Analysis and report by. Record 2007/04. Andrzej P. Radlinski, Dianne S. Edwards, Alan L. Hinde, Rachel Davenport and John M.

Transcription

1 G E O S C I E N C E A U S T R A L I A Hydrocarbon Generation and Expulsion from Early Cretaceous Source Rocks in the Browse Basin, North West Shelf, Australia: a Small Angle Neutron Scattering and Pyrolysis Study Analysis and report by Record 2007/04 Andrzej P. Radlinski, Dianne S. Edwards, Alan L. Hinde, Rachel Davenport and John M. Kennard S PAT I A L I N F O R M AT I O N F O R T H E N AT I O N

2 GEOSCIENCE AUSTRALIA Hydrocarbon Generation and Expulsion from Early Cretaceous Source Rocks in the Browse Basin, North West Shelf, Australia: a Small Angle Neutron Scattering and Pyrolysis Study Analysis and report by Andrzej P. Radlinski, Dianne S. Edwards, Alan L. Hinde, Rachel Davenport and John M. Kennard 2003 Petroleum Promotion and Specialist Studies Research Group, Marine and Petroleum Division Geoscience Australia, PO Box 378, Canberra, ACT, Ph Fax Geoscience Australia Record No 2007/04 ISBN February 2006

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4 Summary Small Angle Neutron Scattering (SANS), Rock-Eval pyrolysis and total organic carbon (TOC) analyses were carried out on 165 organic-rich Upper Jurassic-Lower Cretaceous sedimentary rock samples from nine wells in the Browse Basin (Adele-1, Argus-1, Brecknock South-1, Brewster-1A, Carbine-1, Crux-1, Dinichthys-1, Gorgonichthys-1 and Titanichthys-1). Cutting samples and some sidewall cores have been used. Out of the total 165 samples, 47 samples (22 for Brewster-1A and 25 for Dinichthys-1) were also analysed using the Ultra-small Angle Neutron Scattering (USANS) technique. The focus of the study was to identify potential Lower Cretaceous source rocks and the depth at which the onset of hydrocarbon generation occurred in each well, and to determine the onset of hydrocarbon expulsion in the wells for which USANS data were available. This Record contains a complete description of geochemical and SANS methods and data acquired in 2003 and later selectively used to produce an APPEA publication (Radlinski et al. 2004). This is the first time that such a study has combined the approaches offered by the two disciplines. The neutron scattering and geochemical techniques provide complementary information about petroleum source rocks. Together, the TOC content and Rock-Eval pyrolysis data evaluate source richness, source quality, kerogen type and thermal maturity, whereas SANS/USANS detect the presence of generated bitumen in pores and are pore-size specific. As the pore-size range in mudstones extends from about µm to about 40 µm, the presence of bitumen in the small pores (up to 0.1 µm) detected by SANS indicates the onset of hydrocarbon generation, whereas the presence of bitumen in the largest pores detected by USANS (about 10 µm) indicates a significant saturation and the onset of hydrocarbon expulsion. Brewster-1A and Carbine-1 were drilled with water-based muds which had no detrimental effects on the Rock-Eval pyrolysis and TOC data. Adele-1, Argus-1, Brecknock South-1, Crux-1 and Dinichthys-1 have been drilled using water-based muds containing 'glycol' additives. The shallow sections of the Titanichthys-1 and Gorgonichthys-1 wells were drilled with water-based muds containing glycol additives, and the deeper sections were drilled using synthetic-based muds (SBMs). To determine the hydrocarbon potential of these contaminated samples, extraction procedures with organic solvents were devised, and on analysis, these procedures were observed to have variable success in removing the organic contaminants. The solvent extraction process removes the naturally occurring free hydrocarbons, as well as the organic contaminants, from the whole rock, resulting in the absence of, or a reduction in, the Rock-Eval pyrolysis S 1 peak depending on the rigorousness of the extraction process. Other pyrolysis parameters are also affected if contamination remains; namely S 2 values increase and Tmax values decrease. The affected S 1 and S 2 peaks also result in erratic potential yields (S 1 +S 2 ), an apparent increase in Hydrogen Index (HI = S 2 *100/TOC), and a decrease in, or null value for, the Production Index (PI = S 1 /S 1 +S 2 ). In contrast to the pyrolysis data, the SANS/USANS data obtained on the untreated whole-rock samples do not appear to be influenced by the type of drilling mud used. iii

5 The Lower Cretaceous Echuca Shoals Formation contains some source rocks with the potential to generate and expel liquid hydrocarbons, with the present day values of the hydrogen index, reduced from the original values by the maturity and mineral matrix effects, in the range mg/gTOC. The formation is also sufficiently thermally mature for hydrocarbon generation to occur. SANS/USANS data for Dinichthys-1 show the presence of generated bitumen in pores of all sizes near the base of the formation, but not within the underlying 57 m thick mudstone of the Upper Vulcan Formation juxtaposed between the Echuca Shoals Formation and the Berriasian Brewster Sandstone, which is an important reservoir rock within the Upper Vulcan Formation. It appears that the top mudstone of the Upper Vulcan Formation acts as a barrier for hydrocarbon migration from the Echuca Shoals Formation towards the Berriasian Brewster Sandstone, and, therefore, hydrocarbons generated in the Echuca Shoals Formation have not been expelled into the Berriasian Sandstone reservoir. This is consistent with previous findings based on oil-source correlation that the Upper Vulcan reservoirs have not been charged from Early Cretaceous source rocks. In Brewster-1A there is SANS/USANS evidence of pore-size-specific oil-to-gas cracking within the Echuca Shoals Formation. SANS evidence for bitumen generation in small pores of the Echuca Shoals Formation has also been found in Adele-1, Crux-1, Gorgonichthys- 1 and Titanichthys-1. There is no conclusive SANS evidence for bitumen generation in small pores of Argus-1 (overmature organic matter in this deep well), Brecknock South-1 (potential generation signature possibly overprinted by variable source rock lithology) and Carbine-1 (possible generation signature overprinted by strong sediment compaction in this shallow well). The Lower Cretaceous Jamieson Formation has similar source potential to the underlying Echuca Shoals Formation, but slightly lower organic carbon content and lower thermal maturity. For Brewster-1A and Dinichthys-1, SANS/USANS indicate the presence of bitumen in small pores but not in the largest pores, which indicates that the volume of generated hydrocarbons was insufficient to saturate the pore space and create an effective source charge. There is also SANS evidence of the presence of bitumen in the small pores of this formation in Adele-1, Crux-1, Gorgonichthys-1 and Titanichthys-1. In summary, the Rock-Eval pyrolysis and TOC data imply the existence of a potential source rock in the Lower Cretaceous sediments of the Browse Basin, whereas the SANS/USANS data indicate significant generation but little or no expulsion. This source limitation may explain poor exploration success for liquid hydrocarbons in the area. SANS/USANS data preclude the possibility of an oil charge to the Berriasian Brewster Sandstone from the Echuca Shoals Formation, although some gas charge in Brewster-1A well is possible. iv

6 Contents Summary... iii 1. Introduction Analytical Procedures Samples Analytical Techniques Small Angle Neutron Scattering and Ultra-small Angle Neutron Scattering Rock-Eval Pyrolysis Rock-Eval Pyrolysis Size Fraction Experiments Washing Method Experiments Pyrograms of Water-based Drilling Mud Samples Pyrograms of Glycol Contaminated Samples Pyrograms of SBM Contaminated Samples Results...13 TOC and Rock-Eval Pyrolysis...13 SANS and USANS Analysis Brewster-1A Drilling Fluids, Contaminants and Migrated Hydrocarbons Source Richness Source Quality, Kerogen Type and Maturity Analysis of SANS and USANS data Carbine Drilling Fluids, Contaminants and Migrated Hydrocarbons Source Richness Source Quality, Kerogen Type and Maturity Analysis of SANS data Adele Drilling Fluids, Contaminants and Migrated Hydrocarbons Laboratory Comparisons Source Richness Source Quality, Kerogen Type and Maturity Analysis of SANS data Argus Drilling Fluids, Contaminants and Migrated Hydrocarbons Maturity...61 v

7 3.4.3 Analysis of SANS data Brecknock South Drilling Fluids, Contaminants and Migrated Hydrocarbons Source Richness Source Quality, Kerogen Type and Maturity Analysis of SANS data Crux Drilling Fluids, Contaminants and Migrated Hydrocarbons Source Richness Source Quality, Kerogen Type and Maturity Analysis of SANS data Dinichthys Drilling Fluids, Contaminants and Migrated Hydrocarbons Source Richness Source Quality, Kerogen Type and Maturity Analysis of SANS and USANS data Gorgonichthys Drilling Fluids, Contaminants and Migrated Hydrocarbons Source Richness Source Quality, Kerogen Type and Maturity Analysis of SANS data Titanichthys Drilling Fluids, Contaminants and Migrated Hydrocarbons Source Richness Source Quality, Kerogen Type and Maturity Analysis of SANS data Discussion: Well Comparisons Pyrolysis results: Adele-1 compared to Brewster-1A Pyrolysis results: new Ichthys Field wells compared to Brewster-1A SANS results: new Ichthys Field wells compared to Brewster-1A SANS Results: Adele-1 and Crux-1 compared to Brewster-1A Source Rock Summary Conclusions Recommendations and Further Work References Well Completion Reports vi

8 APPENDICES Appendix 1: List of Wells, Samples and Depository Sequences Appendix 2:Analytical Procedures A2.1 Comparison of the Small Angle Scattering and Geochemical Methods A2.2 SANS/USANS Sample Preparation (extracted from Geoscience Australia Sedimentology Laboratory Operating Procedure) Introduction Purpose Scope Responsibilities Hazards Hazard Control Measures and Limitations Procedural Steps Flow Chart A2.3 Introduction to SANS/USANS and its Applications to Source Rock Generation 179 Introduction Background Application to Petroleum Geology Summary References A2.4 TOC and Rock-Eval Pyrolysis Sample Preparation A2.5 TOC and Rock-Eval Pyrolysis Method Appendix 3: Results of Size Fraction Experiments Appendix 4: Rock-Eval Pyrolysis Definitions Appendix 5: TOC and Rock-Eval Pyrolysis Results vii

9 Figures Figure 1.1 Location of the Browse Basin....2 Figure 1.2. Location of Browse Basin wells sampled in the study....3 Figure 1.3 Browse Basin Mesozoic and Cainozoic stratigraphy (after Blevin et al., 1998a)....4 Figure 2.1a Pyrogram (FID) from Brewster-1A m (# ) for raw cuttings sample showing resolved S 1 and S 2 peaks....6 Figure 2.1b Pyrogram (IR) from Brewster-1A m (# ) for raw cuttings sample showing CO 2 (top trace) and CO (bottom trace) released during pyrolysis....7 Figure 2.1c Pyrogram (IR) from Brewster-1A m (# ) for raw cuttings sample showing resolved CO 2 (top trace) and CO (bottom trace) released during oxidation....7 Figure 2.2 Figure 2.3 Figure 2.4 Figure 2.5 Figure 2.6 Pyrogram (FID) from Crux m (# ) for raw cuttings sample....8 Pyrogram (FID) from Crux m (# ) for extracted cuttings sample....9 Pyrogram (FID) from Crux m (# ) for extracted cuttings sample containing contaminant peaks....9 Pyrogram (FID) from Crux m (# ) for extracted cuttings sample containing contaminant peak Pyrogram (FID) from Crux m (# ) for extracted SWC sample Figure 2.7 Pyrogram (FID) from Gorganichthys-1, m (# ) for extracted cuttings sample drilled using a water-based mud Figure 2.8 Pyrogram (FID) from Gorganichthys m (# ) for extracted cuttings sample drilled using a SBM Figure 3.1 Figure 3.2 Figure 3.3 Depth plots of vitrinite reflectance, TOC and Rock-Eval pyrolysis data for Brewster 1A sediments (HC indicates samples which contain hydrocarbons) TOC and Rock-Eval pyrolysis cross plots for Brewster 1A sediments (HC indicates samples which contain hydrocarbons) TOC and Rock-Eval pyrolysis cross plots for selected sediments in Brewster-1A Figure 3.4. SANS absolute intensity curves for samples of cuttings from Brewster-1A. (a): 11 samples (claystones, 5 m interval each), depth range 2450 m to 2950 m Figure 3.4. SANS absolute intensity curves for samples of cuttings from Brewster-1A. (b): 9 samples (claystones, 5 m interval each), depth range 3000 m to 3600 m viii

10 Figure 3.4. SANS absolute intensity curves for samples of cuttings from Brewster-1A. (c): 4 samples (claystones, 5 m interval each), depth range 3695 m to 4230 m Figure 3.5. SANS intensity versus depth at four Q-values of (a) Å -1, (b) Å -1, (c) Å -1, and (d) Å -1, which corresponds to four pore sizes of 0.01 µm +/-50%, 0.1 µm +/-50%, 1 µm +/-50% and 10 µm +/-50%, for cuttings samples from Brewster-1A...25 Figure 3.6. Variation of the Scattering Length Density (SLD) with depth for Brewster-1A. SLD values were calculated from the elemental composition as determined by a separate X-ray Fluorescence (XRF) measurement Figure 3.7. Pore size distribution at various depths for samples of cuttings from Brewster-1A. (a): 11 samples (claystones, 5 m interval each), depth range is 2450 m to 3055 m. (b): 11 samples (claystones, 5m interval each), depth range 3100 m to 4235 m...29 Figure 3.8. Variation of the pore number density for four selected pore sizes versus depth for Brewster-1A. Note the slight decrease of the pore number density with depth, indicative of compaction. For full discussion see text Figure 3.9. Variation of apparent porosity with depth for Brewster-1A. For discussion see text Figure 3.10 Depth plots of TOC and Rock-Eval pyrolysis data for Carbine Figure 3.11 TOC and Rock-Eval pyrolysis cross plots for Carbine-1 sediments...35 Figure 3.12 TOC and Rock-Eval pyrolysis cross plots for selected sediments in Carbine Figure SANS absolute intensity curves for samples of cuttings from Carbine-1. Data are shown for seven samples (nominally claystones and silty slaystones, 3 m interval each). Depth range is 1349 m to 1559 m Figure SANS intensity versus depth at Q=0.01 A -1 (corresponding to the pore size 25 nm +/-50%, or µm +/-50%) for cuttings samples from Carbine Figure Variation of the Scattering Length Density (SLD) for thermal neutrons with depth for Carbine-1. SLD values were calculated from the elemental composition as determined by a separate X-ray Fluorescence (XRF) measurement Figure Pore size distribution at various depths for samples of cuttings from Carbine-1. Seven samples (nominally claystones and silty claystones, 3 m interval each), depth range is 1349 m to 1559 m Figure Variation of the pore number density for selected pore sizes versus depth for Carbine-1. Note the significant decrease of the pore number density with depth, indicative of compaction. For full discussion see text ix

11 Figure Variation of apparent porosity (within the pore size range 2 nm to 100 nm) with depth for Carbine-1. For discussion see text Figure 3.19 Depth plots of vitrinite reflectance, TOC and Rock-Eval pyrolysis data for Adele Figure 3.20 TOC and Rock-Eval pyrolysis cross plots for Adele-1 samples Figure 3.21 TOC and Rock-Eval pyrolysis cross plots for selected samples from Adele Figure SANS absolute intensity curves for samples of cuttings from Adele Figure SANS intensity versus depth at Q=0.01 A -1 (corresponding to the pore size 25 nm +/-50%, or µm +/-50%) for cuttings samples from Adele Figure Variation of the Scattering Length Density (SLD) for thermal neutrons with depth for Adele-1. SLD values were calculated from the elemental composition as determined by a separate X-ray Fluorescence (XRF) measurement Figure Pore size distribution at various depths for samples of cuttings from Adele-1. A: ten samples (claystones, 5 m interval each), depth range is 2530 m to 2980 m. B: nine samples (claystones, 5 m interval each), depth range 3030 m to 3405 m Figure Variation of the pore number density for selected pore sizes versus depth for Adele-1. Note the slight decrease of the pore number density with depth, indicative of compaction. For full discussion see text Figure Variation of apparent porosity (within the pore size range 2 nm to 100 nm) with depth for Adele-1. For discussion see text Figure Depth plots of vitrinite reflectance, TOC and Rock-Eval pyrolysis data for Argus-1 samples Figure SANS absolute intensity curves for samples of cuttings from Argus-1. Eight samples (seven claystones and one calcareous claystone, 5 m interval each), depth range 4270 m to 4535 m Figure SANS intensity versus depth at Q=0.01 A -1 (corresponding to the pore size 25 nm +/-50%, or µm +/-50%) for cuttings samples from Argus Figure Vitrinite reflectance and thermal maturity data for extracts and condensates for Argus Figure Variation of the Scattering Length Density (SLD) for thermal neutrons with depth for Argus-1. SLD values were calculated from the elemental composition as determined by a separate X-ray Fluorescence (XRF) measurement Figure Pore size distribution at various depths for samples of cuttings from Argus-1. Eight samples (seven claystones and one calcareous claystone, 5 m interval each), depth range is 4270 m to 4535 m x

12 Figure Variation of the pore number density for selected pore sizes versus depth for Argus Figure Variation of apparent porosity (within the pore size range 2 nm to 100 nm) with depth for Argus Figure 3.36 Depth plots of TOC and Rock-Eval pyrolysis data for Brecknock South Figure 3.37 Tmax versus Hydrogen Index for selected samples from Brecknock South Figure SANS absolute intensity curves for samples of cuttings from Brecknock South-1. Ten samples (nominally claystones, 5 m interval each), depth range is 3530 m to 3995 m Figure SANS intensity versus depth at Q=0.01A -1 (corresponding to the pore size 25 nm +/-50%, or µm +/-50%) for cuttings samples from Brecknock South Figure Variation of the Scattering Length Density (SLD) for thermal neutrons with depth for Brecknock South Figure Pore size distribution at various depths for samples of cuttings from Brecknock South-1. Ten samples (nominally claystones, 5 m interval each), depth range is 3530 m to 3995 m Figure Variation of the pore number density for selected pore sizes versus depth for Brecknock South Figure 3.43 Variation of apparent porosity (within the pore size range 2 nm to 100 nm) with depth for Brecknock South-1. For discussion see text Figure 3.44 Depth plots of TOC and Rock-Eval pyrolysis data for Crux-1 (GA data only) Figure 3.45 Depth plots of TOC and Rock-Eval pyrolysis data for Crux Figure 3.46 Tmax versus Hydrogen Index for selected samples from Crux Figure 3.47 SANS absolute intensity curves for samples from Crux Figure SANS intensity versus depth at Q=0.01 A -1 (corresponding to the pore size 25 nm +/-50%, or µm +/-50%) for samples from Crux Figure Vitrinite reflectance versus depth for Crux-1 (after Well Completion Report) Figure Variation of the Scattering Length Density (SLD) for thermal neutrons with depth for Crux Figure Pore size distribution at various depths for samples from Crux Figure Variation of the pore number density for selected pore sizes versus depth for Crux Figure Variation of apparent porosity (within the pore size range 2 nm to 100 nm) with depth for Crux xi

13 Figure Interpretation of SANS data for Crux-1. SANS intensity versus depth at Q=0.01 A -1 (corresponding to the pore size 25 nm +/-50%, or µm +/-50%) for samples from Crux Figure 3.55 Depth plots of vitrinite reflectance, TOC and Rock-Eval pyrolysis data for Dinichthys Figure 3.56 Tmax versus Hydrogen Index for selected samples from Dinichthys Figure 3.57 SANS absolute intensity curves for samples of cuttings from Dinichthys Figure 3.58 SANS intensity versus depth at four Q-values of (a) Å -1, (b) Å -1, (c) Å -1, and (d) Å -1, which corresponds to four pore sizes of 0.01 µm +/-50%, 0.1 µm +/-50%, 1 µm +/-50% and 10 µm +/-50%, for cuttings samp Figure 3.59 Variation of the Scattering Length Density (SLD) for thermal neutrons with depth for Dinichthys Figure 3.60 Pore size distribution at various depths for samples of cuttings from Dinichthys Figure 3.61 Variation of the pore number density for four selected pore sizes versus depth for Dinichthys Figure 3.62 Variation of apparent porosity (within the pore size range 2 nm to 20 µm) with depth for Dinichthys-1. For discussion see text Figure 3.63 Depth plots of vitrinite reflectance, TOC and Rock-Eval pyrolysis data for Gorgonichthys Figure 3.64 Tmax versus Hydrogen Index for selected samples from Gorgonichthys Figure 3.65 SANS absolute intensity curves for samples of cuttings from Gorgonichthys Figure 3.66 SANS intensity versus depth at Q=0.01 A -1 (corresponding to the pore size 25 nm +/-50%, or µm +/-50%) for cuttings samples from Gorgonichthys Figure 3.67 Variation of the Scattering Length Density (SLD) for thermal neutrons with depth for Gorgonichthys Figure 3.68 Pore size distribution at various depths for samples of cuttings from Gorgonichthys Figure 3.69 Variation of the pore number density for selected pore sizes versus depth for Gorgonichthys Figure 3.70 Variation of apparent porosity (within the pore size range 2 nm to 100 nm) with depth for Gorgonichthys Figure 3.71 Depth plots of vitrinite reflectance, TOC and Rock-Eval pyrolysis data for Titanichthys Figure 3.72 Tmax versus Hydrogen Index for selected samples from Titanichthys xii

14 Figure SANS absolute intensity curves for samples of cuttings from Titanichthys Figure 3.74 SANS intensity versus depth at Q = 0.01 A -1 (corresponding to the pore size 25 nm +/-50%, or µm +/-50%) for cuttings samples from Titanichthys Figure 3.75 Variation of the Scattering Length Density (SLD) for thermal neutrons with depth for Titanichthys Figure 3.76 Pore size distribution at various depths for samples of cuttings from Titanichthys Figure 3.77 Variation of the pore number density for selected pore sizes versus depth for Titanichthys Figure 3.78 Variation of apparent porosity (within the pore size range 2 nm to 100 nm) with depth for Titanichthys Figure 4.1 Figure 4.2 Figure 4.3 Figure 4.4 Figure 4.5 Comparison of pyrolysis data from nearby wells drilled using water-based mud and without glycol additives Comparison of pyrolysis data from near-by wells drilled using different mud systems. Depth is expressed in mss Scattering intensity versus depth (below sea level) for stratigraphic formations in Brewster-1A, Dinichthys-1, Gorgonichthys-1 and Titanichthys Interpretation of SANS data for Brewster-1A, Dinichthys-1, Gorgonichthys-1 and Titanichthys Scattering intensity versus depth (below sea level) for stratigraphic formations in Brewster-1A, Crux-1 and Adele Figure 4.6 Comparison of source rock data from Browse Basin study wells In Appendices Diagram 1.0 Set up of sieving apparatus Image 1.0 Sample pot at right, holding jig at left Image 2.0 Sample mount in holding jig ready for sectioning Figure 1 Figure 2 Figure 3 Figure 4 Figure 5. Range of linear sizes that can be observed with various types of neutron optics Neutron scattering length density for major minerals and organic matter types present in sedimentary rocks The comparison of SANS/USANS scattering data for a typical sandstone [24, 25], shale [20, 24] and coal [19] The comparison of SANS/USANS-derived pore size distribution for a sandstone [23, 24], shale [23, 24], and coal [19] The comparison of SANS/USANS-derived specific surface area for a sandstone [23, 24], shale [23, 24] and coal [19] xiii

15 Figure 6. Figure 7. Figure 8. The variation of SANS intensity at a single Q-value versus the annealing temperature for an immature hydrocarbon source rock A schematic representation of the SANS intensity (for a selected Q-value) versus depth within the hydrocarbon generation window The comparison of specific surface area for coals of different rank obtained using SANS and the nitrogen adsorption method. The probe size is 4Å (after Reference 19) xiv

16 Tables Table 3.1. XRF raw data for Adele Table 3.2. XRF data for Argus Table 4.1 Drilling information and depths of lithological units for Brewster-1A, Dinichthys-1, Gorgonichthys-1 and Titanichthys Table A1.1 List of wells studied in this project Table A1.2 Samples analysed in this study from Adele Table A1.3 Samples analysed in this study from Argus Table A1.4 Samples analysed in this study from Brecknock South Table A1.5 Samples analysed in this study from Brewster-1A Table A1.6 Samples analysed in this study from Carbine Table A1.7 Samples analysed in this study from Crux Table A1.8 Samples analysed in this study from Dinichthys Table A1.9 Samples analysed in this study from Gorgonichthys Table A1.10 Samples analysed in this study from Titanichthys Table A1.11. Depository sequences for nine wells in the Browse Basin. Part 1 - Geoscience Australia classification of depository sequences. Part 2 - depository sequences as in Well Completion Reports. All depths are in mrt Table A2.1 Comparison of the SAS and geochemical methods Table A3.1 Reproducibility of data for different size fractions for cuttings sample from Brewster 1A, m (# ) Table A3.2 Reproducibility of data for different size fractions for cuttings sample from Brewster 1A, m (# ) Table A3.3 Comparison of data for different size fractions for cuttings samples from Brewster 1A Table A4.1 Definitions of Rock-Eval pyrolysis parameters (modified after Espitalié et al., 1985; Peters, 1986) Table A4.2. Guidelines for interpreting (a) source rock generative potential and (b) type of petroleum generated from immature sediments (VR <0.6 %), and, c) degree of thermal maturation (modified after Peters, 1986; Espitalié and Bordenave,1993) Table A4.2a Source rock generative potential (richness) for VR < 0.6 % Table A4.2b Source rock quality for VR < 0.6 % xv

17 Table A4.2c Source rock thermal maturity Table A5.1 TOC and Rock-Eval pyrolysis results for cuttings samples from Brewster-1A Table A5.2 TOC and Rock-Eval pyrolysis results for cuttings samples from Carbine Table A5.3 TOC and Rock-Eval pyrolysis results for cuttings samples from Adele-1 extracted with methanol and dichloromethane (90:10). S 1 values are invalid Table A5.4 TOC and Rock-Eval pyrolysis results for cuttings samples from Argus-1 extracted with methanol and dichloromethane (90:10). S 1 values are invalid Table A5.5 TOC and Rock-Eval pyrolysis results for cuttings samples from Brecknock South-1 extracted with methanol and dichloromethane (90:10) Table A5.6 TOC and Rock-Eval pyrolysis results for cuttings and side-wall-core samples from Crux-1. S 1 values are invalid Table A5.7 TOC and Rock-Eval pyrolysis results for cuttings samples from Dinichthys-1. S 1 values are invalid Table A5.8 TOC and Rock-Eval pyrolysis results for cuttings samples from Gorgonichthys-1. S 1 values are invalid Table A5.9 TOC and Rock-Eval pyrolysis results for cuttings samples from Titanichthys-1. S 1 values are invalid xvi

18 1. Introduction The aim of this study was to determine the timing of hydrocarbon generation and expulsion in the Early Cretaceous Echuca Shoals Formation and Jamieson Formation in the Browse Basin (Figs. 1.1, 1.2 and 1.3) using synergies between classical organic geochemistry and the technique of Small Angle Neutron Scattering. The tectonic and stratigraphic evolution of the Browse Basin and its potential for petroleum generation and entrapment have been studied previously (Struckmeyer et al. 1998, Blevin et al. 1998a). Based on the intra-basin oil-oil and oil-source rock correlation, an effective Lower Cretaceous Petroleum System (Westralian W3 Petroleum System) in the Browse Basin has been postulated (Blevin et al. 1998b). The study has been performed on rock cuttings and sidewall cores originating from eight recently drilled wells and one older well (Table A1 in Appendix 1). Small Angle Neutron Scattering (Thiyagarajan et al. 1998), Rock-Eval pyrolysis and total organic carbon (TOC) analyses were carried out on 165 organic-rich Jurassic-Cretaceous sedimentary rock samples from nine wells in the Browse Basin (Table A2 in Appendix 1). Out of the total of 165 samples, 47 (22 for Brewster-1A and 25 for Dinichthys-1) were additionally analysed using the Ultra Small Angle Neutron Scattering (USANS) technique (Hainbuchner et al. 2000). Major findings of this work have been published by Radlinski et al. (2004). Geological applications of SANS and USANS are reviewed by Radlinski (2006). Stratigraphic classification for the Browse Basin wells is at the development stage. Table A1-11 in Appendix 1 lists depositional sequences for the nine wells studied in this work. Uniform classification according to the Geoscience Australia scheme is available for wells Adele 1, Brecknock South 1, Brewster 1A, Crux 1 and Gorgonichthys 1 (part 1 of Table A1-11 in Appendix 1). For wells Argus 1, Carbine 1, Dinichthys 1 and Titanichthys 1 the sequences shown follow the company classification scheme used in Well Completion Reports (part 2 of Table A1-11 in Appendix 1). The focus of the study was to identify potential source rocks and the depth at which the onset of hydrocarbon generation and saturation of pore spaces occurred within each well. However, in the course of the pyrolysis component of the study two other objectives became apparent: firstly, it was necessary to determine whether or not the organic matter in the (>355 µm, <475 µm) size fraction provided was representative of the whole rock sample; and secondly, because the wells were drilled using a variety of drilling fluids, the effect of the these fluids on the quality of the data had to be ascertained. 1

19 Figure 1.1 Location of the Browse Basin WA NT SA QLD Ashmore Platform Vulcan Sub-basin NSW ACT VIC ied) TAS Seringapatam Sub-basin Brecknock 1 Brecknock South 1 Barcoo Sub-basin Buffon 1 North Scott Reef 1 Scott Reef 2, 2A Carbine 1 Caswell 2 Argus 1 Caswell Sub-basin B R O W S E B A S I N Yampi 2 Bassett 1A Echuca Shoals 1 Dinichthys 1 Brewster 1A Titanichthys 1 Gorgonichthys 1 Prudoe Tce Discorbis 1 Columbia 1A Heywood 1 Adele 1 Gwydion 1 Circinus 1 Asterias 1 Cornea 1 Yampi Shelf Crux 1 Londonderry High KIMBERLEY BASIN Psepotus 1 Shallow/exposed Precambrian rocks or Proterozoic basin Leveque 1 Late Palaeozoic to Mesozoic basin Trochus 1 Leveque Shelf Platform of Precambrian / Palaeozoic with thin (<2 km) Mesozoic cover Major Palaeozoic fault Minor Palaeozoic fault Jurassic fault 2

20 2. Analytical Procedures 2.1 Samples A complete list of the samples analysed in this study from the nine Browse Basin wells (Adele-1, Argus-1, Brecknock South-1, Brewster-1A, Carbine-1, Crux-1, Dinichthys-1, Gorgonichthys-1 and Titanichthys-1) are given in Appendix 1. Unless otherwise stated, all depth measurements are given with respect to the rotary table (RT). The selected sedimentary rock samples comprise side-wall-cores (SWCs) and cuttings (CUTT). Given sufficient quantity of the rock material, each rock sample was divided into three portions (in the priority sequence): one for SANS/USANS, one for geochemistry, and one (archived) for possible future palaeontology work. The geochemistry portion was preserved for future biomarker work. Figure 1.2. Location of Browse Basin wells sampled in the study. 13 WA NT SA TAS QLD NSW ACT VIC Seringapatam Sub-basin Brecknock South 1 Barcoo 15 Sub-basin Buffon 1 Caswell 2 Argus 1 B R O W S E Ashmore Platform Caswell Sub-basin Adele 1 Echuca Shoals 1 Dinichthys 1 North Scott Reef 1 Brewster 1A Titanichthys 1 Gorgonichthys 1 Scott Reef 2, 2A Brecknock 1 Carbine 1 Yampi 2 B A S I N Prudoe Tce Gwydion 1 Yampi Shelf Vulcan Sub-basin Londonderry High Crux 1 Cornea KIMBERLEY BASIN Proterozoic basin Late Palaeozoic to Mesozoic basin Precambrian / Palaeozoic Platform

21 Figure 1.3 Browse Basin Mesozoic and Cainozoic stratigraphy (after Blevin et al., 1998a). Age Ma Era MESOZOIC CAINOZOIC System Q TRIASSIC JURASSIC CRETACEOUS TERTIARY NEOGENE PALAEOGENE L E L M E L M E Series/Epoch/Stage CONIACIAN TURONIAN SCYTHIAN PLEISTOCENE PLIOCENE MIOCENE OLIGOCENE EOCENE PALEOCENE MAASTRICHTIAN CAMPANIAN SANTONIAN CENOMANIAN ALBIAN APTIAN BARREMIAN HAUTERIVIAN VALANGINIAN BERRIASIAN TITHONIAN KIMMERIDGIAN OXFORDIAN CALLOVIAN BATHONIAN BAJOCIAN AALENIAN TOARCIAN PLIENSBACHIAN SINEMURIAN HETTANGIAN RHAETIAN NORIAN CARNIAN LADINIAN ANISIAN SPATHIAN NAMMALIAN GRIESBACHIAN Barracouta Fm Oliver Fm Cartier Fm Prion Fm Grebe Fm Bassett Fm Puffin Fm Fenelon and Gibson Fms Woolaston Fm Lower Vulcan Fm Lithostratigraphy Jamieson Fm Echuca Shoals Fm Upper Vulcan Fm Plover Fm Nome Fm Challis Fm Montara Fm Pollard Fm Osprey Fm Mt Goodwin Fm Seq BB22 BB21 BB20 BB19 BB18 BB17 BB16 BB15 BB14 BB13 BB12C BB12B BB12A BB11 BB10 BB9 BB8 BB7 BB6 BB5 BB

22 2.2 Analytical Techniques Small Angle Neutron Scattering and Ultra-small Angle Neutron Scattering Details of the sample preparation for SANS/USANS can be found in Appendix 2.1. An introduction to the SANS/USANS techniques and its application to source rock generation are presented in Appendix 2.2 and 2.3. Briefly, samples for SANS/USANS were prepared by gently crushing the rock material and dry-sieving into three fractions <355 µm; µm; and >475 µm. The dry sieved µm grain size fraction, to be used for the SANS/USANS measurements, was planted in resin and, after curing, two to three 25 mm diameter slices (about 1mm thick and about 0.4mm thick) were cut off with a precision diamond saw. The thick (1 mm) slices were directly used for the SANS measurements and the thin (0.4 mm) slices were used for the USANS measurements. The Standard Operating Procedure for SANS sample preparation is reproduced in Appendix 2.2. Many of the samples submitted for this project were too small to perform a three-way split. Hence, the left over portion of the size-fractionated sample ( µm) from the SANS preparation was submitted for Rock-Eval pyrolysis and TOC analysis. In a series of independent Rock Eval pyrolysis and TOC measurements it was confirmed that this SANS size fraction yielded the same results as the recombined whole rock sample, as detailed in Appendix 3. For the small angle neutron scattering a time-of -flight SANS instrument SAND at the Intense Pulsed Neutron Source, Argonne National Laboratory, USA (Thiyagarayan et al, 1998) and the USANS instrument S18 at the High Flux Reactor in Grenoble, France (Hainbuchner et al., 2000) were used Rock-Eval Pyrolysis The Rock-Eval pyrolysis sample preparation and analytical procedures used in this study are detailed in Appendix 2.4 and 2.5, respectively. Briefly, the dry-sieved sample fractions from wells using water-based drilling muds were powdered and pyrolysed in a Turbo Rock-Eval 6. Samples from wells which were drilled using either Glycol or the synthetic-based mud (SBM), Syntech were extracted with the organic solvent mixture methanol:dichloromethane (90:10 and 50:50, respectively) by sonication after crushing to a fine powder using a mortar and pestle. The sediment was recovered by centrifuging and dried at 40 o C. It was then placed into an oxidized crucible ready for analysis. 2.3 Rock-Eval Pyrolysis Size Fraction Experiments Experiments to determine whether the SANS µm sized fraction was representative of the whole rock sample were carried out on Brewster-1A cuttings samples because this well was drilled using a water-based mud, hence erroneous values arising from drilling fluid contaminants were minimised. 5

23 Rock-Eval pyrolysis was carried out on all three dry-sieved fractions (viz <355 µm; µm; and >475 µm) and a recombined whole rock sample over three depth ranges m (# ), m (# ), and m (# ) in Brewster-1A. These samples were chosen to reflect any differences that may occur between the Jamieson and Echuca Shoals formations, as well as increasing maturity. The results show that the variation seen between the three different size fractions and the recombined sample is generally within experimental error between repeat samples (see Appendix 3; Tables A3.1 and A3.2). The biggest variation in the results is seen between the Tmax, S 3 and TOC values between repeat analyses. Therefore, the µm size fraction was deemed representative of the whole-rock sample and used in the pyrolysis experiments. 2.4 Washing Method Experiments For the samples recovered from wells drilled using glycol additives and synthetic-based muds (SBMs), a method for washing the samples had to be determined to maximise the removal of the contaminants while being practical in terms of laboratory time and use of resources. Initially, the samples were washed in water and then methanol and dichloromethane, prior to crushing and analysis. However, this methodology did not remove the drilling contaminants. Therefore, the extraction method detailed in Appendix 2.4 was employed on the powdered sample Pyrograms of Water-based Drilling Mud Samples On pyrolysis, the cuttings samples from Brewster-1A and Carbine-1, drilled using water-based muds, gave well resolved, individual S 1, S 2 and S 3 peaks, as shown in Figure 2.1. Figure 2.1a Pyrogram (FID) from Brewster-1A m (# ) for raw cuttings sample showing resolved S 1 and S 2 peaks. 6

24 Figure 2.1b Pyrogram (IR) from Brewster-1A m (# ) for raw cuttings sample showing CO 2 (top trace) and CO (bottom trace) released during pyrolysis. Figure 2.1c Pyrogram (IR) from Brewster-1A m (# ) for raw cuttings sample showing resolved CO 2 (top trace) and CO (bottom trace) released during oxidation Pyrograms of Glycol Contaminated Samples On pyrolysis, samples from the five wells; Adele-1, Argus-1, Brecknock South-1, Crux- 1 and Dinichthys-1 showed contamination by glycol additives in the drilling mud. There are large, multiple S 1 and S 2 peaks, as shown in Figure 2.2, due to the contaminant compounds adding to, and obscuring, the indigenous free hydrocarbons (S 1 peak) and the hydrocarbons cracked from the kerogen (S 2 peak) upon pyrolysis. 7

25 Figure 2.2 Pyrogram (FID) from Crux m (# ) for raw cuttings sample. After the solvent extraction, most of the glycol contaminants appear to have been removed from the sample (Fig. 2.3), as well as the free hydrocarbons within the rock. Hence, the S 1 peak in the pyrogram is either small or undetected, resulting in the S 1 peak being unreliable and consequently all values calculated [viz. Bitumen Index (BI), Production Index (PI)] are also unreliable. The kerogen in the rock is unaffected by the solvent extraction process therefore the S 2 peak in the program, and the interpreted Tmax values, should be an accurate measure of the quantity, quality and maturity of the kerogen in the rock, as long as the S 2 peak is fully resolved from any remaining contamination. Although all of the samples were extracted in the same way, the pyrograms of some samples still showed the effects of contaminants (Figs 2.4 and 2.5). The bimodal, and in some cases multimodal, S 2 peak results in an anomalously low Tmax value since Tmax is typically assigned to the peak with the greatest height after 300 o C; in this case the first (lower temperature) peak. The S1 and S2 values are also anomalously high. Despite further extraction, the contaminants remained in some samples. It is undetermined whether the level of contamination in these samples was much greater than the other samples, whether the permeability and/or porosity differed in these samples or that the chemical composition of the contaminant has changed. Furthermore, comparison of the extracted cuttings samples with those of the extracted sidewall core samples in the Adele-1 and Crux-1 wells (Figs 2.5 and 2.6) show that the glycol additive has had a considerable effect on the pyrolysis values of the cuttings samples with respect to the sidewall core samples of similar depth. Despite the fully resolved appearance of the S2 peak in both the pyrograms, the S2 peak in the sidewall core (Fig. 2.6) has a symmetrical and narrow peak shape, whereas a shoulder remains on the broader S2 peak from the cuttings sample (Fig. 2.5). Effects of this additive appear to be inconsistent but generally result in lower than expected Tmax values, enhanced TOC contents and enhanced S2 values. Depending on the relative increases in the TOC and S2 values, the resultant Hydrogen Index values typically increase. 8

26 Figure 2.3 Pyrogram (FID) from Crux m (# ) for extracted cuttings sample. Figure 2.4 Pyrogram (FID) from Crux m (# ) for extracted cuttings sample containing contaminant peaks. 9

27 Figure 2.5 Pyrogram (FID) from Crux m (# ) for extracted cuttings sample containing contaminant peak. Thus, independent of the extraction process, there is an inability to remove all the glycol contaminants, which are still contributing to the S2 peak. Therefore, the Rock- Eval pyrolysis results produced for samples obtained from mud systems with glycol additives should either be used with caution, or not at all, when carrying out source rock appraisal. Figure 2.6 Pyrogram (FID) from Crux m (# ) for extracted SWC sample Pyrograms of SBM Contaminated Samples On pyrolysis, the samples from the two wells Gorgonichthys-1 and Titanichthys-1 showed contamination by mud additives. In Gorgonichthys-1 the well was drilled using water-based drilling mud to a depth of 3930 m, below this depth the mud system was 10

28 changed and SBMs were used to the bottom of the well. Titanichthys-1 was also drilled using two mud systems, an initial water-based mud followed by a SBM being used from a depth of 3905 m to the bottom of the well. All of the cuttings samples were powdered and extracted using methanol and dichloromethane (50:50). Figures 2.7 and 2.8 compare the pyrograms for the extracted cuttings drilled using the water-based drilling fluid and the SBM drilling fluid. The S 2 peak in the SBM pyrogram is much broader than the sample drilled using the water-based mud, resulting in a low Tmax value. Figure 2.7 Pyrogram (FID) from Gorganichthys-1, m (# ) for extracted cuttings sample drilled using a water-based mud. Figure 2.8 Pyrogram (FID) from Gorganichthys m (# ) for extracted cuttings sample drilled using a SBM. 11

29 12

30 3 Results TOC and Rock-Eval Pyrolysis The results for the project are ordered by the type of drilling fluid used in each well (water-based, water-based with glycol additive and SBM-based) and then in alphabetical order of the wells. Pyrolysis data from well completion reports (WCRs) are also included to make the source rock interpretations as complete as possible for each well, to compare the Geoscience Australia s laboratory data with that of service company data, and compare the data from sidewall cores with that of cuttings, which are inherently more prone to contamination issues. Definitions of the Rock-Eval pyrolysis parameters used are given in Appendix 4 Table A4.1 after Espitalié et al (1985) and Peters (1986), with a summary of the criteria used to define a source rock (after Peters, 1986) being listed in Table A4.2. For a sediment to have hydrocarbon potential, the minimum total organic carbon (TOC) content for a carbonate is taken to be 0.2 % and 0.5 % for a clastic sediment (Table A4.2a), although TOC s in excess of 2.0 % are typically required for NW Shelf sediments to have the capacity to generate and expel hydrocarbons. Immature samples often have poorly resolved S 1 and S 2 peaks, therefore Tmax values less than 380 C were excluded from the evaluation of hydrocarbon source potential. Low S 2 values can arise from adsorption of the produced hydrocarbons on the mineral matrix (Espitalié et al., 1980; Orr, 1983), resulting in an underestimation of the Hydrogen Index. The mineral matrix effect was found to be significant in a previous source rock appraisal of the Browse Basin (Blevin et al., 1998b). Therefore, samples with small S 2 peaks (< 0.2 mg hydrocarbons/g rock) were considered to be unreliable and hence such samples have been omitted from the assessment of source rocks. In order to prevent migrated oil and contaminants interfering with the identification of source rocks, samples with anomalously high production indices (PI), and low Tmax values, were excluded from the source rock evaluation sections and included in the discussion of drilling fluids, contaminants and migrated hydrocarbons. The cut-off values applied to the data to allow evaluation of source rocks sensu stricto are as follows; PI 0.1 for immature (VR 0.5 %) sediments, 0.1 > PI 0.25 for early mature (0.5 > VR 0.8 %), sediments and 0.25 > PI 0.4 for mature (0.8 > VR 1.2 %) sediments. Hence, only a proportion of the total number of analyses carried out on sediments from the Browse Basin are shown in some figures. A brief summary of source richness (TOC, potential yield), source quality (oil- or gasprone) and kerogen type is given in this report for the formations in each well. The majority of samples chosen in this study come from the Lower Cretaceous Jamieson, Echuca Shoals and Upper Vulcan formations and the Upper Jurassic Lower Vulcan Formation (Fig. 3.1). A few samples from the Lower-Middle Jurassic Plover Formation and the Triassic Mount Goodwin Formation are also included. In this study, a source rock has been assumed to be gas-prone if the Hydrogen Index is below a minimum of 150 mg hydrocarbons/g TOC, condensate-prone when the HI is between 150 and

31 mg hydrocarbons/g TOC and oil-prone with some gas at higher values. Oil-prone source rocks with HI > 300 mg hydrocarbons/g TOC were not recorded in the Browse Basin samples. An assessment of thermal maturity was made using a combination of Tmax, PI and vitrinite reflectance (VR). The degree of thermal maturity required for the generation of hydrocarbons depends on the type of organic matter present in the source rock. The Mesozoic succession of the Browse Basin comprises thick Lower Jurassic deltaic to coastal plain sediments, thin Upper Jurassic fluvio-deltaic sediments and a thick sequence of Lower Cretaceous prograding fluvio-deltaic and shallow marine sediments (Blevin et al. 1998a, b). These sediments contain varying proportions of indigenous sapropellic material (disseminated remains of bacteria, algae, acritarchs, dinoflagellates etc) and allochthonous land-plant-derived material. Hence, the predominant type of hydrocarbon-prone organic matter within these sediments ranges from Type II to Type III kerogen. Higher maturities are usually required for the generation and expulsion of hydrocarbons from hydrogen-poor Type III kerogens than for Type II kerogens (see Appendix 4, Table A4.2c), thus: Kerogen Type VR oil window Tmax oil window Type II % C Type III % C The peak oil window was taken to correspond to vitrinite reflectances between 0.8 and 0.9 %, peak wet gas at VR = 1.2 % and dry gas at VR > 1.6 %. A minimum temperature of 170 C (VR > 1.2 %) was assumed to be required for the cracking of oil to gas. Sediments in which oxidised organic material (inertinite) or Type IV kerogen is prevalent are considered to be a source of methane and carbon dioxide at high thermal maturities, i.e. within the dry gas window (VR = %). SANS and USANS Analysis The outline of SANS/USANS methodology is given in Appendix 2 (Section A 2.2). The scattering intensity has been measured versus the scattering vector Q for each sample and converted to absolute units. From these data, plots illustrating the variation of the scattering intensity versus depth for several selected pore sizes have been constructed and examined for the existence of characteristic <-shaped patterns, which are indicative of the presence of mobile bitumen within the pores of a particular size. The pore sizes selected for analysis were 100 Å and 860 Å for wells with SANS data only, and 100 Å, 1000 Å, 10,000 Å and 100,000 Å (100 Å = 0.01 µm; 1 µm = 10,000 Å) for wells in which both SANS and USANS data were collected (Brewster-1A and Dinichthys-1). As the pore size range in mudstones extends from about 10 Å to about 40 µm, the presence of bitumen in the pores of the smallest size selected in this work (100 Å) indicates the onset of hydrocarbon generation, whereas the presence of bitumen in the largest pores (10 µm) indicates a significant pore space saturation and an interpreted onset of hydrocarbon expulsion. For wells in which only SANS data are available, only the onset of hydrocarbon generation (if any) could be determined. 14

32 In a separate measurement using X-ray fluorescence (XRF), the atomic composition of the inorganic rock matrix has been determined for a representative number of samples from every depositional sequence in every well. The organic component of the rock is burnt off during sample preparation for XRF measurements. From the atomic composition, values of scattering length density have been calculated and used in conjunction with the absolutely calibrated SANS/USANS data to determine the pore size distribution for every sample. Then, the variation of pore number density versus depth for several selected pore sizes has been calculated. These data have been used to determine the stability of the pore microstructure versus increased lithostatic load at depth, as well as to detect the possible re-arrangement of the pore space caused by changing rock lithology. Finally, the variation of apparent SANS porosity versus depth has been deduced. The apparent SANS porosity is a proxy for the real geometric porosity. The two porosities are approximately equal if the pore space is filled with gas or formation water. If bitumen is present in the pore space, the apparent SANS porosity is generally smaller than the geometric porosity. In the following numerical analysis, it is assumed that the value of SLD for the substance filling the pore space is small compared with the value of SLD for the inorganic rock matrix. In practical terms this assumption works well for brine, saturated hydrocarbons and gas. In the region of liquid hydrocarbon generation, however, the pore space gets filled (at least partially) with bitumen and the SANS characteristics become anomalous, the measured scattering intensity decreases, calculated pore number density decreases, and the calculated porosity decreases. Such anomalies are closely examined to identify regions of hydrocarbon generation and expulsion. This needs to be done with caution, and in conjunction with other geological and geochemical evidence, as there may be other reasons (e.g. overpressure, lithological and organic matter variations) for locally changed microstructural characteristics of the rock matrix. 3.1 Brewster-1A The pyrolysis data for Brewster-1A is given in Appendix 5 Table A5.1. Figure 3.1 is a compilation of vitrinite reflectance, total organic carbon and the Rock-Eval pyrolysis parameters (Tmax, S 1, S 2, HI and BI) plotted against depth (mkb). Figures 3.2 and 3.3 comprise cross plots of the pyrolysis data by laboratory and by formation, respectively. In addition to the cuttings samples analysed in this study, results of Leco TOC and Rock-Eval pyrolysis analyses were also available from previous work by the Australian Geological Survey Organisation (see ORGCHEM, Geoscience Australia s Oracle-based geochemical database and Robertson Research (1986). The three data sets appear comparable despite different instruments being used, as shown by Figures 3.1 and Drilling Fluids, Contaminants and Migrated Hydrocarbons Brewster-1A was drilled with a water-based drilling mud comprising a brine polymer. The well completion report (Woodside, 1980) documents that diesel was added to the side tracked well at 4464 m. This is at a depth below where the SANS cuttings samples 15

33 were taken in this study. Therefore, contamination of the cuttings samples by diesel should not be an issue. Elevated levels in the S 1 abundance, low Tmax values, and high Production Index (PI) and Bitumen Index (BI) values within these sediments indicate the presence of free hydrocarbons (annotated by the open symbols in Figures 3.1 and 3.2) throughout the Echuca Shoals Formation over the depth range m. Two samples within the Jamieson Formation (at 2800 m and 3225 m) may also contain free hydrocarbons. No hydrocarbon staining is evident in the samples analysed by Robertson Research from the Lower Vulcan and Plover formations, even though diesel was added to the drilling mud when the side tracked well penetrated the Plover Formation. Since these free hydrocarbons occur predominantly within the Echuca Shoals Formation, which is currently within the upper oil window, it is believed that they represent in situ generated hydrocarbons from organic-rich units elsewhere within this formation. Figure 3.1 Depth plots of vitrinite reflectance, TOC and Rock-Eval pyrolysis data for Brewster 1A sediments (HC indicates samples which contain hydrocarbons). Brewster -1A GA sequence (a) (b) (c) 1000 Tertiary Maastrichtian Campanian Santonian- Turonian Jamieson Formation Echuca Shoals Formation Upper Vulcan Formation Depth (m KB) Geotrack Geotrack population 2 Geotrack population 1 Robertson Research CUTT Robertson Research CUTT HC AGSO CUTT AGSO CUTT HC GA CUTT SANS GA CUTT SANS HC Lower Vulcan Fm Plover Fm 4500 Diesel added Diesel added GA sequence VR (%) Tmax ( C) TOC (%) (d) (e) (f) 1000 (g) Tertiary Maastrichtian Campanian Santonian- Turonian Jamieson Formation Echuca Shoals Formation Depth (m KB) Upper Vulcan Formation Lower Vulcan Fm Plover Fm Diesel added Diesel added Diesel added Diesel added S1 (mg/g Rock) S2 (mg/g Rock) HI (mg/g TOC) BI 14/OA/ Source Richness The total organic carbon (TOC) contents of the organic-rich sediments of the Lower Cretaceous Jamieson Formation are fair to good, ranging from % (average 16

34 TOC = 0.9 %). The Lower Cretaceous Echuca Shoals Formation source rocks have higher organic richness (range = %; average TOC = 2.1 %; Fig. 3.3). The potential yields of the Jamieson Formation sediments are poor (average S 1 +S 2 = 1.3 mg hydrocarbons/g rock; Fig. 3.3). The Echuca Shoals source rocks (excluding those samples with apparent free hydrocarbons in them) have slightly higher potential yields (average S 1 +S 2 = 2.7 mg hydrocarbons/g rock; Fig. 3.3) Source Quality, Kerogen Type and Maturity Source rock quality is measured by the Hydrogen Index (HI). The Jamieson and Echuca Shoals formation sediments have HI values ranging from 26 to 160 mg hydrocarbons/ g TOC (average = 112 mg hydrocarbons/g TOC and 105 mg hydrocarbons/g TOC, respectively) which indicates that they are presently predominantly gas-prone (Fig. 3.3). The cross plot of HI versus Tmax is routinely used to depict both the type of kerogen present in a source rock and its maturity. Figure 3.3 shows that the Jamieson and Echuca Shoals formation sediments contain Type III to Type IV kerogen. Petrographic analyses (Woodside, 1980) show that the kerogen is predominantly inertinite in the samples analysed. Figure 3.2 TOC and Rock-Eval pyrolysis cross plots for Brewster 1A sediments (HC indicates samples which contain hydrocarbons). (a) Brewster -1A Poor Fair Good Very good (b) S 1-depletion by h/c expulsion Condensate window S1 + S2 (mg/g Rock) Oil Gas Very good Good Tmax ( C) Oil window Fair Immature S 1-enrichment by Poor H/C migration or contamination 14/OA/ TOC (%) Production Index Robertson Research CUTT Robertson Research CUTT HC AGSO CUTT AGSO CUTT HC GA CUTT SANS GA CUTT SANS HC 17

35 There is a significant discrepancy in the vitrinite reflectance values obtained by the two laboratories Robertson Research and Geotrack (Fig. 3.1). Maturity estimates from the Tmax values places the samples closer to the vitrinite reflectance curve of Geotrack than that of Robertson Research. Therefore, the Jamieson Formation sediments are presently believed to be within the early to peak oil window and the Echuca Shoals Formation sediments are within the upper oil window. The Upper and Lower Vulcan formations are currently within the wet gas window and the Plover Formation sediments are within the dry gas window. These sediments may have generated liquid hydrocarbons in the past, hence, their present source potential is not discussed. Of note is that the highest gas readings in the well were encountered within the Lower Vulcan Formation (4285 m m) Analysis of SANS and USANS data Small Angle Neutron Scattering (SANS) and Ultra Small Angle Scattering (USANS) analyses were performed on 22 claystone cuttings from the well Brewster-1A (Table A1.5 in Appendix 2). These cuttings were collected at 50 m to 100 m intervals between depths 2450 mrt to 4235 mrt. Figure 3.4 shows the original SANS data presented in the standard manner: scattering intensity, I(Q) in absolute units, versus the scattering vector Q. Figure 3.5(a-d) illustrates that there is a significant and systematic variation of the scattering intensity with depth. This variation is clearly pore-size-dependent, as shown in Figure 3.5(a-d) for four Q-values of Å -1, Å -1, Å -1 and Å -1, which correspond to four pore sizes of 0.01 µm +/-50%, 0.1 µm +/-50%, 1 µm +/-50% and 10µm +/-50%, respectively. (1 Å = m; 1 µm = 1000 nm = 10,000 Å). In Brewster-1A there are two depth intervals which contain bitumen in the small pores, interpreted as evidence for the onset of hydrocarbon generation: the upper Jamieson Formation and the Echuca Shoals Formation. The characteristic <-shaped intensity curve for the upper Jamieson Formation becomes less accentuated (shallower) for the largest pores (Figure 3.5(a-d)). This indicates that there is not enough hydrocarbon volume generated within the source rock to saturate the largest pores as the bitumen is successively replacing the brine from smaller pores toward the larger ones. This microscopic finding is consistent with the relatively marginal global values of TOC and the early to peak oil window maturity estimate in the Jamieson Formation source rocks (sections and 3.1.3). Within the Echuca Shoals Formation, there is a clear-cut pore-size-dependence of the depth at which the hydrocarbon generation peak is observed, followed, at greater depths, by the oil-to-gas cracking process. For the smallest pore sizes (Figure 3.5(a)), the bitumen saturation signature is strongest at depths near the base of the Jamieson Formation at about 3860 m. As the pore size increases, the position of the bitumen saturation peak shifts upwards through the mid-formation to the top of the Echuca Shoals Formation near the depth of 3500 m (Figure 3.5 (b-d)). Given the vitrinite reflectance values of the order of 1.2% to 1.4% in the mid-formation and at the base, 18

36 respectively, it is most likely that the upward shift of the intensity <-curve is caused by the process of oil-to-gas cracking preferentially taking place in larger pores. Figure 3.3 TOC and Rock-Eval pyrolysis cross plots for selected sediments in Brewster-1A. (a) Brewster -1A Poor Fair Good Very good (b) S 1-depletion by h/c expulsion Condensate window S1 + S2 (mg/g Rock) Oil Gas Very good Good Tmax ( C) Oil window Fair Poor Immature S 1-enrichment by H/C migration or contamination 14/OA/ TOC (%) Production Index (c) 800 I VR = 0.5% Hydrogen Index (mg HC/g TOC) present day II Oil Oil + Gas immature early mature VR = 0.8% Jamieson Formation Echuca Shoals Formation Lower Vulcan Formation Plover Formation 200 Gas + Oil VR = 1.35% 100 Gas III Tmax ( C) mature over mature Figure 3.1(a) illustrates the variation of vitrinite reflectance with depth, based on data provided in the Well Completion Report. These values were used in Figure 3.5 to provide a conventional indication of source rock maturity at various depths. There 19

37 are two sets of data provided by two different laboratories (Robertson Research and Geotrack) which are grossly incompatible within the depth interval 3000 m to 4500 m. As discussed in section 3.1.3, the Geotrack data appear to be closer to maturity estimates based on Tmax values than the Robertson Research data. Figure 3.6 illustrates the calculated values of SLD versus depth for the inorganic component of the rock matrix in Brewster-1A. There is little variation (at most 5%) with depth and, consequently, the average value of SLD = 4.11x10 10 cm -2 was used in subsequent calculations for Brewster-1A. The pore size distributions calculated for various depths from the full SANS/USANS curves (Figure 3.7) indicate that there is little variation of the geometry of the pore space with depth. A detailed analysis of the variation of pore number density (proportional to the pore size distribution) with depth for four pore sizes 0.01µm, 0.1 µm, 1µm and 10µm, indicates a systematic slight compaction with depth throughout the Jamieson Formation and the Echuca Shoals Formation for the smallest pore size, and compaction within the Jamieson Formation followed by expansion in the Echuca Shoals Formation for the larger pore size (Figure 3.8). It appears that the onset of the expansion interval for the larger pores coincides with the "K Aptian sandstone member" (3250 to 3311 mrt) of distinct log characteristics and changed lithology (Figure 3.9), intersected near the base of Jamieson Formation. The smooth and only slight variation of the pore number density with depth indicates both a uniform lithology and mechanical stability of the inorganic rock matrix with depth. Figure 3.9 illustrates calculated porosity (for the very large fraction of total porosity within the pore size range 20 Å to 20 µm) versus depth. Apparent SANS porosity has been computed by adding pore volumes obtained by fitting the combined SANS/ USANS scattering intensity curve using an assumption that all pores are filled with a fluid of low scattering length density, like brine, gas or saturated hydrocarbons. Therefore, the calculated SANS porosity values for depths where pores are filled with bitumen are too low. The apparent SANS porosity values for Brewster-1A lie between 7% and 16%, with a maximum within the Jamieson Formation and at the base of the Echuca Shoals Formation (Figure 3.9). In this particular case, the log porosity of 12% reported in WCR within the 3250 m 3311 m depth interval at the base of the Jamieson Formation remains in good agreement with the SANS/USANS apparent porosity of 13%. Depth intervals characterised by changed conditions are indicated on the left hand side of the figure. The "K Aptian sandstone member" (3250 m to 3311 m) is characterised by a weak gamma ray signal and low penetration rate. Increased mud density was used throughout the Echuca Shoals Formation, which is indicative of overpressure. The depth interval 4335 m to TD at 4703 m (not sampled by SANS) recorded particularly high levels of gas. Significance for hydrocarbon generation The size of the pores found in claystones typically ranges from 1 nm to about 40 µm across. Combined SANS and USANS methods can access pore sizes from about 2 nm 20

38 to 20 µm, which covers nearly total porosity. These data can be used to determine all stages of hydrocarbon generation, saturation and expulsion within source rocks. The microstructure of the inorganic rock fabric changes only slightly throughout the entire depth range studied by SANS in Brewster-1A (Figure 3.7). Therefore, the marked variation of the scattering intensity for all sizes (Figure 3.5) is ascribed to the change of the chemical composition of the organic matter contained in the pores, which affects the neutron scattering contrast. As discussed, in Brewster-1A there are two depth intervals which clearly indicate the presence of bitumen in small pores, interpreted as the evidence of the onset of hydrocarbon generation: the upper Jamieson Formation and the Echuca Shoals Formation. The characteristic <-shape SANS intensity pattern within the upper Jamieson Formation indicates progressive cracking of bitumen to mobile hydrocarbons and migration of hydrocarbons to larger pores with increasing depth within the formation. The largest pores, however, do not appear to be fully saturated which indicates that the upper Jamieson Formation claystones are too organically lean to expel hydrocarbons and become an effective source rock. The average scattering intensity near the top of the Echuca Shoals Formation appears to exhibit a discontinuity when compared to the adjacent region in the Jamieson Formation, which indicates that there is no communication between the pore spaces of these two sedimentary units. Mud weights indicate overpressuring of the Echuca Shoals Formation (Figure 3.9), which suggests that bitumen and other generated hydrocarbons remain trapped within the formation. For the smallest pore size, the trend of decreasing intensity throughout the Echuca Shoals Formation terminates at a sandstone unit deposited within the depth range m (Figure 3.5(a). This might indicate that the sandstone reservoirs mobile hydrocarbons generated within the basal Echuca Shoals Formation. However, the upward shift of the intensity <-shape observed for larger pores (Figure3.5(b-d)) suggests another scenario. Given the vitrinite reflectance values of the order of 1.2% to 1.4% in the mid-formation and at the base, respectively, it is most likely that the upward shift of the intensity <-curve is caused by the process of oil-to-gas cracking preferentially taking place within the larger pores. As the oil-to-gas cracking process occurring in restricted volume regions results in a markedly increased pressure of the reaction products, it would indeed be accelerated in such microstructural environments that can facilitate the release of the extra pressure. Therefore, cracking within the larger pores, which are connected to the outside of the relatively tight claystone matrix of the source rock, can occur at lower temperatures than in the smaller, less easily accessible pores. The set of SANS/USANS results presented in Figure 3.5(a-d) is the first direct evidence for the pore size specificity of the oil-to-gas cracking process in the natural environment and has global implications for the modelling of the hydrocarbon generation kinetics. The USANS results presented in Figure 3.5 (d) show the progressive generation of mobile hydrocarbons within the larger pore network of the upper and lower Jamieson and Echuca Shoals formations (increasing scattering intensity trends). The very rapid increase in scattering intensity in the lower Echuca Shoals Formation is interpreted 21

39 to mark the onset of gas expulsion. As illustrated in Figure 3.5 (e), this interpretation agrees well with the onset of gas expulsion from the geohistory model. Both data sets indicate that all of the source rocks sampled at Brewster-1A are too lean to expel liquid hydrocarbons. It has been pointed out by one of the referees (Dr Chris Boreham) that an alternative interpretation is possible. It is based on an observation that organic matter with vitrinite reflectance values of % may not be mature enough for oil-to-gas cracking to occur and the gas detected by SANS in the pore space might have migrated from deeper, more mature sediments and displaced the liquid hydrocarbons generated in situ. Dr Boreham is also of the opinion that the process of gas-to-oil cracking would be more effective in the small rather than large pores due to greater exposure to heterogeneous catalysis. Figure 3.4. SANS absolute intensity curves for samples of cuttings from Brewster-1A. (a): 11 samples (claystones, 5 m interval each), depth range 2450 m to 2950 m. Figure 3.4(a) Brewster-1A (SANS & USANS) Scattering intensity versus Q for various depths part 1: 2450 m to 2950 m SCATTERING INTENSITY (cm -1 ) m 2500m 2600m 2700m 2750m 2800m 2850m 2900m 2950m SCATTERING VECTOR Q (Å -1 ) 22

40 The relatively low scattering intensity at a depth of 4230 m within the Upper Vulcan Formation indicates that the pores contain significant amount of organic matter with a very low hydrogen-to-carbon ratio. Figure 3.4. SANS absolute intensity curves for samples of cuttings from Brewster-1A. (b): 9 samples (claystones, 5 m interval each), depth range 3000 m to 3600 m. Figure 3.4(b) Brewster-1A (SANS & USANS) Scattering intensity versus Q for various depths part 2: 3000 m to 3600 m SCATTERING INTENSITY (cm -1 ) m 3050m 3100m 3150m 3200m 3325m 3390m 3500m 3600m SCATTERING VECTOR Q (Å -1 ) 23

41 Figure 3.4. SANS absolute intensity curves for samples of cuttings from Brewster-1A. (c): 4 samples (claystones, 5 m interval each), depth range 3695 m to 4230 m. Figure 3.4(c) Brewster-1A (SANS & USANS) Scattering intensity versus Q for various depths part 3: 3695 m to 4230 m SCATTERING INTENSITY (cm -1 ) m 3800m 3850m 4230m SCATTERING VECTOR Q (Å -1 ) 24

42 Figure 3.5. SANS intensity versus depth at four Q-values of (a) Å -1, (b) Å -1, (c) Å -1, and (d) Å -1, which corresponds to four pore sizes of 0.01 µm +/-50%, 0.1 µm +/-50%, 1 µm +/-50% and 10 µm +/-50%, for cuttings samples from Brewster-1A. (a) DEPTH (mrt) vitrinite reflectance: RR KV 0.46% 0.59% 0.61% 0.54% 0.68% ONSET 0.73% 0.80% 0.82% 0.92% 0.89% 0.54% 0.89% 1.17% 1.19% 1.37% 0.52% 1.05% 1.03% permeability or kinetics barrier Gas Sst ONSET ONSET 0.01 µ m (100Å) JAMIESO N ECHUCA SHOALS UPPER 1.65% 1.34% VULCAN % LOWE R PLOVER SCATTERING INTENSITY AT Q=0.025Å -1 (cm -1 ) 25

43 (b) m (1000Å) JAMIESON 3000 DEPTH (mrt) 3500 ECHUCA SHOALS 4000 Gas Sst 3940m 4173m UPPER VULCAN 4500 LOWE R PLOVER SCATTERING INTENSITY AT Q=0.0025Å -1 (cm -1 ) (c) m JAMIESON 3000 permeability or kinetics barrier DEPTH (mrt) 3500 ECHUCA SHOALS m Gas Sst 4173m UPPER VULCAN 4500 LOWER PLOVER SCATTERING INTENSITY AT Q= Å -1 (cm -1 ) 26

44 (d) m JAMIESON 3000 DEPTH (mrt) 3500 permeability or kinetics barrier ECHUCA SHOALS 4000 Gas Sst 3940m 4173m UPPER VULCAN 4500 LOWER PLOVER SCATTERING INTENSITY AT Q= Å -1 (cm -1 ) Figure 3.5(e) Comparison of USANS scattering intensity trends with modelled kerogen transformation (TR Transformation Ratio) and in-situ gas/oil generation and expulsion derived from geohistory and thermal history analysis for Brewster-1A. The good match between the measured Tmax values with the modelled Tmax trend indicates that the thermal and kerogen kinetics models are consistent with the observed pyrolysis data for this well Modelleded Source Rocks TR Tmax Volume (bbl equiv/m 2) µm µ Robertson Research Geoscience Australia Modelled Tmax Gas (in situ) Gas (expelled) Oil light (in situ) Oil light (expelled) U Jamieson M Jamieson L Jamieson DEPTH (mrt) 3500 U Echuca L Echuca Gas Sst 3940m 4173m U Vulcan L Vulcan 8C L Vulcan 8A SCATTERING INTENSITY AT Q= Å -1 (cm -1 ) 27

45 Figure 3.6. Variation of the Scattering Length Density (SLD) with depth for Brewster-1A. SLD values were calculated from the elemental composition as determined by a separate X-ray Fluorescence (XRF) measurement. Brewster-1A, Browse Basin Scattering length density versus depth DEPTH (m) SCATTERING LENGTH DENSITY (x10 10 cm -2 ) 28

46 Figure 3.7. Pore size distribution at various depths for samples of cuttings from Brewster-1A. (a): 11 samples (claystones, 5 m interval each), depth range is 2450 m to 3055 m. (b): 11 samples (claystones, 5m interval each), depth range 3100 m to 4235 m. (a) PORE SIZE DITRIBUTION DENSITY f(r) m 2500m 2600m 2700m 2750m 2800m 2850m 2900m 2950m 3000m 3050m PORE SIZE (Å) 29

47 (b) PORE SIZE DITRIBUTION DENSITY f(r) m 3150m 3200m 3325m 3390m 3500m 3600m 3695m 3800m 3850m 4230m PORE SIZE (Å) 30

48 Figure 3.8. Variation of the pore number density for four selected pore sizes versus depth for Brewster-1A. Note the slight decrease of the pore number density with depth, indicative of compaction. For full discussion see text. (c) 2000 r= 10 m 1 m 0.1 m 0.01 m JAMIESON DEPTH (mrt) ECHUCA SHOALS UPPER VULCAN 4500 LOWER PLOVER PORE NUMBER DENSITY 31

49 Figure 3.9. Variation of apparent porosity with depth for Brewster-1A. For discussion see text changed lithology: gamma ray & penetration rate log porosity 12% 3000 JAMIESON DEPTH (mrt) m 3311m K apt Sst increased mud density ECHUCA SHOALS 4000 Gas Sst UPPER VULCAN 4280m m LOWER TD 4703m high gas readings PLOVER CALCULATED SANS POROSITY (%) 32

50 3.2 Carbine-1 The pyrolysis data for Carbine-1 is given in Appendix 5 Table A5.2. Figure 3.10 is a compilation of total organic carbon and the Rock-Eval pyrolysis parameters (Tmax, S 1, S 2 and HI) plotted against depth (mrt). Figures 3.11 and 3.12 comprise cross plots of the pyrolysis data by laboratory and by formation, respectively. No other data was available for this well Drilling Fluids, Contaminants and Migrated Hydrocarbons Carbine-1 was drilled with a water-based drilling mud comprising a brine polymer, therefore contamination of the cuttings samples should not be an issue. Out of the seven Lower Cretaceous samples analysed from this well, four samples have anomalously low Tmax values, and slightly elevated S 1, Production Index (PI) and Bitumen Index (BI) values, indicating the presence of naturally occurring free hydrocarbons within the Jamieson Formation, as annotated by the open symbols in Figures 3.10 and At this location, all of the Lower Cretaceous sediments analysed are immature for hydrocarbon generation, therefore it is believed that these free hydrocarbons are evidence of migration along more permeable zones from more mature sediments Source Richness Only one sample from 1388 m depth in the Jamieson Formation is considered to be a potential source rock and does not contain any migrated hydrocarbons. The other four samples analysed from this formation appear to have higher S 1 values than could have been generated from the amount and type of organic matter held within the rock. The sample from 1388 m has a good total organic carbon content (1.6 %) but its potential yield is poor (S 1 +S 2 = 1.9 mg hydrocarbons/g rock; Fig. 3.12). The Echuca Shoals sediments have very similar total organic carbon contents (average TOC = 1.7 %) and potential yields (average S 1 +S 2 = 1.7 mg hydrocarbons/g rock) to the Jamieson Formation Source Quality, Kerogen Type and Maturity The Jamieson and Echuca Shoals formation sediments have HI values ranging from between 83 and 118 mg hydrocarbons/g TOC (average = 118 mg hydrocarbons/g TOC and 95 mg hydrocarbons/g TOC, respectively) which indicates that they contain Type III kerogen, being at best gas-prone. However, they are presently immature for hydrocarbon generation to occur (Fig. 3.12). 33

51 Figure 3.10 Depth plots of TOC and Rock-Eval pyrolysis data for Carbine-1. Carbine -1 WRC sequence Borde Marl Puffin Sandstone Fenelon Fm Jamieson Fm Echuca Shoals Formation (g) (b) (c) Depth (m KB) VR (%) Tmax ( C) TOC (%) WRC sequence Borde Marl Puffin Sandstone Fenelon Fm Jamieson Fm Echuca Shoals Formation (d) (e) (f) Depth (m KB) S1 (mg/g Rock) S2 (mg/g Rock) 0 14/OA/ HI (mg/g TOC) GA CUTT GA CUTT HC 34

52 Figure 3.11 TOC and Rock-Eval pyrolysis cross plots for Carbine-1 sediments (a) Carbine -1 Poor Fair Good Very good (b) S 1-depletion by h/c expulsion Condensate window S1 + S2 (mg/g Rock) Oil Gas Very good Good Tmax ( C) Oil window Fair Immature S 1-enrichment by Poor H/C migration or contamination 14/OA/ TOC (%) Production Index GA CUTT SANS GA CUTT SANS HC 35

53 Figure 3.12 TOC and Rock-Eval pyrolysis cross plots for selected sediments in Carbine-1. (a) Carbine -1 Poor Fair Good Very good (b) S 1-depletion by h/c expulsion Condensate window S1 + S2 (mg/g Rock) Oil Gas Very good Good Tmax ( C) Oil window Fair Immature S 1-enrichment by Poor H/C migration or contamination 14/OA/ TOC (%) Production Index (c) 800 I VR = 0.5% Hydrogen Index (mg HC/g TOC) present day II Oil Oil + Gas immature early mature VR = 0.8% Jamieson Formation Echuca Shoals Formation 200 Gas + Oil VR = 1.35% Gas 100 III Tmax ( C) mature over mature 36

54 3.2.4 Analysis of SANS data Small Angle Neutron Scattering (SANS) analysis was performed on 7 claystone and silty claystone cuttings from the well Carbine-1 (Table A1.6 in Appendix 2). These cuttings were collected at about m intervals between depths 1349 m to 1559 m. Figure 3.13 shows the original SANS data presented in the standard manner: scattering intensity, I(Q) in absolute units, versus the scattering vector Q. Except for the out-lying (shallowest) sample at a depth of 1349 m, there is a significant and systematic variation of the scattering intensity with depth. This is illustrated in Figure 3.14 for scattering intensity measured at Q=0.01 Å -1, which corresponds to a pore size of about µm +/-50% (1 Å = m; 1 µm = 1000 nm = 10,000 Å). The scattering intensity slightly decreases by a factor of 1.2 within the depth range 1388 m to 1478 m in the Jamieson Formation, followed by an apparent sharp decrease by a factor of 1.5 to the Echuca Shoals Formation and thereafter remains relatively constant at a low value down to the TD depth of 1561 m. According to the Interpreted Lithology section of the Formation Evaluation Log provided by Santos, the sample of cuttings collected within the depth range m may contain a significant amount of sandstone (cavings?). Consistent lithology is a prerequisite for a successful identification of hydrocarbon generation zones from SANS data. Therefore, results for this sample are shown but treated as anomalous and not taken into account when discussing trends. Figure 3.15 illustrates the calculated values of SLD versus depth for the inorganic component of the rock matrix in Carbine-1. There is little variation (at most 5%) with depth and, consequently, the average value of SLD = 4.38x10 10 cm -2 was used in subsequent calculations for Carbine-1. The pore size distributions calculated for various depths from the full SANS curves (Figure 3.16) indicate that there is little variation of the geometry of the pore space with depth. A detailed analysis of the variation of pore number density (proportional to the pore size distribution) with depth for three pore sizes 100 Å, 316 Å and 630 Å indicates a systematic and significant compaction with depth, but otherwise a consistent pore size distribution in the claystones throughout the Jamieson Formation and Echuca Shoals Formation (Figure 3.17). Figure 3.18 illustrates calculated porosity (only for the fraction of total porosity within the pore size range 20 Å to 1000 Å) versus depth. Most of the values are between 2.5% and 5%, with a maximum within upper Jamieson Formation. Although the general trend of decreasing porosity with depth is consistent both with general expectation and data presented in Figure 3.17, the calculated SANS porosity values need to be calibrated against the log porosities. Gas readings were fairly high throughout the depth interval 1360 m to 1561 m. 37

55 Significance for hydrocarbon generation The size of the pores found in claystones typically ranges from 1nm to about 40 µm across. SANS experiments can access pore sizes at the lower end of this range, from about 2 nm to 100 nm, which typically comprise about 30% of total porosity. These data can be used to determine the early stages of hydrocarbon generation and saturation within source rocks. Owing to significant compaction, the microstructure of the inorganic rock fabric also changes significantly throughout the depth range studied by SANS in Carbine-1 (Figures 3.17, 3.18). For the pore size 316 Å, the pore number density decreases by a factor of about 2 within the depth range of m (Figure 3.17). The SANS intensity for a similar pore size of 250 Å decreases by a similar factor of 1.8 within the same depth range (Figure 3.14). The cause of the apparent marked change in SANS intensity at the top of the Echuca Shoals Formation is not fully understood. Therefore, it is likely that the observed variation of SANS intensity with depth is dominated by the compaction of the inorganic rock matrix. There is no strong indication of progressive bitumen generation and/or cracking. The strong deformation of inorganic matrix with depth observed by SANS in Carbine-1 is unusual since these samples are considerably shallower than other samples previously examined by SANS. This deformation with depth is attributed to normal compaction. 38

56 Figure SANS absolute intensity curves for samples of cuttings from Carbine-1. Data are shown for seven samples (nominally claystones and silty slaystones, 3 m interval each). Depth range is 1349 m to 1559 m Figure 3.13 Carbine-1 Scattering intensity versus Q for various depths 1349m to 1559m SCATTERING INTENSITY (cm -1 ) m m m m m m m SCATTERING VECTOR Q (Å -1 ) 39

57 Figure SANS intensity versus depth at Q=0.01 A -1 (corresponding to the pore size 25 nm +/-50%, or µm +/-50%) for cuttings samples from Carbine m (250Å) 1300 PUFFIN SANDSTONE DEPTH (mrt) FENELON JAMIESON ECHUCA SHOALS SCATTERING INTENSITY AT Q=0.01Å -1 (cm -1 ) 40

58 Figure Variation of the Scattering Length Density (SLD) for thermal neutrons with depth for Carbine-1. SLD values were calculated from the elemental composition as determined by a separate X-ray Fluorescence (XRF) measurement. Carbine 1, Browse Basin Scattering length density versus depth DEPTH (m) SCATTERING LENGTH DENSITY (x10 10 cm -2 ) 41

59 Figure Pore size distribution at various depths for samples of cuttings from Carbine-1. Seven samples (nominally claystones and silty claystones, 3 m interval each), depth range is 1349 m to 1559 m. PORE SIZE DITRIBUTION DENSITY f(r) m m m m m m m PUFFIN SANDSTONE FENELON JAMIESON ECHUCA SHOALS PORE SIZE (Å) 42

60 Figure Variation of the pore number density for selected pore sizes versus depth for Carbine-1. Note the significant decrease of the pore number density with depth, indicative of compaction. For full discussion see text r = 630Å 316Å 100Å PUFFI N SANDSTONE DEPTH (mrt) JAMIESON ECHUCA SHOALS PORE NUMBER DENSITY 43

61 Figure Variation of apparent porosity (within the pore size range 2 nm to 100 nm) with depth for Carbine-1. For discussion see text PUFFI N SANDSTONE m DEPTH (mrt) increased gas reading JAMIESON ECHUCA SHOALS TD 1561m CALCULATED SANS POROSITY (%) 3.3 Adele-1 The pyrolysis data for Adele-1 is given in Appendix 5 Table A5.3. Figure 3.19 is a compilation of vitrinite reflectance, total organic carbon and the Rock-Eval pyrolysis parameters (Tmax, S1, S2 and HI) plotted against depth (mrt). Figures 3.20 and 3.21 comprise cross plots of the pyrolysis data by laboratory and by formation, respectively. In addition to the cuttings samples analysed in this study, results of Leco TOC and Rock-Eval pyrolysis analyses were also available in the well completion report (Shell Development Australia, 1999) carried out on SWCs by Geotechnical Services, and vitrinite reflectance measurements were made by Kieraville Konsultants. There is no mention in the WCR that the SWC samples were washed or extracted using water or organic solvents Drilling Fluids, Contaminants and Migrated Hydrocarbons Adele-1 was drilled with a water-based drilling mud with gel and polymer additives to a depth of 2560 m. Below this depth potassium chloride, PHPA and glycol was used to the bottom of the well. All of the cuttings samples analysed are contaminated with glycol 44

62 additives, and hence they were extracted with methanol and dichloromethane (90:10) as part of the preparative procedure. In the WCR there is no mention that the SWC samples were washed or extracted. From the reported values for S 1, it is surmised that these samples have not been solvent washed. Nevertheless, these samples do not appear to be affected by glycol contamination since the Tmax values are not depressed with respect to the extracted cuttings samples. With the possible exception of the shallowest SWC and deepest two SWC samples, migrated or contaminant hydrocarbons are not evident in the SWC samples from the Jamieson and Echuca Shoals formations in Adele-1 (Fig. 3.19). The samples suspected of containing free hydrocarbons are shown by the open symbols in Fig Of note, petrographic analyses of a SWC sample from 4130 m (within the Echuca Shoals Formation) reported that this sample contained possible oil drops that appear to be in artificial composites and may represent contamination. 45

63 Figure 3.19 Depth plots of vitrinite reflectance, TOC and Rock-Eval pyrolysis data for Adele-1. Adele -1 GA sequence (a) (b) (c) 1000 Tertiary 1500 Maastrichtian Campanian 2000 Santonian - Turonian Jamieson Formation Depth (m KB) Echuca Shoals Formation Vulcan Formation Plover Formation VR (%) Tmax ( C) TOC (%) GA sequence (d) (e) (f) 1000 Tertiary 1500 Maastrichtian Campanian 2000 Invalid data Santonian - Turonian Jamieson Formation Depth (m KB) Echuca Shoals Formation Vulcan Formation Plover Formation S1 (mg/g Rock) S2 (mg/g Rock) 0 14/OA/ HI (mg/g TOC) Kieraville SWC Geotech SWC Geotech SWC HC GA CUTT SANS extracted 46

64 3.3.2 Laboratory Comparisons In general, the TOC content for the extracted cuttings samples tends to be slightly higher than the SWCs over the depth range analysed (Fig. 3.19). This may be due to the cuttings samples being homogenised compared with the SWC samples, or it may be an artifact introduced from residual glycol contaminants. There are some significant differences in the pyrolysis data between the SWC and extracted cuttings samples. The S 1 abundances of the extracted cuttings samples are invalid because any naturally occurring free hydrocarbons (as well as contaminants) are removed during the extraction process, therefore only the S 1, BI and PI values from the SWCs can be interpreted. The S 2 values of the extracted cuttings samples are less than those of the SWC samples (~1 mg hydrocarbons/g rock) which, combined with the apparent higher TOC values, results in their much lower HI values over the depth range analysed. Since the kerogen in the rock is unaffected by the solvent extraction process, the S 2 abundance should be similar for both the cuttings and SWC samples at the same depth. It is difficult to explain this discrepancy but it may be due to the different instruments used or that some contamination is present in the SWCs causing an increase in S 2 and HI, which is not apparent in the TOC results. Despite the abundance of the S 2 peak being less for the cuttings samples than the SWC samples, the derived Tmax values are comparable between the datasets Source Richness The total organic carbon (TOC) contents of the organic-rich sediments of the Lower Cretaceous Jamieson Formation are consistently fair, ranging from % (average TOC = 1.4%; Fig. 3.21). The Lower Cretaceous Echuca Shoals Formation source rocks have more varied but overall similar organic richness (range = %; average TOC = 1.3%). The potential yields of the Jamieson Formation sediments are poor (average S 1 +S 2 = 2.7 mg hydrocarbons/g rock), whereas some of the Echuca Shoals sediments have fair potential yields (S 1 +S 2 = 3.1 mg hydrocarbons/g rock) Source Quality, Kerogen Type and Maturity The Jamieson Formation and Echuca Shoals Formation SWC sediments have similar HI values ranging from between 125 and 270 mg hydrocarbons/g TOC (average = 186 mg hydrocarbons/g TOC and 188 mg hydrocarbons/g TOC, respectively) which indicates that they are presently predominantly gas and condensate-prone. Of note is that the HI values from the extracted cuttings samples are somewhat lower (Fig. 3.21). Conventional interpretation of pyrolysis data would imply that samples which have HI values greater 200 mg hydrocarbons/g TOC have the capacity to generate oil. However, in the case of the majority of samples from both the Jamieson and Echuca Shoals formations in Adele-1, their corresponding TOC contents are typically less than 2 %. At these low-to-moderate TOC levels, any generated oil will probably remain within the source rock and expulsion will not occur until it is substantially cracked to gas at higher maturities. 47

65 Figure 3.21 shows that the Jamieson Formation and Echuca Shoals Formation sediments both contain Type II/III kerogen. A petrographic analysis of a SWC sample from 2580 m in the Jamieson Formation reports that lamalginite, a hydrogen-rich maceral, is common. The maceral assemblage in the majority of the Jamieson Formation sediments is dominated by liptodetrinite (fragments of spores, cuticles etc) with lesser amounts of inertinite, and vitrinite is a rare occurrence. Presently, the Jamieson Formation is immature for hydrocarbon generation, the Echuca Shoals Formation is within the oil window, and the Upper Vulcan Formation is at peak oil generation. Figure 3.20 TOC and Rock-Eval pyrolysis cross plots for Adele-1 samples. (a) Adele -1 Poor Fair Good Very good (b) S 1-depletion by h/c expulsion Condensate window S1 + S2 (mg/g Rock) Oil Gas Very good Good Tmax ( C) Oil window Invalid data 4 Invalid data Fair Geotech SWC 430 Immature 2 S 1-enrichment by Poor H/C migration or contamination 14/OA/ TOC (%) Production Index Geotech SWC HC GA CUTT SANS extracted 48

66 Figure 3.21 TOC and Rock-Eval pyrolysis cross plots for selected samples from Adele-1. (a) Adele -1 Poor Fair Good Very good (b) S 1-depletion by h/c expulsion Condensate window S1 + S2 (mg/g Rock) Oil Gas Very good Good Tmax ( C) Oil window Fair 430 Immature 2 S 1-enrichment by Poor H/C migration or contamination 14/OA/ TOC (%) Production Index Hydrogen Index (mg HC/g TOC) present day (c) II Oil 300 Oil + Gas immature I early mature VR = 0.5% VR = 0.8% Jamieson Formation (SWC) Jamieson Formation (CUTT extracted) Echuca Shoals Formation (SWC) 200 Gas + Oil VR = 1.35% Gas 100 III Tmax ( C) mature over mature Analysis of SANS data Small Angle Neutron Scattering (SANS) analysis was performed on 19 claystone cuttings from the well Adele-1 (Table A1.2 in Appendix 2). These cuttings were collected at 25 m to 60 m intervals between depths 2530 m to 3405 m throughout the Upper Heywood Formation. 49

67 Figure 3.22 shows the original SANS data presented in the standard manner: scattering intensity, I(Q) in absolute units, versus the scattering vector Q. There is a significant and systematic variation of the scattering intensity with depth. This is illustrated in Figure 3.23 for scattering intensity measured at Q = 0.01Å -1, which corresponds to a pore size of about µm +/-50% (1 Å = m; 1 µm = 1000 nm = 10,000 Å). The scattering intensity decreases and increases twice with depth by a factor within the Upper Heywood Formation (equivalent to the Jamieson Formation) within the depth range 2530 m to 3405 m, forming a characteristic double < pattern. The experimental error of the scattering intensity is of the size of the symbol in Figure Although all the samples used for SANS analysis were described as claystones, the XRF analysis of the shallowest sample (2530 m) reveals the presence of 11.8 wt% of CaO compared to wt% in the remaining four samples analysed by XRF (Table 3.1). Therefore, the data for this sample (and possibly nearby samples) may be anomalous due to a different lithology (calcareous claystone) than for the rest of SANS samples (claystone). Figure 3.19(a) illustrates the variation of vitrinite reflectance with depth, based on data provided in the Well Completion Report. These values were used in Figure 3.23 to provide a conventional indication of source rock maturity at various depths. Figure 3.24 illustrates the calculated values of SLD versus depth for the inorganic component of the rock matrix in Adele-1. There is little variation (at most 3%) with depth and, consequently, the average value of SLD = 4.39x10 10 cm -2 was used in subsequent calculations for Adele-1. The pore size distributions calculated for various depths from the full SANS curves (Figure 3.25) indicate that there is little variation of the geometry of the pore space with depth. A detailed analysis of the variation of pore number density (proportional to the pore size distribution) with depth for three pore sizes 100 Å, 316 Å and 630 Å indicates a systematic slight compaction with depth throughout the Upper Heywood Formation, perhaps with a small anomaly in the depth range m (Figure 3.26). For the largest pore size (630 Å) the compaction is least evident. Figure 3.27 illustrates calculated porosity (only for the fraction of total porosity within the pore size range 20 Å to 1000 Å) versus depth. SANS porosity has been computed by adding pore volumes obtained by fitting the corresponding SANS scattering intensity curve using an assumption that all pores are filled with a fluid of low scattering length density, like brine, gas or saturated hydrocarbons. Therefore, the calculated SANS porosity values for depths where pores are filled with bitumen are too low. The porosity values lie between 2.0% and 4.2%, with maximum values at depths 2530 m, 2885 m and 3380 m. The actual porosity values may not be reliable and need to be calibrated against the log porosities. Depth intervals characterised by changed conditions are indicated on the left hand side of the figure. The K Aptian sandstone member equivalent (3414 m to 3595 m) is composed of interbedded glauconitic sandstone, greensand, calcareous sandstone, argillaceous sandstone, claystone and siltstone. Gas and condensate were 50

68 recovered from the depth of m within this unit. The depth interval 3595 m to TD at 4822 m (Lower Heywood Formation, Upper Swan Formation, Lower Swan Formation, Petrel Formation and Londonderry Formation, all not sampled by SANS) recorded high levels of gas, as indicated in Figure Significance for hydrocarbon generation The size of the pores found in claystones typically ranges from 1nm to about 40µm across. SANS experiments can access pore sizes at the lower end of this range, from about 2 nm to 100 nm, which typically comprise about 30% of total porosity. These data can be used to determine the early stages of hydrocarbon generation and saturation within source rocks. Except for the small anomaly in the depth range m, the microstructure of the inorganic rock fabric changes only slightly throughout the entire depth range of m studied by SANS in Adele-1 (Figures 3.25 and 3.26). Therefore, the marked variation of the scattering intensity with depth (Figure 3.23) is ascribed to the change of the chemical composition of the organic matter contained in the pores, which affects the neutron scattering contrast. As discussed above, the low values of the scattering intensity indicate pores filled with bitumen at the onset of mobile hydrocarbon generation, and the high values pores filled with gas, formation brine and/or saturated hydrocarbons. Based on this, two regions of hydrocarbon generation (at different maturity) can be identified (Figure 3.23): (1) near the top of the Upper Heywood Formation at a depth of about 2630m, possibly affected by the presence of the microstructural anomaly, and (2) within the lower Upper Heywood Formation at a depth of about 3180 m. The two generation regions are separated from each other by a permeability barrier at a depth of about 2780 m. The increasing SANS intensity with depth for the two hydrocarbon generation regions within the Upper Heywood Formation indicates progressive cracking of bitumen to mobile hydrocarbons and migration of the hydrocarbons to larger pores with increasing depth within the formation. The deeper of the two trends of increasing intensity within the Upper Heywood Formation ( m and m) terminates close to a K Aptian sandstone member equivalent unit (3414 m to 3595 m), from which gas and condensate were recovered with a FMT tool at the depth of 3514 m. This provides a strong argument that this trend may represent progressive cracking of bitumen into mobile hydrocarbons and migration of hydrocarbons to larger pores within the K Aptian sandstone member equivalent. The permeability barrier apparent within the Upper Heywood Formation at the depth of 2880 m is likely to impede vertical movement of generated hydrocarbons. 51

69 Table 3.1. XRF raw data for Adele-1. AGSO No Loss on SiO2 TiO2 Al2O3 Fe2O3 MnO MgO CaO Na2O K2O P2O5 SO3 ignition Si Ti Al Fe Mn Mg Ca Na K P S (%) (%) (%) (%) (%) (%) (%) (%) (%) (%) (%) (%) AGSO No Sc V Cr Ni Cu Zn Rb Sr Zr Ba Cl (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm)

70 Figure SANS absolute intensity curves for samples of cuttings from Adele- 1. A: ten samples (claystones, 5 m interval each), depth range 2530 m to 2980 m. B: nine samples (claystones, 5 m interval each), depth range 3030 m to 3405 m Figure 3.22(A) Adele-1 Scattering intensity versus Q for various depths part 1: 2530m to 2980m SCATTERING INTENSITY (cm -1 ) m m m m m m m m m m SCATTERING VECTOR Q (Å -1 ) 53

71 Figure 3.22(B) Adele-1 Scattering intensity versus Q for various depths part 2: 3030m to 3405m 10 5 SCATTERING INTENSITY (cm -1 ) m m m m m m m m m SCATTERING VECTOR Q (Å -1 ) 54

72 Figure SANS intensity versus depth at Q=0.01 A -1 (corresponding to the pore size 25 nm +/-50%, or µm +/-50%) for cuttings samples from Adele Ro=0.52% ONSET calcareous? m (250 Å) 3000 Ro=0.56% Ro=0.53% Ro=0.56% UPPER HEYWOOD (JAMIESON) Ro=0.63% ONSET DEPTH (m) Ro=0.62% Ro=0.67% Ro=0.87% Ro=0.97% LOWER HEYWOOD (ECHUCA SHOALS) UPPER SWAN (UPPER VULCAN) LOWER SWAN (LOWER VULCAN) PETREL (PLOVER) LONDONDERRY (SAHUL / NOME ) SCATTERING INTENSITY AT Q=0.01Å -1 (cm -1 ) 55

73 Figure Variation of the Scattering Length Density (SLD) for thermal neutrons with depth for Adele-1. SLD values were calculated from the elemental composition as determined by a separate X-ray Fluorescence (XRF) measurement. Adele-1, Browse Basin Scattering length density versus depth DEPTH (m) SCATTERING LENGTH DENSITY (x10 10 cm -2 ) 56

74 Figure Pore size distribution at various depths for samples of cuttings from Adele-1. A: ten samples (claystones, 5 m interval each), depth range is 2530 m to 2980 m. B: nine samples (claystones, 5 m interval each), depth range 3030 m to 3405 m. PORE SIZE DITRIBUTION DENSITY f(r) m 2580m 2630m 2680m 2730m 2780m 2830m 2880m 2930m 2980m PORE SIZE (Å) 57

75 PORE SIZE DITRIBUTION DENSITY f(r) m 3080m 3130m 3180m 3220m 3280m 3320m 3380m 3405m PORE SIZE (Å) 58

76 Figure Variation of the pore number density for selected pore sizes versus depth for Adele-1. Note the slight decrease of the pore number density with depth, indicative of compaction. For full discussion see text r = 630Å 316Å 100Å DEPTH (m) UPPER HEYWOOD (JAMIESON) LOWER HEYWOOD (ECHUCA SHOALS) UPPER SWAN (UPPER VULCAN) LOWER SWAN (LOWER VULCAN) PETREL (PLOVER) LONDONDERRY (SAHUL / NOME) PORE NUMBER DENSITY 59

77 Figure Variation of apparent porosity (within the pore size range 2 nm to 100 nm) with depth for Adele-1. For discussion see text m calcareous? DEPTH (m) claystone dominated lithology 3226m claystone & siltstone 3414m m; h/c recovered 3595m correlated to fairly "Kapt sandstone good equivalent" gas readings 4057m strong gas readings 4448m good gas readings UPPER HEYWOOD (JAMIESON) LOWER HEYWOOD (ECHUCA SHOALS) UPPER SWAN (UPPER VULCAN) LOWER SWAN (LOWER VULCAN) PETREL (PLOVER) LONDONDERRY (SAHUL / NOME) m POROSITY (%) 3.4 Argus-1 The pyrolysis data for Argus-1 is given in Appendix 5 Table A5.4. Figure 3.28 is a compilation of vitrinite reflectance, total organic carbon and the Rock-Eval pyrolysis parameters (Tmax, S 1, S 2 and HI) plotted against depth (mrt). In addition to the cuttings samples analysed in this study, results of Leco TOC and Rock-Eval pyrolysis analyses were also available in the well completion report (BHPP, 2001) carried out on SWCs by Geotechnical Services, and vitrinite reflectance measurements were made by Kieraville Konsultants. There is insufficient data to enable an inter-laboratory comparison Drilling Fluids, Contaminants and Migrated Hydrocarbons Argus-1 was drilled with a water-based drilling mud with gel additives to a depth of 2483 m. Below this depth potassium chloride, PHPA and glycol was added to the bottom of the well. Therefore, all of the cuttings samples analysed are contaminated with glycol additives, and hence they were extracted with methanol and 60

78 dichloromethane (90:10) as part of the preparative procedure. In the WCR there is no mention that the SWC samples were washed or extracted. With the exception of one SWC sample, all of the samples from the Jamieson Formation contain free hydrocarbons, as indicated by the exceptionally low Tmax values (< 370 o C off the scale of the graphs in Fig. 3.28). These low values are unreasonable for burial depths of over 4000 m and these hydrocarbons could not have been generated by the organic matter within the sediments. Comparison of the Argus-1 dataset with data from samples with identified free hydrocarbons in the Jamieson Formation at Brewster- 1A and Carbine-1 (both drilled with water-based muds), suggests that the anomalous pyrolysis results originate from the incomplete removal of drilling fluid additives in the samples, rather than the occurrence of bona fide thermogenic hydrocarbons within the sediments. The SWC sample from 4598 m appears to have Tmax and PI values in the range expected for a thermally mature sample, however, it has an anomalously high HI value of 484 mg hydrocarbons/g TOC. This places it outside of the range expected for a mature Type II kerogen, hence glycol contamination is suspected in this sample. Therefore, the quality of the data appears compromised by the addition of additives in the drilling fluid and no source rock interpretation was undertaken Maturity Vitrinite reflectance measurements between 4535 m and m indicate that the Jamieson Formation is within the peak oil to peak wet gas windows (0.85 & 1.13%). 61

79 Figure Depth plots of vitrinite reflectance, TOC and Rock-Eval pyrolysis data for Argus-1 samples. Argus -1 WRC sequence (a) (b) (c) Tertiary Depth (m KB) Most values off scale <370 C Bathurst Island Group Jamieson Formation Echuca Shoals Formation VR (%) Tmax ( C) TOC (%) WRC sequence (d) (e) (f) Tertiary Depth (m KB) Bathurst Island Group Jamieson Formation Echuca Shoals Formation Invalid data S1 (mg/g Rock) S2 (mg/g Rock) /OA/ HI (mg/g TOC) Kieraville SWC Geotech SWC (suspect data) Geotech SWC HC GA CUTT SANS extracted 62

80 3.4.3 Analysis of SANS data Small Angle Neutron Scattering (SANS) analysis was performed on eight nominally claystone cuttings from the well Argus-1 (Table A1.3 in Appendix 2). These cuttings were collected at 25 m to 40 m intervals between depths 4270 mrt to 4535 mrt. A cut of cuttings was used to perform X-ray Fluorescence (XRF) analysis for selected samples (Table 3.2). Figure 3.29 shows the original SANS data presented in the standard manner: scattering intensity, I(Q) in absolute units, versus the scattering vector Q. There is a significant variation of the scattering intensity with depth, well beyond the SANS experimental accuracy of about +/-5% (less than symbol size in Figure 3.29). However, no systematic variation in SANS intensity with depth can be seen within the entire depth range 4270 m to 4535 m. This is illustrated in Figure 3.30 for scattering intensity measured at Q=0.01 Å -1, which corresponds to a pore size of about µm +/-50% (1 Å = m; 1 µm = 1000 nm = 10,000 Å). The scattering intensity fluctuates within the range cm -1 throughout the Jamieson Formation and the top of the Vulcan Formation. Although all the samples obtained from BHP Billiton for SANS analysis have been nominally described as claystones throughout the depth range of 4270 m to 4540 m, the Well Completion Report (WCR) provides detailed information indicating that the actual lithology has a significant calcareous component, gradually decreasing with depth within the depth range 4242 m m (cuttings description) or 4242 m m (sidewall cores description) at the top of the Jamieson Formation. Therefore, the shallowest SANS sample (4270m) is likely to be a calcareous claystone of different lithology than the remaining SANS samples. Although the CaO content in this sample (7.23%) is not much larger than for the remaining two samples analysed by XRF (7.01% and 4.13% for samples at the depths of 4390 m and 4535 m, respectively, Table 3.2), based on geological evidence it is treated as anomalous in the following discussion. Figures 3.28(a) and 3.31 illustrate the variation of thermal maturity of the organic matter with depth, based on the petrology and geochemistry data provided in the Well Completion Report. Standard vitrinite reflectance data are reported only for three samples within the depth range m. Thermal maturity indicators, expressed as vitrinite reflectance equivalent (VRe), have been converted from biomarker data (methylphenantrene index, MPI) obtained from three types of samples: mud-filtrate extracts, condensates and mechanical sidewall core (MDCT) extracts. Given their origin, the VRe data are subject to contamination with the mineral oil base present in the drilling fluid (Liquid New Drill) and are reliable only in the relative sense. Only the petrographic VR values were used in Figure 3.30 to provide a conventional indication of source rock maturity at various depths. Figure 3.32 illustrates the calculated values of SLD versus depth for the inorganic component of the rock matrix in Argus-1. There is little variation (at most 2%) with depth and, consequently, the average value of SLD = 3.99x10 10 cm -2 was used in subsequent calculations for Argus-1. 63

81 The pore size distributions calculated for various depths from the full SANS curves (Figure 3.33) indicate that there is little variation of the geometry of the pore space with depth, perhaps with the exception of the 4270 m sample. A detailed analysis of the variation of pore number density (proportional to the pore size distribution) with depth for three pore sizes 100 Å, 316 Å and 630 Å indicates a systematic slight compaction with depth throughout the Jamieson Formation and the top Vulcan Formation for the two smaller pore sizes, and a steady but more scattered trend for the largest pore size (Figure 3.34). The shallowest sample near the top of Jamieson Formation (4270 m) appears to be anomalous, which is consistent with its different lithology. Figure 3.35 illustrates calculated SANS porosity (only for the fraction of total porosity within the pore size range 20 Å to 1000 Å) versus depth. SANS porosity has been computed by adding pore volumes obtained by fitting the corresponding SANS scattering intensity curve using an assumption that all pores are filled with a fluid of low scattering length density, like brine, gas or saturated hydrocarbons. Therefore, the calculated SANS porosity values for depths where pores are filled with bitumen are too low. The porosity values are about % throughout the Jamieson Formation, except for the sample at the depth of 4310 m which has a porosity of 2.8%. The actual porosity values may not be reliable and need to be calibrated against the log porosities. Significance for hydrocarbon generation The size of the pores found in claystones typically ranges from 1 nm to about 40 µm across. SANS experiments can access pore sizes at the lower end of this range, from about 2 nm to 100 nm, which typically comprise about 30% of total porosity. These data can be used to determine the early stages of hydrocarbon generation and saturation within source rocks. Except for shallowest sample (4270 m), the microstructure of the inorganic rock fabric changes only slightly throughout the entire depth range studied by SANS in Argus-1 (Figures 3.33), perhaps with the exception of the pore size 650 Å, for which a significant scatter is observed (Figure 3.34). The variation of the scattering intensity within the Jamieson Formation for pore size 250 Å (Figure 3.30) does not follow any particular pattern. There is no evidence of progressive cracking of bitumen to mobile hydrocarbons and migration of hydrocarbons to larger pores with increasing depth within the formation. This is consistent with the relatively high thermal maturity of the organic matter within the Jamieson Formation (Figure 3.31). The scattering intensity is generally low, which indicates that the small pores contain significant amount of organic matter with a very low hydrogen-to-carbon ratio, e.g. residual bitumen. 64

82 Table 3.2. XRF data for Argus 1. AGSO No Loss on SiO2 TiO2 Al2O3 Fe2O3 MnO MgO CaO Na2O K2O P2O5 SO3 ignition Si Ti Al Fe Mn Mg Ca Na K P S (%) (%) (%) (%) (%) (%) (%) (%) (%) (%) (%) (%) AGSO No Sc V Cr Ni Cu Zn Rb Sr Zr Ba Cl ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm

83 Figure SANS absolute intensity curves for samples of cuttings from Argus- 1. Eight samples (seven claystones and one calcareous claystone, 5 m interval each), depth range 4270 m to 4535 m Figure 3.29 Argus-1 Scattering intensity versus Q for various depths 4270m to 4535m SCATTERING INTENSITY (cm -1 ) m m m m m m m m SCATTERING VECTOR Q (Å -1 ) 66

84 Figure SANS intensity versus depth at Q=0.01 A -1 (corresponding to the pore size 25 nm +/-50%, or µm +/-50%) for cuttings samples from Argus-1. (a) 0.025µ m 4200 weak gas effect m (250 Å) calcareous? 4400 JAMIESON DEPTH (mrt) vitrinite reflectance: 1.04% 0.85% 1.13% gas column top gas 4672m ECHUCA SHOALS ABSENT VULCAN PLOVER NOT CONFIRMED UNDIFFERENTIATED VOLCANICS TD 4878m SCATTERING INTENSITY AT Q=0.01Å -1 (cm -1 ) 67

85 Figure Vitrinite reflectance and thermal maturity data for extracts and condensates for Argus Figure 3.31 Argus-1 Maturity vs depth VR% - vitrinite reflectance, VRe% - VR equivalent calculated from MPI (methyl phenantrene index) Based on geochemistry and petrography data from WCR SAMPLE DEPTH (mrt) VR% cuttings VRe% filtrate extracts VRe% MSCT extracts VRe% condensates VITRINITE REFLECTANCE (%) 68

86 Figure Variation of the Scattering Length Density (SLD) for thermal neutrons with depth for Argus-1. SLD values were calculated from the elemental composition as determined by a separate X-ray Fluorescence (XRF) measurement. Argus 1, Browse Basin Scattering length density versus depth DEPTH (m) SCATTERING LENGTH DENSITY (x10 10 cm -2 ) 69

87 Figure Pore size distribution at various depths for samples of cuttings from Argus-1. Eight samples (seven claystones and one calcareous claystone, 5 m interval each), depth range is 4270 m to 4535 m. PORE SIZE DITRIBUTION DENSITY f(r) m 4310m 4350m 4390m 4430m 4475m 4510m 4535m JAMIESON ECHUCA SHOALS ABSENT VULCAN PLOVER NOT CONFIRMED UNDIFFERENTIATED VOLCANICS PORE SIZE (Å) 70

88 Figure Variation of the pore number density for selected pore sizes versus depth for Argus-1. Note the slight decrease of the pore number density with depth, indicative of compaction. For full discussion see text r = 630Å 316Å 100Å calcareous? DEPTH (mrt ) JAMIESON 4600 ECHUCA SHOALS ABSENT VULCAN PORE NUMBER DENSITY 71

89 Figure Variation of apparent porosity (within the pore size range 2 nm to 100 nm) with depth for Argus-1. For discussion see text calcareous? DEPTH (mrt) JAMIESON 4600 ECHUCA SHOALS ABSENT VULCAN CALCULATED SANS POROSITY (%) Brecknock South-1 The pyrolysis data for Brecknock South-1 is given in Appendix 5 Table A5.5. Figure 3.36 is a compilation of the total organic carbon and Rock-Eval pyrolysis parameters (Tmax, S 1, S 2 and HI) plotted against depth (mrt). Figure 3.37 comprises a graph of Tmax versus Hydrogen Index for potential source rock samples. The ten samples analysed span the Middle Jurassic-Lower Cretaceous. No additional source rock or maturity information was available for this well or for the near-by Brecknock-1 well. Hence, none of the Plover, Vulcan, Echuca Shoals and Jamieson formations are adequately represented Drilling Fluids, Contaminants and Migrated Hydrocarbons Brecknock South-1 was drilled with a water-based drilling mud with gel, guar gum and Flowzan additives to a depth of 3151 m. Below this depth potassium chloride, PHPA and glycol was used to complete the drilling of this well. Therefore, all of the cuttings samples analysed are contaminated with glycol additives, and hence they were extracted with methanol and dichloromethane (90:10) as part of the preparative procedure. As such, the S 1 values and values produced from calculations using the S 1 peak are unreliable (viz. BI, PI). Since the samples are extracted, the presence of naturally occurring free hydrocarbons cannot be determined. The deepest sample (3995 m), still contains free hydrocarbons/ contaminants despite the extraction process. 72

90 3.5.2 Source Richness Given that there is some doubt as to the quality of the pyrolysis data due to the glycol additive remaining in the samples, and the lack of comparative data in adjacent wells, the following interpretation should be viewed with caution, since such contaminants can lead to an over estimation of hydrocarbon potential and an under estimation of thermal maturity. The total organic carbon (TOC) contents of the two sediments from the Jamieson Formation are fair (average TOC = 0.9%), and good for samples from the Echuca Shoals (average TOC = 1.4% for five samples) and Vulcan (average TOC = 1.3% for two samples) formations. The potential yields of the sediments from Brecknock South-1 cannot be discussed due to the removal of the S 1 peak by the preparative processes used to eliminate the glycol contamination. 73

91 Figure 3.36 Depth plots of TOC and Rock-Eval pyrolysis data for Brecknock South-1. Brecknock South -1 GA sequence (b) 1000 (c) Maastrichtian Campanian Santonian - Turonian Jamieson Formation Echuca Shoals Formation Vulcan Formation Plover Formation Depth (m KB) Top Bottom Tmax ( C) TOC (%) GA sequence (d) (e) (f) Maastrichtian Campanian Santonian - Turonian Jamieson Formation Echuca Shoals Formation Vulcan Formation Depth (m KB) Top Plover Formation Invalid data Bottom S1 (mg/g Rock) S2 (mg/g Rock) 0 14/OA/ HI (mg/g TOC) GA CUTT SANS extracted GA CUTT SANS extracted HC 74

92 3.5.3 Source Quality, Kerogen Type and Maturity The Jamieson Formation apparently has the best source quality with HI values ranging from between 163 and 234 mg hydrocarbons/g TOC (average HI = 199 mg hydrocarbons/g TOC; Fig 3.37). However, the TOC contents in these samples are poor, hence any generated liquid hydrocarbons will probably remain within the source rock and expulsion will not occur until it is substantially cracked to gas a higher maturities. The Echuca Shoals Formation has HI values ranging between 123 and 180 mg hydrocarbons/g TOC (average HI = 155 mg hydrocarbons/g TOC) which indicates that they are presently predominantly gas and condensate-prone. The Vulcan Formation samples are at best gas-prone (average HI = 121 mg hydrocarbons/g TOC). Figure 3.37 shows that the Jamieson Formation sediments contain Type II/III kerogen, the Echuca Shoals Formation sediments contain Type III kerogen and the Vulcan Formation sediments contain Type III/IV kerogen. Estimates of maturity from the Tmax values indicate that the Jamieson Formation sediments are presently immature for hydrocarbon generation, whereas the Echuca Shoals Formation and Vulcan Formation sediments are just within the oil window. Having said this, the Tmax values are lower than expected for the given depth range. This would suggest that glycol additives are still present in the samples despite the extraction process. 75

93 Figure 3.37 Tmax versus Hydrogen Index for selected samples from Brecknock South (c) I VR = 0.5% Hydrogen Index (mg HC/g TOC) present day II Oil Oil + Gas immature early mature VR = 0.8% 200 Gas + Oil VR = 1.35% 100 Gas III Tmax ( C) mature over mature Analysis of SANS data Small Angle Neutron Scattering (SANS) analysis was performed on ten nominally claystone cuttings from the well Brecknock South-1 (Table A1.4 in Appendix 1). These cuttings were collected at about m intervals between depths 3530 mrt to 3800 mrt, and the deepest sample (fluvial claystone) was recovered from the depth of 3995 mrt. Figure 3.38 shows the original SANS data presented in the standard manner: scattering intensity, I(Q) in absolute units, versus the scattering vector Q. There is a significant and systematic variation of the scattering intensity with depth. This is illustrated in Figure 3.39 for scattering intensity measured at Q = 0.01 Å -1, which corresponds to a pore size of about µm +/-50% (1 Å = m; 1 µm = 1000 nm = 10,000 Å). The scattering intensity is practically constant ( cm -1 ) within the depth range 3530 m to 3585 m in the Jamieson Formation and top Echuca Shoals Formation, followed by an apparent sharp decrease by a factor of 2.6 at the 76

94 depth of 3675 m in the mid Echuca Shoals Formation and thereafter slightly increases throughout the Echuca Shoals Formation and the Upper Vulcan Formation by a factor of 1.2. The intensity remains at a low value in the Lower Vulcan Formation and at the base of the Plover Formation down to the TD depth of 4008 mrt. There is a significant log change at the boundary between the Jamieson Formation and the Echuca Shoals Formation at 3575 m, and yet there is no scattering intensity change across the boundary until well within the upper Echuca Shoals Formation. This raises the possibility that the cuttings retrieved from the depth interval 3585 m to 3590 m near the top of the Echuca Shoals Formation (used to prepare SANS sample) might have been contaminated by cavings from the overlying Jamieson Formation. Although all the samples obtained from Woodside for SANS analysis have been nominally described as claystones throughout the depth range of 3530 m to 3995 m, the Well Completion Report (WCR) provides detailed information indicating that the actual lithology undergoes significant variation with depth. Within the Jamieson Formation ( m) the gamma log remains constant, except for a sharp jump at the depth of 3570 m due to the presence of 20% glauconite, followed by a jump at the sequence boundary and formation boundary at the depth of 3575 m. In the depth range 3575 m 3664 m within the upper Echuca Shoals Formation there is a slight gradual decrease of the gamma signal, followed by a sudden increase in gamma, density and velocity at the depth of 3664 m. The WCR reports a gradual change of lithology to siltstone throughout the depth range 3664 m 3766 m within the lower Echuca Shoals Formation and throughout the depth range 3776 m m within the Upper Vulcan Formation, but this is not corroborated by the descriptions of sidewall cores. The only swc successfully retrieved within the Jamieson Formation (3570 m) is described as glauconitic claystone (65% siliceous clay, 35% siliceous silt, 10% siliceous sand) and the lithology of sidewall cores within the depth interval 3576 m to 3773 m (within the Echuca Shoals Formation and the Upper Vulcan Formation) is described as predominantly siliceous clay. Since the SANS signal from the organic component of the rock is always superimposed on the SANS signal from the inorganic matrix, a consistent lithology throughout the entire depth range is a prerequisite for a successful identification of hydrocarbon generation zones from SANS data [1]. This is particularly accentuated for organic-lean potential source rocks. Therefore, in the following we first analyse the microstructural properties versus depth. Figure 3.40 illustrates the calculated values of SLD versus depth for the inorganic component of the rock matrix in Brecknock South-1. There is little variation (at most 5%) with depth and, consequently, the average value of SLD = 4.36x10 10 cm -2 was used in subsequent calculations for Brecknock South-1. The pore size distributions calculated for various depths from the full SANS curves are presented in Figure A detailed analysis of the variation of pore number density, proportional to the pore size distribution, with depth for three pore sizes 100 Å, 316 Å and 630 Å (Figure 3.42) indicates a systematic compaction with depth for the pore size 100 Å. For the pore sizes 316 Å and 630 Å, however, the pore number density varies irregularly with depth in a way mirroring the scattering intensity curve (Figure 3.39). Three apparent distinct lithologies can be identified (Figure 3.42). This indicates that 77

95 SANS intensity is most probably dominated by the lithology-dependent scattering on the inorganic matrix, and any organic input is masked by the inorganic matrix signal. Figure 3.43 illustrates calculated porosity (only for the fraction of total porosity within the pore size range 20 Å to 1000 Å) versus depth. The values are between 2.0% and 4.7%, with a maximum near the boundary between the Jamieson Formation and the Echuca Shoals Formation. The general trend with depth follows the pattern observed for the scattering intensity (Figure 3.39) and is also most probably dominated by the microstructure of the inorganic matrix. The calculated SANS porosity values need to be calibrated against the log porosities. Brecknock South-1 is a gas/condensate discovery and the gas-water contact and maximum gas reading are indicated in Figure Significance for hydrocarbon generation The size of the pores found in claystones typically ranges from 1 nm to about 40 µm across. SANS experiments can access pore sizes at the lower end of this range, from about 2 nm to 100 nm, which typically comprise about 30% of total porosity. These data can be used to determine the early stages of hydrocarbon generation and saturation within source rocks. Owing to significant lithology variation, the microstructure of the inorganic rock fabric also changes significantly throughout the depth range studied by SANS in Brecknock South-1 (Figures 3.42, 3.43). For the pore size 316 Å, the pore number density decreases by a factor of about 3 within the depth range of m (Figure 3.42). The SANS intensity for a similar pore size of 250 Å decreases also by a similar factor of 2.6 within the same depth range (Figure 3.39). Therefore, it is likely that the observed marked variation of SANS intensity within the depth interval m is dominated by the lithology variation of the inorganic rock matrix. The slight increase in scattering intensity throughout the depth interval m could indicate (1) a slight systematic change of the microstructure of inorganic matrix or (2) progressive expulsion of mobile hydrocarbons. There is no strong indication of progressive bitumen generation and/or cracking. 78

96 Figure SANS absolute intensity curves for samples of cuttings from Brecknock South-1. Ten samples (nominally claystones, 5 m interval each), depth range is 3530 m to 3995 m Figure 3.38 Brecknock South-1 Scattering intensity versus Q for various depths 3530m to 3995m SCATTERING INTENSITY (cm -1 ) m m m m m m m m m m SCATTERING VECTOR Q (Å -1 ) 79

97 Figure SANS intensity versus depth at Q=0.01A -1 (corresponding to the pore size 25 nm +/-50%, or µm +/-50%) for cuttings samples from Brecknock South glauconitic claystone 3570m cavings? m (250Å) JAMIESON DEPTH (mrt) siliceous claystone to siltstone transition 3664m 3782m interbedded Clst & Sst m ECHUCA SHOALS UPPER VULCAN LOWER 3900 Reservoir interval PLOVER SCATTERING INTENSITY AT Q=0.01Å -1 (cm -1 ) 80

98 Figure Variation of the Scattering Length Density (SLD) for thermal neutrons with depth for Brecknock South-1. SLD values were calculated from the elemental composition as determined by a separate X-ray Fluorescence (XRF) measurement Brecknock South-1 Scattering length density versus depth Calculated from XRF data 3400 average SLD = 4.36x10 10 (cm -2 ) 3500 DEPTH (m) SCATTERING LENGTH DENSITY (x10 10 cm -2 ) 81

99 Figure Pore size distribution at various depths for samples of cuttings from Brecknock South-1. Ten samples (nominally claystones, 5 m interval each), depth range is 3530 m to 3995 m. PORE SIZE DITRIBUTION DENSITY f(r) m 3565m 3585m 3635m 3675m 3705m 3750m 3770m 3800m 3995m PORE SIZE (Å) 82

100 Figure Variation of the pore number density for selected pore sizes versus depth for Brecknock South-1. For the smallest pore size note the significant decrease of the pore number density with depth, indicative of compaction. For full discussion see text r = 630Å 316Å 100Å LITHOLOGY1 JAMIESON 3600 LITHOLOGY2 DEPTH (mrt) LITHOLOGY3 ECHUCA SHOALS UPPER VULCAN LOWER 3900 PLOVER PORE NUMBER DENSITY 83

101 Figure Variation of apparent porosity (within the pore size range 2 nm to 100 nm) with depth for Brecknock South-1. For discussion see text cavings? JAMIESON DEPTH (mrt) m maximum gas reading ECHUCA SHOALS UPPER VULCAN LOWER m gas-water contact PLOVER CALCULATED SANS POROSITY (%) 3.6 Crux-1 The pyrolysis data for Crux-1 are given in Appendix 5 Table A5.6. Figures 3.44 and 3.45 are compilations of total organic carbon and the Rock-Eval pyrolysis parameters (Tmax, S 1, S 2 and HI) plotted against depth (mrt). Figure 3.44 compares the results for raw and extracted samples, and Figure 3.45 compares extracted data from different laboratories. Figure 3.46 comprises a graph of Tmax versus Hydrogen Index for potential source rock samples. In addition to the extracted cuttings and SWC samples analysed in this study, results of Leco TOC and Rock-Eval pyrolysis analyses for both extracted cuttings and SWC samples were available from the well completion report which were analysed by Geotechnical Services (Nippon, 2001). Comparison of the TOC contents and pyrolysis data from extracted samples between the two laboratories reveals that the data sets are comparable despite different preparative and analytical methodologies being used (Fig 3.45) Drilling Fluids, Contaminants and Migrated Hydrocarbons Crux-1 was drilled with water-based drilling mud to a depth of 2120 m. Below this depth potassium chloride, PHPA, glycol and Alplex was used to the bottom of the well. All of the cuttings and SWC samples analysed are contaminated with glycol additives, and hence they were extracted with methanol and dichloromethane (90:10) as part of the 84

102 preparative procedure. There is insufficient information in the WCR to determine the method employed to remove the glycol contamination from the cuttings and SWCs that Geotechnical Services analysed but they did solvent extracted the samples, at least with water (see sections and and table 14; Nippon, 2001). The effects of the glycol additives on the pyrolysis data for both SWC and cuttings samples are demonstrated in Figure 3.44 from comparison of the extracted and unextracted samples. It is apparent that the glycol additive has had a considerable effect on the pyrolysis values. For example, the glycol additive increases the TOC contents, S 1 and S 2 values and the calculated BI and HI values. It also decreases Tmax values which may be variable and show inconsistent trends with increasing depth. Hence, the overall source potential could be overestimated and the maturity of the section underestimated if the type of drilling fluid used is not taken into consideration. After extraction of the sediments with organic solvents (and water in the case of the Geotech-analysed samples), the resultant pyrograms, in most instances, have little or no S 1 peaks and well resolved S 2 and S 3 peaks. This means that the S 1 values, and the calculations involving S 1 values (BI, PI) are invalid and the presence of naturally occurring free hydrocarbons in the sediments cannot be evaluated. Equally, the other pyrolysis parameters must also be interpreted with caution due to the unreliable nature of the S 2 and TOC values. Some samples still had obvious contamination despite multiple extractions and are pronounced in the cuttings samples from to 2390 m to 2650 m (Fig. 3.45), as shown by the open symbols. Below this depth, the Tmax trend shows a fairly uniform increase with depth and the TOC and HI trends increase, albeit in a more erratic manner. Bearing in mind the limitations imposed because of the glycol contamination, the following interpretations are an approximate guide to the greatest hydrocarbon potential that the sediments in Crux-1 may have, and the minimum thermal maturity that they may have attained. The Lower Cretaceous Jamieson Formation is not discussed since these extracted samples are still significantly affected by contamination, as highlighted by the exceptionally low Tmax values and high S 1 values Source Richness The total organic carbon (TOC) contents of the organic-rich sediments of the Lower Cretaceous Echuca Shoals Formation and Upper Vulcan Formation source rocks range from fair to good and have an overall fair TOC content (average TOC = 1%). The source rocks of the combined Upper Jurassic Lower Vulcan and Montara formations range from good to very good and have an overall good TOC content (average TOC = 1.2%). The potential yields of the sediments from Crux-1 cannot be discussed due to the removal of the S 1 peak by the preparative processes used to eliminate the glycol contamination. 85

103 Figure 3.44 Depth plots of TOC and Rock-Eval pyrolysis data for Crux-1 (GA data only). Crux -1 GA sequence Tertiary Maastrichtian Campanian Santonian - Turonian Jamieson Formation Echuca Shoals Fm Upper Vulcan Formation Lower Vulcan Formation Plover Formation Depth (m KB) (b) (c) Tmax ( C) TOC (%) GA sequence (d) (e) (f) 1000 Tertiary Maastrichtian 1500 Campanian Santonian - Turonian Jamieson Formation Echuca Shoals Fm Upper Vulcan Formation Lower Vulcan Formation Plover Formation Depth (m KB) Invalid data S1 (mg/g Rock) 0 14/OA/ S2 (mg/g Rock) HI (mg/g TOC) GA SWC GA SWC extracted GA CUTT GA CUTT extracted 86

104 Figure 3.45 Depth plots of TOC and Rock-Eval pyrolysis data for Crux-1. Crux -1 GA sequence Tertiary Maastrichtian Campanian Santonian - Turonian Jamieson Formation Echuca Shoals Fm Upper Vulcan Formation Lower Vulcan Formation Plover Formation Depth (m KB) (b) (c) Tmax ( C) TOC (%) GA sequence (d) (e) (f) 1000 Tertiary Maastrichtian 1500 Campanian Santonian - Turonian Jamieson Formation Echuca Shoals Fm Upper Vulcan Formation Lower Vulcan Formation Plover Formation Depth (m KB) Invalid data S1 (mg/g Rock) S2 (mg/g Rock) 0 14/OA/ HI (mg/g TOC) Geotech SWC washed GA SWC extracted GA CUTT extracted GA CUTT extracted (HC) 87

105 3.6.3 Source Quality, Kerogen Type and Maturity The Lower Cretaceous Echuca Shoals Formation samples are poor in hydrogen and are at best gas-prone (average HI = 116 mg hydrocarbons/g TOC; Fig. 3.46). The Lower Cretaceous-Upper Vulcan sediments have an average HI value of 178 mg hydrocarbons/g TOC indicating that they have the potential to generate both condensate and gas. Likewise, the Upper Jurassic Lower Vulcan Formation and Montara Formation sediments have similar source quality with average HI values of 194 mg hydrocarbons/g TOC and 197 mg hydrocarbons/g TOC, respectively which indicates that they have the potential to generate both condensate and gas. Figure 3.46 shows that the Echuca Shoals Formation sediments contain immature Type III/IV kerogen. The Upper and Lower Vulcan formations contain Type II/III kerogen that is presently within the early oil window Analysis of SANS data Small Angle Neutron Scattering (SANS) analysis was performed on 25 claystone and silty claystone cuttings as well as five claystone and silty claystone sidewall cores from the well Crux-1 (Table A1.7 in Appendix 2). The cuttings were collected at 20 m to 80 m intervals between depths 2390 mrt to 3550 mrt. Figure 3.47 shows the original SANS data presented in the standard manner: scattering intensity, I(Q) in absolute units, versus the scattering vector Q. Data for sidewall cores are presented separately in Figure 1C. There is a significant and systematic variation of the scattering intensity with depth. This is illustrated in Figure 3.48 for scattering intensity measured at Q=0.01 Å -1, which corresponds to a pore size of about µm +/-50% (1 Å = m; 1 µm = 1000 nm = 10,000 Å). Except for one data point (a sidewall core at a depth of m), there is a good agreement between the intensity values measured from samples of sidewall cores and cuttings Within the Jamieson Formation, the scattering intensity rapidly decreases by a factor of 1.8 within the depth range 2390 m to 2450 m and then sharply increases by a factor of 1.6 within the depth range 2450 m to 2570 m. This is followed by an abrupt decrease at the top of the Echuca Shoals Formation and than a slight decrease throughout the Echuca Shoals Formation and uppermost Upper Vulcan Formation within the depth range 2600 m to m. A general decreasing trend, with somewhat scattered data points, is observed within the top Upper Vulcan Formation within the depth range 2775 m to 2990 m, followed by a roughly constant, relatively low value within the depth range 2990 m to 3110 m. At the base of the Upper Vulcan Formation the scattering intensity increases by a factor of 1.3 ( m). At the top of the Lower Vulcan Formation the scattering intensity returns to a low value and, following the trend exhibited in the mid Upper Vulcan Formation, remains roughly constant throughout the Lower Vulcan Formation, except for one data point (swc) at a depth of m near the base. 88

106 Figure 3.46 Tmax versus Hydrogen Index for selected samples from Crux-1. (a) Crux -1 Poor Fair Good Very good (b) S 1-depletion by h/c expulsion Condensate window S1 + S2 (mg/g Rock) Oil Gas Very good Good Tmax ( C) Oil window 6 4 Fair 2 invalid data Immature Poor S 1-enrichment by H/C migration or contamination 14/OA/ TOC (%) Production Index Invalid data Hydrogen Index (mg HC/g TOC) present day (c) 800 I VR = 0.5% II Oil Oil + Gas Gas + Oil VR = 1.35% Gas III immature early mature VR = 0.8% Tmax ( C) mature over mature Geotech SWC Geotech SWC HC GA SWC GA SWC extracted GA CUTT GA CUTT extracted Echuca Shoals Formation Upper Vulcan Formation Lower Vulcan Formation Figure 3.49 illustrates the variation of the organic matter maturity with depth, using two sets of data: the vitrinite reflectance and FAMM equivalent (CSIRO report in WCR). These values were used in Figure 3.48 to provide a conventional indication of source rock maturity at various depths. 89

107 Figure 3.50 illustrates the calculated values of SLD versus depth for the inorganic component of the rock matrix in Crux-1. There is little variation (at most 3%) with depth and, consequently, the average value of SLD = 4.32x10 10 cm -2 was used in subsequent calculations for Crux-1. The pore size distributions calculated for various depths from the full SANS curves (Figure 3.51) indicate that there is little variation of the geometry of the pore space with depth and that there is little difference between data for sidewall cores and cuttings. A detailed analysis of the variation of pore number density (proportional to the pore size distribution) with depth for three pore sizes 100 Å, 316 Å and 630 Å indicates a systematic slight compaction with depth throughout the entire depth interval 2390 m to 3550 m (Figure 3.52). Superimposed onto this general trend are two anomalies, one located within the Upper Vulcan Formation within the depth range 2690 m to 2850 m and another within the basal Upper Vulcan Formation within the depth range 3110 m to 3200 m. Figure 3.53 illustrates calculated porosity (only for the fraction of total porosity within the pore size range 20 Å to 1000 Å) versus depth. SANS porosity has been computed by adding pore volumes obtained by fitting the corresponding SANS scattering intensity curve using an assumption that all pores are filled with a fluid of low scattering length density, like brine, gas or saturated hydrocarbons. Therefore, the calculated SANS porosity values for depths where pores are filled with bitumen are too low. Most of the values are between 1.6% and 3.2%, with a maximum of about 3.2% at the top of the Jamieson Formation. Crux-1 is a gas discovery well, with a gas cap located within the Nome Formation within the depth range 3635 m to 3884 m (GWC). Significance for hydrocarbon generation The sizes of the pores found in claystones typically range from 1 nm to about 40 µm across. SANS experiments can access pore sizes at the lower end of this range, from about 2 nm to 100 nm, which typically comprise about 30% of total porosity. These data can be used to identify the early stages of hydrocarbon generation and saturation inside source rocks. Except for two relatively weak anomalies within the Upper Vulcan Formation (at a depth of about 2800 m and 3150 m), the microstructure of the inorganic rock fabric changes only slightly throughout the entire depth range studied by SANS in Crux-1 (Figures 3.51 and 3.52). Therefore, the marked variation of the scattering intensity (Figure 3.48) throughout the Jamieson Formation and the Echuca Shoals Formation is ascribed to the change of the chemical composition of the organic matter contained in the pores, which affects the neutron scattering contrast. As discussed above, the low values of the scattering intensity indicate pores filled with bitumen at the onset of hydrocarbon generation, and the high values pores filled with gas, formation brine and/or saturated hydrocarbons. Based on this, three regions of the onset of mobile hydrocarbon generation (at different maturity) can be identified (Figure 3.54): (1) within the upper Jamieson Formation at a depth of about 2450 m, 90

108 (2) at the base of the Echuca Shoals Formation at a depth of about 2690 m, and (3) possibly within the Upper Vulcan Formation at a depth of about m. All three generation regions are separated from each other by barriers, most probably due to low permeability or markedly different thermal kinetics for transformation of organic matter. The increasing SANS intensity with depth for hydrocarbon generation region within the lower Jamieson Formation and at the base of the Upper Vulcan Formation indicates progressive cracking of bitumen to mobile hydrocarbons and migration of hydrocarbons to larger pores with increasing depth within the formation. The low scattering intensity at the base of the Echuca Shoals Formation, as compared to the adjacent region in the Upper Vulcan Formation, indicates that there is no communication between the pore spaces of these two sedimentary units. Claystones within these two units are separated by numerous sandstone layers (up to 10 m thick) intersected within the depth range m. It is possible that these sandstones reservoir mobile hydrocarbons generated at the base of the Echuca Shoals Formation and at the top of the Upper Vulcan Formation. 91

109 Figure SANS absolute intensity curves for samples from Crux-1. (a): 13 samples of cuttings (claystones and silty claystones, 5 m interval each), depth range 2390 m to 2945 m. (b): 12 samples of cuttings (claystones and silty claystones, 5 m interval each), depth range 2990 m to 3550 m. C: five sidewall core samples (claystones and silty claystones, 5 m interval each), depth range m to m Figure 3.47(A) Crux-1 Scattering intensity versus Q for various depths part 1: cuttings 2390m to 2945m SCATTERING INTENSITY (cm -1 ) m m m m m m m m m m m m m SCATTERING VECTOR Q (Å -1 ) 92

110 Figure 3.47(B) Crux-1 Scattering intensity versus Q for various depths part 2: cuttings 2990m to 3550m 10 5 SCATTERING INTENSITY (cm -1 ) m m m m m m m m m m m m SCATTERING VECTOR Q (Å -1 ) 93

111 Figure 3.47(C) Crux-1 Scattering intensity versus Q for various depths part 3: sidewall cores m to m 10 5 SCATTERING INTENSITY (cm -1 ) swc m 135 swc m 136 swc m 137 swc m 138 swc m SCATTERING VECTOR Q (Å -1 ) 94

112 Figure SANS intensity versus depth at Q=0.01 A -1 (corresponding to the pore size 25 nm +/-50%, or µm +/-50%) for samples from Crux MATURITY: Ro% FAMM µ m (250 Å) DEPTH (mrt) % ONSET % 0.42% 0.80% ONSET % 0.38% ONSET % 0.90% 0.44% 0.93% Sst intervals 2676m 2750m kinetics or permeability barrier WOOLASTON JAMIESON ECHUCA SHOALS UPPER VULCAN 0.57% 0.88% LOWER % 0.98% % 1.06% MALITA NOME SCATTERING INTENSITY AT Q=0.01Å -1 (cm -1 ) 95

113 Figure Vitrinite reflectance versus depth for Crux-1 (after Well Completion Report) Figure 3.49 Crux-1 Vitrinite reflectance versus depth circles - vitrinite reflectance results squares - FAMM results SAMPLE DEPTH (mrt) Average VR Minimum Maximum Average FAMM Minimum Maximum VITRINITE REFLECTANCE (%) 96

114 Figure Variation of the Scattering Length Density (SLD) for thermal neutrons with depth for Crux-1. SLD values were calculated from the elemental composition as determined by a separate X-ray Fluorescence (XRF) measurement. Crux1, Browse Basin Scattering length density versus depth DEPTH (m) SCATTERING LENGTH DENSITY (x10 10 cm -2 ) 97

115 Figure Pore size distribution at various depths for samples from Crux-1. (a): 13 samples of cuttings (claystones and silty claystones, 5 m interval each), depth range 2390 m to 2945 m. (b): 12 samples of cuttings (claystones and silty claystones, 5 m interval each), depth range 2990 m to 3550 m. (c): five sidewall core samples (claystones and silty claystones, 5 m interval each), depth range m to m. (a) PORE SIZE DITRIBUTION DENSITY f(r) m 2450m 2500m 2550m 2570m 2600m 2650m 2690m 2775m 2805m 2850m 2900m 2945m PORE SIZE (Å) 98

116 (b) PORE SIZE DITRIBUTION DENSITY f(r) m 3055m 3110m 3150m 3200m 3270m 3325m 3359m 3400m 3460m 3500m 3550m PORE SIZE (Å) (c) PORE SIZE DITRIBUTION DENSITY f(r) swc m swc m swc m swc m swc m PORE SIZE (Å) 99

117 Figure Variation of the pore number density for selected pore sizes versus depth for Crux-1. Note the slight decrease of the pore number density with depth, indicative of compaction. For full discussion see text. (e) 2000 r = 630Å 316Å 100Å WOOLASTON 2500 JAMIESON ECHUCA SHOALS DEPTH (mrt) 3000 UPPER VULCAN 3500 LOWER MALITA NOME PORE NUMBER DENSITY 100

118 Figure Variation of apparent porosity (within the pore size range 2 nm to 100 nm) with depth for Crux-1. For discussion see text WOOLASTON 2500 JAMIESON ECHUCA SHOALS DEPTH (mrt) 3000 UPPER VULCAN 3500 LOWER 3635m GAS MALITA NOME GWC 3884m CALCULATED SANS POROSITY (%) 101

119 Figure Interpretation of SANS data for Crux-1. SANS intensity versus depth at Q=0.01 A -1 (corresponding to the pore size 25 nm +/-50%, or µm +/-50%) for samples from Crux MATURITY: Ro% FAMM µ m (250 Å) DEPTH (mrt) % ONSET % 0.42% 0.80% ONSET % 0.38% ONSET % 0.90% 0.44% 0.93% Sst intervals 2676m 2750m kinetics or permeability barrier WOOLASTON JAMIESON ECHUCA SHOALS UPPER VULCAN 0.57% 0.88% LOWER % 0.98% % 1.06% MALITA NOME SCATTERING INTENSITY AT Q=0.01Å -1 (cm -1 ) 3.7 Dinichthys-1 The pyrolysis data for Dinichthys-1 is given in Appendix 5 Table A5.7. Figure 3.55 is a compilation of vitrinite reflectance, total organic carbon and the Rock-Eval pyrolysis parameters (Tmax, S 1, S 2 and HI) plotted against depth (mrt). Figure 3.56 comprises a graph of Tmax versus Hydrogen Index for potential source rock samples. In addition to the extracted cuttings samples analysed in this study, results of Leco TOC and Rock-Eval pyrolysis analyses for cuttings samples (which were analysed by Geotechnical Services) were available from the well completion report (Inpex, 2001a). Vitrinite reflectance measurements were obtained by Kieraville Konsultants Drilling Fluids, Contaminants and Migrated Hydrocarbons The well completion report states that Dinichthys-1 was drilled with water-based drilling muds with various additives (KCl, Aquadrill and Pyrodrill). However, both the GA cuttings samples and those analysed by Geotechnical Services appear contaminated by glycol additives, as confirmed by subsequent GC-MS work by Geotechnical Services. The samples analysed in this study were extracted with methanol and 102

120 dichloromethane (90:10) as part of the preparative procedure. The Geotech-analysed samples were unwashed cuttings. Comparison of the two laboratory data sets shows that the glycol additive has had a considerable effect on the pyrolysis values (Fig. 3.55). For example, the glycol additive generally (but not always) increases the TOC content, it increases the S 1 and S 2 values and the calculated BI and HI values. It decreases the Tmax values which may be variable and show inconsistent trends with increasing depth. Hence, the overall source potential could be over estimated and the maturity of the section under estimated if the type of drilling fluid used is not taken into consideration. After extraction of the sediments with organic solvent, the resultant pyrograms, in most instances, have little or no S 1 peaks and well resolved S 2 and S 3 peaks. This means that the S 1 values, and the calculations involving S 1 values (BI, PI) are invalid and the presence of naturally occurring free hydrocarbons in the sediments cannot be evaluated. Equally, the other pyrolysis parameters must also be interpreted with caution due to the unreliable nature of the S 2 and TOC values. Bearing in mind the limitations imposed because of the glycol contamination, the following interpretations are an approximate guide to the greatest hydrocarbon potential that the sediments in Dinichthys-1 may have, and the minimum thermal maturity that they may have attained. It must be stated that many samples in Dinichthys-1 still appear to be strongly affected by contamination, as highlighted from the exceptionally low Tmax values and high S 1 values, even after multiple solvent extractions. Therefore, the samples evaluated for their hydrocarbon potential are identified with a black dot in Figure 3.55, and only these data are plotted on the Tmax versus HI plot in Figure Source Richness The total organic carbon (TOC) contents of both the Lower Cretaceous Jamieson Formation and Echuca Shoals Formation samples appear to be good (average TOC = 1.6% and 2.2%, respectively; Fig. 3.56). The potential yields of the sediments from Dinichthys-1 cannot be discussed due to the removal of the S 1 peak by the preparative processes used to eliminate the glycol contamination Source Quality, Kerogen Type and Maturity The Jamieson and Echuca Shoals formations range from being gas-prone to having some liquids potential (average HI = 163 mg hydrocarbons/g TOC and 148 mg hydrocarbons/g TOC, respectively). Figure 3.56 shows that the Jamieson Formation sediments contain immature Type III kerogen, and the Echuca Shoals Formation sediments contains Type III kerogen that is presently within the peak oil window. 103

121 Figure 3.55 Depth plots of vitrinite reflectance, TOC and Rock-Eval pyrolysis data for Dinichthys-1. Dinichthys -1 WCR sequence (a) (b) (c) 1000 Tertiary 1500 Puffin Formation 2000 Fenelon Fm Woolaston Fm Jamieson Formation Depth (m KB) Echuca Shoals Formation Upper Vulcan Fm Lower Vulcan Fm Plover Fm VR (%) Tmax ( C) TOC (%) WCR sequence (d) (e) (f) 1000 Tertiary 1500 Puffin Formation 2000 Fenelon Fm Woolaston Fm Jamieson Formation Depth (m KB) Echuca Shoals Formation Upper Vulcan Fm Lower Vulcan Fm Plover Fm Invalid data S1 (mg/g Rock) S2 (mg/g Rock) /OA/ HI (mg/g TOC) Kieraville SWC Geotech CUTT GA CUTT GA CUTT extracted GA acceptable SR data 104

122 Figure 3.56 Tmax versus Hydrogen Index for selected samples from Dinichthys-1. (a) Dinichthys -1 Poor Fair Good Very good (b) S 1-depletion by h/c expulsion Condensate window S1 + S2 (mg/g Rock) Oil Gas Very good Good Tmax ( C) Oil window 6 Invalid data 440 Invalid data 4 2 Fair Poor 430 Immature S 1-enrichment by H/C migration or contamination 14/OA/ TOC (%) Production Index Hydrogen Index (mg HC/g TOC) present day (c) 800 I VR = 0.5% II Oil Oil + Gas Gas + Oil VR = 1.35% Gas III immature early mature VR = 0.8% Tmax ( C) mature over mature Geotech CUTT GA CUTT GA CUTT extracted Jamieson Formation Echuca Shoals Formation Analysis of SANS and USANS data Small Angle Neutron Scattering (SANS) and Ultra-small Angle Neutron Scattering (USANS) analyses were performed on 25 claystone cuttings from the well Dinichthys-1 (Table A1.8 in Appendix 2). These cuttings were collected at 50 m to 100 m intervals between depths 2550 mrt to 4350 mrt 105

123 Figure 3.57 shows the original SANS/USANS data presented in the standard manner: scattering intensity, I(Q) in absolute units, versus the scattering vector Q. There is a significant and systematic variation of the scattering intensity with depth. This variation is clearly pore-size-dependent, as shown in Figure 3.58(a-d) for four Q- values of Å -1, Å -1, Å -1, and Å -1, which correspond to four pore sizes of 0.01 µm +/-50%, 0.1 µm +/-50%, 1 µm +/-50% and 10 µm +/-50%, respectively (1 Å = m; 1 µm = 1000 nm = 10,000 Å). For the smallest pore size (Figure 3.58(a) the scattering intensity initially increases by a factor of 2 within the depth range 2550 m to 3355m in the Jamieson Formation. The scattering intensity is markedly lower at the top of the Echuca Shoals Formation and it decreases by a factor of 2 within the depth range 3450 m to 3950 m throughout the Echuca Shoals Formation and thereafter remains relatively constant at a low value within the Vulcan Formation. The characteristic <-shaped intensity curve, visible for the smaller pores within the upper Jamieson Formation, effectively washes out for the largest pores (Figure 3.58(ad)). This indicates that there is not enough hydrocarbon volume generated within the source rock to saturate the largest pores as the bitumen is successively replacing brine from smaller pores toward the larger ones. This microstructural evidence is consistent with the marginal global values of TOC and the early to peak oil window maturity estimate in the Jamieson Formation source rocks at nearby Brewster-1A well, for which the TOC values are reliable (sections and 3.1.3). Within the Echuca Shoals Formation, the hydrocarbon generation peak is consistently observed in the depth interval 3850 m 3950 m, and its position moves slightly to shallower depths with increased pore size. The bitumen generation region is not immediately adjacent to the Berriasian Sandstone (regional reservoir rock in the depth interval 4065 m to 4184 m). The depth of the <-shaped intensity curve is smaller for 10 µm pores than for 1 µm pores (Figures 3.58(d) and 3.58(c), respectively). This indicates that the largest pores may not be fully saturated, which would prevent the expulsion of a significant volume of hydrocarbons from the Echuca Shoals Formation. Given the vitrinite reflectance values of the order of 0.63% to 1.16% in the mid-formation and at the base, respectively, it is most likely that the small upward shift of the intensity <-curve is caused by the process of oil generation preferentially taking place in larger pores. Figure 3.59 illustrates the calculated values of SLD versus depth for the inorganic component of the rock matrix in Dinichthys-1. There is little variation (at most 5%) with depth and, consequently, the average value of SLD = 4.40x10 10 cm -2 was used in subsequent calculations for Dinichthys-1. The pore size distributions calculated for various depths from the full SANS curves (Figure 3.60) indicate that there is little variation of the geometry of the pore space with depth, except at the depth of 3350 m near the base of the Jamieson Formation, where an increased number of larger pores is observed. This anomaly coincides with the K Aptian sandstone equivalent region of changed lithology within the depth interval 3340 m 3424 m (Figure 3.62). 106

124 A detailed analysis of the variation of pore number density (proportional to the pore size distribution) with depth for four pore sizes 0.01 µm, 0.1 µm, 1 µm and 10 µm, indicates a systematic slight compaction with depth throughout the Jamieson Formation and slight decompaction throughout the Echuca Shoals Formation, regardless of the pore size (Figure 3.61). The onset of the expansion interval coincides with the different lithology region (Figure 3.62), intersected near the base of Jamieson Formation. The smooth and only slight variation of the pore number density with depth indicates both a uniform lithology and mechanical stability of the inorganic rock matrix with depth. Figure 3.62 illustrates calculated porosity (for the very large fraction of total porosity within the pore size range 20 Å to 20 µm) versus depth. Apparent SANS porosity has been computed by adding pore volumes obtained by fitting the combined SANS/ USANS scattering intensity curve using an assumption that all pores are filled with a fluid of low scattering length density, like brine, gas or saturated hydrocarbons. Therefore, the calculated SANS porosity values for depths where pores are filled with bitumen are too low. The apparent SANS porosity values for Dinichthys-1 lie between 6% and 14%, with a maximum at the base of Jamieson Formation (Figure 3.62). Depth intervals characterised by changed conditions are indicated on the left hand side of the Figure The "K Aptian sandstone equivalent" (3340 m to 3424 m) is characterised by low gamma ray signal and low penetration rate. Gas readings were fairly high throughout the well, and the depth interval 3700 m to 3750 m recorded a particularly elevated level of gas readings. Significant overpressure was recorded within the Echuca Shoals Formation. Significance for hydrocarbon generation The size of the pores found in claystones typically ranges from 1 nm to about 40 µm across. Combined SANS and USANS methods can access pore sizes from about 2 nm to 20 µm, which covers nearly the total porosity. These data can be used to determine all stages of hydrocarbon generation, saturation and expulsion within source rocks. Except for the anomaly at the base of the Jamieson Formation (at 3350 m), the microstructure of the inorganic rock fabric changes only slightly throughout the entire depth range studied by SANS in Dinichthys-1 (Figures 3.60 and 3.61). Therefore, the marked variation of the scattering intensity (Figure 3.58) is ascribed to the change of the chemical composition of the organic matter contained in the pores, which affects the neutron scattering contrast. Typically, the low values of the scattering intensity indicate pores filled with bitumen at the onset of mobile hydrocarbon generation, and the high values pores filled with gas, formation brine and/or saturated hydrocarbons. As discussed above, in Dinichthys-1 there are two depth intervals which clearly indicate the presence of bitumen in small pores, interpreted as the evidence of the onset of hydrocarbon generation: the upper Jamieson Formation and the lower Echuca Shoals Formation. The characteristic <-shape SANS intensity pattern for small pores within the upper Jamieson Formation (Figure 3.58(a) and 3.58(b)) indicates progressive cracking of bitumen to mobile hydrocarbons and migration of hydrocarbons to larger pores with increasing depth within the formation. The largest pores, however, do not appear to 107

125 be saturated at all which indicates that the upper Jamieson Formation claystones are too organically lean to become saturated, expel hydrocarbons and become an effective source rock for hydrocarbons. The average scattering intensity for small pores near the top of the Echuca Shoals Formation appears to exhibit a discontinuity when compared to the adjacent region in the Jamieson Formation (Figure 3.58(a) and 3.58(b)), which indicates that there is no communication between the pore spaces of these two sedimentary units. There is evidence of the presence of bitumen in pores of all sizes in the depth interval 3850 m 3950 m (slightly pore size dependent), but the largest pores are evidently less saturated than the smaller ones (Figures 3.58(d) and 3.58(c), respectively). This indicates insufficient charge volume to fully saturate the pore space of the claystone with hydrocarbons and, therefore, a very limited capacity to expel hydrocarbons. The relatively low scattering intensity at a depth of 4230 m within the Upper Vulcan Formation indicates that the pores contain significant amounts of organic matter with a very low hydrogen-to-carbon ratio, e.g. residual bitumen. 108

126 Figure SANS absolute intensity curves for samples of cuttings from Dinichthys-1. (a): nine samples (claystones, 5m interval each), depth range is 2550 m to 2950 m. (b): nine samples (claystones and claystones plus silty claystones, 5 m interval each), depth range 3000 m to 3760 m. (c) four samples (claystones and claystones plus silty claystones, 5 m interval each), 3850 m to 4190 m. Figure 3.57(a) Dinichthys1 (SANS & USANS) Scattering intensity versus Q for various depths part 1: 2550 m to 2950 m SCATTERING INTENSITY (cm -1 ) m 2610m 2650m 2700m 2740m 2790m 2850m 2895m 2950m SCATTERING VECTOR Q (Å -1 ) 109

127 Figure 3.57(b) Dinichthys1 (SANS & USANS) Scattering intensity versus Q for various depths part 2: 3000 m to 3760 m SCATTERING INTENSITY (cm -1 ) m 3045m 3150m 3250m 3350m 3450m 3550m 3640m 3760m SCATTERING VECTOR Q (Å -1 ) 110

128 Dinichthys1 (SANS & USANS) Scattering intensity versus Q for various depths part 3: 3850 m to 4190 m m 3950m 4040m 4190m SCATTERING VECTOR Q (Å -1 ) 111

129 Figure SANS intensity versus depth at four Q-values of (a) Å -1, (b) Å -1, (c) Å -1, and (d) Å -1, which corresponds to four pore sizes of 0.01 µm +/-50%, 0.1 µm +/-50%, 1 µm +/-50% and 10 µm +/-50%, for cuttings samples from Dinichthys-1. (a) Ro=0.50% ONSET 0.01 µ m (100Å) WOOLASTON Ro=0.53% 3000 Ro=0.59% JAMIESO N Ro=0.61% DEPTH (mrt ) Ro=0.64% Ro=0.63% Ro=0.63% Ro=0.67% Ro=0.70% Ro=1.16% Ro=1.23% ONSET Gas Sst 4065m 4184m permeability or kinetics barrier ECHUCA SHOAL S UPPER VULCAN 4500 Ro=1.48% Ro=1.78% LOWER PLOVER SCATTERING INTENSITY AT Q=0.01Å -1 (b) µ m (1000Å) WOOLASTON 3000 JAMIESO N DEPTH (mrt ) 3500 ECHUCA SHOAL S 4000 Gas Sst 4065m 4184m UPPER VULCAN 4500 LOWE R PLOVER SCATTERING INTENSITY AT Q=0.0025Å

130 (c) µ m 2500 WOOLASTON JAMIESON 3000 DEPTH (mrt) 3500 permeability or kinetics barrier ECHUCA SHOALS 4000 Gas Sst 4065m 4184m UPPER VULCAN LOWER 4500 PLOVER SCATTERING INTENSITY AT Q= Å -1 (d) µ m 2500 WOOLASTON JAMIESON 3000 DEPTH (mrt) 3500 ECHUCA SHOALS 4000 Gas Sst 4065m 4184m UPPER VULCAN 4500 LOWER PLOVER SCATTERING INTENSITY AT Q= Å

131 Figure Variation of the Scattering Length Density (SLD) for thermal neutrons with depth for Dinichthys-1. SLD values were calculated from the elemental composition as determined by a separate X-ray Fluorescence (XRF) measurement Dinichthys1, Browse Basin Scattering length density versus depth 2500 DEPTH (m) SCATTERING LENGTH DENSITY (x10 10 cm -2 ) 114

132 Figure Pore size distribution at various depths for samples of cuttings from Dinichthys-1. (a): 13 samples (claystones, 5 m interval each), depth range is 2550 m to 3250 m. (b): nine samples (claystones and claystones plus silty claystones, 5 m interval each), depth range 3350 m to 4190 m. PORE SIZE DITRIBUTION DENSITY f(r) (a) m 2610m 2650m 2700m 2740m 2790m 2850m 2895m 2950m 3000m 3045m 3150m 3250m PORE SIZE (Å) 115

133 PORE SIZE DITRIBUTION DENSITY f(r) (b) m 3450m 3550m 3640m 3760m 3850m 3950m 4040m 4190m PORE SIZE (Å) 116

134 Figure Variation of the pore number density for four selected pore sizes versus depth for Dinichthys-1. Note the slight decrease of the pore number density with depth, indicative of compaction. For full discussion see text r= 10 µ m 1 µ m 0.1 µ m 0.01 µ m 2500 WOOLASTON 3000 JAMIESO N DEPTH (mrt) ECHUCA SHOALS UPPER VULCAN LOWE R PLOVER PORE NUMBER DENSITY 117

135 Figure Variation of apparent porosity (within the pore size range 2 nm to 20 µm) with depth for Dinichthys-1. For discussion see text. (h) WOOLASTON 3000 changed lithology: gamma ray & penetration rate JAMIESON DEPTH (mrt) m 3424m 3700m 3750m 3350m ECHUCA SHOALS m increased mud density particularly increased gas readings UPPER VULCAN LOWER PLOVER CALCULATED SANS POROSITY (%) 3.8 Gorgonichthys-1 The pyrolysis data for Gorgonichthys-1 are given in Appendix 5 Table A5.8. Figure 3.63 is a compilation of vitrinite reflectance, total organic carbon and the Rock-Eval pyrolysis parameters (Tmax, S 1, S 2 and HI) plotted against depth (mrt). Figure 3.64 comprises a graph of Tmax versus Hydrogen Index for potential source rock samples. In addition to the extracted cuttings samples analysed in this study, results of Leco TOC and Rock-Eval pyrolysis analyses for cuttings samples (which were analysed by Geotechnical Services) were available from the well completion report (Inpex, 2001b). Vitrinite reflectance measurements were obtained by Kieraville Konsultants Drilling Fluids, Contaminants and Migrated Hydrocarbons Gorgonichthys-1 was drilled with a water-based drilling mud with gel and polymer additives to a depth of 3940 m. Below this depth Syntech (a synthetic-based mud) was used to the bottom of the well. The cuttings samples analysed by Geotechnical Services were extracted but no details are given in the WCR. However, it is apparent from these data that the Tmax values were anomalously low (Fig. 3.63) and the S 2, TOC and HI values were high for samples drilled using the water-based mud, as well as the SBMs. This indicates that other organic compounds (possibly glycol) are also present in the water-based mud. Therefore, all of the cuttings samples analysed in this study 118

136 were extracted with methanol and dichloromethane (50:50) as part of the preparative procedure. After extraction of the sediments with organic solvents, the resultant pyrograms, in most instances, have little or no S 1 peaks and well resolved S 2 and S 3 peaks. This means that the S 1 values, and the calculations involving S 1 values (BI and PI) are invalid and the presence of naturally occurring free hydrocarbons in the sediments cannot be evaluated. Equally, the other pyrolysis parameters must also be interpreted with caution due to the unreliable nature of the S 2 and TOC values. Bearing in mind the limitations imposed because of the contamination, the following interpretations are an approximate guide to the greatest hydrocarbon potential that the sediments in Gorgonichthys-1 may have, and the minimum thermal maturity that they may have attained. The samples evaluated for their hydrocarbon potential are identified with a black dot in Figure 3.63, and only these data are plotted on the Tmax versus HI plot in Figure It must be stated that there is a reversal in the Tmax trend from the depth that the SBM was added (Fig. 3.63). This indicates that SBM contaminants remain within the cuttings samples in Gorgonichthys-1. Therefore, data from only the samples above 3940 m are interpreted and shown on the Tmax versus HI plot in Figure It must be noted that the WCR report states that coals are present in the Plover Formation at 4500 and 4530 m. This lithology was not represented in the current sampling suite Source Richness The total organic carbon content of samples from the Lower Cretaceous Jamieson and Echuca Shoals formations appear to range from fair to good with an average TOC of 1.4% and 1.7%, respectively. The potential yields of the sediments from Gorgonichthys- 1 cannot be discussed due to the removal of the S 1 peak by the preparative processes used to eliminate any contamination Source Quality, Kerogen Type and Maturity The source quality of the Jamieson Formation ranges from being gas-prone to having the potential to generate oil (range HI = mg hydrocarbons/g TOC; average HI = 153 mg hydrocarbons/g TOC; Fig ). The Echuca Shoals Formation has similar hydrocarbon potential to the aforementioned formation, with HI values ranging from 128 to 264 mg hydrocarbons/g TOC (average HI = 181 mg hydrocarbons/g TOC). However, in the samples with the highest HI values, the corresponding TOC contents are less than 2%. Hence, any generated oil will probably remain within the source rock and expulsion will not occur until it is substantially cracked to gas at higher maturities. Figure 3.64 shows that the Jamieson Formation contains immature to marginally mature Type II/III to Type III kerogen, and the Echuca Shoals Formation contains Type II/III to Type III kerogen that is presently within the early oil window. Figure 3.63 Depth plots of vitrinite reflectance, TOC and Rock-Eval pyrolysis data 119

137 for Gorgonichthys-1. Gorgonichthys -1 GA sequence (a) (b) (c) 1000 Tertiary 1500 Maastrichtian Campanian 2000 Santonian - Turonian Jamieson Formation Depth (m KB) Echuca Shoals Formation 3500 Upper Vulcan Formation 4000 SBM SBM Lower Vulcan Formation Plover Formation VR (%) Tmax ( C) TOC (%) GA sequence (d) (e) (f) 1000 Tertiary 1500 Maastrichtian Campanian 2000 Santonian - Turonian Jamieson Formation Depth (m KB) Echuca Shoals Formation Upper Vulcan Formation Lower Vulcan Formation Plover Formation Invalid data S1 (mg/g Rock) SBM SBM SBM S2 (mg/g Rock) 8 14/OA/ HI (mg/g TOC) Kieraville Geotech CUTT extracted (glycol) GA CUTT extracted (glycol) GA acceptable SR data Geotech CUTT extracted (SBM) GA CUTT extracted (SBM) 120

138 Figure 3.64 Tmax versus Hydrogen Index for selected samples from Gorgonichthys-1. (a) Gorgonichthys -1 Poor Fair Good Very good (b) S 1-depletion by h/c expulsion Condensate window S1 + S2 (mg/g Rock) Oil Gas Very good Good Tmax ( C) Oil window Invalid data Fair 2 S 1-enrichment by Poor H/C migration Immature or contamination 14/OA/ TOC (%) Production Index 430 Invalid data Hydrogen Index (mg HC/g TOC) present day (c) 800 I VR = 0.5% II Oil Oil + Gas Gas + Oil VR = 1.35% Gas III immature early mature VR = 0.8% Tmax ( C) mature over mature Geotech CUTT extracted (glycol) Geotech CUTT extracted (SBM) GA CUTT extracted (glycol) GA CUTT extracted (SMB) Jamieson Formation Echuca Shoals Formation Analysis of SANS data Small Angle Neutron Scattering (SANS) analysis was performed on 27 claystone cuttings from the well Gorgonichthys-1 (Table A1.9). These cuttings were collected at 50 m to 100 m intervals between depths 2520 mrt to 4770 mrt. 121

139 Figure 3.65 shows the original SANS data presented in the standard manner; scattering intensity, I(Q) in absolute units, versus the scattering vector Q. On the log-log scale the shapes of scattering curves for all samples appear similar, except for the (small) scattering background in the large-q region, which groups into two different values. This is an artifact due to slightly different SANS data processing protocols used in December 2001 and May 2002, and it does not affect the scattering intensity in the small-q region used in the following analysis. There is a significant and systematic variation of the scattering intensity with depth. This is illustrated in Figure 3.66 for scattering intensity measured at Q=0.01 Å -1, which corresponds to a pore size of about µm +/-50% (1 Å = m; 1 µm = 1000 nm = 10,000 Å). On this and many subsequent figures, generalised trend lines have been added to aid interpretation. The scattering intensity initially decreases in the depth range 2620 m to 2870 m and then increases by a factor of 2.3 within the depth range 2870 m to 3360 m in the Jamieson Formation. The scattering intensity is markedly lower at the top of the Echuca Shoals Formation and it decreases by a factor of 1.3 within the depth range 3370 m to 3905 m. The scattering intensity remains at a relatively low value throughout the Vulcan Formation, Plover Formation and Mt Goodwyn Formation, down to a depth of 4720 m. Figure 3.67 illustrates the calculated values of SLD versus depth for the inorganic component of the rock matrix in Gorgonichthys-1. There is little variation (at most 2%) with depth and, consequently, the average value of SLD = 4.49x10 10 cm -2 was used in subsequent calculations for Gorgonichthys-1. The pore size distributions calculated for various depths from the full SANS curves (Figure 3.68) indicate that there is little variation of the geometry of the pore space with depth, except at around the depth of 3320 m, near the base of the Jamieson Formation. A detailed analysis of the variation of pore number density (proportional to the pore size distribution) with depth for three pore sizes 100 Å, 316 Å and 630 Å indicates a more complex picture (Figure 3.69). For the two smaller pore sizes there is a systematic slight compaction with depth, but otherwise, there is a consistent pore size distribution in the claystones throughout the Jamieson Formation, Echuca Shoals Formation and Vulcan Formation. The exception is an anomalous region in the lower portion of the Jamieson Formation. For the pore size 630 Å, the initial compaction trend seems to be reversed in the Echuca Shoals Formation and Vulcan Formation, and the extent of the anomalous region within the lower Jamieson Formation is increased. Figure 3.70 illustrates calculated SANS porosity (only for the fraction of total porosity within the pore size range 20 Å to 1000 Å) versus depth. SANS porosity has been computed by adding pore volumes obtained by fitting the corresponding SANS scattering intensity curve using an assumption that all pores are filled with a fluid of low scattering length density, like brine, gas or saturated hydrocarbons. Therefore, the calculated SANS porosity values for depths where pores are filled with bitumen are too low. Most of the calculated SANS porosity values are about 4%, with a peak of about 11% at the base of the Jamieson Formation. The calculated SANS porosity values appear high and need to be calibrated against the log porosities. Depth intervals characterised by changed conditions are indicated on the left hand side of the figure. The K Aptian sandstone equivalent (3288 m to 3365 m) contains siltstone and sandstone, 122

140 and shows a low gamma ray signal and a low penetration rate. The depth range 3288 m to 3952 m shows varying, elevated levels of gas. Significant overpressure was recorded within the Echuca Shoals Formation. Significance for hydrocarbon generation Except for the anomaly at the base of the Jamieson Formation within the range 3288 m 3365 m, the microstructure of the inorganic rock fabric changes only slightly throughout the entire depth range studied by SANS in Gorgonichthys-1 (Figures 3.68 and 3.69). Therefore, the marked variation of the scattering intensity (Figure 3.66) is ascribed to the change of the density and chemical composition of the organic matter contained within the pores, which affects the neutron scattering contrast. As discussed above, the low values of the scattering intensity indicate pores filled with bitumen at the onset of mobile hydrocarbon generation, and the high values are indicative of pores filled with gas, formation brine and/or saturated hydrocarbons. Based on this, two regions of present-day onset of mobile hydrocarbon generation (at different maturity) can be identified (Figure 3.66): (1) at depth of about m (within the upper Jamieson Formation) and (2) within the Echuca Shoals Formation at a depth of about 3900 m. The increasing SANS intensity with depth within the lower Jamieson Formation indicates progressive cracking of bitumen to mobile hydrocarbons and migration of hydrocarbons to larger pores with increasing depth within the formation. The low scattering intensity within the Echuca Shoals Formation, as compared to the adjacent region in the Jamieson Formation, indicates that there is no communication between the pore spaces of these two sedimentary units. Mud weights indicate overpressuring of this unit (Figure 3.70), which suggests that bitumen and other hydrocarbons generated remain trapped within the formation. The decreasing intensity trend throughout the Echuca Shoals Formation appears to terminate at the top of sandstone intersected within the depth range m, which may indicate that the sandstone reservoirs mobile hydrocarbons generated within the basal Echuca Shoals Formation. The relatively low scattering intensity throughout the Vulcan Formation indicates that the pores contain significant amount of organic matter with a very low hydrogen-to-carbon ratio, e.g. residual bitumen. 123

141 Figure SANS absolute intensity curves for samples of cuttings from Gorgonichthys-1. (a): 13 samples (claystones, 5 m interval each), depth range is 2520 m to 3220 m. (b): 14 samples (claystones and claystones plus silty claystones, 5 m interval each), depth range 3265 m to 4765 m Figure 3.65(a) Gorgonichthys-1 Scattering intensity versus Q for various depths part 1: 2520m to 3220m SCATTERING INTENSITY (cm -1 ) m m m m m m m m m m m m m SCATTERING VECTOR Q (Å -1 ) 124

142 Figure 3.65(b) Gorgonichthys-1 Scattering intensity versus Q for various depths part 2: 3265m to 4765m 10 5 SCATTERING INTENSITY (cm -1 ) m m m m m m m m m m m m m m SCATTERING VECTOR Q (Å -1 ) 125

143 Figure SANS intensity versus depth at Q=0.01 A -1 (corresponding to the pore size 25 nm +/-50%, or µm +/-50%) for cuttings samples from Gorgonichthys µ m (250Å) 2500 Ro=0.54% WOOLASTON 2481m 2536m 3000 Ro=0.51% Ro=0.51% JAMIESON Ro=0.50% DEPTH (mrt) 3500 Ro=0.59% Ro=0.61% Ro=0.75% Ro=0.81% ECHUCA SHOALS 3365m Ro=1.02% Ro=1.03% Ro=1.15% Ro=1.12% 3952m 4115m Gas Sst UPPER VULCAN LOWER m 4218m 4467m PLOVER MT GOODWYN 4718m TD 4772m SCATTERING INTENSITY AT Q=0.01Å -1 (cm -1 ) 126

144 Figure Variation of the Scattering Length Density (SLD) for thermal neutrons with depth for Gorgonichthys-1. SLD values were calculated from the elemental composition as determined by a separate X-ray Fluorescence (XRF) measurement. Gorgonichthys1, Browse Basin Scattering length density versus depth DEPTH (m) SCATTERING LENGTH DENSITY (x10 10 cm -2 ) 127

145 Figure Pore size distribution at various depths for samples of cuttings from Gorgonichthys-1. (a): 13 samples (claystones, 5 m interval each), depth range is 2520 m to 3220 m. (b): 14 samples (claystones and claystones plus silty claystones, 5 m interval each), depth range 3265 m to 4765 m. PORE SIZE DITRIBUTION DENSITY f(r) m 2620m 2720m 2780m 2820m 2870m 2920m 2970m 3020m 3070m 3120m 3170m 3220m PORE SIZE (Å) 128

146 PORE SIZE DITRIBUTION DENSITY f(r) m 3320m 3370m 3420m 3520m 3620m 3720m 3820m 3905m 4120m 4220m 4320m 4720m 4765m PORE SIZE (Å) 129

147 Figure Variation of the pore number density for selected pore sizes versus depth for Gorgonichthys-1. At shallow depths, note slight decrease of the pore number density with depth, indicative of compaction. For full discussion see text r = 630Å 316Å 100Å WOOLASTON 3000 JAMIESON DEPTH (mrt) ECHUCA SHOALS VULCAN 4500 PLOVER PORE NUMBER DENSITY MT GOODWYN 130

148 Figure Variation of apparent porosity (within the pore size range 2 nm to 100 nm) with depth for Gorgonichthys-1. For discussion see text changed lithology: gamma ray & penetration rate WOOLASTON 3000 JAMIESON DEPTH (mrt) m 3365m increased mud density increased gas reading m ECHUCA SHOALS m VULCAN 4500 PLOVER CALCULATED SANS POROSITY (%) MT GOODWYN 3.9 Titanichthys-1 The pyrolysis data for Titanichthys-1 is given in Appendix 5 Table A5.9. Figure 3.71 is a compilation of vitrinite reflectance, total organic carbon and the Rock-Eval pyrolysis parameters (Tmax, S 1, S 2 and HI) plotted against depth (mkb). Figure 3.72 comprises a graph of Tmax versus Hydrogen Index for potential source rock samples. In addition to the extracted cuttings samples analysed in this study, results of Leco TOC and Rock-Eval pyrolysis analyses for cuttings samples (which were analysed by Geotechnical Services) were available from the well completion report (Inpex, 2001c). Vitrinite reflectance measurements were obtained by Kieraville Konsultants Drilling Fluids, Contaminants and Migrated Hydrocarbons Titanichthys-1 was drilled with a water-based drilling mud with gel and polymer additives to a depth of 3905 m. Correspondence with Inpex suggested that glycol additives were also likely to be present in the water-based muds. Below 3905 m Syntech (a synthetic-based mud) was used to the bottom of the well. Irrespective of the drilling mud used, all of the cuttings samples analysed in this study were extracted with methanol and dichloromethane (50:50) as part of the preparative procedure. The cuttings samples analysed by Geotechnical Services were solvent extracted but no details are given in the WCR. 131

149 Comparison of the datasets from the two laboratories (Fig. 3.71) reveals that the values for TOC and Tmax are comparable, whereas Geotechnical Services recorded higher values for the S 1, S 2 and HI parameters, indicating that their extraction process has not removed all of the free organic compounds from within the sediments. After extraction of the sediments with organic solvents, the resultant pyrograms, in most instances, have little or no S 1 peaks and well resolved S 2 and S 3 peaks. This means that the S 1 values, and the calculations involving S 1 values (BI and PI) are invalid and the presence of naturally occurring free hydrocarbons in the sediments cannot be evaluated. Equally, the other pyrolysis parameters must also be interpreted with caution due to the unreliable nature of the S 2 and TOC values. Bearing in mind the limitations imposed because of the contamination, the following interpretations are an approximate guide to the greatest hydrocarbon potential that the sediments in Titanichthys-1 may have, and the minimum thermal maturity that they may have attained. The samples evaluated for their hydrocarbon potential are identified with a black dot in Figure 3.71, and only these data are plotted on the Tmax versus HI plot in Figure It must be stated that there is an offset in the Tmax trend from the depth that the SBM was added (Fig. 3.71). This indicates that SBM contaminants remain within the cuttings samples in Titanichthys-1. Therefore, data from only the samples above 3905 m are interpreted and shown on Figure

150 Figure 3.71 Depth plots of vitrinite reflectance, TOC and Rock-Eval pyrolysis data for Titanichthys-1. Titanichthys -1 WCR sequence (a) (b) (c) 1000 Tertiary 1500 Puffin Formation Fenelon Formation Woolaston Fm Jamieson Formation Depth (m KB) Echuca Shoals Formation 3500 Upper Vulcan Formation 4000 SBM SBM Lower Vulcan Formation 4500 Plover Fm VR (%) Tmax ( C) TOC (%) WCR sequence (d) (e) (f) 1000 Tertiary Puffin Formation Fenelon Formation Woolaston Fm Jamieson Formation Echuca Shoals Formation Upper Vulcan Formation Lower Vulcan Formation Plover Fm Depth (m KB) SBM SBM SBM Invalid data 14/OA/ S1 (mg/g Rock) S2 (mg/g Rock) HI (mg/g TOC) Kieraville Geotech & GA acceptable SR data Geotech CUTT extracted (glycol) Geotech CUTT extracted (SBM) GA CUTT extracted (glycol) GA CUTT extracted (SBM) Source Richness The total organic carbon content gradually increases with depth in Titanichthys-1 until the SBM was used. The samples from both the Lower Cretaceous Jamieson and Echuca 133

151 Shoals formations appear to range from fair to very good with an average TOC of 1.4% and 2.0%, respectively. The potential yields of the sediments from Titanichthys-1 cannot be discussed due to the removal of the S 1 peak by the preparative processes used to eliminate any contamination Source Quality, Kerogen Type and Maturity The source quality of the Jamieson Formation ranges from being gas-prone to having the potential to generate some oil (range HI = mg hydrocarbons/g TOC; average HI = 232 mg hydrocarbons/g TOC; Fig. 3.72). The Echuca Shoals Formation has similar hydrocarbon potential to the aforementioned formation, with HI values ranging from 122 to 336 mg hydrocarbons/g TOC (average HI = 227 mg hydrocarbons/g TOC). The corresponding TOC contents are around 2 %, hence upon maturation some oil expulsion is predicted. Figure 3.72 shows that both the Jamieson and the Echuca Shoals formations contain Type II/III, however it is unknown to the extent that the SBM has contributed to the relatively high HI values. From Tmax values the Jamieson Formation is immature to marginally mature, and the Echuca Shoals Formation is presently within the oil window. Figure 3.72 Tmax versus Hydrogen Index for selected samples from Titanichthys-1. Hydrogen Index (mg HC/g TOC) present day 800 (c) Oil III II Oil + Gas Gas + Oil Gas immature early mature I VR = 0.5% VR = 0.8% VR = 1.35% Tmax ( C) mature over mature Geotech CUTT extracted (glycol) Geotech CUTT extracted (SBM) GA CUTT extracted (glycol) Jamieson Formation Echuca Shoals Formation 134

152 3.9.4 Analysis of SANS data Small Angle Neutron Scattering (SANS) analysis was performed on 20 claystone cuttings from the well Titanichthys-1 (Table A1.10 in Appendix 1). These cuttings were collected at 50 m to 100 m intervals between depths 2450 mrt to 3955 mrt. Figure 3.73 shows the original SANS data presented in the standard manner: scattering intensity, I(Q) in absolute units, versus the scattering vector Q. There is a significant and systematic variation of the scattering intensity with depth. This is illustrated in Figure 3.74 for scattering intensity measured at Q = 0.01 Å -1, which corresponds to a pore size of about µm +/-50% (1 Å = m; 1 µm = 1000 nm = 10,000 Å). The scattering intensity remains roughly constant within the upper Jamieson Formation and then sharply increases by a factor of 1.9 within the depth range 2750 m to 2855 m, followed by a sharp decrease by a factor of 1.3 at the depth of 2900 m. A second sharp increase by a factor of 1.6 occurs in the lower Jamieson Formation within the depth range 3100 m to 3255 m. At the top of the Echuca Shoals Formation the scattering intensity decreases by a factor of 2, down to its original value in the upper Jamieson Formation and remains roughly constant throughout the Echuca Shoals Formation. There is only one data point in the Upper Vulcan Formation with a value 1.2 times higher than the scattering level within the Echuca Shoals Formation. Figure 3.75 illustrates the calculated values of SLD versus depth for the inorganic component of the rock matrix in Titanichthys-1. There is little variation (at most 5%) with depth and, consequently, the average value of SLD = 4.38x10 10 cm -2 was used in subsequent calculations for Titanichthys-1. The pore size distributions calculated for various depths from the full SANS curves (Figure 3.76) indicate that there is little variation of the geometry of the pore space with depth, except around the depth of 3250m, near the base of the Jamieson Formation, where an increased number of larger pores is observed. A detailed analysis of the variation of pore number density (proportional to the pore size distribution) with depth for three pore sizes 100Å, 316Å and 630Å indicates a systematic slight compaction with depth throughout the Jamieson Formation and a systematic expansion throughout the Echuca Shoals Formation (Figure 3.77). There is an anomalous region near the base of the Jamieson Formation, coinciding with the K Aptian sandstone member (3234 to 3305 mrt) which has distinct log characteristics and a changed lithology. Figure 3.78 illustrates calculated porosity (only for the fraction of total porosity within the pore size range 20 Å to 1000 Å) versus depth. SANS porosity has been computed by adding pore volumes obtained by fitting the corresponding SANS scattering intensity curve using an assumption that all pores are filled with a fluid of low scattering length density, like brine, gas or saturated hydrocarbons. Therefore, the calculated SANS porosity values for depths where pores are filled with bitumen are too low. Most of the values are between 4% and 6.5%, with a peak of about 11.5% at the base of Jamieson Formation. The calculated SANS porosity values need to be calibrated against the log porosities. Depth intervals characterised by changed conditions are indicated on the left hand side of the figure. The Kapt sandstone member (3234 m to 3305 m) shows a 135

153 low gamma ray signal and a low penetration rate. Gas readings were somewhat elevated throughout the Echuca Shoals Formation, and within the depth range 4361 m to 4444 m within the Lower Vulcan Formation (not sampled by SANS), particularly high levels of gas were recorded. Significant overpressure was recorded within the Echuca Shoals Formation. Significance for hydrocarbon generation Except for the anomaly at the base of the Jamieson Formation (sample at 3250 m), the microstructure of the inorganic rock fabric changes only slightly throughout the entire depth range studied by SANS in Titanichthys-1 (Figures 3.76 and 3.77). Therefore, the marked variation of the scattering intensity (Figure 3.74) is ascribed to the change of the chemical composition of the organic matter contained in the pores, which affects the neutron scattering contrast. As discussed above, the low values of the scattering intensity indicate pores filled with bitumen at the onset of hydrocarbon generation, and the high values pores filled with gas, formation brine and/or saturated hydrocarbons. Based on this, three regions of the onset of mobile hydrocarbon generation (at different maturity) can be identified (Figure 3.74): (1) within the upper Jamieson Formation at a depth of about m, (2) within the lower Jamieson Formation at a depth of about m, and (3) possibly within the Echuca Shoals Formation at a depth of about 3650 m. All three generation regions are separated from each other by barriers due either to lack of permeability or markedly different thermal kinetics for transformation of organic matter. The increasing SANS intensity with depth for two hydrocarbon generation regions within the Jamieson Formation indicates progressive cracking of bitumen to mobile hydrocarbons and migration of hydrocarbons to larger pores with increasing depth within the formation. The low scattering intensity within the Echuca Shoals Formation, as compared to the adjacent region in the Jamieson Formation, indicates that there is no communication between the pore spaces of these two sedimentary units. Mud weights indicate overpressuring at the base of the Jamieson Formation below a depth of 3170 m and of the entire Echuca Shoals Formation (Figure 3.78), which suggests that bitumen and other hydrocarbons generated remain trapped within these units. This may not apply to the base of the Echuca Shoals Formation and to the top of the Upper Vulcan Formation, which are in close proximity to the sandstone intersected within the depth range m. It is possible that the sandstone reservoirs mobile hydrocarbons generated at the base of the Echuca Shoals Formation and at the top of the Upper Vulcan Formation. In contrast, the permeability barrier apparent within the Jamieson Formation is likely to impede vertical movement of generated hydrocarbons. 136

154 Figure SANS absolute intensity curves for samples of cuttings from Titanichthys-1. (a): 13 samples (claystones, 5 m interval each), depth range 2450 m to 3255 m. (b): seven samples (claystones and one silty claystone, 5 m interval each), depth range 3350 m to 3955 m Figure 3.73(a) Titanichthys-1 Scattering intensity versus Q for various depths part 1: 2450 m to 3250 m SCATTERING INTENSITY (cm -1 ) m m m m m m m m m m m m m SCATTERING VECTOR Q (Å -1 ) 137

155 Figure 3.73(b) Titanichthys-1 Scattering intensity versus Q for various depths part 2: 3350 m to 3950 m 10 5 SCATTERING INTENSITY (cm -1 ) m m m m m m m SCATTERING VECTOR Q (Å -1 ) 138

156 Figure SANS intensity versus depth at Q = 0.01 A -1 (corresponding to the pore size 25 nm +/-50%, or µm +/-50%) for cuttings samples from Titanichthys µ m (250 Å) 2500 Ro=0.53% WOOLASTON Ro=0.46% JAMIESON DEPTH (mrt) Ro=0.52% Ro=0.56% Ro=0.56% Ro=0.55% Ro=0.58% permeability or kinetics barrier Ro=0.56% 4000 Ro=0.60% Ro=0.69% Ro=0.89% Ro=1.06% Sst 3967m 4197m SCATTERING INTENSITY AT Q=0.01Å -1 (cm -1 ) ECHUCA SHOALS UPPER VULCAN LOWER 139

157 Figure Variation of the Scattering Length Density (SLD) for thermal neutrons with depth for Titanichthys-1. SLD values were calculated from the elemental composition as determined by a separate X-ray Fluorescence (XRF) measurement. Titanichthys1, Browse Basin Scattering length density versus depth DEPTH (m) SCATTERING LENGTH DENSITY (x10 10 cm -2 ) 140

158 Figure Pore size distribution at various depths for samples of cuttings from Titanichthys-1. (a): 13 samples (claystones, 5 m interval each), depth range is 2450 m to 3250 m. (b): 12 samples (claystones and claystones plus silty claystones, 5 m interval each), depth range 3350 m to 3950 m. Figure 3.76(a) Titanichthys-1 Pore size distribution part 1: 2450 m to 3250 m PORE SIZE DITRIBUTION DENSITY f(r) m m m m m m m m m m m m m m PORE SIZE (Å) 141

159 Figure 3.76(b) Titanichthys-1 Pore size distribution part 2: 3350 m to 3950 m PORE SIZE DITRIBUTION DENSITY f(r) m m m m m m m PORE SIZE (Å) 142

160 Figure Variation of the pore number density for selected pore sizes versus depth for Titanichthys-1. Note the slight decrease of the pore number density with depth, indicative of compaction r = 630Å 316Å 100Å 2500 DEPTH (mrt) 3000 JAMIESON m ECHUCA SHOALS PORE NUMBER DENSITY UPPER VULCAN 143

161 Figure Variation of apparent porosity (within the pore size range 2 nm to 100 nm) with depth for Titanichthys-1. Figure 3.78 Titanichthys-1 Calculated porosity versus depth in pore size range 2nm to 100nm m 2800 changed lithology: gamma ray & penetration rate JAMIESON DEPTH (mrt) m 3234m 3305m increased gas reading increased mud density ECHUCA SHOALS 3305m m high gas reading 4361m 4444m UPPER VULCAN LOWER PLOVER 3888m 4274m 4459m CALCULATED SANS POROSITY (%) TD 4602m 144

162 4 Discussion: Well Comparisons The following four sections document the effect of mud additives on pyrolysis and SANS/USANS results and the effect of sample age on SANS/USANS results by comparing adjacent wells. The last section gives an overall summary of the source potential of the formations in the wells examined in this study. 4.1 Pyrolysis results: Adele-1 compared to Brewster-1A The use of the glycol additive in the drilling fluid does not appear to have affected the TOC and Tmax results from the unwashed SWCs in Adele-1 when compared to the results obtained from Brewster-1A, drilled using a water-based mud without organic additives. This is shown in Figure 4.1, which plots vitrinite reflectance, TOC and pyrolysis parameters versus depth (mss). However, a relative increase in the S 2 and HI values in the SWCs from Adele-1 are apparent. The integrity of the data from the extracted cuttings samples from Adele-1 which are not compromised by the extraction process (i.e. S 2, Tmax and TOC) is comparable with that of the unwashed cuttings samples from Brewster-1A (Fig. 4.1). 4.2 Pyrolysis results: new Ichthys Field wells compared to Brewster-1A The wells Dinichthys-1, Gorgonichthys-1, Titanichthys-1 and Brewster-1A are in close proximity and penetrate similar stratigraphy, therefore an indication of the effect that different drilling fluids have on pyrolysis data can be obtained. Dinichthys-1 was drilled with a glycol additive. The Gorgonichthys-1 and Titanichthys-1 wells were drilled with water-based drilling mud, however glycol additives are suspected, from the top of the well until around 3900 m, from which depth SBM was used. Figure 4.2 compares TOC and pyrolysis data for extracted cuttings samples (with no apparent contamination) from the wells Dinichthys-1, Gorgonichthys-1 and Titanichthys-1 with cuttings samples from Brewster-1A. No data from samples below 3900 m in Gorgonichthys-1 and Titanichtys-1 are plotted, since these samples have obvious contamination from the SBM. 145

163 Figure 4.1 Comparison of pyrolysis data from nearby wells drilled using waterbased mud and without glycol additives. Depth is expressed in mss. GA sequence (a) (b) (c) 1000 Campanian 1500 Santonian-Turonian Jamieson Formation Echuca Shoals Formation Depth (m SS) Adele-1, Kieraville, SWC Brewster-1A, Robertson Research Brewster-1A, Geotrack Adele-1 Geotech, SWC Adele-1, GA CUTT extracted Brewster-1A, GA & RR CUTT Upper Vulcan Formation Lower Vulcan Fm 4000 Plover Formation 4500 GA sequence VR (%) Tmax ( C) TOC (%) (d) (e) (f) 1000 (g) Campanian 1500 Santonian-Turonian 2000 Jamieson Formation Echuca Shoals Formation Depth (m SS) Upper Vulcan Formation Lower Vulcan Fm 4000 Plover Formation S1 (mg/g Rock) S2 (mg/g Rock) HI (mg/g TOC) BI 14/OA/ Although the vitrinite reflectance trends show that the sediments in these wells have obtained comparable levels of thermal maturity, the Tmax values of Gorganichthys-1 and Titanichthys-1 are slightly lower, indicating that drilling additives are still present in the cuttings samples despite solvent extraction. The Tmax trend for Dinichthys-1 and Brewster-1A are comparable. The TOC trends are fairly comparable, with slightly higher values being obtained in Dinichthys-1, Gorgonichthys-1 and Titanichthys-1 over the depth range m. In general, the S 2 and HI values of the extracted samples from Dinichthys-1, Gorgonichthys-1 and Titanichthys-1 are relatively higher than those from Brewster- 1A, in particular over the depth range m. Since these two trends do not coincide, residual contamination may remain within the cuttings samples, resulting in the apparent enrichment of their source quality and increased hydrocarbon potential. 146

164 Figure 4.2 Comparison of pyrolysis data from near-by wells drilled using different mud systems. Depth is expressed in mss. (a) (b) (c) Depth (m SS) VR (%) Tmax ( C) TOC (%) (e) 1000 (f) Depth (m SS) S2 (mg/g Rock) 0 14/OA/ HI (mg/g TOC) Brewster-1A, Geotrack Gorgonichthys-1, Kieraville Dinichthys-1, Kieraville Titanichthys-1, Kieraville Brewster-1A, GA & RR (water-based) Dinichthys-1, GA CUTT extracted (glycol) Gorgonichthys-1, GA CUTT extracted (glycol or SBM) Titanichthys-1, GA CUTT extracted (glycol or SBM) 147

165 4.3 SANS results: new Ichthys Field wells compared to Brewster-1A The geographical proximity and geological similarities between Brewster-1A, Dinichthys-1, Gorgonichthys-1 and Titanichthys-1 (Figure 1.2 and Table 4.1) enables a meaningful comparison between the corresponding sets of SANS data. Furthermore, owing to the various ages of recovered cuttings and different types of drilling mud used (Tables A1.1 and 4.1), the effect of these factors on the quality of SANS data can be examined. In particular, it is well known that certain types of drilling muds and/ or contaminants render the results of some geochemical analyses unreliable and the question arises whether the same is true for SANS results. Figure 4.3 illustrates the variation of scattering intensity with depth normalised to the sea level datum and measured for the four wells at Q=0.01 Å -1. The general character of the intensity versus depth curve is similar for all four wells: low intensity near the top of the Jamieson Formation, a rapid increase towards a maximum value near the base of the Jamieson Formation, a sharp decrease at the top of Echuca Shoals Formation and gradually decreasing values throughout the Echuca Shoals Formation, with local increase at the base of the Echuca Shoals Formation and top of Vulcan Formation (for Titanichthys-1 and Dinichthys-1 only). For Brewster-1A and Titanichthys-1 there is an additional rapid increase - sharp decrease intra-jamieson cycle. In Section 3 of this report it is demonstrated that for each individual well the pore number density for pore sizes of about 250 Å does not vary significantly with depth except for the narrow region at the base of the Jamieson Formation (61 m to 84 m thick K Aptian sandstone member or K Aptian sandstone member equivalent ). Bitumen has a scattering length density much larger than brine or gas, and being rather similar to that of the rock matrix, which results in the loss of scattering contrast. Therefore, low values of scattering intensity are interpreted as being caused by the presence of generated bitumen in the pore space. Based on this interpretation, depths of the onset of mobile hydrocarbon generation and expulsion to larger pores (referred to as onset below) predicted by SANS are marked in Figure 4.4. The first onset identified by SANS is located at the top of Jamieson Formation within the depth range 2500 m (Dinichthys-1) to 2900 m (Gorgonichthys-1), depending on the well. In this depth region the vitrinite reflectance values are in the range 0.5% (Dinichthys-1) to 0.54% (Brewster-1A, Keiraville data). The second onset was identified only in Titanichthys-1 and Brewster-1A and is located in the mid Jamieson Formation within the depth range m. In this depth region the vitrinite reflectance values are in the range 0.52%-0.56% for Titanichthys-1 and 0.54% for Brewster-1A (Keiraville data). The third onset identified by SANS is located either in the lower Echuca Shoals Formation (Titanichthys-1), basal Echuca Shoals Formation (Dinichthys-1) or the uppermost Vulcan Formation (Gorgonichthys-1 and Brewster-1A) within the depth range m. In this depth region the vitrinite reflectance values are widely spread in the range 0.56% (Titanichthys-1) to 1.03% (Brewster-1A, Gorgonichthys-1). 148

166 The existence of two (three for Titanichthys-1 and Brewster-1A) SANS-identified onsets of mobile hydrocarbon generation and expulsion to larger pores is interpreted to be due to markedly different kinetics for thermal maturation of organic matter deposited in each of the two (three) hydrocarbon generation units (source rocks). The overall magnitude of the scattering intensity versus depth is similar for Gorgonichthys-1 and Titanichthys-1, and for Brewster-1A and Dinichthys-1. The absolute SANS intensity differs between these two groups of wells by a factor of two (Figure 4.3), whereas the experimental error for the absolute intensity does not exceed 10% absolute and is much less in relative terms. The close similarity between SANS data for Brewster-1A (spudded in 1980) and Dinichthys-1 (spudded in 2000) indicates that ageing (weathering) of cuttings stored in sealed plastic bags over a period of many years is most likely not an issue for SANS. This is a very important finding, as it demonstrates that SANS data taken on old cuttings can be reliable. It is possible, however, that the significant scatter of SANS data for Brewster-1A within the Echuca Shoals Formation may be caused by the particle-sizespecific ageing of the cuttings, and more specifically may be related to the size variation of the original cuttings particles used for SANS sample preparations. The original cuttings size was not monitored in this work. The similarity of the SANS data for Gorgonichthys-1 and Titanichthys-1, as opposed to Dinichthys-1, all spudded in 2000, can by interpreted in several ways. Firstly, one reason could be purely geochemical and has to do with differences in the hydrocarbon generation process and/or the composition of bitumen expelled into the pore space. Secondly, the potential influence of the type of drilling mud on the SANS signal needs to be considered. Brewster-1A and Dinichthys-1 were drilled using sea-water based muds, whereas Gorgonichthys-1 and Titanichthys-1 were drilled using synthetic based muds. Although it is unlikely that mud particles could significantly penetrate 150 Å diameter pores in cuttings, such a possibility cannot be entirely discarded. Out of the four wells, Brewster-1A and Titanichthys-1 are geographically closest to each other (about 5 km). Although they exhibit markedly different SANS intensities, in both wells an intra-jamieson permeability/kinetics barrier is observed at a depth of about 2900 mrt. There is no indication of such a barrier in Dinichthys-1 and Gorgonichthys

167 Table 4.1 Drilling information and depths of lithological units for Brewster-1A, Dinichthys-1, Gorgonichthys-1 and Titanichthys-1. Formation Brewster-1A Dinichthys-1 Gorgonichthys- 1 Titanichthys-1 Water Depth (m) RT (m) TD (mrt) Drilling Mud Salt/Polymer Aquadrill/ Pyrodrill Syntec (SBM) Syntec (SBM) below 2366 mrt below 2471 mrt below 2405 mrt below 2337 mrt Mud contaminants diesel fuel glycol, alkenes Spud Date 23-May-80 3-Mar May Sep-00 Top Woolaston (mrt) Jamieson Echuca Shoals Upper Vulcan Lower Vulcan Plover Top Woolaston (m below Jamieson sea level) Echuca Shoals Upper Vulcan Lower Vulcan Plover Thickness (m) Woolaston Jamieson Echuca Shoals Upper Vulcan Lower Vulcan Plover >250 > >

168 Figure 4.3. Scattering intensity versus depth (below sea level) for stratigraphic formations in Brewster-1A, Dinichthys-1, Gorgonichthys-1 and Titanichthys µ m (250 Å) DEPTH (m below sea level ) SCATTERING INTENSITY AT Q=0.01Å -1 Br Jamieson Br Echuca Shoals Br Upper Vulcan Di Jamieson Di Echuca Shoals Di Upper Vulcan Di Lower Vulcan Go Woolaston Go Jamieson Go Echuca Shoals Go Upper Vulcan Go Lower Vulcan Go Mt Goodwyn Ti Jamieson Ti Echuca Shoals Ti Upper Vulcan (cm -1 ) 151

169 Figure 4.4. Interpretation of SANS data for Brewster-1A, Dinichthys-1, Gorgonichthys-1 and Titanichthys ONSET µ m (250 Å) DEPTH (m Below Sea Level) ONSET 2 ONSET 3 BARRIER BARRIER Brewster-1 (depth BSL) Dinichthys-1 (depth BSL) Gorgonichthys-1 (depth BSL) Titanichthys -1 (depth BSL) SCATTERING INTENSITY AT Q=0.01Å -1 (cm -1 ) 4.4 SANS Results: Adele-1 and Crux-1 compared to Brewster-1A Brewster-1A and Adele-1, both located in the Caswell Sub-basin, are geographically close and geologically similar. Crux-1, which has been drilled in the northern part of the Heywood Graben for a Triassic Nome Formation, is located over the Jurassic rift graben overlaid by a proximal portion of the Cretaceous prograde, and has the Jamieson and Echuca Shoals sections much thinner and the Jurassic section much thicker than the other two wells (Figures 1.2 (well location), 3.5 (Brewster-1A), 3.23 (Adele-1) and 3.38 (Crux-1)). Despite these significant differences, the depth of burial of the upper part of 152

170 the Jamieson Formation is similar for all three wells, which enables some meaningful comparison between the corresponding sets of SANS data. Figure 4.5 illustrates the variation of scattering intensity with depth normalised to the sea level datum and measured for the three wells at Q=0.01Å -1. For the Brewster-1A and Adele-1 wells, the general character of the intensity versus depth curve is similar: low intensity near the top of the Jamieson Formation, a rapid increase towards a maximum value in mid-jamieson Formation, followed by another rapid increase - sharp decrease cycle ending at the bottom of the Jamieson Formation. For the Crux-1 well there is a minimum scattering intensity in mid-jamieson Formation, clearly visible despite the relatively low sampling density. In Section 3 of this report it is demonstrated that for each individual well the pore number density for pore sizes of about 250 Å does not vary significantly with depth except for the narrow region at the base of the Jamieson Formation (61 m to 84 m thick K Aptian sandstone member or K Aptian sandstone member equivalent ). Bitumen has the scattering length density much larger than brine or gas, and being rather similar to that of the rock matrix, which results in the loss of scattering contrast. Therefore, low values of scattering intensity are interpreted as being caused by the presence of generated bitumen in the pore space. Based on this interpretation, depths of the onset of mobile hydrocarbon generation and expulsion to larger pores (referred to as onset below) predicted by SANS coincide with the minimum values of the scattering intensity. The first onset identified by SANS is located at the top of Jamieson Formation at the depth of 2700 m for Brewster-1 and 2650 m for Adele-1. In this depth region the vitrinite reflectance values are 0.54% for Brewster-1A (Keiraville data) and 0.52% for Adele-1. The first onset for Crux-1 is located in the mid-jamieson Formation at the depth of 2400 m and the corresponding vitrinite reflectance value is 0.51%. The second onset identified in Brewster-1A and Adele-1 is located in the mid-jamieson Formation at depth of 3050 m and 3200 m, respectively. In this depth region the vitrinite reflectance values are 0.54% for Brewster-1A (Keiraville data) and 0.62% for Adele- 1. The second onset for Crux-1 can be identified at the base of the Echuca Shoals Formation at the depth of about 2690 m, with the corresponding vitrinite reflectance value of 0.42% (directly measured, probably suppressed) or 0.80% (from FAMM). A third onset of hydrocarbon generation has been identified for Crux-1 near the base of the Upper Vulcan Formation (Figure 3.54), with corresponding vitrinite reflectance value of 0.45% (measured directly) or 0.90% (from FAMM). This Formation was not sampled for SANS work neither within Brewster-1A nor Adele-1. The existence of two Cretaceous SANS-identified onsets of mobile hydrocarbon generation and expulsion to larger pores is interpreted to be due to the markedly different kinetics for thermal maturation of organic matter deposited in each of the two hydrocarbon generation units (source rocks). The overall magnitude of the scattering intensity versus depth is similar for Brewster- 1A and Adele-1, and by a factor of two smaller for Crux-1 (Figure 4.5), whereas the experimental error for the absolute intensity does not exceed 10% absolute and is much less in relative terms. 153

171 Figure 4.5. Scattering intensity versus depth (below sea level) for stratigraphic formations in Brewster-1A, Crux-1 and Adele-1. Figure 4.5 Comparison of SANS data for three wells SANS intensity vs depth at Q=0.01Å -1, pore size 250Å+/-50% Br - Brewster-1A, Crux - Crux-1, Adele - Adele Br Jamieson Br Echuca Shoals Br Upper Vulcan 2500 calcareous? Crux Jamieson DEPTH (m below sea level) onset 1 Br onset 2 Br Crux Echuca Shoals Crux Upper Vulcan Crux Lower Vulcan Adele Jamieson Source Rock Summary SCATTERING INTENSITY AT Q=0.01Å -1 (cm -1 ) Rock-Eval/TOC source rock data was obtained from the Jamieson Formation from the wells Brewster-1A, Carbine-1, Adele-1, Dinichthys-1, Gorgonichthys-1 and Titanichthys-1, as is summarised in Figure 4.6. Overall the Jamieson Formation has poor source richness. Although the TOC contents range from 0.6%-2% with average values of 1.3% their potential yields are low (range S 1 +S 2 = mg hydrocarbons/g rock; average S 1 +S 2 = 1.4 mg hydrocarbons/g rock), as summarised from Brewster- 154

172 1A and Carbine-1 (the other wells had the S 1 peak removed). This formation contains Type II/III to Type III kerogen that is immature-marginally mature for hydrocarbon generation (average Tmax = 431 o C). However, those samples with HI values between mg hydrocarbons/g TOC typically have TOC contents less than 1.8%. Therefore, based on the pyrolysis results, where sampled the Jamieson Formation is not expected to have generated liquid hydrocarbons. This conclusion is confirmed by SANS/USANS evidence. Although SANS has detected the presence of bitumen in small pores (about 0.01 µm diameter) within two or three different depth intervals within the Jamieson Formation in Adele-1, Crux-1, Gorgonichthys-1, Titanichthys-1, Dinichthys- 1 and Brewster-1A, USANS data acquired for the two latter wells clearly indicate that the amount of generated bitumen has been insufficient to saturate the pore space and create an effective source rock. SANS data for Brecknock South-1 and Carbine-1 are inconclusive, as they are masked by the varying source rock lithology and strong compaction signal, respectively. Rock-Eval/TOC source rock data were obtained for the Echuca Shoals Formation from the wells Brewster-1A, Carbine-1, Crux-1, Dinichthys-1, Gorgonichthys-1 and Titanichthys-1. Overall the Echuca Shoals Formation has poor source richness. Although the TOC contents range from 0.6%-2.8% with average values of 1.8% their potential yields are low (range S 1 +S 2 = mg hydrocarbons/g rock; average S 1 +S 2 = 2.4 mg hydrocarbons/g rock), as observed in Brewster-1A and Carbine-1 (the other wells had the S 1 peak removed). This formation contains Type II/III to Type III kerogen that is early mature for hydrocarbon generation (average Tmax = 441 o C). The samples with HI values between mg hydrocarbons/g TOC typically have TOC contents between 1% and 2.8%. Therefore, based on the pyrolysis results, some liquid hydrocarbons could have been generated within the Echuca Shoals Formation. SANS has detected the presence of bitumen in small pores (about 0.01 µm diameter) within the Echuca Shoals Formation in Adele-1, Crux-1, Gorgonichthys-1, Titanichthys-1, Dinichthys-1 and Brewster-1A. SANS data for Brecknock South-1 and Carbine-1 are inconclusive, as they are masked by the varying source rock lithology and strong compaction signal, respectively. USANS data, which are crucial for detecting the presence of bitumen in largest pores and, therefore, determine whether hydrocarbon expulsion could occur, have only been acquired for two wells: Dinichthys-1 and Brewster-1A. Combined SANS/USANS data for Dinichthys-1 show the presence of generated bitumen in pores of all sizes near the base of the Echuca Shoals Formation, but not at the depths adjacent to the Berriasian 'Brewster' Sandstone, which is an important reservoir rock. That is, hydrocarbons generated in the Echuca Shoals Formation do not appear to have been expelled into the Berriasian Sandstone reservoir. This is consistent with previous findings based on oil-source correlation that the Berriasian Sandstone reservoirs have not been charged from Early Cretaceous source rocks. In Brewster-1A there is SANS/USANS evidence of pore-size-specific oil-to-gas cracking within the Echuca Shoals Formation. Based on pyrolysis data, the most oil-prone source rocks are apparently found in Gorgonichthys-1 and Titanichthys-1, however there is the possibility that these samples may still contain residual contaminants from the drilling mud. 155

173 The only source rock data available for the Upper and Lower Vulcan formations and the Montara Formation are from Crux-1, therefore no comparisons could be made to other wells. Figure 4.6 Comparison of source rock data from Browse Basin study wells. Browse Basin Source Rocks 800 I VR = 0.5% Hydrogen Index (mg HC/g TOC) present day II Oil Oil + Gas Gas + Oil VR = 1.35% Gas III immature early mature VR = 0.8% 0 14/OA/ Tmax ( C) mature over mature Jamieson Formation Echuca Shoals Formation Upper Vulcan Formation Lower Vulcan Formation 156

174 5 Conclusions Modern drilling practices typically involve the addition of organic compounds to waterbased muds, such as glycol, or the use of SBMs. Not all WCRs list the total additives used while drilling the well, as highlighted by the wells Dinichthys-1, Gorgonichthys-1 and Titanichthys-1. Organic additives present in the sediment samples have a significant effect on TOC and Rock-Eval pyrolysis results; notably low and variable Tmax values, high S 1, S 2, TOC, HI and BI values. Such results can lead to an underestimation of thermal maturity and an overestimation of hydrocarbon source potential. Extraction of samples obtained from mud systems using glycol additives or SMBs with organic solvents removes any organic compounds present to varying degrees. The amount of contamination remaining in the sample depends on the initial concentration of the contaminant, the porosity and permeability of the rock sample and the rigorousness of the extraction process. This means that the validity of the TOC and pyrolysis data is still questionable even after solvent extraction. A full set of data is routinely reported in WCRs for samples that have been extracted with solvents. However, the S 1 abundances of the extracted samples are invalid because any naturally occurring free hydrocarbons (as well as contaminants) are removed during the extraction process. Therefore, the S 1 and the derivatives, BI and PI cannot be used for source rock evaluation. Since the kerogen in the rock is unaffected by the solvent extraction process, the S 2 and derivatives Tmax and HI values should reflect the maturity and source quality of the sediment. In reality, Tmax trends seem to be fairly reliable regardless of the drilling fluid used. However, widely varying TOC, S 2 and HI values were obtained from the extracted samples due to contaminants remaining in the sample. Generally, SWC samples were less affected by contaminants than cuttings samples, as shown by the results from Adele-1. In summary, reliable TOC and pyrolysis data were obtained for Brewster-1A and Carbine-1 which were used in the evaluation of the source potential of the Lower Cretaceous Jamieson and Echuca Shoals formations. Data that were used with caution were obtained from Adele-1, Crux-1, Dinichthys-1, Gorgonichthys-1 and Titanichthys- 1. No useable data were obtained from Argus-1 and the data from Brecknock South-1 were not used in the source rock evaluations due to the lower than expected Tmax values. The Lower Cretaceous Jamieson Formation and Echuca Shoals Formation have similar TOC contents with averages of 1.3% and 1.8%, respectively. Evaluation of their source richness could only be made from the wells Brewster-1A and Carbine-1, since all other samples in the study were extracted, removing the S 1 peak. The data from these wells showed that the sediments had poor generative potential with average S 1 +S 2 values less than 3 mg hydrocarbons/g rock. They contain Type II/III to Type III kerogen. The samples from the Jamieson Formation with HI values between mg hydrocarbons/g TOC typically have TOC contents less than 1.8%. This, coupled with their lack of thermal maturity implies that this formation has not generated and expelled hydrocarbons. The samples from the Echuca Shoals Formation with the highest source rock quality have sufficient maturity to have generated and expelled some liquid hydrocarbons. 157

175 In contrast to Rock-Eval/TOC, drilling mud contamination does not seem to affect SANS/USANS data. Similarly, natural weathering of cuttings stored in sealed plastic bags seems to have little effect (Brewster-1A was drilled in 1980). SANS/USANS results, however, can be strongly affected by microstructural variations caused either by varying sample lithology (Brecknock South-1) or strong compaction caused by shallow burial (Carbine-1). SANS interpretation is also inconclusive for overmature source rocks (Argus-1). For the remaining six wells there is SANS evidence of bitumen generation in the small pores both within the Jamieson Formation and the Echuca Shoals Formation. Depending on the well, there are two or three distinct generative depth intervals within the Jamieson Formation, separated by permeability barriers. USANS data for Brewster-1A and Dinichthys-1 indicate that there is insufficient bitumen saturation of larger pores in the Jamieson Formation to create an effective source rock. Within the Echuca Shoals Formation, for Dinichthys-1 there is USANS evidence of bitumen presence in pores of all sizes, but not at depths adjacent to the Berriasian Brewster Sandstone. There is also USANS evidence of oil-to-gas cracking for Brewster-1A within the Echuca Shoals Formation. 158

176 6 Recommendations and Further Work 1. Modify Extraction Method. Since the glycol contaminant contains a high proportion of alkenes, and the Rock-Eval pyrolysis results appear to be still effected by the contaminant, the washing process should be modified to include an additional wash with petroleum ether to remove the alkenes. However, this residual contamination may reside in smaller, water-wet pores. If this is the case, the petroleum ether will not be able to penetrate the sediments. An alternative extraction method would be to use the Accelerated Solvent Extractor (ASE), as this uses higher temperatures and generally facilitates a higher extraction yield. After extracting the samples by these two methods, use USANS to examine the efficiency of the extraction process in the larger pores. 2. Effect of glycol on S 3 peak. Determine whether glycol decomposes at < 390 o C to liberate CO 2, and hence determine if the S 3 peak is affected despite the Oxygen Index being low in both contaminated and uncontaminated samples. 3. Oil-source rock correlations. Prior to any oil-source rock correlations being run, the composition of the drilling fluid contaminants should be determined and an assessment made of the extent that these contaminants will interfere with biomarker and isotopic measurements which are used as the primary source characterisation parameters. The aromatic components of the drilling fluid need to be assessed to determine their influence on maturity parameters. Geotechnical Services have produced a commercial report Drilling fluids and mud additives: their impact on the interpretation of geochemical data, which documents the chemical compositions of typical fluids used to drill Australian wells. This report will assist in the identification of contaminant compounds. If oil-source rock correlations are carried out on the Jamieson and Echuca Shoals formations, the best samples would be from the wells around the Brewster Field. The Upper and Lower Vulcan Formation could be sampled from Crux-1. However, the effect of the drilling contaminants on the geochemical parameters must first be ascertained. 4. Kinetic Analysis. Carry out kinetic analysis to define the thermal maturity required to generate hydrocarbons from the Jamieson Formation compared with kerogen from the Echuca Shoals Formation. 5. Importance of combined SANS/USANS studies. The abundance, quality and maturity of the kerogen in the source rocks interpreted from conventional Rock- Eval pyrolysis data needs to be compared with the SANS/USANS results to verify which source rocks have generated and expelled liquid hydrocarbons. This study demonstrates that most conclusive results can be obtained when both SANS (generation) and USANS (saturation and expulsion) data are available. 159

177 160

178 7 References Blevin, J.E., Struckmeyer, H.I.M., Cathro, D.L., Totterdell, J.M., Boreham, C.J., Romine, K.K., Loutit, T.S. and Sayers, J. (1998a). Tectonostratigraphic framework and petroleum systems of the Browse Basin, North West Shelf. In: Purcell, P.G. and R.R. (eds) The Sedimentary Basins of Western Australia 2. Proceedings of Petroleum Exploration Society of Australia Symposium, Perth, WA, Blevin, J.E., Boreham, C.J., Summons, R.E., Struckmeyer, H.I.M. and Loutit, T.S. (1998b). An effective Early Cretaceous petroleum system on the North West Shelf: evidence from the Browse Basin. In: Purcell, P.G. and R.R. (eds) The Sedimentary Basins of Western Australia 2. Proceedings of Petroleum Exploration Society of Australia Symposium, Perth, WA, Clementz, D.M. (1979). Effect of oil and bitumen saturation on source-rock pyrolysis. AAPG Bulletin 63, Espitalié, J. and Bordenave, M.L. (1993). Rock Eval pyrolysis. In: Bordenave, M.L. (ed) Applied PetroleumGeochemistry. Éditions Technip, Paris, Espitalié, J., Madec, M. and Tissot, B. (1980). Role of mineral matrix in kerogen pyrolysis: influence on petroleum generation and migration. AAPG Bulletin 64, Espitalié, J., Deroo, G. and Marquis, F. (1985). Rock-Eval pyrolysis and its applications. Rev. Inst. Franç, Pétr., Ref , vol. 2. Hainbuchner M., Villa M., Kroupa G., Bruckner G., Baron M., Amenitsch H., Seidl E. and Rauch H. (2000) The new high resolution ultra small-angle neutron scattering instrument at the High Flux Reactor in Grenoble. J. Appl. Cryst. 33, Horsfield, B and Douglas, A.G. (1980). The influence of minerals on the pyrolysis of kerogens. Geochim. Cosmochim. Acta 44, Horsfield, B. (1984). Pyrolysis studies and petroleum exploration. In: Brooks, J. and Welte, D.H. (eds) Advances in Petroleum Geochemistry, Academic, London, vol. 1, pp Orr, W. L. (1983). Comments on pyrolytic yield in source rock evaluation. In: Bjorøy, M. et al. (eds) Advances in Organic Geochemistry 1981, Wiley, Chichester, pp Peters, K.E. (1986). Guidelines for evaluating petroleum source rock using programmed pyrolysis. AAPG Bulletin 70, Radlinski, A.P., Kennard J.M., Edwards D.S., Hinde A.L. and Davenport, R. (2004). Hydrocarbon generation and expulsion from Early Cretaceous source rocks in the Browse Basin, North West Shelf, Australia: a small angle neutron scattering study. APPEA Journal 2004, Radlinski, A.P. (2006). Small angle neutron scattering and the microstructure of rocks. Rev. Mineral. Geochem. (in press) Robertson Research Australia Pty. Ltd. (1986). Northwest Shelf, Australia Phase II. Petroleum Geology and Geochemistry. Volume 3: Well Summary Reports. 161

179 Thiyagarayan, P., Urban, V., Littrell, K., Ku, C., Wozniak, D.G., Belch, H., Vitt, R., Toeller, J., Leach, D., Haumann, J.R., Ostrowski, G.E., Donley, L.I., Hammonds, J., Carpenter, J.M., and Crawford, R.K. (1998). The performance of the small-angle diffractometer SAND at IPNS. ICANS-XIV, 14th Meeting of the International Collaboration on Advanced Neutron Sources, June , Starved Rock Lodge, Utica, Illinois. Well Completion Reports Brewster-1A WA-35-P Well Completion Report (1980). Woodside Offshore Petroleum Pty. Ltd. Well Completion Report Adele-1 WA-35-P (1February 1999). Shell Development (Australia) Pty. Ltd. Argus-1, AC/P30 Well Completion Report (February 2001). Prepared by C. Ellis, BHP Petroleum Pty. Ltd. Brecknock South-1 Well Completion Report (March 2001). Woodside Australian Energy. Carbine-1, Well Completion Report WA-283-P, Browse Basin, Western Australia (April 2002). Santos Ltd. Crux-1 Final Geological Report Volume 1, AC/P23 Territory of Ashmore and Cartier (March 2001). Nippon Oil Exploration (Vulcan) Pty. Ltd. Well Completion Report Dinichthys-1 (WA-285-P, Browse Basin) (May 2001a). Inpex Browse Ltd. Well Completion Report Gorgonichthys-1 (WA-85-P, Browse Basin) (May 2001b). Inpex Browse Ltd. Well Completion Report Titanichthys-1 (WA-85-P, Browse Basin), (May 2001c). Inpex Browse Ltd. 162

180 APPENDICES 163

181 164

182 Appendix 1: List of Wells, Samples and Depository Sequences Table A1.1 List of wells studied in this project. Well name, water depth, company, spud date Hydrocarbon type Drilling mud type SANS sample depth range (mrt), Formation names Adele 1 (243m) Shell, 7/98 gas + oil shows water-based: KCl/PHPA/ glycol 2530m m (Jamieson Formation equivalent) Argus 1 (572m) BHP Petroleum, 8/2000 gas discovery (noncommercial) water-based: KCl/PHPA/ glycol 4270m m (Jamieson & top Vulcan) Brecknock South 1 (423.7m) Woodside, 8/2000 gas/condensate discovery water-based: glycol 3530m m (Jamieson, Echuca Shoals, Vulcan, Plover) Brewster 1A (256m) Woodside, 5/1980 gas discovery water-based: brine polymer 2450m m (Jamieson, Echuca Shoals, Upper Vulcan) Carbine 1 (54.4m) Santos, 11/2001 dry? water-based: KCl/PHPA 1349m -1559m (Jamieson, Echuca Shoals) Crux 1 (168m) Nippon Oil, 4/2000 gas discovery water-based: KCl/PHPA/ glycol/alplex 2390m m (Jamieson, Echuca Shoals, Upper Vulcan, Lower Vulcan) Dinichthys 1 (263.6m) Inpex Browse, 3/2000 gas/condensate discovery seawater/gel/ KCl to 4100m; Aquadrill below 4100m 2550m m (Jamieson, Echuca Shoals, Upper Vulcan, Lower Vulcan) Gorgonichthys 1 (260m) Inpex Browse, 5/2000 gas/condensate discovery seawater/gel/ KCl to 3950m; Syntech (SBM) below 3950m 2520m m (Jamieson, Echuca Shoals, Upper Vulcan, Lower Vulcan, Mt.Goodwyn) Titanichthys 1 (247m) Inpex Browse, 9/2000 gas/condensate discovery seawater/gel/ KCl to 3900m; Syntech (SBM) below 3900m 2450m m (Jamieson, Echuca Shoals, Upper Vulcan) 165

183 Table A1.2 Samples analysed in this study from Adele-1 AGSO No Upper Depth Lower Depth Sample type Formation WCR Sequence GA Lithology Drilling Fluid (mdf) (mdf) CUTT Upper Heywood 12C Cl KCl/PHPA/glycol CUTT Upper Heywood 12C Cl KCl/PHPA/glycol CUTT Upper Heywood 12C Cl KCl/PHPA/glycol CUTT Upper Heywood 12C Cl KCl/PHPA/glycol CUTT Upper Heywood 12C Cl KCl/PHPA/glycol CUTT Upper Heywood 12C Cl KCl/PHPA/glycol CUTT Upper Heywood 12C Cl KCl/PHPA/glycol CUTT Upper Heywood 12C Cl KCl/PHPA/glycol CUTT Upper Heywood 12C Cl KCl/PHPA/glycol CUTT Upper Heywood 12C Cl KCl/PHPA/glycol CUTT Upper Heywood 12C Cl KCl/PHPA/glycol CUTT Upper Heywood 12C Cl KCl/PHPA/glycol CUTT Upper Heywood 12B Cl KCl/PHPA/glycol CUTT Upper Heywood 12B Cl KCl/PHPA/glycol CUTT Upper Heywood 12A Cl KCl/PHPA/glycol CUTT Upper Heywood 12A Cl KCl/PHPA/glycol CUTT Upper Heywood 12A Cl KCl/PHPA/glycol Table A1.3 Samples analysed in this study from Argus-1 AGSO No Upper Depth Lower Depth Sample Type Formation WCR Sequence GA Lithology Drilling Fluid (mrt) (mrt) CUTT Jamieson 12 Cl KCl/PHPA/glycol CUTT Jamieson 12 Cl KCl/PHPA/glycol CUTT Jamieson 12 Cl KCl/PHPA/glycol CUTT Jamieson 12 Cl KCl/PHPA/glycol CUTT Jamieson 12 Cl KCl/PHPA/glycol CUTT Jamieson 12 Cl KCl/PHPA/glycol CUTT Jamieson 12 Cl KCl/PHPA/glycol CUTT Jamieson 8/9 Cl KCl/PHPA/glycol 166

184 Table A1.4 Samples analysed in this study from Brecknock South-1 AGSO No Upper Depth (mrt) Lower Depth (mrt) Sample Type Formation WCR Sequence GA Lithology Drilling Fluid CUTT Jamieson 12 Cl M glycol CUTT Jamieson 12 Cl glycol CUTT Echuca Shoals 11 Cl glycol CUTT Echuca Shoals 11 Cl glycol CUTT Echuca Shoals 11 Cl glycol CUTT Echuca Shoals 11 Cl glycol CUTT Echuca Shoals 11 Cl glycol CUTT Vulcan 10 Cl glycol CUTT Vulcan 8A Cl glycol CUTT Plover 5A Cl F glycol Table A1.5 Samples analysed in this study from Brewster-1A AGSO No Upper Depth (mrt) Lower Depth (mrt) Sample Type Formation (Equiv GA) Sequence GA Lithology Drilling Fluid CUTT Jamieson 12C Cl Brine polymer CUTT Jamieson 12C Cl Brine polymer CUTT Jamieson 12C Cl Brine polymer CUTT Jamieson 12C Cl Brine polymer CUTT Jamieson 12C Cl Brine polymer CUTT Jamieson 12C Cl Brine polymer CUTT Jamieson 12C Cl Brine polymer CUTT Jamieson 12C Cl Brine polymer CUTT Jamieson 12B Cl Brine polymer CUTT Jamieson 12B Cl Brine polymer CUTT Jamieson 12A Cl Brine polymer CUTT Jamieson 12A Cl Brine polymer CUTT Jamieson 12A Cl Brine polymer CUTT Jamieson 12A Cl Brine polymer CUTT Echuca Shoals 11 Cl Brine polymer CUTT Echuca Shoals 11 Cl Brine polymer CUTT Echuca Shoals 11 Cl Brine polymer CUTT Echuca Shoals 10 Cl Brine polymer CUTT Echuca Shoals 10 Cl Brine polymer CUTT Echuca Shoals 10 Cl Brine polymer CUTT Upper Vulcan 8C Cl Brine polymer 167

185 Table A1.6 Samples analysed in this study from Carbine-1 AGSO No Upper Depth (mrt) Lower Depth (mrt) Sample Type Formation WCR Sequence GA Lithology Drilling Fluid CUTT Jamieson nd Cl KCl/PHPA CUTT Jamieson nd SltCl KCl/PHPA CUTT Jamieson nd Cl KCl/PHPA CUTT Jamieson nd Cl KCl/PHPA CUTT Jamieson/ Echuca Shoals nd SltCl KCl/PHPA CUTT Echuca Shoals nd Cl KCl/PHPA CUTT Echuca Shoals nd Cl KCl/PHPA Table A1.7 Samples analysed in this study from Crux-1 AGSO No Upper Depth (mrt) Lower Depth (mrt) Sample Type Formation WCR Sequence GA Lithology Drilling Fluid CUTT Jamieson 12C Cl KCl/PHPA/glycol/ CUTT Jamieson 12C Cl Alplex CUTT Jamieson 12C Cl KCl/PHPA/glycol/ CUTT Jamieson 12C Cl Alplex CUTT Jamieson 12C Cl KCl/PHPA/glycol/ CUTT Echuca Shoals 11 Cl Alplex CUTT Echuca Shoals 10 Cl KCl/PHPA/glycol/ CUTT Upper Vulcan 9 SltCl Alplex CUTT Upper Vulcan 8C SltCl KCl/PHPA/glycol/ CUTT Upper Vulcan 8C SltCl Alplex CUTT Upper Vulcan 8C SltCl KCl/PHPA/glycol/ CUTT Upper Vulcan 8B SltCl Alplex CUTT Upper Vulcan 8B SltCl KCl/PHPA/glycol/ CUTT Upper Vulcan 8B SltCl Alplex CUTT Upper Vulcan 8B SltCl KCl/PHPA/glycol/ CUTT Upper Vulcan 8B SltCl Alplex CUTT Upper Vulcan 8B SltCl KCl/PHPA/glycol/ CUTT Lower Vulcan 8A SltCl Alplex CUTT Lower Vulcan 8A SltCl KCl/PHPA/glycol/ CUTT Lower Vulcan 8A SltCl Alplex CUTT Lower Vulcan 8A SltCl KCl/PHPA/glycol/ CUTT Lower Vulcan 8A Cl Alplex CUTT Lower Vulcan 8A Cl KCl/PHPA/glycol/ CUTT Lower Vulcan 8A Cl Alplex CUTT Montara 8A Cl KCl/PHPA/glycol/ Alplex swc: SWC Echuca Shoals 11 Cl KCl/PHPA/glycol/ SWC Upper Vulcan 9 SltCl Alplex SWC Lower Vulcan 8B SltCl KCl/PHPA/glycol/ SWC Lower Vulcan 8A SltCl Alplex SWC Lower Vulcan 8A Cl KCl/PHPA/glycol/ Alplex 168

186 Appendix 1: Table A1.8 Samples analysed in this study from Dinichthys-1 AGSO No Upper Depth Lower Depth Sample Type Formation WCR Sequence Lithology Drilling Fluid (mrt) (mrt) GA CUTT Jamieson 12C Cl Seawater/gel/KCl CUTT Jamieson 12C Cl Seawater/gel/KCl CUTT Jamieson 12C Cl Seawater/gel/KCl CUTT Jamieson 12C Cl Seawater/gel/KCl CUTT Jamieson 12C Cl Seawater/gel/KCl CUTT Jamieson 12C Cl Seawater/gel/KCl CUTT Jamieson 12C Cl Seawater/gel/KCl CUTT Jamieson 12C Cl Seawater/gel/KCl CUTT Jamieson 12C Cl Seawater/gel/KCl CUTT Jamieson 12C Cl Seawater/gel/KCl CUTT Jamieson 12A Cl Seawater/gel/KCl CUTT Jamieson 12A Cl Seawater/gel/KCl CUTT Jamieson 12A Cl Seawater/gel/KCl CUTT Jamieson 12A Cl Seawater/gel/KCl CUTT Jamieson 11 Cl Seawater/gel/KCl CUTT Echuca Shoals 11 Cl Seawater/gel/KCl CUTT Echuca Shoals 11 Cl Seawater/gel/KCl CUTT Echuca Shoals 11 Slt Seawater/gel/KCl CUTT Echuca Shoals 11 SltCl Seawater/gel/KCl CUTT Echuca Shoals 11 SltCl Seawater/gel/KCl CUTT Echuca Shoals 9 SltCl Seawater/gel/KCl CUTT Upper Vulcan 9 SltCl Seawater/gel/KCl CUTT Upper Vulcan 9 Cl Aquadrill CUTT Lower Vulcan 8C Cl+some Slt CUTT Lower Vulcan 8C Cl+some Slt Aquadrill Aquadrill/ Pyrodrill 169

187 Appendix 1: Table A1.9 Samples analysed in this study from Gorgonichthys-1 AGSO No Upper Depth (mrt) Lower Depth (mrt) Sample Type Formation WCR Sequence GA Lithology Drilling Fluid CUTT Woolaston 12C Cl Seawater/gel/KCl CUTT Jamieson 12C Cl Seawater/gel/KCl CUTT Jamieson 12C Cl Seawater/gel/KCl CUTT Jamieson 12C Cl Seawater/gel/KCl CUTT Jamieson 12B Cl Seawater/gel/KCl CUTT Jamieson 12B Cl Seawater/gel/KCl CUTT Jamieson 12B Cl Seawater/gel/KCl CUTT Jamieson 12B Cl Seawater/gel/KCl CUTT Jamieson 12B Cl Seawater/gel/KCl CUTT Jamieson 12B Cl Seawater/gel/KCl CUTT Jamieson 12B Cl Seawater/gel/KCl CUTT Jamieson 12A Cl Seawater/gel/KCl CUTT Jamieson 12A Cl Seawater/gel/KCl CUTT Jamieson 12A Cl Seawater/gel/KCl CUTT Jamieson 12A Cl Seawater/gel/KCl CUTT Echuca Shoals 11 Cl Seawater/gel/KCl CUTT Echuca Shoals 11 Cl Seawater/gel/KCl CUTT Echuca Shoals 11 Cl Seawater/gel/KCl CUTT Echuca Shoals 11 Cl Seawater/gel/KCl CUTT Echuca Shoals 10 Cl Seawater/gel/KCl CUTT Echuca Shoals 10 Cl Seawater/gel/KCl CUTT Echuca Shoals 9 Cl Seawater/gel/KCl CUTT Upper Vulcan 9 Cl+Slt Syntech (SBM) CUTT Lower Vulcan 8B Cl+SltCl Syntech (SBM) CUTT Lower Vulcan 8A Cl+SltCl Syntech (SBM) CUTT Mt Goodwin 4 Cl Syntech (SBM) CUTT Mt Goodwin 4 Cl Syntech (SBM) 170

188 Table A1.10 Samples analysed in this study from Titanichthys-1 AGSO No Upper Depth (mrt) Lower Depth (mrt) Sample Type Formation WCR 171 Sequence GA Lithology Drilling Fluid CUTT Jamieson Cl 13 Seawater/gel/KCl CUTT Jamieson Cl 12C Seawater/gel/KCl CUTT Jamieson Cl 12C Seawater/gel/KCl CUTT Jamieson Cl 12C Seawater/gel/KCl CUTT Jamieson Cl 12C Seawater/gel/KCl CUTT Jamieson Cl 12C Seawater/gel/KCl CUTT Jamieson Cl 12C Seawater/gel/KCl CUTT Jamieson Cl 12B Seawater/gel/KCl CUTT Jamieson Cl 12B Seawater/gel/KCl CUTT Jamieson Cl 12A Seawater/gel/KCl CUTT Jamieson Cl 12A Seawater/gel/KCl CUTT Jamieson Cl 12A Seawater/gel/KCl CUTT Jamieson Cl 12A Seawater/gel/KCl CUTT Echuca Shoals Cl 11 Seawater/gel/KCl CUTT Echuca Shoals Cl 11 Seawater/gel/KCl CUTT Echuca Shoals Cl 11 Seawater/gel/KCl CUTT Echuca Shoals Cl 10 Seawater/gel/KCl CUTT Echuca Shoals Cl 10 Seawater/gel/KCl CUTT Echuca Shoals Cl 10 Seawater/gel/KCl CUTT Upper Vulcan SltCl 9 Syntech (SBM) Sample type: Cutt - cuttings swc - side-wall-core Lithology key: Cl - claystone Cl F - fluvial claystone Cl M - marine claystone Slt - siltstone SltCl - silty claystone Water-based drilling muds and additive: Alplex Aquadrill - complex polymer Flowzan - xanthan gum biopolymer KCl - potassium chloride Guar gum - spud mud viscosifier PHPA - partially hydrolyzed polyacrylamides Glycol Pyrodrill Synthetic and oil-based muds: Syntech Synthetic-based mud

189 Table A1.11. Depository sequences for nine wells in the Browse Basin. Part 1 - Geoscience Australia classification of depository sequences. Part 2 - depository sequences as in Well Completion Reports. All depths are in mrt. Sequence Top (Geoscience Australia classification) Adele-1 Brecknock South-1 Brewster- 1A Crux -1 Gorgonichthys-1 Tertiary Maastrichtian Campanian Santonian -Turonian Jamieson Fm (Turonian - Aptian) Echuca Shoals Fm (Aptian - Valanginian) Upper Vulcan Fm (Valanginian - Tithonian) Lower Vulcan Fm (Tithonian - Callovian) Plover Fm (below Callovian) Sequence Top (after WCR) Argus Sequence Top (after WCR) Carbine 1 Sequence Top (after WCR) Dinichthys Titanichthys 1 Tertiary 594 Tertiary 107 Tertiary Bathurst Island Group 4021 Prudhoe Deltaics Member (Mid Maastrichtian) 922 Puffin Fm (Maastrichtian- Campanian) Intra- Campanian 4218 Borde Marl (Late Campanian -Early Maastrichian) 1135 Fenelon Fm (Santonian -Turonian) Jamieson Fm 4242 Puffin Sandstone (Early Campanian) 1263 Woolaston Fm (Cenomanian) Echuca Shoals Fm absent Fenelon Fm (Santonian -Turonian) 1340 Jamieson Fm (Cenomanian- Albian) Vulcan Fm 4535 Jamieson Fm (Cenomanian) 1343 Echuca Shoals Fm (Barremian -Valanginian) Plover Fm not confrmd Echuca Shoals Fm (Aptian - Cenomanian) 1500 Upper Vulcan Fm (Berrasian) undifferentiated volcanics 4700 Lower Vulcan Fm (Tithonian- Oxfordian) Plover Fm (Callovian - Bajocian)

190 Appendix 2: Analytical Procedures A2.1 Comparison of the Small Angle Scattering and Geochemical Methods Table A2.1 Comparison of the SAS and geochemical methods. Diagnostic function Small Angle Scattering Geochemistry General Hydrocarbon source rock applications Hydrocarbon reservoir rock and seal applications Sensitivity to contamination by drilling muds Microstructure of rock matrix (inorganic or organic): pore size distribution (1 nm to 20 µm across) specific internal surface area pore content non-invasive, cores and/or cuttings absolutely calibrated Petroleum fill-spill history: direct evidence organic matter type independent timing of oil generation, oil expulsion, oil-to-gas cracking presence of hydrocarbons in pores (mudrocks) organic matrix reorganisation (coals) pore size specific - follows h/c migration within the pore network of a source rock hydrocarbon saturation in reservoir/seal rocks porosity/permeability in reservoir rocks seal capacity Not evident Composition of organic matter: amount of OM kinetics of thermal decomposition molecular composition (including biomarkers): oilsource correlation isotopic composition (C, H, O,S): gas-oil correlation invasive - crushed rocks, extracts lab protocol dependent Petroleum fill-spill history: indirect evidence organic matter type dependent timing of oil generation, oil expulsion, oil-to-gas cracking sum-of-pores information hydrocarbon saturation in reservoir /seal rocks Strong (S 1, S 2, Tmax) 173

191 A2.2 SANS/USANS Sample Preparation (extracted from Geoscience Australia Sedimentology Laboratory Operating Procedure) Authors: Neil Ramsay, Alex McLachlan and Tony Watson 1.0 Introduction The SANS (Small Angle Neutron Scatter) sample procedures are used in the Sedimentology laboratory to prepare samples for SANS analysis. 2.0 Purpose The purpose of this SOP is to: - Communicate the hazards associated with this operation, - document the control measures that will be used to control the hazards, - document the protocols, methodology and procedures involved in performing the operation, - document the precautions and limitations applicable to this operation, and - define the required qualifications of personnel performing the operation. 3.0 Scope The scope of this SOP covers all aspects of work undertaken in the Sedimentology Laboratory (Petroleum and Marine Division) at Geoscience Australia s Canberra facilities relating to the SANS preparation procedures. Equipment used includes a mortar and pestle, compessed air, drying oven, ultrasonic bath, disposable sieving mesh, electronic balance (accurate to four decimal places), a set of aluminium sieve rings (100mm diameter), low viscosity epoxy resin, Buehler Isomet 1000 precision saw and a micometer. 4.0 Responsibilities This document and procedures are the responsibility of Geoscience Australia. 5.0 Hazards Hazards concerning this SOP include: - Excessive noise when using compressed air to dry/clean equipment, - samples can possibly contain coliforms and/or other harmful micro-organisms, - fine dust particles when grinding or cleaning equipment, - Occupational Overuse Syndrome (OOS), - Epoxy fumes 174

192 6.0 Hazard Control Measures and Limitations 6.1 Personal Protective Equipment (PPE) Control Measures - Laboratory coat must be worn at all times in laboratory, - ear protection is to be used at all times when noise is excessive, - cotton gloves are to be worn at all times when in contact with sample for this proceedure, - face shield or safety glasses are to be worn when using compressed air, - lab coat, gloves and safety glasses must be worn when using potting epoxy, - Store and use Epoxy in a well ventilated area. 6.2 Administrative Control Measures - Operator must have read and be familiar with operating instructions for all equipment and this SOP, - Geoscience Australia s OH&S and OOS policies. 7.0 Procedural Steps Grinding IMPORTANT NOTE: When performing any procedures or analysis on SANS samples it is imperative that cotton gloves are worn. This is to avoid organic contamination of samples. 1. Enter all samples and attached information into pallab database and print off a running spread sheet to work off in the lab. 2. Weigh all of the samples as a bulk weight and record on running spread sheet. 3. Set out the samples on sufficient bench space according to their pallab numbers. 4. For every sample allocate three (3) 20ml vials. These will be labelled coarse fraction, SANS fraction, and fine fraction as well as their respective lab numbers etc. If sub samples are required for geochemistry and palynology then an addition two (2) labelled vials will be needed for these. 5. Use 100mm diameter aluminium sieve rings with base and lid to sieve material, no crushing of sample in the first instance. Place 475um disposable sieve mesh on top ring and 355um disposable mesh on bottom ring (see diagram 1.0) place sample on top mesh attach lid and shake gently. 175

193 Diagram 1.0 set up of sieving apparatus 6. Remove the top dividing ring and pour the coarse fraction of the sample into the mortar. 7. Carefully grind the coarse fraction so that more of it will pass through the sieve cloth. This needs to be done very gently and slowly if there is a limited amount of sample available. Return the coarse sample back to the sieve mesh and repeat the shaking of the sieve. 8. Repeat this process until there is between 1.5 & 2gms of the SANS fraction, do not process whole sample once target SANS yield (<475um >355um) is met. 9. Dismantle the sieving apparatus and transfer the SANS fraction to a piece of weighing paper. Ensure that this is done over clean white paper to catch any falling pieces of sample. Note: dismantle sieves slowly and carefully, keeping hold of the sieve cloth as the ring and cloth may pop out unexpectedly. 10. Weigh SANS fraction then transfer to a glass vial. Record this final weight in the running spreadsheet. 11. Repeat this weighing process for the remaining coarse and fine fractions making sure that the weighing paper is clean between each. In some instances to reach target yield the coarse fraction may be entirely processed. Discard the used sieve cloths and weighing paper. 12. Clean the bench space to prevent contamination. Clean the mortar and pestle, and the sieve sets thoroughly. They can be scrubbed under hot water and placed in an ultrasonic bath to remove any contamination left from the previous sample. 13. After the equipment has been cleaned dry it with compressed air to remove most of the water. 176

194 14. The equipment can then be placed in a warm oven, about 50 C, until it is totally dry and ready to reuse. 15. Repeat this process for any remaining samples. Encapsulation and sectioning of sample 1. Using the SANS fraction place the material into tailor made acrylic mounting pots (20mm internal diameter, 8mm internal height) 3.5mm-4.0mm depth of sample is required this equates to gms of sample (note: differing materials may require assessment for optimum encapsulation and sectioning results). Do not fill pots with sample as this may prevent epoxy from completely immersing the sample. 2. Prepare the Epoxy Resin for sample encapsulation ( Current product is Buehler EPO-THIN 2 pack low viscosity epoxy resin). When mixed, pour gently into potting mount, check base of mount to ensure sample is saturated, leave 24 hours to cure 3. Once cured place sample into sample holding Jig ( see image 1.0) with base outwards. Image 1.0 Sample pot at right, holding jig at left. 4. Mount holding jig into Isomet 1000 precision saw unit (see image 2.0), cut off the mounts plastic base then reset the saw to slice a mm wafer of sample and if possible (consult with project scientist) a mm wafer. Use a micrometer to measure thickness of wafer at it s middle, record this on the clear plastic rim of the wafer along with sample number. Store sample for transport. 177

195 Image 2.0 Sample mount in holding jig ready for sectioning. 8.0 Flow Chart Enter samples into database Weigh each bulk sample and record Label vials for each sample Set up sieving apparatus with balance and mortar and pestle Pour sample into sieve and shake through sieve cloth Pour coarse fraction into mortar Grind coarse fraction Return sample to sieve Repeat until 1.5-2g of SANS fraction has been obtained or all sample used Transfer fractions to respective vials and weigh and record Discard used sieve cloth and weighing paper Clean all equipment and bench space sample encapsulation and sectioning 178