Petroleum System Modelling applied to the evaluation of HC in Place in Unconventional Gas Shale prospects

Transcription

1 Petroleum System Modelling applied to the evaluation of HC in Place in Unconventional Gas Shale prospects Domenico Grigo 28 April,

2 applied to Gas Shale Prospect characterisation Why? In the first phase of a non american gas shale prospect evaluation the well data resolution is so large that the normal approach (quantification of well data only) is not enough to describe properly the properties distribution. American Gas Shale (Barnett) Prospect well data The estrapolation of well data to the entire prospect extension can be succesfully supported by the numerical simulation of the natural processes gouverning the properties distribution. Petroleum System Modelling is the only methodology capable to reproduce natural processes starting from well data at basin scale Non American Gas Shale Prospect well data 250 km 1000 km 2

3 Methods for characterising a Gas Shale The North American analog Key characteristics noted about each system (where available) Time equivalent system Total porosity (%) Basin Age TOC (%) Kerogen type Thermal maturity (%R o ) Gas in place (bcf/section) Shale gas-in-place resource (tcf) Absorbed gas (%) Matrix permeability Relative thickness Reservoir pressure (psi) Bottom-hole temperature ( C) Depositional setting Basin type/ tectonic setting Lithology notes Other notes Hypothesized as potential common denominator 3

4 Methods for characterising a Gas Shale The North American analog 4

5 Gas Shales: unconventional reservoir Gas accumulation is continuous and not related to buoyancy The formation is simultaneously source rock and reservoir Gas presence is not associated to geological traps: the target is a portion of basin Gas production achieved only with fracture stimulation Not all the shale gas plays can commercially produce gas Key geological factors are: TOC >1% with %Ro>1,2 Quality of organic matter: type II kerogene is the most favourable Vshale<40% brittleness Mechanical properties favorable for fracking Presence of natural fractures that can be reactivated No producible water Sealing layers at top and bottom No potential geological risks, namely faults, karst areas and tectonic complexity Adequate depth and thikness of the producing play: if overpressured, depth >3500 m can be acceptable 5

6 Gas Shale Maturity 6

7 Maturity Indicators Depth (m): 1892,5 Sample Type: BC Ro=0.60% - Std Dev. =0.06 Vitrinite Reflectance (Ro%) records only the maximum temperature reached during burial N of Readings Vitrinite Reflectance (Ro%) Apatite Fission Track (AFTA) records also other temperatures but only if younger than the maximun Fluid Inclusions (FI) records all the temperatures 7

8 Equivalent Vitrinite Reflectance (Ro %) Derived by Bitume reflectance Vitrinite is often scarse in carbonate source rocks. Bitumen can be present in this case, in particular when the maturity level is middle/high. By the use of Jacob s formula (Jacob & Hiltmann, 1985) it is possible to convert the bitumen reflectance in equivalent vitrinite reflectance value: Ro eq % = R BIT

9 Equivalent Vitrinite Reflectance (Ro %) Derived by other organisns From Suchy et Al CAI = Conodont Alteration Index 9

10 Equivalent Vitrinite Reflectance (Ro %) Tmax by pyrolysis Rock-Eval This maturity parameter is derived by the Rock-Eval analysis (the analytical technique finalized to source rock evaluation). Tmax is the temperature at which the maximum of residual petroleum potential (by kerogen pyrolysis) occurs. It has not be confused with the maximum temperature (very lower) reached by sample during its burial history. S1 Immature sample T max = 420 C S2 Mature sample T max = 450 C C Heating rate = 25 C per minute Overmature sample T max not available 10

11 Petroleum System Modelling Well Temperature & MaturityCalibration WELL DATA Measured Computed SURFACE TEMPERATURE WELL BURIAL EVALUATION H000 H100 H200 H300 H400 H500 H600 GS H800 H900 TEMPERATURE HISTORY Temperature ( C) TEMPERATURE MATCHING 2000 Depth (m) HEAT FLOW (m) Depth ( H000 H100 H200 H300 H400 H500 H600 GS H800 H Time (ma) H000 H100 H200 H300 H400 H500 H600 GS H800 H Time (ma) Maturity (Ro%) Temperature ( C) Measured Computed Depth (m) MATURITY HISTORY Time (ma) MATURITY MATCHING Ro%

12 Maturity Computation & Potential Gas Shale definition 1000 km Gas Shale Maturity 12

13 Gas Shale Properties 13

14 Kerogen ENVIRONMENT Aquatic KEROGEN TYPE I KEROGEN FORM [ MACERAL] alginite ORIGIN algal bodies structureless debris of algal bodies HC POTENTIAL The potential to generate hydrocarbons and the quality of the products are affected by the quality of the initial kerogen, which is controlled by the quality of the organic input and by the evolution of diagenesis. On the basis of optical examination and physicochemical analyses, kerogens have been gathered into four main groups: Terrestrial II III IV amorphous organic matter exinite vitrinite inertinite (modified, after Merrill, 1991) structureless, planktonic material, primarily of marine origin skins of spores and pollen, cuticle of leaves and herbaceous plants fibrous and woody plant fragments and strcturless collidal humic matter oxydized, recycled woody debris OIL GAS AND SOME OIL NONE GENETIC POTENTIAL

15 Steps of Organic Matter evolution Diagenesis is strongly controlled by the biological activity (bacteria), and by the chemical environment (redox conditions, mineralogy). At the end of diagenesis, the organic matter consists mainly of a policondensed structure which is the kerogen. Catagenesis and Metagenesis, are controlled by thermal stress due to burial Both the absolute temperatures and the heating rate govern the evolution of kerogen transformation m THERMAL EVOLUTION + MACROMOLECULES INITIAL KEROGEN KEROGEN KEROGEN DEGRADATION RESIDUAL KEROGEN (after Bordenave, 1993 modified) early diagenesis diagenesis catagenesis metagenesis C,H,O,N N C,H,O O C,H H C 15

16 Source Rock Evaluation Source rock Evaluation: Geochemical log Quantitative analysis Source potential Qualitative analysis Thermal Maturity FORMATION MARNES DE MADINGO 450 TOC S2 HI KEROGEN TMAX COMPOSITION P F G VG P F G VG III II I IMM M V M DOLOMIE DE LOANGO GRES DE TCHALA CARBONATES DE SENDJI TRACES TRACES SALIFERE DE LOEME Oil prone AOM MPH CHF CWF 2450 ARGILES DE POINT INDIENNE T.D (%) (kg HC/ton of rock) (mg HC/g TOC) (%) Serie ( C) 16

17 Kerogen optical analyses Some kerogen types are shown: Microscope pictures of kerogens Observation in transmitted white light More or less 100 µ 1. Humic Kerogen (woody fragments, and then vitrinite and others coal macerals) 2. Sapropelic Kerogen (spores and pollens) 3. Kerogen constituted by Amorphous Organic Matter (unstructured, unrecognizable OM) 17

18 The Seismic view of a Source Rock 18

19 Source rock lithological model (50-80% shale) (80-90% shale) (90-100% shale) 19

20 Organic matter deposition & preservation modelling OF-Mod 3D: is a process-based software, which reproduce the development and the variation of organic facies in a 3D volume. TOM supply 1 fluvial sediment primary productivity PP (g C m -2 a-1 ) and nutrient supply CO 2 + H 2 O CH 2 O + O 2 PP = g C m-2 a-1 PP = g C m -2 a -1 PP = g C m -2 a carbon flux Fc 4 4 Ctot: 10 wt% Ctot: 7 wt% degradation OF: B OF: C - A 6 MOC (anoxic)= PP PF dilution epibenthic respiration 5 Ctot: 1-3 wt% BFM erosion, bypass and OF: BC-C burial efficiency BE sedimentation processes Ctot: 0.3 wt% OF: D MOC (oxic) = Fc BE dilution water depth (m) TOM = Terrestrial Organic Matter SINTEF Petroleum Research 20

21 Final Outcome: Gas Shale Thickness & Original properties definition Original TOC=15% Original HI=350 mghc/gtoc 1000 km 21

22 Final outcome: Gas Shale Depth & Burial Evolution 1000 km 22

23 Gas Shale original Gas in place 23

24 HC genaration simulation Experimental Kinetic Parameters The parameters defining the reaction scheme are determined experimentally degrading thermically the kerogen samples with the MSSV (Micro Scale Sealed Vessel) pyrolysys experiments OPTIMIZATION OF RESULTS ACCORDING TO A KINETIC SCHEME USE IN THE SIMULATION OF HC GENERATION AND EXPULSION 24

25 Calibration of the Kinetic Model Original properties definition Av. Source Rock Maturity 1.6 Ro% TOC (%) HI mghc/gtoc Measured Measured Computed 4460 (m) Depth ( Computed 4460 (m) Depth ( MODELLED GAS SHALE 15 % TOC HI 350 mghc/gtoc 38 m

26 Expulsion Simulation Why? GENERATED GAS EXPELLED GAS Between Generation and Expulsion of HC a time gap can exists but also a volume gap due to the un-expelled HC remaining in the source and not available for Migration and Charging 26

27 Final outcome: Gas Shale OGIIP Volumes by area The same process of evaluation can be applied at any scale from the basin to the block following the maturation of the Gas Shale exploration project 1000 km 27