Maturity assessment of Middle Cambrian organic-rich rocks in the southern Georgina Basin using geochemical and petrographic comparisons

Transcription

1 Maturity assessment of Middle Cambrian organic-rich rocks in the southern Georgina Basin using geochemical and petrographic comparisons Chris Boreham 1, Jane Newman 2 and Dianne Edwards 1 1 Onshore Energy Group, Resources Division, Geoscience Australia 2 Newman Research, Christchurch, New Zealand Life, Environments and Resources AOGC2014: the 18 th Australian Organic Geochemistry Conference, Adelaide, 30 Nov 2 Dec 2014

2 ACKNOWLEDGMENTS Isotope and Organic Geochemistry Lab. Staff

3 OUTLINE OF TALK Petroleum Systems geology and samples geochemical characteristics of oils and SR Maturity Estimates Organic petrology Tmax anomalies Conclusions

4 LITHOSTRATIGRAPHY E basal Arthur Creek (hot ) shale other source rocks W

5 UNCONVENTIONAL HYDROCARBONS Technically Recoverable Prospective Resource in the Arthur Creek Formation 5 BBL of oil and 33 TCF of gas at mean (Ambrose et al., CABSIII, 2012) max. 2,500 units (1 unit = 200 ppm methane equiv.) PetroFrontier Press Release May 2012

6 Neoproterozoic Paleozoic Exploration Activity PetroFrontier Baldwin 2/2H MacIntyre 2/2H Owen 3/3H Statoil OzAlpha 1 OzBeta 1 OzGamma 1 OzDelta 1 OzEpsilon 1 Central Petroleum JV Total Whiteley 1 Gaudi 1 Southern Georgina Basin UNCONVENTIONAL HYDROCARBONS Inpex 4 November 2014

7 LOCATION MAP Wells sampled for oil stains and source rocks MacIntyre 2H Owen 3H

8 OIL STAINS & BITUMENS strong oil stain Owen-2, m Thorntonia Limestone (Hay River Fm) spotty oil stain/bitumen in vuggy porosity Elkedra-2, m Hagen Member weak oil stain Elkerdra-2, m Hagen Member

9 GC: HEAVY, UNALTERED OIL n-c 22+ waxy n-c 37

10 GC: HEAVY, ALTERED OIL position of n-c 37 unresolved complex mixture (UCM)

11 GC: LIGHT, UNALTERED OIL n-c 19 n-c 22+ waxy

12 GC: LIGHT, ALTERED OIL position of n-c 17 low MW unresolved UCM complex mixture (UCM)

13 HIERARCHICAL CLUSTER ANALYSIS Dendrogram PS Cambrian Petroleum Systems PS Arthur Creek-Hagen (!) PS Variables 13 Carom C19/C23T C22/C21T C24/C23T C26/C25T C24Tet/C23T C28H/C30H C29H/C30H C30X/C30H C31R/C30H C35S/C34S T/H Rearr/Reg %27 %28 %29 S/H PS

14 Georgina HyLogging Arthur Creek Fm Thorntonia Lst Inpex 4 November 2014

15 Source Rock Characterisation Dulcie Syncline Toko Syncline Arthur Creek Fm shales HI >300 to 750 mg/gtoc Type II kerogen, excellent oil & gas source potential Thorntonia/Hay River carbonates HI >300 to 700 mg/gtoc Type II kerogen, excellent oil & gas source potential Inpex 4 November 2014

16 1-D BURIAL HISTORY MODELLING PetroMod 2011 (4-component Georgina compositional kinetics from Tan et al. JMPG submitted) MacIntyre-1 (-2H) uplift/erosion: Alice Springs Orogeny Owen-2 (-3H) present-day geothermal gradient 49 o C/km present-day geothermal gradient 29 o C/km Transformation ratio late oil-early gas window ~80% kerogen transformation early oil window ~20% kerogen transformation

17 SOURCE ROCK MATURITY basal hot shale of the Arthur Creek Formation Ambrose et al CABSIII Symposium, Alice Springs 2012 Insert Title Here <view/master/slidemaster>

18 Netting Fence-1 Tmax o C Tmax 462 (Ro 1.16*) HI Mirrica-1 Tmax o C Tmax 533 (Ro 2.44*) HI Ambrose et al CABSIII Symposium, Alice Springs 2012 *Jarvie et al. 1991; Rc = 0.018Tmax-7.16 Insert Title Here <view/master/slidemaster>

19 MacIntyre-2: Arthur Creek Fm Drilled depth (m) Tmax = 457 o C Rc* = 1.07% *Jarvie et al. 1991; Rc = 0.018Tmax-7.16 Oil staining basal Arthur Creek hot shale

20 Baldwin-1 Rock Eval pyrograms non-extracted solvent-extracted o C 441 o C m, Tmax 441 o C (Rc = 0.78%) (TOC 1.19%; HI 39) m, Tmax 426 o C (Rc = 0.51%) (TOC 0.66%; HI 30) Insert Title Here <view/master/slidemaster>

21 Baldwin-1 Rock Eval pyrograms non-extracted solvent-extracted o C 468 o C 881.8m, Tmax 468 o C (Rc = 1.26%) (TOC 7.70%; HI 30) 881.8m, Tmax 468 o C (TOC 7.75%; HI 21) Insert Title Here <view/master/slidemaster>

22 Baldwin-1 Rock Eval pyrograms non-extracted solvent-extracted 520 o C o C m, Tmax 526 o C (Rc = 2.31%) (TOC 10.12%; HI 30) m, Tmax 520 o C (Rc = 2.20%) (TOC 9.23%; HI 34) Insert Title Here <view/master/slidemaster>

23 Baldwin-1 Rock Eval pyrograms non-extracted solvent-extracted ~470 o C 602 o C o C 880.0m, Tmax 469 o C (Rc = 1.28%) (TOC 6.56%; HI 23) 880.0m, Tmax 602 o C (Rc = 3.68%) (TOC 6.38%; HI 19) Insert Title Here <view/master/slidemaster>

24 Baldwin-1 Rock Eval pyrograms solvent-extracted Standard method 650 o C 602 o C ~470 o C organic concentrate Pure Organic Matter method 800 o C 800 o C 587 o C 880.0m Tmax 602 o C (Rc = 3.68%) 880.0m Tmax 587 o C (Rc = 3.41%) Insert Title Here <view/master/slidemaster>

25 Strongly depressed Tmax ( C) MacIntyre-1, m Tmax 426 o C, transmitted light. Hydrocarbon infilling porosity This impregnating hydrocarbon is translucent which suggests a relatively hydrogen-rich composition. The organic matter has adopted a distinctly systematic 3 D network that suggests impregnation of porosity in a bioclast. Probable origin is a mobile oil.

26 Strongly depressed Tmax ( C) Hydrocarbons in porosity, Netting Fence m Tmax 453 o C; UV light, oil immersion The orange-yellow fluorescing material is inferred to be hydrocarbons in porosity around a quartz grain. The longer wavelength fluorescence colour, which is red-shifted compared to samples with lower Tmax, is tentatively attributed to thermal alteration.

27 Intermediate Tmax o C MacIntyre-1, m Tmax 470 o C Bitumen impregnation in siliceous bioclast, incident nonpolarised light, dry objective. Zooclast, probably graptolitic, incident polarised light, oil immersion. Primary OM is inferred to be dominant. Much of the primary organic matter is likely to be amorphous and cryptically hidden in the rock matrix. However, these examples show mobilised bitumen which does not appear to be coked/carbonised/thermally altered, and a typical zooclast.

28 Elevated Tmax (whole rock 500 C 530 C); Baldwin m Tmax 526 o C Originally highly porous & permeable, coarse silt to fine sand size, matrix poor bioclastic horizon. After precipitation of euhedral carbonate overgrowths (C) a (hydro)thermal event has mobilised and then carbonised organic matter (COM), which infills porosity and hosts shattered crystal fragments (1 & 4) and crushed?faecal pellets (2).

29 Highly elevated Tmax (580 C 600 C) extracted rock Baldwin m Tmax 602 C Coke infilling residual porosity Differences in timing of coke emplacement. Previous slide was highly accessible to hot fluids due to very high initial porosity/permeability. Fracturing and coke emplacement may have been completed at a time when magma was still relatively remote. Here it was not highly accessible to hot fluids because primary porosity/permeability was low hence coke impregnation may not have occurred until magma was more proximal, and temperatures higher. Insert Title Here <view/master/slidemaster>

30 Tmax VR plot for Cambrian marine Type II OM (Arthur Creek Fm)

31 Tmax VR plot for Cambrian marine Type II OM (Arthur Creek Fm)

32 CONCLUSIONS - 1 Three main (unconventional?) petroleum (oil) systems identified in the Georgina Basin early Middle Cambrian Thorntonia (!) PS anoxic platform facies late Middle Cambrian Arthur Creek (!) PS euxinic, deeper water, outer ramp facies early Late Cambrian Hagen (.) PS; anoxic, evaporitic sabkha facies Biodegradation/water washing of oil is a major risk (shallow depth < 1000 m);

33 CONCLUSIONS - 2 For samples past peak oil window (Tmax kerogen > 455 o C; Ro >1%) Strongly depressed Tmax (420 C 455 o C) is inferred to represent impregnation by a relatively hydrogen-rich bitumen mobilised into porosity during a thermal event Intermediate Tmax (455 C 500 C) is inferred to represent primary OM, which may be mostly amorphous (petrographically cryptic) Elevated Tmax (500 C 530 C) is inferred to represent petroleum coke Highly elevated Tmax (580 C 600 C) is inferred to represent strongly carbonised/devolatilised primary or secondary organic matter Tmax (extracted) Rc correlation as per Jarvie et al 1991 for Type II OM The Georgina Basin maturity sample set features mineral hosted oil (and gas) inclusions in samples ranging from low to very high maturity subject of further work (see Jacob Sohn s poster)