Porosity, Permeability and Methane Sorption Capacity of Oil and Gas Shales at different Levels of Thermal Maturation

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1 Porosity, Permeability and Methane Sorption Capacity of Oil and Gas Shales at different Levels of Thermal Maturation Ralf Littke, Bernhard M. Krooss, Alexandra Amann, Amin Ghanizadeh, Matus Gasparik, Benjamin Bruns Introduction Shale gas and shale oil reservoirs are unconventional hydrocarbon plays composed of a variety of finegrained sedimentary rocks including shales, mudstones, marlstones, siliceous shales, limestones and siltstones (Javadpour et al., 2009). Despite considerable gas-in-place (GIP) estimations for shale gas plays, these complex, heterogeneous reservoirs require innovative exploration and completion strategies to produce natural gas or oil economically (Chalmers et al., 2012). Economic gas flow rates in these reservoirs, which commonly have permeability coefficients down to the ndarcy-range, are still technically difficult to achieve, partially due to the poor understanding of the fluid transport processes in these lithotypes (Amann-Hildenbrand et al., 2012; Eseme et al., 2012; Swami and Settari, 2012). Very few studies have experimentally investigated the fluid flow mechanisms in the matrix of organic-rich shales and the characteristics of fluid flow processes within the fracture and matrix systems of these lithotypes are still poorly understood due to the difficulty of measuring the low and extremely-low permeability of shales (e.g. Chalmers and Bustin, 2012; Tinni et al., 2012). Experimental Here, we report data on a series of black shales (Posidonia Shale, Lower Jurassic, North German basin) which reached maturity levels between 0.5 and 1.45 % vitrinite reflectance. Laboratory studies were conducted to investigate the porosity as well as storage and transport of gas. Permeabilty measurements were performed at effective stresses ranging between 6 and 37 MPa and a temperature of 45 C. The effects of different controlling factors including permeating fluid, maturity, anisotropy, moisture content and effective stress on the fluid conductivity were analysed and discussed. Results and Discussion Permeability coefficients measured perpendicular and parallel to bedding ( m 2 ) were within the range previously reported for other shales and mudstones. Among the sample suite studied, the lowest porosity and permeability coefficients were measured on samples of intermediate thermal maturity (0.88% VR r, oil-window). Permeability coefficients (He, CH 4 ) measured parallel to bedding were up to more than one order of magnitude higher than those measured perpendicular to bedding (Ghanizadeh et al., 2014). Conclusions The methane sorption capacities (in dry shales) show a linear positive trend with TOC but significant deviations from this trend exist that are linked to the overprinting effect of thermal maturity. No correlation was observed between the clay content and sorption capacity to methane and we conclude that clay minerals only play a minor role in methane sorption (Gasparik et al., 2014). Results of sorption experiments were implemented in PetroMod software in order to calculate methane sorption in Posidonia Shale on a basin wide scale, based on a previously published 3D basin model (Bruns et al., 2013).

2 Selected References Amann-Hildenbrand, A.; Ghanizadeh, A.; Krooss, B. M., Transport properties of unconventional gas systems. Marine and Petroleum Geology 31, Bruns, B.; di Primio, R.; Berner, U.; Littke, R., Petroleum system evolution in the inverted Lower Saxony Basin, northwest Germany: a 3D basin modeling study. Geofluids 13, Chalmers, G. R. L.; Ross, D. J. K.; Bustin, R. M., Geological controls on matrix permeability of Devonian Gas Shales in the Horn River and Liard basins, northeastern British Columbia, Canada. International Journal of Coal Geology 103, Chalmers, G. R. L.; Bustin, R. M., Geological evaluation of Halfway Doig Montney hybrid gas shale tight gas reservoir, northeastern British Columbia. Marine and Petroleum Geology 38, Eseme, E.; Krooss, B. M.; Littke, R., Evolution of petrophysical properties of oil shales during high-temperature compaction tests: Implications for petroleum expulsion. Marine and Petroleum Geology 31, Gasparik, M., Bertier, P., Gensterblum, Y., Ghanizadeh, A., Krooss, B. M., Littke, R., Geological controls on the methane storage capacity in organic-rich shales. International Journal of Coal Geology, 123, Ghanizadeh, A., Amann-Hildenbrand, A., Gasparik, M., Gensterblum, Y., Krooss, B. M., Littke, R., Experimental study of fluid transport processes in the matrix system of the European organic-rich shales: II. Posidonia Shale (Lower Toarcian, northern Germany). International Journal of Coal Geology, 123, Horsfield, B., Littke, R., Mann, U., Bernard, S., Vu, T.A.T., di Primio, R., Schulz, H.-M., Shale Gas in the Posidonia Shale, Hils Area, Germany Search and Discovery Article #110126, Adapted from oral presentation at session, Genesis of Shale Gas Physicochemical and Geochemical Constraints Affecting Methane Adsorption and Desorption, at AAPG Annual Convention (New Orleans, LA, April 11-14, 2010). Klaver, J., Desbois, G., Urai, J.L., Littke, R., BIM-SEM study of the pore space morphology in early mature Posidonia Shale from the Hils area, Germany. International Journal of Coal Geology, 103, Littke, R., Baker, D.R., Leythaeuser, D. & Rullkötter, J.,1991. Keys to the depositional history of the Posidonia Shale (Toarcian) in the Hils syncline, Northern Germany. - In: Modern and ancient continental shelf anoxia (Tyson, R.V. & Pearson, T., eds), Geol. Soc. Spec. Publ., 58: Littke, R., Baker, D.R. & Leythaeuser, D Microscopic and sedimentologic evidence for the generation and migration of hydrocarbons in Toarcian source rocks of different maturities. - In: Adv. Org. Geochem (Mattavelli, L. & Novelli, L., eds), Org. Geochem., 13, , Pergamon Press, Oxford. Littke, R., Krooss, B.M., Uffmann, A.K., Schulz, H.-M. Schulz & Horsfield, B Unconventional Gas Resources in the Paleozoic of Central Europe.- Oil & Gas Science and Technology Rev. IFP Energies nouvelles, 66, Lüders, V., Plessen, B., Carbon and Nitrogen Isotope Measurements of Gas-Bearing Fluid Inclusions: A Tool For Tracing Gas Sources and Maturity of Source Rocks Search and Discovery Article #40963, Adapted from poster presentation at AAPG Annual Convention & Exhibition (Long Beach, California, April 22-25, 2012). Montgomery, S.L., Jarvie, D.M., Bowker, K.A., Pollastro, R.M., Mississippian Barnett Shale, Fort Worth basin, northcentral Texas: Gas-shale play with multi-trillion cubic foot potential. AAPG Bulletin, 89, Rippen, D., Littke, R., Bruns, B., Mahlstedt, Nicolaj, Organic geochemistry and petrography of Lower Cretaceous Wealden black shales of the Lower Saxony Basin: The transition from lacustrine oil shales to gas shales. Organic Geochemistry, 63, Rullkötter, J., Leythaeuser, D., Littke, R., Mann, U., Müller, P.J., Radke, M., Schaefer, R.G., Schenk, H.J., Schwochau, K., Witte, E.G. & Welte, D.H., Organic matter maturation under the influence of a deep intrusive heat source: A natural experiment for quantitation of hydrocarbon generation and expulsion from a petroleum source rock (Toarcian shale, Northern Germany). - Org. Geochem., 13, 4-6, , Pergamon Press, Oxford.

3 Porosity, Permeability and Methane Sorption Capacity of Oil and Gas Shales at different Levels of Thermal Maturation Ralf Littke, Bernhard M. Krooss, Alexandra Amann, Amin Ghanizadeh, Matus Gasparik, Benjamin Bruns

4 Outline General Aspects Organic Geochemistry and Petrology Petrophysical Data From Reservoir to Basin Scale General Conclusions

5 Conventional Unconventional

6 GAS SHALES Organic-rich argillaceous sedimentary rock Source rock and reservoir in one Very low permeability: micro nano darcy Abundant sorbed and free gas 4

7 Methane in gas shales is stored as free gas on the surface of the organic fraction on the surface of clay minerals in sorbed state matrix porosity (blue) Fracture porosity Fracture gas is produced immediately Adsorbed gas is released due to pressure declines

8 Gas content (Barnett shale) sorbed gas - all non-free gas adsorbed (Langmuir isotherms) absorbed (dissolved) DGMK, Littke und Bayer Montgomery et al.,

9 Remember Scale and Heterogeneity nm Key questions: Regional distribution? Large scale estimation/extrapolation porosity (compaction) GIP (adsorbed & free gas) 10 7 nm 10 4 nm Gas generation/expulsion potential Composition, analysis of OM Storage potential Pore structure/system HP sorption experiment Thermovaporization Flow Production Matrix flow Fracability Fracture flow, flow through proppant filled frac 10 5 nm 10 2 nm

10 Multidisciplinary and Multiscale Approach Basin Modelling Regional Scale Organics TOC - Rock-Eval Pyrolysis; Py-GC, MSSV etc Composition and Phase Prediction Petrography: thin section to synchrotron Biogenic gas generation Inorganics Mineralogy Petrography: thin section to SEM to synchrotron Pore System Low P Gas sorption, MICP, FIB-SEM High PT CH 4 Sorption Single and Multiphase Flow Geomechanics Water and gas permeability, capillary pressure Mechanical characterisation Hydrofrac and proppant embedment Reservoir Scale

11 CASE STUDY WEALDEN SHALE: IMMATURE VS. MATURE, LACUSTRINE-BRACKISH (RIPPEN ET AL., 2013)

12 Wealden Shale

13 Geochemical Properties 3 Wells from the Lower Saxony Basin: Ex-A Ex-B Ex-C

14 Geochemical Properties

15 Organic Petrography

16 Organic Petrography

17 GC & GC/MS

18 GC & GC/MS

19 GC & GC/MS

20 Thermovaporisation-GC/Pyrolysis-GC

21 Basin Modeling

22 Wealden Shales Thick, clay-rich sequence, limited lateral extension Upon maturation loss of primary (Botryococcus) algae Network of solid bitumen predominates Wax-rich oil is generated; large areas in gas window No fractures: effect of lithology? Late oil impregantion of upper gas shale by longdistance intraformation migration?

23 CASE STUDY MARINE POSIDONIA SHALE: NATURAL LAB Regional distribution

24 Regional Scale

25 Posidonia Maturity Series Littke et al., 1991

26 Immature Posidonia Shale: TOC, Sulphur, Carbonate HI Littke et al., 1991

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28 Posidonia Shale (immature) Posidonia Shale (mature + fractures) Littke et al., 1988, 1991

29 Organic Geochemistry TOC (%) T-max ( C) S2 (mg/g) % n-c Paraffinic Oil Low Wax 40 Paraffinic Oil High Wax P-N-A Oil Low Wax Top-Depth (m) Clay marlstone P-N-A Oil High Wax Gas and Condensate Clay marlstone Screening Data (GASHBase) C % Old New Horsfield et al., 2010 n-c % Kerogen Structure Wickensen Harderode Haddessen

30 Mass Balance Posidonia Shale Rullkötter et al., 1988

31 Mass Balance: Organic Carbon Loss and Expelled Products Littke et al., 1993

32 Posidonia Shale: Peak Oil Stage and Beyond: Horizontal Fractures, Solid Bitumen, Oil Inclusions in Carbonate Veins

33 δ 13 C CH 4 [ ] δ 13 C values of CH 4 of fluid inclusions in calcite -50 Haddessen late (?) biogenic gas Harderode Haddessen -45 Horizontal veins R o Harderode -40 Vertical veins -35 R o Haddessen R 0 (%) after Lüders and Plessen, 2012

34 Pore space Sorption capacity GAS STORAGE

35 Porosity Overview: e.g. Posidonia 1.45% Ro Sorbed gas GAS STORAGE Free gas Micro Meso Macro 0.3 nm 1 nm 5 nm 100 nm 200 nm 5 µm Total porosity 8.7% Not detected by Hg 4.3% CO 2-78 C 4.8% Mercury porosity 4.4% FIB/BIB/SEM imaging 1.9% Littke et al., 2011

36 VR r % Which Porosity Changes with Maturity? Total Porosity (Archimedes): Lost then Regained < 5 nm Porosity (CO 2, -78 C): Lost then Regained < 1.5 nm Porosity (CO 2, 0 C): Constant Porosity (%) 0.53% Compaction? 0.9% 1.45% Secondary porosity

37 He-porosity Porosity of Gas Shales 18% 16% 14% 12% 10% 8% 6% 4% 2% 0% HAD (claystone) HAD (marlstone) HAR TOC [wt %] WIC (marlstone) Alum_Skelbro#2 (VRr = 2.4%) Alum_Gislövsh. (VRr = 2.0%) Alum_Ottenby (VRr = 0.9%) Alum_Djupvik (VRr = 0.5%) Posidonia_HAD (VRr = 1.5%) Posidonia_HAR (VRr = 0.9%) Posidonia_WIC (VRr = 0.5%) Barnett_Mesquite#1 (VRr = 1.0%)

38 Pore size characterization: Evolution of porosity Newcastle University (UK) Mature shale (gas shale) Immature shale (oil-shale) Visibly porous organic matter Visibly non-porous organic matter 26

39 HPHT excess sorption isotherms Dependence on Maturity Temperature

40 Sorption dry vs. moist samples

41 [mmol/g] Max. Langmuir sorption capacity n L TOC [wt %] Posidonia (VRr = 1.5%) Posidonia (VRr = 0.9%) Posidonia (VRr = 0.5%) Alum (VRr = 2.4%) Alum (VRr = 2.0%) Alum (VRr = 0.9%) Barnett (VRr = 2.2%) Barnett (VRr = 1.0%)

42 Thermovaporisation S2-normalised Tvap gas yields correlate with Langmuir parameter A new rapid screening tool for sorptive capacity (B. Horsfield and GFZ-group)

43 Klinkenberg-corrected gas (He) permeability (m 2 ) Permeability measurements Porosity-Permeability relationship 1.E-15 1.E-16 1.E-17 1.E-18 Parallel to bedding Perpendicular to bedding Test gas: Helium Effective stress: 30 MPa 1.E-19 1.E-20 1.E-21 1.E He porosity (%) Posidonia Shale Alum Shale Namurian Shale Barnett Shale

44 Klinkenberg-corrected permeability (μdarcy) Single-phase fluid flow - rock matrix - Mature Shale (Haddessen) Horizontal direction %R 0 : 1.45 TOC: 6.7 % Steady state Dry plug He 10 Ar CH Effective stress (MPa) Significant effect of permeating fluid: He > Ar > CH 4 > H 2 O Significant effect of maturity: Lowest permeability values at intermediate maturity level (oil-window) Significant effect of moisture: 2 times higher perm. for dry sample (compared to as-received, 1.9% wt/wt) Significant effect of anisotropy: More than one order of magnitude higher for parallel direction

45 Rock mechanics Ductility increases with porosity, clay content & confining pressure Samples ll to bedding weaker than T provided by G. Dresen and Rybacki, GFZ

46 REGIONAL SCALE CASE STUDY POSIDONIA SHALE Large scale estimation/extrapolation of thermal maturity petroleum generation porosity (compaction) GIP (adsorbed & free gas)

47 Present day maturity Posidonia Shale

48 Present-day bulk adsorption capacity Toarcian

49 Excellent maturity series Posidonia Shale Marlstones with variable clay and carbonate content Secondary porosity & fractures (related to lithology) Porosity, permeability & sorption capacity depend on maturity lowest values close to peak-oil generation! Brittleness depends on porosity and mineralogy First detailed upscaling of petrophysical properties in a basin model Biogenic gas generation in overmature shales?

50 GASH: Gas Shales in Europe ( ) Sponsors Academic partners 3

51 Acknowledgements to our former colleagues at FZ Juelich: Detlev Leythaeuser, Ulrich Mann, Matthias Radke, Juergen Rullkoetter, Rainer G. Schaefer, Dietrich Welte, etc.

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