Gas Generation and Retention in the Bakken Shale, Williston Basin* Brian Horsfield 1, Gary P. Muscio 2, Kliti Grice 3, Rolando di Primio 1, Philipp Kuhn 1, and Ercin Maslen 3 Search and Discovery Article #40330 (2008) Posted November 11, 2008 *Adapted from oral presentation at AAPG Annual Convention, San Antonio, TX, April 20-23, 2008. 1 GFZ-Potsdam, Potsdam, Germany, (horsf@gfz-potsdam.de) 2 Chevron, Houston, TX, 3 Curtin University, Perth, WA, Australia. Abstract The Bakken Shale is charged with high concentrations of indigenous gas at low levels of maturity (Ro = 0.3-0.7%). A good correlation with TOC demonstrates that the gas is adsorbed to indigenous bitumen and kerogen. During the succeeding levels of early catagenesis the kerogen structure loses diaromatic components by generation and migration and/or cross-linking and condensation, and the gas is no longer retained. The origin and fate of the gas seems intrinsically linked to that of the diaromatic structural units in the organic matter which we know are inherited from green photosynthetic sulphur bacteria living in the water column under photic zone euxinia above the site of source rock deposition. Here we employ organic geochemistry and basin modelling to evaluate the shale gas potential of the Bakken Shale and to place findings within a petroleum systems context. Compositional kinetics have been measured to predict GOR development as a function of maturity, and to establish the phase behaviour of the generated fluids. The Bakken Shale is indeed inherently more gas-prone than many marine source rocks worldwide, exhibiting a lower saturation pressure. Carbon and hydrogen isotopes have been utilized to trace the origins and fate of the light hydrocarbons occurring in a free form, the diaromatic units and also the latter s thermal degradation products. To facilitate comparisons with known shale gas provinces, star diagrams based on TOC, Tmax, vitrinite reflectance, Transformation Ratio and light hydrocarbon concentrations have been constructed. Potential sweet spot definition will be presented.
Gas Generation and Retention in the Bakken Shale, Williston Basin Brian Horsfield 1, Gary Muscio 2, Kliti Grice 3, Rolando di Primio 1, Philipp Kuhn 1, Ercin Maslen 3 1 GFZ-Potsdam, Germany 2 Chevron Energy Technology Company, USA 3 Curtin University of Technology, Australia Partners in the GFZ IPP Project Shallow Gas
Take home messages 1. Shale oil and shale gas exploration and production source rock properties of paramount a importance 2. Organic matter properties help govern disfunctionality in the case of the Bakken Shale 3. Is HI of 300 mg/gtoc critical? Change in adsorptive properties related to disappearance of certain aromatic units from the kerogen. 4. Bakken is a low GOR system overall - variability in field GOR is complex: generation kinetics and phase behavior are important.
Paleozoic Source Rock The Bakken Shale Uniform facies Type II (basin centre) Broad maturity range 0.3 1.6 %Ro TOC 6-20% Overpressured where mature In-Situ Petroleum Paraffinic composition High API gravity High in gasoline Low in sulphur
Selected References WILLIAMS (1974) Correlation of Madison oils with Bakken source MEISSNER (1978) Regional overpressuring of Bakken in-source reservoir PRICE (1984) Comprehensive Organic Geochemical Characterisation of Bakken Significance of Gas for Migration Behaviour of Bakken Petroleum JARVIE & ELSINGER (1996) Oil systems MUSCIO ET AL. (1994) Early gas generation MUSCIO AND HORSFIELD (1996) Unusual maturation characteristics
Today s Presentation Physical and chemical changes that t take place during maturation Adsorptive properties GOR Saturation pressure Bulk petroleum characteristics Part 1: natural maturation series Part 1: natural maturation series Part 2: simulated maturation series
Samples
Early Gas in the Bakken Shale
Gas Yield as a function of maturity
Gas Yield as a function of maturity Chattanooga Woodford Posidonia
Kerogen Structure Depletion of labile aromatic units in kerogen Photic zone anoxia during deposition
Hydrogen Index Zonation (approximate) Zone of lowered adsorption capacity due to structural changes in kerogen
Petroleum Quality in Reservoirs Kerogen Type Ecosystem Traditional View Qualitative Source Control Realistic View Quantitative Carrier Control Maturity Chemical PVT behaviour Physical
Simulated Maturation using MSSV pyrolysis (Horsfield et al., 1989) Distillation fractions Compound classes Individual compounds 20.00 T Sample: Bouvard 1 Depth: 1315m Sample type: SWC Comment: G003224, heated to 415C APT-ID: 33947 Analysis: TE-GC-FID 15.00 8 Abundance: FID: 1.709e+5 Don t even think about trying to read this 10.00 B E M P 13 Y Z 22 5.00 X 10 min. 20 30 40 50 60 70 8
Compositional Kinetic Model Gases Individual components, tuning Liquids Boiling ranges, molecular weight and density Liquids Boiling ranges molecular weight and density 35 30 100 a 90 b 80 25 70 20 15 60 50 40 10 30 5 20 10 0 0 42 kcal/mol 43 kcal/mol 44 kcal/mol 45 kcal/mol 46 kcal/mol 47 kcal/mol 48 kcal/mol 49 kcal/mol 50 kcal/mol 51 kcal/mol 52 kcal/mol 53 kcal/mol 54 kcal/mol 55 kcal/mol 56 kcal/mol 57 kcal/mol 58 kcal/mol 59 kcal/mol 60 kcal/mol 61 kcal/mol 62 kcal/mol 63 kcal/mol 64 kcal/mol 65 kcal/mol 42 kcal/mol 43 kcal/mol 44 kcal/mol 45 kcal/mol 46 kcal/mol 47 kcal/mol 48 kcal/mol 49 kcal/mol 50 kcal/mol 51 kcal/mol 52 kcal/mol 53 kcal/mol 54 kcal/mol 55 kcal/mol 56 kcal/mol 57 kcal/mol 58 kcal/mol 59 kcal/mol 60 kcal/mol 61 kcal/mol 62 kcal/mol 63 kcal/mol 64 kcal/mol 65 kcal/mol d 35.00 30.00 25.00 20.00 15.00 C56-80 C46-55 C36-45 C26-35 C16-25 C7-15 n-c6 n-c5 c TR 10 30 50 70 90 n-c1 23.05 25.04 25.53 26.82 34.48 n-c2 11.21 11.42 11.66 11.81 10.39 n-c3 10.46 11.43 11.61 11.59 10.16 i-c4 0.84 0.70 0.70 0.65 0.66 n-c4 5.24 4.74 4.40 4.30 3.67 i-c5 2.34 1.54 1.25 1.17 0.90 n-c5 3.09 3.07 3.08 2.91 2.42 n-c6 9.89 11.69 11.58 11.42 11.20 C7-15 17.00 15.82 16.07 16.22 15.37 C16-25 9.13 8.15 8.07 7.76 6.75 C26-35 4.23 3.61 3.48 3.18 2.52 C36-45 1.96 1.60 1.50 1.30 0.94 C46-55 0.91 0.71 0.65 0.53 0.35 C56-80 0.67 0.49 0.43 0.33 0.19 Potential (%) 10.00 5.00 0.00 i-c5 n-c4 i-c4 n-c3 n-c2 n-c1 42 kcal/mol 43 kcal/mol 44 kcal/mol 45 kcal/mol 46 kcal/mol 47 kcal/mol 48 kcal/mol 49 kcal/mol 50 kcal/mol 51 kcal/mol 52 kcal/mol 53 kcal/mol 54 kcal/mol 55 kcal/mol 56 kcal/mol 57 kcal/mol 58 kcal/mol 59 kcal/mol 60 kcal/mol 61 kcal/mol 62 kcal/mol 63 kcal/mol 64 kcal/mol 65 kcal/mol
Cumulative GOR versus maturity Range: 200 600 m 3 /m 3 800 2400 scf/bbl 10000 GOR (Sm 3 /Sm 3 ) 1000 100 G0853 G0848 G0842 G0832 G0817 G0795 G0684 Bakken Shale Bakken Shale Bakken Shale Liptinitic brown coal Vitrinite Alabama lignite Indonesian coal 10 10 30 50 70 90 TR % 0.01 0.1 1 10 kg/kg Scf/bbl 50 500 5000 50000 10 100 1000 10000 Sm 3 /Sm 3
GOR of Bakken Tested Fluids
Predicted Phase Envelopes 2 Bakken samples at 3 stages of maturation ti 350 300 250 Fractu ure Pressure 30% TR 50% TR 70% TR 350 300 250 Fracture Pressure 30% TR 50% TR 70% TR Press sure, bara 200 150 100 50 Hyd drostatic Pressure e sure, bara Press 200 150 100 50 Hyd drostatic Pressure e 0-100 0 100 200 300 400 500 Temperature, C 0-100 0 100 200 300 400 500 600 Temperature, C Bakken Fm. G000852 Bakken Fm. G000842 Philipp Kuhn (unpublished)
Predicted Phase Envelopes 2 Bakken samples at 3 stages of maturation ti 350 300 250 Fractu ure Pressure 30% TR 50% TR 70% TR 350 300 250 Fracture Pressure 30% TR 50% TR 70% TR Press sure, bara 200 150 100 50 Hyd drostatic Pressure e sure, bara Press 200 150 100 50 Hyd drostatic Pressure e 0-100 0 100 200 300 400 500 Temperature, C 0-100 0 100 200 300 400 500 600 Temperature, C Bakken Fm. G000852 Bakken Fm. G000842 Philipp Kuhn (unpublished)
Predicted Phase Distribution
Conclusions 1. Shale oil and shale gas exploration and production source rock properties of paramount importance 2. Organic matter properties help govern disfunctionality in the case of the Bakken Shale 3. Is HI of 300 mg/gtoc critical? Change in adsorptive properties related to disappearance of certain aromatic units from the kerogen. 4. Bakken is a low GOR system overall - variability in field GOR is complex: generation kinetics and phase behavior are important. 5. Evolution of bulk petroleum properties within petroleum system model is the next step
References Horsfield, B., U. Disko and F. Leistner, 1989, The micro-scale simulation of maturation; outline of a new technique and its potential applications, in Geologic modeling, aspects of integrated basin analysis and numerical simulation: Geologische Rundschau, v. 78/1, p. 361-374. Jarvie, D.M., R.J. Elsinger, R.F. Inden, and J.G. Palacas, 1996, A comparison of the rates of hydrocarbon generation from Lodgepole, False Bakken, and Bakken Formation petroleum source rocks, Williston Basin, USA: AAPG Bulletin, v. 80/6, p. 973. Meissner, F.F., 1978, Petroleum geology of the Bakken Formation, Williston Basin, North Dakota and Montana: in Montana Geological Society, The Economic geology of the Williston Basin; Montana, North Dakota, South Dakota, Saskatchewan, Manitoba, p. 207-227. Muscio, G.P.A., and B. Horsfield, 1996, Neoformation of inert carbon during the natural maturation of a marine source rock; Bakken Shale, Williston Basin: Energy Fuels, v. 10/1, p. 10-18. Muscio, G.P.A., B. Horsfield, and D.H. Welte, 1994, Occurrence of thermogenic gas in the immature zone; implications from the Bakken insource reservoir system: Organic Geochemistry, v. 22/3-5, p. 461-476. Price, L.C., T. Ging, T. Daws, A. Love, M. Pawlewicz, and D. Anders, 1984, Organic metamorphism in the Mississippian-Devonian Bakken Shale, North Dakota portion of the Williston Basin: in Rocky Mountain Association of Geologists, Hydrocarbon source rocks of the Rocky Mountain region, p. 88-133. Williams, J.A., 1974, Characterization of oil types in Williston Basin: AAPG Bulletin, v. 58/7, p. 1243-1252.