Unconventional hydrocarbons in shales: source rock or waste zones?
Nachiketa Mishra A , John Kaldi B and Ulrike Schacht AA Australian School of Petroleum, The University of Adelaide.
B CO2CRC, Australian School of Petroleum, The University of Adelaide.
The APPEA Journal 55(2) 474-474 https://doi.org/10.1071/AJ14109
Published: 2015
Abstract
This extended abstract summarises the objectives of a research project that will provide insight into hydrocarbon generation and accumulation in continuous-source reservoirs and how to best exploit such unconventional resources in Australia, specifically in the Cooper Basin. It compares and contrasts a productive shale from the US—the Bakken Formation—with shales from the Cooper Basin.
Unconventional resources, such as the Devonian-Mississippian Bakken Formation, have been assumed to be continuous source-reservoirs where the oil is generated from organic-rich shales with minimal migration. It is possible, however, that the shale intervals are a waste zone (a leaked seal). These waste zones form when the buoyancy pressure of the hydrocarbon exceeds the capillary forces in the seal, resulting in tertiary migration. Oil saturation values strongly correlate with the hydrocarbon content parameter (S1/TOC) from Rock-Eval. Values of 120 mgHC/gC are typically indicative of non-indigenous or migrated hydrocarbons (reservoirs or leaked seals). Mercury injection capillary pressure (MICP) analysis of core samples can also diagnose whether a shale is a source or a seal. Organic shales with high capillary entry pressures generally have low hydrocarbon content, in line with in-situ generation; shales with low entry pressures have comparatively higher hydrocarbon content and indicate migration from an underlying accumulation.
Once these waste zones are identified on a basin-scale, specific samples from the Bakken Formation will be analysed using micro-scale sealed vessel pyrolysis, combined with monitoring of the biomarkers and other organic compounds using mass spectrometry. As the composition of organic compounds is altered during migration, this will confirm whether they are generated locally or migrated.
Nachiketa Mishra is a postgraduate research candidate at the Australian School of Petroleum, University of Adelaide. His research involves studying unconventional shale hydrocarbons and their generation and migration in continuous source reservoirs (mixed source, reservoir and sealing facies). He completed his bachelor degree in natural resources (geosciences) and honours degree in petroleum geology and geophysics at the Australian School of Petroleum, University of Adelaide. He recently represented the Australian School of Petroleum in the AAPG International Barrel Award in which the team placed 1st in the Asia-Pacific regional competition. |
John Kaldi is the chief scientist for CO2CRC and professor and chair of geosequestration at the Australian School of Petroleum, University of Adelaide. John’s expertise is in CO2 storage (containment, injectivity, capacity), seal evaluation, petroleum reservoir geology, carbonate sedimentology and diagenesis. John has worked in academia for 12 years at the University of Adelaide and in the petroleum industry for more than 18 years with Shell, Arco and Vico, serving in both technical and managerial roles. He obtained his bachelor's degree and studied for his master's at Queens College, City University of New York, and he received a PhD from Cambridge University for a dissertation on Permian carbonates (hydrocarbon reservoir rocks) in the North Sea. He became Director of the National Centre for Petroleum Geology and Geophysics at University of Adelaide, Australia (1998–2003), and then was the inaugural Head of School of the Australian School of Petroleum, also at the University of Adelaide (2003–2005). |
Ulrike Schacht is a geochemist at CO2CRC, responsible for conducting natural analogue studies for CO2 storage and assurance monitoring for CO2 storage sites such as the Otway Project demonstration site. Her interests include CO2 storage, caprock systems for CO2 storage, environmental monitoring and CO2-related diagenesis. She obtained her bachelor's in geo-engineering sciences and masters in applied geochemistry from the Technical University of Berlin, Germany, and completed her PhD studies in marine geochemistry at the University of Kiel, Germany. She has been a senior research fellow at Australian School of Petroleum, University of Adelaide and CO2CRC since 2007. |
References
Alexander, E.M., Gravestock, D.I., Cubitt, C., and Chaney, A., 1998—Lithostratigraphy and Environments of Deposition. In: The Petroleum Geology of South Australia, Vol. 4. Adelaide: Government of South Australia, 69–116.Apak, S.N., Stuart, W.J., Lemon, N.M., and Wood, G. (1997). Structural evolution of the Permian-Triassic Cooper Basin, Australia; relation to hydrocarbon trap styles. AAPG Bulletin 81, 533–55.
Cox, S.A., Cook, D.M., Dunek, K., Daniels, R., Jump. C., and Barree, B., 2008—Unconventional Resource Play Evaluation: a look at the Bakken Shale Play of North Dakota. SPE Unconventional Resources Conference Proceedings, Keystone, Colorado, 10–12 February, SPE 114171.
Dow, W.G. (1974). Application of oil correlation and source rock data to exploration in Williston basin. AAPG Bulletin 58, 1,253–62.
Downey, M.W. (1984). Evaluating seals for hydrocarbon accumulations. AAPG Bulletin 68, 1,752–63.
Hunter, C.D., and Young, D.M., 1953—Relationship of natural gas occurrence and production in Eastern Kentucky (Big Sandy Gas Field) to joints and fractures in Devonian bituminous shales. AAPG Bulletin 37, 282–99.
Jenkins, C.C., 1989—Geochemical correlation of source rocks and crude oils from the Cooper and Eromanga Basins. In: O’Neil, B.J. (ed.) The Cooper and Eromanga Basins, Australia. The Cooper and Eromanga Basins Conference Proceedings, Adelaide, 26–27 June, 525–40.
Lowe-Young, B.S., Mackie, S.I., and Heath, R.S., 1996—Geological controls on hydrocarbon accumulations in the Eromanga Basin, south west Queensland: a petroleum system perspective. In: Mesozoic ’96. Mesozoic Geology of the Eastern Australia Plate Conference Abstracts, Brisbane, 23–26 September, 356–65.
Meissner, F.F., 1978—Petroleum geology of the Bakken Formation, Williston Basin, North Dakota and Montana. In: Rehrig, D. (ed.) The economic geology of the Williston Basin, Montana, North Dakota, South Dakota, Saskatchewan, Manitoba. Billings: Montana Geological Society, 207–27.
Minescu, F., Popa, C., and Grecu, D. (2010). Theoretical and practical aspects of tertiary hydrocarbon migration. Petroleum Science and Technology 28, 555–72.
Noble, R.A., Kaldi, J.G., and Atkinson, C.D. (1997). Oil saturation in shales: applications in seal evaluation. AAPG Memoir 67, 13–30.
Schowalter, T.T. (1979). Mechanics of secondary hydrocarbon migration and entrapment. AAPG Bulletin 63, 723–60.
Schowalter, T.T., and Hess, P.D. (1982). Interpretation of subsurface hydrocarbon shows. AAPG Bulletin 66, 1,302–27.
Seifert, W.K., and Moldowan, J.M. (1978). Applications of steranes, terpanes and monoaromatics to the maturation, migration and source of crude oils. Geochimica et Cosmochimica Acta 42, 77–95.
Tissot, B.P., and Welte, D.H., 1984—Petroleum formation and occurrence. New York: Springer-Verlag, 699.
Webster, R.L., 1984—Petroleum source rocks and stratigraphy of the Bakken Formation in North Dakota. In: Woodward, J., Meissner, F.F., and Clayton, J.L. (eds.) Hydrocarbon source rocks of the Greater Rocky Mountain region. Denver: Rocky Mountain Association of Geologists, 57–81.
