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AAPG Bulletin

Abstract

(Begin page 1033)

AAPG Bulletin, V. 85, No. 6 (June 2001), P. 1033-1053.

Copyright ©2001. The American Association of Petroleum Geologists. All rights reserved.

Lake-type controls on petroleum source rock potential in nonmarine basins

Alan R. Carroll,1 Kevin M. Bohacs2

1Department of Geological and Geophysical Sciences, University of Wisconsin, 1215 W. Dayton St., Madison, Wisconsin, 53706; email: [email protected]
2ExxonMobil Upstream Research Co., 2189 Buffalo Speedway, Houston, Texas, 77252; email: [email protected]

AUTHORS

Alan R. Carroll has been an assistant professor at the University of Wisconsin, Madison, since 1996, specializing in sedimentary basins in western China and the western United States. He received geology degrees from Carleton College (B.A. degree, 1980), the University of Michigan, Ann Arbor (M.Sc. degree, 1983), and Stanford University (Ph.D., 1991). He worked as an exploration geologist for Sohio (1983-1986) and a research geologist for Exxon Production Research Company (1991-1995). He is an associate editor of the AAPG Bulletin.

Kevin M. Bohacs is a sedimentologist and stratigrapher with the Petroleum Geochemistry section of ExxonMobil Upstream Research Company (URC) in Houston, Texas. He received his B.Sc. (honors) degree in geology from the University of Connecticut in 1976 and his Sc.D. degree in experimental sedimentology from M.I.T. in 1981. At URC, he leads the application of sequence stratigraphy and sedimentology to organic-rich rocks from deep sea to swamps and lakes in basins around the world. As a research associate, his primary focus is to keep the geo- in geochemistry, integrating field work, subsurface investigation, and laboratory analyses. He has written numerous articles on the stratigraphy and sedimentology of mudrocks, hydrocarbon source rocks, and lake systems. He was co-recipient of the AAPG Jules Braunstein Memorial Award for best poster session paper in 1995 for work on coal sequence stratigraphy and the AAPG International Paper Award in 1998 and was an AAPG Distinguished Lecturer for 1999-2000.

ACKNOWLEDGMENTS

This article benefited from discussions with many individuals, including S. C. Brassell, Y. Y. Chen, R. Cunningham, D. J. Curry, G. Genik, K. S. Glaser, G. J. Grabowski Jr., G. B. Hieshima, G. H. Isaksen, B. J. Katz, M. R. Mello, K. Miskell-Gerhardt, J. E. Neal, P. Olsen, D. J. Reynolds, C. Scholz, and K. O. Stanley. G. J. Grabowski and H. B. Lo collected some of the data used in this article. M. Wartes provided useful comments on an early draft of the manuscript. Field studies in the Junggar basin in 1987, 1988, and 1992 were funded by the Stanford-China Industrial Affiliates, a group of companies that included AGIP, Amoco, Anschutz, BHP Petroleum, Chevron, Conoco, Elf-Aquitaine, Enterprise Oil, Exxon, Mobil, Occidental, Pecten, Phillips, Sun, Texaco, Transworld Energy International, and Unocal. Conoco provided additional support for this article. The Donors of The Petroleum Research Fund, administered by the American Chemical Society, also provided support for this research. We thank Exxon Production Research Co. for permission to publish this article. J. A. Curiale, B. J. Katz, B. Wiggins, and an anonymous reviewer all provided very helpful reviews.

ABSTRACT

Based on numerous empirical observations of lacustrine basin strata, we propose a three-fold classification of lacustrine facies associations that accounts for the most important features of lacustrine petroleum source rocks and provides a predictive framework for exploration in nonmarine basins where lacustrine facies are incompletely delineated.

(1) The fluvial-lacustrine facies association is characterized by freshwater lacustrine mudstones interbedded with fluvial-deltaic deposits, commonly including coal. Shoreline progradation dominates basin fill, resulting in the stacking of indistinctly expressed cycles up to 10 m thick. In map view, the deposits may be regionally widespread but laterally discontinuous and contain strong facies contrasts. Transported terrestrial organic matter contributes to mixed type I-III kerogens that generate waxy oil (type I kerogen is hydrogen rich and oil prone; type III kerogen is hydrogen poor and mainly gas prone). The Luman Tongue of the Green River Formation (Wyoming) and the Honyanchi Formation (Junggar basin, China) provide examples of this facies association, which is also present in the Songliao basin of northeastern China, the Central Sumatra basin, and the Cretaceous Doba/Doseo basins in west-central Africa.

(2) The fluctuating profundal facies association represents a combination of progradational and aggradational basin fill and includes some of the world's richest source rocks. Deposits are regionally extensive in map view, having relatively homogenous source facies containing oil-prone, type I kerogen. Examples include the Laney Member of the Green River Formation (Wyoming), the Lucaogou Formation (Junggar basin, China), the Bucomazi Formation (offshore west Africa), and the Lagoa Feia Formation (Campos basin, Brazil).

(3) The evaporative facies association represents dominantly aggradational fill related to desiccation cycles in saline to hypersaline lakes and may include evaporite and eolianite deposits. Sublittoral organic-rich mudstone facies are relatively thin but may be (Begin page 1034) quite rich and widespread. The highest organic enrichment coincides with the deepest lake stages. Low input of land plant organic matter results in minimal lateral contrasts in organic content. In some cases a distinctive type I-S (sulfur-rich) kerogen may generate oil at thermal maturities as low as 0.45% vitrinite reflectance equivalent. Examples include the Wilkins Peak Member of the Green River Formation (Wyoming), the Jingjingzigou Formation (Junggar basin, China), the Jianghan and Qaidam basins (China), and the Blanca Lila Formation (Argentina).

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