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Abstract

AAPG Bulletin, V. 88, No. 5 (May 2004), P. 587-611.

Copyright copy2004. The American Association of Petroleum Geologists. All rights reserved.

Modification of the petroleum system concept: Origins of alkanes and isoprenoids in crude oils

James Collister,1 Robert Ehrlich,2 Frank Mango,3 Glenn Johnson4

1SGS Control Services, 22934 Lochness Ave., Torrance, California 90105; [email protected]
2Residuum Energy, Inc., 1048 S. Oak Hills Way, Salt Lake City, Utah 84108; [email protected]
3Department of Chemical Engineering, Rice University, PO Box 1892, Houston, Texas 77079-5201; [email protected]
4University of Utah, Energy and Geoscience Institute, 423 Wakara Way, Suite 300, Salt Lake City, Utah 84108; [email protected]

AUTHORS

James Collister received a B.A. degree in biochemistry and geology from the University of California at Santa Barbara and an M.S. degree and a Ph.D. in biogoechemistry from Indiana University. He is currently working at SGS Control Services in California and is also a private consultant. His interests include isotopic biogeochemistry of ancient and modern sedimentary depositional environments, oil and source rock characterization, and tracing biogenic inputs into petroleum source rocks and crude oils in an attempt to refine petroleum systems analysis.

For the past 30 years, Robert Ehrlich has been engaged in developing and applying image analysis and pattern recognition procedures in the earth and environmental sciences. He received his B.A. degree in geology at the University of Minnesota. He received his M.S. degree and his Ph.D. from Louisiana State University. After a 30-year career in the academe at Michigan State University, the University of South Carolina, and the University of Utah, he is currently vice president of Residuum Energy Incorporated and heads Residuum's Salt Lake City office. He current interests lie in the general field of data mining.

Frank Mango received his B.S. degree in chemistry from San Jose State College and his Ph.D. in organic chemistry from Stanford University. He joined Shell Development at Emeryville, California, working in catalysis and petroleum chemistry and later switched to organic geochemistry at Bellaire Research Center in Texas. He was adjunct professor in the Department of Geology and Geophysics at Rice University and a research scientist in the Department of Chemical Engineering, where he carried out research on the role of transition metals in the origin of oil and natural gas.

Glenn Johnson received his M.S. degree from the University of Delaware and his Ph.D. from the University of South Carolina. Both research programs focused on the application of multivariate techniques to geological and geochemical data. He spent seven years between degrees, as an environmental consultant with Roux Associates, Inc., and McLaren/Hart Environmental Engineering Corp., where his work focused on investigation of contaminated sites, environmental forensics, and associated litigation support. Since 1995, Johnson has been a research assistant professor at the Energy and Geoscience Institute at the University of Utah, where he teaches in the Department of Civil and Environmental Engineering, and continues research in chemometrics applied to environmental and petroleum geochemical systems.

ACKNOWLEDGMENTS

The Timan-Pechora oils and rock extracts were analyzed in the laboratory of the Energy and Geoscience Institute, University of Utah. The high quality of the analyses owes much to the care and prowess of Nicolas Dahdah.

ABSTRACT

Kerogen, the source material for petroleum, can have a long history of alteration and diagenesis before crude oil forms. A common assumption is that the bulk composition of the expressed oil reflects so much of these progressive alterations that most of the primary biological information of the original fixed carbon has been lost. Exceptions are trace constituents, the biomarkers that comprise only a fraction of the organic material in most pristine crude oils. Analysis of the alkane/acyclic isoprenoid fraction of a large number of crude oils and rock extracts from the Timan-Pechora basin (Russia) suggest that this fraction, the main constituent of most crude oils, is a direct product of liquefaction of biological debris that was preserved essentially unaltered to the point of oil generation. Therefore, the primary biological provenance of this fraction is preserved in the oil fraction.

A set of gas-chromatographic analyses of 242 crude oils as well as 83 solvent extracts from upper to middle Paleozoic putative source rocks from the Timan-Pechora basin (Russia) were analyzed by a multivariate data-analytical procedure new to organic geochemistry. The distributions of n-alkanes and acyclic isoprenoids (24 in all) in the 325 samples could be reproduced by linear combinations of six end-member compositions attributed to distinct biological inputs. Four of the six are assigned to primary producers (waxes from higher plants, cyanobacteria, microalgae, and the microorganism Gloeocapsomorpha prisca). These end members account for most of the n-alkanes and acyclic isoprenoids in our samples. The other two represent the products of secondary bacterial alteration of primary organics during sedimentation and low-level bacterial alteration in the reservoir (biodegradation). Each end member is composed of a spectrum of analytes whose abundances are related to one another by fixed ratios. We surmise that each primary end member represents the breakdown of a resistant biopolymer that forms cell walls and partitions of a given biological group. The n-alkanes and acyclic isoprenoids in crude oils represent the weighted signatures of their various ancestors (i.e., their primary organic inputs). If the precursors of most oils are the products of a small set of chemically simple biopolymers, then many of our assumptions concerning the importance of total organic carbon and the nature of the oil window must be reexamined.

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