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Geochemical Evaluation of Oils and Source Rocks from the Western Siberian Basin, U.S.S.R.

PETERS, KENNETH E., Chevron Overseas Petroleum, Inc., San Ramon, CA, J. M. MOLDOWAN, Chevron Oil Field Research Company, Richmond, CA, A. E. KONTOROVICH and O. STASOVA, Siberian Scientific Research Institute for Geology, Geophysics and Mineral Resources, Novosibirsk, U.S.S.R., B. J. HUIZINGA, Chevron Overseas Petroleum, Inc., San Ramon, CA, and G. J. DEMAISON, Consultant, Capitola, CA

Although the Western Siberian basin is among the most prolific in the world, there has been disagreement among Soviet geoscientists on the origin of the petroleum within this basin. Screening geochemical analyses were used to select several oils and potential source rocks for a preliminary study using detailed biomarker and supporting geochemistry. Possible sources for this petroleum include rocks of Middle Jurassic, Upper Jurassic, and Lower Cretaceous age.

Results indicate that most of the analyzed Western Siberian oils, occurring in reservoirs from Middle Jurassic to Late Cretaceous in age, are derived from the Upper Jurassic Bazhenov Formation. The locations of the samples in the study generally correspond to the distribution of the most effective oil-generative parts of the Bazhenov Formation. Analyses show that the Bazhenov rock samples contain abundant marine algal and bacterial organic matter, preserved under anoxic depositional conditions.

Biomarkers show that thermal maturities of the samples range from the early to late oil-generative window and that some are biodegraded. For example, the Salym No. 114 oil, which flowed directly from the Bazhenov Formation, shows a maturity equivalent to the late oil window. The Van-Egan No. 110 oil shows maturity equivalent to the early oil window and is biodegraded. This oil shows preferential microbial conversion of lower homologs of the 17a, 21b(H)-hopanes to 25-nor-17a(H)-hopanes.


AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)