--> Abstract: Occurrence of Oil and Gas Fields and Source Rock Transformation in the West Siberian Basin and Barents Sea Platform, by N. Lopatin; #90990 (1993).

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LOPATIN, NIKOLAI, Institute of Geochemistry, Moscow, Russia

ABSTRACT: Occurrence of Oil and Gas Fields and Source Rock Transformation in the West Siberian Basin and Barents Sea Platform

The West Siberian and Barents Sea basins contain the largest demonstrated reserves of gas in the world (more than 55 trillion cu m) and very large recoverable reserves of oil (about 19 billion tons). The main productive reservoirs are of the Jurassic and Cretaceous and are composed of marine and alluvial sandstones. Major gas fields of the West Siberian basin are located north of the Arctic Circle, from which they extend into the Yamal Peninsula and offshore into the Kara Sea. Oil fields of the basin are found mainly in the middle Ob region. Only one giant gas-condensate field has been found in the Barents Sea; however, this area has excellent potential for gas-condensate discoveries in the future. Both basins contain Kimmeridgian-Tithonian black-shale formations, which are prolific o l source rocks.

In the Barents Sea basin, Kimmeridgian black shales contain 7 to 9% of organic carbon; total pyrolysis yield ranges from 5.3 to 84.2 mg HC/g rock, and hydrogen index ranges from 270 to 630 mg HC/g TOC. Our pyrolysis data and basin modeling (GALO version) indicate that the realization of the initial petroleum potential in the Shtokmanov field area has not begun because the volume of generated oil (about 8 mg HC/g TOC) is insufficient to start expulsion (threshold of expulsion is equal to 96 mg HC/g TOC).

The Bazhenov Formation shales in the central part of the West Siberian basin are characterized by extremely high values of pyrolysis measurements. The organic carbon content ranges from 10 to 25%; the residual petroleum potential varies from 50 to 190 mg HC/g rock; the maturity typically corresponds to the oil window zone; and the amount of expelled hydrocarbons ranges from 40 to 60 mg HC/g rock. The expulsion of oil commenced 90 to 35 m.y. In the northern part of the West Siberian basin, the Bazhenov shales are lean source rocks.

AAPG Search and Discovery Article #90990©1993 AAPG International Conference and Exhibition, The Hague, Netherlands, October 17-20, 1993.