--> Abstract: Separate Prognosis and Formation of Hydrocarbon Systems in West Siberia, by N. Nemchenko, A. Rovenskaya, and V. Podshibyakin; #90990 (1993).

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NEMCHENKO, N., State Commission for Mineral Reserves of Russia, Moscow, Russia; A. ROVENSKAYA, Institute of Geological, Geochemical, and Geophysical Systems, Moscow, Russia; and V. PODSHIBYAKIN, Ymalneftegasgeologiya, Salekhard, Russia

ABSTRACT: Separate Prognosis and Formation of Hydrocarbon Systems in West Siberia

The west Siberian oil and gas province occupies an area of more than 2.5 million sq km. More than 1900 oil and gas pools have been discovered there. A study of the vertical and regional distribution of hydrocarbons suggests that there is a regular zonation of the various phase state. Within the Mesozoic to Cenozoic series, five major zones have been identified, each with its own typical phase state.

The first zone, which incorporates Aptian, Albian, and Cenomanian rocks is dominantly gaseous; this zone contains all principal gas accumulations of the province (95% of west Siberian gas). They are predominantly dry-gas bearing in the northern and Arctic regions. A number of super giant and giant dry-gas fields have been discovered, which include the Urengoy, Medvezhoye, Yamburg, Zapolyarnoye, Gubkin, and Komosomolskoye fields. Reservoir temperature varies from 9 to 20 degrees C.

The second zone includes Valanginian through lower Aptian rocks. The zone contains many gas condensate and oil-gas condensate pools. A group of wet-gas fields is located between the Nadym and Taz rivers, and also on the Yamal and Gydan peninsulas. The total thickness of the Neocomian is 1000 m. Reservoir temperature varies from 30 to 75 degrees C.

The third zone contains mainly oil pools. This zone embraces Valanginian-Hauterivian and Berriasian-Valanginian productive horizons of the middle Ob region. The great majority of fields were discovered there, including Samotlor, Bistrin, and Fedorovo. Reservoir temperature is between 70 and 100 degrees C.

The fourth zone comprises Middle and Upper Jurassic rocks and contains oil and gas condensate pools, oil with associated gas-bearing Upper and Middle Jurassic sandstones in the Salym and Krasnolensk region. The oil is lower density than the Neocomian oil, and production generally is smaller. Reservoir temperature reaches 120 to 140 degrees C.

The fifth zone is distinguished in deeply buried rocks of the Achimov Formation and Lower-Middle Jurassic strata of the Urengoy field in the northern part of the basin. The zone contains gas condensate, and the reservoir temperature is more than 140 degrees C.

The specific feature of the West Siberian basin is the genetic character of the vertical and areal zonation; the distribution and type of hydrocarbons is a function of primary kerogen type, and of in situ generation and entrapment.

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