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ABSTRACT: Petroleum Geology of the West Siberian Basin

James A. Peterson, James W. Clarke

The West Siberian oil and gas province comprises the largest flat land area in the world (3.5 million km2, 1.3 million mi2). Over most of the region, elevations rarely exceed 100 m (330 ft). The basin is bounded on the west by the Uralian and Novaya Zemlya uplifts, on the east by the Siberian craton and Taymyr uplift, on the south by the Kasakh and Altay-Sayan uplifts, and on the north by the North Siberian sill. Structurally, the basin is a broad, relatively gentle downwarp filled with 3-10 km (10,000-33,000 ft) of post-Paleozoic marine, nearshore marine, and continental clastic sedimentary rocks. The basement is composed of Precambrian and Paleozoic fold systems with large areas of partly metamorphosed Paleozoic carbonate and clastic rocks and nume ous areas of Paleozoic or older granitic and mafic igneous bodies. In the central part of the basin, the basement is cut by an extensive, northerly oriented Triassic rift system.

Paleostructural and stratigraphic trapping are important aspects of West Siberian petroleum geology. Oil source rocks are mainly marine Jurassic and Lower Cretaceous bituminous shales. Gas source rocks are mainly Upper Cretaceous humic and coaly shales. Petroleum production in the basin occurs in four major areas: (1) Middle Ob, primarily oil from Lower Cretaceous deltaic-marine clastic reservoirs on broad regional uplifts; the Samotlor and other supergiant fields are located in this area; (2) Near Ural, primarily oil in the south and gas in the north from Upper Jurassic and Lower Cretaceous clastic reservoirs in paleostructural-stratigraphic traps; (3) Southern basin, oil and oil-gas from Jurassic clastic reservoirs, mainly on anticlines or arches inherited from basement highs; (4) N rthern basin, gas primarily from Upper Cretaceous (Cenomanian) and gas condensate from Lower Cretaceous and Jurassic clastic reservoirs on large anticlinal traps sealed by Cretaceous shales or permafrost; Urengoy, the world's largest gas field, and several other supergiant gas fields are located in this area. Large parts of the basin are relatively unexplored, particularly the northern offshore segments. The interrelated paleostructural and depositional character of this enormous basin provides excellent prospects for stratigraphic trap accumulations. An estimated 70 billion bbl of oil and 1000 tcf of gas have been found in the basin. U.S. Geological Survey estimates of undiscovered conventionally recoverable petroleum resources are 30 billion bbl of oil and 350 tcf of gas.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990