Western Siberian Oil and Gas Basin

the largest oil and gas basin in the world; situated within the Western Siberian Lowland in the territory of Tiumen’, Omsk, Kurgan, and Tomsk oblasts and parts of Sverdlovsk, Cheliabinsk, and Novosibirsk oblasts and Krasnoiarsk and Altai krais, in the RSFSR. Area, approximately 3.5 million sq km.

Technically the Western Siberian oil and gas basin is located in the Western Siberian plate and is bounded on the west by the Hercynian structures of the Urals, on the east by the ledges of the ancient (Baikal) substructure of the Siberian platform, and on the south by the Caledonian and Hercynian structures of the Kazakh, Altai, Tom’-Kolyvan, Alatau, and Zapadnyi Saian fold systems; all these structures and systems have buried continuations beneath a sedimentary covering plate.

The possibility of the existence of oil and gas in the Western Siberian plate was first expressed by I. M. Gubkin in 1932-34. Systematic geological prospecting with the use of geophysical investigations and deep orientation well drilling was begun in 1947. The first gas deposit was found in 1953 with a test well drilled in the Berezovskii Raion, in the lower reaches of the Ob’ River (Seve roSos’va anticline); six years later, the first oil deposit was discovered in the Shaim region, on the Konda River (Shaim mega-swell). The commercial petroleum content of the central group of anticlines in Tiumen’ and Tomsk oblasts and the commercial gas-bearing capacity of the northern part of the Western Siberian oil and gas basin were established between 1959 and 1965, when the commercial gas content of the Severo-Sos’va anticline and the commercial oil-bearing capacity of the Shaim mega-swell and the Krasnoleninskii anticline were also confirmed. By March 1971, 168 oil, gas, and combination oil-and-gas deposits had been discovered.

The basin area is composed of terrigenous deposits from the Jurassic, Cretaceous, Paleocene and, to a lesser degree, the Neocene periods; older deposits (Triassic, Paleozoic) are developed only in depressions making up the substructure. The Lower and Middle Jurassic deposits are represented by continental sand and argillaceous rocks with a maximum thickness in the north of 1,000 m (200-600 m over a large area of the basin). The Upper Jurassic and Lower Cretaceous (Valanginian) rocks are composed of argillites and sandstones; the thickness of the Upper Jurassic deposits seldom exceeds 300 m, and that of the Valanginian, 500 m; the remainder of the early Cretaceous section is composed of lagoon and marine argillaceous sandstones (600 m in the central part of the basin and up to 1,000 m in the north). The Upper Cretaceous, Paleocene, and Eocene deposits are represented by marine and, to a lesser degree, continental argillaceous and sandstone rocks ranging in thickness from 800 to 1,600 m. The Oligocene, no more than 700 m thick, is expressed by continental sands and clays. The maximum thickness (more than 5 km) of the sedimentary deposits occurs in the northern part of the basin.

A series of large uplifts (anticlines and mega-swells), depressions, and downwarps is recorded in the sedimentary layer. The basin includes the Surgut, Nizhnevartovsk, Aleksandrovskoe, Kaimysovy, Srednii Vasiugan, Sen’kino-Sil’ginskii, and Pudino anticlines in the central part, and the Severo-Sos’va, Krasnoleninskii, and Liamino anticlines in the west; the northern part of the basin includes the Medvezh’e-Iamal, Urengoi, Messoiakha-Rassokha, Tazovskii, and Iubileino-Var”egan mega-swells. The depth of the substructure stratification at the locations of the anticlines varies from 1,500 to 4,000 m. The anticlines are separated by depressions and downwarps; the largest are the Nadym and the Khanty-Mansiisk depressions, which divide the western from the central group of anticlines, and the Ust’-Enisei depression in the northeastern part of the basin.

Local upthrusts, including large (40 x 20 km), medium (15 x 10 km), and small (3x 5 km) upthrusts, have evolved in the large uplift areas and the depressions. More than 100 local upthrusts have been proved to bear oil or gas.

The basin’s oil- and gas-bearing capacity is associated with Jurassic and Cretaceous deposits which, in section, include more than 40 productive sandstone formations. In the Berezovo gas-bearing region, gas flows are also obtained from fissured gneissic granites and metamorphic shales underlying the sedimentary rocks. Two productive strata are distinguished in the Jurassic deposits: the middle Lower Jurassic and the Upper Jurassic. The first has four to six productive beds, each up to 20 m thick; the stratum is productive throughout the entire basin. The Upper Jurassic stratum is productive in the western and central parts of the basin. The productive beds are 10-15 m thick. In the Cretaceous deposits, both Lower Cretaceous Neocomian (Aptian) and Upper Cretaceous rocks contain oil and gas. In the Neocomian there are up to 20 productive beds, each 15-20 m thick. These are most developed in the deposits of the central group of anticlinal uplifts. In the Aptian deposits, oil-bearing capacity has been established in the western and northern areas of the basin. The gas-bearing capacity of the northern group of deposits is associated with Upper Cretaceous sandstones. The thickness of the gas-bearing beds here reaches 120 m.

Most of the oil- and gas-bearing deposits (more than 80 percent) are located at depths of 2,000-3,000 m; gas and gascondensate deposits are developed for the most part (approximately 80 percent) at depths of 2,000 m. Both oil and gas deposits of the basin have high yields: up to 200 tons of oil per day and 5 million cu m of gas per day. The petroleum from the Western Siberian oil and gas basin is a valuable raw material for the chemical industry. Its density is no more than 880 kg/m3, sulfur content is low (to 1.1 percent), paraffin content is less than 0.5 percent, and gasoline fraction content is high (40-60 percent). The petroleum of the Jurassic deposits is lighter than that of the Cretaceous deposits. The gas contains 90-98 percent methane, 1-4 percent heavy hydrocarbons, 3-6 percent nitrogen, and 0.1-2 percent carbon dioxide. Light petroleum in a dissolved state (gas-condensate deposits) occurs in some gas deposits, including Myl’dzhino, Ust’-Sil’ginskii, and Tazovskii. (See Table 1.)

In accordance with the directives of the Twenty-Fourth Congress of the CPSU, the nation’s largest petroleum industry center, producing no less than 120-125 million tons of oil in 1975, is to be created in Western Siberia. Petroleum production will reach 230-260 million tons by 1980, in accordance with the decree of the Central Committee of the CPSU and the Council of Ministers of the USSR (dated January 1970) on measures for the rapid development of the petroleum industry in Western Siberia.

The petroleum from the Western Siberian oil and gas basin is sent to oil refineries in Omsk and Angara. The gas is shipped to the Urals.