Volga-Ural petroliferous province
VOLGA-URAL PETROLIFEROUS PROVINCE (RU: Волго-Уральская нефтегазоносная провинция) is situated within the limits of the Perm, Sverdlovsk, Kirov, Ulyanovsk, Kuibyshev, Orenburg, Saratov, Volgograd provinces of the Russian Federation, and within the Tatar ASSR, Bashkir ASSR, and Udmurt ASSR (see the Map). The area is 700 thousand square kilometres.
The first petroleum field has been discovered during the 1929 near the Verhnechusovskie towns, later during the 1932, there has been discovered the Ishimbaevskoe petroleum field, which is confined to the reefs of the Lower Permian, and the Devonian petroleum has been identified during the 1944. By the 1982, there have been discovered approximately 920 petroleum fields. The most known petroliferous fields are: Romashkinskoe, Novoelhovskoe, Arlanskoe, Shkapovskoe, Tuymazinskoe, Yarin-Kamennolozhskoe, Bavlinskoe, Muhanovskoe, Pokrovskoe, Kuleshovskoe, Sokolovogorskoe, Bobrovskoe, Osinovskoe, Chutyrsko-Kiengopskoe (the petroleum fields); Orenburgskoe, Korobkovskoe, Stepnovskoe (the gas fields, and gas condensate fields). Geographically, the province is situated within the eastern part of the Eastern European plain. The major water arteries are the Volga, Kama, Belaya, Ural, and Chusovaya rivers. The northern part of the Volga-Ural petroliferous province is situated within the forest zone and forest-tundra, while the southern part is situated within the forest-steppe and steppe zones. The major routes of communication are the well developed network of the automotive roads and railways. The transport of the petroleum and gas is performed through the local and trunk petroleum and gas pipelines. The processing of the petroleum, which is extracted, is performed mainly within the limits of the province, except the petroleum, which is transported into the countries, which are the members of the Council for the mutual economic assistance. The major centres of the extraction are the Almetyevsk, Osa, Neftekamsk, Tuymazy, Octyabrskiy, Igra, Otradnyi, Buguruslan, Buzuluk, Zhigulyovsk, and other cities.
The Volga-Ural petroliferous province is confined to the eastern part of the Eastern European craton, and to the Ural foredeep; this province is bounded at the north and east by the Timan ridge, and Ural mountains, borders the Caspian syneclise to the south, the Voronezh vault and Tokmovsko-Syselskay system of the vaults to the west. The basement of the craton is pre-Cambrian, heterogeneous. The thickness of the cratonic Riphean-Vendian and Paleozoic cover (with the non-significant development of the rocks of the Mesozoic) within the eastern part of this craton is 9-12 kilometres. The cross-section of the sedimentary cover is represented by the continental, coastal-marine, and marine (terrigenous and carbonate) formations, namely, of the Riphean-Vendian, Devonian, Carboniferous, and Permian complexes of the rocks. There has been identified the series of the large vaults (Tatar, Perm-Bashkir, Zhigulyovsk-Orenburg, and others), depressions, embankments and troughs, which are complicated by more than 2 thousand local uplifts, which are characterized by the sizes from 1x2 to 10x50 kilometres, and by the amplitudes from 10 to 100 metres and more. There are industrial the petroliferous depositions of the Devonian, Carboniferous, and Permian, and the petroleum manifestations have been noted within the rocks of the Riphean-Vendian age. The productive horizons have been identified at the depth from 0.5 to 5 kilometres and more. The reservoirs are mostly tabular vaulted, tabular vaulted lithologically shielded, massive, and in the small quantity tectonically shielded. The yields of the boreholes under the conditions of the normal hydrostatic pressures are medium (up to 100-200 tonnes per second) and small. The development of the reservoirs is performed, as a rule, with the maintainance of the layer pressure.
The petroleums are mainly of the paraffinic type, with the medium and high density (820-890 kilograms per cubic metre), with the high sulfur content (0.5-3.0%), and with the high tar content. The free gases within the Lower Permian depositions are of the methane type, with the high sulfur content (5.5%), and with the low nitrogen content. The gas caps and dissolved gases within the petroleums of the Carboniferous depositions of the northern regions contain up to 98% of the nitrogen gas. As a whole throughout the province, from the north to the south, and from the west to the east, there are observed the gradual decreasing of the density of the petroleums, decreasing of the sulfur content within these petroleums, and increasing of the content of the dissolved gas there, transition to the paraffinic-naphthenic type.
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