Northern Caspian Oil and Gas Region

(also Caspian Oil and Gas Region), a region situated primarily in the western part of the Kazakh SSR and partly in the Astrakhan, Gur’ev, Volgograd, Saratov, and Orenburg oblasts of the RSFSR. The total area is approximately 640,000 sq km. The largest deposits, in terms of petroleum reserves, are those of Prorva, Martyshi, Aktiube, and Kenkiiak.

The presence of commercial reserves was established with the discovery of the Dossor (1911), Makat (1915), Koschagyl (1930), Baichunas (1931), and other deposits. During the Great Patriotic War (1941–45), the region became an important supplier of petroleum. By 1975, more than 50 oil deposits had been discovered, of which 32 were being exploited as of 1974.

A considerable part of the Northern Caspian Oil and Gas Region is confined to the Caspian syneclise of the Eastern European Platform. It is bounded in the south by buried Hercy-nian folded structures and in the east by mountain structures of the Southern Urals and Mugodzhars. The three major structural complexes into which the platform mantle of the Caspian syneclise is divided are the subsaline, saline, and suprasaline, the total thickness of which exceeds 20 km.

The subsaline complex (Upper Proterozoic-Paleozoic) comprises terrigenous (in the east and south) and carbonaceous rocks, which form a gently sloping depression complicated by steplike ruptures (flexures, troughs). A series of large arched uplifts is located in the eastern and southern parts of the complex.

The saline complex is composed of rock salt, mainly of Kun-gurian (Permian) age. The rock salt forms numerous (more than 1,000) salt domes, arches, and ridges, which occupy approximately 30 percent of the entire depression.

The suprasaline complex comprises terrigenous carbonaceous rocks of the late Permian period and of the Mesozoic and Cenozoic eras. Thicknesses range from several hundred meters to 1,500 m in the arches of salt domes to several thousand meters in areas between domes. The complex forms arches and archlike uplifts, the structural plan being inherited from the subsaline complex.

The commercial reserves of oil and gas in the region are associated with the subsaline and suprasaline complexes.

A large number of the region’s petroleum deposits, which are located in the southeast, in the area between the Emba and Ural rivers, and in the eastern part of the region, are linked to the Ural-Emba Oil and Gas Region. Petroleum deposits are found at depths ranging from 300 m to 4,200 m, with most deposits at 1,500 m.

The petroleum varies in composition (0.02 to 2.76 percent sulfur) and properties (densities from 0.782 to 0.962 g/cm³). In particular, it contains high-grade oils (Martyshi, Kenkiiak, Baichunas, Sagiz) and considerable amounts of gasoline (Kulsary, Iskine, Martyshi Severnye).

The Paleozoic subsaline complex, which occurs at depths of 5,000–6,000 m, and the suprasaline complex hold the greatest promise for the region’s future development.