Oil and Gas Potential of the Pre-Caspian Depression

The Pre-Caspian depression is one of the largest basin of the Soviet Union measured by sedimentary volume. The area of basin is more than 500,000 km{sup 2}, and the thickness of sedimentary mantle is 20 km in the central part of depression (Central-Pre-Caspian graben). About one-tenth of the initially recoverable hydrocarbons in the Soviet Union hook up with this basin. The sequence of sedimentary mantle of the depression is divided by salt massives of Kungarian age on subsalt (Riphean-Aptian) and supersalt (Upper Permian-Quaternary) structural-formational complexes. The first complex contain a large part (96%) of the initial recoverable hydrocarbons of the region; the remaining resources are in the supersalt complex. Deposits from Middle Devonian to Aptian age are productive in the subsalt complex. More than 30 fields of hydrocarbons (including giant fields: Astrakhan gas-condensate, Tengiz oil and gas-condensate, and Karachaganak oil and gas condensate) have been discovered in these deposits. Most commercial oil and gas reserved have been found in the carbonate reservoirs, but development of capacious terrigenous reservoirs have been predicted for the subsalt complex. Terrigenous reservoirs have received exceptional development in the supersalt complex, but large oil and gas accumulation areas are absent there. Discovered commercial oil fields (aboutmore » 50) have, usually, small reservoirs in this complex. On the whole, the Pre-Caspian depression is characterized by poorly known oil and gas potential. This permits the authors to predict discoveries of new, hydrocarbon accumulations.« less