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Vitaly G. Kuznetsov1
(1) Russian State University of Oil & Gas, Moscow, Russia

Abstract: Reservoir properties and petroliferous of the Upper Devonian - Tournaisian deep marine carbonate sediments, Volga-Urals basin, Russia

Relatively deep marine clayey-carbonate sediments of the Frasnian - Tournaisian (domanicits) are distributed at the East of the East - European craton. The sediments of Domanic horizon (Upper Frasnian) have a thickness of 10 - 40 m and are developed in the limits of the whole Volga-Urals province. The younger sediments of that type including Tournaisian are developed in Kama-Kinel depression. This is a narrow (25 - 100 km) and long (not less than 1400 - 1500 km) and meandering depression. Total thickness of such sediments in depression make 100 - 300 m. Domanicits are one of important source rocks of Volga-Urals basin, but several tens oil pools and several hundreds oil inflow have been obtained. Main rock types are mudstones, rarely wackestones, as a rule clayey, siliceous and bituminous and also lime - and dolomitic argillites. Porosity of those rocks is small - 2 - 5 % usually and very seldom to 10 - 15 %. Sandstone-like dolomites are found relatively rarely. They form pinching beds and lens with thickness up to 2 - 5 m. Dolomites is medium crystalline subhedral. Crystals are adjoined by corners and rarely by sides. It forms open-worked spongy structure with high intercrystal porosity (to 20 - 25%). The size of those pores is 0.1 to 0.2 mm and interporosity channels from 0.04 to 0.08 mm. It is supposed that dolomitization is early diagenetic and stipulated by alkali and pH increase as a result of decay of organic matter. Tectonic jointing is of great importance for filtration. The character of distribution of rocks with intercrystal porosity and high jointing cause lithological sealing limiting the pools, which do not clear structure control and are disposed on the slopes of anticlinal folds and its periclinal ends.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana