Carbonate reservoirs of subsalt deposits of the Caspian syneclise

The Caspian syneclise is one of the most promising hydrocarbon regions in Russia and Kazakhstan, which is confirmed by the discovery in recent years of large oil and gas fields within its borders. The presence in the Caspian syneclise at several stratigraphic levels of clay-carbonate deposits enriched with dispersed organic matter, a sufficiently high degree of their catagenetic transformation, the passage of the so-called «oil window» – all indicates a favorable situation for the generation of hydrocarbons in the region under consideration. The spread of possible accumulations of oil and gas in the subsalt sediments of the syneclise is mainly controlled by the quality of the reservoirs and impermeable layers. The proposed article illustrates the authors’ attempt to create a generalized model for the formation of subsalt strata and to develop a scheme for the interrelationship between the processes of accumulation of carbonate sediments and their hydrocarbon productivity. The application of the obtained results to the practice of oil and gas prospecting can be of great importance, since the evaluation of the hydrocarbon productivity of the subsoil is impossible without the prediction of the spatial distribution of differentfacial deposits playing the role of accumulating and preserving strata. The revealed regularities of the space-time relationships of the formation of the main elements of natural reservoirs responsible for the oil and gas content in the subsalt sediments can serve to some extent as a base for the growth of hydrocarbon reserves, which is so necessary for the Caspian region

Sedimentation-capacity model of the subsalt deposits of the Southern Urals and adjoining territories

The junction zone of the Caspian syneclise, the Russian Plate and the Pre-Ural trough is characterized by a complex structure. It has been studied in some detail during large-scale geological, geophysical, and drilling operations in the search for mineral deposits. Subsalt deposits are associated with the main prospects for the growth of hydrocarbon reserves in this region. This makes it important to rethink the available data and conduct scientific analysis to identify patterns of formation of sedimentary complexes and an integrated assessment of their possible hydrocarbon productivity by means of sedimentation modeling. The structure and history of the formation of five large sedimentary complexes: the Ordovician-Lower Devonian, the Central Middle Devonian, the Frasnian-Tournaisian, the Visean-Upper Carboniferous, and the Permian are considered in detail. For each complex, a structural-formational position and sedimentation conditions are determined, which should determine the hydrocarbon productivity of local objects. The revealed relationship between the conditions of carbonate sediments accumulation and their potential reservoir properties served as the basis for forecasting the productivity of regional natural reservoirs. The paper presents a generalized model of the formation of subsalt strata and the forecast of the spatial distribution of different facies deposits, which play the role of accumulating and preserving strata. The results obtained are applicable in the practice of oil and gas exploration in the regio