Autoclave Type of the Hydrocarbon Systems in the Pricaspian Oil-and-Gas Province (Russia): Conditions of Formation at Great Depth

— On the basis of modern ideas about the structural organization of the geological shell of the Earth, the authors substantiate the geofluid dynamics patterns of the localization of hydrocarbon systems (and their elements) at great depths. According to the authors, under conditions of high compressive loads exerted by overlying deposits, reliable all-round lithological shielding of reservoirs, hydrodynamic stagnation in deep-seated complexes of evaporite basins, a special type of hydrocarbon system, that is, autoclaved, can be developed. The authors predict that in the Pricaspian oil-and-gas province in the subsalt oil and gas bearing stage (in the Lower Devonian–Lower Permian deposits), an autoclave hydrocarbon system could have formed due to the sealing of a salt-bearing complex of significant thickness (i), the unrealized generation potential of oil and gas source strata represented by deep-water deposits 4–6 km and deeper (ii), and hydrodynamic stagnation of the water drive system (iii). Under the control of these conditions, paleo-drive objects and intra-basin carbonate structures near contact with oil and gas source rocks act as high-capacity reservoirs for the products of catagenic fluid generation and the segregation of a single-phase fluid with phase separation of hydrocarbons during periods of a sharp decrease in reservoir pressure completes the formation of unique and large hydrocarbon fields.