South-western part of Caspian petroleum province: structural features and aspects of oil and gas accumulation zone occurrence in subsalt and suprasalt sequences

Relying on structural features and aspects of oil and gas occurrence within the Caspian Petroleum Province, the authors substantiate the need for geopetroleum zoning with separate identification of oil and gas accumulation zones in subsalt and suprasalt sequences. Principles of identification, as well as structural features and aspects of subsalt and suprasalt oil and gas accumulation zone petroleum potential are discussed by the example of the south-western part of Caspian Petroleum Province. At the current low exploration maturity of the subsalt sequence, it seems appropriate to identify subsalt oil and gas accumulation zones confined to large first-order structural elements and differing from each other by structural features and settings of hydrocarbon accumulation formation. These include, first of all, positive structural elements (Astrakhansky arch, Karasal’sky monocline, Karakul’sky-Smushkovsky zone of highs) with the development of thick Upper Devonian-Middle Carboniferous sequences typical in the subsalt section, as well as the Sarpinsky trough with Carboniferous-Lower Permian terrigenous and clastic-carbonate fans formed within it. A single approach to identify oil and gas accumulation zones (salt dome, salt ridge) within a salt-dome structure and neighbouring flanks of between-dome basins is proposed for suprasalt sequence. They make the independent petroleum systems within which the processes of generation, migration (including inflow from subsalt deposits), and accumulation of hydrocarbons occur