The paper deals with the subsalt megacomplex in the Kazakhstan sector of the Caspian depression and with the scheme of oil and gas field geological zoning. Due to the insufficient study of the region, its interior zoning used to vary substantially over the history of making quantitative estimates. Therefore, practically any subsequent quantitative re-estimation of the resources resulted in ‘vanishing’ of some earlier discovered and ‘emerging’ of some new oil and gas-bearing regions and even oil- and gas-bearing areas. To optimize quantitative estimations of oil and gas forecasted resources, the proposed zoning variant is based on the methodic approaches of basin modeling and consists in estimating the provision degree of the processes of oil and gas pool formation with migrated, preserved hydrocarbons. Identification of the oil and gas gathering areas (OGGA) – drainage zones – is grounded on the recent structural plan of the bottom of the Kungurian regional salt-bearing cap rock. To make semiquantitative comparative estimates of the HC potential resources that provide for the migration and accumulation processes in every OGGA, the factor of the migration flow specific density is used; this is represented by the ratio of the total amount of preserved migrated HC to the length of the ‘migration finite barrier’ closing the OGGA in question.
Two oil-and-gas-bearing areas have been recognized: the North Caspian (Volgograd-Orenburg) and the South Caspian (Astrakhan-Aktyubinsk) ones, with dominantly oil-and-gas-bearing regions within them.
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