M.N. Babasheva, V.N. Babasheva, V.F. Pankratov, F.M. Kuanyshev, A.P. Pronin
Prospecting for unconventional subsalt hydrocarbon fields in Caspian Depression
Key words: basin; pressure; concentration; field; oil; gas; reservoir; type; porosity; permeability; effective capacity; catagenesis; destruction; parameter; facies; sandstone; siltstone; flow rate; plankton; jointing.
For citation: Babasheva M.N., Babasheva V.N., Pankratov V.F., Kuanyshev F.M., Pronin A.P. Prospecting for unconventional subsalt hydrocarbon fields in Caspian Depression. Geologiya nefti i gaza. 2023;(1):67–74. DOI: 10.31087/0016-7894-2021-1-67-74. In Russ.
Topicality of the work responds to assessment of the reasons for low prospecting efficiency in the Caspian zone of depression using the conventional methodologies for determination of prospecting objects. Traditional reservoir rocks of deepwater genesis (sandstone, siltstone, carbonate reservoirs) are thin and have low to very low porosity and permeability. The discovery of a highly productive oil pool in the mainly argillaceous Akzhar Vostochny area is a key factor in understanding the petroleum potential of the subsalt deposits in the depression. Deciding on the reservoir model and mechanism of commercial reservoir rock formation in argillaceous deposits allows not only uncovering the cause of effective capacity formation in argillaceous rocks, but also determining the discriminating factors for identification of the areas, where probability of high-capacity oil-saturated reservoirs are highly probable. The extremely high content of the Organic Matter (Tasmanites plankton) in the highly productive argillaceous sequence is a distinctive feature of the Akzhar Vostochny field. Effective capacity formation in argillaceous rocks synchronically with oil pool is associated with catagenesis of plankton having chemical composition perfect for hydrocarbon formation. Identification of areas favourable for reservoir rock formation is identification of the area favourable for prospecting. Discriminating factors are the conditions having a fundamental influence on producing capacity of saltwater plankton, and thermal conditions of subsoil (relatively high areas of deepwater basin’s bottom and thermal conditions of subsoil). Undulation of the basin floor topography is estimated from the distribution of thicknesses of rock sequence between seismic subsalt reflectors. The evolution of the thermal regime of the subsalt sediments, which is largely a function of rock density, reflects an integrated indicator: the seismic wave propagation velocity. Seismic data-based model of promising area identification allows efficient prospecting of unconventional subsalt oil pools in the Caspian deepwater zones.