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.

Mansiya N. Babasheva
Candidate of Technical Sciences,
Deputy Director
Timal Consulting Group LLP,
Building 33, Nursaya, Yelorda Avenue, Atyrau,
063709, Kazakhstan
e-mail: Babasheva.M@timal.kz

​Viktor N. Babashev
Candidate of Technical Sciences,
Director
Timal Consulting Group LLP,
7, building 5A, prospect Al-Farabi, Almaty,
050059, Kazakhstan
e-mail: Victor@timal.kz

Vladimir F. Pankratov
Project head manager
Geophysical Support Services LLP,
15V, ul. Kanysh Satpaeva, Almaty,
E02M0M9, Kazakhstan
e-mail: vlad1950@yandex.ru

Farukhat M. Kuanyshev
Candidate of Geological and Mineralogical Sciences
KazKorReserch LLP,
32 Severnaya Promzona, Atyrau, 060026, Kazakhstan
e-mail: f.kuanyshev@zhahancompany.kz

Alexey P. Pronin ORCiD
Manager
KazKorReserch LLP,
32 Severnaya Promzona, Atyrau, 060026, Kazakhstan
e-mail: kcr@zhahancompany.kz

1. Yatskevich S.V. Litologo-petrograficheskaya kharakteristika porod produktivnoi tolshchi Vostochno-Akzharskoi ploshchadi i usloviya osadkonakopleniya [Lithological and petrographic characteristics of reservoir rocks in Akzhar Vostochny field and depositional environment]. Nedra Povolzh’ya i Prikaspiya. 1993;(5):35–41. In Russ.
2. Dal’yan I.B. Sedimentatsionnye podsolevye kompleksy vostochnoi okrainy Prikaspiiskoi vpadiny v svyazi s neftegazonosnost’yu [Eastern margin of Caspian Depression: subsalt depositional sequences in the context of oil and gas occurrence]. Neft’ i gaz Kazakhstana 1998;(4):3–17.
3. Dal’yan I.B., Golovko A.Yu. The oil-bearing chert-argillo-carbonaceous formation of Eastern Kaspian area. Ural’skii geologicheskii zhurnal. 2003;31(1):17–23. In Russ.
4. Sherman G.Kh., Slukin A.V., Nikishov V.V. «Akzharity» — novyi tip kollektorov, obrazuyushchikh neftegazovye rezervuary Prikaspiya? [Akzharite is the new reservoir type that form Caspian petroleum accumulations?]. Nedra Povolzh’ya i Prikaspiya. 1993(5):27–35. In Russ.
5. Oreshkin I.V., Zholtaev G.Zh., Kulumbetova G.E., Oreshkin A.I. Characteristics of carbonate and terrigenous subsalt formations of the Caspian Depression and formation of hydrocarbon traps within them. Geologiya nefti i gaza. 2019;(4):5–16. DOI: 10.31087/0016-7894-2019-4-5-16.
6. Savvin V.A. Modeli stroeniya tipichnykh produktivnykh rezervuarov podsolevykh mestorozhdenii Prikaspiya [Structural models of typical productive reservoirs in Caspian subsalt fields]. Nedra Povolzh’ya i Prikaspiya. 1999(17):3–11. In Russ.
7. Azhgaliev D.K. Carbonate thickness in the paleozoic complex on the eastern board of the Caspian basin. News of the national academy of sciences of the Republic of Kazakhstan series of geology and technical sciences. 2017;5(425):69–78. In Russ.
8. Iskaziev K.O., Savinova L.A., Almazov D.O., Lyapunov Yu.V. Prospects of oil and gas potential of deep-water Lower Permian deposits within the eastern part of the Pre-Caspian basin. Neftyanoe khozyaistvo. 2021(5):22–25. DOI: 10.24887/0028-2448-2021-5-22-25. In Russ.
9. Taskinbaev K.M., Nursultanova S.N., Azhgaliev D.K., Voronov V.G., Obryadchikov O.S., Nysanova A.S. Neantklinal’nye lovushki nefti i gaza v Respublike Kazakhstan [Non-anticline oil and gas traps in Republic of Kazakhstan]. Almaty; 2020. 271 p. In Russ.
10. Taskinbayev K.M., Pankratov V.F., Obryadchikov O.S., Nyssanova A.S. Uncommon oil field Akzhar Vostochny: another version of the structure and oil and gaz content. News of the Academy of Sciences of the Republic of Kazakhstan Series of geology and Technical Sciences. 2021;448(4):83–90. DOI: 10.32014/2021.2518-170X.85.
11. Zdobnova E.N. Alga Tasmanites Newton, 1875 in Lower Permian Sediments within the Western Part of the Pre Caspian Depression and their Role in Stratigraphy and Geology Oil and Gas. Izvestiya Saratovskogo universiteta. Novaya seriya. Seriya Nauki o Zemle. 2011;11(2):57–63. In Russ.