Geology, geography and global energy

Scientific and Technical Journal

Carbonate collectors of the Caspian hollow

2018. №4, pp. 118-125

Fedorova N.F. - C.Sc. in Geology and Mineralogy, Associate Professor, Astrakhan State University, 1 Shaumyan sq., Astrakhan, 414000, Russian Federation,

Bystrova I.V. - C.Sc. in Geology and Mineralogy, Associate Professor, Astrakhan State University, 1 Shaumyan sq., Astrakhan, 414000, Russian Federation,

Zaskokina A.V. - Master, Astrakhan State University, 1 Shaumyan sq., Astrakhan, 414000, Russian Federation,

The article presents the comparative characteristics of subsalt oil and gas fields of the Caspian Basin. To further explore the prospects for oil and gas presence in the depression, it is advisable to show the role of cracks in carbonate reservoirs. K.A. Kleshchev and other scientists proposed an unconventional geological concept based on the idea that the accumulation of thick sedimentary strata in the Caspian depression is connected not with a cup-shaped region of long subsidence of the earth's crust, but with the formation of heterogeneous tectonic structures such as passive continental margins, rifts, plate collision orogens. The development of block tectonics in the basement with the formation of fracture and other large subsalt structures led to the presence of rift zones (avlocogens) and multi-oriented faults in the depression. All these processes contributed to the appearance of faults, the formation of thrusts, drastic changes in thickness and the stratigraphic completeness of the cuts. Fissure systems divide rocks into equally-sized, equally-sized blocks. The discovery of oil and gas deposits in clayey, dense carbonate and crystalline rocks changed the idea of the reservoir role of fracturing. Their role is recognized as decisive in fluid filtration. In the Late Paleozoic, within the Caspian Basin there was a favorable environment for the accumulation of carbonate strata and the formation of a carbonate platform. Intense carbonate accumulation occurred in a wide time range - from late Devonian to early Permian. The onboard zones of the Caspian Basin in modern times are characterized by a fairly wide development of Late Paleozoic carbonate complexes, which form isolated zones, called "intrabasin carbonate platforms". Tengiz, Karachaganak, Astrakhan and other deposits are discovered in the onboard parts of the depression. Collectors at the Tengiz field are carbonate coal deposits, which are represented by voids with primary and secondary pores, cavities and fractures. The carbonate sections of the Astrakhan field are extremely variegated. There are strata with increased porosity and permeability, but they form separate insulated lenses. At the Karachaganak field, the productive stratum is represented by carbonate rocks of the Upper Devonian-Lower Permian age. The section is composed of limestones, dolomites and their transitional differences. The formation of a carbonate stratum is associated with two large organogenic structures.

Key words: впадина, месторождение, нефть, газ, коллектор, трещиноватость, поры, depression, field, oil, gas, reservoir, fracturing, pores