Current problems in the North Caspian depression geology and oil and gas prospects

The deep structure and formation of the North Caspian (Precaspian) depression have not been fully understood due to the scarcity of depth studies at 18–22 km. The existing concepts and hypotheses are clearly insufficient to interpret the unexplained facts. New approaches and research efforts are necessary to solve the old problems. The current state of the depression deep structure problems is reviewed, and the existing explanation flaws are demonstrated. The depression consolidated crust has oceanic and riftogenic origin as it has been suggested by the author before. This explanation is supported by the Astrakhan deposit D-2 deep well core data. The Astrakhan-Aktobe zone arched uplift genesis, formation and role in the carbonate platforms emergence are discussed. Deep geothermy and fluid dynamics problems, as well as recent geophysical data are considered in view of the North Caspian depression hydrocarbon prospects.

CHOICE AND GENERALIZATION OF INTERPRETATION METHODS IN RELATION TO THE SOUTH CASPIAN DEPRESSION

Geological structure and bathymetry of the seabed of the deep water part of the Caspian Sea testifies to the formation of significant volumes of gas hydrates. In this regard, it was necessary to study the sedimentary deposits of the Caspian Sea in order to distinguish areas of gas hydrates and evaluate their potential, as well as obtaining new data. A significant volume of data published in scientific journals and reports was analyzed. Much attention was paid to the thermodynamic conditions of gas hydrates formation, as well as the analysis interpretation of geological and geophysical data. Experimental, theoretical and practical data indicates that maximal temperature, at which gas hydrates can be formed on methane is 24 °C. Therefore, an attempt was made to establish the depth at which there is a boundary with temperature in 24 С in the upper part of the section. Gas hydrates zones distinguishing as per data of geophysical methods with determination of BSR boundary or other diagnostic features are considered to be the main diagnostic indicator of gas hydrates. Keywords: gas, seismic investigations, pressure and temperature, BSR

Tectonic Criteria of Oil and GAS Potential at the Transitional Part of the Susha-sea Along the Western Coast of the South Caspian Depression

The southern part of the South Caspian oil and gas Basin (SCB) is one of the main oil and gas producing regions in the central part of Eurasian continent. The large number of offshore oil and gas fields is located here, therefore the basin considered as a promising direction for the further perspective zones survey. The basin is located between the uneven-aged mountain structures of the Lesser and Greater Caucasus in the west, the Great Balkhan and Kopet-Dag in the east, the Talish and Elbrus ridges in the south. In the north, it is limited by a sub-latitudinal regional deep fault, which fixes the northern slope of the complex Absheron-Balkhan zone of uplifts, which is part of the South Kura and Western Turkmenistan depressions. Among the structural elements of the second order, the South Absheron depression, the complex Abikh swell and the Javadkhan-Natevan zone in the west should be noted; Turkmen terrace, Ogurchinskaya step and Chikishlyar-Fersmanovskaya-Weber-Western zone in the east (Fig. 1). The central place in the structure of the basin is occupied by the South Caspian Mega Depression (SCMD), in the most submerged part of which - the pre Elbrus Basin - the basement lies at a depth of about 25 km, and the sedimentary stratum, including Mesozoic, Cenozoic and Quaternary formations, is largely represented by the Pliocene - post-Pliocene sediments, reaching a total thickness of 8–10 km and more in the troughs (Fig. 2, 3).

Structural features of the lower Permian salt-bearing series and the character of salt-tectogenesis manifestations in the Caspian Depression. Paper II

The article presents the analysis of the inner structure of the salt-bearing series within the Caspian Depression. Certain salt-bearing complexes of various ages, compositions and plastic properties are distinguished. Their structural relations and the features of salt-tectogenesis manifestation are evaluated. Up to the present no subsalt uplifts have been confirmed in the Russian sector of the Caspian Depression and no HC fields have been discovered. Therefore, any search for additional criteria for predicting the salt-bed structure from the character of salttectogenesis manifestation is conductive to predicting the zones of subsalt structure development over the Caspian Depression area.

Structural features of the lower permian salt-bearing series and the character of salt-tectogenesis manifestations in the northern and northwestern margins of the Сaspian depression. Paper 1

The detailed evaluation of the accumulated geological-geophysical data, particularly on the inner structure of the saltbearing series in the margins of the Caspian Depression, the mechanism of salt-tectogenesis manifestation, its reflection in the structure of the salt table and association with the structural inhomogeneities of the subsalt bed is presented. The authors attempt to acquire additional indirect criteria for predicting the structure of the subsalt bed by means of analyzing the structure of the salt-bearing series and the character of salt-tectogenesis manifestation. The problem solution is based on the complex analysis of the data from drilling and seismic prospecting.

Winter months’ temperature rises effect on duration of phenological phases for Spermophilus pygmaeus Pallas, 1778 populations located in Caspian depression (Astrakhan oblast)

This article provides comparison analysis between 1950–1959’s and 2000–2009’s periods for duration and schedule dates of awakening, spreading and hibernation phases for Spermophilus pygmaeus populations located in the Caspian Depression (by example of Astrakhan Oblast). We learned that within a period of maximum temperature rise in February 2000–2009’s durations of S.pygmaeus’ populations of every phonological phase have shortened and been rescheduled with earlier dates (in comparison to 1950–1959’s). The study also shows that these changes caused its population reduction on the Caspian Depression’s territory.

Role of abnormally high formation pressures in the distribution of oil-gas bearing content in South Caspian depression

The paper reviews and compares the state of South Caspian depression to the large oil-gas bearing regions of the world genetically not associated but similar to the major geological factors. Geological data on the development and distribution of abnormally high formation pressures (AHFP) and anomaly ratio in the sections of sedimentary strata in various regions of the world has been analyzed. The appearance of abnormally high formation pressure in different geological conditions within South Caspian depression has been reviewed and compared to the corresponding results of similar basins, on the basis of which an adequate model developed as well. In the context of the fields with AHFP within South Caspian basin, it is shown that the significant amount of hydrocarbon reserves may be associated with AHFP zones. The paper presents a brief analysis of views development on the regulations of the distribution of hydrocarbon accumulations in the soil depth. Based on the graphic materials and mathematical statistics, the inequality of distribution of oil reserves on the territory of mentioned basins is justified. Therefore, data analysis on geobaric characteristics of perspective structures, particularly, in deep water zones of SCB, which is top priority for conducting exploration survey may contribute to more reasonable choice.