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The paper deals with the South Kara regional depression covering the southern part of the Kara Sea. A comparative analysis of the geologic structure of major petroleum-promising sedimentary complexes in the water area and on the land is carried out. Regional tectonic processes are considered, and the main stages of the formation of large tectonic elements are reconstructed. A brief comparative analysis of the anticline traps on the land of the study area and in the Kara Sea is made.

We have analyzed the predictions of the petroleum potential of West Siberia made by Academician I.M. Gubkin in his public reports and scientific works. We outline the strategy of oil exploration in the area east of the Urals, set up in the early postwar period, and the current state of research into the petroleum potential of the province. Special attention is focused on Jurassic deposits, which were regarded by I.M. Gubkin as oil-promising. At present, the largest volumes of predicted oil and gas resources of the province are concentrated in Jurassic and Neocomian plays.

Results of regional seismic exploration and drilling testify to the occurrence of moderately dislocated thick Upper Proterozoic and Lower Paleozoic deposits of subplatform type west of the Yenisei River. The deposits are buried beneath the Meso-Cenozoic sedimentary cover in the east of the West Siberian geosyneclise and form the Cis-Yenisei sedimentary basin. A comprehensive analysis of the new geological and geophysical data has refined the seismogeological model of sedimentary complexes, including 2D sections, structural and geological maps, and tectonic scheme. The Neoproterozoic and Paleozoic geodynamic evolution of the western margin of the Siberian craton is discussed.

The paper presents new paleotectonic data on the Bovanenkovo, Taz, and Gubkin arch uplifts and the Novyi Port, Urengoi, Kharampur, and Medvezh’e swells, with implications for the history of zone J2 and the Jurassic reservoir as a whole. Most of the large uplifts originated in the Early-Middle Jurassic and completed their evolution in the early Late Cretaceous (latest Cenomanian), generally (Bovanenkovo, Novyi Port, Kharamp, and Taz) or to a large extent (Urengoi and Gubkin), except for the much younger Medvezh’e swell, which formed in the Paleogene-Quaternary interval. The conditions for oil storage and retention in anticlinal traps of Jurassic zones J1 and J2 were the most favorable between the middle Late Cretaceous and the Eocene, inclusive. Gas accumulation lasted for a much longer time, from the Late Jurassic to the Present, and was especially rapid in the Late Cretaceous-Paleogene.

It is proposed to separate a regionally persistent member of fine-dispersed mudstones as the individual Kogalym Member within the Lower Vasyugan Subhorizon (Uppermost Bathonian-Lowermost Oxfordian). We present data on the lithologic composition, geophysical characteristics, and geochemical properties of the organic matter and depositional environments of the member. The Tyumenskaya SDB-6 well is proposed as a type section of the Kogalym Member, where a biostratigraphic approach has yielded the Middle-Upper Callovian volume of the member. We also discuss the aspects of specification and detalization of the Callovain-Oxfordian part of the Callovian and Upper Jurassic regional scheme of West Siberia.

The paper presents approaches to characterization of shale source rocks using geochemical data for the case of the Bazhenov petroleum system in West Siberia. Regional patterns of oil distribution in the Bazhenov shale are shown to depend on their original total organic carbon (TOC) content and thermal maturity. The existing thermal maturity model for the Bazhenov Formation based on vitrinite reflectance ( R ^o_Vt) of nearby beds has been updated using parameters measured by Rock-Eval pyrolysis ( T max, HI, PC, and RC) for the shale itself. The results were used to quantify hydrocarbon resources in different maturity zones. The relationship between total organic carbon and presence of expelled oil found for logged zones in the Bazhenov section allows allocation and quantifying oil resources in unlogged beds.

The petroleum potential of the Bazhenov Formation reservoir has been assessed on the regional scale using several criteria inferred from published evidence, available geological and geophysical data, and well logging results from Upper Jurassic reservoirs.

Based on results of comprehensive lithological and geochemical analysis, we have established the regularities of the spatial distribution of major rock-forming components of the Bazhenov Formation in the West Siberian Basin (WSB), namely, siliceous, argillaceous, and carbonate material. According to the SiO2/Al2O3 ratio, the most siliceous rocks of the Bazhenov Formation are biomorphic siliceous mudstones (radiolarites) (>20), cryptocrystalline siliceous mudstones (8-20), and the most argillaceous rocks are argillaceous mudstones (<3). Intermediate SiO2/Al2O3 values (3-8) are observed in mudstones of different types. North-south distribution profiles of the SiO2/Al2O3 ratio and CaO content in different areas of the WSB were constructed. The areas of occurrence of radiolarites (potential reservoirs) and a “coccolith” member with the highest content of organic matter have been clarified. The thickest radiolarite bed (3-4 m) has been found in the Salym area. In some sections of the North Surgut area, a “coccolith” member is 2 m thick and is carbonatized. In most of the sections of the North Surgut, South Tomsk, and West Tomsk regions, rocks of this type are observed as 1 cm thick intercalates, and in the Novosibirsk region they are virtually lacking. We have established that a “coccolith” member, localized mostly in the upper part of the Bazhenov Formation, occurs not only in the Salym and Krasnoleninsk regions but also in the North Surgut region. It was also found in the Northern region in the southern and central parts of the South Nadym megamonoclise. Coccolithophorid relics are occasional in the South and West Tomsk regions and are lacking in the Novosibirsk region and in the Northern region of the South Nadym megamonoclise.

The composition of saturated and aromatic hydrocarbons and the structural-group characteristics of resins and asphaltenes of four oils of northern West Siberia have been studied. As follows from the distribution of hydrocarbons, the Cenomanian oils (pools in the beds PK and K2c) of the Russkoe, Barsukovskoe, and Pangodinskoe fields are naphthenic and the Pangodinskoe oil sample from the Lower Cretaceous pool (bed BN9) is paraffinic. The hydrocarbon composition pattern of the saturated fraction and the characteristics of the heterocyclic components of these oils point to their formation from dispersed organic matter of mixed genesis in the oil window. Hence, the oil source rocks are localized at depths much greater than the present-day level of the oil pools. Secondary (cryptohypergene) alterations (oxidation and biodegradation) in the shallow-depth oils determined their current predominantly naphthenic composition and considerably hamper the reconstruction of the types of dispersed organic matter. We assume that the mixed genetic type of the studied oils is not only due to their heterogeneous source but also due to the reorganization of primary oil pools at the Cenozoic stage of tectogenesis. The Cenomanian Russkoe and Pangodinskoe naphthenic oils are saturated with adamantoids, which can selectively accumulate during biodegradation.

Results of comprehensive geochemical studies of dispersed organic matter of the Bazhenov Formation are presented. The maximum contents of total organic carbon are found in the areas of the Surgut arch and South Nadym megamonoclise. The contents of organic matter are high (up to 24%) at the top of the formation section and gradually decrease to its bottom. By pyrolysis parameters and the composition of hydrocarbon biomarkers, the organic matter is referred to as type II kerogen (sapropelic organic matter) and is localized in the oil window.