The regularities of changes in the lithological and geochemical composition of Bazhenov Formation (BF) rocks characterized by different degrees of organic matter transformation are determined. From МК1 2–МК2 (140–170 C–170–195 C), the following tendency is revealed: a) increasing of the number of calcareous-dolomitic interlayers and content of the dolomite in them; b) reducing of the content of S in the whole section; c) reducing of the OM and sulfide sulfur contents in "pyrite-kerogen" layers of roof of BF; d) reducing of the ratios of C/S; d) increasing of the "pyrite" layer thickness in the transition zone of BF and the overlying sediments and the content of pyrite in it. It is concluded that in the period between the stages corresponding to the grades МК1–МК2, there is a transformation of OM, migration of its transformation products, dolomitization of rocks, and pyritization of low-carbon rocks of the overlying BF Podachimov strata.
The composition of Bazhenov and Abalak Formation rocks of Western Siberia is presented. Correlations of macro- and micro-components concentration with the base mineral and organic matter content in rocks are showed. Investigations of trace elements allow determining sedimentation conditions: redox conditions, hydrogen sulfide contamination and the source of the sedimentary material. The results showed that the rocks of the Bazhenov Formation were formed at low flows of clastic material under reducing conditions and a periodic hydrogen sulphide mode.
The Bazhenov Formation of Western Siberia is one of the most important and promising high-carbon formations. Its peculiarity is a huge area of distribution and high generation potential of its constituent deposits. Another feature of the formation is the predominance of silicides in its composition, among which the most interesting are radiolarites, which are often associated with hydrocarbon inflows. However, the mechanism of the forecast and the nature of their distribution still do not have an unambiguous solution. Based on a study of the composition and textural features of the structure of radiolarite layers in the clayey-siliceous rocks of the Bazhenov formation, a model of their formation based on the interaction of plankton (radiolarians) and currents is proposed.
The analysis of Bazhenov high-carbon formation organic matter catagenesis zonal distribution in connection with its own reservoir's organic matter porosity made in this work. Realized research helped to articulate regional prospecting criteria for oil deposits in Bazhenov's formation unconventional reservoir with organic porosity.
The most prospective section intervals in the Bazhenov formation (Tutleimskoy) and Abalak formation are composed of interbedded siliceous and carbonate rocks. Based on the core analysis, genetic typing of carbonate rocks was performed to improve the quality of their prediction, the most promising of them for finding of oil-saturated reservoirs are identified.
The Bazhenov high-carbon formation is a part of the Bazhenov formation, characterized by a high content of aquagenic organic matter. Formation is a perspective source for expanding the hydrocarbon resource base. The article presents a combination of the results of core studies, interpretation of well logging and seismic data. A multi-faceted approach to the study of rocks made it possible to divide the West Siberian basin into 13 structur- al-facies zones, each of which has its own structural features of the bazhenov high-carbon formation section. This typification of the section will make it possible in the future to simplify the modeling of the properties of bazhenov high-carbon formation and predicting the most prospective areas.
As part of this work, various sedimentation environments were identified in the Middle-Late Jurassic (J2k–J3v1) on the territory of the Krasnoleninsky arch in Western Siberia. The heterogeneity of the seabed topography and the presence of islands formed by protrusions of the pre-Jurassic basement led to the formation of the Vogulka strata as a result of the removal of clastic material from the land. At the same time, far from the islands, in relatively calm shallow environments, clayey and glauconite-clayey sediments of the Abalak Formation accumulated. Gravelites and sandstones of the Vogulka strata were formed unevenly. The greatest thickness of these deposits is observed to the west of the central upland. The difference in the thickness of clastic strata on the western and eastern slopes could probably be caused by the specific horseshoe shape of the island and the absence of active currents on the western part of the slope, as well as its greater steepness. The upper member of the Vogulka strata, composed of detrital limestones, is extremely thin (no more than 1 m), and contains numerous unconformities. Probably, these traces of erosion can be indirect evidence of the influence of the Late Oxford regression on the structure of the section, which was previously noted in adjacent territories.
Fluid inclusions in quartz crystals from the Abalak formation carbonate rocks of 5 wells on the Em-Egovskaya summit of the Krasnoleninsky arch (Western Siberia) were investigated. Two-phase fluid inclusions with water-salt solutions, inclusions containing organic liquid, and single-phase gas fluid inclusions were found. For fluid inclusions with two-phases, the values of the homogenization temperature were obtained. For single-phase inclusions, the temperature of the second phase forming was revealed. It was established that two types of primary inclusions are present in one well, with oil and with water-salt solution. The homogenization temperature of the primary fluid inclusion containing a water-salt solution is 267°C, the homogenization of the oil-containing inclusion exceeds 300°C. In primary-secondary inclusions, the homogenization temperature reached 136 °C. Studies of the composition of inclusions by infrared spectrometry have shown that in single-phase inclusions, the gas is represented by methane. In primary-secondary inclusions, the composition may vary, while in the gas phase, the predominant components may be hydrocarbons with two or more carbon atoms. Studies of organic matter from the deposits of the Tutleim source-rock formation overlying the Abalak formation have shown that the stage of catagenetic transformation of kerogen in the studied wells changes. It was found that in wells in which organic matter is most transformed, the homogenization temperature of fluid inclusions exceeds 130°C. Thus, it is proved that on the territory of the Em-Egovskaya summit of the Krasnoleninsky arch, Jurassic deposits were effected by heat flows created by high-temperature fluids. Not only rocks of the Abalak formation were exposed by thermal processes, but also organic matter from the Tutleim formation was changed, as a result its maturity increased and the generation of hydrocarbon compounds was stimulated. The results obtained explain the difference in the catagenetic transformation of the organic matter of the Tutleim formation in this area. The study of the molecular composition of inclusions will allow us to more accurately reconstruct the conditions of hydrothermal processes. The study of fluid inclusions makes it possible to develop new criteria for the search for oil and gas deposits.
