Introduction. The subject of the study of this work is the deposits of the anomalous section of the Bazhenov formation (ASB) of Western Siberia, the disturbed occurrence of which was recorded by 2D, 3D seismic exploration and borehole data at many fields of the Frolov oil and gas region. The research area unites the company’s assets in the KhMAO and the Tyumen region, which are part of the large hydrocarbon cluster “ZIMA”. Aim. In order to typify various complexes of rocks of the Bazhenov formation and further localization of deposits, a comprehensive core analysis, GIS and seismic studies were performed. Materials and methods. According to the results of lithological study of the core and petrophysical interpretation of logging diagrams, have been identified various types of rocks in the interval of the Bazhenov formation. According to the results of the interpretation of the seismic survey materials, contoured zones that differ in the wave pattern by different coherence of the axes of common phase. The revealed differences in seismic sections compared with borehole data and geological bodies mapped based on the obtained patterns. Results. Based on a comprehensive interpretation of the core, GIS and seismic studies, established the zonality of the distribution of various types of deposits of the Bazhenov formation, the relationship of the development of ASB zones with the introduction of Early Cretaceous sedimentary bodies and showed the introduction of detrital material from the overlying rocks. Conclusions. The authors of the article conclude that the development of anomalous sections of the Bazhenov formation involves several stages of the introduction of landslide bodies of overlying rocks, according to the gradation of Neocomian clinocyclites in the north-west direction. Within the study area, mapped three large landslide bodies in the Bazhenov formation interval, each of which was formed an internal zonality and because of the introduction of rocks from the overlying interval.

Background. In the process of studying productive Domanik deposits of the Frasnian-Famennian, numerous uncertainties arise in identifying their effective thickness. Although several approaches have been recently proposed for identifying promising intervals in Domanik sediments, e.g. determination of the effective thickness using gas logging during geological and technical studies, the use of the interpretation method presented in the article and other methods continue to develop. Therefore, studies aimed at increasing their efficiency remain to be relevant.Aim. To develop basic methodological approaches to interpretation of well logging data with the purpose of identifying promising Domanik deposits rich in mobile hydrocarbons.Materials and methods. Geological and geophysical data obtained when investigating the wells of the according to published data of geological and geophysical resources of drilled wells in the Buzuluk depression were used to build the main well logging dependencies. In addition, the materials of core and geophysical studies of wells in the Volga-Ural oil and gas basin conducted by Gazprom Neft (PJSC) were used. Extended well logging data were collected for the wells under consideration. A number of tests and core studies, including geochemical experiments, which were carried out in deposits of Fran age, the density of resources of 5—10 samples per 1 meter of core.Results. For the first time, basic methodological approaches for identifying effective oil-saturated strata in Domanik sediments according to well logging data were developed. The developed approaches are based on the integration of geological-geophysical and geochemical data characterizing the material and mineralogical composition of rocks, the content of organic matter, the group composition of hydrocarbons and the genesis of reservoirs. In the section under study, rocks saturated with hydrocarbons were identified. The hydrocarbons were different in terms of group composition, which determined their mobility. Boundary values were obtained when interpreting data obtained by well logging methods for Domanik rocks containing mobile and stationary hydrocarbons. The proposed methodological approaches were tested on other wells in the Domanik deposits in the Orenburg region. As a result of repeated practical application and testing of the developed methodology, its effectiveness was confirmed.Conclusions. The proposed basic methodological approaches for interpretation of well logging data when identifying effective oil-saturated strata were substantiated by the geological-geophysical and geochemical properties of Domanik deposits.

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Properties of unconventional prospective deposits are interconnected by the rocesses of reservoir formation and oil and gas formation. Dispersed dolomite in situ formed during the maturation of TOC from syngenetic magnesium in the rock matrix increases the void space of the rock, thereby forming an unconventional reservoir filled with autochthonous hydrocarbons and oil components. In the process of TOC maturation and hydrocarbon migration, the TOC components are redistributed in the void space, thereby, the released volume of rocks is filled with stationary resinous asphaltene substances, which sharply reduces the reservoir properties of unconventional reservoirs. As a result, the definition of “organic” porosity includes a broader concept than just the porosity of kerogen. This is a more complex physicochemical process of transformation of the organic matter itself and the redistribution of elements within the formation as a result of the maturation of TOC components and hydrocarbon migration. When assessing the oil and gas potential in the section, we distinguish three groups of rocks: unconventional reservoirs with an increased TOC content and the presence of mobile hydrocarbons; bituminous rocks, in which part of the pore volume is filled with resinous-asphaltene substances and host dense carbonate rocks without organic matter. Also, sporadically developed traditional reservoirs are distinguished throughout the section of the Domanik type of rocks.

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