Replenishment of oil reserves requires searching, exploration and production of new unconventional objects. Among these objects is Domanik formation, which is widespread in the Volga-Ural basin. The Domanic high-carbon formation is presented by thin-layered carbonate-siliceous rocks with a high content of organic matter, capable of both producing hydrocarbons with its own oil and gas potential, and concentraring them in reservoirs [Stupakova et al., 2017]. Study of lithological composition of rocks help to obtain information about the nature of hydrocarbon accumulations and understand possibilities of estracting hydrocarbon of them. The lithological and geochemical characteristics of rocks are an integral part of the study such types of deposits.
Domanic deposits have already been studied in sufficient details. Various aspects of their study were described previosly in many works, but so far, these deposits have been considered mainly as source rocks. Domanic deposits are distributed in a wide stratigraphic range from the Middle Frasnian of the Late Devonian to the Tournaisian of the Early Carboniferous. In this paper, domanic formation is considered as an unconventional reservoir. Due to the complex and heterogeneous structure of rocks, their uneven saturation with organic matter and low porosity values, the methodology for assessing reservoir properties is at a low stage of production. An integrated study of the void space in such deposits, including macro- and microdescription of the core, analytical studies, makes it possible to predict zones with best quality of reservoirs and helped successfullу produce such deposits. In the section of domanic formation were identified the main lithotypes and characterized of each of them. Comparison of the types of void space identified in thin sections and reservoir properties made it possible to classify the main types of reservoirs and assess their quality.
The paper describes the structure and depositional conditions of a domanicoid high-carbon formation (HCF) in the central part of the Volga-Ural oil and gas basin. The structure of the HCF depends on the structural relatedness and paleogeographic conditions of the Late Devonian period, where the time of maximum sea level standing within the basin led to deposition of high organic carbon content intervals. The structural-facies zonation of the HCF distribution area is associated with the zone of relatively deep-water depressions, the zone of slopes, highs and the shallow water shelf with numerous bioherm buildups. The boundaries of the zones were determined by the position of large structural elements of the Tatar and Bashkir arches and depressions of the Kama-Kinel system of troughs. These zones differ not only in the distribution of the thickness of HCF deposits, but also in the nature of the distribution of intervals of the section enriched in organic matter. The maximum number of interlayers enriched by organic matter of the siliceous-carbonate rocks is observed in the section of the Frasnian and Famennian deposits within the central part of the Kama-Kinel system of troughs. Numerous of oil shows from the HCF intervals indicate the potential for further study and spotting of promising areas for hard-to-recover hydrocarbon reserves exploration.
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