Hayevska Y. Lithofacial features of the deposits of Eocene of the BoryslavPokuttia zone of the Carpathian foredeep and advanced Units of the Skyba zone of the Ukrainian Carpathians in connection with their oil and gas potential

The dissertation represents a complex study of lithologic-facial and mineralogical-petrographic features of Eocene deposits and revealing of oil and gas prospective areas for the hydrocarbon prospecting in the Boryslav-Pokuttya zone of the Carpathian foredeep and the Beregova and Oriv napes of the Skyba zone of the Ukrainian Carpathians. According to the results of the analysis and interpretation of the well-log data, the spatial distribution of the Eocene deposits was determined and the areas of distribution of sandstones and siltstones, which constitute potential reservoirs for hydrocarbons, were identified. The material composition of potential reservoir rocks has been studied on the basis of the analysis and generalization of materials of lithological, lithogenetic, petrographic, structural and textural studies of Eocene rocks. The depositionalenvironments within the Carpathian segment of continental margin of Tethys in Eocene and their control on formation of potential reservoir rocks for hydrocarbons has been studied. It has been found that the placement of aleuro-psammitic Eocene rocks with maximum and minimum sandstone content has a mosaic, mosaic-linear feature, which reconstructs fragments of Carpathian fans; areas with high sandstone content are dominated by porous reservoir rocks while the fractured reservoir rocks occur in the areas with low sandstone content. It was revealed that the best reservoir properties in terrigenous Eocene deposits are characteristic for the reservoir rocks with pore, contact-pore, film-pore matrix, and comparatively worse – for those containing pore-basal or basal type of matrix. An important factor that significantly affects the conservation of high reservoir properties by the reservoir rocks at large depths is the thickness of the layers. It was found that within the studied area both sandstones and siltstones represent the potential fracture and mixed type reservoirs and only in rocks at considerable depths (up to 4-5 km) where processes of secondary pore space formation occurred due to the formation of lithogenetic and tectonic fracturing, such rocks represent potential poretype reservoirs. According to the results of the performed investigations, the features of the spatial development of different lithological types of rocks are distinguished, which differ in the specificity of catagenetic transformations and types of potential reservoirs for hydrocarbons, maps of distribution of potential reservoir rocks in Eocene sequence are constructed, and the location of prospective for oil and gas areas for hydrocarbons prospecting within the northwestern, central and southeastern regions of the study area are established