On the perspectives of oil and gas bearing of the Paleocene deposits of the Berehova and Oriv units of the Ukrainian Carpathians

Abstract

On the basis of the analysis of the occurrence of the main Paleocene lithological complexes of the Berehova and Oriv units of the Ukrainian Carpathians, four areas with different distribution of sandstones, siltstones and mudstones were distinguished. The selected areas are promising for the planning of oil and gas prospecting and for the increase of oil and gas reserves. Areas of distribution of lithologically sealed hydrocarbon traps are situated where sandstone formations occur. It is established that sandstones and siltstones of the Yamna suite are represented by both densely and poorly cemented varieties, which differ in cement composition, degree of cementation and porosity. The reservoir properties of the oil and gas bearing Paleocene sediments of the northwestern part of the study area were largely controlled by the factors that contributed to the preservation of high filtration and reservoir properties of the rocks at great depths - the thickness of the layers and the type of cementation of the clastic material. At the same time, the formation of the secondary pore space occurred due to the lithogenetic and tectonic fractures, as well as the decarbonization of sandstone and siltstone cement. The varying degrees of catagenetic changes in the rocks of the northwestern and southeastern parts of the study area indicate that tectonic processes had a significant impact on the lithogenesis of oil and gas bearing deposits and the formation of their reservoir properties. It is revealed that the most prospective from the point of view of potential reservoir rocks occurrence in the sequence of the Yamna suite, which is represented mainly by sandstones, is the northwestern part of the study area, where the high reservoir properties of the oil- and gas-bearing Paleocene sediments are largely determined by the factors that facilitated their preservation in the rocks at great depths. These factors are the thickness of the layers and the type of cementation of the clastic material. The complex of obtained results of investigations allowed allocation of the areas of potential reservoir rocks occurrence in the Paleocene sequence prospective for hydrocarbons accumulations.