Tectonic and geochemical criteria of organic matter evolution of the Carpathians Krosnen zone in the context of oil and gas potential

Abstract

Statement of the general problem. The article provides an analysis of the geological and tectonic factors that influenced the formation of deposits of the Krosnenskaya zone of the Outer Carpathians. The authors considered several questions related to the stratigraphy and tectonics of this zone. In the geological structure of the Krosnenskaya cover, we distinguish two separate cover units - the Turkivskaya and Bitlyanskaya subcovers, based on their lithologic and facies characteristics. The problems of finding hydrocarbon deposits in this region are associated with an insufficient understanding of their structure. This problem was solved with the emergence of the concept of scaly-thrust structure of the Krosnenskaya zone. Productive horizons with unstable tides are revealed in the Oligocene sediments of Golovetsk. These horizons are not currently developed. We believe that it is possible to obtain stable industrial gas flows from such collectors.

Research materials and methods. The history of the study of the geological structure of 7 deposits located on the territory of Poland and Ukraine within the considered and adjacent regions is presented: Borynskyi (well 1, 2), Hryniavskyi, Khaschiv-Lopushanskyi, Pobuk, Sanok, Strahotsina and Grabovnica. In total, 13 measurements of the composition of gas mixtures were included in the calculation. The depth range for the considered samples is within 875-5077 m, which allowed us to draw conclusions about changes in geochemical coefficients with depth.

Presentation of the main research material. The analysis of the history of the evolution of organic matter was carried out using the method of geochemical coefficients and thermodynamic modeling using the methods of independent chemical reaction constants and entropy maximization. According to the results of the analysis, it was established that tectonic criteria directly affect thermobaric conditions, control the evolutionary processes of destruction of organic matter. We discovered that the source of gases in the deposits of the Krosnenskaya zone is only kerogen. On the other hand, part of the deposits of the zones adjacent to Krosnenskaya show deviations from this regularity, and we assume that part of the gases in these deposits are formed because of oil cracking. The article shows that the values of the i-C₄/n-C₄ coefficient vary slightly for the deposits of the considered region. Obviously, this indicates that the evolution of organic matter for the considered deposits took place in close conditions, both in terms of thermobaric conditions and in terms of the composition of the parent material. This conclusion is confirmed by the results of calculations of the formation depths of equilibrium gas mixtures both by entropy maximization and by the method of constants of independent chemical reactions.

Conclusions. Geochemical analysis of kerogen depletion by the methane generation rate proved that the kerogen deposits of the region are not completely depleted and retain the potential for further evolution with the formation of hydrocarbon gases. Based on the above considerations, we believe that the oil and gas potential of this region has not been studied enough and requires additional analysis, including the laying of new exploratory wells.