Khokha Y. Evolution of sedimentary complexes organic matter of Ukraine oil and gas regions from the thermodynamics standpoint

The dissertation is devoted to the research of the evolution of systems of organic and inorganic substances in a wide range of pressures, temperatures and initial ratio of elements by equilibrium thermodynamics methods. These systems are part of the structural-material complexes of oil and gas regions of Ukraine. A multifactor method of thermodynamic modeling of the geochemical systems evolution based on entropy maximization using the provisions of Jaynes' formalism is made. The method makes it possible not only to calculate the composition of systems containing geopolymers, hydrocarbons and non-hydrocarbon compounds in a wide range of thermobaric conditions, but also allows to establish the chemical structure of the solid phase. The method does not require the introduction of assumptions about the initial chemical structure of geopolymers, to perform calculations enough information about the elemental composition of the system at the beginning of transformations and assumptions about its component composition. The application of the developed technique for modeling the equilibrium composition of the geopolymer / gas-liquid fluid system convincingly showed that in the depth range of 2-6 km there is a stability area for hydrocarbon and non-hydrocarbon components existing in equilibrium with kerogen or carbonized material solid phase. The obtained results correlate well with the hypothesis of the "oil window", where in this range of depths the existence of a zone of maximum generation of heavy hydrocarbons by destructive changes of organic matter is located within 2-4 km. Thermodynamic analysis of organic matter transformations according to the data on the composition of modern fields of oil and gas regions of Ukraine indicates both the possibility of biogenic and the probability of abiogenic origin, ie the "polygenesis of oil". Based on thermodynamic modeling by entropy maximization, a method for estimating kerogen depletion by its methanogeneration has been developed. This method was applied to three oil and gas regions of Ukraine, and based on the results of the simulation, conclusions were made about the residual gas generation potential for each of them; the corresponding maps are constructed. It is shown that: • the gas-generating potential of kerogen of most of Boryslav-Pokutsk oil and gas district can be considered exhausted, while the kerogen of Bilche-Volytsk oil and gas district still retains sufficient potential to generate hydrocarbons; • the kerogen of the central axial part of the DDD has not yet exhausted its gas generation potential; however, local areas on both sides of the rift were depleted due to high paleothermic gradients, which significantly affected the depth of kerogen degradation; • the kerogen of the Kerch-Taman interpericlinal depression of the Southern oil and gas region is maximally depleted, while the kerogen of the southern side of the Karkinitsky-North-Crimean depression retains a high potential for gas generation.