THERMODYNAMICS OF THE EVOLUTION OF ORGANIC MATTER IN THE CONTEXT OF POLYGENESIS OF FOSSIL HYDROCARBONS

• Дата: 2020
• Автори: Khokha, YU.V., Pavlyuk, M.I., Naumko, I.M.
• Формат: Стаття
• Мова: Ukrainian
• Опубліковано: Institute of Geological Sciences, NAS of Ukraine 2020
• Теми: органічна речовина; полігенез; еволюція; Карпатська нафтогазоносна провінція; рівноважна термодинаміка; 84; 552.58; органическое вещество; полигенеза; эволюция; Карпатская нефтегазоносная провинция; равновесная термодинамика; organic matter; polygenesis of oil and gas; evolution; Carpathian oil and gas province; equilibrium thermodynamics
• Онлайн доступ: http://geojournal.igs-nas.org.ua/article/view/214800
• Назва журналу: Geological journal

The dominant concepts of organic matter evolution, which are based on various theories – the synthesis of inorganic compounds in the Earth’s asthenosphere, the destruction of organic compounds in the sedimentary layer, and other hybrid and alternative models, are comprehensively considered. A possibility is accessed of using the equilibrium thermodynamics methodology to calculate the change in the composition of the geochemical system under changing geodynamic regimes in a wide range of lithosphere conditions. The main factors that control the kerogen/gas system composition are temperature, pressure, and the initial composition expressed in molar fractions of elements. Some ways to calculate by thermodynamic methods the composition of geochemical systems consisting of organic and inorganic compounds are shown. All methods were divided into two main groups: “stoichiometric”, based on independent chemical reactions in equilibrium, and “non-stoichiometric”, when the calculation is based on the chemical potentials of the components. It is shown that the entropy maximization method is most suitable for estimating the evolution of organic matter in sedimentary rock strata, and the method of independent chemical reaction constants – for calculation within the Earth’s asthenosphere. Both methods are applied to hydrocarbon deposits in the Carpathian oil and gas province. The temperatures and depths of the formation of gases mixture identical in composition to those found in modern deposits are determined. Schematic maps of formation depths on both models are composed and regularities of spatial distribution of depths and temperatures of the formation of deposits in region are established. According to the thermodynamic analysis, the gases component composition of oil and gas fields of the Western oil and gas region of Ukraine indicates both the possibility of biogenic and the probability of abiogenic origin, i.e. the “oil polygenesis”. The consistency of the “oil window” concept with thermodynamic calculations by the method of entropy maximization according to Jaynes’ formalism is shown. It was found that among thermodynamic models for calculating the kerogen/gas geochemical systems composition, the most suitable method is entropy maximization by Jaynes’ formalism, and for determining the composition by abiogenic model of deep genesis – the method of independent chemical reactions constants. It is assumed that the concept of polygenesis of oil and gas equates the views on the genesis of natural hydrocarbons in the bowels of the Earth: abiogenic, abiogenic-biogenic, and biogenic.