Thermodynamic model of the deep origin of oil and its phase "freezing"

Abstract

Based on the deep inorganic concept of the origin of oil and gas deposits, the evolution of these petrogenic reservoirs in the lithosphere is considered. The analysis of phase diagrams and experimental data made it possible to determine two trends in the evolution of non-methane hydrocarbons in the Earth's interior. In the upper mantle, the "metastability" of heavy (with a lower H/C ratio) hydrocarbons increases with depth. However, at temperatures and pressures corresponding to the surface mantle-crustal hydrothermal conditions, the “relative metastability” of heavy hydrocarbons increases with approach to the surface. When deep HCs fluids rise to the surface, petrogenic oil reservoirs are formed as a result of a drop in hydrogen fugacity and a gas → liquid oil phase transition. Under the physical and chemical conditions of an oil reservoir, metastable reversible phase equilibria are established between liquid oil, gas hydrocarbons and CO2 and solid (pseudocrystalline) "mature" and "immature" kerogens of "oil source" rocks. A decrease in hydrogen pressure and temperature leads to a stoichiometric phase transition (“freezing”) of liquid oil into solid kerogens. This occurs as a result of oil dehydrogenation in the processes of high-temperature CO2 fixation and low-temperature hydration of oil hydrocarbons, which are the main geochemical pathways for its transformation into kerogen. Thus, the formation of carbon matter in petrogenic reservoirs is the result of regressive metamorphism of deep hydrocarbon fluids, natural gas, liquid oil, and emerging accumulations of naphthides.