Geochemistry of kerogen type III transformations in the process of rocks diving according to the thermodynamic simulation results

Abstract

The publication considers the processes that accompany the transformation of organic matter (OM), which is the basis of kerogens different types, are characterized by incredible complexity and predictable diversity. Here is a summary of the basic reactions that occur with the components of the biota after passing the biodegradation barrier: first destruction due to hydrolysis, and then - different types of condensation. It is shown that the complexity of the processes of organic matter degradation does not allow to develop an adequate model of its transformations after sedimentation only on the basis of understanding the kinetics of individual reactions and groups of reactions. We believe that the analytical apparatus of equilibrium thermodynamics is best suited for such descriptions of these complex systems. Using a thermodynamic model based on Jayne's formalism, we calculated the changes in the organic matter of type III-A kerogen in contact with organic and inorganic gases during the rocks dipping. The results of the calculations are the molar fractions of 44 additive components, which describe the solid phase of kerogen III for each depth up to 20 km inclusive, and organic and inorganic individual substances. It is established that the consolidating effect of pressure is an important factor influencing the composition of the geochemical system, including type III kerogen, in the depth range of 6-13 km, at the same time with subsequent dipping, the destructive temperature factor prevails. Entropy has shown that the depth range from 6 to 15 km with a maximum of 7.5 km can be considered the most suitable for the formation of hydrocarbon fluid. The branching coefficients proposed in this work for solid (type III kerogen) and gas-fluid phases confirm experimental works on estimating the direction of kerogen transformation processes with immersion. The complex nature of the balance between constitutional water and kerogen, depending on the heat flux and depth, has been established. To analyze this equilibrium, a simple equilibrium constant of dehydration is proposed, which generalizes the conversion of water in the kerogen matrix.