Solid-liquid organic matter interaction mechanism between kerogen and aromatic compounds

Abstract

Under geological conditions, the initial generation of oil and gas in source rocks reaches saturation before being expelled and migrating, with the adsorption of hydrocarbons by kerogen being a key factor influencing oil saturation. The hydrocarbons produced by pyrolysis interact with kerogen macromolecules. Understanding the solvency and adsorption capacities of solid kerogen organic matter for liquid hydrocarbons can clarify the selective retention of hydrocarbons by source rocks and their characteristics in hydrocarbon generation and expulsion. Aromatic hydrocarbons are crucial components of petroleum hydrocarbons. Based on a three-dimensional model of kerogen, this study employed Autodock software to perform semi-flexible docking calculations between different types of aromatic hydrocarbon molecules (including benzene, polycyclic aromatic hydrocarbons, and their derivatives) and kerogen molecules of varying maturities. The Gibbs free energy required for their binding was calculated to study the characte-risticsof the interaction between aromatic hydrocarbons and kerogen. This study investigated the mechanism of kerogen adsorption of aromatic hydrocarbons at the molecular level, revealing the nature of solid and liquid organic matter interactions. When binding with kerogen of the same maturity, the larger the molecular weight of the polycyclic aromatic hydrocarbons, the greater the number of methyl groups in the compound, and the higher the degree of molecular condensation, the lower the Gibbs free energy required for binding with kerogen molecules. The interaction between aromatic hydrocarbons and kerogen molecules was influenced by three factors: the molecular mass of the aromatic hydrocarbons, the degree of molecular condensation, and the number of methyl groups in the system. After reaching the peak of hydrocarbon generation, kerogen with higher content of aromatic carbon methyl groups showed a stronger adsorption capacity for aromatic hydrocarbons. Polycyclic aromatic hydrocarbons and their derivatives with larger molecular mass and higher degrees of condensation demonstrated stronger binding abilities with kerogen. Conversely, smaller aromatic molecules with conventional connectivity exhibited weaker retention capacities in kerogen, making them more prone to hydrocarbon expulsion, migration, and accumulation into reservoirs.

Keywords

• kerogen
• aromatic hydrocarbon
• molecular docking
• adsorption effect
• gibbs free energy
• hydrocarbon generation and expulsion