Retention ability of different hydrocarbon molecules during the thermal evolution of lacustrine kerogen: Insights from molecular simulation and docking

Kerogen selectively binds to hydrocarbon molecules, influencing shale oil properties. Molecular simulations of its retention capacity help explain compositional differences between expelled and retained hydrocarbons. Lacustrine Kerogen from the Shahejie Formation in the Bohai Bay Basin was selected for artificial thermal simulation experiments. Structural information of kerogen at various maturity levels was obtained using ¹³C NMR, based on which 2D and 3D modeling was performed. The binding energies of n-alkanes, cycloalkanes, and aromatics with various kerogens were calculated by molecular docking. Results show that kerogen loses long aliphatic chains, reducing oil potential in the thermal evolution. In the late oil window, kerogen rapidly evolves and strongly retains hydrocarbons, especially aromatics with higher carbon numbers. The binding stability of aromatics exceeds that of n-alkanes and cycloalkanes, with Gibbs free energy for aromatics being over 300 % lower than for n-alkanes at higher carbon numbers. For saturated hydrocarbons, kerogen is more likely to retain larger liquid alkane molecules. Methylation of small molecules may be an important factor affecting their ability to bind to the kerogen. The application of molecular docking into petroleum geochemistry has achieved initial success, offering novel insights into hydrocarbon expulsion processes within kerogen. The molecular docking results are consistent with existing findings and provide a rapid, effective approach for simulating and validating oil retention mechanisms.