Energetics of Interfacial Interactions of Hydrocarbon Fluids with Kerogen and Calcite Using Molecular Modeling

Understanding of the fluid-rock interactions is essential to characterize the behavior of petroleum fluids in reservoir formations. Such knowledge is difficult to obtain due to the heterogeneous nature of hydrocarbon systems. This study investigated the interactions of light oil molecules with kerogen and calcite using molecular dynamics simulations. Specifically, octane and octanthiol were used as model molecules for non-polar and polar oil compounds; a kerogen fragment molecule was employed as the building block for kerogen, the major constituent of reservoir rock organics; calcite was used as a model system for hydrophilic materials in reservoir rocks. Umbrella sampling method combined with the weighted histogram analysis method was deployed to calculate the free energy profiles of oil molecule interactions with kerogen and calcite surfaces. The effects of surface composition, oil molecular polarity, surface water, and size of the oil molecular cluster on the interfacial interactions were evaluated based on the free energy profiles. The results show that the minimal energy required to recover oil molecules significantly decreases at both kerogen and calcite surfaces if water is presented. The kerogen surface exhibits stronger binding energies with oil molecules than that of the calcite. These findings suggest that (1) polar oil compounds require more effort to be recovered from the reservoir rocks than non-polar molecules, (2) isolated oil molecules or oil clusters of a smaller size are harder to be displaced from the surfaces than a larger size of molecular clusters, and (3) the presence of water reduces the effort to recover oil at both surfaces. The results provide an energetic perspective of the interfacial interactions for the oil recovery in reservoir formations. This study demonstrates the capability of MD simulations in evaluating the energetics of the oil-rock interactions under different interface conditions, which can provide valuable implications for developing novel technologies of oil recovery.