Atomistic simulation of calcite interaction with ionic species and oil components in water-flooding

Density functional theory (DFT) trends in Gibbs free energies and enthalpies were thoroughly studied in calcite. Different coordination was applied for ionic species that exist in smart-water as well as for carboxylic acids presented in crude oil at distinct two primary hydration sites: CO3H, CaOH. The studied hydration sites were proposed based on previous electro-kinetics besides surface titration experimental studies. Interfacial energy runs using molecular modeling approaches, with Becke's three parameter exchange and Lee Yang Parr corrected correlation functional (B3LYP) and 3-21G basis set, were performed to account for stability, reactivity and wettability alteration. The calculations predict the most stable complexes for calcite are, CO3H, CaO-, CO3Ca+, CO3Mg+, CaCO3-, CaHCO3, CaH2O+ and CaSO4-. We also demonstrate that free ion species are having a higher free energy in seawater than in case of a complex and thus indicates a more reactivity of complex species to interact with rock sites. This study proposes a numerical correlation between thermochemistry profiles and wettability alteration, which expresses to us how the surface affinity for a certain organic compound compares with its affinity for water. The calculations agrees with previous experiment findings especially in case of Ca+2, Mg+2, SO4-2, MgOH+1, OH-1, and NaCl. Some reversed trend can be explained by the smaller size of the basis set used in the calculations. The results of this insights help in understanding the interaction mechanism of this unique systems in order to modify reactivity for enhancing oil recovery (EOR) purposes, and to use the outcomes of this study to pose questions and directions for continuing theoretical efforts destined at linking macroscopic reactivity in case of altering wettability with molecular-level understanding.