First-principles calculations of carboxylic acid adsorption on carbonate surfaces: Chain size and aqueous interface effects

In enhanced oil recovery (EOR), low salinity water (LSW) is an essential condition to change wettability in carbonate reservoirs for organic compound desorption. However, the nature of the water-oil-carbonate interactions remains challenging. Accordingly, we performed first-principles calculations to determine the adsorption energies of the propanoic and octanoic acids on the calcite and dolomite surfaces with water interface and implicit solvation medium. Our results confirm that the Mg sites are less selective for adsorption of both acidic oil components, whereas the Ca sites keep retaining the acid molecules. The differentiated influence from the carbonate surfaces is enhanced through the aqueous environment. In presence of Mg, the aqueous environment may act mainly on the unoccupied electronic levels of the dolomite carbonate sites instead of the Ca sites in calcite, which in turn has a stronger interaction with the acid molecules. The effect of the acid chain size is less pronounced. The acid desorption process could be then reached from the carbonate sites as the surface hydrophilicity is mainly increased in dolomite, which has a favourable ionic exchange and water adsorption. Therefore, our simulation models help to shed light on some important interaction properties in complex water-oil-carbonate interfaces under LSW conditions for EOR.

Automated summary

In this study, first-principles calculations were used to determine the adsorption energy of propanoic and octanoic acids on calcite and dolomite surfaces under low salinity water conditions. The results showed that the adsorption selectivity of acidic oil components was lower on magnesium sites, while calcium sites retained the acid molecules more effectively. The influence of the carbonate surfaces was enhanced in the presence of an aqueous environment. Additionally, the aqueous environment may predominantly affect the unoccupied electronic levels of dolomite carbonate sites, resulting in a stronger interaction with the acid molecules. The size of the acid chain had a less pronounced effect. The desorption of the acid molecules could occur from the carbonate sites, especially in dolomite, due to increased surface hydrophilicity and favorable ionic exchange and water adsorption. Overall, these simulation models provide important insights into the interaction properties of complex water-oil-carbonate interfaces under low salinity water conditions for enhanced oil recovery.