New insights from nanoscale in-depth investigation into wettability modification in oil-wet porous media

In the context of fluid-surface studies of oil reservoirs, wettability alteration plays an important role, especially in carbonate reservoirs. This investigation, utilizing molecular dynamics simulation, delves into the effect of oil movement during interactions with brine ions. The calculation of adsorption energy, radial distribution function, diffusion coefficient, and configurational changes of the NaCl brine molecules allowed for an examination of the role of ions in oil movement from an oil-wet calcite surface. Findings indicate that the polarity of oil has a marked influence on oil detachment, as evidenced by the more than 30% adsorption energy for the acrylic acid system compared to the decane system. The diffusion coefficient of Na${}^{+}$ ions in the acrylic acid system was found to be five times as high as in the decane system. Configuration changes showed that brine ions are more active — in a regular eight shape — in interacting with the acrylic acid-wet surface as opposed to the decane-wet surface. The hierarchical significance of oil polarity $>$ brine ions $>$ mineral surface in altering the wettability of the system demonstrates the significance of sodium ions in the presence of the polar oil component. The findings greatly contribute to the development of effective Smart Water flooding technology.