the effect of monovalent ions on the oil/brine electrical behavior using a novel surface complexation model

Oil/brine electrical behavior could control the wettability of the oil/brine/rock system during low salinity water flooding. however, there is a lack of understanding of chemical reactions occurring on the oil surface. there are a few surface complexation models (scms) for the oil/brine interface, and all of them assume that the surface site density is a fixed number, like the mineral surface. the current study assessed two existing models on this subject (model a and b). these models ignore the dynamic nature of the oil/brine interface. therefore, they failed to capture experimentally measured ζ potentials appropriately. therefore, this study constructed a novel diffuse layer scm (model c) considering the interfacial concentration of surface carboxylic acid as a function of brine salinity for each salt, including nacl, na2so4, cacl2, mgcl2, and nahco3. model c matches the experimental data of the literature far better than a and b. based on model c, na+, cl-, and so42- cannot be adsorbed on the oil/brine interface; however, the role of these ions in the electrical behavior of crude oil/brine is only to affect the interfacial concentration of -cooh. for example, an increase in na+ reduced the oil/brine ift. therefore, more carboxylic groups would be available at the oil/brine interface. as a result, -coo- concentration increases, and the crude oil surface becomes more negatively charged. the current study indicated that ca2+ and mg2+ are not the only factors that make the interface more positively charged. however, an increase in ift (in this study by salinity reduction) significantly makes the oil/brine interface more positive, too.