Thermodynamic Aspects of pH and Wettability Changes in Low Salinity Water Flooding Oil Recovery

Low salinity water flooding has for decades emerged as a technically and economically viable enhanced oil recovery scheme due to its environmentally attractive nature. In the literature, several reasons have been proposed for its immense success, some of which have been experimentally proven. Among the reasons given, wettability and pH increase have been greatly highlighted. In this paper, we have developed a pH and salinity dependent Gibbs free energy of adsorption model, using established thermodynamic concepts to prove the viability of hydrogen ions adsorption which can lead to pH and wettability increase. Accordingly, we have shown based on theoretical calculations that as salinity decreases, adsorption free energy for hydrogen ions decreases, leading to pH decrease at lower salinities. Our theoretical calculations also agree with optimum salinity ranges reported in the literature.