Experimental and theoretical study of wettability alteration during low salinity water flooding-an state of the art review

Initially oil-wet carbonate reservoirs as the carbonate rock is positively charged and crude oil is negatively charged at reservoir conditions (pH ∼ 7-8, T ≈ 100 °C), therefore, the oil adheres strongly onto the carbonate rock that makes it oil-wet (left). Low saline with potential determining ions (pdi) injected into carbonate reservoirs will increase the negative surface charge/potential due to chemisorption, therefore, enhance the repulsive part of disjoining pressure and changes the wettability to water-wet. At equilibrium, a stable thin film will be formed by double layer expansion mechanism (right).