Synchronous impact of divalent ions on formation damage and wettability alteration during smart water injection: static and dynamic assessment

Smart water injection into oil fields is an efficient EOR method but has significant challenges due to incompatibility between the formation brine and the injecting water. The presence of reactive ions in smart water can change the wettability of reservoir rock to increase oil production. However, the possibility of formation damage due to inorganic scales may increase. In this research, static and dynamic experiments were conducted to investigate the competition between rock wettability alteration and formation damage due to smart water injection. The experiments were performed in two parts including waters compatibility tests and rock wettability measurements for various concentrations of potential-determining ions in smart water. The crystal size and morphology of the sulfate scales were inspected visually using scanning electron microscopy images. In static compatibility tests, the maximum amount of sulfate scales was detected in the mixture containing 40% injection water. The experimental data indicated that the simultaneous increase in the concentration of sulfate and magnesium ions improves the carbonate rock wettability 18% more compared to increasing sulfate concentration alone. As a result, SW_1Ca.2 Mg.1.5S revealed the highest effect on rock wettability changes from oil-wet to water-wet conditions in both static and dynamic tests. The formation damage analysis through core-flooding experiments showed that increasing the concentration of sulfate ions twice the sea water causes an 88% reduction in core permeability. However, doubling the magnesium concentration in the presence of sulfate ions reduces the permeability decline to 77%. The maximum recovery factor (i.e., 35%) was attained by injecting SW_1Ca.2 Mg.1.5S into the carbonate core, and core permeability was enhanced twofold. The findings show that simultaneous changes in the concentration of potential-determining ions in smart water, in addition to increasing oil production, also prevent formation damage, which is often neglected in previous studies.