Effects of dissolved binary ionic compounds and different densities of brine on interfacial tension (IFT), wettability alteration, and contact angle in smart water and carbonated smart water injection processes in carbonate oil reservoirs

In this communication, K2SO4, KI, MgSO4, Na2SO4, CaCl2, MgCl2, KCl, and NaCl salts, as binary ionic compounds, were used for producing smart water with concentrations of 1000 + 1000, 2000 + 2000, 5000 + 5000, and 10,000 + 10,000 ppm. Then, the effects of dissolution of these salts on interfacial tension and contact angle between water, oil, and carbonate rock were studied. In addition, CO2 was added to the ionic solution with optimal compositions and densities in terms of minimum interfacial tension under the pressures of 6894.7, 10,342.1, and 13,789.5 kPa, and its effects on the latter two parameters were investigated. After that, the effects of ions dissolved in seawater (10 times diluted seawater) on water-oil interfacial tension, wettability of carbonate rock and contact angle under the pressure of 101.4 kPa in the absence of CO2, and under the pressures of 6894.7, 10,342.1, and 13,789.5 kPa in the presence of CO2 were studied. All tests were conducted at constant temperature of the reservoir (75 °C). The minimum interfacial tension was obtained for MgCl2 + K2SO4 composition (6.73 mN/m), which was lower than the interfacial tension between the initial amount of fresh water and oil (24.145 mN/m) by 72%. This reduction reached 83% after carbonating the solution under 2000 ppm and 75 °C conditions. The minimum contact angle in the aged segment for KCl + MgCl2 composition with concentration of 2000 + 2000 ppm was recorded as 39.80°, which decreased by 49.62% and reached 20.05° by adding CO2 under 13,789.5 kPa condition. The interfacial tension between seawater (initial density) and crude oil, under 101.4 kPa and 75 °C conditions, was obtained as 27.464 mN/m. The interfacial tension values under 6894.7, 10,342.1, and 13,789.5 kPa conditions were obtained as 25.315 mN/m, 25.146 mN/m, and 21.464 mN/m, respectively. These results reveal a decreasing trend after each dilution stage. In addition to trend, reduction of the initial contact angle in the aged segment in the solution after each dilution step indicates better performance of ionized seawater relative to normal seawater.