LAUSR

Abstract The injection of optimized water in terms of desired salinity range and ionic composition into a reservoir to enhance oil recovery is widely known as SmartWater flooding. The synergistic effects of different SmartWater brines with alkali on wettability alteration of carbonates is investigated in this study by measuring the ζ-potentials at calcite/brine and oil/brine interfaces. The ζ-potential at calcite/brine/oil interfaces indicate that a higher concentration of sulfates is necessary to result in a favorable wettability alteration. Both alkalis (NaOH and Na2CO3) increase the negative ζ-potential at the two interfaces for low salinity Na2SO4 brine. A slight increase in negative charge is observed at the two interfaces using NaCl brine with Na2CO3 alkali while there is no much change in ζ-potentials with alkali in SmartWater (10-times reduced salinity seawater). Sodium carbonate effects on the ζ-potential of calcite is more pronounced when compared to NaOH due to the availability of carbonate ions as excess potential determining ions. The surface complexation modeling results quantitatively agree with the experimental data at the calcite/brine interface. For the oil/brine interface, a reasonable match is obtained and further calibration of carboxylic acid group and nitrogen based crude oil reactions is recommended to improve these predictions. These results indicate that Na2SO4 brine is highly suitable for alkaline-assisted water-flooding processes in carbonates. The negligible impact of adding alkali on measured dielectric constant as well as strong agreement obtained between the polarity of ζ-potentials at both calcite/brine and oil/brine interfaces with contact angle results confirm the robustness of the reported experimental ζ-potential values.