Effect of Low-Salinity Water Ionic Composition on Wettability and Heavy-Oil Recovery in Berea Sandstone

Engineered low-salinity water (LSW) injection was investigated as an environmentally favorable enhanced oil recovery strategy for heavy oil in Berea sandstone. A Taguchi L9 design was used to formulate nine brines (861–4483 ppm total dissolved solids) with systematically varied Na+, Ca2+, Mg2+, and SO42− concentrations and to evaluate their effects on interfacial tension (IFT), wettability, zeta potential, and oil recovery. Among the nine engineered low-salinity brines, BR6 (2877 ppm) yielded the lowest IFT, whereas BR8 (4059 ppm) yielded a contact angle of 20°, compared with 38° for FW. Contact angles were measured after brine exposure and provided comparisons among the tested brine conditions. Zeta potential became increasingly negative as salinity decreased, suggesting stronger electrostatic repulsion at the rock–brine interface and conditions favorable for wettability modification. Optimization of the ionic composition yielded an engineered brine (OPT) predicted by Taguchi design analysis and experimentally validated. In microcosm tests, OPT and BR6 achieved oil recoveries of 53.8% and 51.6%, respectively; corresponding packed-column recoveries were 38.8% and 42.0%. Moreover, tertiary BR6 injection after formation-water flooding recovered an additional 12.2% of the original oil in place. Overall, the results suggested that engineered LSW performance is governed by ionic composition rather than salinity reduction alone.