Role of divalent ions, temperature, and crude oil during water injection into dolomitic carbonate oil reservoirs

Although wettability alteration has been shown to be the main control mechanism of Low Salinity and Smart Water (LS-SmW) injection, understanding of the phenomena resulting in wettability changes still remains incomplete. Thus, direct measurement of wettability through contact angle measurement at ambient and elevated temperatures (28°C and 90°C) during LS-SmW injection to identify trends in wettability alteration was carried out. Zeta potential measurement was applied as an indirect technique for wettability assessment in rock/brine and oil/brine interfaces in order to validate the contact angle measurements. The results provided a new understanding to the effect of temperature and different ions on the wettability state of dolomite particles during an enhanced oil recovery process. Observations showed that increasing temperature from 28°C to 90°C reduced the contact angle of oil droplets from 140 to 41 degrees when Seawater (SW) was injected. Additionally, changing crude oil from crude-A (low asphaltene content) to crude-B (high asphaltene content) contributed to more negative surface charges at the oil/brine interface. The results suggested that the sulfate ion (SO^2-₄ ) was the most effective ion for altering dolomite surface properties, leading to less oil wetness. Wettability alteration at ambient and elevated temperatures during LS-SmW injection could be explained by Electrical Double Layer (EDL) theory.