The Effect of Salinity, Rock Type and pH on the Electrokinetics of Carbonate-Brine Interface and Surface Complexation Modeling

Laboratory studies reveal that reducing brine salinity and altering pH can shift carbonate rock wettability toward a less oil-wetting state, driven by changes in surface charge. This effect is consistent across different carbonate rock types—including Stevns Klint chalk, limestone, and dolomite—though chalk exhibits the highest reactivity to pH and salinity changes, while dolomite shows the least. Surface complexation modeling suggests that surface species like >CaSO4-, >CO3Ca+, and >CO3Mg+ significantly influence total surface charge, with pH increasing the zeta-potential by converting negatively charged moieties into neutral ones. These findings provide insights into reservoir behavior under varying salinity and pH conditions, offering a tractable approach to predicting carbonate rock electrokinetic properties.

Mahani, H., Keya, A. L., Berg, S., & Nasralla, R. (2015). The Effect of Salinity, Rock Type and pH on the Electrokinetics of Carbonate-Brine Interface and Surface Complexation Modeling. SPE Reservoir Characterisation and Simulation Conference and Exhibition. https://doi.org/10.2118/175568-ms