Electrostatic Characterization of the −COOH–Brine–Clay System: Implications for Wettability Alteration during Low Salinity Waterflooding in Sandstone Reservoirs

Wettability alteration is a critical physiochemical effect for enhanced oil recovery during low salinity waterflooding in sandstone reservoirs. While electrostatic adsorption of polar groups on clay basal planes and edges has been perceived to govern the wettability alteration, the relative contribution of adsorption on basal plane and edges to wettability alteration has not been elucidated, which hinders the prediction of low salinity effects. We therefore coupled PHREEQC and PEST to quantify the acid component (−COOH) adhesion on the kaolinite surface against adsorption tests of 4-tert-butyl benzoic acid (PTBBA) on kaolinite powder. The −COOCa+ and −COO– adsorption on kaolinite basal planes and edges was calibrated against the measured PTBBA adsorption at different salinity and pH values. The new calibrated model shows that the PTBBA adsorption mainly occurs on the basal plane. This geochemical modeling corrects the overestimation of electrostatic force from previous geochemical modeling at low pH and provides further insights beyond the quinoline adsorption model from Chen et al. Salinity governs the PTBBA adsorption at pH > 6 (>Na + −COOCa+ = > –COOCa + Na+), while the pH determines the PTBBA adsorption at pH < 6. This work adds new geochemical data sets to the existing geochemical reactions, quantifying the relative contribution between edge- and basal-charged minerals of acid component (−COOH) adhesion and hence the wettability alteration at different pH and salinity values.