Electrostatic Characterization of -COOH-Brine-Clays System: Implications for Wettability Alteration during Low Salinity Waterflooding in Sandstone Reservoirs

Wettability alteration is a critical physiochemical effect for enhanced oil recovery in sandstone reservoirs during low salinity waterflooding. While electrostatic adsorption of polar groups on basal planes and clay edges has been perceived to govern the wettability alteration, 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 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 were calibrated against the measured PTBBA adsorption at different salinity and pH. The new calibrated model shows that the PTBBA adsorption mainly occurs on the basal plane. This geochemical modelling corrects the overestimation of electrostatic force from previous geochemical modelling 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 pH determines the PTBBA adsorption at pH < 6. This work adds new geochemical datasets to the existing geochemical reactions, quantifying the relative contribution between edge- and basal-charged minerals of acid component (-COOH) adhesion hence wettability alteration at different pH and salinity.