Influence of aqueous pH and ionic strength on the wettability of quartz in the presence of dense non-aqueous-phase liquids

The location, distribution, and migration of non-aqueous-phase liquids (NAPLs) in porous media are strongly influenced by the wettability of aquifer solids. Changes in wettability can significantly affect capillary pressure, relative permeability, residual saturation, and fluid displacement potential. In this study, mineral wettability by DNAPLs was evaluated as a function of aqueous pH and ionic strength for a water-DNAPL-quartz system. Contact angle and DNAPL-water interfacial tension, which is related to contact angle, were experimentally determined for trichloroethylene and carbon tetrachloride in aqueous solutions of varying pH and ionic strength. Both DNAPLs exhibited the following results: Contact angles were at a maximum near the pH of the point of zero surface charge of quartz (pH similar to 2) and decreased as pH and ionic strength were increased. DNAPL-water interfacial tension was invariant with respect to pH and ionic strength (up to 0.1 M). Observed variations in contact angle yield calculated changes in capillary pressure as high as 10%, which may affect the mobility of DNAPLs in settings where capillary pressures are close to displacement entry pressures for porous media.