Zeta Potential of a Natural Clayey Sandstone Saturated With Carbonated NaCl Solutions at Supercritical CO₂ Conditions

The zeta potential is a measure of electric potential at the mineral-electrolyte interfaces. The zeta potential of natural sandstones depends on mineralogy, electrolyte pH, concentration, composition, amount of dissolved CO₂, and temperature. We report for the first time the zeta potential measured on clayey sandstone comprising quartz, kaolinite, illite, albite and microcline saturated with NaCl solutions at supercritical CO₂ conditions. Our results demonstrate that zeta potentials in clayey sandstone samples at supercritical CO₂ conditions are significantly different from similar measurements conducted under ambient conditions and from those obtained with clean sandstones. Supercritical CO₂ zeta potential remains negative but is influenced by clays and feldspars due to their significant presence and exposure to large pores, which yields less negative zeta potential compared to quartz, under identical conditions. Our results have significant implications to natural subsurface systems such as CO₂ geo-sequestration sites, aquifers, geothermal sources and hydrocarbon reservoirs.