Effects of Salinity-Induced Chemical Reactions on Biotite Wettability Changes under Geologic CO₂ Sequestration Conditions

The wettability of rocks and minerals significantly affects the safety and efficiency of energy-related subsurface operations. Salinity is an important controlling factor in terms of wettability but has received limited attention. We studied the effects of salinity-induced chemical reactions on biotite's wettability changes under relevant subsurface conditions. Biotite was reacted at 95 °C and 102 atm of CO₂ for 70 h in solutions with salinities of 0, 0.1, 0.5, and 1.0 M NaCl. Then, static and dynamic water contact angles on reacted biotite basal surfaces were measured using a captive drop method. As a result of enhanced biotite dissolution at higher salinities, increased roughness, more negatively charged surfaces, and higher densities of hydroxyl groups on the biotite surfaces made biotite basal surface more hydrophilic. These results provide new information about the interplay of chemical reactions and wettability alterations of minerals, providing a better understanding of CO₂ transport in subsurface environments.