Geochemical Interactions Among Rock/CO₂/Brine Systems: Implications for CO₂ Geo-Storage

Carbon Capture and Storage (CCS) is one of the promising techniques to mitigate carbon dioxide emissions and move towards net zero targets. The efficiency of a geological storage process is, however, a complex function of CO₂/rock/brine interactions. In particular, the effect of geochemical interactions among CO₂/rock/brine systems in an aquifer and its associated impact on wetting behavior has not been rigorously investigated before. In this work, we study the effect of the critical parameters affecting the CO₂/rock/brine system wettability from a geochemical perspective. In particular, we study the effect of temperature, pressure, and salinity on the wettability of the CO₂/calcite/brine system. The wettability was assessed based on the disjoining pressure, which was calculated from calcite surface potential. The geochemical simulator used is based on surface complexation modeling and takes dissolution and precipitations reactions of the minerals and aqueous species into account. The results show that increasing pressure decreases the concentration of calcite surface species >CaOH₂⁺ and >CO₃^-, while it increases the calcite surface species >CaCO₃^-. However, increasing temperature increases the concentration of calcite surface species >CaCO₃^- and >CO₃^-, while it slightly decreases the calcite surface species >CaOH₂⁺. The results also show higher calcite surface potential and disjoining pressure at higher temperatures and lower salinity, which reflects an increase in water wettability (or a decrease in CO₂-wetness) and greater CO₂ storage potential in calcite-rich aquifers at these conditions. This paper provides insight into the effect of different influencing parameters on the CO₂/rock/brine interactions and CO₂/rock/brine wettability, which can help understand the geochemical processes involved in CCS projects under a wide range of operating conditions.