Geochemical Transient Modeling of Temperature and Pressure Effects on Long-Term CO2 Storage Integrity

Abstract This study explores the long-term geochemical interactions between CO2 and calcite, a predominant mineral in caprocks that plays a crucial buffering role, focusing on their implications for CO2 sequestration in geological formations. Using open-source geochemical modeling software, we examined the effects of varying temperature (25°C to 120°C), CO2 partial pressure (0.01 to 100 atm), and brine molality (1M and 5M) on caprock stability over a 10,000-year period. Across all scenarios, geochemical equilibrium was reached within 1000 to 2000 years, as indicated by the stabilization of pH, calcium concentration, and the calcite saturation index (si_Calcite). Calcite dissolution increased Ca2+ concentrations and buffered acidification from CO2 dissolution, while elevated temperatures and CO2 pressures accelerated this process. Higher salinity slightly reduced the solubility of both calcium and carbon species. The consistent convergence to si_Calcite ≈ 0 under all conditions confirms calcite's role in sustaining chemical stability and maintaining caprock integrity. Although the model applies a fixed reaction rate and assumes closed-system conditions, it provides a robust baseline for understanding fluid–mineral interactions in CO2-rich environments. Future work should incorporate reactive transport and geomechanical processes to more fully evaluate long-term caprock performance. This research contributes to improving the predictive capability and safety of CO2 storage systems as part of climate change mitigation efforts.