Geochemical Analysis Strengthens Assessment of CO2 Storage in Different Reservoir Rocks

Abstract The efficiency of CO2 trapping in geological formations is strongly influenced by their mineralogical composition and physical properties. This study investigates the geochemical interactions governing CO2 trapping in three distinct formations: basalt, carbonate, and sandstone. A three-dimensional reactive transport model was developed to simulate the long-term fate of injected CO2, incorporating key trapping mechanisms, including supercritical CO2 retention, dissolution in brine, and mineralization. Additionally, changes in formation porosity and the geomechanical response to injection were evaluated to assess potential reservoir alterations. Simulation results revealed significant variations in CO2 trapping behavior in different types of formations. In sandstone and carbonate formations, CO2 is primarily retained in its supercritical phase through structural and residual trapping, with dissolution contributing to a lesser extent. Mineral trapping is more pronounced in carbonate formations than in sandstone, but basalt exhibits the highest degree of CO2 mineralization, with mineral trapping eventually surpassing dissolution over extended time. This extensive mineralization in basalt leads to a reduction in porosity, with an observed maximum change of −0.001 porosity units, whereas carbonate formations show only minimal porosity alteration. In contrast, sandstone formations retain positive porosity changes, indicating limited mineral precipitation. Additionally, CO2 plume evolution differs among formations, with basalt formations demonstrating the most significant long-term shrinkage due to mineral trapping. A geomechanical analysis further indicated a localized subsidence of approximately 0.3 feet at the injection site, emphasizing the need to monitor formation stability. This study highlights the critical role of geochemical processes in CO2 storage and their implications for long-term containment. The findings provide essential insights into how formation mineralogy influences CO2 storage, aiding in the refinement of Area of Review (AoR) delineation and regulatory frameworks for Class VI permit applications. These results contribute to a more robust understanding of CO2 storage in diverse geological settings and support the advancement of carbon capture and storage (CCS) initiatives.