Modeling the long-term fate of injected CO 2 in saline aquifers: An integrated framework coupling multiphase flow, dissolution, reaction, and ripening

Abstract. Geological carbon sequestration (GCS) mitigates climate change by storing anthropogenic carbon dioxide (CO2) in geological formations. CO2 undergoes complex physical and chemical transformations in deep geological formations, governed by various interacting trapping mechanisms. Because the trapping mechanisms operate over a wide range of different timescales, their long-term interplay remains unclear. We develop an integrated numerical modeling framework to analyze and track the plume footprint and phase transition processes that occur throughout the entire cycle of the injected CO2 in saline aquifers. The key novelty of the modeling framework lies in its capability to describe multiple hydrodynamic processes and their interactions, including injection, dissolution-driven convection, reactive transport, and gravity-induced Ostwald ripening. The results suggest that dissolution reduces the lateral migration of free-state CO2, while geochemical reactions generate preferential pathways for CO2-rich flow. For the scenarios we analyze, after 500 years of mass transfer, dissolved CO2 accounts for 42.80 % of total trapped CO2 mass, while reactive CO2 contributes less than 1 %. The results also illustrate that low vertical permeability is unfavorable for the long-term transition of CO2 from physical trapping to dissolution trapping. When the permeability anisotropy index γ increases from 0.5 to 10, the total dissolution storage amount within the domain is reduced to one-third over the 500-year simulation period. This integrated modeling framework provides critical insights into the long-term evolution of CO2 plume migration and phase transition behavior, thereby offering a practical tool to quantitatively assess the long-term fate of the injected CO2 in saline aquifers.