Influence of Ion Evolution–Controlled ScCO2 Acidification-Induced Mineral Dissolution on Carbon Sequestration Efficiency

Supercritical carbon dioxide–enhanced coalbed methane ( ScCO 2 - ECBM ) is a pivotal strategy for mitigating the global greenhouse effect; however, the postinjection evolution of coal seam physical structures and fluid behaviors remains insufficiently understood. This study systematically investigated the carbon dioxide–water–coal interaction mechanisms in deep coal seams and establishes a fully coupled multiphysics model incorporating ion transport and mineral dissolution. Using this model, the influence of acidified fluids on calcite dissolution and its consequent impact on carbon sequestration performance was investigated comprehensively. The results demonstrate that, following ScCO 2 injection, its solubility markedly increases, leading to a pronounced decrease in the potential of hydrogen (pH) of the fracture water system. Hydrogen ions ( H + ) subsequently interact with fracture surfaces carbonate minerals, releasing calcium ions ( Ca 2+ ) and carbonate ions ( CO 3 2 − ) into the aqueous phase, thereby causing their concentrations to rapidly peak in the short term. As ionic activity exceeds the dissolution equilibrium constant of calcite, secondary precipitation of Ca 2 + and CO 3 2 − occurs, resulting in a gradual reduction in their concentrations. A comparative analysis based on global monitoring between models with and without CO 2 - water - coal interactions indicated that calcite dissolution exerts a significant promotive effect on carbon sequestration efficiency. This enhancement can be sustained over extended periods, although it is partially offset by secondary precipitation of carbonate minerals. This study provides a robust theoretical foundation for advancing the understanding of CO 2 - water - coal interaction mechanisms in ScCO 2 - ECBM processes.