Long distance migration assisted structural trapping during CO

Long-distance migration-assisted structural trapping represents an optimal configuration for offshore geological CO₂ storage. In this study, the trapping efficiency of CO₂ was quantitatively analyzed using CMG software, taking into account aqueous solubility and geochemical reactions. The investigation focused on CO₂ migration behavior, mineralogical changes, pH and porosity variations induced by geochemical processes, and their respective contributions to overall carbon storage. Simulation results show that CO₂ tends to accumulate near the injection wells and subsequently migrates upward along the slightly dipping strata due to density differences between CO₂ and formation brine. After the injection wells are shut in, the CO₂ plume continues to migrate up-dip toward the crest of the anticline structure. A substantial portion of CO₂ remains trapped in the dipping strata due to capillary pressure hysteresis. As CO₂ dissolves into the saline aquifer, it generates H⁺ ions, which promote the dissolution of anorthite, releasing Ca²⁺ and Al³⁺ necessary for the precipitation of calcite and kaolinite over time. Results indicate that kaolinite and calcite predominantly precipitate within the aqueous phase, while anorthite is continuously dissolved throughout the simulation. The interplay of mineral dissolution and precipitation dynamically alters both pH and porosity. Anorthite is not the sole source of Ca²⁺; minerals such as dolomite and limestone can also readily contribute to Ca²⁺ availability, depending on the rock’s mineral composition. A localized pH decrease is observed along the CO₂ migration pathway. Porosity slightly decreases in the near-well zone but increases in the structurally elevated areas. The proportion of structurally trapped CO₂ increases during the injection phase but decreases during the subsequent long-distance migration phase. Residual gas trapping exhibits an initial rise followed by a decline, driven by capillary pressure hysteresis. Overall, the mechanism of long-distance migration-assisted structural trapping significantly enhances the long-term security and effectiveness of CO₂ geological storage.