Long-distance migration assisted structural trapping during CO2 storage in offshore basin

Abstract

Long-distance migration assisted structural trapping is an optimal structure for offshore geological carbon storage. Qualitative analysis of carbon trapping efficiency was investigated using CMG software, considering aqueous solubility and geochemistry reactions. CO₂ migration, mineral mole changes, geochemical induced PH and porosity variations and carbon storage contribution were also examined. CO₂ concentrates near the injection wells and migrates upward along the slightly dipping strata the disparity in density between CO₂ and aqueous. After CO₂ injection wells shut in, CO₂ plume continues to migrate upward along the slightly dipping strata, transporting towards the upper anticline. A large amount of CO₂ is still being trapped in the dipping strata due to wettability and capillary effects. Being dissolved CO₂ into saline aquifer forming H+, the dissolution of anorthite provided Ca₂₊ and Al₃₊ required for the precipitation of calcite and kaolinite over time. Calcite is initially in the dissolved state, gradually converting to the state of precipitation. Dynamics of mineral dissolution and precipitation influence PH and porosity changes. There is a PH decrease area during CO₂ migration. The porosity particularly near the wellbores showed a slightly decrease due to the deposition of previously dissolved minerals. The porosity around the top anticline experienced a substantial increase due to mineral dissolution in the formation. The proportion of structural trapping is continuously increasing during the CO₂ injection period, and is decreasing during CO₂ long-distance migration stage. Residual gas trapping displays the initially increasing and then decreasing trend due to wettability and capillary effects throughout the CO₂ migration period. It is observed that long-distance migration assisted structural trapping enhances the long-term security of CO₂ storage.