Influence of supercritical CO₂ on the mobility and desorption of trace elements from CO₂ storage rock sandstone and caprock shale in a potential CO₂ sequestration site in Taiwan

Excess carbon dioxide emission was considered as the most important cause of increased trend of global warming. Significant amounts of research were devoted to the reduction of CO₂ emission and CO₂ sequestration. Sequestration of CO₂ in empty oil reservoirs was considered as one of the most promising options. However, the effects of metal release and mobility as a result of CO₂ injection were not studied in detail, particularly under super-critical CO₂ (scCO₂) conditions. In this study, the release of selected metals immersed in distilled water for varying amounts of time in the absence and presence of scCO₂ was assessed in simulated conditions at 90°C and 24 MPa. Significant increases in dissolution of Fe, Sr, and Ba by 3, 8, and 24 times were found when the storage rock sandstone or caprock shale was immersed in DI water for different time period. However, in the presence of scCO₂, the dissolution of these metals was reduced by 80% for Fe, suggesting permanent sequestration of scCO₂ into carbonate minerals. The trend in changes of pore water chemistry in the sandstone and shale after being immersed in DI water showed dissolution of Sr-bearing mineral and precipitation of Ba-bearing mineral.