Geological Carbon Storage in Saline Aquifers: Factors Governing Residual & Solubility Trapping

Abstract Carbon dioxide (CO2) storage in saline aquifers holds offers a promising solution for mitigating greenhouse gas emissions. Deep saline formations are considered optimal for CO2 storage given their substantial capacity. This study examines the research on the two primary trapping mechanisms, solubility trapping and residual trapping, which are essential for the secure and stable containment of injected CO2 within saline aquifers. Solubility trapping and residual trapping are rapid and pervasive mechanisms in CO2 storage within saline aquifers. A simulation-assisted sensitivity analysis was performed to investigate how various reservoir characteristics, fluid transport properties, and engineering parameters affect the spatiotemporal evolution and interactions of these two trapping mechanisms under diverse geological, fluid, and engineering conditions. Residual trapping becomes the dominant mechanism for long-term CO2 storage, with volumes generally doubling those of solubility trapping after 50 years of monitoring, even though solubility trapping initially surpasses residual trapping at the end of the injection phase. Water imbibition post-injection notably enhances residual trapping, which more than doubles with an injection rate increase from 1 MMT/y to 10 MMT/y. Initially, higher porosity aquifers have high solubility trapping, but this shifts to significant residual trapping as injection continues and ends. Temperature significantly impacts CO2 residual trapping, with a six-fold increase observed at 40°C after injection. Thicker aquifers exhibit pronounced post-injection residual trapping increases, contrasting with stable solubility trapping levels. High-pressure aquifers maintain higher levels of residual trapping, especially noticeable 15 years post injection. Aquifers with high pressure, high permeability, high anisotropy and low temperature show a drastic increase in residual trapping after injection concludes, highlighting their important role in long-term, stable CO2 storage.