Compositional simulation of the synergistic impact of impurities and geochemical reactions on the efficiency of impure CO₂ sequestration at a Korean CCS site

Carbon capture and storage involves CO2 injection into geological structures to mitigate industrial CO2 emissions. CO2 capture processing can lead to inclusion of impurities such as H2S and CH4, which alter the properties of CO2, influencing geochemical reactions in reservoirs and CO2 storage efficiency. In this study, the impact of impurities and geochemical reactions on CO₂ storage efficiency was analyzed using reservoir simulation. The impurities altered the properties of CO₂ depending on both their type and concentration. CO2 mixture density decreased by up to 74.8 % with 20 % CH4 impurity. Also, the concentrations of aqueous hydrogen ions and metal ions varied compared to those in pure CO2 injection scenarios. As the results, geochemical reactions with CO₂ mixtures altered the pore volume by <1 %. These findings indicate that impurities influence the gas storage capacity differently: H2S impurities increase the storage capacity, while CH4 impurities reduce it. The differences in CO2 storage capacity become more pronounced as the impurity concentrations rise. Specifically, at 20 % impurity, H2S increased CO2 storage capacity by 1.44 %, CH4 reduced it by 6.68 %. Impurities modify CO2 properties, and the resulting decrease in CO2 density and volume percentage negatively affects the residual trapping efficiency, particularly when CH4 is included. Overall, these findings demonstrate that impure CO2 injection influences geochemical reactions and CO2 properties, with combined effects on storage efficiency in saline aquifers.