Coupling effects of native H2S and different co-injected impurities on CO2 sequestration in layered saline aquifers

Abstract Impurity effects are an intricate issue in CO2 geological storage, involving both pre-dissolved impurities in the geological medium and co-injected impurities. Numerical simulations were carried out in this study to investigate the coupling effects of pre-dissolved H2S and different co-injected impurities (H2S, CH4 and N2) on CO2 sequestration in layered sour saline aquifers. The native H2S would be exsolved out of the sour formation brine and pushed ahead by the injected plume. The exsolved H2S reduced the concentrations of the injected gases at the two-phase interface. Particularly, when H2S was co-injected with CO2 into the sour saline aquifers, both dissolved CO2 inventory and dissolved CO2 ratio would reduce by nearly half compared with that in the regular saline aquifers without native H2S. It was observed that the decrease of the dissolved CO2 ratio due to the existence of the native H2S was much compensated by the co-injection of CH4 or N2. Nevertheless, the native impurity seemed to have more profound effects on CO2 sequestration than the co-injected impurities. The results should be considered in selecting appropriate sequestration sites and establishing risk assessment strategies.