Convective Dissolution Analysis of Long-term Storage of Acid Gas in Saline Aquifers

Abstract

Geological storage of acid gas in subsurface formations is considered one of viable strategies to reduce emissions of greenhouse gases into the atmosphere. During acid gas such as CO2-H2S injected into saline aquifers, the density difference between the acid gas–rich brine and the brine may induce an unstable hydrodynamic state favorable for natural convection. The dissolution-diffusion-convection (DDC) process of acid gas in brine is numerically simulated. We focus on the effect of acid gas composition on DDC process and find that the dissolved H2S has an inhibitive effect on the convective mixing in the brine phase, the criterion for the diffusive-convective transition and the corresponding critical acid gas composition are illustrated and clarified. The apparent average cumulative amount of dissolved multi-component acid gas in the saline aquifer is also presented. It is decided by the solubility of the acid gas and the density-driven convective mixing, and either of the two affecting factors may become the dominate one due to the variation of acid gas composition with different geological conditions. This implies that for the long-term acid gas storage, the convection effect and the solubility of the acid gas should be paid more attention to reduce the risk of acid gas storage at subsurface formations. The results provide insights into the optimal composition of acid gas for storage at subsurface formations, and facilitate the screening of candidate sites for the geological sequestration.