Geochemical Trapping Efficiency of H2S and CO2 in Saline Aquifers: Individual vs. Co-Injection Strategies

This study models the geochemical trapping of single CO2, H2S, and their mixture in a Cretaceous carbonate-clastic aquifer from the Middle East. The system simulates injection into a high-salinity brine (220 g/L) equilibrated with siderite, calcite, albite, chlorite, and quartz at reservoir conditions.

Key results show distinct mineral reactions: H2S completely transforms siderite to pyrite, while CO2 drives the dissolution of albite and chlorite, producing kaolinite, silica, and dolomite. The pH evolution occurs in three stages, each buffered by specific minerals, with sharp transitions at critical gas/rock ratios, when the corresponding buffering mineral becomes fully consumed.

Solubility trapping of the gas mixture is 7% lower than the additive sum of pure gases, reflecting their non-ideal behavior. However, co-injection enhances long-term mineral trapping by 42% through complementary reactions: CO2 sequesters via Mg/Ca silicates and carbonates, while H2S reacts with Fe-rich phases.

The study concludes that co-injection in Fe- and Mg-rich formations optimizes storage by leveraging synergistic mineral reactions, despite a slightly reduced solubility trapping. These findings support targeted deployment of acid gas storage in polymineralic aquifers, with implications for long-term sequestration strategies in the Middle East and analogous basins.