Application of natural and artificial tracers to constrain CO₂ leakage and degassing in the K-COSEM site, South Korea

Although Carbon Capture and Storage (CCS)has been demonstrated successfully on many occasions, the potential leakage of deep sequestrated CO₂ into shallow groundwater remains a concern. To address this, an artificial injection experiment was performed at the K-COSEM test site in Eumseong, South Korea, that involved the release of CO₂–infused water (16.9 kg of CO₂ in 5 m³)containing He and Kr tracers into a shallow, heterogeneous, weathered-granite aquifer. The initial CO₂–fluid was slightly oversaturated at the subsurface injection point, and thus the plume was expected to initially degas CO₂ before equilibrating at in-situ conditions. Monitoring of carbonate system parameters in nearby observation wells helped define the evolution of the injected fluids, while the noble gas tracers were used to clearly define the physical behavior of the CO₂ plume (including an estimate of degassed CO₂ equal to 0.9–3.1%). This study demonstrates the potential use of noble gases for monitoring CO₂ leakage in shallow aquifers, constraining mass balance and phase changes of leaking fluids, and better understanding local flow pathways. Furthermore, breakthrough of noble gases in this study was different from some previous experiments, suggesting that monitoring efficiency of these tracers may depend on leakage and site conditions.