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 m(3)) 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.