Constraining the effectiveness of inherent tracers of captured CO₂ for tracing CO₂ leakage: Demonstration in a controlled release site

Geological storage of carbon dioxide (CO₂) is an integral component of cost-effective greenhouse gas emissions reduction scenarios. However, a robust monitoring regime is necessary for public and regulatory assurance that any leakage from a storage site can be detected. Here, we present the results from a controlled CO₂ release experiment undertaken at the K-COSEM test site (South Korea) with the aim of demonstrating the effectiveness of the inherent tracer fingerprints (noble gases, δ¹³C) in monitoring CO₂ leakage. Following injection of 396 kg CO_2(g) into a shallow aquifer, gas release was monitored for 2 months in gas/water phases in and above the injection zone. The injection event resulted in negative concentration changes of the dissolved gases, attributed to the stripping action of the depleted CO₂. Measured fingerprints from inherent noble gases successfully identified solubility-trapping of the injected CO₂ within the shallow aquifer. The δ¹³C within the shallow aquifer could not resolve the level of gas trapping, due to the interaction with heterogeneous carbonate sources in the shallow aquifer. The time-series monitoring of δ¹³C_DIC and dissolved gases detected the stripping action of injected CO_2(g), which can provide an early warning of CO₂ arrival. This study highlights that inherent noble gases can effectively trace the upwardly migrating and fate of CO₂ within a shallow aquifer.