Numerical Estimation and Interpolation of Released CO2 Fluxes and Concentration at Vadose Zone with Controlled-injection

Directly storing CO₂ in the geologically safe underground formations is considered to be an effective way to reduce CO₂ concentration in atmosphere. However, CO₂ can be leaked through faults or abandoned wells from the targeted storage formations. When abundant CO₂ is leaked to the surface, elevated CO₂ concentration can significantly damage the groundwater and ecological system. Released CO₂ to the surface could be affected by various factors such as soil moisture, rainfall, atmospheric pressure and temperature. Therefore, the purpose of the research is to simulate CO₂ transport through the unsaturated zone and investigate various external forces affecting CO₂ fluxes and concentration.

In Eumseong, Repulic of Korea, the controlled CO₂ release site was developed by the Korea CO₂ Storage Environmental Management (K-COSEM) Research Center. CO₂ was released from the 50 m PVC pipe buried at 2.5 m-depth unsaturated zone and CO₂ fluxes and concentration were monitored in addition to extra parameters such as weather data, soil moisture, and soil temperature. The HYDRUS-1D simulation package was utilized with SOILCO2 and predicted CO₂ fluxes and concentration in the unsaturated zone. Furthermore, simulated surface CO₂ fluxes were compared with field-observed data to validate the CO₂ transport model and evaluate CO₂ leakage process more precisely.

Our research concluded that, without CO₂ release, the Hydrus-SOILCO2 model predicted the variation in soil CO₂ natural background fluxes at surface precisely. Nevertheless, the model requires additional assumption to simulate CO₂ fluxes during the release test. Both measured and simulated data indicated that major external factors controlling the surface CO₂ fluxes were atmospheric temperature and precipitation. In addition, to improve the simulated prediction of CO₂ fluxes, biological and soil hydraulic factors must be considered.