Simulating natural variations of CO2 gas concentration in the vadose zone wells and a simple application for predicting CO2 leakage

Abstract:

To mitigate the climate changes, the geologic carbon sequestration has been proposed as an appropriated technique by injecting CO₂ into the safety geologic layers. However, because there are unrecognized risks, detecting the signal of potential CO₂ leaking is one of the important rules and especially CO₂ gas monitoring near the surface is critical because it is not only the last detection boundary of leaked CO₂ but also the area closest zone to the surface. Thus, to understand the impact of CO₂ leakage on the surface environment and to develop a CO₂ monitoring technique that is available near the surface, the controlled CO₂ release (CCR) test was planned in the K-COSEM study area. However, the background concentration of CO₂ gas was high with over 12,000 ppm (vol./ vol.) before the test and the daily variations of CO₂ gas concentration were very significantly varied according to day and night. Thus, this study intended to simulate the natural variations in CO₂ gas concentration and to reproduce the pattern of CO₂ gas concentration when performing field tests to address this problem by using a numerical model. The result of the numerical model provided the good matched signals and magnitude of gas concentrations with the real-time observed CO₂ gas concentration. It is expected that these primary results of the model will provide useful data for separating CO₂ gas leakage signals mixed with the naturally occurring CO₂ gas, as well as predicting a detectable signal during the CCR test later using the gas monitoring wells near the surface.

Acknowledgment

Financial support was provided by the “R&D Project on Environmental Management of Geologic CO₂ Storage” from the KEITI (Project Number: 2018001810002).