Seminar Seung-Wook Ha

The occurrence of gas in shallow subsurface environments is increasingly driven not only by natural processes but also by emerging subsurface technologies, including geological CO₂ storage, underground hydrogen storage, and hydrocarbon production. Shallow subsurface environments such as weathered soils/rocks commonly exhibit multiscale heterogeneity, including fracture traces that can strongly perturb flow and transport. This study investigates how open fractures embedded in porous media govern the spatiotemporal behavior of CO₂ under shallow, heterogeneous conditions.
We first conducted a field-scale controlled CO₂ release experiments under induced groundwater-flow conditions to monitor CO₂ behavior in a realistic shallow subsurface environment. Based on field observations indicating fractured porous domains as likely migration pathways, we then performed laboratory visualization experiments to directly observe CO₂ migration and dissolution in fractured porous media. Additional experiments systematically examined the combined effects of fracture orientation and background flow on CO₂ distribution.
Across field and laboratory scales, results show that open fractures can exert a dominant control on CO₂ behavior. Depending on their orientation relative to groundwater flow, fractures may function not only as preferential pathways but also as effective barriers, even when apertures are present. Moreover, the pathway–barrier behavior was further modulated by the background flow velocity. These findings are supported by high-resolution maps of gas-phase and dissolved CO₂ reconstructed through image-based analysis, providing intuitive and diagnostic signatures of fracture-controlled transport.

These results highlight the necessity of explicitly considering fracture traces in the shallow subsurface for effective gas monitoring, and this improved understanding is expected to enable more realistic predictions of gas behavior and support successful environmental management.