Dissolution trapping is one of the primary mechanisms of carbon dioxide (CO2) storage in a geological formation. In this study, a numerical model was used to examine the impacts of single and multiple fractures on the transport of dissolved CO2 plumes in various geological settings. The effects of the fracture angle, fracture-matrix permeability ratio, fracture intersection, and matrix heterogeneity on density-driven CO2 convection were systematically investigated. The fractures were found to play time-varying roles in both homogeneous and heterogeneous media by serving as preferential pathways for both CO2-rich plumes (fingers) and CO2-free water. The competition between the enhancement of convective mixing and the inhibition of finger growth by the upward flow of freshwater generated a complex flow system. The interaction between the strong upward flow of freshwater through the fractures and the falling CO2-rich fingers through the porous matrix induced a positive feedback, resulting in accelerated domain-scale circulation and CO2 dissolution. While the CO2-rich fingers grew relatively evenly at the top boundary in the homogeneous media, they selectively developed through the high permeable zones in the heterogeneous media. Compared with homogeneous media, the heterogeneous media preserving fractures particularly generated a more dynamic fracture-matrix mass transfer, resulting in more rapid CO2 dissolution. The findings of this study were extended to examine the effects of fracture connectivity on the enhancement of CO2 transport and dissolution on a field scale.
All Science Journal Classification (ASJC) codes
- Water Science and Technology