EXPERIMENTAL EVIDENCE FOR PARTIAL FRACTURE SEALING DURING scCO2-H2O FLOW THROUGH FRACTURED EAGLE FORD SHALE (Invited Presentation)

Geologic sequestration provides a potential method to isolate large amounts of anthropogenic CO₂ away from the atmosphere. However, a potentially serious limitation to this approach is that it depends on the integrity of the caprock sealing CO₂ in the subsurface, as fractures in this seal may constitute a potentially significant leakage pathway. In order to determine whether interactions with the solution will change the fracture permeability, experiments have been conducted in which a scCO₂-water solution was flowed through a synthetically fractured sample of Eagle Ford shale at reservoir-like conditions. The results showed that, in parts of the core with pre-existing increased permeability, dissolution of the reactive mineral matrix (often calcite) tended to further increase the permeability, generating channelization and specific flow paths along the fracture plane. In other parts of the core, other cations (primarily ferrous iron) reacted with both the aqueous carbonate in the solution and calcium liberated from calcite dissolution in the matrix to precipitate mixed-carbonate mineral phases (Ca-siderite) that sealed the fracture. Thus, the results of these experiments showed that fractured caprocks containing small fractions of reactive, non-calcite minerals have the potential either to seal themselves in the presence of a scCO₂-water fluid, improving the chances of successful geologic CO₂ sequestration or, in the absence of such phases, to develop enhanced permeability.