fracture network modeling results for GCA submission

Chemical weathering in fractured bedrocks will dissolve minerals and change the fracture geometry, leading to the re-distribution of water flow paths. This study investigated the dynamic coupling and feedback between mineral dissolution and flow re-distribution, and its effects on mineral dissolution rates and rate scaling. A fracture network model with a capability of simulating coupled reactions and transport in individual fractures was developed that can simulate the dynamic changes of fracture aperture, flow field, and mineral dissolution in complex fracture network. Simulation results indicate that mineral dissolution rates increase significantly with increasing hydraulic gradient, fracture aperture size, and fracture network connectivity under transport-limited conditions. The dynamic feedback between mineral dissolution rate and flow path re-distribution strongly depends on the type of flow boundary conditions. When transport limits the weathering, the weathering rate increases with increasing flow velocity, showing positive feedback between dissolution rate and flow velocity under constant hydraulic gradient conditions. The feedback, however, becomes negative under constant flow flux conditions due to the effect of flux-redistribution on the overall dissolution rate. Under mixed hydraulic gradient and flow flux boundary conditions that are common with the progress of weathering process, the feedback is initially positive, and then gradually changes to negative. The overall weathering rate in a fracture-network can be effectively scaled using Da number when there is no dynamic feedback between the dissolution rate and transport. However, in presence of the dynamic feedback, the Da-based scaling approach has to be corrected to account for the feedback-induced changes of physical heterogeneity and flow flux redistribution.