REACTIVE TRANSPORT IN DISCRETE FRACTURE NETWORKS

We analyze reactive flow and transport behavior in discrete fracture networks with a focus on how reaction-induced changes in physical and chemical properties affect connectivity and thus overall flow capacity within the network. As an example of a relevant geochemical process, we consider the mitigation of atmospheric CO₂ via carbonate mineral sequestration and used two-dimensional reactive flow and transport simulations to analyze the impacts on a natural discrete fracture network. We conclude that reaction-induced changes in discrete fracture segment properties can substantially alter the connectivity of the system. We see this occur where fluid mixing at a fracture intersection results in carbonate mineral precipitation in one fracture segment while leaving other segments nearly unaffected. The reactive transport processes taking place in the fracture network present the possibility of wholesale reorganization of the flow system due to changes in connectivity. In a second set of simulations, we considered the problem of natural weathering of fractured mafic and ultramafic rocks in the partially saturated Earth’s critical zone (CZ) and how this could contribute to the mitigation of atmospheric CO₂. To the highly local and selective dissolution and precipitation occurring in the fractures, we add the effect of drainage within the fracture network that contributes to a heterogeneous liquid saturation distribution, and thus to highly variable reactive gas diffusion rates. In the partially saturated fractured CZ, the system is largely diffusion-controlled as the precipitation of carbonate phases depends on the ability of reactive gases to diffuse through the fracture network system.