Fluid flow and mixing in rough-walled fracture intersections

[1] Fracture intersections play a basic role in contaminant transport through fracture networks because they allow different fluids to mix and disperse along the flow paths. We use experimental and numerical methods to understand and improve predictions of these phenomena. Laboratory experiments of mixing between two miscible fluids were performed within an artificial, rough-walled fracture intersection made of textured glass. We also develop a numerical model of mixing based on local application of streamline routing within the irregular aperture distribution of the intersection. This model shows good agreement with the laboratory experiments, both in the amount of average mixing and in the spatial distribution of dye streamlines. The numerical model is used to generalize our results based on aperture statistics, and shows that mixing is significantly affected by how well apertures correlate across the intersection, especially as fractures are closed. We conclude that flow channelization through rough-walled intersecting fractures significantly enhances physical mixing compared to intersecting parallel plates. Relative to transport through parallel plate aperture networks, surface roughness may reduce solute dilution and increase solute dispersion.