1 Introduction Subsurface modeling of flow for geologic fracture networks has numerous critical applications including contaminant transport, hydrocarbon extraction, and C O 2 ${\mathrm{C}\mathrm{O}}_{2}$ sequestration (Hyman, 2020; Kang et al., 2020). It is a challenging problem in geophysics, because not only do simulations typically require solving large-scale systems of linear equations, but in many cases a large number of simulations are needed to quantify uncertainty.
