Fluid flow partitioning between fractures and a permeable rock matrix

Field data‐based finite‐element simulations of flow partitioning between fractures and a permeable rock matrix reveal critical fracture aperture values that mark the transition from matrix to fracture dominated flow. For matrix permeabilities of 0.00 1–1 D, the matrix either dominates or contributes significantly to the total flow. The percentage of the flow‐normal cross‐section that is occupied by fractures, A f , strongly influences the fracture‐matrix permeability ratio, above which fractures will dominate flow. This ratio is 10 2 –10 4 for A f = 10 −4 –10 −3 (mean = 5 × 10 −3 ), but also depends on the proportion of fractures which fully penetrate the representative elementary volume. Fluid‐velocity spectra for the fractured rock have three important characteristics: (1) Darcy velocity is only poorly correlated with permeability, (2) flow velocities have characteristic values, even if fracture‐length frequency relations are self similar, and (3) fracture and matrix velocities overlap.