To verify CanFracEnv hydrological modeling, the code was used to conduct an analysis of water flow into an open pit in fractured rock. The domain was discretized into continuum elements and several fracture-distribution models were applied to the domain grid (one fracture distribution at a time) to examine their effects on water flow into the open pit.
Appendix A of the publication “Fracture-Based Continuum Modeling of Coupled Geomechanical-Hydrological Processes in Numerical Simulation of Hydraulic Fracturing” (https://doi.org/10.1016/j.jrmge.2023.07.009) describes the verification analysis in detail.
The calculated history of water discharge into the open pit and magnitudes of the steady-state discharge show attributes that verify that (1) the model calculations represent fracture flow explicitly and (2) the calculated discharge manifests progressive relative contributions of matrix flow and fracture flow as fracture aperture decreases.
First, the results show the pit discharge is greatest with fracture models that produce the shortest flow paths to the open pit. The results show that fracture flow is dominant in the models, such that the calculated pit discharge follows a relationship consistent with the input fracture orientations, both for constant fracture orientations and statistical distribution of fracture orientations.
Second, steady-state conditions were attained in only approximately 10 min. after perturbation for models with constant fracture orientation and approximately 20 min. for models with statistical distribution of fracture orientations. This attribute of the results shows fracture flow was dominant and modeled explicitly. In contrast, a system based on modeling matrix flow (with or without fracture effects on transmissivity) would reach steady state in much longer time, as can be shown using the publication “Modeling Directional Water Flux in Fractured Rock” (https://doi.org/10.1007/978-3-031-00808-5_65).
Third, the steady state discharge into the open pit increases linearly with b^3 for b>~0.025 mm, where b is the fracture aperture. In contrast, for smaller fracture aperture (b<~0.025 mm), the discharge exceeds the linear relationship. The difference between the calculated discharge and the linear relationship can be explained as resulting from matrix flow. For b>~0.025 mm, fracture flow is dominant and the calculated discharge follows a relationship with fracture aperture consistent with fracture behavior. In contrast, the matrix-flow contribution increases relative to the fracture-flow contribution as the fracture aperture decreases below 0.025 mm.
Geological processes modeling (GPM) research Institute 