Effective method for identification of preferential flow paths in two-dimensional discrete fracture networks based on a flow resistance method

Abstract

Preferential flow is usually characterized by rapid and concentrated fluid flow in fractured geological media, and preferential flow paths (PFP) dominate the fluid flux and velocity. Therefore, the identification of PFP is significant for quantitatively characterizing fluid flow in fractured media, especially in discrete fracture networks (DFN). The traditional methods of identifying PFP need to solve groundwater flow models; however, such models are limited by complex groundwater-related problems, the need for detailed hydrogeological survey data, and a high computational workload. In this study, a graph-theory-based flow resistance method is proposed for identifying the PFP in DFN. The method uses the flow resistance of fracture trace lines to identify the corresponding minimum resistance path. The flow resistance is defined as the weighted factor between the adjacent nodes in the fracture network based on the formula of the modified cubic law, and then the Dijkstra algorithm is used to determine the minimum resistance path. The flow resistance method is verified through case analysis by numerical simulation with COMSOL Multiphysics. The results show that the fluid tends to flow along the path with less flow resistance, and the minimum resistance path is essentially consistent with the preferential flow path. The method only needs to extract flow resistance values from the geometric parameters of the fractures, and then quickly analyze the fracture-network pathways to identify the preferential flow path. The method provides an effective and efficient way of identifying the preferential flow path without resorting to complex groundwater flow models to find the solution.