Fluid flow and connectivity in fractured rock

Abstract

A numerical simulation using the boundary integral element method is used to solve fluid flow through a network of discrete fractures. The fracture network is composed of three orthogonal fracture sets, with fracture length, density, and location characterized by appropriate probability distributions. Emphasis is placed on understanding how fracture connectivity influences fluid flow within a network of fractures. Based on the percolation process, a three-dimensional discrete fracture model has been developed to investigate the effect of the percolation factor and the percolation frequency on connectivity and flowrate. The numerical model results indicate that there exists a sharp threshold flowrate for the case of constant mean fracture length and varying fracture volume density as well as for the case of constant fracture volume density and varying mean fracture length. The values of percolation threshold and critical percolation frequency are predicted to be approximately 1.1 and 0.35, respectively, for circular fractures. The results also indicate that an increase in the percolation factor increases the degree of interconnection and, thus, increases the flowrate of a fracture network.