Impact of connectivity characteristics on the permeability of three-dimensional fracture networks

• A rapid 3D Fracture Network Modeling and Seepage Simulation Approach was developed. • Key Factors Affecting Connectivity and Permeability of 3D Fracture Networks were demonstrated. • Quantitative Relationships Between Connectivity and Permeability were established A program for rapid modelling, connectivity evaluation, and seepage simulation of a three-dimensional fracture network was developed based on COMSOL using MATLAB to accurately evaluate the seepage characteristics of a rock fracture network. A Monte Carlo algorithm was used to generate the fracture geometry parameters, and the Euler angle was introduced to establish a three-dimensional fracture model. The bounding box method was used to calculate the fracture network connectivity, and the Darcy module was used to simulate the seepage process. The fracture density, dip direction, dip angle, and length were selected as the experimental factors. Orthogonal numerical experiments were conducted to explore the primary factors controlling the connectivity, permeability, and permeability anisotropy of a three-dimensional fracture network. The results show that connectivity and permeability were primarily affected by the fracture density, length, and dip direction. Moreover, the permeability anisotropy was primarily affected by the fracture dip direction. The quantitative relationship among the connectivity index, permeability coefficient, and permeability anisotropy coefficient was determined based on numerical analysis. The results show that the permeability coefficients in various directions increased with the connectivity index and gradually stabilized. The permeability anisotropy weakened rapidly with increasing connectivity. It stabilized when the connectivity index exceeded 15. The research results have positive significance for revealing the seepage mechanism of complex three-dimensional fracture networks and for preventing and controlling water disasters in fractured rock masses.