Simulation of seepage and heat transfer in 3D fractured rock mass based on fracture continuum method

The main challenge of simulating the processes of seepage and heat transfer in fractured rock mass is the heterogeneity of rock mass at various scales. In order to balance the efficiency and accuracy of numerical simulation, the two-dimensional fracture continuum method is extended to a three-dimensional one. Based on the depth-first search algorithm, the effective fractures contributing to the permeability of rock blocks are collected. The block permeability tensor is obtained by considering the contribution of effective fractures and rock matrix. The finite element software COMSOL Multiphysics is integrated with Matlab to generate a three-dimensional fracture continuum model that contains multiple blocks with various permeabilities. The simulation results show that due to the combination between stochastic continuum model and discrete fracture model, the fracture continuum model can avoid the complexity of addressing fracture networks and consider the spatial variability of rock mass permeability, thus both the simulation efficiency and accuracy are balanced. As the order of magnitude for the ratio of rock matrix permeability to fracture permeability ranges from 10-4 to 10-6, the discharge calculation error of the effective fracture network model exceeds 5%.