Discrete fracture network modelling of multiphysics processes in fractured media for geoenergy applications

Abstract

Fractures such as joints and faults are prevalent discontinuity features in the Earth’s crust, forming hierarchical networks in the subsurface and controlling the bulk behaviour of geological media. They play an important role in various multiphysical processes such as stress transfer, pressure diffusion, heat transport, earthquake generation, wave scattering, and chemical dissolution, which are crucial for many geoenergy applications ranging from geothermal energy exploitation and critical mineral extraction to nuclear waste disposal and underground hydrogen storage. Thus, it is of central importance to advance our capability of realistically representing these ubiquitous discontinuity features and further accurately modelling the associated seismo-thermo-hydro-mechanical processes. Over the past years, I have established a powerful fractured media simulation platform based on the discrete fracture network concept to simulate coupled multiphysical processes in fractured rocks. The model can explicitly represent the distribution of a large number of fractures in both 2D and 3D space as well as accurately compute their multiphysical responses/interactions over both space and time domains. No a priori assumption about the representative elementary volume is needed, rendering this approach as an appropriate tool to study hierarchical fractured rocks that may have no characteristic length scale. Using this modelling paradigm, diverse macroscopic phenomena in fractured media can be captured as emergent properties physically arising from the collective behaviour of numerous existing/growing fractures and interacting rock blocks. This multiphysics modelling framework can serve as a useful tool to bridge experimentally-established constitutive relationships of fracture/rock samples at the laboratory scale to phenomenologically-observed macroscopic properties of fractured geological formations at the site scale. A series of case studies are presented, where high-fidelity multiphysics simulations are combined with high-quality laboratory measurements and/or high-resolution field observations to address different geoenergy-related problems. The research findings and insights obtained have important implications for understanding and predicting the behaviour of fractured rocks for safe and sustainable geoenergy development.