A novel LBM-DEM based pore-scale thermal-hydro-mechanical model for the fracture propagation process

Fracture propagation in rocks is a complex thermal-hydro-mechanical (THM) phenomenon present in geotechnics, such as enhanced geothermal systems, CO₂ sequestration, and shale gas exploitation. Numerical simulation is an essential way to study its mechanism. In this study, a pore-scale model combined with the lattice Boltzmann method (LBM) and the discrete element method (DEM) is developed, in which the comprehensive THM coupling phenomena are considered, consisting of convective heat transport, conjugate heat transfer, hydrodynamic force, and thermal strain. In addition, to couple the temperature and anisotropic thermal expansion of rock in LBM-DEM, a novel method based on the deformation of sphero-triangle particle is presented, where the deformation is calculated using the principle of minimum potential energy. The main features of the proposed THM model are that it can accurately calculate the fluid flow in fractures and the temperature in both fractures and DEM particles, and it takes full consideration of multiple anisotropic properties in rock. After validations, the THM fracturing mechanism is preliminarily investigated using the proposed model.