A Coupled Thermo-Mechanical Model Based on TOUGH-FEMM for Simulating Thermal Cracking in Rocks

In this paper, the algorithm of the hybrid finite-element meshfree method (FEMM) is first used to simulate three-dimensional thermal cracking in the context of the TOUGH-FEMM simulator. The TOUGH-FEMM simulator combines two existing codes sequentially, TOUGH2 and FEMM. The temperature distribution of the system is analyzed using TOUGH2, which is able to solve coupled problems of nonisothermal, multiphase, multicomponent fluid flow in complex geological systems. Recently, hydro-mechanical models based on FEMM and TOUGH2 have been coupled together for the analysis of hydraulic fracturing in fractured rock. The thermal stress, rock deformation and cracking induced by temperature change are modeled by FEMM. The finite element meshfree method (FEMM) is presented to model mechanical deformation and discontinuities. With the concept of partition of unity, the accuracy of global approximation can be improved without adding extra degrees of freedom (DOF), and various local approximation functions can be used for modeling strong or weak discontinuities. Linear elastic fracture mechanics (LEFM) with mixed-mode stress intensity factors are employed to determine the initiation and direction of crack propagation. Several benchmark examples, including stress intensity factor calculation, steady-state heat conduction, transient heat conduction, and deformation induced by thermal stress, are provided to validate TOUGH-FEMM in dealing with thermo-mechanical problems with cracking. Additionally, a numerical experiment of crack propagation induced by thermal stress is also given, and its results are compared with the experimental results. The simulation results agree well with the analytical solutions or experimental results, indicating that the proposed approach is effective for thermal cracking simulation.