Simulation of thermal cracking in anisotropic shale formations using the combined finite-discrete element method

Thermal cracking widely exists in many geoengineering practices (e.g., geothermal exploitation, nuclear waste disposal and CO2 sequestration), and highly affects the efficiency and safety of the engineering applications. Some of these projects are constructed in shale formations with anisotropic thermal/mechanical properties, which affect the thermal cracking behavior. It is therefore imperative to understand and correctly model the thermo-mechanical (TM) coupling behavior of anisotropic shale rocks for better and safer designs. In this paper, a novel anisotropic TM coupled model, named as Y-TManiso, is proposed to study the heat transfer and thermal cracking process in the anisotropic shale formations based on the combined finite-discrete element method (FDEM). In particular, some inherent characteristics of the shale formations (e.g., material anisotropy, preexisting discontinuities and multiple layers) can be well handled in this model. The performance of this model on temperature field calculation and thermal cracking modelling are confirmed by numerical tests with analytical or experimental solutions. An application test concerned with the thermal cracking in a shale formation is investigated. The results show that the proposed Y-TManiso has implications in the application and design of TM coupling problems in anisotropic shale formations.