An equivalent thermo-hydro-mechanical model for gas migration in saturated rocks

Gas transport process in saturated rocks is gaining increasing attention in the environmental/energy geomechanical engineering fields, e.g., shale gas exploitation, carbon dioxide sequestration and nuclear waste disposal, etc., as it is closely associated with gas production rate, sealing capability of caprocks. To investigate gas migration behavior through saturated rocks which induces microcracking inside the material, an equivalent thermo-hydro-mechanical (THM) model is developed that considers coupled behavior of fractures. The fractured rock material is considered as the equivalent continuum, which consists of isotropic porous matrix and parallel fracture set. The mathematical formulations are constructed within the thermodynamic framework, where the THM constitutive relations are proposed. Compared to the model without considering fracture behavior, the equivalent model improves the calculation accuracy of about 60% against laboratory experiments (e.g., observed gas flow rate), which proves the model capability. Furthermore, the sensitivity analysis shows that highlypressurized gas induced microcracking has significant influence on the coupled process, which greatly contributes to the observed gas flow phenomenon.