A Pore–Fracture Permeability Model for Rocks, Considering Temperature-Induced Damage and Creep Deformation

Deep rock engineering is affected by coupled thermal, mechanical, and hydraulic processes, and the accurate prediction of permeability evolution is important for underground energy development and engineering safety. Existing permeability models often consider either temperature or creep, but the coupled effect of temperature and creep on permeability evolution remains insufficiently described. In this study, a coupled temperature–creep–permeability model is proposed by decomposing the total permeability into pore permeability and fracture permeability. Temperature-induced damage is defined based on elastic modulus degradation, and creep damage is mainly introduced for the accelerated creep stage. Pore permeability is described using the Kozeny–Carman (K-C) equation, while fracture permeability is described using the cubic law with an empirical transition function for fracture aperture increment. The model is verified using published experimental data at different levels, including temperature-dependent creep tests, creep-permeability tests at room temperature, and creep-permeability tests under different temperatures. The results show that permeability evolution during creep is controlled by the competition between pore compaction and fracture contribution. During the primary and secondary creep stages, pore compaction dominates and permeability decreases. In the accelerated creep stage, fracture aperture and connectivity increase rapidly, leading to permeability recovery or a sharp increase. The proposed model captures delayed permeability recovery during creep and describes the transition from pore-dominated to fracture-dominated permeability evolution. It provides a useful framework for analyzing the permeability evolution of rocks under coupled temperature and creep conditions.