Temperature-Dependent Permeability Model of Granite After Thermal Treatment Based on Energy Dissipation Theory and Fractal Theory

For many years, the relationship between permeability and temperature of rocks after high temperature was described by a classical exponential model based on thermos-elastic theory. However, recent experiments have shown that the thermal damage incurred by rocks after high temperatures is irreversible plastic damage. This paper aims to propose a new approach for creating a temperature-dependent permeability model that considers this irreversibility of thermal damage. To achieve this, energy dissipation theory and fractal theory were used to develop a model that describes the irreversible thermal damage evolution and temperature-dependent permeability of rocks after high temperature. The new model was verified through CT and gas permeability experiments. The results indicate that: 1. in the temperature range of 200 similar to 800 celcius, thermal damage develops into an irreversible plastic state due to energy dissipation; 2. the thermal damage of granite exhibits a porous structure at 50 similar to 600 celcius, which turns into a mixed pore-fracture structure at 600 similar to 800 celcius; 3. the granite matrix followed fractal distribution patterns after thermal treatment, demonstrating a quadratic correlation with temperature; 4. based on the fractal evolution of granite after high temperature, the temperature permeability model is derived. The new model is compared to the two commonly used models. The new model showed smaller fitting relative errors, and produced a better representation of the causes of plastic thermal damage, offering a promising solution for similar problems.