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 ~ 800 ℃, thermal damage develops into an irreversible plastic state due to energy dissipation; 2. the thermal damage of granite exhibits a porous structure at 50 ~ 600 ℃, which turns into a mixed pore-fracture structure at 600 ~ 800 ℃; 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. Highlights: The classical exponential model between temperature and permeability is based on thermos-elastic theory. But in this paper, the development of plastic irreversible thermal damage is explained by energy dissipation Fractal theory is used to describe the evolution of thermal damage quantitatively Based on the fractal expression of thermal damage, a new temperature-dependent permeability model is deduced The fractal expression of thermal damage and the new temperature-dependent permeability model are verified by meso-CT test and gas permeability test [ABSTRACT FROM AUTHOR]