CT 3D reconstruction and analysis of mesoscale damage and permeability evolution in salt rock under thermo-mechanical coupling

The effects of thermo-mechanical coupling on the mesoscale damage and seepage evolution mechanisms in salt rock remain insufficiently understood. To simulate high-temperature underground storage conditions, triaxial loading and permeability experiments were conducted on thermally treated salt rock specimens. Detailed pore-fracture networks and equivalent pore network models were conducted using X-ray CT scanning and 3D reconstruction techniques to capture structural changes. Both qualitative and quantitative analyses revealed that temperature and confining pressure significantly affect the development of the pore-fracture network. Pore counts decrease with increasing radius, particularly in the 0–100 μm range, while pores larger than 600 μm dominate volumetrically. Elevated confining pressure suppresses pore-fracture expansion, thereby reducing porosity, connected porosity, fractal dimension, and permeability. In contrast, high temperatures under lower confining pressures increase these parameters. At high confining pressures, increasing temperatures further reduce these properties. A 3D bivariate linear function was developed to characterise the coupled effects of temperature and pressure on the evolution of porosity, fractal dimension, and permeability. Additional analysis revealed statistically significant correlations among these factors, emphasising that pore-fracture connectivity governs seepage pressure, flow rate, and gas migration. These findings provide essential theoretical insights to assessing the long-term safety and sealing performance of salt cavern gas storage.