The efficient exploitation of hot dry rock (HDR) geothermal resources critically depends on the enhancement of reservoir permeability. Thermal stimulation through low-temperature fluid injection represents a promising reservoir stimulation technique. However, the thermal-induced damage mechanisms in high-temperature rocks under different cooling methods remain unclear, limiting the optimization of permeability enhancement strategies. This study experimentally investigates the microstructural damage characteristics of granite subjected to different cooling methods (air cooling, liquid nitrogen (LN 2 ) cooling, and water cooling) after heat treatment at 300–600°C. X-ray computed tomography (CT) and scanning electron microscopy (SEM) were employed to quantitatively characterize the pore structure evolution. The results demonstrate that water cooling significantly increases porosity from 5.88% to 11.67% over the 300–600°C range, with 10–20 μm pores constituting 40.0% of the total porosity at 600°C and forming interconnected three-dimensional fracture networks. A secondary yet distinct increase in porosity is also observed under LN 2 cooling (from 2.02% to 9.41%). Air cooling yields the weakest improvement (1.60%→5.78%). Consequently, water cooling emerges as the optimal approach for enhanced geothermal system (EGS) reservoir stimulation, owing to its ability to generate uniform damage networks and irreversible permeability enhancement. This study provides an experimental foundation for permeability enhancement technologies in deep geothermal resource development and proposes a hybrid stimulation strategy combining cyclic water cooling with hydraulic fracturing. • Thermal stimulation efficacy: Water cooling (300–600°C) induces the most significant porosity increase in granite (5.88%→11.67%), outperforming liquid nitrogen and air cooling. • Pore network optimization: Water cooling generates interconnected 10–20 μm pores (40% of total porosity at 600°C) and 3D fracture networks, ideal for Enhanced geothermal systems permeability enhancement. • Mechanistic insight: Water cooling’s uniform microstructural damage and irreversible permeability enhancement make it optimal for hot dry rock reservoir stimulation.
Wang et al. (Sun,) studied this question.