Fractures in hot dry rock (HDR) reservoirs are the locations where heating fluid flows exchange heat with the HDR matrix. Cold shock with liquid nitrogen is one method for stimulating cracks. This study investigates the evolution law of fracture aperture under cold shock with liquid nitrogen. The real‐time high‐temperature triaxial servo control rock testing machine was used to conduct permeability experiments to examine the fracture aperture of single‐fracture granite during liquid nitrogen shock cycles at various temperatures. The effects of pore pressure, temperature, and shocking cycles on the fracture aperture are analyzed, and the difference in fracture aperture variation under liquid nitrogen cooling and natural cooling modes is compared. The results showed that (1) during liquid nitrogen cooling, the fracture aperture expands as pore pressure rises; the effect of pore pressure on the fracture aperture becomes more robust as the number of liquid nitrogen shocking cycles and initial temperature increases; (2) under 1‐2 soaking cycles, fracture aperture decreases as the temperature rises. Under two or more soaking cycles, the fracture aperture first increases and then decreases with increasing temperature; (3) when the initial temperature of fractured granite is 100°C, the fracture aperture is not significantly changed by repeated cold soaking cycles. However, with a higher initial temperature, the fracture aperture develops with more liquid nitrogen cold soaking cycles. The liquid nitrogen cooling method is more conducive to increasing the fracture aperture than natural cooling. The experimental results can provide primary experimental data for future research into controlling the evolution of granite cracks.

Summary: The dynamic behavior of coal structure under stress is of significant importance for enhancing coalbed methane (CBM) production in low-permeability and highly heterogeneous reservoirs. In this study, we systematically investigated the multiscale pore evolution of coal by analyzing four key parameters—pore volume, pore volume increment, equivalent length increment, and dominant transport channels under confining stress–gas pressure coupled conditions. More critically, the fundamental regulating mechanisms of methane (CH4) migration within coal seams were elucidated. The key findings reveal that stress-dependent pore compression exhibits scale-selective characteristics. Pores with diameters greater than 5.3 μm are proved to be of heightened sensitivity to confining stress variations. The pore volume decreases linearly under low confining stress and exponentially under high confining stress. Based on the magnitude of pore volume increment, the pores can be classified into the three categories of limited compression pores, transitional pores, and strong compression pores. The cumulative pore volume increments of these pores all demonstrate an exponential decrease with increasing confining stress. The strong compression pores contribute the most to pore volume change, with a cumulative pore volume increment of approximately −87.41%. In contrast, the equivalent length compression is more pronounced in limited compression pores, with a maximum equivalent length compression of about 31.20 mm occurring at a pore diameter of 0.03 μm. In addition, two fundamental regulatory mechanisms of gas seepage pressure on CBM migration are quantitatively characterized. First, the distribution of pores responsible for transport is dynamically reconstructed, and second, the threshold aperture for CH4 migration is regulated. The results demonstrate a good exponential relationship between the porosity of pores responsible for transport (ηx) and gas seepage pressure. As gas seepage pressure increases, the pore diameter threshold decreases, leading to changes in the dominant mechanism of CH4 migration.