# Experimental Study on the Influence of Low Temperature on the Gas Permeability of Granite
## 4 Conclusions  
In this paper, 1D intrinsic gas permeability tests and nuclear magnetic resonance (NMR) tests were conducted before and after freeze-thaw cycles on coarse- and fine-grained granite. The effect of low temperature on the gas permeability of different particle sizes was analyzed in conjunction with 2D intrinsic gas permeability tests under real-time low-temperature conditions. The main conclusions drawn are as follows:  
1. The low dispersion of the 1D and 2D gas permeability test results of coarse-grained granite in the initial state indicates that the pore structure between different specimens of coarse-grained granite is more stable than that of fine-grained granite. As the freezing temperature decreases, the 1D intrinsic gas permeability of granite increases. Due to differences in the freezing point of pore water corresponding to pores of different sizes, the change trend in intrinsic gas permeability in different freezing temperature intervals varies significantly. At the same freezing temperature, the change in intrinsic gas permeability of fine-grained granite is significantly higher than that of coarse-grained granite, indicating that fine-grained granite is more sensitive to freeze-thaw damage.
2. In real-time cryogenic environments, both granites exhibit a linear increase in 2D gas permeability with a gradual decrease in freezing temperature. Additionally, the greater the 2D gas permeability of the granite at room temperature, the faster the rate of increase in permeability with decreasing temperature.
3. In real-time cryogenic environments, the two granites exhibited a linear increase in 2D gas permeability with a gradual decrease in freezing temperature. In addition, the greater the 2D gas permeability of the granite at room temperature, the faster the rate of increase in permeability with decreasing temperature.
4. Coarse-grained granite contains micropores (r < 0.1 \(\upmu\)m), mesopores (0.1 \(\upmu\)m \(\leq\) r \(\leq\) 1 \(\upmu\)m), and macropores (r > 1 \(\upmu\)m), with macropores being the dominant pore structure. In contrast, fine-grained granite consists of micropores and mesopores, with mesopores occupying a dominant position. As the freezing temperature decreases, the volume proportion of micropores and macropores in coarse-grained granite decreases, while  
Figure 19: Contributing porosity versus intrinsic gas permeability of fine-grained granite.  
mesopores increase. In fine-grained granite, the volume proportion of micropores decreases, and mesopores increase. (5) Among the factors influencing freeze-thaw damage in rocks, lithology plays a dominant role. When the freezing temperature is relatively low, the two types of granite exhibit distinct patterns of freeze-thaw damage evolution. In coarse-grained granite, the damage is primarily manifested in the initiation and expansion of newly formed pores, with new micropores continuously forming and developing into mesopores. In contrast, the freeze-thaw damage in fine-grained granite is more prominently reflected in the intensified expansion of pre-existing pores, with original micropores continuously developing and eventually transforming into mesopores. (6) In the temperature range of 20 \({}^{\circ}\)C to \(-\)20 \({}^{\circ}\)C, the intrinsic gas permeability of coarse-grained granite is primarily controlled by macropores, while fine-grained granite is dominated by micropores. When the temperature decreases further to the \(-\)60 \({}^{\circ}\)C to \(-\)120 \({}^{\circ}\)C interval, the intrinsic gas permeability of coarse-grained granite is influenced by a combination of mesopores and macropores, whereas fine-grained granite is primarily controlled by mesopores.