# Experimental Study on the Influence of Low Temperature on the Gas Permeability of Granite
## 3 Results and Discussion
### Relationship Between Pore Structure and Permeability
#### 3.5.2 Relationship Between Pore Size Distribution and Gas Permeability  
To gain a deeper understanding of how low temperatures affect the gas permeability properties of granite, the 1D intrinsic gas permeability before and after freeze-thaw cycles is analyzed in conjunction with the contributing porosity. This investigation explores how freeze-thaw cycles alter the pore structure within granites of two different grain sizes, coarse and fine, leading to changes in its permeability properties. The relationship between each contributing porosity and the permeability of granite before and after freeze-thaw cycling can be determined across different pore size distributions. Based on the findings in Section 3.4.2, it is evident that the pore size distribution of both granites shows a clear distinction at \(-60\)\({}^{\circ}\)C. Therefore, when analyzing the relationship between pore size distribution and gas permeability of granite before and after freeze-thaw cycles, the analysis should be conducted with \(-60\)\({}^{\circ}\)C as the cut-off point.  
The 1D intrinsic gas permeability under a confining pressure of 5 MPa is studied as an example. The relationship between each contributing porosity and the permeability  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Particle** & \multicolumn{3}{c}{**Coarse-Grained Granite**} & \multicolumn{3}{c}{**Fine-Grained Granite**} \\ \hline \multirow{2}{*}{**Temperature**} & \multicolumn{3}{c}{**Pore Size Distribution Range**} \\  & **\textless{0.1 }\(\mathbf{\mu}\)m** & **0.1-1 \(\mathbf{\mu}\)m** & **\textgreater{1 }\(\mathbf{\mu}\)m** & **\textless{0.1 }\(\mathbf{\mu}\)m** & **0.1-1 \(\mathbf{\mu}\)m** \\ \hline
20 \({}^{\circ}\)C & 0.003 &  
of granite is shown in Figures 18 and 19. As shown in Figure 18, within the freezing temperature range of 20 \({}^{\circ}\)C to \(-\)40 \({}^{\circ}\)C, a strong positive correlation exists between the contributing porosity of macroopres (pore size >1 \(\upmu\)m) and intrinsic gas permeability, with a correlation coefficient of 0.989. The correlation coefficients for macroopres with a pore size of <0.1 \(\upmu\)m and mesopores (pore size between 0.1 \(\upmu\)m and 1 \(\upmu\)m) are 0.152 and 0.709, respectively. This indicates that, in the temperature interval from 20 \({}^{\circ}\)C to \(-\)40 \({}^{\circ}\)C, the change in intrinsic gas permeability of coarse-grained granite is primarily controlled by macroopres during freeze-thaw cycles. In the temperature range from \(-\)60 \({}^{\circ}\)C to \(-\)120 \({}^{\circ}\)C, both mesopores and macroopres show highly correlated positive relationships with intrinsic gas permeability, with correlation coefficients of 0.992 and 0.944, respectively. This suggests that during this temperature range, freeze-thaw cycling affects the intrinsic gas permeability of coarse-grained granite through a combined influence of mesopores and macroopres.  
From Figure 19, it can be observed that in the temperature range from 20 \({}^{\circ}\)C to \(-\)40 \({}^{\circ}\)C, the contributing porosity of micropores and the intrinsic gas permeability exhibit a strong positive correlation, with a correlation coefficient of 0.998. In contrast, the correlation coefficient for mesopores is only 0.319. This suggests that, in the temperature interval from 20 \({}^{\circ}\)C to \(-\)40 \({}^{\circ}\)C, the changes in the intrinsic gas permeability of fine-grained granite are primarily controlled by micropores. When the temperature ranges from \(-\)60 \({}^{\circ}\)C to \(-\)120 \({}^{\circ}\)C, the contributing porosity of mesopores and the intrinsic gas permeability show a  
Figure 18: Contributing porosity versus intrinsic gas permeability of coarse-grained granite.  
highly correlated positive relationship, with a correlation coefficient of 0.985. This indicates that, within this temperature range, the changes in the intrinsic gas permeability of coarse-grained granite due to freeze-thaw cycles are primarily controlled by mesopores.