# Experimental Study on the Influence of Low Temperature on the Gas Permeability of Granite
## 3 Results and Discussion
### Two-Dimensional Gas Permeability
#### 3.3.2 Changes in 2D Intrinsic Gas Permeability  
The scatter plot illustrating the relationship between 2D gas permeability of granite and freezing temperature is shown in Figure 11. The corresponding fitted curves and coefficients of determination (R\({}^{2}\)) are also provided. The results indicate a linear increase in 2D gas permeability with decreasing freezing temperature for both types of granite. This is because the test was conducted using dry specimens, and the dry specimens' gas permeability was affected by real-time low temperatures. Change is primarily caused by the rock's contraction and deformation during the freezing process; the rock's pores will widen as a result of the contraction of the rock skeleton. The differing thermal contraction coefficients of the mineral phases lead to incompatible deformations during freezing, disrupting the internal structure and generating additional permeable pathways, thereby increasing the gas permeability.  
\begin{table}
\begin{tabular}{c c c c c} \hline \multirow{2}{*}{**Specimen No.**} & \multicolumn{3}{c}{**Apparent Permeability**} & \multirow{2}{*}{**Intrinsic Permeability**} \\ \cline{2-2} \cline{4-5}  & **5 Bar** & **10 Bar** & **15 Bar** & \\ \hline TB1 & 2.52 \(\times\)\(10^{-19}\) & 1.89 \(\times\)\(10^{-19}\) & 1.74 \(\times\)\(10^{-19}\) & 1.27 \(\times\)\(10^{-19}\) \\ TB2 & 4.92 \(\times\)\(10^{-19}\) & 3.52 \(\times\)\(10^{-19}\) & 2.93 \(\times\)\(10^{-19}\) & 1.88 \(\times\)\(10^{-19}\) \\ TB3 & 1.58 \(\times\)\(10^{-19}\) & 1.26 \(\times\)\(10^{-19}\) & 1.07 \(\times\)\(10^{-19}\) & 8.59 \(\times\)\(10^{-20}\) \\ \hline \end{tabular}
\end{table}
Table 4: Two-Dimensional gas permeability of fine-grained granite(m\({}^{2}\)).  
\begin{table}
\begin{tabular}{c c c c c} \hline \multirow{2}{*}{**Specimen No.**} & \multicolumn{3}{c}{**Apparent Permeability**} & \multirow{2}{*}{**Intrinsic Permeability**} \\ \cline{2-2} \cline{4-5}  & **5 Bar** & **10 Bar** & **15 Bar** & **Permeability** \\ \hline TA1 & 3.25 \(\times\)\(10^{-18}\) & 2.75 \(\times\)\(10^{-18}\) & 2.49 \(\times\)\(10^{-18}\) & 2.16 \(\times\)\(10^{-18}\) \\ TA2 & 3.83 \(\times\)\(10^{-18}\) & 3.32 \(\times\)\(10^{-18}\) & 2.97 \(\times\)\(10^{-18}\) & 2.59 \(\times\)\(10^{-18}\) \\ TA3 & 2.94 \(\times\)\(10^{-18}\) & 2.86 \(\times\)\(10^{-18}\) & 2.58 \(\times\)\(10^{-18}\) & 2.45 \(\times\)\(10^{-18}\) \\ \hline \end{tabular}
\end{table}
Table 3: Two-Dimensional gas permeability of coarse-grained granite(m\({}^{2}\)).  
The fitted relationship between 2D gas permeability and freezing temperature is described by a first-order linear function. The slope of the fitting curve reflects the rate at which the 2D gas permeability increases with decreasing temperature--the steeper the slope, the more sensitive the granite is to real-time low-temperature conditions. The 2D gas permeability of coarse-grained granite exhibits a more pronounced increasing trend compared to fine-grained granite. This can be attributed to the denser solid skeleton of fine-grained granite, which undergoes more uniform strain under real-time low-temperature conditions, leading to less significant changes in the internal pore structure. This behavior contrasts with the one-dimensional gas permeability observed in granite specimens subjected to freeze-thaw cycles. The differing trends in gas permeability under these two testing conditions can be explained by the fact that dry granite specimens, when exposed to real-time low temperatures, experience damage primarily due to the cold contraction of the rock. In contrast, saturated granite specimens subjected to freeze-thaw cycles undergo additional complex damage due to the water-ice phase transition, which further contributes to the degradation of the rock's internal structure.