# Analysis and Characterization of Micro-Nano Pores in Coal Reservoirs of Different Coal Ranks
## 3 Results and Discussion
### Pore Network Stick Model
A comparison between Table 5 and Figure 11 reveals that the medium-rank coal exhibited more developed large-medium pores compared with the low- and high-rank coal, while the low- and high-rank coal exhibited relatively more micro-pores. The variance between the average pore size and the maximum and minimum pore sizes, as well as the pore equivalent radius distribution histogram, indicated that the pore sizes span a wide range, resulting in an uneven distribution. Figure 12 depicts the histogram of the coordination number distribution of each sample. The statistical analysis revealed that, under micro-CT scanning, the coordination number was concentrated between a 0 and 25 distribution, whereas, under nano-CT scanning, the coordination number was concentrated between 0 and 15. The maximum coordination number, a critical parameter describing the local pore connectivity, was 79, with an average coordination number of 5.67. Under nano-CT, the maximum value was 49, and the average coordination number was 4.76. The uneven distribution of the coordination numbers indicated that the pore throat distribution was more complex. Despite the complex distribution, particularly with coordination numbers ranging from 0 to 20, a significant portion of the samples exhibited excellent connectivity, making them suitable for seepage simulation. \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{ \begin{tabular}{c} **CT** \\ **Type** \\ \end{tabular}  } & \multirow{2}{*}{**Samples**} & \multirow{2}{*}{**Total**} & \multicolumn{2}{c}{**Equivalent Radius of Pore**} & \multicolumn{2}{c}{**Coordination Number**} & \multicolumn{2}{c}{**Surface Area (\(\upmu\)m\({}^{2}\)/nm\({}^{2}\))**} \\ \cline{3-10}  & & & \multicolumn{2}{c}{**(um/nm)**} & & & & & & & & \\ \cline{3-10}  & & & **Max** & **Avg** & **Min** & **Max** & **Avg** & **Min** & **Max** & **Avg** & **Min** \\ \hline \multirow{3}{*}{Micro-CT} & LL & 193,056 & 1062 & 166 & 25 & 79 & 5.67 & 0 & \(2.52\times 10^{10}\) & \(6.36\times 10^{8}\) & \(5.05\times 10^{6}\) \\ \cline{2-10}  & XJ & 59,998 & 1272 & 182 & 25 & 75 & 6.58 & 0 &  
low-rank coal XJ was the least, which was 197,303. The total number of LL throats of the medium-rank coal under nano-CT scan was the largest, which was 175,483. The total number of throats of the low-rank coal XJ was the least, which was 7846. This indicated that the pore connectivity between the different samples varied significantly. In comparison with the throat equivalent radius and throat length data of the micro-nano-CT scans, the throat parameters under micro-CT exceeded those under nano-CT due to a higher total number of throat counts, resulting in a larger throat surface area. Figure 13 depicts the throat equivalent radius distribution histogram of each sample. Notably, the throat equivalent radius distribution under a micro-CT scan exhibited a single peak, primarily concentrated within 200 \(\upmu\)m, while, under a nano-CT scan, it was unimodal and concentrated within 2000 nm, indicating that the homogeneity of each sample was excellent. Upon comparing Table 6 and Figure 12, it was observed that the medium-rank coal LL exhibited the largest number of throats under micro-nano conditions, followed by the high-rank coal ZZ, with the low-rank coal XJ exhibiting the fewest throats. However, XJ exhibited a more compact distribution regarding the throat equivalent radius compared with ZZ,