## 4 Results
### \(N_{2}\) Adsorption and Desorption Isotherms  
According to IUPAC classification, there are four types of N\({}_{2}\) adsorption isotherms [61; 62]. In this study, there were obvious hysteresis loops in the samples, and all of the hysteresis loops were closed. The existence of a hysteresis loop shows that evaporation from the pores is obviously different from condensation in the pores, and that capillary condensation occurs in mesoporous pores [71]. Useful information about the pore structure can be obtained from the shape of the hysteresis loop. The hysteresis loops of 16 samples were analyzed and it was found that there was only one type of hysteresis loop: type H3 (Figure 4). H3 hysteresis occurs with the accumulation of plate-like particles that produce slit-shaped pores, which corresponds to the slit-shaped and acicular intergranular pores of clay minerals observed under a scanning electron microscope (SEM) (Figure 2). The sample crush size may have an influence on the behavior of low-pressure gas adsorption and desorption. Through experimental analysis, [PERSON] et al. showed that the macro-pore volume in N\({}_{2}\) adsorption and desorption increased if the particle-crush \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Pore** & **Length (\(\mu\)m)** & **Width (\(\mu\)m)** & **Average Pore Size (nm)** \\ \hline
1 & 0.245308312 & 0.160560518 & 202.9344146 \\
2 & 0.55289136 & 0.387186408 & 470.0388843 \\
3 & 0.320037996 & 0.275904161 & 297.9710785 \\
4 & 0.191697886 & 0.081227918 & 136.4629019 \\
5 & 0.141878096 & 0.084477035 & 113.1775655 \\
6 & 0.14810557 & 0.104242495 & 126.1740323 \\
7 & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Parameters of each organic pore obtained from sample SK1-S-1 after PCAS software processing. Length: longest diameter; width: shortest diameter; average pore size: average diameter (longest+ shortest)/2. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Porosity**} & \multirow{2}{*}{**Number**} & \multicolumn{3}{c}{**Pore Size (nm)**} & **Average** & **Average** \\ \cline{3-6}  & & **Max** & **Min** & **Average** & **Shape** & **Probability** \\ \hline Inorganic pores & 6321 & 3083 & 103 & 225 & 0.54 & 0.926294 \\ Organic pores & 161 & 1616 & 112 & 329 & 0.56 & 0.628375 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Average pore parameters of organic pores and inorganic pores obtained from K\({}_{2}\)n\({}^{1+2}\) by PCAS software. Figure 4: Nitrogen adsorption–desorption isotherms of K\({}_{2}\)n\({}^{1+2}\) samples. size was too small [71]. In this study, the crushed size of the samples was in the range of 178-425 \(\upmu\)m, which was chosen to take into account the shale matrix and the particle size distribution within the mineral. This size range falls into the medium particle size range in the study of [PERSON] et al. (2018), which showed no significant influence on the N\({}_{2}\) adsorption and desorption results [71]. At the same time, the surface chemistry of the sample also affects the results of the pore characterization by nitrogen adsorption [72]. The presence of a catalyst on the sample surface attracts the adsorption of nitrogen molecules, resulting in a decrease in the ability of gas molecules to enter the pores and a shift in the measured pore size distribution curve toward smaller pore sizes [72]. The adsorption behavior of nitrogen molecules is also affected by the hydrophilicity or hydrophobicity of the sample surface. The hydrophilic surface attracts nitrogen molecules, resulting in a high measured specific surface area, while the hydrophobic surface repels nitrogen molecules, resulting in a low measured specific surface area [72]. This effect was minimized in the pre-treatments of the experiments to accurately characterize the pore structure. Some useful information about the surface area, pore volume, and pore size distribution (PSD) can be provided by N\({}_{2}\) adsorption experiments.