## 4 Results
### Organic Geochemistry  
The hydrocarbon generation potential of shale can be evaluated according to the TOC content and hydrogen enrichment. Although the crushed particle size has an effect on the rock analysis results, the rock pyrolysis and the total organic carbon content (TOC) were analyzed more than twice in parallel strictly according to the national standards GB/T 18602-2012 and GB/T 19145-2003 [78] so as to guarantee analytical precision. Flame ionization detector (FID) saturation during pyrolysis is a common source of error found in the analysis of organic-rich rocks, especially those that generate large quantities of hydrocarbons from kerogen during pyrolysis (large S2 yields). FID saturation usually occurs when analyzing type II kerogen with thermal evolution in the immature-to-medium oil window range or with high TOC samples. Considering the TOC content of the samples and the type of kerogen, the experimental results would not have FID saturation [79; 80; 81; 82].  
The S2 value of the K\({}_{2}\)n\({}^{1+2}\) shale in the Songliao Basin varied greatly, with an average of 24.43 mg HC/g rock, ranging from 0.39 to 75.41 mg HC/g rock. The content of TOC ranged from 0.3 to 8.74 wt.%, with an average of 3.21 wt.% (Table 4). The S2-TOC diagram shows that there is type I kerogen in the shale of K\({}_{2}\)n\({}^{1+2}\)[45] (Figure 7). S2 and the TOC had a good linear correlation, and the correlation coefficient was R\({}^{2}\) = 0.9781 (Figure 7). The slope (S2/TOC) indicates that the trend-based HI (hydrogen index) had a value of about 980 mg HC/g TOC (Slope \(\times\) 100 = HI = 980 mg HC/g TOC), and the sample was of type I kerogen oil-prone.  
The value of free hydrocarbon (S1) was between 0.04 and 3.38 mg HC/g rock, with an average of 0.79 mg HC/g rock. S1 had a positive correlation (R\({}^{2}\) = 0.8973, T \(>\) 2.58, \(p\)\(<\) 0.01) with the TOC (Figure 7). The range of HI was 131 to 975 mg HC/g TOC, and the average was 600.8 mg HC/g TOC. The value of the oil saturation index (OSI) ranged from 7.87 to 43.9 mg HC/g TOC, and the average was 18.62 mgHC/g TOC. The T\({}_{\rm max}\) value represents the temperature at which the S2 peak reached its maximum, ranging from 434 \({}^{\circ}\)C to 443 \({}^{\circ}\)C, with an average of 439 \({}^{\circ}\)C (Table 6).  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Sample** & **Quartz** &
\begin{tabular}{c} **Potash** \\ **Feldspar** \\ \end{tabular} & **Plagioclase** & **Calcite** & **Dolomite** & **Siderite** & **Pyrite** & **Clay** \\ \hline SK1-S-1 & 35.5 & 2.2 & 8.1 & 2.3 & 3.4 & / & 0.5 & 48 \\ SK1-S-2 & 35.6 & 1.5 & 5.1 & 2.2 & 1.3 & / & 1.9 & 52.4 \\ SK1-S-3 & 21.8 & 2 & 6.5 & 8.4 & 8.3 & / & 4.3 & 48.7 \\ SK1-S-4 & 17.8 & 1.8 & 5.1 & 3.4 & 0 & / & 2.4 & 47.2 \\ SK1-S-5 & 21.7 & 1.7 & 4.8 & 11.2 & 8.6 & / & 3.6 & 48.4 \\ SK1-S-6 & 18.9 & 1.7 & 6.1 & 8.8 & 8.2 & 7.1 & 2.8 & 46.4 \\ SK1-S-7 & 19.3 & 1.8 & 5.5 & 12.8 & 3.5 & 4.5 & 0.6 & 52 \\ SK1-S-8 & 17 & 1.8 & 5.2 & 3.8 & 20.5 & / & 0.1 & 51.6 \\ SK1-S-9 & 21.5 & 2.6 & 7.1 & 6.8 & 2.8 & 5.7 & 1.4 & 52.1 \\ SK1-S-10 & 20.6 & 1.7 & 6.7 & 11.2 & 4.9 & / & 2.9 & 52 \\ SK1-S-11 & 28.4 & 1.5 & 8.1 & 1.6 & 14.9 & / & 1.9 & 43.6 \\ SK1-S-12 & 21.1 & 1.7 & 7.3 & 5.8 & 7.7 & / & 4.2 & 52.2 \\ SK1-S-13 & 19.7 & 1.9 & 7.7 & 8.3 & 5.9 & / & 0.4 & 56.1 \\ SK1-S-14 & 24.9 & 2.8 & 11.3 & 9 & 4.2 & / & 2.9 & 44.9 \\ SK1-S-15 & 20.5 & 1.8 & 13.3 & 3.5 & 8.5 & / & 5.5 & 46.9 \\ SK1-S-16 & 20.3 & 1.5 & 12 & 17.1 & 4.3 & / & 4.6 & 40.2 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Mineral composition of K\({}_{2}\)n\({}^{1+2}\) by XRD (unit: wt.%).