## 4 Results
### n-Alkanes and Isoprenoids, Light Hydrocarbons, and Diamondoids  
Figure 2a shows the molecular fingerprints of light oils from the Ordovician reservoirs in the F1 zone, based on whole oil gas chromatography analysis. The chromatograms of the studied samples are all strikingly similar, with a complete distribution of normal alkanes (n-alkanes) without a significant unresolved complex mixture (UCM) \"hump\" (Figure 2a). The distribution pattern of n-alkanes in the studied oil samples is dominated by low molecular weight n-alkanes (C\({}_{8}\)-C\({}_{10}\)), with the abundance decreasing sharply with the increasing carbon number. Accordingly, the two thermal maturity parameters calculated from n-alkanes, the carbon preference index (CPI) and the odd-even dominance index (OEP), are calculated to range from 1.00 to 1.16 and from 0.99 to 1.00, with averages of 1.05 and 0.99, respectively (Table 3). Apparently, the abundance of isoprenoids (Figure 2a), such as pristine (Pr) and phytane (Ph), is lower compared to the adjacent n-alkanes. As \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**Well** & **Depth (m)** & **Formation** & \begin{tabular}{c} **Density** \\ **(g/cm\({}^{3}\))** \\ \end{tabular} & \begin{tabular}{c} **Viscosity** \\ **(mm\({}^{2}\)/s)** \\ \end{tabular} & \begin{tabular}{c} **Sulfur** \\ **(\%)** \\ \end{tabular} & \begin{tabular}{c} **Wax** \\ **(m\({}^{3}\)/m\({}^{3}\))** \\ \end{tabular} & \begin{tabular}{c} **GOR** \\ **(\%)** \\ \end{tabular} & \begin{tabular}{c} **Sat** \\ **(\%)** \\ \end{tabular} & \begin{tabular}{c} **Aro** \\ **(\%)** \\ \end{tabular} & \
\begin{tabular}{c} **Sat/Aro** \\ **(\%)** \\ \end{tabular} &
\begin{tabular}{c} **\(\xi^{13}\)C/\%** \\ \end{tabular} \\ \hline S1-3 & 7256–7358 & O\({}_{23\text{j}}\) & 0.802 & 3.04 & 0.105 & 4.99 & 367 & 72.8 & 14.3 & 5.1 & \(-31.53\) \\ S1-18 & 7302–7821 & O\({}_{2\text{j}\text{j}}\)+O\({}_{1-2\text{j}}\) & 0.808 & 2.93 & 0.102 & 9.72 & 457 & 83.6 & 9.1 & 9.1 & \(-32.05\) \\ S1-7H & 7339–7456 & O\({}_{2\text{j}\text{j}}\) & 0.800 & 3.28 & 0.121 & 6.03 & 354 & 83.2 & 9.0 & 9.2 & \(-31.39\) \\ S1-20H & 7387–7578 & O\({}_{2\text{j}\text{j}}\)+O\({}_{1-2\text{j}}\) & 0.800 & 2.58 & 0.132 & 3.75 & 173 & 89.4 & 6.1 & 14.7 & \(-32.20\) \\ S1-1H & 7458–7558 & O\({}_{2\text{j}\text{j}}\) & 0.794 & 2.58 & 0.107 & 4.28 & 349 & 75.0 & 6.1 & 12.3 & \(-31.74\) \\ S1-5H & 7475–7576 & O\({}_{2\text{j}\text{j}}\) & 0.802 & 2.59 & 0.100 & 7.43 & 353 & 67.8 & 5.6 & 12.2 & \(-32.12\) \\ S1-11 & 7527–7732 & O\({}_{2\text{j}\text{j}}\) & 0.793 & 2.56 & 0.106 & 4.58 & 266 & 83.0 & 8.7 & 9.5 & \(-32.06\) \\ S1-14 & 7589–710 & O\({}_{2\text{j}\text{j}}\) & 0.798 & 2.71 & 0.114 & 4.06 & 240 & 85.5 & 8.8 & 9.7 & \(-32.66\) \\ S1-15 & 7614–8007 & O\({}_{2\text{j}\text{j}}\)+O\({}_{1-2\text{j}}\) & 0.794 & 2.52 & 0.115 & 3.94 & 256 & 87.1 & 7.6 & 11.4 & \(-32.16\) \\ S1-16 & 7619–7822 & O\({}_{2\text{j}\text{j}}\)+O\({}_{1-2\text{j}}\) & 0.803 & 2.80 & 0.157 & 3.70 & 262 & 86.8 & 8.5 & 10.2 & \(-31.34\) \\ S1-9 & 7373–7630 & O\({}_{2\text{j}\text{j}}\)+O\({}_{1-2\text{j}}\) & 0.798 & 2.57 & 0.108 & 4.59 & 324 & 73.4 & 8.7 & 8.4 & \(-31.42\) \\ SP3H & 7396–7640 & O\({}_{2\text{j}\text{j}}\)+O\({}_{1-2\text{j}}\) & 0.795 & 2.55 & 0.102 & 4.48 & 302 & 87.4 & 6.6 & 13.2 & \(-31.96\) \\ SL1 & 7262–7710 & O\({}_{2\text{j}\text{j}}\) & 0.809 & 3.97 & 0.150 & 3.62 & - & 68.3 & 13.4 & 5.1 & \(-32.39\) \\ \hline \hline \end{tabular} Note: GOR = gas to oil ratio. Sat/Aro = Saturate/Aromation. “-” = no data or not determined.  
\end{table} 
Table 1: Physical properties and the carbon isotopic compositions of the studied oils.