## 5 Discussion  
### Maturity Assessment of Crude Oils  
In this study, the bulk properties of the studied oils, such as low oil density (an average value of 0.80 g/cm\({}^{3}\)) (Table 1) and high saturated/aromatic hydrocarbons (an average value of 9.89%) are indicative of the higher thermal maturity of the studied oil samples. Similarly, the predominance of low molecular weight n-alkanes, the absence of odd-even dominance (OEP and CPI values close to 1.0), and the low Pr/n-C\({}_{17}\) and Ph/n-C\({}_{18}\) (Table 3), based on whole oil chromatography, also signify the relatively high thermal maturity of the studied oils [45]. Based on the GC-MS analysis of saturated hydrocarbon fractions, the predominance of C\({}_{20}\) TFs rather than C\({}_{23}\) TFs, the depletion or absence of high molecular weight tricyclic terpenes and pentacyclic terpen, and the dominance of C\({}_{21}\) pregames all indicate that high molecular weight steranes and terpen have undergone thermal cracking, which further suggests the higher thermal maturity of the studied oil samples. C\({}_{5}\)-C\({}_{7}\) light hydrocarbons and diamondoids play a significant role in evaluating the geochemical correlation of high-maturity crude oils [35; 38; 39; 43; 46]. C\({}_{7}\) light hydrocarbon compounds have been widely applied for crude oil maturity evaluation [20; 46]. Generally, the ratio of nC\({}_{7}\)/MCH has been commonly used to denote the degrees of thermal maturity [47]. A value of nC\({}_{7}\)/MCH? 1.5 is considered to be an indication of the high maturity of light oils, corresponding to an equivalent vitrinite reflectance (Rc) of?1.2% [48]. Here, the nC\({}_{7}\)/MCH values of the samples ranged from 1.52 to 2.0, with an average value of 1.76 (Table 4), signifying that the studied oils are at an excessively high maturity stage. Moreover, [PERSON] [49] proposed two parameters, heptane value (H) and isoheptane value (I), to evaluate the maturity of source rocks, the parent source type, and the maturity of crude oil. In this study, according to [PERSON] [49] and [PERSON] [50], the cross-plot of H versus I suggests that the Rc of the oil ranged from 1.2% to 1.5%, mostly being closer to 1.50% (Figure 5). In addition, [PERSON] [35] showed that MDI values increase with the increase in the thermal evolution of hydrocarbon rocks in the Tarim Basin, and there is a clearly expressed linear relationship between MDI and Ro (Ro = 2.4389 \(\times\) MDI + 0.4363). The equivalent vitrinite reflectance (Rc1) of the crude oils in this study is obtained in the range of 1.55 to 1.63% with an average value of 1.58%, based on the relationship between MDI and Ro (Table 3). Figure 4: The GC-MS spectrogram of the naphthalene, phenanthrene, and dibenzothiophene series of the studied oil samples (\(m/z=142\), 156, 170, 178, 184, 192, 198, and 212). Abbreviations: 2-MN/1-MN = 2-/1-methylnaphthalene; EN = ethylnaphthalene; DMN = dimethylnaphthalene; TMN = trimethylnaphthalene; DBT = dibenzothiophene; P = phenanthrene; MDBT = methyldispen-zothiophene; MP: methylphenanthrene; DMDBT: dimethyldibenzothiophene. Additionally, aromatic hydrocarbon parameters are equally more reliable for evaluating the maturity of high-maturity oil [51]. According to [PERSON] [36], the DNR parameter (DNR = (2,6-DMN + 2,7-DMN)/1,5-DMN) can be used as a specific parameter for evaluating the maturity of higher thermal maturity crude oil, as shown in Table 3, where the calculated equivalent vitrinite reflectance (Rc2) of crude oils varies from about 1.06% to 1.67%, with an average value of 1.48%. Similarly, alkyl dibenzothiophene (e.g., MDR = 4-/1-MDBT and DMDBr = 4,6-DMDBT/(1,4-DMDBT + 1,6-DMDBT)) indicators can also effectively determine the maturity of high-maturity crude oils [52; 53]. According to [PERSON] [37], the calculated equivalent vitrinite reflectance (Rc3) of crude oils ranges from 0.87% to 1.84%, with a mean of 1.51% (Table 3).