## 5 Discussion
### Alteration Processes of Hydrocarbons
In this study, the H\({}_{2}\)S content varies from 0.003% to 2.224% (Table 1), this being the highest value for S1-18H, indicating the occurrence of limited TSR effects. Moreover, previous studies have suggested that the TSR alteration increases the DBT/P ratio, while the thermal maturation process decreases it [68]. [PERSON] et al. [69] concluded that oils subjected to TSR in the Tarim Basin are usually characterized by an elevated DBT/P ratio of \(>2\). The Middle Cambrian strata comprise a suite of supratidal anhydrite dolomites that evolved over a large area, with 400-1400 m thick anhydrite and salt beds. The reactive sulfate used for TSR is likely to be derived from the dissolution of anhydrite in the Middle Cambrian strata. The unusually high concentration of DETs in the gas condensate may be due to the reverse reaction of H\({}_{2}\)S with hydrocarbons. In the case of TSR occurrence, higher temperatures of over 160 \({}^{\circ}\)C were necessary in the Tarim Basin [69]. As shown in the figure, the DBT/P ratios of the studied oil samples are in the range of 0.34 to 1.25 (Table 3), indicating that the occurrence of TSR effects in the study area is limited. In addition, the TSR is typically likely to change the composition of light hydrocarbons. Previous studies have suggested that TSR alteration results in a significant increase in K1 (K1 = 2-MH + 2,3-DMP)/(3-MH + 2,4-DMP) [38; 52; 70]. The K1 values of the studied oil samples were all around 1.0 (Table 4),  
Figure 7: The cross-plot of nC\({}_{7}\)/MCH versus Tol/nC\({}_{7}\) (after Thompson [48]), demonstrating the secondary alteration in the studied oils. with the highest value of 1.04 for S1-18H, indicating that no significant TSR alteration was experienced. In conclusion, the integrated analysis, based on the H\({}_{2}\)S content, the DBT/P ratios, and the K1 values of light hydrocarbons, suggests that the studied oils experienced limited TSR effects. In the study area, the lower Cambrian Shayilike formation (E2s) and Awatage formation (E2a) play an important role in the development of anhydrite and salt beds, which offer a favorable environment for TSR reactions. However, the low geothermal gradient and the rapid burial depth may have prevented a more pronounced TSR effect from occurring in this area. Evaporative fractionation, also known as gas washing, thereby emphasizing the additional gas introduced into the reservoir rather than the dissolved gas from the oil, is important for investigating light oil or condensate. Their escape from the gas phase results in light-end compounds in the liquid phase that are readily soluble in gas entering the gas phase and migrate as part of the gas, resulting in the enrichment of heavy components that are not readily soluble with gas in the liquid phase [48]. [PERSON] et al. [71] and [PERSON] et al. [72] noted that the logarithm of the molar concentration of n-alkanes (Lg[MC(n)]) from unaltered petroleum is correlated with the corresponding carbon number and is widely used to reflect light component accumulation or depletion. As shown in Figure 10, the studied oil samples display two main types of relationships between the carbon number and the logarithm of the molar fraction of n-alkanes; one shows a very good linear relationship between them (Figure 10a), indicating that no significant evaporative fractionation occurred, while the other shows a slope break at about C\({}_{24}\) (Figure 10b), where significant evaporative fractionation occurred. In addition, toluene/n-heptane (Tol/nC\({}_{7}\)) and n-heptane/methylcyclohexane (nC\({}_{7}\)/MCH), as proposed by [PERSON] [48], have frequently been used to evaluate the evaporative fractionation. The increased nC\({}_{7}\)/MCH values and lower Tol/nC\({}_{7}\) values of the studied oils in Figure 7 also support this view. Figure 8: The cross-plot of Ln (C\({}_{1}\)/C\({}_{2}\)) versus Ln (C\({}_{2}\)/C\({}_{3}\)), demonstrating the origin and maturity of natural gases in this study region (after [PERSON] et al. [73]).