Study on hydrocarbon accumulation process in the western section of south slope of Kuqa foreland basin

In recent years, significant breakthroughs have been achieved in the exploration of the Kuqa Depression in the Tarim Basin. However, previous studies on the hydrocarbon accumulation process in the study area are relatively scarce. In this study, organic geochemistry, fluid inclusion experiments, and basin simulation techniques are employed to systematically analyze the source, accumulation period, and accumulation process of crude oil in the study area. The results show that two oil groups, namely Group Ⅰ and Group Ⅱ, can be identified in the study area. The tricyclic terpenoids of Group Ⅰ crude oil follow the pattern of C₁₉<C₂₀<C₂₁>C₂₂<C₂₃ (up - down - up type), and they have light carbon isotopes. The oil and source correlation indicates that their source rocks are the Huangshanjie Formation in the Triassic system. The tricyclic terpenoids of Group Ⅱ crude oil exhibit the pattern of C₁₉>C₂₀>C₂₁>C₂₂<C₂₃ (down-down-up type), and the carbon isotope value is heavy. The oil-source correlation reveals that the source rock is the Jurassic Qiakemake Formation. Based on the distribution patterns of homogenization temperature, the evolutions of burial and thermal history, as well as the two-dimensional accumulation models of representative profiles, the results show that Group Ⅰ oils were generated from Triassic source rocks, migrated to the buried-hill reservoirs, and then accumulated between 16 and 5 Ma. Group Ⅱ oils originated from Jurassic source rocks, migrated to the Cretaceous strata, and then accumulated in the Cretaceous and Paleogene reservoirs between 5 and 2 Ma. The planar distributions of oil groups may be attributed to the distribution of fold areas in the Qiulitage tectonic belt, which formed in different periods. In the early period (16~5 Ma), the folding area of the Qiulitage tectonic belt led to the obstruction of the oil and gas transmission system in the western portion of the study area.As a result, Group Ⅰ oils were predominantly distributed in the eastern part of the study area. However, in the second period (5~2 Ma), the folded area of the Qiulitage structural belt caused the blockage of the oil and gas transmission system in the eastern part of the study area, thereby giving rise to the distribution of Group Ⅱ oils in the western part of the study area. Although well Qiucan 1 is close to the source rock and lies on the path of oil and gas migration during the two accumulation stages, it failed because no effective traps were developed. Well Xiqiu 2 failed due to engineering reasons. The study found that there is a high possibility of oil in the buried hill reservoir of this well, so it is suggested to deepen the drilling. Meanwhile, it is found that the western Qiulitage paleo-uplift around the source kitchen in the study area has the conditions for the formation of large-scale oil and gas accumulation zones. Therefore, the research results in this paper may play a crucial role in further petroleum exploration in this area.