Abstract: Low oil saturation reservoirs of the Jurassic Badaowan Formation have been discovered in the shallow and middle layers of the slopes of Mahu Sag in Junggar Basin,but the production rates of the old wells are different after the production test, and it is difficult to identify the "sweet spots" of the reservoirs. Therefore, the geochemical characteristics of Badaowan Formation reservoirs were investigated using oil and gas geochemical parameters. The results show that the biomarker compounds of the crude oils from low oil saturation reservoirs of Badaowan Formation are of great significance in identifying the similarities and differences of crude oils and analyzing the genesis of crude oils. The crude oils are generally characterized by a high abundance of β-carotene and γ-cerane, which are the products of the typical hydrocarbon source rocks of the Permian Fengcheng Formation. Among them, the γ-cerane abundance of crude oils from low-production wells is relatively low, and Ts/Tm is large; the γ-cerane abundance of crude oils from high-production wells is high, and Ts/Tm is small. The chromatography effect is the main reason for the differences in biomarker compounds among crude oils. Comprehensive analysis shows that the fault communication mode and reservoir filling process affect the oil and gas accumulation, and the low oil saturation reservoirs in Badaowan Formation formed by tectonic tilts and adjustments in the late period have more exploration potential. Study results could provide ideas and directions for the next exploration and development in Mahu Sag.

Key words: biomarker compound, low oil saturation reservoir, chromatography effect, crude oil genesis, Badaowan Formation, Mahu Sag