Junggar Basin is rich in hydrocarbon resources. After decades of exploration, numerous hydrocarbon resources have been found in Junggar Basin, among them, the reserve of heavy oil dominated above one-second of the total amount of heavy oil resources in China. In the world, heavy oil is a hot and difficult point for scholars to study, and the research on the origin of heavy oil is the basis of exploration and development. Heavy oil resource abundance in Junggar Basin, but the inherent laws and chemical molecular characteristics of crude oil are diverse in different regions. The origin and understanding of heavy oil in Pingdiquan Formation of Permian system in the eastern of Junggar Basin are not clear, which severely strain further prospecting and planning. In view of the understanding of inherent laws of heavy oil, combined with its carbon isotope and saturated hydrocarbon chromatography, this paper comprehensively analyzed the origin, source and accumulation pattern of heavy oil in Pingdiquan Formation of Permian. The results show that Pr/Ph of heavy oil is between 1.08 and 1.6 in this area. Its carbon isotope distribution ranges from −30.1‰ to −34.6‰. Sterane maturity parameter C₂₉ββ/(αα+ββ) ranges from 0.24 to 0.41. Heavy oil in this area should be the product of source rock of Pingdiquan Formation of Permian. The maturity of crude oil in Huobei area is basically the same as the evolution of its source rocks, which should provide hydrocarbons for in-situ source rocks. Low density crude oil of mature stage exists in the Huoshaoshan area, which indicates that there are many stages of crude oil mixing in this area.

Dongdaohaizi area is an important hydrocarbon-rich depression in the Junggar Basin. Early resource evaluation has revealed that it has superior hydrocarbon generation conditions. No major exploration breakthrough has been observed in the hydrocarbon from the Permian Pingdiquan Formation source rocks, which are widely distributed and have a large sedimentary thickness. The unclear recognition of the genesis, the sources, and the hydrocarbon evolution history of the formation seriously restricted further exploration and development. Sixty-four samples were acquired during the study, consisting of 30 source rocks, 13 crude oil samples, and 21 natural gas samples. Studying the geochemical characteristics of the source rock extract and the surrounding structural crude oil in the Dongdaohaizi Depression, the differences in the stable carbon isotope, the biomarker compound, and the molecular relative composition of the three sets of main source rock products in the research fields are summarized. The results reflect that the drying coefficient of natural gas in the study area is generally low, and the fractional distillation value of methane and ethane is 0.32, which is most likely due to the loss of oil and gas migration and the mixing of different types of natural gases. The carbon isotope value is relatively low, with the Pr/Ph being generally less than 3.0. The content of sterane C₂₉ is the highest in the relative composition of steranes, followed by the content of sterane C₂₈, which together account for more than 80% of the total sterane content, and then followed by a lower content of C₂₇ sterane, accounting for only 5-20% of the total content, which generally conforms to the characteristics of Permian Pingdiquan Formation source rock products. The carbon isotope value of crude oil ranges from -30.94 to -28.31‰, which is different from the characteristics of typical Permian source rocks (values range from -34.49 to -28.21‰), while it is related to typical Carboniferous products (values range from -29.98 to -24.1‰), indicating that small amounts of Carboniferous source rock products were mixed in different degrees in the Dinan fault area. According to the distribution law of oil and gas, the geochemical characteristics and hydrocarbon sources were considered the oil source in the east of the Dongdaohaizi Depression, mainly from the source rocks of the Permian Pingdiquan Formation. The products of the peak period of hydrocarbon generation in the source rocks of the Pingdiquan Formation have not been transported to the high structural positions on a large scale to form reservoirs. They may still exist in the deep part of the Depression and the slope area. The low-amplitude structural and lithologic traps in the slope area of the Dongdahaizi Depression are promising targets for finding the products of the peak period of hydrocarbon generation. This is of great significance to reveal the Permain hydrocarbon evolution in the Junggar Basin and guide further research on the oil-source correlation of natural gas from the paleo-strata.

The NMR of the Trinity reservoir indicate that changes in crude oil compositions result in differences in NMR characteristics. On this basis, the chemical properties of crude oil are analyzed, and two criteria affecting the NMR characteristics of crude oil with different physical properties are presented. The research shows that the chromatographic characteristics of crude oils with different maturity and biodegradability correspond well with NMR characteristics. Lateral relaxation time of heavy oil at low maturity stage and experiencing strong biodegradability is shortened. Two parameters, maturity index and biodegradation level, can be reliably applied to the evaluation and production of heavy oil reservoir.

Many heavy oil wells have been found in the Jilantai shallow depression in the Hetao Basin. The origin of heavy oil in the study area was analyzed comprehensively according to the physical properties and geochemical characteristics of heavy oil. Two sets of source rocks were detected in the Guyang and Linhe groups, in the Hetao Basin. During the Guyang Formation, the differences of sedimentary environments resulted in brackish water sedimentary environment in the south of the study area and freshwater reducing environment in the north of the study area. The high content of boron in the source rocks of Linhe Formation indicates its saltwater environment. By the method of oil source comparison, it is found that the Pr/Ph of the crude oil in Jilantai area and Linhe Formation is lower than 0.50, and the Pr/nC₁₇ is between 0.7 and 3.5, which should come from the source rock of the first segment of the southern moderate lacustrine Guyang Formation. The C₂₉ sterane 20S/(20S+20 R) and C₂₉ sterane ββ/(αα+ββ) parameters indicate that the low maturity of crude oil is the main cause of heavy oil formation. The research on the genesis and geochemical characteristics of Jilantai crude oil indicates that the northern and central depression of the Hetao Basin is a rich area of favorable resources.