Geochemical Characteristics and Oil-Gas Source Identification of The SN31 Oil and Gas Reservoir in The Junggar Basin

Recently, with the improvement of exploration levels, there has been disputes about the geochemical characteristics and sources of oil and gas reservoirs in the SN31 well block of the Junggar Basin, and they need to be re-evaluated. By collecting crude oil and natural gas samples from key wells, testing, and analysing the components, stable carbon isotopes, and biomarkers of the samples using laboratory physical calibration, chromatography-mass spectrometry, and other methods, the physical and chemical characteristics, genetic types, and sources of oil and gas can be identified. The results show that the relatively low API value indicates a light to medium oil. The crude oil has a relatively high carbon isotope content, distributed between -29.4‰ to -28.7‰. The ratio of pristane (Pr) to phytane (Ph) indicates that the crude oil originates from humus-rich source rocks. The higher content of tricyclic terpenes and rearranged steranes indicates higher maturity. The content of C27>C29>C28 indicates that the crude oil is mixed with a certain proportion of higher plants. The natural gas content is high, and the drying coefficient is 0.86~0.94, which is indicted mainly wet gas. The non-hydrocarbon components are mainly N2 and CO2. The carbon isotope characteristics show that the methane carbon isotope distributes from -33.4‰ to -35.3‰ and the ethane carbon isotope distributes from -24.7‰ to -26.6‰.