Abstract
AbstractThe Sangonghe Formation in Mahu sag of Junggar basin is a new target for middle and shallow oil and gas exploration. In order to study the geochemical characteristics of crude oil from the Sangonghe Formation, typical oil sand samples from the Sangonghe Formation in the Mahu Sag and Xiayan High in the east were selected, and the group composition, saturated hydrocarbon chromatography, and GC-MS tests were carried out for the oil sand extracts. The origin and maturity of crude oil, as well as the depositional environment and sources of hydrocarbon-generating parent material, are studied. The results show that the carbon isotope composition of crude oil from the Sangonghe Formation is lighter (δ13C value is about −30‰). The oil group composition from the Sangonghe Formation has high content of saturated hydrocarbon. Part of the shallowly buried crude oil was affected by secondary effects such as biodegradation, and its saturated hydrocarbon content is relatively low. The normal alkanes in crude oil all show low-carbon advantage (nC17, nC19). The values of C29 sterane ββ/(αα + ββ) and C29 sterane 20S/(20S + 20R) are greater than 0.45, which indicates mature crude oil. The Pr/Ph value is between 0.58 and 1.12. Crude oil contains a certain amount of gammacerane and β-carotane, indicating that the hydrocarbon-generating parent material was deposited in the reducing-weak reducing environment, and the water body had a certain salinity. The distribution and composition of steroids and terpanes in crude oils from the Sangonghe Formation in Mahu sag and Xiayan High are similar. The ααα-20R regular steranes of C27, C28 and C29 show an inverse “L” distribution. Tricyclic terpenes are mainly C20, C21, C23. The high content of C20, C21, C23 tricyclic terpenes and abundant C29 steranes came from the contribution of microorganisms and algae. The crude oils have the same source of parent material.KeywordsCrude oil geochemistryTricyclic terpaneSangonghe formationMahu sagJunggar Basin
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