Stable Carbon Isotope Compositions of Liquid Hydrocarbon Molecules and their Application

Key words: 
• Junggar Basin /
• carbon /
• isotopic /
• composition of individual hydrocarbon

Abstract: This paper reports carbon isotopic compositions of individual n-alkanes and isoprenoids from crude oil and source rock samples in the Junggar Basin. Between nC₁₁ and nC₃₄ , the most part of isotopic compositions of n-alkanes originating from the Jurassic limnetic factes is-27.0‰, to-32.4‰,,heavier than that of the crude oil from the marine factes strata, characterized by ¹³C-rich isotope.The n-alkane δ¹³C values of the crude oil from the type Ⅱ A source rock are lighter than that of the type Ⅱ B oil, it suggests that n-alkane be richer in ¹²C relatively.If crude oils are derived from the same group of organism or,at least,from organism using the same carbon source, the δ¹³C values of these n-alkanes and isoprenoids have a similar distributional range and total variational trend. Therefore, these data can be used in the source rock/oil correlation.The isotopic compositions of individual n-alkanes of the oil from the Cainan oil field become similar to that from the lower Jurassic Sangonghe source rock, they show a variation from-26.0‰,to-32.0‰,in the nC₁₁ to nC₃₂ range, among the same carbon numbers, the δ¹³C differences is less than 2‰,especially the δ¹³C value of n-alkanes in the Cainan oil matches that in the saturated hydrocarbon fractions from the lower Jurassic Sangonghe source rock.In the Pencan-2 well, the δ¹³C values of crude oil n-alkanes coincide with that of the Badaowan source.The Du-71 well is located on the southern margin of the Junggar Basin, its productive strata are shallower.The δ¹³C values of C₁₁ -C₂₃ n-alkanes vary from heavier to lighter with increasing of the carbon number, ranging from - 25. 4‰, to - 33.0‰, These values have a similar trend to the Toutunhe source rock. Through the study on microbiology, it has been proved that there is a great amount of Methanococcus in the Toutunhe hydrocarbon source rock.Therefore, the origin of the Dushanzi oil is possibly related to archaeobacteria.