银额盆地查干凹陷原油地化特征及油源对比

Geochemical Characteristics of Oil and Source Rock Correlation in the Chagan Sag of Yingen-Ejinaqi Basin, NW China

银额盆地东部查干凹陷首次发现轻质低硫成熟原油 ,其饱和烃含量在 90 %以上 ,成熟度相当于镜煤反射率Ro1.0 %左右 ,是生油高峰阶段的产物 ;原油全碳同位素δ13C值 - 31.1‰。原油生物标志物中类异戊二烯含量较高 ,植烷与姥鲛烷均势 ;三环萜烷含量高于五环萜烷 ;含有较高的TsC2 9、TsC30 重排藿烷、伽马蜡烷 ;藿烷中以C30 藿烷为主 ,C32 以上升藿烷含量极低 ;孕甾烷含量高 ;甾烷中以C2 9甾烷为主 ,C2 7甾烷含量也较高 ,异胆甾烷含量高于胆甾烷 ;重排甾烷含量低 ;甾烷的含量与萜烷含量相当 ,是典型的湖相原油。已发现的天然气中甲烷含量达 80 % ,为湿气。原油和源岩生物标志物组成特征分析对比表明下白垩统巴音戈壁组源岩是主要油源岩。

It is the first time that some crude oil has been discovered in the Chagan Sag, the eastern of the Yingen Ejinaqi basin, NW China. The geochemical characteristics of the oils (including oil sands) and source rock have been studied in this paper. The oils, in which saturated hydrocarbon accounts for more than 90%, belongs to maturated oils with a lower density and lower sulfur content at the generaton peak stage (equal to R o=1.0%±). The δ 13 C value of the whole oil is -31.1‰. The features of the biomarkers in the oils are as follows: relatively high abundance of isoprenoidies, no preference between pristane and phytane; the proportion of tricyclic terpanes over pentacyclic terpanes; relatively high amounts of Ts, C 29 Ts, C 30 diahopane and gammacerane; the significant amounts of C 30 hopane and much lower concentration of homohopanes (higher than C 32 ); high amounts of pregnanes; the significant proportion of C 29 sterane, relatively high abundance of C 27 sterane, the proportion of isocholestane over cholestane; low concentration of diacholestane; equivalent amounts between steranes and terpanes. The proportion of methane in the discovered natural gas is up to 80%, reflecting that it belongs to wet gas.The oil source correlation shows that the crude oils in Chagan Sag are generated from Lower Cretaceous Bayingebi Formation, and can be described as typical lacustrine oils. Biomarkers reveal that the oil has a certain migration effect.