藏北羌塘盆地羌资1井中侏罗统沥青脉生物标志化合物分布特征及其意义

藏北羌塘盆地羌资1井中侏罗统沥青脉生物标志化合物含有丰富的正烷烃、类异戊二烯烷烃、萜类化合物和甾类化合物。正烷烃图谱形态以单峰形态占优势,主碳峰以nC₁₆、nC₁₇、为主,次为nC₁₈、nC₂₀、nC₁₅,轻烃组分占有绝对优势,OEP值介于0.69-1.22之间,平均值为0.96,偶碳数优势不明显;Pr/Ph值介于0.35~0.78之间,平均值为0.59,具有明显的植烷优势。萜烷相对丰度表现为五环三萜烷 > 三环萜烷 > 四环萜烷,γ-蜡烷普遍存在,但相对含量较低;甾烷主要为规则甾烷,少量孕甾烷,规则甾烷Σ(C₂₇+C₂₈) > ΣC₂₉,ΣC₂₇/ΣC₂₉介于0.61~2.18之间,平均值为1.06,显示弱的C₂₇甾烷优势或弱的C₂₉甾烷优势。有机质母质构成中,除有丰富的藻类等低等水生生物外,可能还有陆生高等植物输入混合。成熟度参数和镜质体反射率均显示沥青脉中的有机质处于成熟-过成熟阶段。沥青脉形成环境为还原环境。另外,除饱和烃和芳烃含量上有明显差别外,中侏罗统夏里组砂泥岩中的沥青脉与布曲组碳酸盐岩中的沥青脉的生物标志化合物无明显区别。

Origin, distribution and significance of the biomarkers from the Middle Jurassic bitumen veins in the Qiangtang Basin, northern Xizang

The biomarkers from the Middle Jurassic bitumen veins in the Qiangzi-1 well in the Qiangtang Basin, northern Xizang are reported for the first time, including n-alkanes, isoprenoid hydrocarbons, terpanes and steranes. Chromatograms for saturated hydrocarbons, terpanes and steranes show that n-alkanes contain a relatively wide range of nCl6, nCl7, nCl8, nC20 and nC15. Examination of the relative abundance also shows an absolute dominance of light hydrocarbon compositions. OEP ratios range between 0.69 and 1.22, with an average of 0.96. Pr/Ph ratios vary from 0.35 to 0.78 with an average of 0.59, indicating an obvious dominance of phytanes. The relative abundances of terpanes display the tendency of pentacyclic triterpane 〉 trieyclic terpane 〉 quartcyclic terpane. Gammacerane is common, but has relatively low content. Steranes display the tendency of ∑（C27＋C28）〉∑C29,∑C27/∑C29 ratios ranging between 0.61 and 2.18 with an average of 1.06. The maturity parameters and vitrinite reflectanees also show that the organic matter in bitumen veins is now in the mature to overmature stages. The biomarkers in the bitumen veins from the Middle Jurassic Xiali Formation sandstone and mudstone are similar to those from the Buqu Formation carbonate rocks apart from different contents of saturated hydrocarbons and aromatic hydrocarbons.