四川盆地古生界泥页岩的地球化学特征

Geochemical characteristics of Paleozoic shale in Sichuan Basin and their gas content features

通过四川盆地古生界不同层系的探井及典型剖面样品的地球化学分析,从有机碳含量、有机碳同位素,热成熟度以及生物标志化合物特征讨论了四川盆地古生界4套泥/页岩地球化学特征及其生烃潜力。研究结果表明:古生界下寒武统、上奥陶统、下志留统3套黑色页岩有机碳含量高,平均值分别为6.31%,3.53%,1.87%,有机质类型主要为生烃能力极强的I型干酪根,δ13C分布在-29.0‰^-32.0‰,低碳数正构烷烃相对丰度高、C27规则甾烷优势分布、三环二萜烷的相对含量较高等生物标志化合物分布特征表现了腐泥型有机质特征,有机质来源为低等水生生物和藻类;上二叠统龙潭组泥/页岩有机碳含量平均为4.0%,有机质类型为II,III型,生物标志化合物研究表明龙潭组页岩既有丰富的水生生物输入,又有一定数量的陆生生物来源,煤和炭质泥岩母质来源以陆源有机质输入为主。

Through geochemistry analysis of core and outcrop samples from different Paleozoic strata in Sichuan Basin,geochemical characteristics and hydrocarbon generation potential of the 4 sets shales were discussed from organic carbon isotope,thermal maturity and biomarker characteristics.The results show that three sets of Paleozoic high quality black shales（i.e.Lower Cambrian Qiongzhushi Formation,Upper Ordovician Wufeng Formation,and Lower Silurian Longmaxi Formation） have high organic abundance,with an average percentage of 6.31%,3.53% and 1.87%,respectively.The main type of organic matter for all three sets of Paleozoic high quality black shales is of sapropalic Type I,with δ13C for TOC（total organic carbon） ranging from-29.0‰ to-32.0‰.The higher relative abundance of low-molecular n-alkanes,C27 regular steranes,and tricyclic terpanes show that the organic matters in the Paleozoic high quality black shales are derived from lower hydrobiont and algae.The average organic carbon abundance of Upper Permian Longtan shale is 4.0%,and the organic matter is of Type II and III.The study of biomarkers indicates that the organic matter in Longtan shale is mainly of aquatic and continental organic matter input,whereas the organic mater in Longtan coal and mudstone are terrestrial organic matter input.