桂中坳陷东部下石炭统鹿寨组泥页岩有机地球化学特征

摘要

基于对桂中坳陷东部下石炭统鹿寨组泥页岩总有机碳含量(TOC)、有机质成熟度(Ro)、显微组分、饱和烃色谱-质谱等有机地球化学特征分析,发现其TOC主体>2.0%,Ro为0.84%~2.95%,有机质类型属于Ⅱ1-Ⅱ2型.通过对比国内外主要页岩气盆地富有机质泥页岩有机地球化学特征和分析研究区页岩气保存条件,判断下石炭统鹿寨组泥页岩具有较好生烃潜力.在此基础上,分析了鹿寨组泥页岩的沉积环境和有机质来源,发现:Pr/Ph<1,伽马蜡烷/αβC30霍烷比值为0.72~0.75,具有升霍烷系列,C27重排甾烷/C27规则甾烷比值为0.13~0.15,孕甾烷/C29-20R规则甾烷比值为0.03~0.04,研究区属于高咸度贫氧-缺氧的强还原环境;正构烷烃分布范围宽,C、N原子比为42.23~50.89,三环萜烷中C21、C23、C24呈倒"V"形分布, αβC30霍烷/∑C29甾烷比值为0.48~0.51,C29具有明显优势,伽马蜡烷指数平均值为0.37>0.2,不同显微组分在剖面上对TOC贡献率不同,判断鹿寨组泥页岩有机质来源多样,以高等植物和水生生物为主,顶部和底部层位有机质来源以低等细菌、藻类为主,具有较好的生烃潜力.%Based on the analysis of TOC, Ro, organic matter type, saturated hydrocarbon chromatogram-mass spectrometry and other organic geochemical characteristics of the shales in the Lower Carboniferous Luzhai Forma -tion in the east of Guizhong Depression, it is found that the subject of TOC>2.0%, Ro is between 0.84% and 2.95%, the organic matter type is II 1-II2.The shales of the Lower Carboniferous Luzhai Formation have better hydrocarbon potential by comparising organic geochemical characteristics of organic-rich shales in the main basin of having discovered shale gas in domestic and foreign and analyzing the storage conditions of shale gas in the study area.On this basis,the sedimentary environment and the organic matter source of shales in Luzhai Formation were analyzed.The results show that,the ratio of Pr/Ph<1,the ratio of the γ-wax /the αβC30octane is 0.72~0.75, it has the series of the lumine, the ratio of the C27rearrangement of sterane/the C27regular sterane is between 0.13~0.15,the ratio of the prostane /the C29-20R regular sterane is between 0.03~0.04 in the shales of Luzhai Formation.And accordingly,the study area belongs to the highly degraded, oxygen-deficient and strong reducing environment.At the same time,the distribution of n-alkanes was wide,the atomic ratio of C/N is between 42.23~50.89,C21,C23and C24are distributed in inverted"V"shape,the ratio of the αβC30octane/the ∑C29sterane is between 0.48 and 0.51,C29has obvious advantages,the average of the index of γ-wax is 0.37>0.2 in the shales of Luzhai Formation,and different microstructures have different contribution to TOC in the profile.Accordingly,it is concluded that the organic matter of shales in Luzhai Formation is diverse and it is mainly included in higher plants and aquatic organisms.The organic matter of shales in the top and bottom of Luzhai Formation is mainly in-cluded in the low bacteria and algae,which has better hydrocarbon potential.