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研究采用索氏抽提、饱和烃色谱-质谱分析及干酪根碳同位素等分析方法,针对重庆城口地区下寒武统黑色岩系有机地球化学特征,页岩气的有机质生源构成、成熟度、沉积环境等进行分析。结果表明所有样品中氯仿沥青“A”含量均较低,正构烷烃、类异戊二烯烃、甾萜类化合物含量丰富。GC-MS图中,正构烷烃显示明显的双峰型优势,碳数分布范围为C14~C31,双峰型前后主峰分别为nC18和nC23,单峰型主峰为nC16或nC18,OEP值为1.05~1.19,接近平衡值1.0,无明显奇偶优势,(nC21+nC22)/(nC28+nC29)比值大于1.5,nC17/nC31值为0.24~2.96,均值1.35,显示轻烃组分占绝对优势。干酪根δ13 CPDB值为-31.4‰~-34.7‰,变化较小,为腐泥型干酪根。萜类化合物中,五环三萜类化合物>三环萜烷>四环萜烷,可见少量伽马蜡烷和奥利烷。三环萜烷中C21,C23,C24和规则甾烷C27,C28,C29分别呈倒“V”字形和“V”字型分布,含量相差不大,推断有机质母质主要为菌藻类等低等水生物和海洋浮游生物。藿烷中C31αβ22S/(22S+22R)值为0.57~0.61,Ts/(Tm+Ts)值为0.43~0.50,βα-莫烷/αβ-藿烷比值0.12或0.11,Tm/Ts比值为1.0~1.35大于生油门限下限,甾烷中C29ααα20S/(20S+20R)值为0.41~0.46,C2920Rαββ/(ααα+αββ)值为0.40~0.46,反映有机质已达成熟~过成熟阶段。Pr/Ph值除个别大于1外皆为0.45~0.91,C27重排甾烷/C27规则甾烷值0.08~0.43,γ-蜡烷指数绝大部分都小于0.2,处于0.12~0.19之间,孕甾烷/C29-20R规则甾烷值为0.18~0.61,皆反映缺氧还原环境且沉积水体盐度不高,与前期元素地球化学研究结果所反映的缺氧环境一致。
Soxhlet extraction, saturated hydrocarbon chromatography-mass spectrometry and kerogen carbon isotope analysis were used to study the organic geochemical characteristics of the Lower Cambrian black rocks in the Chengkou area of Chongqing, the composition of organic matter sources of shale gas, maturity, Sedimentary environment and other analysis. The results showed that the content of chloroform bitumen in all samples was low, and n-alkanes, isoprenoids and terpenoids were abundant. In GC-MS, n-alkanes showed obvious bimodal advantages with carbon number distribution ranging from C14 to C31, nC18 and nC23 before and after bimodal, nC16 or nC18 with monomodal peak, and OEP value of 1.05 ~ 1.19, close to the equilibrium value of 1.0, no obvious even advantage, (nC21 + nC22) / (nC28 + nC29) ratio greater than 1.5, nC17 / nC31 value of 0.24 to 2.96, mean 1.35, indicating the absolute advantage of light hydrocarbon components. The kerogen δ13 CPDB values ranged from -31.4 ‰ to -34.7 ‰, with little change, which was sapropel kerogen. Among the terpenoids, pentacyclic triterpenoids> tricyclic terpanes> tetracyclic terpanes, a small amount of gamma-alkanes and orylenes were observed. The tricyclic terpanes C21, C23, C24 and regular steranes C27, C28, C29 were inverted “V ” shape and “V ” shape distribution, the content is not much difference, it is concluded that the organic matter is mainly composed of bacteria and algae Other low water creatures and marine plankton. In the hopane, the values of C31αβ22S / (22S + 22R) were 0.57-0.61, the values of Ts / (Tm + Ts) were 0.43-0.50, the ratio of βα-molylamine to αβ-hopane was 0.12 or 0.11, 1.35 is greater than the lower limit of the oil production threshold. The values of C29ααα20S / (20S + 20R) in sterane are 0.41-0.46, and the values of C2920Rαββ / (ααα + αββ) are 0.40-0.46, indicating that the organic matter has reached the mature to over mature stage. Pr / Ph values were all 0.45 to 0.91 except for a few greater than 1, C27 rearrangement sterane / C27 regular sterane value of 0.08 to 0.43, γ-wax index most of less than 0.2, between 0.12 to 0.19, pregnancy The sterane / C29-20R regular sterane has a value of 0.18-0.61, both of which reflect the environment of oxygen deficit reduction and the salinity of sedimentary water is not high, which is consistent with the anoxic environment reflected by the previous elemental geochemical study.