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塔里木盆地下古生界存在中—下寒武统和中—上奥陶统两套有效烃源层。前者 R。已达2.0％以上,只能作为有效气源岩;后者成熟度适中且有一定分布范围,是塔里木盆地最现实的烃源层,可分为三段,其中以上奥陶统中部的印干组和良里塔格组最具重要意义。对盆地中海相原油与寒武系和奥陶系岩石抽提物中甲基甾垸、三芳甲基甾烷及降胆甾烷的分布进行直观对比,表明原油与中—上奥陶统存在亲缘关系,而与寒武系无明显相关。全盆地所有钻遇的寒武系岩样,C_(27)—C_(28)—C_(29)甾烷碳数分布呈“斜线”型或反“L”型,而绝大部分中一上奥陶统岩样则呈不对称“V”字型分布。所分析的储层沥青的甾烷碳数分布与上述寒武系岩样一致,说明寒武系生油岩在地质历史上确曾生过油。包括塔中4、轮南、桑塔木和东河塘等在内的工业性油田产出的油,其甾烷碳数都呈不对称“V”字型分布,只有极少数的油样呈“斜线”或反“L”型分布,因此塔里木盆地的原油主要与中—上奥陶统相关,而与寒武系相关极少。运用C_7温度参数评价原油成熟度,结果为塔里木盆地主要油区原油的形成温度在117～133℃之间,对应的 R。值为0.78％～0.92％,只相当于中等成熟阶段,可以推断它们不可能源于寒武系,只能源于奥陶系。
Lower Paleozoic in the Tarim Basin there are two sets of effective hydrocarbon source layer of the Middle-Lower Cambrian and Middle-Upper Ordovician. The former R. Which has reached more than 2.0% and can only serve as effective gas source rocks. The latter is moderately matured and has a certain distribution range. It is the most realistic hydrocarbon source layer in the Tarim Basin and can be divided into three sections. Among them, The group and the Lianglitage group the most significant. An intuitive comparison between the distributions of methylstestarch, triarylmethylstesthane and cholestane in the marine facies oil of the basin and the Cambrian and Ordovician rock extracts shows that there is a close relationship between the crude oil and the Middle-Upper Ordovician Relationship, but no significant correlation with the Cambrian. For all the Cambrian rocks encountered in the whole basin, the carbon number distribution of C 27 C 28 C 29 Cys is “diagonal” or anti “L” The Upper Ordovician rock samples are asymmetric “V” shaped distribution. The analyzed bitumen carbon isotopic distribution is consistent with the above Cambrian rock samples, indicating that the Cambrian source rock did have oil in the geological history. Oil produced in industrial fields, including Tazhong 4, Lunnan, Santarum and Donghitang, showed asymmetric “V” carbon numbers in their steranes and only a few oil samples “Slash” or anti-“L” type distribution, so the oil in the Tarim Basin is mainly associated with the Middle-Upper Ordovician, while there is very little correlation with the Cambrian. The C_7 temperature parameter was used to evaluate the crude oil maturity. As a result, the formation temperature of the crude oil in the main oil region of Tarim Basin was between 117 and 133 ° C, corresponding to R. The value of 0.78% ~ 0.92%, equivalent to only moderately mature stage, we can infer that they can not originate from the Cambrian, only from the Ordovician.