塔里木盆地柯坪露头剖面中上奥陶统烃源岩地球化学特征与海相油源对比

采用有机地球化学扫描分析方法,对塔里木盆地柯坪地区6条剖面上发育的中上奥陶统烃源岩进行了细致分析。大湾沟剖面、喀马提坎剖面、通古斯布隆剖面中上奥陶统萨尔干组烃源岩较为发育,泥页岩有机碳含量大多大于1.0%;上奥陶统印干组烃源岩仅在大湾沟剖面发育。结合肖尔布拉克剖面、苏盖特布拉克剖面、于提西剖面下寒武统玉尔吐斯组烃源岩地球化学分析,发现柯坪地区玉尔吐斯组、萨尔干组、印干组在分子地球化学参数上显示出相似性,呈现以C23三环萜烷为主峰、伽马蜡烷和C28甾烷含量较高的特征,烃源岩生物标志物面貌趋同与烃源岩较高成熟度有关。而海相原油中C28甾烷含量大多小于25%,与柯坪地区寒武系-奥陶系烃源岩具有较大的差异性。在组分碳同位素组成上,下寒武统玉尔吐斯组烃源岩均显示比中上奥陶统烃源岩值偏低的特点,特别是玉尔吐斯组干酪根碳同位素值,偏低超过5‰。中上奥陶统萨尔干组和印干组烃源岩组分碳同位素之间差异并不十分显著。在排除油气藏的TSR作用前提下,烃源岩干酪根碳同位素可以作为潜在的油源对比指标。

The geochemical characteristics of Middle-Upper Ordovician source rocks in Keping outcrops profiles and marine oil-source correlation,Tarim Basin,NW China

The Middle-Upper Ordovician source rocks developed in six outcrop profiles in Keping area,Tarim Basin,NW China were analyzed using organic geochemical scanning method. Source rocks of Middle-Upper Ordovician Salgan Formation developed in Dawangou,Kamatikan and Tonggusibulong outcrop profiles,with most TOC value greater than 1.0%. Whereas source rocks of the Upper Ordovician Yingan Formation only developed in the Dawangou outcrop profile. Combined with the analysis results of Lower Cambrian Yuertusi Formation developed in Xiaoerbulake,Sugaitebulake and West Yuti outcrops profiles,the source rocks of Yuertusi Formation,Salgan Formation and Yingan Foramtion showed similar molecular geochemical characteristics,with lower Pr/Ph value,C23 greater than C21 tricyclic terpane,higher gamacerane and higher C28 steranes content. The similarity in molecular compounds of Cambrian to Ordovician source rocks in Keping area may be a result of the high maturity. In the relative content of C27-C29 steranes,the most marine oils with C28 sterane lower than 25% showed great difference with that of the source rocks of Cambrian to Ordovician source rocks in Keping area. In the fraction carbon isotopes,the source rocks of the Lower Cambrian Yuertusi Formation have lower carbon isotopes,compared with that of the Middle-Upper source rocks. Especially in kerogen carbon isotopes,Lower Cambrian Yuertusi Formation is 5‰ lower than that of Middle-Upper Ordocivian source rocks.Overall,the carbon isotopic fractionation of saturate,bitumen,aromatic fraction,non-hydrocarbon fraction,asphaltenes and kerogen is small in source rocks from Middle-Upper Ordovican Salgan and Yingan Formation in Keping area. The carbon isotopes of kerogen of source rocks can be used as a parameter for oil-source correlation excluding the TSR of the oil reservoirs.