塔河油田原油沥青质包裹烃地球化学特征及油源判识

Geochemical Characteristics of Hydrocarbons Occluded in Asphaltene and Oil Source Identification in Tahe Oilfield

为解决塔里木盆地塔河油田的油源争议问题,选择该油田主体区TK772井原油,对原油和沥青质温和氧化产物包裹烃的地球化学特征进行了对比研究。结果表明,沥青质包裹烃具有正构烷烃偶碳优势、姥植比低、C_(29)藿烷/C_(30)藿烷低、C_(35)藿烷/C_(34)藿烷低、成熟度低、Ts/(Ts+Tm)高和伽马蜡烷指数高等特点,说明其母源形成于局限台地、高盐度、强还原、水体分层的蒸发岩环境,代表了塔河油田最早期充注原油的特征。而TK772井原油的饱和烃生物标志化合物特征则与沥青质包裹烃明显不同,反映其母源形成于水体开阔、盐度较低的碳酸盐岩沉积环境,代表了塔河油田主体区多数原油的特征。根据这些新的地球化学证据,结合前人关于塔北地区烃源岩分布与沉积相关系的研究结果,认为塔河油田存在3期成藏,第一期是寒武系台内凹陷蒸发岩烃源岩的贡献,第二期是上奥陶统碳酸盐岩烃源岩的贡献,第三期是塔河外围晚期高熟轻质油充注。

To solve the disputes on oil source in Tahe oilfield of Tarim basin,the paper selects the oil obtained from Well TK772 in the ma-jor area of the oilfield to comparatively study the geochemical characteristics of the crude oil and the hydrocarbons occluded in the asphal-tene oxidation products.The results show that the hydrocarbons occluded in asphaltene are characterized by even carbon preference in N-alkanes,low pristane to phytane ratio,low C29/C30 hopane ratio,low C35/C34 hopane ratio,low maturity,high Ts/(Ts+Tm)ratio and high gam-macerane index and so on,indicating that its oil source was formed in an evaporite environment with restricted platform,high salinity,strong reduction and zonal water body,which represents the oil charging characteristics at the earliest stages in Tahe oilfield.The character-istics of the biomarkers of saturated hydrocarbon in Well TK772 which is significantly different from that of the hydrocarbons occluded in asphaltene reflects that its oil source was formed in a depositional environment of carbonate rocks with broad water body and low salinity,representing the characteristics of the most oil in Tahe oilfield.Based on these newly obtained geochemical evidence and combined with the previous research results on the relationship between source rock distribution and sedimentary facies in the northern Tarim basin,it is considered that the oil accumulated in 3 periods in Tahe oilfield,the first-period oil originated from the Cambrian source rocks of evaporite facies in the platform;the second-period oil from the Upper Ordovician carbonate source rocks and the third-period from the high-maturity light oil charging at the late stage in the periphery of Tahe oilfield.