塔里木盆地北部地区上奥陶统烃源条件

塔里木盆地北部地区已有大量钻井揭示上奥陶统恰尔巴克组、良里塔格组和桑塔木组。对钻井样品烃源条件系统分析表明,上奥陶统特点是有机质丰度低,有机质类型以腐殖-腐泥型为主。塔河南地区上奥陶统镜质体反射率为1%左右,烃源岩不发育,基本不具备形成规模油气的烃源条件。塔里木盆地北部上奥陶统碳酸盐岩具有既可能是烃源岩又可能是储层的双重特点,常规的油-岩对比可能成为实际意义上的油-油对比。文中采用了两种油-岩对比方法,以岩心直接抽提物及经抽提处理后的热模拟产物分别与原油进行对比。结果表明,塔河原油与上奥陶统烃源岩基本没有源属关系,上奥陶统烃源岩直接抽提物的地球化学特征介于原油与岩心热解模拟产物之间,而原油与上奥陶统岩心热解模拟产物则主要表现为差异性。新的油-岩对比方法在研究思路上解决了上奥陶统作为储集层与烃源岩于一体、不能直接进行常规油-岩对比的局限性。

Upper Ordovician source rocks in northern Tarim Basin

Many wells have encountered the Qrebake,Lianglitaga and Sangtamu formations in Upper Ordovician of northern Tarim Basin.A systematic analysis of source rock samples from the sequence indicates that it was characterized by low abundance of organic matters and mixed organic types.In southern Tahe area,the Upper Ordovician source rock is poorly developed with a vitrinite reflectance (R_o) of about 1%,thus could not be the source of commercial oil and gas reservoirs.In contrast,in northern Tarim Basin,the Upper Ordovician carbo-nates are both source rocks and reservoirs,making conventional oil-source correlation impossible.The study adopted two oil-source correlation methods to compare the properties of direct extracts from source rocks and their pyrolysis yields with that of crude oil from the reservoirs.The result shows that there is no source-product relationship between the crude from Tahe oilfield and source rocks from the Upper Ordovician.The geochemical characteristics of direct extracts from the Upper Ordovician source rocks are something between that of crude oil and pyrolysis yield,while the geochemical characteristics of crude oil and the pyrolysis yield are quite different.The new method of oil-source correlation solved the problem of the conventional oil-source correlation method not applicable to the Upper Ordovician as it is both source rocks and reservoirs at the same time.