塔里木盆地一类新海相原油的地球化学特征

Geochemical Characteristics of A Novel Kind of Marine Oils from Tarim Basin

对塔中52等井奥陶系储层产出的原油进行的分析结果表明,它们的三环萜烷系列较为特殊,主要表现为其相对丰度呈C19>C20>C21>C23>C24>C25>C26阶梯状的模式,C24四环萜烷异常丰富,且其丰度远高于C26三环萜烷,这一分布模式一般出现在淡水沼泽相和浅湖相沉积地层与原油中。在三萜烷分布特征上,其伽马蜡烷含量很低,甾烷系列和藿烷系列的分布与组成特征与该地区来源于中上奥陶统烃源岩的海相原油十分接近,同时它们的全油均具有轻的碳同位素组成,其δ13C值都小于-30‰,具有海相成因原油的特征。而塔中12井上奥陶统良里塔格组4-5段烃源岩中生物标志物的分析结果进一步证实了该类原油与那些富含宏观藻残片,且有机质类型偏腐殖型的上奥陶统海相烃源岩关系密切,是该地区油气勘探中值得关注的对象。

The crude oils from Ordovician reservoir in TZ52 and TZ162 well have been analyzed,the results showed that there are some evident differences in the distributions and compositions of their biomarker from two kinds of the known marine oils in the middle zone of Tarim Basin.For example,it is firstly reported that its trycyclic terpane series is of special step-like model with C19〉C20〉C21〉C23〉C24〉C25〉C26 in relative abundance,C24 tetracyclic terpane is abnormally abundant and it relative abundance is much more than C26 tricyclic terpanes,which occurs in those source rocks and the crude oils deposited under fresh water swamp and shallow lacustrine facies.As for their triterpane series,the abundance of gammacerane is much less than C31 homohopanes,but the distributions of their sterane and hopane series are very similar to the marine oils derived from middle to middle-upper Ordovician source rocks such as with abnormally abundant pregnane and homopregnane,relatively lower C28 sterane in C27-29 steranes and more abundant C29 norhopane secondary to C30 hopane.In addition,their stable carbon isotope of whole oil is very light and their δ13C values are less than-30‰ like other marine oils,showing that this kind of crude oil is marine.Based on the biomarker data in the source rocks with abundant benthic marco-algae from 4-5 member of Lianglitage formation of upper Ordovician in TZ12 well,it is found that their distribution and the relative composition of its C19-26 tricyclic terpane,C24 tetracyclic terpane and gammacerane is very similar to this kind of crude oils,showing that there is a close relationship between this kind of novel crude oils and the source rocks.Therefore,it should pay much more attention to the source rocks and their exploration potential from Lianglitage Formation of upper Ordovician in Tarim Basin.