塔里木盆地英买力地区原油地球化学特征与族群划分

塔里木盆地英买力地区油气成因复杂,采用多馏分、多组分化学成分分析及单体烃碳同位素分析途径,对该区海相、陆相油进行精细分析。结果表明,英买力油田主要有两大类油组,分别是南部YM2井区的海相油(I类)和北部YM7井区的陆相油(Ⅱ类),各自具有典型的海相油与陆相油的特征。进一步分析表明,两大油组内部仍有分异。将第二油组进一步分为两亚类,以中、古生界产层为主的正常黑油和重质油为一类(Ⅱa),以古近系为主的凝析油为另一类(Ⅱb)。两亚类原油正构烷烃单体烃同位素稍有差异,芳烃组成与分布具有显著差异。较之于Ⅱa原油,Ⅱb原油富含联苯系列与氧芴系列、不同类型芳烃系列中以低分子量同系物占绝对优势,其正构烷烃单体烃碳同位素更重,与相邻的羊塔克地区原油表现出一定的相似性,表明两者之间有一定的成因联系,前者可能为混源油,由位于库车坳陷中拜城凹陷提供两种陆相烃源岩。英买力地区陆相油并非以往确认的一种成因类型,可能至少由两套性质迥异的中生界烃源岩供烃。英买力地区第一类海相油(I类)尽管生物标志物特征相近,但分析原油的单体烃碳同位素具有显著差异,同样存在油气混源的可能。英买力地区海、陆相原油特征与成因的深入剖析,对于该区精细油源确认、油气成藏机制乃至油气资源评价具有重要意义。

Geochemical Characteristics and Families of the Crude Oils in the Yingmaili Oilfield, Tarim Basin

The genetic type of the oil in the Yingmaili Oilfield in the Tarim Basin is rather complex.Multiple geochemical approaches,including GC and GC/MS analysis of hydrocarbons in a gasoline range,biomarkers and aromatics fractions as well as compound specific isotope analysis of n-alkanes,are adopted to characterize and classify oils in the area.Two main genetic oil families have been recognized in the Yingmaili Oilfield,namely marine oil family(I) in the YM2 well-block and terrestrial oil family(Ⅱ) in the YM7 well-block,which have typical characteristics of marine and terrestrial oils respectively.However,further investigations show that there are still some differences in either of the oil families.The oil family Ⅱ is divided into two sub-groups: One is primarily normal black and heavy oils produced form the Palaeozoic and Mesozoic intervals(Ⅱa),the other(Ⅱb) mainly condensate oils from the Eogene.There are some disparities of compound specific carbon isotope of n-alkanes and distinctive differences of the composition and relative distribution of aromatics in the oils.The Ⅱb oil is distinguished from Ⅱa by relatively high abundances of diphenyl and dibenzofurane series in aromatics,and significant advantages of various aromatics,such as naphthalene,phenanthrene and chrystane,each of which has a low molecular weight relative to that of the homologues with a high molecular weight.Furthermore,the Ⅱb oil is also characterized by a little heavier compound specific carbon isotope of n-alkanes as compared with the Ⅱa.All those features of Ⅱb are similar to those of the oils in the adjacent Yangtake oilfield,suggesting that there must be a certain genetic relationship between them and that the former is likely to be mixed-source oils from the Mesozoic source rocks in the north Baicheng Depression of the Kuqu sub-basin,which does not agree with the previous opinion about one genetic type of oil discovered there.Despite some similar biomarkers observed for the oil of family I in the YM2 well-block,the distribution pattern of the compound specific carbon isotope of n-alkanes in the oil of YM2(O1) and YM201(O) wells in the block is impressively distinct,suggesting different sources and oil mixing probabilities.This study might be helpful for further source rock identification and hydrocarbons accumulation mechanisms unravelment as well as petroleum resource evaluation in the area.