惠州凹陷原油成因研究

Study on oil genesis in Huizhou Depression

采用单质谱、串联质谱及单体烃碳同位素分析技术,分析检测了惠州凹陷24个原油样品,对部分复杂成因类型原油的来源取得了新认识。惠州凹陷主要分布3类原油:来源于文昌组中深湖相烃源岩的原油;来源于恩平组河沼相烃源岩的原油;成因类型复杂的混源油。混源油可能是文昌组与恩平组不同类型原油的混源,或是由于文昌组烃源岩中原始有机质母质输入不同造成的。混源油的异戊二烯烷烃分子碳同位素表现出2种不同的分布特征,为δ13CPr>δ13CPh和δ13CPr<δ13CPh。Ph较Pr明显贫13C的特征在一定程度上说明甲烷生成菌脂类对植烷的重要贡献。来源于文昌组中深湖相烃源岩贡献的原油单体烃碳同位素相对富集δ13C,可能与藻类的勃发导致的13C富集有关。

Using the analysis technology of single mass spectrometry,tandem mass spectrometry and single hydrocarbon carbon isotope,24 oil samples in Huizhou Depression were detected and the new understanding of the sources of complex crude oil types was made.The study results show that the oils in Huizhou Depression can be divided into three types.The first type mainly originates from the middle-deep lacustrine source rocks in Wenchang Formation.The second type derives from the river mash source rocks of Enping Formation.The third type is mixed oil having complex genetic types,which are mix sources of oils from Wenchang and Enping Formation,or are caused by different parent materials in the source rocks of Wenchang Formation.The carbon isotope of isoprenoid hydrocarbons of mixed oils show two different characteristics,which are δ13CPrδ13CPh and δ13CPrδ13CPh.Pr is rich in 13C relative to Ph,which shows that methanogenic bacteria can constitute additional inputs of phytane.Oils originated from the middle-deep lacustrine source rocks in Wenchang Formation generally have heavy δ13C value.Blooming of algae can result in an enrichment of 13C.