利用芳烃参数探讨塔里木盆地库车坳陷原油中高丰度重排藿烷类的成因

Using Aromatic Paramaters to Study the Origin of High Abundance of Rearranged Hopanes in Crude Oils in Kuche Depression,Tarim Basin

通过色谱-质谱技术,系统剖析了塔里木盆地库车坳陷具有不同丰度重排藿烷的原油饱和烃与芳烃分子组成特征,并应用芳烃参数对原油中高-异常高丰度重排藿烷的成因进行了探讨。研究发现,具有高-异常高丰度重排藿烷的原油其二环+三环芳烃占总芳烃相对百分含量很高,平均值大于98%;而低丰度重排藿烷类的原油中其相对百分含量较低,说明陆源高等植物可能为重排藿烷的重要生物来源。原油中重排藿烷类化合物相对丰度与氧芴(OF)含量具有正相关性,揭示两者形成过程可能具有相似的沉积环境。研究区原油甲基菲比值MPR值主要介于1.00~1.18之间,对应的Ro值分布范围为0.88%~0.92%,暗示这些原油中重排藿烷类化合物相对丰度的高低与成熟度关系不大。有鉴于此,塔里木盆地库车坳陷原油中重排藿烷类化合物的相对丰度主要受控于烃源岩沉积环境和生物来源。在弱氧化-弱还原环境中,水体盐度较低,陆源高等植物的贡献越大越有利于重排藿烷类化合物的形成。

By Gas chromotography- mass spectrometry technique,and based on the systematic analysis of molecular components characteristics of saturated hydrocarbons and aromatic hydrocarbons in crude oils with different abundance of diahopanes from the Kuche depression,Tarim basin,the discussion on the origin of the high- abnormal high abundance of diahopanes in the crude oils was carried out by the application of aromatic parameters. It was found that the relative content of bicyclic and tricyclic aromatic hydrocarbons was very high in the crude oils with high-abnormal high abundance of rearranged hopanes,the average content was above 98%,while the crude oils with low abundance of diahopanes had a relative lower content of them,it could be deduced that terrigenous higher plants may be an important biological sources of diahopanes; and a positive correlation were observed between the relative abundance of diahopanes and the ratios of OF /（ F ＋ OF）,the result showed that they maybe have a similar depositional environment; and the MPR values of crude oils from the researched area were mainly between 1. 00 and 1. 18,and the corresponding Ro values range was 0. 88%-0. 92%,which suggested that the correlation of the relative abundance level of diahopanes and the maturity of crude oils was not significant.Thus,the relative abundance of diahopanes in crude oil from Kuche depression,Tarim basin was mainly controlled by the sedimentary environment and biological input of source rocks. Then the greater the contribution of terrigenous higher plants were more favorable to the formation of diahopanes under the weak oxidation to weak reduction environment and with a low salinity water.