原油中芳烃及其碳稳定同位素组成特征

Characteristics of aromatic hydrocarbons and its stable carbon isotope compositions in crude oils

  • 摘要: 芳烃作为原油的主要组分之一,蕴含丰富的地球化学信息,常用原油中芳烃的分布及其碳稳定同位素组成来评价原油的有机质来源和热成熟度等指标。为了补充油品化学指纹的基础鉴别指标和数据,找出适用于油样鉴别的芳烃地球化学指标以及碳稳定同位素组成,本文主要测定了来自不同地区七种原油芳香烃组分的相对含量以及碳稳定同位素组成,并计算分析了甲基萘比值(MNR)、二甲基萘比值(DNR)、三甲基萘比值(TNR)、甲基菲比值(MPR)、甲基菲指数(MPI1)和甲基菲分馏系数(MPDF)等常见的芳烃特征比值。从原油中芳烃组分相对含量分布来看,七种原油均显示出了各自的特点;从原油芳烃的特征比值来看,成熟度参数(MNR、TNR1、TNR2、MPR、MPI1、MPDF1和MPDF2)均反映出所有原油的高成熟度,其它芳烃参数如DNR1、DNR2和TNR4等比值反映原油的母质来源及生物降解等信息,由芳烃特征比值的单因素方差分析(ANOVA)结果可知,与成熟度参数MNR和MPI1相比,DNR1、DNR2和TNR4在不同原油间的差异更加明显;从原油芳烃碳稳定同位素组成来看,不同地区原油间差别较大,其中巴西原油最富集13C,阿曼原油和委内瑞拉原油最亏损13C,二甲基萘和菲的碳稳定同位素组成在不同油样间的差异最明显。将显著性差异大的芳烃参数与芳烃δ13C值联用,结果表明,该方法可以更加有效区分七种原油。最后使用主成分分析方法分析原油芳烃碳稳定同位素组成,七种原油显示出各自不同的碳稳定同位素组成特征和明显的区分效果,利用不同油样芳烃的碳稳定同位素组成差异可实现对油样来源的鉴别。

     

    Abstract: Aromatic hydrocarbons contain plenty of geochemistry information as ubiquitous constituents of crude oils.Characteristics of aromatic hydrocarbons and its stable carbon isotope compositions are usually used to assess the source and thermal maturity.In order to find out the aromatics geochemical index and the stable carbon isotope compositions which are suitable for oil samples identification.The composition of aromatics and their stable carbon isotope composition in different areas were studied.In this paper, relative contents, characteristic ratios and stable carbon isotope compositions of aromatic hydrocarbons in crude oils were determined from different areas.In terms of aromatic hydrocarbons relative contents, seven kinds of crude oils have shown their own features.From the characteristics of the ratios of aromatic hydrocarbon in crude oil, the maturity parameters (MNR、TNR1、TNR2、MPR、MPI1、MPDF1 and MPDF2) reflected high maturity of all the crude oil, other parameters, such as DNR1、DNR2 and TNR4, revealed the organic source and biodegradation of crude oil and other information.From the one-way analysis of variance (ANOVA) results of aromatics feature ratios, it was found that the differences between DNR1, DNR2 and TNR4 in different crude oils were more obvious than those of MNR and MPI1. From the compositions of stable carbon isotope of aromatic hydrocarbons in crude oils, crude oils between the various regions have the differences which the Brazil crude oil enriched 13C while of Oman crude oil and Venezuelan crude oil showed depleted 13C.Plots of aromatic hydrocarbon ratios versus δ13C values of dimethylnaphthalene and phenanthrene were constructed to discriminate crude oils from different areas.The results demonstrate that this method can distinguish different kinds of crude oisl more effectively.Finally, principal component analysis (PCA) were applied to the compositions of stable carbon isotope of aromatic hydrocarbons data sets in order to evaluate their different features.Indeed, there are diverse stable carbon isotope compositions characteristics and clear distinction among these crude oils.the use of aromatics stable carbon isotopic compositions of diverse oils can be applied on the identification of oil samples source.

     

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