应用石油中“三芴”系列判识沉积环境的几个问题

Several Problems on the Use of Relative Abundances of Fluorenes, Dibenzofurans and Dibenzothiophenes in the Study of Depositional Environment

摘要: 石油和沉积有机质中芴、二苯并噻吩、二苯并呋喃通常合称“三芴”系列，其相对含量与有机质的沉积环境密切相关，已成为判识沉积环境的重要分子标志物。本文采用三种不同的方法，即只统计母核分子、考虑一个甲基取代、考虑两个甲基取代同系物系列，考查其对“三芴”系列相对含量计算结果的影响。结果表明无论是来自典型氧化沉积环境的湖相泥岩成因原油，还是来自典型还原沉积环境的海相碳酸盐岩成因原油，不同计算方法对芴的相对含量值没有明显的影响，而对二苯并噻吩和二苯并呋喃相对含量具有较大的影响。考虑的甲基取代个数越多，二苯并呋喃的相对含量增高越多，最大可达15%左右，而二苯并噻吩相对含量相应降低。本文从“三芴”系列的成因、甲基化和去甲基化等角度进行了分析。最后指出在利用“三芴”系列进行沉积环境判识和油-油(源)对比时，要采用相同的统计方法，统计到多甲基取代同系物系列。

Abstract: The relative abundances of fluorene (F), dibenzofuran (DBF) and dibenzothiophene (DBT) and their methyl substituted homologues in oils and sedimentary organic matters are important geochemical parameters indicating the depositional environments. This paper discusses the relative contents of Fs, DBFs and DBTs using three different methods, i.e. only considering parent molecules, including methyl- and dimethyl-homologues, respectively. It suggested that the relative abundances of fluorenes keep an approximately constant value in oils originated from both typical oxic terrestrial lacustrine shales and anoxic marine carbonate source rocks. In comparison, the relative abundance of DBFs is relatively higher when methyl- and dimethyl-dibenzofurans were considered. Correspondingly, the relative abundances of DBTs decrease by a maximum of 15%. The paper preliminarily analyzes the chemical mechanism that results in these differences between Fs, DBFs and DBTs. It is concluded that it is better to consider more methylated homologues and same statistic method must be applied in data sets with different sources.