Characteristics of aromatic hydrocarbons in crude oils

Abstract

Crude oils from different basins in China, Australia and New Zealand were analyzed to character ize aromatic hydrocarbons produced in different environments by means of GC/MS. The distributions of some common compounds such as naphthalene, phenanthrene, ehrysene, pyrene, fluoranthene, fluorene, dibenzothiophene and dibenzofuran were found to be related to sedimentary environments. Especially the relative contents of fluorenes, dibenzofurans and dibenzothiophenes can be used to divide the oils into three types: (1) saline or marine carbonate environment; (2 ) fresh-brackish water lake; (3) swamp and coal-bearing sequence. Aromatic biomarkers (e.g. retene, nor-abietene, derivatives of lupeol and β-amyrin) represent higher plant inputs with respect to the precursors of crude oils. High contents of sulphur-containing compounds like benzothiophene and dibenzothiophene series indicate a reducing sulphur-abundant diagenetic condition. The benzohopane series (C32–C35) was identified both in hypersaline and coal-bearing basins, and it is postulated to be the result of strong bacteria activity. In all the samples, a complete series of alkyl benzenes was analyzed. The similarity of its carbon-number distribution with that of n-alkanes probably suggests their genetic relationship. The distribution of the methylphenanthrene series reflects the evolution degree of crude oils, MPI holding a positive correlation with C29-sterane 20S/(20S+20R).