Geological Implications of Polycyclic Aromatic Hydrocarbons in Oils Derived from Terrigenous Materials

LI, CINDY XINYU, University of Oklahoma, Norman, OK

The aromatic fractions of 20 oil samples from different basins in China, Australia, and New Zealand were analyzed by means of infrared spectroscopy, H nuclear magnetic resonance spectroscopy, organic elemental analysis, and gas chromatography/mass spectrometry. The results demonstrate that the depositional environment exerted as important an influence upon the proportions of aromatic components and the polycyclic aromatic hydrocarbon (PAHs) distribution as did the level of thermal maturity. The PAHs of oils from swamp environments of Australia and New Zealand with higher plant input show a high degree of aromatization and a low level of alkyl side-chain substitution. By contrast the PAHs of oils from the saline lake environment of China show a high level of alkyl side-chain substituti n and have a lower degree of aromatization.

The distribution of PAHs in crude oils were controlled by organic matter types, depositional environment, and thermal maturity. The biomarkers indicative of higher plants include cadalene, retene, norabietene, beta-amyrin, and lupeol derivatives. Organic sulfur compounds were identified in oils from hypersaline, reducing, and sulfur-abundant environments. The benzohopane series [C(32+)-C(35+)] were identified in oils from both swamp and hypersaline environments, probably reflecting high levels of early bacterial activity. The relative abundance of fluorene, dibenzothiophene, and dibenzofuran series in oils can differentiate the depositional environment of source rocks. Methylphenanthrene indices (MPIs) proved to be good maturity parameters and could be compared with maturity parameter based on sterane and hopane isomers.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)