Aromatic hydrocarbons as indicators of origin and maturation for light oils from Panyu lower uplift in Pearl River Mouth basin

Abstract

Aromatic fractions of six light oils and two source rock samples from Panyu (番禺) lower uplift of Pearl River Mouth basin were analyzed using GC-MS (gas chromatography-mass spectrometric) technique. Thirteen aromatic series of hydrocarbons detected such as biphenyls, naphthalenes, phenanthrenes, dibenzothiophenes (more than two hundred aromatic hydrocarbon compounds) were used to analyze the origin and maturity of the light oils. This study indicates that the distribution of aromatic hydrocarbon compounds in the light oils of wells L1 and P1 differs from those of wells P2, P3 and P4. The light oil samples from wells L1 and P1 contain more dibenzofuran and fluorence hydrocarbons and less naphthalene hydrocarbons. The contents of fluorene, dibenzothiophene and dibenzofuran in the two groups of light oils also show their difference in sedimentary environment. Moreover, the diversity of the relative distributions of biphenyl and naphthalene is apparent between the two groups of light oils. As mentioned above, the origin of the light oils from wells L1 and P1 varies from that of wells P2, P3 and P4. According to the result of oil-source correlation, the light oils from wells P2, P3 and P4 mainly originated from the source rocks in the Enping (恩平) Formation. Accordingly, the light oils from wells L1 and P1 may have been derived from the lacustrine shales in the Wenchang (文昌) Formation or from the mixed source of the Wenchang Formation and the Enping Formation. Applying maturity parameters of methylnaphthalenes, methylphenanthrenes and methyldibenzothiophenes from the aromatic hydrocarbons to the study of the maturity of light oils from Panyu lower uplift indicates that the maturity has reached the high mature stage.