Directory UMM :Data Elmu:jurnal:O:Organic Geochemistry:Vol31.Issue12.Dec2000:
Organic Geochemistry 31 (2000) 1441±1449
www.elsevier.nl/locate/orggeochem
Carbon isotopic composition of individual n-alkanes in
asphaltene pyrolysates of biodegraded crude oils from the
Liaohe Basin, China
Yongqiang Xiong, Ansong Geng *
The State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Wushan,
Guangzhou 510640, PR China
Abstract
Biodegraded oils are widely distributed in the Liaohe basin, China. In order to develop eective oil-source correlation tools speci®cally for the biodegraded oils, carbon isotopic compositions of individual n-alkanes from crude oils
and their asphaltene pyrolysates have been determined using the gas chromatography±isotope ratio mass spectrometry
technique. No signi®cant fractionation in the stable carbon isotopic ratios of n-alkanes in the pyrolysates of oil
asphaltenes was found for anhydrous pyrolysis carried out at temperatures below 340 C. This suggests that the stable
carbon isotopic distribution of n-alkanes (particularly in the C16±C29 range) in the asphaltene pyrolysates can be used
as a correlation tool for severely biodegraded oils from the Liaohe Basin. Comparison of the n-alkane isotopic compositions of the oils with those of asphaltene pyrolysates shows that this is a viable method for the dierentiation of
organic facies variation and post-generation alterations. # 2000 Elsevier Science Ltd. All rights reserved.
Keywords: GC±IRMS; Biodegraded oil; Asphaltene pyrolysis; n-alkane; d13C; Oil correlation; Liaohe basin
1. Introduction
The Liaohe basin is one of the most important Cenozoic sedimentary basins in NE China. Since the ®rst oil
discovery from the Xinglongtai ®eld in 1975, the Liaohe
basin has become the third largest oil-producing province in China, with 22 oil®elds in production. Previous
studies have shown that the fourth (Es4) and third (Es3)
members of the Eocene-Oligocene Shahejie formation
are the main source rocks in this basin (Editorial Committee for Petroleum Geology of China, 1993). In addition to normal gravity oils, heavy to extra-heavy oils
(
www.elsevier.nl/locate/orggeochem
Carbon isotopic composition of individual n-alkanes in
asphaltene pyrolysates of biodegraded crude oils from the
Liaohe Basin, China
Yongqiang Xiong, Ansong Geng *
The State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Wushan,
Guangzhou 510640, PR China
Abstract
Biodegraded oils are widely distributed in the Liaohe basin, China. In order to develop eective oil-source correlation tools speci®cally for the biodegraded oils, carbon isotopic compositions of individual n-alkanes from crude oils
and their asphaltene pyrolysates have been determined using the gas chromatography±isotope ratio mass spectrometry
technique. No signi®cant fractionation in the stable carbon isotopic ratios of n-alkanes in the pyrolysates of oil
asphaltenes was found for anhydrous pyrolysis carried out at temperatures below 340 C. This suggests that the stable
carbon isotopic distribution of n-alkanes (particularly in the C16±C29 range) in the asphaltene pyrolysates can be used
as a correlation tool for severely biodegraded oils from the Liaohe Basin. Comparison of the n-alkane isotopic compositions of the oils with those of asphaltene pyrolysates shows that this is a viable method for the dierentiation of
organic facies variation and post-generation alterations. # 2000 Elsevier Science Ltd. All rights reserved.
Keywords: GC±IRMS; Biodegraded oil; Asphaltene pyrolysis; n-alkane; d13C; Oil correlation; Liaohe basin
1. Introduction
The Liaohe basin is one of the most important Cenozoic sedimentary basins in NE China. Since the ®rst oil
discovery from the Xinglongtai ®eld in 1975, the Liaohe
basin has become the third largest oil-producing province in China, with 22 oil®elds in production. Previous
studies have shown that the fourth (Es4) and third (Es3)
members of the Eocene-Oligocene Shahejie formation
are the main source rocks in this basin (Editorial Committee for Petroleum Geology of China, 1993). In addition to normal gravity oils, heavy to extra-heavy oils
(