Carbon isotopic composition of individual n-alkanes in asphaltene pyrolysates of biodegraded crude oils from the Liaohe Basin, China

Biodegraded oils are widely distributed in the Liaohe basin, China. In orde r to develop effective oil-source correlation tools specifically for the bi odegraded oils, carbon isotopic compositions of individual n-alkanes from c rude oils and their asphaltene pyrolysates have been determined using the g as chromatography-isotope ratio mass spectrometry technique. No significant fractionation in the stable carbon isotopic ratios of n-alkanes in the pyr olysates of oil asphaltenes was found for anhydrous pyrolysis carried out a t temperatures below 340 degreesC. This suggests that the stable carbon iso topic distribution of n-alkanes (particularly in the C-16-C-29 range) in th e asphaltene pyrolysates can be used as a correlation tool for severely bio degraded oils from the Liaohe;Basin. Comparison of the n-alkane isotopic co mpositions of the oils with those of asphaltene pyrolysates shows that this is a viable method for the differentiation of organic facies variation and post-generation alterations. (C) 2000 Elsevier Science Ltd. All rights res erved.