Pyrolysis of petroleum asphaltenes from different geological origins and use of methylnaphthalenes and methylphenanthrenes as maturity indicators for asphaltenes

摘要

Asphaltenes separated from two different crude oils from upper Assam, India, having different geological origins, viz. DK (Eocene) and JN (Oligocene-Miocene) were pyrolysed at 600°C and the products were analysed by gas chromatography-mass spectrometry (GC/MS) especially for the generated alkylnaph-thalenes and alkylphenanthrenes. Both the asphaltenes produced aliphatic as well as aromatic compound classes. Alkylnaphthalenes and alkylphenanthrenes were identified by using reference chromatograms and literature data and the distributions were used to assess thermal maturity of the asphaltenes. The ratios of β-substituted to a-substituted isomers of both alkylnaphthalenes and alkylphenanthrenes revealed higher maturity of the JN asphaltenes than the DK asphaltenes. For both the asphaltenes the abundance of 1-methylphenanthrene dominated over that of 9-methylphenanthrene showing the terrestrial nature of the organic matter.