Keywords: 
• biodegradation oil /
• aromatic hydrocarbon /
• methylphenanthrene index /
• methyl-dibenzothiophene index /
• oil source correlation /
• Qiangtang Basin

Abstract: As an ipmortance component of crude oil and source rocks, aromatic biomarkers have been analysed for source, depositional envirment and maturity. Particularly, it’s more difficult biodegradation than the saturated hydrocarbon, so aromatic biomarkers perhaps  will  be widely used for the study of biodegradation oil. The biodegradation oil exsits  widely in the Qiangtang Basin, Tibet plateau. In order to effectively carry out the oil source correlation analysis, aromatic fractions of six oils from Longeni area of Qiangtang Basin were analyzed using GC-MS techique. Fifteen aromatic series of hydrocarbon detected such as naphthalene, phenanthrene, terfluorene( more than One hundred and seventy aromatic hydrocarbon compounds) were used to analyze the origin and maturity of the oil. Oils are characterized by a high abundance of phenanthrene and low of naphthalene, in the meantime, a certain amount of components  regarded as the marker  of terrestrial high plant were detected, such as cadalene, pimanthrene, retene and so on, which indicate the oil have derived from the source containing predominantly lower aquatic organisms combined with a small amount terrestrial higher plant deposited in a marine environment. The maturity stduy indicates methylnaphthalene index due to mixed source influence and cannot be used alone for maturity evaluation, but methylphenanthrene index and methyldibenzothiophene index are effective parameter for the maturity research of crude oil in Qiangtang Basin. Applying maturity parameters of methylnaphthalene, methylphenanthrene and methyldibenzothiophene from the aromatic hydrocarbon to the study of the maturity of oil from Longeni erea indicates that the maturity has reached the matrue stage in Qiangtang Basin.