Characteristics of Aromatic Geochemistry in Light Oils from Xihu Sag in East China Sea Basin

Key words: 
• Xihu Sag /
• light oils /
• aromatic hydrocarbon /
• geochemical characteristic /
• crude oil maturity

Abstract: Aromatic geochemical characteristics of thirteen light oil samples from nine Wells have been studied systematically by using GC-MS experimental technique. The results show that the distribution and relative content of aromatic compounds in the light oils from Well NB14-1, Well NB14-2 and well NB14-3 in the north of Pinghu slope belt are different from those of Well NB25-1 and Well NB25-2 in the middle of Pinghu slope belt, Well HY1-1 in the Xiciao, and Well HY2-1 and Well HY2-2 in Huangyan tectonic belt. The major components of aromatic fraction in light oils are bicyclic and tricyclic compounds. The light oil samples from the former wells contain more phenanthrene hydrocarbons and less naphthalene and biphenyl hydrocarbons. Meanwhile, the latter wells contain more naphthalene and biphenyl hydrocarbons and less phenanthrene hydrocarbons. The study on the source and depositional environment shows that the source material of light oils is mainly terrestrial higher plants input, and the depositional environment is oxidizing environment, but the latter wells has a higher 1,2,5-TMN and 1,2,5,6-TeMN relative content, and has a greater relative content of dibenzofuran and Pr/Ph value, reflecting that which has a greater degree of higher terrestrial plants input, with a stronger oxidative deposition environment. Alkyl-naphthalene, alkyl-phenanthrene and alkyl-dibenzothiophen are found to be optimal parameters for assessing thermal maturity characteristics, and the study shows that the light oils have reached mature-high mature oil characteristics, and the light oils in Well NB14-1, Well NB14-2 and NB14-3 have a higher maturity relatively.