Composition Characteristics and Geochemical Significance of Aromatic  Hydrocarbons of Crude Oils from the Banqiao Depression

Key words: 
• aromatic hydrocarbon /
• maturity /
• depositional environment /
• Banqiao Depression

Abstract: Most of crude oils from the Banqiao Depression are condensate or light oils with lower density, lower viscosity, lower sulfur content and higher solidifying point as well as higher wax. The result of aromatic hydrocarbon fraction in oils by GCMS indicate that the content of regular polycyclic aromatic hydrocarbon series vary from 66.33% to 80.81%, the content of dibenzothiophene (SF), dibenzofuran (OF) and fluorene (F) series is 15% to 30%, and the content of fragrant sterane series is merely 5.55%. The naphthalene series and phenanthrene series are main components of regular polycyclic aromatic series. The maturity RC calculated from methylphenanthrene index (MPI1) showa that the crude oils from the Banqiao Depression are mature to higher mature, and the RC of Banshen 35 (Es3，4731m) reaches highly 1.60%. The correlation between the content of low carbon triaromatic sterane in all triaromatic sterane and MDR shows well, and the correlation of fragrant sterane content in aromatic hydrocarbon fraction and methylphenanthrene index (MPI3) or methyldibenzothiophene ratio (MDR) are also good. The distributed characteristics of SF, OF, and F series show that the primary depositional environments of the oils are pooroxidation and deoxidation environments with secondary paludal facies.