Genetic Characteristics of Crude Oils from Yakela Oilfield in Tabei Uplift

Key words: 
• Tabei Uplift

Abstract: Geochemical analysis was completed for crude oils from Yakela oilfield to investigate geochemical characteristics and genetic type of crude oils. The heptane value, isoheptane value and MCYC₆ index of crude oils in Yakela oilfield provided excellent evidence for marine oils characteristics. Compoundspecific carbon isotope of light hydrocarbons indicated that oils in Yakela oilfield were marine oils with relative high maturity for lower oils. C₂₁/C₂₃  tricyclic diterpane and C₂₈ steranes relative content in C₂₇~C₂₉steranes were consistent with oils derived from O₃source rock in Tarim Basin. Characteristics of triaromatic steroids and methyl triaromatic steroids further proved the O₃ source rock was the source of oils in Yakela oilfield. A significant difference was found in carbon isotope composition of whole oil and fractions of TD2 well ,T904 well and Yakela oilfield，which suggested the crude oils among deeper and shallower layers in Yakela oilfield were marine oils and had obvious diffrences with crude oils derived from ∈—O1. Based on the ight hydrocarbons, tricyclic terpanes, C₂₈steranes, triaromatic steranes and methyl triaromatic steranes, and carbon isotope composition of whole oil and fractions, it is suggested that the crude oils of Yakela oilfield in deeper and shallower layers had the common source and derived from O₃ source rock. 