Compositional characteristics and geochemical significance of light hydrocarbons for crude oils in Tarim Basin, China

摘要

Light hydrocarbons, especially C-7 isoalkanes, cyclopentanes, cyclohexanes and n-heptane in 540 oils from the Tarim Basin were studied systematically. The results suggested the K-1 values [(2-MH+2,3-DMP)/(3-MH+2,4-DMP)] of crude oils vary from a lowest value of {0.78}, to a highest value of {1.54}, but the K-1 values of the majority of oil samples (80%) range from {0.90} to {1.20}. However, the absolute contents of (2-methylhexane+ 2,3-dimethylpentane) and (3-methylhexane+2,4-dimethylpentane) in the total light hydrocarbons (C-4-C-7) show a similar variation trend. The variation of K-1 values of crude oils can suggest a typical sedimentary environment for source rocks. Therefore, according to the compositional characteristics of C-7 light hydrocarbons in light of the steady-state catalytic hypothesis, non-marine oils from the Yingmaili area and marine oils from the Tazhong uplift in the Tarim Basin were genetically classified.