Vertical Distribution Characteristics and Its Geological Significance for  Carbon Isotopic Composition of Oils and Its Group Components of Deep  Marine Oil Reservoirs in Tabei Uplift, Tarim Basin

Key words: 
• Tabei Uplift /
• deep /
• marine oil /
• group component

Abstract: The carbon isotopic compositions of the oils and its group components, which collected from the deep marine oil reservoirs in Tabei Uplift of Tarim Basin, were analyzed by the MAT252 Isotope Mass Spectrometer. The results showed that carbon isotopic compositions of these deep oils are mainly controlled by their parent material, and less affected by the thermal effects. Reversely, the carbon isotopic compositions and its reversed distributions and fractionations of these deep oil group components, on the basis of inheriting the carbon isotopic composition of parent materials, are evidently affected by the thermal effects. The carbon isotopic compositions of saturated hydrocarbons, with the increasing oil reservoirs depth and the enhancing thermal effect, gradually became heavy, but the carbon isotopic compositions of asphaltenes obviously lighten. The reversed distribution degree and fractionation degree of carbon isotope for these deep oil group components also increased, and there are totally reversed distribution in some samples that the distribution of δ13C values of the group components is saturated hydrocarbons﹥aromatics﹥nonhydrocarbons﹥asphaltenes. The vertical distribution characteristics of oil group components of deep marine oil reservoirs in Tabei Uplift may indicate the influences of thermal effects on oil stability.