Research on the stable isotope composition characteristics of crude oils

In this study, GC/MS, GC/IRMS and EA/IRMS as the analytical methods were used to determine the characteristic ratios, bulk δ¹³C values and carbon isotope composition of the individual n-alkanes from six crude oils in different areas, which were compared and analyzed subsequently.The results showed that C₁₉+C₂₀/(C₁₉~C₂₂), OEP₁ and CPI_13-22 of different oils were not sharply demarcated t and even may be consistent, which can't be used as effective indicators to distinguish different types crude oils.The bulk δ¹³C values of six crude oils showed pronounced differences, which the most depleted was Oman and most enriched was Brazil, another four crude oils ranked among them.The results of GC/IRMS demonstrated that different carbon stable isotope composition characters existed in diverse types crude oils and significant differences could be found for δ¹³C values and profiles of n-alkanes.ANOVA results indicated that the deviations of the bulk δ¹³C and δ¹³C of nC₂₀ were significant among any two types oils (P < 0.05) except for exceptional oil samples. The study furthered evidences that the characteristic differences of stable carbon isotope composition in petroleum could provide an effective method support for identification and traceability of crude oils.It was worth noting that woul carbon isotope composition combined with characteristic ratioscound prominently improve the discernibility ability of crude oils from different origins.