Geochemical characterization of selected Western Canada oils by C-5-C-8 Compound Specific Isotope Correlation (CSIC)

Forty-two oils/condensates from the Western Canada Sedimentary Basin (WCSB) ranging in reservoir age from Devonian to Cretaceous are compared using th e stable carbon isotopic ratio of individual hydrocarbons in the gasoline-r ange fraction (C-5-C-8) Of these oils. Continuous Flow-Isotope Ratio Mass S pectrometry (CF-IRMS), using a modified solid dilution, purge and trap inle tting system can provide reproducible isotopic ratios for the ca. 26 domina nt n-, iso-, and cyclo-alkanes and aromatics in the gasoline range. The res ulting isotopic signatures, or gasoline "isotopograms", for oils/condensate s provide a diagnostic geochemical technique for oil-oil and oil-source cor relations. In many instances, the non-straight-chained hydrocarbons are mor e diagnostic than n-alkanes. Hierarchical cluster analysis provides a non-s ubjective approach to the treatment of individual isotopic information. Thi s study confirms that oils from similar or the same sources produce isotopi c signatures that are highly correlated. Clear carbon isotopic relationships between individual hydrocarbon compound s in the oils suggest a steady-state kinetic relationship for the generatio n of oil and gas, as opposed to a thermodynamic equilibrium relationship. T his mechanism explains the consistent shift in isotopic ratios between simi lar compounds, such as the methylalkanes and dimethylalkanes. (C) 1999 Else vier Science Ltd. All rights reserved.