Abstract

In this investigation the hydrocarbons and sulphur compounds in the gas oils of the Athabasca, Cold Lake and Lloyd-minster heavy oils have been studied by a combination of liquid, gas-liquid and gas-solid chromatographic techniques coupled with mass spectrometry. The results were compared with those for the Medicine River oil which is lighter, thermally mature and lies in a reservoir of the same geological age.

The distillates were fractionated into hydrocarbon types (i.e., saturates, mononuclear, dinuclear and polynuclear aromatics). This allowed a comparative study of the normal alkanes and isoprenoid hydrocarbons, pristane and phytane, in the C₁₆ to C₁₉ range of the saturates. Also the structural changes in the aromatic hydrocarbon types, as indicated by both gas chromatography coupled with mass spectometry, have been followed up. The results were interpreted geochemically with reference to the thermal and biological aspects of degradation.

It is quite clear that these oils are closely related although there are some distinct differences. The number of isomers of the sulphur compounds appears to be low in comparison with the number of possible isomers, suggesting some selective mechanism of formation.