Nature and geochemistry of high molecular weight hydrocarbons (above C4o) in oils and solid bitumens

Al~traet--Series of hydrocarbons ranging up to C75 have been detected by high temperature gas chromatography (HTGC) in a number of geochemical samples, including oils and waxes precipitated in drill stem pipes. A saturated hydrocarbon fraction isolated from a fossil bitumen, ozocerite, and enriched in branched/cyclic compounds, was analysed by direct insertion probe mass pectrometry (DIP/MS) and showed the presence of cyclic structures in the high molecular weight region (>C40). The asphaltene fractions isolated from the various samples were analysed by flash pyrolysis-high temperature gas chromatography (P-HTGC). Similar distributions of high molecular weight hydrocarbons were produced from the asphaltenes of both the oils and waxes. In vitro simulation experiments of the asphaltene fractions produced a similar distribution of high molecular weight hydrocarbons as observed from Py-HTGC, suggesting that thermal breakdown of asphaltenes may be responsible for the production, or release, of some naturally occurring high molecular weight hydrocarbons. Key words--oils, waxes, asphaltenes, high molecular weight hydrocarbons (C40 +), high temperature gas chromatography (HTGC), flash pyrolysis-HTG