Abstract

Traditional Gas Chromatographic (GC) techniques for the analysis of petroleum provide information on components with carbon numbers less than ~C₃₅. The newly available analytical method, High Temperature Gas Chromatography (HTGC), which uses new thermally stabile GC columns and GC oven temperatures as high as 470°C, makes possible the routine analysis of C₃₅ to C₁₂₀ hydrocarbons present in petroleum and related materials. HTGC provides information useful in both exploration and production, and is well suited for the analysis of high-wax oils, such as those produced in Central Sumatra and surrounding areas.

Paleoenvironmental information on the geologic source of oils and bitumens can be provided by HTGC analyses. One series of C₄₀ to C₆₀ HTGC peaks, shown to be coeluting monocyclic and acyclic branched saturated hydrocarbons of differing carbon number, often dominate HTGC profiles in this higher molecular weight range. These HTGC peaks frequently show a distinct predominance pattern in which alternating peaks are enhanced or diminished in intensity relative to neighboring peaks in the series. Saline lacustrine-sourced oils show one predominance pattern for these C₄₀ to C₆₀ HTGC peaks, while open marine-sourced oils show the opposite predominance pattern; oil from fresher water lacustrine sources typically show very weak lacustrine predominance patterns or no detectable predominance. The C₄₀ to C₆₀ predominance intensities of lacustrine oils can be affected by thermal maturation. Oil from the Salawati Basin in Irian Jaya and Telisa Shale extracts from Central Sumatra show HTGC profiles consistent with their marine sources. Central Sumatran high-wax oils show HTGC profiles consistent with a fresher water lacustrine source.

Chromatographic resolution, analytical reliability, and molecular weight range differ for various HTGC columns and instrumental sample injection systems. New metal capillary columns employing on-column injection techniques provide good chromatographic resolution and long column life for analyses in the C₄₀ to C₆₀/C₇₀ range, a molecular weight range suitable for many applications.