Applications and limitations of Mangoʹs light hydrocarbon parameters in petroleum correlation studies

Mango (1987) reported on the remarkable invariance of four isoheptanes in petroleums: regardless of the absolute concentration, the ratio of sums of concentration of (2-methylhexane + 2,3-dimethylpentane)/(3-methylhexane +2,4-dimethylpentane) remains constant, the K1 ratio value being around unity. Gas chromatographic analyses of an additional 500 oils contradict this invariance, as a suite of oils from the Cretaceous Northwest Basin (Argentina) deviate significantly by having a ratio of 1.67. Still, oils derived from the same structural kerogen have invariant ratios that can vary from a lowest value of 0.79 found for the Midland oil set (Mango, 1990) up to a highest value of 1.67 found for the Cretaceous Northwest Basin. Mango (1990) postulated so-called parent-daughter schemes having an invariance in the ratio of isoheptanes and dimethylcyclopentanes, an invariance unique for a homologous set of oils, but possibly distinctly different from another suite of homologous oils. It will be shown here that this difference in invariance can be used in oil/oil correlation studies, and that this technique is especially powerful for oil/condensate correlation, condensates in which the concentration of biological markers is quite often below the limit of detection. Further, the concentration of light hydrocarbons, needed for this approach, can be determined from whole-oil gas chromatography without any pre-treatment, thus providing a rapid and cheap tool for correlation studies.