UNRAVELING MANGOES MYSTERIES - A KINETIC SCHEME DESCRIBING THE DIAGENETIC FATE OF C-7-ALKANES IN PETROLEUM SYSTEMS

Analyses of the composition of the light (gasoline range) hydrocarbons in oils are widely used to assess oil maturity or to track petroleum alteration. As Mango observed, the concentration ratios of some isomer ic alkanes in the gasoline range do not match their relative thermodyn amic stabilities, although these compounds are probably derived from t he same alkene precursors. This indicates that light hydrocarbon isome risation is proceeding via a kinetically rather than an energetically controlled reaction mechanism. We present here a reaction scheme for t he formation of isomeric C-7-heptanes from heptenes and kinetic calcul ations based on this scheme, that result in 2-methylhexane/3-methylhex ane ratios very similar to those observed in sediments. As such, these results provide a useful theoretical backbone for the utilisation of the gasoline range hydrocarbon compounds in petroleum geochemistry. (C ) 1997 Published by Elsevier Science Ltd. All rights reserved.