Question

State of the art of research in kinetic modeling of oil formation and expulsion

Answer 1

The last ten years have seen a rapid development in the understanding of petroleum generation and expulsion by a combined use of natural series and experimental simulation. This knowledge is now used to develop mathematical models which reproduce the kinetics of petroleum generation and migration in the purpose of basin evaluation. By a combination of observation of homogeneous geochemical series, experimental simulation and mathematical modelling, it has been now established that parameters governing the quantity and composition of petroleum are temperature, type of organic matter, time (or heating rate). Catalysis by clay minerals, which would produce important amounts of isoalkanes is not necessary to produce petroleum. The role of minerals, although still controversial, is rather to retain the heavy fraction of petroleum. Pressure seems to have a limited influence within the range for effective source rocks.

Kerosene is a tremendously complex macromolecule which is now insufficiently characterized to develop fundamental, predictive models of thermal cracking (i.e. involving intermediates such as radicals and olefins). Such models presently apply only to the cracking of simple molecules (hexane, hexadecane) at limited degrees of cracking.

For this reason kinetic models are still empirically calibrated on pyrolysis experiments and/or on natural maturation trends. The most popular models involve a series or a continuous distribution of parallel reactions to describe primary cracking (i.e. direct formation of mobile compounds . These are generally calibrated against open system pyrolysis with various temperature programs. Consideration of natural maturation trends (i.e. decrease in petroleum potential) may be used also for calibration, but discrepancies of organic matter properties, availability of deep samples and uncertainties on thermal history limit the effectiveness of such methods. Whatever the method, main activation energies are found in the range 45–60 kcal/mol.