An unusual application of chemical reaction engineering: the evolution of a crude oil reservoir. Of the use of intelligent lumping.
Advancing the chemical engineering fundamentals
Chemical Reaction Engineering: Advanced Concepts (T2-2b)
Keywords: chemical reaction engineering, thermal cracking, oil reservoir, lumping, radical reaction mechanisms
Title: An unusual application of chemical reaction engineering: the evolution of a crude oil reservoir. Of the use of intelligent lumping.
Authors:
R. Bounaceur1), G. Scacchi1), P.M. Marquaire1), G. Wild1)*, F. Dominé2), R. Michels 3)
1)Département de Chimie Physique des Réactions (DCPR), Nancy-Université, CNRS, ENSIC, 1, rue Grandville, F – 54001 Nancy
2) Carbochem, 12 chemin de Maupertuis, F - 38240 Meylan
3) Géologie et gestion des ressources minérales et énergétiques (G2R) Faculté des Sciences, BP 239 F — 54506 Vandœuvre-lès-Nancy
Abstract:
Petroleum industry will still be with us for some time and the exploration of new reservoirs is still an important topic. Our knowledge about the origin of petroleum made tremenduous progresses the last decades, however, it is still not possible to predict the actual form of a petroleum in a basin of a given age and approximately well known pressure and temperature history. The aim of the present paper is to use the tools of chemical reaction engineering to try to predict the approximate composition of an oil contained in a reservoir after secondary cracking.
The challenges are multiple: for a typical oil reservoir, the time scale is a few millions of years (a long time, even in academia), the pressure is high (some 20 MPa), the temperature relatively low (about 200 °C), the chemical composition of the mixture extremely complex; furthermore the reservoir may contain water and a lot of solids, some of which may react (sulfates can be reduced, other particles may have catalytic properties). It is however currently assumed that the main reactions happening are radical pyrolysis reactions. In the present paper, we will therefore neglect non radical reactions (catalytic or molecular).
Since the relevant pyrolysis reactions are very slow at the actual reservoir conditions, reaction rates have to be measured at higher temperatures, and the results extrapolated to the low temperatures of interest. Furthermore, it is of course impossible to handle separately all the numerous constituents of petroleum and their interactions during pyrolysis: different lumping strategies have been used to handle this complexity.
The classical approach of geochemistry consists in lumping the constituents of petroleum in a limited number of pseudo-compounds, as Kuo & Michael (1994): C1 (methane), C2 (ethane and ethene), C3-C5, C6-C14, stable aromatics (benzene, toluene, xylene, naphthalene), C15+ saturates, C15+ aromatics, resins, asphaltenes and coke. Arbitrary stoichiometry and rate laws are established using measurements at different temperatures usually between 300 °C and 500 °C.
Unfortunately the Arrhenius law used to extrapolate holds true for elementary reactions, but not for empirical rate laws obtained by fitting. For this reason, another approach was proposed (e.g. Dominé et al., 2002), in which the oil is supposed to be a mixture of a limited number of model compounds the pyrolysis of which is described by a rigorously built set of radical reactions, whose rate equations are established. Since the resulting mechanism is still too complicated to be used directly, lumping has still to be done. Three ways of model reduction are proposed. The advantages and drawbacks of these are compared. Due to the principle used, they can be extrapolated to smaller temperatures, as long as no new reactions appear.
Presented Monday 17, 16:20 to 16:40, in session Chemical Reaction Engineering: Advanced Concepts (T2-2b).
