Elaboration of a new compositional kinetic schema for oil cracking

• Published in: Organic geochemistry Vol. 39; no. 6; pp. 764 - 782
• Main Authors: Behar, Françoise, Lorant, François, Mazeas, Laurent
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.01.2008; Elsevier Science; Elsevier
• Subjects: Earth sciences; Earth, ocean, space; Environmental Sciences; Exact sciences and technology; Geochemistry; Hydrocarbons; Sedimentary rocks; Soil and rock geochemistry; Saudi Arabia; Middle East; Arabian Peninsula; Asia; experimental studies; models; crude oil; resins; gas chromatograms; thermal effects; hydrocarbons; reservoirs; liquid chromatography; case studies; hydrogen; natural gas; maturation; pyrolysis; cracking(refining); methane; temperature; kinetics; petroleum; chemical composition; stability; CRAQUAGE DU PETROLE; SCHEMA DE COMPOSITION
• ISSN: 0146-6380; 1873-5290
• DOI: 10.1016/j.orggeochem.2008.03.007

The aim of this work is to get new insights into oil cracking mechanisms. The investigation was focused on the thermal stability of the heavy chemical classes such as the C 14+ saturates, C 14+ aromatics, and the polar fraction (resins + asphaltenes). Artificial maturation was performed in closed pyrolysis system in the temperature range 300–375 °C for following a large range of conversion for the three initial chemical classes. Pyrolysis products are described as H 2S, C 1, C 2, C 3–C 4 gases, C 6–C 14 saturates, C 6–C 14 aromatics, C 14+ saturates, C 14+ aromatics, NSOs and prechar. In a first step, the total C 14+ aromatics of the initial oil was isolated and artificially matured. They generated a significant part of saturated compounds and new heavy aromatics which were assumed to be methylated structures. The proportion of initial and produced aromatics was determined based on the decrease of the hydrogen content. Then, a kinetic model was elaborated for their specific bulk and compositional kinetic parameters which was taken as an initial guess when optimising the global kinetic model for the total C 14+ oil. A tentative global kinetic model for the total C 14+ oil was elaborated which well simulated laboratory experiments for both global conversions and yields of generated products. When this model is used for extrapolating laboratory results to natural reservoirs assuming a geothermal heating rate of 2 °C/Ma, predicted oil thermal behavior is not in contradiction with observed field data. Indeed, aromaticity is decreasing above 140 °C whereas, the yield of C 14+ saturates starts to decrease above 170–180 °C. However this comparison is only qualitative since this model was not integrated into a real case study in which the full process of generation–expulsion and oil cracking must be totally described. The reverse relative thermal stability of the C 14+ saturates and aromatics between laboratory and geological conditions is explained by the large difference of A and E of the two chemical classes. Finally, this model was elaborated on a Type II oil only and needs to be tested also on other oils of different chemical composition, either paraffinic or enriched in NSOs.