Heavy Oil Rheology as a Function of Asphaltene and Resin Content and Temperature
J-F. Argillier (Institut Français du Petrole) | C. Coustet (Institut Français du Petrole) | I. Henaut (Institut Français du Petrole)
Because of very important reserves that are of the same order of magnitudethan conventional oils, heavy oils represent a strategic source ofhydrocarbons. The major difficulty for producing and transporting these crudescomes from their very high viscosities. The success of exploitation of thesepetroleum products requires new treatments to improve their transport. Such atarget implies to better understand the relationship between the composition ofheavy oils, in particular in terms of asphaltenes and resins content and theirflow properties. Influence of asphaltenes content in the crude has beenparticularly studied in our lab : the experimental work revealed the existenceof a critical concentration C* above which the asphaltenes particlesoverlapp. This structural change dramatically increases the viscosity andintensifies the elastic character of heavy crude oils. A further series ofexperiments has focused on the influence of resins: they show that in diluteregime (C*), resins increase the viscosity of the crude and inconcentrated regime (C>C*), which corresponds to the case of aheavy oil, they lower the asphaltenes effect on viscosity. Experiments werefirst carried out with asphaltenes and nonylphenol as a model of resins andfollowed by experimental work on real crude that confirmed the trends. Tounderstand the rheological behavior of a heavy crude oil in relation with itsinternal structure, asphaltenes and resins have to be simultaneouslyconsidered. From this study we conclude that the origin of the high viscositiesof heavy oils comes from to the entanglement of solvated asphaltene particlesstabilized by resin molecules. A strong influence of temperature on therheology is also revealed by high activation energy measurements. This thermaldependent rheological behavior shows that the internal organization of theheavy crude oil is partly based on thermal dependent physical bonds. Using thereversibility of these physical links, we should be able to modify thestructure of heavy crude oils to facilitate their transport.
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