Résumé -Rhéologie des bruts lourds en relation avec leur composition -La forte demande en énergie conduit les industries pétrolières à exploiter les réserves de bruts lourds et extralourds. Ces bruts sont en particulier caractérisés par leur forte viscosité qui rend leur transport en surface impossible sous leur état naturel (pertes de charge importantes). Plusieurs méthodes de traitement existent ; afin de les améliorer, il est nécessaire de comprendre l'origine de ces fortes viscosités. Notre démarche a été de réa-liser des études rhéologiques et structurales (diffusion de rayons X ou SAXS) afin de relier les propriétés macroscopiques et microscopiques des bruts lourds. Nous avons étudié l'influence des deux composés les plus lourds et les plus polaires des bruts que sont les asphaltènes et les résines. Les résultats ont montré le rôle prépondérant des asphaltènes sur la viscosité des bruts lourds. Deux régimes de viscosité, confirmés en SAXS, ont montré l'existence d'une concentration critique à partir de laquelle les asphaltènes ne sont plus des particules indépendantes et se recouvrent. Le rôle des résines a été développé dans un solvant aromatique puis en ajoutant une molécule modèle des résines : le nonylphénol. Il a été montré que la pré-sence de résines réduit l'influence des asphaltènes sur la viscosité. Leur mode d'action sur les asphaltènes est double : d'une part, elles ont un rôle stabilisant en recouvrant les asphaltènes ; d'autre part, elles ont un effet dissociant en diminuant la taille des asphaltènes et en réduisant leur masse. L'influence des résines a été également confirmée dans le brut réel. Enfin, il a été montré que l'addition modérée d'un alcool dans un solvant aromatique réduisait l'association des asphaltènes. Abstract -Composition and Heavy Oil Rheology -Increasing energy demand persuades oil companies to exploit heavy crude oil and extra-heavy crude oil resources. These crudes are essentially characterized by high viscosity that makes impossible surface transportation in their natural state (high pressure drops). Our investigation procedure was to perform both rheological and structural experiments (Small Angle X-ray Scattering SAXS) in order to

A major flow assurance challenge in the near future is the production and transport of heavy oils: although these petroleum products represent very important reserves, their exploitation is limited by their high viscosity. The paper discusses the origin of this high viscosity in order to ultimately develop operating guidelines. It focuses on the relationship between the composition of heavy oils, in particular their asphaltenes and resins contents, and their flow properties. The structural analysis and rheological measurements that were performed revealed how strongly the transportability of heavy oils depends on thermal conditions, especially in deepwater ones. From this study, we conclude that the high viscosity of a heavy oil comes essentially from the overlapping of its asphaltenes. We observed that as temperature decreases, not only the viscosity increases but also the rheological behavior of heavy oils becomes non Newtonian. Dynamic tests carried out on several crudes show that at low temperatures, they develop a shear thinning behavior with no yield stress appearance. It was checked that this phenomenon comes from the particular structure of asphaltenes and that it is not due to the presence of waxy crystals. It is therefore recommended to take into account this non Newtonian behavior if heavy oils are to be transported in deepwater conditions. Introduction. A major flow assurance challenge in the near future is the production and transport of heavy oils. Despite very large reserves, their exploitation is limited by their high viscosity. Actually, the very low mobility of these petroleum products is making an as such pipeline transportation impossible. Advanced methods are necessary. They include upgrading, dilution, formation of oil-in-water emulsions and heating. These technologies imply high operational and investment costs so that optimized transport conditions have to be found. With this aim in view, a detailed study of the rheology of heavy oils was carried out. It deals with the link between the constitution and the flow properties of the crude, and lays emphasis on the role played by temperature. The understanding of the origin of the high viscosity of heavy oils will help to improve their methods of transportation, especially at low temperatures like in expected deepwater discoveries. The overlapping of asphaltenes inside a heavy oil and its consequence on viscosity. One main chemical characteristics of a heavy oil is its large content in asphaltenes. These molecules constitute a class of substances defined on the basis of their solubility in organic solvents: they are soluble in toluene but insoluble in alkanes such as n-pentane. Asphaltenes are the heaviest and most aromatic and polar fraction of a crude oil. These particular components are described as molecules composed of polycondensed aromatic rings carrying aliphatic chains that contain acid-base and polar groups at their edge. It is well recognized that thanks to these chemical characteristics, asphaltenes can self assemble through physical interactions and increase the viscosity of a medium in which they are added. Most of these studies were realized with simple organic solvents [Reerink and Lijzenga (1973), Sheu et al. (1991), Yudin et al. (1998), Acevedo et al. (1999).].

Model compound vulcanization in combination with reversed-phase high-performance liquid chromatography and NMR spectroscopy was used to elucidate the reactions of accelerator, sulfur, zinc stearate and zinc-2-mercaptopyridine-N-oxide (ZPNO) in natural rubber vulcanization. Studies of different curing ingredient formulations in squalene have been done to determine the influence of each component during the vulcanization. It was found that 2-mercaptopyridine-N-oxide bridged adducts (R-Sx-Pyr(O)) were formed when squalene was heated in the presence of sulfur, curing ingredients and 2,2′-dithiobis(pyridine-N-oxide) (PyrO-S2-PyrO). Possible interactions of R-Sx-Pyr(O) with carbon black have been proposed.

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Sulfur vulcanization was carried out with 5-phenyl hex-2-ene serving as a model of e-SBR. Various accelerators have been used to study and compare the reactivity in a system containing sulfur and activators. Both HPLC and GC-MS analytical tools were used to identify the reaction products. It has been observed that the vulcanization in the presence of N-cyclohexyl-2-benzothiazole sulfenamide (CBS) generates a large amount of 2-marcaptobenzothiazole (MBT), which continuously increases and finally decreases suggesting further participation in vulcanization generating new crosslinks. The sulfenamide, N-cyclohexyl-4,6 dimethyl-2-pyrimidine sulfenamide (CDMPS) behaves different. Although it generates considerable amount of corresponding thiol, (4,6-dimethyl pyrimidine-2-thiol, DMMP) at the beginning of the reaction, no decrease has been observed during the course of further reaction suggesting that the accelerator, DMMP, somehow remains deactivated and therefore no changes in network is feasible. Identical differences exist between bis(2,2′benzothiazyl) disulfide (MBTS) and corresponding bis (4-methyl-2,2′benzothiazyl)disulfide (M-MBTS) in the reaction kinetics.