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Asphaltene deposition is one of the important problems of oil production that requires an accurate predictive modelling. We developed an asphaltene deposition model in a pipeline. The model is based on data, which are obtained by experiments performed in a Couette device, where the inner cylinder rotates, and deposition on the outer wall is studied. A detailed theoretical analysis of an applicability of a Couette device for imitation of the asphaltene deposition in a pipe flow is presented. The model developed is based on first principles and consists of the two major modules: (1) a sub-model describing the particle size distribution evolution in time in a Couette device, and along a pipe; (2) a sub-model for calculating the particle transport to the wall. A population balance model is employed for modelling the particle size evolution. A concept of the critical particle size is introduced; only particles that are smaller than the critical size can deposit. The model developed contains only three parameters that are determined experimentally using a Couette device. The model of asphaltene deposition in a Couette device allows accurate describing the deposit mass growth in time. Performance of the deposition model for a pipeline with the coefficients obtained by a laboratory Couette device is also illustrated.Le dépôt d'asphaltènes est un des problèmes majeurs de l'industrie pétrolière et nécessite des modèles prédictifs fiables. Nous avons développé un modèle de dépôt d'asphaltènes en conduite pétrolière. Le modèle est basé sur des données obtenues expérimentalement par un système Couette avec cylindre intérieur tournant. Le dépôt sur les parois extérieures, fixes, est alorsétudié. Une analyse théorique détaillée de l'applicabilité d'un système Couetteà l'étude du dépôt d'asphaltènes enécoulement dans une conduite pétrolière est présentée. Le modèle développé est basé sur des principes fondamentaux et consiste en deux principaux modules: (1) un premier module décrivant l'évolution de la distribution de taille des particules avec le temps dans un système Couette et le long d'une conduite, (2) un deuxième module pour le calcul du transport des particules vers la paroi. Un modèle d'équilibre de population (population balance model) est utilisé pour modéliser l'évolution de la taille des particules. Un concept de « taille critique » est alors défini: seules les particules plus petites que cette taille peuvent se déposer. La modélisation contient seulement trois paramètres qui sont déterminés expérimentalement sur un appareil de type Couette. Le modèle permet une description fiable de l'augmentation de la masse de dépôt avec le temps. Les résultats de ce modèle appliquésà une conduite pétrolière avec les paramètres obtenus en laboratoire sur un système Couette sontégalement démontrés.

Asphaltene properties vary with separation method and sometimes with individual technique. Factors such as contact time, solvent-to-crude oil ratio, and temperature influence asphaltene precipitation and are somewhat standardized. However, the final step in most separations, washing the asphaltene filter cake with solvent, is not standardized. Asphaltene properties can be very sensitive to small amounts of resins and therefore may be sensitive to the amount of washing. Asphaltenes were extracted with three different levels of washing from four source oils (Athabasca, Cold Lake, Lloydminster, and Peace River). In all cases, increased washing decreased asphaltene yield and slightly increased asphaltene density. Increased washing significantly increased molar mass and decreased the solubility of the extracted asphaltenes. A new washing method using a Soxhlet apparatus removed the largest amount of resinous material and yielded asphaltenes with significantly different properties from conventionally washed asphaltenes. Since more resinous material was removed, the Soxhlet method allows a more direct comparison between asphaltenes from different sources. Asphaltenes were also extracted using three standard separation methods, IP 143, ASTM D4124, and a method proposed by Speight. Some property variations between the methods were observed and a set of criteria to obtain consistent samples is proposed.

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in Wiley Online Library (wileyonlinelibrary.com).Asphaltene deposition phenomena are investigated both theoretically and experimentally. A Couette device, where the inner cylinder rotates and particles deposit on the outer wall, is used for deposition laboratory studies. A deposition modeling approach, recently proposed by the authors is improved. Empirical parameters of the model are obtained from Couette device experiments. The deposition mechanism peculiarities are explained based on an analogy between the deposition and water in oil emulsion stabilization by asphaltenes, and on an analysis of interaction of asphaltene molecules. The model performance is illustrated by modeling oil production, accompanied with asphaltene deposition, from a cylindrical reservoir through vertical tubing. The computations, performed for a reservoir depleting over time, demonstrate a good qualitative agreement with the field data reported in literature.

The Peng-Robinson equation of state (EoS) was adapted using group contribution methods to model asphaltene precipitation from solutions of toluene and an n-alkane and from n-alkane diluted bitumens. A liquid-liquid equilibrium was assumed between a primary liquid phase and a second dense asphaltene phase. Bitumen was characterized in terms of solubility fractions: saturates, aromatics, resins, and asphaltenes. Critical properties of the saturates, aromatics, and resins were determined that fit their measured densities and compared well with existing critical property correlations. The saturate and aromatic critical properties were also tuned to fit asphaltene precipitation data from solutions of the saturate and toluene or the aromatic and heptane. Asphaltenes were divided into fractions of different molar masses using a gamma distribution function. EoS parameters for asphaltenes were determined that fit the measured densities, fit precipitation data for mixtures of asphaltenes, toluene, and heptane, and compared well with existing critical property correlations. The model successfully fitted and predicted the onset and amount of precipitation over a broad range of compositions, temperatures from 0 to 100 °C, and pressures up to 7 MPa. The model results were within the error of the measurements except for high dilutions with n-pentane.

A regular solution model, previously used to model asphaltene precipitation from Western Canadian bitumens, was tested on four international heavy oil and bitumen samples. The input parameters for the model are the mole fraction, the molar volume, and the solubility parameter for each component. Heavy oils and bitumens were divided into four main pseudo-components, corresponding to the SARA fractions (saturates, aromatics, resins, and asphaltenes). Asphaltenes were divided into fractions of different molar mass, based on a gamma molar mass distribution. The molar volumes and solubility parameters of the pseudo-components were calculated using solubility, density, and molar mass measurements and previously developed correlations. Model predictions were compared with the measured onset and the amount of asphaltene precipitation for solutions of asphaltenes in toluene and n-heptane and for heavy oils diluted with n-alkanes, all under ambient conditions. The overall average absolute deviations (AAD) of the predicted fractional precipitation or yields were <0.031 for the asphaltene solutions and <0.008 for the diluted heavy oils. A methodology for characterizing heavy oils and modeling asphaltene precipitation from n-alkane-diluted heavy oils is proposed.