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Asphaltene deposition is a very serious and complex problem. The damaging effects of this problem are common in all facets of petroleum production, processing and transportation. The mechanisms of asphaltene precipitation are still not fully understood due to the lack of understanding of the physicochemical behavior of asphaltene as it exists in the crude oil system. In this paper, a model based on the statistical thermodynamics of polymer solution is described for the phase behavior of asphaltenes. A Vapor-Liquid-Liquid Equilibria (VLLE) model is employed, using separate VLE and LLE calculations to predict the phase splits (vapor, asphaltene and crude oil fractions). The model uses the concept of material balance by coupling with the Flory-Huggin theory of polymer solution. Various theoretical equations of state are employed as options for the estimation of the component properties for the lighter fraction. The properties of the heavy fractions in the crude oil system are determined using empirical correlations. The resulting model allows us to predict the onset of asphaltene flocculation as a function of temperature, pressure and compositional changes in the crude oil system. This model can be used as a basis for designing petroleum production systems, including separator design, production well performance analysis, pipelines and EOR projects.
Asphaltene deposition, whether it is in the reservoir, production tubings or facilities, is a very serious and complex problem. The devastating effects of this problem are well known in the petroleum industry and have been studied quite extensively in the research and scientific community for the past several years. Numerous articles have been published each year pertaining to asphaltene deposition, but the subject is still minimally understood and extensive investigations are still under way. A comprehensive overview of asphaltene deposition problem in the petroleum industry can be obtained by referring to the paper published by Leontaritis and Mansoori. Studies have shown that the complexity of asphaltene itself vastly contributes to the anomalous behavior of this fraction of the crude oil. Hitherto, "why", "how" and "when" asphaltene will flocculate and precipitate in the production tubings and pipelines still remain a subject of controversy and ambiguity. These controversy and ambiguity arise largely because of the lack of chemical definition of asphaltene in the crude oil mixtures. One such controversy is whether asphaltene exists in the crude oil in the forms of true solutions, colloidal particles, or a combination of both.
Despite all the controversy, at least one thing is clear - the research community seems to agree that the perpetual internal changing of the crude oil system, and perhaps, its surroundings cause the asphaltene particles and other similar derivatives to separate from the crude. The condition or the "threshold point" at which the asphaltenes precipitate in the crude oil system is still subject to ongoing investigations. To date, no model has satisfactorily been formulated to completely describe the mechanism of asphaltene precipitations. Nonetheless, several researchers have put some efforts to formulate the phase behavior of asphaltene precipitation by applying various models (solubility and colloidal theories).
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