Development of asphaltene phase equilibria predictive model

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 physico-chemical 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.