Cubic-Plus-Association Equation of State for Asphaltene Precipitation in Live Oils

Abstract

We apply a cubic-plus-association equation of state (CPA-EOS) to study the asphaltene precipitation in live oils from temperature, pressure, and composition effects. The live oils are characterized by considering the pure components, the pseudo-hydrocarbon components, and the hydrocarbon residue. The hydrocarbon residue is further divided into the “heavy” component and asphaltenes. The asphaltene precipitation is modeled as liquid−liquid equilibrium between the upper onset and bubble point pressures and as gas−liquid−liquid equilibrium between the bubble point and lower onset pressures. In our work, the self-association between asphaltene molecules and the cross-association between asphaltene and “heavy” molecules are taken into account. The EOS parameters are either directly available, from our recent work, or from fitting the bubble point pressure. The cross-association energy between asphaltene and “heavy” molecules depends upon the temperature but is independent of the pressure. We reproduce the exper...