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

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 selfassociation 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 experiments of the amount and onset pressures of asphaltene precipitation in several live oils over a broad range of composition, temperature, and pressure conditions.