In this work, an effort has been made to further improve the predictions of the wax formation conditions based on the previously proposed wax model ( Zuo, J. Y.; Zhang, D.; Ng, H.-J. An improved thermodynamic model for wax precipitation from petroleum fluids. Chem. Eng. Sci. 2001, 56 ( 24), 6941− 6947 ). The model framework consists of the three-parameter Peng−Robinson equation of state for describing the nonideality of the vapor and liquid phases and the predictive universal quasi-chemical (UNIQUAC) model proposed by Coutinho for the solid (wax) phase. The characterization procedure for plus fractions proposed by Zuo and Zhang ( Zuo, J. Y.; Zhang, D. Plus fraction characterization and PVT data regression for reservoir fluids near critical conditions. SPE 64520, 2000. ) has been modified and extended to reservoir fluids using high-temperature gas chromatography (HTGC) data. The wax model developed in this study has been applied to predict wax appearance temperature (WAT) and wax cut curves for a number of defined component systems, diesel fuels, and reservoir fluids. The average deviation of the predicted WAT is within 1.5 K at low and high pressures for defined component systems. For reservoir fluids, the predicted thermodynamic WAT locus tends to be much higher than the measured WAT. It is observed that a very small amount of wax precipitated in the fluids could shift the WAT to the measured WAT. The prediction of wax compositions in the solid phase is in good agreement with the experimental data. The results indicate that the proposed wax model is a useful tool to the flow assurance industry.
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