Thermodynamics Prediction of Wax Precipitation Using the Patel-Teja Equation of State

Abstract

Abstract Flow assurance is a problem which plagues the petroleum industry. The purpose of this study is to predict wax precipitation in crude oil pipelines. The industry spends millions of dollars to remediate this problem. As a result, ways are being sought to reduce the occurrence of the phenomenon by predicting as accurately as possible, the wax appearance temperature, which is a very important parameter when analysing the problem of wax precipitation. Experimental methods have been employed in times past, but in recent times, thermodynamic modeling of wax formation allows better prediction of wax deposition in pipelines. A three parameter equation of state, the Patel-Teja EOS is used to describe the non-ideality of the liquid phase (oil) while the UNIQUAC model is used to describe the solid phase (wax). Solid precipitation is measured as temperature drops below the wax appearance temperature. The introduction of the third parameter increases the accuracy of results. The results from this study are in agreement with observations made by Pedersen et al. (1995) and Lira Galeana et al. (1996). This study has shown that the Patel-Teja EOS gives better predictions of wax precipitation when compared with the Peng Robinson EOS. This paper is based on theoretical data only. Accurate prediction of wax precipitation reduces loss time, maintenance cost and production loss due to shut-in. Although a kinetic model is required to estimate the wax deposition rate, accurate thermodynamics model is a key requirement for both wax deposition and precipitation calculations as the kinetics is being controlled by the thermodynamics driving force. The thermodynamic model proves successful and compares favourably with results obtained from the experimental data.