Experimental study and a proposed new approach for thermodynamic modeling of wax precipitation in crude oil using a PC-SAFT model

Taraneh Jafari Behbahani

doi:10.1007/s12182-015-0071-4

Abstract

A powerful method is necessary for thermodynamic modeling of wax phase behavior in crude oils, such as the perturbed-chain statistical associating fluid theory (PC-SAFT). In this work, a new approach based on the wax appearance temperature of crude oil was proposed to estimate PC-SAFT parameters in thermodynamic modeling of wax precipitation from crude oil. The proposed approach was verified using experimental data obtained in this work and also with those reported in the literature. In order to compare the performance of the PC-SAFT model with previous models, the wax precipitation experimental data were correlated using previous models such as the solid solution model and multi-solid phase model. The results showed that the PC-SAFT model can correlate more accurately the wax precipitation experimental data of crude oil than the previous models, with an absolute average deviation less than 0.4 %. Also, a series of dynamic experiments were carried out to determine the rheological behavior of waxy crude oil in the absence and presence of a flow improver such as ethylene–vinyl acetate copolymer. It was found that the apparent viscosity of waxy crude oil decreased with increasing shear rate. Also, the results showed that the performance of flow improver was dependent on its molecular weight.

Highlights

Crude oil is a complex mixture of hydrocarbons, consisting of waxes, asphaltenes, resins, aromatics, and naphthenics
The performance of the perturbed-chain statistical associating fluid theory (PC-statistical associating fluid theory (SAFT)) model for calculating WAT and the weight percent of wax precipitation has been compared with those obtained using the Ji model from the solid solution (SS) category and the Lira-Galeana model from the multi-solid (MS) phase category for the experimental data given in this work and given in the literature
The PC-SAFT model was used to estimate precipitated wax weight percent in crude oil and the model was verified using the experimental data obtained in this work and given in the literature

Summary

Introduction

Crude oil is a complex mixture of hydrocarbons, consisting of waxes, asphaltenes, resins, aromatics, and naphthenics. In the transportation of waxy crude oil in a cold environment at temperatures below the oil pour point, the temperature gradient of the oil creates a concentration gradient of the dissolved waxes due to their difference in solubility. The first important approach for modeling of wax precipitation uses a cubic equation of state (EOS) for vapor–liquid equilibrium and an activity coefficient model for solid–liquid equilibrium. These models are based on solid solution (SS) theory which assumes that all the components in the solid phase are miscible in all proportions (Won 1968, 1989; Hansen et al 1988; Pedersen et al 1991; Zuo et al 2001; Ji et al 2004). These models are based on solid solution (SS) theory which assumes that all the components in the solid phase are miscible in all proportions (Won 1968, 1989; Hansen et al 1988; Pedersen et al 1991; Zuo et al 2001; Ji et al 2004). Chen et al (2009)

Methods

Results

Conclusion