Reliable Wax Predictions for Flow Assurance

Abstract

A number of wax models currently in use by the oil industry are based on parameters that were empirically determined to match available data for black oils. These data are often not very precise. The recently developed predictive local composition model is, however, a predictive, theoretically well-defined model based on highaccuracy thermodynamic data. The paper describes how the predictive local composition model can be used in conjunction with conventional cubic equations of state to perform wax equilibrium calculations for black oils. Examples are given that show how the model can predict both wax appearance temperature and the amount of wax precipitated at varying temperatures with or without detailed n-paraffin analyses. The examples presented include the effect of pressure on live oils. The improved thermodynamic modeling of wax formation will allow for better prediction of wax deposition rates for flow assurance.

On the effect of wax content on paraffin wax deposition in a batch oscillatory baffled tube apparatus

“…petroleum fluids [3]; the prediction of the viscosity of waxy oils [4,5]; the improved thermodynamic model for wax precipitation [6]; the prediction of the phase behaviour of petroleum fluids [7]; the prediction of wax deposition for flow assurance [8]; and the new thermodynamic model validated with wax disappearance temperature [44].…”

An investigation on the sensitivity analysis of the parameters of proposed wax precipitation model

“…1 presents a comparison of different models used to predict wax appearance temperature. In this figure the results of the proposed model were compared with experimental data (Metivaud et al, 1999) and three different models; ideal solid solution, multi-pure-solid, and Coutinho's Uniquac in which the solid phase non-ideality is described by UNIQUAC model (Pedersen, 1993;Pan et al, 1996;Coutinho et al, 2002). As shown in this figure, the proposed model predictions are very good over a wide range of compositional distributions.…”

Studies of Wax Deposition Onset in the Case of Indian Crude Oil

“…The temperature, at which the first crystal appears, called wax appearance temperature, is an important parameter. The wax appearance temperature represents a thermodynamic boundary at which crystalline paraffins form stable nuclei and precipitate from the bulk hydrocarbon fluid (Coutinho, Edmonds, Moorwood, Szczepanski, and Zhang, 2002).…”

“…But, the study of their relative position/boundaries within pressure temperature (P-T) diagrams as well as the rate of wax deposition and accumulation is also essential. The major factors include oil composition, temperature/cooling rate, pressure, paraffin concentration, molecular mass of paraffin molecules, paraffin molecular weight distribution, occurrence of nucleating materials such as asphaltene, formation fines and corrosion products, water oil ratio, and shear environment (Coutinho, Edmonds, Moorwood, Szczepanski, and Zhang, 2002;Forsdyke, 1996;Pedersen, 1995;Hammami, 1994;Hammami, 1997;Monger McClure, Tackett, and Merrill, 1999;Pan, Firoozabadi, and Fotiand, 1997;Vazquez and Mansoori, 2000).…”