Reliable Wax Predictions for Flow Assurance

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 high-accuracy 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.