Wax Deposition Measurement and Scale-Up Modeling for Waxy Live Crudes under Turbulent Flow Conditions

Abstract

Abstract A wax deposition scale-up model has been developed to scale-up laboratory wax deposition results for waxy crude production lines. The wax deposition model allows users to predict wax deposition profile along a cold pipeline and predict potential wax problems and pigging frequency. Consideration of the flow turbulence effect significantly increases prediction accuracy. Accurate wax deposition prediction should save capital and operation investments for waxy crude production systems. Many wax deposition models only apply a molecular diffusion mechanism in modeling and neglect shear effect. However, the flow turbulence effect has significant impact on wax deposition and cannot be neglected in wax deposition modeling. Wax deposition scale-up parameters including shear rate, shear stress, and Reynolds number have been studied. None of these parameters can be used as a scaler. Critical wax tension concept has been proposed as a scaler. A technique to scale up shear effect and then wax deposition is described. For a given oil and oil temperature, the laboratory wax deposition data can be scaled up by heat flux and flow velocity. The scale-up techniques could be applied to multiphase flow conditions. Examples are presented in this paper to describe profiles of wax deposition and effective inside diameter along North Sea and West Africa subsea pipelines. The difference of wax deposition profiles from stock tank oil and live oil is also presented. Introduction When transporting a waxy oil through a cold pipeline, wax will be deposited on the cold pipe wall through molecular diffusion and shear dispersion mechanisms. Many wax deposition models only apply molecular diffusion mechanism in modeling, but neglect shear effect. However, our previous results 6 show that the flow turbulence effect has a significant impact on wax deposition and cannot be neglected in wax deposition modeling. The shear effect on wax deposition is difficult to interpret with correlations or dynamic equations. A semi-empirical technique is proposed to scale up shear effect and then apply conventional modeling techniques to predict wax deposition for waxy crude production lines. THEORETICAL BACKGROUND When transporting a waxy oil through a cold pipeline, wax will be deposited on the cold pipe wall through molecular diffusion, shear dispersion, Brownian and settling mechanisms. P. 241