Wax Deposition Scale-Up Modeling for Waxy Crude Production Lines
Authors: Hsu J.J.C. , Brubaker J.P. 
Published: October 2008

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 Doffing mechanism in modeling and neglect shear effect. However, the flow turbulence erect has significant impact On wax deposition and can not be neglected in wax Deposition modeling. Wax deposition scale-we parameters Including shear rate, shear stress, and Reynolds number Have been studied. None of these parameters can be used as A scalar. Critical wax tension concept has been proposed as A scalar. 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 represented in this paper to describe profiles of Wax deposition and effective inside diameter along North Sea and West Rica subset pipelines. The difference of wax Deposition profiles fem. stock tank oil and live oil is also Presented.

INTRODUCTION

When transporting waxy oil through a cold pipeline, wax will be deposited on the cold pipe wall throe h molecular Diffusion and shear dispersion mechanisms 1,2,3. Much wax deposition modelsl1,2,3,4,5,only apply molecular diffusion Mechanism in modeling, but neglect shear effect, However, Our previous results6 show that the flow turbulence effect Has a significant impact on wax deposition and can not 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 waxy oil through a cold pipeline, wax will be deposited on the cold pipe wall through molecular Diffusion, shear dispersion, Brownian and settling Mechanisms. Our data shows that shear dispersion effect conditions1,2,3,4,5. However, when flow velocity exceeds a certain value, shear effect becomes significant and affects wax deposition rate6, especially under turbulent flow conditions. Molecular diffusion and shear effect on wax deposition are discussed and a model is created. Wax deposition controlled by molecular diffusion mechanism only

The wax deposition rate on the pipe wall due to molecular diffusion mechanism only has been discussed elsewhere 7 and expressed as (Available In Full Paper)

The wax density may be a function of oil composition, temperature and flow conditions. However, the variation is not significant because a large portion of wax-deposit is trapped oil (up to 80%). Therefore, for simplicity, it is assumed that the wax density is constant in the range of the studied operating conditions. Equation (1) may be rearranged to a different format.