Wax-Deposition Experiments Decouple Hydrodynamic Parameters To Aid Scaleup
Authors: Wilson Adam 
Published: October 2017

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper OTC 27757, “Effect of Hydrodynamic Parameters on Wax Mass Density: Scaleup From Laboratory Flow Loop to Crude Production Pipelines,” by N. Daraboina, SPE, J. Agarwal, SPE, S. Ravichandran, SPE, and C. Sarica, SPE, The University of Tulsa, prepared for the 2017 Offshore Technology Conference, Houston, 1–4 May. The paper has not been peer reviewed. Copyright 2017 Offshore Technology Conference. Reproduced by permission.

Oil- and gas-production pipelines typically operate at high Reynolds number and low wall shear stress. Current wax-deposition-prediction models, however, were developed on the basis of laboratory flow-loop experimental data obtained at high shear stress and low Reynolds number. In this study, the effects of the hydrodynamic parameters are decoupled with specially designed flow-loop experiments. The results enhance understanding of the deposition behavior at various hydrodynamic conditions and aid in scaling up from laboratory to field conditions.

Introduction

Subsea production faces both fluid- and flow-based challenges, which eventually can lead to shutdowns, safety issues, and intermittency in production. Among these challenges, the deposition of paraffin, or wax, in the pipelines has gained attention as a flow-assurance problem. The severity can be realized in terms of lost production from reduced flow area, large changes in the pressure drops across pipelines, and changes in fluid properties such as an increase in viscosity of oil with wax precipitation. Accuracy in determining wax buildup across a pipe is critical for designing and applying remediation techniques. For example, accurate prediction of deposition parameters is necessary to manage the pigging process in production lines—including pigging frequencies and mechanical designs of pigs—and treatment of deposits with inhibitors. The assessment of the overall mass flux from the bulk to the interface is a prerequisite for accurate prediction of wax deposition, followed by the prediction of aging and growth individually of the deposit.

The existing models predicting paraffin deposition use nonrepresentative parameters that cannot be scaled up to field conditions because of the empiricism associated with the parameters. The failure of the parameters may partly be because of the application of incorrect variables used in development of empirical relationships for the parameters. These models show inconsistency in predicting field data. Selecting the correct hydrodynamic parameter for scaleup studies, therefore, is important.

Experimental Program

Fluid Characterization. The experimental fluids used in this study are laboratory-synthesized model oil containing 5 wt% food-grade wax and  Garden Banks condensate.

Experimental Facility. A small-scale facility is used to conduct flow-loop deposition experiments. This facility has three 8-ft pipeline test sections with different diameters. This enables effectively decoupling the effect of Reynolds number and shear stress at the wall on wax deposition. The test sections are configured as pipe-in-pipe to allow for countercurrent flow of oil and glycol.