Research Papers: Petroleum Transport/Pipelines/Multiphase Flow

Transient Wax Gel Formation Model for Shut-In Subsea Pipelines

[+] Author and Article Information
Chiedozie Ekweribe1

Faruk Civan

 University of Oklahoma Norman, OKfcivan@ou.edu


Current address: Chevron North America, LA.

J. Energy Resour. Technol 133(3), 033001 (Oct 03, 2011) (5 pages) doi:10.1115/1.4004965 History: Received March 19, 2010; Revised August 20, 2011; Accepted August 24, 2011; Published October 03, 2011

Physics of wax gel formation during shut-in is analyzed and described over a cross-section of a typical subsea pipeline. Two regions are identified during this process: the liquid and gel regions. Phase transition is assumed to occur at the liquid-gel interface. Unsteady-state heat and mass transfer models are proposed for each region. Two diffusion streams are evaluated: the dissolved wax molecules moving from the pipe center toward the wall due to temperature gradient and subsequently concentration gradient and the wax molecules diffusing from the liquid-gel interface into the gel deposit. This model is essentially the modification of the model given by Bhat [1] which considered transient heat transfer and neglected mass transfer of wax molecules through the gel deposit and the model by Singh [2] which considered transient mass transfer of molecules with carbon numbers higher than the` critical carbon number (CCN) necessary for wax diffusion into gel deposit but did not consider transient heat transfer effects during the cooling process. This paper presents a transient-state formulation circumventing the limitations of these previous models and better represents the true cooling and gelation process occurring in a shut-in subsea pipeline filled with waxy crude.

Copyright © 2011 by American Society of Mechanical Engineers
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Grahic Jump Location
Figure 1

Cross-sectional view of a pipe showing possible phase regions in solids deposition (after Bhat and Mehrotra [1])

Grahic Jump Location
Figure 2

Growth of waxy gel from pipe wall and subsequent aging due to diffusion of wax molecules into gel layer

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Figure 3

Schematic of the evolution of waxy crude gel inside a cross-section of a shut-in subsea pipeline



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