0
RESEARCH PAPERS

A Two-Layer Paraffin Deposition Structure Observed and Used to Explain the Removal and Aging of Paraffin Deposits in Wells and Pipelines

[+] Author and Article Information
Peter Toma

 P.R. Toma Consulting Ltd., 7328 Rowland Road, Edmonton, AB, Canada T6A 3W1ptoma@telus.net

John Ivory

 Alberta Research Council, Heavy Oil & Oil Sands, 250 Karl Clark Road, Edmonton, AB, Canada T6N 1E4ivory@arc.ab.ca

Gerard Korpany

 Alberta Research Council, Heavy Oil & Oil Sands, 250 Karl Clark Road, Edmonton, AB, Canada T6N 1E4ivory@arc.ab.ca

Mario deRocco

 Alberta Research Council, Heavy Oil & Oil Sands, 250 Karl Clark Road, Edmonton, AB, Canada T6N 1E4ivory@arc.ab.ca

Larry Holloway

 Alberta Research Council, Heavy Oil & Oil Sands, 250 Karl Clark Road, Edmonton, AB, Canada T6N 1E4ivory@arc.ab.ca

Chris Goss

 Alberta Research Council, Heavy Oil & Oil Sands, 250 Karl Clark Road, Edmonton, AB, Canada T6N 1E4ivory@arc.ab.ca

Jamal Ibrahim

Petroleum Engineering Group, PETRONAS Research and Scientific Services, Lot. 3288 & 3289, Off Jalan Ayer Itam, Kawasan Institusi Bangi, 43000 Kajang, Selangor, Mallot 3, Bangi, 4300 Kagang, Selanoor, Malaysiajamalir@petronas.com.my

Ismail Omar

Petroleum Engineering Group, PETRONAS Research and Scientific Services, Lot. 3288 & 3289, Off Jalan Ayer Itam, Kawasan Institusi Bangi, 43000 Kajang, Selangor, Mallot 3, Bangi, 4300 Kagang, Selanoor, Malaysiajamalir@petronas.com.my

J. Energy Resour. Technol 128(1), 49-61 (May 31, 2005) (13 pages) doi:10.1115/1.2126989 History: Received July 28, 2004; Accepted May 31, 2005

Paraffin fouling of pipelines and wells is a dynamic process involving deposition and removal. Deposited wax growth and hardening have been observed in the field. They must be properly evaluated at the design stage in order to develop a suitable and economic flow assurance strategy. Laboratory studies and direct observations on the nature and composition of the deposited wax have been made possible with the aid of a novel, axial wax deposition apparatus. This study resulted in an improved understanding and calculation of wax removal and aging rates. A turbulent burst mechanism was used to explain experimental observations made during this study as well as results recently published by other laboratories and field knowledge of wax removal and the aging/hardening process. Direct observations of the wax deposit nature and composition which were performed on samples removed from the deposited wax, provided essential information on the nature and composition of the deposit resulting from different flow regimes. These observations suggested that two distinct flowing zones (layers) and a wall-attached, thin, solid deposit are part of the flow-related deposition-removal process. A turbulent burst action, which is promoted in the near-wall area by the turbulent flow core zone, was used to explain experimental and field observations suggesting a selective removal of n-paraffin fractions. While the proposed removal mechanism acts selectively depending on the size of nonattached, crystallized wax, the transport of liquid n-alkanes components from the bulk, warmer zone to the near-wall colder region is considered as an overall “n-alkane” transport as accepted and used in calculations so far. The proposed two fluid layer model offers a framework for improving the design and operation (pigging and additive) strategies as well as for revisiting the accepted (safe) ranges of design velocities for waxy crude production and transport limes. This work aims to offer a better tool for estimating the pigging frequency, the optimal flow regime and a better additive testing and application strategy with considerable costs-saving to industry.

FIGURES IN THIS ARTICLE
<>
Copyright © 2006 by American Society of Mechanical Engineers
Your Session has timed out. Please sign back in to continue.

References

Figures

Grahic Jump Location
Figure 1

The two-layer flow model including bulk and “float” layers (where the “float” layer is defined for temperatures tFL<tWAT)

Grahic Jump Location
Figure 2

Conceptual description of deposition-removal. The feedback interaction between key controlling factors.

Grahic Jump Location
Figure 3

Schematic of the three-flow zone, paraffin deposition apparatus with deposition on the outside of a central, glycol-cooled sliding central pipe, used in this study (dimensions for the ARC variant)

Grahic Jump Location
Figure 4

View of the annular-axial flow deposition apparatus (deposition pipe removed for sampling and photographic study of the deposit)

Grahic Jump Location
Figure 5

Variation of composition (n-alkanes, oil, HTC) of circulated oil with time

Grahic Jump Location
Figure 6

Postrun direct observation of deposit and direct sampling (Test 2 high-shear rate Test 3 low-shear rates - a very thin wall-attached deposit and a gel, layer altered immediately after warm crude circulation is interrupted)

Grahic Jump Location
Figure 7

Measured carbon-number distribution for n-alkanes obtained from deposited wax: (a) the inner layer and (b) outer layer sampled for Test 2 (12 CMH) and (c) full deposit for Test 3 (6 CMH, indiscernible layers)

Grahic Jump Location
Figure 8

Schematic diagram of turbulent burst (10)

Grahic Jump Location
Figure 9

Minimum required flowrate and respective average velocity required for removal of a certain n-alkane equivalent size [calculation based on Shields’ curve Eqs. 5,6 and ARC deposition apparatus, flow area A=0.001m2, dh=0.011m]

Grahic Jump Location
Figure 10

“Equivalent particle size” and the relative removal tendency [Eq. 16] function of carbon number n-alkane carbon number (calculated for 18°C WAT as the float reference temperature)

Grahic Jump Location
Figure 11

Critical shear velocity (ucr*) required for removal of crystallized paraffin particles from the float layer as a function of particle diameter—a three-zone model (14)

Grahic Jump Location
Figure 12

Elliptical burst areas disposed on the control area exposed to turbulent burst-removal [after Cleaver and Yates 10]

Grahic Jump Location
Figure 13

Selective removal of n-paraffin crystals and aggregates as a function of carbon number (calculated for two flow rates and ARC’s deposition apparatus 42 API at 16.5°C bulk temperature)

Grahic Jump Location
Figure 14

Comparison of experimental (4) and calculated aging of paraffin deposit

Tables

Errata

Discussions

Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Related Journal Articles
Related eBook Content
Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In