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RESEARCH PAPERS

An Experimental Study on Mechanics of Wax Removal in Pipeline

[+] Author and Article Information
Qian Wang

TUFFP, The University of Tulsa, Tulsa, OK 74104

Cem Sarica

TUFFP, The University of Tulsa, Tulsa, OK 74104

Tom X. Chen1

Texaco Inc.

1

Now with Shell Int’l Exploration & Production Inc., Houston, TX.

J. Energy Resour. Technol 127(4), 302-309 (Jan 07, 2005) (8 pages) doi:10.1115/1.2047591 History: Received November 26, 2001; Revised January 07, 2005

Pigging has been recognized as the most cost-effective method for preventing flow restriction by wax deposits in subsea flowlines. However, the pigging mechanics for wax removal in pipelines is still very poorly understood. A unique test facility was designed and constructed for experimental studies on the mechanics of wax removal in pipelines. The test facility consisted of a test section, a support structure, an apparatus to pull the pig through the test pipe, and a computer-based data acquisition system. The test section was 6.4m(21ft) long and was made from 0.0762m(3in.) inner diameter schedule-40 steel pipe. The mixture of commercial wax and mineral oil was cast inside the test section at different wax thickness and oil contents. A series of experiments was performed to investigate the wax removal mechanics with three different types of conventional pigs, i.e., cup, disc, and foam pigs. The experiments showed that a typical wax removal process using a pig followed four distinct phases, namely, wax breaking, plug formation, accumulation, and production phases. Wax accumulation can be very significant and is expected to be the dominating factor for the force required for moving a pig in long pipelines. As wax thickness and hardness increases, the required force to move the pig increases. The shape and material of the pig have a profound effect on the wax removal performance. While the disc pig provides the most efficient wax removal, the force requirement is excessive, especially for thicker and harder wax deposits. The wax removal performance of a cup pig is very similar to that of a disc pig. However, the cup pig can withstand higher load without mechanical damages than the disc pig. The foam pig offers the poorest wax removal performance.

Copyright © 2005 by American Society of Mechanical Engineers
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References

Figures

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Figure 16

Foam pig force data for 50% oil content and 2mm wax thickness

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Figure 5

Forces acting on a pig

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Figure 6

Test data for 50% oil content and 4mm wax thickness (disc pig 1)

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Figure 7

Typical force vs. distance behavior

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Figure 8

Baseline test results

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Figure 9

Test data for 50% oil content and different wax thicknesses (disc pig 1)

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Figure 10

Test data for 50% oil content and different wax thicknesses (cup pig)

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Figure 11

Test data for 4mm wax thicknesses and different oil contents (disc pig 1)

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Figure 12

Disc pig data for 75% oil content and 2mm wax thickness (disc pig 2)

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Figure 13

Data for 4mm wax thickness and different oil contents (cup pig, first run)

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Figure 14

Data for 4mm wax thickness and 35% oil content (cup pig, second run)

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Figure 15

Foam pig test data for 75% oil content

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Figure 17

Foam pig force data for 50% oil content and 4mm wax thickness

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Figure 18

Comparison of force data for first runs (2 and 4mm wax thicknesses and 50% oil content)

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Figure 19

Reverse foam pig force data for 50% oil content and 4mm wax thickness

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Figure 1

Schematic of test setup

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