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Technical Briefs

Prebending Coiled Tubing and Its Fatigue Life Prediction

[+] Author and Article Information
Li Zifeng

 Petroleum Engineering Institute of Yanshan University, Qinhuangdao 066004, Chinazfli@ysu.edu.cn

Li Xuejiao

 Petroleum Engineering Institute of Yanshan University, Qinhuangdao 066004, Chinalijunjiao-11@163.com

Wang Peng

 Petroleum Engineering Institute of Yanshan University, Qinhuangdao 066004, Chinalittle_well@126.com

J. Energy Resour. Technol 134(3), 034502 (Jul 30, 2012) (5 pages) doi:10.1115/1.4006960 History: Received February 01, 2012; Accepted June 05, 2012; Published July 30, 2012; Online July 30, 2012

Coiled tubing is widely used in oil drilling and production operations. However, extreme high stress variation of coiled tubing during the processes of pulling out, rolling in the reel, and passing through the gooseneck makes coiled tubing fatigue failure easily. Thus, it is of great importance to increase coiled tubing fatigue life. This paper introduces the new technology to improve the fatigue life of coiled tubing—the prebending coiled tubing technology; proceeds mechanical analysis and strength check of the prebending coiled tubing; analyzes stress cycling characteristics of the prebending coiled tubing in field operations; establishes the fatigue life prediction model of prebending coiled tubing under arbitrary cycle, on the basis of fatigue experimental data under the symmetric cycle and the pulsating cycle, with fitting and interpolation method; makes simple comparison of the fatigue life of the prebending coiled tubing with that of the straight coiled tubing. Preliminary calculations show that the prebending coiled tubing technology may improve the fatigue life of coiled tubing multiple times.

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Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Diagram of coiled tubing bending cycle

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Figure 2

Prebending coiled tubing

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Figure 3

Stress-strain curve

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Figure 4

Asymmetric stress cycle of prebending coiled tubing

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Figure 5

S–N curves of coiled tubing under symmetry cycle, pulsation cycle, and arbitrary cycle

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Figure 6

Nx -x curve under arbitrary cycle

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Figure 7

Equivalent stress cycle curve of two types of coiled tubing

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