Summary
As early as 1999, the need for industry guidelines regarding the use of
coiled tubing (CT) in sour wells was recognized (Luft and Wilde 1999).
Small-scale standard National Assocation of Corrosion Engineers (NACE) tests
(i.e., proof-ring, C-ring, double-cantilever-beam, and slow-strain-rate tests)
have been performed to evaluate the behavior of CT materials in sour
environments (Cayard and Kane 1997; McCoy 2005; McCoy and Thomas 2006; Luft
2003). Although these tests evaluate the crack-resistance properties of the
material in sour conditions, they do not give data regarding the low-cycle
fatigue performance of CT after sour exposure that could be used for CT-string
management in real operating conditions.
By 2003, uniaxial low-cycle corrosion fatigue tests of short, full-body CT
samples were used to evaluate the sour performance of Grade-70 and -80
materials (Luft 2003). These tests, although they considered fatigue
performance, were based on uniaxial reversing loads rather than reversing
bending strains, which is what occurs in CT operations. In addition to this,
the need for high-strength CT materials (i.e., 90-grade and higher) in sour
wells required additional knowledge regarding their sour performance.
By the end of 2004, a joint-industry project (JIP) among ExxonMobil
Development Company, Shell Canada Limited, and BJ Services Company was
initiated to investigate the serviceability of high-strength CT in sour
environments, with the main emphasis on the measurement of low-cycle
bending-fatigue life after sour exposure using full-body CT samples. Some of
the early results of this project were included in a previous paper (Luft et
al. 2007).
The present paper summarizes more than 4 years of laboratory testing aimed
at establishing the effect of sour exposure on the low-cycle fatigue life of CT
materials. Other aspects related to the possible CT degradation from sour
exposure are also included, such as the effect of varying sour-environment
severities, performance of anticracking (H2S) inhibitors, effect of
prefatigue, butt- and bias-weld performance, and tensile-strength integrity.
The results have led to changes in the current operating procedures regarding
CT-strings management and CT-material selection criteria for sour service.
© 2010. Society of Petroleum Engineers
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History
- Original manuscript received:
9 March 2010
- Meeting paper published:
23 March 2010
- Revised manuscript received:
6 June 2010
- Manuscript approved:
17 June 2010
- Published online:
18 November 2010
- Version of record:
9 December 2010
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