Summary
The increased use of corrosion resistant alloys (CRAs) in deep
high-pressure/high-temperature (HP/HT) wells has led to production-tubing
cracking failures throughout the industry. Many of these failures have occurred
from the outside (annulus side) and have been attributed to environmentally
assisted cracking (EAC) and, hence, are best described as annular EAC (AEAC).
Examination of these failures points to a serious incompatibility of the
production tubing metallurgy with the packer fluid under stress.
In 2003, combining expertise in fluid chemistry and metallurgy, the authors
formed a research alliance to address the AEAC problem by examining the
compatibility of a wide spectrum of completion fluids with various martensitic
stainless steel (MSS) metallurgies. This unique research collaboration,
involving extensive stress-cracking testing performed with different
metallurgies and different fluids under simulated well conditions, has resulted
in an extensive database (more than 4,000 test entries for 27 fluids and six
MSS metallurgies) and a new body of knowledge regarding the causes behind AEAC
failures.
Conventional wisdom holds that chloride ion and oxygen play major causative
roles. The authors' findings, however, identify other contaminants in
completion/packer fluids that play the dominant role in the chemical mechanism
of the crack failures. Such contaminants include sulfur-containing species,
oxidants other than oxygen, and select basic ionic species. This paper
addresses the effect of the new information and identifies serious
misconceptions regarding the role of completion /packer fluids in the tubular
failures.
The authors' comprehensive study has advanced the industry's knowledge of
the causes of AEAC by detailing the previously unrecognized importance of
various contaminants present in the fluids. As a consequence, the need for
quality assurance and best-practice fluid management throughout the life cycle
of the fluids is now recognized. Misconceptions with respect to the chemical
mechanisms and causative factors of AEAC failures are discussed. Such
information should expand the industry's AEAC knowledge base and minimize the
risk of tubular failure.
© 2010. Society of Petroleum Engineers
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History
- Original manuscript received:
24 February 2009
- Meeting paper published:
21 April 2009
- Revised manuscript received:
28 September 2009
- Manuscript approved:
5 November 2009
- Published online:
22 June 2010
- Version of record:
2 December 2010
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