Chemistry and Mechanisms of Completion/Packer Fluids: Annular Environmentally Assisted Cracking (AEAC) of Martensitic Stainless Steel Tubing: Misconceptions Regarding the Chemical Role of Completion/Packer Fluids
Jeffrey S. McKennis, Nam Bae, Enrico J. Termine, Ken Shimamoto and Mitsuo Kimura, International Symposium on Oilfield Chemistry, 20-22 April 2009, The Woodlands. Texas. doi:10.2118/121433-MS
The increased use of corrosion resistant alloys (CRAs) in deep HPHT wells has led to production-tubing cracking failures throughout the industry. Many of these failures have occurred from the outside (annulus side) and been attributed to Environmentally Assisted Cracking (EAC) and hence, 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 (> 4000 test entries for 27 fluids and 6 MSS metallurgies) and 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 impact 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.
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