Coiled Tubing and Sour Service – Are We There Yet?

Abstract Research and field experience have given technical bases to accept the use of CT80, 90, and 100 coiled tubing (CT) for sour service, including their limitations. New higher strength Grades are now available (CT110 to CT140), but there is not enough awareness about potential issues, suitability, and boundaries regarding their use in H2S environments. This paper presents the potential issues and indicates the aspects that should be considered for the qualification of new CT Grades. This paper gathered research data from the review of technical publications related to CT and sour service since 1982, and also included field experiences regarding the use of CT in wells containing H2S, in order to establish the potential problems of working with CT in sour environments, and define what should be considered for the qualification of the new CT Grades available in the market, including the testing options that will cover the aspects needed for that qualification. The analysis of the information allowed establishing that the potential problems of using CT in sour service include the reduction of fatigue life available and different forms of H2S cracking. Considering this, it was established that the aspects that should be included for qualifying a CT Grade for sour service are: sour fatigue performance for pipe and bias weld, boundaries limits regarding H2S partial pressure, and finally the effectiveness of anti-cracking inhibitors for protecting the pipe against H2S cracking. The testing options proposed include bending fatigue testing of CT samples after being exposed to H2S, and small scale samples NACE TM0177 testing (Methods A, B, or C). More awareness about potential issues of using high strength CT Grades in sour service is required, and also there is no formal industry guidelines regarding their qualification for sour service. This paper summarizes the potential problems that can occur from the exposure of CT to H2S (lab data and field failures examples) and establish what should be considered for the qualification of a CT Grade to be used in sour service, including the testing options.