A joint industry project (JIP) among ExxonMobil Development Company, Shell Canada Limited and BJ Services Company Canada was initiated approximately 2 years ago to extend the prior research conducted into the serviceability of coiled tubing (CT) for under-balanced sour well drilling and work-over operations, to the higher strength (90 to 110 ksi SMYS) grades. A significantly different and unique laboratory testing protocol is employed in the present JIP research. The methodology entails full-body tubing specimens that have been immersed in a sour solution of varying severity followed by testing in a bend fatigue machine to determine the low cycle fatigue performance of high strength CT materials degraded by prior exposure to the sour environment. In addition, there are several important aspects of possible CT degradation from exposure to sour wells that were not adequately investigated previously. These include the incubation times for cracks to form due to hydrogen induced cracking (HIC) or sulphide stress cracking (SSC), the tensile strength integrity of coiled tubing strings in which HIC and/or SSC have formed, the relative resistance of different CT strength grades to HIC and SSC, the benefits of H2S corrosion inhibitors and the effects of different sour environment severities and external mechanical damage. Detailed metallographic examinations of the CT material characteristics that define their relative susceptibility to failure under sour conditions were also performed. Although the JIP research is still in progress, this presentation will reveal many of the significant results obtained to date with emphasis on CT operational implications and considerations. The newly obtained test results are also being exploited for the preparation of Alberta Industry Recommended Practices (IRP- 21) currently under development in Canada.
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