The causes and associated remediation practices of most coiled tubing failures are well-known and detailed in multiple technical papers (Crabtree 2008, van Ardrichem & Larsen 2002, Burgos et al. 2007). One type of failure that has more limited exposure is excessive wall loss due to abrasion, occurring primarily in chrome completions. Significant wall loss over a large area typically requires the string be retired from service. On occasion, this damage has occurred during only a few operating runs. Retiring strings early is financially unacceptable, and in certain global locations, replacement strings can take months to arrive, resulting in a failure to meet operational objectives. This paper will detail the background on this type of failure observed in Azerbaijan, New Zealand and the USA, the failure analysis, results from pipe inspections, mitigation plans, and their associated results in reducing the frequency of incidents.
Analysis of incidents in the three markets started with an early notice of wear on a concentric string for offshore use in chrome completions. This wear detection resulted in a full string inspection to determine future life. While this string was retired, mitigation practices included mandating a wetted and/or lubricated wellbore and greater tracking of wall loss. The second market experienced a significant number of cases of premature failure, primarily on 1 ¾-in. coiled tubing (CT) run in chrome completions. Significant tracking of pipe movement versus location of the damage was completed to optimally target the use of friction-reducing lubricants. The third market used a 2-in. concentric string for 14 runs in a single L80 well. Here, flat spots exceeded 60% of wall loss, and several compressive failures occurred on the reel. In addition, galling with material transfer was observed. Mitigation practices include the use of pipe straighteners, wetted and lubricated completion in areas of high contact force.
Mitigation practices have significantly reduced the extreme wall loss issues in the first market, and similar programs have been recently implemented in the other two. Features common to all wells, such as deviation profile, will be presented to identify high-risk wells and permit pre-job mitigation planning.
This paper covers data from 19 wells and various mitigation practices and the associated positive results. The information will enable operators to better plan for success with CT well intervention operations.