Defying Conventional Wisdom; Reversing Tapered Coiled Tubing Strings for Extended Life

Abstract It is common practice in the coiled tubing industry to manage the fatigue of straight wall coiled tubing (CT) strings by reversing the string on a work reel. The benefit is to shift the fatigue profile along the string by moving high fatigue sections away from high cycle depths in the well. This often helps extend the working life of the coiled tubing. For tapered CT strings, however, this is not a common practice. Tapered strings are traditionally not considered reversible as the effectiveness of the taper would be lost, and in some cases, pulling out of hole would exceed the yield strength of the tapered section of the string. In a large unconventional gas play, a tapered string was designed to be utilized for a number of completion activities on extended reach wells. String costs had a significant impact on the economics of the project. The strings were utilized until a given section exceeded 80% of the predicted fatigue life of the coil, and then in a conventional fashion, the strings were taken out of service. By evaluating the upcoming work on the project and the location of the fatigue spikes in the string the coiled tubing service company was able to develop a procedure to remove the fatigue spikes and manipulate sections of the string to gain additional useful life out of the string. Forward planning, special operating procedures and engineering analysis were used to gain over 60% longer working life of coiled tubing strings on this campaign.