This paper presents the recent development of 140-ksi specified minimum yield strength (SMYS) coiled tubing (CT). The introduction provides background on the development. This includes the history of high-strength CT developments and potential new markets. It also defines the testing necessary to verify that the appropriate strength levels are achieved through all welding processes and compatibility with typical CT field equipment.
The tubing properties verification, steel selection process, and the welding procedure development and testing are discussed. Verification of manufacturability using current CT manufacturing equipment, which includes high-frequency induction welding, is also discussed. Compatibility testing verifies that the tubing can be used with typical CT equipment, such as injectors, blowout preventers (BOPs), and typical connections to pressure pumping equipment.
The target market for high-strength tubing is high-pressure well intervention and completion operations. Therefore, sour gas compatibility testing should be performed because even modest amounts of hydrogen sulfide (H2S) become severely sour in high-pressure environments. The testing program verifies that while using the available chemical inhibition methods, the tubing/inhibitor system is not susceptible to sulfide stress cracking (SSC), even at extremely sour H2S partial pressures in acidic environments. Finally, testing to verify low-cycle fatigue life caused by exposure with inhibition is discussed based on full-tube fatigue testing, both with and without sour gas exposure.
The paper concludes with lessons learned during the development process and presents the conclusions regarding the development, applicable markets for use, and any future steps.