Research and Development of Advanced Coiled-Tubing Construction and Performance
- T. Urayama (Japan Natl. Oil Corp.) | T. Yonezawa (Japan Natl. Oil Corp.) | M. Hamada (Sumitomo Metal Industries Ltd.) | M. Sugino (Sumitomo Metal Industries Ltd.) | H. Takabe (Sumitomo Metal Industries Ltd.) | A. Ikeda (Sumitomo Metal Technology Inc.)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- June 2001
- Document Type
- Journal Paper
- 83 - 90
- 2001. Society of Petroleum Engineers
- 1.7.5 Well Control, 3 Production and Well Operations, 4.2.3 Materials and Corrosion, 4.3.4 Scale, 4.1.2 Separation and Treating, 2 Well Completion, 1.6 Drilling Operations
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This paper describes joint industry project DEA107, in which BP plc, Amoco, Eni SpA. Div. Agip, Scottish Enterprise Operations, and Japan Natl. Oil Corp. (JNOC) participated. Objectives of this project were to investigate and to report on the low-cycle fatigue phenomena of coiled tubing (CT), to present a rational fatigue-life prediction model for CT, and to develop an advanced CT which could be applied to CT drilling of deep wells. In this paper, the effect of various factors on the cyclic bending performance of parent CT materials is predicted in relation to ballooning and low-cycle fatigue phenomena; corrosion and low-cycle fatigue phenomena of CT after long-term exposure in a mud environment are discussed, followed by fatigue performance and improvement of circumferential joining techniques.
A trial section of advanced CT of 2 3/8-in. outer diameter (OD) and 0.190-in. wall thickness (WT) with a total length of 3,000 ft was manufactured by means of joining short lengths of seamless tubing using the amorphous diffusion bonding (ADB) technique. A CT drilling test at the JNOC Kashiwazaki test field in Japan was completed successfully using this advanced CT.
The objective of this project is closely related to the future development of CT drilling technology. A deep well application of CT technology is seen as being one of the industry's major technology breakthroughs, especially when applied to slimhole drilling. This new area uses a larger diameter CT than that used for normal workover; its size and expected internal pressure has led to higher strength requirements for the material. The scope of work in this project has concentrated on three aspects.
Theoretical fundamental research of life-cycle prediction of drilling strings using CT, ballooning, and low-cycle fatigue phenomena.
Assessment of CT materials performance and development of a test method for fatigue, and corrosion.
Development of advanced materials for CT drilling; study of materials and joining or welding process; and trial production of advanced CT with the total length more than 3,000 ft.
CT manufactured using the electric resistance welding (ERW) process is the only type commercially available now. Available sizes and strengths are restricted to the tube-manufacturing mill capacity. In considering a technology breakthrough, we have focused on the development of CT using seamless pipe in this project. To use seamless pipes, we had to develop a circumferential joining process with both excellent quality and high productivity. Gas tungsten arc welding (GTAW) and amorphous diffusion bonding (ADB) had been selected for the candidate joining process in the preceding feasibility study.1
Fig. 1 illustrates the ADB process1,2 for tubes. After an amorphous thin film filler metal that has lower melting points than the tubes is inserted to the bonding interface, the bonding portion is heated under the melting point of steel. The bonding portion of the tubes is in the ADB chamber shown in Fig. 2, which is shielded by inert gas or evacuated during the ADB operation. At elevated temperatures, the amorphous film creates a thermal diffusion of atoms across the interface and produces a rigid bonding mechanism resulting from the interatomic forces between the atoms in the area of the abutment of the joint. After the ADB operation, some suitable heat treatment is applied to the bonding portion if it is needed.
Table 1 lists the tested materials. Samples of commercial CT's were purchased and tested to obtain information on conventional CT. All materials were certified with chemical composition analysis, tensile test, and microstructure.
Full-Scale Fatigue Test
Full-scale fatigue tests were carried out using the Stewart-Stevenson Service Model 200 CT life-cycle test stand shown in Fig. 3, which was considered as a standard type of fatigue-testing machine for CT. Test specimens for a full-scale fatigue test were full body pipes and tubes 2 m in length. The ends were sealed using caps with VAM connections to apply internal pressure easily. The fatigue life of materials is assessed by the number of bending cycles to internal pressure leakage. The process of ballooning was examined by the precise measurement of the OD and WT at various stages in the bending cycle. Plastic deformation behavior of full-scale test specimens in the early test stages was measured with strain gauges.
Material strength, OD, bending radius, and internal pressure are factors affecting fatigue phenomena and fatigue life. Bending radii at 48, 72, and 120 in. and internal pressures of 1,500, 3,000, 6,000, and 9,000 psi were studied.
Circumferential-joining processes for developing advanced CT from seamless pipe were examined. It has been recognized that any butt-welding process applied to CT has not satisfied performance requirements, particularly the fatigue life. Even though a GTAW process with improved quality could be developed, it would be inferior to the ADB process during production of large-diameter and heavy-wall CT. Therefore, the development of a joining process using the ADB process has been highlighted in this project.
It was shown in the feasibility study1 that ADB joints with a well-controlled bead configuration effectively improved the low-cycle fatigue life. With the goal of improving the bench-test fatigue life of API-5CT L80 tubes, the effects of various factors for the ADB joining process, particularly post-heat treatment and ADB joining environments, have been examined with the full-scale fatigue tester. As API-5CT L80 is manufactured using the quench-and-tempered process, a suitable post-weld heat treatment after ADB joining is necessary for L80 tubes. Fig. 4 shows that controlling oxygen potential is effective in improving the fatigue life of ADB joints. Both control of environment using inert-gas replacement and evacuation of oxygen in ADB joints effectively improved fatigue resistance. Evacuation proved to be better in stabilizing the quality of ADB joinings than inert-gas replacement. The average fatigue life of ADB is currently 70% of the L80 parent material.
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