Evaluation of Mechanical Performance and Stress-Corrosion-Cracking Resistance of Post Expanded Carbon Steel and CRA Casing Grades
- Andrea Bufalini (Centro Sviluppo Materiali) | Roberto Morana (Centro Sviluppo Materiali) | Perry Ian Nice (Statoil ASA) | Havard Nasvik (Statoil Hydro) | Halvor Kjorholt (Statoil ASA) | Bill M. Bailey (Baker Oil Tools) | Mark Kendall Adam (Baker Oil Tools) | Dennis G. Jiral (Baker Oil Tools) | Robert Chapman Ross (Baker Oil Tools) | Bob Smith (Baker Oil Tools) | Masakatsu Ueda (Sumitomo Metals Industries Ltd.) | Taro Ohe (Sumitomo Metals Industries Ltd.)
- Document ID
- Society of Petroleum Engineers
- SPE Annual Technical Conference and Exhibition, 19-22 September, Florence, Italy
- Publication Date
- Document Type
- Conference Paper
- 2010. Society of Petroleum Engineers
- 4.6 Natural Gas, 4.2.3 Materials and Corrosion, 4.3.4 Scale, 1.6 Drilling Operations, 4.2 Pipelines, Flowlines and Risers, 1.10 Drilling Equipment
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While expandable tubular technology significantly increased traction within the oil&gas industry in the last few years, materials behavior knowledge for expandable casing has not progress sufficiently. This is due to the lack of a diffused definition of the most appropriate procedures to verify post-expansion material performance and to the difficulties in performing investigation activity. These investigations rely on post-expanded material, which is costly and time-consuming to obtain, especially for the range of very large plastic deformations applicable to Monobore applications.
Consequently, an extensive testing program was started by Statoil to define an appropriate testing procedure for the evaluation of material performance after expansion and to characterize candidate materials. This paper presents the testing methodologies developed and the results obtained for several carbon steel grades and CRAs. These evaluations included tests of the mechanical performance and the resistance to aggressive environments.
The assessment of mechanical performance was carried out through several conventional and innovative tests and evaluation activities. Conventional tests included tensile tests in longitudinal and transverse direction, at room and elevated temperature, impact tests and residual stress evaluation. Collapse tests were performed on expanded pipes. Novel methods with optical strain measurements were adopted for improved tensile tests. Finite Element Analysis of the expansion process was also used to further investigate post-expansion mechanical performance. The resistance to stress corrosion cracking or sulphide stress corrosion was evaluated by means of FPB and C-ring tests. Carbon grades were tested in a mild sour environment while CRAs were tested in aggressive environments representative of possible field conditions. All experimental tests were carried out on materials before and after expansion. The effect of strain aging was also evaluated for carbon steel grades applying a defined aging cycle to expanded material.
The experimental methods adopted are described and discussed. The test results highlighted the main mechanical parameters to be considered and allowed ranking the different materials tested. At least one carbon steel grade and one CRA possess adequate mechanical and environmental performance even after 30% expansion. The test methodology adopted was therefore considered adequate for the aimed purpose.
Downhole casing expansion is nowadays a well established option for consideration in the well construction process. However, Monobore well construction concept has not maintained the pace that advocates of this technology had envisaged or the potential of its achievements.
One of the most important factors that prevent the diffusion of the expandable casing is related to the partial knowledge of the casing material behavior once subject to the large plastic deformation introduced by the expansion process. Despite an increasing number of applications, involving different levels of expansions, there is not a generally accepted view on how the casing material should be evaluated, or a clear knowledge of the performance of post-expanded material from the point of view of the mechanical and stress corrosion cracking resistance. This lack of knowledge presents a considerable obstacle for applications of successive Monobore sections. Not only do these successive Monobore applications involve expansion ratios easily exceeding 20% and possibly reaching 30%, they also depend on expandable tubulars for longer duration than the common expandable drilling liners.
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