Mechanical Performance and Stress-Corrosion-Cracking Resistance of Expanded Casing
Authors: Bybee Karen 
Published: February 2015

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 133382, ’Evaluation of Mechanical Performance and Stress- Corrosion-Cracking Resistance of Post Expanded Carbon Steel and CRA Casing Grades,’ by A. Bufalini, SPE, and R. Morana, Centro Sviluppo Materiali; P.I. Nice, H. Nasvik, SPE, and H. Kjorholt, SPE, Statoil; B.M. Bailey, M.K. Adam, SPE, D.G. Jiral, SPE, R.C. Ross, SPE, and R.C. Smith, Baker Hughes; and M. Ueda, and T. Ohe, Sumitomo Metal Industries, originally prepared for the 2010 SPE Annual Technical Conference and Exhibition, Florence, Italy, 19-22 September. The paper has not been peer reviewed.

While use of expandable tubular technology has significantly increased within the oil and gas industry in the last few years, materials-behavior knowledge for expandable casing has not progressed sufficiently. This is because of the lack of a definition of the most appropriate procedures to verify post-expansion material performance and because of the difficulties in performing investigations. 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.   

Introduction

One of the most important factors that prevent the widespread use of expandable casing is related to the only-partial knowledge of the casing-material behavior once it is subject to the large plastic deformation introduced by the expansion process. Despite an increasing number of applications, involving different levels of expansion, there is not a generally accepted view on how the casing material should be evaluated, nor is there a clear knowledge of the performance of post-expanded material from the point of view of mechanical and stress-corrosion-cracking (SCC) resistance. This lack of knowledge presents a large 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. An extensive testing program was carried out to evaluate the mechanical performance and the SCC resistance of post-expanded material.

The assessment of mechanical performance involved two types of activities. Conventional tensile tests were performed as the main way to define the mechanical behavior after the expansion. Tensile tests were carried out before and after expansion in longitudinal and transverse directions. Tests on carbon-steel grades included the evaluation of possible strain-aging effects, while tests on corrosion-resistant alloys (CRAs) also involved the effect of temperature. Impact tests were performed to gain a basic understanding of post-expanded material toughness. Because collapse resistance is the historical weakness for expandables, full-scale collapse tests were performed on expanded tubes.

Additional tests provided enhanced knowledge of the material capability to withstand the large plastic deformation required by monobore applications. A novel test was adopted, involving the use of an optical method for strain measurement to determine extended stress/strain relation for the materials. As part of the evaluation process, the effect of the real pipe configuration was considered by means of finite-element analysis (FEA) of the expansion process made with a 3D model of the casing.