Study of Expandable-Tubular Collapse Leads To Risk-Based Strength Development
Authors: Wilson Adam 
Published: June 2018

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 187460, “The Study on Expandable-Tubulars Collapse Performance and the Development of Risk-Based Design-Collapse Strength,” by X. Long, S.M. Roggeband, H. Pasaribu, and M. Jabs, Shell, and F.J. Klever, SPE, BetaTech Consulting, prepared for the 2017 SPE Annual Technical Conference and Exhibition, San Antonio, Texas, USA, 9–11 October. The paper has not been peer reviewed.
Solid expandable technology is helping the industry reach more challenging wells. The objective of this study is to investigate comprehensively the effects of the expansion process on the pipe mechanical properties and collapse performance and to develop a reliable risk-based collapse-strength design for the expandables.
Introduction
Expansion technology allows for tubulars to expand in situ, thus maintaining downhole size. It has been used successfully for zonal isolation in depleted or trouble zones as a drilling liner. It was also found to be very useful for extended reach in brownfields without losing the tubular diameter for maximum production. Another application is to repair existing casing worn by drilling. Several expansion technologies have been developed since the first concept test was performed in 1993. Currently, an expansion system called top anchor and pull (TAAP) is being developed, and multiple liners have been installed in the Gulf of Mexico.
The TAAP expansion system currently uses 50-ksi-grade expandable seamless tubulars. This material exhibits a large degree of work-hardening and, therefore, is suited for use in expandable tubulars. The collapse strength of tubulars, one of the major concerns during well design, is generally determined by the diameter-to-thickness (D/t) ratio as well as pipe material yield strength and geometric factors such as ovality, eccentricity, and residual stresses. Earlier studies have shown that the expansion process can affect the factors influencing tubular collapse performance significantly.
One of the objectives of this study is to develop a better understanding of collapse-failure mechanisms of expanded tubulars.
The other objective is to develop collapse-strength design formulas and methodologies for expanded tubulars with the same reliability level used currently, taking into account the additional aspects and uncertainties related to expandable tubulars.
Expandable Tubular Collapse Mechanisms
On the basis of a review of the literature, factors such as expanded pipe yield strength, stress/strain curve, geometry factors, and residual stresses, as well as their effects on pipe-collapse performance, have been investigated in the present study by both experimental measurements and numerical finite-element analysis (FEA).
Residual Stresses. The split-ring and hole-drilling methods for pipe residual-stress determination produce approximate or average measurements that do not accurately represent residual-stress distribution through the pipe wall thickness. In this study, through-wall residual stresses in an expanded pipe were measured by X-ray diffraction (XRD).