Strength Analysis of Expandable Tubular for Well Applications
Authors: Caldas Aguiar Ana Carolina 
Published: June 2014

Abstract
Solid expandable tube technology has many advantages when compared to conventional wells. The expansion of tubes in situ allows developing reserves in many of the challenging scenarios found in oil industry, as pre-salt layer, HPHT wells, deep reservoirs, or ultra-deep water. Besides, this procedure has good compatibility with directional and horizontal wells and facilitates side-tracks operations. Although the expansion of tubes is very attractive, a better understanding of its influence on the tube mechanical strength is necessary. In this work, experimental tests and numerical analyses were performed in order to determine the effect of parameters such as diameter-to-thickness ratio and expansion rate on the collapse resistance of expandable tubes. An experimental apparatus was designed and built to reproduce full-scale tube expansion. Three 2 meter long specimens were expanded 10% their original diameters and subjected to hydrostatic pressure inside a vessel until collapse. Three non-expanded tubes were also tested for comparison. At the same time, non-linear numerical models were developed using the finite element method. After calibration, they were used to further analyze the mechanical behavior of solid expandable tubes and the influence of expansion on its resistance against collapse.

1. Introduction
A 2 - 3% annual increase of the already high demand for energy, oil in particular, is expected for the next few decades (Energy Information Administration, 2006). Because of this, oil companies are intensifying efforts to meet the global demand. These efforts must be made in the E&P area, especially on the discovery and development of new reservoirs, and in the overshoot of challenges, by improving the performance, developing feasible new technologies and reducing costs. Once drilling and completion represent a major percentage of the field development cost, it will not be surprise if companies concentrate their efforts on those segments. Some of the current challenges in drilling and completion segments are the following: HP/HT drilling; Drilling through salt layer; Deep wells; Ultra-deep water horizon; Extend reach wells; Complicated trajectory wells; Rigs availability.
With over 1000 installations in place, solid expandable tubular has proved to be an economically and viable alternative to conventional drilling technology as a means to overcome the mentioned challenges. Originally developed to extend well depth while maintaining larger borehole diameter (mono-diameter or slim well system), expandable tubes can also be used as a contingency drilling liner in any well during the drilling phase. The mentioned process maintains hole size when a geographical anomaly or problem is encountered. Another application is the open hole cladding system. It consists in an expandable string with elastomers that is run and installed against the formation to isolate specified areas. The cladding differs from the previous system because it is not tied back into the base casing. Expandable tubular technology can be used in cased holes as well. The expandable cased hole liner system enables operators to repair existing damage or worn casing in deep drilling or other contingencies.