Next Generation Expandable Liner Applications
Authors: Metcalfe Paul , Innes Gareth , Johnston Gary , Gardiner Colin 
Published: October 2008

Expandable tubular technology is gradually becoming mainstream. However, many of the early products released to the industry utilized basic expansion concepts and their designs were compromised by the inclusion of other conventional techniques such as cementing.

This paper looks at the evolution of various expansion concepts and how increased understanding of such techniques is now being fed into the next generation of expandable tubular based products. The paper discloses newly developed expansion techniques, discusses the FEA and analytical test results that have allowed improvements in design and shows how conventional, limiting techniques have been removed.

Field case histories are discussed as an illustration of progress made with these next generation expandable liners.

Introduction

The term "Solid Expandable Tubular" or SET encompasses a broad range of potential products and applications. SET refers to methods involving the expansion of whole tubulars, without slots or perforations.

Two primary techniques are in use within the industry today, fixed cone and rotary expansion. Fixed cone expansion is an extrusion process in which a swage (figure 1) is used to expand the tubulars. In its simplest form, the pipe behind the swage is fixed in position while the swage is drawn towards the free end. This stretches the circumference of the pipe, and is normally accompanied by a shortening of the pipe length from its free end (since the total volume of pipe material remains unchanged). Additional dimensional change is a 4-7% reduction in wall thickness. In oilfield applications, the high loads required to force the swage through the pipe are usually applied through hydraulic pressure behind the swage, sometimes supplemented by pulling tension in the workstring. Hence swage expansion of solid tubulars is usually conducted from the bottom upwards.

Rotary expansion tools (figure 2) usually consist of one or more rollers positioned so as to impart a radial force upon discreet zones of a tubular's circumference. In order to apply this radial force to the entire inner circumference of a pipe, the tools are rotated about their longitudinal axis. The result of successive passes of rollers is a diametric expansion of the tubular combined with a gradual thinning of the pipe wall. While a rotary expander is being traversed through a tubular, this "roll forging" is not usually accompanied by a corresponding shortening of the pipe length. The use of rollers having a specific profile shape assists in maintaining a concentration of point loading and in minimizing tool friction. These provide for solid tubular expansion with relatively low axial loads. Typical axial loads for rotary expansions are of the order of 20% of those of equivalent swage expansions. Hence the attributes of high radial contact force, low tool-to-pipe friction, low axial tool loads facilitate the expansion of tubulars from any direction both "top down" and "bottom up". The top down method allows the expansion tool to be recovered partway through the operation (if necessary), and then re-deployed to continue the expansion process.

Rotary expansion processes fall into two distinct categories, i.e. with fixed and compliant roller systems. With the fixed roller system, the expansion characteristics are dictated by the geometry of the rolling elements that, combined with the expansion pitch, control the expansion demands for axial force and torque.