Expandable tubulars include casing, casing liners, tubing and sand screens that can have their diameter mechanically increased downhole. A special mandrel is drawn upward through the pipe once it is in position in the well, reducing the pipe wall thickness while increasing both outside and inside diameter. Current systems increase the diameter of the pipe between 5 and 16 percent, which in turn results in a reduction in wall thickness of between 2 and 5 percent, depending on the process. The steel used in expandable pipe has been specially processed for ductility, reduced sensitivity to metallurgical defects and increased fracture resistance, enabling it to be permanently deformed during the expansion process.

The potential benefits of expandable tubular technology are significant. With conventional casing, each new casing string set in the hole reduces the internal diameter of the hole by approximately 20 percent. This "telescoping" means that a deep well requiring multiple casing strings must either start with a very large diameter surface casing or end with a small diameter production casing, or both. This increases the cost and may limit the ultimate production capacity of a deep well. Expandable tubulars aim to avoid this decrease in well diameter with the installation of each successive casing string.

Expandable tubulars have found application as:

• openhole liners hung from inside a conventional casing string,
• perforated or slotted screens for lining a producing zone when sand production is a problem,
• cased-hole liners for repairing casing or shutting off perforations,
• specially designed junctions for multilateral wells, and as
• successive segments of casing that result in a mono-diameter borehole.

In addition to the primary goal of enabling an increase in the diameter of a deep completion zone, expandable tubulars can help simplify drilling through high pressure zones, allow continued use of conventional logging tools at greater depths, and extend the life of older wells (rehabilitative cladding). Several hundred expandable liners and screens have been installed since the advent of this technology in 1999-2000. However, the greatest potential for expandable technology lies in its widespread use as a means to create a mono-diameter wellbore.

In September 2002, Shell Exploration & Production Co. and Enventure Global Technology (a joint venture of Shell and Halliburton to develop expandable tubular technology) became the first to achieve a mono-diameter wellbore interval by using a series of 9 5/8-in. expandable liners run consecutively. Future improvements in the characteristics of expandable pipe could ultimately make it possible for a well to be cased with a single string of casing (MonoDiameter™ is Enventure's name for this system). If this type of application becomes mainstream, it would vastly reduce well construction costs and improve production capability.