A new expandable wellbore casing could prove to be a boon to small-hole drilling. It is the first expandable casing designed to work economically in boreholes with diameters smaller than 4 inches.

Under the auspices of the U.S. Department of Energy’s Natural Gas and Oil Program, a cost-shared project led by Dynamic Tubular Systems Inc. has successfully completed all essential steps in developing an innovative expandable wellbore casing that could prove to be a boon to small-hole drilling. This is the first expandable casing that can be designed to work economically in boreholes with diameters smaller than 4 inches, and it has the potential to become the first expandable casing capable of protecting coiled-tubing drilling systems from harsh drilling conditions.

The new wellbore casing is expected to benefit a variety of extraction industries where it could extend the reach of traditional telescoping wellbore designs that sometimes run out of hole and fall short of target. The casing has great potential to reduce costs and improve operations in the shallow-gas and petroleum industries, including remedial work and patches for well repair, and recovery of bypassed and stranded resources, unconventional resources, and coalbed methane. Environmental, civil and mineral extraction fields also should find this technology useful.

Existing technology has limitations with extrusion (expansion) in small-diameter holes, but the new self-expanding split-tube design nowworks ably in them. A significant advantage is that the expandable casing can be controlled to create a high-pressure mechanical seal of the drill hole in lieu of cement. This is important because cementing is difficult to perform reliably in small-diameter wells since they typically have minimal clearance between the casing and borehole. And unexpected difficulties often arise, making the cost of cementing the most expensive item in a drilling project and rendering the small diameter hole uneconomical.

Development of the expandable casing progressed from initial concept to demonstration in just two years, and has attracted industry interest as an affordable approach for maintaining borehole stability and well control. The project was supported by the Microhole Technology Initiative, an Office of Fossil Energy effort begun in 2005 to reduce the costs and environmental impact of shallow-gas and petroleum gas well-drilling, and to make possible the economical development of the vast untapped reserves that exist in America’s declining or depleted reservoirs.

Microhole technologies also are being pursued for their potential value to applications such as drilling shallow development wells, drilling reservoir data monitoring holes, drilling shallow re-entry wells, and lateral drilling from deep exploration holes. Microholes are projected to reduce drilling wastes by 20 percent, and reduce overall field development costs by around 50 percent compared to conventional wells.

The Microhole Technology Initiative is managed by the National Energy Technology Laboratory. For more information about the initiative, please visit the Office of Fossil Energy’s Microhole Systems Research and Development Web site at www.fossil.energy.gov.