Sandia National Laboratories’ Well-field Construction activity, previously called the Drilling Technology Program, supports the U.S. Department of Energy’s Geothermal Technologies Program (GTP) through development activities aimed at making geothermal drilling and related wellfield construction cheaper and more reliable. This is critical to attaining GTP objectives because drilling not only is involved in almost all aspects of a geothermal development cycle  exploration, production and injection, and well maintenance  but also is expensive relative to other cost elements. When constructing a geothermal power plant, the cost of the (production and injection) well field can be as much as 50 percent of the total capital investment. Although much of the equipment for geothermal drilling comes from the oil and gas industry, the drilling itself is qualitatively different. Rocks are hard, abrasive, fractured and, by definition, hot.

Formation fluids often are highly corrosive and underpressured (pore pressure is less than an equivalent column of water). These harsh conditions mean that many of the tools used to reduce cost in other types of drilling cannot be used in geothermal reservoirs. The requirement for geothermal wells to produce large volumes of fluid also means that they are larger in diameter than other wells of the same depth. All of these factors can drive up the cost of typical geothermal wells.

Sandia’s goal is to develop, and transfer to industry, technology that will lower the costs and risks associated with drilling geothermal wells. Reducing these new technologies to “standard practice” will sustain the existing geothermal industry and enable expansion into more challenging resource areas.

For near-term hydrothermal systems:

• By 2010, develop and implement near-term improvements to drilling processes for geothermal applications to reduce costs by 25 percent, e.g., $300 per foot to $225 per foot.
  
  
• By 2010, develop and implement advanced technology solutions to reduce the risk of lost or unproductive, due to drilling problems, wells by 25 percent to 50 percent.

For Engineered Geothermal Systems (EGS):

• By 2010, demonstrate and implement drilling, completion and maintenance technologies that support successful first-generation EGS demonstrations.
  
  
• By 2020, develop the long-term revolutionary drilling advances needed to allow drilling twice today’s depths for the same cost.

Sandia’s approach to planning for wellfield construction is to aggressively address needs across the full spectrum of activities associated with creating the well field. While there is no silver bullet (that is, any single element of the process with potential for dramatically reducing total cost), opportunities for significant cost reduction exist across the range of activities that, taken as a whole, can achieve its cost goals. In this regard, the folks at Sandia have rethought this entire element of the program and are working on a range of activities both broader and deeper than previous program directions.