The costs and risks associated with the exploration for and assessment of geothermal reservoirs are high and the results are not predictable. Geothermal resources have the advantage of base-load generation, but this does not command a premium price in the utility market. Internationally, there are a number of different business models that contribute to the viability of geothermal power generation. Often, the resource is government owned, and national companies undertake exploration and delineation drilling. Once the resource has been identified, private firms are brought in to build the power plants and deliver power to the grid. In the US, although the resource may be on Federal land, the government is not involved in exploration and assessment activities, and exploration and assessment risk is assumed by the developer. However, the government does participate by sponsoring research in exploration methodology, as illustrated by DOE’s Geothermal Play Fairway program. We would extend this approach with the use of slim hole drilling and testing to collect and archive subsurface data. Slim hole drilling involves a spectrum of options that can extend from measurement of temperatures and analysis of geologic conditions to full reservoir testing. Although echoed by others, this approach has not been widely adapted. We describe the slim hole assessment of a hidden system at Mountain Home Air Force Base in Idaho, USA to illustrate an intermediate option between temperature gradient and full reservoir testing. Our present efforts at Camus Prairie, Idaho illustrate the process of flow testing an exploration slim hole.

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