Historical Exploration and Drilling Data from Geothermal Prospects and Power Generation Projects in the Western United States

Abstract

In 2005, Idaho National Laboratory was conducting a study of historical exploration practices and success rates for geothermal resources identification. Geo Hills Associates (GHA) was contracted to review and accumulate copies of published literature, Internet information, and unpublished geothermal exploration data to determine the level of exploration and drilling activities that occurred for all of the currently operating geothermal power generation projects and undeveloped geothermal prospects in the western United States. GHA found that there is published exploration and drilling data from twenty-two (22) geothermal power generation projects and at least three hundred fifteen (315) geothermal prospects in the western United States compared to the one hundred forty (140) geothermal resource sites examined in the July 2005 resource estimation workshop, which formed the basis for the Western Governors’ Association Geothermal Task Force Report of 2006. GHA also evaluated the geophysical methods presented in historical databases that appear to be the most definitive in providing the necessary data for successful citing of geothermal exploration, production, and injection wells, which appears to be electrical geophysical surveys. Most potential geothermal resource areas have exploration and drilling data accumulated during the late 1970s and early 1980s, primarily by petroleum companies, that exists in published literature and should be thoroughly evaluated before new exploration surveys and investigations are planned, funded, and conducted. For example, there are 2,737 thermal gradient boreholes in the GHA database for Nevada; however, of the 122 geothermal prospects and power generation projects only 39 have slim holes, exploration, and/or commercial wells. Therefore, there may be as many as 83 potential geothermal prospects in Nevada to be reassessed and confirmed as viable geothermal reservoirs with electrical geophysical surveys and intermediate-depth slim holes.