| Abstract |
Allis et al. (2014, 2015) and others have made the case that hot stratigraphic geothermal reservoirs may host considerable thermal energy within an economic temperature-depth window of 150 to 200 oC at 2 to 4 km. One such area recently identified in Idaho’s fold and thrust belt (Welhan et al., 2014) was evaluated to provide a first-order estimate of stored thermal energy and electric power-generating potential in areas where reservoir conditions have been identified. Elevated heat flows, determined from data in more than 30 deep oil and gas exploration wells drilled in Idaho’s thrust belt, range from 90 to more than 120 mW/m2 in the most favorable areas, with depths of 2.5 to 3.3 km to the 150 oC isotherm and corrected bottom-hole temperatures up to 220 oC. Potential reservoir rocks known to be oil and gas producers in northern Utah, several of which also host productive aquifers in the study area, were encountered in all deep wells drilled in the high-heat flow areas. Based on the formations encountered, potential reservoir rocks in the area of highest heat flow have aggregate thicknesses of 100 to 700 meters in an area of 250 to 500 km2, as defined by four boreholes whose conductive gradients indicate temperatures of 185 to 240 oC at 4 km. Using the reservoir stored-heat method and a range of thermal recovery and energy conversion factors documented in operating geothermal power plants worldwide, the median electric power-generating potential of the area of highest-heat flow is conservatively estimated at 1.1 to 1.3 GWe. An area of moderately elevated heat flow and lower reservoir temperatures, with depths to the 150 oC isotherm of 4 to 4.2 km, has 75 to 90 MWe of power-generation potential, but the greater depths and high fluid salinities suggest that development potential in this area is marginal. A third area, defined by a single high heat-flow well with reservoir temperatures of 150-195 oC at depths between 3.1 and 4 km, appears to have the best potential for near-term development. It is located within 25 km of the phosphate mining and processing center of Soda Springs and less than 10 km from a regional high-voltage transmission corridor; the power-generating potential in the area near this well is conservatively estimated at 160 to 200 MWe but may be much higher, depending on how large an area is eventually identified as having suitable reservoir temperatures. |