Evaluation of the geothermal potential of the Snake River Plain, Idaho, based on three exploration holes

Over the period of September 2010 to January 2012 three exploratory wells were drilled on the Snake River Plain in Idaho as part of the Snake River Plain Geothermal Drilling Project (Project Hotspot). These wells were intended to help document the existence of geothermal potential in the Snake River Plain area; specifically, along the axis of the eastern Snake River Plain, along the margin of the plain, and in the western Snake River Plain.;I examined five water samples that were collected from the three wells (one each from Kimama and Mountain Home, and three from Kimberly) and analyzed for 24 ion concentrations. The Kimama waters are Na-chloride, Kimberly waters are Na- bicarbonate, and Mountain Home waters are Na-sulfate. These chemical results were used in seven solute geothermometers to estimate reservoir temperatures at depth. Three of the water samples were also analyzed for the stable isotopes 2H, 13C, and 18O. Temperature logs were used to calculate geothermal gradients in the wells.;The Mountain Home well had the highest recorded water temperature (140 °C), the highest geothermometer results, and highest geothermal gradient for the entire well (73 °C/km). Mountain Home isotopic properties indicate it is not meteoric water. Kimama had a maximum recorded temperature of 59.3 °C, and geothermometer results only slightly lower than at Mountain Home. The Snake River Plain aquifer suppresses the geothermal gradient in the upper portion (0-960 m) of the Kimama well to 5.5 °C/km, while below a depth of 960 m the gradient increased to 88.9 °C/km. Kimama isotopic properties indicate that it is meteoric water. Kimberly had a maximum recorded temperature of 57.3 °C, the lowest geothermometer results of 112.9 °C, and a geothermal gradient of 15.1 °C/km. The gradient from 800-1,953 m is only 5 °C/km. Mountain Home and Kimama had the strongest indicators of future geothermal potential with high temperatures, high geothermometer results, and high geothermal gradients.