EVALUATION OF THE GEOTHERMAL POTENTIAL OF THE SNAKE RIVER PLAIN, IDAHO, BASED ON THREE EXPLORATORY COREHOLES

Three exploratory coreholes were drilled at Kimama, Kimberly and Mountain Home on the Snake River Plain, Idaho, to evaluate its geothermal potential. We used chemical data from water samples collected from the three coreholes in seven solute geothermometers to estimate reservoir temperatures at depth. The water samples were also analyzed for the stable isotopes deuterium, oxygen-18, and carbon-13. Temperature log data from the coreholes were used to calculate geothermal gradients. Also, core samples from Kimama were analyzed for clay content and composition using X-ray diffraction.

The X-ray diffraction data suggest that the base of the Snake River Plain aquifer at Kimama is located 960 m below the surface, much deeper than previously suspected. Below 960 m the core shows signs of alteration including color change, formation of clay, and filling of secondary minerals in vesicles and fractured zones. Increased temperatures favor the formation of smectite clay below 960 m, which clogs pore spaces and reduces porosity and permeability to create a natural base to the aquifer.

Mountain Home has the strongest indicators of geothermal potential, with the highest recorded water temperature, the highest geothermometer results, and the highest geothermal gradient for the entire hole (73 degrees C/km). Mountain Home isotopic properties indicate that it is not meteoric water. Kimama also appears to have good geothermal potential, as its geothermometer results were only slightly lower than Mountain Home’s. Although the Snake River Plain aquifer suppressed the gradient above 960 m at Kimama to 5.5 degrees C/km, below 960 m the gradient increased to 89 degrees C/km. Kimama isotopic properties indicate that it is meteoric water. Kimberly does not appear to have as much geothermal potential as Mountain Home and Kimama, as it had the lowest recorded water temperature, geothermometer results, and geothermal gradient.