Geothermal Reservoir Temperatures in Southeastern Idaho, USA Using Multicomponent Geothermometry

Abstract

The thrust zone of southeastern Idaho and western Wyoming exhibits numerous warm springs, warm water from shallow wells, and hot water within oil and gas test wells that indicate a potential for geothermal development in the area. Although the area exhibits several thermal expressions, the measured geothermal gradients varies substantially (19 – 61 oC/km) within this area, potentially suggesting a redistribution of heat in the overlying ground water from deeper geothermal reservoirs. We have estimated reservoir temperatures from measured water compositions using an inverse modeling technique (RTEst) that calculates the temperature at which multiple minerals are simultaneously at equilibrium while explicitly accounting for the possible loss of volatile constituents (e.g., CO2), boiling and/or water mixing. As an extension of an ongoing project that investigates the geothermal potential of the adjacent Eastern Snake River Plain (ESRP) system, we have applied the RTEst model to water compositions measured in the 1980s from a limited number of wells and thermal springs to estimate the underlying geothermal reservoir temperature in the thrust zone. The temperature estimates of this zone are compared to the estimated temperatures for the adjacent ESRP system.