This paper evaluates our ability to predict geothermal reservoir temperatures using water compositions measured from surface hot springs or shallow subsurface wells at four geothermal sites prior to the startup of geothermal energy production using RTEst, a multicomponent equilibrium geothermometer we have developed and are testing. The estimated reservoir temperatures of these thermal expressions are compared to measured bottom-hole temperatures of production wells at Raft River, ID; Neal Hot Springs, OR; Roosevelt Hot Springs, UT; and Steamboat Springs, NV geothermal sites. In general, temperatures of the producing reservoir estimated from the composition of water from surface expressions/shallow wells using RTEst are similar to the measured bottom-hole temperatures. For example, estimates for the Neal Hot Springs system are within ±10 șC of the production temperatures. However, some caution must be exercised in evaluating RTEst predictions. Estimated temperature for a shallow Raft River well (Frazier well) is found to be slightly lower (ca. 15 șC) than the bottom-hole temperatures from the geothermal plant production wells. For the Raft River system, local geology and fluid mixing model indicate that the fluid source for this shallow well may not have originated from the production reservoir. Similarly, RTEst results for Roosevelt Hot springs and Steamboat Springs geothermal areas were found consistent with the reservoir temperatures obtained from deep wells. These results suggest that the RTEst could be a valuable tool for estimating temperatures and evaluation geothermal resources.

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