James F. Kohler

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Recent awareness of the finite nature of fossil-fuel resources has resulted in an increased interest in alternate sources of energy such as geothermal. To evaluate the geothermal energy potential of the hot springs system near Midway, Wasatch Co., Utah, consideration was given to heat flow, water chemistry, and structural controls.

Abnormal heat flow was indicated qualitatively by snow-melt patterns and quantitatively by heat-flow measurements that were obtained from two of four temperature-gradient wells drilled in the area. These measurements indicated that the area north of the town of Midway is characterized by heat flow equal to 321.75 mW/m2, which is over four times the value generally considered as "normal" heat flow.

Chemical analyses of water from six selected thermal springs and wells were used in conjunction with the silica and Na-K-Ca geothermometers to estimate the reservoir temperature of the thermal system. Because the calculated temperature was more than 25 degrees C above the maximum observed temperature, a mixing model calculation was used to project an upper limit for the reservoir temperature. Based on these calculations, the system has a reservoir temperature ranging from 46 to 125 degrees C.

Structural information obtained from published from published geologic maps of the area and from an unpublished gravity survey, enabled two models to be developed for the system. The first model, based geologic relationships in the mountains to the north and west of Midway, assumes that the heat for the thermal system comes from a relatively young intrusive or related hydrothermal convection system in the vicinity of the Mayflower mine. Meteoric waters would be heated as they approach the heat source and then move laterally to the south through faults and fractures in the rocks. These thermal waters then rise to the surface through fractures in the crest of an anticline underneath the Midway area. The second model, based on the gravity survey, assumes an igneous intrusion directly beneath Midway as the heat source. The first model is considered more likely.

The Midway geothermal system is a low temperature resource, suitable for space-heating and other direct-use applications.


DOE/ET/28393-19 Utah Geological and Mineral Survey, Report of Investigation, no. 142, preliminary report. Published by Utah Geological and Mineral Survey, a division of Department of Natural Resrouces, State of Utah. Prepared for Department of Energy/Division of Geothermal Energy