Abstract

Development of geothermal resources in southwest Utah’s Sevier thermal area continued in the early 1990s with expansion of existing power-generation facilities. Completion of the Bud L. Bonnett geothermal power plant at the Cove Fort-Sulphurdale geothermal area brought total power generation capacity of the facility to 13.5 MWe (gross). At Cove Fort-Sulphurdale, recent declines in steam pressures within the shallow, vapor-dominated part of the resource prompted field developers to complete additional geothermal supply wells into the deeper, liquid-dominated portion of the resource. At Roosevelt Hot Springs near Milford, Intermountain Geothermal Company completed an additional supply well for Utah Power and Light Company’s single-flash, Blundell plant. With the increased geothermal fluid supply from the new well, the Blundell plant now produces about 26 MWe (gross).

The authors conducted several geothermal resource studies in undeveloped thermal areas in southwest Utah, Previous studies at Newcastle revealed a well-defined, self-potential minimum coincident with the intersection of major faults and the center of the heat-flow anomaly. A detailed self-potential survey at Wood’s Ranch, an area in northwest Iron County where thermal water was encountered in shallow wells, revealed a large (5,900 × 2,950 feet [1,800 × 900 m]) northeast-oriented self-potential anomaly which possibly results from the flow of shallow thermal fluid. Chemical geothermometry applied to Wood’s Ranch water samples suggest reservoir temperatures between 230 and 248°F (110 and 120°C). At the Thermo Hot Springs geothermal area near Minersville, detailed self-potential surveys have also revealed an interesting 100 mV negative anomaly possibly related to the upward flow of hydrothermal fluid.