Beowawe Geothermal Field

The geothermal area at Beowawe Geysers straddles the Eureka-Lander County line in Whirlwind Valley, about 10 km west of the small community of Beowawe, Nevada. It is one of the largest geothermal fields in Nevada with some of the highest reported subsurface temperatures in the state (reservoir temperatures of 213-216C), making it an ideal area for the development and production of geothermal power.

The most conspicuous feature of the Beowawe Geysers area is an enormous, symmetrical sinter terrace (formed by evaporation of hot spring water) standing some 75m above the valley floor. The top of the terrace, which measures 30 m wide and 850 m long, is remarkably level. The hot springs, geysers, and fumaroles have temperatures up to 94-95.5C, and in 1932 several geysers were reported to erupt to heights of more than 1m.

The Beowawe geothermal area was actively prospected by several energy companies beginning about 1959 and continuing through the 1960s and early 1970s, leading to the development of the area as a power source. Exploration efforts have confirmed that the field is a geologically interrelated system. Drilling of geothermal exploration wells on the main sinter terrace in the early 1960s resulted in the disruption of natural geyser activity; however, geysers on the valley floor to the west of the terrace became noticeably more active after the wells were drilled, erupting to heights of 1-2 m. Vandals destroyed the caps from four steam wells on the main terrace sometime prior to 1972, and one of these released large volumes of steam and water, after which geyser activity ceased.

Between 1959 and 1965, twelve exploratory geothermal wells were drilled by Magma Power Company, Vulcan Thermal Power Company, and Sierra Pacific Power Company, demonstrating support for geothermal power. The deepest well drilled during this period was 625 m and several of the wells had temperatures of 208-212C at depths of 213-244 m. Between 1974 and 1978, three more wells were drilled, one of them to a depth of 2,915 m. Continued exploration drilling in the 1970s and early 1980s confirmed the presence of sufficient hot water and steam at shallow enough depths to support development of geothermal power. Geothermal production is from highly fractured and permeable zones in the sedimentary rocks below 2040 m.

The Beowawe flash power plant came on line in 1985, producing 16.7 MW from a 200C resource. During the first year of plant operation, injection of spent brine outside of the Beowawe reservoir caused the reservoir pressure to reduce, which allowed cold ground water to flow into and cool the geothermal reservoir. The cold water inflow stabilized the reservoir pressure but over eight years it reduced the temperatures of the production wells by as much as 21C. A large new production well was drilled, which temporarily restored full plant output but accelerated the decline in reservoir pressure, causing a reduction in the power plant output. The problem was resolved over the next two years, and full production resumed.

In 2005, Sierra Pacific Power Company signed a 20-year contract to purchase geothermal power from Beowawe Power. Operated by Caithness Operating Company, the Beowawe plant will supply Sierra Pacific 17.7 MWe in January 2006. An additional 30 MWe of power from geothermal sources, up from the current 95 MWe, is expected to be on line by mid-2008.

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