Abstract

The Heber Geothermal field is located in Imperial County, California along the extension of the East Pacific Rise into the North American continent. Initial exploration in 1945 was for oil and gas, but this changed to geothermal exploration when high thermal gradients were discovered in shallow holes. Several geophysical surveys were run: gravity, reflection seismic, ground noise, resistivity and spontaneous potential. However, the best data for picking the explortory well location was provided by temperature holes up to 500 feet (152 M) deep. The first geothermal well was drilled in 1972. Curently, the field is outlined by data from sixteen wells. These indicate a convective hot water plume of 375°F (190°C) or higher in a predominantly sand reservoir. A predominantly shale section provides a cap above 2,000 feet (610 M) where heat flow is primarily conductive. Development, planned in zones from 2,000 feet (610 M) to 10,000 feet (3050 M), is expected to support a generating capacity of 500 megawatts for at least 30 years. Initial development will produce brine from Zone I (2000-4000 feet) and Zone 2 (4000-6000 feet). Producing wells will be directionally drilled to bottom hole targets in the temperature high. Cooled brine will be injected into wells located at the periphery of the reservoir. An operting unit has been formed by the leaseholders: Chevron Resources Company, Union Oil Company of California and New Albion Resources Company. Chevron is the Unit Operator and has signed a contract to supply 2-phase geothermal fluid to a 50 megawatt gross double-flash power generation plant to be built by Southern California Edison Company. Start-up is planned for early 1984.