The Geysers

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The Sonoma Calpine 3 power plant is one of 22 power plants at The Geysers

The Geysers is a complex of 22 geothermal power plants, drawing steam from more than 350 wells, located in the Mayacamas Mountains 72 mi (116 km) north of San Francisco, California. The largest in the world, the Geysers has 1517 MW[1] of active installed capacity with an average production factor of 63% (955 MW).[2] Calpine Corporation operates and owns 19 of the 22 active plants in the Geysers and is currently the United States' largest producer of geothermal energy. Two other plants are owned jointly by the Northern California Power Agency and the City of Santa Clara's municipal Electric Utility (now called Silicon Valley Power). The Bottle Rock Power plant owned by the US Renewables Group was expected to be reopened in 2007.[3] Another plant is under development by Ram Power Corp,[4] formerly Western Geopower, with operation set to begin in 2010.

Description

The Geysers geothermal development spans an area of around 30 square miles (78 km2) in Sonoma, Lake and Mendocino counties in California, located in the Mayacamas Mountains. Power from The Geysers provides electricity to Sonoma, Lake, Mendocino, Marin, and Napa counties. It is estimated that the development meets 60% of the power demand for the coastal region between the Golden Gate Bridge and the Oregon state line.[5]

Steam used at The Geysers is produced from a greywacke sandstone reservoir, that is capped by a heterogeneous mix of low permeability rocks and underlaid by a silicic intrusion.[6] Gravity and seismic studies suggest that the source of heat for the steam reservoir is a large magma chamber over 4 mi (7 km) beneath the ground, and greater than 8 mi (14 km) in diameter.[7] Unlike most geothermal resources, the Geysers is a dry steam field, which means it mainly produces superheated steam. Because the power plant turbines require a vapor phase input, dry steam resources are generally preferable. Otherwise, a two-phase separator is required between the turbine and the geothermal wells to remove condensation that is produced with the steam. The Geysers complex is now recharged by injecting treated sewage effluent from the City of Santa Rosa and the Lake County sewage treatment plant. This effluent, which used to be discharged into waterways such as the Laguna de Santa Rosa, is now piped to the geothermal field where it replenishes the steam reservoir.

Seismicity

Prior to the beginning of geothermal exploitation at The Geysers, seismicity was very low. However, the seismic coverage of stations was also very low. Nevertheless, according to USGS historical records for Northern California, no events were detected (above magnitude 2) before 1969— in a two degree box centered on The Geysers. Current studies of The Geysers Geothermal Field seismicity have reached the conclusion that deep-well injection in the field produces mostly microseismic events, with magnitudes on the Richter Scale (M) mostly between 0.5 and 3.0. The seismicity between magnitude 3.0 and 4.6 (the largest event recorded in The Geysers field, which was in 1973) is on the order of a few magnitude 4 events per year and on the order of 20 to 30 magnitude 3 events per year. Although the magnitude 4 events have been increasing, the number of magnitude three events has been relatively constant since the mid 1980s, despite the rate of injection increasing since then. [8]


Worldwide, the largest induced seismic event to date linked to Enhanced Geothermal System (EGS) activity was M3.7[9] in the Cooper Basin of Australia. However, research based on maximum fault lengths indicates that a M5.0 is the largest possible (but not probable) event in the Geysers. A magnitude 4.5 earthquake struck near the Geysers on January 12, 2014.[10]

A concern to the residents is not only the amount of seismicity but the magnitude of the largest seismic event likely to occur. Although no one can accurately predict earthquakes, the magnitude of an earthquake is dependent on the surface area that can slip — the length times the depth or width of the fault. Therefore, a large earthquake can occur only on a large fault.[11] There are no mapped faults of large length in The Geysers, so it is extremely unlikely that induced seismicity caused by activities in The Geysers will lead to a large earthquake.

History

Drilling a geothermal well, 1977 (USGS).

The first recorded discovery of The Geysers was in 1847 during John Fremont's survey of the Sierra Mountains and the Great Basin by William Bell Elliot. Elliot called the area "The Geysers," although the geothermal features he discovered were not technically geysers, but fumaroles. Soon after, in 1852, The Geysers was developed into a spa for The Geysers Resort Hotel, which attracted the likes of Ulysses S. Grant, Theodore Roosevelt, and Mark Twain.[12]

It was here that Pacific Gas and Electric began operation of the first successful geothermal electric power plant in the United States in 1960.[13] The original turbine lasted for more than 30 years and produced 11 MW net power.[14]

Future

The Geysers electrical plant reached peak production in 1987, at that time serving 1.8 million people. Since then, the steam field has been in gradual decline as its underground water source decreases. Currently, the Geysers produce enough electricity for 1.1 million people.

Techniques developed from Enhanced Geothermal Systems research will increase the production of the region in the future. By reinjecting greywater from the nearby city of Santa Rosa, existing wells will be recharged. This water will be naturally heated in the geothermal reservoir, and be captured by the existing power plants as steam. The project should increase electrical output by 85 MW, enough for about 85,000 homes.[15]

See also

References

  1. ↑ DiPippo, Ronald. Geothermal Power Plants, Second Edition: Principles, Applications, Case Studies and Environmental Impact. Butterworth-Heinemann. ISBN 978-0-7506-8620-4. 
  2. ↑ Lund, John W.; Bloomquist, R. Gordon; Boyd, Tonya L.; Renner, Joel (24–29 April 2005), "The United States of America Country Update", Proceedings World Geothermal Congress, Antalya, Turkey, retrieved 2009-11-09 
  3. ↑ Baker, David R. (January 14, 2007). "Steamy industry may clear the air". San Francisco Chronicle (Lake County). p. page F-1. Retrieved 2009-11-09. 
  4. ↑ http://www.ram-power.com
  5. ↑ "Calpine Corporation - The Geysers" (http). Retrieved 2008-06-11. 
  6. ↑ RESERVOIR RESPONSE TO INJECTION IN THE SOUTHEAST GEYSERS, 1991 (pdf) Steve Enedy, Kathy Enedy, John Maney, Sixteenth Workshop on Geothermal Reservoir Engineering 1991. (accessed 2007-05-16)
  7. ↑ "Cascades Volcanic Observatory (USGS) - Clear Lake Volcanic Field, California". Retrieved 2007-05-16. 
  8. ↑ http://esd.lbl.gov/research/projects/induced_seismicity/egs/geysers_history.html
  9. ↑ "EGS: The Geysers: What is the history of seismicity at The Geysers?" (http). Retrieved 2010-08-01. 
  10. ↑ http://earthquake.usgs.gov/earthquakes/eventpage/nc72141176#summary
  11. ↑ "Earthquake Size" (http). Retrieved 2010-08-01. 
  12. ↑ "A History of Geothermal Energy in the United States" (http). Retrieved 2007-05-17. 
  13. ↑ Lund, J. (September 2004), "100 Years of Geothermal Power Production", Geo-Heat Centre Quarterly Bulletin (Klamath Falls, Oregon: Oregon Institute of Technology) 25 (3): 11–19, ISSN 0276-1084, retrieved 2009-04-13 
  14. ↑ McLarty, Lynn; Reed, Marshall J. (October 1992). "The U.S. Geothermal Industry: Three Decades of Growth". Energy Sources, Part A: Recovery, Utilization, and Environmental Effects (London: Taylor & Francis) 14 (4): pp. 443–455. doi:10.1080/00908319208908739. ISSN 1556-7230. 
  15. ↑ "National Renewable Energy Laboratory - Enhanced Geothermal Sources" (pdf). Retrieved 2007-06-01. 

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Coordinates: 38°47′26″N 122°45′21″W / 38.79056°N 122.75583°W / 38.79056; -122.75583

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