Enhanced Geothermal Systems

T Coso geothermal project, located in California’s Coso volcanic field and about 100 miles (161 kilometers) north of Los Angeles, produces 260 megawatts of geothermal energy. Without tapping into any new geothermal resources (just by fracturing the existing reservoir), Coso will soon produce another 20 megawatts of electricity. The additional power will come from applying technology designed to improve the production of fields like Coso. Known as enhanced geothermal systems (EGS), this technology should more than double the amount of recoverable geothermal energy in the U.S., as well as extend the productive life of existing geothermal fields.


T he Coso geothermal project, located in
California's Coso volcanic field and about 100 miles (161 kilometers) north of Los Angeles, produces 260 megawatts of geothermal energy. Without tapping into any new geothermal resources (just by fracturing the existing reservoir), Coso will soon produce another 20 megawatts of electricity. The additional power will come from applying technology designed to improve the production of fields like Coso. Known as enhanced geothermal systems (EGS), this technology should more than double the amount of recoverable geothermal energy in the U.S., as well as extend the productive life of existing geothermal fields. The enhanced production at Coso will come as DOE's partners at the University of Utah's Energy & Geoscience Institute (EGI) and Caithness Corporation pump water under high pressure into a portion of the Coso field to reopen sealed fractures in subsurface rocks. Water pumped into the ground from injection wells will then circulate through the fractured rocks, flow to the surface through existing geothermal wells, and drive steam turbines. The process, called "hydrofracturing," is commonly used in oil and gas production. "We are attempting to tap into less

Geysers Project, California
The Geysers, about 120 miles (193 kilometers) north of San Francisco, is the world's largest dry-steam geothermal steam field, reaching 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.
EGS techniques will also increase the production and extend the life of The Geysers geothermal steam field. The wastewater from the Santa Rosa project will be injected into underground wells at a depth of 7,000 to 10,000 feet (2,134 to 3,048 meters), and at a rate of 11 million gallons (50 million liters) a day for the next 30 years. This water will be naturally heated in the geothermal reservoir, and the resulting steam will be used in nearby power plants to produce electricity. The project should increase electrical output by 85 megawatts, enough for about 85,000 homes. ORMAT Nevada, Inc., a major geothermal operator, plans to apply EGS techniques at a prospective geothermal site east of the operating Desert Peak geothermal field in Churchill County, Nevada. They will fracture a low permeability zone under the ground to enable production of an estimated 2 to 5 megawatts of electricity. If successful, this project could have wide application to other geothermal sites in the Great Basin, due to the many similarities of subsurface features throughout this geologic province.

EGS Around the West
The DOE will share the cost of the Phase I feasibility study of a three phase, five-year program to develop a commercial EGS power plant project. ORMAT's objective will be to develop and demonstrate EGS techniques at its geothermal leasehold area, east of the existing Desert Peak Geothermal Facility in Churchill County, Nevada. The objectives of subsequent phases A similar project with the Lake County Sanitation District (website at: geysers-pipeline.org/ index.htm) called the Southeast Geysers Wastewater Recycling System has been operating successfully since 1997. This system delivers about 2.8 billion gallons (10.6 billion liters) of effluent annually, and has delivered more than 16 billion gallons (60.5 billion liters) of fluid to The Geysers since operations began. This project was described in the 1999 Geothermal Today in an article titled Turning Wastewater into Clean Energy.
EGS seeks to tap a continuum of geothermal resources, ranging from conventional hydrothermal resources to hot dry rock. Nature has been prolific in providing large quantities of heat in the earth's crust, but fluids and permeability are less abundant.
With EGS, we hope to "engineer" new and improved reservoirs, and foster the economic production of that heat over long periods of time. Similar research and demonstration efforts are well underway in of this project will be the drilling, logging, hydraulic fracturing, and testing of the reservoir, followed by the construction and operation of a facility employing EGS technology for commercial power generation.
The project seeks to demonstrate that: 1) hydraulic fracturing technology can be applied commercially to geothermal systems; 2) adequate analytical techniques (such as subsurface stress analysis, fracture definition through seismic monitoring, numerical simulation of fluid flow and heat transfer in fractured media, etc.) required for an EGS project are already available; 3) neither water loss nor cooling of the produced fluid is a prohibitive barrier to a well-designed EGS project; and 4) commercial power can be generated reliably from an EGS project. The project relies upon proven technology for reservoir characterization and routine wellfield/power plant operation, and the application of existing fracturing technology to EGS.
Europe (websites at www.dhm.ch/dhm.html and www.soultz.net) and Australia (website at: hotrock.anu.edu.au), and show the promise of EGS technology worldwide.
EGS technology will initially enable greater efficiency and sustainability in the extraction of heat energy from producing hydrothermal fields. The technology developed will also set the stage for eventually recovering the abundant heat contained in areas not associated with commercial hydrothermal fields, but with huge resource potential. This broadening use of geothermal resources will strengthen security and develop needed, clean, domestic energy resources. ■

DOE Program Goal -Enhanced geothermal systems should
increase geothermal production to 20,000 MW by 2020.
The Steamboat geothermal power plant, originally built and now owned by ORMAT, in Steamboat Springs, Nevada.