For nearly 40 years, The Geysers Geothermal Field in Northern California has been a leading source of safe, low-cost and environmentally sound electric power. From a modest start in the 1920s through large-scale development beginning in the 1960s, The Geysers became the world's largest source of geothermal power.

According to Pacific Gas & Electric's Senior Engineer Dean Cooley, "Despite reservoir pressure and electricity production declines during the past decade, The Geysers retains its first-place status, with a peak capability of nearly 1,100 megawatts (MW) -- enough electricity to supply a city of over a million Californians."

About the Author
Paul Atkinson is a Special Engineering Consultant for Unocal Corporation, based in Sugar Land, Texas. He holds B.Sc., M.Sc. and Ph.D. degrees in petroleum engineering from Stanford University. Since 1977, he has worked for Unocal, first in the company's geothermal division, then in its oil and gas division.
Atkinson's geothermal work includes reservoir engineering and operations assignments in California (Santa Rosa) and The Philippines (Manila). He was technical program chairman for the 1993 GRC Annual Meeting. His professional interests include resource evaluation, well performance analysis and technology management.
Atkinson can be reached at Unocal, 14141 Southwest Freeway,
Sugar Land, TX 77478, USA.
Telephone: 281-287-5237
Fax: 281-276-9404.
E-mail
Historical Overview
Geothermal energy was first tapped commercially at The Geysers in the 1920s, when steam from shallow wells generated electricity for a resort on Big Sulphur Creek. Full-scale commercial development began by 1955, and the 11-megawatt (MW) Geysers Unit 1 power plant was commissioned in 1960. By 1989, installed generating capacity at The Geysers was 1,967 MW. Since 1987, The Geysers has experienced a decline in steam pressure and electricity production that has coincided with older power plants in the area reaching the end of their useful lives. Initial pressure in most Geysers production wells was above 500 pounds per square inch (psi), but by the mid-1990s many fell below 200 psi. And because pressure determines production rate, it is no longer practical in most areas of The Geysers to drill new wells to supplement steam supply.
Declines in reservoir pressure and steam production at The Geysers, however, have moderated considerably since 1987, and computer models indicate that a softening of decline rate should continue. Reservoir heat remains near its original temperature. Injecting water into these parts of The Geysers reservoir can result in recovery of additional heat. Water injection has helped mitigate fluid losses from the reservoir since 1969. More than 25 percent of fluid produced as steam is reinjected to the reservoir, and a number of wells in the area have shown production increases due to injection.

Operators at The Geysers are committed to reservoir management that maximizes energy recovery and power generation. Research has been ongoing since the early days of development, and a number of efficiency improvements and steam conservation measures have been implemented. Many power plants at The Geysers are now operated at lower turbine inlet pressures or modified for lower pressure operation, reducing back pressure on production wells and fostering higher steam production. This practice also increases the amount of steam ultimately recovered at The Geysers by lowering field abandonment pressure.

"The Geysers will be operating for a long, long time, but in the process, things will continue to change." This 1994 comment from the Geysers Geothermal Association is as true today as it has been since the beginning of commercial geothermal electricity generation in the area. Indeed, by the early 1990s, computer modeled forecasts indicated that field life at The Geysers will exceed 50 years. Power plant operators and steam suppliers continually seek new operating strategies to maximize future power generation-coupled with daily injection of millions of gallons of reclaimed municipal wastewater from Lake County since late 1997 and a proposed second effluent pipeline from Santa Rosa to The Geysers, those predictions seem assured.

Resource and institutional developments at The Geysers during the past 10 years have been described in several publications (see references). This article will pick up where those summaries left off-describing recent activities at The Geysers. These include new developments on the organizational, resource and institutional fronts, including injection of reclaimed municipal wastewater, electric utility deregulation, and power plant sales, auctions and closures.

Geothermal Projects Status