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WGP Geysers

Flowing WGP-1 Flowing WGP-1
Flowing WGP-1 From Plant Site Flowing WGP-1 From Plant Site

In Depth

WGP Project – Geysers, California

Project Description and Location

U.S. Geothermal acquired Ram Power Corp’s Western GeoPower (“WGP”) project, located in the Geysers geothermal field on April 4, 2014. The acquisition included the Ram subsidiaries of Western Geopower, Inc., Skyline Geothermal Holdings, Inc., and Etoile Holdings, Inc. These in turn, include all membership interests in Mayacamas Energy LLC and Skyline Geothermal LLC.

WGP #1 – flow test June 2015

The WGP project is located at the site of the former Pacific Gas and Electric (PG&E) Unit 15 project, which once had a 62 megawatt (gross) capacity power plant. During 10 years of operation, the PG&E plant declined in production to approximately 35 megawatts before it was shut down in l989 and all of the wells were plugged and abandonded. The project is located within the broader Geysers geothermal field which covers a total of approximately 20,000 acres in the Mayacamas Mountains in Sonoma County, California, approximately 75 miles north of San Francisco. The broader Geysers geothermal resource is the largest producing geothermal field in the world, and has been generating greater than 850 megawatts of power for more than 30 years.

Two development approaches are currently being considered for the WGP project. The first involves obtaining a power purchase agreement and constructing a power plant, while the second option involves selling steam to one of several companies currently operating power plants at The Geysers.

The WGP Project includes geothermal leases (covering 3,809 acres), detailed engineering design plans, and permits for a proposed 26 net megawatt power plant. This property contains 4 of the 5 existing geothermal wells immediately available for production or injection. The 5th well is located on an adjacent property where the project owns a 50% undivided interest in the geothermal mineral rights relating to the property, with the remaining 50% ownership under lease.

At the time Western Geopower was merged into Ram, Western Geopower had successfully drilled four wells with an initial steam flow totaling 462,000 pounds per hour. A report prepared in 2012 by Geothermex, a third party reservoir engineering firm, states that the total initial power capacity from these existing wells is estimated at about 30 megawatts. The report further estimated that the sustainable long-term production from the resource is conservatively estimated at approximately 30 megawatts gross (26 megawatt net), assuming only 25% of the withdrawn geothermal fluid is injected back into the reservoir.

Accessibility, Climate, Local Resources, Infrastructure and Physiography

The WGP project site is accessed via an existing county road called the Healdsburg-Geysers Road. This is an all-weather asphalt road currently utilized by other geothermal operators. Rail and road transportation from Los Angeles and Oakland, California ports is adequate for the shipment of heavy equipment to the WGP Project site and the Healdsburg-Geysers Road is adequate to support construction of the WGP Project.

Geothermal power plants at The Geysers typically operate 24 hours per day, 365 days per year without limitation due to climatic conditions or operating seasons. Existing structures remaining on the WPG site include over-land steam lines from the well pads, several concrete slabs, two sheds, two steel separator vessels, a concrete sedimentation basin, and a vent station with a concrete rock muffler. The WPG site is crossed by a California Independent System Operator (“CAISO”) controlled, PG&E operated 115 kV transmission line. The Geysers Project power plant is planned to interconnect with this line. A Large Generator Interconnection Agreement (“LGIA”) was signed between WGP, PG&E and CAISO in February 2009.

The WGP Project is located within the larger Geysers geothermal area, where there are 18 operating geothermal power plants. This infrastructure supports a large and qualified work force. In addition, suppliers, contractors and specialty consultants are readily accessible. The topography of the Geysers is characterized by rugged terrain and steep slopes. The ambient temperatures range from 46o F to 104o F. The plant elevation is 2,427 ft. above mean sea level. The WGP Project site receives an average of 80 inches of rain per year, with rainfall predominantly in the months of October to April.

History of the Property

Geological Setting

The site is located within a seismically active region dominated by the San Andreas Fault system, which is approximately 30 miles to the southwest. The nearest active fault identified by the California Geological Survey is the Mayacamas Fault, approximately 3.5 miles southwest of the project. The WGP Project site is located northwest of the Alexander Valley, in eastern Sonoma County within the Coast Range Geomorphic Province of Northern California. This province is generally characterized by northwest-trending mountain ranges and intervening valleys, which are a reflection of the dominant northwest structural trend of the bedrock in the region. The basement rock in the northern portion of this province is presumed to consist of the Franciscan Complex, a diverse group of igneous, sedimentary, and metamorphic rocks of Upper Jurassic to Cretaceous age (140 to 65 million years old). The Franciscan Complex is part of a northwest-trending belt of material immediately adjacent to the eastern edge of the San Andreas Fault system. In the WPG project site vicinity, the Franciscan Complex rocks are overlain by Tertiary age continental and marine sedimentary and volcanic rocks. These Tertiary age rocks are locally overlain by younger Quaternary alluvial, colluvial and landslide deposits.


Commercial electric power generation at The Geysers began in 1960 and reached a peak in the mid-1980s. Steam pressure began declining in the 1980s, but in the 1990’s efforts across The Geysers by geothermal operators and utilities, were successful in slowing and nearly halting the overall decline in the rate of steam production. These efforts include the reinjection of steam condensate, the injection of excess creek water, and the injection of reclaimed wastewater into The Geysers reservoir. Although there is no current injection into wells located on the WPG site, injection near the WPG project boundaries may be benefiting the project now and contemplated future injection measures may provide additional benefits in the future.


The four new wells were drilled during 2008-2009 under a geothermal exploration permit through the California Division of Oil and Gas and Geothermal Resources. These four wells were directionally drilled to targets within known production zones identified in the original development drilling for PG&E Unit 15 in the 1970s and 1980s. All wells were drilled to production diameter through the steam production zone. Drilling was completed using sump-less mud drilling in the upper section of the well bore. Air drilling was used in the geothermal steam production zone.

Resource Estimates

GeothermEx was retained to develop and calibrate a reservoir model of the WGP project that incorporates all of The Geysers in its entirety to study the planned WGP project.  The field-wide model was necessary to assess the interference between the WGP project and those of other operators who produce steam at The Geysers.  Using data obtained from flow tests of 3 of the 4 production wells conducted in 2015, the model confirmed the WPG steam supply is sufficient to support a 30 MW power plant.

Exploration and Development

Additional drilling to increase steam production beyond the existing four production wells and the development of an injection well strategy is underway. Economic models encompassing both production options are also being developed to optimize the project.

Preliminary power plant and switchyard design for a 26 megawatt (net) power plant at the project has been performed by Power Engineers, Inc., a power plant and electric transmission design engineering firm. Development of the geothermal reservoir will be managed by U.S. Geothermal. Design and construction of a power plant, will be incorporated into an EPC Agreement with a third party contractor.

Completed and Ongoing Development Activities

A major milestone was completed in the first quarter of 2016 when WPG received an approved transmission interconnection agreement with the California Independent System Operator (CAISO) and Pacific Gas and Electric (PG&E).  WGP has provided funding and authorized PG&E to begin the design, engineering and construction of the new interconnection facilities, which will support up to 35 MW of transmission capacity.

In the first quarter of 2016, CAISO provided a Deliverability Study Report to WGP.  It found that no payments from WGP are required for system upgrades to accommodate power delivered from the planned WGP power plant.

An application for an updated Conditional Use Permit from Sonoma County has been submitted and issuance of the permit is expected in the second quarter of 2016.

Discussions for a Power Purchase Agreement with several interested parties are continuing.  Shortly after finalizing a Power Purchase agreement it is anticipated that construction financing will be obtained.

WGP has engaged Power Engineers to provide engineering services for the construction a 30 MW power plant on the WGP leases at The Geysers.  The services include preparation of the specifications and drawings necessary to initiate discussions with equipment suppliers as well as assistance in the equipment suppliers bidding process and the evaluation of those bids.

Progress Report

  • Flowing WGP-1
  • Flowing WGP-1 From Plant Site