Geothermal

Absolute Commitment: Geothermal Operations at The Geysers

Issue 2 and Volume 2.

Nestled among the peaks of the rugged Mayacamas Mountains above California’s famous wine country is “The Geysers,” a vital source of clean power in a state always hungry for more. Two miles beneath the dry oak and pine forest landscape, a high-temperature geothermal energy resource boils to steam–locked in fractured sandstone made super-hot by ancient volcanic magma that has yet to cool.

The Geysers produced the nation’s first commercial geothermal electricity in 1960 at Pacific Gas & Electric’s (PG&E’s) 11 MW Unit 1 power plant. Covering 30 square miles, The Geysers went on to become the world’s largest commercial geothermal field by the mid-1980s, with nearly a score of power plants approaching 2,000 MW of installed capacity. (Left: Steam lines along the road leading to NCPA Plant 1 at The Geysers. Coutresy Ted J. Clutter)

Against this backdrop of rapid growth, the Northern California Power Agency (NCPA) built two 110 MW power plants in the southeast corner of The Geysers.

“During the late-1970s, NCPA was searching for a reliable renewable energy source,” says Murray Grande, who served as the agency’s Geothermal Facilities Manager for a decade. Shell Oil Co. discovered 300 C dry steam at the site in 1975, at a depth of 4,947 feet. After proving around 70 MW, the agency signed an exclusive contract with Shell to supply steam for its new operations. In January 1983, NCPA started up twin turbine generators at its 110 MW Plant 1, the first publicly owned geothermal power facility to operate at The Geysers. In 1985, NCPA bought the geothermal wells, field production facilities and all rights for future development. The purchase marked the first integrated approach to geothermal resource management at The Geysers.

“It created a synergy that made it easier to meet our need for steam while efficiently adapting operations to the dynamic geothermal reservoir,” Grande says. An aggressive two-year exploration and development program expanded the number of wells plying the NCPA field from 13 to more than 60, which ensured enough steam for a second NCPA power plant. Two turbine generators went online at NCPA Plant 2 in December 1985 and reached their rated capacity of 110 MW the following spring.

Geysers Reservoir Crisis

In the late-1980s disaster struck. Steam flow across the geothermal field nosedived, threatening millions of dollars in capital investment and a renewable baseload power source for the California grid. Intensive geologic investigations showed The Geysers reservoir was not recharging with surface water as quickly as believed. A nearly impervious carbonate “cap” beneath a layer of low permeability rock allowed little new water to percolate into the reservoir.

Developers responded by closing inefficient power plants and throttling back others as they improved cooling tower efficiencies. Like other Geysers operators at the time, NCPA replaced only about 20 percent of the mass it tapped from the reservoir back to the deep geothermal reservoir, injecting condensate from its power plants.

“When the steamfield pressure drop was first detected, we knew that the decline was not about the heat source it was about water,” says Grande.

An NCPA performance analysis showed the geothermal reservoir could not provide enough steam to operate at full capacity for the project’s designed 30-year life.

“There was a lot of disappointment among our member/owners, Grande says. They were willing to invest millions of dollars to conserve clean energy resource well before the issues of renewable portfolio standards, global warming and carbon footprints. An important factor in NCPA’s favor was steamfield ownership. Compared with other Geysers power plant operators during the 1980s, NCPA was “poised to quickly implement our development and management strategies to extend the productive life of the geothermal reservoir,” says Grande.

Recognizing that operating efficiency requires balancing steam pressure to its turbines, NCPA created a “Four Zone Operating Plan” in 1999.

“Wells near the edge of the field produce lower-pressure steam than those at the center,” Grande says. “Separate gathering systems for various steam pressures–and turbines modified to accept those pressures–promotes maximum steam flow to our power plants.”

NCPA modified its Unit 2 generator at Plant 1 with a low-pressure turbine in 1997. After confirming positive benefit, the agency similarly modified Unit 1 at the same power plant in 2002. With these changes, the turbines have made far better use of steam from the lowest pressure edges of the geothermal reservoir.

To produce more steam from those areas, NCPA developed an innovative drilling technique called a “forked completion.” The idea is to get more steam to a wellhead by boring a new “leg” from an existing well into an untapped area of the reservoir. The agency has drilled 12 forked completions at its wells. The technique successfully expanded the geothermal field’s productive area by about 1,200 acres.

A major change to NCPA’s operating plan is scheduled for May 2010 when the agency will decommission its Unit 3 turbine at Plant 2 and rebuild Unit 4 to low-pressure specifications. The new Unit 4 turbine is designed for high flows, so it can handle all the steam currently used by both units.

“Our total power generation of over 100 MW will remain the same, but we will shift to a three-zone operating plan,” Grande says.

Wastewater to the Rescue

Injection from improved condensed steam collection and rainwater ponds raised mass replacement to the reservoir from around 20 percent to 33 percent by 1988. But to reduce reservoir losses still further, more water had to be found. The problem was solved by an unusual proposition. During the 1980s, aging infrastructure and rapid population growth were overwhelming the Lake County Sanitation District’s (LACOSAN) wastewater systems. A study in the early 1990s confirmed a “green” solution that would resolve the county’s pollution problem and help sustain The Geysers’ geothermal energy resource. (Left: Murray Grande, former NCPA facilities manager, in front of a turbine-generator set at the agency’s Plant 2 at The Geysers. One turbine will be shut down permanently in May 2010 and the other rebuilt for high flows and low pressure. Courtesy Ted J. Clutter)

After years of negotiation, design and construction, the Southeast Geysers Effluent Project (SEGEP) pipeline started delivering millions of gallons of secondary treated wastewater to injection wells at The Geysers in September 1997.

“The 26-mile-long pipeline delivers around 8 million gallons of effluent to the southeastern portion of The Geysers geothermal field every day from Lake County,” says NCPA Steamfield Superintendent Steve Enedy.

When the $45-million project started pumping water to The Geysers, NCPA owned a one-third interest in the pipeline and pump stations and received a similar amount of its flow. By taking on larger shares of the millions of dollars spent on SEGEP maintenance, upgrades and pump station installations during the past decade, the agency increased its project ownership share to 50 percent.

Notable improvements paid for solely by NCPA include a 1 MW solar power system for the original SEGEP pump station at Clear Lake that is jointly owned with project partners LACOSAN and Calpine.

“The six-acre array generates 100 percent of NCPA’s share of power for the facility,” Enedy says, “using one renewable energy source to help sustain another.” A second solar-powered booster pump station at Middletown, Calif. started deliveries of an additional 400 to 500 gallons of effluent each minute to The Geysers in January 2010. With that, NCPA will now receive half of project water.

“SEGEP was a perfect marriage of economic and environmental interests for the State of California, LACOSAN and Geysers geothermal power plant operators,” Enedy says. “It helped reduce reservoir decline to only 3 to 4 percent per year.” Through 2009, the project had delivered over 35 billion gallons of effluent to The Geysers. More than one third of that– almost 14 billion gallons–flowed to the NCPA leasehold.

The pipeline provides NCPA with 55 percent of the fluid it injects back to The Geysers reservoir. “With other measures to augment injection, we now replace 96 percent of fluid we take from the reservoir every year, compared to 33 percent in the 1980s,” Enedy says. “We distribute the water at variable rates to 10 injection wells, creating steam more efficiently and minimizing microseismic events.”

Earthquake Mitigation

As steam production and fluid injection increased at The Geysers over the years so did “microearthquakes” as pressures fluctuated within the deep geothermal formations. During 2009, the U.S. Geological Survey recorded 1,007 seismic events at The Geysers, but few were felt by nearby residents. No major structural damage has been caused by microearthquakes at The Geysers, but they are of continuing concern for geothermal power operators.

For the past five years, NCPA has worked with Calpine Corp. and the local community to address the nuisance that microearthquakes can cause for them.

“It was our idea to form a mitigation committee with representatives from Anderson Springs, Lake County, Calpine and NCPA to review damage claims,” Enedy says. “We set up a fund budgeted at $30,000 per year to pay for repairs–typically to cracked sidewalks, siding, chimneys and windows.”

NCPA has also sought new technology to reduce seismic events. “With the California Energy Commission in 2003, we invested close to $12 million drilling the first horizontal injection wells at The Geysers,” says Enedy. By intersecting near-vertical fractures, the two wells distribute injected water more evenly within the hot rock for more rapid boiling and faster steam recovery.

At the end of 2009, the microseismicity issue figured prominently in a decision to shut down a U.S. Department of Energy “Enhanced Geothermal Systems” (EGS) project at NCPA’s leasehold. Led by AltaRock Energy Inc. based in Seattle, the experiment was to drill to a depth of 12,500 feet into an area beneath The Geysers reservoir where the rock is hot but dry. High-pressure injection would then fracture the rock to create a manmade geothermal reservoir.

The project had hardly begun when it was stopped following a New York Times article about earthquakes at a similar experiment in Basel, Switzerland.

“Our project was shut down because of drilling problems and public perceptions that had little relationship to conditions here at The Geysers,” says Grande. “That’s too bad, because it might have ultimately reduced earthquakes by increasing distribution of injection water to new areas.”

Low-pressure technologies, innovative drilling techniques, augmented injection and participation in the unique SEGEP wastewater pipeline project successfully staved off The Geysers steam pressure crash. NCPA geothermal power operations have continuously operated for 27 years and have produced 33 million megawatt-hours of electricity, far exceeding expectations of the agency’s gloomy performance analysis in 1988.

“Though current production from our power plants at The Geysers is only half of nameplate, it is much better than if nothing had been done about declining reservoir steam pressure,” Grande says. “NCPA maintained 150 MW of geothermal generation for 10 years after the reservoir problem occurred. We have produced at least a million MWh almost every year since 1985 and achieved 116 MW of gross generation capacity in 2009.”

With continued injection of Lake County wastewater, NCPA expects to continue its geothermal operations at The Geysers until at least 2035, extending the project 20 years past its 30-year designed life. NCPA estimates it will tap 319 billion pounds of steam production over the next 20 years–enough to generate an additional 18.8 million MWh of clean electricity for its consumers.

In late January 2010, NCPA offered Grande a new and challenging assignment as director of renewable resources development. His task: to find 350 MW of new power projects–especially geothermal–for the agency’s renewable portfolio. Replacing Grande is another veteran of geothermal development at The Geysers, Kevin Cunningham, who comes to the position via PG&E and Calpine Corp.

“The NCPA Geysers team has made excellent decisions and aggressively pursued projects that address steam pressure issues,” Cunningham says.

Even so, he says he believes that enhancing future operations will be more difficult as the geothermal resource continues to decline.

“I believe our next steps require looking at the resource as a whole, with more cooperation and information sharing among all power producers at The Geysers.” Cunningham says he will have no lack of support, because NCPA believes in the long-term economic future of its geothermal power plants. “We are absolutely committed to renewable energy development.”

Left: Roughnecks on the floor of NCPA Drill Rig #1 maneuver a new piece of drill pipe into place. Worth about $15 million, the drill rig was built for NCPA at the start of its Geysers projects in 1979. NCPA’s drilling program is small, with only two wells scheduled for cleanouts each year. Without a rig of its own, a wait of up to two years might be necessary before a portable rig could become available. A plugged well that loses 1 MW of steam a year costs NCPA around $700,000 in generation revenue. NCPA offsets rig ownership costs by leasing it to other geothermal power operators at The Geysers, including Calpine Corp., Bottlerock Power and Ram Power Corp., formerly Western GeoPower. Thermasource Inc. provides management and crews for NCPA rig operations.

Author: Ted J. Clutter is a former Executive Director for the Geothermal Resources Council (Davis, Calif). He can be reached at [email protected]