Small earthquakes can be triggered from geothermal efforts like the one proposed for Newberry Crater, which use water pressure to create a network of tiny cracks deep below the Earth’s surface.
“When they fracture rock, they’re automatically creating earthquakes,” said Dennise Templeton, a seismologist with the Lawrence Livermore National Laboratory in California. “The whole issue is how big they are, and can they be mitigated so they’re not affecting people at the surface.”
In Basel, Switzerland, an enhanced geothermal project was shut down last week because of earthquakes that rattled homes. And at the Geysers in California, a project has been put on hold while the company addresses drilling problems and the Energy Department reviews seismic information in response to news reports.
But developers of the Newberry project, which recently received $25 million in federal stimulus funds, say the geology and the fracturing techniques proposed for the site south of Bend lessen the chances that people would feel any ground movement locally.
“We’re causing what are basically microscopic cracks in the rock to move,” said Don O’Shei, CEO of AltaRock, which is working with Davenport Energy on the Newberry geothermal project.
While seismometers measuring ground movement might pick up on that activity, he said, the vast majority of the quakes would be less than around 1.0 magnitude, and people would be “completely unaware they’re happening.”
Earthquakes produced by enhanced geothermal systems happen when crews drill a well, then inject pressurized water thousands of feet below the surface to fracture the rock.
The idea is to later circulate water through these fractures, heating it up before it’s pumped back to the surface to generate power from the heat.
AltaRock and Davenport are proposing to test the technique west of the Newberry National Volcanic Monument, but still have to go through the permitting and environmental review process with the Bureau of Land Management, which will take months. Davenport previously drilled exploratory wells in the area but didn’t find the steam or hot water necessary for traditional geothermal power.
In the enhanced geothermal technique, “as you inject water down in the well to mine the heat, it opens up fractures,” said John Lund, director of the Geo-Heat Center at the Oregon Institute of Technology in Klamath Falls.
“And as these fractures pop open, they release energy, and that energy is picked up on a seismograph.”
Most of the earthquakes from enhanced geothermal projects are small, he said, with some reaching around a magnitude of 3.0 — which is about the size at which people will feel some movement.
“Some of the lodges in the (Newberry) caldera might feel some of them,” he said, adding “I think it’s not going to be anything serious.”
During the permitting process for a project like Newberry, a seismologist would probably study the area and say whether earthquakes might be felt in nearby communities, he said.
Still, because the fracturing is happening at depths shallower than earthquakes normally occur, people might be able to feel smaller earthquakes, said John Vidale, director of the Pacific Northwest Seismic Network.
“The closer it is to the surface, the smaller magnitude you can feel,” he said — and people might be able to feel a shallow magnitude 2.0 quake.
But with the geothermal issue, problems can stem from people’s perception of the quakes — whether or not they feel them.
“If there’s a lot of little earthquakes, even if there’s not much damage, people get really nervous,” he said. And that nervousness can be a legitimate concern for project developers, Vidale added.
Seismologists are realizing that there are areas of rock deep below the surface that are under stress and could generate earthquakes, he said. And the only way to know for sure what will happen at Newberry is to start the project.
“The only real way to know how many earthquakes will be generated is to start pumping fluids (into the rock),” Vidale said. “It’s hard to predict ahead of time.”
But O’Shei with AltaRock said that the Newberry project has key differences from the Switzerland effort.
In Basel, crews intentionally drilled into a large fault, hoping to use the pent-up energy of the fault to create fractures.
But Newberry is seismically stable, he said, and the local project’s engineers don’t want to create the whole network of faults at once — they want to generate multiple smaller systems.
“We can control it and do much smaller fracturing,” he said.
Crews will have sensitive monitoring equipment that will be able to tell them where the fractures are occurring, O’Shei said.
And if too much rock is moving, or the cracks are going in an unwanted direction, they can ramp down the volume or pressure of the water to stop the process, he said.
The Basel drilling rig was right in the middle of the city, he said, where many buildings were built hundreds of years ago.
“There’s all kinds of medieval construction there that’s very fragile,” O’Shei said.
And because Basel is on a major fault, while Newberry isn’t, the rocks at Newberry should be less likely to move, he said.
“A place that generally is seismically active is likely to be more sensitive to anything you would do there,” O’Shei said.
Kate Ramsayer, Bend Bulletin – http://www.bendbulletin.com/apps/pbcs.dll/article?AID=/20091215/NEWS0107/912150393/-1/RSSNEWSMAP