Enhanced geothermal systems (EGS) don't attempt to create new cracks in rocks. Instead, they seek to expand the ones that are already there.
That's the explanation from Will Osborn, vice president at AltaRock Energy, which plans on erecting a demonstration of EGS near the Newberry National Volcanic National Monument in Oregon over the next three years. If it works, AltaRock will move onto the next stage, i.e., planting a generator next to the wells to see how much -- and at what price -- power can be generated. Davenport Newberry is participating in the project with AltaRock, which is funded by Department of Energy grants.
A successful set of pilots would be a seismic event in the geothermal industry because it effectively would allow geothermal developers to begin to examine sites outside of the "Ring of Fire" on the Pacific Coast. A study conducted by MIT researchers in 2007 estimated that close to ten percent of the power requirements for the U.S. could be extracted from geothermal sources within 50 years. Khosla Ventures, Google, Kleiner Perkins and others have invested in AltaRock, while other companies such as Potter Drilling have received outside investments in recent years because of geothermal's potential.
Lately, though, it's been a bumpy road for EGS. In September of 2009, AltaRock’s EGS demo at The Geysers in Northern California suspended its drilling operations due to the bore-hole collapsing as a result of unstable geologies (previous permitting studies had not uncovered the problem). In a different trial in Switzerland, seismic activity in an EGS project resulted in $9 million in damages.
Conventional geothermal drillers sink wells into areas where the rock underground is already hot, fractured, and permeated to some degree with water. Electricity is generated by bringing the subterranean hot water to the surface, turning it into steam for a turbine, and returning it to the ground where it can be re-heated. By contrast, EGS developers seek out areas where the rock is hot, dry and crumbly. Pressurized cold water is pumped underground at a pressure that will be high enough to expand existing fractures in rock, but, ideally, won't create new fissures in the rock.
"You don't want to exceed the tensile strength of rock" in the process, known as hydroshearing, said Osborn. Newberry is actually located within the Ring of Fire, but the geology at the particular site resembles the dry, veined sort of geology that EGS developers will encounter when trying to expand the process to sites nationwide.
This type of EGS actually does create micro-seismic events, but the key word is micro. The activity might register 1 to minus 1 on the Richter scale and the seismic activity will take place a mile below the ground.
Davenport has already dug two wells for EGS testing. Temperatures in the rock exceed 600 Fahrenheit. The next step will revolve around creating an underground fracture network and then testing the water flow and heat output.