Is Fracking for Enhanced Geothermal Systems the Same as Fracking for Natural Gas?The U.S. geothermal industry recently scored a big win when its first enhanced geothermal system (EGS) project went online in April. ORMAT was able to stimulate a previously unproductive well at its Desert Peak project with EGS technology — injecting fluid into a well to reopen cracks and create a resource reservoir — and found an additional 1.2 megawatts (MW) of capacity. Renewable energy experts applauded the project, dubbing it a "game-changer" and a "shining moment" for the industry.
Though the project represents a breakthrough for EGS technology and the geothermal industry in general, EGS has come under fire, with opponents accusing it as being just as dangerous as oil or natural gas hydraulic stimulation, commonly known as fracking. While traditional geothermal energy is viewed as clean renewable energy, could EGS technology, with its similar "fracking methodology," coupled with its rocky past, come under the same intensive scrutiny as natural gas fracking?
According to Hollett, the fundamental difference between natural gas fracking and EGS fracking is the injection process. The oil and gas industry injects water and a proppant (a mix of sand and chemicals), at a very high pressure of around 9,000 psi or more, which breaks though the rock and holds the cracks open; otherwise they would close when the fluid stops flowing.
EGS, however, uses water, and sometimes acid, to shear the rock and cause a "slip." "You're trying to make two rock faces slide past each other slightly, which creates a little bit more space between them," said Lauren Boyd, EGS program manager at the DOE. This is where fractures or weaknesses in the rock likely existed already and were plugged by mineral deposits over time. Boyd compared the process to putting an ice cube in a glass of hot liquid: "cracks will form where there are existing deformities in the ice, which is similar to what happens in the subsurface with closed fractures," she said.
As for long-term effects, "we are talking about very small fractures very deep in the earth — there is really little or negligible long-term impact there," said Hollett.
Since many believe EGS technology to be similar to natural gas fracking, the same concerns about leakage, spills and resulting groundwater and soil contamination exist for both technologies. After all, according to Popular Mechanics, in the past two years alone, natural gas fracking has caused numerous surface spills including several projects that have contaminated groundwater.
AltaRock plans to combat these problems at the Newberry project by using a multizone stimulation process. Water is injected into a single well at a pressure of about 2,000 psi to stimulate cracks in the rock, which eventually spider out to create a "zone." Once a zone is complete, pressure is dropped to 1,000 psi and a diverter made of biodegradable plastic (similar to plastic developed that allows water bottles to biodegrade in landfills) is injected into the well to "gum up" the cracks, according to Stowe. Pressure is then increased to 2,000 psi to start a new fracture zone, and then a new batch of diverter is made to plug up holes at hotter temperatures. The process repeats until all zones are created, and water flow is then stopped to allow the well to heat up. It takes about one week for the diverter to break down into water and CO2, which is eventually used to generate power once the plant is built, said Stowe.
According to several experts, many of the issues related to natural gas fracking can be prevented with the same type of proper protocol and procedures in use at the Newberry project. For example, in 2011 Chesapeake Energy reportedly lost control of a well in Pennsylvania. The well cracked, spilled and contaminated a nearby stream - this could have been prevented by using stronger cement and casings to ensure an impermeable seal.
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