Earthquakes are a serious drawback and side effect of geothermal drilling and that could be damaging to the industry, especially after Japan’s nuclear experience. GTherm, a Connecticut-based company founded in 2008, thinks they can overcome the issue through their proprietary geothermal extraction process that doesn’t involve fracturing rock, which is apparently causing the quakes.
The phenomenon of “induced seismicity” has already been experienced in Basel, Switzerland, in 2009 and in North America, where it had the potential of damaging private property. Enhanced geothermal systems (EGS) have been used in these cases, and they had been fracturing solid rock by pumping fluids into wells at high pressure.
Herbert Einstein, a professor of rock mechanics at MIT, says that “you can get seismic events with any kind of fracturing. If you do it close to a city, it’s an issue.”
GTherm’s approach uses a “heat nest,” basically a solid-state heat exchanger, which can extract heat from the surrounding rock more efficiently. For that matter, it uses a highly conductive grout that encases it.
A fluid travels the length of the well in a closed loop and carries the heat from the nest back to the surface. There, a second fluid in a separate loop is turned into gas, which drives a turbine, generating electricity. “We’re basically a heat pump on steroids,” says Michael Parrella, CEO and founder of GTherm.
Tests on this technology could be starting as soon as 2012, with the company now being in the validation process with the Electric Power Research Institute. Depleted oil and gas wells could be exploited first, since their inside temperature is already known.
GTherm says the price of the electricity they intend to produce with this method could get as low as 10 cents per kilowatt-hour. Although MIT’s Einstein doubts the fact the process will be quake-free, the company is extremely optimistic and thinks of building several hundreds of megawatts, with each well producing as low as one megawatt, in a distributed and scalable configuration.
[via technologyreview]
