Seismic events from geothermal sites called a red herring

“I think that’s a red herring,” says MIT Professor of Geophysics M. Nafi Toksoz, a DoE geothermal grant recipient, referring to the issue of  earthquakes induced by activity at geothermal energy sites. “We know that every time we drill into the Earth, we alter the state of the stress in the rock.” As a result, small earthquakes do occur regularly near oil and gas wells, deep mine shafts for coal or minerals, and even from the pressure of water when a reservoir fills up behind a new dam. “Wherever there are existing faults, they will induce mostly minor quakes.”

Toksoz, with research scientists Michael Fehler and Haijian Zhang of MIT’s Dept. of Earth, Atmospheric and Planetary Sciences as collaborators, will be doing research at a test Engineered Geothermal System installation in Utah, Nevada and California to develop ways of detecting and analyzing the fractures that form in deep rock and how water actually flows through them.

DoE last year awarded $336 million in grants to help resolve uncertainties about geothermal energy, and three of those grants, totaling more than $2 million, went to MIT researchers.

MIT professor Herbert Einstein is is one of the grants to develop computer programs that can aid in the evaluation of geothermal sites, assessing both the potential power output and any potential risks, such as the triggering of seismic activity. Such triggering has already resulted in the premature closing two years ago of one test installation, in Basel, Switzerland, after some minor earthquakes (the largest being magnitude 3.4) were felt in the area.

The planned software is based on programs Einstein has developed to assess proposed tunnel sites and landslide risks. “What these decision tools do is allow you to consider the uncertainties, of which there are a lot,” he says.

As is the case with tunnel construction, a great deal of the uncertainty with EGS has to do with the kind of rock encountered in the drilling and how that rock will fracture under pressure. Einstein’s software will be adapted to address the higher pressures encountered in the very deep boreholes needed for geothermal fields.

Einstein suggests that the risks from seismic triggering are largely sociological, because the events seen so far, at least, are too small to produce any serious damage.

More info is available at the MIT site: http://web.mit.edu/newsoffice/2010/geothermal-0126.html