Hydraulic fracturing — the process of drilling and then pumping fluid deep into a formation to generate fractures or cracks, typically for extracting natural gas from shale formations — has been under fire lately, owing to concerns that it contaminates drinking water. But while Congress debates proposed legislation that would impose new restrictions on the technology, an entirely different concern related to fracturing — or "fracking" — is emerging: It may trigger earthquakes.
The claim is not new, but attention to it has been renewed following a June 2 earthquake recorded at Cleburne, Texas — the first in the town’s 140-year history — and four subsequent smaller quakes, none with a magnitude greater than 2.8. Speculators assert that what’s causing the temblors is fracking, which began in earnest in 2001 in the Barnett Shale, a geologic formation said to be the nation’s richest gas field. A geologist has yet to confirm the claim.
At the same time, fracking-related quake concerns are mounting in northern California, around The Geysers region, where start-up company AltaRock Energy is looking to tap geothermal energy in a demonstration of Engineered Geothermal Systems technology. The technology essentially pumps water into the earth, creating fractures in the hot dry rock (Figure 3). The water then flows into the fissures, creating a reservoir of very hot geothermal fluid that is continuously heated, and when it is returned to the surface, the pressure decrease produces steam, which is used to turn a turbine. That project has secured more than $36 million from the DOE and has the backing of several large venture capital firms.
3. Cracks that run deep. Hydraulic fracturing—a process that involves drilling and then pumping fluid deep into a formation to generate fractures or cracks—has been thought to cause earthquakes, most recently in Cleburne, Texas, where fracturing, or “fracking,” is used to extract natural gas from shale. But Alta Rock’s geothermal demonstration plant, which uses Engineered Geothermal Systems technology (shown here) has also come under scrutiny because the project proposes fracturing hard rock more than 2 miles deep in an area overlying two fault lines. Courtesy: Department of Energy
But it has caught bad press from The New York Times, which points out that the project proposes fracturing hard rock more than 2 miles deep in an area overlying two fault lines. The newspaper draws similarities between the Alta Rock demonstration and a Swiss geothermal prospecting project in Basel, which is believed to have triggered a massive earthquake on Dec. 8, 2006, after prospectors drilled 3 miles into a significant fault.
Alta Rock has disputed the comparison, saying that Basel sits on top of a large (200-km long) "locked" fault that previously ruptured and heavily damaged the city in the 14th century. "We carefully chose our site to avoid Basel’s problems," the company said in a statement. "There has been geothermal energy production at the Geysers since 1965. AltaRock’s project is located in a seismically active area adjacent to smaller faults (the closest faults are 3 and 11 km long) which are not ‘locked’ due the constant stress relief resulting from small seismic movements."
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