Drilling for Earthquakes

Drilling for Earthquakes

To Cathy Wallace, the earthquakes that have been rattling her tidy suburban home in Dallas feel like underground thunderstorms. First comes a distant roar, then a boom and a jolt. Her house shakes and the windows shudder. Framed prints on the walls clatter and tilt. A heavy glass vase tips over with a crash.

The worst moments are the ones between the rumble and the impact. “Every time it happens you know it’s going to hit, but you don’t know how severe it’s going to be,” she says. “Is this going to be a bigger one? Is this the part where my house falls down? It’s scary. It’s very scary.”

Until 2008 not a single earthquake had ever been recorded by the U.S. Geological Survey from the Dallas-Fort Worth area, where Wallace has lived for more than 20 years. Since then, close to 200 have shaken the cities and their immediate suburbs. Statewide, Texas is experiencing a sixfold increase in earthquakes over historic levels. Oklahoma has seen a 160-fold spike in quakes, some of which have sent people to hospitals and damaged buildings and highways. In 2014 the state’s earthquake rate surpassed California’s.

Fonte: USGS

Source: USGS

The rise in quakes coincides with an increase in drilling activity. Wallace’s house, for instance, sits above the Barnett Shale Formation, a layer of hard black rock that holds the U.S.’s second-largest deposit of natural gas. Between 1998 and 2002 companies started drilling this deposit using hydraulic fracturing, or fracking, which involves pumping millions of gallons of water, plus sand and chemicals, into the ground at high pressure to crack the rock and release the gas. As the gas comes up the well so does the fracking fluid, along with volumes of brine so salty it is hazardous. The fluids are pumped back down a different hole drilled far below the shale into porous rock for permanent disposal. As more and more fluid is injected into these wastewater wells, pressure can start to build up on deep geologic faults. Eventually one can slip, causing an earthquake.

Researchers at the USGS and other institutions have tied earthquake surges in eight states, including Texas, Oklahoma, Ohio, Kansas and Arkansas, to oil and gas operations. Some state regulators have been slow to accept scientists’ findings. Residents have become increasingly angry, and environmental groups have sued. “This is a public safety issue, and there’s been a lot of denial and ignoring of the problem,” says Wallace, who has joined neighbors to push for the shutdown of nearby wastewater wells.

As scientists continue to study the phenomenon, they have found more reason for concern. Evidence suggests that earthquake risks can spread for miles beyond the original disposal sites, and can persist for a decade or more after drilling stops. And although the biggest earthquake from wastewater injection was a 5.6 on the Richter scale, near Oklahoma City in 2011, scientists think that temblors as powerful as 7.0 – enough to cause fatalities and damage buildings across a wide area – are possible, although unlikely.

Source: Scientific American

Date: March 2016

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