SOURCE: The Washington Post
DATE: August 30, 2018
SNIP: Each day across the United States, 2 billion gallons of fossil-fuel-industry wastewater flies through thousands of underground tubes. The injection wells descend into porous rock, filling gaps with brine and chemicals that are the result of extracting oil and gas from the ground. The goal of the wells is for the wastewater to be out of sight, out of drinking water and out of harm’s way.
Except the wells can cause earthquakes. In some cases, the quakes begin as far as 15 miles from the wells. In a new study in the journal Science, scientists describe for the first time how earthquakes can be triggered so far away from the wells. An efficient practice by the oil and gas industry is creating a ripple effect far beyond its drilling locations.
Geologists have linked injection wells to quakes, with findings based on years of observation. Human-made earthquakes, though most are moderate in size, put 1 in 50 people in the United States at risk, according to a recent U.S. Geological Survey analysis. Wastewater injection wells are concentrated in Oklahoma, Texas, California and Kansas, according to the Environmental Protection Agency.
“Induced earthquakes are becoming more and more of an issue in central and the eastern U.S.,” said University of California at Santa Cruz seismologist Thomas Goebel. In 2011, an injection well in Oklahoma was responsible for a magnitude-5.6 earthquake that damaged a highway, shook buildings and generated a dozen aftershocks.
The study authors were able to identify two types of earthquakes triggered by wastewater wells, having everything to do with what kind of rock the water is being injected into.
One kind of earthquake formed close to the injection well but stopped abruptly at about a half-mile from the site, Goebel said. If a well dumped its wastewater into rigid bedrock, earthquakes occurred within a close distance. There, pressure from water that spilled into a fault triggered the earthquake.
The other kind had a “very long-distance tail” — the quakes could appear far from the well, with the triggers petering out only after several miles. This occurred if a well dumped its wastewater into softer sedimentary rock. This was a result of what the researchers called “poro-elasticity.”