WASHINGTON — A new study explains how just four wells forcing massive amounts of drilling wastewater into the ground are probably shaking up Oklahoma.
Those wells seem to have triggered more than 100 small-to-medium earthquakes in the past five years, according to a study published Thursday by the journal Science. Many of the quakes were much farther away from the wells than expected.
Combined, those wells daily pour more than 5 million gallons of water a mile or two underground into rock formations, the study found. That buildup of fluid creates more pressure that “has to go somewhere,” said study lead author Cornell University seismologist Katie Keranen.
Researchers originally figured the water diffused through underground rocks slowly. But instead, it is moving faster and farther and triggers quake fault lines that already were likely ready to move, she said, adding, “You really don’t need to raise the pressure a great deal.” The study shows the likely way in which the pressure can trigger fault lines — which already existed yet were not too active— but researchers need more detail on the liquid injections themselves to absolutely prove the case, Ms. Keranen said.
The wastewater is leftover from unconventional wells that drill for oil and gas with help of high pressure liquids — nicknamed fracking — and from the removal of water from diluted oil. These new methods mean much more wastewater has to be discarded.
While there are about 8,000 deep injection wells in the region, the amount of water injected at the four wells — named Chambers, Deep Throat, Flower Power and Sweetheart — has more than doubled since the drilling boom started about a decade ago.
From 1976 to 2007, Oklahoma each year averaged about one quake of magnitude 3 or more — strong enough to feel locally, but too weak to cause damage. But from 2008 to 2013, the state averaged 44 earthquakes of that size every year. So far this year, there have been another 233, Ms. Keranen said, getting her earthquake figures from the U.S. Geological Survey database. The rattling has led some Oklahomans to push for restrictions on the use of injection wells.United States - North America - Oklahoma