FORT WORTH — States where hydraulic fracturing is taking place have seen a surge in earthquake activity, raising suspicions that the unconventional drilling method could be to blame, especially the wells where the industry disposes of its wastewater.
Fracking, as the procedure is commonly called, generates vast amounts of wastewater, far more than traditional drilling methods. The water is pumped into injection wells, which send the waste thousands of feet underground. No one knows for certain exactly what happens to the liquids after that.
Scientists wonder whether they could trigger quakes by increasing underground pressures and lubricating faults.
Oklahoma has recorded nearly 250 small-to-medium earthquakes since January, according to statistics kept by the US Geological Survey. That’s close to half of all the magnitude 3 or higher earthquakes recorded this year in the continental United States.
Seven small earthquakes shook central Oklahoma in about 14 hours Sunday. They ranged from magnitude 2.6 to 2.9.
A study published this month in the journal Science suggests that just four wells injecting massive amounts of drilling wastewater into the ground are probably shaking up much of the state, accounting for one out of every five quakes from the eastern border of Colorado to the Atlantic coast.
Another concern is whether injection well operators could be pumping either too much water into the ground or pumping it at exceedingly high pressures.
Most of the quakes in areas where injection wells are clustered are too weak to cause serious damage or endanger lives. Yet they have led some states, including Ohio, Oklahoma, and California, to introduce new rules compelling drillers to measure the volumes and pressures of their injection wells as well as to monitor seismicity during fracking operations.
Researchers are debating the appropriate way for measuring the link between injection wells and earthquakes, including at what distances injections can possibly stimulate quakes. Previously, seismologists had linked injection wells to earthquakes occurring within 3 miles of injection sites, but a new study tracks earthquakes as far as 20 miles away from wells.
No injuries or deaths have been reported from these earthquakes, but there have been varying degrees of property damage.
Most of the quakes are big enough to be felt but too small to do damage like classic California or Japanese quakes. In the North Texas city of Azle, which has endured hundreds of small earthquakes since fracking and injection well activity began, residents have reported sinkholes, cracks in the walls of homes, and air and water quality concerns. Two structures collapsed during Oklahoma’s 5.7-magnitude earthquake in 2011.
Studies on the swarms of temblors in central Oklahoma, Ohio, and North Texas have found probable links between injection wells and earthquakes, with the caveat that a dearth of information on conditions underground before the injections began makes it difficult to unequivocally link them to quakes. However, studies more than 50 years old have linked injection wells to tremors in Colorado.
The oil and gas industry officials generally maintain that there is no link between quakes and drilling.