When oil producers in Oklahoma were ordered by regulators to severely cut back the volume of waste water injected into the earth to lessen man-made earthquakes, the number of tremors fell to fewer than two a day, from more than five.
But now quakes are occurring in relatively new areas of Oklahoma, the SCOOP and STACK plays, and almost no waste water is injected deep underground in these plays, Bloomberg reported.
That has drawn attention back to hydraulic fracturing, specifically, is fracking causing tremors?
To some industry proponents in Oklahoma, low-level tremors infrequently are the price to pay for the positives oil and gas exploration and production bring, Kallanish Energy learns.
In 2009, Oklahoma, suddenly began to experience numerous quakes, just as oil output, and fracking, started to increase. By 2014, Oklahoma was more seismically active than California, Bloomberg reported.
Seismologists and geologists concluded the main reason by far was the reinjection into disposal wells of waste water. These high-pressure blasts of water can impact fault lines that had been quiet for centuries.
Limiting the quantity that could be shot back into the earth and slowing the speed at which it was discharged made a difference. Earthquakes of at least 2.7 magnitude dropped to a daily average of just 1.7 last year, from a high of 5.4 in 2015, according to the Oklahoma Corporation Commission, which regulates the industry.
Late in 2016, the tremors began to be felt around the SCOOP and STACK, shale plays in the Anadarko Basin.
Central Oklahoma "started seeing some relatively small earthquakes," Jeremy Boak, director of the Oklahoma Geological Survey, told Bloomberg, "and some slightly up-in-arms residents."
And now the quakes "are rising to a number to where you can count them," Matt Skinner, a spokesman for the commission, told Bloomberg.