Fracking not to blame for Oklahoma earthquakes

The Oklahoma Geological Survey has cleared hydraulic fracturing, or fracking, as the cause of a skyrocketing incidence of small earthquakes in the state. Instead, the agency attributed the increase to the practice of injecting wastewater from oil and gas drilling operations—including but not limited to fracked production—into deep disposal wells.

According to a 21 April report from the survey, the average number of magnitude 3 or greater temblors within the state has grown to 2½ per day, up from last year’s rate of 2 per week, and a historic average of 1½ per year.

“The primary suspected source of triggered seismicity is not from hydraulic fracturing,” which accounts for only a small percentage of the wastewater, the report stated. “Produced water is naturally occurring within the Earth that is often high in salinity and coexists with oil and gas in the subsurface. As the oil and gas is extracted/produced, so is the water. This water is then separated and re-injected into disposal wells, often at greater depth from which it was produced.”

Only a small percentage of the wastewater injected into so-called Class II disposal wells comes from fracking operations, the agency stated. The earthquakes are occurring in an area of the state where wastewater disposal volumes have significantly increased over the last several years, it noted.

The current rate of seismic activity is 600 times greater than its historical occurrence and “is very unlikely the result of a natural process,” the report said. The state and the US Geological Survey warned a year ago that the growing number of events has “significantly increased” the threat of a damaging earthquake of magnitude 5.5 or greater. The state’s biggest recorded quake, a magnitude 5.6, occurred in 2011 and damaged a number of homes and a historic building. The USGS suggested that that event was triggered by fluid injection.

Christi Craddick, chair of the Texas Railroad Commission, which regulates oil and gas production in that state, said that information to date indicates that the quakes are not caused by fracking. The commission has hired a seismologist and is looking into their cause, she said.

Donald Siegel, chair of the department of Earth sciences at Syracuse University, said at the 23 April hearing that the seismic events were probably caused by injecting wastewater at “extremely high rates.” Slowing injection, increasing the number of wells, and spreading them out geographically should reduce earthquakes, he said, noting that most of the quakes have been too small to feel.

About 800 billion gallons (3 cubic kilometers) of water from unconventional oil and gas production—a category that includes fracking—are generated each year and must be disposed of or managed, Elgie Holstein of the Environmental Defense Fund testified.