Cliff Frohlich figures his new study has good news and bad news for the oil and gas drilling business.
First, the bad news. The senior research scientist at the University of Texas' Institute for Geophysics found that deep injection of oil and gas wastewater appears to be causing more earthquakes than previously thought.
The good news, though, is that although drillers have to go where the oil and gas is to produce it, they can choose where they dispose of their wastewater.
"There are different levels of good news," Frohlich said in an interview. "Even if things do turn out to be more serious than we thought, they do have options."
But however one views it, Frohlich said, industry and government officials need to take the issue of man-made earthquakes seriously as drilling spreads across the country to more densely populated areas.
"There are organizations that would like to ignore this. My study suggests you can't ignore it," Frohlich said. "I don't see a major problem. But it does need to be addressed."
Frohlich took advantage of a dense seismic array installed in the Barnett Shale around Dallas from November 2009 to September 2011 to measure small earthquakes taking place near injection wells. His peer-reviewed study, published in the Proceedings of the National Academy of Sciences, was released yesterday.
All 24 of the earthquakes for which he was able to get precise location information were within 2 miles of an injection well. Most of the earthquakes were too small to be felt, magnitude 2 or smaller, and would not have been detected without the extra seismographs.
The earthquakes were concentrated around several wells near the Dallas/Fort Worth International Airport; nearby in Denton County; and in Johnson County around Cleburne, about 25 miles south of Fort Worth.
The study period ended in September 2011, but since then there have been 16 small earthquakes around Cleburne, 13 of those in the past two months.
Frohlich did not find any suggestion that the earthquakes were caused by hydraulic fracturing, or fracking. But fracturing creates millions of gallons of briny, toxic wastewater that drillers must eventually dispose of, usually by injecting it into the type of injection wells Frohlich was studying.
Advances in fracturing technology that involve blasting high volumes of water into production wells have led to a surge in gas production in shale formations such as the Barnett in Texas and the Marcellus in Ohio, Pennsylvania and the Northeast.
It is well understood among scientists that injecting wastewater underground -- whether from energy production or something else -- can lubricate faults and create earthquakes.
Chesapeake Energy Corp. shut down two wells near the Dallas/Fort Worth Airport in 2009 after Frohlich's research linked them to larger, magnitude-3.3 quakes (Greenwire, March 11, 2010).
But there are about 40,000 oil and gas disposal wells in the country, and only a few have been linked to earthquakes. There has never been a death or serious injury from such a quake.
State officials in Ohio also shut down several waste injection wells earlier this year after linking a magnitude-4 quake and a host of smaller ones to a well in Youngstown.
Scientists are investigating whether other earthquakes in Colorado, Oklahoma and Texas are linked to drilling activities such as waste injection (EnergyWire, July 25). Seismologists at the U.S. Geological Survey have suggested that some of those quakes, along with the Arkansas swarm, are part of a "remarkable" increase in the number of earthquakes in the middle of the country that is "almost certainly man-made" and likely linked to oil and gas operations (EnergyWire, March 29).
With the additional instruments installed, Frohlich was able to detect 67 earthquakes. Only eight of those were picked up and reported by the Geological Survey's National Earthquake Information Center. The 24 earthquakes clustered around injection wells were the ones where he was able to determine the most precise location of the epicenters.
All the wells that had earthquakes nearby took in a high volume of wastewater, more than 150,000 barrels a month (6.3 million gallons). But there are more than 100 other high-volume wells in the Barnett Shale area that had no earthquakes.
That suggests, he said, that earthquakes occur only if there is a fault nearby that is susceptible to being triggered by high volumes of fluid.
Chris Tucker of the industry campaign Energy in Depth said the study highlights that merely injecting drilling wastewater doesn't automatically cause the ground to shake.
"Instead, it argues that the fluids themselves can contribute to those events, but only if they reach a fault line, and even then only under fairly unusual circumstances," said Tucker, whose campaign was created by the Independent Petroleum Association of America. "With the technology available to us now, it's a lot easier to seismically map the subsurface and detect those minor fault lines today than it was 10 or 20 years ago, when many of these EPA-regulated [injection] wells were first sited."
Frohlich did not see any connection between earthquakes and the amount of pressure used to inject the brine. Some seismologists have suggested that injection wells are more likely to cause earthquakes if pressure must be used to push the water in.
He said it's not his call whether the wells he identified as possible causes of earthquakes should be closed. But he said there are steps that can be taken to prevent new injection wells from setting the earth rumbling.
"If I was a company that operated lots of these wells, I might stay away from an urban area," Frohlich said. "And I might stay away from putting high-volume wells in an area where there's been earthquakes."
Click here to read a copy of the study.