Texas Campaign for the Environment: News
Dallas Morning News, June 16, 2012 By Randy Lee Loftis and Kira Witkin
Waste-disposal wells from gas drilling linked to North Texas quakes
North Texas historically has been a sleepy backwater for earthquakes. But as the region has converted into a natural-gas frontier, things have gotten shakier. People in Johnson County felt new evidence of the trend early Friday. The U.S. Geological Survey said a 3.1-magnitude quake hit at 2:02 a.m. about 11 miles north-northeast of Cleburne and was felt as far away as Plano and Denton. The agency said the quake occurred 3.1 miles below ground.
Scientists said Friday that they think they know why North Texas is seeing more quakes, and it’s probably not from the hydraulic fracturing of thousands of natural-gas wells in the Barnett Shale gas field. A National Research Council panel said the increased earthquake risk probably comes from a related activity: injecting large amounts of saltwater drilling waste underground for disposal.
The Barnett Shale, which stretches from Dallas County to the west past Fort Worth, has nearly 20,000 natural-gas production wells. Almost all were drilled in the past five years. But the region has only about 100 waste injection wells. Scientists have tied the timing and locations of earthquakes to the injection wells.
‘Whole house shook’
Injection wells can cause earthquakes strong enough for people to feel, said the panel, which examined possible links between quakes and several energy-related activities.
The latest Cleburne quake brought more than a hundred 911 calls to the Johnson County sheriff’s office, said Lt. Tim Jones. The temblor, which lasted 15 to 20 seconds, woke up plenty of people but apparently hurt no one and damaged no property.
Scott Carpenter, who lives in nearby Keene, said the quake roused him from a deep slumber.
“I mean, honestly, I was passed out dead asleep, and I heard this boom and then a real deep rumble,” he said. “My whole house shook. My bed shook. When I first woke up to it, I thought it was either a tree falling down or one of those oil pipelines blowing up.”
Mark Hayes of Mansfield, 24 miles away from Cleburne, said he was awakened — “felt like someone hit the wall on the house” — and believes the quake was responsible.
The possibility that shoving large volumes of material underground might trigger earthquakes has been a frequent theme for critics of hydraulic fracturing, or fracking. In fields such as the Barnett Shale and the Northeast’s Marcellus Shale, gas companies pump millions of gallons of chemically treated water and sand into a well to break up the rock and free trapped gas. The injection takes place under high pressure, leading to questions about whether the fluid’s force might cause tremors along geological faults.
The research council’s report, Induced Seismicity Potential in Energy Technologies, found little evidence that fracking can trigger earthquakes but did find a probable link to injection wells. Injection wells use lower pressure than fracked production wells but deal with much bigger volumes of liquid. Much of the waste injected into those disposal wells is the fluid that comes back out of gas production wells after fracking.
Dallas decision nears
The report said mild earthquakes in recent years near Cleburne and at Dallas/Fort Worth International Airport were probably linked to disposal wells. At the airport, the timing and locations of earthquakes in 2008 and 2009 “strongly suggest” that injection of drilling waste was the cause, the report said. The finding about the airport quakes was based on a 2010 study by researchers at Southern Methodist University and the University of Texas at Austin.
The gas company Chesapeake Energy shut down one waste-injection well near Cleburne in 2009 after nearby earthquakes. A Chesapeake spokesman did not respond to a request for comment Friday.
Dallas City Council members are considering new rules on fracking that would not allow disposal wells in the city. The council is set to discuss gas drilling in the city on Aug. 1.
The research report said the biggest risk of induced earthquakes probably would accompany large-scale projects to capture carbon dioxide and store it underground as a measure against global warming. Although no such projects are under way, Texas is considered prime potential territory for the practice because of geology and the state’s long experience with using carbon dioxide for enhanced recovery from old oil wells.
The full report by the research council, an arm of the National Academy of Sciences, is available free at nap.edu/catalog.php?record_id=13355.