Human activity associated with oil and gas production can sometimes cause earthquakes, but the problem is not hydraulic fracturing, a seismologist from the University of Texas told researchers gathered for a two-day conference on Marcellus shale-gas drilling.
When the rare quakes do occur, they’re typically linked to the disposal of drilling fluids in underground injection wells, Cliff Frohlich said in September at West Virginia University. And the vast majority of injection wells don’t cause quakes, either, he said.
Frohlich cited six earthquakes since 2008 in Texas, Arkansas, Colorado, Ohio and Oklahoma, ranging from magnitude 3.3 to magnitude 5.7.
Their locations show that human-caused earthquakes are geographically widespread and geologically diverse, but “very rare,” given the amount of petroleum produced and the amount of waste being disposed of.
Why some injection wells cause earthquakes and others don’t remains unclear, he said. Frohlich hypothesizes that quakes occur when a “suitably oriented” fault lies near an injection site.
“Hydraulic fracturing almost never causes true earthquakes,” he told the group gathered for the National Research Council workshop. “It is the disposal of fluids that is a concern.”
Texas has 10,000 injection wells, Frohlich said, and some have been in use since the 1930s. That effectively makes the state a giant research lab for the shale-gas drilling issues now facing Appalachian states including West Virginia, Pennsylvania, Ohio and New York.
If injection wells were “hugely dangerous,” he said, “we would know.”
“Texas would be famous as a state that just rocks with major earthquakes,” Frohlich said. “That is not true.”
West Virginia University hosted the conference for the National Research Council, which is the operating arm of the National Academy of Sciences.
Fred King, the WVU vice president for research, says the reports the workshop generates should be available before the start of West Virginia’s legislative session in January and could help guide future regulatory discussions.
Frohlich urged policymakers to consider cultural and population differences if they are weighing regulation aimed at minimizing the risk of earthquakes through either the spacing between or monitoring of injection wells.
“There’s places in West Texas you could have a 5.2 earthquake and it wouldn’t bother anyone,” he said. “If you’re going to operate in urban areas, I think you need to invest in incredibly stringent regulations. But in other areas, you probably don’t.”
Jay Cole, WVU chief of staff, said the university has a special obligation to help industry and government identify critical issues as shale-gas development grows and to identify questions that remain to be answered.
The workshop featured representatives of industry and government, including the National Energy Technology Laboratory, U.S. Geological Survey and U.S. Environmental Protection Agency, as well as researchers from 12 universities.
Ray Boswell, technology manager for natural-gas technology programs at Morgantown’s national lab, said drillers tapping the Marcellus are producing more gas even as they sink fewer wells, and are outpacing production estimates made by the U.S. Energy Information Administration.
The region’s reserves, he said, easily can sustain strong production through 2040.
Joseph Frantz, vice president of engineering for the Texas-based oil and gas producer Range Resources, said drillers in the Appalachian basin are producing nearly 12 billion cubic feet of oil and gas per day from the Marcellus, a figure that has skyrocketed since 2009 as drillers rapidly embrace and deploy technology developed in the nation’s other shale-gas fields.
Range and other companies are casing their wells with as many as four layers of steel and cement, redundancies that Frantz said dramatically reduce any risk of groundwater contamination. Range also is using rubber containment pads and berms under every piece of equipment to stop pollution from soaking in the ground or migrating off-site, he said.
It’s an expensive way to do business, Frantz said, but “this is the right thing to do.”
“We talk about this social license to operate,” he said. “We always have to be transparent and honest and open with everybody. ... If we don’t do our job, someone’s going to come in and tell us how it should be done, and that may not be a pleasant day.”