| NEW YORK
NEW YORK A blowout at a Pennsylvania natural gas well late Tuesday could heighten concerns about the safety of a controversial process to extract gas from shale rock.
The accident comes at a sensitive time for energy drillers, exactly one year after an explosion that led to the massive BP Gulf of Mexico oil spill, and just as regulators mull whether to allow the technique in New York state.
The well in Bradford County, operated by Chesapeake Energy, spewed thousands of gallons of drilling fluid used in hydraulic fracturing, county emergency management officials said.
The process, also called fracking, releases natural gas from shale rock by blasting it with water, sand and chemicals.
Local residents were evacuated from Leroy Township, about 25 miles from the New York border, though Chesapeake said no one was hurt.
"An equipment failure occurred during well-completion activities, allowing the release of completion fluids," Chesapeake said in a statement.
The fluid initially spilled into a nearby waterway but tests found no adverse affects on aquatic life as yet, said a spokeswoman for the Pennsylvania Department of Environmental Protection.
Environmentalists and residents have complained that fracking can pollute water supplies. That has raised calls for increased regulation on the use of the process to produce natural gas, which is a cornerstone fuel of the Obama Administration's energy policy.
Advances in drilling technology such as fracking have revolutionized U.S. energy markets, opening up the potential of vast reserves of natural gas in shale deposits. Surging production from these areas have pushed natural gas prices down, making it relatively cheap compared to oil.
Gas drilling in Pennsylvania, and in particular in the Marcellus Shale, has drawn the attention of major energy companies due to estimates that the region holds enough gas to meet total U.S. needs for a decade or more.
The blowout, which happens when a driller loses control of a well, could stoke the fierce debate about whether fracking should be allowed to continue unabated in the United States.
The timing is particularly problematic for the industry. On April 20, 2010, a blowout of a BP Plc well in the Gulf of Mexico led to an explosion that killed 11 workers and released nearly 5 million barrels of oil that fouled the shorelines of four Gulf Coast states.
"This event is likely to provide fuel for those who oppose fracking. Blowouts are pretty uncommon onshore like this," said Jeremy Boak, director of the Center for Oil Shale Technology and Research at the Colorado School of Mines.
"When they happen, they're the kind of thing that keep people up at night, including oil company CEOs."
A well in Pennsylvania operated by Houston-based oil and gas producer EOG Resources had a blowout last June, resulting in a natural gas leak that took a day to control and spewed gas and wastewater into the environment.
That incident led to an investigation by regulators in the state, and heightened environmental concerns.
"Considering the sad state of regulatory enforcement in Pennsylvania and other drilling states, (the blowout) is sadly not at all surprising," said Deborah Goldberg of environmental group Earthjustice in a statement.
The incident comes two months after Chesapeake shut natural gas wells in the Marcellus Shale in western Pennsylvania, after a fire in natural gas liquids storage tanks injured three people.
(Additional reporting by Joshua Schneyer, Janet McGurty and Kristina Cooke; Editing by Matthew Robinson and Martin Howell)