Chesapeake Energy has stemmed the flow of leaking drilling fluids from a natural gas well that suffered a blow-out late on Tuesday in Pennsylvania and prompted the company to suspend a controversial gas production technique in the state. Chesapeake, one of Pennsylvania’s biggest shale gas producers, used a mix of plastic, ground-up tires and heavy mud to plug the well — an operation that echoes BP’s “top kill” effort to seal its ruptured Gulf of Mexico oil well last year. “Late Thursday afternoon, efforts to seal the leak and regain control of well pressure were successful,” Chesapeake said in a statement on Thursday evening. The company said it still did not know the cause of the blowout nearly two days after it occurred. It was planning to start an investigation into the accident, the statement said.

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.