Chevron Appalachia LLC has temporarily ceased operations at seven wells across Pennsylvania over concerns about wellhead configurations and their ability to handle high pressures after a fatal explosion and fire at one of the company's sites in Greene County, PA on Feb. 11.

Scott Perry, deputy secretary of the Pennsylvania Department of Environmental Protection's (DEP) Office of Oil and Gas Management, said the company identified 27 wells across the state that were constructed in a similar way to two that caught fire after an explosion at a three-well pad in Dunkard Township, about 70 miles south of Pittsburgh (see Daily GPI, Feb. 11).

It remains unclear what caused the explosion, which left Cameron International's Ian Mckee, 27, dead and another contractor injured (seeDaily GPIFeb. 18). Initially, state regulators suspected a blowout, but they now believe gas leaked from the wellhead and was ignited by something on the surface (seeDaily GPIFeb. 12).

"These all have similar wellhead configurations, and there's concerns about pressure within the wells and valves on the wellhead that can handle those pressures," Perry said of the seven wells Chevron shut down.

Perry said the DEP recently asked Chevron to assess its wells across the state, but added that the company had already started to do so. The 27 wells the company has identified for further review are awaiting pipeline connections or being readied for sales, Perry said.

At the time the explosion occurred at the Dunkard site, a crew was preparing to run tubing ahead of a production start-date for the Lanco 7H, which caught fire along with the Lanco 6H. Another well, the Lanco 8H, was likely damaged in the blaze too.

"We did ask them to assess their wells, but they had already started that work," Perry said. "They're prioritizing the wells they want to get back to work on and providing us with information on what they're going to do and how they're evaluating those wells so they're comfortable with resuming operations."

It remains unclear exactly which wells the company has shut down or even where they are located in the state. The company did not provide any additional details. According to state records, Chevron has 447 active Marcellus Shale wells across Pennsylvania.

The fire at the Dunkard site stopped burning on Feb. 15, and after more than a week of work to stop the flow of gas at the site, Houston-based Wild Well Control capped the Lanco 7H on Sunday after cutting the wellhead and installing a capping stack.

The section of the 7H wellhead where the leak occurred will be transported offsite for further analysis by an independent third party as part of the investigation into the cause of the incident, according to Chevron.

Perry said efforts to cap the Lanco 6H were taking place on Monday and were expected to continue on Tuesday. After that well is capped, Wild Well will assess the integrity of the Lanco 8H and make any necessary repairs to secure its wellhead equipment.

Wild Well also plans to install plugs as a protective barrier 8,000 feet below the surface in all three wells to prevent gas pressure from reaching the wellheads.

"The continuing well intervention efforts involve many steps and have to be executed in a precise, controlled, methodical manner," Chevron said in a statement. "We are working to be efficient in our efforts to minimize the duration however. The safety of the workers and operations will determine the appropriate pace."