A fire that erupted Tuesday morning at a Chevron Appalachia LLC natural gas well site in Greene County, PA continued to burn Wednesday, and it may not be clear for some time what caused it, officials said.

Pennsylvania Department of Environmental Protection (DEP) spokesman John Poister said local emergency management officials and specialists from Houston-based Wild Well Control were letting the intense fire burn as they worked with Chevron officials and public safety crews to craft a strategy to tame it (see Shale Daily, Feb. 11).

“I liken it to a gas stove; the fire on the surface is being fed by gas from the well,” Poister said. “It’s pretty much burned everything on the well pad that it will burn. We’re monitoring it and awaiting word from Wild Well Control.”

The explosion, heard for miles, was reported Tuesday by Chevron at 6:45 a.m. EST. It sent one person to the hospital with minor injuries, while another remained unaccounted for Wednesday and was presumed dead. The fire was complicated by a loaded propane truck near the well pad that ignited in the blaze, Poister said.

Chevron has 40 permits to drill in Dunkard Township, about 70 miles south of Pittsburgh near the West Virginia border, where the explosion happened. Dunkard is in one of the most heavily drilled counties in the state, where operators continue to target a liquids-rich window throughout southwest Pennsylvania (see Shale Daily, Dec. 12, 2013).

The Lancor 7H well, which caught fire, shared its pad with two others and was spud in March 2012 and hydraulically fractured (fracked) a year later. There were no additional fracking or drilling operations taking place at the site, Chevron spokesman Kent Robertson told NGI’s Shale Daily. At the time of the incident, Robertson said a crew was preparing to run tubing ahead of a production start-date for the Lancor 7H.

“The wells were in the final stages of preparation before being placed into production,” Robertson said. “We do not yet know the cause of the incident. Chevron has mobilized representatives from Wild Well Control, who are currently on-site and working with Chevron to develop plans to safely address the situation.”

Specialists from Wild Well have opted to let the fire keep burning, not unusual for a large fire, according to DEP officials. The company has an office in Canonsburg, PA and a staging area for equipment and personnel in Clearfield, PA.

Given the fact that there were no drilling or fracking operations at the time of the blast, Poister said a blowout was not likely the cause.

“We believe it was ignited on the surface, although that is conjecture right now and I wouldn’t go to the bank on this,” he said. “We probably won’t know for sometime what caused it. It appears when you see the pictures and footage from the air that the explosion occurred on the surface, not in the well. Whatever sparked the fire, likely sparked it from the surface, but that is pure conjecture and we won’t know until we can get close enough to look into the cause.”

U.S. Sen. Bob Casey (D-PA) urged a thorough investigation.

“My office has been in contact with the Occupational Safety and Health Administration (OSHA) and has encouraged them to investigate this well explosion,” Casey said. “I’ve repeatedly encouraged the administration and companies to make the safety of pipelines and gas wells a priority. Moving forward, it’s critical that all stakeholders increase their vigilance and oversight of these issues in order to better protect public safety.”

The rural well site poses no danger to the public, Poister said. State and local officials plan to conduct air quality tests once the fire dies down.

A series of lengthy investigations is to be undertaken in the coming weeks by, among others, the Pennsylvania State Police and the DEP, with OSHA expected to be involved as well, Poister said.