EQT Corp. has launched a pilot program to begin converting its Marcellus Shale drilling rigs from diesel-powered equipment to run on liquefied natural gas (LNG), the Pittsburgh-based company said Thursday.

The initial rig conversion is operating in northern West Virginia and the company hopes to convert additional rigs in West Virginia and Pennsylvania after evaluating the pilot program, EQT said. The LNG being used in the pilot program is produced locally from Marcellus natural gas reserves.

Natural gas emits 20-30% less carbon dioxide and a fraction of nitrogen oxides, sulfur oxides and particulates compared with diesel, and LNG is about 40% less expensive than diesel, EQT said.

“We want to be a leader in reducing the environmental impacts related to drilling, and we are proud to be the first operator in the Marcellus to launch such a program,” said Steve Schlotterbeck, president of exploration and production for EQT. “Along with safety, protection of the environment is top-of-mind for our employees, contractors and, of course, communities.”

EQT owns or maintains drilling rights to 3.5 million acres in the Appalachian Basin. In 2010 the company drilled 489 gross wells, including 326 horizontal wells — 90 targeting the Marcellus Shale and 236 targeting the Huron play — and 95 vertical coalbed methane wells.

The Marcellus remains one of the most active shale plays in the country, despite a recent slip in activity. There were 126 rigs operating in the Marcellus in the week ending June 29, according to NGI’s Shale Daily Unconventional Rig Count, unchanged from the week before and a 19-rig (13%) decline from a year ago. Only the Eagle Ford Shale (251 rigs) and the Bakken/Sanish/Three Forks (219 rigs) had more rigs running.

EQT posted a 20.6% increase in wells spud in Pennsylvania’s Marcellus in the first five months of 2012 compared with the same period last year, even as some major operators saw year/year declines (see Shale Daily, June 28). Pennsylvania’s Marcellus Shale gas drilling declined nearly 7% January-May this year from the same period of 2011 in part as operators began moving from dry gas to wetter targets, according to data from the state’s Department of Environmental Protection.