It also may provide a way for drilling companies to improve their image on environmental issues after sustaining criticism for air quality problems around gas wells and the practice of lacing hydraulic fracturing fluids with chemicals.
The U.S. Environmental Protection Agency calls reducing pollution from diesel engines one of the county's most important air quality challenges. Diesel engines can produce large quantities of smog-forming nitrogen oxides and soot, which can cause lung and heart problems. Soot also plays a significant role in climate change, researchers say.
Saving the truck trips will improve air quality, but the size of the benefit from replacing diesel engines with natural gas is less clear, according to environmental advocates.
That's because new diesel engines are subject to strict environmental standards and natural gas-powered engines give off only slightly less pollution, said Joe Osborne, legal director of the Pittsburgh-based Group Against Smog and Pollution.
Regardless, the economic benefit appears enormous for an industry that used more than 700 million gallons of diesel domestically in hydraulic fracturing last year, according to Apache estimates.
The cost to convert the engines is far less than the roughly $3.5 million per frack spread that Apache can save if it completes 140 planned wells in a year with the two units, Bahorich said.
For PGE and Universal, the cost of conversion and engineering will be several million dollars, said Roger Willis, Universal's president. After that, the fuel price savings are eye-popping: A gallon of diesel fuel costs about $3.60, while equivalent amount of the natural gas blend replacement currently costs about 47 cents, Kuntz said.
PGE, which plans to drill 35 to 40 new Marcellus Shale wells in 2013 all with the natural gas-powered frack spread, expects to save 750,000 gallons of diesel a year, or 55 percent of the diesel in its fracking operations.
"Keeping this frack spread busy over the course of a year, you'll be on the positive side in less than a year," Kuntz said.