WASHINGTON (AP) — In Pennsylvania's gas drilling boom, newer and unconventional wells leak far more often than older and traditional ones, according to a study of state inspection reports for 41,000 wells.
The results suggest that leaks of methane could be a problem for drilling across the nation, said study lead author Cornell University engineering professor Anthony Ingraffea, who heads an environmental activist group that helped pay for the study.
The research was criticized by the energy industry. Marcellus Shale Coalition spokesman Travis Windle said it reflects Ingraffea's "clear pattern of playing fast and loose with the facts."
The Marcellus shale formation of plentiful but previously hard-to-extract trapped natural gas stretches over Pennsylvania, West Virginia and New York.
The study was published Monday by the Proceedings of the National Academy of Sciences.
A team of four scientists analyzed more than 75,000 state inspections of gas wells done in Pennsylvania since 2000.
Overall, older wells — those drilled before 2009 — had a leak rate of about 1 percent. Most were traditional wells, drilling straight down. Unconventional wells — those drilled horizontally and commonly referred to as fracking — didn't come on the scene until 2006 and quickly took over.
Newer traditional wells drilled after 2009 had a leak rate of about 2 percent; the rate for unconventional wells was about 6 percent, the study found.
The leak rate reached as high as nearly 10 percent horizontally drilled wells for before and after 2009 in the northeastern part of the state, where drilling is hot and heavy.
The researchers don't know where the leaky methane goes — into the water or the air, where it could be a problem worsening man-made global warming.
The scientists don't know the size of the leaks or even their causes and industry officials deny that they are actual leaks. The study calls it "casing and cement impairment," but the study's lead author says that is when methane is flowing outside the pipe.