Drilling at several natural gas wells in southwestern Pennsylvania released methane into the atmosphere at rates that were 100 to 1,000 times higher than federal regulators had estimated, new research shows.
Using a plane equipped to measure greenhouse gas emissions in the air, scientists found that drilling activities at seven well pads in the Marcellus shale formation emitted 34 grams of methane per second, on average. The Environmental Protection Agency has estimated that such drilling releases between 0.04 grams and 0.30 grams of methane per second.
The study, published Monday in the Proceedings of the National Academy of Sciences, adds to a growing body of research suggesting that the EPA is seriously underestimating methane emissions from oil and gas operations. The agency is expected to issue its analysis of methane emissions from the oil and gas sector as soon as today, which will give outside experts a chance to assess how well regulators understand the problem.
Carbon dioxide released by the combustion of fossil fuels is the biggest contributor to climate change, but methane – the chief component of natural gas – is 20 to 30 times more potent when it comes to trapping heat in the atmosphere. Methane emissions make up 9 percent of the country’s greenhouse gas emissions and are on track to increase, according to the White House.
The researchers determined that the wells leaking the most methane were in the drilling phase, a period that has not been known for high emissions. Experts had thought that methane was more likely to be released during subsequent phases of production, including hydraulic fracturing, well completion or transport through pipelines.
The airborne readings were a snapshot over two days, said Paul Shepson, an atmospheric chemist at Purdue University who helped lead the study. Further research over a longer period and at other sites are needed to know whether the Pennsylvania measurements are typical, he cautioned.