So-called “green” completions are very effective at cutting methane emissions when used on new natural gas wells, but other equipment allows more gas to escape than previously estimated, a new study shows. Overall, the emissions from natural gas well sites were in line with current estimates by the U.S. Environmental Protection Agency.
The University of Texas at Austin conducted the $2.3 million study, which was mostly financed by nine energy producers and included funding from the Environmental Defense Fund. Researchers said it was the first study to take on-site measurements rather than relying on estimates. Fort Worth-based XTO Energy, a subsidiary of Exxon Mobil, was one of the producers that allowed researchers access to well sites in the Barnett Shale and other U.S. shale gas fields.
Methane, the principal component in natural gas, is a potent greenhouse gas. There has been continuing controversy over whether methane emissions during production and processing could offset the lower carbon dioxide emissions from burning natural gas instead of coal and other fossil fuels. After hydraulic fracturing, gas and fracturing fluid flow back from the well, typically for days. Without equipment that captures or burns that gas, a significant amount of methane would be vented into the atmosphere.
The study measured emissions at 27 completion flowbacks. In the 18 jobs that used reduced-emissions equipment, 99 percent of methane was captured or burned in a flare. The other nine were vented, but were “low-emitting” wells, the study said. In all, total emissions at all 27 jobs were 97 percent lower than current EPA estimates.
The UT study said that 0.42 percent of the natural gas produced from wells escapes on the well site. It said that, using EPA estimates for other segments of the natural gas supply chain, 1.3 percent of all natural gas produced escapes. That is low enough to produce immediate climate benefits when burning natural gas instead of coal to generate electricity, using the gas in a high-efficiency power plant. Those benefits increase over time, because natural gas leaves the atmosphere faster than carbon dioxide.
“The way in which wells are drilled and brought into production has been evolving,” said David Allen, professor of chemical engineering at UT’s Cockrell School of Engineering and the study’s principal author. “The net emissions for completion flowbacks is significantly lower than previous estimates, indicating the type of emission control activities observed during these events are very effective.”
Drew Nelson, Texas manager of special projects for the Environmental Defense Fund in Austin, said the study shows that the EPA is right to regulate methane emissions in the field. Leaks and venting from valves and pneumatic controls accounted for 40 percent of methane emissions at well sites, the UT study found.
“There are still plenty of opportunities to reduce emissions,” Nelson said.
-- Jim Fuquay