- 17 сентября 2013, 04:00
- Natural Gas Europe
A new study released today by researchers at the University of Texas, Austin, generally tracks with U.S. EPA's most recent estimates for the amount of methane released into the atmosphere each year by natural gas production.
The study, which will be published this week in the Proceedings of the National Academy of Sciences, was conducted by UT Austin with participation from the Environmental Defense Fund and nine major petroleum producers. It was intended to help end the debate over methane emissions from natural gas production -- and to solidify the role gas use can play in helping to limit man-made climate change.
Emissions data for gas have been incomplete. EPA released its annual "Inventory of U.S. Greenhouse Gas Emissions and Sinks" in April, which showed that hydraulic fracturing released about 1.5 percent of total output into the atmosphere in 2011. Natural gas systems overall were responsible for 144.7 teragrams of carbon dioxide equivalent in that year, more methane than any other sector, the agency estimated.
But EPA's calculations were based on reported estimates, not empirical data. They were panned by industry groups as an overestimation of the sector's emissions, while some reports showed much higher levels of methane leakage.
Researchers at the National Oceanic and Atmospheric Administration and the University of Colorado, Boulder, for example, released a study finding that leaks in two U.S. drilling sites were between 4 and 9 percent.
But the UT Austin study used direct measurements from wellheads being operated by participating companies, including Anadarko Petroleum Corp. and Chevron Corp. and arrived at estimates that tracked closely with the ones in EPA's analysis.
The new study also showed that so-called green completions, which capture methane at the wellhead, are effective at limiting the amount of methane leaked during production. EPA promulgated a rule last year that will require operators to phase in the use of green completions by 2015, and the UT study showed that the use of that technology had proved even more effective in limiting methane leakage than the agency assumed in its inventory.
"EPA has largely gotten it right, both in terms of the amount of methane the production side is producing as well as the need to have regulations for green completions," said Drew Nelson, who worked on the study for EDF.
But the study also found that the agency had underestimated the amount of methane leaked by pneumatics -- or valves that keep natural gas moving and maintain pressure in pipelines.
Interest in the climate-forcing properties of gas has grown as it continues to displace coal in electric generation. EPA is set to release a new carbon dioxide rule by Friday that industry expects will give further advantages to gas at coal's expense (Greenwire, Sept. 13).
Environmentalists, meanwhile, have argued that EPA should consider promulgating a New Source Performance Standard to rein in methane emissions from natural gas production. Nelson said today's study and subsequent ones EDF is collaborating on may help inform future regulatory actions by the agency.
"I think the study clearly shows that the regulations that are in place are effective, but it also clearly shows that there are many other opportunities for regulations and to bring these emissions down even further," he said.
"The good news from an environmental perspective is that these emissions are much lower than some of the previous estimates that have been put out there, but I don't think this study shows that the problem is solved and we can all go home now and worry about other issues," Nelson added. Understanding the life-cycle greenhouse gas footprint of gas is key to understanding the fuel's overall climate benefits or liabilities, he noted.
The gas industry hailed the study as further evidence that more use of its product is a boon to the environment.
"The study provides further support for the findings of other credible researchers -- that greater use of natural gas can substantially reduce greenhouse gas emissions," said Erica Bowman, vice president of research and policy analysis for America's Natural Gas Alliance. "We are continually putting into operation equipment and practices that demonstrate our commitment to lower emissions in the production process. We look forward to working with stakeholders to ensure the best science is applied in future study of this issue and that as an industry we continue the substantial progress we have made through ongoing innovation."
Jean Chemnick, E&E reporter
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