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Air pollution from fracked wells measured Research team finds some facets of natural gas production give off less greenhouse gas emissions than previously estimated Wesley Loy For Petroleum News
Anew study from University of Texas and other researchers finds that air pollution from natural gas production might be lower than previously estimated.
The research involved direct measurements of methane emissions from 190 onshore natural gas production sites in the Lower 48, including the Gulf Coast, Midcontinent, Rocky Mountain and Appalachian regions.
Methane is the primary component of natural gas and is also a greenhouse gas, says the six-page research article published online Sept. 16 by the journal Proceedings of the National Academy of Sciences.
The article is available at http://bit.ly/1gqeTkA.
The shale gas boom, with its extensive use of horizontal drilling and hydraulic fracturing, forms the backdrop for the research.
The tested sites included 150 production sites with 489 wells, all of which were hydraulically fractured.
“In addition to the 150 production sites, 27 well completion flowbacks, 9 well unloadings, and 4 well workovers were sampled,” the article says.
Nine different companies operated the sites: Anadarko, BG Group, Chevron, Encana, Pioneer Natural Resources, Shell, Southwestern Energy, Talisman and XTO Energy.
Comparing with EPA inventory The researchers attempt to determine the accuracy of methane emission estimates reflected in the Environmental Protection Agency’s latest national inventory of greenhouse gas emissions.
These published estimates possibly are outdated, given the significant change in gas production processes during the past two decades, the article says.
The researchers, however, found they were able to make useful comparisons only for certain gas production activities.
One of these was well completion flowbacks.
“After a well is drilled, the well is ‘completed.’ Completion is the process of making a well ready for continuous production,” the article says. “Specifically, after drilling and fracturing, before natural gas production can begin, the well must be cleaned of sand and liquid of various types that had been injected into the well. The recovery of these liquids is referred to as a flowback, and gas, including methane, can be dissolved or entrained in the flowback liquids. Some of the methane in the liquids can be sent to sales or emission control devices, but some can be emitted.”
Flowback emissions overstated The researchers took measurements of methane emissions during 27 completion flowback events.
“The completions with the lowest emissions were those in which the flowback from the well was sent immediately, at the start of the completion, to a separator, and all of the gases from the separator were sent to sales,” the article says.
Based on their testing, the researchers estimate the annual national methane emissions from completion flowbacks at wells with hydraulic fracturing is far less than what the EPA inventory shows.
Measurements made from certain equipment that releases or leaks methane, however, suggested an increase in the national emission estimate, the researchers found.
The lead author, David T. Allen, is with the Center for Energy and Environmental Resources at the University of Texas.
The article acknowledges the Environmental Defense Fund as a sponsor of the work.
“This study tackles one of the most hotly debated issues in environmental science and policy today,” said Mark Brownstein, of the Environmental Defense Fund. “It shows that when producers use practices to capture or control emissions, such as green completions, methane can be dramatically reduced. The study also demonstrated, however, that certain methane emissions are larger than previously thought, indicating that there are many further opportunities to reduce emissions.”
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