title: Measurements of methane emissions at natural gas production sites in the United States.
abstract: Engineering estimates of methane emissions from natural gas production have led to varied projections of national emissions. This work reports direct measurements of methane emissions at 190 onshore natural gas sites in the United States (150 production sites, 27 well completion flowbacks, 9 well unloadings, and 4 workovers). For well completion flowbacks, which clear fractured wells of liquid to allow gas production, methane emissions ranged from 0.01 Mg to 17 Mg (mean = 1.7 Mg; 95% confidence bounds of 0.67-3.3 Mg), compared with an average of 81 Mg per event in the 2011 EPA national emission inventory from April 2013. Emission factors for pneumatic pumps and controllers as well as equipment leaks were both comparable to and higher than estimates in the national inventory. Overall, if emission factors from this work for completion flowbacks, equipment leaks, and pneumatic pumps and controllers are assumed to be representative of national populations and are used to estimate national emissions, total annual emissions from these source categories are calculated to be 957 Gg of methane (with sampling and measurement uncertainties estimated at ± 200 Gg). The estimate for comparable source categories in the EPA national inventory is ~1,200 Gg. Additional measurements of unloadings and workovers are needed to produce national emission estimates for these source categories. The 957 Gg in emissions for completion flowbacks, pneumatics, and equipment leaks, coupled with EPA national inventory estimates for other categories, leads to an estimated 2,300 Gg of methane emissions from natural gas production (0.42% of gross gas production).
authors.affiliation: Center for Energy and Environmental Resources, University of Texas, Austin, TX 78758.
authors.forename: David T
authors.initials: DT
authors.lastname: Allen
authors.forename: Vincent M
authors.initials: VM
authors.lastname: Torres
authors.forename: James
authors.initials: J
authors.lastname: Thomas
authors.forename: David W
authors.initials: DW
authors.lastname: Sullivan
authors.forename: Matthew
authors.initials: M
authors.lastname: Harrison
authors.forename: Al
authors.initials: A
authors.lastname: Hendler
authors.forename: Scott C
authors.initials: SC
authors.lastname: Herndon
authors.forename: Charles E
authors.initials: CE
authors.lastname: Kolb
authors.forename: Matthew P
authors.initials: MP
authors.lastname: Fraser
authors.forename: A Daniel
authors.initials: AD
authors.lastname: Hill
authors.forename: Brian K
authors.initials: BK
authors.lastname: Lamb
authors.forename: Jennifer
authors.initials: J
authors.lastname: Miskimins
authors.forename: Robert F
authors.initials: RF
authors.lastname: Sawyer
authors.forename: John H
authors.initials: JH
authors.lastname: Seinfeld
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D002849:Chromatography, Gas; D004784:Environmental Monitoring / Q000706:statistics & numerical data*; D019652:Extraction and Processing Industry / Q000706:statistics & numerical data*; D008697:Methane / Q000032:analysis*; D059206:Natural Gas; D014481:United States
chemical_list: D000393:Air Pollutants; D059206:Natural Gas; D008697:Methane
keywords: greenhouse gas emissions; hydraulic fracturing
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