title: Methane emissions from process equipment at natural gas production sites in the United States: liquid unloadings.
abstract: Methane emissions from liquid unloadings were measured at 107 wells in natural gas production regions throughout the United States. Liquid unloadings clear wells of accumulated liquids to increase production, employing a variety of liquid lifting mechanisms. In this work, wells with and without plunger lifts were sampled. Most wells without plunger lifts unload less than 10 times per year with emissions averaging 21,000-35,000 scf methane (0.4-0.7 Mg) per event (95% confidence limits of 10,000-50,000 scf/event). For wells with plunger lifts, emissions averaged 1000-10,000 scf methane (0.02-0.2 Mg) per event (95% confidence limits of 500-12,000 scf/event). Some wells with plunger lifts are automatically triggered and unload thousands of times per year and these wells account for the majority of the emissions from all wells with liquid unloadings. If the data collected in this work are assumed to be representative of national populations, the data suggest that the central estimate of emissions from unloadings (270 Gg/yr, 95% confidence range of 190-400 Gg) are within a few percent of the emissions estimated in the EPA 2012 Greenhouse Gas National Emission Inventory (released in 2014), with emissions dominated by wells with high frequencies of unloadings.
authors.affiliation: Center for Energy and Environmental Resources, University of Texas at Austin , 10100 Burnet Road, Building 133, M.S. R7100, Austin, Texas 78758, United States.
authors.forename: David T
authors.initials: DT
authors.lastname: Allen
authors.forename: David W
authors.initials: DW
authors.lastname: Sullivan
authors.forename: Daniel
authors.initials: D
authors.lastname: Zavala-Araiza
authors.forename: Adam P
authors.initials: AP
authors.lastname: Pacsi
authors.forename: Matthew
authors.initials: M
authors.lastname: Harrison
authors.forename: Kindal
authors.initials: K
authors.lastname: Keen
authors.forename: Matthew P
authors.initials: MP
authors.lastname: Fraser
authors.forename: A
authors.initials: A
authors.lastname: Daniel Hill
authors.forename: Brian K
authors.initials: BK
authors.lastname: Lamb
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*; D004864:Equipment and Supplies; D008697:Methane / Q000032:analysis*; D059206:Natural Gas / Q000032:analysis*; D061329:Oil and Gas Fields; D013997:Time Factors; D014481:United States
chemical_list: D000393:Air Pollutants; D059206:Natural Gas; D008697:Methane