National Academy of Sciences of the
United States of America
Measurements of methane emissions at natural gas
production sites in the United States
This work reports direct measurements of methane emissions at 190
onshore natural gas sites in the United States.
The measurements indicate that well completion emissions are
lower than previously estimated; the data also show emissions from
pneumatic controllers and equipment leaks are higher than
Environmental Protection Agency (EPA) national emission projections.
Estimates of total emissions are similar to the most recent
EPA national inventory of methane emissions from natural gas
These measurements will help inform policymakers,
researchers, and industry, providing information about some of the
sources of methane emissions from the production of natural gas, and
will better inform and advance national and international scientific
and policy discussions with respect to natural gas development and
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
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
David T. Allena,1,
Vincent M. Torresa,
David W. Sullivana,
Scott C. Herndonc,
Charles E. Kolbc,
Matthew P. Fraserd,
A. Daniel Hille,
Brian K. Lambf,
Robert F. Sawyerh, and
John H. Seinfeldi
Edited by Susan L. Brantley, Pennsylvania State University,
University Park, PA, and approved August 19, 2013 (received for
review March 20, 2013)