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March 26, 2015
By E-Mail
Mr. Leif Hockstad
Environmental Protection Agency
Climate Change Division (6207J)
1200 Pennsylvania Ave., NW
Washington, DC 20460
hockstad.leif@epa.gov
Re: Comments of America’s Natural Gas Alliance on the Draft Inventory of U.S. Greenhouse
Gas Emissions and Sinks: 1990-2013 (February 2015)
Dear Mr. Hockstad:
America’s Natural Gas Alliance (ANGA) appreciates the opportunity to submit these
comments on the U.S. Environmental Protection Agency’s (EPA) Draft Inventory of Greenhouse
Gas Emissions and Sinks: 1990-2013 (2015 Draft GHG Inventory).
Representing America’s leading independent natural gas exploration and production
companies, America's Natural Gas Alliance works with industry, government and customer
stakeholders to promote increased demand for and continued availability of our nation’s
abundant natural gas resource for a cleaner and more secure energy future.
The safe and environmentally responsible development of our domestic stores of natural
gas has been, and increasingly will be, an important component of America’s energy supply and
economic health. Natural gas is a clean-burning, efficient, and cost-effective fuel that offers the
potential for both significantly decreasing air pollution emissions and promoting America’s
energy independence.
This new draft inventory shows that production emissions have dropped by 36 percent
since 2005 even as production has grown 28 percent and emissions from natural gas systems still
account for just 2 percent of all anthropogenic greenhouse gas emissions. As these comments
1 will show, there clearly is opportunity for continued emissions reductions across the supply chain
through industry innovation and through collection of more comprehensive data and we are
committed to continuing those reductions.
For the past several years, ANGA has submitted comments on EPA’s Draft GHG
Inventories. In recent GHG Inventories, EPA has addressed some of these concerns, including
adjusting the methodologies for estimating the frequency of well re-fracturing, emissions from
hydraulically fractured well completions and workovers, and emissions from liquids unloading.
ANGA supported these changes, which more accurately accounted for actual field practices.1
We encourage EPA to continue upgrading the GHG Inventory with net emission factors in place
of potential emission factors as more data become available. We believe more accurate data will
show lower methane emissions from the natural gas sector.
In the 2014 GHG Inventory, EPA adjusted the methodology for completions and
workovers with hydraulic fracturing. These adjustments established four technology specific
emissions factors for wells with hydraulically fractured completions and workovers using data
from the 2011 and 2012 Greenhouse Gas Reporting Program (GHGRP) Subpart W.
In the 2015 Draft GHG Inventory, these emissions factors are updated using additional
data from the 2013 GHGRP. These updates result in reductions for the emissions factors for
three of the four well categories. Additionally, the updated data show more wells using RECs
and fewer wells that directly vent all flowback emissions in 2012 compared to the 2014 GHG
Inventory. These activity data better reflect actual industry practices, including the voluntary use
of RECs by many producers. ANGA supports these changes, which address inaccuracies found
in previous GHG Inventories that we have commented on in the past. We would also support
further sub-categorization to recognize the differences between hydraulically fractured
completions and hydraulically fractured workovers.
While ANGA supports the new emission factors for uncontrolled well completions as
more accurately representing actual industry practices, they remain higher than measured results
from the recent study by researchers at the University of Texas-Austin and supported by
1
Comments submitted by Erica Bowman to Mr. Leif Hockstad. Comments of America’s Natural Gas Alliance on
the Draft Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2012, March 26, 2014.
2 Environmental Defense Fund (UT Austin/EDF study).2 At 36.8 metric tons (MT) methane per
vented well completion, for example, the estimate in the Draft 2015 GHG Inventory is one order
of magnitude higher than similarly configured completions in the UT Austin/EDF Study, which
found a range of 0.5-4 MT methane per completion event for those wells vented directly to
atmosphere. Much of this difference can be attributed to the choke flow calculation
methodology option in the GHGRP. The choke flow calculation methodology was not designed
for use in multi-phase flow applications, and as such can often deliver erroneous results when
compared to direct measurement. While ANGA supports continued use of the GHGRP data to
update emission factors, ANGA encourages EPA to remove outlier data from the emission factor
calculation and use only measured data in the GHGRP for the calculation of emission factors, not
data derived from the choke flow equation methodology.
As noted above, ANGA supports the use of GHGRP data to establish emission factors
and encourages EPA to continue using this data source to refine the emission factors for
hydraulically fractured well completions and workovers. As industry technology and practices
improve to further reduce methane reductions and the GHGRP continues to update its calculation
and reporting methodologies, the emission factors for hydraulically fractured wells and
completions should be adjusted accordingly. In addition to improving the accuracy of the GHG
Inventory, creating emissions factors that more closely match the GHGRP data will provide
public confidence in and increase uniformity across EPA’s data programs.
While ANGA continues to believe that EPA’s estimate of the number of uncontrolled
well completions and workovers is too high, we understand that this number will decrease
significantly in future GHG Inventories because they will factor in requirements included in the
2012 Oil and Gas NSPS. This rule requires the use of RECs for almost all completions and
workovers after January 1, 2015 and required flowback emissions to be routed to a completion
combustion device starting in October 2012. The impact of this rule can clearly be seen in the
Draft 2015 GHG Inventory, which reports methane emissions from these activities decreasing by
nearly 52 tons from 2012 to 2013.
2
Allen et al. (2013) Measurement of methane emissions at natural gas production sites in the United States. Proc
Natl Acad Sci USA 110(44): 17601-17602. 3 In response to EPA’s request for feedback on possible changes to the methodologies for
estimating emissions from pneumatic controllers and liquids unloading, ANGA supports the use
of direct measurements to develop technology- and/or process/function-specific emissions
factors. Additionally, ANGA supports the development of emissions factors and activity data on
a regional as opposed to national basis. We believe that aggregation of regional data to calculate
national emissions provides a more accurate estimate that accounts for regional variation in gas
composition, production practices, and regulation.
Given the magnitude of the changes that the Agency has made over the past five years
both increasing and decreasing estimated emissions from natural gas production, the underlying
data and assumptions must be rigorous and well supported. ANGA appreciates the changes EPA
has made to its methodology for estimating emissions from liquids unloading, its estimate of the
frequency of workovers, and its methodology for hydraulically fractured well completions and
workovers. We encourage EPA to continue updating its methodology and emissions factors with
technology specific and region specific emissions factors based on valid data, assumptions and
calculations. However, given the underlying uncertainties of the current data, ANGA does not
support the use of the emissions estimates presented in the GHG Inventory as the basis for any
analysis or regulatory action.
ANGA stands ready to continue to work with EPA to develop valid emission factors and
estimates for additional Natural Gas System components and activities that can serve as the basis
for more accurate emissions estimates. If you have any questions, please contact Erica Bowman
at ebowman@anga.us or (202) 789-2642.
Sincerely,
Erica Bowman
Vice President, Research and Policy Analysis
4