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Better documentation of actual GHG emissions is needed
CAMBRIDGE, Mass. (August 24, 2011) – Estimates
used by the United States Environmental Protection Agency (EPA) and others for
greenhouse gas emissions from upstream shale gas production are likely
significantly overstated, according to a new report by IHS Cambridge Energy
Research Associates (IHS CERA). The estimates are based on assumptions that do
not reflect current industry practice and should be reevaluated, it says.
emissions have become a very important and controversial issue given their
potency as a greenhouse gas,” said Mary Barcella, IHS CERA director of North
American natural gas. “Unfortunately, such emissions are not being measured.
Estimates are being used that are not supported by data, do not reflect current
industry practice and would be unreliable to use as a base for
report cites as one example the EPA’s 2010 revised estimates of methane
emissions during well completion—the period after the well has been drilled but
before it is placed into production. The current EPA methodology for estimating
methane emitted during this phase was based on a small sample of wells and primarily
measured methane that was captured
rather than released into the
atmosphere, the report says.
EPA estimates were based on two workshop presentations describing methane
captured during “green completions”—operations designed to capture as much
methane as possible. The EPA assumed that (1) similar levels of methane were
produced at every other well in the United States and (2) that those emissions
went completely uncaptured. Such assumptions do not conform to current industry
practices, the report says.
assumption that all methane recovered from these sample wells would otherwise
have been flared or vented is questionable at best, given that common industry
practice is to capture gas for sale as soon as it is technically feasible,”
said Surya Rajan, IHS CERA director. “Gas that cannot be sold is generally
flared rather than vented for safety reasons. If the methane emissions at wells
were as high as some methodologies assume, you would have extremely hazardous
conditions at the well site that neither regulators nor industry would permit.”
key mischaracterization found in the EPA estimates and other recent reports,
such as a study led by Cornell University professor Robert W. Howarth, is the
assumption that wells in flowback contain methane in quantities equal to their
post-completion daily production, the report says. This assumption results in a
significant overestimation of methane emissions. (The flowback phase is the
phase of production when fluids injected into the well flow back out ahead of
the tapped gas.)
IHS CERA report notes that data on unconventional gas well GHG emissions is currently
lacking due to the fact that they are not adequately measured. More reliable
data is needed in order to produce estimates with any degree of certainty.
report says that the most productive result of additional regulations proposed
by the EPA in July could be better documentation of actual GHG emissions which would
provide the accurate measurement that is needed. Some of the other proposed
regulations, such as requiring green completions and flaring of any produced
gas that is not suitable for sale, are already common practice in the industry,
The complete IHS CERA report is available at:
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