Shale gas life-cycle emissions about half those of coal: study
Houston (Platts)--24Jul2014/410 am EDT/810 GMT
A new study finds that the life-cycle of greenhouse gas emissions for
electric power produced from shale gas are on par with emissions from
conventional gas and on average about half those of coal.
The research, published in "Proceedings of National Academy of
Sciences," is the most recent study to examine the GHG emissions of gas
versus those of other fossil fuels and contradicts some of that earlier
research.
The study examines and "harmonizes" the existing literature on the
subject of GHG emissions from natural gas to create an "apples to apple"
comparison, Garvin Heath senior scientist with the National Renewable
Energy Laboratory in Golden, Colorado, and lead author of the study,
said in an interview Wednesday.
"The systematic and robust conclusion, based on the previously published
literature and our analysis is that shale gas when used to generate
electricity has comparable life-cycle greenhouse gas emissions to
conventionally produced natural gas," Heath said.
The researchers found that on the basis of grams of CO2 equivalent per
kilowatt hour, the median level of emissions from shale gas were 460 g
CO2e/kWh, about equal to that of conventional natural gas and less than
half the median estimate of 980 g CO2e/kWh for coal.
"The best performing coal facilities could have small overlap" with the
life-cycle emissions of the least efficient gas-fired facilities, Heath
said.
In addition, the study found that assumptions about the lifetime
production of wells and the practice of liquids unloading to have the
greatest influence on how the estimated life-cycle GHG emissions are
calculated.
ACTUAL MEASUREMENTS
In the study, Heath and co-authors -- Patrick O'Donoughue of NREL and
Douglas Arent and Morgan Bazilian of the Joint Institute for Strategic
Energy Analysis -- emphasized that it is important that future research
should include taking actual measurements of GHG emissions from various
power-generating fuel sources, rather than relying on estimates.
"Harmonization of prior estimates of GHG emissions provides greater
precision, but does not fully address the questions of accuracy of our
knowledge of GHG emission sources in the natural gas supply chain,"
Arent said in a statement.
"Verified measurements of emissions from components and activities
throughout the natural gas supply chain, and robust analysis of lifetime
well production and the prevalence of practices to reduce emissions can
help create a more robust understanding of our energy options," he said.
Robert Howarth, a Cornell University researcher whose earlier published
findings conclude that the life-cycle GHG emissions for natural gas are
greater than those of coal, disputed the conclusions of the NREL/JISEA
study.
"I disagree, and disagree strongly, with the conclusion of the Heath et
al. paper. Using the best available and most up-to-date science, I think
the conclusion is inescapable that natural gas has a larger greenhouse
gas footprint than do other fossil fuels," Howarth said in an email
statement Wednesday.
Howarth argued that the authors of the more recent report relied for the
most part on studies performed in 2011 and the first part of 2012 and
ignored more recent studies that showed higher levels of emissions of
methane, a potent greenhouse gas, from natural gas operations.
"Bottom line? There is a lot more methane being emitted than Heath et
al. assume," he said.
METHANE LEAKAGE
In addition, Howarth said the research the NREL/JISEA team looked at
measured methane and carbon dioxide emissions on a 100-year time scale.
"This hugely underestimates methane's importance at shorter time
scales," he said. "I believe it is quite simply wrong to focus just on
the 100-year time scale, as do a growing number of other earth study
scientists."
Heath said that the NREL/JISEA researchers included Howarth's research
results in their harmonization of the existing scientific literature.
"His estimates were at the high end of the other ones in the
literature," he said. "Harmonization is not meant to make every estimate
the same. There are legitimate differences in opinion and data resources
and also the focus of different studies can differ."
He called the issue of methane leakage from the natural gas supply chain
"an open scientific question," and one that not all of the studies in
the literature addressed. "We ensured that all studies included the same
set of activities," Heath said.
Shawn Bennett, a spokesman for pro-energy industry group Energy In
Depth, endorsed the results of the NREL/JISEA study. "What this study
does is emphasize we are seeing a definite environmental benefit from
the burning of natural gas," he said.
--Jim Magill, jim.magill@platts.com
--Edited by Richard Rubin, richard.rubin@platts.com
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