Fugitive emissions from shale gas: our Q&A
- 29 May 2012, 14:00
- Chris Peters
A report released today by the International Energy Agency
suggests a series of Golden Rules
for a Golden Age of Gas. One of the proposed rules is that the
question of 'fugitive emissions' from shale gas extraction is
addressed. The IEA writes:
"Greenhouse-gas emissions must be
minimised both at the point of production and throughout the entire
natural gas supply chain. Improperly addressed, these concerns
threaten to curb, if not halt, the development of unconventional
The question of fugitive emissions - how significant they are,
and what they mean for the extraction of shale gas in the UK and
elsewhere, remains remains highly contested. In the Q&A below,
we have laid out the state of play as we understand it.
What are fugitive emissions?
The process of extracting shale gas, also known as fracking,
is not perfect at the moment. Not all the gas released from shale
rock formations is captured, so some leaks out.
Gas also leaks during the refining process and when transporting
the end product to our homes, from example from damaged or poorly
maintained pipes - although this doesn't just apply to shale gas
but to conventional gas as well. According to one paper, leaks from
the Russian long distance natural gas pipeline network account for
0.6 per cent of the natural gas transported.
In both cases, these accidental leaks are known as fugitive
How does it happen?
When shale gas is extracted, large volumes of pressurised water
- along with small amounts of sand and chemicals - are forced
into shale formations deep underground in a process called
hydraulic fracturing, which has become known as "fracking".
A significant portion of the water returns to the surface
accompanied by large quantities of methane, which flows naturally
into boreholes and is collected at wells. Some methane,
however, escapes into the atmosphere during well completion. This
makes up the majority of so-called fugitive emissions, even taking
into account leakage that occurs when the gas is being
How big a problem is it?
Methane is a greenhouse
gas, which, although short-lived in the atmosphere relative to
carbon dioxide, is approximately
25 times more powerful over a 100 year timescale. So leakage of
methane directly into the atmosphere isn't a good idea if you want
to keep greenhouse gas emissions down.
The problem is that we don't really know how much methane leaks
out during the fracking process and researchers currently don't
agree on the figures.
It's important that we get a clearer idea because more and more
countries are exploring the potential for indigenous production of
unconventional gas, which has really taken
off in the US. It looks like we could see the same happening
elsewhere as reserves of
shale have been identified in Europe, China and Russia - although
it looks like this will be easier in some
countries than others, depending on their geography and legal
What does the data show so far?
study by Cornell University (Cornell study 2011) concluded that
fugitive emissions mean that shale gas would be even more
environmentally polluting than coal. The study has come under a
great deal of criticism (Cathles et al, 2011), however, by
people who question its methodology.
Other studies including a literature
survey by the Manchester Tyndall Centre and
two different papers in Environmental
Research Letters indicate that emissions from shale gas are
only slightly higher than conventional gas - much less than the
amount given by the Cornell researchers.
But the authors of the Cornell study have disagreed
with the criticisms (Howarth et al, 2012) of their paper - and
early bits of hard data on methane emissions from the process
appear to back them up.
That's not the end of the disagreement either - the group
critical of the original Cornell University study has recently
published a paper in the Geochemistry, Geophysics, Geosystems
journal, which insists that replacing coal with gas power plant is
still an efficient method of reducing emissions and tackling
Our graphic below compares different researchers' assessments of
fugitive emissions as a percent of the total emissions from both
conventional gas and shale gas wells. It shows just how much
disagreement there is between scientists on the subject:
EPA figures calculated by Howarth et al 2012.
Fugitive emissions expressed as percentage of total emissions
over the lifecycle of the well.Source:
Methane Emissions from Natural Gas Systems (2012)
Who is claiming what?
The disagreement amongst researchers gives everyone an
opportunity to cite figures that appear to support their case.
ExxonMobil's vice president of public and government affairs
Ken Cohen, for example, prefers the lower estimates - but then
bet high on the US shale gas revolution. Energy In
Depth, the industry-backed group that supports shale gas
exploration in the US, has also been keen to
discredit the first Cornell study.
In contrast, environmentalists like
Tony Juniper have cited the higher figures from the 2011
Cornell study in support of the contention that shale gas is "comparable
to coal" in terms of emissions. Research
from the Canadian site DeSmogBlog, which opposes fracking, also
higher figures to argue that shale gas isn't as clean as many
suggest. The US Environmental Protection Agency acknowledges that
previous estimates it made about overall fracking emissions could
underestimated the real figures.
Where do we go from here?
Initial drilling by Cuadrilla was found to be "
highly probably" responsible for two minor
earthquakes near Blackpool last year. Cuadrilla have since
suspended their drilling in the area.
report released in April of this year concluded that "DECC
see no need for any moratorium on shale gas." The
DECC consultation on the report ended last Friday, and
media reports the government is likely to give the
go-ahead to fracking in the next few weeks.
So where does that leave us? The question of how much fugitive
emissions really do add to the impact of shale gas on climate
change remains essentially unanswered. Should the UK proceed with a
major expansion of production from shale gas, the consequent impact
on our emissions also remains an unknown quantity until further
research is carried out.
UPDATE 5pm 29th May: The section on the suspension of fracking by
Cuadrilla was altered in response to the first comment below.