Methane emissions undermine switch from coal to gas
- 07 Jan 2013, 17:00
- Mat Hope
Questions are being asked about the emissions benefits of shale
new research shows high levels of methane emissions
leaking from two gas fields in the United States.
Natural gas has
about half the carbon emissions of coal when it is burnt, so
burning gas instead of coal can significantly lower emissions. But
there would be less benefit in switching to gas if significant
amounts of greenhouse gases like methane leak into the atmosphere
when gas is extracted from unconventional sources like shale.
The process of extracting shale gas is not perfect. Not all the
gas released from shale rock formations is captured, and some leaks
out - so-called fugitive
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, or fracking. A significant portion of the
water returns to the surface accompanied by large quantities of the
greenhouse gas methane, which flows naturally into boreholes and is
collected at wells. Some methane,
however, escapes into the atmosphere while the wells are being
built, and this makes up the majority of fugitive emissions.
Research from the Environmental Defense Fund and Princeton
University suggests that for there to be significant climatic
benefits of switching to gas from coal, as the US is doing, the
amount of methane that leaks into the atmosphere from all
natural-gas sources needs to be less than 3.2 per
The new research from the National Oceanic and Atmospheric
Administration (NOAA) and the University of Colorado in Boulder
nine per cent of the methane produced from two fields in Utah
and Colorado was leaking out.
If methane is leaking from other fields at a similar rate then the
apparent emissions benefit of switching to gas is lost, and so
nailing down exactly how much gas escapes in general is important
to take into account when making choices about the amount of gas to
include the energy mix.
Uncertain emissions and energy choices
While the study adds to the body of information on fugitive
emissions, the larger picture is still unclear - and
study by Cornell University in 2011 concluded that fugitive
emissions meant that shale gas would be even more polluting than
coal, but that study has come under a great deal of criticism by
question its methodology. The authors of the Cornell study have
with the criticisms of their paper, suggesting that
four per cent of the methane produced in the fields they
examined was leaking.
It remains difficult to know the precise level of fugitive
emissions and how it would affect choices about the role of gas in
the energy mix.
There is a lot riding on getting better information about fugitive
emissions. If the fugitive emissions from fracking were generally
as high as the NOAA research indicates, it would presumably
undermine the benefits of the US switching from coal to gas - as
far as emissions go, at least.