Yes. At the moment it is
considered likely that there will be some gas leakage from wells but no one
knows whether it will be insignificant, moderate or large. Despite this, the
replacement of coal generation with gas generation has the potential for
reducing methane emissions to the atmosphere considerably.
A pedant would say that this is a
certain outcome of extracting the gas and using the gas in the first place: We
extract the gas, burn the gas to extract its useful energy, and then vent the
resulting CO2 to the atmosphere, where its presence contributes to global
climate change.
An extremely environmentally sensitive
individual would point out that we must stop burning fossil fuels altogether,
but few eschew the advantages that fossil fuels provide, and those that do are
perhaps among the most moral on Earth (but they won’t be reading this blog, or
eating Mars bars as these behaviours require fossil fuels).
The government wants energy security,
and that means its own sources of energy. Of course it would also like the
price of gas to come down because that serves its political ends, but no one
seriously expects that to happen.
What do most men and women in the UK
want? Well, I think they want correct information, delivered clearly and used
to make sensible decisions. They may be getting the sensible decisions, but
many do not trust that to be the case because of the lack of evidence-based
information delivered in a straightforward manner.
Coal vs. Gas
It has been pointed out that shale gas
is a non-ideal solution, but one that is better than the current norm of
burning coal. Indeed, a number of policy makers consider shale gas to be a
bridge-fuel allowing us time to develop and roll-out renewables as well as
smoothing the problem of demand when depending on intermittent solar and wind
sources.
The argument is that for each megawatt
hour (MWh) you get from shale gas much less CO2 is produced than if you used
coal generation to provide it. In fact an average coal would give
about 975 kg of CO2 per MWh compared to about 550 kg of CO2 per MWh for natural
gas.
In other words shale gas is about half as bad for the climate as coal if burned
efficiently to produce electricity. The
gain is significant because, in the unlikely event that we could replace all
coal-fired power stations with gas-fired ones, we would be able to reduce annual
CO2 emissions from 11 billion tonnes of CO2 to 6.2 billion tonnes of CO2,
which is a whopping 4.8 billion tonnes of CO2. That saving of CO2 would also
take place if we replaced the coal-fired generation by building over 851,000 wind turbines, each with a capacity of 5MW like
those offshore UK, and having them work constantly all year! This argument alone has led to claims that
shale gas is a green-alternative. It is not ideal, but a
step in the right direction.
Moreover, if we look at the lifecycle
NOx, SOx, and mercury emissions, we find that those from
coal are 1.3, 18, and 27 times higher than those from natural gas,
respectively. The amount of freshwater consumed for coal production and
electricity generation is over twice the amount consumed by natural gas. Yes,
fracking uses a lot of water, but less than coal mining has always done on a
per kilowatt basis.
There are also benefits to human
health. According to a recent
report from the Breakthrough
Institute that was highlighted in an article by the
energy collective,
“Coal
combustion releases toxic chemicals including arsenic, mercury, lead, and
numerous others. In addition to CO2, coal combustion also emits
oxides of sulphur (mainly SO2), and oxides of nitrogen (NOx),
which can cause adverse respiratory conditions. Hydrogen cyanide (HCN), sulphur
nitrate (SNO3), and other toxic substances are also produced. SO2 reacts
with atmospheric gases to produced sulphuric acid, which returns to the earth
as acid rain, harming ecosystems and human health. Pollutant emissions from
coal plants cause more than 20,000 heart attacks, nearly 10,000
hospitalizations, and more than 13,000 premature deaths annually in the United
States.”
By comparison, gas is much cleaner,
leading to less than 30% of the deaths per terawatt hour associated with coal,
that is a saving of over 8000 lives per year in the USA alone.
If we could replace all of our coal
burning power stations with clean gas burning power stations, then there would
indeed be an advantage for the atmosphere. It is ironic to think that it is
solely due to their development of coal gas that
(i) the
USA would have already met its Kyoto goals if it has signed-up to them,
(ii) the
USA now exports of the coal that it does not now need, keeping UK power
stations burning dirty fuel, and
(iii) the
USA and Canada are converting most of its public transport systems (yes it does
have some!) to run on gas.
Effect of CH4
on the climate
But perhaps there is a problem. If the
shale gas leaks to the atmosphere directly, it provides a much greater contribution
to climate change than CO2. The potential for methane to cause global climate
change depends on the timescale
because it is efficiently removed from the atmosphere by natural processes.
However, it is a stronger green house gas than CO2, so its effects are
nevertheless greater in general. Over a 20 year timescale the IPCC
2001 report (Scientific Basis, Chapter 4) calculates methane to be 62 times
as damaging as CO2, dropping to 23 times after 100 years and 7 times after 500
years.
The current annual emissions rate of
methane into the atmosphere is about 598 million tonnes per year, which adds to that
already there, which is about 4850 million tonnes, and there is also an annual
loss of methane from the atmosphere of about 576 million tonnes per year. Of
the emissions no more than 200 million tonnes per year are from natural
sources, leaving the rest caused by various human activities, amongst which
mining is a large fraction, together with ruminants and rice farming. The
difference between the emissions and the losses is about 22 million tonnes, so
anything that can reduce this gap will be important, as we will see in the
following sections.
Coal’s
contribution to CH4
A study by the National
Renewable Energy Laboratory has estimated that surface and underground
mining of coal releases 1.91 grams and 4.23 grams of methane per kilogram of
coal mined, respectively. In 2011
8.12 billion tonnes of coal was consumed. If we take 3 grammes of methane
per kg as a convenient mean for both surface and underground mining, we get a
figure of 22.1 million tonnes of methane released into the atmosphere as the
result of coal power generation.
Coal
vs. gas - Part II
Hence, if there were no methane losses
associated with shale gas production and consumption to generate power,
and we could replace all of the coal plants with shale gas plants, the amount
of methane released to the environment would decrease to such an extent that we
would solve climate change from that source.
This is clearly an incredible and heartening piece of information.
However, shale gas
production and consumption will inevitably release some methane into the
atmosphere,
and if gas wells leak, it could be considerable. The question is whether they
leak more than 22.1 million tonnes of it. If not, we are already in the black
on the climate calculation, if not the green.
The figure 22.1 million
tonnes of methane is incredibly difficult to imagine, but calculating its
volume at atmospheric pressure and 25oC is about 3.23 km3.
It is also about 0.1% of the annual global natural gas production (3201 km3,
data from 2010 and 2011 compiled from the 2012 CIA
World Factbook ). In other words, it’s a huge leak, but equally it would
only require a 0.1% of production to leak from each gas well (of all types)
around the world!
Methane
leaks from shale gas wells
So, reading the earlier posting on
aquifer contamination, it is clear that shale gas wells can and do leak. There
are leakage mechanisms between the cement and the casing, the cement and the
rock, through the cement and occasionally through breaks in the casing.
The leaks seem small, but are
difficult to quantify. It seems like they will become larger as the well ages,
even if maintenance is carried out, and is due to casing rust and degrading
cement. The question is whether these leaks are or ever will be significant
enough to invalidate the advantage that natural gas has over the coal that it
will replace.
Other
pollutants from shale gas wells
There has been some concern that gases
leaking from shale gas wells could carry with them toxic pollutants in the form
of an aerosol. This could happen if there were a significant blow-out from a
well. Fortunately, with modern technology and safety procedures these are vanishingly
rare. The low slow leakage that may happen through casing and cement is not
likely to carry significant aerosol-borne contaminants as these will stay
within the pores of the cement.
Testing for
leaks scientifically
My view is that there should be a
scientific study into the potential problem that is presented in a transparent
manner. If the UK had a growing shale
gas industry, it would be possible. However, the industry in the UK is simply
too immature to carry out such a study. It is interesting to note that
Cuadrilla have engaged an independent environmental consultancy to test the back-ground environmental levels at
the Balcombe drill site, finding elevated natural levels of methane and ethane
in the ground water environment. Only when we have post drilling and
post-fracking measurements, over a reasonable period, will we be able to start
quantifying the fraction, if any, of leaked gases.
My recent analysis and that of the BBC http://www.bbc.co.uk/news/science-environment-23724657 of two recent scientific
papers shows how difficult it is to carry out this type on monitoring accurately.
In general, the use of data from the USA is not possible because the sampling
protocols skewed, and they do not carry out back-ground level checks which
would be necessary to prove the leakage. The two scientific papers that I
discuss in another
blog posting represent the best of the studies from the USA. One reports a
correlation between shale gas wells and methane in groundwater, but since there
were no background tests, it is impossible to be sure.
What is
certain is that it is absolutely necessary to ensure that all UK wells are
monitored for atmospheric pollution and leakage.
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