Tuesday, 20 August 2013
Issue 10: Fracking can and will release gas into the atmosphere
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.