Tuesday, 8 January 2013

Worried about gas wells leaking methane

Even without fracking, gas wells can leak methane. Some surveys have found high methane levels close to wells but unless you have a baseline reading before the well was drilled you can't be absolutely sure it is caused by the well. However, it only takes leakage of a few % to make 'clean' gas as bad as coal for greenhouse gas emissions. Energy companies are in denial over the issue and there isn't enough good data to evaluate the magnitude of the problem.


There have been reports of serious leakage through the ground around wells in Australia [1] and in the USA. A recent article in Nature [2] reports on work done by the National Oceanic and Atmospheric Administration (NOAAA) which suggests leaks of up to 4% at a field near Denver, Colorado and maybe even 9% in the Uinta Basin of Utah. These numbers are contested by the gas industry. Some of these wells have been fracked, some not. The Australian gas wells are from coal seams which are relatively shallow compared to many shale gas wells and the researchers from Southern Cross Univerity suspect that 'depressurisation (fracking, groundwater pumping) of the coal seams during gas extraction changes the soil structure (i.e., cracks, fissures) that enhance the release of greenhouse gases such as methane and carbon dioxide.' [1]


Global Warming Impact of methane leaks compared to coal and oil: data from [3],[4],[5]
You need about 67g of methane to get 1 kWh of gas [3]. This generates 185g of CO2. If the methane leaks and is not consumed, then it has a global warming impact far greater - over 20 years 72 times the same mass of CO2 [4]. That means the 67g of methane is equivalent to 4.8 kg CO2. Over a longer timescale, the relative impact is not so bad because methane does not last very long - half will be oxidised to CO2 in 12 years - so it is 'only' 25 times as bad as CO2 over 100 years. The graph shows the impact of different leakage rates of methane compared to the CO2 released from full combustion of either coal (as used in power stations) or fuel oil. Over the 20 year time scale methane is as bad as coal at 3.5% leakage, but over the 100 year timescale you need 10% leakage.

We need more data on this - but there are powerful interests involved wishing to bury the problem. It may well be that most wells are OK but the shallower ones are high risk. Sometimes a well which has been abandoned starts to leak because of drilling nearby opening up fissures and then there is a question as to who is responsible for plugging it [6] - assuming that someone even notices the problem. We need to ensure that gas fields are thoroughly and accurately surveyed before, during and after drilling - and learn how to identify high risk areas before it is too late.



[1] Methane leaking from coal seam, testing shows (Sydney Morning Herald, November 2012)
[2] Methane leaks erode green credentials of natural gas Nature Jan 2013
[3] About Natural Gas: Reference Guides www.natural-gas.com.au
[4] IPCC Direct Global Warming Impact Potentials
[5] Guidelines to Defra /DECC GHG Conversion Factors for Company Reporting Defra 2012
[6] Pennsylvania investigating methane leaks in Sullivan County www.ohio.com Jan 2013

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