New Estimates of Methane Emissions from Fracking


20th September 2013.

A study published in PNAS has reported new measurements of methane emissions associated with shale gas production sites.  The research included 150 production sites with nearly 500 wells produced through fracking, as well as measurements of 27 “well completion flowbacks”.  After a well is drilled it has to be cleaned of sand and liquids that had been injected into it during its creation, and during this cleaning (the “flowback”) methane can be emitted.  An average value of 1.7 Mg of methane was reported for the flowbacks, with a range of approximately 0.01 – 16 Mg.  The large range is partially due to the duration of flowbacks, some of which lasted for two weeks and featured large amounts of gas flaring.  This figure is substantially lower than the average value of 81 Mg per flowback cited by a recent EPA inventory, and the authors of the PNAS paper suggest that this discrepancy is due to efficient capture and control of potential methane emissions.

As well as flowbacks, the study also examined “unloadings”; during the lifetime of a well, water and liquid hydrocarbons accumulate and periodically need removing.  For the 9 unloadings measured, the average release of methane was 1.1 Mg (range 0.02 – 3.7 Mg), although the frequency of unloading events varied between wells.  Taking this into account, the average emission per well per year was calculated as 5.8 Mg.  Whilst acknowledging the limited sample size and large uncertainty, the authors state that current EPA estimates overpredict measured unloading emissions.

Finally, the paper looked at 150 well sites that were under routine operation.  Methane emissions from pneumatic chemical injection pumps averaged 3.7 g CH4 per minute, slightly lower than EPA estimates.  However, intermittent pneumatic devices averaged 5.9 g CH4 per minute, whilst the average for low bleed pneumatic devices was 1.7 g CH4 per minute; both higher than EPA estimates.  Equipment leaks averaged 1.2 g CH4 per minute which is similar to the EPA inventory.

If these figures are scaled up the cited figure is that these sources emit 957 Gg CH4 per year, compared with EPA’s estimate of 1211-1250 Gg CH4 per year.  The authors do cite the caveat that their estimated uncertainty in this calculation is 200 Gg.  Adding this to other associated sources gives a total of 2300 Gg of methane from US natural gas production.  To conclude, it seems that methane emissions from natural gas production may be decreasing, partly due to federal regulations and EPA standards.

Reference: Allen et al, 2013. Measurements of methane emissions at natural gas production sites in the United States. PNAS, 10.1073/pnas.1304880110.

Photo: By Joshua Doubek (Own work) [CC-BY-SA-3.0] via Wikimedia Commons.


UK Government Announces Tax Breaks for Fracking


19th July 2013.

The UK government has given a huge boost to the fracking industry after announcing tax breaks for onshore shale gas production. The proposal outlines a 30% tax rate, which is approximately half that of new gas operations in the North Sea. The chancellor, George Osborne, hopes that the move will allow the shale gas industry to flourish rapidly, thus providing increased energy security for the UK. Fracking has proved to be a controversial issue and, in an attempt to get the public on side, Osborne has promised that communities hosting shale gas sites will receive £100,000, plus up to 1% of production revenues.

However, there is likely to be widespread hostility to the news, and both Greenpeace and Friends of the Earth have voiced their opposition to shale gas extraction. Part of the concern arises from the possibility of water contamination, as various fluids are injected into the ground during the process. Some of these fluids are carcinogenic, but more alarming is the fact that the identity of some chemicals can be withheld on the grounds of “trade secrets”. A second concern is that of fracking inducing seismic activity; although any tremors up to date have been small, these have been enough to cause public consternation. Finally, there is the fact that fracking results in significantly higher methane release to the atmosphere when compared to conventional gas extraction.

Clearly there is a need for new sources of energy, as traditional fossil fuels fall out of favour. Nevertheless, some may question the UK government’s approach of offering incentives to the burgeoning shale gas industry, considering that, once successfully established, the business is likely to be a lucrative one.

Relevant references:

Howarth, R.W., Santoro, R., Ingraffea, A. 2011. Methane and the greenhouse-gas footprint of natural gas from shale formations. Climatic Change, 106, 679-690.

Howarth, R.W., Ingraffea, A., Engelder, T. 2011. Natural gas: should fracking stop? Nature, 477, 271-275.

Photo credit: Daniel Foster.

Fracking Study: Shale Gas Impact

Shale gas groundwater

20th May 2011.

Fans of MethaneNet’s Twitter feed will lately have seen plenty of references to ‘fracking’. This follows a study published in PNAS (1) in which methane contamination of groundwater is reported in northeastern Pennsylvania and upstate New York, in areas where gas is being extracted from underlying shales using directional drilling and hydraulic fracturing (fracking) technologies. The issue is relevant to UK-based readers as the first attempt at fracking shale to extract gas from rocks in England, operated by Cuadrilla Resources, got underway at Preese Hall Farm near Blackpool in March this year.

In the USA, the production of shale gas, deemed by its supporters to be a cheap, clean and relatively low carbon fuel, has increased dramatically in the past decade. Development of this ‘non-conventional gas’ source has not been without controversy. In 2010, a contentious US independent film ‘Gasland’, highlighted in emotive fashion what its director Josh Fox sees as the case against the shale gas industry.

The veracity of several of the more controversial scenes in Fox’s film, notably one in which tap water is set alight, have been disputed (2), but questions remain about the environmental impact of several aspects of shale gas exploitation.

The main concerns relate to the potential for leakage into drinking water aquifers, of gas from the wells and of the water/chemicals mix used to enhance the efficacy of the high pressure shale fracturing process. The study by Osborn et al. sought to establish some hard facts, amidst the controversy. The good news for supporters of shale gas production was that this study found no evidence that fracture fluids and chemicals had contaminated ground water supplies in the gas extraction areas studied. The bad news is that the researchers found methane concentrations were significantly elevated, up to 64 mg L-1 – a potential explosion hazard – within 800 m of the gas wells. Using the d13C –CH4 signature, the origin of the methane was shown to be thermogenic, i.e. associated with the shales, and not from an alternative biogenic source.

The study has been criticised by shale gas industry representative John Conrad (3) for not including baseline data, the suggestion being that the high gas levels measured may have pre-dated drilling of the shale-gas wells. The general consensus is that further work on the environmental impact of shale gas production – including the potential for increased methane emissions to the atmosphere – is badly needed. A report from the Tyndall Centre for Climate Change Research (4) went so far as to recommend a moratorium on exploitation of shale gas in the UK until more is known about the risks. Their conclusion is starkly at odds with the views of UK petroleum geologist Dick Selley of Imperial College, an enthusiastic proponent of UK shale gas production long before the idea became fashionable, who in this month’s Geological Society publication Geoscientist Online (2) continues to plead for a more rational debate about what he considers a much needed and environmentally benign additional energy source.


(1) Osborn, S.G., Vengosh, A., Warner, N.R. and Jackson, R.B. (2011). Methane contamination of drinking water accompanying gas-well drilling and hydraulic fracturing. PNAS Early Edition:

(2) Selley, R. (2011). Shale Gas – blessing or curse? Geoscientist Online:

(3) Transcript of interview on National Public Radio on 13 May 2011:

(4) Shale Gas – a provisional assessment of climate change and environmental impacts. A report by researchers at the Tyndall Centre, University of Manchester: