Gas is more abundant than ever thought and offers secure supplies with lower greenhouse gas emissions. But is this too good to be true and nothing more than a pipedream, asks Janet Wood?
Gas was considered a strictly limited resource until the USA’s experience with shale gas. Hydraulic fracturing – or fracking – has brought huge reserves of gas to the nation at an affordable cost and the impact has been profound.US energy prices have dropped and gas imports are now minimal. Crucially though, gas has replaced the nation’s use of coal in electricity generation and carbon dioxide emissions have dropped as methane, the main component of gas, burns more cleanly than coal.
These developments have caught the attention of policymakers worldwide. As Dieter Helm, economist and former UK special advisor to the EU Commissioner for Energy, recently told a UK parliamentary committee: “The climate change problem over the next 10 to 20 years is almost entirely about heading off the already enormous and increasing coal burn globally.”
Although gas offers an opportunity to use less coal and cut carbon dioxide emissions, many with an interest in the energy industry are calling for all fossil fuels to be firmly left in the ground. These restrictions would include gas, be it from conventional drilling or fracking.
Gas has been seen as a means of generating electricity when renewable generation isn’t available, acting as a ‘balancing fuel’ compensating for the highs and lows of renewable power. However, some argue that this isn’t necessary. These proponents of renewable generation say that if adequate interconnections between pan-European energy markets and energy storage were in place, the need for such a ‘balancing fuel’ would disappear.
What’s more, gas has been seen as a ‘bridge’ to a renewable-based low-carbon future, but some fear that further development of the fossil fuel will divert resources from much-needed investment in low-carbon generation.
And now there are concerns over the gas leaks, notably methane, that can take place during production, storage and transmission. Methane emissions are far from ideal as the gas has been calculated to be 25 times more potent than carbon dioxide. Any future with gas should hinge on better understanding the extent of methane leaks and the impact on climate.
Gas emissions
So where are the methane emissions? The transport of gas from source to buyer leads to some methane leakage but, to date, emissions during extraction have proven to be more contentious, particularly for shale gas.
Resources may be abundant, but technical challenges during shale-gas extraction can increase the potential for methane escapes relative to conventional gas. Indeed, some commentators have argued that emissions are so high the climate effect could be on par with that of coal power.
There are several phases to the lifetime of a shale gas well. Initial exploration requires a number of wells to be drilled and tested before production wells can be drilled and lined to a depth of 1-2km.
When production starts, horizontal channels are drilled from the production wells. The shale rock is fractured by pumping in a mix of water, sand and chemicals, which enables gas trapped in the pores of the rock to flow through the fractures and into the well.
At the end of production some fracking fluid returns to the surface – known as flowback – and this must be cleaned and managed. Finally, the well is closed and plugged.
All these processes have emissions, some of which are well understood, as they are similar to conventional gas extraction. However, some only take place in shale gas extraction and, as such, the scale of emissions is unknown. For starters, when the shale production well reaches the end of its life, large methane releases can take place when the flowback fracking fluid is expelled from the well before it is capped. Also, methane may or may not be deliberately vented depending on the expense of gas capture.
During a well’s lifetime, so-called fugitive gas emissions are likely to occur. Possible sources range from continuous leakage at valves and well heads to accidental releases.
How large are all these different sources? Vented emissions, for one, are dropping as tighter regulation twinned with rising gas prices encourages operators to cut the amount of gas ‘flared’ to the atmosphere. But for other sources of leaks, the answer still isn’t clear.
In 2011 Robert Howarth from the Department of Ecology and Evolutionary Biology, Cornell University, published a paper called ‘Methane and the greenhouse gas footprint of natural gas from shale formations’ in the journal Climate Change. He estimated that gas emissions during the flowback and close period of a well’s lifetime could come close to those across its full production.
However, in a later Climate Change commentary on Howarth’s paper, Lawrence Cathles of Cornell University and colleagues argued that Howarth’s emissions estimates were technically and economically unlikely. Estimates have since swung back and forth.
Similarly, the extent of fugitive emissions has been debated. Some estimates from measurements at individual US fracking sites put these as high as 12 per cent of production but, again, these have been disputed.
Indeed, the UK-based Tyndall Centre for Climate Change recently issued a paper reporting that fugitive emissions could “increase the footprint of shale gas substantially”. However, it also concluded that “with effective capture and process technologies, emissions levels not dissimilar from those associated with natural gas extraction appear possible in principle”.
UK conclusions
UK energy policy assumes that a significant tranche of electricity supply will continue to come from gas in some form, despite uncertainties over methane leaks. As conventional natural gas supplies from the North Sea have dwindled, investments in pipelines and LNG terminals to import gas from European neighbours and the global market have risen. Some 80 per cent of the population relies on gas for domestic heat so clearly this energy source is not going to disappear from the nation’s energy mix any time soon.
Government, keen to maintain domestic gas supplies, asked Department of Energy and Climate Change chief scientist Professor David Mackay and Dr Timothy Stone, senior advisor to the Secretary of State, to assess the potential greenhouse gas emissions from UK shale gas production.
The Mackay-Stone report, published in September 2013, stated: “As long as venting scenarios are excluded, data indicate that the total carbon footprint of shale gas exploration, extraction and transmission and use is likely to be similar to that of gas derived from conventional wells in the UK, LNG and non-EU piped gas.”
Crucially, Mackay and Stone also reported: “All gas sources are likely to be significantly less polluting, in terms of emissions per unit energy produced, than coal.”
While the authors point out that their conclusions are UK-specific, their thoughts are echoed by Daniel Schrag, director of the Center for the Environment at Harvard University and a member of President Obama’s Council of Advisors on Science and Technology.
Hardly a supporter of long-term gas use, Schrag agrees: “Even if shale gas production results in large methane emissions, burning natural gas is still much better for the climate system than burning coal.”
Be it a better option or not, the effects on individual countries of extracting shale gas are still far from clear. Most countries have only just started investigating and characterising reserves and few understand the real cost of extracting gas.
Still, for many, important arguments exist in fracking’s favour. First, local resources provide an indigenous source of gas that could be lower in emissions than imports.
Critically, indigenous supply brings control. This allows national authorities to set tight licence conditions and emissions standards and police them.
As Schrag puts it: “The answer to whether shale gas is good or bad for climate change mitigation depends on what policies are used to regulate it.”
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