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The heavy price of shale gas

5/18/16

Since 2009, the quantity of ethane in the atmosphere has been increasing by 5% per year. Prior to this, concentrations of the gas had actually been decreasing over a twenty-year period thanks to successful political initiatives. This gas tends to lead to peak ozone levels in the air we breathe and increase the atmospheric lifetime of greenhouse gases. Ethane essentially comes from the exploitation of oil and natural gas. It is also a good indicator of anthropogenic emissions of methane. A multiple study initiated by the University of Liege using measurements and modelling has clearly identified the main cause of the increase of ethane in the atmosphere: the sudden expansion of shale gas exploitation in the US.

The observation occurred almost anecdotally. Whitney Bader and Bruno Franco had just improved the technique for measuring atmospheric ethane from the Jungfraujoch station. Together with Emmanuel Mahieu, a researcher at the FNRS and head of GIRPAS (InfraRed Group of Atmospheric and Solar Physics of the University of Liege), they re-analysed and updated their ethane time series. It was at that moment, as they were observing the data gathered that they noticed an intriguing trend upturn. “At the Jungfraujoch observatory”, explains Emmanuel Mahieu, “We have been collecting atmospheric data since the mid-1980s. This data has enabled us to study the stratosphere and the troposphere, and therefore the quality of surface air. And since then, we have observed a progressive decrease in the burden of ethane (C2H6) of 1% to 2% per year. This decrease was due, in particular, to efficient political measures”. Certainly, this environmental awareness placed restrictions on the behaviour of industrial organisations, such as, for example, prohibition of the use of CFCs (see article: New threat to the ozone layer?).

atmosphere

“Because this decrease remained constant”, continues the researcher, ”We were quite casual in our approach to checking ethane levels until our improved time series alerted us to a startling trend reversal. Since 2009, the concentration of ethane in the troposphere has been increasing by 5% per year”. Having made this observation (see article, the butterfly effect of shale gas), the team could not remain in possession of this data without investigating further. The researchers had lots of theories, but they had no proof. In order to verify their theories the researchers needed to match their observations with models. The result of this work has just been published (1). The result was unequivocal and the cause was clearly identified. The increase in the concentration of ethane is directly linked to exploitation of shale gas by means of hydraulic fracturing.  

A harmful gas for the environment

“One of the beneficial components of the atmosphere is the hydroxyl radical (OH)”, explains Emmanuel Mahieu. “We could call it the detergent of the troposphere because it is a highly reactive molecule which consumes other elements by oxidising them. Among these elements is methane (CH4), for example, which is an even more efficient greenhouse gas than CO2. Ethane consumes this hydroxyl radical. It becomes oxidised to form carbon monoxide with the carbon it contains. Therefore, the higher the quantity of ethane in the atmosphere, the less hydroxyl radical there is to consume the methane and the longer the lifetime of the latter will be. A second harmful effect concerns the quality of the air, because ethane, during its degradation, promotes the formation of tropospheric ozone (O3). “And we have all heard warnings about ozone peaks in summer. While it is true that the ozone present in the stratosphere protects us from the UV rays of the sun, in the troposphere and the surface air, it is, in excess of a certain threshold, harmful not only for health but also for the development of plants etc.”

Ethane is a gas which is essentially emitted due to human activity. Two-thirds of its emission is caused by the exploitation and transportation of natural gas. This natural gas, trapped in rock, results from a mixture of hydrocarbons which notably include methane, ethane and propane. Every gas leak simultaneously releases all of its compounds. The last third is divided between the consumption of bio-fuels and combustion of the biomass (forest fires, for example). “As its emission is essentially anthropogenic, government initiatives taken to reduce emissions were immediately effective. Following this, each year the levels were decreasing. The atmosphere consumed more ethane than was being emitted up to 2009. But since then, we have wiped out 30 years of effort in just a few years”.  This sobering fact was the object of the first publication. It still remained to understand what was happening, to identify the sources and quantify them. “We did not know what this increase represented in tonnes of gas emitted, for example”.

Pointing the finger at the US

The recordings by the Jungfraujoch instruments were therefore a first step. “The second was to contact some of our colleagues in the NDACC (Network for the Detection of Atmospheric Composition Change), who work on the American continent. We informed them about the detection of this trend reversal and asked them to analyse their data to see what the result would be. In the end, the stations at Toronto in Canada, the Great North, Greenland, Colorado and Hawaii sent us their series”. The stations in the North and in Hawaii, which were further away from the gas wells, should provide a background level, an indication of the average state of the atmosphere over the Northern Hemisphere. On the other hand, those of Colorado and Toronto are closer to many drilling zones and here we were able to observe a higher concentration of ethane. 

 USA extraction Shale

Emissions seen to be increasing

All over the world, studies aim to estimate and create inventories of the emissions of harmful constituents into the atmosphere and to make them freely available. One of the most recognised inventories is the HTAP2, which combines the results from all the regions of the globe. This is as much information as it is possible to integrate into and use in atmospheric models. “In the context of our research, Louisa Emmons, of NCAR in Colorado, integrated this data into a model to compare them with our measurements. She noticed that the estimates for ethane emissions in these inventories were too low and this also applied to the decade before 2009. This signifies that these inventories under-estimate gas emissions and therefore the degradation of the air. In order to obtain a result that is a reliable indication of the average emission from the 2000s, these needed to be multiplied by two”.

But that wasn’t all, the researcher then suggested as a supplementary theory, that the responsibility for the recent increase in ethane production was attributable only to the US. “Beyond the initial multiplication, it was still necessary to increase annual emissions by 75% in order to model the growth observed between 2009 and 2014”. In more concrete terms, in the inventory, the emission of ethane in North America was estimated at 0.8 million tonnes per year before 2009 while, in reality, it had risen to 1.6 million tonnes. But in 2014, the emissions reached the startling figure of 2.8 million tonnes. “The result was quite unequivocal”, says Emmanuel Mahieu. “The researcher fully succeeded in reproducing the trends we had observed. This meant that it was even more possible to identify the exploitation of shale gas as a real cause of the problem”.

And if only ethane was the only problem

However, these were only the results of a first model and the intention was to make the observations even sounder. When its origin is well-targeted, ethane is a good indicator of methane emissions. This is another harmful consequence for the atmosphere because exploitation by hydraulic fracturing also releases methane more or less in the same proportions as ethane. This property was useful to the researchers for the creation of a second model simulation.  

“For the first model, which was based on inventories, we used a ‘bottom-up’ technique, from the bottom to the top. We used inventories for calculating the content of the atmosphere. This did not constitute sufficient proof to verify our theories. We needed an extra lever. We wanted to verify this data by means of a “top-down”, approach, from top to bottom. We therefore wanted to record the fluxes by satellite and deduce new inventories from these”. Though direct measurements of ethane fluxes by satellite are not available, methane is very observable from space. It then became possible, based on the quantity of methane emitted from the region identified as the culprit to get an approximate deduction of the ethane flux. “This was the objective of Emily Fischer and her group, also based in Colorado. For this they used the GEOS-Chem model, developed by Harvard. This model takes account of high-definition measurements of methane. The fine resolution available makes it possible to precisely map these fluxes. In parallel with this, they drew up a map of the wells of which there are more than 500,000 today, and they compared this distribution of wells with the intensity of methane emissions. They were therefore able to quantify these fluxes, to attribute them to this activity and deduce an estimate of the ethane emission completely independently of our observations and calculations from the first model. And all our results concur completely. This means that we can confidently point the finger of blame at the American oil industry and the massive exploitation of shale gas because we know where these emissions are coming from and in what quantity”.

Evolution ethane rate 

Methane, a difficult gas to model

Now, if the emission of ethane has increased by 75% due solely to shale gas exploitation, the methane flux has also increased proportionately given that the overall concentration ratio of these gases is the same. This is not good news either but is also very difficult to observe. “Paddy-fields, marshes, permafrost or cattle to name but a few: there are more than ten natural or anthropogenic sources of methane which must be taken into account when we want to model its emission around the globe. Therefore, if oil activity increases, the amount of methane released into the atmosphere will be less visible than in the case of ethane. The ratio of methane to ethane is a real asset for achieving a more reliable estimate of methane due to the oil industry. We were therefore able to observe that, in 2009, shale gas extraction generated 20 million extra tonnes of methane into the atmosphere. By increasing this flux by 75%, we get a figure of 35 million tonnes emitted in 2014. To put this in context, methane increased by 1% per year up to 2000 before reaching a plateau during 5 years, even though we have yet to understand why. But since then, it has been increasing again by 0.3% per year. We estimate that a third of this increase is due to an increase in gas exploitation in the United States”.

By combining ethane with methane and by associating them with the extraction of natural gas, the publication points to two types of harmful effects which affect both air quality and global warming. But the researchers did not stop there. “We are no longer in the realm of theory. Since our study, it is an incontrovertible truth. We are going to continue studies on a global level and then accelerate proceedings by trying to influence decisions based on our results. Our information should be available and reliable, and we are going to continue working to achieve that. We have a colleague in Colorado who is currently measuring the concentration of gas with a much shorter lifetime at dozens of sites. One of the advantages of these gases is that if they are measured somewhere, this is because their source is very close, while we have detected ethane emissions several thousand kilometres from their source. If the results are significant, we will be better able to identify the harmful effects of shale gas extraction. We are also going to study the data from all the sites in the NDACC network, to obtain a global map of these emissions. We would also like to produce a high-resolution map to better identify the variations in these emissions. For example, we would like to determine if the losses are higher in active wells or in abandoned wells which have been poorly sealed or whether these fluxes are more significant in certain very precise areas in accordance with geological layers. These are all different aspects which we have not been able to discern for the moment. I am not saying that I am asking for a ban on shale gas extraction, but perhaps that, at least, this type of knowledge could lead to more efficient means of extraction in order to drastically reduce emissions”.

(1) Evaluating ethane and methane emissions associated with the development of oil and natural gas extraction in North America, Franco et al, Environmental Research Letters, Vol. 11, April 2016. http://orbi.ulg.ac.be/handle/2268/194574


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