What the peer-reviewed science says about shale gas
Shale gas exploration and extraction via hydraulic fracturing is a controversial and polarizing topic in New Brunswick. The public is divided on the issue and, as is often the case these days, social media are being used to rally supporters to one side or the other. Inflammatory rhetoric and exaggerated claims appear to dominate the discussion. That being said, it is far from clear yet whether NB has a sufficiently large and economically extractable reserve of gas to create a significant industry; it may turn out that shale gas may not exist in sufficient quantities, or prices may not be sufficient to justify development at this time. On the other hand, the gas is a public asset and so discussion of how to develop (or not develop) and utilize the asset is merited. For a useful outline of the shale industry in New Brunswick, see an article by A. Park of UNB (16) and an opinion piece by various UNB researchers.
The development of hydraulic fracturing technologies over the past 30 years or so has made extraction of shale gas economically feasible and attractive prices have allowed the industry to expand rapidly. An abundance of gas in the marketplace pushed down prices in 2011-2012 and the expansion of the industry has slowed somewhat. Information in the peer-reviewed scientific literature with respect to adverse environmental and health impacts from shale gas extraction is now beginning to appear. A number of these articles are available for free download and I would encourage people to read them, rather than accept the interpretations that appear in various media (or my interpretations, for that matter). It is fine to have opinions, but much better to have opinions based in verifiable data. Then we can have a rational discussion.
The objective of this post is to review what the peer-reviewed scientific data say about shale gas extraction and its environmental impacts. I have put together a list of peer-reviewed science journal articles related to shale gas environmental effects, and have added some comments on the results obtained by the researchers (If anyone knows of any that are not listed below, please forward to me). The numbers in parentheses below refer to the scientific citation with the same number. Let’s look at what the science says with respect to some of the major environmental issues:
- Contamination of groundwater by extracted methane.
Methane is the largest component of natural gas; other hydrocarbon gases, such as ethane and propane, are generally removed from natural gas during the purification process. Because it is a potent greenhouse-gas, methane releases into the atmosphere have long been a concern. More recently, methane contamination of groundwater used for drinking has become an issue, due to the potential of hydraulic fracturing technologies that allow methane to escape from deep reserves and potentially mix with groundwater reservoirs.
In two widely-reported studies (11, 15), researchers at Duke University’s Nicholas School of the Environment found high levels of gas from thermogenic (i.e. likely from deep gas reserves) sources in a number of drinking water wells that were located less than 1 km from gas well sites, mainly located in Pennsylvania. Groundwater samples taken further way from gas wells has significantly lower levels of methane, and the methane in those latter sites was a mix of thermogenic and biogenic (i.e. likely from shallow gas reserves adjacent to groundwater) methane. However, the authors reported that methane was found in 85% (15) and 82% (11), respectively, of all water samples taken from houses in the research areas. In other words, the research took place in an area where biogenic and likely thermogenic methane already were common contaminants, and the nearby presence of gas wells increased methane concentration in the water supplies of houses close to those wells. Methane is known to be naturally present in drinking water in different locations in North America, including NB. Those are the regions that would seem to be the most likely to see increased methane levels in drinking water, when the gas wells are close by. In other areas, the likelihood of gas leaking into groundwater may be related to the geology of the region. Houses less than 1 km from gas wells also had propane and ethane contaminants, presumably from the same natural deep underground sources that provided the higher levels of methane.
These two studies suggest that if gas wells are located 1 km or more from the house, the chances increased contamination by methane are fairly low. The authors of the 2013 study (11) concluded that the source of the higher levels of methane, propane and ethane was probably faulty well casing construction that resulted in gas leaks into water. In other words, the problem was not the hydraulic fracturing process itself, but poor well construction. Davies (4), Saba and Orzechowski (18) and Schon (19) criticized Osborn (15) for characterizing the additional methane as resulting from hydrofracturing and emphasized that the most likely cause, faulty well-casing, was not inherently related to hydraulic fracturing technology. If correct, that sounds like a fixable problem, provided there is sufficient monitoring to detect the leaks.
Finally, I’d note that the Jackson (11) article reported that the Pennsylvania Department of Environmental Protection issued 90 violations in 2010 and 119 violations in 2011 for faulty casing and cementing of gas wells. That points out the need for careful and vigorous monitoring of gas wells by independent agencies, although, to keep things in perspective, it is worth noting that by 2011 there were over 8000 gas wells in Pennsylvania. Jackson (11) also recommended extensive pre-drilling data collection on groundwater quality and public disclosure of same. It follows that public agencies would need to have the resources to oversee or carry out those tasks.
- Contamination by fluids used in hydraulic fracturing
In the 2011 study referred to above, Osborn (15) did not detect drinking water contamination by hydraulic fracturing fluids. Data showing contamination of drinking water from fracking fluids are hard to find in the peer-reviewed scientific literature. The United States EPA, in 2011, reported contamination of groundwater in Wyoming by such fluids. The EPA test wells were drilled near domestic water wells where residents had complained about water quality for several years and those wells were within a few hundred metres of gas wells. The EPA has tried without apparent success to develop a peer-review evaluation of the methods and data used in that study. The area in question has had intensive gas drilling for decades, using both conventional and hydraulic fracturing techniques, and the reported contamination may or may not be due to the latter technology. Waste pits from oil and gas drilling activities and containing various contaminants are found in the area. It sounds like some errors were made in site selection and those errors resulted in data that cannot be conclusively linked to hydraulic fracturing.
Some have mischaracterized the EPA results and claimed that the EPA could not reproduce the results showing contamination. In fact, repeated sampling has shown detectable levels of contamination, and those contaminants might indeed be the cause of the odour, taste and possible health effects reported by residents at the Wyoming site. The problem encountered by the EPA in connecting their results to hydraulic fracturing seems to be site selection. The EPA chose sites where groundwater contamination may have occurred from causes other than hydraulic fracturing, and consequently the EPA cannot properly test the hypothesis that fluids used in fracturing are responsible for the contaminants found in ground water. It is important that sites selected for study of contamination be areas where traditional oil and gas exploration and drilling have not been done, in order to separate the effects of past practices from new practices. Additionally, you would prefer a site where baseline data are available, in order to separate out naturally-occurring problems or other ‘human-induced’ problems from those caused by gas development.
It is clear from the Wyoming example that the oil and gas industry does not exactly have a stellar track record with respect to environmental stewardship, and that proper regulation and monitoring are required to reduce risk. However, the Wyoming case does not help much either way with respect to the impact of hydraulic fracturing on groundwater contamination.
The data presented in these two studies from Duke University on the other hand suggest that water wells 1 km or more from gas well sites are not likely to become contaminated with methane and that fluid contamination from hydraulic fracturing is unlikely. Properly constructed and monitored gas wells might reduce that distance even further, but differing geologies might affect gas migration.
- Surface water contamination
Olmstead (14) found higher levels of contaminants (they used chloride as a ‘marker’ for contaminants and found increases of approx 10% per treatment facility) in surface water (rivers, streams) samples collected downstream from fracking fluid water treatment facilities, compared to samples from control locations. The presence of gas wells upstream increased (5% per 18 additional well pads) the amount of total dissolved solids downstream, but this appeared to be related to land-clearing or other actions related to construction of the gas wells rather than fracking fluid contamination per se.
These data suggest that water treatment facilities may be releasing contaminants into watersheds. Contaminants are also released into watersheds by domestic water treatment facilities, but proper regulation and monitoring can be used to maintain drinking water standards. There have also been reports in the media of spills of fluids causing surface water contamination. Rozell (17) used a risk analysis procedure to determine that leaks and spills during wastewater disposal posed a large threat to drinking water supplies. It sounds reasonable, therefore, to require independent and transparent monitoring of surface waters near water treatment facilities, and that contamination levels in treated water be regulated to meet at least drinking water standards. It is also important to note that water discharged from municipal sewage treatment plants is not free of contaminants; there is a difference between a water source that is free of contaminants and one that meets water drinking standards.
- Methane leaks into atmosphere
Methane is a potent greenhouse gas and increased methane emissions into the atmosphere will certainly contribute to global warming. There is a great deal of concern about release of methane from thawing Arctic permafrost for that very reason.
When used as a fuel in power generation, natural gas (NG) releases fewer CO2 emissions than coal or oil. Low prices for NG, following the expansion in supply resulting from hydraulic fracturing, have led to replacement of coal by NG in power generation in some parts of the US. Greenhouse-gas emissions have fallen slightly in the US and that decline might be a consequence of the switch from coal and oil to NG. That would seem to suggest benefits where shale gas replaces ‘dirtier’ fuels such as coal or oil for power generation.
A report by Howarth (9) caused alarm as it suggested that large amounts of methane might be escaping from natural gas wells. They calculated that, largely because of these methane emissions, the GHG ‘footprint’ of shale gas might be greater than that of coal. Howarth et al’s calculations were based largely on an EPA report. However, the EPA has now issued a revised report that significantly reduces the amounts of methane they expect to be released from shale gas wells [EPA (2011a) Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2009. April 14, 2011. U.S. Environmental Protection Agency, Washington DC]. Jiang (12) also calculated GHG emissions related to shale gas extraction (methane leakage, flaring/venting of gas from wells during flow testing, and CO2 emissions related to operation of diesel equipment at well sites). They concluded, in contrast to Howarth (9), that shale gas had a lower GHG footprint than coal, when used for electricity generation.
Cathles (2, 3) also concluded that shale gas would provide marked reductions in GHG emissions if it replaced coal and oil as an energy source. Cathles (2) stress that, while methane is a potent GHG, it persists in the atmosphere for about 20 years, while CO2 emissions from coal and oil consumption persist for hundreds of years. Even with leakage from gas wells, they concluded that the use of gas is vastly less damaging in terms of global warming than coal and oil. Howarth (10) responded in 2012 with a defense of their position. The different conclusions appear to be based largely on whether one believes we should look at the impacts of emissions over a decadal or 100 year time scale. Both groups of authors agree that more independent data on methane emissions are needed.
Interestingly, the Cathles group and the Howarth group are both based at Cornell University in upstate New York – I can imagine the ‘angry words’ during coffee breaks! For a commentary on this dispute, see here.
If a company is in the business of selling methane (i.e. natural gas), you’d think they would try to reduce any leakage as much as possible. After all, loss of gas by venting into the atmosphere is a potential loss of profit – they have already invested in the well, so would they tolerate such a loss? Of course, the higher the value of the gas, the greater will be their interest in capturing as much of it as possible. By contrast, when gas is cheap, the cost of capture might be greater than the value of the gas. It’s true that the oil industry may at times vent off large amounts of gas in order to secure the more valuable oil from underground reserves, but the shale gas industry is in the gas business. According to the EPA, the industry has made significant strides in reducing emissions of methane from wells. That, plus the reduction in GHG emissions in the US referred to above, would suggest Howarth’s calculations are off the mark. Lu (20) found that CO2 emissions fell between 2008 and 2009 in the US and attributed that decline to a switch in the use of gas for coal in power generation. Indeed, other scientific publications (2, 3, 12) have claimed that the methane emissions from shale gas wells, and their impacts, are small enough that the use of this gas results in a net reduction in GHG emissions, where the shale gas replaces coal or oil in power generation. The weight of the evidence appears to support the use of natural gas as a transition fuel.
- Seismic events
It has been claimed that earthquakes may be triggered by hydraulic fracturing technologies. The word ‘earthquake’ tends to conjure up visions of massive seismic events resulting in large amounts of destruction and loss of life. It’s helpful to consider that most earthquakes are minor seismic events and cause no discernible damage. While most earthquakes are natural events, minor man-made events can occur as a result of blasting (road construction, mining). The force or magnitude of an earthquake is measured on a logarithmic scale: those below a magnitude of 5 rarely cause damage; those below a magnitude of 3 (i.e. 100 times less intense) are rarely felt, although they will be recorded on the seismographs used to record earthquake events.
Earthquakes Canada provides data on earthquakes occurring in Canada and New Brunswick earthquake information can be found here also. For example, in 2012 there were 91 earthquakes recorded in the New Brunswick region (because regions are defined by longitude and latitude, the NB region also includes parts of Maine, PEI and Nova Scotia. You can adjust the settings provided by Earthquakes Canada to expand or reduce the area to be reported on.). Of the 91, 89 had a magnitude of 2 or less. Only 31 of the 91 were reported by members of the public. Many of these were from the earthquake ‘swarm’ that occurred in the Macadam area. In 2013, 19 events were recorded from January through June. Seventeen of those were magnitude 2 or less. So earthquakes are not uncommon, but very few earthquakes in New Brunswick cause damage. If you check the Earthquakes Canada site you can see for yourself whether or not seismic testing for shale gas over the past couple of years has resulted in an increase in the number of recorded quakes in New Brunswick.
Can hydraulic fracturing cause earthquakes? The scientific evidence suggests that either fracturing itself or wastewater injection may induce small earthquakes, but there does not seem to be evidence that these are normally damaging to infrastructure or the environment (13). For example, Holland (7) concluded that hydraulic fracturing of an oil well in Oklahoma triggered earthquakes. A series of 116 earthquakes resulted. These occurred from 17-23 January 2011 with no other similar earthquakes identified at other times prior to or post-hydraulic fracturing. In other words, the earthquakes ended when the fracking stopped. The identified earthquakes ranged in magnitude from 0.6 to 2.9, with only 16 of 116 earthquakes of magnitude 2 or greater. Very minor earthquakes such as these would not be expected to cause damage and none was reported.
Brodsky and Lajoie (1) found a good correlation between the volume of fracturing fluids injected or extracted from a well and seismic activity in California. In this case, the objective of fracturing was not to obtain shale gas but to develop geothermal energy sources. As the fracturing continued over a series of decades, the number of earthquakes per amount of fracturing activity appeared to decline. That might suggest a limit in earthquake activity in response to fracturing, but, again, that might depend upon the geology of the region. Ellsworth (5) noted that earthquakes induced by fracturing appear to be mainly minor events, but cautioned that deep injection of wastewater might result in larger earthquakes. He noted that wastewater injection was the likely cause of major quakes in the U.S. in 2011 and 2012, in particular the 5.6 Magnitude quake that struck Oklahoma and destroyed several homes. Horton (8) found similar swarms of seismic events in Kansas that were apparently associated with wastewater injection. It is possible therefore that wastewater injection, as opposed to fracturing itself, might pose a particular hazard. Ellsworth suggested increased monitoring, especially near wastewater injection sites. Van der Elst (6) reached similar conclusions, noting that fracturing seismic activity in a region increased the likelihood that the region might be hit by larger earthquakes originating at remote locations. Again, that might be dependent upon local geology; increased monitoring at well-injection sites was recommended.
Overall, there does seem to be a relationship between the deep injection of wastewater and seismic activity. For the most part, that activity does not appear to be dangerous, but there are some reports suggesting that these minor events might make a region more susceptible to quakes that originate elsewhere. That possibility needs further investigation and, again, underlies the need for transparent and public monitoring.
- Brodsky, E. and Lajoie, L. 2013. Anthropogenic Seismicity Rates and Operational Parameters at the Salton Sea Geothermal Field. Science 1239213 (Published online 11 July 2013) [DOI:10.1126/science.1239213]
- Cathles, L., Brown, L., Taam, M., and Hunter, A.2012. A commentary on ‘The greenhouse-gas footprint of natural gas in shale formations’ by R.W. Howarth, R. Santoro, and Anthony Ingraffea,” Climatic Change 113, no. 2: 525-535.
- Cathles, L. M. 2012. Assessing the greenhouse impact of natural gas. Geochemistry, Geophysics, Geosystems 13: 1525-2027 doi 10.1029/2012GC004032
- Davies, R. 2011. Methane contamination of drinking water caused by hydraulic fracturing remains unproven. Proceedings of the National Academy of Sciences 108, no. 37: E871.
- Ellsworth, W.L. 2013. Injection-Induced Earthquakes. Science (July 12) Vol.341 (6142) doi: 10.1126/science.1225942
- van der Elst, NJ; Savage, HM; Keranen, KM,; Abers, GA.2013. Enhanced remote earthquake triggering at fluid-injection sites in the midwestern United States. Science (Jul 12) 341(6142):164-167. doi:10.1126/science.1238948.
- Holland, A. 2013. Earthquakes triggered by hydraulic fracturing in south-central Oklahoma. Bulletin of the Seismological Society of America 103(3):1784-1792
- Horton, S. 2012. Disposal of Hydrofracking Waste Fluid by Injection into Subsurface Aquifers Triggers Earthquake Swarm in Central Arkansas with Potential for Damaging Earthquake. Seismological Research Letters, March/April 2012, v. 83, p. 250-260, doi:10.1785/gssrl.83.2.250.
- Howarth, RW., Santoro, R., and Ingraffea, A. 2011. Methane and the greenhouse-gas footprint of natural gas from shale formations. Climatic Change 106, no. 4 : 679-690
- Howarth, RW., Santoro, R., and Ingraffea, A. 2012. Venting and leaking of methane from shale gas development: response to Cathles et al. Climatic Change 113, no. 2 : 537-549
- Jackson, R., Vengosh, A., Darrah, T., Warner, N., Down, A., Poreda, R., Osborn, S., Zhao, K., and Karr, J. 2013. Increased stray gas abundance in a subset of drinking water wells near Marcellus shale gas extraction. Proceedings of the National Academy of Sciences 110, no. 28: 11250-11255.
- Jiang, M., Griffin, WM., Hendrickson,C., Jaramillo, P., VanBriesen, J., and Venkatesh, A. 2011. Life cycle greenhouse gas emissions of Marcellus shale gas, Environmental Research Letters 6, no. 3. 034014.
- National Research Council. Induced Seismicity Potential in Energy Technologies . Washington, DC: The National Academies Press, 2012.
- Olmstead, S., Muehlenbachs, L., Shih, J-S., Chu, Z., and Krupnick, A. 2013. Shale gas development impacts on surface water quality in Pennsylvania. Proceedings of the National Academy of Sciences 110, no. 13: 4962-4967.
- Osborn, S., Vengosh, A., Warner, N., and Jackson, R. 2011. Methane contamination of drinking water accompanying gas-well drilling and hydraulic fracturing.Proceedings of the National Academy of Sciences 108, no. 20: 8172-8176
- Park, A. 2012. Shale Gas in New Brunswick: Promise, Threat, or Opportunity? Journal of New Brunswick Studies / Revue d’études sur le Nouveau-Brunswick, North America, 3, Dec. 2012. Available at: <http://journals.hil.unb.ca/index.php/JNBS/article/view/20081/23218>. Date accessed: 19 Jul. 2013.
- Rozell, D. J. and Reaven, S. J. (2012), Water Pollution Risk Associated with Natural Gas Extraction from the Marcellus Shale. Risk Analysis 32: 1382–1393. doi: 10.1111/j.1539-6924.2011.01757.x
- Saba, T., and Orzechowski, M. 2011. Lack of data to support a relationship between methane contamination of drinking water wells and hydraulic fracturing. Proceedings of the National Academy of Sciences 108, no. 37: E663.
- Schon, S. 2011. Hydraulic fracturing not responsible for methane migration. Proceedings of the National Academy of Sciences 108, no. 37: E664.
- Xi Lu, Salovaara, J. , McElroy, M. 2012. Implications of the Recent Reductions in Natural Gas Prices for Emissions of CO2 from the US Power Sector. Environ. Sci. Technol., 2012,46 (5), pp 3014–3021 DOI: 10.1021/es203750k