Literature Review on Fracking Chemical Abstracts; 2011 June 2013

Transcription

1 Literature Review on Fracking Chemical Abstracts; 2011 June 2013 ; 8 August Executive summary This report provides a summary of the scientific literature on hydraulic fracturing (fracking) published from 2011 to June 2013, obtained primarily from a search of Chemical Abstracts. Fracking is conducted by first drilling into the rock vertically and then horizontally into the desired shale formation, followed by pumping a fluid into the well under high pressure to fracture the rock formation. One of the main issues associated with fracking is the potential for groundwater contamination. Although the horizontal well bore may be hundreds or thousands of meters below groundwater aquifers, hydraulic connectivity between the well fracture region and the aquifers, mainly via natural fissures in the rock, has been demonstrated. This connectivity may allow displaced deep toxic brines and gases (such as methane), in addition to the fracking fluid itself, to contaminate groundwater aquifers making them less suitable as potable water sources. Because the former two components (brines and gases) are naturally occurring, it is important that baseline monitoring data, collected before a fracking operation begins, is available to provide conclusive evidence regarding the cause of groundwater contamination. Such conclusive scientific evidence on the health and environmental impacts of fracking is currently limited, and is mainly circumstantial. Coupled with the fact that over a million fracking operations have been conducted in the US alone, it might be concluded that the risk of groundwater contamination from fracking is minimal. However, an important consideration in this regard is that the migration of fluids from deep fracked formations into a higher groundwater aquifer may take up to 10 years after the fracking operation has been completed, as has been shown by mathematical modeling. Therefore, it may take several years after fracking is completed for human health to be impacted through groundwater contamination, again stressing the need for pre fracking baseline data. A more immediate issue is what to do with the high volumes of toxic water that flow out of the well after the fracking operation and throughout the lifetime of the well. Although this water is reused in other fracking operations, it will eventually need to be treated as gas field development is completed. While processes exist for treating this fluid, their economics may be prohibitive and much research is still needed in this area. In summary, one scientific report stated: A conclusion that may be drawn from a review of recent scientific studies and incidences is that horizontal drilling accompanied

2 by hydraulic fracturing poses threats to local environmental conditions and the health and safety of persons using land, water, and air resources (Hatzenbuhler, 2012). 2 Introduction Wells for natural gas and oil production are drilled vertically to a depth of a kilometer or more, and then horizontally for a similar distance (EPA, 2012). The horizontal drilling increases the exposure of the bore to the geologic formation containing the gas and oil. Once the well has been drilled, hydraulic fracturing (fracking) is conducted by pumping large volumes of an aqueous solution/suspension into the well at high pressure to fracture the rock formation and increase the flow of hydrocarbon product into the well bore. Issues around fracking include: 1. The fracking fluid is toxic and may contaminate groundwater that is used for drinking 2. The fracking fluid may displace toxic deep brines into shallower groundwater sources 3. Additional fissures created by fracking may cause contamination of groundwater and air by methane and other gases 4. Surface spills of fracking water may result in groundwater and surface water contamination Although the shale gas basins in the U.S., which are located in about 20 states (Vengosh, 2013), have been the sight of extensive fracking operations, rigorous scientific data is slim for determining health risks from fracking, as there have been relatively few relevant publications in the open scientific literature (Mitka, 2012; Thompson, 2012; Batley, 2012). The purpose of this review was to summarize the scientific literature on fracking that was cited primarily in Chemical Abstracts, with a focus on papers published from 2011 to June The Chemical Abstracts computer searchable database contains the contents of over 8,000 scientific journals and other scientific publications. 3 Fracking water The fluid that is pumped into the ground during a fracking operation is typically an aqueous solution/suspension of several chemicals as outlined in the table below. This is only a short list of the estimated 750 chemicals that have been used in fracking fluid (Batley, 2012). Many of these chemicals are toxic. Page 2 of 8

3 From Vidic (2013) 4 Groundwater contamination 4.1 Connectivity between deep shale and groundwater Even though horizontal well bores can be a kilometer or more below drinkable groundwater sources, suggesting that they are effectively isolated from one another, connectivity has, however, been observed, which could provide pathways for deep toxic brine, gases and fracking fluid to migrate into groundwater aquifers. For example, the ratios of various chemical species present in groundwater including Br, Cl, Ca 2+, Na +, HCO 3, and 87 Sr/ 86 Sr, have been used to establish that shallower groundwater aquifers have become contaminated by deeper highly saline and toxic groundwaters. These brines have apparently migrated upward through natural fissures in the rock (Vengosh, 2013; Warner, 2012). Does fracking itself enhance or cause connectivity between hydrocarbon bearing deep shale and drinkable groundwater? In this regard, Mayers (2012) pointed out that fracking is not intended to affect surrounding formations, but shale properties vary Page 3 of 8

4 over short ranges and out of formation fracking is not uncommon. In the Marcellus shale, out of formation fracks have been documented 500 m above the top of the shale. These fractures could contact higher conductivity sandstone, natural fractures, or unplugged abandoned wells above the target shale. Also, fluids could reach surrounding formations just because of the volume injected into the shale, which must displace natural fluid, such as the existing brine in the shale (Mayers, 2012). 4.2 Fracking fluid contamination of groundwater Given that most (70 90 %; Gross, 2013) of the hundreds of thousands of liters of fracking fluid per well remain in the ground after fracking, and that there may be connectivity between the deep shale fracking region and much shallower groundwater as discussed above, it is possible that fracking fluid may contaminate groundwater that is used for drinking. However, although more than 1 million hydraulic fracturing treatments have been conducted, there are only a few documented cases of direct groundwater pollution resulting from injection of hydraulic fracturing chemicals used for shale gas extraction (Vidic, 2013), including the following: 1. Fracking fluid was found in aquifers in the Marcellus region (DiGiulio et al. 2011; EPA 1987), although the exact source and pathways had not been determined (Mayers, 2012). 2. A U.S. EPA study reported that two deep monitoring wells near an aquifer in Pavillion, Wyoming, tested positive for glycols, alcohols, and high levels of methane, all of which were thought to originate from hydraulic fracturing activity conducted below the aquifer (Gross, 2013). In contrast, there are studies that report no groundwater contamination in fracking areas. For example, Kresse (2011) found no elevated levels of metals and chloride in drinking water wells in a shale gas producing area. Methane found in some wells was presumably biogenic in origin. Does this suggest that fracking is relatively safe? At least 2 factors do not support this. Firstly, in North America, unconventional oil and gas drilling (which employs fracking) currently sees extensive public support as being a modern day gold rush in the energy sector (Pairitz, 2013). Therefore, it is not surprising that there are political, legal and financial impediments to peer reviewed research into the environmental impacts of fracking (Vidic, 2013). In other words, it is difficult to study fracking in a scientific unbiased way. Secondly, the effects of fracking may be slow to emerge. In this regard, a recent study applied a groundwater transport model to estimate the risk of groundwater contamination with hydraulic fracturing fluid by using pressure changes reported for gas wells in the Marcellus Shale region. The study concluded that changes induced by hydraulic fracturing could allow advective transport of fracturing fluid to groundwater aquifers in less than 10 years (Vidic, 2013). This implies that it may take several years after completion of a fracking operation for groundwater aquifer contamination to Page 4 of 8

5 occur (Myers, 2012), making causal association of this pollution to fracking even harder to prove. 4.3 Methane contamination of groundwater The documentary film Gasland, released in 2010, shows a scene where tap water appears to be burning, presumably due to the presence of mainly methane. At the time of writing, YouTube contained numerous additional clips of burning tap water events. While little scientific knowledge can be gained from this video evidence, it highlights the possibility that methane contamination of groundwater might serve as an indicator of gaseous pollution caused by fracking. More than 40 million U.S. citizens drink water from private wells. In some areas, methane the main component of natural gas seeps into these private wells from either natural (biogenic) or anthropogenic (thermogenic) sources (Vidic, 2013). Thermogenic gas is formed by compression and heat at depth (and is associated with fracking operations), whereas bacteriogenic (biogenic) gas is formed by bacteria breaking down organic material. The source can be distinguished based on both C and H isotopes and the ratio of methane to higher chain gases (ethane, propane, etc.). Thermogenic gas can reach drinking water aquifers only by leaking from the well bore or by seeping vertically from the source. In either case, the gas must flow through potentially very thick sequences of sedimentary rock to reach the groundwater aquifers (Mayers, 2012). Nonetheless, many studies which have found thermogenic gas in water wells, found more gas near (natural) fracture zones, suggesting that fractures are pathways for gas transport (Mayers, 2012). This means that if thermogenic methane contamination of groundwater is detected in an area where fracking was conducted, natural causes cannot be ruled out unless baseline data exist that show the absence of contamination before fracking began. The scientific evidence on whether fracking causes methane contamination of drinkable groundwater has been largely circumstantial, mainly due to the difficulties in establishing the methane source. For example, many agency reports and legal citations and peer reviewed articles have found more gas in water wells near areas being developed for unconventional natural gas (where fracking is used) (Mayers, 2012). In another report: a study of 60 groundwater wells in the Dimock PA area, including across the border in upstate New York, showed that both the average and maximum methane concentrations were higher when sampled from wells within 1 km of active Marcellus gas wells as compared with those farther away (Vidic, 2013). In both these scientific reports, the cause of methane contamination (natural or due to fracking) could not be conclusively identified. 5 Contamination from surface spills During a fracking operation, high volumes of fracking solution are pumped into a well under high pressure. On depressurization, initially fracking water emerges from the well; Page 5 of 8

6 this is called flowback water. After the flowback water exits the well, it is followed by natural water from the depths of the well which is called produced water, and may be continuously produced along with the gas/oil during the lifetime of the well. This produced water may be toxic due to its high salt and naturally occurring radioactive materials (NORMs) contents (Kharaka, 2013; Barbot, 2013). Given that the volume of this wastewater may be quite high (26 million barrels per year recorded in Pennsylvania during 2008 to 2011; Vidic, 2013), it presents a significant challenge for treatment and disposal. However, early on in oilfield development, much of the fracking wastewater may be reused. But this is only a temporary solution to wastewater management until there are no new fracking operations in the area and the field becomes a net wastewater producer. Therefore, there is a need to develop additional technical solutions (such as effective and economical approaches for separation and use of dissolved salts from produced water and treatment for naturally occurring radioactive material) that would allow continued development of this important natural resource in an environmentally responsible manner. Considering very high salinity of many produced waters from shale gas development, this is truly a formidable challenge. Research focused on better understanding of where the salt comes from and how hydrofracturing might be designed to minimize salt return to the land surface would be highly beneficial (Vidic, 2013). 6 Air pollution Methane, which has a global warming potential of 72 times greater than carbon dioxide, is released during flowback in fracking operations. This increases the methane pollution footprint of fracking operations by about 30 % compared to conventional gas drilling (Howarth, 2011). While methane has relatively low human toxicity, there have been reports of serious human health effects caused by atmospheric pollution associated with fracking, suggesting that other gases are released during this process. For example: Subchronic health effects, such as headaches and throat and eye irritation reported by residents during well completion activities, are consistent with known health effects of BTEX hydrocarbons associated with gas/oil production (McKenzie, 2012). McCarron (2013) documented severe human health effects in an area where fracking was conducted. Analytical results on atmospheric samples showed that these people were likely exposed to a wide variety of gases/vapours including chlorinated hydrocarbons, propylene and acrolein, the latter two compounds being associated with DNA alkylation. Page 6 of 8

7 These data show that it is important to include air pollution in the national dialogue on unconventional natural gas development that, to date, has largely focused on water exposures to hydraulic fracturing chemicals (McKenzie, 2012). 7 Conclusion Please see Executive summary. 8 References Barbot, Elise; Natasa S. Vidic, Kelvin B. Gregory, and Radisav D. Vidic. Spatial and Temporal Correlation of Water Quality Parameters of Produced Waters from Devonian Age Shale following Hydraulic Fracturing. Environ. Sci. Technol. 2013, 47, Batley, Graeme E., and Rai S. Kookana. Environmental issues associated with coal seam gas recovery: managing the fracking boom. Environ. Chem. 2012, 9, Boyer, Elizabeth W., Ph.D., Bryan R. Swistock, M.S., James Clark, M.A., Mark Madden, B.S., and Dana E. Rizzo, M.S.The Impact of Marcellus Gas Drilling on Rural Drinking Water Supplies. The Center for Rural Pennsylvania EPA: Study of the Potential Impacts of Hydraulic Fracturing on Drinking Water Resources PROGRESS REPORT. US Environmental Protection Agency Office of Research and Development Washington, DC. December 2012 EPA/601/R 12/011 Gross, Sherilyn A., Heather J. Avens, Amber M. Banducci, Jennifer Sahmel, Julie M. Panko & Brooke E. Tvermoes. Analysis of BTEX groundwater concentrations from surface spills associated with hydraulic fracturing operations. Journal of the Air & Waste Management Association, 63(4): , 2013 Hatzenbuhler, Heather and Terence J. Centner Regulation of Water Pollution from Hydraulic Fracturing in Horizontally Drilled Wells in the Marcellus Shale Region, USA. Water 2012, 4, Howarth, Robert W. Renee Santoro, Anthony Ingraffea. Methane and the greenhousegas footprint of natural gas from shale formations. Climatic Change (2011) 106: Kharaka, Y. K., J. J. Thordsen, C. H. Conaway, R. B. Thomas. The energy water nexus: potential groundwater quality degradation associated with production of shale gas. Procedia Earth and Planetary Science 7 ( 2013 ) Kresse, Timothy M., Nathaniel R. Warner, Phillip D. Hays, Adrian Down, Avner Vengosh, Robert B. Jackson. Shallow Groundwater Quality and Geochemistry in the Fayetteville Shale Gas Production Area, North Central Arkansas, U.S. Geological Survey Scientific Investigations Report , 31 p. McCarron, Geralyn. The Australian gas fields; personal insights into the health impacts and limitations of regulation. January 26th Published at Page 7 of 8

8 McKenzie, LM, Witter RZ, Newman LS, Adgate JL. Human health risk assessment of air emissions from development of unconventional natural gas resources. Sci Total Environ May 1;424: Mitka, Mike. Rigorous Evidence Slim for Determining Health Risks From Natural Gas Fracking. JAMA, May 23/30, 2012 Vol 307, No. 20, pg 2135 Osborn, Stephen G., Avner Vengosh, Nathaniel R. Warner, and Robert B. Jackson Methane contamination of drinking water accompanying gas well drilling and hydraulic fracturing. Pairitz, C. Fracking: The Modern Day Gold Rush. Posted on July 12, the modern day gold rush/ Struchtemeyer, Christopher G., Michael D. Morrison, Mostafa S. Elshahed A critical assessment of the efficacy of biocides used during the hydraulic fracturing process in shale natural gas wells. International Biodeterioration & Biodegradation 71 (2012) 15e21 Thompson, Helen. Fracking Boom Spurs Environmental Audit. Scientific American, May 29, Vengosh, Avner, Nathaniel Warner, Rob Jackson, Tom Darrah.The effects of shale gas exploration and hydraulic fracturing on the quality of water resources in the United States. Procedia Earth and Planetary Science 7 ( 2013 ) Vidic, R. D. S. L. Brantley, J. M. Vandenbossche, D. Yoxtheimer, J. D. Abad. Impact of Shale Gas Development on Regional Water Quality. 17 MAY 2013 VOL 340 SCIENCE. Warner, Nathaniel R., Robert B. Jackson, Thomas H. Darrah, Stephen G. Osborn, Adrian Down, Kaiguang Zhao, Alissa White, and Avner Vengosh. Geochemical evidence for possible natural migration of Marcellus Formation brine to shallow aquifers in Pennsylvania. PNAS July 24, 2012 vol. 109 no Page 8 of 8