Unconventional shale gas development: challenges for environmental policy and EA practice

Figures & data

Figure 1. Drilling installation schema.

Table 1. Chemical classes of additives identified in hydraulic fracturing fluids.

Additive	% by weight	Purpose	Examples
Proppant	9	Props open fractures	Sand (0.4–0.8 mm in diameter), aluminium ceramic beads
Acid	0.400	Cleans up perforations, dissolve some rocks	Hydrochloric acid
Breaker	<0.001	Reduces viscosity, promotes flowback	Peroxydisulfates
Bactericide/biocide	0.020	Control bacterial growth	Gluteraldehyde, formaldehyde, methylisothiazolinone
Buffer agent		Adjusts/controls acidity	Sodium (or potassium) carbonate, acetic acid
Clay stabiliser		Prevents clay swelling/migration	Potassium chloride
Corrosion inhibitor	0.001	Prevents rusting of pipes	Ammonium bisulphate, methanol
Cross linker		These have higher viscosities and break down less	Potassium hydroxide, borate esters, vinylidene chloride/methyl acrylate copolymer
Friction reducer	0.090	Reduces friction between the fluid and the wellbore	Sodium acrylate, acrylamide copolymer, petroleum distillates (benzene, ethylbenzene, toluene, xylene, naphthalene)
Gelling agent	0.001	Increases fluid viscosity to carry more proppants into fractures	Guar gum, cellulose polymers, petroleum distillates (benzene, ethylbenzene, toluene, xylene, naphthalene)
Iron control	0.02	Prevents precipitation of iron oxides	Ammonium chloride, ethylene glycol
Solvent			Various polyaromatic hydrocarbons (PAHs), benzene, toluene
Surfactant	0.100	Reduce the fluid surface tension to aid fluid recoverys	Methanol, isopropanol, ethoxylated alcohol, ethylene dichloride

Sources:

Cooley & Donnelly 2012; CCA (2014); Stoiber et al. (2015).

Figure 2. Contaminant pathways in shale gas development (after Rozell & Reaven 2011).

Table 2. Summary of what is known and what is not.

Area of concern	Known	Not known
Process chemicals and wastewaters generated	• Seventy three per cent of HF fluid products with CAS numbers associated with 6–14 adverse health effects on skin, eye, sensory organ and reproduction • Marcellus shale region – Flowback and produced water contain levels of salinity (TDS), toxic chemicals and NORM exceeding regulatory thresholds • Wyoming – high levels of poly aromatic hydrocarbons (PAH) in groundwater • Pennsylvania Industrial and municipal WWTF do not effectively remove high levels of TDS and NORM • Minor earthquakes observed in Marcellus and Barnett shale regions attributed to reinjection of wastewater, not fracturing process; two events observed in Alberta Canada attributed to fracturing treatment	• Identity of over half of estimated 750 chemicals used in HF fluids • Outcomes of possibly synergistic interaction between HFF chemicals and formation chemicals under high pressure and temperature • Whether frequent and successive minor seismic events eventually trigger a big one
Release mechanisms and transport pathways to chemical contamination of water resources	• Major routes for toxic chemicals and NORM include spills, well casing leaks, leaks through fractured rock, drilling site discharge and wastewater disposal • Canada – ‘fracture communication’, between wells >600 m apart	• Baseline information on groundwater quality for different sites • Extent of well integrity failure • Extent of inter wellbore communication
Risks posed to human and ecosystem health	• Positive association between density and proximity of pregnant mothers to SGD and congenital heart defects and possibly neural tube defects in newborns • Colorado – water samples from areas with intensive SGD have significant higher endocrine disruption activity than samples from sites with fewer or no operations • High levels of iodide and bromide in HFW react with disinfection chemicals to form known mutagens and carcinogens • Pennsylvania – increased radon readings in buildings after SGD above MCLs • Arkansas – individual gas wells fully changed about 2.5 ha of land and modified an additional 0.5 ha of natural forest.	• Level, duration and source of exposure to water and air pollutants • Confounding variables in existing studies • Occupational health hazards posed by NORM in HFW • Source of radon emissions increase • Long-term impacts of land use changes on species diversity, composition, dynamics and ecosystem functioning
Risk of increased GHG and fugitive methane emissions	• Routes are leaks from well casing and through fractured rock	• Source of fugitive methane emissions, whether biogenic or thermogenic
Disruptive and psycho social effects on communities	• Mostly self-reported impacts on quality of life from traffic noise, increased population and threats to health from HFW	• Baseline health studies • Confounding variables on reported health impacts
Existing impact mitigation measures	• Microbial activity degrades organic compounds in produced waters • Pennsylvania – Aerobic micro-organisms dominate in pre-fracturing fluids, decline in produced water with an increase in anaerobes • Anaerobic micro-organisms successfully cultivated in produced water	• Impacts on flowback reuse

Cooley H, Donnelly K. 2012. Hydraulic fracturing and water resources. Separating the Frack from the Fiction. Oakland, CA: Pacific Institute.

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[CCA] Council of Canadian Academics. 2014. En1130-1137. Environmental impacts of shale gas extraction in Canada: the expert panel on harnessing science and technology to understand the impacts of shale gas extraction. Ottawa: The Council of Canadian Academies; p. 262.

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Stoiber T, Walker B, Allayaud B. 2015. California’s toxic hydraulic fracturing fluids. The chemical recipe. Washington: EWG; p. 35.

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Rozell DJ, Reaven SJ. 2011. Water pollution risk associated with natural gas extraction in Marcellus Shale. Risk Analysis. 1539–6924.

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