AEA: Support to the identification of potential risks for the environment and human health arising from hydrocarbons operations involving hydraulic fracturing in Europe

AEA: Support to the identification of potential risks for the environment and human health arising from hydrocarbons operations involving hydraulic fracturing in Europe by the European Commission DG Environment, prepared by AEA Technology plc under contract to the European Commission DG Environment ref 07.0307/ENV.C.1/2011/604781/ENV.F1., August 10, 2012, Ref: AEA/ED57281/Issue Number 17

Surface and groundwater contamination
The study found that there is a high risk of surface and groundwater contamination at various stages of the well-pad construction, hydraulic fracturing and gas production processes, and during well abandonment. Cumulative developments could further increase this risk.

                                                           Source:  EU Fracing Study, August 2012, Page 27

Cuttings produced from wells also need to be properly handled to avoid for instance the risk of radioactive contamination.

The risks of surface water and groundwater contamination during the technical hydraulic fracturing stage are considered moderate to high. … If wastewater is used to make up fracturing fluid, this would reduce the water requirement, but increase the risk of introducing naturally occurring chemical contaminants and radioactive materials into aquifers in the event of well failure or of fractures extending out of the production zone. The potential wearing effects of repeated fracturing on well construction components such as casings and cement are not sufficiently understood and more research is needed.

In the production phase, there are a number of potential effects on groundwater associated however with the inadequate design or failure of well casing, leading to potential aquifer contamination. Substances of potential concern include naturally occurring heavy metals, natural gas, naturally occurring radioactive material and technologically enhanced radioactive material from drilling operations. The risks to groundwater are considered to be moderate-high for individual sites, and high for development of multiple sites.

The hydraulic fracturing process is water-intensive and therefore the risk of significant effects due to water abstraction could be high where there are multiple installations. … The risk of contamination would increase in situations where casings are of inadequate depth. ….wellbore casings provide the primary line of defence against contamination of groundwater, and any loss of integrity from catastrophic failure of well casing to poor cement seals can lead to a contamination event. Poor casing quality can thus lead to pollution of groundwater during subsequent well development stages, such as hydraulic fracturing, flowback or gas production activities. … The risks from these activities would increase linearly with the number of wells and the time period over which the risk exposure arises. Any significant increase in groundwater pollution during this phase could potentially affect health in the event that members of the public were exposed to pollution in drinking water.

Wells also produce cuttings which need to be properly handled. For example, a vertical well with surface, intermediate and production casing drilled to a total depth of 2,100 metres produces approximately 120 cubic metres of cuttings, while a horizontally drilled well with the same casing program to the same target depth with an example 1,200 metre lateral section produces a total volume of approximately 170 cubic metres of cuttings (i.e., about 40% more). … It is important to ensure proper storage and disposal of cuttings. … The introduction of wide scale shale gas extraction would result in a significant increase in the quantities of potentially contaminated material requiring storage, handling, treatment and disposal. Depending on the nature of shales in Europe, this material may have elevated levels of radioactivity.

USEPA (2011a PR) states that “drilling muds are known to contain a wide variety of chemicals that might impact drinking water resources. This concern is not unique to hydraulic fracturing and may be important for oil and gas drilling in general.”

Source: EU Fracing Study, August 2012, Page 43

The lack of baseline monitoring carried out in the US prior to shale gas development may partly explain why the evidence of contamination associated with shale gas extraction is complex and uncertain.

At one such site setting (Pavillion, Wyoming), hydraulic fracturing occurred in gas production wells at a depth as shallow as 372 metres below ground surface (EPA, 2011c NPR (draft)). Overlying the gas field, there is an aquifer in a formation where water wells are excavated to depths of 15m to 230m or more. These wells are the principal source of domestic, municipal and agricultural water in the area of Pavillion. Groundwater contamination has been found in this area. The US EPA (2011c NPR) draft report concluded that the data indicate likely impact to ground water which can be explained by hydraulic fracturing. The USEPA’s draft report concluded that the observed contamination was linked to inadequate vertical well casing lengths and a lack of well integrity (USEPA 2011c NPR p37, p38). However, the initial sampling will need to be completed in a next phase of testing. (Wyoming State Governor; the Northern Arapaho and Eastern Shoshone Tribes, and US EPA Administrator, 3 March 2012 NPR).

Broderick et al (2011 NPR page 81) notes that once installed, wellbore casings provide the primary line of defence against contamination of groundwater, and states that any loss of integrity from catastrophic failure of well casing to poor cement seals can lead to a contamination event. … The EPA indicates that the potential effects of repeated hydraulic fracturing treatments on well construction components (e.g., casing and cement) are not well understood. This is an area where additional information is needed to draw firm conclusions with regard to potential impacts, and is highlighted as an issue of high potential significance. …

For individual sites with less than 600 m separation between the fracturing zone and groundwater, the risk was judged “high”.

As discussed above, the potential exists in principle for the fugitive gases, chemical additives in the fracturing liquid or the liberated, naturally occurring substances to reach underground sources of drinking water raises concerns over the risks to human health. This could potentially occur, for example, if extended fractures are linked to aquifers via faults or preexisting manmade structures.

Research indicated that predicted and actual fracture lengths often differ (Daneshy, 2003 NPR ; Warpinski et al. 1998 NPR , quoted in EPA 2011a PR ; Damjanac et al, 2010 NPR). Due to this uncertainty in fracture location, fracturing may lead to fractures intersecting local geologic or man-made features, potentially creating subsurface pathways that allow fluids or gases to contaminate drinking water resources. Broderick et al (2011 NPR page 81) identified common subsurface pathways as the outside of the wellbore itself, incomplete or plugged wellbores from abandoned wells, fractures and other natural cracks, fissures and interconnected pore spaces.

The potential also exists for pre-existing manmade structures (e.g. abandoned oil and gas wells) in the vicinity of injection zones or wells to serve as conduits increasing the reach of contaminated groundwater. The existence of
abandoned wells is a significant issue in the US, where oil and gas extraction has proceeded for decades. The existence and location of many of these wells is not recorded.

A proportion (25% to 100%) of the water used in hydraulic fracturing is not recovered, and consequently this water is lost permanently to re-use, which differs from some other water uses in which water can be recovered and processed for re-use.

This impact on the drinking water system can lead to the need for engineering solutions for reduced aquifer levels – for example lowering of pumps or deepening of wells as required in the area of the Haynesville Shale. Further consequences of reduced water levels mentioned include:
• The potential for chemical changes to aquifer water, including altered salinity, as a result of the exposure of naturally occurring minerals to an oxygen rich environment.
• stimulated bacterial growth, causing taste and odour problems in drinking water.
• upwelling of lower quality water or other substances (e.g. methane – shallow deposits) from deeper and subsidence or destabilization of geology

Well integrity could potentially be affected by seismic activity – either activity induced by the hydraulic fracturing process, or other seismic events. … As reported by Broderick et al (2011 NPR), one study indicated a maximum induced magnitude of around 3, for that location, which was considered insufficient to cause surface structural damage but to potentially damage the wellbore itself.

Re-fracturing may be needed during the production phase. It is estimated that re-fracturing may take place up to four times from an individual well, as described in Section 2.2. USEPA (2011a PR p82) highlights concerns that the potential effects of repeated pressure treatments on well construction components (e.g., casing and cement) are not well understood. … Nevertheless, in view of the possible evidence for methane migration into potable groundwater (Osborn et al. 2011) and uncertainty around the risks associated with re-fracturing, the potential for increased risk due to re-fracturing remains an area of uncertainty, and hence has been assigned a risk ranking of “high” for installations with less than 600 m distance between fracturing zone and groundwater and “moderate” for installations with more than 600 m distance.

Prohibit venting of gases…. [Emphasis added]

[Refer also to: Restrict shale gas fracking to 600m from water supplies, says study

Shale gas fracking needs tighter regulation EU reports  

EU raises fresh concerns over environmental impact of Shale Gas, Series of major new reports increase prospect of EU level regulation to tackle Shale Gas risks 

Études de la Commission européenne sur les gaz de schiste: risques élevés pour l’environnement ]

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