Barnaby Harding, principal hydrogeologist at environmental consultancy ESI, explores the real science behind fracking, the risks to water resources it presents, and how these can best be managed to safeguard public health.
It is clear that there remain some very major concerns, certainly amongst the public and environmental groups, around the fracking process and its implications for both the water environment and public safety.
With the UK Government currently in the process of awarding energy companies new licences to explore for both conventional and unconventional oil and gas (including via hydraulic fracking) – a move which has been met with a great degree of opposition from environmental campaigners – and with the government’s support for fracking, it appears that the fracking debate is very much back on the front burner.
“Historically, the exploration and production of natural gas and oil has been primarily focused on readily available conventional resources that are relatively easy to develop. However, with growing energy needs, political concerns over energy security, and mounting pressures on current resources, the proposition of finding alternative extraction methods has become increasingly attractive. Whilst considered to be controversial by some, following on from its commercial success in the United States, the exploitation of oil and gas through fracking is seen as having the potential to be a strong component of the energy mix both here in the UK and worldwide.
Fracking – or hydraulic fracturing – emerged in the US in the 1940s and is the process of drilling down into the earth before a high-pressure fluid consisting of water, chemicals and proppant (most commonly sand) is injected into underground rock formations. The proppant holds open the newly formed millimetre-sized fractures (or cracks) upon release of the injection pressure, facilitating the flow to the surface of previously-trapped oil and gas. Subsequent technological developments, including horizontal and directional drilling, have opened up previously inaccessible resource.
The story so far
It is estimated that over 2.5 million fracture treatments (‘fracks’) have taken place across the globe to date, with an estimated 25,000 – 30,000 new wells drilled and hydraulically fractured in the US between 2011 and 2014 alone. In the UK, forms of hydraulic fracturing for conventional oil and gas extraction have been performed off-shore many thousands of times in the North Sea since the late 1970s, as well as on-shore sites since the early 1980s – although this did not become subject to real public attention until the mid ‘noughties’ when its use was proposed for onshore shale gas wells.
The fracking process itself is initiated at the start of a well’s life with fracks repeated several times thereafter. An individual frack can typically last up to two hours with a number taking place over several weeks, during which time selected parameters are continually monitored. Once fracking is completed a well can produce gas for between 30-50 years without the need for further treatments.
The extensive use of fracking in the US – where it has truly revolutionised the energy industry – has unsurprisingly prompted a number of environmental concerns. These include not only the risk of contamination to the surrounding land and groundwater as a result of accidental chemical leaks, but also its direct impact on the water resources, particularly in areas with low water availability, due to the significant amounts of water necessary to perform the process.
Assessing the risks
Over 90% of the fluid injected into a hydraulically-fractured well is water, with each fracking operation requiring between 10,000 and 30,000m3 (10,000 to 30,000 tonnes or 2 to 6 million gallons). If not accessible from the site via extraction, the water must be transported to the location, with operators choosing to use either a nearby river, lake or coastal source, or groundwater, sometimes in addition to the use of trucks to transport water to the site. Whilst in isolation this is not a large volume, in the context of most surface or groundwater resources the cumulative impacts of large numbers of wells, if unregulated, could result in local water stress. The effects would be naturally highest in areas of high fracturing water use and existing low water availability. Nationally, however, the experience in the US and current forecasts in the UK suggest that water use for unconventional oil and gas would not exceed 1% of the total non-potable water use. Such issues relating to water supply will need to be dealt with very much on a local level and in collaboration with relevant bodies, including the EA, which may restrict the industry’s operations in such areas.
A further concern raised by fracking components is groundwater contamination. In comparison to conventional methods of extracting oil and gas, the fracking process requires the high pressure introduction of water and chemicals hundreds or thousands of metres underground – chemicals used to date typically include polyacrylamide, hydrochloric acid, and biocides, amongst others. These and other chemicals are stored at surface and introduced into the ground as part of the fracking process. Once the fracking procedure is complete, fluids along with the gas released from the formation, will flow back to the surface. Both stored and introduced chemicals have the potential to contaminate the surface and /or groundwater via various pathways if not properly managed.
EC study highlights
key areas of concern
A study published by the European Commission in 2012, which was co-authored by ESI, highlighted that, if not managed adequately, there would be a high risk of surface and groundwater contamination at various stages of the process, with poorly designed well construction – and the subsequent failure of the cement or casing surrounding the wellbore enabling the leakage of contaminating fluids – a key factor.
As well as the introduced fluids and the released gas, on some fracking sites, drilling and flow-back fluid can contain low levels of naturally occurring radioactive minerals (NORM) such as radium, similar to those found in granite rock. These occur naturally at depth but can be brought to the surface entrained with the fluids in the well.
Fortunately, the whole process of fracking in the UK, including the composition of fracking fluid and the construction of wells, is tightly regulated and associated risks can therefore be mitigated and managed. The latest round of Petroleum Exploration and Development Licensing was preceded by a Strategic Environmental Assessment which looked at the potential environmental impacts of conventional and unconventional oil and gas development. In order to secure a Petroleum Exploration and Development Licence (PEDL), operators needed to demonstrate their awareness of the environmental issues and their proposals for mitigating impact through the development of an Environmental Awareness Statement. Even if an operator is lucky enough to secure a PEDL, before any operations can commence, operators must go through an in-depth planning process which requires a comprehensive hydrogeological and hydrological assessment, including investigations into potential contaminants in surface or groundwater, with further long-term monitoring of conditions scheduled throughout the site’s lifetime.
What is expected of operators?
Operators need to outline clearly their drilling, fracturing design, and operational practices, as well as any environmental, safety and health risks and how they are to be addressed, to provide the public with a clear understanding of the challenges, risk and benefits. Operators will need to inform of the nature of chemicals they propose using in the hydraulic fracturing process, including carrier fluids, at pre-application and planning application stages. This will ensure that the proposed borehole construction, casing and completion can be assessed as adequate. The regulation and best practice guidance published by DECC specifically states that there must be no direct discharge of pollutants into groundwater and that the indirect entry of non-hazardous pollutants must be limited so as not to cause pollution. Applications will only be granted if the proposals are deemed to not pose a threat to the environment and the aquifers and watercourses that provide potable water supply. In particularly sensitive areas DECC has gone further and has limited what fracking can take place.
The Onshore Hydraulic Fracturing (Protected Areas) Regulations 2015, which were approved by MPs in December 2015, describe such sensitive areas (which include National Parks, Areas of Outstanding National Beauty, the Broads and World Heritage Sites) and ensure that the process of hydraulic fracturing can only take place below 1200 metres in these areas. Ministers have also committed to ensure that fracking cannot be conducted from wells that are drilled in the surface of National Parks and other protected areas.
Once a site has been approved and viability of operations assessed, there is also a requirement for fracking site operators to dispose of all flowback fluid safely and efficiently to avoid any environmental contamination. As the fluid is categorised as mining waste, an environmental permit is required and a waste management plan must be agreed with the relevant environmental regulator. Disposal methods may include on-site treatment with re-use of water and disposal of remaining liquids and solids; off-site removal to a suitable licensed waste treatment and disposal facility; or via a special sewer with permission of the relevant wastewater utility.
Approval for the use of certain chemicals should also be considered on an individual case basis. Permission to use a chemical at one site may not mean it is automatically allowed elsewhere as the site conditions and environmental risks may vary.
The overall picture
Whilst controversies surrounding hydraulic fracking will undoubtedly continue to propagate as the process evolves and more wells are put forward to be fracked, evidence suggests that the core issues relating to water resources and contamination are predominantly down to poor practice rather than any inherent risks associated with the technique itself. Public Health England’s Dr John Harrison himself outlined that potential risks to public health from exposure to emissions associated with the shale gas extraction process are considered low if operations are properly run and regulatedi. It is my opinion also that, with the right regulatory regime and effective and specialist support in the exploration of unconventional oil and gas extraction, the risks to the environment and public safety can be significantly minimised.”