You can read the full case study of this project here.
The extraction of shale gas using hydraulic fracturing techniques, also known as 'unconventional' gas extraction but more commonly as 'fracking', has attracted a great deal of public attention. Essentially it is similar to 'conventional' onshore gas extraction whereby seams of methane gas are 'mined' using a combination of drilling and pumping to get the methane gas to the surface for onward transmission, storage and use.
The big difference between conventional and unconventional extraction is the location of the gas deposits and the additional measures required to extract it. Conventional gas is trapped in pockets in coal seams which lie about 500 metres below the surface. Coal is permeable and the gas can be recovered more easily. Shale gas, however, lies much deeper however, and is trapped within the shale or mudstone layer which lies between 2,500 and 5,000 metres below the surface. In order to extract the gas, the shale, or mudstone, has to be fractured by injecting the surrounding area with a combination of water, chemicals and minerals at very higher pressure through perforations in the well bore before it is possible to recover it to the surface.
The earliest fracking wells were drilled purely vertically but, since the 1990's, once the vertical drill has reached a certain depth it turns to extend horizontally for significant distances to maximise extraction from a single well-head at the surface. The drilled bore is lined with a steel casing to transmit the fracturing fluid into the shale and to retrieve the resulting shale gas mixture to the surface. It is perforated by detonations along its horizontal length to let the fracturing fluid out and return the flowback mixture to the surface as necessary and re-sealed before the operations recommences at the next point along the horizontal bore.
The noise from shale gas extraction comes purely from the equipment and processes located on the surface and consists of that from the following operations:
The equipment required for the short-term construction and restoration processes is standard construction plant (excavators, loaders, dump trucks, cement trucks, vibratory or non-vibratory rollers etc). For the longer term drilling operations, the equipment required consists of the main drilling rig which has a hydraulically or electrically powered top drive [Image 1], which moves up and down the drilling rig as each section of the drill string is driven into the ground. Aside from the drive itself, noise comes from the generators or compressors used to power it together with mud pumps and shale shakers and their associated power requirements. The fracturing process uses high pressure fracturing pumps, again with their associated power requirements.
The pumps and other equipment are generally spread around the rig itself [Image 2] and can be individually treated by acombination of enclosure, lagging and anti-vibration mounts. Screening of larger areas can be provided, for critical directions, by strategic placing of ISO containers which make for an easily available, if somewhat rudimentary, modular screening system. In extreme circumstances screening of the entire drilling rig may be necessary [Image 3].
Although noise predictions can be straightforward with knowledge about the planned equipment distribution on the site, sound power level data may be more difficult to come by for more specialised equipment and operations due to the current lack of horizontally bored fracking sites in the UK. It is of particular note that the horizontal drilling proposed for many intended sites, once the shale depth has been reached, can be significantly higher than for vertical drilling.
Once up to date information has been obtained on the intended equipment, there is nothing unconventional about assessing the noise and noise sources. What can, however, be of particular concern is the fact that drilling / extraction sites are often located in rural areas where noise from other (background) sources are low. The drilling operation, in particular, needs to be continuous day and night and may extend for months at a time. Siting of the drilling rig and all surface works is therefore crucial to minimise the effects on the nearest noise sensitive properties which should be at distances sufficient to prevent noise disturbance to residents at night. The fracking operation itself is not usually carried out at night but is likely to be noisier.
Shale gas extraction is considered under the minerals planning regime and planning applications for the surface works are consequently judged by the relevant minerals planning authority (MPA). Consent for the underground processes are determined by the government Department for Energy and Climate Change (DECC) and the Environment Agency, and are not considered by the MPA. Planning for the surface works therefore needs to have specific regard to the Planning Practice Guidance on Minerals (PPG-M) [i] which has a specific section on planning for hydro-carbon extraction but no separate noise advice beyond that contained in the main 'noise emissions' section.
The noise emissions section defines separate limits on noise for day-time (0700-1900), evening (1900-2200) and night-time (2200-0700) periods. The day-time limit is set at 10 dB above the LA90,1hr background noise level although how this background level is set, bearing in mind typical variation in background noise level, is not defined. Some variation is allowed to avoid 'imposing unreasonable burdens on the mineral operator' but the limit should be as close to this a possible and should not exceed 55 dB LAeq. The evening limit is similar but there is no variation allowed for a perceived 'unreasonable burden'. At night the limit should be set 'to reduce to a minimum any adverse impacts, without imposing unreasonable burdens on the mineral operator, subject to a maximum of 42 dB LAeq'. This last item can be particularly challenging in the case of shale gas drilling if inappropriate sites are selected for development, due to the requirement for the 24 hour drilling operation. The lack of a specified lower limiting value is not helpful although it could be expected to be informed by good sense and what would be required to provide a good standard of night-time noise environment in the specific circumstances under consideration. It is almost inevitable, however, that there will be at least some debate as to what constitutes an 'un-reasonable burden' in terms of additional mitigation beyond what would normally be considered practicable for the drilling operation.
We recently took part in the Public Inquiry which was held in February and early March 2016 to consider applications for two shale gas exploration sites in Lancashire, acting on behalf of Lancashire County Council; the relevant minerals planning authority. Although it's not particularly relevant here, something which many people are unaware of is that the planning authority can only consider the application on its specific planning merits such as appearance of the equipment in the landscape, noise, traffic, effects on cultural heritage etc.. Hence the Inquiry was also only able to cover these issues; what goes on under the ground is subject to rules laid down by the Environment Agency and the Department of Energy and Climate Change and are not open to debate as part of the planning process.
A good deal of the debate on noise came down to consideration of what constitutes the lowest observed adverse effect level, the significant observe adverse effect level, as referred to in the Noise Policy Statement for England [ii], and indeed the unacceptable adverse effect level which was introduced as additional criterion by Planning Practice Guidance on Noise (PPG-N) [iii] and the relevance of these to the night-time limit. This was, in turn, informed by discussion of sleep disturbance effects and the relevance of the various WHO publications on this issue [iv,v,vi]. The crux of the sleep disturbance discussions appears to be not the level of disturbance to a sleeping person from noise from transportation, on which the majority of sleep effects research is based, but the effect on individuals who may be awoken by other sources, and their ability to be able to return to sleep in the face of an audible noise which they may have significant objection to. The Inspector in this case, and the Secretary of State to whom she will make her report, will need to consider this carefully.
Despite the clear remit for shale gas extraction judged according to Planning Practice Guidance on Minerals Extraction, a distinction has been made by some between the length of time a conventional (surface) minerals site could be expected to operate for and the time when the noisy operations of drilling and fracturing will occur on a shale gas extraction site. The reduced timescale of the occurrence of noisy activities gives rise to a further debate as to whether it is appropriate to use noise assessment guidance aimed at long-term mineral extraction for assessment of the drilling and fracturing process required for shall gas extraction or whether it would be more appropriate to use noise guidance such as BS5228 [vii] which is aimed at construction work, which tends to be shorter term in duration.
There is clearly a certain amount of overlap between the guidance with BS5228 referring to 'open sites' which are defined in the standard as a 'site where there is significant outdoor excavation, levelling or deposition of material'. Examples are provided of 'quarries, mineral extraction sites, an opencast coal site or other site where an operator is involved in the outdoor winning or working of minerals' with an additional note that 'waste disposal sites and long term construction projects can, in most cases, be treated as open sites'. This advice has the clear potential to introduce a certain amount of ambiguity into whether even a conventional (surface) minerals site should be assessed using the guidance in BS5228 or that in PPG-M but since the potential significance criteria presented at Appendix E of BS5228 are only presented as examples this may be irrelevant.
BS4142 [viii], similarly, has the potential to provide additional useful guidance with shale gas drilling falling under its general umbrella of 'industrial and commercial sound' but the situation is much more clear cut here with sources 'falling within the scopes of other standards or guidance' specifically being scoped out of its remit.
There is clearly a requirement for detailed noise assessments to be carried out on sites identified for shale gas exploration and extraction. This is likely to increase following the recent planning consent by North Yorkshire County Council and due to the unequivocal support by the current UK Government. Careful attention needs to be paid to the noise limits to be applied, particularly at night due to the necessity for continuous 24 hour drilling for long periods but also during the day when background noise levels can be low in rural areas and when the noisier fracking operations are carried out.
by Andy McKenzie
[i] Online Planning Practice Guidance on Minerals, UK Government Department for Communities and Local Government, Last Updated October 2014
[ii] Noise Policy Statement for England, UK Government Department for Environment Food and Rural Affairs, March 2010
[iii] Planning Practice Guidance on Noise, UK Government Department for Communities and Local Government, Last Updated December 2014
[iv] Night Noise Guidelines for Europe, World Health Organization, 2009
[v] Night Noise Guidelines for Europe, World Health Organization, 2007
[vi] Guidelines for Community Noise, World Health Organization, 1999
[vii] BS5228, Code of practice for noise and vibration control on construction and open sites – Part 1: Noise, British Standards Institution, 2014
[viii] BS4142, Methods for rating and assessing industrial and commercial sound, British Standards Institution, 2014.
01 Apr 2016Back to news