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 in the last few years.
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
flow-back 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 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 and can be individually treated by a combination 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.
Although noise predictions can be straight-forward
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 L
A90,1hr
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 L
Aeq. 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 L
Aeq‘.
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 made her report, had 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.
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