Although there is widespread potential for
unconventional gas exploration in the
UK, according to the British Geological Survey (BGS) there
are a number of steps that need to be taken first to protect
BGS geologist Rachel Bell told delegates at the
Extractive Industry Geology (EIG) Conference 2014 last
month that before further development of shale gas occurs,
groundwater resource demand and potential pollutant pathways
with regards to exploration need to be considered.
|Shale plays in the UK extend to around 30%
of England and Wales
shale gas will use and mobilise extraction of chemicals
that are potential pollutants, so these risks will need to be
fully assessed and managed effectively from evaluation stage to
post abandonment as well, Bell said.
Shale plays in the UK extend to around 30% of England and
Wales, with the USGS identifying two specific areas with
potential for shale gas development.
Shale gas development to date has been limited to the north
Cuadrilla Resources, but proposals have already been put
forward for further developments in South Wales, North
Yorkshires, West Sussex, Kent and Northern Ireland, which have
led to concerns regarding additional water resource
In the UK, groundwater provides around 30% of the water
supply, with some areas in the south east and East Anglia
sourcing up to 80% of their public water supply from
According to Bell, in order to carry out shale gas
exploration in the UK, a lot of water would need to be produced
in a small amount of time.
Existing data from the US estimate that a maximum of
4,000m3 water is needed to drill, and around 23,000
m3 water is need for fracking, though figures vary
depending on geology, drilling complexity and well length.
However, based on the assumption that 100 wells are drilled
and fracked in one year, annual water usage would not be
unreasonably high the challenge lies rather with
managing overlap between exploration and areas with limited
The water that shale gas will potentially use is
actually a very small percentage 0.02% for shale gas
extractions, Bell said.
The issue is more because there are challenges in
areas where there are very limited water resources, in areas of
the south east and also large chunks of the midlands as there
isnt much resource available, she added.
Aside from additional water pressure, contamination of
groundwater is also a concern.
One potential contamination source to groundwater from shale
gas exploration is the
fracturing (fracking) fluid used to prop open the
The fluid contains additives such as sand and acids, although
these make up only around 0.1-0.2% of the total volume, and
disposal of any of these chemicals requires prime
|Principle acquifers in England and Wales
Another potential contaminant is the flowback water used in
fracking as 20-80% of water used in the process is returned
to the surface.
That can contain things like heavy metals and also
naturally occurring radioactive materials so its really
important that we look into the safe handling, storage and
disposal of this kind of water, Bell cautioned.
She added that the last source of potential contamination is
the shale gas itself, which is composed of methane and other
According to Bell, the presence of higher hydrocarbons
enables a distinction to be made between thermogenic methane,
formed in deep shales, from biogenic methane, formed in much
shallower environments such as marshes, bogs and landfills.
One study, which was carried out in the US, used the
distinction between thermogenic and biogenic methane to
determine methane concentration based on distance to the
nearest gas well and found much higher methane concentrations
close to the active extraction sites.
However, Bell noted that monitoring was important before any
activity even begins: Because they didnt know how
much methane was there before they started extracting the
shale, they werent sure about the migration pathways, and
how exactly it was getting into the groundwater.
Groundwater contamination pathways
With contaminant sources such as chemicals and oils,
produced water and shale gas, Bell said it was important to
note how contaminants can get into groundwater and the likely
We can then examine where this is going to be a
problem in the UK, Bell added.
|Shale clay units in England and Wales
Pathways can include factors such as surface spills,
well integrity failure such as leaks or poor
construction the fracking process itself and natural
To pinpoint problem areas in the UK, the BGS has carried out
work on a national 3D geological model, which has identified
areas where aquifers overlie source rocks as a potential
Now that we know where shale gas is overlying
principle aquifers, were going out and collecting
baseline methane samples in public water drinking supplies and
in any private drinking supplies near shale gas rock,
All the data collected so far has been collated and the BGS
plans to extend its research into northern areas, eventually
looking to publish all the data on the BGS website.
The results collected so far have shown that biogenic
methane is present in all UK aquifers but at low levels.
In spite of this, methane isnt actually a
contaminant of concern in terms of human health it has
no impact really but it could be an early warning
indicator of other contaminants that might come through from
shale gas operations, Bell added.
The future of UK shale
According to Bell, though the UK has significant shale gas
potential, this is not yet a proven resource.
Additionally, before any exploration takes place, local
needs must first be considered, and relevant regulation and
monitoring be put into place.
We do have an existing extraction licencing system
which is well used to dealing with competing water
demands, Bell said.
We also have groundwater contamination regulations
which are well developed, and baseline and groundwater
monitoring is essential and needs to be implemented throughout
the whole lifecycle of the shale gas process, she
Frac sand sufficient
In order to sufficiently exploit the UKs shale
resource, however, a secure proppant supply is also needed.
According to BGS industrial mineral specialist, Clive
Mitchell, the UK is nearly self-sufficient in silica sand, with
40 sand quarries producing 4m tonnes of silica sand.
While all frac sand is made from silica sand, not all silica sand is suitable for use as
frac sand, with some grades far more efficient than
According to Mitchell, the closest equivalent to the frac
sand suggested by the British Standards for proppants used in
Europe is foundry sand. This has high-quartz content and
features round grains, with good sphericity and a similar size
range to frac sand grains (100-500 microns).
There are 20 quarries producing foundry sand in the
UK. The main sources are the Sandringham Sand Formation
(Norfolk), Woburn Sand Formation (Bedfordshire), Folkestone
Formation (Surrey & Kent), Chelford & Congleton Sands
(Cheshire) and Wind Blown sand (North Lincolnshire),
There is of course also potential for ceramic
proppants composed of sintered bauxite or kaolin
within Europe, however these are more expensive to
produce, and until exploration gets underway it will be
difficult to tell if the shale within Europe requires them.