By Clive Mitchell, Industrial Minerals Specialist,
British Geological Survey
Frac sand is composed mainly of quartz grains. It is used in
the fracking process, hence the name "frac" sand. The sand is
entrained in water and is pumped under great pressure into
fractures created in the reservoir rock. The sand is packed
tightly into the fractures and props them open, hence they are
also referred to as "proppants". This forms a permeable pathway
for the oil and gas to escape from otherwise impermeable rock
formations, such as shale.
Approximately 70% of the proppants used in fracking are
naturally-occurring silica sand. Other types of proppants
include resin-coated silica sand, and ceramic proppants, which
are most commonly comprised of calcined bauxite or kaolin.
The current specification for proppants used in fracking in
the UK is the British Standard (BS) European (EN) International
Standards Organisation (ISO): 13503-2:2006 + A1:2009 Petroleum
and natural gas industries. Completion fluids and materials.
Measurement of properties of proppants used in fracking and
The standard covers the testing and specification of those
properties that are important for a good quality proppant, such
as frac sand, including particle size distribution, roundness,
sphericity and turbidity.
UK frac sand sources
Silica sand in the UK is currently produced for several
different end markets, such as glass, ceramics, foundry, water
filtration and horticulture.
In 2012, a total of 3.9m tonnes silica sand was produced in
the UK from 39 silica sand workings.
However, not all of these workings contain sand of the right
specification for fracking. The silica sand product that is the
closest equivalent to frac sand, in terms of its composition
and physical properties, is foundry sand.
Frac sand and foundry sand are both composed of high-purity
silica sand (greater than 98-99% SiO2), consisting
of well rounded, spherical sand grains with a narrow particle
size distribution. The silica sand workings in the UK that
produce foundry sand and are therefore potential sources of
frac sand and are listed as follows:
Upper Carboniferous sandstones
The Upper Carboniferous sands produced in Scotland were
deposited in a shallow marine environment and form part of a
cyclical sequence with siltstones and mudstones.
|Good quality frac sand is tested by
looking at particle size distribution, roundness,
sphericity and turbidity.
Source: Fairmount Santrol
The Passage Formation is an extensive, important resource
that occurs across the Midland Valley of Scotland. A thick
alternating sequence of fine- to coarse-grained, friable
sandstone is worked at Levenseat Quarry near Fauldhouse, West
Lothian, and Burrowine Moor and Devilla Forest quarries near
The Upper Limestone Formation occurs in North Ayrshire,
Scotland. It is characterised by a cyclical sequence of
limestone, mudstone, siltstone and sandstone. A 10 metre thick
sequence of white sandstone is worked at Hullerhill Sand
Lower Triassic sandstone
The Nottingham Castle Sandstone Formation, part of the
Sherwood Sandstone Group, occurs in Nottinghamshire and south
Yorkshire and is a thick sequence (100 metres) of pinkish-red
or buff-grey, medium- to coarse-grained, friable sandstone. The
sand was deposited by fast-flowing braided rivers in an
actively subsiding continental basin. It is currently worked at
Two Oaks Farm Quarry, 4km south of Mansfield.
Middle Jurassic sandstone
The Scalby Formation in North Yorkshire is represented by
medium- to coarse-grained sandstone with thin siltstone and
mudstone beds up to 60 metres. It is worked at Burythorpe
Quarry near Malton and is a small occurrence of sand with only
Lower Cretaceous sands and
Collectively, the Lower Cretaceous sands and sandstones of
eastern and southern England are significant sources,
accounting for approximately 40% of the silica sand used in the
The Leziate and Mintlyn members occur in west Norfolk and
form the upper part of the Sandringham Sands Formation. The
Leziate Member is up to 30 metres in thickness and consists of
pale grey, fine- to medium-grained quartz sand with subordinate
bands of silt or clay. The Mintlyn Member is up to 15 metres in
thickness and consists of glauconitic, clayey, grey and green
sands. It is thought that the sands were derived from
Carboniferous sandstones to the west and were deposited in a
near shore marine environment adjacent the north-south trending
coastline. They are currently worked at Leziate Quarry near
The Folkestone Formation, part of the Lower Greensand Group,
occurs around the circumference of the Weald basin in south
east England, from Hampshire in the west, to Kent in the east.
It consists of fine- to coarse-grained, well-sorted sands and
weakly cemented sandstones. It was deposited in a shallow
marine, near shore environment and varies in thickness from
0.5-85 metres. The formation is worked at eight quarries in
Kent and Surrey.
The Woburn Sands Formation, part of the Lower Greensand
Group, occurs in Bedfordshire and Cambridgeshire between
Leighton Buzzard and Cambridge. This formation was deposited in
a shallow marine basin and is typically 30-60 metres thick. It
mostly consists of fine- to medium-grained, yellowish quartz
sandstone or loose sand. In Leighton Buzzard, the upper part
contains a layer, up to 20 metres, of pure white sand known as
the Upper Woburn Sands or the Silver Sands. This sand is worked
at 14 quarries in Bedfordshire.
The St Agnes Formation occurs as an outlier of Palaeogene
sand, thought to be of marine origin, near St Agnes Head,
Cornwall. It is approximately 10 metres in thickness. The sand
occurs interbedded with clay with both being worked at Beacon
Pit on a small scale.
The Chelford Sand Formation, which includes the Congleton
Sand, in Cheshire, is a significant source, accounting for
approximately 40% of the silica sand used in the UK.
The Chelford Sand Formation occurs as irregular sheets of
quartz sand, which infill troughs in the underlying Triassic
Mercia Mudstone Group. The formation is up to 20 metres in
thickness and consists of white- to buff-coloured, well-sorted,
well-rounded medium-grained quartz sand.
It is thought that the sands are an aeolian deposit derived
from sandstones to the west of the Cheshire basin, such as
those in the Carboniferous Millstone Grit and the
Permo-Triassic Sherwood Sandstone groups. The sand is currently
worked at Arclid Quarry near Sandbach, Bent Farm and Eaton Hall
quarries near Congleton, and Dingle Bank Quarry near Lower
Withington. The Chelford Sand Formation is the only sand to
have been used in exploratory fracking of shale in the UK at
the Preese Hall-1 well, Lancashire, in 2011.
The Lowestoft Formation in Suffolk is a chalky till of
variable thickness that contains outwash sand and gravels. It
is worked at Blyth River Pit near Mells.
The future for UK frac sand
Given that the scale of any shale gas development in the UK
is likely to be modest in the near future, it seems likely that
the UK has the resources and the production capability to meet
the domestic demand for frac sand.
At this stage, it is difficult to predict the amount of frac
sand that would be required if the UK shale gas industry
developed at pace. The experience from production in the US is
that each well would require in the order of 2,000 to 10,000
tonnes frac sand depending on the length of the well and the
number of fracking treatments.
It is estimated that the demand for frac sand in the UK
could be as little as 10,000 tpa or as large as 380,000 tpa,
depending on the amount of fracking carried out (Mitchell,
The UK is actively looking at the potential for the
production of oil and gas from shale. As a result, many
companies in the UK extractive industry sector are looking to
see how they could meet the potential future demand for frac
sand if development goes ahead.
The key parameters for frac sand are: a high silica content
(quartz); a narrow particle size distribution; sand grains with
a high sphericity and roundness; resistance to crushing; and a
low silt and clay content. Existing sand resources that meet
these requirements do exist in the UK, with the closest
parallel being those used to produce foundry sand.
The most likely sources for the future production of frac
sand in the UK are the Upper Carboniferous sandstones in the
Midland Valley of Scotland, the Lower Cretaceous sands and
sandstones of eastern and southern England, and the Pleistocene
sands of Cheshire.
It is difficult to predict the amount of frac sand that will
be required. It depends on the number of wells that are
drilled, their length and the number of fracking treatments
carried out. The amount of frac sand required could be as
little as 10,000 tpa or as much as 380,000 tpa. Before this
point is reached, many years of exploratory drilling and
fracking are needed before the first shale hydrocarbon
production goes ahead in the UK.
You can read the full version of this article in
IM’s June issue, which contains a 30-page section
dedicated to oilfield minerals.