The BGS has an important, impartial role to play in terms of better understanding the environmental risks and impacts that might arise from shale gas industry operations. 

Shale gas is extracted from the impermeable shale rock through a process called hydraulic fracturing (also known as hydrofracking or fracking).

What are the risks associated with extracting shale gas?

Groundwater contamination

On average, around 20 million litres of water are needed during the life cycle of a well. The waste water (‘flow back’) needs to be treated properly and kept isolated from the surrounding aquifers. Other potential pathways for contamination of groundwater include poor well design or construction and the migration of contaminants along natural pathways into overlying aquifers.

Climate

Concerns include the emissions of carbon dioxide (CO₂), methane (CH₄) and other greenhouse gasses when the shale gas play is exploited. This also includes ‘fugitive’ emissions, which are composed of CH₄ that flows to the surface after fracking and can affect the atmosphere.

Air quality

There can be a negative effect on local air quality and noise pollution caused by the many truck movements during the life cycle of a shale gas well.

Induced tremors

Induced, low-magnitude tremors, such as those experienced in Lancashire in 2011, can be a consequence of the process of hydraulic fracturing.

How does BGS research help?

The BGS is the coordinator for the pan-European Horizon2020 (SECURe) project, which gathers scientific evidence relating to monitoring the environment and mitigating risk in order to guide subsurface geoenergy development.

We are also a major contributor of the NERC-funded Unconventional Hydrocarbons in the UK Energy System project. This aims to improve the understanding of unconventional hydrocarbon development in the UK, taking a holistic, interdisciplinary approach to identifying the potential environmental, social and economic impacts.

Our research is currently focused in the following main areas.

Environmental impacts and monitoring

Basin analysis

Further reading

Shale gas deposits are regarded as commercially exploitable when the organic matter contained within the shale is of the right type — of marine origin — the net shale thickness exceeds 25 m and when it is found at a depth of more than 1500 m.

Where is shale gas found in the UK?

In the UK, four areas have been identified as potentially viable for the commercial extraction of shale gas:

• the Carboniferous Bowland–Hodder area in north-west England (Lancashire and the Midlands)
• the Carboniferous Midland Valley in Scotland
• the Jurassic Weald Basin in south England
• the Wessex area in south England

Between 2013 and 2016, the BGS was commissioned by the Department of Energy and Climate Change (DECC; now the Department for Business, Energy and Industrial Strategy (BEIS)) to provide for these areas.

How much shale gas do we have in the UK?

Because there is no established shale gas industry in the UK, there is no production data available, which makes estimating the size of the resource extremely difficult. Therefore, in the DECC-commissioned reports, we took a bottom-up estimation approach whereby we used available rock materials from drill cores stored in the National Geological Repository.

Many of the drill cores used for the estimates we developed were not drilled for the purpose of a shale gas resource estimate, resulting in a wide total range of volume estimates.

Shale gas exploration in the UK

The main rock formation of interest for shale gas exploration in the UK is called the , which occurs across a large area of central Britain. These shales were deposited in marine basins during the Visean and Namurian stages of the Carboniferous period (between 347 and 318 million years ago) when the UK was located around the equator. Carboniferous marine shales can reach thicknesses of up to 5000 m and contain enough organic matter (1–3 per cent, but locally over 10 per cent) to generate hydrocarbons.

The Bowland Shale Formation is not restricted to the onshore environment; the basins extend offshore beneath the Southern North Sea and the East Irish Sea.

Andrews (2013) estimated a total gas-in-place estimate for the Bowland Shale Formation and Hodder Mudstone Formation between 822 and 2281 trillion cubic feet (tcf). As a comparison, the total gas consumption in 2018 in the UK was 2.98 tcf. Since then, other estimates have suggested the total gas-in-place volume could be considerably less (around 140 tcf; Whitelaw et al., 2019).

Scotland

Middle Carboniferous, organic-rich shales are also found in the subsurface Midland Valley of Scotland (Girvan to Greenock in the west; Dunbar to Stonehaven in the east) as part of the and the . There, the shales reach a thickness of about 3000 m, contain 2–6 percent organic carbon and are considered as a potential target for shale gas exploration. Monaghan (2014) suggested a total of 49.4–134.6 tcf gas-in-place for the Midland Valley of Scotland.

Wales

In Wales, a paucity of publicly available data currently prevents the calculation of reliable resource estimates. Potential unconventional gas resources in Wales are most likely to be found in association with coal seams or shales. In North Wales, middle Carboniferous shales include the Bowland Shale Formation, thought to be contiguous with strata in north England. Early Carboniferous shales are found in South Wales as part of the Avon Group. However, more research is needed to establish this group’s prospectivity for shale gas.

Much of Wales and central England are underlain by older Palaeozoic rocks, which may be prospective for shale gas. These successions have not been investigated extensively and no evaluation has been conducted by either the BGS or exploration companies.

References

How is shale gas extracted?

Hydraulic fracturing

Shale gas or unconventional gas is extracted from the impermeable shale through a process called hydraulic fracturing (also known as hydrofracking or fracking). A crude form of this technique, involving nitroglycerine, was used for the first time around the 1860s to explore for oil and gas.

During hydraulic fracturing, a mixture of water, chemicals and sand is pumped down a borehole at high pressure. The water pressure opens up cracks in the rock and the sand grains lodge into the spaces to keep them open, allowing the released gas to flow out of the rocks and travel back up the borehole.

The hydraulic fracturing technique is not new; it has been used for over 50 years to improve recovery of conventional oil and gas. 

The moratorium on hydraulic fracturing in the UK (2019)

Shale gas extraction is not presently allowed to proceed in the UK.

In November 2019, the UK Government announced a moratorium on hydraulic fracturing in shale in England. This decision was taken on the basis of a by the Oil & Gas Authority.

In January 2015, the Scottish Government put a moratorium on unconventional oil and gas development in Scotland in place, following the publication of a of an independent, expert, scientific panel.

Since 1 October 2018, licensing powers in Wales have been , which has taken the decision not to support applications for hydraulic fracturing in Wales or fracking consents.

Shale is a fine-grained, sedimentary rock formed as a result of the compaction of clay, silt, mud and organic matter over time and is usually considered equivalent to mudstone. Shales were deposited in ancient seas, river deltas, lakes and lagoons and are one of the most abundant sedimentary rock types, found at both the Earth’s surface and deep underground.

Shale gas is natural gas found in shale deposits, where it is trapped in microscopic or submicroscopic pores. This natural gas is a mixture of naturally occurring hydrocarbon gases produced from the decomposition of organic matter (plant and animal remains). Typically, shale gas consists of 70 to 90 per cent methane (CH₄), the main hydrocarbon target for exploration companies. This is the gas used for generating electricity and for domestic heating and cooking.

How is shale gas different from conventional gas?

Hydrocarbons, such as oil and gas, are produced by the transformation of organic matter (plants; animals; algae, etc.) as a result of increased temperature and pressure. This occurs when a potential source rock, rich in organic matter, is buried and heated at considerable depth (usually thousands of metres below the surface).

The hydrocarbons migrate upwards where they may find their way into porous reservoir rocks, typically a sandstone or a porous limestone. If the reservoir rock is overlain by an impermeable cap or seal rock, such as one rich in clay, the hydrocarbons become trapped in the reservoir rock. Conventional hydrocarbons can be extracted by drilling directly into the reservoir rock.

Shale gas is a form of unconventional hydrocarbons because the rock it is extracted from acts as the source, reservoir and cap rock. The gas is produced, stored and sealed within impermeable shale and can be released only after the shale is drilled and artificially fractured during an extraction process.  

Our role and research

The BGS’s role is to provide independent, expert and impartial geological and environmental advice to industry, government and the public, regarding shale gas in the UK.

We research all aspects relevant to shale gas in the UK and internationally. Our research spans from resource estimation to the environmental impacts associated with shale gas extraction, such as investigating groundwater contamination and microseismicity.

Whilst shale gas extraction is not presently permitted in the UK, we continue to conduct research related to shale gas. We actively publish reports and academic papers on a variety of topics related to shale gas.