Geology of Onshore Oil and Gas


  • Oil and natural gas was formed millions of years ago

  • Oil and gas can be trapped by rocks or within rocks

  • Oil and gas can be found anywhere in the UK

  • Shale gas has been found in basins around Northern and Central England


Shale oil and gas, unlike conventional hydrocarbons, are produced directly from the source shale rock, which acts as the source rock, reservoir and seal

All of the oil and gas we use today began as microscopic plants and animals living in the ocean millions of years ago. When they died, they sank to the bottom and over the years, layer after layer built up forming a spongy material called kerogen.

This kerogen was covered by sand, clay and other minerals which over time turned into rock called shales.

After oil and natural gas was formed, it travelled through tiny pores in the surrounding rock until it either reached the surface or was trapped under or against a layer of rock that it couldn’t move through. Very slowly, the oil and gas built up. As it did, reservoirs were formed. These trapped deposits are where we find oil and natural gas today, for example, in the North Sea and many parts of onshore Britain.

A conventional well can also be hydraulically fractured to help extraction by improving flow rates

In some cases the oil and gas became trapped within the shale rock itself and did not form traditional conventional reservoirs. This type of hydrocarbon is typically found at far greater depths than conventional oil and gas. As the shale is much less permeable (or easily penetrated by liquids or gases), it requires a lot more effort to extract the hydrocarbons from the rock.

The key outward difference is the rate at which the natural gas flows or the ‘flow rate’. Drilling into a conventional accumulation would normally result in at least some flow of oil and gas immediately. An accumulation trapped within the rock has to be stimulated in some way before it will even begin to flow.

geologyHydraulic fracturing is merely a method used to stimulate the oil or gas either to begin or continue flowing. A conventional well can also be hydraulically fractured to help extraction by improving flow rates. This does not mean it has become an unconventional well as the nature of the hydrocarbon accumulation has not changed.

In 2013, the British Geological Survey (BGS) and others prepared a comprehensive report detailing their shale gas resource estimates of the carboniferous Bowland-Hodder, which covers much of Northern and Central England. Their total central gas-in-place estimate amounted to 1,329 trillion cubic feet (tcf) of gas. With the UK using around 2.81 tcf of gas every year, if just 10% of the resource was recovered and utilised, the Bowland could meet the UK's gas demand for nearly 50 years.

Since 2017, the onshore oil and gas industry has been exploring for shale gas in Lancashire and North Nottinghamshire. Four exploratory wells were drilled across three sites: Preston New Road, Springs Road and Tinker Lane. The cores from these wells were taken to Aberdeen for analysis, where they were found to contain high-quality gas in large volumes. A visual representation of this, of one of the IGas cores in North Nottinghamshire, can be seen in the video below.

As a result of the highly encouraging results gained from these inital exploration wells, UKOOG updated its shale gas forecasts in 2019 to demonstrate what just 100 shale gas sites could do for the UK. These benefits include:

  • A CO2 saving of 69 million tonnes compared with importing the same quantity of LNG
  • A reduced import dependency of just 10%
  • £600m in local community benefits
  • £1.2bn in Business Rates
  • £33bn in supply chain and industry spending

The full revised forecasts report can be found in the downloads section of this website.



shale gas study

Andrews, I.J. (2013) The Carboniferous Bowland Shale gas study: geology and resource estimation.

British Geological Survey for Department of Energy and Climate Change: London, UK.



The shale resource in the UK is estimated to be much thicker than in the US



The total volume of potentially productive shale in central Britain was estimated using a 3D geological model generated using seismic mapping, integrated with outcrop and deep borehole information