Extracting onshore oil and gas
Find out about conventional and unconventional gas and how it is extracted
Conventional and unconventional oil and gas
The difference between conventional and unconventional natural oil and gas simply refers to the types of rock within which the oil and gas are found, and the method by which they are extracted. In general terms, conventional oil and gas are found in relatively permeable materials in which the oil or gas can flow relatively freely towards a production well. In contrast, unconventional oil and gas are trapped within rocks such as shale or coal, making it more difficult to extract.
Testing, investigating underground formations, and drilling processes are integral to all forms of oil and gas development. Regardless of how they are extracted or the rock they come from, unconventional oil and gas are essentially the same as their conventional counterparts.
The regulatory regimes covering conventional and unconventional oil and gas are the same. Find out more about our role and the regulation of onshore oil and gas in Wales.
Unconventional gas and its extraction
Unconventional gas reserves can take a number of forms. These are summarised as follows:
Shale gas refers to gas held in fractures and pore spaces, or gas adsorbed on organic material (the remains of organisms such as plants and animals) within shale rock. It is extracted by cracking the rock using hydraulic fracturing techniques.
Hydraulic fracturing or “fracking” is a technique that uses fluid, usually water, pumped at high pressure into the rock to create narrow fractures which provide paths for the gas to flow into the production well and then to the surface. Once the fractures have been created, small particles, usually of sand, are pumped into them to keep the fractures open. The fracking water normally contains small quantities of other non-hazardous substances to improve the efficiency of the process, for example friction reducers are used to reduce the friction forces experienced by tools. All such substances must be approved by Natural Resources Wales.
For more information go to the Department of Energy and Climate Change's guidance about shale gas and hydraulic fracturing (fracking).
Coal bed methane
Coal bed methane refers to the natural gas extracted from unmined coal seams. It is recovered through the drilling of a series of vertical or horizontal wells directly into the coal seam and then pumping water out to release the pressure in a process known as 'dewatering'. Reducing the pressure within the coal seams allows the methane to be released and flow to the production well and then to the surface.
Underground coal gasification
Underground coal gasification (UCG) is the process of partially combusting coal underground to produce a gas comprising of hydrogen, carbon monoxide and methane (known as 'syngas'). The UCG process typically involves drilling two wells into the coal, one for the injection of oxidants to enable combustion (water/air or water/oxygen mixtures) and another well, some distance away, to bring the gas to the surface.
How we use unconventional gas
Unconventional gas does not yet contribute to the energy we use in the UK. The technology is being used in a limited way to explore the quantity of available resources.
Oil and gas development phases
The exploitation of oil and gas reserves typically occurs in four key phases (not all of these phases apply to underground coal gasification). The four phases are outlined below:
- Exploration is likely to involve the drilling of a borehole to assess the rock formations and the potential quantity of resources available at a specific site
- Appraisal is likely to include an increase in the number of boreholes and a small element of oil or gas extraction, to assess the technical feasibility and costs of extracting the oil or gas at a specific site
- Production refers to full-scale commercial extraction. This is likely to require a larger number of boreholes and associated surface operations (for example gas storage and processing facilities)
- Site remediation and abandonment refers to the permanent removal of wells and infrastructure
Permissions and permits
For each of the first three stages (exploration, appraisal and production), the developer will be required to secure separate planning permissions, environmental permits and other notifications. The process will likely take operators a number of years to progress from exploration to production. Separate permissions may also be required if the developer wishes to significantly change their activities, ie drilling to a greater depth than originally permitted.
Cumulative environmental impact
The environmental impact of an oil and gas activity is considered cumulatively at each phase of a development (ie exploration, appraisal and production). Therefore, should a developer receive permissions and permits for the exploratory phase, the cumulative impact will be considered when deciding whether to issue permissions and permits for the appraisal or production phases.