What is Unconventional Gas (aka Fracking)
The term ‘Unconventional Gas’ refers to natural gas, which is trapped in deep underground rocks that are hard to reach, such as shale rock or coal beds. Technological advances mean it could be economically viable to extract methane from these sources.
Unconventional gas exploration includes:
- Shale Gas
- Coal Bed Methane
- Underground Coal Gasification
Shale Gas & Fracking
Shale gas is natural methane gas that is trapped in impermeable shale rock. The most common way to extract shale gas is by cracking the rock using hydraulic fracturing. This is often referred to as ‘fracking’.
Fracturing fluid, which is a combination of millions of gallons of water, sand and potentially toxic chemicals, is pumped at high pressure into the rock to create narrow fractures that allow the gas to flow into the well bore and to the surface.
The potentially toxic cocktail of chemicals used in the process have the capability to contaminate the land and water supply. Once the fractures have been
created, small particles, usually sand, are pumped into the fractures to keep them open when the fluid is taken back up the well.
Coal Bed Methane
Coal Bed Methane, sometimes called Coal Seam Gas is methane gas trapped in coal seams underground.
To extract the gas, the basic method is to drill into the coal seam. Then, if the seam is permeable enough, pumping water out of the seam will be enough to start gas flowing from the well. If not, it is often also necessary to frack the seam to extract the gas.
Methane gas within deep coal seams is held on the coal surface (adsorbed) by pressure of surrounding water and rock. If pressure is released, gas can flow through rock fractures, and be extracted from boreholes.
Techniques to release CBM gas include:
- Dewatering (pumping large amounts of water out of the coal seam over several months)
- Nitrogen gas fracturing/fracking by injection of nitrogen under pressure into the coal seams
- Higher pressure hydraulic fracturing / fracking
- A series of techniques may be necessary to reactivate flow, as the initial gas pressure decreases
Underground Coal Gasification
Underground coal gasification and extraction involves the partial burning of coal underground to produce a mixture of gases.
This involves drilling boreholes into a coal seam, injecting water/oxygen mixtures down one pipe, igniting and partially combusting the coal and extracting the gasification products (known as syngas) through another pipe.