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Opponents to shale fracking (a process used to get gas out of the ground) claim that coal seam gas (CSG) extraction endangers underground aquifers, while the industry itself says it is possible to set up protective measures to ensure that coal seam and shale gas can be safely extracted.
Hydraulic fracturing or fracking, refers to the use of high-pressure fluid explosions to break apart shale or other underground rock to release and then capture natural gas. Fracking is necessary for all shale gas extraction and although the process requires large amounts of chemical accelerants and water, the actual fracking events are unlikely to effect underground water resources because shale occurs between 3 to 4 kilometres below the surface, while fresh water aquifers occur between 200 meters and 1.5 kilometres down.
Fracking is less commonly used to extract CSG and is applied to between 15 and 40 per cent of extraction projects, depending on the structure of the coal seam. However, CSG occurs between 500 metres and 1.5 kilometres below the surface and as such, the potential for fracking events to contaminate underground water is greater because of the relative proximity of these deposits to aquifers. To mitigate any threat to the water supply, fracking projects require detailed understanding of the local stratigraphy, as well as the presence of an elastic layer such as clay between aquifers and the fracture zone. In some parts of Australia, the process is further complicated because usable aquifers can occur both above and below the coal seam. In both coal seam and shale extraction, the principle point of weakness is often the well that captures the gas. A thick multilayered tube constructed from an impermeable mixture of steel and concrete, this well must ensure the gas is totally isolated to protect both the gas and the surrounding environment from contamination. Jeanne-Vida Douglas