“Fracking, in natural gas and petroleum production, injection of a fluid at high pressure into an underground rock formation in order to open fissures and allow trapped gas or crude oil to flow through a pipe to a wellhead at the surface.
“Employed in combination with improved techniques for drilling horizontally through selected rock layers, fracking has opened up vast natural gas deposits in the United States and elsewhere.
“At the same time, the rapid rise of the practice, frequently in regions with no history of intensive oil and gas drilling, has raised concerns over its economic and environmental consequences.”
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