Fracking, or “Hydraulic Fracturing”, is a technique used to crack rock underground, usually for the purpose of extracting oil or gas. It involves injecting a fluid down a well under massive pressure, in order to force open cracks in the rock. Conventional hydraulic fracturing has been used since the 1950s to create small cracks, just around well-bores, to speed the flow of oil or gas into the well.
More recently “massive slickwater hydraulic fracturing” has been developed for the purpose of extracting gas from more much impermeable rock formations, such as shale. Hydraulic fracturing of a typical shale gas or oil well requires the use of around 5 to 7 million gallons of slickwater (a mixture of water, sand and chemicals) to fracture the rock in up 40 stages along a horizontal distance of a mile or more.