Hydraulic fracturing is the propagation of fractures in a rock layer caused by the presence of a pressurized fluid. Some hydraulic fractures form naturally, as in the case of veins or dikes, and are a means by which gas and petroleum from source rocks may migrate to reservoir rocks. Induced hydraulic fracturing or hydrofracking, commonly known as fracking, is a technique used to release petroleum, natural gas (including shale gas, tight gas and coal seam gas), or other substances for extraction.[a] This type of fracturing creates fractures from a wellbore drilled into reservoir rock formations.
The first use of hydraulic fracturing was in 1947, though the fracking technique which made the shale gas extraction economical was first used in 1997 in the Barnett Shale in Texas. The energy from the injection of a highly pressurized fracking fluid creates new channels in the rock which can increase the extraction rates and ultimate recovery of fossil fuels.
Proponents of fracking point to the vast amounts of formerly inaccessible hydrocarbons the process can extract. Detractors point to potential environmental impacts, including contamination of ground water, risks to air quality, the migration of gases and hydraulic fracturing chemicals to the surface, surface contamination from spills and flowback and the health effects of these. For these reasons hydraulic fracturing has come under scrutiny internationally, with some countries suspending or even banning it.