Hydraulic fracturing or fracking creates fractures in the shale formation to release the gas.
A fracturing fluid is pumped under high pressure (ca. 100 bar) into the drilling pipe to widen fractures in the rock or to create new ones.
The fluid consists mainly of water. It is usually mixed with quartz sand and three to twelve chemicals which amount for 0.5 to 2 %. The exact compositions are kept secret by the drilling companies.