Info graphic illustration. Overview of oil fracking operation. Hydraulic fracturing (also hydro fracturing, hydrofracking, fracking or fraccing), is a well-stimulation technique in which rock is fractured by a hydraulically pressurized liquid made of water, sand, and chemicals. Diagram illustration, schematic illustration. Specially engineered fluids are pumped at high pressure and rate into the reservoir interval to be treated, causing a vertical fracture to open. The wings of the fracture extend away from the well bore in opposing directions according to the natural stresses within the formation. Proppant, such as grains of sand of a particular size, is mixed with the treatment fluid to keep the fracture open when the treatment is complete.