Fracking drill rig. Fracking or hydraulic fracturing is a drilling technique used to extract gas from shale deposits. A mixture of sand, chemicals and water is pumped under high pressure from the surface to underground horizontal wells. The pressure forms fissures (fractures) in the shale. The sand keeps the fissures open, allowing gas to flow into the well and rise to the surface. The main drill rig is used to drill a well prior to the hydraulic fracturing process. This drill rig is in the Bakken oil field in Stark County, western North Dakota. Photographed in 2012.