Hydraulic fracturing and horizontal drilling are two techniques that have helped to unleash the boom in natural gas from shale deposits, which are often thin layers of rock spanning a broad area. Drills bore long, horizontal holes deep underground, following the shale like a skewer piercing through the filling in a layer cake. Operators then inject huge volumes of water, chemicals, and sand under high pressure to crack the shale and release oil or gas trapped inside.
The FracFocus chemical disclosure registry, a partnership between federal and state governments and private companies, lists more than 50,000 gas and oil wells nationwide where companies have voluntarily reported using fracking. Zoom in to see gas wells (red) or oil wells (blue).