Hydraulic fracturing is the process of injecting water, sand, and certain chemicals underground at high pressures to crack open rocks that hold oil and gas. It is called fracking for short. Petroleum producers use fracking on more than 90 percent of oil and gas wells in the United States. Fracking occurs after a well has been drilled downwards and, sometimes, sideways. Such wells may be 4 miles (6.4 kilometers) deep, and more than a mile or several kilometers long. Hydraulic fracturing allows oil and gas to flow to the surface from wells that could not otherwise be profitably mined.
The fluid used in a hydraulic fracture is typically water that contains sand or other small solids called proppants. These solid particles “prop” open the cracks that form in the rocks when the mixture is pumped underground. The fracking fluid also contains such chemicals as benzene, methanol, and hydrochloric acid. The added chemicals perform a variety of functions. For example, they help kill microbes that might grow in the well. They dissolve rocks underground to help oil or gas flow more easily. They also reduce rust inside the well tubing.
Fracking is often done in stages. Large fracking projects involving sideways drilling can require up to 5 million gallons (19 million liters) of water, over 2 million pounds (1 million kilograms) of proppant, and hundreds of pounds or kilograms of added chemicals. The fracking fluid is injected underground at extremely high pressures. Once a well is fractured, some of the fracking liquid flows from underground back to the surface. This produced water is often toxic. Petroleum producers must capture and dispose of it to avoid contaminating the environment. Some fracked wells create millions of gallons or liters of produced water.
Some people oppose fracking due to concerns about potential environmental contamination by fracking fluid, produced water, or petroleum escaping fractured deposits. Hydraulic fracturing can also contribute to seismic activity (underground shaking), leading to fears of earthquake damage. In the United States, some state and local governments have passed laws banning the practice. Supporters of fracking argue that the method yields cheap natural gas, which burns much more cleanly than the coal used in many U.S. power plants. They also argue that fracking in the United States could help free the country from reliance on foreign imports of oil and gas.
See also Petroleum (Stimulating production) .
