Natural-gas processing is a range of industrial processes designed to purify raw natural gas by removing impurities, contaminants and higher molecular mass hydrocarbons to produce what is known as pipeline quality dry natural gas. Natural gas has to be processed in order to prepare it for final use and ensure that elimination of contaminants. Natural-gas processing starts underground or at the well-head. If the gas is being produced, for instance, alongside crude oil, the separation process already transpires as the fluid flows through the reservoir rocks until it reaches the well tubing. The process beginning at the wellhead extracts the composition of natural gas according to the type, depth, and location of the underground deposit and the geology of the area. Oil and natural gas are often found together in the same reservoir. The natural gas produced from oil wells is generally classified as associated-dissolved gas meaning that the gas had been associated with or dissolved in crude oil. Natural gas production not associated with crude oil is classified as “non-associated.” In 2009, 89 percent of U.S. wellhead production of natural gas was non-associated. Non-associated gas that produce a dry gas in terms of condensate and water are sent directly to a pipeline or gas plant without undergoing any separation process. Natural-gas processing plants purify raw natural gas by removing contaminants such as solids, water, carbon dioxide (CO2), hydrogen sulfide (H2S), mercury and higher molecular mass hydrocarbons. Some of the substances which contaminate natural gas have economic value and are further processed or sold. An operational natural gas plant delivers pipeline-quality dry natural gas that can be used as fuel by residential, commercial and industrial consumers, or as a feedstock for chemical synthesis. Types of raw-natural-gas wells Raw natural gas comes primarily from any one of three types of wells: crude oil wells, gas wells, and condensate wells. Natural gas that comes from crude oil wells is typically called associated gas. This gas can have existed as a gas cap above the crude oil in the underground reservoir or could have been dissolved in the crude oil, coming out of solution as the pressure is reduced during production. Natural gas that comes from gas wells and condensate wells, in which there is little or no crude oil, is called non-associated gas. Gas wells typically produce only raw natural gas, while condensate wells produce raw natural gas along with other low