Abstract

Natural gas is a mixture of naturally occurring hydrocarbon and non-hydrocarbon gases found in porous geologic formations beneath the earth's surface. Methane is a principal constituent and the mixture may contain higher hydrocarbons such as ethane, propane, butane, and pentane. Gases such as carbon dioxide, nitrogen, hydrogen sulfide, various mercaptans, and water vapor along with trace amounts of other inorganic and organic compounds can also be present. Natural gas is found in a variety of geological formations including sandstones, shales, and coals. Worldwide natural gas reserves have continued to increase as the demand for gas has increased and exploration efforts have expanded. Natural gas production on a worldwide basis has also continued to increase. The composition of natural gas at the wellhead depends on the characteristics of the reservoir and is highly variable with respect to both the constituents present and the concentrations of these constituents. Natural gas obtained at the wellhead usually undergoes some type of treatment or processing prior to its use for safety, economic, or system and material compatibility reasons. Gases are odorless, but for safety reasons, natural gas is odorized before distribution to provide a distinct odor to warn users of possible gas leaks in equipment.

Natural gas is used as a fuel and source of heat throughout the industrialized countries for a broad range of residential, commercial. Both natural gas and natural gas liquids are used as feedstocks in the chemical industry. Production takes place both at onshore installations and on offshore platforms which service wells drilled to provide access to reservoirs located below the floor of the ocean.