Natural gas is a naturally occurring mixture of gases found in geological formations, consisting mainly of methane (CH₄), with smaller quantities of other hydrocarbons and nonhydrocarbon compounds. It is a fossil fuel used as a source of energy and as a raw material for chemical manufacturing. Commercial natural gas is usually processed to remove liquids and contaminants before distribution through pipelines or transport in liquefied form. Its composition at the wellhead differs from that of the gas delivered to consumers. (eia.gov)
Composition and properties
Raw natural gas can contain ethane, propane, butanes, and heavier hydrocarbons, together with carbon dioxide, nitrogen, hydrogen sulfide, helium, and water vapor. The proportions depend on the deposit. Gas containing substantial recoverable hydrocarbon liquids is commonly called wet gas; processed, methane-rich gas meeting pipeline specifications is called dry gas. These commercial terms describe composition and processing rather than a single, universal chemical formula. (eia.gov)
Processed natural gas is colorless and normally odorless. Odorants, often sulfur-containing compounds such as mercaptans, are added to distributed gas to make leaks detectable by smell. Natural gas is combustible, and leaks can create explosion hazards when gas accumulates and encounters an ignition source. Its production, storage, transportation, and use therefore require safety controls. (eia.gov)
Formation and geological occurrence
Most natural gas resources are thermogenic: they form as buried organic matter undergoes chemical alteration under elevated temperature and pressure over geological time. Another portion is generated through microbial processes. These different origins can produce gas with different chemical and isotopic characteristics. (pubs.usgs.gov)
Conventional deposits contain gas in rock formations from which it can flow relatively readily into wells. Unconventional resources include shale gas and tight gas held in formations with restricted flow, as well as coalbed methane associated with coal deposits. Natural gas may also occur alongside petroleum and be produced from the same wells. The conventional–unconventional distinction concerns geological occurrence and extraction requirements, not different kinds of methane. (eia.gov)
Exploration, extraction, and processing
Exploration commonly uses seismic surveys to investigate subsurface structures. Exploratory drilling then establishes whether a formation contains gas in quantities and conditions suitable for development. Production wells may be vertical or horizontal. In low-permeability formations, hydraulic fracturing introduces fluid under high pressure to fracture the rock and improve gas flow into the well. (eia.gov)
Gathering pipelines carry produced gas to treatment facilities. Processing can include separation of oil and condensate, dehydration, removal of hydrogen sulfide and carbon dioxide, and recovery of hydrocarbon liquids. Amine solutions are commonly used to absorb acid gases. Dehydration limits problems caused by water condensation and hydrate formation in pipelines. Recovered liquids can be separated into individual products according to their boiling points and sold independently of the methane-rich gas. The required treatment sequence depends on the incoming gas composition. (eia.gov)
Transportation and storage
Gas delivery relies on extensive infrastructure. Long-distance transmission pipelines carry processed gas toward consuming regions; smaller distribution mains and service lines deliver it to buildings. Storage balances relatively steady short-term production against daily and seasonal changes in demand. Underground facilities include depleted oil and gas fields, salt caverns, and suitable aquifers beneath impermeable rock layers. (eia.gov)
Liquefied natural gas (LNG) is produced by cooling natural gas to approximately −162°C. Liquefaction reduces its volume to roughly one six-hundredth of its gaseous volume, facilitating storage and transport where pipelines are unavailable or impractical. Specialized ships carry LNG in insulated tanks. At receiving terminals, it is stored and subsequently regasified before entering pipeline systems. Liquefaction and handling require additional energy and specialized equipment. (eia.gov)
Energy and industrial uses
Natural gas supplies space heating, water heating, cooking, and industrial process heat. It also fuels electricity generation and some vehicles. Industrial users employ it both as a combustible fuel and as a feedstock for manufacturing chemicals and fertilizers. (eia.gov)
In a combined-cycle power plant, a gas turbine generates electricity, while its hot exhaust produces steam for a steam turbine that generates additional power. Recovering exhaust heat increases the useful output obtained from the fuel compared with operating the combustion turbine alone. (energy.gov)
Natural gas also provides a feedstock for hydrogen production. In steam-methane reforming, methane reacts with high-temperature steam in the presence of a catalyst, producing hydrogen and carbon monoxide. A subsequent water-gas shift reaction converts carbon monoxide and additional steam into carbon dioxide and more hydrogen. Purification removes remaining impurities from the hydrogen stream. (energy.gov)
Markets and environmental effects
Natural gas prices respond to supply and demand, including production, inventories, imports, exports, weather, and competing fuel prices. Cold weather increases heating demand, while hot weather can increase demand for gas-fired electricity supporting air conditioning. Pipeline constraints and limited short-term fuel-switching capacity can intensify price changes. (eia.gov)
Burning natural gas generally produces less carbon dioxide and fewer emissions of many air pollutants than burning coal or petroleum products for an equal amount of energy. Nevertheless, combustion releases carbon dioxide, and methane escaping from wells, processing plants, pipelines, or storage facilities is a potent greenhouse gas. Assessing effects on climate change therefore requires consideration of both combustion and supply-chain emissions. (eia.gov)
Extraction and transportation can disturb land and water resources and generate noise, air pollution, and contaminated wastewater. Hydraulic fracturing produces wastewater requiring treatment or controlled disposal. Underground wastewater injection can induce earthquakes. Flaring unwanted gas converts much of its methane into carbon dioxide but also produces other pollutants, with emissions depending on gas composition and combustion conditions. (eia.gov)