It is formed when layers of decomposing plant and animal matter are exposed to intense heat and pressure under the surface of the Earth over millions of years.
The energy that the plants originally obtained from the sun is stored in the form of chemical bonds in the gas.
Natural gas is a non-renewable hydrocarbon used as a source of energy for heating, cooking, and electricity generation.
It is also used as a fuel for vehicles and as a chemical feedstock in the manufacture of plastics and other commercially important organic chemicals.
Natural gas has a complicated effect on climate change; it itself is a greenhouse gas, and it releases carbon dioxide when burned.
However, natural gas use often supplants coal use, which is far more environmentally damaging, leading to lower net carbon dioxide emissions in countries such as the United States.
Natural gas is found in deep underground rock formations or associated with other hydrocarbon reservoirs in coal beds and as methane clathrates.
Petroleum is another resource and fossil fuel found close to and with natural gas. Most natural gas was created over time by two mechanisms: biogenic and thermogenic.
Biogenic gas is created by methanogenic organisms in marshes, bogs, landfills, and shallow sediments.
Deeper in the earth, at greater temperature and pressure, thermogenic gas is created from buried organic material.
In petroleum production, gas is sometimes burned as flare gas.
Before natural gas can be used as a fuel, most, but not all, must be processed to remove impurities, including water, to meet the specifications of marketable natural gas.
The by-products of this processing include ethane, propane, butanes, pentanes, and higher molecular weight hydrocarbons, hydrogen sulfide (which may be converted into pure sulfur), carbon dioxide, water vapor, and sometimes helium and nitrogen.
Natural gas is sometimes informally referred to simply as «gas», especially when compared to other energy sources such as oil or coal.
However, it is not to be confused with gasoline, especially in North America, where the term gasoline is often shortened in colloquial usage to gas.
The search for natural gas begins with geologists who study the structure and processes of the earth.
They locate the types of geologic formations that are likely to contain natural gas deposits.
Geologists often use seismic surveys on land and in the ocean to find the right places to drill natural gas and oil wells.
Seismic surveys create and measure seismic waves in the earth to get information on the geology of rock formations.
Seismic surveys on land may use a thumper truck, which has a vibrating pad that pounds the ground to create seismic waves in the underlying rock.
Sometimes small amounts of explosives are used.
Seismic surveys conducted in the ocean use blasts of sound that create sonic waves to explore the geology beneath the ocean floor.
If the results of seismic surveys indicate that a site has potential for producing natural gas, an exploratory well is drilled and tested.
The results of the test provide information on the quality and quantity of natural gas available in the resource.
If the results from a test well show that a geologic formation has enough natural gas to produce and make a profit, one or more production (or development) wells are drilled.
Natural gas wells can be drilled vertically and horizontally into natural gas-bearing formations.
In conventional natural gas deposits, the natural gas generally flows easily up through wells to the surface.
In the United States and in a few other countries, natural gas is produced from shale and other types of sedimentary rock formations by forcing water, chemicals, and sand down a well under high pressure.
This process, called hydraulic fracturing or fracking, and sometimes referred to as unconventional production, breaks up the formation, releases the natural gas from the rock, and allows the natural gas to flow to and up wells to the surface.
At the top of the well on the surface, natural gas is put into gathering pipelines and sent to natural gas processing plants.
Because natural gas is colorless, odorless, and tasteless, natural gas companies add mercaptan to natural gas to give it a distinct and unpleasant odor to help detect leaks in natural gas pipelines.
Mercaptan is a harmless chemical that smells like rotten eggs.
Natural gas is processed for sale and consumption
Natural gas withdrawn from natural gas or crude oil wells is called wet natural gas because, along with methane, it usually contains NGL-ethane, propane, butanes, and pentanes-and water vapor.
Wellhead natural gas may also contain nonhydrocarbons such as sulfur, helium, nitrogen, hydrogen sulfide, and carbon dioxide, most of which must be removed from natural gas before it is sold to consumers.
From the wellhead, natural gas is sent to processing plants where water vapor and nonhydrocarbon compounds are removed and NGL are separated from the wet gas and sold separately.
Some ethane is often left in the processed natural gas.
The separated NGL are called natural gas plant liquids (NGPL), and the processed natural gas is called dry, consumer-grade, or pipeline quality natural gas.
Some wellhead natural gas is sufficiently dry and satisfies pipeline transportation standards without processing.
Chemicals called odorants are added to natural gas so that leaks in natural gas pipelines can be detected.
Dry natural gas is sent through pipelines to underground storage fields or to distribution companies and then to consumers.
A generalized flow diagram of the natural gas industry from the well to the consumer.
In places where natural gas pipelines are not available to take away associated natural gas produced from oil wells, the natural gas may be reinjected into the oil-bearing formation, or it may be vented or burned (flared).
Reinjecting unmarketable natural gas can help to maintain pressure in oil wells to improve oil production.
Coalbed methane can be extracted from coal deposits before or during coal mining, and it can be added to natural gas pipelines without any special treatment.
Most of the natural gas consumed in the United States is produced in the United States.
Some natural gas is imported from Canada and Mexico in pipelines.
A small amount of natural gas is also imported as liquefied natural gas.