Natural gas, sometimes just called gas, is a gaseous fossil fuel that is usually found along with petroleum deposits, but it can also be found alone in natural gas deposits within the crust of Earth. It is a mixture of hydrocarbons (molecules that contain only carbon and hydrogen) and gases. Natural gas is an indispensable energy resource throughout most of the industrialized world. Natural gas is used in furnaces, stoves, water heaters, clothes dryers, and other appliances. The fuel also supplies energy for numerous industrial processes and provides raw materials essential to the production of an array of products

Like oil, widespread use of natural gas can make it a tool in political struggles between producing and dependent nations. Such struggles also include disputes with countries hosting natural gas pipelines. There are, for example, ongoing disputes between Russia, a major gas producer, and neighboring nations that were former Soviet republics. The disputes have occasionally resulted in closure or partial closure of gas pipelines ultimately supplying countries in Europe. Disruptions in gas supply, whether accidental or deliberate, usually result in substantial hardship and economic loss.

Natural gas production, transport, and use also present special hazards. As early as 1937, a leak of natural gas caused an explosion that killed about 300 students and teachers in the East Texas town of New London. Their school, located in the middle of a large oil and natural gas field, was connected to the wet-gas lines that ran near it for cost savings. In September 2010, an oil and gas production platform exploded in the Gulf of Mexico. A week later, a deadly gas pipeline explosion near San Francisco, California, destroyed more than 50 homes in a residential neighborhood, producing flames so intense that they melted pavement and required the use of heavy firefighting aircraft normally reserved for large wildfires. On September 13, 2018, a series of natural gas lines owned by Columbia Gas of Massachusetts exploded in the towns of Lawrence, Andover, and North Andover due to excessive pressure. One person died and more than 30,000 were forced to evacuate their homes. There were more than 80 individual fires and extensive damage to up to 100 homes. The total cost of this incident was estimated to be greater than $1 billion.

Normally, approximately 85 percent of natural gas is methane (CH₄), around 10 percent of ethane (C₂H₆), and 5 percent or less of butane (C₄H₁₀), propane (C₃H₈), pentane (C₅H₁₂), other alkanes, and impurities, which exist naturally in rocks beneath the surface of Earth. Other gases such as oxygen, argon, and carbon dioxide make up the rest of most natural gas sources.

Natural gas is transported using pipeline networks that allow faster transport from production areas to cities and towns. (Denys Prykhodov/Shutterstock) (Denys Prykhodov/Shutterstock)

Natural gas is the product of the decaying of living matter over millions of years (as is also true for petroleum). Specific conditions (including low oxygen levels) are necessary for this to occur. The hydrocarbon gases are trapped in geological formations known as anticlines. Each of the major hydrocarbon components of natural gas is used as a fuel source.

The Chinese were the first people documented to have discovered and used natural gas. As early as 940 BCE, records show use of gas found underground and piped through hollow bamboo poles to the seashore, where it was burned to boil ocean water and reduce it to treasured salt. By 615 BCE, the Japanese were producing gas from similar wells. Other ancient civilizations may have accidentally discovered natural gas seeping up from the ground. When they learned that the gas would burn continuously, they built temples to house seemingly mysterious eternal fires.

In colonial North America, several natural gas seepages were discovered when they were accidentally set on fire. In the 1770s, French missionaries reported “pillars of fire” in the Ohio River valley, and George Washington (1732–1799), the first US president, described in wondering terms a “burning spring” on the banks of a river in West Virginia. Most scientists believe that natural gas was created by the same forces that formed petroleum, another fossil fuel.

 
Table 1.

In 1821, American gunsmith William Aaron Hart drilled the first natural gas well in the United States. It was covered with a large barrel, and the gas was directed Page 3023  |  Top of Articlethrough wooden pipes that were replaced a few years later with lead pipe. Although the well was only 27 ft (8.2 m) deep, it produced enough gas to illuminate nearby houses and stores in Fredonia, New York. Through the 1830s and 1840s, a few other gas wells were drilled in New York, Pennsylvania, and West Virginia. The first company to distribute and sell natural gas was established in Fredonia in 1865. However, by then, oil had been discovered near Titusville, Pennsylvania, and in the oil rush that followed, natural gas was practically forgotten. In addition, about 300 companies were already selling manufactured gas, which was made from coal or oil. Gas lighting systems that burned manufactured gas had been established in many cities long before natural gas was discovered.

For many years, natural gas was used only in places that happened to be near gas wells, mainly because early pipes were unable to transport it much farther. In some towns that used natural gas for street lighting, the lights were left on during the day because it cost more to turn them off than it did to burn the gas. When new wells produced gas along with oil, the gas was usually just burned off, or flared.

In the late 1800s, the introduction of electric lighting nearly killed off the gas industry. However, customers of manufactured gas continued to use the fuel for cooking and heating, so gas companies never completely died out. Gradually, the natural gas industry began to recover as pipeline technology was improved and as larger quantities of natural gas were discovered. The first long-distance pipeline—only about 25 mi (40.2 km) long and less than 1 ft (30 cm) in diameter—was built in the early 1870s to serve Rochester, New York. It was made of pine logs with holes bored through them. Iron pipe was also tested at that time in a 5.5-mi (8.8-km) pipeline serving 250 customers in Titusville, but for decades pipelines remained relatively short in length and small in diameter.

Then, in the early 1900s, huge amounts of natural gas were found in Texas and Oklahoma, and in the 1920s, modern seamless steel pipe was introduced. The strength of this new pipe, which could be electrically welded into long sections, allowed gas to be carried under higher pressures and thus in greater quantities. For the first time, natural gas transportation became profitable, and the US pipeline network grew rapidly through the 1930s and 1940s. By 1950, almost 300,000 mi (482,700 km) of gas pipelines had been laid—a length greater than that used to pipe oil. Soon it became routine for natural gas to be transported over distances of several hundred miles to the major centers of population and industry. As natural gas became available at prices lower than manufactured gas, customers switched to the cheaper fuel and consumption of natural gas increased phenomenally. Despite the loss of the lighting market, natural gas emerged as the most important heating and cooking fuel, and it gradually increased its share of the industrial market as well. Between 1940 and 1955, production of natural gas in the United States multiplied more than threefold. Today, natural gas now supplies more than one-fourth of all energy consumed in the United States.

In western Europe, however, the use of natural gas was virtually unknown until after World War II (1939–1945), when gas fields began to be developed in France and the Netherlands in the 1950s and in the North Sea, by the United Kingdom and Norway, in the 1960s. A US company came up with the idea of exporting natural gas to Europe by liquefying it at very cold temperatures and shipping it. In 1959, the first cargo of liquefied natural gas (LNG) crossed the Atlantic and was delivered to a specially built terminal in the UK.

Despite the huge amounts of natural gas that have been produced and consumed, new discoveries have continued to increase gas reserves—the amount of gas that is potentially recoverable. Exploring for natural gas is a complex process that demands the skills of geologists, physicists, chemists, and engineers. Once the right clues have been found above ground, surveyors map the area and samples of surface rocks are closely examined. Then, underground structures are explored from the surface by means of instruments that identify rock layers from sound waves (seismographs) or from changes in gravity and magnetism (gravity meters and magnetometers). Still, no aboveground technique can prove the presence of gas, Page 3024  |  Top of Articleand an expensive well must be drilled for confirmation. On land, wells typically cost about $500,000. Unusually deep wells, and offshore wells drilled in water, cost much more. However, when all costs are considered, including land acquisition, drilling, facilities, and processing/transport, the total cost balloons to between $4.9 million and $8.3 million, according to the US Energy Information Administration (EIA).

Natural gas satisfies more than 38 percent of US power requirements, according to preliminary data for 2019, up from 25 percent only a few years prior. Increasing demand has made it economically profitable to tap methane reserves in layers of subsurface shale via a process known as hydraulic fracturing, or fracking, which accounts for the substantial jump of the share of natural gas in electricity generation. In fracking, injections of highly pressurized water and sand fracture shale formations. Producers then collect the gas released from the shattered shale. The fracking process has become increasingly controversial and is the subject of litigation. Whereas the process is profitable for some landowners, others complain that it is a nuisance and environmentally destructive. In some cases, released gases and drilling mud have contaminated water wells and groundwater reserves. Studies are ongoing to learn how fracking affects groundwater and local seismic activity. There are, however, environmentalists who counter that extraction of natural gas by fracking lowers overall carbon emissions because natural gas is a lower emission energy source than automobile gasoline, heating oil, or coal. As of 2020, fracking is still a highly controversial method for natural gas extraction, with many people expressing grave concerns that environmental damage outweighs the benefits.

Natural gas consumption is expected to decrease by 7 percent in 2020 when compared to 2019, due to the significant effects of the COVID-19 pandemic and related restrictions, including the overall decline in economic activity. Prior to the COVID-19 pandemic, natural gas consumption in the US industrial sector was forecast to continue growing by more than 4 percent per year, and its share of electricity generation to remain stable at over 37 percent.

Natural gas has its origins in decayed living matter, most likely as the result of the action of bacteria upon dead animal and plant material. In order for most bacteria to effectively break down organic matter to hydrocarbons, there must be low levels of oxygen present. This would mean that the decaying matter was buried (most likely underwater) before it could be completely degraded to carbon dioxide and water. Conditions such as this are likely to have been met in coastal areas where sedimentary rocks and marine bacteria are common. The actions of heat and pressure along with bacteria produced a mixture of hydrocarbons. The smaller molecules that exist as gases were then either trapped in porous rock or in underground reservoirs where they formed sources of hydrocarbon fuels.

The exact composition of different sources of natural gas varies slightly, but in all cases, methane is by far the most common component, with other hydrocarbons also being very common. The largest sources of natural gas in the United States are found in Alaska, Texas, Oklahoma, western Pennsylvania, and Ohio. It is estimated that the supply of natural gas in this country may be sufficient to last for two centuries, although the more readily accessible sources have been used, meaning that it will be more expensive to obtain natural gas in the future.

As the technology for piping gas from the source began to improve, it became possible to pipe natural gas over thousands of miles. This has meant that natural gas has become as convenient as petroleum and coal to use as a fuel source, and often with far less pollution. Natural gas burns with almost no by-products except for carbon dioxide and water (as opposed to coal that often has large amounts of sulfur in it), and the heat released from the reaction (combustion of any of the hydrocarbon components of natural gas is an exothermic process). The combustion of methane, the most prevalent component of natural gas, is described by the following reaction:

CH₄ + O₂ → CO₂ + H₂O + heat energy

Ethane is used less as a fuel source than as a starting material for the production of ethylele (acetylene), which is used in welding.

Both butane and propane are relatively easy to liquefy and store. Liquefied propane and butane are used in disposable lighters and as camping fuels.

Because gases take up large amounts of space, they can be inconvenient to transport and store. The ability to liquefy the components of natural gas (either as a mixture or in isolation) has made natural gas much more practical as an energy source. The liquefaction of natural gas takes advantage of the different boiling points of methane, ethane, and other gases as a way of purifying each substance. A combination of refrigeration and increased pressure allows the individual gases to be stored and transported conveniently. At one time, the natural gas that often Page 3025  |  Top of Articleaccompanied petroleum in the ground was simply burned off as a means of getting rid of it. Recently, however, this gas has been collected, liquefied, and used along with the petroleum.