Natural Gas

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Natural Gas

Formation and composition of natural gas

Natural gas, sometimes just called gas, is a gaseous fossil fuel that is usually found along with petroleum deposits but 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. Its usual composition is 85% methane (CH₄), around 10% of ethane (C₂H₆), and 5% 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.

It is widely used as a heating source, and in some cases specific portions of the natural gas are used as starting materials in industrial processes. In fact, natural gas is an indispensable energy resource throughout most of the industrialized world. In American homes, 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 for making many products that Americans use every day.

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.

History

The Chinese were the first people known to have discovered and used natural gas. As early as 940 BC, they found gas underground and piped it through hollow bamboo poles to the seashore, where they burned it to boil off ocean water and collect the leftover salt. By 615 BC, 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 mysterious eternal fires. People traveled from faraway lands to visit these temples and marvel at this supernatural phenomenon.

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, the first U.S. president, described in

Table 1. (Thomson Gale. )
Gases and mole percentages
Substance	Mole %
Methane (CH₄)	76
Ethane (C₂H₆)	6
Propane (C₃H₈)	4
Butane (C₄H₁₀)	2
Nitrogen (N₂)	10

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.

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 through wooden pipes that were replaced a few years later with lead pipe. Although the well was only 27 feet (8.2 meters) 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 miles (40.2 km) long and less than one foot (30 m) 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 mile (8.8 km) pipeline serving 250 customers in Titusville, Pennsylvania, 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 American pipeline network grew rapidly through the 1930s and 1940s. By 1950, almost 300,000 miles (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, when gas fields began to be developed in France and the Netherlands in the 1950s and in the North Sea, by England and Norway, in the 1960s. An American 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 England.

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 above-ground technique can prove the presence of gas, and 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.

Formation and composition of natural gas

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 under water) 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 which exist as gases were then either trapped in porous rocks 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.

Use of natural gas

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 byproducts 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 reaction below:

CH₄ + O₂ → CO₂ + H₂O + heat energy

Ethane is used less as 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.

Liquefied natural gas

Since 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

Key Terms

Anticline —An upward fold in a geological formation that traps gases.

Combustion reaction —A form of oxidation that occurs so rapidly that noticeable heat and light are produced.

Exothermic reaction —A chemical process that releases heat (hydrocarbon combustion reactions are exothermic).

Fossil fuel —A fuel that is derived from the decay of plant or animal life; coal, oil, and natural gas are the fossil fuels.

Hydrocarbon —Compound made from atoms of hydrogen and carbon. Methane (CH₄) and propane (C₃H₈) are simple, gaseous hydrocarbons. Oil can vary from tar to very light liquid hydrocarbon to natural gas.

gases to be stored and transported conveniently. At one time, the natural gas that often accompanied 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.

Resources

BOOKS

Darley, Julian. Standard High Noon for Natural Gas: The New Energy Crisis. White River Junction, VT: Chelsea Green Publishing Company, 2004.

Lyons, William C., and Gary S. Plisga, eds. Standard Handbook of Petroleum and Natural Gas Engineering. Amsterdam, Netherlands, and Boston, MA: Elsevier, 2005.

Seddon, Duncan. Gas Usage and Value: The Technology and Economics of Natural Gas Use in the Process Industries. Tulsa, OK: PennWell, 2006.