Natural Gas

Natural gas is a gaseous fossil fuel consisting primarily of methane but including significant quantities of ethane, butane, propane, carbon dioxide, nitrogen, helium and hydrogen sulfide.   It is found in oil fields and natural gas fields, and in coal beds as coalbed methane.   When methane-rich gases are produced by the anaerobic decay of non-fossil organic material, these are referred to as biogas.   Sources of biogas include swamps, marshes, and landfills as well as sewage sludge and manure by way of anaerobic digesters, in addition to enteric fermentation particularly in cattle.   Natural gas is often informally referred to as simply gas, especially when compared to other energy sources such as electricity.   Before natural gas can be used as a fuel, it must undergo extensive processing to remove almost all materials other than methane.   The by-products of that processing include ethane, propane, butanes, pentanes and higher molecular weight hydrocarbons, elemental sulfur, and sometimes helium and nitrogen.   The processed gas then is converted to fuel and many other useful products. ^{Wiki n.p.}

The primary component of natural gas is methane , CH₄, the shortest and lightest hydrocarbon molecule.   It also contains heavier gaseous hydrocarbons such as ethane, C₂H₆; propane, C₃H₈; and butane, C₄H₁₀.   Other constituents are sulfur-containing gases in varying amounts.   Natural gas also contains the primary market source of helium.   Typical components (by weight) of natural gas are the following: ^{Wiki n.p.}

• Methane, 70-90%
• Ethane, 5-15%
• Propane & Butane, < 5%
• CO₂, N₂, H₂S, etc., balance

Water and odorants can also be present.   Mercury is also present in small amounts in natural gas extracted from some fields.   The exact composition of natural gas varies between gas fields.   Organosulfur compounds and hydrogen sulfide are common contaminants which must be removed prior to most uses.   Gas with a significant amount of sulfur impurities, such as hydrogen sulfide, is called sour gas; gas with sulfur or carbon dioxide impurities is acid gas.   Processed natural gas that is available to end-users is tasteless and odorless.   However, before gas is distributed to end-users, it is odorized by adding small amounts of odorants (mixtures of t-butyl mercaptan, isopropyl mercaptan, tetrahydrothiophene, dimethyl sulfide and other sulfur compounds), to assist in leak detection.   Processed natural gas is harmless to the human body, but it is a simple asphyxiant and can kill if it displaces air to the point where the oxygen content will not support life.   Natural gas can also be hazardous to life and property through an explosion.   Natural gas is lighter than air, and so tends to dissipate into the atmosphere but when it is confined, such as within a house, gas concentrations can reach explosive mixtures and, if ignited, result in blasts that can destroy buildings.   Methane has a lower explosive limit of 5% in air, and an upper explosive limit of 15%.   Explosive concerns with compressed natural gas used in vehicles are almost non-existent due to the escaping nature of the gas, and the need to maintain concentrations between 5% and 15% to trigger explosions. ^{Wiki n.p.}

Quantities of natural gas are measured in normal cubic meters (corresponding to 0° C at 1 atm) or in standard cubic feet (corresponding to 60° F and 30 inHg).   The gross heat of combustion of one normal cubic meter of commercial quality natural gas is around 39 megajoules (˜10.8 kWh), but this can vary by several percent.   In US units, one standard cubic foot of natural gas produces around 1000 British Thermal Units (BTUs).   The actual heating value when the water formed does not condense is the net heat of combustion and can be as much as 10% less. ^{Wiki n.p.}

Natural gas is commercially produced from oil fields and natural gas fields.   Gas produced from oil wells is called casinghead gas or associated gas.   The natural gas industry is producing gas from increasingly more challenging resource types: sour gas, tight gas, shale gas and coalbed methane.   The world's largest gas field by far is Qatar's offshore North Field, estimated to have 25 trillion cubic metres (900 trillion cubic feet) of gas in place, enough to last more than 200 years at optimum production levels.   The second largest natural gas field is the South Pars Gas Field in Iranian waters in the Persian Gulf.   Actually an extension of Qatar's North Field, it has estimated reserves of 8 to 14 trillion cubic metres (280-500 trillion cubic feet) of gas. ^{Wiki n.p.}

Town gas is a mixture of methane and other gases that can be used in a similar way to natural gas and can be produced by treating coal chemically.   This is a historic technology, still used as 'best solution' in some local circumstances, although coal gasification is not usually economic at current gas prices.   However, depending upon infrastructure considerations, it remains a future possibility. ^{Wiki n.p.}

Methanogenic archaea are responsible for all biological sources of methane, some in symbiotic relationships with other life forms, including termites, ruminants, and cultivated crops. Methane released directly into the atmosphere would be considered a pollutant, however, methane in the atmosphere is oxidised, producing carbon dioxide and water. Methane in the atmosphere has a half life of seven years, meaning that every seven years, half of the methane present is converted to carbon dioxide and water. ^{Wiki n.p.}

The major difficulty in the use of natural gas is transportation and storage because of its low density.   Natural gas pipelines are economical, but are impractical across oceans.   Many existing pipelines in North America are close to reaching their capacity, prompting some politicians in colder climates to speak publicly of potential shortages.   LNG carriers can be used to transport liquefied natural gas (LNG) across oceans, while tank trucks can carry liquefied or compressed natural gas (CNG) over shorter distances.   They may transport natural gas directly to end-users, or to distribution points such as pipelines for further transport.   These may have a higher cost, requiring additional facilities for liquefaction or compression at the production point, and then gasification or decompression at end-use facilities or into a pipeline. ^{Wiki n.p.}

In the past, the natural gas which was recovered in the course of recovering petroleum could not be profitably sold, and was simply burned at the oil field (known as flaring).   This wasteful practice is now illegal in many countries, especially since it adds greenhouse gas pollution to the earth's atmosphere.   Additionally, companies now recognize that value for the gas may be achieved with LNG, CNG, or other transportation methods to end-users in the future.   The gas is now re-injected back into the formation for later recovery.   This also assists oil pumping by keeping underground pressures higher.

In Saudi Arabia, in the late 1970s, a "Master Gas System" was created, ending the need for flaring.   The natural gas is used to generate electricity and heat for desalinization.   Similarly, some landfills that also discharge methane gases have been set up to capture the methane and generate electricity. ^{Wiki n.p.}

Natural gas is often stored in underground caverns formed inside depleted gas reservoirs from previous gas wells, salt domes, or in tanks as liquefied natural gas.   The gas is injected during periods of low demand and extracted during periods of higher demand.   Storage near the ultimate end-users helps to best meet volatile demands, but this may not always be practical. ^{Wiki n.p.}

To 1859

The first natural gas well was drilled and began production in Fredonia, NY, in 1821.   The gas was piped to the Fredonia Hotel and used for lighting and cooking. ^{Carruth 165}

1859-1869

1870-1879

1880-1889

1890-1899

1900-1909

1910-1919

1920-1929

1930-1939

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1990-1999