Natural gas is a naturally occurring hydrocarbon gas mixture
consisting primarily of methane, but commonly including varying
amounts of other higher alkanes, and sometimes a small percentage of
carbon dioxide, nitrogen, hydrogen sulfide, or helium. 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 fossil fuel 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.
Fossil fuel based
natural gas is a non-renewable resource.
Natural gas is found in deep underground rock formations or associated
with other hydrocarbon reservoirs in coal beds and as methane
Petroleum is another resource and fossil fuel found in
close proximity 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
In petroleum production gas is often burnt as flare gas. The World
Bank estimates that over 150 cubic kilometers of natural gas are
flared or vented annually. 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 often 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.
2.1 Natural gas
2.3 Town gas
2.5 Crystallized natural gas — hydrates
Natural gas processing
5 Storage and transport
5.1 Floating liquefied natural gas
6.1 Mid-stream natural gas
6.2 Power generation
6.3 Domestic use
6.7 Animal and fish feed
7 Environmental effects
7.1 Effect of natural gas release
Carbon dioxide emissions
7.3 Other pollutants
8 Safety concerns
8.3 Added odor
8.4 Risk of explosion
8.5 Risk of carbon monoxide inhalation
9 Energy content, statistics, and pricing
9.1 European Union
9.2 United States
Natural gas as an asset class for institutional investors
11 Adsorbed natural gas (ANG)
12 See also
14 External links
Natural gas coming out of the ground in Taiwan
Natural gas was discovered accidentally in ancient China, as it
resulted from the drilling for brines. The natural gas was used to
boil brine to make salt.
Natural gas was first used by the Chinese
in about 500 BC (possibly even 1000 BC). They discovered a way to
transport gas seeping from the ground in crude pipelines of bamboo to
where it was used to boil salt water to extract the salt, in the
Ziliujing District of Sichuan. The world's first industrial
extraction of natural gas started at Fredonia, New York, United
States, in 1825. By 2009, 66 000 km³ (or 8%) had been used
out of the total 850 000 km³ of estimated remaining recoverable
reserves of natural gas. Based on an estimated 2015 world
consumption rate of about 3400 km³ of gas per year, the total
estimated remaining economically recoverable reserves of natural gas
would last 250 years at current consumption rates. An annual increase
in usage of 2–3% could result in currently recoverable reserves
lasting significantly less, perhaps as few as 80 to 100 years.
See also: List of natural gas fields, List of countries by natural gas
proven reserves, and List of countries by natural gas production
Natural gas drilling rig in Texas.
In the 19th century, natural gas was usually obtained as a by-product
of producing oil, since the small, light gas carbon chains came out of
solution as the extracted fluids underwent pressure reduction from the
reservoir to the surface, similar to uncapping a soft drink bottle
where the carbon dioxide effervesces. Unwanted natural gas was a
disposal problem in the active oil fields. If there was not a market
for natural gas near the wellhead it was prohibitively expensive to
pipe to the end user.
In the 19th century and early 20th century, unwanted gas was usually
burned off at oil fields. Today, unwanted gas (or stranded gas without
a market) associated with oil extraction often is returned to the
reservoir with 'injection' wells while awaiting a possible future
market or to repressurize the formation, which can enhance extraction
rates from other wells. In regions with a high natural gas demand
(such as the US), pipelines are constructed when it is economically
feasible to transport gas from a wellsite to an end consumer.
In addition to transporting gas via pipelines for use in power
generation, other end uses for natural gas include export as liquefied
natural gas (LNG) or conversion of natural gas into other liquid
products via gas to liquids (GTL) technologies. GTL technologies can
convert natural gas into liquids products such as gasoline, diesel or
jet fuel. A variety of GTL technologies have been developed, including
Fischer–Tropsch (F–T), methanol to gasoline (MTG) and syngas to
gasoline plus (STG+). F–T produces a synthetic crude that can be
further refined into finished products, while MTG can produce
synthetic gasoline from natural gas. STG+ can produce drop-in
gasoline, diesel, jet fuel and aromatic chemicals directly from
natural gas via a single-loop process. In 2011, Royal Dutch
Shell's 140,000 barrels (22,000 m3) per day F–T plant went into
operation in Qatar.
Natural gas can be "associated" (found in oil fields), or
"non-associated" (isolated in natural gas fields), and is also found
in coal beds (as coalbed methane). It sometimes contains a
significant amount of ethane, propane, butane, and pentane—heavier
hydrocarbons removed for commercial use prior to the methane being
sold as a consumer fuel or chemical plant feedstock. Non-hydrocarbons
such as carbon dioxide, nitrogen, helium (rarely), and hydrogen
sulfide must also be removed before the natural gas can be
Natural gas extracted from oil wells is called casinghead gas (whether
or not truly produced up the annulus and through a casinghead outlet)
or associated gas. The natural gas industry is extracting an
increasing quantity of gas from challenging resource types: sour gas,
tight gas, shale gas, and coalbed methane.
There is some disagreement on which country has the largest proven gas
reserves. Sources that consider that
Russia has by far the largest
proven reserves include the US CIA (47 600 km³), the US
Energy Information Administration
Energy Information Administration (47 800 km³),[verification
needed] and OPEC (48 700 km³). However, BP credits Russia
with only 32 900 km³, which would place it in second place,
Iran (33 100 to 33 800 km³, depending on the
source). With Gazprom,
Russia is frequently the world's largest
natural gas extractor. Major proven resources (in cubic kilometers)
are world 187 300 (2013),
Iran 33 600 (2013),
Russia 32 900 (2013),
Qatar 25 100 (2013), Turkmenistan 17 500 (2013) and the United States
It is estimated that there are about 900 000 km³ of
"unconventional" gas such as shale gas, of which 180 000 km³ may
be recoverable. In turn, many studies from MIT, Black & Veatch
and the DOE predict that natural gas will account for a larger portion
of electricity generation and heat in the future.
The world's largest gas field is the offshore South Pars / North Dome
Gas-Condensate field, shared between
Iran and Qatar. It is estimated
to have 51,000 cubic kilometers (12,000 cu mi) of natural
gas and 50 billion barrels (7.9 billion cubic meters) of
natural gas condensates.
Because natural gas is not a pure product, as the reservoir pressure
drops when non-associated gas is extracted from a field under
supercritical (pressure/temperature) conditions, the higher molecular
weight components may partially condense upon isothermic
depressurizing—an effect called retrograde condensation. The liquid
thus formed may get trapped as the pores of the gas reservoir get
depleted. One method to deal with this problem is to re-inject dried
gas free of condensate to maintain the underground pressure and to
allow re-evaporation and extraction of condensates. More frequently,
the liquid condenses at the surface, and one of the tasks of the gas
plant is to collect this condensate. The resulting liquid is called
natural gas liquid (NGL) and has commercial value.
The examples and perspective in this article deal primarily with the
United States and do not represent a worldwide view of the subject.
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The location of shale gas compared to other types of gas deposits.
Shale gas is natural gas produced from shale. Because shale has matrix
permeability too low to allow gas to flow in economical quantities,
shale gas wells depend on fractures to allow the gas to flow. Early
shale gas wells depended on natural fractures through which gas
flowed; almost all shale gas wells today require fractures
artificially created by hydraulic fracturing. Since 2000, shale gas
has become a major source of natural gas in the United States and
Canada. Because of increased shale gas production, the United
States is now the number one natural gas producer in the world.
Following the success in the United States, shale gas exploration is
beginning in countries such as Poland, China, and South
Main article: History of manufactured gas
Town gas is a flammable gaseous fuel made by the destructive
distillation of coal. It contains a variety of calorific gases
including hydrogen, carbon monoxide, methane, and other volatile
hydrocarbons, together with small quantities of non-calorific gases
such as carbon dioxide and nitrogen, and is used in a similar way to
natural gas. This is a historical technology and is not usually
economically competitive with other sources of fuel gas today.
Most town "gashouses" located in the eastern US in the late 19th and
early 20th centuries were simple by-product coke ovens that heated
bituminous coal in air-tight chambers. The gas driven off from the
coal was collected and distributed through networks of pipes to
residences and other buildings where it was used for cooking and
Gas heating did not come into widespread use until the last
half of the 20th century.) The coal tar (or asphalt) that collected in
the bottoms of the gashouse ovens was often used for roofing and other
waterproofing purposes, and when mixed with sand and gravel was used
for paving streets.
Main article: Biogas
Methanogenic archaea are responsible for all biological sources of
methane. Some live in symbiotic relationships with other life forms,
including termites, ruminants, and cultivated crops. Other sources of
methane, the principal component of natural gas, include landfill gas,
biogas, and methane hydrate. When methane-rich gases are produced by
the anaerobic decay of non-fossil organic matter (biomass), these are
referred to as biogas (or natural biogas). Sources of biogas include
swamps, marshes, and landfills, as well as agricultural waste
materials such as sewage sludge and manure by way of anaerobic
digesters, in addition to enteric fermentation, particularly in
Landfill gas is created by decomposition of waste in landfill
sites. Excluding water vapor, about half of landfill gas is methane
and most of the rest is carbon dioxide, with small amounts of
nitrogen, oxygen, and hydrogen, and variable trace amounts of hydrogen
sulfide and siloxanes. If the gas is not removed, the pressure may get
so high that it works its way to the surface, causing damage to the
landfill structure, unpleasant odor, vegetation die-off, and an
explosion hazard. The gas can be vented to the atmosphere, flared or
burned to produce electricity or heat.
Biogas can also be produced by
separating organic materials from waste that otherwise goes to
landfills. This method is more efficient than just capturing the
landfill gas it produces. Anaerobic lagoons produce biogas from
manure, while biogas reactors can be used for manure or plant parts.
Like landfill gas, biogas is mostly methane and carbon dioxide, with
small amounts of nitrogen, oxygen and hydrogen. However, with the
exception of pesticides, there are usually lower levels of
Landfill gas cannot be distributed through utility natural gas
pipelines unless it is cleaned up to less than 3% CO
2, and a few parts per million H
2S, because CO
2 and H
2S corrode the pipelines. The presence of CO
2 will lower the energy level of the gas below requirements for the
Siloxanes in the gas will form
deposits in gas burners and need to be removed prior to entry into any
gas distribution or transmission system. Consequently, it may be more
economical to burn the gas on site or within a short distance of the
landfill using a dedicated pipeline.
Water vapor is often removed,
even if the gas is burned on site. If low temperatures condense water
out of the gas, siloxanes can be lowered as well because they tend to
condense out with the water vapor. Other non-methane components may
also be removed to meet emission standards, to prevent fouling of the
equipment or for environmental considerations. Co-firing landfill gas
with natural gas improves combustion, which lowers emissions.
Biogas, and especially landfill gas, are already used in some areas,
but their use could be greatly expanded. Experimental systems were
being proposed[when?] for use in parts of Hertfordshire, UK, and Lyon
in France. Using materials that would otherwise
generate no income, or even cost money to get rid of, improves the
profitability and energy balance of biogas production.
in sewage treatment plants is commonly used to generate electricity.
For example, the Hyperion sewage plant in Los Angeles burns
8 million cubic feet (230,000 cubic meters) of gas per day to
generate power New York City utilizes gas to run equipment in the
sewage plants, to generate electricity, and in boilers. Using
sewage gas to make electricity is not limited to large cities. The
city of Bakersfield, California, uses cogeneration at its sewer
plants. California has 242 sewage wastewater treatment plants, 74
of which have installed anaerobic digesters. The total biopower
generation from the 74 plants is about 66 MW.
Crystallized natural gas — hydrates
Huge quantities of natural gas (primarily methane) exist in the form
of hydrates under sediment on offshore continental shelves and on land
in arctic regions that experience permafrost, such as those in
Siberia. Hydrates require a combination of high pressure and low
temperature to form.
In 2010, the cost of extracting natural gas from crystallized natural
gas was estimated to be as much as twice the cost of extracting
natural gas from conventional sources, and even higher from offshore
In 2013, Japan Oil,
Gas and Metals National Corporation (JOGMEC)
announced that they had recovered commercially relevant quantities of
natural gas from methane hydrate.
The McMahon natural gas processing plant in Taylor, British Columbia,
Natural gas processing
Natural gas processing
The image below is a schematic block flow diagram of a typical natural
gas processing plant. It shows the various unit processes used to
convert raw natural gas into sales gas pipelined to the end user
The block flow diagram also shows how processing of the raw natural
gas yields byproduct sulfur, byproduct ethane, and natural gas liquids
(NGL) propane, butanes and natural gasoline (denoted as pentanes
Schematic flow diagram of a typical natural gas processing plant.
Natural gas production in the US reached a peak in 1973, and went over
a second lower peak in 2001, but recently has peaked again and is
continuing to rise.
Storage and transport
Polyethylene plastic main being placed in a trench.
Because of its low density, it is not easy to store natural gas or to
transport it by vehicle.
Natural gas pipelines are impractical across
oceans, since the gas needs to be cooled down and compressed, as the
friction in the pipeline causes the gas to heat up. Many existing
pipelines in America are close to reaching their capacity, prompting
some politicians representing northern states to speak of potential
shortages. The large trade cost implies that natural gas markets are
globally much less integrated, causing significant price differences
across countries. In Western Europe, the gas pipeline network is
already dense.[better source needed][full citation
needed] New pipelines are planned or under construction in Eastern
Europe and between gas fields in Russia,
Near East and Northern Africa
and Western Europe. See also List of natural gas pipelines.
Whenever gas is bought or sold at custody transfer points, rules and
agreements are made regarding the gas quality. These may include the
maximum allowable concentration of CO
2S and H
2O. Usually sales quality gas that has been treated to remove
contamination is traded on a "dry gas" basis and is required to be
commercially free from objectionable odours, materials, and dust or
other solid or liquid matter, waxes, gums and gum forming
constituents, which might damage or adversely affect operation of
equipment downstream of the custody transfer point.
LNG carriers transport liquefied natural gas (LNG) across oceans,
while tank trucks can carry liquefied or compressed natural gas (CNG)
over shorter distances. Sea transport using
CNG carrier ships that
are now under development may be competitive with
LNG transport in
Gas is turned into liquid at a liquefaction plant, and is returned to
gas form at regasification plant at the terminal. Shipborne
regasification equipment is also used.
LNG is the preferred form for
long distance, high volume transportation of natural gas, whereas
pipeline is preferred for transport for distances up to 4,000 km
(2,500 mi) over land and approximately half that distance
CNG is transported at high pressure, typically above 200 bars
(20,000 kPa; 2,900 psi). Compressors and decompression
equipment are less capital intensive and may be economical in smaller
unit sizes than liquefaction/regasification plants.
Natural gas trucks
and carriers may transport natural gas directly to end-users, or to
distribution points such as pipelines.
Gas Manlove Field natural gas storage area in Newcomb
Township, Champaign County, Illinois. In the foreground (left) is one
of the numerous wells for the underground storage area, with an LNG
plant, and above ground storage tanks are in the background (right).
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 in a process known as flaring. Flaring is now
illegal in many countries. Additionally, higher demand in the last
20–30 years has made production of gas associated with oil
economically viable. As a further option, the gas is now sometimes
re-injected into the formation for enhanced oil recovery by pressure
maintenance as well as miscible or immiscible flooding. Conservation,
re-injection, or flaring of natural gas associated with oil is
primarily dependent on proximity to markets (pipelines), and
Natural gas can be indirectly exported through the absorption in other
physical output. A recent study suggests that the expansion of shale
gas production in the US has caused prices to drop relative to other
countries. This has caused a boom in energy intensive manufacturing
sector exports, whereby the average dollar unit of US manufacturing
exports has almost tripled its energy content between 1996 and
A "master gas system" was invented in
Saudi Arabia in the late 1970s,
ending any necessity for flaring. Satellite observation, however,
shows that flaring and venting are
still practiced in some gas-extracting countries.
Natural gas is used to generate electricity and heat for desalination.
Similarly, some landfills that also discharge methane gases have been
set up to capture the methane and generate electricity.
Natural gas is often stored underground inside depleted gas reservoirs
from previous gas wells, salt domes, or in tanks as liquefied natural
gas. The gas is injected in a time of low demand and extracted when
demand picks up. Storage nearby end users helps to meet volatile
demands, but such storage may not always be practicable.
With 15 countries accounting for 84% of the worldwide extraction,
access to natural gas has become an important issue in international
politics, and countries vie for control of pipelines. In the first
decade of the 21st century, Gazprom, the state-owned energy company in
Russia, engaged in disputes with
Belarus over the price of
natural gas, which have created concerns that gas deliveries to parts
of Europe could be cut off for political reasons. The United
States is preparing to export natural gas.
Floating liquefied natural gas
Floating liquefied natural gas
Floating liquefied natural gas (FLNG) is an innovative technology
designed to enable the development of offshore gas resources that
would otherwise remain untapped due to environmental or economic
factors it is nonviable to develop them via a land-based LNG
LNG technology also provides a number of environmental and
Environmental – Because all processing is done at the gas
field, there is no requirement for long pipelines to shore,
compression units to pump the gas to shore, dredging and jetty
construction, and onshore construction of an
LNG processing plant,
which significantly reduces the environmental footprint. Avoiding
construction also helps preserve marine and coastal environments. In
addition, environmental disturbance will be minimised during
decommissioning because the facility can easily be disconnected and
removed before being refurbished and re-deployed elsewhere.
Economic – Where pumping gas to shore can be prohibitively
LNG makes development economically viable. As a result, it
will open up new business opportunities for countries to develop
offshore gas fields that would otherwise remain stranded, such as
those offshore East Africa.
Many gas and oil companies are considering the economic and
environmental benefits of floating liquefied natural gas (FLNG). There
are currently projects underway to construct five F
Petronas is close to completion on their FLNG-1 at Daewoo
Shipbuilding and Marine Engineering and are underway on their FLNG-2
project at Samsung Heavy Industries.
Shell Prelude is due to start
production 2017. The Browse
LNG project will commence FEED in
Natural gas is primarily used in the northern hemisphere. North
America and Europe are major consumers.
Mid-stream natural gas
Often well head gases require removal of various hydrocarbon molecules
contained within the gas. Some of these gases include heptane,
pentane, propane and other hydrocarbons with molecular weights above
4). The natural gas transmission lines extend to the natural gas
processing plant or unit which removes the higher molecular weighted
hydrocarbons to produce natural gas with energy content between
950–1,050 British thermal units per cubic foot (35–39 MJ/m3).
The processed natural gas may then be used for residential, commercial
and industrial uses.
Natural gas flowing in the distribution lines is called mid-stream
natural gas and is often used to power engines which rotate
compressors. These compressors are required in the transmission line
to pressurize and re-pressurize the mid-stream natural gas as the gas
travels. Typically, natural gas powered engines require
950–1,050 BTU/cu ft (35–39 MJ/m3) natural gas to
operate at the rotational name plate specifications. Several
methods are used to remove these higher molecular weighted gases for
use by the natural gas engine. A few technologies are as follows:
Cryogenic or chiller system
Chemical enzymology system
Natural gas is a major source of electricity generation through the
use of cogeneration, gas turbines and steam turbines.
Natural gas is
also well suited for a combined use in association with renewable
energy sources such as wind or solar and for alimenting peak-load
power stations functioning in tandem with hydroelectric plants. Most
grid peaking power plants and some off-grid engine-generators use
natural gas. Particularly high efficiencies can be achieved through
combining gas turbines with a steam turbine in combined cycle mode.
Natural gas burns more cleanly than other fuels, such as oil and coal.
Because burning natural gas produces both water and carbon dioxide, it
produces less carbon dioxide per unit of energy released than coal,
which produces mostly carbon dioxide. Burning natural gas produces
only about half the carbon dioxide per kilowatt-hour (kWh) that coal
does. For transportation, burning natural gas produces about 30%
less carbon dioxide than burning petroleum. The US Energy Information
Administration reports the following emissions in million metric tons
of carbon dioxide in the world for 2012:[clarification needed]
Natural gas: 6,799
Coal-fired electric power generation emits around 2,000 pounds
(900 kg) of carbon dioxide for every megawatt-hour (MWh)
generated, which is almost double the carbon dioxide released by
natural gas-fired generation. Because of this higher carbon
efficiency of natural gas generation, as the fuel mix in the United
States has changed to reduce coal and increase natural gas generation,
carbon dioxide emissions have unexpectedly fallen. Those measured in
the first quarter of 2012 were the lowest of any recorded for the
first quarter of any year since 1992.
Combined cycle power generation using natural gas is currently the
cleanest available source of power using hydrocarbon fuels, and this
technology is widely and increasingly used as natural gas can be
obtained at increasingly reasonable costs.
Fuel cell technology may
eventually provide cleaner options for converting natural gas into
electricity, but as yet it is not price-competitive. Locally produced
electricity and heat using natural gas powered Combined
Heat and Power
plant (CHP or
Cogeneration plant) is considered energy efficient and a
rapid way to cut carbon emissions.
Natural gas generated power has increased from 740 TWh in 1973 to 5140
TWh in 2014, generating 22% of the worlds total electricity.
Approximately half as much as generated with coal.[verification
needed][full citation needed] Efforts around the world to reduce the
use of coal has led some regions to switch to natural gas.
Natural gas dispensed in a residential setting can generate
temperatures in excess of 1,100 °C (2,000 °F) making it a
powerful domestic cooking and heating fuel. In much of the
developed world it is supplied through pipes to homes, where it is
used for many purposes including ranges and ovens, gas-heated clothes
dryers, heating/cooling, and central heating. Heaters in homes and
other buildings may include boilers, furnaces, and water heaters. Both
North America and Europe are major consumers of natural gas.
Domestic appliances, furnaces, and boilers use low pressure, usually 6
to 7 inches of water (6" to 7" WC), which is about 0.25 psig. The
pressures in the supply lines vary, either utilization pressure (UP,
the aforementioned 6" to 7" WC) or elevated pressure (EP), which may
be anywhere from 1 psig to 120 psig. Systems using EP have a regulator
at the service entrance to step down the pressure to UP.[citation
In the US compressed natural gas (CNG) is used in rural homes without
connections to piped-in public utility services, or with portable
Natural gas is also supplied by independent
natural gas suppliers through Natural
Gas Choice programs throughout
the United States. However, as CNG costs more than LPG (liquefied
petroleum gas), LPG is the dominant source of rural gas.
Washington, D.C. Metrobus, which runs on natural gas.
CNG is a cleaner and also cheaper alternative to other automobile
fuels such as gasoline (petrol) and diesel. By the end of 2014 there
were over 20 million natural gas vehicles worldwide, led by
China (3.3 million),
Pakistan (2.8 million),
India (1.8 million), and
Brazil (1.8 million). The
energy efficiency is generally equal to that of gasoline engines, but
lower compared with modern diesel engines. Gasoline/petrol vehicles
converted to run on natural gas suffer because of the low compression
ratio of their engines, resulting in a cropping of delivered power
while running on natural gas (10%–15%). CNG-specific engines,
however, use a higher compression ratio due to this fuel's higher
octane number of 120–130.
Besides use in road vehicles, CNG can also be used in aircraft.
Compressed natural gas
Compressed natural gas has been used in some aircraft like the Aviat
Aircraft Husky 200 CNG and the Chromarat VX-1 KittyHawk
LNG is also being used in aircraft. Russian aircraft manufacturer
Tupolev for instance is running a development program to produce LNG-
and hydrogen-powered aircraft. The program has been running since
the mid-1970s, and seeks to develop
LNG and hydrogen variants of the
Tu-204 and Tu-334 passenger aircraft, and also the Tu-330 cargo
aircraft. Depending on the current market price for jet fuel and LNG,
fuel for an LNG-powered aircraft could cost 5,000 rubles (US$100) less
per tonne, roughly 60%, with considerable reductions to carbon
monoxide, hydrocarbon and nitrogen oxide emissions.
The advantages of liquid methane as a jet engine fuel are that it has
more specific energy than the standard kerosene mixes do and that its
low temperature can help cool the air which the engine compresses for
greater volumetric efficiency, in effect replacing an intercooler.
Alternatively, it can be used to lower the temperature of the exhaust.
Natural gas is a major feedstock for the production of ammonia, via
the Haber process, for use in fertilizer production.
See also: Industrial gas
Natural gas can be used to produce hydrogen, with one common method
being the hydrogen reformer.
Hydrogen has many applications: it is a
primary feedstock for the chemical industry, a hydrogenating agent, an
important commodity for oil refineries, and the fuel source in
Animal and fish feed
Protein rich animal and fish feed is produced by feeding natural gas
Methylococcus capsulatus bacteria on commercial scale.
Natural gas is also used in the manufacture of fabrics, glass, steel,
plastics, paint, and other products.
See also: Environmental impact of the energy industry
Effect of natural gas release
See also: Atmospheric methane
Natural gas is mainly composed of methane. After release to the
atmosphere it is removed by gradual oxidation to carbon dioxide and
water by hydroxyl radicals (OH−) formed in the troposphere or
stratosphere, giving the overall chemical reaction CH
4 + 2O
2 → CO
2 + 2H
2O. While the lifetime of atmospheric methane is relatively
short when compared to carbon dioxide, with a half-life of about 7
years, it is more efficient at trapping heat in the atmosphere, so
that a given quantity of methane has 84 times the global-warming
potential of carbon dioxide over a 20-year period and 28 times over a
Natural gas is thus a more potent greenhouse gas than
carbon dioxide due to the greater global-warming potential of
methane. 2009 estimates by the EPA place global emissions of
methane at 85 billion cubic meters (3.0 trillion cubic feet)
annually, or 3% of global production, 3.0 trillion cubic
meters or 105 trillion cubic feet (2009 est). Direct
emissions of methane represented 14.3% by volume of all global
anthropogenic greenhouse gas emissions in 2004.
During extraction, storage, transportation, and distribution, natural
gas is known to leak into the atmosphere, particularly during the
extraction process. A
Cornell University study in 2011 demonstrated
that the leak rate of methane may be high enough to jeopardize its
global warming advantage over coal. This study was criticized
later for its over-estimation of methane leakage values.
Preliminary results of some air sampling from airplanes done by the
National Oceanic and Atmospheric Administration indicated
higher-than-estimated methane releases by gas wells in some areas,
but the overall results showed methane emissions in line with previous
Carbon dioxide emissions
Natural gas is often described as the cleanest fossil fuel. It
produces 25%–30% and 40%–45% less carbon dioxide per joule
delivered than oil and coal respectively, and potentially fewer
pollutants than other hydrocarbon fuels. However, in absolute
terms, it comprises a substantial percentage of human carbon
emissions, and this contribution is projected to grow. According to
the IPCC Fourth Assessment Report, in 2004, natural gas produced about
5.3 billion tons a year of CO
2 emissions, while coal and oil produced 10.6 and 10.2 billion tons
respectively. According to an updated version of the
Special Report on
Emissions Scenario by 2030, natural gas would be the source of 11
billion tons a year, with coal and oil now 8.4 and 17.2 billion
respectively because demand is increasing 1.9% a year.
Natural gas produces far lower amounts of sulfur dioxide and nitrous
oxides than other fossil fuels. The pollutants due to natural gas
combustion are listed below:
Comparison of emissions from natural gas, oil and coal burning
Natural gas extraction also produces radioactive isotopes of polonium
(Po-210), lead (Pb-210) and radon (Rn-220).
Radon is a gas with
initial activity from 5 to 200,000 becquerels per cubic meter of gas.
It decays rapidly to Pb-210 which can build up as a thin film in gas
A pipeline odorant injection station
Some gas fields yield sour gas containing hydrogen sulfide (H
2S). This untreated gas is toxic. Amine gas treating, an industrial
scale process which removes acidic gaseous components, is often used
to remove hydrogen sulfide from natural gas.
Extraction of natural gas (or oil) leads to decrease in pressure in
the reservoir. Such decrease in pressure in turn may result in
subsidence, sinking of the ground above.
Subsidence may affect
ecosystems, waterways, sewer and water supply systems, foundations,
and so on.
Main article: Environmental impact of hydraulic fracturing
Releasing natural gas from subsurface porous rock formations may be
accomplished by a process called hydraulic fracturing or "fracking".
It's estimated that hydraulic fracturing will eventually account for
nearly 70% of natural gas development in North America. Since the
first commercial hydraulic fracturing operation in 1949, approximately
one million wells have been hydraulically fractured in the United
States. The production of natural gas from hydraulically fractured
wells has utilized the technological developments of directional and
horizontal drilling, which improved access to natural gas in tight
rock formations. Strong growth in the production of unconventional
gas from hydraulically fractured wells occurred between 2000-2012.
In hydraulic fracturing, well operators force water mixed with a
variety of chemicals through the wellbore casing into the rock. The
high pressure water breaks up or "fracks" the rock, which releases gas
from the rock formation. Sand and other particles are added to the
water as a proppant to keep the fractures in the rock open, thus
enabling the gas to flow into the casing and then to the surface.
Chemicals are added to the fluid to perform such functions as reducing
friction and inhibiting corrosion. After the "frack," oil or gas is
extracted and 30–70% of the frack fluid, i.e. the mixture of water,
chemicals, sand, etc., flows back to the surface. Many gas-bearing
formations also contain water, which will flow up the wellbore to the
surface along with the gas, in both hydraulically fractured and
non-hydraulically fractured wells. This produced water often has a
high content of salt and other dissolved minerals that occur in the
The volume of water used to hydraulically fracture wells varies
according to the hydraulic fracturing technique. In the United States,
the average volume of water used per hydraulic fracture has been
reported as nearly 7,375 gallons for vertical oil and gas wells prior
to 1953, nearly 197,000 gallons for vertical oil and gas wells between
2000-2010, and nearly 3 million gallons for horizontal gas wells
Determining which fracking technique is appropriate for well
productivity depends largely on the properties of the reservoir rock
from which to extract oil or gas. If the rock is characterized by
low-permeability — which refers to its ability to let substances,
i.e. gas, pass through it, then the rock may be considered a source of
tight gas. Fracking for shale gas, which is currently also known
as a source of unconventional gas, involves drilling a borehole
vertically until it reaches a lateral shale rock formation, at which
point the drill turns to follow the rock for hundreds or thousands of
feet horizontally. In contrast, conventional oil and gas sources
are characterized by higher rock permeability, which naturally enables
the flow of oil or gas into the wellbore with less intensive hydraulic
fracturing techniques than the production of tight gas has
required. The decades in development of drilling technology
for conventional and unconventional oil and gas production has not
only improved access to natural gas in low-permeability reservoir
rocks, but also posed significant adverse impacts on environmental and
The US EPA has acknowledged that toxic, carcinogenic chemicals, i.e.
benzene and ethylbenzene, have been used as gelling agents in water
and chemical mixtures for high volume horizontal fracturing
(HVHF). Following the hydraulic fracture in HVHF, the water,
chemicals, and frack fluid that return to the well's surface, called
flowback or produced water, may contain radioactive materials, heavy
metals, natural salts, and hydrocarbons which exist naturally in shale
rock formations. Fracking chemicals, radioactive materials, heavy
metals, and salts that are removed from the HVHF well by well
operators are so difficult to remove from the water they're mixed
with, and would so heavily pollute the water cycle, that most of the
flowback is either recycled into other fracking operations or injected
into deep underground wells, eliminating the water that HVHF required
from the hydrologic cycle.
In order to assist in detecting leaks, an odorizer is added to the
otherwise colorless and almost odorless gas used by consumers. The
odor has been compared to the smell of rotten eggs, due to the added
tert-Butylthiol (t-butyl mercaptan). Sometimes a related compound,
thiophane, may be used in the mixture. Situations in which an odorant
that is added to natural gas can be detected by analytical
instrumentation, but cannot be properly detected by an observer with a
normal sense of smell, have occurred in the natural gas industry. This
is caused by odor masking, when one odorant overpowers the sensation
of another. As of 2011, the industry is conducting research on the
causes of odor masking.
Risk of explosion
Gas network emergency vehicle responding to a major fire in Kiev,
Explosions caused by natural gas leaks occur a few times each year.
Individual homes, small businesses and other structures are most
frequently affected when an internal leak builds up gas inside the
structure. Frequently, the blast is powerful enough to significantly
damage a building but leave it standing. In these cases, the people
inside tend to have minor to moderate injuries. Occasionally, the gas
can collect in high enough quantities to cause a deadly explosion,
disintegrating one or more buildings in the process. The gas usually
dissipates readily outdoors, but can sometimes collect in dangerous
quantities if flow rates are high enough. However, considering the
tens of millions of structures that use the fuel, the individual risk
of using natural gas is very low.
Risk of carbon monoxide inhalation
Natural gas heating systems may cause carbon monoxide poisoning if
unvented or poorly vented. In 2011, natural gas furnaces, space
heaters, water heaters and stoves were blamed for 11 carbon monoxide
deaths in the US. Another 22 deaths were attributed to appliances
running on liquified petroleum gas, and 17 deaths on gas of
unspecified type. Improvements in natural gas furnace designs have
greatly reduced CO poisoning concerns. Detectors are also available
that warn of carbon monoxide and/or explosive gas (methane, propane,
Energy content, statistics, and pricing
Natural gas prices
See also: Billion cubic metres of natural gas
Natural gas prices
Natural gas prices at the
Henry Hub in US dollars per million BTUs
Comparison of natural gas prices in Japan, United Kingdom, and United
Quantities of natural gas are measured in normal cubic meters (cubic
meter of gas at "normal" temperature 0 °C (32 °F) and
pressure 101.325 kPa (14.6959 psi)) or standard cubic feet
(cubic foot of gas at "standard" temperature 60.0 °F
(15.6 °C) and pressure 14.73 psi (101.6 kPa)), one
cubic meter ≈ 35.3147 cu ft. The gross heat of
combustion of commercial quality natural gas is around 39 MJ/m3
(0.31 kWh/cu ft), but this can vary by several percent. This
is about 49 MJ/kg (6.2 kWh/lb) (assuming a density of
0.8 kg/m3 (0.05 lb/cu ft), an approximate value).
Gas prices for end users vary greatly across the EU. A single
European energy market, one of the key objectives of the EU, should
level the prices of gas in all EU member states. Moreover, it would
help to resolve supply and global warming issues, as well as
strengthen relations with other Mediterranean countries and foster
investments in the region.
Gas Marketed Production 1900 to 2012 (US EIA data)
Trends in the top five natural gas-producing countries (US EIA data)
In US units, one standard cubic foot (28 L) of natural gas
produces around 1,028 British thermal units (1,085 kJ). 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.
In the United States, retail sales are often in units of therms (th);
1 therm = 100,000 BTU.
Gas sales to domestic consumers are often
in units of 100 standard cubic feet (scf).
Gas meters measure the
volume of gas used, and this is converted to therms by multiplying the
volume by the energy content of the gas used during that period, which
varies slightly over time. The typical annual consumption of a single
family residence is 1,000 therms or one Residential Customer
Equivalent (RCE). Wholesale transactions are generally done in
decatherms (Dth), thousand decatherms (MDth), or million decatherms
(MMDth). A million decatherms is a trillion BTU, roughly a billion
cubic feet of natural gas.
The price of natural gas varies greatly depending on location and type
of consumer. In 2007, a price of $7 per 1000 cubic feet ($0.25/m3) was
typical in the United States. The typical caloric value of natural gas
is roughly 1,000 BTU per cubic foot, depending on gas
composition. This corresponds to around $7 per million BTU or around
$7 per gigajoule (GJ). In April 2008, the wholesale price was $10 per
1000 cubic feet ($10/MMBTU). The residential price varies from
50% to 300% more than the wholesale price. At the end of 2007, this
was $12–$16 per 1000 cubic feet ($0.42–$0.57/m3). Natural gas
in the United States is traded as a futures contract on the New York
Mercantile Exchange. Each contract is for 10,000 MMBTU or
10 billion BTU (10,551 GJ). Thus, if the price of gas
is $10/MMBTU on the NYMEX, the contract is worth $100,000.
Canada uses metric measure for internal trade of petrochemical
products. Consequently, natural gas is sold by the gigajoule (GJ),
cubic meter (m3) or thousand cubic meters (E3m3). Distribution
infrastructure and meters almost always meter volume (cubic foot or
cubic meter). Some jurisdictions, such as Saskatchewan, sell gas by
volume only. Other jurisdictions, such as Alberta, gas is sold by the
energy content (GJ). In these areas, almost all meters for residential
and small commercial customers measure volume (m3 or ft3), and billing
statements include a multiplier to convert the volume to energy
content of the local gas supply.
A gigajoule (GJ) is a measure approximately equal to half a barrel
(250 lbs) of oil, or 1 million BTUs, or 1,000 cu ft or
28 m3 of gas. The energy content of gas supply in
Canada can vary
from 37 to 43 MJ/m3 (990 to 1,150 BTU/cu ft) depending
on gas supply and processing between the wellhead and the customer.
In the rest of the world, natural gas is sold in gigajoule retail
LNG (liquefied natural gas) and LPG (liquefied petroleum gas)
are traded in metric tonnes (1,000 kg) or MMBTU as spot
deliveries. Long term natural gas distribution contracts are signed in
cubic meters, and
LNG contracts are in metric tonnes. The
LNG and LPG
is transported by specialized transport ships, as the gas is liquified
at cryogenic temperatures. The specification of each LNG/LPG cargo
will usually contain the energy content, but this information is in
general not available to the public.
In the Russian Federation,
Gazprom sold approximately 250 billion
cubic meters (8.8 trillion cubic feet) of natural gas in 2008. In
2013 they produced 487.4 billion cubic meters
(17.21 trillion cubic feet) of natural and associated gas.
Gazprom supplied Europe with 161.5 billion cubic meters
(5.70 trillion cubic feet) of gas in 2013.
In August 2015, possibly the largest natural gas discovery in history
was made and notified by an Italian gas company ENI. The energy
company indicated that it has unearthed a "supergiant" gas field in
the Mediterranean Sea covering about 40 square miles (100 km2).
It was also reported that the gas field could hold a potential
30 trillion cubic feet (850 billion cubic meters) of natural
gas. ENI said that the energy is about5.5 billion barrels of oil
equivalent [BOE] (3.4×1010 GJ). The field was found in the deep
waters off the northern coast of Egypt and ENI claims that it will be
the largest ever in the Mediterranean and even the world.
Natural gas as an asset class for institutional investors
Research conducted by the World Pensions Council (WPC)[when?] suggests
that large US and Canadian pension funds and Asian and
MENA area SWF
investors have become particularly active in the fields of natural gas
and natural gas infrastructure, a trend started in 2005 by the
formation of Scotia
Gas Networks in the UK by
OMERS and Ontario
Teachers' Pension Plan.
Adsorbed natural gas (ANG)
Another way to store natural gas is adsorbing it to the porous solids
called sorbents. The best condition for methane storage is at room
temperature and atmospheric pressure. The used pressure can be up to 4
MPa (about 40 times atmospheric pressure) for having more storage
capacity. The most common sorbent used for ANG is activated carbon
(AC). Three main types of activated carbons for ANG are: Activated
Carbon Fiber (ACF), Powdered Activated Carbon (PAC), activated carbon
Sustainable development portal
Renewable energy portal
Associated petroleum gas
Gas oil ratio
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The future of Natural
A Comparison between
China and Unconventional Fuel
Development in the United States: Health, Water and Environmental
Risks by Paolo Farah and Riccardo Tremolada. This is a paper presented
at the Colloquium on Environmental Scholarship 2013 hosted by Vermont
Law School (11 October 2013)
New Technology For High BTU Natural
GA Mansoori, N Enayati, LB Agyarko (2016), Energy: Sources,
Utilization, Legislation, Sustainability, Illinois as Model State,
World Sci. Pub. Co., ISBN 978-981-4704-00-7
Manufactured fuel gas
Underground coal gasification
Blast furnace gas
Natural gas storage