Natural gas is a fossil fuel. Like other fossil fuels such as coal and oil, natural gas forms from the plants, animals, and microorganisms that lived millions of years ago.
There are several different theories to explain how fossil fuels are formed. The most prevalent theory is that they form underground, under intense conditions. As plants, animals, and microorganisms decompose, they are gradually covered by layers of soil, sediment, and sometimes rock. Over millions of years, the organic matter is compressed. As the organic matter moves deeper into Earth’s crust, it encounters higher and higher temperatures.
The combination of compression and high temperature causes the carbon bonds in the organic matter to break down. This molecular breakdown produces thermogenic methane—natural gas. Methane, probably the most abundant organic compound on Earth, is made of carbon and hydrogen (CH4).
Natural gas deposits are often found near oil deposits. Deposits of natural gas close to Earth’s surface are usually dwarfed by nearby oil deposits. Deeper deposits—formed at higher temperatures and under more pressure—have more natural gas than oil. The deepest deposits can be made up of pure natural gas.
Natural gas does not have to be formed deep underground, however. It can also be formed by tiny microorganisms called methanogens. Methanogens live in the intestines of animals (including humans) and in low-oxygen areas near the surface of Earth. Landfills, for example, are full of decomposing matter that methanogens break down into a type of methane called biogenic methane. The process of methanogens creating natural gas (methane) is called methanogenesis.
Although most biogenic methane escapes into the atmosphere, there are new technologies being created to contain and harvest this potential energy source.
Thermogenic methane—the natural gas formed deep beneath Earth’s surface—can also escape into the atmosphere. Some of the gas is able to rise through permeable matter, such as porous rock, and eventually dissipate into the atmosphere.
However, most thermogenic methane that rises toward the surface encounters geological formations that are too impermeable for it to escape. These rock formations are called sedimentary basins.
Sedimentary basins trap huge reservoirs of natural gas. In order to gain access to these natural gas reservoirs, a hole (sometimes called a well) must be drilled through the rock to allow the gas to escape and be harvested.
Sedimentary basins rich in natural gas are found all over the world. The deserts of Saudi Arabia, the humid tropics of Venezuela, and the freezing Arctic of the U.S. state of Alaska are all sources of natural gas. Outside Alaska, U.S. basins are primarily around the states bordering the Gulf of Mexico, including Texas and Louisiana. Recently, the northern states of North Dakota, South Dakota, and Montana have developed significant drilling facilities in sedimentary basins.
Types of Natural Gas
Natural gas that is economical to extract and easily accessible is considered “conventional.” Conventional gas is trapped in permeable material beneath impermeable rock.
Natural gas found in other geological settings is not always so easy or practical to extract. This gas is called “unconventional.” New technologies and processes are always being developed to make this unconventional gas more accessible and economically viable. Over time, gas that was considered “unconventional” can become conventional.
Biogas is a type of gas that is produced when organic matter decomposes without oxygen being present. This process is called anaerobic decomposition, and it takes place in landfills or where organic material such as animal waste, sewage, or industrial byproducts are decomposing.
Biogas is biological matter that comes from plants or animals, which can be living or not-living. This material, such as forest residues, can be combusted to create a renewable energy source.
Biogas contains less methane than natural gas, but can be refined and used as an energy source.
Deep Natural Gas
Deep natural gas is an unconventional gas. While most conventional gas can be found just a few thousand meters deep, deep natural gas is located in deposits at least 4,500 meters (15,000 feet) below the surface of Earth. Drilling for deep natural gas is not always economically practical, although techniques to extract it have been developed and improved.
Shale
Shale gas is another type of unconventional deposit. Shale is a fine-grained, sedimentary rock that does not disintegrate in water. Some scientists say shale is so impermeable that marble is considered “spongy” in comparison. Thick sheets of this impermeable rock can “sandwich” a layer of natural gas between them.
Shale gas is considered an unconventional source because of the difficult processes necessary to access it: hydraulic fracturing (also known as fracking) and horizontal drilling. Fracking is a procedure that splits open rock with a high-pressure stream of water, and then “props” it open with tiny grains of sand, glass, or silica. This allows gas to flow more freely out of the well. Horizontal drilling is a process of drilling straight down into the ground, then drilling sideways, or parallel, to Earth’s surface.
Tight Gas
Tight gas is an unconventional natural gas trapped underground in an impermeable rock formation that makes it extremely difficult to extract. Extracting gas from “tight” rock formations usually requires expensive and difficult methods, such as fracking and acidizing.
Acidizing is similar to fracking. An acid (usually hydrochloric acid) is injected into the natural gas well. The acid dissolves the tight rock that is blocking the flow of gas.
Coalbed Methane
Coalbed methane is another type of unconventional natural gas. As its name implies, coalbed methane is commonly found along seams of coal that run underground. Historically, when coal was mined, the natural gas was intentionally vented out of the mine and into the atmosphere as a waste product. Today, coalbed methane is collected and is a popular energy source.
Gas in Geopressurized Zones
Another source of unconventional natural gas is geopressurized zones. Geopressurized zones form 3,000-7,600 meters (10,000-25,000 feet) below Earth’s surface.
These zones form when layers of clay rapidly accumulate and compact on top of material that is more porous, such as sand or silt. Because the natural gas is forced out of the compressed clay, it is deposited under very high pressure into the sand, silt, or other absorbent material below.
Geopressurized zones are very difficult to mine, but they may contain a very high amount of natural gas. In the United States, most geopressurized zones have been found in the Gulf Coast region.
Methane Hydrates
Methane hydrates are another type of unconventional natural gas. Methane hydrates were discovered only recently in ocean sediments and permafrost areas of the Arctic. Methane hydrates form at low temperatures (around 0°C, or 32°F) and under high pressure. When environmental conditions change, methane hydrates are released into the atmosphere.
The United States Geological Survey (USGS) estimates that methane hydrates could contain twice the amount of carbon than all of the coal, oil, and conventional natural gas in the world, combined.
In ocean sediments, methane hydrates form on the continental slope as bacteria and other microorganisms sink to the ocean floor and decompose in the silt. Methane, trapped within the sediments, has the ability to “cement” the loose sediments into place and keep the continental shelf stable. However, if the water becomes warmer, the methane hydrates break down. This causes causes underwater landslides, and releases natural gas.
In permafrost ecosystems, methane hydrates form as bodies of water freeze and water molecules create individual “cages” around each methane molecule. The gas, trapped in a frozen lattice of water, is contained at a much higher density than it would be in its gaseous state. As the ice cages thaw, the methane escapes.
Global warming, the current period of climate change, influences the release of methane hydrates from both permafrost and ocean sediment layers.
There is a vast amount of potential energy stored in methane hydrates. However, because they are such fragile geological formations—capable of breaking down and disrupting the environmental conditions around them—methods for extracting them are developed with extreme caution.
Drilling and Transportation
Natural gas is measured in normal cubic meters or standard cubic feet. In 2009, the United States Energy Information Administration (EIA) estimated that the world’s proven natural gas reserves are around 6,289 trillion cubic feet (tcf).
Most of the reserves are in the Middle East, with 2,686 tcf in 2011, or 40 percent of total world reserves. Russia has the second-highest amount of proven reserves, with 1,680 tcf in 2011. The United States contains just over four percent of the world’s natural gas reserves.
According to the EIA, total world consumption of dry natural gas in 2010 was 112,920 billion cubic feet (bcf). That year, the United States consumed a little more than 24,000 bcf, the most of any nation.
Natural gas is most commonly extracted by drilling vertically from Earth’s surface. From a single vertical drill, the well is limited to the gas reserves it encounters.
Hydraulic fracturing, horizontal drilling, and acidizing are processes to expand the amount of gas that a well can access, and thus increase its productivity. However, these practices can have negative environmental consequences.
Hydraulic fracturing, or fracking, is a process that splits open rock formations with high-pressure streams of water, chemicals, and sand. The sand props open the rocks, which allows gas to escape and be stored or transported. However, fracking requires huge quantities of water, which can radically reduce an area’s water table and negatively impact aquatic habitats. The process produces highly toxic and frequently radioactive wastewater that, if mismanaged, can leak and contaminate underground water sources used for drinking, hygiene, and industrial and agricultural use.
In addition, fracking can cause microearthquakes. Most of these temblors are far too tiny to be felt on the surface, but some geologists and environmentalists warn that the quakes may cause structural damage to buildings or underground networks of pipes and cables.
Due to these negative environmental effects, fracking has been criticized and banned in some areas. In other areas, fracking is a lucrative economic opportunity and providing a reliable source of energy.
Horizontal drilling is a way of increasing the area of a well without creating multiple expensive and environmentally sensitive drilling sites. After drilling straight down from Earth’s surface, drilling can be directed to go sideways—horizontally. This broadens the well’s productivity without requiring multiple drilling sites on the surface.
Acidizing is a process of dissolving acidic components and inserting them into the natural gas well, which dissolves rock that may be blocking the flow of gas.
After natural gas is extracted, it is most frequently transported through pipelines that can be from two to 60 inches in diameter.
The continental United States has more than 210 pipeline systems that are made up of 490,850 kilometers (305,000 miles) of transmission pipelines that transfer gas to all 48 states. This system requires more than 1,400 compressor stations to ensure that the gas continues on its path, 400 underground storage facilities, 11,000 locations to deliver the gas, and 5,000 locations to receive the gas.
Natural gas can also be cooled to about -162°C (-260°F) and converted into liquified natural gas, or LNG. In liquid form, natural gas takes up only 1/600 of the volume of its gaseous state. It can easily be stored and transported places that do not have pipelines.
LNG is transported by a specialized insulated tanker, which keeps the LNG at its boiling point. If any of the LNG vaporizes, it is vented out of the storage area and used to power the transport vessel. The United States imports LNG from other countries, including Trinidad and Tobago and Qatar. However, the U.S. is currently increasing its domestic LNG production.
Consuming Natural Gas
Although natural gas takes millions of years to develop, its energy has only been harnessed during the past few thousand years. Around 500 B.C.E., Chinese engineers made use of natural gas seeping out of the earth by building bamboo pipelines. These pipes transported gas to heat water. In the late 1700s, British companies provided natural gas to light streetlamps and homes.
Today, natural gas is used in countless ways for industrial, commercial, residential, and transportation purposes. The United States Department of Energy (DOE) estimates that natural gas can be up to 68 percent less expensive than electricity.
In residential homes, the most popular use for natural gas is heating and cooking. It is used to power home appliances such as stoves, air conditioners, space heaters, outdoor lights, garage heaters, and clothes dryers.
Natural gas is also used on a larger scale. In commercial settings, such as restaurants and shopping malls, it is an extremely efficient and economical way to power water heaters, space heaters, dryers, and stoves.
Natural gas is used to heat, cool, and cook in industrial settings, as well. However, it is also used in a variety of processes such as waste treatment, food processing, and refining metals, stone, clay, and petroleum.
Natural gas can also be used as an alternative fuel for cars, buses, trucks, and other vehicles. Currently, there are more than five million natural gas vehicles (NGV) worldwide, and more than 150,000 in the United States.
Although NGVs initially cost more than gas-powered vehicles, they are cheaper to refuel and are the cleanest-running vehicles in the world. Gasoline- and diesel-powered vehicles emit harmful and toxic substances including arsenic, nickel, and nitrogen oxides. In contrast, NGVs may emit minute amounts of propane or butane, but release 70 percent less carbon monoxide into the atmosphere.
Using the new technology of fuel cells, the energy from natural gas is also used to generate electricity. Instead of burning natural gas for energy, fuel cells generate electricity with electrochemical reactions. These reactions produce water, heat, and electricity without any other byproducts or emissions. Scientists are still researching this method of producing electricity in order to affordably apply it to electric products.
Natural Gas and the Environment
Natural gas usually needs to be processed before it can be used. When it is extracted, natural gas can contain a variety of elements and compounds other than methane. Water, ethane, butane, propane, pentanes, hydrogen sulphide, carbon dioxide, water vapor, and occasionally helium and nitrogen may be present in a natural gas well. In order to be used for energy, the methane is processed and separated from the other components. The gas that is used for energy in our homes is almost pure methane.
Like other fossil fuels, natural gas can be burned for energy. In fact, it is the cleanest-burning fuel, meaning it releases very few byproducts.
When fossil fuels are burned, they can release (or emit) different elements, compounds, and solid particles. Coal and oil are fossil fuels with very complex molecular formations, and contain a high amount of carbon, nitrogen, and sulfur. When they are burned, they release high amounts of harmful emissions, including nitrogen oxides, sulfur dioxide, and particles that drift into the atmosphere and contribute to air pollution.
In contrast, the methane in natural gas has a simple molecular makeup: CH4. When it is burned, it emits only carbon dioxide and water vapor. Humans exhale the same two components when we breathe.
Carbon dioxide and water vapor, along with other gases such as ozone and nitrous oxide, are known as greenhouse gases. The increasing amounts of greenhouse gases in the atmosphere are linked to global warming and could have disastrous environmental consequences.
Although burning natural gas still emits greenhouse gases, it emits almost 30 percent less CO2 than oil, and 45 percent less CO2 than coal.
Safety
As with any extractive activity, drilling for natural gas can lead to leaks. If the drill hits an unexpected high-pressure pocket of natural gas, or the well is damaged or ruptures, the leak can be immediately hazardous.
Because natural gas dissipates so quickly into the air, it does not always cause an explosion or burn. However, the leaks are an environmental hazard that also leak mud and oil into the surrounding areas.
If hydraulic fracturing was used to expand a well, the chemicals from that process can contaminate local aquatic habitats and drinking water with highly radioactive materials. The uncontained methane released in the air can also force people to temporary evacuate the area.
Leaks can also occur slowly over time. Until the 1950s, cast iron was a popular choice for distribution pipelines, but it allows a high amount of natural gas to escape. The cast iron pipes become leaky after years of freeze-thaw cycles, heavy overhead traffic, and strains from the naturally shifting soil. Methane leaks from these distribution pipelines make up more than 30 percent of the methane emmissions in the U.S. natural gas distribution sector. Today, pipelines are made out of a variety of metals and plastics to reduce leakage.
Burning of natural gas coming out of the ground
Natural gas (also called fossil gas, methane gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane (97%)[1] in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbon dioxide, nitrogen, hydrogen sulfide, and helium are also usually present.[2] Methane is colorless and odorless, and the second largest greenhouse gas contributor to global climate change after carbon dioxide.[3] Because natural gas is odorless, odorizers such as mercaptan (which smells like sulfur or rotten eggs) are commonly added to it for safety so that leaks can be readily detected.[4]
Natural gas is a fossil fuel and non-renewable resource that is formed when layers of organic matter (primarily marine microorganisms)[5] decompose under anaerobic conditions and are subjected to intense heat and pressure underground over millions of years.[6] The energy that the decayed organisms originally obtained from the sun via photosynthesis is stored as chemical energy within the molecules of methane and other hydrocarbons.[7]
Natural gas can be burned for heating, cooking,[8] and electricity generation. It is also used as a chemical feedstock in the manufacture of plastics and other commercially important organic chemicals and less commonly used as a fuel for vehicles.
The extraction and consumption of natural gas is a major and growing contributor to climate change.[9][10][11] Both the gas itself (specifically methane) and carbon dioxide, which is released when natural gas is burned, are greenhouse gases.[12][13] When burned for heat or electricity, natural gas emits fewer toxic air pollutants, less carbon dioxide, and almost no particulate matter compared to other fossil and biomass fuels.[14] However, gas venting and unintended fugitive emissions throughout the supply chain can result in natural gas having a similar carbon footprint to other fossil fuels overall.[15]
Natural gas can be found in underground geological formations, often alongside other fossil fuels like coal and oil (petroleum). Most natural gas has been created through either biogenic or thermogenic processes. Biogenic gas is formed when methanogenic organisms in marshes, bogs, landfills, and shallow sediments anaerobically decompose but are not subjected to high temperatures and pressures. Thermogenic gas takes a much longer period of time to form and is created when organic matter is heated and compressed deep underground.[16][6]
During petroleum production, natural gas is sometimes flared rather than being collected and used. Before natural gas can be burned as a fuel or used in manufacturing processes, it almost always has to be processed to remove impurities such as water. The byproducts 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 must also be removed.
Natural gas is sometimes informally referred to simply as "gas", especially when it is being compared to other energy sources, such as oil, coal or renewables. However, it is not to be confused with gasoline, which is also shortened in colloquial usage to "gas", especially in North America.[17]
Natural gas is measured in standard cubic meters or standard cubic feet. The density compared to air ranges from 0.58 (16.8 g/mole, 0.71 kg per standard cubic meter) to as high as 0.79 (22.9 g/mole, 0.97 kg per scm), but generally less than 0.64 (18.5 g/mole, 0.78 kg per scm).[18] For comparison, pure methane (16.0425 g/mole) has a density 0.5539 times that of air (0.678 kg per standard cubic meter).
Name
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In the early 1800s, natural gas became known as "natural" to distinguish it from the dominant gas fuel at the time, coal gas.[19] Unlike coal gas, which is manufactured by heating coal, natural gas can be extracted from the ground in its native gaseous form. When the use of natural gas overtook the use of coal gas in English speaking countries in the 20th century, it was increasingly referred to as simply "gas."[20] In order to highlight its role in exacerbating the climate crisis, however, many organizations have criticized the continued use of the word "natural" in referring to the gas. These advocates prefer the term "fossil gas" or "methane gas" as better conveying to the public its climate threat.[21][22][23] A 2020 study of Americans' perceptions of the fuel found that, across political identifications, the term "methane gas" led to better estimates of its harms and risks.[24]
History
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A gas bill from Baltimore, Maryland, 1834, for manufactured coal gas, before the introduction of ground-extracted methane gas.Natural gas can come out of the ground and cause a long-burning fire. In ancient Greece, the gas flames at Mount Chimaera contributed to the legend of the fire-breathing creature Chimera. In ancient China, gas resulting from the drilling for brines was first used by about 400 BC.[25] The Chinese transported 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.[26][27]
Natural gas was not widely used before the development of long distance pipelines in the early twentieth century. Before that, most use was near to the source of the well, and the predominant gas for fuel and lighting during the industrial revolution was manufactured coal gas.[28]
The history of natural gas in the United States begins with localized use. In the seventeenth century, French missionaries witnessed the American Indians setting fire to natural gas seeps around lake Erie, and scattered observations of these seeps were made by European-descended settlers throughout the eastern seaboard through the 1700s.[29] In 1821, William Hart dug the first commercial natural gas well in the United States at Fredonia, New York, United States, which led in 1858 to the formation of the Fredonia Gas Light Company.[30] Further such ventures followed near wells in other states, until technological innovations allowed the growth of major long distance pipelines from the 1920s onward.[29]
By 2009, 66,000 km3 (16,000 cu mi) (or 8%) had been used out of the total 850,000 km3 (200,000 cu mi) of estimated remaining recoverable reserves of natural gas.[31]
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Natural gas
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Natural gas drilling rig in Texas, USIn the 19th century, natural gas was primarily obtained as a by-product of producing oil. 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. The gas was often viewed as a by-product, a hazard, and a disposal problem in active oil fields. The large volumes produced could not be used until relatively expensive pipeline and storage facilities were constructed to deliver the gas to consumer markets.
Until the early part of the 20th century, most natural gas associated with oil was either simply released or burned off at oil fields. Gas venting and production flaring are still practised in modern times, but efforts are ongoing around the world to retire them, and to replace them with other commercially viable and useful alternatives.[32][33] Unwanted gas (or stranded gas without a market) is often returned to the reservoir with 'injection' wells while awaiting a possible future market or to re-pressurize the formation, which can enhance oil 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.[34] In 2011, Royal Dutch Shell's 140,000 barrels (22,000 m3) per day F–T plant went into operation in Qatar.[35]
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).[36] 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 transported.[37]
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, unconventional 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 Central Intelligence Agency (47,600 km3)[38] and Energy Information Administration (47,800 km3),[39][40] as well as the Organization of Petroleum Exporting Countries (48,700 km3).[41] Contrarily, BP credits Russia with only 32,900 km3,[42] which would place it in second, slightly behind Iran (33,100 to 33,800 km3, depending on the source).
Countries by natural gas proven reserves (2014), based on data from The World FactbookIt is estimated that there are about 900,000 km3 of "unconventional" gas such as shale gas, of which 180,000 km3 may be recoverable.[43] In turn, many studies from MIT, Black & Veatch and the US Department of Energy predict that natural gas will account for a larger portion of electricity generation and heat in the future.[44][better source needed]
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.
Shale gas
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The location of shale gas compared to other types of gas depositsShale gas is natural gas produced from shale. Because shale's matrix permeability is 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.[45] Because of increased shale gas production the United States was in 2014 the number one natural gas producer in the world.[46] The production of shale gas in the United States has been described as a "shale gas revolution" and as "one of the landmark events in the 21st century."[47]
Following the increased production in the United States, shale gas exploration is beginning in countries such as Poland, China, and South Africa.[48][49][50] Chinese geologists have identified the Sichuan Basin as a promising target for shale gas drilling, because of the similarity of shales to those that have proven productive in the United States. Production from the Wei-201 well is between 10,000 and 20,000 m3 per day.[51] In late 2020, China National Petroleum Corporation claimed daily production of 20 million cubic meters of gas from its Changning-Weiyuan demonstration zone.[52][unreliable source?]
Town gas
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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 was 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 lighting. (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.
Crystallized natural gas – clathrates
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Huge quantities of natural gas (primarily methane) exist in the form of clathrates 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 2013, Japan Oil, Gas and Metals National Corporation (JOGMEC) announced that they had recovered commercially relevant quantities of natural gas from methane hydrate.[53]
Processing
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Natural gas processing plant in Aderklaa, Lower AustriaThe 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 markets.
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 +).[54][55][56][57]
Schematic flow diagram of a typical natural gas processing plantDemand
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Natural gas extraction by countries in cubic meters per year around 2013As of mid-2020, natural gas production in the US had peaked three times, with current levels exceeding both previous peaks. It reached 24.1 trillion cubic feet per year in 1973, followed by a decline, and reached 24.5 trillion cubic feet in 2001. After a brief drop, withdrawals increased nearly every year since 2006 (owing to the shale gas boom), with 2017 production at 33.4 trillion cubic feet and 2019 production at 40.7 trillion cubic feet. After the third peak in December 2019, extraction continued to fall from March onward due to decreased demand caused by the COVID-19 pandemic in the US.[58]
The 2021 global energy crisis was driven by a global surge in demand as the world quit the economic recession caused by COVID-19, particularly due to strong energy demand in Asia.[59]
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Polyethylene plastic main being placed in a trench Construction close to high pressure gas transmission pipelines is discouraged, often with standing warning signs.[60]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 the US 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.[61][better source needed][full citation needed] New pipelines are planned or under construction between Western Europe and the Near East or Northern Africa.[62]
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
2, H
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 carrier ships transport liquefied natural gas (LNG) across oceans, while tank trucks can carry LNG or compressed natural gas (CNG) over shorter distances.[63] Sea transport using CNG carrier ships that are now under development may be competitive with LNG transport in specific conditions.[citation needed]
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 offshore.
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.
Peoples 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.[64] 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 regulatory restrictions.
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 2012.[65]
A "master gas system" was invented in Saudi Arabia in the late 1970s, ending any necessity for flaring. Satellite and nearby infra-red camera observations, however, shows that flaring[66][67][68][69] and venting[70] are still happening in some 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 [references about geological storage needed]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.[71] In the first decade of the 21st century, Gazprom, the state-owned energy company in Russia, engaged in disputes with Ukraine and 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.[72] The United States is preparing to export natural gas.[73]
Floating liquefied natural gas
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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 which currently make them impractical to develop via a land-based LNG operation. FLNG technology also provides a number of environmental and economic advantages:
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 FLNG facilities. Petronas is close to completion on their FLNG-1[76] at Daewoo Shipbuilding and Marine Engineering and are underway on their FLNG-2 project[77] at Samsung Heavy Industries. Shell Prelude is due to start production 2017.[78] The Browse LNG project will commence FEED in 2019.[79]
Uses
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Natural gas is primarily used in the northern hemisphere. North America and Europe are major consumers.
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 methane (CH
4). The natural gas transmission lines extend to the natural gas processing plant or unit which removes the higher-molecular weight hydrocarbons to produce natural gas with energy content between 35–39 megajoules per cubic metre (950–1,050 British thermal units per cubic foot). The processed natural gas may then be used for residential, commercial and industrial uses.
Mid-stream natural gas
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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 repressurize the mid-stream natural gas as the gas travels. Typically, natural gas powered engines require 35–39 MJ/m3 (950–1,050 BTU/cu ft) natural gas to operate at the rotational name plate specifications.[80] Several methods are used to remove these higher molecular weighted gases for use by the natural gas engine. A few technologies are as follows:
Power generation
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Domestic use
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Manhole for domestic gas supply, London, UKIn the US, over one-third of households (>40 million homes) cook with gas.[3] 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.[83] Stanford scientists estimated that gas stoves emit 0.8–1.3% of the gas they use as unburned methane and that total U.S. stove emissions are 28.1 gigagrams of methane.[3] In much of the developed world it is supplied through pipes to homes, where it is used for many purposes including ranges and ovens, heating/cooling, outdoor and portable grills, and central heating.[84] 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 with a standard preassure around 1.7 kilopascals (0.25 psi) over atmospheric preassure. The pressures in the supply lines vary, either the standard utilization pressure (UP) mentioned above or elevated pressure (EP), which may be anywhere from 7 to 800 kilopascals (1 to 120 psi) over atmospheric pressure. Systems using EP have a regulator at the service entrance to step down to UP.[85]
Natural gas piping systems inside buildings are often designed with pressures of 14 to 34 kilopascals (2 to 5 psi), and have downstream pressure regulators to reduce pressure as needed. In the United States the maximum allowable operating pressure for natural gas piping systems within a building is based on NFPA 54: National Fuel Gas Code,[86] except when approved by the Public Safety Authority or when insurance companies have more stringent requirements.
Generally, natural gas system pressures are not allowed to exceed 5 psi (34 kPa) unless all of the following conditions are met:
Generally, a maximum liquefied petroleum gas pressure of 20 psi (140 kPa) is allowed, provided the building is used specifically for industrial or research purposes and is constructed in accordance with NFPA 58: Liquefied Petroleum Gas Code, Chapter 7.[87]
A seismic earthquake valve operating at a pressure of 55 psig (3.7 bar) can stop the flow of natural gas into the site wide natural gas distribution piping network (that runs (outdoors underground, above building roofs, and or within the upper supports of a canopy roof). Seismic earthquake valves are designed for use at a maximum of 60 psig.[88][89]
In Australia, natural gas is transported from gas processing facilities to regulator stations via transmission pipelines. Gas is then regulated down to distributed pressures and the gas is distributed around a gas network via gas mains. Small branches from the network, called services, connect individual domestic dwellings, or multi-dwelling buildings to the network. The networks typically range in pressures from 7 kPa (low pressure) to 515 kPa (high pressure). Gas is then regulated down to 1.1 kPa or 2.75 kPa, before being metered and passed to the consumer for domestic use.[90] Natural gas mains are made from a variety of materials: historically cast iron, though more modern mains are made from steel or polyethylene.
In some states in the USA natural gas can be supplied by independent natural gas wholesalers/suppliers using existing pipeline owners' infrastructure through Natural Gas Choice programs.
LPG (liquefied petroleum gas) typically fuels outdoor and portable grills. Although, compressed natural gas (CNG) is sparsely available for similar applications in the US in rural areas underserved by the existing pipeline system and distribution network of the less expensive and more abundant LPG (liquefied petroleum gas).
A Washington, D.C. Metrobus, which runs on natural gasTransportation
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CNG is a cleaner and also cheaper alternative to other automobile fuels such as gasoline (petrol).[91] By the end of 2014, there were over 20 million natural gas vehicles worldwide, led by Iran (3.5 million), China (3.3 million), Pakistan (2.8 million), Argentina (2.5 million), India (1.8 million), and Brazil (1.8 million).[92] 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.[93]
Besides use in road vehicles, CNG can also be used in aircraft.[94] Compressed natural gas has been used in some aircraft like the Aviat Aircraft Husky 200 CNG[95] and the Chromarat VX-1 KittyHawk[96]
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.[97] 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.[citation needed]
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.[citation needed]
Fertilizers
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Natural gas is a major feedstock for the production of ammonia, via the Haber process, for use in fertilizer production.[84][98] The development of synthetic nitrogen fertilizer has significantly supported global population growth — it has been estimated that almost half the people on the Earth are currently fed as a result of synthetic nitrogen fertilizer use.[99][100]
Hydrogen
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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 hydrogen vehicles.
Animal and fish feed
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Protein rich animal and fish feed is produced by feeding natural gas to Methylococcus capsulatus bacteria on commercial scale.[101][102][103]
Natural gas components(alkanes) can be converted into olefins(alkenes) or other chemical synthesis. Ethane by oxidative dehydrogenation converts to ethylene, which can be further converted to ethylene oxide, ethylene glycol, acetaldehyde or other olefins. Propane by oxidative hydrogenation converts to propylene or can be oxidized to acrylic acid and acrylonitrile.
Other
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Natural gas is also used in the manufacture of fabrics, glass, steel, plastics, paint, synthetic oil, and other products.[104]
Fuel for industrial heating and desiccation processes.
Raw material for large-scale fuel production using gas-to-liquid (GTL) process (e.g. to produce sulphur-and aromatic-free diesel with low-emission combustion).
Environmental effects
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Deaths caused by use of fossil fuels such as natural gas (areas of rectangles in chart) greatly exceed those resulting from production of renewable energy (rectangles barely visible in chart).[105]Greenhouse effect and natural gas release
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The warming influence (called radiative forcing) of long-lived greenhouse gases has increased substantially in the last 40 years, with carbon dioxide and methane being the dominant drivers of global warming.[106]Human activity is responsible for about 60% of all methane emissions and for most of the resulting increase in atmospheric methane.[107][108][109] Natural gas is intentionally released or is otherwise known to leak during the extraction, storage, transportation, and distribution of fossil fuels. Globally, methane accounts for an estimated 33% of anthropogenic greenhouse gas warming.[110] The decomposition of municipal solid waste (a source of landfill gas) and wastewater account for an additional 18% of such emissions. These estimates include substantial uncertainties[111] which should be reduced in the near future with improved satellite measurements, such as those planned for MethaneSAT.[13]
After release to the atmosphere, methane 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.[112][113] While the lifetime of atmospheric methane is relatively short when compared to carbon dioxide,[114] 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 100-year period. Natural gas is thus a potent greenhouse gas due to the strong radiative forcing of methane in the short term, and the continuing effects of carbon dioxide in the longer term.[109]
Targeted efforts to reduce warming quickly by reducing anthropogenic methane emissions is a climate change mitigation strategy supported by the Global Methane Initiative.[110]
Greenhouse gas emissions
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When refined and burned, natural gas can produce 25–30% less carbon dioxide per joule delivered than oil, and 40–45% less than coal.[115] It can also produce potentially fewer toxic pollutants than other hydrocarbon fuels.[115][116] However, compared to other major fossil fuels, natural gas causes more emissions in relative terms during the production and transportation of the fuel, meaning that the life cycle greenhouse gas emissions are about 50% higher than the direct emissions from the site of consumption.[117][118]
In terms of the warming effect over 100 years, natural gas production and use comprises about one fifth of human greenhouse gas emissions, and this contribution is growing rapidly. Globally, natural gas use emitted about 7.8 billion tons of CO
2 in 2020 (including flaring), while coal and oil use emitted 14.4 and 12 billion tons, respectively.[119] The IEA estimates the energy sector (oil, natural gas, coal and bioenergy) to be responsible for about 40% of human methane emissions.[120] According to the IPCC Sixth Assessment Report, natural gas consumption grew by 15% between 2015 and 2019, compared to a 5% increase in oil and oil product consumption.[121]
The continued financing and construction of new gas pipelines indicates that huge emissions of fossil greenhouse gases could be locked-in for 40 to 50 years into the future.[122] In the U.S. state of Texas alone, five new long-distance gas pipelines have been under construction, with the first entering service in 2019,[123] and the others scheduled to come online during 2020–2022.[124]: 23
Installation bans
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To reduce its greenhouse emissions, the Netherlands is subsidizing a transition away from natural gas for all homes in the country by 2050. In Amsterdam, no new residential gas accounts have been allowed since 2018, and all homes in the city are expected to be converted by 2040 to use the excess heat from adjacent industrial buildings and operations.[125] Some cities in the United States have started prohibiting gas hookups for new houses, with state laws passed and under consideration to either require electrification or prohibit local requirements.[126] New gas appliance hookups are banned in New York State[127] and the Australian Capital Territory.[128] Additionally, the state of Victoria in Australia is set to implement a ban on new natural gas hookups starting from January 1, 2024, as part of its gas substitution roadmap.[129]
The UK government is also experimenting with alternative home heating technologies to meet its climate goals.[130] To preserve their businesses, natural gas utilities in the United States have been lobbying for laws preventing local electrification ordinances, and are promoting renewable natural gas and hydrogen fuel.[131]
Other pollutants
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Although natural gas produces far lower amounts of sulfur dioxide and nitrogen oxides (NOx) than other fossil fuels,[116] NOx from burning natural gas in homes can be a health hazard.[132]
Radionuclides
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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 extraction equipment.[133]
Safety concerns
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A pipeline odorant injection stationThe natural gas extraction workforce face unique health and safety challenges.[134][135]
Production
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Some gas fields yield sour gas containing hydrogen sulfide (H
2S), a toxic compound when inhaled. Amine gas treating, an industrial scale process which removes acidic gaseous components, is often used to remove hydrogen sulfide from natural gas.[136]
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.[137]
Fracking
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Releasing natural gas from subsurface porous rock formations may be accomplished by a process called hydraulic fracturing or "fracking". Since the first commercial hydraulic fracturing operation in 1949, approximately one million wells have been hydraulically fractured in the United States.[138] The production of natural gas from hydraulically fractured wells has used the technological developments of directional and horizontal drilling, which improved access to natural gas in tight rock formations.[139] Strong growth in the production of unconventional gas from hydraulically fractured wells occurred between 2000 and 2012.[140]
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 formation.[141]
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 and 2010, and nearly 3 million gallons for horizontal gas wells between 2000 and 2010.[142]
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.[143] 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.[144] 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.[145][146] The decades in development of drilling technology for conventional and unconventional oil and gas production have not only improved access to natural gas in low-permeability reservoir rocks, but also posed significant adverse impacts on environmental and public health.[147][148][149][150]
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).[151] 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.[152] 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 are 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.[153]
Historically low gas prices have delayed the nuclear renaissance, as well as the development of solar thermal energy.[154]
Added odor
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In its native state, natural gas is colorless and almost odorless. In the USA, the New London School explosion that occurred in 1937 in Texas caused a push for legislation requiring the addition of an odorant to assist consumers in detecting leaks. An odorizer with an unpleasant smell, such as thiophane or tert-Butylthiol (t-butyl mercaptan) may be added. Situations have occurred in which an odorant cannot be properly detected by an observer with a normal sense of smell despite being detectable by analytical instruments. This is caused by odor masking, when one odor overpowers the sensation of another. As of 2011, the industry is conducting research on the causes of odor masking.[155][needs update]
Risk of explosion
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Gas network emergency vehicle responding to a major fire in Kyiv, UkraineExplosions 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. Leaks often result from excavation work, such as when contractors dig and strike pipelines, sometimes without knowing any damage resulted. 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, destroying one or more buildings in the process. Many building codes now forbid the installation of gas pipes inside cavity walls or below floor boards to mitigate against this risk. Gas usually dissipates readily outdoors, but can sometimes collect in dangerous quantities if flow rates are high enough.[156] However, considering the tens of millions of structures that use the fuel, the individual risk of using natural gas is low.
Risk of carbon monoxide inhalation
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Natural gas heating systems may cause carbon monoxide poisoning if unvented or poorly vented. Improvements in natural gas furnace designs have greatly reduced CO poisoning concerns. Detectors are also available that warn of carbon monoxide or explosive gases such as methane and propane.[157]
Energy content, statistics, and pricing
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Comparison of natural gas prices in Japan, United Kingdom, and United States, 2007–2011Quantities of natural gas are measured in standard cubic meters (cubic meter of gas at temperature 15 °C (59 °F) and pressure 101.325 kPa (14.6959 psi)) or standard cubic feet (cubic foot of gas at temperature 60.0 °F and pressure 14.73 psi (101.6 kPa)), 1 standard cubic meter = 35.301 standard cubic feet. 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 50 to 54 MJ/kg depending on the density.[158][159] For comparison, the heat of combustion of pure methane is 37.7 MJ per standard cubic metre, or 55.5 MJ/kg.
Except in the European Union, the U.S., and Canada, natural gas is sold in gigajoule retail units. LNG (liquefied natural gas) and LPG (liquefied petroleum gas) are traded in metric tonnes (1,000 kg) or million BTU 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. The European Union aimed to cut its gas dependency on Russia by two-thirds in 2022.[160]
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). This was named the Zohr gas field and could hold a potential 30 trillion cubic feet (850 billion cubic meters) of natural gas. ENI said that the energy is about 5.5 billion barrels of oil equivalent [BOE] (3.4×1010 GJ). The Zohr 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.[161]
European Union
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Gas prices for end users vary greatly across the EU.[162] 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,[163] as well as strengthen relations with other Mediterranean countries and foster investments in the region.[164] Qatar has been asked by the US to supply emergency gas to the EU in case of supply disruptions in the Russo-Ukrainian crisis.[165]
United States
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US Natural 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.[166]
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. The typical caloric value of natural gas is roughly 1,000 BTU per cubic foot, depending on gas composition. Natural gas in the United States is traded as a futures contract on the New York Mercantile Exchange. Each contract is for 10,000 million BTU or 10 billion BTU (10,551 GJ). Thus, if the price of gas is $10/million BTU on the NYMEX, the contract is worth $100,000.
Canada
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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 80 litres (0.5 barrels) of oil, or 28 m3 or 1,000 cu ft or 1 million BTUs 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.
Adsorbed natural gas (ANG)
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Natural gas may be stored by adsorbing it to the porous solids called sorbents. The optimal condition for methane storage is at room temperature and atmospheric pressure. Pressures up to 4 MPa (about 40 times atmospheric pressure) will yield greater storage capacity. The most common sorbent used for ANG is activated carbon (AC), primarily in three forms: Activated Carbon Fiber (ACF), Powdered Activated Carbon (PAC), and activated carbon monolith.[167]
See also
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References
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