Natural gas 1 Natural gas Natural gas extraction by countries in cubic meters per year. Natural gas is a naturally occurring hydrocarbon gas mixture consisting primarily of methane, with up to 20 percent [1] concentration of other hydrocarbons (usually ethane) as well as small amounts of impurities such as carbon dioxide. Natural gas is widely used and is an important energy source in many applications including heating buildings, generating electricity, providing heat and power to industry and vehicles and is also a feedstock in the manufacture of products such as fertilizers. Natural gas is found in deep underground natural rock formations or associated with other hydrocarbon reservoirs, in coal beds, and as methane clathrates. 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 material. [2] Before natural gas can be used as a fuel, it must undergo processing to clean the gas and remove impurities including water in order to the specifications of marketable natural gas. The by-products of processing include ethane, propane, butanes, pentanes, and higher molecular weight hydrocarbons, hydrogen sulphide (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. Sources Natural gas Natural gas drilling rig in Texas. In the 19th century, natural gas was usually obtained as a byproduct 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 bottle of soda pop 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 virtually valueless since it had to be piped to the end user. In the 19th century and early 20th century, such unwanted gas was usually burned off in the 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 economically feasible to move the gas from the wellsite to the end consumer.
Transcript
Natural gas 1
Natural gas
Natural gas extraction by countries in cubic meters per year.
Natural gas is a naturally occurringhydrocarbon gas mixture consistingprimarily of methane, with up to 20percent[1] concentration of otherhydrocarbons (usually ethane) as wellas small amounts of impurities such ascarbon dioxide. Natural gas is widelyused and is an important energy sourcein many applications including heatingbuildings, generating electricity,providing heat and power to industryand vehicles and is also a feedstock inthe manufacture of products such as fertilizers.
Natural gas is found in deep underground natural rock formations or associated with other hydrocarbon reservoirs, incoal beds, and as methane clathrates. Most natural gas was created over time by two mechanisms: biogenic andthermogenic. 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 material.[2]
Before natural gas can be used as a fuel, it must undergo processing to clean the gas and remove impurities includingwater in order to the specifications of marketable natural gas. The by-products of processing include ethane, propane,butanes, pentanes, and higher molecular weight hydrocarbons, hydrogen sulphide (which may be converted into puresulfur), 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 asoil or coal.
Sources
Natural gas
Natural gas drilling rig in Texas.
In the 19th century, natural gas was usually obtained as a byproduct of producingoil, since the small, light gas carbon chains came out of solution as the extractedfluids underwent pressure reduction from the reservoir to the surface, similar touncapping a bottle of soda pop where the carbon dioxide effervesces. Unwantednatural gas was a disposal problem in the active oil fields. If there was not amarket for natural gas near the wellhead it was virtually valueless since it had tobe piped to the end user. In the 19th century and early 20th century, suchunwanted gas was usually burned off in the oil fields. Today, unwanted gas (orstranded gas without a market) associated with oil extraction often is returned tothe reservoir with 'injection' wells while awaiting a possible future market or torepressurize the formation, which can enhance extraction rates from other wells.In regions with a high natural gas demand (such as the US), pipelines areconstructed when economically feasible to move the gas from the wellsite to theend consumer.
Another possibility is to export the natural gas as a liquid. Gas-to-liquids (GTL) is a developing technology thatconverts stranded natural gas into synthetic gasoline, diesel, or jet fuel through the Fischer-Tropsch processdeveloped during World War II Germany. Such fuel can be transported to users through conventional pipelines andtankers. Proponents claim GTL burns cleaner than comparable petroleum fuels. Most major international oilcompanies are in an advanced stage of GTL production, with a world-scale (140000 barrels (22000 m3) a day) GTLplant in Qatar scheduled to be in production before 2010.Natural gas can be "associated" (found in oil fields) or "non-associated" (isolated in natural gas fields), and is alsofound in coal beds (as coalbed methane). It sometimes contains significant amounts of ethane, propane, butane, andpentane—heavier hydrocarbons removed for commercial use prior to the methane being sold as a consumer fuel orchemical plant feedstock. Non-hydrocarbons such as carbon dioxide, nitrogen, helium (rarely), and hydrogen sulfidemust also be removed before the natural gas can be transported.[3]
Natural gas is commercially extracted from oil fields and natural gas fields. Gas extracted from oil wells is calledcasinghead gas or associated gas. The natural gas industry is extracting gas from increasingly more challengingresource types: sour gas, tight gas, shale gas, and coalbed methane.The world's largest proven gas reserves are located in Russia, with 4.757×1013 m³ (1.68×1015 cubic feet). With theGazprom company, Russia is frequently the world's largest natural gas extractor. Major proven resources (in billioncubic meters) are world 175,400 (2006), Russia 47,570 (2006), Iran 26,370 (2006), Qatar 25,790 (2007), SaudiArabia 6,568 (2006) and United Arab Emirates 5,823 (2006).It is estimated that there are about 900 trillion cubic meters of "unconventional" gas such as shale gas, of which 180trillion may be recoverable.[4] In turn, many studies from MIT, Black & Veatch and the DOE -- see natural gas --will account for a larger portion of electricity generation and heat in the future.[5]
The world's largest gas field is Qatar's offshore North Field, estimated to have 25 trillion cubic meters[6]
(9.0×1014cubic feet) of gas in place—enough to last more than 420 years at optimum extraction levels. The secondlargest natural gas field is the South Pars Gas Field in Iranian waters in the Persian Gulf. Located next to Qatar'sNorth Field, it has an estimated reserve of 8 to 14 trillion cubic meters[7] (2.8×1014 to 5.0×1014 cubic feet) of gas.Because natural gas is not a pure product, as the reservoir pressure drops when non-associated gas is extracted from afield under supercritical (pressure/temperature) conditions, the higher molecular weight components may partiallycondense upon isothermic depressurizing—an effect called retrograde condensation. The liquid thus formed may gettrapped as the pores of the gas reservoir get deposited. One method to deal with this problem is to re-inject dried gasfree 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 to collect this condensate.The resulting liquid is called natural gas liquid (NGL) and has commercial value.
Town gasTown gas, a synthetically produced mixture of methane and other gases, mainly the highly toxic carbon monoxide, isused in a similar way to natural gas and can be produced by treating coal chemically. This is a historical technology,not usually economically competitive with other sources of fuel gas today. But there are still some specific caseswhere it is the best option and it may be so into the future.Most town "gashouses" located in the eastern US in the late 19th and early 20th centuries were simple by-productcoke ovens which heated bituminous coal in air-tight chambers. The gas driven off from the coal was collected anddistributed 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) thatcollected in the bottoms of the gashouse ovens was often used for roofing and other water-proofing purposes, andwhen mixed with sand and gravel was used for paving streets.
BiogasWhen methane-rich gases are produced by the anaerobic decay of non-fossil organic matter (biomass), these arereferred to as biogas (or natural biogas). Sources of biogas include swamps, marshes, and landfills (see landfill gas),as well as sewage sludge and manure[8] by way of anaerobic digesters, in addition to enteric fermentation,particularly in cattle.Methanogenic archaea are responsible for all biological sources of methane, some in symbiotic relationships withother life forms, including termites, ruminants, and cultivated crops. Methane released directly into the atmospherewould be considered a pollutant. However, methane in the atmosphere is oxidized, producing carbon dioxide andwater. Methane in the atmosphere has a half life of seven years, meaning that if a tonne of methane were emittedtoday, 500 kilograms would have broken down to carbon dioxide and water after seven years.
U.S. natural gas extraction, 1900–2005. Source: EIA.
Other sources of methane, the principalcomponent of natural gas, includelandfill gas, biogas and methanehydrate. Biogas, and especially landfillgas, are already used in some areas, buttheir use could be greatly expanded.Landfill gas is a type of biogas, butbiogas usually refers to gas producedfrom organic material that has not beenmixed with other waste.
Landfill gas is created from thedecomposition of waste in landfills. Ifthe 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 produceelectricity or heat. Experimental systems were being proposed for use in parts of Hertfordshire, UK and Lyon inFrance.
Once water vapor is removed, about half of landfill gas is methane. Almost all of the rest is carbon dioxide, but thereare also small amounts of nitrogen, oxygen and hydrogen. There are usually trace amounts of hydrogen sulfide andsiloxanes, but their concentration varies widely. Landfill gas cannot be distributed through utility natural gaspipelines unless it is cleaned up to less than 3% CO2, and a few parts per million H2S, because CO2 and H2Scorrode the pipelines.[9] It is usually more economical to combust the gas on site or within a short distance of thelandfill using a dedicated pipeline. Water vapor is often removed, even if the gas is combusted on site. If lowtemperatures condense water out of the gas, siloxanes can be lowered as well because they tend to condense out withthe water vapor. Other non-methane components may also be removed in order to meet emission standards, toprevent fouling of the equipment or for environmental considerations. Co-firing landfill gas with natural gasimproves combustion, which lowers emissions.Gas generated in sewage treatment plants is commonly used to generate electricity. For example, the Hyperionsewage plant in Los Angeles burns 8 million cubic feet ( m3) of gas per day to generate power [10] New York Cityutilizes gas to run equipment in the sewage plants, to generate electricity, and in boilers.[11] Using sewage gas tomake electricity is not limited to large cities. The city of Bakersfield, California uses cogeneration at its sewerplants.[12] 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.[13]
Biogas is usually produced using agricultural waste materials, such as otherwise unusable parts of plants and manure. 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. Using materials that would otherwisegenerate no income, or even cost money to get rid of, improves the profitability and energy balance of biogasproduction.Anaerobic lagoons produce biogas from manure, while biogas reactors can be used for manure or plant parts. Likelandfill 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 contaminants.
The McMahon natural gas processing plant inTaylor, British Columbia, Canada.[14]
Crystallized natural gas – hydrates
Huge quantities of natural gas (primarily methane) exist in the form ofhydrates under sediment on offshore continental shelves and on land inarctic regions that experience permafrost such as those in Siberia(hydrates require a combination of high pressure and low temperatureto form). However, as of 2010 no technology has been developed toextract natural gas economically from hydrates.
In 2010, using current technology, the cost of extracting natural gasfrom crystallized natural gas is estimated to 100%–200% the cost ofextracting natural gas from conventional sources, and even higher fromoffshore deposits.[15]
Natural gas processingThe image below is a schematic block flow diagram of a typical natural gas processing plant. It shows the variousunit 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 +).[16] [17] [18] [19] [20]
Schematic flow diagram of a typical natural gasprocessing plant.
DepletionSee main article, Gas depletion
Uses
Power generationNatural gas is a major source of electricity generation through the use of gas turbines and steam turbines. 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 Hydrocarbon fuels, such as oil and coal, and produces less carbon dioxide per unit of energyreleased. For an equivalent amount of heat, burning natural gas produces about 30% less carbon dioxide than burningpetroleum and about 45% less than burning coal.[21] Combined cycle power generation using natural gas is thus thecleanest source of power available using hydrocarbon fuels, and this technology is widely used wherever gas can beobtained at a reasonable cost. Fuel cell technology may eventually provide cleaner options for converting natural gasinto electricity, but as yet it is not price-competitive.
Domestic useNatural gas dispensed from a simple stovetop can generate heat in excess of 2000°F (1093°C) making it a powerfuldomestic cooking and heating fuel.[22] In much of the developed world it is supplied to homes via pipes where it isused for many purposes including natural gas-powered ranges and ovens, natural gas-heated clothes dryers,heating/cooling, and central heating. Home or other building heating may include boilers, furnaces, and waterheaters. Compressed natural gas (CNG) is used in rural homes without connections to piped-in public utilityservices, or with portable grills. Natural gas is also supplied by independent natural gas suppliers through NaturalGas Choice programs throughout the United States. However, due to CNG being less economical than LPG, LPG(propane) is the dominant source of rural gas.
A Washington, D.C. Metrobus, which runs onnatural gas.
Transportation
CNG is a cleaner alternative to other automobile fuels such as gasoline(petrol) and diesel. As of 2008 there were 9.6 million natural gasvehicles worldwide, led by Pakistan (2.0 million), Argentina (1.7million), Brazil (1.6 million), Iran (1.0 million), and India(650,000).[23] [24] The energy efficiency is generally equal to that ofgasoline engines, but lower compared with modern diesel engines.Gasoline/petrol vehicles converted to run on natural gas suffer becauseof the low compression ratio of their engines, resulting in a cropping ofdelivered power while running on natural gas (10%–15%).CNG-specific engines, however, use a higher compression ratio due tothis fuel's higher octane number of 120–130.[25]
FertilizersNatural gas is a major feedstock for the production of ammonia, via the Haber process, for use in fertilizerproduction.
AviationRussian aircraft manufacturer Tupolev is currently running a development program to produce LNG- andhydrogen-powered aircraft.[26] The program has been running since the mid-1970s, and seeks to develop LNG andhydrogen variants of the Tu-204 and Tu-334 passenger aircraft, and also the Tu-330 cargo aircraft. It claims that atcurrent market prices, an LNG-powered aircraft would cost 5,000 roubles (~ $218/ £112) less to operate per ton,roughly equivalent to 60%, with considerable reductions to carbon monoxide, hydrocarbon and nitrogen oxideemissions.The advantages of liquid methane as a jet engine fuel are that it has more specific energy than the standard kerosenemixes do and that its low temperature can help cool the air which the engine compresses for greater volumetricefficiency, in effect replacing an intercooler. Alternatively, it can be used to lower the temperature of the exhaust.
HydrogenNatural gas can be used to produce hydrogen, with one common method being the hydrogen reformer. Hydrogen hasmany applications: it is a primary feedstock for the chemical industry, a hydrogenating agent, an importantcommodity for oil refineries, and the fuel source in hydrogen vehicles.
OtherNatural gas is also used in the manufacture of fabrics, glass, steel, plastics, paint, and other products.
Storage and transport
Polyethylene plastic main beingplaced in a trench.
Because of its low density, it is not easy to store natural gas or transport byvehicle. Natural gas pipelines are impractical across oceans. Many existingpipelines in America are close to reaching their capacity, prompting somepoliticians representing northern states to speak of potential shortages. In Europe,the gas pipeline network is already dense in the West.[27] New pipelines areplanned or under construction in Eastern Europe and between gas fields inRussia, Near East and Northern Africa and Western Europe. See also List ofnatural gas pipelines.
LNG carriers transport liquefied natural gas (LNG) across oceans, while tanktrucks can carry liquefied or compressed natural gas (CNG) over shorterdistances. Sea transport using CNG carrier ships that are now under developmentmay be competitive with LNG transport in specific conditions.
Gas is turned into liquid at a liquefaction plant, and is returned to gas form atregasification plant at the terminal. Shipborne regasification equipment is alsoused. LNG is the preferred form for long distance, high volume transportation of natural gas, whereas pipeline ispreferred for transport for distances up to 4,000 km over land and approximately half that distance offshore.
CNG is transported at high pressure, typically above 200 bars. Compressors and decompression equipment are lesscapital intensive and may be economical in smaller unit sizes than liquefaction/regasification plants. Natural gastrucks and carriers may transport natural gas directly to end-users, or to distribution points such as pipelines.
Peoples Gas Manlove Field natural gas storagearea in Newcomb Township, Champaign County,
Illinois. In the foreground (left) is one of thenumerous wells for the underground storage area,
with an LNG plant, and above ground storagetanks are in the background (right).
In the past, the natural gas which was recovered in the course ofrecovering petroleum could not be profitably sold, and was simplyburned at the oil field in a process known as flaring. Flaring is nowillegal in many countries.[28] Additionally, companies now recognizethat gas may be sold to consumers in the form of LNG or CNG, orthrough other transportation methods. The gas is now re-injected intothe formation for later recovery. The re-injection also assists oilpumping by keeping underground pressures higher.
A "master gas system" was invented in Saudi Arabia in the late 1970s,ending any necessity for flaring. Satellite observation, however, showsthat flaring[29] and venting[30] are still practiced in some gas-extractingcountries.
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 generateelectricity.
Natural gas is often stored underground inside depleted gas reservoirs from previous gas wells, salt domes, or intanks 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 importantissue in international politics, and countries vie for control of pipelines.[31] 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 priceof natural gas, which have created worries that gas deliveries to parts of Europe could be cut off for politicalreasons.[32]
Floating Liquefied Natural Gas (FLNG) is an innovative technology designed to enable the development of offshoregas resources that would otherwise remain untapped because due to environmental or economic factors it isnonviable to develop them via a land-based LNG operation. FLNG technology also provides a number ofenvironmental and economic advantages:• 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 anLNG processing plant, which significantly reduces the environmental footprint.[33] Avoiding construction alsohelps preserve marine and coastal environments. In addition, environmental disturbance will be minimised duringdecommissioning because the facility can easily be disconnected and removed before being refurbished andre-deployed elsewhere.
• Economic – Where pumping gas to shore can be prohibitively expensive, FLNG makes developmenteconomically viable. As a result, it will open up new business opportunities for countries to develop offshore gasfields that would otherwise remain stranded, such as those offshore East Africa.[34]
Many gas and oil companies are considering the economic and environmental benefits of Floating Liquefied NaturalGas (FLNG)However, for the time being, the only FLNG facility now in development is being built by Shell,[35] duefor completion in around 2017.[36]
Environmental effects
CO2 emissionsNatural gas is often described as the cleanest fossil fuel, producing less carbon dioxide per joule delivered than eithercoal or oil[21] and far fewer pollutants than other hydrocarbon fuels. However, in absolute terms, it does contributesubstantially to global carbon emissions, and this contribution is projected to grow. According to the IPCC FourthAssessment Report (Working Group III Report, chapter 4), in 2004, natural gas produced about 5.3 billion tons ayear of CO2 emissions, while coal and oil produced 10.6 and 10.2 billion tons respectively (figure 4.4). According toan updated version of the SRES B2 emissions scenario, however, by the year 2030, natural gas would be the sourceof 11 billion tons a year, with coal and oil now 8.4 and 17.2 billion respectively because demand is increasing 1.9% ayear[37] (Total global emissions for 2004 were estimated at over 27,200 million tons)In addition, natural gas itself is a greenhouse gas more potent than carbon dioxide. Although natural gas is released into the atmosphere in much smaller quantities, methane is oxidized in the atmosphere, and hence natural gas affects the atmosphere for approximately 12 years, compared to CO2, which is already oxidized, and has effect for 100 to 500 years. Natural gas is composed mainly of methane, which has a radiative forcing twenty times greater than carbon dioxide. Based on such composition, a ton of methane in the atmosphere traps as much radiation as 20 tons of carbon dioxide; however, it remains in the atmosphere for 8–40 times less time. Carbon dioxide still receives the lion's share of attention concerning greenhouse gases because it is released in much larger amounts. Still, it is inevitable when natural gas is used on a large scale that some of it will leak into the atmosphere. (Coal methane not captured by coal bed methane extraction techniques is simply lost into the atmosphere; however, most methane in the atmosphere is currently from animals and bacteria, not from industrial leaks.) Current estimates by the EPA place
global emissions of methane at 3 trillion cubic feet (85 km3) annually,[38] or 3.2% of global production.[39] Directemissions of methane represented 14.3% of all global anthropogenic greenhouse gas emissions in 2004.[40]
Other pollutantsNatural gas produces far lower amounts of sulfur dioxide and nitrous oxides than any other hydrocarbon fuel.[41]
Carbon dioxide produced is 117,000 ppm vs 208,000 for burning coal. Carbon monoxide produced is 40 ppm vs 208for burning coal. Nitrogen oxides produced is 92 ppm vs 457 for burning coal. Sulfur dioxide is 1 ppm vs 2,591 forburning coal. Mercury is 0 vs .016 for burning coal.[42] Particulates are also a major contribution to global warming.Natural gas has 7ppm vs coal's 2,744ppm.[43]
ExtractionThe practice of hydraulic fracturing, the process of using a combination of chemicals ranging from harmless to toxicto force natural gas to the surface from reservoirs with low permeability, has come under scrutiny internationally dueto concerns about environmental and health safety, and has been suspended or banned in some countries. See also:Environmental concerns with hydraulic fracturing
Safety concerns
A pipeline odorant injection station
Production
In mines, where methane seeping from rock formations has no odor,sensors are used, and mining apparatus such as the Davy lamp has beenspecifically developed to avoid ignition sources.
Some gas fields yield sour gas containing hydrogen sulfide (H2S). Thisuntreated gas is toxic. Amine gas treating, an industrial scale processwhich removes acidic gaseous components, is often used to removehydrogen sulfide from natural gas.[44]
Extraction of natural gas (or oil) leads to decrease in pressure in thereservoir. 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.
Releasing the gas from low-permeability reservoirs is accomplished by a process called hydraulic fracturing or"hydrofracking". To allow the natural gas to flow out of the shale, oil operators force one to 9 million US gallons(34000 m3) of water mixed with a variety of chemicals through the wellbore casing into the shale. The high pressurewater breaks up or "fracks" the shale, which releases the trapped gas. Sand is added to the water as a proppant tokeep the fractures in the shale open, thus enabling the gas to flow into the casing and then to the surface. Thechemicals are added to the frack fluid to reduce friction and combat corrosion. During the extracting life of a gaswell, other low concentrations of other chemical substances may be used, such as biocides to eliminate fouling, scaleand corrosion inhibitors, oxygen scavengers to remove a source of corrosion, and acids to clean the perforations inthe pipe.Dealing with fracking fluid can be a challenge. Along with the gas, 30% to 70% of the chemically-laced frack fluid,or flow back, returns to the surface. Additionally, a significant amount of salt and other minerals, once a part of therock layers that were under prehistoric seas, may be incorporated in the flow back as they dissolve in the frack fluid.
UseIn order to assist in detecting leaks, a minute amount of odorant is added to the otherwise colorless and almostodorless gas used by consumers. The odor has been compared to the smell of rotten eggs, due to the added butylmercaptan. Sometimes a related compound, thiophane may be used in the mixture.Explosions caused by natural gas leaks occur a few times each year. Individual homes, small businesses and otherstructures are most frequently affected when an internal leak builds up gas inside the structure. Frequently, the blastwill be enough to significantly damage a building but leave it standing. In these cases, the people inside tend to haveminor 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 sometimescollect in dangerous quantities if flow rates are high enough. However, considering the tens of millions of structuresthat use the fuel, the individual risk of using natural gas is very low.Natural gas heating systems are a minor source of carbon monoxide deaths in the United States. According to the USConsumer Product Safety Commission (2008), 56% of unintentional deaths from non-fire CO poisoning wereassociated with engine-driven tools like gas-powered generators and lawn mowers. Natural gas heating systemsaccounted for 4% of these deaths. Improvements in natural gas furnace designs have greatly reduced CO poisoningconcerns. Detectors are also available that warn of carbon monoxide and/or explosive gas (methane, propane, etc.).
Energy content, statistics, and pricing
Natural gas prices at the Henry Hub in US dollars per million BTUs ($/mmbtu) for2000–2010.
Quantities of natural gas are measured innormal cubic meters (corresponding to 0 °Cat 101.325 kPa) or in standard cubic feet(corresponding to 60 °F (16 °C) and 14.73psia). The gross heat of combustion of onecubic meter of commercial quality naturalgas is around 39 megajoules (≈10.8 kWh),but this can vary by several percent. Thiscomes to about 49 megajoules (≈13.5 kWh)for one kg of natural gas (assuming0.8 kg/m^3, an approximate value).
The price of natural gas varies greatlydepending on location and type ofconsumer. In 2007, a price of $7 per 1000cubic feet (28 m3) was typical in the UnitedStates. The typical caloric value of naturalgas is roughly 1,000 British thermal units (BTU) per cubic foot, depending on gas composition. This corresponds toaround $7 per million BTU, or around $7 per gigajoule. In April 2008, the wholesale price was $10 per 1000 cubicfeet (28 m3) ($10/MMBTU).[45] The residential price varies from 50% to 300% more than the wholesale price. Atthe end of 2007, this was $12–$16 per 1000 cu ft (28 m3).[46] Natural gas in the United States is traded as a futurescontract on the New York Mercantile Exchange. Each contract is for 10,000 MMBTU (~10,550 gigajoules), or 10billion BTU. Thus, if the price of gas is $10 per million BTUs on the NYMEX, the contract is worth $100,000.
European UnionAs one of the world's largest importers of natural gas, the EU is a major player on the international gas market.Gas prices for end users vary greatly across the EU.[47] A single European energy market, one of the key objectivesof the European Union, should level the prices of gas in all EU member states.
United StatesIn US units, one standard cubic foot of natural gas produces around 1,028 British thermal units (BTU). The actualheating value when the water formed does not condense is the net heat of combustion and can be as much as 10%less.[48]
In the United States, retail sales are often in units of therms (th); 1 therm = 100,000 BTU. Gas meters measure thevolume of gas used, and this is converted to therms by multiplying the volume by the energy content of the gas usedduring that period, which varies slightly over time. Wholesale transactions are generally done in decatherms (Dth),or in thousand decatherms (MDth), or in million decatherms (MMDth). A million decatherms is roughly a billioncubic feet of natural gas. Gas sales to domestic consumers may be in units of 100 standard cubic feet (Ccf).As of 2009, the Potential Gas Committee estimated that the United States has total future recoverable natural gasresources approximately 100 times greater than current annual consumption.[49]
CanadaCanada uses metric measure for internal trade of petrochemical products. Consequently, natural gas is sold by theGigajoule, a measure approximately equal to 1/2 of a barrel (250lbs) of oil, or 1 million BTUs, or 1000 cu ft of gas,or 28cu metres of gas.
ElsewhereIn the rest of the world, Natural gas is sold in Gigajoule retail units. LNG (liquefied natural gas) and LPG (liquefiedpetroleum gas) are traded in metric tons or mmBTU as spot deliveries. Long term Natural gas distribution contractsare signed in cubic metres, and LNG contracts are in metric tonnes (1,000kg). The LNG and LPG is transported byspecialized transport ships, as the gas is liquified at cryogenic temperatures. The specification of each LNG/LPGcargo 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 metres of natural gas in 2008.
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