The natural gas is a fossile fuel, it acts of a mixture of Hydrocarbure S naturally found in form Gaz euse. It is the second energy source most used in the world after the Pétrole and its use develops quickly.
Types of natural gas
There exist several natural gas shapes, being characterized by their origin, their composition and the type of tanks in which they are. Nevertheless, the gas is always made up mainly of methane and resulting from disintegration from old living organisms. With the various types of natural gases quoted hereafter, one could associate the Biogaz, a renewable substitute .
Nonassociated conventional gas
It is the most exploited form natural gas. Its formation process is similar to that of the Pétrole. One distinguishes primary gas thermogenic, directly resulting from the Pyrolyse of the Kérogène, and the secondary gas thermogenic, formed by the pyrolysis of oil. The gas thermogenic includes/understands, in addition to methane, a heavier hydrocarbon fluctuating rate, being able to go until the Heptane (CH). One can also find there carbon dioxide (), sulfur dioxide (), sulfide of hydrogen called also “acid gas” (), and sometimes of the Azote (NR) and minor amounts of Hélium (He).
It is about gas present in solution in oil. It is separate during the extraction of this last. For a long time, he was regarded as a waste and was destroyed in Torchère, which constitutes a wasting of nonrenewable energy resources and an useless pollution. Today, essence either is reinjected in the reservoirs oil (contributing there to maintain the Pression and to maximize the extraction of oil), or developed. Nevertheless, the destruction in flare is still of topicality in certain areas.
The gas biogenic is resulting from the Fermentation by Bactérie S of organic sediments. Following the example Peat, it is a fossile fuel but whose cycle is relatively fast. The layers biogenic small and are in general located at a shallow depth. They account for approximately 20% of the known conventional gas reserves. The gas biogenic has less of value per cubic meter than gas thermogenic, because it contains a considerable gas share noncombustible (in particular of) and provided not hydrocarbons heavier than methane.
The coal naturally contains methane and in its pores. Historically, this gas especially was known for the threat mortal which it presents on the safety of the minors - it then remained in the collective memory under the name of Grisou. However, its exploitation is under development full, in particular in the United States. The exploitation relates to coal layers rich in gas and too deep to be exploited in a conventional way. There were tests in Europe also, but the majority of European coals are rather low in methane. China is interested also more and more in the exploitation of this type of natural gas.
Some Schiste S contain also methane trapped in their crackings. This gas is formed by the degradation of the kerogen present in the schist, but, as for coal gas, there exist two great differences compared to gas reserves conventional. First is that the schist is at the same time the rock source of gas and its tank. Second is that accumulation is not discrete (many gases joined together in a point) but continues (the gas is present in weak concentration in an enormous volume of rock), which makes the exploitation much more difficult.
See also: Hydrate of methane
The methane Hydrates are structures of ice containing of captive methane. They result from the relatively recent accumulation of ice containing of organic waste, degradation is biogenic. One finds these hydrates in the Permafrost or on the ic floor Océan. The volume of existing gas in this form is unknown, variable several orders of magnitude according to the studies. No technology currently makes it possible to exploit these resources.
Industry of gas
Upstream: extraction and treatmentThe natural gas and crude oil often associated and are extracted simultaneously from the same layers, or from the same production zones. The liquid hydrocarbons come from crude oil for an average proportion about 80 %; 20 % remaining, among the lightest fractions, propane and butane are almost always liquefied to facilitate transport of it.
Exploration (search for layers) and the extraction of the natural gas use techniques about identical to those of the oil industry. Most of the gas layers known throughout the world was found besides during campaigns of exploration whose objective was to find oil.
During the extraction, the relaxation with the wellhead causes the condensation of the C5 hydrocarbons in C8. Liquids recovered, called “condensates of natural gas” or “ liquid of gas naturel  well; ” correspond to an extremely light oil, of very high value (giving gasoline and Naphta). All the remainder (C1 hydrocarbons with C, and He) gas with room temperature and is conveyed by Gazoduc towards a treatment plant of gas. One thus needs two collecting systems, for gas and for the condensates.
In this factory (which can be close to the layers, or close to the places of consumption), the gas undergoes then a Déshydratation by Dewpoint, then the various components are separate. The hydrocarbons C with C are sold under the name of Petroleum gas liquefied (LPG, and not Natural gas liquefied (GNL)). Is generally simply rejected into the atmosphere, except if there is a close user. Sometimes, one reinjects it in an underground formation (Séquestration of CO2) to reduce the gas emissions to Greenhouse effect. The acid gas is sold with chemical industry or is sequestered. Helium is separated and marketed, if it is present in sufficient quantity - in certain cases, it represents a very important addition with the incomes generated by the layer.
The condensates and the LPG have such a commercial value that certain layers are exploited only for them, the “ gas pauvre ” (methane) being reinjected progressively, for lack of local outlets. Even when the essence of producer gas is sold, one often reinjects of it a part in the layer, to slow down the decrease in pressure, and to recover with final most of the condensates and LPG.
The other part (largest) is transported by gas pipeline or Méthanier towards the places of consumption.
The transport of treated gas (producer gas, almost exclusively of methane) is by nature much more difficult than for oil. That explains why, for a long time, the gas layers did not interest the companies that if they were relatively close to the places of consumption, while the layers found in isolated places were developed only if their size justified the infrastructures necessary. Knowing that the profitability of the gas layers has improved considerably for several years, several layers which were seen as “sub-commercial” are now advantageous.
To transport natural gas of the layers towards the places of consumption, the gas pipelines are the means more running. But an increasing share of consumed gas is transported in liquid form, with -162°C and atmospheric pressure, in Méthanier S of the place of production towards the places of consumption: it is what one calls the GNL, or Liquefied Natural gas. In this liquid form, the natural gas offers, with equal volume with the domestic fuel, a calorific value which corresponds to more half of the calorific value of this one.
But this solution which makes it possible “to condense” gas energy under a reduced volume requires very heavy investments, both for the Liquéfaction transport. As an indication, the cost of a factory of liquefaction, minimal size about 45 Gthermies/an (3,5 million tons of liquefied natural gas) is about 400 with 500 million USD and if one wants to double this capacity, 85  should be added; % more at this cost.
The ships of transport, which has cryogenic tanks, also cost very expensive: in 2006, more than 200 million Euro S for a capacity of 100 000 tons, is the price of a tanker of some 300 000 tons.
But, seen the continuous increase of the energy needs of all kinds and flamed it of the oil price since the beginning of the 21e century, all these investments are amply justified. The die of the Natural gas liquefied requires an important size however to be economically viable, one thus needs a strong production to be exported to justify the construction of a factory of liquefaction and, conversely, important need for importation to build a terminal of reception. In 2006, there does not exist any project in lower part of 2 or 3 million tons per annum for export, 1 for the importation.
On arrival with the places of consumption, the natural gas is split, if necessary, to separate it from the ethane, the Propane and the Butane, then the regazéfier. Here still, one needs enormous investments for the reception, storage and gasification.
For the treatment, and if one wants to separate LPG before transport, starting from the layers of gas and condensates (if those are close), one installs two collecting systems, for the natural gas and another for the condensates. The gas and the condensates are directed towards installations of treatment and desulfurisation.
See also: Natural gas liquefied
UseThe natural gas is one of the energy means least polluting. Indeed, when its combustion is complete, it emits only water and carbon dioxide:
CH4 + 2O2 --> CO2 + 2:00 2O
Like all fossile fuels, after combustion, it rejects Carbonic gas, but only 55 kg by giga Joule of produced heat, against 75 for crude oil, and approximately 100 for the coal. The advantage of natural gas is even larger if one takes account of the emissions on the complete cycle “of the well with the burner” and not only of those resulting from the final use of fuel: indeed, the extraction and the treatment of natural gas consume much less energy.
The use of natural gas practically does not produce a oxides of nitrogen (Nox), and almost no local pollution like sulfur oxides, dust, etc This interest ecological has a direct economic consequence: an installation (Powerplant, boiler room, cement factory or other) burning coal needs devices of depollution, to extract the Soufre, Nox and dust of smoke. These installations are very expensive to build and maintain. With natural gas, this equipment is useless, from where an important economy. Moreover, the natural gas does not leave ashes.
It is used as source of energy in industry in order to produce heat (heating, furnaces…) and of the electricity. In 2006, on a world level, more 20 % of electricity is produced starting from natural gas, and this share does not cease increasing. At the private individuals, the natural gas is used for the heating, warm water and the cooking of food. Lastly, for a few years, the natural gas compressed in bottles has been used in France like fuel for the vehicles (GNV). But already more than one million vehicles to natural gas roll already in the world, countries like Argentina and Italy.
The natural gas is also the raw material of a good part of chemical industry and petrochemical: with the near total of the production of Hydrogen, Methanol and Ammonia, three basic commodities, which in their turn are useful in various industries:
Hereafter is the presentation of the chemistry of methane in petrochemical industry:
It is as starting from methane as one synthesizes the ammonia () and the Urée (CO (NH2) 2), which are the starting point of the industry of the Engrais.
In 2006, overall, the use of the natural gas is expanding, the majority of the country supporting its use increased everywhere where it can replace oil. It indeed has several advantages in comparison with this last: less expensive in general, less pollutant, it also allows a diversification of the energy supplies of the importing countries (Géopolitique), even if the crisis between the Ukraine and Russia with the beginning of the year 2006 shows that it is not " LA" miracle solution. In certain countries, like the Russia or the Argentinian , the use of natural gas even exceeded that of oil.
The natural gas became a total industry, which slices singularly with the time (until the years 1950, well later in certain countries), where it before was very perceived like a cumbersome and dangerous coproduit of the oil wells.
Calorific value of natural gas
The calorific value of a fuel is the quantity of heat expressed in kWh or MJ, which would be released by the complete combustion of one (1) normal cubic meter (m ³ (N)) dry gas in the air with a constant absolute pressure and equalizes with 1,01325 bar, the gas and air being at an initial temperature of 0°C (zero degree Celsius), all products of combustion being brought back to 0°C and a pressure of 1,01325 bar.
The calorific value of natural gas is expressed in MJ or kWh per cubic meter.
One distinguishes 2 calorific values.
GCV = NCV + Latent heat of evaporation
GCV = higher calorific value
It is the quantity of heat expressed in kWh or MJ, which would be released by the complete combustion of one (1) normal cubic meter of gas. The water formed during combustion being brought back in the liquid state and the other products being in a gas state.
- NCV = lower calorific value
It is calculated while deducing by convention, of the GCV the heat of condensation (2 511 kJ/kg) of the water formed during combustion and possibly of the water contained in fuel.
- Latent heat of vaporization
the combustion of a product generates, inter alia, of water to the vapor state. For the vaporization of 1 kg of water, 2 511 kJ/kg is necessary. This energy is lost with combustion gases evacuated by the chimney unless condensing the steam and to try to recover heat there being accumulated. Certain techniques make it possible to recover the quantity of heat contained in this water of combustion by condensing it (boilers with condensation)
The natural gas contains however more Hydrogène, consequently, the loss of energy is more important during combustion because of the formation of steam evacuated by the chimney. Approximately 10 % of the supplied energy is lost in this case.
Report/ratio PCI/PCS for natural gas: approximately 0,9028 (3,25/3,6)
For the natural gas , one distinguishes:
gases “ B  type; ” (or “ L  type; ”)
distributed in the North of France. They have a higher calorific value ranging between 9,5 and 10,5 kWh/m ³ (N). It is primarily the case of gas of Groningue (coming from the Netherlands). This gas is characterized by its high percentage of Azote.
- gases “ H  type; ”
distributed on the remainder of the French territory. They have a higher calorific value ranging between 10,7 and 12,8 kWh/m ³ (N).
For the majority of the domestic apparatuses, these two types of gas are interchangeable, certain apparatuses will require an adjustment however.
The natural gas, as an abundant resource, not very expensive and available is not any more topicality. Indeed, the countries which lay out of the resources most important (Russia at the head with a third of world reserves, but also Algérie, Bolivia, etc) use it henceforth with fine policies and diplomatic. The gas is becoming a major stake and the perenniality of the provisioning is a concern illustrated by the many debates within the European Union around the signature of the European Charter of energy by Russia or not.
The countries of the old Soviet block, which sought to leave the Russian sphere of influence not to depend more on Moscow, depend today mainly on Gazprom, the group which the Kremlin constituted to ensure a domination of this economic sector but also to increase the dependancy of the European countries with respect to the Russian deliveries.
The current context, marked by an insecurity of the provisioning coming from the Middle East (with the question of Iran and its nuclear program), increases the tensions on the worldwide markets of hydrocarbons. Russia seeks to benefit from it in order to give its economy on the way but also to find the lost power. It is thus described as " super power énergétique" (Richard Lugar) or of " énergocratie" (Francoise Thom).
In 2005, according to BP, the world produced 2743 billion cubic meters of natural gas, in rise of 2,5% compared to the previous year (whereas the production of oil increased only by 1%). The Russia accounts for 22% of the worldwide production.
The figures of production of natural gas are rather complex to interpret, according to the ways of calculating one can or not count associated gas flaring in flare, to count volumes of gas before or after extraction of the pollutants, etc the figures of the IEA are besides different from those of BP, with a worldwide production of 2871 G (m) for the same year, is nearly 5% more than BP.
For more information on the production by country, one will be able to refer to the series oil-bearing Régions. The principal exporting countries, according to the EIA, are:
Here still, these data require some note:
- It acts of rough exports, i.e. the quantum of imports is not deduced from it. For example, Canada exported 105 G.m3 in the United States, but also imported 10 G.m3 of this country. In the same way, Russia imports Turkmen gas.
- These data do not include the exportations of products directly derived from gas, like methanol or ammonia.
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