Natural gas is a natural fossil fuel gas usually found in the continental or marine subsoil. This product is preserved in great underground deposits (gas basins or fields).
Natural gas was formed millions of years ago when a number of decomposed organisms, including animals and plants, were buried under mud and sand at the very bottom of ancient lakes and oceans. As mud, sand and sediment accumulated, layers of rock were formed at great depth. The pressure exerted by their weight together with the heat from the earth slowly transformed the organic material into crude oil and natural gas.
Gas accumulates in deposits between porous underground rocks. Sometime it gets trapped underground by solid cap rocks that prevent the gas from filtering out, leading to the formation of a reservoir. Gas is extracted from these natural deposits by perforating the ground or the seabed. This is called a well.
A mixture of hydrocarbons is obtained with a predominant amount of methane (85% - 95%), and also includes ethane, propane, butane and pentane. Furthermore, it usually includes other compounds like metals and sulphur, which are removed before taking it to the transmission systems or the liquefaction plants.
Natural gas is measured in energy units as opposed to volume or weight. In other words, on the basis of its lower calorific value or the heat it emits during its combustion. The amount is usually given in kilowatts-hour per cubic metre (kWh/m3). The range is between 10 and 13 kWh/m3 measured at 0ºC and 1 atmosphere.
While oil reservoirs are concentrated in the Middle East (65%), the location of natural gas reservoirs is more widespread, which is a guarantee that must be taken into account. The main deposits are in Russia and the Middle East but there are also important reservoirs elsewhere. Proven reserves have increased in recent years, with the USA emerging as one of its main producers. This has resulted in increased supply security. As prospecting and technology advance, the time period will be longer.
At the beginning of the 21st century, European proven reserves (especially those in Norway, Great Britain and the Netherlands) accounted for 3.5% of the world total; Asia accounted for 7%; Africa 7.67%; America 9.31%; the Middle East 33.9%, and those in the Russian Federation 38.8%.
Spain has its main supplier of natural gas in Algeria, a country that provides about 50 % of the imported total. Other suppliers include Norway, Qatar, Nigeria, Trinidad and Tobago or Peru.
Because it makes it safer to handle and easier to transport. When liquefied, the product reduces its volume 600 times, which makes its maritime transport over long distances possible. Furthermore, as a liquid, the gas does not burn or explode, thus significantly increasing navigation safety.
Liquefaction is achieved by cooling gas to 160 degrees below zero at a pressure close to that of atmospheric pressure. The plants where this procedure is carried out are located on the coast, usually close to the reservoirs. They have one or more LNG trains making up independent units sharing the same shipping terminal.
Liquefied natural gas has a great strategic advantage because it ensures market freedom as fuel suppliers and fuel origin are diversified, as opposed to gas pipeline imports, where supplier and consumer mutually depend on each other.
Natural gas is odourless, although sometimes, as extracted from the deposits, it may include some chemical that gives it a certain smell, which is removed at initial processing. Spanish law establishes that the natural gas must be odorised for safety reasons so that its smell may function as an alert in the event of a leak.
All plants are equipped with odorisation systems through which, once regasified, substances are injected that add smell in amounts of some parts per million. These organic compounds contain both sulphur and tetrahydrotiophene.
Natural gas is the fossil fuel with the least environmental impact. Its use contributes to a reduction in the emission of greenhouse gases. In homes, it may advantageously replace other products. In road transport, it prevents all the drawbacks gasoline and diesel as regards emissions to the atmosphere.
As far as maritime transport, LNG is the ideal fuel to meet the requirements resulting from the establishment of emission control areas for greenhouse effect gases. Besides its environmental advantages, its availability and its competitive price mean that it will be in great demand for both merchant and fishing fleets.
As to power generation, it is the most environmentally friendly non-renewable technology. Compared to other fossil fuels, the advantages of natural gas are very clear: it produces less carbon dioxide during its combustion, hardly any sulphur or heavy metal emissions, much less nitrogen oxide and does not leave any solid waste.
LNG plants in Spain were initially designed for the reception, storage and regasification of liquefied natural gas, a service that is provided to major clients who own the fuel. However, over the last few years they have evolved to become major logistic hubs, as they can also re-dispatch maritime shipments in large ships or for small-scale distribution.
The availability of LNG plants provides the energy market with freedom as it gives access to a variety of importers and ensures the strategic stocks that any country needs. The activity of the terminals is essential for ensuring the efficient operation of the national gas network, of power plants and other industrial facilities.