Natural gas field

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As a natural gas field one is natural gas - deposit referred to in porous sedimentary layers of the earth's crust which is economically viable or is conveyed from the gas already. For the most part, they arise from marine deposits from marginal seas, in Central Europe e.g. B. from the so-called Zechstein Sea or the late phases of the Tethys Sea .

Oil and gas fields on the Greek shelf near Kavala-Thasos

Natural gas fields require the existence of sufficiently porous sediments that can serve as storage rock for the gases and mostly also for other hydrocarbons such as petroleum. The mostly biogenic gases collect in pores or crevices beneath an air-impermeable layer. A distinction is made between saddle-shaped bulges under a sealing layer or sloping storage sites with sealing on overlapping layers, on salt dome flanks or on faults.

Oil or gas höffige areas are first through geological and geophysical exploration vorerkundet, later followed by exploratory drilling and the success of the production well . The conveyance to the earth's surface is carried out by gas pressure or (less often) by pressing salt water into the subsoil.

Formation of the deposits

Natural gas is produced by processes similar to , but more frequently than, oil and is based on biogenic deposits from warm geological ages . If it occurs together with petroleum, it is dissolved in it or is deposited on top of it. It forms under high pressure and temperature from the digested sludge of dead microorganisms of the oceans, especially from planktonic algae , provided that they are deposited in the substantial absence of free oxygen and subsequently covered by further sediments. As a result of tectonic processes or simple sedimentary load and their own buoyancy, these gases can migrate into porous rocks and collect under sealing layers. Larger amounts of natural gas were also produced on site (without significant migration) through bacterial decomposition of organic substances, for example under the Alpine foothills in the Young Tertiary (around 20 million years ago ).

Natural gas deposits are mostly mixed hydrocarbon fields that contain biogenic gases in variable compositions and often also crude oil. The latter can hardly be found alone, but pure natural gas fields often because the gas can migrate more easily due to its lower density.

The USA , Russia , Canada , Iran and Norway achieve high funding rates . In 2008, these five countries accounted for around 52% of world production of 3,065 billion cubic meters. Large deposits are also in some CIS countries in Central Asia (especially Turkmenistan ), in northern regions of Siberia and on its Pacific coast near Sakhalin , in countries of the Persian Gulf such as Saudi Arabia , Qatar and Iran, in Algeria and in South America. The largest European deposits are located under the North Sea : the Norwegian troll field , the Dutch Uithuizen and some fields towards England. More recent finds were u. a. known from Bolivia and central Ukraine , while z. B. those in Lower Saxony are coming to an end.

Production plant in the Vučkovec natural gas field in northern Croatia

According to the BGR, the world's known natural gas reserves amounted to around 180,000 billion m³ in 2007 , which would be sufficient for around 60 years if world consumption remained the same. Russia holds 26 percent of the reserves, Iran 15 and Qatar 14 percent, followed by Central Asia and the USA. A problem in estimating future gas production is - in contrast to oil fields - the sudden drop in productivity, which applies to individual fields as well as to the statistics of world stocks.

composition

Natural gas is a gas mixture, the composition of which strongly depends on the location. however, methane (swamp gas, CH 4 ) always makes up the largest part . The proportion of higher hydrocarbons such as the alkanes ethane , propane , butane and ethene fluctuates, as does water vapor , carbon dioxide , small proportions of hydrogen sulfide and inert gases ( helium , other noble gases and nitrogen). Natural gas with a higher proportion of gases that can be liquefied under pressure is called wet natural gas .

For example, North Sea gas consists on average of 89% methane and 8% other alkanes, while Siberian gas contains 97–99% methane. Type L natural gas, on the other hand, has an inert gas content of 11%.

history

It is uncertain when the first discovery of natural gas took place, but it was presumed to have been given by volcanic events in antiquity. In Europe and the USA, targeted funding goes back to the 19th century. The first find in Europe took place in Vienna in 1844 on the area of ​​the Ostbahnhof. The deposit found in 1892 near Wels (Upper Austria) when drilling wells was larger , where it was soon extracted from 150 boreholes and is still there today.

Larger extraction areas in the early 20th century were the Vienna Basin , the gas deposits in Lower Saxony and the large fields in North America (USA and Mexico), which soon exceeded the yield in other regions by far. In 1938, around 35 billion standard cubic meters (Nm³) were extracted in North America , a maximum of a tenth of that in Europe. During the Second World War, production in Russia increased significantly and amounted to 10–11 billion Nm³ in 1956, and that in the USA 260 billion Nm³. In 1956 Canada and Italy each accounted for 4–5 billion, Mexico and Indonesia 3–4 billion Nm³, and Austria and Brunei each around 1 billion Nm³.

In Germany (especially Lower Saxony and Upper Bavaria) production was highest between 1975 and 1980 with up to 20 billion Nm³ (1979 20.3), but has been falling since then. The German natural gas reserves that can be extracted with today's extraction technology are estimated at 218 billion m³, the economically / technically not extractable resources at ~ 200 billion m³. In Austria they are around a quarter of these values, in Switzerland they are significantly lower.

See also

Literature and Sources