Geology
How was natural gas created?
More than 300 million years ago, in the early Carboniferous period, all the land masses of the Earth began to merge into a new supercontinent called Pangaea. Surrounding Pangaea was a single global ocean - called Panthalassa.
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This supercontinent stretched from the equator to the poles. In the Carboniferous period, the climate on Earth was warm and humid. Central Europe was in the tropical region at that time and large swamps with abundant life formed in many areas. There were no trees as we know them today, but mainly club-foot plants and horsetails.The first conifers and seed ferns also developed. Insects, scorpions and amphibians dominated the land, while sharks ruled the seas. The organic material that was deposited in these swamps has become coal layers and source of the natural gas.
Where is the natural gas?
After the Carboniferous period with the beginning of the Permian period, the climate became drier and huge desert areas developed in the continental interior of Pangaea, where today's Central and Northern Europe were also located at that time. These desert areas most likely resembled today's Sahara desert. The climate here was very dry and the few water supplies were mostly in salt lakes, similar to today's Dead Sea.
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The landscape was dominated by sand dunes or sand seas that were moved by the wind. Today, this desert sand, in the form of sandstone, is the storage rock for natural gas.
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At the end of the Rotliegend (Early Permian) and with the transition to the Zechstein (Late Permian), seawater flooded most of present-day northern Europe and Germany and formed a huge inland sea from the east coast of England to eastern Poland. Because of the persistent hot and dry climate, the water evaporated and the remaining salt settled - as we know it today from the Dead Sea. Deposits of this salt, known as Zechstein salt, have thicknesses of 700 - 1000 metres near Zehdenick. Since salt rock is impermeable, it seals the gas-bearing rock very well.
The Rotliegend desert sand is known to be a good reservoir rock and natural gas is extracted from this reservoir rock in many places from England through Holland and Germany to Poland. Today, the Rotliegend desert sand lies more than 3800 to 4000 metres below Zehdenick. In comparison, the groundwater is at a depth of 0 - 250 metres. During the drilling carried out by VEB Erdöl-Erdgas Gommern in the 1970s, several hundred metres of Rotliegend sandstone, in whose pores natural gas is found, were discovered near Zehdenick. These gas deposits are conventional deposits and not unconventional shale gas deposits. The gas deposit in Zehdenick can be produced using conventional technologies including horizontal drilling.
What is a natural gas trap?
Gas and oil is created from organic material deposited millions of years ago together with clay or limestone. Once this rock has been exposed to heat and pressure oil and gas will over time be generated. The rock from which oil and gas is generated is called a source rock. The source rock is surrounded by rocks whose pores are filled with salt water. Once generated Gas or oil will move into these pores, and since the gas and oil are lighter than salt water, it will rise and "float on water". If the gas and oil are not stopped by impermeable rocks, they migrate to the earth's surface and can on the surface be seen as nature oil or gas seeps. ​
Some of the oil and gas will be stopped by an impermeable layer of rock, such as rock salt, clay, or some other tight rocks. The oil or gas would be trapped below the tight or sealing rock and the rock where the oil and gas is trapped is called reservoir rocks. The oil and gas is trapped in the pores within the reservoir rock and does not form a “pool” of oil or gas within the underground. Reservoir rocks can consist of porous sandstone or limestone.
