Oil shale

from Wikipedia, the free encyclopedia
Oil shale in Holzmaden
Oil shale at Kimmeridge
Digestion in Estonian oil shale ( kuckersite )
Fossil-bearing cuckersite from Estonia

As oil shale dark gray to black are, clayey and marly sedimentary rocks called that up to 20%, in some deposits to 30% kerogen , a precursor of petroleum contain. The kerogens are converted into crude oil-like substances (shale or smoldering oil) and gas by heating them to 340 to 530 ° C.

According to today's petrographically correct name, oil shale is not slate in the actual sense, but a layered, but not schisted sedimentary rock . The kerogens are formed in the absence of oxygen from dead plankton , seawater and freshwater algae and bacteria . In chromatographic investigations, amino acids and chlorophyll breakdown products can be determined. Under certain geological conditions, oil shale can develop from oil shale in the course of the earth's history through increasing overburden and temperature increase.

Oil shale is one of the so-called " unconventional deposits ", the exploitation of which is not yet worthwhile due to the very high production costs.

Emergence

Oil shale can form from microorganisms (algae, plankton and bacteria) that were originally deposited in swamps , freshwater and saltwater lakes as well as in shallow marine, subtidal areas if they sink to a poorly ventilated, low -oxygen lake or sea floor after they die . In the absence of oxygen, the organic biomass could not rot , but went through a biochemical putrefaction and conversion process. The organic substance was broken down into its components ( proteins , fats and carbohydrates with small amounts of sulfur and nitrogen ), from which kerogens can be formed as a precursor of petroleum in the course of the earth's history. In contrast to petroleum, oil shale has not yet passed through all stages of the bitumen formation process and is therefore referred to as immature petroleum mother rock.

properties

The calorific value of the raw substance fluctuates between 3.3 MJ / kg and 8 MJ / kg depending on the kerogen content  . The specific sulfur content in relation to the fuel substance can be up to 10%. The kerogens are released from the rock by thermal treatment (in situ or in smoldering reactors, so-called retorts) and so smoldering or shale oil is obtained. The oil obtained from oil shale is distinguished from natural crude oil by a lower hydrogen and higher oxygen content. In order to be able to use oil shale economically, a minimum kerogen content of 4% is required in the rock. The oil content of the rock is compared in the different deposits in the laboratory using a standardized smoldering method developed by Franz Fischer and Hans Schrader ( Fischer Assay ).

Oil shale can be radioactive .

Occurrence

Worldwide there are a large number of oil shale deposits from different geological ages in 40 countries. The German Federal Institute for Geosciences and Natural Resources (BGR) currently estimates the amount of global oil shale resources at 97  gigatons (data status: end of 2011), whereby it must be stated that the resource estimate has been made several times since 2009 (119 GT) (2011: 112 GT) had to be corrected downwards. According to the BGR and the USGS, an estimate of the resources that can be extracted is not possible due to the lack of and vague data and the different energy content of the individual deposits in many countries. The largest deposits are in the USA (73%), followed by Russia (10%) and Brazil, Italy and the Republic of the Congo (together 9%). The largest deposit is in the Green River area in the USA. The deposit extends over 65,000 km².

Europe

Germany

In Germany, oil shale was mined on a larger scale in the last few years of World War II . At the moment, oil shale is only extracted from a cement plant near Dormettingen in Baden-Württemberg and used on site to generate electricity. According to the Federal Institute for Geosciences and Raw Materials (BGR), the use of energy is only economical because the burnt oil shale is used as the starting product for special Portland cements .

In the southeast of Lower Saxony in the area of Schandelah near Braunschweig there is an occurrence of approx. 2 billion tons with an oil content of less than 10%. This occurrence also opens up sedimentary rocks of the Lias .

In the southern Emsland in the region around Salzbergen you can find oil shale. This was the reason to found the Salzbergen refinery in 1860 . However, oil shale processing was abandoned in 1861. It still exists as a later oil refinery and today's lubricant refinery.

The Messel pit in Hessen in the Darmstadt-Dieburg district is an example of an oil shale deposit with a significant fossil deposit. Unlike the following examples, the formation here took place in a maar lake , i.e. under freshwater conditions. The fossils of this fossil deposit belong to the Eocene period .

Other

Seefeld formation

The largest European deposits are in Russia . Here were Olenjok basin, the Baltic shale basin in St. Petersburg , in the Volga basin and Vychegodsky mined oil shale basin and exports by 2005 to Estonia for electricity with.

In Estonia , the most important occurrences of kukersite are located near Narva and Kohtla-Järve . Kukersit, named after the former Baltic German Gut Kukruse (German Kuckers ), is a marine Gyttja . This fossil-rich clay marl sediment alternates between layers of lime , which also contains fossils from the Ordovician . Estonia currently covers over 60% of its electricity needs from burning oil shale.

In Italy, on the island of Sicily , large deposits of oil shale are known.

In Tyrol there are oil shale deposits in the Seefeld strata around Scharnitz , Seefeld and Reith as well as in the Achensee area in the Bächental . The rocks near Seefeld were used from the middle of the 14th century to extract Tyrolean stone oil , which is widely sold and was also used industrially in the 19th century for asphalt production. The hope of making big profits with the distillation of the popular lamp fuel, petroleum , which began in 1858 , was dashed with the cheaper petroleum made from petroleum, which was imported a little later . The industrial production was given up and from the mid-1860s the stone oil distillery was operated by local residents again. From 1884 onwards, the sulphonation of stone oil laid the foundation for marketing it under the brand name Ichthyol . The production was stopped in 1964, the local production now processes rocks from France. The oil shale deposits in the Achensee area have been exploited since the beginning of the 20th century and processed into rock oil in Pertisau . This is used in the production of special cosmetics and medical products.

Smaller, partly historically used oil shale deposits are known from Romania ( Anina mine), Great Britain in various deposits in Scotland , France (Autun, Sévérac-le-Château ), Switzerland ( Meride ), Sweden (Kvarntorp).

Worldwide

By far the largest oil shale deposit in the world is the Eocene Green River Formation, which extends over parts of the US states of Utah , Colorado and Wyoming . The American Geological Survey (USGS) gives the total in place reserves , i.e. the total amount of shale oil suspected in the earth in the Green River Formation, as around 4.29 trillion barrels , of which 1.44 goes to the Greater Green River Basin Trillion barrels, the Uinta Basin 1.32 trillion barrels and the largest reservoir, the Piceance Basin, 1.53 trillion barrels. The actual amount of shale oil that can be extracted in the Green River Formation cannot be estimated at the moment, as, according to the USGS, no method has yet been developed to extract the oil from the Green River Formation at a cost-covering level.

Major deposits of oil shale are currently being explored and mined in Brazil, China, Canada, Israel, Jordan, Libya, Morocco, Syria and Thailand. In 2010 it became known that a large oil shale deposit was discovered in Anatolia ( Turkey ). In South America, particularly in Patagonia ( Argentina ), a large deposit of oil shale has been drilled in the Vaca Muerta Formation in recent years and is one of the largest deposits discovered in the last three decades.

Extraction, extraction and use of oil shale

A 1920s kerogen extraction retort near Kilve, West Somerset

Dismantling

The extraction of oil shale can be carried out in open pit mining if there is little loose rock cover of up to 40 m. An overburden / oil shale ratio of less than 5: 1, with a minimum thickness of the oil shale layer of 3 m, is currently considered economically viable. The deposits in Estonia, China and Brazil are currently among the largest open-cast oil shale mines.

In the future, the kerogens are to be extracted in situ in the deposit in deeper oil shale deposits without mining the adjacent rock. Various pilot plants with different extraction processes are currently in the test phase.

Extraction process

In this process, the kerogen in oil shale is converted into shale oil through pyrolysis , hydrogenation or thermal decomposition . The shale oil obtained in this way can be used as fuel or further refined in a refinery by adding hydrogen and removing sulfur and nitrogen.

Pyrolysis and gasification of kerogen from oil shale

The numerous processes for the extraction of kerogen from oil shale, which were extracted in the open pit, can be divided into two groups: horizontal and vertical retorts. Examples of vertical retorts include the Paraho method, the Petrosix method, Fushun method (China), and the Kiviter method (Estonia). In the horizontal retort process, the oil shale is heated in a horizontal furnace. Examples of extraction processes with horizontal retorts are the TOSCO II process, the ATP process and the Galoter process . The kerogen contained in oil shale is largely extracted by pyrolysis to form shale oil (synthetic crude oil) and oil shale gas. The decomposition of the kerogen begins at 300 ° C and runs optimally at temperatures between 450 ° C and 530 ° C. In most processes, the pyrolytic decomposition takes place in an oxygen-free environment. In addition to the condensable, synthetic oil, this process also produces oil shale gas and solid residues, some of which can be disposed of and some can be reused.

In-situ procedure

Shell in-situ pilot facility in the Piceance Basin, Colorado

In order to minimize land use , numerous methods are currently being tested to remove the kerogen in situ from the rock. The underground carbonization can be achieved either by electrical heating of the rock or by supplying oxygen through boreholes in the area of ​​ignited oil shales. The latter method proved to be of limited use due to the difficulty in controlling the underground combustion and the air pollution. In the in-situ conversion process (Shell In-Situ Conversion Process) developed by the Shell Group , a rock package with a volume of around 0.6  cubic kilometers is electrically heated to a temperature of around 350–370 ° C for a period of 4 years become. Shell assumes that the controllable, electrical heating of the rock can have a beneficial effect on the catagenesis process.

To do this, it is necessary to sink around 50 holes per hectare. According to the RAND study, a continuous electrical output of around 1.2 gigawatts is required for the rock package mentioned above  . In order not to heat the surrounding groundwater-bearing layers, in this process the rock around the heated rock package is to be frozen through a so-called freezing wall . With this technique, which originates from shaft construction, a liquid at around −50 ° C is circulated through specially designed bores so that the rock around the bores slowly freezes and thus becomes hydraulically impermeable.

Various in-situ charring processes have also been developed by other mineral oil companies, which are currently in the laboratory or pilot stage, such as the Electrofrac process from ExxonMobil . In this process, separating surfaces are created or expanded in the oil shale by hydraulic fracturing and filled with an electrically conductive cement in which a heating element is implemented. The kerogen is released from the rock in situ via the heating element and carried to the surface via production wells.

The Chevron Crush process, developed by the mineral oil company Chevron Corporation together with the Los Alamos National Laboratory , is also currently in a pilot phase. In this process, similar to the Electrofrac, the interfaces in the oil shale are expanded with the help of hydraulic fracturing. Hot carbon dioxide is injected into the subsoil through injection holes, which heats the kerogen in the subsoil and dissolves it from the rock. To monitor the deep-lying aquifers , monitoring boreholes are being drilled in the area.

All in-situ processes are characterized by the fact that a period of at least 5 to 6 years passes from the first drilling to production, with the heating process taking 12 to 18 months.

For some oil shale deposits, such as the Devonian Black Shale Formation in the east of the USA, only in-situ methods can be considered for exploration due to the depth of the deposit.

use

Burning oil shale
Production of oil shale, after Pierre Allix, Alan K. Burnham

Oil shale has been mined and processed since 1837. The first dismantling took place in Autun , France.

Towards the end of the Second World War the National Socialists tried in the so-called Enterprise Desert to extract mineral oil for tanks and aircraft from the oil shale deposits in the foreland of the Swabian Alb , but this did not bring the desired success. The oil was so inferior that it could only be burned in special engines. In addition, the kiln method used was inefficient. To extract one ton of oil, 35 tons of slate were needed. By the end of the war, around 1500 tons of oil had been extracted. The extraction of the slate was carried out in forced labor by prisoners from several subcamps of the Natzweiler-Struthof concentration camp .

The economic use is more economical if the oil shale is burned directly. When the organic substances are extracted by distillation , considerable residues remain in the slate. In the case of large-scale use, both processes leave a considerable amount of rock residue that has to be stored as overburden. Around 50 liters of oil can be extracted from one ton of oil shale.

The largest power plant that is fired with oil shale is located in Narva, Estonia . A cement plant in Dotternhausen (Baden-Württemberg) produces a small amount of electricity from oil shale for its own use. Other projects such as the Suncor development in Australia were discontinued in 2004 due to the low energy yield and the bankruptcy of the operator.

Given the possible global oil production peak , oil shale is a possible alternative to fuel production. Financially, with rising oil prices, the extraction of crude oil from oil shale can again make sense.

In addition, ammonium bituminosulfonate is obtained from shale oil through sulfonation and subsequent neutralization of certain fractions of the shale oil. This is used in medicine against skin diseases and as a pulling ointment , and is marketed as Ichthammol or Ichthyol .

Environmental aspects

Depending on the extraction method, the environment is more or less affected by the oil shale mining and processing. When mining in an open pit, the land consumption of the landscape and the high demand for water are factors to be considered. Some authors assume that the availability of water in arid areas can become a limiting factor for the extraction of oil shale. Burning oil shale to generate electricity, for example in Estonia, releases a large amount of the greenhouse gas CO 2 and has a negative impact on air quality. The lime content of the adjacent rock is of great importance for the CO 2 balance, since at temperatures of 700–1100 ° C the carbonate is completely decomposed and can lead to high emission values. Compared to modern coal-fired power plants, burning carbonate-rich oil shale in Estonia produces around 60% higher CO 2 emissions (1,600 g CO 2 eq / kWh). Compared to conventional fuels, the production of fuels from oil shale leads to 30 to 75% higher greenhouse gas emissions. The energy-intensive extraction of kerogens from the oil shale also means that the emissions balance of CO 2 is around 75% higher than that of conventionally extracted oil.

The Rand study states that about 3 barrels of water are required for one barrel of smoldering oil. When oil shale is burned, residues, slag and ash are left over, some of which can be enriched with heavy metals such as lead , zinc , cadmium , chromium , but also uranium and vanadium and water-polluting substances, phenols and sulfur compounds. There are currently no scenarios for the disposal of these incineration residues in many deposits. In some cases, these by-products can also be used economically, since most black shales have significant geogenic concentrations of heavy metals, as well as silver and, more rarely, gold, but also uranium and vanadium.

Current developments

In recent years, numerous new oil shale deposits have been re-prospected and the extraction process optimized. Numerous processes for the in-situ extraction of shale oil are currently in the development stage; the first pilot plants in the USA are delivering the first large-scale results. The pyrolytic decomposition in retorts has been optimized so that the extraction costs are around 30 US dollars / barrel in order to be able to compete better with conventional crude oil in the future. Major oil shale deposits have been discovered in Argentina in the Vaca Muerta Formation in recent years . The extent to which the deposits can be mined economically is currently being investigated.

literature

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Web links

Commons : Oil Shale  - Collection of images, videos and audio files

Individual evidence

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