There are two kinds of oil shale in Estonia, both of which are sedimentary rocks laid down during the Ordovician geologic period. Graptolitic argillite is the larger oil shale resource, but, because its organic matter content is relatively low, it is not used industrially. The other is kukersite, which has been mined for more than a hundred years. Kukersite deposits in Estonia account for 1% of global oil shale deposits.
Oil shale (; literally 'burning rock') has been defined as a strategic energy resource in Estonia and the oil shale industry in Estonia is one of the most developed in the world.IEA (2013), p. 20 Historically, most of mined oil shale was used for electricity generation. Of all the oil shale fired power stations in the world, the two largest are in Estonia. Although its share decreased in the decade to 2022, direct and indirect use of oil shale still generates about half of Estonia's electricity. About half of mined oil shale is used to produce shale oil, a type of synthetic oil extracted from oil shale by pyrolysis, which is sufficient to keep Estonia as the second largest shale oil producer in the world after China. In addition, oil shale and its products are used in Estonia for district heating and as a feedstock material for the cement industry.
In the 18th and 19th centuries, Estonian oil shale was described by several scientists and used as a low-grade fuel. Its use in industry commenced in 1916. Production of shale oil began in 1921 and oil shale was first used to generate electrical power in 1924.Ots (2004), pp. 15–16 Shortly thereafter, systematic research into oil shale and its products began, and in 1938 a department of mining was established at Tallinn Technical University. After World War II, Estonian oil shale gas was used in Saint Petersburg (then called Leningrad) and in northern cities in Estonia as a substitute for natural gas. Increased need for electricity in the north-west of the Soviet Union led to the construction of large oil shale-fired power stations. Oil shale extraction peaked in 1980. Subsequently, the launch of nuclear reactors in Russia, particularly the Leningrad Nuclear Power Station, reduced demand for electricity produced from oil shale, and, along with a post-Soviet restructuring of the industry in the 1990s, led to a decrease in oil shale mining. After decreasing for two decades, oil shale mining started to increase again at the beginning of the 21st century. Most oil-shale fuelled electricity generation is planned to be phased out by 2030.
The industry continues to have a serious impact on the environment producing ordinary and hazardous waste and greenhouse gas emissions, lowering groundwater levels, altering water circulation, and spoiling water quality. Leachates from waste heaps pollute surface and groundwater. Former and current oil shale mines cover about one percent of Estonia's territory.
Resource
Graptolitic argillite
Estonian graptolitic argillite (also known as dictyonema argillite, dictyonema oil shale, dictyonema shale or alum shale) is a marine-type of black shale, belonging to the marinite-type of oil shales. Although the name dictyonema argillite is widely used instead of graptolitic argillite, it is now considered a misnomer as the graptolite fossils in the rock, earlier considered dictyonemids, were reclassified during the 1980s as members of the genus Rhabdinopora.Aaloe et al. (2007), pp. 3–4
Graptolitic argillite was formed some 480 million years ago during the Early Ordovician under a marine environment. In mainland Estonia, it occurs at the foot of the North Estonian Klint, ranging from the Pakri Peninsula to Narva in an area covering about .Aaloe et al. (2007), p. 4 When findings in the western Estonian islands are included, its extent increases to about . The thickness of the layer varies from less than to a maximum of in western Estonia, and its depth below the surface varies from .
Resources of graptolitic argillite in Estonia have been estimated at 60–70 billion tonnes. Although resources of graptolitic argillite exceed that of kukersite, attempts to use it as an energy source have been unsuccessful due to its low calorific value and high sulfur content. Its organic content ranges from 10 to 20% and its sulfur content from 2 to 4%. Correspondingly, its calorific value is only 5–8 megajoules per kilogram (MJ/kg; 1,200–1,900 kcal/kg) and its Fischer Assay oil yield is 3–5%. However, the graptolitic argillite resource in Estonia contains a potential 2.1 billion tonnes of oil. In addition, it contains 5.67 million tonnes of uranium – making it one of the main potential sources of uranium in Europe – 16.53 million tonnes of zinc, and 12.76 million tonnes of molybdenum. There is as yet no economical and environmentally friendly technology to extract either the metals or the oil.
Kukersite
Kukersite is a light-brown marine-type Late Ordovician oil shale formed some 460 million years ago.Aaloe et al. (2007), p. 8 It was named kuckers by the Baltic German geologist Carl Friedrich Schmidt in the mid-19th century, and kukersite by the Russian paleobotanist Mikhail Zalessky in 1916. The name reflects the German name for Kukruse Manor, where oil shale samples were obtained.Aaloe et al. (2007), p. 30
Kukersite deposits in Estonia are the world's second highest-grade oil shale deposits after the Australian torbanite. Its organic content varies from 15% to 55%, averaging over 40%. Correspondingly, its mean calorific value is 15 MJ/kg (3,600 kcal/kg). The conversion ratio of its organic content into usable energy (shale oil and oil shale gas) is between 65 and 67%,Aaloe et al. (2007), pp. 6–7 and its Fischer Assay oil yield is 30 to 47%.
The principal organic component of kukersite is telalginite, which originated from the fossil green alga Gloeocapsomorpha prisca, deposited in a shallow marine basin. Kukersite lies at depths of . The most significant kukersite deposits in Estonia – the Estonian and the Tapa – cover about ,Francu et al. (2007), p. 14 and together with the Leningrad deposit (an extension of the Estonian) form the Baltic Oil Shale Basin.Aaloe et al. (2007), pp. 10–12 The Estonian deposit, which covers about , is used industrially. It consists of 23 exploration and mining fields. The Tapa deposit is not accounted as a reserve due to its lower calorific value, which makes its extraction economically inexpedient. In northern Estonia there are 50 layers of kukersite; the six lowest of these form a thick mineable bed. In this area kukersite lies near the surface. To the south and west it lies deeper and its thickness and quality decrease.
According to the International Energy Agency, Estonia's kukersite represents about 1.1% of global and 17% of European oil shale resources.IEA (2013), p. 71 The total kukersite resources in Estonia are estimated to be about 4.8 billion tonnes, including 1.3 billion tonnes of economically proven and probable reserves. Economically proven and probable reserves consist of mineable deposits with energy ratings of at least 35 gigajoules per square metre and calorific values of at least 8 MJ/kg, located in areas without environmental restrictions. Up to 650 million tonnes of economically proven and probable reserves are designated as recoverable.
History
Early history It is often reported that 18th-century naturalist and explorer Johann Anton Güldenstädt had mentioned a discovery of a "burning rock" near Jõhvi in 1725, but his published travel notes mention neither oil shale nor Estonia. It is also often reported that the earliest documented record of oil shale in Estonia, authored by the Baltic German publicist and linguist August Wilhelm Hupel, dates to 1777. However, this is based on a misinterpretation of the German word Steinöhl (meaning: stone oil), which was used by Hupel but which most likely did not mean oil shale in the context of his publication.
In the second half of the 18th century, the St. Petersburg Free Economic Society started to search for information about combustible minerals which as fuels would replace the decreasing stock of trees in the European part of Russia. As a result of these inquiries, the Society received information about a combustible mineral found at the Kohala Manor near Rakvere. According to the landlord of the Kohala estate, Baron Fabian Reinhold Ungern-Sternberg, the 'burning rock' was discovered at a depth of about ten meters when a spring was opened on the slope of a sandy hump, as it was during the digging of a well some years earlier on the same slope. This discovery was briefly mentioned in a paper prepared by the German chemist Johann Gottlieb Georgi and presented by the Actual State Councillor Anton-Johann Engelhardt at the meeting of the Society in 1789. The first scientific research into the rock's oil yield, using samples from the village of Vanamõisa of the Kohala Manor, was published by Georgi at the Russian Academy of Sciences in 1791. In 1838 and 1839, the Baltic German geologist Gregor von Helmersen published a detailed description of the deposits of kukersite in Vanamõisa and graptolitic argillite in Keila-Joa. In 1838 he made a thorough experiment to distil oil from the Vanamõisa oil shale deposit.
During the 1850s, large-scale works were undertaken in Estonia to transform excessively wet land into land suitable for agriculture; this included the digging of drainage ditches. In the process, previously unknown layers of oil shale were discovered in several locations. In the years 1850–1857, the territory of Estonia was explored by the Baltic German geologist Carl Friedrich Schmidt who studied these findings of oil shale. Russian chemist Aleksandr Shamarin, who at the end of the 1860s had studied the composition and properties of oil shale originating from the Kukruse area, concluded it made sense to use oil shale for the production of gas and as a solid fuel. However, he considered shale oil production unprofitable. During the remainder of the 19th century oil shale was used locally as a low-grade fuel only.Ots (2004), p. 14 For example, in the 1870s, Robert von Toll, landlord of the Kukruse Manor, started to use oil shale as a fuel for the manor's distillery. There were failed attempts to use graptolitic argillite as fertilizer in the 19th century. In the beginning of the 20th century, geologist and engineer Carl August von Mickwitz studied self-ignition of graptolitic argillite near Paldiski. At the University of Tartu oil shale geology and chemistry analyses were conducted during the 19th century by Georg Paul Alexander Petzholdt, Alexander Gustav von Schrenk, and Carl Ernst Heinrich Schmidt, among others.
Beginning of the oil shale industry
Analysis of Estonian oil shale resources and mining possibilities intensified during the early 20th century while Estonia was part of the Russian Empire. Industrial development was under way in Saint Petersburg (known as Petrograd in 1914–24), but regional fuel resources were in short supply. A large shale oil extraction plant for processing Estonian oil shale was proposed in 1910. The outbreak of World War I, coupled with a fuel supply crisis, accelerated the pace of the research.