Product has been added to the basket

Shale of the Century

A Wirtgen cold milling machine in action in Kivoli. Image courtesy, Heikki Bauert

Geoscientist 17.2 February 2007

Are oil shales a dead duck, or about to take off? For one European country where oil shale provides 93% of its electricity, an answer is keenly awaited. Ted Nield investigates…

Believe it or not there is a modern European country, with an annual GDP growth rate of 12%, which today relies almost completely on oil shale for its electricity. Oil shale (box) is that country's chief mineral resource (both for power generation and chemical industry feedstock) and it digs up about 13 million tonnes of the stuff every year. Even more surprising, these undeformed organic sediments date from the Ordovician, and they're a two hour Easyjet hop away from Stansted Airport.

The country in question is Estonia (box). But environmental campaigners there are finding themselves at loggerheads with the industry, which is set to grow markedly in coming years after a period of decline. They claim it is environmentally unfriendly, while the industry counters that campaigners are living in the past. Thanks to improvements in mining and combustion technology, the industry's environmental record is now clean, they say.

In fact, the future for oil shales worldwide may be brighter than even its Estonian enthusiasts are saying. New in situ combustion techniques being trialled in the USA may make oil shale one of the greenest fuel sources around, with all waste remaining locked firmly in the ground.

What is oil shale?

The brachiopod Estlandia from the Oil Shale (Kukruse Formation - Ordovician Caradoc) of Estonia. Both genus and family are endemic to this terrane, indicating how isolated Baltica was in the Ordovician. Photo Phil Crabb. © Natural History Museum. In the history of misnomers, "oil shale" must rate as one of the greatest, since it isn't shale and contains no oil. So forget about those foul-smelling bituminous Jurassic shales of Kimmeridge Bay, or parts of the Carboniferous. These oil shales are fine-grained, toffee-coloured sediments of low density, containing high proportions of kerogen that give off liquid of gaseous hydrocarbons when heated. The proper mineralogical term for this rock is "kukersite", derived from the type locality near Kukruse, in Estonia (picture).

Kukersite is really a source rock that has not passed through the "oil window". So the organic matter, having not been changed into an oil-like substance, has to be heated in a retort, in the absence of air, to between 350 and 650°C (depending on feedstock). The kerogen undergoes the chemical process known as pyrolysis, and the hydrocarbons are driven off. The industrial process is called "retorting". Generally, only those shales yielding over 40 litres of oil per tonne are considered economic. The Estonian oil shales are particularly rich, yielding over three times that much. While some of Estonia's oil shale is used in this way, more is simply burned in power stations - usually after it has been further concentrated ("beneficated") to minimise the amount of low-calorific value gangue mixed with it.

The kerogen in oil shale owes its origin to the same organic processes as the hydrocarbons in conventional reservoirs – and like them is composed of carbon, hydrogen, oxygen, with a dash of nitrogen and sulphur. However its complex macromolecular structure is insoluble in the usual organic solvents.

Oil shale was first researched scientifically in Estonia at the end of 18th Century. In 1838 first experiments were made to obtain oil by distillation from a small batch of kukersite mined near the town of Rakvere. Although the rock could be used as solid fuel and, after processing, as liquid or gaseous fuel, kukersite was not exploited until shortages created by World War I bit for the first time. In fact the history of the exploitation of oil shale globally has been marked by cycles of renewed interest based on shortages, or threats of shortages that have inflated the price of oil. Thus, under Jimmy Carter, America threw large amounts of money at "Synfuels Corp." during the 70s oil shock. It closed in 1985. The current high oil prices, concerns over "Hubbert's Peak" and security of future supply, have re-awakened interest in this vast and largely untapped global resource.

Estonia at a glance

Area – 45,227 km2
Population – 1.4 million
GDP - €6.2bn
GDP (purchasing power standards per person, % of EU Average) – 40%
Wages per hour (2000) – €3.03
Unemployment – 12.4%
Agricultural workers – 7.1%

The rock that burns

The first genuine historical record of the unusual properties of the mineral that would be named kukersite was made about 1725 - a report about local shepherds using the shale to build the nighttime fires by which to watch their flocks. Another reference appeared in 1777, in a report by August Hupel, (1737-1819), Lutheran minister, savant and man of letters in the city of Põltsamaa.

The occurrence of oil shale (kukersite) in the Baltic oil Shale Basin (courtesy, Heikki Bauert)
<Fig 1 Location of shale deposits in the Baltic Oil Shale Basin (Heikki Bauert) > 

Kukersite occurs in two main units in Estonia. In the North East part of the republic is the "Estonian" deposit, which comes from the base of the Viivikonna Formation (Kukruse Stage) of Upper Ordovician age (actually the precise stratigraphic position of the oil shale is still uncertain. Conodonts indicate Upper Ordovician (in the recent global timescale), while graptolites, which are very rare in limestones, support a topmost Middle Ordovician age.) The Estonia Deposit forms the western part of the Baltic Oil Shale Basin, covering an area about 5000km2. Easternward extension of the Baltic Oil Shale Basin into Russian territory is called the Leningrad deposit. The Tapa deposit in central Estonia which is slightly younger in age, lies at a depth of 60 to 170 metres. It is not well explored.

Kukersite is a light brown rock flecked with abundant fossil remains. Unlike in monotonous black shales as well as in microlaminated Green River oil shales, specific cell structures can be observed in kukersite microscope studies, particularly well distinguished under SEM. The kukersite organic matter derives from a colonial microorganism called Gloeocapsomorpha prisca – thought either to be an alga or cyanobacterium. G. prisca also shows many morphological similarities to the modern cyanobacterium Entophysalis major, which forms intertidal and subtidal mats in places like Shark Bay, Australia. The calorific value of the kukersite deteriorates to the south, falling from 10 Megajoules per kilogram in the north to about half that in the south and southwest. The thickness of the commercial horizon also decreases in that direction.

Because of the chemical and isotopic characteristics of the organic fraction, the accumulations are thought to have originated in shallow subtidal marine lagoons of the Baltic epicontinental sea. More than 300 different species of fossil have been recorded from them, and they tend to have a rather low pyrite content – all indicative of good oxygenation. Palaeomagnetic data suggest a palaeolatitude of 30 to 50 degrees south, suggesting a temperate environment.

Since 1916-18, when commercial oil shale mining began in Estonia, it has had an enormous influence on the country's economy, particularly when it was part of the Soviet Union, and subsequently in the modern Estonian Republic. By 1955 annual output had reached seven million tonnes and was mainly used a power station/chemical plant feed, and in the production of cement (using the ash). The opening of the 1400 MW Baltic Thermal Power Station (1965), followed in 1973 by the 1600 MW Estonian Thermal Power Station, again boosted production, and annual output peaked in 1980 at 31 million tonnes.

The decline in oil shale production started in 1981, when the fourth reactor was launched at the Leningrad Nuclear Power Plant located in Sosnovy Bor and it became clear that no additional thermal power plant will be built in Estonia. By 1999 annual oil shale production had fallen to 10 million tonnes. Most was used for electricity and heat generation, and 1.3 million tonnes were distilled to produce 151,000 tonnes of shale oil. Estonian oil shale resources are currently put at 5 billion tonnes, including 1.5 billion tonnes of active (mineable) reserves. Since the turn of the century, each subsequent year has seen small recoveries in production, reflecting the rising power demand in Estonia as its economic recovery has gathered pace.

Future trends

As the consumption of oil globally begins to outstrip the discovery of new fields, oil-poor countries like Estonia can be forgiven for looking upon their oil shale as a blessing. But the shale has, as well as its actual overburden, an invisible one – namely, opposition from environmentalists.

It is not hard to see why environmentalists instinctively oppose the industry. First, like most industries dating mainly from the Soviet era, it has had a dubious environmental past. The shale (mostly) needs to be strip-mined; typically, Estonian opencast oil shale mines have to take out 20-30 metres of overburden to excavate a mere 3-4 metres of kukersite. Although new Wirtgen milling machines have improved the efficiency of this mining process (picture), relieving the need for further enrichment of the product before burning, all overburden must be replaced and the landscape restored and re-vegetated. 

It is also widely asserted by environmental campaigners that the sludgy material left behind by retorting and burning, because of a so-called "popcorning effect" unique to oil shale, occupies 30% more volume than the original unburned material. The hole it came out of being too small to receive all this waste, the result has been large mountains of ash that are a familiar feature of the NE Estonian landscape. Moreover, environmentalists say, this residue contains phenol-rich organic molecules that then leach into groundwater.

However, Heikki Bauert, an expert on Estonian oil shales, but who no longer works in the industry says: "the popcorning effect…exists only in fantasy. The actual mass balance for kukersite oil shale and retorted waste are similar. Kukersite…is really a lightweight rock… and during retorting at least 10% of mass is removed as raw oil."

The main reason for not dumping the sludge back into mines was not because it wouldn't fit, but to avoid contaminating groundwater. And as for those toxic phenols, the environmentalists' argument is also misleading and deceptive, according to Bauert. "During the Soviet time, all kinds of oil processing industry waste was dumped together into the same hills. Today, retorting waste may even be free of phenol compounds” he says.

But the biggest single charge levelled by environmental campaigners against oil shale is that because burning it also decomposes carbonates as well as hydrocarbons, it creates more than four times as much greenhouse gas as conventional hydrocarbon fuel. This assertion again, industry supporters say, is highly misleading because the central assertion (that burning oil shale decomposes carbonates) is outdated. The German cold milling engines are highly selective and have much improved the quality of the power-plants' feedstock. Also those plants now employ much more advanced combusting technology.

Bauert says: "We are not "burning carbonates" in power plants any more". The companies who have developed the circulating bed combustors now employed in Estonian power plants say that while during conventional burning, as during the Soviet era, 30% extra CO2 emissions could result from decomposing the carbonate gangue, in modern circulating bed combustors roughly 25% of the included carbonate stays intact." Also, the nitrogen content in kukersite is very low, Bauert says. These improvements have made it possible to consider expanding oil shale mining within emissions guidelines imposed by the EU.

Since 2001 the Estonian government has phased in liberalizing measures in its electricity sector. However, the government was chary of wholesale adoption of EU energy policy for the simple domestic reason that opening Estonia's energy market to competition from abroad would likely put mines, quarries and two huge power stations out of business – precipitating an economic and social crisis in the NE of the country. Estonia therefore pushed for the EU to recognise that most of its power would continue to come from oil shales until 2015 at least. In this they were largely successful.

Although a recent Estonian Economic Development Plan stated that oil shale's share in the country's national primary energy balance must fall to 52-54% by 2005 and to 47-50% by 2010, thanks to technological improvements in mining and combustion, the country's most recent governmental projection is able to project a marked increase in mining in the near future, with output rising to 31 million tonnes by 2015. Mining permits for this amount have already been issued.

Interestingly, regulatory hurdles have not only afflicted the power generation side of the oil shale industry. In May 2006, the European Parliament approved the Registration, Evaluation and Authorisation of Chemicals Directive (REACH). By June, the Estonian chemical industry was already complaining that it was now put at a competitive disadvantage because its unconventional feedstock meant that it had to re-test all its products to ensure compliance - even if the molecule in question was already on the EU approved list.

But while the country's major chemical producer Viru Keemia Grupp (VKG) has struggled with gaining certification for its chemical products, Estonia as a whole is finding that improved technology has saved it from a very uncomfortable situation, despite the continuing opposition of green lobbies. Where once it seemed that Estonia's main mineral product and energy source had either to be reformed beyond the efficiency of any proven technology, or abandoned in favour of imports, the industry is now looking at a renaissance.

Shale renaissance

Estonia's response to its very singular energy problems is being watched intently by others with strategic concerns of their own. Outside Estonia, oil shales are exploited only sporadically – notably the Permian Irati Formation (Brazil), and Tertiary lake sediments at Fushun, Liaoning Province, China. However the energy potential of oil shale globally is truly vast. According to the BP Statistical Review of World Energy, the world's remaining oil and gas reserves total 2.1 trillion barrels. The total estimated global resources of oil shale are thought to be well over 2.6 trillion barrels. The total energy resource represented by the Tertiary Green River Formation is said to exceed the total oil and gas reserves of Saudi Arabia.

The amazing fact is that oil shales in Australia, Brazil, Canada, China, Estonia, France, Russia, Scotland, South Africa, Spain, Sweden and the USA have an energy potential exceeding all known conventional oil reserves. So how can all the valuable organic material contained in them be converted into energy at a market price, and without environmental damage?

Last year Royal Dutch Shell completed a demonstration project that produced 1400 barrels of oil plus associated gas from oil shale in the ground – without any of that shale ever seeing light of day, and without (as far as they can tell) any damage to groundwater. The process they used is called the In-situ Conversion Process, or ICP.

The tale began in 1981 when researchers at Shell's division of "unconventional resources" spent some time and money thinking about how to make oil shale productive. In 1996 Shell successfully performed a small field test on its Mahogany property in Rio Branco County, Colorado, about 320 kilometres west of Denver. Four related tests have since been carried out, the most recent, the Mahogany Ridge Project, being the largest to date. The basic idea is simple in principle but difficult in practice. As oil shale is an immature source rock, what it needs is a good dose of pressure-cooking.

Shell's process puts an array of down-hole electrical heaters into the formation, which heat the surrounding shale to temperatures as high as 400°C. Over three to four years, dense oil and gas is expelled from the kerogen; lighter components are sheared off the denser compounds and the available hydrogen becomes concentrated in lighter fractions that then change to gas. This moves to surface through fractures – induced or natural – via producing wells.

Shell believes the process produces up to 70% of the original carbon in the shale – 10 times more product per unit of shale than conventional mining-based methods. Also, when these wells dry up, they do so suddenly – unlike conventional oil wells, with their long and costly tail of poor productivity. The last stage involves injecting water, which flashes to steam and carries the final organics to surface for stripping. Then all the operator has to do is turn everything off and move along to the next plot.

The most cunning aspect of ICP is how groundwater is protected from contamination during the process. Shell drills a line of wells a few metres apart around the perimeter of the site and uses these to pass refrigerant. The groundwater then freezes, and the frozen columns coalesce to form a coffer dam of ice c. 10 metres thick. This technology is essentially the same as sometimes used for example by tunnellers to prevent groundwater ingress in saturated terrain.

The whole process is clearly energy intensive; but Shell estimate that – on the basis of the complete life-cycle of a field – 3.5 units of energy would be produced for every unit used in production. That is a very favourable ratio, compared to heavy crude fields using steam injection enhanced oil recovery, and certainly much more efficient than strip mining. The oil produced is light, and the lightest fractions come off first – which means a faster return on investment.

There is no evidence yet that this can work at greater depths on a commercial scale, but the results are promising. In Green River, Shell believe they could harvest a million barrels per acre – which is a billion barrels per square mile in a field covering a thousand square miles, with (they hope) none of the environmental deficits of conventional oil shale mining. Shell also believe that the whole process – if it scales up – could be economic at a crude price of only $30 per barrel, and before them lies the prospect of being able to recover between 500 billion and 1.1 trillion barrels – just from Green River Formation rocks in Colorado, Utah and Wyoming. The mid-point on that range – 800 billion barrels is three times Saudi Arabia's oil reserves.

Shell are now conducting a $50 million two- to four-year study of the ice-wall technology in Rio Branco County, and hope to decide by 2010 whether the ICP process is commercial. Meanwhile the US Department of Energy has signed an agreement with the Estonian Ministry of Economic Affairs and Communications for scientific and technology cooperation on oil shale research and utilization.

The era of home-brew oil may just be dawning. And that might just be the good news that Estonia needs.


I am deeply indebted to Heikki Bauert, Olle Hints and Rein Raudsep for help with this article, and for many of the pictures that accompany it. The piece also benefited by reference to online articles by Dan Denning, Vermund Jensen, Ingo Valgma, Randall Parker, Katharine Sanderson, Linda Seebach.

Suggested further reading

• Oil Shale – an alternative energy resource? O M Sather, GEO ExPro 2004 pp 26-32.

• Oil Shale Development in the United States Prospects and Policy Issues. RAND Corporation J T Bartis, T LaTourrette, L. Dixon, D J Peterson, and G Cecchine, MG-414-NETL, 2005.

• The chemistry and mineralogy of waste from retorting and combustion of oil shale. O M Sather et al., from Gieré, R & Stille, P (eds) 2004: Energy, Waste and the Environment: a Geochemical Perspective. Geological Society, London, Special Publication 236, 263-284.

Want to see the Estonian oil shale for yourself?

An unprecedented opportunity to see the Estonian oil shale industry first hand will be available at MAEGS-15, Georesources and public policy: research, management, environment 16-20 September 2007, Tallinn, Estonia. For more details and registration