CHAPTER 10 – Shale Oil
Shales are geologic formations composed of thinly layered sedimentary rocks,
and these are widely dispersed on the Earth.
It has partially decomposed and metamorphosed over the ages until it now
exists as a mixture of organic substances locked within the shale. The organic
material contained in shale is called kerogen.
The shale itself contains no oil as it is known today. However, if the shale is
pretreated and fractionated at elevated temperatures, the kerogen
decomposes and part of it is discharged as an oily vapor, which can be
condensed into a viscous liquid referred to as shale oil.
Unlike typical crude oil, this shale oil contains large amounts of compounds of
nitrogen and large amounts of sulfur. These must be removed before a product
like crude oil results.
Oil shale has been used since ancient times. It was first used for industrial
purposes in the early seventh century.
The world’s first commercial use of shale oil was based on mining operations
in the Lothian region of Scotland in the middle of the nineteenth century, after
the scientist James “Paraffin” Young devised a process of removing the oil by
roasting the rock in ovens and draining away the fluid that it gave off.
Following the 1973 oil crisis, the oil shale industry was resurrected in several
countries, including the United States. However, in the 1980s, when oil prices
fell, the industry again declined. The industry grew in full force at the start of
the twenty-first century.
Availability/Distribution and Characterization
United States has a considerable fraction of the world’s oil shale deposits
(approximately 73 percent according to an earlier 1974 World Energy
Huge amounts of oil are also found along the Athabasca River in Alberta,
Canada, where the tar sand deposits are near enough to the surface to be
removed by a method like strip mining.
The oil produced per ton is directly proportional to the amount of kerogen per
unit of mass. The mass of oil is typically two-thirds of the mass of kerogen;
however, it varies from 10 to 80 percent for various formations throughout the
Oil shale must be hydrogenated to form a high-quality Syncrude oil for Refinery
Availability/Distribution and Characterization
Oil can also be extracted from bituminous tar sands that contain elevated
quantities of hydrocarbons. The “Alberta Sands” of Canada, for example,
average 83 percent sand, 13 percent bituminous matter, and 4 percent water.
The heavy oils from shale are characterized by an unfavorable
hydrogen/carbon ratio. These issues are typically corrected when hydrogen is
added during the refining operation.
Shale gas is also widely distributed throughout the U.S. Recent advances in
hydrofracturing techniques have allowed for the development of these here-to-
fore untapped resources.
Shale gas resources are also being developed abroad as well.
Oil shale is mined either by (1) traditional underground mining or (2) surface
The two methods of surface mining are:
(1) open pit mining and
(2) strip mining.
A method of subsurface mining is the room-and-pillar method, where the shale
is extracted across a horizontal plane while leaving pillars of untouched
material to support the roof.
The main recovery technique involves first removing as much as 150 feet of
overburden to allow huge mechanical diggers to start scooping out the shale.
The operation is complex and expensive since huge digging machines are
required to handle more than 6,000 tons of material an hour.
Another type of oil that can be recovered by mining rather than drilling is found
in grayish rocks known as shales. The oil is chemically combined with the
shales. Very high temperatures are again required to force the rock to
decompose so that it will discharge its oil content. However, this is a costly
The four earlier commercially acceptable aboveground retorting processes
required crushing shale and heating it to an elevated temperature to
decompose the organic material. Each differs in the manner of heating. These
methods yield shale oil and gas.
In the Tosco process, the mined shale is crushed and fed to a preheat tower
where it is heated by hot gas. This material is then fed into a rotary drum,
where it mixes with marble-sized ceramic balls that have been preheated. The
hot ceramic balls pulverize and heat the shale until oil and gas boil off. The
spent shale is removed in the bottoms. The vapors can be sent to a distillation
Finally, power plants can directly use oil shale as a fuel to employ two types of
combustion methods. The traditional method is pulverized combustion, which
is used in the older units in Estonia. The more advanced method is fluidized
bed combustion, which is used in Germany and Israel. The two main fluidized
bed technologies are the bubbling fluidized bed and circulated fluidized bed
Environmental concerns with oil shale are broad and encompass not only the
industrial complex, but also the effect on the surrounding socioeconomic area
and region. There is a considerable amount of air pollution, including the
release of particulate, SO2, NOX, CO, and hydrocarbons from any of the
processes discussed in the previous section. Blasting, mining, crushing, and
transporting the oil shale all contribute to air quality particulate levels, and the
transportation and storage of spent shale contributes even more.
Air pollution will still be a major obstacle to oil shale development.
It is estimated that slightly more than three barrels of water will be required for
every barrel of oil produced from shale oil.
Water obtained from the oil shale itself is also contaminated with organics such
as phenols and carboxylic acids.
Summarizing, oil shale processes involve a number of environmental impacts;
they are more pronounced in surface mining than in underground mining. They
include acid drainage induced by the sudden rapid exposure and subsequent
oxidation of formerly buried materials; the introduction of both organics and
metals into surface water and groundwater; and increased erosion, sulfur
emissions, particulate matter, and other forms of air pollution. The processes
can also damage the biological and recreational value of land and the
ecosystem in the area. The extensive use of water in arid regions is an
extremely sensitive environmental issue.
Future Prospects and Concerns
In the future, it may be possible to produce oil from shale without costly
excavation and processing. Some pyrolysis processes have been
recommended and are currently under study. One of the processes involves
combining a fluidized bed and a circulated fluidized bed for the purpose of
burning the by-products of pyrolysis. Perhaps the most promising process is a
pressurized fluid bed combustion process; however, this process is in the