OIL SHALE
Oil shale, also known as kerogen shale, is an organic-rich
fine-grained sedimentary rock containing kerogen (a solid mixture oforganic
chemical compounds) from which liquid hydrocarbons called shale oil (not to be
confused with tight oil—crude oil occurring naturally in shales) can be
produced. Shale oil is a substitute for conventional crude oil; however,
extracting shale oil from oil shale is more costly than the production of
conventional crude oil both financially and in terms of its environmental impact.[1][2]
Deposits of oil shale occur around the world, including major deposits in the
United States. Estimates of global deposits range from 2.8 to 3.3 trillion
barrels (450×109 to 520×109 m3) of recoverable oil.
Heating oil shale to a sufficiently high temperature causes
the chemical process of pyrolysis to yield a vapor. Upon cooling the vapor, the
liquid shale oil—an unconventional oil—is separated from combustible oil-shale
gas (the term shale gas can also refer to gas occurring naturally in shales). Oil
shale can also be burned directly in furnaces as a low-grade fuel for power
generation and district heating or used as a raw material in chemical and
construction-materials processing.[2][6]
Oil shale gains attention as a potential abundant source of oil
whenever the price of crude oil rises.[7][8] At the same time, oil-shale mining
and processing raise a number of environmental concerns, such as land use,
waste disposal, water use, waste-water management, greenhouse-gas emissions and
air pollution.[9][10] Estonia and China have well-established oil shale
industries, andBrazil, Germany, and Russia also utilize oil shale.[2]
General composition of oil shales constitutes inorganic
matrix, bitumens, and kerogen. Oil shales differ from oil-bearing shales, shale
deposits that contain petroleum (tight oil) that is sometimes produced from
drilled wells. Examples of oil-bearing shales are theBakken Formation, Pierre
Shale, Niobrara Formation, and Eagle Ford Formation.
Contents
[hide]
• 1 Geology
• 2 Reserves
• 3 History
• 4 Industry
• 5 Extraction
and processing
• 6
Applications and products
• 7 Economics
•
Geology[edit]
Main article: Oil shale geology
Outcrop of Ordovician oil shale (kukersite), northern
Estonia
Oil shale, an organic-rich sedimentary rock, belongs to the
group of sapropel fuels.[11] It does not have a definite geological definition
nor a specific chemical formula, and its seams do not always have discrete
boundaries. Oil shales vary considerably in their mineral content, chemical
composition, age, type of kerogen, and depositional history and not all oil
shales would necessarily be classified as shales in the strict sense.[3][12]
According to the petrologist Adrian C. Hutton of the University of Wollongong,
oil shales are not "geological nor geochemically distinctive rock but
rather 'economic' term."[13] Their common feature is low solubility in
low-boiling organic solvents and generation of liquid organic products on
thermal decomposition.[14]
Oil shale differs from bitumen-impregnated rocks (oil sands
and petroleum reservoir rocks), humic coals and carbonaceous shale. While oil
sands do originate from the biodegradation of oil, heat and pressure have not
(yet) transformed the kerogen in oil shale into petroleum, that means that its
maturation does not exceed early mesocatagenetic.[2][14][15][16]
General composition of oil shales constitutes inorganic
matrix, bitumens, and kerogen. While the bitumen portion of oil shales is
soluble incarbon disulfide, kerogen portion is insoluble in carbon disulfide
and can contain iron, vanadium, nickel, molybdenum, and uranium.[17] Oil shale
contains a lower percentage of organic matter than coal. In commercial grades
of oil shale the ratio of organic matter to mineral matter lies approximately
between 0.75:5 and 1.5:5. At the same time, the organic matter in oil shale has
an atomic ratio of hydrogen to carbon (H/C) approximately 1.2 to 1.8 times
lower than for crude oil and about 1.5 to 3 times higher than for
coals.[2][11][18] The organic components of oil shale derive from a variety of
organisms, such as the remains of algae, spores, pollen, plant cuticles and
corky fragments of herbaceous and woody plants, and cellular debris from other
aquatic and land plants.[2][19] Some deposits contain significant fossils;
Germany's Messel Pit has the status of a Unesco World Heritage Site. The
mineral matter in oil shale includes various fine-grained silicates and
carbonates.[6][11] Inorganic matrix can contain quartz,feldspars, clays (mainly
illite and chlorite), carbonates (calcite and dolomites), pyrite and some other
minerals.[17]
Geologists can classify oil shales on the basis of their
composition as carbonate-rich shales, siliceous shales, or cannel shales.[20]
Another classification, known as the van Krevelen diagram, assigns kerogen
types, depending on the hydrogen, carbon, and oxygen content of oil shales'
original organic matter.[12] The most commonly used classification of oil
shales, developed between 1987 and 1991 by Adrian C. Hutton, adapts
petrographic terms from coal terminology. This classification designates oil
shales asterrestrial, lacustrine (lake-bottom-deposited), or marine (ocean
bottom-deposited), based on the environment of the initial biomass
deposit.[6][21] Known oil shales are predominantly aquatic (marine, lacustrine)
origin.[14][21] Hutton's classification scheme has proven useful in estimating
the yield and composition of the extracted oil.[2]
Reserves[edit]
Main article: Oil shale reserves
Fossils in Ordovician oil shale (kukersite), northern
Estonia
As source rocks for most conventional oil reservoirs, oil
shale deposits are found in all world oil provinces, although most of them are
too deep to be exploited economically.[22] As with all oil and gas resources,
analysts distinguish between oil shale resources and oil shale reserves.
"Resources" refers to all oil shale deposits, while
"reserves", represents those deposits from which producers can
extract oil shale economically using existing technology. Since extraction
technologies develop continuously, planners can only estimate the amount of
recoverable kerogen.[1][6] Although resources of oil shale occur in many
countries, only 33 countries possess known deposits of possible economic value
.[23][24] Well-explored deposits, potentially classifiable as reserves, include
the Green River deposits in the western United States, the Tertiary deposits in
Queensland, Australia, deposits in Sweden and Estonia, the El-Lajjun deposit in
Jordan, and deposits in France, Germany, Brazil, China, southern Mongolia and
Russia. These deposits have given rise to expectations of yielding at least 40
liters of shale oil per tonne of oil shale, using the Fischer Assay.[6][12]
A 2005 estimate set the total world resources of oil shale
at 411 gigatons — equivalent to yield of 2.8 to 3.3 trillion barrels (450×109
to 520×109 m3) of shale oil though only a part of it is recoverable.[3][4][5]
According to the 2010 World Energy Outlook by the International Energy Agency,
the world oil shale resources may be equivalent of more than 5 trillion barrels
(790×109 m3) of oil in place of which more than 1 trillion barrels (160×109 m3)
may be technically recoverable.[22] For comparison, the world's proven
conventional oil reserves were estimated at 1.317 trillion barrels (209.4×109
m3), as of 1 January 2007.[25] The largest deposits in the world occur in the
United States in the Green River Formation, which covers portions of Colorado,
Utah, and Wyoming; about 70% of this resource lies on land owned or managed by
the United States federal government.[26] Deposits in the United States
constitute 62% of world resources; together, the United States, Russia and
Brazil account for 86% of the world's resources in terms of shale-oil
content.[23] These figures remain tentative, with exploration or analysis of
several deposits still outstanding.[2][6] Professor Alan R. Carroll of
University of Wisconsin–Madison regards the Upper Permian lacustrine oil-shale
deposits of northwest China, absent from previous global oil shale assessments,
as comparable in size to the Green River Formation.[27]
History[edit]
Main article: History of the oil shale industry
Production of oil shale in millions of metric tons, from
1880 to 2010. Source: Pierre Allix, Alan K. Burnham.[28]
Humans have used oil shale as a fuel since prehistoric
times, since it generally burns without any processing.[29]Britons of the Iron
Age also used to polish it and form it into ornaments.[30] The first UK patent
for extracting oil from oil shale was British Crown Patent 303 granted to
Becker and Serle in 1684.[17][31][32] Modern industrial mining of oil shale
began in 1837 in Autun, France, followed by exploitation in Scotland, Germany,
and several other countries.[2][33]
Operations during the 19th century focused on the production
of kerosene, lamp oil, and paraffin; these products helped supply the growing
demand for lighting that arose during the Industrial Revolution.[34] Fuel oil,
lubricating oil and grease, and ammonium sulfate were also produced.[35] The
European oil-shale industry expanded immediately before World War I due to
limited access to conventional petroleum resources and to the mass production
of automobiles and trucks, which accompanied an increase in gasoline
consumption.
Although the Estonian and Chinese oil-shale industries
continued to grow after World War II, most other countries abandoned their
projects due to high processing costs and the availability of cheaper
petroleum.[2][6][33][36] Following the 1973 oil crisis, world production of oil
shale reached a peak of 46 million tonnes in 1980 before falling to about 16
million tonnes in 2000, due to competition from cheap conventional petroleum in
the 1980s.[9][23]
On 2 May 1982, known in some circles as "Black
Sunday", Exxon canceled its US$5 billion Colony Shale Oil Project near
Parachute, Colorado because of low oil-prices and increased expenses, laying
off more than 2,000 workers and leaving a trail of home-foreclosures and
small-business bankruptcies.[37] In 1986, President Ronald Reagan signed into
law the Consolidated Omnibus Budget Reconciliation Act of 1985 which among
other things abolished the United States' Synthetic Liquid Fuels Program.[4]
The global oil-shale industry began to revive at the
beginning of the 21st century. In 2003, an oil-shale development program
restarted in the United States. Authorities introduced a commercial leasing
program permitting the extraction of oil shale and oil sands on federal lands
in 2005, in accordance with the Energy Policy Act of 2005.[38][39]
Industry[edit]
Main article: Oil shale industry
A photograph of Shell Oil's experimental in situ shale oil
extraction facility in the Piceance Basin of northwestern Colorado. In the
center of the photo, a number of oil recovery pipes lie on the ground. Several
oil pumps are visible in the background.
Shell's experimental in-situ oil-shale facility, Piceance
Basin, Colorado, USA
As of 2008, industry uses oil shale in Brazil, China,
Estonia and to some extent in Germany, and Russia. Several additional countries
started assessing their reserves or had built experimental production plants,
while others had phased out their oil shale industry.[2] Oil shale serves for
oil production in Estonia, Brazil, and China; for power generation in Estonia,
China, and Germany; for cement production in Estonia, Germany, and China; and
for use in chemical industries in China, Estonia, and Russia.[2][36][40][41]
As of 2009, 80% of oil shale used globally is extracted in
Estonia, mainly due to the Oil-shale-fired power plants.[40][42]
Oil-shale-fired power plants occur in Estonia, which has an installed capacity
of 2,967 megawatts (MW), China (12 MW), and Germany (9.9 MW).[23][43]Israel,
Romania and Russia have in the past run power plants fired by oil shale, but
have shut them down or switched to other fuel sources such as natural
gas.[2][23][44] Jordan and Egypt plan to construct power plants fired by oil shale,
while Canada and Turkey plan to burn oil shale along with coal for power
generation.[2][23][45] Oil shale serves as the main fuel for power generation
only in Estonia, where the oil-shale-fired Narva Power Plants accounted for 95%
of country's electrical generation in 2005.[46]
According to the World Energy Council, in 2008 the total
production of shale oil from oil shale was 930,000 tonnes, equal to 17,700
barrels per day (2,810 m3/d), of which China produced 375,000 tonnes, Estonia
355,000 tonnes, and Brazil 200,000 tonnes. In comparison, production of the
conventional oil and natural gas liquids in 2008 amounted 3.95 billion tonnes
or 82.12 million barrels per day (13.056×106 m3/d).[2]
Extraction and processing[edit]
Main article: Shale oil extraction
A vertical flowchart begins with an oil shale deposit and
follows two major branches. Conventional ex situ processes, shown on the right,
proceed through mining, crushing, and retorting. Spent shale output is noted.
In situ process flows are shown in the left branch of the flowchart. The
deposit may or may not be fractured; in either case, the deposit is retorted
and the oil is recovered. The two major branches converge at the bottom of the
chart, indicating that extraction is followed by refining, which involves
thermal and chemical treatment and hydrogenation, yielding liquid fuels and
useful byproducts.
Overview of shale oil extraction.
Most exploitation of oil shale involves mining followed by
shipping elsewhere, after which one can burn the shale directly to generate
electricity, or undertake further processing. The most common methods of
surface mining involve open pit mining and strip mining. These procedures
remove most of the overlying material to expose the deposits of oil shale, and
become practical when the deposits occur near the surface. Underground mining
of oil shale, which removes less of the overlying material, employs the room-and-pillar
method.[47]
The extraction of the useful components of oil shale usually
takes place above ground (ex-situ processing), although several newer
technologies perform this underground (on-site or in-situ processing).[48] In
either case, the chemical process of pyrolysis converts the kerogen in the oil
shale to shale oil (synthetic crude oil) and oil shale gas. Most conversion
technologies involve heating shale in the absence of oxygen to a temperature at
which kerogen decomposes (pyrolyses) into gas, condensable oil, and a solid
residue. This usually takes place between 450 °C (842 °F) and 500 °C (932
°F).[1] The process of decomposition begins at relatively low temperatures (300
°C or 572 °F), but proceeds more rapidly and more completely at higher
temperatures.[49]
In-situ processing involves heating the oil shale
underground. Such technologies can potentially extract more oil from a given
area of land than ex-situ processes, since they can access the material at
greater depths than surface mines can. Several companies have patented methods
for in-situ retorting. However, most of these methods remain in the
experimental phase. One can distinguish true in-situ processes (TIS) and
modified in-situ processes (MIS). True in-situ processes do not involve mining
the oil shale. Modified in-situ processes involve removing part of the oil
shale and bringing it to the surface for modified in-situ retorting in order to
create permeability for gas flow in a rubble chimney. Explosives rubblize the
oil-shale deposit.[50]
Hundreds of patents for oil shale retorting technologies
exist;[51] however, only a few dozen have undergone testing. As of 2006, only
four technologies remained in commercial use: Kiviter, Galoter, Fushun, and
Petrosix.[52]
Applications and products[edit]
Industry can use oil shale as a fuel for thermal
power-plants, burning it (like coal) to drive steam turbines; some of these
plants employ the resulting heat for district heating of homes and businesses.
In addition to its use as a fuel, oil shale may also serve in the production of
specialty carbon fibers, adsorbent carbons, carbon black, phenols,
resins,glues, tanning agents, mastic, road bitumen, cement, bricks,
construction and decorative blocks, soil-additives, fertilizers, rock-wool insulation,
glass, and pharmaceutical products.[40] However, oil shale use for production
of these items remains small or only in its experimental stages.[2][6] Some oil
shales yield sulfur, ammonia, alumina, soda ash, uranium, and nahcolite as
shale-oil extraction byproducts. Between 1946 and 1952, a marine type of
Dictyonema shale served for uranium production in Sillamäe, Estonia, and
between 1950 and 1989 Sweden used alum shale for the same purposes.[6] Oil
shale gas has served as a substitute for natural gas, but as of 2009, producing
oil shale gas as a natural-gas substitute remained economically
infeasible.[53][54]
The shale oil derived from oil shale does not directly
substitute for crude oil in all applications. It may contain higher
concentrations of olefins, oxygen, and nitrogen than conventional crude oil.[4]
Some shale oils may have higher sulfur or arsenic content. By comparison with
West Texas Intermediate, the benchmark standard for crude oil in
thefutures-contract market, the Green River shale oil sulfur content ranges
from near 0% to 4.9% (in average 0.76%), where West Texas Intermediate's sulfur
content has a maximum of 0.42%.[55] The sulfur content in shale oil from
Jordan's oil shales may rise even up to 9.5%.[56] The arsenic content, for example,
becomes an issue for Green River formation oil shale. The higher concentrations
of these materials means that the oil must undergo considerable upgrading
(hydrotreating) before serving as oil-refinery feedstock.[20] Above-ground
retorting processes tended to yield a lower API gravity shale oil than the in
situ processes. Shale oil serves best for producing middle-distillates such as
kerosene, jet fuel, and diesel fuel. Worldwide demand for these middle
distillates, particularly for diesel fuels, increased rapidly in the 1990s and
2000s.[4][57] However, appropriate refining processes equivalent to
hydrocracking can transform shale oil into a lighter-range hydrocarbon
(gasoline).[4]
Economics[edit]
Main article: Oil shale economics
A graph of NYMEX light-sweet
crude oil price changes from 1996 to 2009 (not adjusted for inflation). In
1996, the price was about US$20 per barrel. Since then, the prices saw a sharp
rise, peaking at over $140 per barrel in 2008. It dropped to about $70 per
barrel in mid-2009.
NYMEX light-sweet crude oil prices 1996–2009 (not adjusted
for inflation)
The amount of economically recoverable oil shale is
unknown.[22] The various attempts to develop oil shale deposits have succeeded
only when the cost of shale-oil production in a given region comes in below the
price of crude oil or its other substitutes. According to a survey conducted by
the RAND Corporation, the cost of producing a barrel of oil at a surface
retorting complex in the United States (comprising a mine, retorting plant,
upgrading plant, supporting utilities, and spent shale reclamation), would
range between US$70–95 ($440–600/m3, adjusted to 2005 values). This estimate
considers varying levels of kerogen quality and extraction efficiency. In order
to run a profitable operation, the price of crude oil would need to remain
above these levels. The analysis also discusses the expectation that processing
costs would drop after the establishment of the complex. The hypothetical unit
would see a cost reduction of 35–70% after producing its first 500 million
barrels (79×106 m3). Assuming an increase in output of 25 thousand barrels per
day (4.0×103 m3/d) during each year after the start of commercial production,
RAND predicts the costs would decline to $35–48 per barrel ($220–300/m3) within
12 years. After achieving the milestone of 1 billion barrels (160×106 m3), its
costs would decline further to $30–40 per barrel ($190–250/m3).[40][47] Some
commentators compare the proposed American oil-shale industry to the Athabasca
oil-sands industry (the latter enterprise generated over 1 million barrels
(160,000 m3) of oil per day in late 2007), stating that "the
first-generation facility is the hardest, both technically and
economically".[58][59]
In 2005, Royal Dutch Shell announced that its in-situ
process could become competitive for oil prices over $30 per barrel
($190/m3).[60] A 2004 report by the United States Department of Energy stated
that both the Shell technology and technology used in the Stuart Oil Shale
Project could be competitive at prices above $25 per barrel, and that theViru
Keemia Grupp expected full-scale production to be economical at prices above
$18 per barrel ($130/m3).
To increase efficiency when retorting oil shale, researchers
have proposed and tested several co-pyrolysis processes.
A 1972 publication in the journal Pétrole Informations (ISSN
0755-561X) compared shale-based oil production unfavorably with coal
liquefaction. The article portrayed coal liquefaction as less expensive,
generating more oil, and creating fewer environmental impacts than extraction
from oil shale. It cited a conversion ration of 650 litres (170 U.S. gal; 140
imp gal) of oil per one ton of coal, as against 150 litres (40 U.S. gal; 33 imp
gal) of shale oil per one ton of oil shale.[33]
A critical measure of the viability of oil shale as an
energy source lies in the ratio of the energy produced by the shale to the
energy used in its mining and processing, a ratio known as "Energy
Returned on Energy Invested" (EROEI). A 1984 study estimated the EROEI of
the various known oil-shale deposits as varying between 0.7–13.3[67] although
known oil-shale extraction development projects assert an EROEI between 3 to
10. According to the World Energy Outlook 2010, the EROEI of ex-situ processing
is typically 4 to 5 while of in-situ processing it may be even as low as 2.
However, according to the IEA most of used energy can be provided by burning
the spent shale or oil-shale gas.[22]
The water needed in the oil shale retorting process offers
an additional economic consideration: this may pose a problem in areas with
water scarcity.
