Alberta is only slightly above 0
C the surface temperature in Venezuela is much higher (>20
C) and the oil
therefore needs less heating to reduce its viscosity.
Much of the oil in Venezuela is heavy oil and it
occurs in a foreland basin in front of the Cordilleran
Mountains in a similar plate tectonic position to the
heavy oil in Alberta. Also the oil in the Middle East is
located in a similar foreland basin but here the
reservoirs have not been uplifted so close to the surface and are therefore in most cases not so
biodegraded.
It is possible to make an emulsion between bitumen
and water which has low viscosity and which can flow
in pipelines and be burned directly to produce electric
power. The heavy oil and bitumen is rather rich in
sulphur which should be removed to avoid pollution. It
can also be mixed with gas so that it can be used to
produce normal oil products.
There are other important tar sand deposits in the
USA (Utah) and Africa (Congo and Madagascar).
Tar sand has only recently been included in data on
world oil reserves and as a result Canada has become
one of the nations with the highest oil reserves.
23.2 Oil Shales
Oil shales are source rocks, usually mudstones and
shales, with a high organic content (TOC), which
have not been buried deeply enough to become sufficiently mature for most of the hydrocarbons to be
generated. Although they may contain some
hydrocarbons they must be heated in an oven (pyrolysis) to 400–500
C so that most of the petroleum can be
generated from the remaining kerogen.
Oil shales must therefore be mined near the surface
in quarries and then heated in large ovens so that the
petroleum can be distilled off.
Source rocks may be uplifted close to the surface
after deeper burial; it is the temperature history that
determines how much of the kerogen is altered to oil
and gas.
Some source rocks may have been buried to more
than 5–6 km (160–170
C) and they have then
generated and expelled most of the hydrocarbons, but
some oil and particularly gas may remain. The Upper
Cambrian alum shale which is found in the Oslo
region is a good example of a rich source rock which
has been buried to at least 200
C (5–7 km) and lost
most of its hydrocarbons during the Caledonian folding in the late Silurian and early Devonian. In Sweden
the Upper Cambrian alum shales have not been buried
so deeply and therefore contain more oil which can be
distilled off by pyrolysis at 400–500
C.
In the Baltic region the lowermost Ordovician shales
are even less mature so that more of the kerogen remains
and in Estonia this shale is mined for oil on a large
scale. Here the reserves are very large (0.6 Â10
9 sm
3
oil equivalents – o.e).
Oil shales are used in electric power generation and
provide 60% of Estonia’s stationary energy. It is also
used for oil production and refining. The waste is
70–80 Mt. of semi-coke and the mounds exceed
100 m in height. The waste is very fine grained and
is alkaline with significant concentrations of sulphides
and heavy metals.
On a global basis oil shales represent a reserve
almost as large as conventional oil. Reserves of oil
which can be produced from oil shale are difficult to
estimate but they may total close to 5 trillion barrels
(800 Â10
9 sm
3 ). This is about equivalent to the
estimated world reserves of conventional oil and gas
(480 sm
3 o.e.). More than 80% of the well known
reserves are located in the US but there are probably
other regions with oil shales which have not been
recorded and evaluated.
The Green River Shale in Colorado, Utah and
Wyoming is a gigantic source of hydrocarbons. This
organic-rich mudstone was deposited in very large
lakes during the Eocene and the organic matter was
mostly freshwater algae (Fig. 23.5a, b).
In Australia there are also very large reserves of oil
shale and they have been used for oil production
already in the latter part of the 19th Century when
more than 100,000 tonnes of shale were processed.
In areas including Queensland and South Australia
there are Cenozoic shales or mudstones deposited in
freshwater associated with coal deposits but there are
also older (Permian) oil shales. Strict environmental
restrictions on oil shale mining have been imposed
here, particularly because of the association with The
Great Barrier Reef.
Also in other parts of the world oil shales may
represent large potential oil reserves but they may
not be produced with the present technology.
Oil shales must however be mined and heated in
ovens (pyrolysis) to generate the petroleum and the
energy for the heating is taken from the burning of the
23 Unconventional Hydrocarbons: Oil Shales, Heavy Oil. . .
585
C the surface temperature in Venezuela is much higher (>20
C) and the oil
therefore needs less heating to reduce its viscosity.
Much of the oil in Venezuela is heavy oil and it
occurs in a foreland basin in front of the Cordilleran
Mountains in a similar plate tectonic position to the
heavy oil in Alberta. Also the oil in the Middle East is
located in a similar foreland basin but here the
reservoirs have not been uplifted so close to the surface and are therefore in most cases not so
biodegraded.
It is possible to make an emulsion between bitumen
and water which has low viscosity and which can flow
in pipelines and be burned directly to produce electric
power. The heavy oil and bitumen is rather rich in
sulphur which should be removed to avoid pollution. It
can also be mixed with gas so that it can be used to
produce normal oil products.
There are other important tar sand deposits in the
USA (Utah) and Africa (Congo and Madagascar).
Tar sand has only recently been included in data on
world oil reserves and as a result Canada has become
one of the nations with the highest oil reserves.
23.2 Oil Shales
Oil shales are source rocks, usually mudstones and
shales, with a high organic content (TOC), which
have not been buried deeply enough to become sufficiently mature for most of the hydrocarbons to be
generated. Although they may contain some
hydrocarbons they must be heated in an oven (pyrolysis) to 400–500
C so that most of the petroleum can be
generated from the remaining kerogen.
Oil shales must therefore be mined near the surface
in quarries and then heated in large ovens so that the
petroleum can be distilled off.
Source rocks may be uplifted close to the surface
after deeper burial; it is the temperature history that
determines how much of the kerogen is altered to oil
and gas.
Some source rocks may have been buried to more
than 5–6 km (160–170
C) and they have then
generated and expelled most of the hydrocarbons, but
some oil and particularly gas may remain. The Upper
Cambrian alum shale which is found in the Oslo
region is a good example of a rich source rock which
has been buried to at least 200
C (5–7 km) and lost
most of its hydrocarbons during the Caledonian folding in the late Silurian and early Devonian. In Sweden
the Upper Cambrian alum shales have not been buried
so deeply and therefore contain more oil which can be
distilled off by pyrolysis at 400–500
C.
In the Baltic region the lowermost Ordovician shales
are even less mature so that more of the kerogen remains
and in Estonia this shale is mined for oil on a large
scale. Here the reserves are very large (0.6 Â10
9 sm
3
oil equivalents – o.e).
Oil shales are used in electric power generation and
provide 60% of Estonia’s stationary energy. It is also
used for oil production and refining. The waste is
70–80 Mt. of semi-coke and the mounds exceed
100 m in height. The waste is very fine grained and
is alkaline with significant concentrations of sulphides
and heavy metals.
On a global basis oil shales represent a reserve
almost as large as conventional oil. Reserves of oil
which can be produced from oil shale are difficult to
estimate but they may total close to 5 trillion barrels
(800 Â10
9 sm
3 ). This is about equivalent to the
estimated world reserves of conventional oil and gas
(480 sm
3 o.e.). More than 80% of the well known
reserves are located in the US but there are probably
other regions with oil shales which have not been
recorded and evaluated.
The Green River Shale in Colorado, Utah and
Wyoming is a gigantic source of hydrocarbons. This
organic-rich mudstone was deposited in very large
lakes during the Eocene and the organic matter was
mostly freshwater algae (Fig. 23.5a, b).
In Australia there are also very large reserves of oil
shale and they have been used for oil production
already in the latter part of the 19th Century when
more than 100,000 tonnes of shale were processed.
In areas including Queensland and South Australia
there are Cenozoic shales or mudstones deposited in
freshwater associated with coal deposits but there are
also older (Permian) oil shales. Strict environmental
restrictions on oil shale mining have been imposed
here, particularly because of the association with The
Great Barrier Reef.
Also in other parts of the world oil shales may
represent large potential oil reserves but they may
not be produced with the present technology.
Oil shales must however be mined and heated in
ovens (pyrolysis) to generate the petroleum and the
energy for the heating is taken from the burning of the
23 Unconventional Hydrocarbons: Oil Shales, Heavy Oil. . .
585