Chapter 23
Unconventional Hydrocarbons: Oil Shales, Heavy Oil,
Tar Sands, Shale Oil, Shale Gas and Gas Hydrates
Knut Bjørlykke
For many decades conventional oil which could be
produced at low cost was present in abundance. A
low oil price gave no incentive to look for other
types of resources. It is now clear, however, that we
are gradually running out of new sedimentary basins to
explore and that the reserves of conventional oil which
can be produced cheaply are limited.
This is the reason why many of the major oil
companies now invest in what is often called unconventional hydrocarbons. There are large reserves of these
and the main types are oil shales, heavy oil, tar sand,
shale oil and shale gas. Production of hydrocarbons
from these sources occurs mainly in onshore basins
and may be challenging environmentally.
Gas hydrates may also become an important source
of hydrocarbons but the development of methods to
produce from such accumulations is still at an early
stage.
The reserves of unconventional hydrocarbons are
very large, probably larger than those of conventional
oil. We will therefore not run out of fossil hydrocarbons
for a long time but the prices will be higher because
these sources are more difficult to produce, particularly
if strict environmental standards should be met.
23.1 Heavy Oil and Tar Sands
Heavy oil seeping out on the surface has been known
for a long time and this was easy to exploit for use in
small quantities. Even after drilling for oil became
successful (in 1857 in Pennsylvania), mining for
heavy oil continued in many parts of the world including Germany. In southern California (Ventura and Los
Angeles basins) oil was mined from the early 1860s to
the 1890s because the heavy oil there would not flow
to the wells (Fig. 23.1).
Tar sands are sandstone reservoirs which have been
filled with oil at shallow depth <2 km (<70–80
C) so
that the oil has become biodegraded. Reservoir rocks
which have been buried more deeply and then uplifted
before the oil migration may be sterilised at higher
temperatures and are less likely to be biodegraded.
When the sandstone has not been buried to more
than about 2 km depth the sand will remain mostly
uncemented as loose sand because of a lack of quartz
cement.
Tar sand contains asphaltic oil rich in asphaltenes
and resins. It has a high content of aromatics and
naphthenes compared to paraffins, and a high content
of nitrogen, sulphur and oxygen (NSO). Most of the
hydrocarbon molecules have more that 60 carbon
atoms and the boiling point and viscosity are therefore
very high.
The viscosity of the biodegraded oil is very low and
the oil must be heated so that the viscosity is reduced
before it can be produced by drilling wells. There are
transitions between reservoirs with heavy oil and nearly
solid bitumen. Heating can be achieved by soaking the
reservoir with injected steam so that the heat of condensation to water helps to heat the oil. This is called cyclic
steam injection when the steam is injected in the production well and left to soak for a few weeks before
production starts when the oil is warmer. The steam
may also be injected in a nearby well and driven
towards the production well. Much of the energy is
K. Bjørlykke (*)
Department of Geosciences, University of Oslo, Oslo, Norway
e-mail: knut.bjorlykke@geo.uio.no
K. Bjørlykke (ed.), Petroleum Geoscience: From Sedimentary Environments to Rock Physics,
DOI 10.1007/978-3-642-34132-8_23, # Springer-Verlag Berlin Heidelberg 2015
581
Unconventional Hydrocarbons: Oil Shales, Heavy Oil,
Tar Sands, Shale Oil, Shale Gas and Gas Hydrates
Knut Bjørlykke
For many decades conventional oil which could be
produced at low cost was present in abundance. A
low oil price gave no incentive to look for other
types of resources. It is now clear, however, that we
are gradually running out of new sedimentary basins to
explore and that the reserves of conventional oil which
can be produced cheaply are limited.
This is the reason why many of the major oil
companies now invest in what is often called unconventional hydrocarbons. There are large reserves of these
and the main types are oil shales, heavy oil, tar sand,
shale oil and shale gas. Production of hydrocarbons
from these sources occurs mainly in onshore basins
and may be challenging environmentally.
Gas hydrates may also become an important source
of hydrocarbons but the development of methods to
produce from such accumulations is still at an early
stage.
The reserves of unconventional hydrocarbons are
very large, probably larger than those of conventional
oil. We will therefore not run out of fossil hydrocarbons
for a long time but the prices will be higher because
these sources are more difficult to produce, particularly
if strict environmental standards should be met.
23.1 Heavy Oil and Tar Sands
Heavy oil seeping out on the surface has been known
for a long time and this was easy to exploit for use in
small quantities. Even after drilling for oil became
successful (in 1857 in Pennsylvania), mining for
heavy oil continued in many parts of the world including Germany. In southern California (Ventura and Los
Angeles basins) oil was mined from the early 1860s to
the 1890s because the heavy oil there would not flow
to the wells (Fig. 23.1).
Tar sands are sandstone reservoirs which have been
filled with oil at shallow depth <2 km (<70–80
C) so
that the oil has become biodegraded. Reservoir rocks
which have been buried more deeply and then uplifted
before the oil migration may be sterilised at higher
temperatures and are less likely to be biodegraded.
When the sandstone has not been buried to more
than about 2 km depth the sand will remain mostly
uncemented as loose sand because of a lack of quartz
cement.
Tar sand contains asphaltic oil rich in asphaltenes
and resins. It has a high content of aromatics and
naphthenes compared to paraffins, and a high content
of nitrogen, sulphur and oxygen (NSO). Most of the
hydrocarbon molecules have more that 60 carbon
atoms and the boiling point and viscosity are therefore
very high.
The viscosity of the biodegraded oil is very low and
the oil must be heated so that the viscosity is reduced
before it can be produced by drilling wells. There are
transitions between reservoirs with heavy oil and nearly
solid bitumen. Heating can be achieved by soaking the
reservoir with injected steam so that the heat of condensation to water helps to heat the oil. This is called cyclic
steam injection when the steam is injected in the production well and left to soak for a few weeks before
production starts when the oil is warmer. The steam
may also be injected in a nearby well and driven
towards the production well. Much of the energy is
K. Bjørlykke (*)
Department of Geosciences, University of Oslo, Oslo, Norway
e-mail: knut.bjorlykke@geo.uio.no
K. Bjørlykke (ed.), Petroleum Geoscience: From Sedimentary Environments to Rock Physics,
DOI 10.1007/978-3-642-34132-8_23, # Springer-Verlag Berlin Heidelberg 2015
581