256 PETROLEUM TECHNOLOGY, ECONOMICS, AND POLITICS
with depth, with the richer portions appearing much darker. For
example, in Colorado, the richest layers are termed the Mahogany
Zone after the rich brown color.
Oil shale does not contain oil and only produces oil when it is
heated to about 500°C (about 932°F), when some of the organic
material is transformed into a distillate. The potential for liquids
production potential from oil shale is measured by a laboratory
pyrolysis method called Fischer Assay (Scouten, 1990; Speight,
1994) and is reported in barrels (42 gal) per ton. Rich zones can yield
more than 40 gallons per ton, while most shale falls in the range of
10 to 25 gallons per ton. Oil shale yields more than 25 United States
gal/ton are generally viewed as the most economically attractive,
and hence, the most favorable for initial development. Shale oil can
be refined into synthetic crude oil and the known resources of the
United States could translate into as much as 2.2 trillion (2.2 x 10
12
)
barrels of synthetic crude oil.
Surface processes for the production of liquids involve mining
the shale followed by heating at the surface in a reactor, referred to
as retorting, produces shale oil, which is often referred to referred to
as synthetic crude oil both before and after hydrotreating. However,
with the exception of in situ processes, oil shale must be mined
before it can be converted to shale oil. Depending on the depth and
other characteristics of the target oil shale deposits, either surface
mining or underground mining methods may be used.
In-situ processes avoid the need to mine the shale but introduce
heat to the kerogen while it is still embedded in its natural geological formation and the product is recovered as distillate through a
well. There are two general in-situ approaches; true in-situ in which
there is minimal or no disturbance of the ore bed, and modified insitu, in which the bed is given a rubble-like texture, either through
direct blasting with surface up-lift or after partial mining to create void space. In situ processes tend to operate slowly and may
require one or more years to produce shale oil.
Modified in-situ processes involve mining beneath the target oil
shale deposit prior to heating. Such processes attempt to improve
performance by exposing more of the deposit to the heat source and
by improving the flow of gases and liquids through the rock formation, and increasing the volumes and quality of the oil produced.
Shale retorting processes produce oil with almost no highboiling residuum. With upgrading, shale oil is a light boiling premium product more valuable than most crude oils. However, the
with depth, with the richer portions appearing much darker. For
example, in Colorado, the richest layers are termed the Mahogany
Zone after the rich brown color.
Oil shale does not contain oil and only produces oil when it is
heated to about 500°C (about 932°F), when some of the organic
material is transformed into a distillate. The potential for liquids
production potential from oil shale is measured by a laboratory
pyrolysis method called Fischer Assay (Scouten, 1990; Speight,
1994) and is reported in barrels (42 gal) per ton. Rich zones can yield
more than 40 gallons per ton, while most shale falls in the range of
10 to 25 gallons per ton. Oil shale yields more than 25 United States
gal/ton are generally viewed as the most economically attractive,
and hence, the most favorable for initial development. Shale oil can
be refined into synthetic crude oil and the known resources of the
United States could translate into as much as 2.2 trillion (2.2 x 10
12
)
barrels of synthetic crude oil.
Surface processes for the production of liquids involve mining
the shale followed by heating at the surface in a reactor, referred to
as retorting, produces shale oil, which is often referred to referred to
as synthetic crude oil both before and after hydrotreating. However,
with the exception of in situ processes, oil shale must be mined
before it can be converted to shale oil. Depending on the depth and
other characteristics of the target oil shale deposits, either surface
mining or underground mining methods may be used.
In-situ processes avoid the need to mine the shale but introduce
heat to the kerogen while it is still embedded in its natural geological formation and the product is recovered as distillate through a
well. There are two general in-situ approaches; true in-situ in which
there is minimal or no disturbance of the ore bed, and modified insitu, in which the bed is given a rubble-like texture, either through
direct blasting with surface up-lift or after partial mining to create void space. In situ processes tend to operate slowly and may
require one or more years to produce shale oil.
Modified in-situ processes involve mining beneath the target oil
shale deposit prior to heating. Such processes attempt to improve
performance by exposing more of the deposit to the heat source and
by improving the flow of gases and liquids through the rock formation, and increasing the volumes and quality of the oil produced.
Shale retorting processes produce oil with almost no highboiling residuum. With upgrading, shale oil is a light boiling premium product more valuable than most crude oils. However, the