153
Recovery of Heavy Oil and Tar Sand Bitumen
sand handling, and (4) bringing a partially upgraded product to the surface. The extent of the
upgrading can, hopefully, be adjusted by adjusting the exposure of the bitumen of heavy oil to the
underground thermal effects.
In the modified in situ extraction processes, combinations of in situ and mining techniques are
used to access the reservoir. A portion of the reservoir rock must be removed to enable application
of the in situ extraction technology. The most common method is to enter the reservoir through a
large-diameter vertical shaft, excavate horizontal drifts from the bottom of the shaft, and drill injection and production wells horizontally from the drifts (Meszaros et al., 1990). Thermal extraction
processes are then applied through the wells. When the horizontal wells are drilled at or near the
base of the tar sand reservoir, the injected heat rises from the injection wells through the reservoir,
and drainage of produced fluids to the production wells is assisted by gravity.
Generally, as opposed to heavy oil recovery, bitumen recovery requires a higher degree of thermal stimulation because bitumen, in its immobile state, is extremely difficult to move to a production well. Extreme processes are required, usually in the form of a degree of thermal conversion that
produces free-flowing product oil that will flow to the well and reduce the resistance of the bitumen
to flow.
Bitumen recovery processes can be conveniently divided into two categories: (1) mining methods
also called oil mining and (2) nonmining methods.
In the former type of process, the tar sand must first be removed from the formation by a mining
technique and then transported to a bitumen recovery center. In the latter type of process, usually
(but not always correctly) termed in situ, bitumen (or a portion of the bitumen in-place) is recovered
from the formation by a suitable thermal method, leaving the formation somewhat less disturbed
than when the mining method is employed.
7.2 MINING
The alternative to in situ processing is to mine the tar sands, transport them to a processing plant,
extract the bitumen value, and dispose of the waste sand. Such a procedure is often referred to as
oil mining. This is the term applied to the surface or subsurface excavation of petroleum-bearing
formations for subsequent removal of the heavy oil or bitumen by washing, flotation, or retorting
treatments. Oil mining also includes recovery of heavy oil by drainage from reservoir beds to mine
shafts or other openings driven into the rock, or by drainage from the reservoir rock into mine openings driven outside the tar sand but connected with it by bore holes or mine wells.
Oil mining is not new. Mining of petroleum and bitumen has occurred in the Sinai Peninsula,
the Euphrates valley, and in Persia prior to 5000 BC. In addition, subsurface oil mining was used in
the Pechelbronn oil field in Alsace, France, as early as 1735. This early mining involved the sinking
of shafts to the reservoir rock, only 100–200 ft (30–60 m) below the surface and the excavation of
the tar sand in short drifts driven from the shafts. These tar sands were hoisted to the surface and
washed with boiling water to release the bitumen. The drifts were extended as far as natural ventilation permitted. When these limits were reached, the pillars were removed and the openings filled
with waste. This type of mining continued at Pechelbronn until 1866, when it was found that oil
could be recovered from deeper, and more prolific, sands by letting it drain in place through mine
openings with no removal of sand to the surface for treatment. Nevertheless, mining for petroleum
is a new challenge facing the petroleum industry.
Oil mining methods should be applied in reservoirs that have significant residual oil saturation
and have reservoir or fluid properties that make production by conventional methods inefficient or
impossible. The high well density in improved oil mining usually compensates for the inefficient
production caused by reservoir heterogeneity. However, close well spacing can also magnify the deleterious effects of reservoir heterogeneity. If a high-permeability streak exists with a lateral extent
that is less than the inter-well spacing of conventional wells but is comparable to that of improved
oil mining, the channeling is more unfavorable for the improved oil mining method.
Recovery of Heavy Oil and Tar Sand Bitumen
sand handling, and (4) bringing a partially upgraded product to the surface. The extent of the
upgrading can, hopefully, be adjusted by adjusting the exposure of the bitumen of heavy oil to the
underground thermal effects.
In the modified in situ extraction processes, combinations of in situ and mining techniques are
used to access the reservoir. A portion of the reservoir rock must be removed to enable application
of the in situ extraction technology. The most common method is to enter the reservoir through a
large-diameter vertical shaft, excavate horizontal drifts from the bottom of the shaft, and drill injection and production wells horizontally from the drifts (Meszaros et al., 1990). Thermal extraction
processes are then applied through the wells. When the horizontal wells are drilled at or near the
base of the tar sand reservoir, the injected heat rises from the injection wells through the reservoir,
and drainage of produced fluids to the production wells is assisted by gravity.
Generally, as opposed to heavy oil recovery, bitumen recovery requires a higher degree of thermal stimulation because bitumen, in its immobile state, is extremely difficult to move to a production well. Extreme processes are required, usually in the form of a degree of thermal conversion that
produces free-flowing product oil that will flow to the well and reduce the resistance of the bitumen
to flow.
Bitumen recovery processes can be conveniently divided into two categories: (1) mining methods
also called oil mining and (2) nonmining methods.
In the former type of process, the tar sand must first be removed from the formation by a mining
technique and then transported to a bitumen recovery center. In the latter type of process, usually
(but not always correctly) termed in situ, bitumen (or a portion of the bitumen in-place) is recovered
from the formation by a suitable thermal method, leaving the formation somewhat less disturbed
than when the mining method is employed.
7.2 MINING
The alternative to in situ processing is to mine the tar sands, transport them to a processing plant,
extract the bitumen value, and dispose of the waste sand. Such a procedure is often referred to as
oil mining. This is the term applied to the surface or subsurface excavation of petroleum-bearing
formations for subsequent removal of the heavy oil or bitumen by washing, flotation, or retorting
treatments. Oil mining also includes recovery of heavy oil by drainage from reservoir beds to mine
shafts or other openings driven into the rock, or by drainage from the reservoir rock into mine openings driven outside the tar sand but connected with it by bore holes or mine wells.
Oil mining is not new. Mining of petroleum and bitumen has occurred in the Sinai Peninsula,
the Euphrates valley, and in Persia prior to 5000 BC. In addition, subsurface oil mining was used in
the Pechelbronn oil field in Alsace, France, as early as 1735. This early mining involved the sinking
of shafts to the reservoir rock, only 100–200 ft (30–60 m) below the surface and the excavation of
the tar sand in short drifts driven from the shafts. These tar sands were hoisted to the surface and
washed with boiling water to release the bitumen. The drifts were extended as far as natural ventilation permitted. When these limits were reached, the pillars were removed and the openings filled
with waste. This type of mining continued at Pechelbronn until 1866, when it was found that oil
could be recovered from deeper, and more prolific, sands by letting it drain in place through mine
openings with no removal of sand to the surface for treatment. Nevertheless, mining for petroleum
is a new challenge facing the petroleum industry.
Oil mining methods should be applied in reservoirs that have significant residual oil saturation
and have reservoir or fluid properties that make production by conventional methods inefficient or
impossible. The high well density in improved oil mining usually compensates for the inefficient
production caused by reservoir heterogeneity. However, close well spacing can also magnify the deleterious effects of reservoir heterogeneity. If a high-permeability streak exists with a lateral extent
that is less than the inter-well spacing of conventional wells but is comparable to that of improved
oil mining, the channeling is more unfavorable for the improved oil mining method.