86 PETROLEUM TECHNOLOGY, ECONOMICS, AND POLITICS
production wells horizontally from the drifts. 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.
3.4 Bitumen Recovery
In the case of tar sand bitumen, 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.
The API gravity of tar sand bitumen is usually less than 10°
depending upon the deposit, and whereas conventional crude
oils may have a viscosity of several poise (at 40°C, 105°F), the tar
sand bitumen has a viscosity of the order of 50,000 centipoises to
1,000,000 centipoises or more at formation temperatures (approximately 0°C to 10°C, 32°F to 50°F depending upon the season). This
offers a formidable but not insurmountable obstacle to bitumen
recovery.
3.4.1 Mining Methods
The mining method of recovery has received considerable attention since it was chosen as the technique of preference for the only
two commercial bitumen recovery plants in operation in North
America. In situ processes have been tested many times in the
United States, Canada, and other parts of the world and are ready
for commercialization. There are also conceptual schemes that are
a combination of both mining (above-ground recovery) and in situ
(non-mining recovery) methods.
production wells horizontally from the drifts. 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.
3.4 Bitumen Recovery
In the case of tar sand bitumen, 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.
The API gravity of tar sand bitumen is usually less than 10°
depending upon the deposit, and whereas conventional crude
oils may have a viscosity of several poise (at 40°C, 105°F), the tar
sand bitumen has a viscosity of the order of 50,000 centipoises to
1,000,000 centipoises or more at formation temperatures (approximately 0°C to 10°C, 32°F to 50°F depending upon the season). This
offers a formidable but not insurmountable obstacle to bitumen
recovery.
3.4.1 Mining Methods
The mining method of recovery has received considerable attention since it was chosen as the technique of preference for the only
two commercial bitumen recovery plants in operation in North
America. In situ processes have been tested many times in the
United States, Canada, and other parts of the world and are ready
for commercialization. There are also conceptual schemes that are
a combination of both mining (above-ground recovery) and in situ
(non-mining recovery) methods.