EXPLORATION, RECOVERY, AND TRANSPORTATION 89
since the early 1960s. In situ combustion has been field tested under
a wide variety of reservoir conditions, but few projects have proven
economical and advanced to commercial scale.
Other variations on this theme include the use of steam and the
means of reducing interfacial tension by the use of various solvents. The solvent extraction approach has had some success when
applied to bitumen recovery from mined tar sand but when applied
to unmined material, losses of solvent and bitumen are always a
major obstacle. This approach should not be rejected out of hand
because a novel concept may arise that guarantees minimal but
acceptable losses of bitumen and solvent.
In situ combustion is normally applied to reservoirs containing
low-gravity oil but has been tested over perhaps the widest spectrum of conditions of any enhanced oil recovery process. In the
process, heat is generated within the reservoir by injecting air and
burning part of the crude oil. This reduces the oil viscosity and partially vaporizes the oil in place, and the oil is driven out of the reservoir by a combination of steam, hot water, and gas drive. Forward
combustion involves movement of the hot front in the same direction as the injected air; reverse combustion involves movement of
the hot front opposite to the direction of the injected air.
Finally, by all definitions, the quality of the bitumen from tar
sand deposits is poor as a refinery feedstock. As in any field in
which primary recovery operations are followed by secondary
or enhanced recovery operations and there is a change in product quality, such is also the case for tar sand recovery operations.
Thus, product oils recovered by the thermal stimulation of tar sand
deposits show some improvement in properties over those of the
bitumen in-place.
Although this improvement in properties may not appear to
be too drastic, nevertheless it usually is sufficient to have major
advantages for refinery operators. Any incremental increase in the
units of hydrogen/carbon ratio can save amounts of costly hydrogen during upgrading. The same principles are also operative for
reductions in the nitrogen, sulfur, and oxygen contents.
Many innovative concepts in heavy oil production have been
developed and several major new technologies have positively
affected the heavy oil industry in the last 10 years.
Steam assisted gravity drainage (SAGD) was developed first
in Canada for reservoirs where the immobile bitumen occurs and
uses paired horizontal wells. Low-pressure steam continuously
since the early 1960s. In situ combustion has been field tested under
a wide variety of reservoir conditions, but few projects have proven
economical and advanced to commercial scale.
Other variations on this theme include the use of steam and the
means of reducing interfacial tension by the use of various solvents. The solvent extraction approach has had some success when
applied to bitumen recovery from mined tar sand but when applied
to unmined material, losses of solvent and bitumen are always a
major obstacle. This approach should not be rejected out of hand
because a novel concept may arise that guarantees minimal but
acceptable losses of bitumen and solvent.
In situ combustion is normally applied to reservoirs containing
low-gravity oil but has been tested over perhaps the widest spectrum of conditions of any enhanced oil recovery process. In the
process, heat is generated within the reservoir by injecting air and
burning part of the crude oil. This reduces the oil viscosity and partially vaporizes the oil in place, and the oil is driven out of the reservoir by a combination of steam, hot water, and gas drive. Forward
combustion involves movement of the hot front in the same direction as the injected air; reverse combustion involves movement of
the hot front opposite to the direction of the injected air.
Finally, by all definitions, the quality of the bitumen from tar
sand deposits is poor as a refinery feedstock. As in any field in
which primary recovery operations are followed by secondary
or enhanced recovery operations and there is a change in product quality, such is also the case for tar sand recovery operations.
Thus, product oils recovered by the thermal stimulation of tar sand
deposits show some improvement in properties over those of the
bitumen in-place.
Although this improvement in properties may not appear to
be too drastic, nevertheless it usually is sufficient to have major
advantages for refinery operators. Any incremental increase in the
units of hydrogen/carbon ratio can save amounts of costly hydrogen during upgrading. The same principles are also operative for
reductions in the nitrogen, sulfur, and oxygen contents.
Many innovative concepts in heavy oil production have been
developed and several major new technologies have positively
affected the heavy oil industry in the last 10 years.
Steam assisted gravity drainage (SAGD) was developed first
in Canada for reservoirs where the immobile bitumen occurs and
uses paired horizontal wells. Low-pressure steam continuously