162
The Chemistry and Technology of Petroleum
When there is some natural reservoir energy, steam stimulation normally precedes steam drive.
In steam stimulation, heat is applied to the reservoir by the injection of high-quality steam into the
produce well. This cyclic process, also called huff and puff or steam soak, uses the same well for
both injection and production. The period of steam injection is followed by production of reduced
viscosity oil and condensed steam (water). One mechanism that aids production of the oil is the
flashing of hot water (originally condensed from steam injected under high pressure) back to steam
as pressure is lowered when a well is put back on production.
Cyclic steam injection is the alternating injection of steam and production of oil with condensed
steam from the same well or wells. This process is predominantly a vertical well process, with each
well alternately injecting steam and producing heavy oil and steam condensate. In practice, steam
is injected into the formation at greater than fracturing pressure followed by a soak period after
which production is commenced. The heat injected warms the heavy oil and lowers its viscosity.
A heated zone is created through which the warmed heavy oil can flow back into the well. This is
a well-developed process; the major limitation is that less than 30% (usually less than 20%) of the
initial oil in place can be recovered.
Steam drive involves the injection of steam through an injection well into a reservoir and the
production of the mobilized bitumen and steam condensate from a production well. Steam drive is
usually a logical follow-up to cyclic steam injection. Steam drive requires sufficient effective permeability (with the immobile bitumen in place) to allow injection of the steam at rates sufficient to raise
the reservoir temperature to mobilize the bitumen.
Two expected problems inherent in the steam drive process are steam override and reservoir
plugging. Any in situ thermal process tends to override (migrate to the top of the effected interval)
because of differential density of the hot and cold fluids. These problems can be partially mitigated
by rapid injection of steam at the bottom or below the target interval through a high-permeability
water zone or fracture. Each of these options will raise the temperature of the entire reservoir by
conduction and to a lesser degree, by convection. The bitumen will be at least partially mobilized
and the effectiveness of the following injection of steam into the target interval will be enhanced.
For a successful steam drive project, the porosity of the reservoir rock should be at least 20%;
the permeability should be at least 100 mD; and the bitumen saturation should be at least 40%. The
reservoir oil content should be at least 800 bbl per acre-foot. The depth of the reservoir should be
less than 3000 ft and the thickness should be at least 30 ft; other preferential parameters have also
been noted on the basis of success with several heavy oil reservoirs.
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 since a novel concept may arise, which guarantees minimal (acceptable) losses of bitumen
and solvent.
7.3.2 ComBustIon ProCesses
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 EOR 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.
During in situ combustion or fire flooding, energy is generated in the formation by igniting bitumen in the formation and sustaining it in a state of combustion or partial combustion.
The high temperatures generated decrease the viscosity of the oil and make it more mobile.
The Chemistry and Technology of Petroleum
When there is some natural reservoir energy, steam stimulation normally precedes steam drive.
In steam stimulation, heat is applied to the reservoir by the injection of high-quality steam into the
produce well. This cyclic process, also called huff and puff or steam soak, uses the same well for
both injection and production. The period of steam injection is followed by production of reduced
viscosity oil and condensed steam (water). One mechanism that aids production of the oil is the
flashing of hot water (originally condensed from steam injected under high pressure) back to steam
as pressure is lowered when a well is put back on production.
Cyclic steam injection is the alternating injection of steam and production of oil with condensed
steam from the same well or wells. This process is predominantly a vertical well process, with each
well alternately injecting steam and producing heavy oil and steam condensate. In practice, steam
is injected into the formation at greater than fracturing pressure followed by a soak period after
which production is commenced. The heat injected warms the heavy oil and lowers its viscosity.
A heated zone is created through which the warmed heavy oil can flow back into the well. This is
a well-developed process; the major limitation is that less than 30% (usually less than 20%) of the
initial oil in place can be recovered.
Steam drive involves the injection of steam through an injection well into a reservoir and the
production of the mobilized bitumen and steam condensate from a production well. Steam drive is
usually a logical follow-up to cyclic steam injection. Steam drive requires sufficient effective permeability (with the immobile bitumen in place) to allow injection of the steam at rates sufficient to raise
the reservoir temperature to mobilize the bitumen.
Two expected problems inherent in the steam drive process are steam override and reservoir
plugging. Any in situ thermal process tends to override (migrate to the top of the effected interval)
because of differential density of the hot and cold fluids. These problems can be partially mitigated
by rapid injection of steam at the bottom or below the target interval through a high-permeability
water zone or fracture. Each of these options will raise the temperature of the entire reservoir by
conduction and to a lesser degree, by convection. The bitumen will be at least partially mobilized
and the effectiveness of the following injection of steam into the target interval will be enhanced.
For a successful steam drive project, the porosity of the reservoir rock should be at least 20%;
the permeability should be at least 100 mD; and the bitumen saturation should be at least 40%. The
reservoir oil content should be at least 800 bbl per acre-foot. The depth of the reservoir should be
less than 3000 ft and the thickness should be at least 30 ft; other preferential parameters have also
been noted on the basis of success with several heavy oil reservoirs.
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 since a novel concept may arise, which guarantees minimal (acceptable) losses of bitumen
and solvent.
7.3.2 ComBustIon ProCesses
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 EOR 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.
During in situ combustion or fire flooding, energy is generated in the formation by igniting bitumen in the formation and sustaining it in a state of combustion or partial combustion.
The high temperatures generated decrease the viscosity of the oil and make it more mobile.