161
Recovery of Heavy Oil and Tar Sand Bitumen
finds at a pressure such that fracturing (parting) is achieved. Such a technique therefore changes the
reservoir profile and introduces a series of channels through which fluids can flow from the injection well to the production well. On the other hand, the technique may be disadvantageous insofar
as the fracture occurs along the path of least resistance, giving undesirable (i.e., inefficient) flow
characteristics within the reservoir between the injection and production wells, leaving a large part
of the reservoir relatively untouched by the displacement or recovery fluids.
In principle, the nonmining recovery of bitumen from tar sand deposits is an EOR technique and
requires the injection of a fluid into the formation through an injection well. This leads to the in situ
displacement of the bitumen from the reservoir and bitumen production at the surface through
an egress (production) well. There are, however, several serious constraints that are particularly
important and relate to the bulk properties of the tar sand and the bitumen. In fact, both must be
considered in toto in the context of bitumen recovery by nonmining techniques.
Another general constraint to bitumen recovery by nonmining methods is the relatively low
injectivity of tar sand formations. It is usually necessary to inject displacement/recovery fluids at
a pressure such that fracturing (parting) is achieved. Such a technique, therefore, changes the reservoir profile and introduces a series of channels through which fluids can flow from the injection
well to the production well. On the other hand, the technique may be disadvantageous insofar as
the fracture occurs along the path of least resistance giving undesirable (i.e., inefficient) flow characteristics within the reservoir between the injection and production wells which leave a part of the
reservoir relatively untouched by the displacement or recovery fluids.
In steam stimulation, heat and drive energy are supplied in the form of steam injected through
wells into the tar sand formation. In most instances, the injection pressure must exceed the formation fracture pressure in order to force the steam into the tar sands and into contact with the oil.
When sufficient heating has been achieved, the injection wells are closed for a soak period of variable length and then allowed to produce, first applying the pressure created by the injection and then
using pumps as the wells cool and production declines.
Steam can also be injected into one or more wells with production coming from other wells
(steam drive). This technique is very effective in heavy oil formations but has found little success
during application to tar sand deposits because of the difficulty in connecting injection and production wells. However, once the flow path has been heated, the steam pressure is cycled, alternately
moving steam up into the oil zone, then allowing oil to drain down into the heated flow channel to
be swept to the production wells.
If the viscous bitumen in a tar sand formation can be made mobile by admixture of either a
hydrocarbon diluent or an emulsifying fluid, a relatively low-temperature secondary recovery process is possible (emulsion steam drive). If the formation is impermeable, communication problems
exist between injection and production wells. However, it is possible to apply a solution or dilution
process along a narrow fracture plane between injection and production wells.
7.3.1 steAm-BAsed ProCesses
The steam processes are the most advanced of all EOR methods in terms of field experience and
thus have the least uncertainty in estimating performance, provided that a good reservoir description is available. Steam processes are most often applied in reservoirs containing viscous oils and
tars, usually in place of rather than following secondary or primary methods. Commercial application of steam processes has been underway 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.
Steam drive injection (steam injection) has been commercially applied since the early 1960s. The
process occurs in two steps: (1) steam stimulation of production wells (i.e., direct steam stimulation),
and (2) steam drive by steam injection to increase production from other wells (i.e., indirect steam
stimulation).
Recovery of Heavy Oil and Tar Sand Bitumen
finds at a pressure such that fracturing (parting) is achieved. Such a technique therefore changes the
reservoir profile and introduces a series of channels through which fluids can flow from the injection well to the production well. On the other hand, the technique may be disadvantageous insofar
as the fracture occurs along the path of least resistance, giving undesirable (i.e., inefficient) flow
characteristics within the reservoir between the injection and production wells, leaving a large part
of the reservoir relatively untouched by the displacement or recovery fluids.
In principle, the nonmining recovery of bitumen from tar sand deposits is an EOR technique and
requires the injection of a fluid into the formation through an injection well. This leads to the in situ
displacement of the bitumen from the reservoir and bitumen production at the surface through
an egress (production) well. There are, however, several serious constraints that are particularly
important and relate to the bulk properties of the tar sand and the bitumen. In fact, both must be
considered in toto in the context of bitumen recovery by nonmining techniques.
Another general constraint to bitumen recovery by nonmining methods is the relatively low
injectivity of tar sand formations. It is usually necessary to inject displacement/recovery fluids at
a pressure such that fracturing (parting) is achieved. Such a technique, therefore, changes the reservoir profile and introduces a series of channels through which fluids can flow from the injection
well to the production well. On the other hand, the technique may be disadvantageous insofar as
the fracture occurs along the path of least resistance giving undesirable (i.e., inefficient) flow characteristics within the reservoir between the injection and production wells which leave a part of the
reservoir relatively untouched by the displacement or recovery fluids.
In steam stimulation, heat and drive energy are supplied in the form of steam injected through
wells into the tar sand formation. In most instances, the injection pressure must exceed the formation fracture pressure in order to force the steam into the tar sands and into contact with the oil.
When sufficient heating has been achieved, the injection wells are closed for a soak period of variable length and then allowed to produce, first applying the pressure created by the injection and then
using pumps as the wells cool and production declines.
Steam can also be injected into one or more wells with production coming from other wells
(steam drive). This technique is very effective in heavy oil formations but has found little success
during application to tar sand deposits because of the difficulty in connecting injection and production wells. However, once the flow path has been heated, the steam pressure is cycled, alternately
moving steam up into the oil zone, then allowing oil to drain down into the heated flow channel to
be swept to the production wells.
If the viscous bitumen in a tar sand formation can be made mobile by admixture of either a
hydrocarbon diluent or an emulsifying fluid, a relatively low-temperature secondary recovery process is possible (emulsion steam drive). If the formation is impermeable, communication problems
exist between injection and production wells. However, it is possible to apply a solution or dilution
process along a narrow fracture plane between injection and production wells.
7.3.1 steAm-BAsed ProCesses
The steam processes are the most advanced of all EOR methods in terms of field experience and
thus have the least uncertainty in estimating performance, provided that a good reservoir description is available. Steam processes are most often applied in reservoirs containing viscous oils and
tars, usually in place of rather than following secondary or primary methods. Commercial application of steam processes has been underway 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.
Steam drive injection (steam injection) has been commercially applied since the early 1960s. The
process occurs in two steps: (1) steam stimulation of production wells (i.e., direct steam stimulation),
and (2) steam drive by steam injection to increase production from other wells (i.e., indirect steam
stimulation).