EXPLORATION, RECOVERY, AND TRANSPORTATION 85
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.
Cyclic steam injection (steam soak, huff 'n' puff) is the alternating injection of steam and production of oil with condensed
steam from the same well or wells. A cyclic steam injection process
includes three stages. In the first stage is injection, during which
a measured amount of steam is introduced into the reservoir. In
the second stage (the soak period) requires that the well be shut in
for a period of time of usually several days to allow uniform heat
distribution to reduce the viscosity of the oil, alternatively, to raise
the reservoir temperature above the pour point of the oil. Finally,
during the third stage, the now-mobile oil is produced through the
same well. The cycle is repeated until the flow of oil diminishes to
a point of no returns.
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.
The relatively small portion of the oil that remains after these
displacement mechanisms have acted becomes the fuel for the in
situ combustion process. Production is obtained from wells offsetting the injection locations. In some applications, the efficiency
of the total in situ combustion operation can be improved by
alternating water and air injection. The injected water tends to
improve the utilization of heat by transferring heat from the rock
behind the combustion zone to the rock immediately ahead of the
combustion zone.
In 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
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.
Cyclic steam injection (steam soak, huff 'n' puff) is the alternating injection of steam and production of oil with condensed
steam from the same well or wells. A cyclic steam injection process
includes three stages. In the first stage is injection, during which
a measured amount of steam is introduced into the reservoir. In
the second stage (the soak period) requires that the well be shut in
for a period of time of usually several days to allow uniform heat
distribution to reduce the viscosity of the oil, alternatively, to raise
the reservoir temperature above the pour point of the oil. Finally,
during the third stage, the now-mobile oil is produced through the
same well. The cycle is repeated until the flow of oil diminishes to
a point of no returns.
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.
The relatively small portion of the oil that remains after these
displacement mechanisms have acted becomes the fuel for the in
situ combustion process. Production is obtained from wells offsetting the injection locations. In some applications, the efficiency
of the total in situ combustion operation can be improved by
alternating water and air injection. The injected water tends to
improve the utilization of heat by transferring heat from the rock
behind the combustion zone to the rock immediately ahead of the
combustion zone.
In 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