Role of Water in Recovery and Production of Raw Fuels
25
and expands the volume of oil causing fluid movement. This action facilitates oil
recovery from the reservoir. The well begins its production level after the soaking
period until the flow of oil slows down. Once this occurs, the process is repeated.
After much of oil is recovered, cyclic steam flood is converted to steam injection.
In this process, steam is injected from one well and the oil is recovered from other
nearby wells [16,17].
Steam flood in some reservoirs results in a dramatic increase in oil production.
This method which accounts for about 20% of EOR processes, has gained more
popularity in recovery of unconventional oils such as heavy oils, tar sands, and shale
oil [16,17]. The technique works well because of the crude oil expansion due to
increased temperature, which continues as pressure drops. Steam flood wells are
drilled on an ~5-acre spacing and require a reservoir depth of ~10 ft or more. The
method is most effective in wells no deeper than 5000 ft.
2.3.2.2 hot Water injection
Besides steam injection, hot water injection is often pursued. This method is, however, not as effective because of heat loss and resulting fingering phenomenon and
loss of sweep efficiency [16,17].
2.3.2.3 In Situ Combustion
In situ combustion can be dry (only using air) or wet or partially wet. In this process, fire
is ignited by injecting compressed air into the injection wells and driven across the reservoir. The heat from fire reduces oil viscosity leading to drop in pressure and expansion
of oil. The vapor can also be collected from the well and condensed at the well mouth.
The process is not very efficient because a large amount of heat is not utilized.
The in situ combustion can be forward combustion or reverse combustion. In
the forward combustion process, fire is ignited in the formation near the injection
well, and with continuing air injection, the fire and produced oil are driven toward
nearby producing wells. In the reverse combustion process, the fire is started near
the compressed air injection well and allowed it to progress toward nearby wells.
The process is then reversed; the air is injected from nearby wells and the original
air injection well is used to collect the oil that is produced. The reverse combustion
is often considered to be more efficient than the forward combustion. The combustion process is more effective for heavy crude oil. In wet and partially wet injection
processes, steam accompanies air [16,17].
As the existing oil well ages and new oil wells are discovered in more difficult
locations, the use of EOR techniques to recover oils will significantly increase in
future. This will require an additional usage of water or steam.
2.4 rOle OF Water in the FraCKinG PrOCess
The natural gas can occur in the oil fields (known as associated gas), in coal seams
(known as coal bed methane), in sandstone (tight and deep gas) or shale (shale gas),
or in the fields not associated with oil or coal (i.e., nonassociated gas). The gas is also
found in geopressurized zones. The most important game changer in recent years is
shale gas largely due to the novel but controversial process of fracking [18–36].
25
and expands the volume of oil causing fluid movement. This action facilitates oil
recovery from the reservoir. The well begins its production level after the soaking
period until the flow of oil slows down. Once this occurs, the process is repeated.
After much of oil is recovered, cyclic steam flood is converted to steam injection.
In this process, steam is injected from one well and the oil is recovered from other
nearby wells [16,17].
Steam flood in some reservoirs results in a dramatic increase in oil production.
This method which accounts for about 20% of EOR processes, has gained more
popularity in recovery of unconventional oils such as heavy oils, tar sands, and shale
oil [16,17]. The technique works well because of the crude oil expansion due to
increased temperature, which continues as pressure drops. Steam flood wells are
drilled on an ~5-acre spacing and require a reservoir depth of ~10 ft or more. The
method is most effective in wells no deeper than 5000 ft.
2.3.2.2 hot Water injection
Besides steam injection, hot water injection is often pursued. This method is, however, not as effective because of heat loss and resulting fingering phenomenon and
loss of sweep efficiency [16,17].
2.3.2.3 In Situ Combustion
In situ combustion can be dry (only using air) or wet or partially wet. In this process, fire
is ignited by injecting compressed air into the injection wells and driven across the reservoir. The heat from fire reduces oil viscosity leading to drop in pressure and expansion
of oil. The vapor can also be collected from the well and condensed at the well mouth.
The process is not very efficient because a large amount of heat is not utilized.
The in situ combustion can be forward combustion or reverse combustion. In
the forward combustion process, fire is ignited in the formation near the injection
well, and with continuing air injection, the fire and produced oil are driven toward
nearby producing wells. In the reverse combustion process, the fire is started near
the compressed air injection well and allowed it to progress toward nearby wells.
The process is then reversed; the air is injected from nearby wells and the original
air injection well is used to collect the oil that is produced. The reverse combustion
is often considered to be more efficient than the forward combustion. The combustion process is more effective for heavy crude oil. In wet and partially wet injection
processes, steam accompanies air [16,17].
As the existing oil well ages and new oil wells are discovered in more difficult
locations, the use of EOR techniques to recover oils will significantly increase in
future. This will require an additional usage of water or steam.
2.4 rOle OF Water in the FraCKinG PrOCess
The natural gas can occur in the oil fields (known as associated gas), in coal seams
(known as coal bed methane), in sandstone (tight and deep gas) or shale (shale gas),
or in the fields not associated with oil or coal (i.e., nonassociated gas). The gas is also
found in geopressurized zones. The most important game changer in recent years is
shale gas largely due to the novel but controversial process of fracking [18–36].