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oil production. Today, there are different nanomaterials that have been developed
for stimulating the increase in the recovery of the crude oil in a much efficient way,
compared to available methods. Oil is recovered primarily by using the earth geological pressure, known as primary recovery (Rellegadla et al. 2017). With time the
amount of oil recovered reduces with decreasing pressure. At this moment a variety of injected fluids like water is injected for enhancing the sweep efficiency of
the displacing fluid. Although the recovery of crude oil increases till 35% of the
original oil in place (OOIP), but with time it gradually decreases due to increased
viscous fingering (Rellegadla et al. 2017). Tertiary methods known as enhanced oil
recovery are later employed at this point for increasing the recovery of residual oil in
place. A number of tertiary methods have been developed for increasing the recovery
potential. Owing to the reservoir heterogeneity issues, different types of enhanced
oil recovery methods are currently been used in the fields to recover crude oil.
The three major types of tertiary recovery methods used currently are (Alvarado
and Manrique 2010; Ayatollahi and Zerafat 2012; Kong and Ohadi 2010; Silva et al.
2007; Viebahn et al. 2015):
Thermal Methods—Thermal methods involve introducing heat in the bottom-hole
of the heavy oil reservoirs to promote crude oil mobility by affecting its physical
properties (lowering of density and viscosity). There are different thermal methods
such as cyclic steam simulation, steam assisted gravity drainage (SAGD) and steam
flooding.
Chemical Methods—Chemical flooding involves altering the properties of the
injected fluids. Secondary flooding results in increase of viscous fingering, thereby
lowering the efficiency of the recovery potential. Henceforth, long chain polymers are
added to the injection water to increase the viscosity of the drive fluid with improved
sweep efficiency. Besides, surfactants are also added to the injection fluid to lower
the interfacial tension (IFT) of the oil–rock interface and alter wettability of the rock
surface toward water wet.
Gas Methods—Different gaseous hydrocarbons (such as methane, propane or natural gases) and non-hydrocarbons (N 2 or CO 2 ) are injected into the reservoir during
gas flooding. These gases dissolve in the oil layer and further reduce their viscosity
by expanding its volume leading to increased recovery.
But all the above-mentioned methods have their own limitations. Cost of application is a common issue for thermal and chemical methods. Besides, low thermal
conductivity of reservoir rocks and fluids, an escape of heat in a two-stage process,
that is, during flooding from heat generator to the reservoir and loss to undesired
layers create an issue during steam flooding. Formation damage can be a big issue
during chemical flooding due to incompatibility issues. The injected chemicals could
have lower effect on IFT and wettability alteration, whereas during gas flooding fingering can occur at bottom-hole leading to early breakthrough. Besides, deposition
of asphaltene has been reported during gas flooding. In brief, summarizing the effects
of the above-mentioned processes includes many advantages, such as decreasing oil
viscosity, improved mobility, lowering IFT, wettability alteration, oil expansion and
R. Sandeep et al.
oil production. Today, there are different nanomaterials that have been developed
for stimulating the increase in the recovery of the crude oil in a much efficient way,
compared to available methods. Oil is recovered primarily by using the earth geological pressure, known as primary recovery (Rellegadla et al. 2017). With time the
amount of oil recovered reduces with decreasing pressure. At this moment a variety of injected fluids like water is injected for enhancing the sweep efficiency of
the displacing fluid. Although the recovery of crude oil increases till 35% of the
original oil in place (OOIP), but with time it gradually decreases due to increased
viscous fingering (Rellegadla et al. 2017). Tertiary methods known as enhanced oil
recovery are later employed at this point for increasing the recovery of residual oil in
place. A number of tertiary methods have been developed for increasing the recovery
potential. Owing to the reservoir heterogeneity issues, different types of enhanced
oil recovery methods are currently been used in the fields to recover crude oil.
The three major types of tertiary recovery methods used currently are (Alvarado
and Manrique 2010; Ayatollahi and Zerafat 2012; Kong and Ohadi 2010; Silva et al.
2007; Viebahn et al. 2015):
Thermal Methods—Thermal methods involve introducing heat in the bottom-hole
of the heavy oil reservoirs to promote crude oil mobility by affecting its physical
properties (lowering of density and viscosity). There are different thermal methods
such as cyclic steam simulation, steam assisted gravity drainage (SAGD) and steam
flooding.
Chemical Methods—Chemical flooding involves altering the properties of the
injected fluids. Secondary flooding results in increase of viscous fingering, thereby
lowering the efficiency of the recovery potential. Henceforth, long chain polymers are
added to the injection water to increase the viscosity of the drive fluid with improved
sweep efficiency. Besides, surfactants are also added to the injection fluid to lower
the interfacial tension (IFT) of the oil–rock interface and alter wettability of the rock
surface toward water wet.
Gas Methods—Different gaseous hydrocarbons (such as methane, propane or natural gases) and non-hydrocarbons (N 2 or CO 2 ) are injected into the reservoir during
gas flooding. These gases dissolve in the oil layer and further reduce their viscosity
by expanding its volume leading to increased recovery.
But all the above-mentioned methods have their own limitations. Cost of application is a common issue for thermal and chemical methods. Besides, low thermal
conductivity of reservoir rocks and fluids, an escape of heat in a two-stage process,
that is, during flooding from heat generator to the reservoir and loss to undesired
layers create an issue during steam flooding. Formation damage can be a big issue
during chemical flooding due to incompatibility issues. The injected chemicals could
have lower effect on IFT and wettability alteration, whereas during gas flooding fingering can occur at bottom-hole leading to early breakthrough. Besides, deposition
of asphaltene has been reported during gas flooding. In brief, summarizing the effects
of the above-mentioned processes includes many advantages, such as decreasing oil
viscosity, improved mobility, lowering IFT, wettability alteration, oil expansion and