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R. Sandeep et al.
higher viscosity that can help improving the mobility ratio of the drive fluid. Hence,
nanoemulsions prove an advantage over polymers, as polymers are retained due to
adsorption on rock surface (Binks et al. 2005; Binks and Rodrigues 2005). These
properties make its applications extended to large-scale field jobs.
A number of NPs have been developed to be used as nanoemulsions. Silica NPs
have found wide use as nanoemulsions in many of the recent studies. The concentration of silanol groups in the silica NPs containing nanoemulsions plays an important role in many of its intrinsic characters, such as the wettability, hydrophilicity
and hydrophobicity. Wettability character is controlled with the amount of silanol
groups present on the surface (Mcelfresh et al. 2012). Hydrophilicity behavior of
the nanoemulsion increases with increasing percentage (over 90%) of silanol groups
on the surface. This helps in forming stable oil-in-water (o/w) emulsions. When the
concentration is only 10% on the surface, the hydrophobic character yields water-inoil (w/o) emulsions. This change helps control the formation of o/w emulsions and
w/o emulsions, which further improves interaction with non-polar oils or polar oils,
respectively (Aveyard et al. 2003).
The emulsification behavior has also been observed in some micro-model experiments earlier. The key reasons for such behavior of NPs on emulsion are also
mentioned by some studies. Images viewed by an optical microscope also show
the uniform size of the NPs generating a compact, well-structured unilayer at the
aqueous/non-aqueous interface, thereby making the emulsions highly stable under
extreme temperatures (Alomair et al. 2014).
3.3 Nanocatalysts
Nanocatalysts act as nanodimensional-sized metal particles with an increased surface
area of contact that helps in better interaction of the surface of oil with nanocatalysts
(Hashemi et al. 2013, 2014). These catalysts are therefore used for upgrading the
properties of crude oil by reacting with bitumen in the crude oil to convert it into
lighter products by some chemical reactions. Such type of reactions is referred as
aquathermolysis. These occur while injection of nanocatalysts during steam injection
into heavy oil reservoirs. The presence of nano-sized metal particles, such as nickel
and iron, provides an increased surface area for catalyzing the breaking of carbon
sulfur bonds within asphaltenes. This, therefore, increases the amount of saturates
and aromatics present in the heavy oil (Hyne 1986).
The percentage of carbon monoxide produced during this reaction reacts with
water to produce hydrogen (during thermal EOR process at 200–300 °C). These
hydrogen molecules that have been produced later react with the unsaturated
molecules of heavy oil, thereby producing lighter, saturated crude oil components
by hydrogenolysis (Callaghan 2006).
Aquathermolysis also helps in decreasing the viscosity of the heavy oils. When
metal NPs were used as catalysts they caused a greater reactivity compared to micronsized particles. As noted by Shokrlu et al., nickel NPs were able to reduce oil viscosity
R. Sandeep et al.
higher viscosity that can help improving the mobility ratio of the drive fluid. Hence,
nanoemulsions prove an advantage over polymers, as polymers are retained due to
adsorption on rock surface (Binks et al. 2005; Binks and Rodrigues 2005). These
properties make its applications extended to large-scale field jobs.
A number of NPs have been developed to be used as nanoemulsions. Silica NPs
have found wide use as nanoemulsions in many of the recent studies. The concentration of silanol groups in the silica NPs containing nanoemulsions plays an important role in many of its intrinsic characters, such as the wettability, hydrophilicity
and hydrophobicity. Wettability character is controlled with the amount of silanol
groups present on the surface (Mcelfresh et al. 2012). Hydrophilicity behavior of
the nanoemulsion increases with increasing percentage (over 90%) of silanol groups
on the surface. This helps in forming stable oil-in-water (o/w) emulsions. When the
concentration is only 10% on the surface, the hydrophobic character yields water-inoil (w/o) emulsions. This change helps control the formation of o/w emulsions and
w/o emulsions, which further improves interaction with non-polar oils or polar oils,
respectively (Aveyard et al. 2003).
The emulsification behavior has also been observed in some micro-model experiments earlier. The key reasons for such behavior of NPs on emulsion are also
mentioned by some studies. Images viewed by an optical microscope also show
the uniform size of the NPs generating a compact, well-structured unilayer at the
aqueous/non-aqueous interface, thereby making the emulsions highly stable under
extreme temperatures (Alomair et al. 2014).
3.3 Nanocatalysts
Nanocatalysts act as nanodimensional-sized metal particles with an increased surface
area of contact that helps in better interaction of the surface of oil with nanocatalysts
(Hashemi et al. 2013, 2014). These catalysts are therefore used for upgrading the
properties of crude oil by reacting with bitumen in the crude oil to convert it into
lighter products by some chemical reactions. Such type of reactions is referred as
aquathermolysis. These occur while injection of nanocatalysts during steam injection
into heavy oil reservoirs. The presence of nano-sized metal particles, such as nickel
and iron, provides an increased surface area for catalyzing the breaking of carbon
sulfur bonds within asphaltenes. This, therefore, increases the amount of saturates
and aromatics present in the heavy oil (Hyne 1986).
The percentage of carbon monoxide produced during this reaction reacts with
water to produce hydrogen (during thermal EOR process at 200–300 °C). These
hydrogen molecules that have been produced later react with the unsaturated
molecules of heavy oil, thereby producing lighter, saturated crude oil components
by hydrogenolysis (Callaghan 2006).
Aquathermolysis also helps in decreasing the viscosity of the heavy oils. When
metal NPs were used as catalysts they caused a greater reactivity compared to micronsized particles. As noted by Shokrlu et al., nickel NPs were able to reduce oil viscosity