Effects of Nanoparticles on Rheological Behavior of Polyacrylamide Related to Enhance Oil Recovery- Juniper Publishers
JUNIPER
PUBLISHERS- ACADEMIC JOURNAL OF POLYMER SCIENCE
Abstract
The effect of nanoparticles SiO2, TiO2 and Fe2O3 on
the rheological behavior of anionic polyacrylamide and a mixed assembly
of polymer and cationic surfactants were measured systematically by
shear viscosity and oscillatory testing at different concentration of
Nano-materials. The results of shear viscosity measurement indicate that
for all of the systems, the shear viscosity increases with the addition
of nanoparticles and show shear thinning behavior at low shear rate. In
the oscillatory test, all of the systems show elastic behavior, which
depend on the concentration of nanoparticles. The storage modulus (G’)
and loss modulus (G’’) increased as nanoparticles concentration
increase. The core flooding experiment were also done with
polymer-surfactant solution in presence and absence of nanoparticles and
the obtained result indicates the higher oil recovery in presence of
nanomaterials. In enhance oil recovery process; the viscosity and
viscoelasticity are key parameters for the success of the recovery
process.
Keywords: Wettability; Viscoelasticity; Displacement efficiency; NanoparticlesIntroduction
Due to the increasing demand of energy and
diminishing amount of conventional oil, the oil industries have been
relying on enhanced oil recovery methods for decades. Presently, lots of
researches are being carried out globally to improve enhanced oil
recovery techniques to fulfill the demands of oil. Recently, the use of
nanoparticles in enhance oil recovery has been proved very efficient.
With a nano size and large surface area to volume ratio, nanoparticles
have the potential to penetrate the pores in the reservoir rocks where
conventional enhance oil recovery process are unable to. The
nanoparticles can alter the oil reservoir characteristics such as
mobility ratio, wettability, interfacial tension, injected fluid
viscosity and are stable than the polymer-surfactant at harsh and saline
conditions [1-3]. The oil recovery decreases by increasing the salt
concentration during the polymer flooding, whereas in the case of
flooding with a suspension of nano-silica in the polymer, decreasing the
rate of oil recovery is lower [4]. The nanoparticles are more capable
of the reduction of interfacial tension and the alteration of
wettability in the case of light oil reservoir [5].
In the last decade, nanoparticles have attracted many
researcher’s attention in the field of enhance oil recovery due to
their unique properties. Maghzi et al., [6] reported that at the same
salinity, the oil recovery is 10% higher with nanoparticles than the
polymer flooding in the absence of nanoparticles. Hu et al., [7]
reported that with 5ppm concentration of nanoparticles recovered the
original oil in place about 35.8%, with 10ppm of nanoparticles
it is 41.8% and with 20ppm of nanoparticles, 39.8% of original oil in
place was recovered. At low nanoparticles concentrations, the rate of
recovery of oil increases with an increase of nanoparticles
concentration and reaching a peak value at 20ppm, above which it starts
to decline.
Joonaki et al., [8] reported in his result, the total
oil recovery by using nanoparticles is 92.5%, 88.6% and 95.3% in the
three scenarios. This result indicates that the oil recovery will be
higher, and less amount of oil is remaining trapped within the porous
media, if the nano fluid injection begins earlier. In the experiment of
Pei et al., [9], 50% of the OOIP were recovered with silica
nanoparticles. These results demonstrate that the injection of
nanoparticles with polymer and surfactant system can significantly
increase the wettability, reduce the mobility ratio and thus leads to
the improvement of enhance oil recovery. Yousefvand et al., [10]
reported in his paper that the oil recovery factor after one pore volume
of the injected fluid has been obtained and results indicate that in
the presence of nano silica an improvement about 10% in the ultimate oil
recovery can be achieved and this is due to the viscosity enhancement
of the injected fluid. Also, nanoparticles have ability to change the
wettability to water-wet in some portions of the micro model.
In this study, we have organized a series of
experiments to know the potential effects of nano-materials on the
rheological behavior of polyacrylamide solution. The sample viscosities
in different concentrations of nanoparticles, shear rates,
temperature were measured. Because the viscosity plays a very
important role in enhance oil recovery. Also, this paper presents
a comparison between the effects of different nanoparticles on
the rheology of polyacrylamide in the presence of surfactants.
In addition, the viscoelasticity of polyacrylamide solution in the
presence of different nanoparticles was also measured.
Procedure
Materials
For this study, polyacrylamide (PAM) of molecular weight
150000, was purchased from Sigma Aldrich, U.S.A. CTAB
surfactant (≥99.0%, Merck, Germany) was used as received.
Gemini surfactants α,ω- bis (hexadecyldimethylammonium)
alkane dibromides (16-6-16 and 16-5-16) were prepared and
purified. Also, three types of nanoparticles were used for this
study. These nanoparticles are Silica fumes (particle size 0.007μm,
specific surface area 395 ± 25m2/g, density 36.8424649kg/m3),
TiO2 (particle size < 100nm, purity 99.5% trace metal basis,
specific surface area 50 -100nm) and Fe2O3 (particle size 50-
100nm, purity 97% trace metal basis, specific surface area 40-
60m2/g) was purchased from Sigma Aldrich, St. Lucia, U.S.A. All
the experiments were conducted at 50 °C and all the solution was
prepared in double distilled water (Table 1).
Preparation of solution
The polymer solution of 1.0wt% concentration was
prepared in distilled water. The nanoparticle of SiO2, TiO2,
Fe2O3 in a concentration of 0.2wt% to 1.0wt% was mixed with
polyacrylamide solution. After conducting several tests of polymer
and nanoparticle mixture, we add cationic surfactants with these
solutions. It is also observed that above 1.0wt% of a nanoparticle
of SiO2 and TiO2 (except Fe2O3), the solution of polymer and Gemini
surfactants gets precipitated. This will set the limit and we add the
nanoparticle at low concentration very carefully. The solutions of
polymer-surfactant-nanoparticle are not easily mixed with each
other and the solution will require a heating and agitation for
several hours.
Methods
There is a wide range of rheological measurement techniques
are available and each one has its advantages and disadvantages.
To maximize the value of the data generated it is obviously
important to ensure that the most appropriate technique is used
for the application. The shear viscosity of the prepared solution as
a function of shear rate and concentration were measured using
Anton Paar’s Modular Compact Rheometer (series 102) with
cone shaped measuring geometry at 50°C. The shear viscosity at
all solution concentrations, over a shear rate range of 0 to 500s-
1 was measured. The oscillatory frequency test was also carried
out at an angular frequency of 0.1 to 100 rad. s-1. Generally, the
oscillatory tests were carried out to determine the viscoelastic
behavior of the solution.
Core flooding experiment were performed to measure the
recovery of crude oil by using sand pack system. The crude oil
was obtained from Rajasthan oil field, India with API of 19.2 at
28 °C. The sandstone with the permeability of 2.5 milli Darcy and
porosity 0.19 was used for the test. During the test, the sand pack
was flooded with crude oil at 30psig. Then, the polymer-surfactant
and polymer-surfactant-nanoparticle solution was introduced in
a sand pack when water cut exceeded 95%.
Results and Discussion
Effect of different concentration of nanoparticles on viscosity
The rheological properties of the injected fluid are an important
parameter in a chemical flooding process. The additional increase
in viscosity of injected fluid, the oil displacement efficiency is
increased, and more oil recovered from the porous rock. To
observe the effect of silica nanoparticles on the viscosity of
polymer solution, the viscosity measurement test was performed
with 1.0 wt.% of a polymer solution and also with polymersurfactants
system containing different silica concentration at 50
0C. From a Figure 1, the viscosity of polymer solution increases
with increase in a concentration of Nano-silica. The ion-dipole
interaction is developed between cations and oxygen atoms in
the tetrahedral structure of silica. Thus, the attack of cations to polymer molecules is reduced to some extent and the increase
in viscosity of the solution is observed in the presence of silica
nanoparticles. Consequently, the oil recovery increases during
chemical flooding test by increasing the silica nanoparticles
concentration [4].
The same effect of nano-TiO2 and nano-Fe2O3 on the rheology
of polyacrylamide was also obtained at the same operating
conditions (Figure 2&3). The viscosity of the polymer increases
with increase in the concentration of nano-TiO2 and nano-Fe2O3
as expected. But there is a more drastic change in the viscosity
of polyacrylamide is observed with the nano- materials of metal
oxides. TiO2 shows the ability to provide much better result in
enhance oil recovery process while chemical flooding. Comparing
with the nano-silica, the nano- TiO2 increases the viscosity of
polymer solution up to 83.33% and the nano-Fe2O3 increases the
viscosity of about 64.28%. Also, some research studies suggested
that the reduction of oil viscosity is possible via nanoparticles of
metals oxide. A Bayat et al., [11] reported in his work, that SiO2,
TiO2, Al2O3 and nano-fluids flooding at 60 ͦC caused 8, 24 and 34%
viscosity reduction compared to the original oil viscosity at the
same temperature, respectively. This is because TiO2, Al2O3 and
Fe2O3 have higher thermal conductivity than SiO2.
The effect of nanoparticles on the mixed assembly of polymer
and surfactant are shown in Figure 4,5 and 6. The concentration
of polymer and surfactants are fixed and the test was conducted at
50 0C. The shear viscosity of all the systems increases with nanosilica
concentration. As shown in Figure 4, the polymer solution
with CTAB surfactant shows a more drastic change in the viscosity
with a given Nano-silica concentration range. In a case of TiO2 and
Fe2O3, the Gemini (16-5-16) surfactant shows more effect on the
rheological property of polyacrylamide. The interaction between
the polymer and nanoparticles are affected by the presence of
a surfactant (Figure 5&6). The surfactants in the solution can
dislocate and relocate on the surface of the nanomaterial and
ultimately created new surfactant coated particles. This will lead
to increase in the viscosity of the solution.
Effect of shear on the rheological properties of the polymer-nanoparticles and polymer-surfactant-nanoparticles hybrid system
In this section, the effects of shear rate on the viscosity of
polymer-nanoparticles and polymer-surfactant-nanoparticles
hybrid system were studied. The results are plotted in Figure 7,
8 and 9 for a fixed PAM concentration of 0.5 wt.% with varying
concentration of nano-Si, nano-TiO2 and nano-Fe2O3 from 0.5 to
1.0 wt.%. The results indicate that the addition of nanoparticles in
the polyacrylamide solution leads to increase in viscosity. Because
of the irreversible adsorption of polyacrylamide on nanoparticles,
the resultant macro-molecular structure is stable and not easily
broken, and it leads to increase in viscosity of the system. The
viscosity of polymer-nanomaterial system is greater than the
viscosity of polyacrylamide solution at same temperature and
shear rate. Figure 10, 11 and 12 shows the viscosity variation of
polymer-surfactant-nanoparticles hybrid system. Across all the
polymer, surfactants and nanoparticles concentrations, it is found
that the samples revealed non-Newtonian shear thinning behavior
at low shear rate (γ < 25 s-1). But at high shear rate the solution
loses it’s non-Newtonian and shows shear thickening behavior
[12]. At low shear rate, the viscosity of the system is obviously
dropped. The bond between the polymer and nanoparticles are
not easily broken in normal state, but progressively weakens
as shear rate increases, thus the flow of the suspension is shear
thinning [13]. The shear thinning behavior and incremental shear
viscosity with concentration of polyacrylamide and nanoparticles
can be responsible for strong interaction between polymer and
nanoparticles.
On the basis of results, adding a small amount of nanoparticles
can improve the pseudo-plasticity behavior of polymer solution
at a given shear rate. From the above discussion, it is observed
that the nano-suspension increases the viscosity of the solution
in comparison to polymer viscosity. It indicates that the
nanoparticles can increase the sweep efficiency of the polymer
solution and oil recovery will be higher with nanoparticles. The
more nanoparticles transportation will be the more effective the
wettability alteration and better effective sweep efficiency of the
polymer-surfactant solution.
Effect of nanoparticles on viscoelastic behavior of polymer
The viscoelastic properties of polymer solution are widely
used to gain insight into structure strength of polymer in the
solution. The viscoelastic property of polymer plays an important
role in increasing the oil recovery. Larger the viscoelasticity,
greater will be the sweep efficiency of the polymer solution.
Figure 13 shows the plots of storage modulus (G’) as a function
of oscillatory angular frequency (ω) for polyacrylamide solution
and polymer-silica mixed system at 50 0C. For all the solutions,
storage modulus G’ is a strong function of angular frequency and
increases over the entire range. The elastic part of the polymer is
called the storage modulus (G’) and it is a measure of the energy
stored and recovered. The viscous part is called the loss modulus
G” which is a measure of the energy dissipated [14]. The value
of storage modulus increases with increases the concentration
of nanoparticles due to the more numbers of nanoparticles
available in the solution. With the addition of silica nanoparticles,
storage modulus of polymer-silica system greater than that of the
polyacrylamide solution. This indicates that the polyacrylamidenanosilica
mixed system undergoes microstructural changes and they have ability to increase the oil recovery. In the polymersilica
mixed system, the interaction between the amide group
of polyacrylamide and silanol functional group of nano-silica
occurred. So, the structure of polyacrylamide strengthened, and
the elasticity of the mixed system becomes more pronounced.
The elastic property is more dominant than the viscous i.e., G’ is
greater than G’’. This indicates that there is a significant buildup of
network structure that is responsible for imparting a significant
elasticity to the polymer solutions [12].
Figure 14 shows the loss modulus (G’’) as a function of
increasing angular frequency for PAM and PAM-silica mixed
system. The loss modulus (G’’) is the characteristic of the viscous
behaviors of the solution. When the value of storage modulus is
greater than the loss modulus, it represents the solution exhibits
viscoelastic gel like behavior and when the value of loss modulus
is greater than storage modulus, the system displays a liquid
like behavior. The value of G’ and G’’ increased with the angular
frequency. On comparing the viscoelastic effect of nano-silica on
polymer solution with TiO2 and Fe2O3 from Figure (15&17), the
storage modulus (G’) of TiO2 is much larger than that of nano-Si
and Fe2O3. G’ and G’’ increases with increase in a concentration
of nanoparticles. The increase in a concentration of nanoparticles
found to strengthen the network structure of polyacrylamide
solution and this leads to increase the viscoelastic properties.
At 1.0wt.% of TiO2, the flow curve is constant with the increase
of angular frequency and G’ > G’’, this means the elastic effect is
more dominant. The elastic behavior of all the above systems is
more than that of loss modulus because the decreased friction
at the polymer-nanoparticles interface led to the slight decrease
in the loss modulus. From (Figure 16 & 18), the loss modulus is
also increasing with the addition of nanoparticles, but the value
of loss modulus is slightly less than the storage modulus at all
concentration. Also, the value of loss modulus never exceeds to
zero [15].
Core flooding Results
From Figure 19, the core flooding test was conducted by
injecting a polymer and surfactant solution. First, the sandstone
system saturated with the crude oil and then brine solution is
injected to measure the porosity. The porosity of the sandstone
system was found 0.19 or 19%. Then the crude oil was flooded
with 30psi pressure. Brine solution is then injected in a sand pack
system to displace the oil via secondary recovery and around 39%
of oil is recovered. After that the polymer and surfactant solution
were injected to recover the remaining oil as tertiary recovery.
Additional recovery of 5.5%, 13.5%, and 17.3% were obtained for
1.0wt. PAM+50mmol CTAB, 1.0wt. PAM+50mmol G5 and 1.0wt.
PAM+50 mmol G6 respectively. The polyacrylamide renders
the mobility to the oil rich phase by increasing the viscosity of
injected fluid. The crude oil droplets are mobilized by reducing the
interfacial tension between the oil-water interfaces. As the spaces
length of Gemini surfactant increases from 16-5-16 to 16-6-16,
the crude oil saturation increases due to improved coalescing of
mobilized crude oil droplets to form an oil bank and this result
in better oil displacement and hence greater oil recovery. In
presence of nanoparticles, the oil recovery percentage is improved
as shown in Figure 20. The nanoparticles increase the viscosity
of polymer solution significantly and this will lead to increase in
storage modulus and loss modulus of polyacrylamide solution,
results in the oil recovery will increase. The nano titanium oxide
shows good result as compare to nano silica and nano iron oxide
material.
Conclusion
In the present study, the rheological behavior of
polyacrylamide and polymer-surfactant solution in the presence of
nanoparticles was examined. The result reveals that the presence
of nanoparticles strongly influences the rheological properties of
solutions. It is found that the shear viscosity of polyacrylamide
solution increased with the addition of nanoparticles. With the
introduction of nanoparticles in the polymer solution, the polymer
chains adsorb on the nanoparticles surface and complex micelle
type structure is formed and this interaction leads to increase the
viscosity, which indicates that increase in sweep efficiency. A non-
Newtonian shear thinning behavior was observed at low shear
rate (γ < 25s-1). The titanium oxide shows the promising prospects
for potential application in enhance oil recovery. The addition of
nanoparticles improves the viscoelastic properties of polymer. The
additional 11.5%, 17.5% and 22% of oil recovery were observed
in presence of nanoparticles. It means nano-suspension can be
used in enhance oil recovery and more beneficial than chemical
flooding without nanoparticles.
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