Application of Electromagnetic Waves and Dielectric Nanoparticles in Enhanced Oil Recovery
Transcript of Application of Electromagnetic Waves and Dielectric Nanoparticles in Enhanced Oil Recovery
Application of Electromagnetic Waves and Dielectric Nanoparticles in Enhanced Oil Recovery
Hasnah Mohd Zaid1, a, Noor Rasyada Ahmad Latiff2,b, Noorhana Yahya1,c, Hassan Soleimani1,d, Afza Shafie1,e
1Fundamental and Applied Sciences Department, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 31750 Tronoh, Perak, MALAYSIA
2Enhanced Oil Recovery Centre, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 31750 Tronoh, Perak, MALAYSIA
[email protected] (corresponding author), [email protected], [email protected], [email protected],
[received: 5.7.2013, accepted]: 3.9.2013]
Keywords: Enhanced Oil Recovery, Dielectric nanoparticles, Electromagnetic irradiation
Abstract. Enhanced oil recovery (EOR) refers to the recovery of oil that is left behind in a reservoir
after primary and secondary recovery methods, either due to exhaustion or no longer economical,
through application of thermal, chemical or miscible gas processes. Most conventional methods are
not applicable in recovering oil from reservoirs with high temperature and high pressure (HTHP)
due to the degradation of the chemicals in the environment. As an alternative, electromagnetic (EM)
energy has been used as a thermal method to reduce the viscosity of the oil in a reservoir which
increased the production of the oil. Application of nanotechnology in EOR has also been
investigated. In this study, a non-invasive method of injecting dielectric nanofluids into the oil
reservoir simultaneously with electromagnetic irradiation, with the intention to create disturbance at
oil-water interfaces and increase oil production was investigated. During the core displacement
tests, it has been demonstrated that in the absence of EM irradiation, both ZnO and Al2O3
nanofluids recovered higher residual oil volumes in comparison with commercial surfactant sodium
dodecyl sulfate (SDS). When subjected to EM irradiation, an even higher residual oil was recovered
in comparison to the case when no irradiation is present. It was also demonstrated that a change in
the viscosity of dielectric nanofluids when irradiated with EM wave will improve sweep efficiency
and hence, gives a higher oil recovery.
Introduction
Most of the existing oil reservoirs nowadays are maturing fields and categorized as the conventional
oil reservoirs which are simply defined as reservoirs that are easily recoverable at low cost and
without the need of applying advanced technology. However, this type of reservoir is depleted and
most of the newly discovered reservoirs could be categorized as unconventional oil, e.g. heavy oil,
tar sands, reservoir located deep water regions and high temperature and high pressure reservoirs
[1]. The major methods in tertiary oil recovery or EOR, which is the recovery of oil that is left
behind in a reservoir after primary and secondary recovery methods, are thermal, miscible and
chemical. In the thermal method, thermal energy is transferred into the reservoir to heat up the oil
formation and therefore reducing oil viscosity for easier displacement [2,3]. Meanwhile in the
miscible flooding method, various types of solvents are used to fully mix up with the residual oil to
overcome capillary forces and hence, increase oil mobility. In the chemical method or flooding,
polymers, surfactants and alkalis are mixed up with water before injection. Chemical flooding
methods work either by reducing interfacial tension between oil and water, increasing sweep
efficiency or changing the wettability of the rock surfaces.
As the depth of the reservoir increases, high pressure and high temperature (HTHP)
environments are also present. Some methods work efficiently at increasing depth e.g. hydrocarbon
Journal of Nano Research Vol. 26 (2014) pp 135-142Online available since 2013/Dec/06 at www.scientific.net© (2014) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/JNanoR.26.135
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miscible and fireflood, by manipulating the highly pressurized environment. However, this is
limited to reservoirs with low water saturation and high oil saturation i.e. more than 600 barrels of
oil initially present in the reservoir and has an oil reservoir thickness of at least 1.5 meter. Chemical
flooding methods are not feasible since most of the chemicals e.g. polymer and alkaline suffer
degradation due to the extreme temperature created by the pressure at more than 2100 meter depth.
An invasive approach e.g. insertion of electrode or any stimulating devices in the extreme
temperature and pressure environment will cause failure to the electronic circuits and the device
itself. Injection of external stimulating agents or fluids into the reservoir under this extreme
condition is not feasible when their stability could not be sustained and degraded with increasing
temperature and pressure.
These problems could be treated by employing a method that can withstand a HTHP
environment. Since conventional methods are no longer applicable to the extreme reservoir
conditions, a new method with highly advanced technology has to be designed. A non-invasive
approach to stimulate oil in the reservoir could be applied with the application of a low frequency
electromagnetic (EM) wave. At low frequency, the penetration depth of the wave will be higher and
therefore, a transmitter is not necessarily located in the wellbore which means that the low
frequency EM wave transmitter may be located on the seafloor and transmit EM energy remotely.
Furthermore, the usage of nanotechnology has the potential to enhance this method, due to
interaction at the molecular level [4]. Dielectric nanoparticles suspension injected into the porous
medium and activated by the low frequency EM wave will be polarized in an electric field and
create highly dense charges on the surfaces, creating surface active interfaces. Interaction of charges
at the interfaces will disturb the compatibility between oil/water/rock interfaces and therefore oil
can be released more easily.
Viscosity modification mechanisms are not restricted to dielectric particles only. An
electrorheological (ER) fluid will change its properties e.g. apparent viscosity, shear stress and yield
stress under external electric field and revert back to its original state when the field is removed [5].
This phenomenon has been widely applied in automotive industries e.g. in clutches, brakes and
dampers. Based on previous research, it was found that the crucial factor for the ER effect is the
interfacial polarization, which occurs in the frequency range of 102
− 105 Hz [6]. Application of an
electrorheological fluid in subsurface engineering is still uncommon but could potentially enhance
the hydrocarbon detection, enhanced oil recovery and mobility control.
In this study, a new EOR method of injecting nanoparticles suspensions, or simply known as
nanofluids, is proposed. For this application, the dielectric properties of the nanomaterials are the
most significant properties to be considered. It is desirable to create interaction between dielectric
particles and elements present in the oil reservoir with the application of electric or electromagnetic
field. Two types of dielectric materials, zinc oxide (ZnO) and aluminum oxide (Al2O3) are used in
this study. Al2O3 based material is chosen due to the chemical inertness and textural stability upon
high temperature application [7,8]. ZnO will crystallize to the hexagonal structure when annealed at
temperature 300°C and beyond, to give the most stable wurtzite phase [9]. Sol gel was identified as
the synthesis method to be used in this study based on the high repeatability and ability to control
morphology, structure and uniform size distribution of the end products [10]. Nanofluids were
injected into the porous medium, with and without the presence of electromagnetic waves, to
recover oil by conducting core flooding tests and the roles of nanofluids, surfactant and
electromagnetic waves on the recovery process were distinguished by measuring the interfacial
tension (IFT), viscosity and recovery efficiency.
Methodology
Preparation of Porous Medium and Petrophysical Characterization. Silica beads were
homogeneously mixed in equal ratio according to their average sieve size, 90-150µm and
450-600µm. Figure 1 represents the measurement column fabricated for this purpose. The glass
beads mixture was placed in a transparent acrylic tube with diameter of 50mm by 46mm, sealed
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with aluminium caps with O-rings, at both ends. The aluminium caps were held by two aluminium
holders at both sides to ensure safety and pressure trapping. A 1/8″ stainless steel fitting with PVC
tubing of 1/8″ diameter was inserted on both caps to serve as inlet and outlet of the closed system.
Petrophysical characterization such as permeability, porosity and pore volume of the porous
medium was determined by using the equation:
PA
LqΚ
∆=
µ
(1)
where K is the permeability in mD, q the flow rate in cm3/s, µ the viscosity of the test fluid in cP,
L the length of the porous medium in meter, A the cross-sectional area of the porous medium in cm2
and ∆P is the differential pressure between inlet and outlet, in atm.
Fig. 1 Measurement column serves as unconsolidated cores for petrophysical characterization and
core flooding experiment.
Preparation of the Dielectric Oxides Nanofluid. 0.05 wt% of the as-synthesized zinc oxide, ZnO
and aluminium oxide, Al2O3 nanoparticles was dispersed in the base fluid separately. The average
crystallite size of ZnO and Al2O3 nanoparticles was measured as ~45 nm and ~38 nm, based on
XRD analysis. The base fluid consists of 0.3wt% of sodium dodecyl sulfate (R&M, 99.5% purity)
diluted in deionized water. The purpose of adding anionic surfactant in the base fluid is to stabilize
the nanoparticles suspension for a longer period, since the particles tend to agglomerate due to high
surface energy. The nanoparticles suspensions were then magnetically stirred for 1 hour and
subsequently subjected under ultrasonic agitation for another 1 hour to disperse agglomerated
particles homogeneously.
Oil-aqueous phase interfacial tension (IFT) measurement. Interfacial tension between oil and
injection fluids e.g. ZnO and Al2O3 nanofluids, aqueous SDS and brine were measured by using a
Spinning Drop Video Tensiometer. The measurements were conducted by controlling the tilt angle
and rotation of the oil drop present in the capillary block, known as drop phase into the excess
injection fluids, known as outer phase at 10,000 rpm. If the IFT is not low enough and the length of
the oil drop captured by the charged-coupled device (CCD) camera is smaller than 4 times its
diameter; IFT, γ measured in mN/m is calculated based on spinning drop contours according to
Laplace-Young method shown in the following equation:
( )C
ωρρ dh
2
3 2.74156e γ
−= −
(2)
Acryllic tube
filled with
glassbeads
Aluminium cap with O-
ring
Aluminium
holder
1/8” stainless steel fitting
with 1/8” PVC
tubing
Journal of Nano Research Vol. 26 137
where ρh is the density of the heavy (outer) phase (g/cm3), ρd is the density of the light (drop) phase
(g/cm3), ω is the rotational velocity (rpm), and C is a coefficient determined by the ratio of the
length to the width of the oil drop.
Viscosity Measurement. The viscosity of the fluids was measured by using a Brookfield CAP
2000+ Viscometer, in maximum rotation of 100 rpm at ambient temperature, 25°C.
Core flooding experiment. Using the fabricated measurement column described in Figure 1, glass
beads were packed homogeneously and saturated with brine of 30,000 ppm. Its significant
properties e.g. permeability, porosity and pore volume were determined at this stage. Subsequently,
crude oil was injected into the porous medium horizontally until irreducible water saturation, Swi is
achieved. Brine was injected for the second time to replicate the waterflooding process and
continued until 30% watercut level is reached. EOR stage took place by the injection of the
nanofluids and surfactant, SDS. All fluids were injected at a constant flow rate of 2.5ml/min.
Result and Discussion
Interfacial tension of oil-injection fluid. Interfacial tension values between crude oil and various
injection fluids containing nanoparticles and surfactant were measured and compared, as shown in
Figure 2. There are 3 types of fluids involved in the measurement, Al2O3, ZnO, and SDS. Dynamic
or time dependent measurement methods are often used to obtain equilibrium tension values in a
prolonged duration [11].
Fig. 2 Dynamic IFT values measured in 1600s duration for all injection fluids.
Initially, the oil-brine IFT value was measured as 19.59 mN/m, almost in the range of typical oil-
brine IFT, which is around 20−50 mN/m[12]. When 0.3wt% of aqueous SDS solution is in contact
with the crude oil, the IFT value was tremendously decreased to 2.82 mN/m. When the same
aqueous SDS solution was used as the base fluid for the nanoparticles suspensions, the IFT values
slightly increases as compared to that of the base fluid itself. In mixed systems, the more rapidly
adsorbing surfactant was originally located at the interface, and gradually, particles will be
irreversibly adsorbed at the interface to replaced surfactant molecules, leading to an increase in
surface tension. Once at the interface, a particle can be thought of as being irreversibly absorbed, a
behaviour unlike surfactants, which are generally thought to be in a state of dynamic equilibrium,
absorbing and desorbing on a fast timescale [13]. Another factor which contributes to the increase
Al2O3
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in IFT values is the particles size. Kinetic study of CdSe nanoparticles on oil-water interface
conducted by S. Kutuzov et al. shows that when the nanoparticle size decreases, the rate of
adsorption of the nanoparticles will subsequently decreases, which explains the lower IFT value
observed in ZnO nanofluids, in comparison with Al2O3 nanofluids [14].
Viscosity of the injection fluids. Table 1 shows the kinematic viscosity of the base fluid and the
nanoparticles suspension. As predicted earlier, viscosity of the suspensions will be higher than its
base fluid with nanoparticles addition. Among those three injection fluids, the Al2O3 suspension has
a slightly higher viscosity which could be due to particle clustering and interactions and also
interparticle potential such as Van der Waals forces [15]. Again, particle size exhibits a significant
effect on the properties of the suspension as their viscosity increases in proportion to the particle
size reduction. This was proven from calculation using the Derjaguin–Landau–Verwey–Overbeek
(DLVO) theory) which states that the total inter-particle potential energy is mainly the sum of van
der Waals attraction and electrical double layer repulsion. Therefore, when the particle size is
reduced, the interparticle repulsion force increases as the total surface area increases, resulting in a
net increase of bulk viscosity of the suspension [16].
Table 1 - Kinematic viscosity of the injectant
Injectant Viscosity (cP)
SDS 0.94
NanoZnO 1.24
NanoAl2O3 1.6
Effect of nanoparticles addition on the recovery efficiency. In a series of core flood experiments,
the performance of both types of nanofluid were evaluated. In the first experiment, brine was
injected continuously at a rate of 2 ml/min during water flooding stage, followed by 2 pore volume
(PV) injection of the base fluid, 0.3 wt% SDS, which serves as the controlled experiment. In other
experiments, the same amount of nanofluids was injected and their performances were compared.
As shown in Figure 3, the incremental recovery curves for SDS and ZnO injection resembled
similarities between them in terms of patterns although 26.4% more residual oil in place (ROIP)
was recovered with ZnO.
Fig. 3 Comparison of the incremental recovery versus pore volume injected in the absence of EM
waves for all injection fluids.
Journal of Nano Research Vol. 26 139
After 0.6 PV of SDS injections, oil production was declining and a plateau region observed on the
curve after 0.8 PV and beyond indicates that no more oil could be displaced. With ZnO nanofluid
injection, a steady increase in the oil production was observed until 0.8 PV and shows a sudden
decline in the production before reaching plateau beyond 1.0 PV injection. However, a dissimilar
pattern was observed for Al2O3 nanofluid injection with a slower increment of oil being displaced
after each 0.1 PV of fluid injected. Even though the rate of oil production is slower than the other
two fluids, production of oil was continuously observed before it begins to decline after 1.8 PV of
fluid injection. Due to this condition, the injection was prolonged and stopped at 2.5 PV since oil
production remains stagnant after 2.1 PV. In total, Al2O3 nanofluid injection gives the highest
recovery of 32.88% ROIP, which is 11.8% more oil recovered compared to that of ZnO nanofluid
and 41.2% more oil recovered in comparison with the SDS injection.
Effect of electromagnetic irradiation on the recovery efficiency. Irradiation of electromagnetic
waves on the porous medium during nanofluid injection showed a dramatic increase in the amount
of oil recovered, as shown in Figure 4. In the case of ZnO nanofluid injection, 63.9% of ROIP
more oil was recovered in the presence of 50 MHz of electromagnetic waves. A similar trend was
observed during Al2O3 nanofluid injection, where 54.2% of ROIP was successfully recovered when
subjected to an electromagnetic field. In contrast, only 5.12% more ROIP recovered in Al2O3
nanofluid injection when compared with ZnO nanofluid in the presence of an electromagnetic wave.
Fig. 4 Comparison of the incremental recovery versus pore volume of both types of nanofluids
injected in the presence/absence of EM waves.
It can be concluded that the higher recovery observed was due to the change in the apparent
viscosity of the nanofluid when subjected to an electromagnetic field. In an electromagnetic field,
dielectric particles undergo polarization which in turn creates electric dipoles caused by the
separation of positive and negative charges. These dipoles will align with the applied field and, as a
result, creates a temporary chain-like structure which contributes to the increase in apparent
viscosity of the nanofluid [17]. Therefore, a better sweep efficiency can be achieved with the
increase in apparent viscosity, as in the case of polymer flooding. Addition of nanoparticles could
increase the viscosity of water; therefore the water-oil mobility ratio could be minimized to achieve
a better sweep efficiency. Furthermore, it has been widely presumed that with the reduction in the
mobility ratio, a shorter time will be needed to reach residual oil saturation, which was clearly
140 Journal of Nano Research Vol. 26
observed during Al2O3 nanofluid injection [18]. Although SDS reduces the IFT of water and oil, this
reduction is not large enough to cause significant oil dispersion in the fluid. Even though the IFT
values become slightly higher with the presence of nanoparticles, tiny globules of oil are formed
and are better dispersed in the mixture of nanofluid, brine and oil [19].
Possible recovery mechanism. During core flooding experiments, some observations were done on
the effluent collected at the outlet, as shown in Figure 5. Initially, only a clear solution of brine is
displaced when 0.1-0.2 PV of nanofluid is injected. This marks the process of mobilization of
dispersed oil ganglion to form connections between other oil ganglions and become a large oil bank.
However, when the fluid injection is continued, continuous oil drops flow through the outlet for the
next 0.5 to 0.7 PV.
Fig. 5 Effluent collected at the outlet during core flooding experiment
Beyond those injection volumes, mixtures of oil, brine and nanofluid started to be produced in the
form of a cloudy, opaque brown solution which came out from the outlet mostly after 0.5 PV of the
injection fluids are injected through the inlet. The cloudy solution was found to be a
macroemulsion, which is the formation of tiny droplets of oil in an aqueous phase due to a reduction
in IFT between oil and water by the presence of surfactant (SDS) in the base fluid [14].
After waterflooding, disconnected oil ganglia left behind a flood front and dispersed in the swept
zones. Therefore, an EOR agent is needed to connect these oil ganglia and mobilize them to flow.
As the nanofluids interact with the formation, two processes are expected to occur. First, low
concentration of SDS present in the base fluid reduces the IFT between oil and water, therefore
induced coalescence between previously dispersed oil ganglia. Subsequently, formation of an
emulsion increases the viscosity of the flood front and also the viscosity of the nanofluids are found
to be higher than brine, thus the sweep efficiency is improved and results in higher residual oil
recovery.
Conclusion
After a series of core flooding, the recovery mechanism of the novel EOR method was studied and
explained. It was found that at low concentration of nanoparticles, a tremendous reduction in IFT
was not achieved. Therefore, based on the measurement, it is proven that a viscosity increase plays
an important role in enhancing the production of an oil reservoir. By reducing the mobility ratio
between oil and water, a better sweep efficiency was achieved and more oil could be swept in
shorter time. The highest recovery by nanofluid flooding itself was achieved in Al2O3 nanofluid
injection with 32.88% ROIP, which is 11.8% more oil recovered, compared to that of the ZnO
nanofluid and 41.2% more oil recovered in comparison with the SDS. In the presence of an
electromagnetic wave, apparent viscosities of the nanofluids were expected to be higher due to their
electrorheological properties. By injection of Al2O3 nanofluid, 54.2% of ROIP was successfully
recovered when subjected to an electromagnetic field, 5.12% more oil recovered compared to ZnO
nanofluid.
Journal of Nano Research Vol. 26 141
Acknowledgment
The corresponding author would like to thank Universiti Teknologi PETRONAS for all the
facilities and research grants; EOR Center Operational Budget (15-8205-005), STIRF Research
Fund (STIRF 88.09/10) and YUTP Fundamental Research Grant (YUTP-FRG15-8209-002).
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