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

ahasnamz@petronas.com.my (corresponding author), bsyasya.latiff@gmail.com, cnoorhana_yahya@petronas.com.my, dhassan.soleimani@petronas.com.my,

eafza@petronas.com.my

[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

136 Journal of Nano Research Vol. 26

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

138 Journal of Nano Research Vol. 26

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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