Effect of native and injected nano-particles on the efficiency of heavy oil recovery by radio frequency electromagnetic heating

Author’s Accepted Manuscript Effect of Native and Injected Nano-Particles on the Efficiency of Heavy Oil Recovery by Radio Frequency Electromagnetic Heating Achinta Bera, Tayfun Babadagli www.elsevier.com/locate/petrol

PII: DOI: Reference:

S0920-4105(17)30414-X http://dx.doi.org/10.1016/j.petrol.2017.03.051 PETROL3939

To appear in: Journal of Petroleum Science and Engineering Received date: 29 February 2016 Revised date: 18 December 2016 Accepted date: 29 March 2017 Cite this article as: Achinta Bera and Tayfun Babadagli, Effect of Native and Injected Nano-Particles on the Efficiency of Heavy Oil Recovery by Radio Frequency Electromagnetic Heating, Journal of Petroleum Science and Engineering, http://dx.doi.org/10.1016/j.petrol.2017.03.051 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Effect of Native and Injected Nano-Particles on the Efficiency of Heavy Oil Recovery by Radio Frequency Electromagnetic Heating Achinta Bera, Tayfun Babadagli* University of Alberta *Corresponding author: [email protected]. Department of Civil and Environmental Engineering, School of Mining and Petroleum Eng., 7-277 ICE Bldg., 9211 – 116 St., Edmonton, AB, Canada T6G 1H9.

Abstract Previous attempts of EM heating have been made on the estimation of reservoir heating capabilities through numerical or analytical modeling. Experimental efforts, however, are needed, especially to test the oil property changes under EM radiation, temperature rise profile, and its effects on oil recovery. In this study, we introduced a conceptually scaled model (125 × 50 × 40 cm) filled with sand to investigate the feasibility of EM heating for heavy oil recovery. For this purpose, a microwave antenna with a frequency of 2.45 GHz and 2 kW Magnetron based power generator was used to obtain the EM waves. Temperatures at different distances from the antenna were measured by fiber optic temperature sensors. Oil recovery experiments were conducted by placing the oil saturated sand samples in Buchner funnels at different distances from the antenna. The effect of temperature on viscosity of crude oil before and after exposure of EM radiation was also examined through the oil samples in Buchner funnels located in the model. The produced gases and oil collected were analyzed through GC to ensure the loss of component from the original oil and upgradation study. The experiments were repeated using Ni and Fe nanoparticles with oil and silica bead mixture, which can absorb EM waves. They improved the efficiency of the methods yielding a faster heating and thereby a quicker viscosity reduction. Finally, the experiments were repeated with high clay contents representing shale reservoirs. The recoveries and the change in oil properties were correlated to the power of the EM source and distance from this antenna. Temperature was raised by Ni nanoparticles (up to~200°C) and therefore higher oil recovery (~30% of OOIP) was also obtained with Ni nanoparticles. Experimental observations and quantitative analyses could provide a vision for further development of EM heating as an alternative for situations where aqueous heating is not feasible.

Keywords:

Metal

Nanoparticles,

Native

Nanoparticles,

Heavy

Oil,

Electromagnetic

Heating,

Microwave/Radiofrequency Antenna Introduction Steady depletion of conventional oil resource has brought about new environmentally-friendly and economical methods to recover heavy/extra heavy oil, bitumen, oil sands, and oil shales by the oil industry. Due to extremely

high viscosity of these types of oils, thermal methods are necessary. The main objective of thermal oil recovery methods is to improve heavy oil recovery by increasing the temperature of the reservoir and thereby reducing the viscosity of oil. This is commonly achieved by steam but alternative solutions are sought to overcome the inherent operational and environmental problems associated with aqueous heating. Aqueous thermal methods such as hot water flooding and steam injection processes, namely steam flooding, cyclic steam stimulation, and steam assisted gravity drainage (SAGD) are used commercially for heavy oil recovery. However, SAGD problematically requires a large amount of fresh water to produce required steam. Another problem with these methods is the geological properties of the reservoirs. Steam related thermal methods are not effective for deep or very shallow reservoirs as well as heterogeneous ones and low permeability formations (Clark 2007; Sahuquet et al. 1990). Recently, more attention has been paid to electromagnetic (EM) (radiofrequency/microwave) heating method not only for these reasons but also due to technical limitations such as heterogeneous, low permeable, deep shale reservoirs, and even for off-shore fields. Yet, this technique is not ready for commercial application (Bera and Babadagli 2015). Although environmental issues are not as critical as in the aqueous methods, EM heating requires more efficient application procedures to make it an economically viable process.

The basic principle of EM heating technology is to install an antenna into the downhole formation to radiate radiofrequency waves into the oil-bearing formation to be absorbed by the dielectric materials present in the reservoir to raise the temperature and heat heavy oil. As a result, the viscosity of heavy oil is reduced and its mobility is increased. Note that this process is characteristically indirect; i.e., water present in the reservoir is heated and the heat generated is transmitted to the heavy oil. Over the last six decades, several concepts and ideas have been proposed to implement this type of heating method in field. Radiation heating for enhanced heavy oil/bitumen recovery was first proposed by Ritchey (1956) who filed a patent in 1956 for a design to transfer the EM waves to the wellbore from the surface through a coaxial system of internal and external tubings and casings. Different scale field tests were carried out since that time by Sayakhov et al. (1980, 1992a, 1992b), Kasevich et al. (1994), Bridges et al. (1979), Spencer (1987), and Davidson (1995).

Meanwhile, modeling works have been published and showed the efficiency of EM heating for heavy oil

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recovery. In a recent study, Bera and Babadagli (2015) documented an extensive and critical review of these studies and concluded that most of the modeling studies were computational and therefore more experimental works are needed to clarify the physics and optimal application condition of the method. A limited number of experimental studies on heavy oil recovery by EM heating have been published (Kasevich et al. 1994; Gunal and Islam 2000; Sierra et al. 2001; Jackson 2002; Hascakir et al. 2008, 2009, 2010; Kovaleva et al. 2010; Alomair et al. 2012; Greff and Babadagli 2013) and a great portion of them were conducted using a household cooking microwave oven. This idealistic model cannot be applied to account for the field scale performance; i.e., upscaling may not be possible. Beyond the upscaling issue, understanding the actual physics of the process and recovery potential from EM heating cannot be extracted from a microwave type experiment. To understand the efficiency of EM hating on heavy oil recovery, Bientinesi et al. (2013a) conducted laboratory experiments on EM heating of nearly 2000 kg of oilsands in a sandbox up to 200ºC using a dipolar antenna. 2.45 GHz was used to irradiate heat with a variable power (1-2 kW). The temperature of the oil sand and the boundary was recorded and in several specific points of the setup throughout the experiment. On the basis of the experimental results they concluded that EM irradiation is capable of heating oil sands, even above the boiling temperature of connate water. Another approach to test the microwave energy on heating of heavy oil and reservoir was made by Callarotti and Paez (2014). They measured the electromagnetic frequency response of heavy oil by enclosing the sample with high purity quartz vials placed in an alluminium cylindrical resonator. The experimental results of their studies indicated that the absorbed power by the oil can increase the reservoir temperature around ~18 °C which indicates the reduction of oil viscosity in electromagnetic heating but not catalytic upgrading of crude oil.

It is worth noting that the role of metal nanoparticle in reduction of heavy oil viscosity during EM heating (and other thermal methods) is significantly important to improve the mobility of oil. Metal nanoparticles are potential candidates to absorb EM waves and thereby can increase the temperature of the surroundings of the system. To investigate this, Hamedi Shokrlu and Babadagli (2010) tested the efficiencies of iron and nickel nanoparticles on viscosity reduction of heavy oil by catalytic effect. They found that the concentration, type and size of the nanoparticles can potentially influence the viscosity reduction of heavy crude oil. Later, Li et al. (2014) studied that upgrading of heavy crude by carbon nanocatalysts under microwave irradiation. They concluded that the microwave heating in presence of carbon nanocatalysts can perform the upgrading of lighter oil at 150°C. The

carbon nanocatalysts can reduce the viscosity of oil, and shorten the reaction time for upgrating the crude. As a further attempt, we propose a design of EM heating setup to improve the efficiency of this process using nanometal particles. This setup consists of a conceptually scaled sand box model (122 × 50 × 40 cm) filled with sand for application of EM heating for enhanced heavy oil recovery.

The main objectives of the experiments are to study the temperature response of the formation and heavy oil recovery under EM heating when metal nano-particles are used. In a sense, this is an improved version of the EM heating model we used in an earlier study (Greff and Babadagli 2013) in which a commercial microwave oven system was used to heat the oilsands. We propose a more “realistic” and scaled model representing a heating unit installed in a formation where heat is transferred through a porous medium made of sands.

Experimental Setup Design of RF Antenna Setup The parts of the radiofrequency (RF)/microwave heating unit attached together to generate EM power and transmit through a flexible coaxial transmission line are shown schematically in Figure 1. The RF power generator consists of (1) a power supply and (2) a magnetron heat unit. The RF power generator is connected to directional coupler through an isolator. A tuner is available between directional coupler and waveguide step transition. Coaxial cable is connected from waveguide coax transition to antenna. The antenna is placed into the application field and the entire system is controlled by software.

The RF output power level varies from 210 to 2000 W. As a high radiation preventative, 1 sec E-field probe field meter is also included for safety purposes. The suggested E-field safety limit is considered to be in the range of 60-100 V/m in Canada. The recommended maximal RF power reflection coefficient is 0.5 for the RF heating system.

Magnetron and isolator have certain temperature limits and they should be controlled at 30°C and 40°C, respectively. The joints of the lid and box and other small open portions of the sandbox that the antenna is

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attached to are properly sealed with alumina tape to prevent the leakage of radiation of EM waves.

Fig. 1. Schematic diagram of RF antenna setup.

Design of Experiment for Oil Recovery and Temperature Measurement The antenna used to generate radio waves is attached to a sandbox (reservoir model) shown in Figure 2. Round silica beads were used to create a sandpack. Fiber optic cables were used to determine temperature in the sandpack inside the stainless steel box.

Fig. 2. Instrumental setup of EM heating system with conceptual sand box.

Conceptual designs of stainless steel box and Buchner filter funnel. A conceptual stainless steel box with

dimensions 125 cm × 50 cm ×40 cm was made to contain the sands up to 3/4 of the box depth from the bottom. Silica sands (average grain size ~250-500 micron) were used to fill up the stainless steel box. The antenna was place at one side of the box (~10 cm from the one side wall of the box) through a cavity on the lid of the box. Figures 3a and 3b show the dimensions of the hole for antenna and the picture of the antenna that was used in the experiment for radiating EM radio frequency waves.

Two small holes made on the lid of the model are shown in Figure 2 (right photo). The distances from the holes to the antenna are 40 and 70 cm, through which the gas release tube and oil collection tube of two Buchner filter funnels were placed. The Buchner funnels contain oil saturated glass bead. Figure 4 shows the the Buchner filter funnel. The holes are made on top of the lid and also the bottom of the box at the same position to properly set the Buchner funnel to collect produced oil and generates gas from the lower and upper parts respectively.

Fig. 3. (a) Cavity for the antenna placed inside the box and (b) microwave antenna inside the box before putting sands to fill up the box.

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Fig. 4. Photograph of specially designed Buchner Filter Funnel for experimental purpose.

Silica beads and heavy oil mixture sample for oil recovery experiment. Heavy oil mixed silica beads were added into the Buchner funnel for the oil recovery experiment. Different amounts of nanoparticles were added

to the crude oil and silica bead mixture in the Buchner funnel. After addition of nanoparticles, the mixture was tried to homogenize by a spatula. The same procedure was followed for all samples. The used silica glass beads in this experiment were procured from Potters Industries LLC., Canada. For experimental purposes, 100 g silica beads were properly mixed with ~25 g of heavy oil. The mixture was carefully transferred to the Buchner filter funnel. The oil left at the mixing container was measured to calculate the initial amount of heavy oil (original oil in place or OOIP). The initial appearance of the silica beads and heavy oil mixture inside the Buchner filter funnel is shown in Figure 5.

Fig. 5. Initial appearance of silica beads with heavy oil inside the Buchner funnel filter before experiment.

Heavy oil with viscosity of 67,424 cP (at 23°C) was used in the experiments. The properties of the heavy oil sample are given in Table 1. Ni and Fe nanoparticles were added to the silica glass bead + heavy oil mixture in the funnel to investigate the effect of added metal nanoparticles on the oil recovery as well as the change in temperature. The nanoparticles used in the present study were procured from Sigma Aldrich, Canada. The detailed properties of nanoparticles (Ni and Fe) are given in Table 2. In some experiments, clay (Fuller’s Earth) purchased from BASF Chemical Company, Germany was used as nanoparticles instead of metal. The main composition of this clay is attapulgite. The color of the clay is yellow-ish white. The details of Buchner filter funnel model is given in Table 3. Table 1 Properties of the used heavy oil for experimental purpose. Heavy oil from eastern Oil Alberta, Canada Viscosity at 25 °C 67,424 cP Viscosity at 50 °C 5301 cP Viscosity at 90 °C 379 cP

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Density at 25 °C °API Gravity Water Content Saturates Asphaltenes Resin Aromatic

1.004 g/ml 12.46 at 60 °F 2.52 wt% 25.57 wt% 31.17 wt% 26.77 wt% 16.30 wt%

Table 2. Properties of used metal nanoparticles in the EM heating experiments. Properties Nickel metal nanoparticles Iron metal nanoparticles Assay ≥ 99% trace metal basis 99.5+ % metal basis. Form Nanopowder Nanopowder Resistivity 6.97 µΩ-cm at 20 °C 9.71 µΩ-cm at 20 °C Particle size < 100 nm 95-105 nm Boiling point 2732 °C (l) 2750 °C Melting point 1453 °C (l) 1535 °C 3 3 Density 8.9 g/cm at 25 °C (l) 7.90 g/cm Appearance Blackish Black Table 3. Properties of Buchner funnel filter. Product type Filter funnels Material Borosilicate glass Disc diameter (mm) 40 Funnel capacity (ml) 60 Stem diameter (mm) 12 Joint size near the filter 24/40 Pore size 25-25 µm porosity Total length (Bottom 55 cm funnel and top cap)

Temperature measurement and oil recovery. Oil recovery experiments were conducted by placing the two Buchner filter funnels saturated with heavy oil-silica bead mixture inside the sandpack through the holes on the box. The Buchner funnel was fully covered with sand; hence it represented a volume element of a heavy-oil reservoir heated by RF waves. The system was run at different power levels such as 500, 800, 1000, and 1200 W. The produced oil was collected from the bottom of the box through the lower tubing neck of the Buchner funnel. In all cases, the experiment was conducted up to 10 h for a general comparison of the efficiency of the power level and the effect of nano-metal/clay additives mixed with the silica beads and heavy oil mixtures into the sand formation. For Ni and Fe nanoparticles, the experiments were run for 8 h as maximum high temperature was found to be reached within this time span. The oil recovery was measured at different time intervals. The schematic diagram of the whole experimental setup is shown in Figure 6.

The temperature was recorded using Neoptix fiber cables with time-intervals during experiments. The fiber wires were placed inside the funnel attached to the heavy oil-silica bead mixture and temperature change was continuously recorded by an automatic data acquisition system.

Fig. 6. Schematic diagram of the laboratory experimental setup of EM heating.

Results and Discussion EM Heating Experiment without Metal Nanoparticles Temperature increment profile without nanoparticles Effect of different energies of power levels on temperature rise during radiofrequency heating of sand formation is shown in Figure 7. Four different power levels (500, 800, 1000, and 1200 W) were applied. In all cases, the experiments were run for 10 h and the corresponding temperatures were recorded by fiber optic cables. Interestingly, the temperatures of funnels at 70 cm distances were higher than the 40 cm distances cases after a certain time. This can be attributed to the “wall effect” of radiofrequency heating. As the funnel at 70 cm was surrounded by three walls of the stainless steel box (Figs. 2 and 6), the radiowaves were reflected from the near

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walls and again acting on the funnel. In addition, the hot surfaces of the three walls also supplied more heat to the funnels at 70 cm than located at 40 cm distance from the antenna. In case of funnel at 40 cm distance, there are also three walls present but wall along the length of the box is situated at a longer distance to be critically effective on the process. As a result, heating of the model (funnel) was influenced by two phenomena, which were stronger on the one placed 70 cm away from the antenna. Bientinesi et al. (2013a,b) also observed the similar trend of temperature profile affected by dielectric properties of the materials placed higher distance from the antenna. Hence, one may conclude that the change in the temperature profile of an EM absorbing medium is directly proportional to the distance of the EM antenna irrespective of any other influencing factor. Moreover, one should pay attention to the influences of any reflecting or absorbing materials in the system, which may affect the temperature profile increment in the negative way while working on the the practical design of EM heating applications.

Major observations from the four plots in Figure 7 are as follows: (1) In all four cases, temperature in the funnel located 70 cm away from the antenna reached 100oC within ~5,000 sec. The final temperatures reached after 35,000 sec were 113oC, 114oC, 115oC and 126oC for the 500, 800, 1000, and 1200 W cases, respectively. (2) In all four cases, temperature in the funnel located 40 cm away from the antenna reached 100 oC within ~7,500, 15,000, 15,000, and 20,000 sec for the 500, 800, 1000, and 1200 W cases, respectively. The final temperatures reached for these cases were 103oC, 106oC, 113oC and 114oC. (3) Within the range applied in these experiments, the effect of power was seen at the final temperature but increasing power yielded slower heating in both funnels.

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Oil recovery without nanoparticles at different power levels On the basis of above the observations, one may conclude that the differences in the final temperatures and time to reach these values are not critically high for the given power range. However, the effect of power on oil recovery from recovery rates and the ultimate recovery reached is highly significant. Figure 8 shows the oil recovery for four different (500, 800, 1000, and 1200 W) power levels. In all cases, oil recovery was started after few hours, which is proportional to the power applied. While it was 9 h for the 500 W case (Fig. 8a), production starting time was only 3 h when 1200 W power was applied (Fig. 8d). These times were 5 and 4 h for the 800 and 1000 W cases, respectively.

Also noticeable is the variations in the ultimate recoveries reached with the power applied. Ultimate recoveries systematically increased with power (up to 5% and 7.5% OOIP at 1200 W, while it was only 2% and 0% at 500 W for the funnels at 40 cm and 70 cm distances from the antenna respectively). Hence, the ultimate recoveries are

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not proportional to the temperature values (and profiles) given in Figure 7. This can be attributed to the effects other than heating on the change of oil properties. Up-grading oil (breaking C-S or C-C bonds) or even the change of surface properties could be possible under EM radiation field (Dreher et al. 2013). This effect deserves more investigation. Note that most of the studies on the use of EM heating are based on the reservoir heating capability of the method and rarely consider oil recovery (Bera and Babadagli 2015). Our results presented in Figures 7 and 8 reveal that these two effects should be mutually considered in selecting the optimal power.

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Fig. 8. Oil recovery efficiency of EM heating at different power levels: (a) 500 W; (b) 800 W; (c) 1000 W; and (d) 1200 W.

EM Heating Experiment with Ni and Fe Nanoparticles As seen in the previous section, the process may not be as effective as expected. More heat needs to be transferred to the reservoir and absorbed by oil to render more recovery or to obtain a more economically viable application. One of the ways to do this is to add nano-metal catalyst into the reservoir; i.e., inject to the catalyst during different thermal techniques such as in-situ combustion (Hamedi et al. 2012), microwave heating (Greff and

Babadagli 2013), and cyclic steam injection (Hamedi and Babadagli 2014a). This requires the introduction of nanoparticles at a certain stage of the application (Hamedi and Babadagli 2013, 2014a) for steam injection. How to introduce them into the reservoir is the next issue to focus on and further analysis can be done following the procedure suggested by Hamedi and Babadagli (2014b) for cyclic steam injection.

We adopted the procedure applied by Greff and Babadagli (2013) and added the nanoparticles into the model during preparation. Contrary to this study where the oil + sand + nanoparticle mixtures were exposed to microwave heating directly, we conducted the tests in a model representing a reservoir and placed this mixture in the Buchner funnel (Fig. 5) located in a sand packmodel shown in Figure 6. Two aspects of the effect of nanoparticles on the process are discussed: (1) Improvement of heating efficiency and (2) improvement of oil recovery.

Temperature increment profile with Ni nanoparticles Figure 9 a-d shows the temperature variation with time under EM heating of silica beads and heavy oil mixture in the presence of Ni nanoparticles at different concentrations (0, 0.1, 0.7 and 1.5%) at 1200 W. Experiments were run until the temperature reached stabilization in each case (about 4-5 h when Ni particles were added). The following observations can be made from the plots given in Figure 9: (1) Considerably higher temperatures were observed when nickel particles were added. The ultimate temperatures reached for the funnel located 70 cm away from the antenna were quite similar regardless of the concentration. This value (200-220oC) was almost twice that of the one obtained without metal particles indicating the microwave absorption capability of Ni. (2) Similar patterns were followed in the Ni cases (Figs. 9b-d) for the funnel at 70 cm distance in the model. The initial jump in the temperature for the 0.1% Ni was much higher (160-170oC) than those of higher concentrations (100oC) (Figs. 9c-d). A decline in temperature at the late stages was characteristically observed in all three Ni cases. Further analysis is needed to clarify whether this systematic behavior is due to heat loss or to the EM wave absorption capacity of Ni particles. (3) In the case of the funnel at 40 cm distance, 0.1 and 0.7% Ni concentrations yielded similar behavior and

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the temperature profile was similar to the zero concentration case (Fig. 9a); i.e., Ni particles did not result in any additional temperature increase. When the Ni concentration was increased to 1.5% (Fig. 9d), additional 60 °C increase in the temperature was observed (up to ~175oC). (4) The distance from the antenna and boundary conditions may result in different propagation of EM waves and temperature distribution.

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Fig. 9. Effect of Ni nanoparticles on temperature profile during oil recovery and EM heating at 1200 W: (a) 0% Ni nanoparticles; (b) 0.1 % Ni nanoparticles; (c) 0.7 % Ni nanoparticles and (d) 1.5 % Ni nanoparticles.

Oil recovery with Ni nanoparticles at 1200 W For all concentrations of Ni nanoparticles, oil recovery experiments were run for 8 h. Figures 10 a-d show the oil recovery performances in the presence of 0.1, 0.7, 1.5 and 0% Ni nanoparticles, respectively. Marked increase in the recovery was observed with addition of Ni reaching 30% OOIP from the sample 70 cm away from the antenna (Fig. 10c).

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With increasing concentration of Ni nanoparticles, oil recovery increases and production starts earlier. First drop of oil was produced at 3, 2, and 2 h for 0.1, 0.7, and 1.5% Ni nanoparticle concentrations for the 70 cm distance funnel. Maximum oil recovery was found in case of 1.5% Ni and was reported as around 30% of OOIP whereas 12 and 20% of OOIP recoveries were obtained for 0.1 and 0.7% Ni concentrations (Figs. 10a-b). For comparison purposes, the case without Ni particles is shown in Figure 10d and indicates that ~4 h were needed to start the production and the ultimate recovery reached was 7.5% within 10 hours.

For the funnel at 40 cm distance, the recovery without Ni particles jumped from 5% OOIP (Fig. 10d) to 6, 12, and 16% of OOIP for 0.1, 0.7 and 1.5% Ni concentrations, respectively. The production started after 6 hours of heating without Ni particles, while this time was reduced to 5, 3, and 3 h with 0.1, 0.7, and 1.5 % Ni

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concentrations, respectively (Figs. 10a-c).

Ni nanoparticles act as microwave absorber and therefore they increase the temperature of the mixture very fast and stabilize the high temperature for 10 h, which is very important for thermal oil recovery operation. As a result of this, oil viscosity reduced faster and recovery was accelerated to higher value. In other words, Ni nanoparticles acted as catalyst in upgrading of heavy oil under thermal conditions. During microwave heating, there may be cracking reactions as small amount of water is present in the crude oil. Hence, aquathermolysis process may take place during radiofrequency heating with Ni nanoparticles.

Temperature increment profile with Fe nanoparticles Fe nanoparticles were also tested considering the cost of nano particles. Figures 11a-d show the temperature profiles of 0, 0.1, 0.7 and 1.5% Fe nanoparticle concentration cases. The trends are similar to the base case (no Ni nanoparticles) given in Figure 11a when nano particles were added and no significant improvements were obtained when Fe particles were added. The only exception was the profile obtained from the funnel located 40 cm away from the antenna with 1.5% Fe concentration. A sudden jump was observed (i.e., quicker heating) in the beginning and the temperature was stabilized to the same value of the other cases (~120oC).

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Fig. 11. Effect of Fe nanoparticles on temperature profile during oil recovery and EM heating at 1200 W: (a) 0% Fe nanoparticles; (b) 0.1 % Fe nanoparticles; (c) 0.7 % Fe nanoparticles and (d) 1.5 % Fe nanoparticles.

Oil recovery with Fe nanoparticles at 1200 W Although the effects of metal nano particles were not as strong as in the Ni cases, we observed some improvements in the ultimate recovery and time to start oil production. Based on the plots given in Figures 12ad, the following ultimate recoveries and time to start oil production were obtained from two different funnels: (1)

Recovery from 70 cm distance funnel: 7.5, 9, 10, and 13% of OOIP for the 0, 0.1, 0.7, and 1.5% Fe nanoparticle concentrations.

(2)

Recovery from 40 cm distance funnel: 5, 6, 7, and 8% of OOIP for the 0, 0.1, 0.7, and 1.5% Fe nanoparticle concentrations.

(3)

Time to start oil production from 70 cm distance funnel: 4, 3, 3 and 2 hours for 0, 0.1, 0.7, and 1.5, respectively.

(4)

Time to start oil production from 40 cm distance funnel: 6, 5, 4 and 3 hours for 0, 0.1, 0.7, and 1.5, respectively.

18

14

14

40 cm from antenna 70 cm from antenna 1200 Watt

40 cm from antenna 70 cm from antenna 0.1% Fe Nanoparticle, 1200 Watt

12

8

6

4

8

6

4

2

2

0

0 -1

0

1

2

3

4

5

6

7

8

9

10

-1

11

0

1

2

3

4

5

6

7

8

9

10

11

7

8

9

10

11

Time, h

Time, h 14

14

40 cm from antenna 70 cm from antenna 0.7% Fe nanoparticle, 1200 Watt

12

40 cm from antenna 70 cm from antenna 1.5% Fe nanoparticle, 1200 Watt

(c) 12

(d)

10

Oil recovery, % OOIP

10

Oil recovery, % OOIP

(b)

10

10

Oil recovery, % OOIP

Oil recovery, % OOIP

12

(a)

8

6

4

8

6

4

2

2

0

0 -1

0

1

2

3

4

5

6

7

8

9

10

11

-1

Time, h

0

1

2

3

4

5

6

Time, h

Fig. 12. Oil recovery efficiency of EM heating with Fe nanoparticles at 1200 W: (a) 0% Fe nanoparticles; (b) 0.1 % Fe nanoparticles; (c) 0.7 % Fe nanoparticles and (d) 1.5 % Fe nanoparticles.

Effect of Clay on Temperature Rise and Oil Recovery In an earlier attempt, Greff and Babadagli (2013) tested clays as nanoparticles in replacement of metal ones for a more economical process. In general, heavy oil reservoirs and high permeable unconsolidated oil sands contain a significant amount of clay. Their microwave heating results showed positive effects of clays on the process. With this inspiration, in the present paper the tests were repeated with Fuller’s earth clay particles.

Figure 13 shows that maximum temperatures and oil recovery of the clay experiments at 1200 W power for two different clay concentrations (10 and 30%). Clay minerals can efficiently absorb EM waves and increase the temperature of the system. Thus, temperatures values of 149 (10% clay) and 160°C (30% clay) were obtained for the funnel at 70 cm distance. The final temperature reached for the control case (no nanoparticles) was 120 oC (Figs. 9a and 11a). Temperatures at the funnel 40 cm away from the antenna were found to be 144 and 150 °C for

10 and 30% clay concentrations, respectively. The control case temperature (no nanoparticles) was 110 oC (Figs. 9a and 11a).

Despite ~40 °C additional increase in temperature in the presence clay, oil recovery was not high. The ultimate oil recoveries with 10% concentration of clay were 3 and 6% of OOIP for the funnels at 40 and 70 cm distances, respectively. No oil was recovered for 30% clay concentration from both funnels. These values were even lower than the control case (Fig. 8d). This can be attributed to the negative effects of clay, such as reverse wettability and permeability reduction. Addition of clay can increase the temperature of the system but the oil recovery is reduced. Clay has also irreversible oil absorption power which can substantially reduce oil recovery. Figure 14 displays the photographs of the samples after microwave exposure at 1200 W. It is clear that in the case of 10%

Temperature (°C) and Oil recovery (% OOIP)

clay, very little oil was recovered (whitish color glass beads) and no oil was recovered from the 30% clay sample.

180

10% Clay 30% Clay

160 140 120 100 80 60 40 20 0 fF rature o Tempe

t 70 unnel a

cm fF rature o Tempe

t 40 unnel a

cm m very fro Oil reco

Funnel

m at 70 c

ery from

v Oil reco

Funnel

m at 40 c

20

Fig. 13. Temperatures and oil recoveries of clay experiments at 1200 W power.

Fig. 14. Samples after electromagnetic heating at 1200 W with (a) 10% clay and (b) 30% clay.

Upgradation of Heavy Oil by EM Heating Viscosity reduction of heavy oil requires decomposition and breaking of large asphaltene molecules. The dissociation energy of the C-S bonds is less than the dissociation energy of the other bonds of the molecules. Therefore, they are the first bonds, which will start to dissociate and as a result the viscosity of oil will be reduced. The dissociation energy can be provided by exothermic chemical reactions between metal particles and oil phase in the presence of heat (Hascakir et al. 2008; Hamedi Shokrlu and Babadagli 2014a). To clarify these effects, the viscosity of oil samples was measured using a Brookfield DV-II+ Pro viscometer. Temperature dependent viscosity variations of the produced oil after microwave exposure with and without nanoparticles and original dead oil viscosity are shown in Figure 15. The initial dead oil viscosity was found to be 67,424 cP at 25°C. The microwave treated oils at 1000 and 1200 W power levels show lower viscosity than original oil. When Ni nanoparticles (1.5% at 1200 W) were used, the viscosity of the collected oil was reduced even more.

The reduced viscosity indicates that the cracking and upgrading of heavy oil occurred during the heating of oil under microwave exposure. In case of 1.5% Fe, viscosity of the produced oil sample also shows reduced values of viscosity. Therefore, during the microwave heating with and without metal nanoparticles, there should be dissociation or breakage of large asphaltene molecules causing a reduction in oil viscosity.

To further investigate the upgrading and change in oil characteristics, gas chromatography (GC) was run with original oil and oils after microwave exposure. The composition of the original and irradiated oil is shown in Figure 16. Original oil shows a higher mass percentage yield than the treated oil under microwave with and without metal nanoparticles. Mass percentage yields were also higher for the oil treated at 1200 W for Ni nanoparticles than Fe. The experiment was run for 10 h for 1200 W, therefore, in some cases it showed lower mass percentage yields. Ultimately, the mass percentage yields for original oil were higher than the produced oil after microwave exposure.

This apparent upgrading could be caused by preferential removal of lighter

hydrocarbons, thermal cracking, or reactions between the hydrocarbons and the steam (if generated from the existing water).

Original oil 1200 Watt 1000 Watt 1.5% Ni Nanoparticle, 1200 Watt 1.5% Fe Nanoparticle, 1200 Watt

Viscosity, cP

100000

10000

1000

100 20

30

40

50

60

70

80

90

100

Temperature, °C Fig. 15. Viscosity of original oil and produced oil by microwave heating with temperature.

22

100 90

Mass% yield

80

Original Oil 1200 W 1.5% Ni at 1200 W 1.5% Fe at 1200 W

70 60 50 40 30 20 10 0 100

200

300

400

500

600

700

Temperature, °C Fig. 16. Mass percentages of original oil and microwave treated wave with and without metal nanoparticles.

Comparison of the Results with and without Metal Nanoparticles From the data and results presented in this paper, a comparative analysis can be performed. Figure 17 shows the maximum temperatures and corresponding oil recoveries for the funnel placed at 70 cm from the antenna. The results of all experiments are tabulated in Table 4.

Out of all powers, nanoparticle type, and concentration cases, maximum temperature and oil recovery were obtained using Ni nanoparticles with 1.5% concentration. Also, increasing power level resulted in a slight increase in temperature but significant change in recovery. Interestingly, in every case, the funnel located furthest (70 cm distance) from the antenna showed a higher recovery and temperature rise. Hence, for given distance range, radiofrequency heating produced homogeneous heating in the model.

Although they contributed to oil recovery, Fe nanoparticles were not as effective, especially from a heating point of view as compared to Ni. The results also reveal that there there is an optimal concentration of nanoparticles. Different photographs of the upper surfaces of the silica beads and heavy oil mixture are given in Figure 18 for

visual validation of the recovery performances presented above. It is worth mentioning that the metal nanoparticles in EM heating method are used for multi-purposes, i.e., the absorption of EM radiation to act as localized heat source to the surroundings due to EM energy transfer (Keblinski et al., 2006) as well as catalytic action on upgrading of heavy crude to reduce its viscosity (Greff and Babadagli 2013, Hamedi-Shokrlu and Babadagli, 2010, 2011, 2013, 2014a).

Temperature (°C) and Oil recovery (% OOIP)

240 220 200

Tempertaure at 40 cm funnel Temperature at 70 cm funnel Oil recovery at 40 cm funnel Oil recovery at 70 cm funnel

180 160 140 120 100 80 60 40 20 0

W W W W W W W W W W 500 800 1000 1200 , 1200 , 1200 , 1200 , 1200 , 1200 , 1200 i i i e e e % N .7 % N .5 % N 1 % F 7 % F 5 % F 1 . 0 0 1 0. 0. 1. Fig. 17. Comparative results of EM heating with and without metal nanoparticles.

24

Fig. 18. Silica beads and heavy oil mixture (a) before microwave exposure; after microwave exposure at (b) 800 W, (c) 1000 W, (d) 1200 W, (e) 1.5% Ni nanoparticle with 1200 W, and (f) 1.5% Fe nanoparticles with 1200 W. Table 4. Results of EM heating experiment with and without metal nanoparticles. Exp. No.

Particle type

Nanopartic le conc. (wt %)

Microwave power level (W)

Heating time (h)

Maximum temperature reached (°C) 40 cm 70 cm from from antenna antenna

Total oil recovery (% OOIP) 40 cm 70 cm from from antenna antenna

1 2 3 4 5

None None None None Nano-nickel

0 0 0 0 0.1

500 800 1000 1200 1200

10 10 10 10 8

103 106 113 114 121

113 114 115 125 170

0 1.2 4.4 5.3 6.2

2.2 4.5 6 7.5 12.9

6 7 8 9 10

Nano-nickel Nano-nickel Nano-iron Nano-iron Nano-iron

0.7 1.5 0.1 0.7 1.5

1200 1200 1200 1200 1200

8 8 8 8 8

144 175 112 115 121

171 194 119 124 127

12 16 6 7 8.8

20 31.8 8.8 9.8 13.1

EM Heating Experiment with Wet Sand Note that all the experiments were run within a sandpack composed of dry sand only. Existence of water in the system would affect electromagnetic heating. Therefore, oil recovery and temperature increment experiments were also performed for wet sand at 1200 W. The sands were made partially wetted with addition of water. The experiments were run for 10 h; the same time period as the dry sand experiments. Temperature profiles are shown in Figure 19. The increase of temperature is slower than the dry sand case (Fig. 11a) and the stabilization temperature was lower for both 40 and 70 cm distance cases. What is more interesting is that the funnel 40 cm away from the antenna showed faster heating that the 70cm distance one. This is opposite to the dry sand case given in Figure 11a.

High water content produces a large amount of steam, which will change the heating process and temperature distribution as can be observed in Figures 11a and 19.

Also, in this closed system, the vaporised water

condensates on the metal box (boundaries of the sandpack model). This may affect the radiation heating, which makes the 70 cm away funnel heat quicker. Therefore, drying of the sand was not fully possible and increase of temperature was slower in the case with wet sand than with dry sand.

100 90

Temperature, °C

80 70 60 50 40

70 cm from antenna 40 cm from antenna Wet sand, 1200 W

30 20 10 0

10000

20000

30000

40000

50000

Time, seconds Fig. 19. Temperature profile of wet sand at 1200 W.

Conclusions In this study, we introduced a conceptual sand box experimental study for heavy oil recovery from oilsands by electromagnetic heating. The interstitial water present in the heavy oil and moisture content of sand help to absorb the microwave energy to reduce the viscosity and enhance the production. We showed to what extent this process can be improved by adding nanoparticles into the model (reservoir). The following conclusions can be withdrawn from the observations and analyses made in this work.

1. Different powers (500, 800, 1000, and 1200 W) were used in a 2.45 GHz microwave generator. It was observed that temperature and oil production increase with an increase in microwave power level. 1200

26

W produced the maximum amount of oil and achieved the maximum equilibrium temperature of 125°C. Due to laboratory safety limitations, we were unable to test higher powers. 2. As metal nanoparticles are good microwave absorbers, Ni and Fe nanoparticles were added to the oilsands model. Different concentrations (0.1, 0.7 and 1.5 wt%) were used at a high power levels (1200 W). 1.5% Ni and Fe nanoparticles produced the largest amount of oil and achieved the highest temperature (194 and 127°C for the funnel at 70 cm distance from the antenna respectively due to wall effect). Ni and Fe nanoparticles produced 32% and 13% OOIP, respectively. Hence, Ni nanoparticles are more effective than Fe nanoparticles during EM heating. 3. Most of the earlier studies on the use of EM heating are based on the reservoir heating capability of the method and rarely consider oil recovery. Our results revealed that these two effects should be mutually considered in selecting the optimal power. In fact, ultimate recoveries were not proportional to the temperature values (and profiles), and even though the same temperature (heating) values were reached at different powers, oil recoveries might significantly change. This can be attributed to the effects other than heating on the change of oil properties. Up-grading oil (breaking C-S or C-C bonds) or even the change of surface properties could be possible under EM radiation field (Dreher et al. 2013). This effect deserves more investigation. 4. Viscosity measurement and GC analysis of produced and original oil samples indicate upgrading of heavy oil by electromagnetic heating. Significant reduction of viscosity was observed after microwave exposure. GC analysis showed the reduction of mass fraction of heavy as well as light components of the original oil after heating under microwave exposure. Upgradation was enhanced when metal nanoparticles were used and Ni was found to be more effective than Fe in this process. 5. Clay (as nanoparticles) can increase the temperature of the system but the oil recovery is reduced when clay is used as additive in EM heating. But, having clays in the system might inversely affect oil recovery due to the blockage of pore spaces or unfavorable wettability conditions. Only 6% of OOIP recovery was obtained in case of the funnel at 70 cm (wall effect) from the antenna with clays addition, which is similar to the control cases (no nanoparticles) at 1200 W. 6. One experiment was run with wet sand at 1200 W to compare the heating conditions with the dry sand case, which was used as a medium in all experiments. Temperature rise with wet sand was not high in the

funnel at 40 cm from the antenna (maximum temperature reached was 98°C only). The produced steam condensated and reduced the sand temperature in the surroundings of the funnels. In this case, higher temperature was reached at the funnel located 40 cm from the antenna than the one at 70 cm distance. This is opposite to what was observed in the dry sand cases.

Acknowledgements This research was conducted under the second author’s (TB) NSERC Industrial Research Chair in Unconventional Oil Recovery (the industrial partners are CNRL, SUNCOR, Petrobank (Touchstone Inc.), Sherritt Oil, APEX Eng., PEMEX, Saudi Aramco, and Husky Energy) and an NSERC Discovery Grant (No: RES0011227). This paper is a substantially revised and modified version of SPE 176113 that was submitted to be presented (presentation was not made, paper included in the proceedings) at the SPE Asia Pacific Oil & Gas Conference and Exhibition held in Bali, Indonesia, 20–22 October 2015.

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HIGHLIGHTS 1. We introduced a conceptual experimental study for heavy oil recovery by electromagnetic heating. 2. We showed to what extent this process can be improved by adding nanoparticles. 3. Ni nanoparticles are more effective than Fe nanoparticles during electromagnetic heating. 4. Using clay (as nanoparticles) can increase the temperature but the oil recovery is reduced.

30