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Effects of Nanoparticles on Thermal Conductivity
Enhancement in Different Oils
Mustafin, Robert
Mustafin, R. (2018). Effects of Nanoparticles on Thermal Conductivity Enhancement in Different
Oils (Unpublished master's thesis). University of Calgary, Calgary, AB.
http://hdl.handle.net/1880/109361
master thesis
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UNIVERSITY OF CALGARY
Effects of Nanoparticles on Thermal Conductivity Enhancement in Different Oils
by
Robert Mustafin
A THESIS
SUBMITTED TO THE FACULTY OF GRADUATE STUDIES
IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE
DEGREE OF MASTER OF SCIENCE
GRADUATE PROGRAM IN CHEMICAL ENGINEERING
CALGARY, ALBERTA
DECEMBER, 2018
© Robert Mustafin 2018
ii
Abstract
In recent years, depleting amount of energy extracted from conventional oil reservoirs, together
with an industrial shift towards heavy oil/bitumen recovery has become more pronounced. Today,
steam injection heating methods are primary used by industry for heavy oil/bitumen recovery.
However, these methods have a detrimental effect on the environment, high-energy consumption
and limited application, especially for the deep reservoirs. Therefore, there is a high priority to
investigate alternative approaches. To date, the most progressive alternative technique that has
proven its potential during pilot-plant tests is “Nanocatalytic in-situ heavy oil/bitumen upgrading
via hot-fluid injection,” developed by Catalysis and Adsorption for Fuels and Energy (CAFE)
research group at the University of Calgary. Nevertheless, continual improvement of the technique
is of utmost importance. Therefore, this study is intended for proposal of new nanofluid system
suitable for high-temperature injection into the reservoir with consecutive heavy oil/bitumen
upgrading. New nanofluid system posses enhanced thermal properties represented by thermal
conductivity, which is one of the critical parameters that affects the performance of oil recovery.
Experimental studies on the thermal conductivity of oil-based medias were conducted and the
effects of particle type, solid mass fraction, particle size distribution and temperature augmentation
were evaluated. The results showed that the thermal conductivity values of nanofluid systems is
substantially higher than that of the base fluids. Thermal conductivity enhancement trend was
found to increase with increase in particle dosage. The highest thermal conductivity enhancement
was determined for nanofluids with smaller average hydrodynamic particle size. Moreover,
presence of chemo-physical interactions between nanoparticles and base fluid led to additional
intensification of thermal conductivity. Also, the temperature augmentation in a range from 80 to
110°C exhibited a positive effect on thermal conductivity enhancement of vacuum residue-based
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nanofluid system. The present study holds great promise for the application of nanoparticle
technology in enhancing heavy oil upgrading and recovery.
Keywords: nanofluids, thermal conductivity, oil recovery, in-situ upgrading, nanoparticles.
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Acknowledgements
“The harder the struggle, the more glorious the triumph.”
This work would not have been possible without the financial support of the Tatarstan Ministry of
Education that sponsored my MSc study in the University of Calgary. I am especially indebted
to my supervisor Dr. Nashaat N. Nassar for his support, comprehensive understanding, believe in
myself, motivational speeches, helpful discussions and vital life advices – without him, this work
would be impossible not only to finish but even to start. Dr. Nassar made this education process
unforgettable, I have memories that I will cherish forever. Dr. Nassar Group for Nanotechnology
Research is the most profound research group that I had a pleasure to be a part of, the group that
changed my attitude from such fundamental things as life views to the educational process overall.
My special thanks go to Dr. Abdallah Manasrah, a postdoctoral fellow in Dr. Nassar’s group, who
become more than my mentor during these years of education – my friend and my brother, who
guided me for the whole road from the beginning, kindly sharing his knowledge and experience,
uncomplainingly providing feedbacks on my thoughts and writing, always reminding me of that I
am almost there. I wish to extend my gratitude to Prof. Pedro Pereira-Almao, Dr. Gerardo
Vitale, Dr. Azfar Hassan, Dr. Josefina Scott, Dr. Carlos Scott, Dr. Lante Carbognani, and Dr.
Hossein Hejazi for their valuable assistance through my research.
I am grateful to all of those with whom I have had the pleasure to work and interact with during
this research: Afif Hithnawi, Nedal Marei, Tatiana Montoya, Ghada Nafie, Maysam Alnajjar,
Farad Sagala, Milad Kamkar and all members of Dr. Nassar Research Group for Nanotechnology
Research. Each of the members has provided me extensive personal and professional guidance and
taught me a great deal about both scientific research and life in general.
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The most important, I wish to express my deepest gratitude to all my family back home:
grandparents Vyacheslav and Ludmilla, dauani Roza parents Ramil and Eleni, sister Emma, aunt
Nonna, uncle Yura, cousins Eugeniya and Vlad. I would gratefully acknowledge my friends:
Musa Gilyazov, Timur Kamalov, Daniel Belyalov, Nail Salyahov-Aminov, Adel Zamaliev and
Ildar Gusamov for their mental help and being beside even when far away. Also, I would like to
acknowledge Maxim Krekhovetski and Torleif Landsgaard, who helped me with editing this
manuscript and will always remind me of how small and tiny the world is.
The last but not the least, I am profoundly thankful to Nastasya Pavlova, love of my life, the light
of my soul, the warmth of my heart, for giving me the companionship and emotional support I
needed to embark on and complete this arduous journey. Thank you from the bottom of my heart.
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Dedication
Моей семье
Моим друзьям
Моей любви, Настасечке
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Table of Contents
Abstract ............................................................................................................................... ii Acknowledgements ............................................................................................................ iv Dedication .......................................................................................................................... vi Table of Contents .............................................................................................................. vii List of Tables ..................................................................................................................... ix
List of Figures and Illustrations ...........................................................................................x List of Symbols, Abbreviations and Nomenclature .......................................................... xii
Chapter 1 Introduction .........................................................................................................1 1.1 Global energy demand ...............................................................................................1 1.2 Unconventional oil deposits and their challenges ......................................................3
1.2.1 Shale oil and oil sands .......................................................................................4 1.3 Thermal recovery processes and their challenges ......................................................8
1.3.1 Hot water flood ..................................................................................................9 1.3.2 Steam injection processes ................................................................................11
1.3.2.1 Steam flooding .......................................................................................11 1.3.2.2 Cyclic Steam Stimulation .......................................................................13 1.3.2.3 Steam Assisted Gravity Drainage ..........................................................14
1.3.3 In-situ combustion ...........................................................................................16 1.4. NPs integration in oil industry ................................................................................19
1.4.1 NPs in EOR .....................................................................................................20 1.4.1.1 IFT reduction .........................................................................................21 1.4.1.2 Wettability alteration and disjoining pressure ......................................22
1.4.2 Damage inhibition by NPs ...............................................................................23
1.4.3 In-situ heavy oil/bitumen upgrading ...............................................................26 1.5 Thermal conductivity study .....................................................................................29 1.6 Objectives ................................................................................................................34
Chapter 2 Experimental Work ...........................................................................................36 2.1 Materials ..................................................................................................................36 2.2 Preparation of nanomaterials ...................................................................................37
2.2.1 CuSi nanocrystalline particles synthesis .........................................................37 2.2.2 Copper oxide NPs synthesis ............................................................................38 2.2.3 CuAeg NPs synthesis ......................................................................................38
2.3 Characterization of synthesized nanomaterials ........................................................39
2.3.1 X-ray diffraction (XRD) ..................................................................................39 2.3.2 Textural properties ...........................................................................................39 2.3.3 Scanning electron microscopy (SEM) .............................................................40
2.4 NF systems preparation ...........................................................................................40 2.5 Characterization of nanofluids .................................................................................41
2.5.1 Thermal conductivity measurements ...............................................................41 2.5.2 DLS analysis ....................................................................................................43 2.5.3 Viscosity measurements ..................................................................................43
Chapter 3 Results and Discussion ......................................................................................45
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3.1 Materials Characterization .......................................................................................45
3.2 TC measurements ....................................................................................................51
3.2.1 Mineral oil base fluid .......................................................................................51 3.2.2 Glycerol base fluid ..........................................................................................55 3.2.3 VGO base fluid ................................................................................................60 3.2.4 Effect of 2wt% CuAeg NPs on VGO and VGO-VR mixture base fluids .......63 3.2.5 Effect of CuAeg NPs on TC and viscosity of VR ...........................................65
Chapter 4 Conclusion and Recommendations ...................................................................69 4.1 Conclusion ...............................................................................................................69 4.2 Recommendations ....................................................................................................70
References ..........................................................................................................................71
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List of Tables
Table 3.1 Crystalline domain sizes obtained by XRD. ................................................................. 47
Table 3.2 Surface area and particle size obtained from BET analysis .......................................... 48
Table 3.3 Viscosity and TC value of VGO-VR mixtures ............................................................. 63
x
List of Figures and Illustrations
Figure 1.1. Proven-probable conventional oil discoveries and consumption rates . ....................... 2
Figure 1.2. Unconventional oil definition by physical characteristics............................................ 4
Figure 1.3. Total proven global bitumen and heavy oil reserves .................................................... 6
Figure 1.4. Bituminous oil sands products...................................................................................... 7
Figure 1.5. The current thermal EOR methods. .............................................................................. 9
Figure 1.6. Cold water flooding method of oil recovery. ............................................................. 10
Figure 1.8. Steam flooding method of oil recovery ..................................................................... 12
Figure 1.9. Cyclic Steam Stimulation method of oil recovery. .................................................... 13
Figure 1.10. Steam assisted gravity drainage method of oil recovery ........................................ . 14
Figure 1.11. In-Situ Combustion method of heavy oil recovery. ................................................. 16
Figure 1.12. Toe-to-Heel Air Injection method of oil recovery. .................................................. 18
Figure 1.13. Schematic representation of role of nanoparticle application in oil industry. .......... 20
Figure 1.14. Schematic representation of IFT reduction mechanism ........................................... 21
Figure 1.15. Schematic representation of different wettability states of oil reservoir. ................. 22
Figure 1.16 Mechanism of oil displacement by disjoining pressure ............................................ 23
Figure 2.1 Schematic representation of the two-step preparation method of nanofluid. .............. 41
Figure 2.2. TC measurements with a thermal needle TP08 .......................................................... 42
Figure 2.3. TP08 needle probe.. .................................................................................................... 42
Figure 2.4 Field Point Relay system. ............................................................................................ 43
Figure 3.1. XRD patterns and their comparison with targeted materials...................................... 46
Figure 3.2. Corey-Pauling-Koltun (CPK) surface representation ................................................. 48
Figure 3.3. SEM images of CuSi nanocrystalline material at different magnifications. .............. 49
Figure 3.4. SEM images of CuO nanocrystalline material at different magnifications. ............... 50
Figure 3.5. SEM images of CuAeg nanocrystalline material at different magnifications. ........... 50
xi
Figure 3.6. TC enhancement as a percent value against particles concentration for MO-based
fluid. ...................................................................................................................................... 52
Figure 3.7. Hydrodynamic particle size distribution from DLS analysis for MO-based fluid. .... 54
Figure 3.8. TC enhancement as a percent value against particles concentration for glycerol-
based fluid ............................................................................................................................. 56
Figure 3.9. Hydrodynamic particle size distribution from DLS analysis for glycerol-based
fluid. ...................................................................................................................................... 58
Figure 3.10. Schematic representation of aggregation of NPs inside solution ............................. 59
Figure 3.11. TC enhancement as a percent value against particle concentrations for VGO-
based fluid. ............................................................................................................................ 61
Figure 3.12. Hydrodynamic particle size distribution for VGO-based fluid. ............................... 62
Figure 3.13. TC values against VR concentrations in VGO (a) and TC percentage
enhancement against VR concentration in VGO (b). ........................................................... 64
Figure 3.14. (a) TC values over temperature and (b) TC enhancement as a percentage over
temperature. .......................................................................................................................... 66
Figure 3.15 (a) Viscosity values at 80°C for VR and VR-CuAeg NF system against shear
rate, and (b) viscosity values at fixed shear rate against temperature increase for VR and
VR-CuAeg NF system. ......................................................................................................... 67
xii
List of Symbols, Abbreviations and Nomenclature
Symbol Definition
AVR
BET
Athabasca Vacuum Residue
Bruneur-Emmett-Teller
CSS
COSH
DLS
EG
Cyclic Steam Stimulation
Combustion Override Splitproduction
Horizontal-well
Dynamic Light Scattering
Ethelene Glycol
EOR
ICS
IFT
MO
MF
MP
Enhanced Oil Recovery
In-Situ Combustion
Interfacial Tension
Mineral Oil
Microfluid
Microparticle
NF Nanofluid
NP Nanoparticle
SAGD
SEM
THAI
TC
Steam Assisted Gravity Drainage
Scanning electron microscopy
Toe-to-Heel Air Injection
Thermal Conductivity
UD
VAPEX
Ultradispersed
Vapor Assisted Petroleum Extraction
xiii
VGO
VR
XRD
Vacuum Gas Oil
Vacuum Residue
X-Ray diffraction
1
Chapter 1 Introduction
It is clear from the current world situation that it will take indefinite time to omit the systemic use
of hydrocarbons. Thus, until alternative sources of energy are found to replace petroleum, the
growth of energy consumption from the oil and gas industry will continue [1]. Moreover,
consistent depletion of conventional petroleum reserves has led to greater reliance on
unconventional oil resources to fill the energy demand [2]. Accordingly, researchers and oil and
gas companies have deemed necessary to improve thermal enhanced oil recovery (EOR)
techniques used for unconventional oil reservoirs. Our sphere of interest aims to develop an
environmentally-friendly and cost-effective approach suitable for unstable oil market conditions,
by implementing the latest scientific developments in nanotechnology to the petroleum industry.
For this special case, a novel technique, “in-situ catalytic upgrading of heavy oil/bitumen via hot
fluid injection,” was proposed and developed by CAFE group at the University of Calgary. The
main goal of the current work is to provide insight on one possible way of improving this novel
technique by enhancing thermal properties of injecting fluid, which might lead to high oil
recovery/upgrading rates.
This introductory chapter includes the literature review on global energy demand, thermal methods
of heavy oil recovery, challenges faced during thermal extraction, review of application of
nanoparticles in EOR, and a summary of current research on nanofluids thermal conductivity
enhancement.
1.1 Global energy demand
The global energy consumption growth rate has been remarkably stable since mid-19th century [3]
and shows no evidence of further backward trend up to the 2040 year [4]. By the mid-21st century,
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the global total energy demand might be 35% higher than that in 2017 [5]. At present, abundant
amount of energy needed to maintain the balance between demand and supply are extracted from
more than 70,000 conventional oil fields [6]. However, from these large number of fields only 507
giant fields account for more than 60% of total production [7], of which 261 are already
experiencing a decline in output [8]. Campbell et al. [9] in 1998 proposed the widening gap
between growing demand and declining production of energy from conventional oil reservoirs.
Later in 2010, this forecast was confirmed by Owen et al. [6], who plotted proven-probable
conventional oil discovery and consumption rates based on data from open sources which can be
seen in Figure 1.1.
Figure 1.1. Proven-probable conventional oil discoveries and consumption rates [6].
3
One can note from Figure 1.1 that the peak of conventional oil discoveries in the 1960s wherein
the last giant field was found [10], subsequent declining trend of new discoveries suggesting the
opportunity to find new fields with significant oil output is improbable. Eventually, additional
production from small fields will become insufficient to compensate dwindling of large fields’
production. To set this inevitable problem aside for the time being before alternative sources of
energy will extend their influence on the energy market, it is necessary to investigate thermal EOR
methods applicable for unconventional oil reservoirs. Heavy oil, oil shale and oil sands contain a
significantly greater amount of energy in comparison with conventional reservoirs on a global
scale and according to Schlumberger oilfield review, up to 70% of total oil resources reside in
unconventional reservoirs [11].
1.2 Unconventional oil deposits and their challenges
General definition of unconventional oil can be expressed by its physical and chemical
characteristics. Even highest-quality unconventional oil is significantly heavier, denser, more sour
than conventional oil and traditional industry’s methods can neither recover nor transport it [12].
The graphical distinction of unconventional oil from conventional by its API gravity and viscosity
is represented in Figure 1.2.
4
Figure 1.2. Unconventional oil definition by physical characteristics. Modified from Banerjee
[13].
1.2.1 Shale oil and oil sands
To date, approximately 600 deposits of shale oil are found on a worldwide scale [14]. The majority
of them are located in the United States, Canada, Russian Federation, Democratic Republic of
Congo, Jordan and some European countries [15], [16]. Shale oil is a fine-grained sedimentary
rock and can be identified as “immature oil” since it has not been affected by naturally occurring
heat long enough for actual crude oil to be generated and expelled out from the source rock [15].
The composition of oil shale is mainly characterized by high concentration of kerogen ~15%,
which consists of carbon ~80%, hydrogen ~10%, as well as small amounts of oxygen, nitrogen
and sulfur [17]. If these components are represented by a sufficient amount of polyaromatic
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compounds and oxygenated functional groups, then the kerogen mainly consists of aliphatic
structures which are inclinable to form hydrocarbon vapors in response to pyrolysis, that can be
processed into oil and gas [15]. However, oil shale industry faces challenges in economically
feasible extraction as it is a highly energy-consuming process [18]. There are two major methods
that are commonly reported for oil extraction from oil shale reservoirs: surface and in-situ
processing. The latter one involves drilling wells into the oil shale then proceeding to insert electric
heaters, or by introducing heated gases or liquids to heat up the rocks and then collecting the oil
as it is freed from the rocks [19]. This in-situ method is the key in developing deep oil shales, as
richest oil shale is buried beneath hundreds of meters of rocks, where mining is inapplicable [20],
[21]. However, the most commonly used method is still surface mining. It is simpler and a less
cost-intense technique but leaves enormous land use territory and destroys all the vegetation in the
area [22]. In surface processing, the oil rich-rock is brought to the surface after mining and heated
to very high temperatures ranging from about 350°C to 550 °C with addition of hydrogen [22],
[23]. In general, mechanism for thermal cracking of the oil shale consists of two steps. First,
decomposition of the kerogen to bitumen, gas and carbon residue and second, subsequent
decomposition of the bitumen to oil, gas and char [24]. Initially, higher concentration of valuable
bitumen ~10-18% is contained in oil sands, that are sedimentary rocks composed of quartz, clay,
water, and high content of sulfurs ~ 7% [12]. The world’s largest deposits of bitumen are located
in the Canadian Province of Alberta including Athabasca McMurray, Cold Lake Clearwater, and
Peace River Bluesky-Gething regions [13]. Globally, 21 other countries have bitumen resources,
including the USA, Venezuela, Republic of Congo, Madagascar, Nigeria, and Russian Federation
[25]. However, the USA and other countries’ bitumen reserves are currently considered to be
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smaller in comparison to Canada’s deposits and majority of them are harder to recover, due to
different physical and chemical compositions. The pie chart shown in Figure 1.3 is representing
global proven bitumen and heavy oil reserves.
Figure 1.3. Total proven global bitumen reserves (a) and bitumen reserves together with heavy
oil (b). Chart modified from Hein et al. [25]
Understanding the complex chemistry of bitumen in oil sands is of utmost importance. Its main
distinctions from conventional petroleum are poor concentration or even devoid of hydrocarbons
with low molecular weight such as alkanes and the large quantity of high molecular weight
polymeric materials [26], [27]. In respect to bitumen in general, Athabasca bitumen is rich in
aromatic, paraffinic, olefinic and heterocyclic structures (N, O, and S) with various functional
groups; presence of trace metals and organometallic compounds were identified as well [27]. Such
intensely complex hydrocarbon mixture can be synthetically processed into valuable products as
gasoline, diesel, jet fuel, etc. as shown in Figure 1.4 [28].
7
Figure 1.4. Bituminous oil sands products
Overall, bitumen can be treated as a constitute of four fractions: saturates, aromatics, resins and
asphaltenes [29]. The difficulty of Alberta oil sands underground recovery is strongly interrelated
with extremely high viscosity of bitumen for which asphaltene content (16-25% for Athabasca
bitumen) is ultimately responsible [26]. Thus, where applicable, surface mining of bitumen is the
most common method to use. For example, in the northern part of Alberta where overburden depth
of bituminous sands is relatively shallow and less than 75 m [13], an undeniable advantage of the
mining process is low energy consumption with overall possibility to recover more than 90% of
the bitumen in place [30]. However, the major problem with the mining industry is that it leaves a
severe environmental footprint by huge surface land use and creation of oil sands tailings as a
8
byproduct of bitumen extraction process. Such tailings are a complex mixture of residual toxic
solids, containing ∼90 wt% water [31]. The water contained in such mixture is hard to separate
from the solids and other chemical compounds (e.g. naphthenic acid) as the stable matrix is formed.
To date, the total size of tailing ponds in Alberta is covering an area of more than 220 km2 [32].
At the same time with environmental challenges, about 80% of the known bitumen reserves are
located at depths greater than 75 m and cannot be extracted by mining operations [13]. However,
most of these large amounts of oil can be recovered with application of thermal EOR processes
that are discussed in the following sections.
1.3 Thermal recovery processes and their challenges
Since 1950’s application of thermal EOR methods into the fields have been widely put to use. So
far, they have been recognized as the most advanced among EOR methods [33]. As was mentioned
previously, the most critical characteristics of heavy oil that makes primary recovery not feasible
are low API gravity and extreme-high viscosity. This is precisely why reservoir heating is
necessary to mobilize the oil in place by reducing its viscosity, allowing oil to flow to the
production well. Generally, current thermal EOR processes can be divided into two main
categories [30]: (1) processes in which hot water or steam is injected into the reservoir and (2)
processes in which heat is generated within the reservoir itself, such as the combustion processes
as shown in Figure 1.6.
9
Figure 1.5. The current thermal EOR methods.
1.3.1 Hot water flooding
Different types of injecting fluid such as natural gas, carbon dioxide, exhaust gases, and solvents
are applied in the fields, but the simplest form is a hot-water flooding (hot-water drive) [34], [35].
Water is usually preheated at the surface by boilers or heaters and then injected into a relatively
cold reservoir, sometimes downhole heat exchangers are also applied [36]. Hot-water flooding has
many similarities with conventional cold-water flooding, demonstrated in Figure 1.6, which is an
oil displacement process.
10
Figure 1.6. Cold water flooding method of oil recovery. Modified from Shah et al. [30].
Because of the temperature affect, the viscosity of oil is reduced and oil displacement from the
rocks occurs with higher efficiency than that from a conventional water flooding. This leads to
increase of oil recovery rate by at least 45% [35]. However, the heated front of the injected hot
water rapidly loses heat while penetrating deeper inside the core and quickly reaches the initial
reservoir temperature. Thus, most of the heat from injection is concentrated in the oil-depleted
portions of the reservoir [37]. Consequently, displaced oil loses its mobility while going through
regions where water has a lower temperature and becomes stored in unswept portions of the
reservoir. It leads to displacement front instability and will cause premature water breakthrough
with further reduction of the oil recovery [34]. A number of modifications aimed to improve the
11
efficiency of the process are proposed [38], but still the two main approaches used in oil industry
to heat reservoir are in-situ combustion of part of reservoir or steam injection [30].
1.3.2 Steam injection processes
In terms of field experience concerning viscous oils and oil sands recovery, steam-based processes
are the most understood of all EOR methods [34]. Similar to all thermal EOR techniques, the main
target of steam-based injection is viscosity reduction. However, it is believed that mechanisms
such as steam distillation [39], thermal expansion, emulsion drive, solution gas drive, capillary
imbibition [40], and CO2 generation also take place and play a significant role during steam
injection [41], [42].
1.3.2.1 Steam flooding
Steam flooding (steam drive) method is schematically presented in Figure 1.7. Its recovery rates
range from 50 to 60%, leading up to 75% of oil in place in some cases [43], [44].
12
Figure 1.7. Steam flooding method of oil recovery. Modified from Shah et al. [30].
The continuous injection of steam generates large amount of heat, thereby reducing oil viscosity
and together with accumulated pressure, improves the fluidity of oil towards the production well
[30]. A major characteristic property of steam flooding method is sensibility of steam injection
control: high injection rate can induce early steam breakthrough, whereas low rate will cause heat
loss [45]. Despite high recovery rates, the process has long payout and substantial operational cost,
even if compared to other steam-based thermal methods. Reports have shown that steam flooding
method is better suited for conventional oil reservoirs, as they contain more steam-distillable
components than oil sands [46].
13
1.3.2.2 Cyclic Steam Stimulation
The cyclic steam stimulation (CSS), also known as “steam soak” or “huff and puff” method, is a
three-stage recovery process (steam injection, soaking stage and production), schematically
represented in Figure 1.8.
Figure 1.8. Cyclic Steam Stimulation method of oil recovery. Modified from Shah et al. [30]
During the first stage, steam under high pressure and temperature conditions is persistently injected
into the oil-bearing zone. After the heat is fully dispersed, the hot pressurized reservoir is closed
for a period of time mandatory for the steam to “soak” the formation, consequently decreasing oil
viscosity and mobilizing the oil in sands [30]. As the reservoir temperature decreases, the well is
put into production and an occurred pressure drop allows mobilized oil to expel out from the rock
and move towards the well. Production rates are high at first, but then gradually declining as rock
14
formations begin losing the heat. Every next cycle repeats with increased steam to oil ratio, as
more heat is needed to maintain high production rates [47]. The major drawback of CSS is
comparingly low recovery factor that ranges only from 10% to 40% of oil in place, however, this
method is still considered to be applicable in regions where formation thickness is too low for
steam assisted gravity drainage (SAGD) process [30], [34].
1.3.2.3 Steam Assisted Gravity Drainage
SAGD process, schematically represented in Figure 1.9., was introduced by Dr. Roger Butler in
the late 1970s, then first tested for production in a field scale at Cold Lake in Alberta in the 1980s
[30], [48].
Figure 1.9. Steam assisted gravity drainage method of oil recovery. Modified from Shah et al.
[30]
15
In this method two nearly horizontal parallel wells, vertically separated 4 to 10 m apart from one
another, are drilled at the bottom of the thick reservoir. At the beginning of the process, both wells
can be used for steam injection before the moment when formation around wells warms up [49].
Afterwards, the bottom well turns to production regime and the top well continually serves for
steam injection. The latter generates a high-temperature steam chamber, which gradually expands
in both vertical and horizontal directions, consequently reducing the viscosity of bitumen [50].
Condensed steam and mobilized oil drive down by gravity forces to the production well from
which the fluids are pumped to the surface for further upgrading. SAGD technique is the most
commonly applied method for heavy oil/bitumen recovery; characteristically exhibiting high
recovery rates between 40-60%, but very sensitive to operational and geological conditions [30].
According to Kisman and Yeung [51], the main parameter to consider is rock permeability.
However, the effect of reservoir heterogeneity [52], oil reservoir thickness, depth of burial and
steam injection rate are of great concern [53]. The abundance of water resources and water
processing facilities are required as well: SAGD process uses up to 40 barrels of water to one
barrel of produced oil in early stage, then decreased to 4-6 barrels of water/oil [54]. Moreover,
SAGD is highly energy demanding process which exhibits necessity supply of fuel as a heat source
for steam generation. Together, it not only impeaches its cost-effectiveness amid slumping oil
prices but also generates detrimental effect represented by emission of greenhouse gases in large
quantities and produced water with high organic and metal content. These limitations led to the
development of alternative processes such as non-thermal counterpart of SAGD named vapor-
assisted petroleum extraction (VAPEX) [55], expanding solvent steam assisted gravity drainage
(ES-SAGD) [56] (wherein up to 13% of solvent is added to the steam [57]), and steam and gas
16
push (SAGP) [58]. Nonetheless, the SAGD is still one of the most successful and commonly
applied thermal technique for bitumen recovery in western Canada [37], [59].
1.3.3 In-situ combustion
In-situ Combustion (ISC) or fire flooding method, which schematic representation can be seen in
Figure 1.10, was first tried at field scale in 1920s [60]. Since that time the application of technology
is still limited and usually performed only for reservoirs whereby steam injection is not relevant
[60]. On the one side, ICS provides some indisputable benefits over other thermal EOR methods.
Instead of highly energy-consuming steam injection, viscosity reduction occurs due to flux of air
or oxygen which burns a portion of hydrocarbons in place (~10%) that heat surrounding formation
and mobilizes the flow of the unburned oil fraction [33], [61]. It leads not only to higher cost-
effectiveness by lowering production and capital cost, but environmental benefits by minimizing
the usage of natural gas, fresh water and significant reduction of greenhouse gases emission.
Figure 1.10. In-Situ Combustion method of heavy oil recovery. Modified from Shah et al. [30].
17
The main possible advantage from ISC technique is partial in-situ upgrading of crude oil which
takes place while the combustion front propagates through the oil-bearing area. Catanier and
Birgham [62] observed existence of segregated zones between the injection and production wells
and defined them as follows: burned zone, combustion zone, cracking region, evaporation and
visbreaking region, steam plateau, water bank, oil bank and initial zone. Numerous and complex
chemical reactions which occur in these zones over temperature range can be classified into two
main exothermic chemical reaction modes: low-temperature oxidation (50-350 ºC) and high-
temperature oxidation (300-800 ºC) [63], [64]. Reaction kinetics and their products are easier to
predict in boundaries of laboratory studies, but, unfortunately, in consequence of poor combustion
front controlling, which is a key operational parameter, ICS has not gained wide acceptance and
the process has not achieved the success predicted by the theory [65]. In order to overcome main
challenges such as gas override, oil banking, and viscous fingering that causes low displacement
efficiency, early gas breakthrough and gas flow channel blocking, some modification of ISC are
proposed [66]. Among other presented modifications, such as combustion override splitproduction
horizontal-well (COSH) [67], top-down in-situ combustion (TD-ISC) [68], high air pressure
injection, etc. the one that took more attention is Toe-to-Heel Air Injection (THAI) [69] and its
catalytic variation of upgrading process in-situ (CAPRI) [70], [71]. THAI process has lower
operational temperature and theoretically significantly better control of the process as the
combustion front propagates over the length of horizontally-placed producer from “toe” part of the
well to the “heel”, as shown at Figure 1.11 [30].
18
Figure 1.11. Toe-to-Heel Air Injection method of oil recovery. Modified from Shah et al. [30].
Such combination of wells together with combustion process already provide an opportunity to
obtain partially upgraded product, whereas catalytic modification CAPRI stimulates the outcome
of converted light oil by surrounding production well with refinery catalysts [34], [72], [73].
Traditionally used commercial catalysts are in mm or micrometre scale. Together with their “fixed
bed” arrangement around the production well it leads to fast deactivation of active sites due to their
small surface area and surface covering with different materials and components such as heavy
metals and residual coke present in a reservoir [72], [74]. THAI and THAI CAPRI processes still
have to overcome several challenges and need more investigation to gain wide acceptance and
application.
19
Overall, integration of commercial catalyst into oil and gas industry is not a new idea, however,
the use of nanocatalysts and nanoparticles (NPs) is different from their larger counterparts and
nowadays attracts greater attention in oil industry [75]. Huge amounts of water consumption and
high energy intensity, especially for the most commonly applied SAGD process, together with
deployment problems of traditional and novel combustion techniques questioning the feasibility
of future realization of the current technologies [76]. For the foregoing reasons, it is essential to
search for various new pathways in the field of heavy oil recovery and improve current
technologies or develop new ones to obtain environmentally friendly and cost-effective methods.
For that special case, an exceptionally appropriate solution would be an integration of NPs in
thermal EOR methods.
1.4. Nanoparticle integration in oil industry
In nanoscale, particles perform entirely differently from their large-scale counterparts and classical
physics or quantum laws can only partially explain the outstanding behavior of NPs. Since 1980’s
extensive research in nanotechnology sphere and its practical expansion into different applications
has been conducted [77]. To date, research progress on NPs has moved from the laboratory
experiments to real life applications and enabled their use in different areas such as electronics
[78], medicine [79], food agriculture [80], industrial area [81], renewable energy [82], environment
[83], etc. The development of nanotechnology also affected the oil industry, and high potential of
NPs in the upstream petroleum industry has been discovered [84]–[86]. Overall, researchers
mainly focus on NPs application in non-thermal EOR methods and formation damage inhibition,
but to this end, current interest is making much headway toward the area of heavy oil/bitumen
upgrading and recovery [87]. Some research originates in other spheres of oil industry, such as
20
exploration [88], drilling [89], water treatment [90]–[92], etc. Figure 1.12 visualizes the role of
potential application of NPs in oil industry.
Figure 1.12. Schematic representation of role of nanoparticle application in oil industry.
1.4.1 Nanoparticles in EOR
Several mechanisms for EOR with NPs such as interfacial tension (IFT) reduction, wettability
alteration, and disjoining pressure have been recently reported. The following sections briefly
discuss the aforementioned EOR mechanisms.
21
1.4.1.1 IFT reduction
IFT is one of the main parameters used to determine fluids’ movement in porous media.
Mechanism of IFT reduction can be seen in Figure 1.13. Capillary forces restrict the oil flow in
porous media [93] and their value is determined by the IFT between oil/water, rock wettability and
pore geometry [94]. Lower interfacial tension results in reduced capillary trapping, the oil pass
through pores more easily and followed up higher recovery rates can be obtained.
Figure 1.13. Schematic representation of IFT reduction mechanism between oil droplets and
water. Modified from Olajire [95].
Significant IFT reduction is already possible with surfactant addition, however, use of NPs has
provided evidence to enhance IFT reduction. Synergistic studies of surfactants and NPs have
shown that surfactant adsorption on rock surface can be reduced by integration of NPs [96], [97].
To date, alumina, titanium, zinc and zirconium oxides NPs, as well as silica-based, CNTs and
Janus (bifacial) NPs, have been proven to reduce IFT, demonstrating their potential for use as EOR
agents [98]–[103]. Hendraningrat et al. [104] used an elevated concentration of NPs and proved
direct dependence between higher NPs loading and better IFT reduction.
22
1.4.1.2 Wettability alteration and disjoining pressure
Wettability can be defined as predisposition of the fluid to adhere on rock surface in the presence
of another immiscible fluid [105]. Originally, majority of reservoirs are water-wet, but during the
oil recovery its characteristic changes to oil-wet state, which leads to a decrease in reservoir
production. Such effect results from temperature and pressure augmentation as well as chemical
and physical properties of injected fluids. These changes are also dependent on the previously
described interfacial tension between fluids present in the reservoir. Normally, to return reservoir
back to high production rates wettability alteration towards water-wet state is performed, its
schematic representation can be seen in Figure 1.14 [106].
Figure 1.14. Schematic representation of different wettability states of oil reservoir.
As one can mention, increased surface contact angel in the water-wet system will allow oil droplets
to be displaced more easily from the rock surface during recovery. In order to diminish rock/oil
interface forces and alter wettability to water-wet state, addition of NPs can be performed. NPs
rather than oil droplets can coat the rock surface and prevent further oil adhesion. For instance,
Karimi et al. [107] performed a process of wettability alteration by using ZrO2 nanofluids.
Adsorption of NPs to the rock surface and continuous slow aggregation growth were observed.
23
Obtained formation of nanotextured layer on a core surface improved water-wetting behavior of
carbonate rock. Recently, a new view of oil displacement from a solid surface has been proposed
by Wasan and Nikolov [108], who used nanofluids containing surfactant micelles in a nanometer
range. They claimed that micelles are organizing into the ordered layer between soil droplet and
surface, so-called “wedge film”, that progressively displace soil from surface as can be seen in
Figure 1.15.
Figure 1.15 Mechanism of oil displacement by disjoining pressure
Later studies proved the applicability of NPs instead of micelles [109], [110]. The dosage
increment of NPs will exert pressure on the wedge film and will favor structural disjoining which
governed by electrostatic, solvation and Van-der-Waals’ forces between the NPs [110], [111].
Disjoining pressure effectiveness realization is affected by several parameters, such as the NPs
size, their concentration, charge density, operating temperatures, salinity, and surface
characteristics [111]. Kondiparty et al. [112] concluded that higher concentration and smaller size
of NPs leads to increased disjoining pressure.
1.4.2 Formation damage inhibition by nanoparticles
According to Bennion [113], formation damage comprised of wide spectrum of processes that
might take place during different stages of oil recovery and cause reduction in the production rates.
24
It can be caused by reason of various biological, hydrodynamic, chemical, and thermal interactions
between formation pores, particles, and fluids [114], [115]. However, one of the most commonly
reported formation damage, especially for heavy oil/bitumen recovery processes, is caused by
presence of asphaltenes [116]. These hydrocarbons with extraordinary molecular weight exhibit a
tendency to deposit onto mineral surfaces [117], coherently reducing oil effective permeability and
altering wettability of reservoir to oil-wet state [118], which has an adverse impact on oil recovery.
Self-association of asphaltenes results in increased viscosity of crude oil which limits its flow in
the piping system and can cause deposition on steel surfaces of pipelines with consequent
corrosion and pipeline breaking [119]. Furthermore, in the event of oil spills probable asphaltene
adsorption onto soil grains can cause detrimental effect to nature, as the clean-up process is very
problematic. The above-mentioned and other problems such as negative asphaltene stabilization
effect on water-oil emulsion, catalyst deactivation, coke formation, etc. aimed scientific
community to investigate into implementation of NPs as efficient adsorbents for asphaltenes
removal from heavy oil. The adsorption and subsequent oxidation, pyrolysis and gasification of
asphaltenes on metal oxide NPs was introduced by Nassar et al. [120]–[126] and has since been
tested by several investigators [127], [128]. Nassar et al. investigated the adsorption/oxidation of
Athabasca asphaltenes using different metal oxide NPs (i.e., NiO, Co3O4, Fe3O4). The authors
reported a monolayer adsorption isotherm. After the adsorption process, the authors evaluated the
catalytic effect of the NPs; the oxidation temperature of asphaltene decreased by 140 °C, 136 °C,
and 100 °C relative to the noncatalytic oxidation of virgin asphaltenes in the presence of NiO,
Co3O4, and Fe3O4 NPs, respectively. Further, the NPs significantly decreased the activation
energy, confirming their catalytic activity toward asphaltene decomposition. The authors
25
confirmed that the asphaltene adsorption/oxidation is metal oxide specific. In fact, a correlation
between the adsorption affinity and the catalytic activity of the metal oxide NPs was reported,
indicating that higher adsorption affinities increase the catalytic activity. In other studies, Nassar
and coworkers have improved the catalytic steam gasification of adsorbed asphaltenes onto silica
or kaolin supported NPs and reported a significant decrease in the gasification temperature (around
600 oC in comparison with at least 850 oC with the conventional gasification process) [129]. In a
more recent study, our group has investigated the effects of different-sized NiO (80 to 5 nm) NPs
for adsorption asphaltene model molecule and post-adsorption catalytic oxidation [130]. It was
revealed that the smaller NiO NPs 5 and 15 nm, followed by the NPs of 30 and 40 nm, have the
fastest oxidative ability of Quinolin-65, which was used as asphaltene model compound. These
findings were later confirmed with real asphaltenes which evidenced that the increase in adsorption
affinity, catalytic activity and decrease of asphaltene aggregation degree are directly interrelated
with decreasing the size of NiO NPs [131]. The aforementioned studies become a precursor for
the development of low-cost and effective silicate-based NPs that might be an alternative for
metals oxide NPs. For this reason, in a more recent study our research group proposed aegirine
(NaFeSi2O6, PY) as naturally-driven, new environmentally-safe and cost-effective NPs for
enhancing heavy oil upgrading and recovery [132]. It was concluded that the adsorption capacity
and affinity of aegirine NPs for Violanthrone-79 as a compound mimicking polar hydrocarbons
was the highest for NPs in the range between 30 and 60 among the different particle sizes ranging
from 1-100 nm. Moreover, followed-up oxidation reactions tests of VR-C5 asphaltenes adsorbed
on different-sized aegirine NPs were conducted at noticeably lower temperatures than origin VR-
C5 asphaltenes, proving catalytic properties of aegirine NPs [133].
26
Asphaltene adsorption and further catalytic reactions are accompanied with a reduction in density
and viscosity of the crude oil, providing significant advantages such as improved fluid flow in
porous media and further transportation possibility of deasphalted crude oil via pipelines [134].
1.4.3 In-situ heavy oil/bitumen upgrading
As it was mentioned in previous sections, heavy oils and bitumen transportability via pipeline
systems is not conceivable without a priori upgrading which favors their viscosity reduction,
removing corrosive substances and asphaltenes. Traditionally, such effect is obtained by the use
of cost-intensive surface upgrading facilitates via applying severe heat/pressure conditions or use
of diluents [135, Ch. 6]. Surface upgrading projects require key investments to produce synthetic
crude oil (SCO) and capacity of existing facilities is not enough to cover raw bitumen production
amounts, thus, around 57% of total bitumen remained non-upgraded in the 2017 year, and only as
small as 4.8% were upgraded in-situ. Moreover, surface upgraders are hazardous industrial
facilities, in 2016-2017-year period explosions and leaks on plants led to sufficient ex-situ bitumen
upgrading production cut. In the absence of new planned projects, together with complicated
marked conditions, in-situ upgrading growth is expected to gain attraction by following years
[136]. Some projects for in-situ upgrading of heavy oil/bitumen already have been tested at pilot
plants and a few of them implemented at field scales: previously described THAI CAPRI process
[69], [73], steam distillation [137], solvent-based propane deasphalting [138], visbreaking [139],
hydrogenation and hydroprocessing [140], aquathermolysis [141].
Upgrading of heavy oil/bitumen in-situ via hot fluid injection with ultra-dispersed nanocatalysts
is a novel technique which minimizes an environmental footprint and requires significantly less
operational costs than traditional thermal recovery methods [142]. In this approach, the reservoir
27
itself acts as a high-temperature reactor wherein such chemical reactions hydrocracking,
hydrotreating, etc. are conducted under catalytic hydrogenation [143]. The obtainable product has
high quality and can be transported via pipelines without use of diluents [144], [145]. For the
process to be successful several bullet points need to be satisfied: 1) transportation of nanocatalysts
through the sand medium inside the formation; 2) presence of hydrogen injection to mobilize
heavy oil/bitumen and co-reactants; 3) maintain sufficient temperature and pressure conditions for
targeted upgrading degree [76]. It should be noted that catalytic upgrading of heavy oil/bitumen
in-situ via hot fluid injection is a new approach and available published literature is limited.
However, recent studies have already proven economic and environmental predominance of this
approach over other commonly applied thermal recovery methods, conferring its possibility to
become “next generation” of oil sands industry improvement [146].
In 2013 Coy [147] prepared experimental simulation of hot fluid injection in sand pack media,
using Athabasca vacuum residue (AVR) as a carrier for tri-metallic (NiMoW) nanocatalysts and
dispersed hydrogen. It was proven by this study that in-situ upgrading with ultradispersed (UD)
catalysts suspended in AVR is plausible since an increase API gravity and a reduction in viscosity
of oil in place were observed. In addition, irreversible retention of nanocatalysts on porous media
throughout the whole reactor was detected. Deactivation of nanocatalysts was not observed during
the experimental test. Late 2013, Hashemi [143] conducted experiments with VGO as a carrier
fluid for the same UD tri-metallic catalysts. He confirmed retention of nanocatalysts inside the
porous media with their possibility to enhance the quality of produced liquids. The targeted
transport depth can be achieved by manipulating a number of factors, such as injection
temperature, pressure and flow rate. As well, he claimed that transport of nanocatalysts is possible
28
with VGO as the carrier fluid and increasing its concentration enhances recovery of bitumen.
Furthermore, catalytic upgrading coupled with hydrogen injection enhanced the
hydrodesulfurization and hydrodenitrogenation reactions, leading to less environmental impact.
Silvia in 2016 [148] performed experiments that operated at near reservoir conditions for
Athabasca and Mexican reservoirs. In her work, she used VR as a carrier for the same UD
trimetallic nanocatalysts and hydrogen injection. She came to the conclusion that VR acts as heat
carrier at the same time, providing required amount of energy for hydroprocessing reactions.
Moreover, the presence of exothermic reactions was observed, which plausibly helped the
confined oil to expel out from the matrix with subsequent increased oil recovery rates. Hovsepian
in 2016 [146] proposed a two-dimension bench-scale plant in order to investigate the production
and upgrading mechanism of the novel technology. His experiments were based on the injection
of VR, containing UD NiMoW nanocatalysts, same as in previously mentioned studies, and
moderated flow of hydrogen. He verified the choice of using VR as an injecting fluid, as its
reactivity and heat capacity is the highest among other crude distillates, whereas economic value
is the lowest. As well, he confirmed the improvement of the feedstock if the product is maintaining
its stability. His study included life cycle assessment modelling which demonstrated that the
catalytic upgrading in-situ via dense hot fluid injection could produce synthetic crude oil that met
requirements of pipeline transportation, while generating enough VR to maintain the stability of
the process. Moreover, process could produce less greenhouse gases emission in comparison to
SAGD. In 2017 a study by Rodriguez [149] indicated that the key to a successful in-situ upgrading
technology depends on the ability to achieve high conversion levels of the VR fraction while
controlling the formation of coke precursors, which will minimize potential damage that it may
29
cause. He claimed that such levels only achievable with the use of catalysts. Additionally, his study
confirms Coy’s and Hashemi’s findings that nanocatalysts retention on reservoir surface with
monotonic decrease from enter to the exit of porous media. Needed to mention here, that no
agglomerations of nanocatalysts were observed in injecting fluid dispersion. In 2015, Suarez [150]
performed research focused on understanding the main mechanisms which can cause heavy-oil
production during nanocatalytic in-situ upgrading process. Outcomes from his experiments
demonstrated that the UD nanocatalysts play an important role in upgrading not only oil in place,
but a carrier fluid (VR in his case) as well. He claims, that increased recovery factor from 30% to
60% is possible in carbonate rocks. Another valuable finding was his analytical model, in which
he mentioned that thermal conduction plays a significant role in nanocatalytic in-situ upgrading
process.
In my thesis, continious expansion of hot fluid injection approach is attempted, but from an
alternative focus point. Our primary target is to propose new naturally-driven nanofluid system
with enhanced thermal properties represented by thermal conductivity, as I believe it will have
favorable effects on heavy oil/bitumen upgrading and recovery rates.
1.5 Thermal conductivity study
Thermal conductivity (TC) is a property of a material to conduct heat, and a higher TC value is
responsible for faster heat transfer through the material. Conduction is the primarily heat transfer
mechanism in thermal EOR methods, and forming high TC is a key parameter to conduct heat
transfer in a reservoir [151]. Therefore, higher TC of reservoir will lead to an increase of its heating
rates followed up by greater oil production. However, Sommerton et al. [152] concluded that linear
TC decrease, and reservoir temperature increase are in direct dependence with each other. Due to
30
specific properties of a reservoirs core and its volume components, the oil sand formation can lose
up to 25% from the initial TC value while experiencing temperature augmentation from original
to steam/hot fluid injection temperature [153]. Thus, it is of utmost importance to investigate TC
of hot fluid injection in order to obtain higher upgrading degree and higher recovery rates.
To the best of our knowledge, no research has been published in terms of TC enhancement for
thermal EOR methods or upgrading purposes. One exceptional study conducted by Berna Hascakir
et al. [154] who investigated the addition of Fe, Fe2O3 and FeCl3 microparticles (MPs) with average
diameter more than 10 µm under 0.1wt% and 0.5wt% into the shale oil. It was reported that MPs
increased TC of the system, caused a reduction in the viscosity of the shale oil and subsequently
enhanced oil recovery in laboratory conditions. The authors believed that their results stem from
intensified heat transfer by the presence of large MPs. However, their findings more probably
attributed to catalytic properties of ferrum powders, rather than MPs effect on TC enhancement.
The authors applied electrical heating which creates an electrical field which, in turn, stimulates
adsorption and catalytic reactions that lead to observed viscosity reduction and enhanced oil
recovery [155]. Even though observed TC increase and heat transfer intensification might be
attributed to MPs introduction, the injection of such large particles inside the reservoir should be
avoided as it can cause pore clogging and additional flow resistance. A few studies are presented
in terms of TC enhancement in boundaries of thermal recovery processes. Barahoei et al. [156]
proposed water and ethylene glycol (EG)-based stabilized CuO nanofluid systems for enhancing
TC of reservoir. They reported that injection of water-based CuO nanofluid led to TC enhancement
of the core up to 48% at highest NPs concentration. It should be mentioned that application of
water is not suitable for severe temperature conditions that can be faced during thermal EOR and
31
more study should be done on this area. However, their proposed mechanism of reservoir’s TC
enhancement formulated as “TC of reservoir enhances due to occurrence of conductive paths by
NPs saturation on core surface” sounds entirely plausible. One more study on enhanced TC of
porous medium with CuO-based nanofluid is performed by Rokhforouz et al.[157], however, only
numerical. They claimed that it is possible to enhance heat transfer of reservoirs by injection of
nanofluid with increased TC. Injection of water-based CuO nanofluid with concentration 0.01 M
led to effective TC increase in 11.7%. Moreover, it was found that TC enhancement trend
experiencing an increase with decreasing core porosity and CuO concentration increment. Another
study reported by Shokrlu and Babadagli [158] proved that the presence of different CuO and iron
NPs/MPs leads to higher TC value and faster distribution of heat during thermal recovery
processes. Worth mentioning here that outcomes from their study confirmed that the effect of NPs
is more noticeable than that of MPs.
The aforementioned studies have proven the occurrence of TC enhancement and consequent heat
transfer intensification during thermal recovery processes with the presence of MPs/NPs. Thus, it
is profoundly important to study their effects on TC enhancement of injected fluid. However,
information available on this topic is not enough to elaborate mechanisms that stand behind the
TC enhancement phenomenon of oil medium. Moreover, to the extent of our knowledge, no one
reported the effects of NPs on TC enhancement of such complicated media as VGO nor VR, that
might be used as a catalyst carrier during hot fluid injection where SAGD is inapplicable or as
alternative to it. For this reason, the decision was made to investigate more deeply into
conventional TC enhancement applications with further expansion of obtained knowledge to
thermal EOR application.
32
The single-phase heat transfer fluids such as water, engine oil, glycerol, transformer oil, etc are
mainly used in process industries, chemical and thermal power plants. However, their heat transfer
performance is relatively poor due to their low TC values. Addition of solid particles with respect
to enhancement in TC value was first proposed and observed by Maxwell in 1881 [159]. Almost
century later, Masuda et al. [160] dispersed Al2O3, SiO2 and TiO2 MPs in a base fluid and
confirmed TC enhancement, however, major problems such as particle sedimentation were faced.
To overcome this drawback, Choi in 1995 proposed that nanometer-sized particles can be
suspended in industrial heat transfer fluids to enhance their TC values, later the author proposed
the term nanofluids (NFs) for this new class of engineered colloidal fluids. Metal oxides NPs such
as Al2O3 and CuO are the most common and inexpensive NPs used by many researchers in their
experiments [161]. Other metal oxide NPs such as MgO, Fe2O3, SiO2, TiO2 and ZrO2 [162]–[164];
metal NPs such as Cu, Au, Ag and Fe [165], different carbon materials like carbon nanotubes,
graphite and diamonds are used as well [161], [163]–[166]. To the best of knowledge, carbon-
based materials such as carbon nanotubes (CNT), multi-walled carbon nanotubes (MWCNTs) and
single-walled carbon nanotubes (SWCNTs) exhibiting the highest TC enhancement due to their
disparate TC properties, but in our work their use was avoided due to the expensiveness of
materials and our target to have naturally-driven NPs with catalytic properties. As copper by itself
is inexpensive, highly conductive and well-understood material, for this study it was decided to
fix three types of NPs containing copper.
The TC enhancement trend of NF system being favourably affected by decreasing particle size
was claimed firstly by Lee et al. in 1999 [167]. Later such relationship was proven by most of the
studies [163], [165]. However, Pac and Cho [168] based on their results from experiments with
33
metal oxides came to conclusion that better heat transfer performance and greater TC enhancement
can be obtained by introducing particles of larger size. Beck et al. [169] sustained this assumption
by testing Al2O3 NPs ranged from 8 to 282 nm in water and ethylene glycol. As well, such
conclusion can be done by comparing results from Xie et al. [170], Wang et al. [171] and Das et
al. [172] who investigated Al2O3 water-based NFs with different NPs size. Hwang et al. [173] also
found that that CuO (33 nm) NPs has more significant effect on TC enhancement base fluids when
compared to smaller-sized SiO2 (12 nm) NPs. From these contradictious findings, it was decided
to fix one of copper-based materials for such particles type which shows an existence of micronic-
scale particles. As our target is to test the effect of particles that at the same time would exhibit
catalytic properties, an appropriate choice would be copper-silicate materials, also as known as
Egyptian blue or cuprorivaite material (CaCuSi4O10). The catalytic properties of copper-silicate
were investigated by Manasrah [174] who successfully performed catalytic oxy-cracking of
petcoke into water for humic acid production. The second chosen copper-based NPs that do exhibit
catalytic properties, but are significantly smaller in size, are as known as nano-pyroxene or aegirine
NPs (NaFeSi2O6, PY), whose surface were doped with ~7.5% of copper. Their catalytic properties
in catalytic oxidation of visbroken residue-C5 asphaltenes were discovered and proved by
Hmoudah [133]. A third type of copper-based material was decided to fix for traditional CuO NPs,
as it is one of the most-studied material in boundaries of TC enhancement.
Study of base fluid and its effect on TC enhancement is not well-understood yet and very limited
reliable information is available in the literature. In general, it can be taken into consideration from
Timofeeva et al. [175] and Moosavi et al. [176] outcomes that TC enhancement is higher for base
fluids with initially lower TC value. As well, it was reported that viscosity might have an effect on
34
TC enhancement. Tsai et al. [177] concluded that higher viscosity of base fluids leads to lower TC
increase. Thus, mineral oil and glycerol as base fluids with different initial TC values and
viscosities were chosen for screening experiments along with VGO. Effect of temperature
augmentation on TC enhancement of NF systems overall shows upward trend, linear or non-linear,
with respect temperature increase [163], [165]. However, temperature range is usually limited to
60°C, only a few studies investigated TC under higher temperatures. As our focus is proposing a
NF for hot fluid injection, temperature experiments were decided to carry out for proposed NF
system with particle type that exhibited the highest TC enhancement during the screening
experiments.
1.6 Thesis objectives
The main objective of this thesis is to propose a new nanoparticle-based injecting fluid system for
future investigations in the boundaries of study “In Situ Upgrading of Bitumen/Heavy Oils via
Nanocatalytic Hot Fluid injection.” The specific objectives are:
1. Prepare different types of copper-based nanocrystalline materials (7.5Cu-doped
FeNaO6Si2, PY; copper-silicate (CaCuSi4O10); and CuO), confirm their structural identity
and investigate their textural properties using X-Ray Diffraction (XRD), Bruneur-Emmett-
Teller (BET) test, and Scanning electron microscopy (SEM) analysis. Determine particle
size distribution inside medias by applying Dynamic Light Scattering (DLS) analysis.
2. Investigate experimentally the effects of NPs/MPs type, size and concentration on thermal
conductivity of mineral oil, glycerol and VGO. Provide a plausible explanation of
mechanisms that stand behind TC enhancement.
35
3. Determine and optimize the lead nanocrystalline material type and concentration which
exhibited the highest TC enhancement among presented NF systems.
4. Conduct TC experiments using VR as the matrix for the injecting fluid with proposed lead
NPs under elevated temperature.
36
Chapter 2 Experimental Work
This chapter includes the list of used materials as well as description of nanocrystalline material
preparation methods. In addition, the chapter introduces two-step method of NF/MF systems
preparation followed-up by TC measurements procedure for NF/MF systems.
2.1 Materials
In this study, for copper-doped aegerine (7.5Cu-dopped FeNaO6Si2, PY named in boundaries of
this study as CuAeg) NPs preparation, the following chemicals and reagents were purchased from
Sigma-Aldrich (Ontario, Canada): sodium hydroxide (NaOH) (99 wt.% purity), anhydrous ferric
chloride (FeCl3) (97 wt.% purity), sulfuric acid (H2SO4) (98 wt.% purity), cupric acetate
monohydrate (Cu(CH3COO)2.H2O)(99 wt.% purity), sodium silicate (27 wt. % SiO2, 10.85 wt%
Na2O).
For preparation of copper-silicate (CaCuSi4O10, named in boundaries of this study as CuSi)
material, the sequential chemical reagents were purchased as well from Sigma-Aldrich and used:
nitric acid (HNO3), 70 wt% purity; cupric acetate monohydrate (Cu(CH3COO)2.H2O), 99 wt%
purity; sodium silicate (27 wt% SiO2, 10.85 wt.% Na2O); calcium hydroxide (Ca(OH)2,), 99 wt%
purity; and 99 wt% purity sodium hydroxide (NaOH, VWR, Ontario, Canada).
For copper oxide (CuO) NPs preparation, copper (II) nitrate (Cu(NO3)2) precursor, 98% purity;
was purchased from Sigma Aldrich, Ontario, Canada.
For preparation of NF systems four types of oils were used: vacuum residue from Athabasca
bitumen (obtained industrially by Suncor Energy Inc. at their upgraded facilities), vacuum gas oil
(obtained from Nexen, Alberta, Canada), glycerol (obtained from Sigma-Aldrich Ontario,
37
Canada), mineral oil was purchased from Calumet Penreco LLC, Pennsylvania, USA. All
chemicals were used as received without further purifications.
2.2 Preparation of nanomaterials
2.2.1 Synthesis of CuSi nanocrystalline particles
The CuSi nanocrystalline materials were synthesized using a co-precipitation method followed by
a thermal treatment. First, 12 mL of nitric acid was carefully diluted into 600 mL deionized water
under magnetic stirring (300 rpm) to prepare an acidic solution, this step was followed by the
addition of 10.254 g copper (II) acetate. Second, after complete dissolution of copper (II) acetate
in the acid solution, approximately 45.492 g of sodium silicate was gradually added and agitated
for 5 min until homogenized solution was achieved. Afterwards, by the addition of NaOH pellets
under magnetic stirring (300 rpm), an increment of pH level to 8.0-8.5 was achieved and a blue
gel was formed. This gel was allowed to stand for 10 min in order to ensure the stability of pH
level in a range of 8.0-8.5. Then the solution was filtered and washed with deionized water under
vacuum suction at room temperature conditions in order to remove excess salts. Subsequently,
filtered product was allowed to stand under vacuum suction with circulating air through it for 15
min. After that, 3.762 g of calcium hydroxide was added and gently mixed with the wet cake until
a smooth homogeneous pale blue paste was obtained. The pale blue paste was dried overnight in
an oven at 200 oC, then grinded using a marble mortar and pestle and calcined in a muffle furnace
at 850 C for 3 h with a heating ramp of 10 C/min. The furnace was then cooled down to room
temperature and the powdered CuSi nanocrystalline materials were obtained.
38
2.2.2 Synthesis of copper oxide nanoparticles
The copper (II) oxide (CuO) NPs were synthesized by calcination method from copper (II) nitrate
(Cu(NO3)2) precursor. 10 g of Cu(NO3)2 were powdered in porcelain capsule and immersed into
Barnstead 62700 Furnace for 12 h under 300 oC with the heating step rate 15 C/min. After
calcination, black CuO NPs powder was obtained, cooled overnight and grinded for the further
characterizations.
2.2.3 Synthesis of CuAeg nanoparticles
CuAeg NPs were prepared by controlled time and low-temperature hydrothermal synthesis route.
First, an acidic solution was prepared by careful addition of ~12.798 g of concentrated H2SO4 to
65 g of deionized water under magnetic stirring (300 rpm), followed by dissolving ~9.023 g of
anhydrous FeCl3 in diluted sulfuric acid solution and subsequent dissolution of ~4.534 g of
Cu(CH3COO)2×H2O. Second, basic solution was prepared by dissolving ~21.507 g of NaOH in
45 g of distilled water under magnetic stirring (300 rpm) and then, 43.329 g of sodium silicate was
added to this alkaline solution and agitated until complete homogenization. Further, an acid
solution was slowly added to the basic solution under 300 rpm and stirred for 15 min at 25 ºC to
produce a homogeneous fluid-like brown gel. Then, the prepared gel was transferred to a 300 mL
stainless-steel PARR reactor (series 2950), heated up to 180 ºC and allowed to stay for 72 h with
agitation at 300 rpm. After reaching the desired crystallization time, substance was cooled down;
filtration and washing with distilled water were carried out to obtain pH level close to 7, and then
the gel was allowed to dry overnight. Finally, the dried mass was grinded until homogeneous
powder and CuAeg NPs were obtained.
39
2.3 Characterization of synthesized nanomaterials
2.3.1 X-ray diffraction (XRD)
To identify the structure of the obtained nanomaterials, X-ray diffraction (XRD) analysis was
conducted, providing crystalline structural identity to targeted materials. XRD was also performed
in order to estimate particle crystalline domain size by using X-ray Ultima III Multi-Purpose
Diffraction System (Rigaku Corp., The Woodlands, TX) with Cu K radiation operating at 40 kV
and 44 mA with a -2 goniometer. The analyzer had a 0.5 mm in depth glass sample holder that
was filled with uniformly distributed material for analysis and provided scans in the range of 3–
90° 2-θ degrees using a 0.02° step and a counting time of 1.0° per min. The crystalline domain
sizes of the prepared NPs were estimated using the Scherrer’s equation as implemented in the
software JADE by fitting the experimental profile to a pseudo-Voigt profile function, and then,
calculating the full width at half maximum of the peak.
2.3.2 Textural properties
To investigate surface area and porosity of the prepared material, Bruneur-Emmett-Teller (BET)
tests were carried out using a surface area and porosity analyzer (TriStar II 3020, Micromeritics
Instrument Corporation, Norcross, GA). Before the analysis, samples were dried and pre-treated
inside the sample holder cells, with a flow of nitrogen gas and simultaneously heated up to 423 K
overnight. After that, the pre-treated samples were submitted to nitrogen physisorption at 77 K to
produce the adsorption-desorption isotherms. Finally, using BET equation the surface area of NPs
was estimated.
40
2.3.3 Scanning electron microscopy (SEM)
A field emission electron microscope Quanta 250, manufactured by FEI, was a type of scanning
electron microscope (SEM) that was used to investigate size and morphology of the prepared
materials. The samples for analysis were prepared by placing tiny amount of powder over a carbon
tape. Then the carbon tape sample holder was taped in order to allow an extra amount of powder
to release out. After that, the tape with material powder was inserted inside the microscope
chamber. Selected images of materials were taken by analyzer under different magnifications.
2.4 Nanofluid systems preparation
Two-step preparation method was used to prepare all tested NF systems. First, nanocrystalline
materials were produced as dry powders, as explained in Section 2.2. Second, a specified amount
of nanopowder was slowly and gradually added under magnetic agitation force (300 rpm) to
previously weighted 80 mL of base fluid under room temperature conditions. Afterwards, solution
was allowed to stir for 2 h. For high-viscous VR-based NF system preparation, it was decided
firstly to heat VR up to 190˚C to decrease its initial viscosity and only then gradually add NPs into
the media under 300 rpm magnetic stirring. The same heating temperature for VR and equal
agitation force were applied to prepare VR-VGO based matrix and VR-VGO NF systems.
Schematic representation of the two-step method is shown in Figure 2.1. In order to physically
stabilize NF/MF systems after magnetic stirring by breaking Van-der-Waals’ forces between
NPs/MPs, ensuring better distribution of NPs/MPs, it was decided to transfer the prepared
solutions to ultrasonic bath with 2700 GHz for 60 min.
41
Figure 2.1 Schematic representation of the two-step preparation method of nanofluid.
2.5 Characterization of nanofluids
2.5.1 Thermal conductivity measurements
Samples for TC experiments were collected right after sonication process and placed in such way
to ensure equal conditions of measurements for each sample. Measurements were performed with
the use of a TP08 probe (Hukseflux, Holland;) which was connected to a personal computer via
FieldPoint system (National Instrument, USA). Figure 2.2 shows an image of the complete TC
setup.
42
Figure 2.2. TC measurements with a thermal needle TP08 inserted into tested media (1) and
connection to personal computer via FieldPoint system (2).
TP08 is a probe that offers the possibility to perform a practical and fast measurement of thermal
conductivity (or thermal resistivity) of the medium in which needle is inserted at a high accuracy
level +/− (3% + 0.02%); operational temperature ranges from -55 to +180 °C [178].
Figure 2.3. TP08 needle probe. The probe consists of a needle (3) with a single thermocouple
junction (6) and a heating wire (5) which is inserted into the medium. In the base (2), a
temperature sensor (4) is mounted. The needle is connected to PC by a built-in cable.
43
The analyzed thermal conductivity parameters were measured and registered every three seconds
over a period of 200 seconds; synchronization with PC had established via Field Point relay system
which was fulfilling the role of controller unit for data collecting and voltage supply (Figure 2.4).
In order to determine the TC of the analyzed materials, a function of the amount of heat released
by a heater installed inside the probe was presented graphically against a natural logarithm of time
and automatically interpreted. The thermal conductivity of each sample was analyzed in 5
replications each of 2 rounds of measurements right after complete NF/MF system preparation and
temperature stabilization, then averaged to obtain final value.
Figure 2.4 Field Point Relay system.
2.5.2 Dynamic light scattering analysis
Dynamic Light Scattering (DLS) analysis was performed to estimate the average hydrodynamic
particle size of NPs in the base fluid, where applicable. For this purpose, the Zetasizer Nano Series
system from Malvern Instruments Ltd. was utilized to analyze the size of solid particles in liquid media.
2.5.3 Viscosity measurements
Viscosity values for base fluids available for measurements under room temperature conditions
were evaluated using DV2T Viscometer. The rheological behavior of VR and VR-based NF was
44
evaluated using a rheometer (MCR 302, Anton Paar) equipped with a 25 mm cone and plate (a
cone angle of 1 and truncation of 47μm) geometry at temperature range from 80 to 110 ºC.
45
Chapter 3 Results and Discussion
To investigate the effect of in-house prepared copper-based nanomaterials on thermal conductivity
(TC) enhancement, XRD, BET and SEM analyses for the prepared powders were conducted first.
Then, the effects of different types of NPs on TC enhancement of chosen base fluids was
investigated. First, synthesized CuSi, CuO and CuAeg nanomaterials were tested under different
concentrations (wt%) in mineral oil (MO), glycerol and vacuum gas oil (VGO) base fluids in order
to detect the highest TC enhancement among the prepared nano/microfluid (NF/MF) systems.
Second, material type and concentration with the best effect on TC enhancement were selected to
propose NF for high-temperature applications, then TC measurements were conducted under
elevated temperatures for the lead NF.
3.1 Material characterization
Figure 3.1 shows the XRD patterns for in-house prepared materials in comparison with the
reported values of targeted material from the COD database: cuprorivaite #010850158, ternorite
#1011148, and aegirine #9000327 pdf cards for CuSi, CuO, and CuAeg powders, respectively.
Sharp peaks appearing in the expected positions (COD file numbers) confirmed the formation of
the crystalline material to all synthesized powders. Positions and relative intensities of the
diffraction peaks of the samples are in a great agreement with previously reported studies [133],
[174], [179].
46
Figure 3.1. XRD patterns and their comparison with targeted materials for a) CuSi, b) CuO, and
c) CuAeg materials.
47
Table 3.1 displays the obtained crystalline domain sizes for the prepared particles that were
estimated with the commercial software JADE [180] by fitting the experimental profile to a
pseudo-Voigt profile function and calculating the full width at half maximum (FWHM) of the peak
using the Scherrer’s equation.
Table 3.1 Crystalline domain sizes obtained by XRD.
Particle type Crystalline domain size by XRD (nm)
CuSi 93.0 0.5
CuO 15.6 1
CuAeg 10.3 2
As seen in Table 3.1, CuO and CuAeg NPs have lower crystalline domain sizes than CuSi, that
might favorably affect TC enhancement as smaller-sized NPs can possibly enhance TC much
better [163], [165]. Moreover, surface area plays a significant role in TC enhancement, as heat
transfer takes place at the surface of the particles [181]. For this reason, BET analysis was
conducted to determine surface area of synthesized nanomaterials. In addition, to get an insight
about surface atomic structure, the optimized (001) surfaces of presented nanocrystalline materials
are depicted in Figure 3.2. Figure 3.2a is obtained from work of Sebakhy et al. [182], who prepared
7.5Ni-doped Aegirine, which atomic structure should be similar to our CuAeg. In our work, instead
of Ni, dispersion of the metallic Cu clusters on the surface of the aegirine-carrier was
accomplished. Figure 3.2b represents top and side views of CaCuSi4O10 (CuSi) and Figure 3.2c
represents surface of 15 nm spherical CuO NP.
48
Figure 3.2. Corey-Pauling-Koltun (CPK) surface representation of the surface (001) of (a) CuAeg,
(b) CuSi (left part represents side view of the surface, right part is top view) ; representation of a
15 nm spherical nanoparticle (c) CuO. Blue atoms represent copper atoms, red atoms represent
oxygen, yellow atoms represent silicon, dark green atoms represent sodium while the light green
represents calcium and light blue atoms represent iron.
As seen in Figure 3.2., significantly more Cu atoms is dispersed on a surface of CuO NPs, which
might be one of the possible factors for higher TC enhancement. However, according to the
literature [163]–[166], TC enhancement is more dependent on particle size. Thus, to get an idea
about particle size, an estimation of the actual particle diameter (assuming an equivalent spherical-
size particle) for prepared materials was performed. This was accomplished by using the measured
specific surface area and the derived equation 𝑑 = 6000 ⁄ (𝑆𝐴×𝜌material) [182], where 𝑑 - particle
size in nm, 𝑆𝐴 is the experimentally measured specific surface area (m2 /g), and - material density
(g/cm3). The obtained results can be seen in Table 3.2.
Table 3.2. Surface area and particle size values obtained from BET analysis.
Particle type CuSi CuO CuAeg
BET surface area
(m2/g) 0.6 3.0 151
BET particle size
(nm) 2945 307 11
49
Referring to Table 3.2, the largest surface area was obtained for CuAeg NPs, which means the
possible highest TC enhancement as significantly more surface-liquid interaction will be
happening inside the media. Estimated particle diameter calculated for CuAeg NPs was the
smallest among the presented materials and in a good agreement with the average crystalline
domain sizes obtained by XRD. However, for CuO and CuSi particles diameters obtained with
BET are significantly higher than the respective crystalline domain sizes. Taking into
consideration their low surface areas, it can be suggested that these two prepared nanomaterials
were aggregated producing particles comprising smaller ones. To sustain or dispose of this
assumption and also to investigate the morphologies of the prepared materials, SEM analysis was
conducted. Obtained SEM images of CuSi, CuO and CuAeg under different magnifications are
presented in Figures 3.3, 3.4, and 3.5, respectively.
Figure 3.3. SEM images of CuSi nanocrystalline material at different magnifications.
It can be seen from Figure 3.3. that CuSi nanocrystalline material is made up of coarse fused
crystals of different sizes and shapes with characteristic steps, ridges, and terraces on the surface.
Needed to mention here that no tendency of adhesion between big particles was observed, and the
size of larger particles was in the scale of a few microns (the largest particles were between 10 and
50
30 µm), which leads to the low surface area obtained and confirms findings from BET diameter
size calculations.
Figure 3.4. SEM images of CuO nanocrystalline material at different magnifications.
Figure 3.4 shows that mono-dispersive micronic-scale dandelion-like aggregates of smaller CuO
NPs resided in spherical and rod shapes in a range of 60-450 nm. Which may be agreed on when
compared with BET and XRD data. It may be attributed to the fact that CuO NPs have tendency
to agglomerate due to their structure, high surface energy and high surface tension. Same tendency
to reside in aggregated state was observed for CuAeg NPs in Figure 3.5.
Figure 3.5. SEM images of CuAeg nanocrystalline material at different magnifications.
51
When CuAeg SEM images were compared with the XRD and BET data, they seemed to suggest
that these aggregates were composed of smaller-sized NPs in a range from 60 to 200 nm which
were more visible at higher magnifications. At the same time, elongated fibrous-like monoclinic
prismatic crystals of about 1 μm in the longest direction that look like spear point could be noticed.
This is similar to what can be observed for the natural aegirine counterparts but with a difference
in scale [133]. Noteworthy mentioning, the actual hydrodynamic size of all tested particles inside
the medias was measured with DLS analysis. DLS analysis results are presented in the following
section. In order to get permissible level of optical transparency in dilution, it was decided to fix
concertation of NPs at 20 ppm (0.002 wt%) and repeat the procedure of NF/MF preparation. After
sonication bath, DLS analysis was conducted. Needed to mention here, Zetasizer was able to detect
particles with hydrodynamic particle size up to 5 μm, whereas existence of some fused grains of larger
size for CuSi materials were found with SEM.
3.2 TC measurements
3.2.1 Mineral oil-based fluid
The TC enhancement of prepared MO-based NF systems was investigated by dispersing the
nanomaterials into the MO matrix. Figure 3.6 represents the enhancement of TC against particle
concentrations (wt%) in MO-based fluid. It is clearly seen that a general upward trend of TC
enhancement with respect to increase in particle dosage is obtained for the all tested systems. This
trend is confirmed by most of the studies, where the main factors for such a trend are related to the
type, size of particles and their interactions with the base fluids such as water, EG, various oils,
etc [165], [183]. Needed to mention here that viscosity of MO is the lowest among tested base
fluids and equals 178 cP at room temperature, initial TC value ~0.118 W/m K.
52
Figure 3.6. TC enhancement as a percent value against particles concentration for MO-based fluid.
As shown in Figure 3.6, the highest TC enhancement is observed for CuAeg NPs with the peak at
20.6% for 2wt% concentration. This enhancement is almost twice as large as TC enhancement of
MO-based fluid obtained by Chiesa and Das [184] with 1 vol% loading concentration of SiC NPs
in the presence of surfactant. It might be possible to obtain better TC enhancement results if
surfactant is employed to improve the compatibility between the added material and the oil-based
fluid [185], [186]. However, the use of surfactant is avoided in this work. The TC of surfactants is
53
lower than that of chosen base fluids, therefore, addition of it, while improving stability, will
reduce the TC of suspension [187]. Despite the fact that the use of surfactant leads to lowering of
TC value and total cost appreciation, one of the biggest disadvantages in their application is the
occurrence of foaming when the NF is flowing or experiencing temperature augmentation [188].
It would have straight adverse impacts on targeted application of our NF systems. At the same
time, surfactants might have a corrosion effect on the pipelines and unstable under high-
temperature conditions, which disables the bonding between NPs and surface modifiers [189].
Another important finding is an enhancement of TC for CuO NPs with the peak at 15% for 2wt%
dosage. At this concertation, the difference between CuO and CuAeg NPs became more
pronounced. It can be attributed to the fact that according to DLS analysis CuAeg NPs have less
tendency to form aggregations, as seen in Figure 3.7.
54
Figure 3.7. Hydrodynamic particle size distribution from DLS analysis for MO-based fluid.
For the same mass concentration, CuAeg NF systems will have remarkably more well-distributed
active material inside the MO matrix, thereby, higher TC enhancement. Such dependence of higher
TC enhancement on smaller particle size and higher surface area correlates with the results
obtained by Chopkar et al., [190], [191] who investigated the impact of Al2Cu, Ag2Al NPs on TC
of water and ethylene glycol. It was confirmed that under higher concentration the deviation of TC
enhancement between NPs of different sizes became more vivid. Moghadassi et al. [192] also
confirmed the relationship between higher TC enhancement of monoethylene glycol (MEG) and
55
smaller-sized NPs. Consequently, it is not surprising that the lowest trend of TC enhancement is
obtained for CuSi particles with the peak at 9.32% for 2wt% of particle dosage. DLS analysis
revealed that CuSi particles exhibit the strongest tendency to form aggregates, XRD detected the
largest crystalline domain size and SEM showed existence of large fused particles grains in a range
of micrometre. Viscosity of MO is low enough to create favorable conditions to settle large
aggregates and microparticles out from the solution, which leads to poor distribution and
occurrence of regions with “particle free” liquid. According to Keblinski et al. [193], such “particle
free” regions have high thermal resistance that oppositely affects TC enhancement. To prevent
sedimentation of larger particles and investigate how initially higher TC value of more-viscous
media is affected by particle dosage, glycerol-based fluid was chosen for TC measurement
experiments.
3.2.2 Glycerol-based fluid
Figure 3.8 represents the percentage enhancement in TC at different concentrations of the three
nanomaterials in the glycerol-based fluid. As shown, a similar trend of TC enhancement is
observed for all tested types of particles and the TC increases linearly with the increase in the
particle loading [165], [183], [194]. Glycerol has the highest initial TC ~0.280 W/m K and high
viscosity value of 648 cP at room temperature.
56
Figure 3.8. TC enhancement as a percent value against particles concentration for glycerol-based
fluid
Compared with MO-based fluid, the highest TC enhancement trends are still determined for
CuAeg and CuO NPs with a reduction in the TC from 20.6% and 15% to 18.3% and 14.5%,
respectively at 2 wt% concentration. Despite the fact that the effect of base fluid properties on TC
of NF/MF systems is not well-understood yet, it can be assumed that the distinction in TC
enhancement between glycerol and MO systems can be referred to their differences in viscosity
and TC values. Glycerol has higher initial TC value than MO, and according to Timofeeva et al.
[175] and Moosavi et al. [176] it leads to lowering TC enhancement trend. Moreover, it has been
57
proven by Tsai et al. [177] that the alteration of the base fluid viscosity from 4.2 to 5500 cP resulted
in a decrease in the thermal conductivity of the Fe2O3 suspension as the viscosity of the base fluid
increased. Furthermore, it was reported that the high viscous fluids reduce the ability of NPs to
interact with one another, less particle-to-particle interactions occurring inside the solution, thus
the heat transfer inside the solution is reduced [192]. In our case, lower heat transfer between the
NPs was observed in glycerol-based fluid compared with MO, leading to diminishment of TC
enhancement for CuO-glycerol and CuAeg-glycerol NF systems. Our findings can be confirmed
by a research study performed by Nikkam et al. [194] who revealed that higher-viscous diethylene
glycol-based fluid leads to lower TC enhancement in comparison with less-viscous ethylene
glycol. Worth noting here, according to DLS analysis shown in Figure 3.9 the size of CuAeg and
CuO NPs in glycerol was found to be higher than that in MO.
58
Figure 3.9. Hydrodynamic particle size distribution from DLS analysis for glycerol-based fluid.
Possibly, NPs are staying in a form of so-called “highly concentrated clusters” (HCC) [195]
without an intra-liquid level, as shown in Figure 3.10. Whereas extended agglomerates can provide
increased TC [196], as can possibly be observed for CuO-MO and CuAeg-MO NF systems, such
HCC-clustering of NPs results in undesirable TC decrease. In addition, our findings can be
affirmed by experiments performed by Hong et al. [197] who investigated the effect of
clusterization for Fe EG-based NF systems. It was revealed that larger cluster size leads to lower
TC enhancement. The fact that HCC clusters are presented in glycerol CuO and CuAeg NF systems
59
and omitting better distribution of NPs across the volume, as a result, full potential effect on TC
enhancement, can be described by the lack of sonication time as more time is needed to break Van
der Waals’ forces between NPs inside the more-viscous solution. In this study, the sonication time
was fixed and equal for all tested NF systems and deep understanding of sonication effect is out
of the scope of this thesis. Nonetheless, to support the aforementioned assumption we can refer to
work of Kwak et al. [198] who proposed that CuO NPs dispersed in an ethylene glycol have the
smallest average diameter value when the duration of sonication equals 9 h.
Figure 3.10. Schematic representation of aggregation of NPs inside solution
However, in the case of the larger-sized CuSi particles, it is not surprising that more intense effect
on glycerol TC enhancement is observed with the peak at 13.4% for 2 wt% concentration. TC
enhancement is always a synergized effect of many parameters and mechanisms, in the case of
CuSi MF the stability factor overcome higher initial TC value of glycerol-based fluid. CuSi
particles demonstrate better stability in more-viscous glycerol media than in MO as can be seen in
Figure 3.9. Consequently, a better distribution of active material across the media with less
particle-free zones existence was observed, which obviously leads to higher TC enhancement.
Based on that, it can be concluded that the mechanism mainly responsible for TC enhancement is
60
the distribution of particles inside the solution. Concurrently, the stability of NF/MF system has a
significant impact on TC enhancement as well. To fulfil the aforementioned requirements for
higher TC enhancement, we are the first group to introduce a complicated base fluid such VGO
with more complex structure for the TC experiments.
3.2.3 VGO-based fluid
Figure 3.11 represents the TC enhancement results as a function of nanomaterials concentration
(wt%) in VGO-based fluid. As expected, a significant increase in the TC of NF was observed with
increasing the concentration of NPs [163], [165], [194]. However, the TC enhancement trend of
the VGO has increasing rate different from that of MO and glycerol base fluids. This difference
can be attributed not only to the viscosity and initial TC of the base fluid but the complexity of
chemical structure of VGO [199]. Viscosity of VGO was 500 cP under room temperture and the
inintial TC value ~0.112 W/m K.
61
Figure 3.11. TC enhancement as a percent value against particle concentrations for VGO-based
fluid.
VGO as a product of distillation fractions of crude oil contains a minor amount of asphaltenes
[200]–[202] that can interact with particle surface [120], [132], [203]. Two surface-derived effects
such as interfacial tension and adsorption make the asphaltenes a vivid interface that will connect
solid sufaces to the oil matrix [204]. Therefore, the particles that involved in interaction with
asphaltenes will positively affect their distribution across the base fluid and remain stable inside
62
the solution, thus favourably affect TC enhancement. The DLS results show a good stability of
nanomaterials as presented in Figure 3.12.
Figure 3.12. Hydrodynamic particle size distribution for VGO-based fluid.
Another possible mechanism of TC enhancement could be also related to the interfacial properties
of the particles and base fluid. For example, TC of NF is influenced by a molecular-level layering
of the fluid at a solid interface [193]. It can be represented as a more-ordered interfacial shell
around the particles with higher TC value than in surrounding fluid. As the thickness of this shell
increases, there is a corresponding increase in the volume of the interface, which results in higher
63
TC enhancement. Since the CuAeg NPs exhibited the highest TC enhancement among all tested
materials with the maximum peak of 21.3%, we decided to use only this nanomaterials with 2wt%
concentration for further investigations and perform experiments using VGO-VR mixtures as a
possible injecting fluid for thermal EOR methods.
3.2.4 Effect of 2wt% CuAeg NPs on VGO and VGO-VR mixture-based fluids
Viscosities and initial TC values of VGO-VR based fluids are presented in Table 3.3. As can be
noted, continuous increase in TC and viscosity values of base fluid derives from increased VR
concentration in a matrix.
Table 3.3 Viscosity and TC value of VGO-VR mixtures
VR concentration in VGO (%) 0 5 10 15 20
Viscosity, cP 500 817 1179 1786 2750
TC value (W/m K) 0.112 0.115 0.122 0.125 0.130
The effect of VR addition to VGO on the TC value with and without NPs loading is shown in
Figure 3.13, where a) the TC values (W/m K) and b) the TC percentage enhancement between
base fluid and NF system. It is clearly seen that with increasing amount of VR from 0 wt% to 20
wt% a linear increase in TC value is observed without NPs addition. This observation can be
supported by the fact that VR contains conductive metals such as Fe, Al, Ni, V and others [205],
which might have a positive effect on TC value of VGO-VR matrix in the absence of NPs [199].
Moreover, adding NPs to the VGO-VR matrix leads to enhanced TC as well.
64
Figure 3.13. TC values against VR concentrations in VGO (a) and TC percentage enhancement
against VR concentration in VGO (b).
2wt%CuAeg-5%VR-VGO NF has lower TC enhancement rate of only 8.42% when compared to
21.3% for 2wt%CuAeg-VGO NF. This interesting finding can be described as follows; first, a
significant drop in TC enhancement occurs due to the solid status of VR at the room temperature
conditions which has a critical effect on viscosity and complexity of the base fluid after dissolution.
Second, it is possible that formation of cluster network structure of matrix being introduced after
5% of VR dosage [29], [206], [207]. This possibly means that another mechanism will be
responsible for TC enhancement with addition of NPs. Phenomenon of subsequent growth of TC
enhancement rate despite the continuous increase of initial TC and viscosity of the base fluid
containing from 5 wt% to 20 wt% of VR in VGO contradicts with previous studies [175], [177].
However, plausible explanation arises once physico-chemical interaction between NPs and media
had taken into considerations. From study of Hmoudah [133] we can extrapolate knowledge that
CuAeg NPs will tend to adsorb asphaltenes onto their surfaces, moreover, we are aware that
65
increased VR concentration in matrix leads to higher asphaltene concentration in a matrix. It was
believed that the more asphaltenes being presented in the solution, the higher possibility of NPs to
be engaged in formation of well-diffused fractal and porous structures [208], [209] across the
media. Keeping in mind, that asphaltenes exhibit amphiphilic behavior [210], it can be assumed
that adsorption process onto NPs surface from solution wherein asphaltenes are present as
associated clusters, will lead to formation of smaller-sized clusters that consist of NPs
interconnected by asphaltenes molecules. In that case, structural behavior of asphaltenes might be
mimicking the graphene-like materials in terms of heat transfer mechanism, thereby acting as heat
conductive paths inside the solution. In addition, such smaller-sized clusters will be stabilized by
short-range attractive forces between NPs and long-range repulsive forces between clusters
themselves, leading to the high stability of system [211]. As we are claiming the similarity between
the role of graphene materials and asphaltenes regarding TC enhancement and assume the
formation of network inside the solution that will be percolated by interconnected NPs, one of
plausible mechanisms to describe a phenomenon that stands behind such enhancement can be
describe by the work of Tahmooressi et al. [195]. They observed percolation network via
dispersing carbon materials to the silicone oil. As our target is proposing NF system with higher
TC value, it was decided to support our hypothesis by introducing a novel VR-based NF with the
use of CuAeg NPs and conduct TC experiments under temperature augmentation.
3.2.5 Effects of CuAeg NPs on TC performance and viscosity of VR
The effects of our proposed CuAeg NPs on TC value and viscosity of VR were studied at different
temperatures. Figure 3.14 represents a) TC values of VR-NF with and without 2wt% CuAeg NPs
loading as a function of the temperature; and b) represents percentage enhancement of TC as a
66
function of the temperature. As shown in the figure, with the temperature augmentation, both VR
and VR-based NF system experiencing an increase in TC values. In the case of VR without NPs,
it can be observed almost unnoticeable enhancement in TC which can be attributed to chemical
characteristics of media. The existence of metals, multi-hydroxy and multi-amine molecules in VR
matrix are playing role in TC enhancement under elevation of the temperature [199], [212], [213].
The high temperature will increase the mobility of these metals and thus increasing their ability
to transfer the heat.
Figure 3.14. (a) TC values over temperature and (b) TC enhancement as a percentage over
temperature.
For 2wt%CuAeg-VR NF system, the enhancement in TC is more noticeable, which correlates with
major studies on NF and their TC dependence on temperature [163], [165], [214]. A plausible
explanation of mechanism that stands behind TC enhancement is strongly interrelated with CuAeg
NPs interaction with asphaltenes. It should be pinpointed here, inside solution with sufficient
asphaltene content as VR, the asphaltene clusters tend to form a stable viscoelastic network [202],
[215], [216]. However, after addition of CuAeg NPs to the VR, the physical interaction might be
67
taken place via adsorption process which forces them for disaggregation and migration of
asphaltenes from the solution to the surface of NPs [217]. Therefore, the NPs will be a part of
viscoelastic network that will consist of smaller-sized fractal clusters of NPs interconnected by
asphaltenes. To provide evidence of smaller-sized clusters formation viscosity measurements for
VR and CuAeg-VR NF systems were conducted, the viscosity results of the VR-based fluids with
and without CuAeg NPs are presented in Figure 3.15a,b. Along with TC enhancement, a decrease
in viscosity was observed after CuAeg NPs loading and under elevation of temperature.
Figure 3.15 (a) Viscosity values at 80°C for VR and CuAeg-VR NF system against shear rate, and
(b) viscosity values at fixed shear rate against temperature increase for VR and CuAeg-VR NF
system.
The fact that decrease in viscosity aligned with reduction of cluster size was proven by the study
of Nassar et al. [217] and Eyssautier et al. [218], who confirmed that NPs could change the
aggregation mechanism of asphaltene and cease its growth. Moreover, it can be concluded that
with the temperature augmentation more small-sized clusters are formed. Higher number of
smaller-sized clusters has more effect on TC enhancement than existence of less but larger clusters,
68
as confirmed by Tahmooressi et al. [195]. However, this mechanism is not likely to be solely
responsible for TC enhancement, as it can be expressed as synergistic effect of different
mechanisms. Another potential mechanism of TC enhancement is due to the intensification of NPs
vibrations as well as the resultant micro-convection with temperature augmentation [219]. Such
NPs vibrations can play a role in more inter-cluster connections generation and coherent clusters
disassociation. In addition, asphaltenes contain multi-hydroxy and multi-amine molecules that
exhibit an increase in TC properties with an elevation of the temperature. Hence, asphaltenes will
transfer heat more effectively through the connections between NPs at higher temperatures. Since
this study is a first attempt proposing such complicated NF for high-temperature applications, more
deep and careful studies are needed not only to understand VR TC intensification mechanisms
more thoroughly but also make the ground for reaching practical models to be employed in oil
industries in the future.
69
Chapter 4 Conclusion and Recommendations
4.1 Conclusion
This research study fosters the understanding of the main factors that stand behind TC
enhancement of oil-based NF systems, which might have favorable effects on heavy oil/bitumen
recovery while applied during thermal EOR methods. CuAeg, CuO and CuSi nanocrystalline
materials effect on TC properties of MO, glycerol and VGO were investigated under 0.5, 1.0 and
2.0 wt% concentrations. The highest TC enhancement rate was determined for 2wt% of CuAeg
NPs, which have the smallest crystalline domain size and demonstrated the smallest average
hydrodynamic particle size inside the base fluid medias. This type and concentration of CuAeg
NPs were fixed and experiments with VGO-VR mixtures were conducted. It has been proven that
increase of VR concentration in VGO matrix from 0 wt% to 20 wt% leads to higher TC value of
base fluid. Moreover, the linear increase in TC as percent value to the respect base fluid was
observed from 5 wt% to 20 wt% concentration of VR in a matrix with 2 wt% loading of CuAeg
NPs. Thus, as our target is proposing NF with higher TC, it was decided to perform experiments
for proper VR media under temperature augmentation from 80 to 110 °C. It was found that TC of
VR without NPs dosage with rising temperature underwent minor, almost unnoticeable increase,
whereas 2 wt%CuAeg-VR NF system exhibited stable upwards trend with respect temperature
augmentation. At 110 °C TC was determined to be 0.254 W/m K, which is 23.5% higher than TC
of VR without NPs. This is a valuable result that can open doors for further investigations of NF
systems’ TC properties in boundaries of study of in-situ nanocatalytic upgrading of heavy
oil/bitumen via hot fluid injection.
70
4.2 Recommendations
The injection of CuAeg-VR NF system with enhanced TC is a promising approach that will
plausibly lead to higher heavy oil/bitumen recovery and upgrading rates. However, more studies
are needed to be carried out to more profoundly understand the mechanisms and effect of NPs on
TC of VR and consequent effect of such NF on in-situ upgrading.
▪ It is substantial to conduct TC enhancement measurements of VR-based NF with modified
CuAeg NPs, especially with increased amount of doped copper on aegirine surface.
▪ Conduct experiments with different-sized CuAeg NPs under different concentrations to
obtain optimal conditions.
▪ Additional material characterizations techniques of NPs might be applied (XPS, TGA,
HRTEM, FT-IR).
▪ It is needed to investigate TC enhancement behavior under flow conditions of NF. Find an
appropriate way to study TC of flowing NF at increased temperatures, higher than 250 °C.
▪ Propose a model for CuAeg-NF TC enhancement behavior under elevated temperatures
based on validated mechanisms that responsible for intensification.
▪ Validate the catalytic properties of CuAeg NPs during hot fluid injection simulation tests
on Athabasca bitumen.
▪ Measure TC of reservoir before, during and after hot fluid injection and compare results
with other nanocatalysts that already in use.
71
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