A review of nanomaterials and their applications in oil & petroleum industries

The swiftly growing global economies remain the root cause of the soaring demand for oil and gas to satisfy their excessive energy demands, thus making the oil and gas sector one of the most important industrial sectors. Though renewable energy technologies are the more sustainable option, technological advances are required to make them more accessible to the common people. Therefore, due to the limitation of renewable energy technologies, oil and gas continue to be a more viable alternative. Extensive research is being conducted on the applications of nanotechnology to make the upstream, midstream, and downstream processes efficient in the oil and gas sector. Nanomaterials make the activities in processing and transportation more economical, efficient, and environment-friendly than their conventional counterparts. In this review, we have highlighted the need for nanomaterials in oil and gas, for example, in crude oil exploration, including drilling and EOR, separation techniques, refining, transportation, and other related activities. Further, this review summarizes novel nanomaterials developed and used in the activities mentioned above, and at the end, we have briefly described the synthesis mechanism of these nanomaterials. Finally, we emphasize the current challenges and future work prospects in this area of study.


Introduction
Emerging engineered nanomaterials have shown a broad spectrum of applications in science and technology, showcasing their growth and development.Nanomaterials have extensive applications in the biotechnology, biomedical, natural sciences, and civil & industrial areas [1].The tendency is primarily related to the unique properties that nanoparticles show, such as their small size, and the novel properties they exhibit which vary highly from the bulk properties and can be modified to fit the desired applications [2].Unlike the bulk counterparts, when the size of a particle is decreased to near or less than the wavelength of the conducting electrons, several properties such as optical behaviour, magnetism, thermal resistance, catalytic and chemical activities, internal pressure, and melting point are changed.The application and study of extremely small materials (about 1-100 nm) is the fastest-growing research field in various science and technology fields [3].The advances in nanotechnology have given researchers a pathway to fabricate collections of various enhanced nanomaterials, nanotools, and nanodevices, which can be used in multiple fields such as electronics, aerospace, medical and biomedical, smart materials and manufacturing, pharmaceutical, photography, energy, etc.In addition, nanomaterial technology is a cost-effective and efficient industrial process with an accurate design and conduction of atoms and molecules besides complete control of their unique properties [4].
Nanotechnology has advanced in the oil and gas industry due to its unique physicochemical properties.Nanofluids prepared using functional nanomaterials may exhibit better performance in oil production processes, and nanocatalysts have improved the efficiency in oil refining and petrochemical processes.Nanomembranes enhance oil, water, and gas separation, oil and gas purification, and the separation of impurities from wastewater [5].There are numerous methods available for the production of nanomaterials.Usually, the synthesis of nanomaterials produces a toxic effect on the surrounding environment and is very expensive.Thus, cost-effective, simple, and green chemistry principles are highly required for synthesizing nanomaterials.Different oil and gas industry operations have used many nano-sized materials such as metal oxide nanoparticles, metallic nanoparticles, carbon nanotubes, and magnetic nanoparticles [6].The preparation of nanoparticles can be done through various methods, including the sol-gel and hydrothermal processes, which are efficient in producing crystalline nanoparticles [7].Many studies on the synthesizing and functionalizing of such nanoparticles have been widely found in the literature.Significant challenges in the petroleum industry have been discussed, including the early stage of exploration, such as reservoir mapping and management and drilling processes, and production processes, such as refining and processing.Researchers have potentially solved similar industrial problems in almost every aspect of the oil and gas industry, from upstream to downstream.Significant practices, efforts, and innovations have been dedicated to developing precise design and characterization of nanomaterials, specifically for oil and gas industry-based applications [8].
The utilization of nanoparticle suspension injections into reservoirs for improved oil recovery (EOR) has recently gained attention in the literature.Various methods, such as altering the surface of reservoir rocks to make them more wettable by using different nanomaterials, have been conducted.Polystyrene nanomaterials as nanocarriers for surfactants, silica nanoparticles dispersion in polyethylene glycol, and nanomaterials as emulsion stabilizers have shown great potential in the EOR [3].Many studies have also identified nonionic surfactants, mesoporous silica systems, aluminum oxide, and magnesium oxide nanoparticles as potential in chemical flooding oil recovery.By altering the fluid's properties, altering the rock's wettability, reducing drag more effectively, strengthening sand consolidation, lowering interfacial tension, and increasing the permeability of the capillary-trapped oil, adding nanoparticles to fluids may significantly improve enhanced oil recovery and well drilling [9].By improving cake quality and lowering tube sticking issues, nanomaterials can also help with oil drilling issues.Depending on the quality of the slime cake, which can be effectively modified utilizing nanomaterials, damage issues near the reservoir can be resolved [2,10].The concentration and average size of the nanoparticles influence the characteristics and functionality of the drilling fluids.According to studies, these nanoparticles increase the surface area to volume ratio and improve the rheological characteristics of the drilling fluid [11].Nanoparticles have tangibly improved the oil recovery process, various drilling processes, and every other significant process, such as exploration, monitoring, and generation in the oil and gas industry.
This review lists several synthetic methods for different nanoparticles and several functionalization strategical methods for them that can be used in oil and gas applications.The variety of applications of the wide range of nanoparticles in the oil and petroleum industry is also discussed.Furthermore, the recent progress on consistent nanotechnological studies and their requirements for various major oil and gas processes will be summarized.

Need for nanomaterials in the oil & petroleum industry
Nanomaterials are becoming one of the most emerging technologies used in many different fields of applications.Examples such as nanoelectronics, nanomedicine, and nanodevices justify the efficiency and benefits of nanomaterials in many practical applications.These nanomaterials can be vital in the oil and petroleum industries.
Figure 1 is a pictorial description of the requirement of nanomaterials in different operations in the oil and petroleum industry.These nanomaterials can be useful in tracing, enhancing the production of petroleum products, increasing the water separation rate from oil, and many more.It can be clearly explained that there is a strong urge to use nanomaterials in the oil and petroleum industries.These nanomaterials can be used in the oil and petroleum industries in various following ways: 1. Carbon Quantum Dots as a tracer: Franco et al used Vaccinium Meridionale Swartz (also known as Mortiño) as the main raw material for fabricating Carbon Quantum Dots (CQDs).The CQDs were produced by means of a carbonization methodology with the assistance of microwaves.These CQDs were then observed for their reliability as a tracer to trace out the presence of pollutants and toxic agents in the crude oil.These CQDs turned out to be a promising nanomaterial to be used as a tracer.The CQDs produced do not tend to change any interaction between the crude oil and water.Also, there was no evidence of emulsion formation and particle agglomeration.The CQDs are mixed with the injection fluid (here brine was used as an injection fluid).The CQDs do not change the physical and chemical properties of the injection fluid.Hence this example can explain the need of nanomaterials in the oil and petroleum industry as a tracer [1].
2. Nanomaterials in the process of drilling and completion: Nanomaterials can be utilized in the process of drilling and completion in various aspects.The nanomaterials are a useful agent to stabilize the wellbore by preventing the water swelling phenomena and the collapsing of the wellbore.These nanomaterials also seal off the micro or nanopores that are present on the wellbore, which results in a decrease in the filter loss.The drilling fluid's viscosity and dynamic shearing force can also be increased by introducing the nanomaterials in the fluid.The rise in viscosity and dynamic shearing force enhances the rheological properties of the drilling fluid.Nanomaterials help enhance the system's thermal stability due to their tolerance against high temperatures [12].
3. Preventing corrosion in pipes using nanomaterials: Nanocontainers like halloysite/polyelectrolyte can be an excellent anti-corrosion agents in pipelines.This need for nanomaterials in oil and petroleum industries can save a huge amount of money spent in recovering the accidents due to corrosion occurring within the pipelines.This need can also resolve the issue of oil leakage.Shchukin et al [13] made this possible by producing a halloysite/polyelectrolyte anti-corrosion nanocontainer.The corrosion-preventing agent (or the corrosion inhibitor) is stuffed inside the halloysite nanotubes, then coated with a pH-sensitive electrolyte.This coating ensures that the release of the inhibitor is at a controlled rate.
4. Nanomaterials catalyzing the refineries: Catalysts are one of the most important substances required in any chemical industry to speed up the reaction and give more products in less time.These catalysts are immensely used in oil and petroleum industries, especially in cracking and reforming.Nanomaterials can fulfill the demand for catalysts as their high aspect ratio gives them some unique catalytic properties.Nano-sized carbon catalysts, for instance, can be used to reduce the viscosity of heavy oils.Metallic nanoparticles such as ruthenium, iron, nickel, and cobalt can be a promising catalysts for the Fischer-Tropsch reaction.These metallic nanoparticle catalysts tend to catalyze the Fischer-Tropsch reaction.The Fischer-Tropsch reaction produces liquid hydrocarbons with the help of a series of carbon monoxide and hydrogen reactions.Hence, there is a need for nanomaterials as a catalyst in the oil and petroleum industries.

Separation techniques using nanomembranes:
The basic application of any membrane is to carry out a separation process between the constituents of a mixture in the same or different phases.The membranes whose thicknesses are in the order of nanometers are called nanomembranes.These nanomembranes can fulfill the need to effectively separate oil from other impurities, especially water.Since the crude oil is obtained underneath the sea level during offshore/onshore drilling, these crudes have a high chance of containing some water and forming an emulsion.These water particles must be removed from the emulsion to get the highest crude purity.Nanomembrane-like micro/nano dual-scaled porous nitrocellulose (NC) membrane is one of the examples that can perform a separation of oil and water with higher efficiency.Nanomembranes play an important role in oil purification, gas separation, and CO 2 capture and storage.Nanomembranes can also contribute to gas separation.Hazardous gas like CO 2 needs to be removed from the oil.Different nano/ hybrid membranes are some examples that can fulfill the need for nanomembranes in the separation of gas from oil.

Nanomaterials & their properties suitable for oil & petroleum industry
As discussed in the previous section, it has been demonstrated that nanomaterials play a significant role in the oil and petroleum industry and there is a necessity of such nanomaterials to enhance the operational efficiency of the petroleum industry.But it is also important to understand the chemistry and the suitable properties of these nanomaterials that are responsible for increasing the efficiency of the oil and petroleum industry.This section explores the various applications of the nanomaterials in the oil and petroleum industries and the properties that contributes to these applications.Figure 2 shows a Venn diagram that represents the involvement of nanomaterials in the oil and petroleum industry and their various applications.

Drilling
Drilling fluids should be appropriately synthesized and changeable according to the formation to be drilled in order to perform efficiently during the drilling operation.The drilling fluid serves a variety of purposes.However, the primary function of the drilling fluid is to clean the wellbore's bottom, remove trimmings, lubricate and cool the drilling bit, maintain wellbore stability by controlling formation pressure, and prevent fluid inflow [11].Nanomaterials possess unique properties such as high thermal conductivity, large surface area, and pollution resistance, which make them suitable for making drilling-based products to improve the rheology of fluid and reduce fluid loss.Even at a very low concentration of nanomaterials, it shows excellent fluid properties [8].Researches have been conducted on the impact of carbon nanotubes on the rheological and filtration properties of drilling fluids.It has been found that adding 0.01 ppb Multi-Walled Carbon Nanotubes (MWCNTs) to an oil-based drilling fluid improves yield strength, gel strength, and emulsion stability.Because of their propensity to form ionic bonds, metal oxide nanoparticles are expected to increase drilling fluids' yield point, viscosity, and gel strength.Metallic oxide nanoparticles are preferred because of their availability and economic viability, although oxides of particular transition metals can be toxic and detrimental to the environment [11].Nano silica increased wellbore stability by 10-100 times through the reduction of water invasion, which was especially beneficial in shale formation.Using these nontoxic nanoparticles in drilling fluid can significantly cut drilling and disposal costs, resulting in significant environmental benefits [6].Ferric hydroxide nanoparticles have also been used to reinforce wellbore walls during drilling operations.These nanoparticles are being used as a loss circulation material (LCM), resulting in a stronger wellbore and decreased fluid losses.Sandstone core samples were used to test the ferric hydroxide nanoparticle compositions.The ultimate compressive strength of exposed cores is 70 percent higher than that of unexposed cores (16.5 versus 27.5 MPa) [14].
Another drilling sector where nanoparticles show promise is in the design of drilling fluids for severe environments, where temperatures over 120 °C impact drilling fluid shear response due to thermal deterioration of the viscosifiers in the fluid.Cellulose nanofibrils (CNF) have the ability to modify the rheology of water-based fluids, such as drilling fluids for use in oil wells or injection water for improved oil recovery (EOR).Heat aging was used to age CNF dispersions made mechanically, utilizing TEMPO-mediated oxidation, carboxymethylation as a pre-treatment, and cellulose nanocrystals (CNC).Temperature stability was highest for CNC and mechanically manufactured CNF, which remained stable after three days of heating to 140 °C.The effect of additions was investigated; cesium formate and sodium formate improved the temperature stability of the dispersions, whereas phosphate buffer had no effect [15].Different nanomaterials and their applications are mentioned in table 1, along with their role in enhancing different parameters.

Flooding
For oil recovery, energy is needed to transport the oil from the reservoir rock into a producing well which is given from the surface via induced pressure.Various parameters including temperature, salt compositions, different salinity, and initial wettability of rock have an impact on enhancing the oil recovery process [9].Nanoparticles are added to fluids in order to alter fluid characteristics, rock wettability, and sand consolidation, decrease interfacial tension, advanced drag reduction, and enhance the mobility of capillary-trapped oil.These enhancements greatly improve oil recovery and well drilling [9].One of the primary functions of nanoparticles is their ability to diffuse through fractures easily.Therefore, they can fill cracks, tights, and pores and cause fundamental permeability changes because of their strong effect on pore plugs [30].The type, size, and concentration of nanoparticles impact the mechanism used to reduce viscosity in heavy oil/bitumen.Surfactant flooding is enhanced by adding nanoparticles, which increases oil recovery [31].Slightly hydrophobic nanoparticles improve surfactant flooding efficiency, and the reservoir rock wettability is changed from hydrophobic to hydrophilic.The presence of nanoparticles alters the rheological properties of the surfactant solution and boosts their ability to enhance oil recovery operations.The observed decrease in interfacial tension

Surface-functionalized nanocellulose
Improve recovery of oil through water flooding using green technology.
EOR [29] and wetting properties is due to nanoparticles at the interfacial layers.A 19% increase in oil recovery is obtained when nanoparticles are used with surfactants [31].A higher polymer concentration, higher formation-damage coefficient, and higher value of mobility ratio lead to a higher recovery factor.The oil mobility ratio is increased from the large migration of the polymer solution from the high-permeability layers to the low-permeability layers [30].In porous media and fluids, nanoparticles have unique properties that have a variety of consequences under various conditions.The nanofluid is a colloidal suspension solution containing nanoparticles with distinct properties.This multiphase fluid system consist of different components that alter the properties of the base fluid.Nanofluids achieve a total oil recovery of more than 88%.Cheraghian et al [4] studied how nanoparticles and surfactants can release oil trapped in pores and throats.The responsible mechanisms are an increase in injection fluid viscosity, a reduction in oil viscosity, surface and interfacial tension, and a change in wettability in the rock formation.Due to the techno-economic feasibility, higher efficiency, and lower capital expense, polymer flooding has received prior attention as a chemical-enhanced oil recovery (CEOR) method.HPAM (partially hydrolyzed polyacrylamide) is the most commonly used polymer in CEOR because of its wide availability, ease of handling, and cost.The concentration of 2.0 to 3.0% of silica NP injected in core flooding, Silica nanoparticles have been frequently used in flooding because of their availability and unique physiochemical qualities (hydrophobic to hydrophilic).The adsorption of nanoparticles at the water-rock interface may alter the wettability of rock surface and improve HCS recovery factor [4]. Numerous factors exert a significant influence on controlling nanoparticle migration.Some are the rise of pressure drop and increasing flow velocity during the low-salinity water-flooding procedures [30].Some of the nanoparticles, including silicon dioxide for improved foam stability, titanium oxide and zinc titanate aluminum oxide for reduced oil viscosity and mobility, and graphene oxide for improved oil recovery, are utilized in these applications.

Demulsification property
The extraction of crude oil accompanies a significant amount of water with oil and thus forms an emulsion.This water and oil mixture can pose a great challenge during refining activities due to the presence of dissolved salts in the emulsion.These salts can contaminate the catalysts in various reactors and cause fouling and scaling.Therefore, we need to separate the oil and water emulsion to avoid these issues in later operations.For the past many years, chemical de-emulsifiers have been used.However, their applications have been limited due to concerns about their toxicity to the environment and their complicated production methods.Various studies have reported using SiO 2 nanoparticles, and carbon-based nanomaterials, for example, carbon nanotubes, graphene oxide, etc, as de-emulsifying agents.Recently, novel nanomaterials like CNTs/SiO 2 have been introduced, demonstrating positive de-emulsification and environment-friendly results.Here, CNTs are the basic nanomaterial from which other nanomaterials have been synthesized.Oxidized CNTs have been prepared by the chemical oxidation of CNTs with the help of HNO 3 and H 2 SO 4 .Furthermore, CNTs/SiO 2 nanomaterial is prepared by grafting SiO 2 nanoparticles on the surface of oxidized CNTs [32].
Wettability is one of the major properties that can indicate the demulsification properties of these nanomaterials.The three-phase contact angle is measured to investigate wettability.CNT nanomaterials like CNTS, Ox-CNTs, and CNTs/SiO 2 exhibited different contact angles.The contact angles for CNTs, Ox-CNTs, and CNTs/SiO 2 were 107.8, 83.0°and 92.8°respectively.The reduced contact angle for oxidized CNTs and, furthermore, for CNTs/SiO 2 shows the presence of various hydrophilic groups at the surface.Thus, there is more wettability in the water phase.Moreover, in the case of CNTs/SiO 2 , the contact angle further reduces due to SiO 2 grafting on its surface.This reduction takes place since these nanomaterials get attached to the oil-water interface.The results from these studies showed that θ of 90°has better demulsification performance.Regarding the interfacial activity of these nanomaterials, CNTs get dispersed into the oil phase, and Ox-CNTs go into the water phase.Still, CNTs/SiO 2 remains at the oil-water interface even after a very long time.The nanomaterial was easily able to coalesce the water molecules.The experiments show a demulsification efficiency of 87.4% exhibited by CNTs/SiO 2 [32].Various other carbon-based nanomaterials have been used as de-emulsifiers which are able to break the strong viscoelastic film between the oil-water interface due to π−π and p−π bonds between nanomaterials and film components [33,34].In addition to these, rhodium borate nanoparticles were studied as de-emulsifiers.The demulsification efficiency is given by the ratio of the volume of water separated and water present in the emulsion.Compared with a commercial demulsifier with an efficiency of 78.9%, rhodium borate nanoparticles provide an efficiency of 84.2%.The studies also suggested that when the concentration of a demulsifier has increased, the separation also increases as the surface tension of the water molecules gets reduced.Due to this greater number of water molecules come together.Also, an increase in temperature results in better separation [35].

Catalytic property
One important use of nanomaterials in the petroleum industry is to upgrade the low-grade crude (with < 20°A PI gravity) to a high-grade crude by cracking the low-grade crude.This process usually takes a long time and should be performed at high temperatures.However the use of carbon nanoparticles in this process can reduce the reaction time to less than an hour, and products could be attainable at temperatures less than 150 °C.As a result, this process will not only reduce the environmental impact of the effluents but also cut down the operating cost of the process to a significant level.Since nanoparticles are very small in size, they have a large surface when compared to the bulk solid.This helps to increase the reaction on its surface and reduce the activation energy of the thermal cracking process [2].A few of the most widely used nanomaterials in petroleum refineries are ZSM-5 of MFI, FAU topologies and zeolite Y. Since 1960, zeolites with Face Centered Cubic (FCC) structures have been widely used as catalysts in the process of converting heavy crude oil into lighter ones.Another important application of nanomaterials is in Fischer-Tropsch synthesis (FTS).FTS is one of the most coherent ways to convert natural gas, biomass, and coal into hydrocarbons.Synthesis gas (H 2 +CO) is the intermediate product of this process.A study reported that synthesis gas shows 60% (by weight) conversion into C 2 through C 4 alkenes, using the catalyst that contains Fe nanoparticles evenly spread on weakly interactive carbon nanofibers or α-alumina supports.
Every day, the amount of carbon emissions are increasing, and all the countries pledge to decrease and cut down their carbon footprint by taking measures and imposing strict regulations on industries.One of the main sectors contributing to emissions is the petroleum industry.In order to decrease the carbon emissions, oil and gas manufacturers had to remove harmful compounds like Sulphur compounds (mostly oxides of Sulphur) and reduce their level to less than 10 ppm in petroleum products.Nanomaterials derived from nickel, cobalt, and molybdenum dispersed on different supports, are widely used as effective catalysts for confiscating Sulphur from petroleum and its products.It has been observed that carbon nanotubes (CNTs) are very good supports for nano-catalysts such as CoMo particles.These supports provide homogeneous distribution of the catalysts on the bulk of carbon nanotubes (CNTs) [5].

Chemical synthesis mechanisms 4.1. Synthesis of magnetic nano-silica using barley husk
The petroleum industry can benefit greatly from magnetic silica nanoparticles.So far, the most common uses have been water invasion control in shale, filtration and rheology control in fluids, oil well cementing, foam and emulsion stability for better oil recovery, and drag reduction in porous media [3].
The barley husk was broken into smaller pieces and dried.The straws were properly rinsed with distilled water to eliminate clinging sand, soil, or other visible particles.The sample was then dried in the oven.A miller was used to crush the dry barley husk into powder form.After that, the barley husk powder was refluxed in HCl.The material was filtered and rinsed with distilled water after the acid reflux followed by heating.After dissolving the sample in HNO 3 , it was rinsed with distilled water, filtered, and allowed to cool, resulting in precipitation of nano-silica.The organic substance of the barley was removed by heating, while metallic contaminants were removed by acid reflux.The nano-silica powder that resulted was utilized to make a nano-silica solution.
To make Magnetic nano-silica (M-NS), it was necessary first to prepare the magnetic solution, which was then mixed with the nano-silica solution.The magnetic nanoparticles were made using iron (III) chloride (FeCl 3 ) as a precursor.Barley leaf extract is mixed in FeCl 3 solution.The resulting mixture was agitated, and the color of the mixture changed to a very dark brown during this process, suggesting the creation of magnetic nanoparticles.The mixture was centrifuged and rinsed twice with alcohol.The magnetic nano-silica (M-NS) particles were made by gently pouring the magnetic solution into the nano-silica solution while continuously mixing, centrifuging, and drying in the oven.Magnetic nano-silica particles with an average diameter of 162 nm and a vast surface area of 120 m 2 gm −1 were discovered to be hydrophobic.Because of these properties, magnetic nano-silica was employed as an adsorbent to remove petrol pollutants from water.The experimental approach revealed that with the use of just 0.6 gm. of M-NS on a petroleum concentration of 40 mg l −1 , can result in an absorption efficiency of 85 percent.Because a large volume of petroleum was removed, sorption proved to be a successful procedure.The study also shows that as the amount of sorbent grows, so does the sorption capacity until an equilibrium is attained [36].

Synthesis of HPAM (hydrolyzed polyacrylamide) -based Al 2 O 3 PNFs (polymeric nanofluids)
Nanoparticles (NPs) have been thoroughly explored for their usage in enhanced oil recovery (EOR) due to their special features and availability in large numbers.A new trend in nanotechnology is incorporating nanoparticles as an additive with polymer to create unique materials known as polymeric nanofluids (PNFs) for EOR.The most productive and effective method for recovering hydrocarbons from depleted reservoirs is polymer flooding, a chemical EOR strategy.For polymer floods in the field, partially hydrolyzed polyacrylamide (HPAM) is the most widely used polymer.HPAM is preferred in EOR field applications because it is resistant to bacteria, has high water solubility and mobility control, and is a relatively low-cost polymer.Al 2 O 3 NP is a metal oxide nanoparticle with excellent qualities as a nanofluid.They have slightly high thermal conductivity and can easily disperse heat from fluids using Brownian motion.As a result, fluids with Al 2 O 3 NPs are less impacted by temperature changes [37].
HPAM polymer was added directly to deionized water to make the polymer solutions.Varying polymer concentrations from 500 to 5,000 ppm were used to establish the critical concentration of HPAM molecules.A fixed concentration of HPAM above the critical concentration was used for rheological characterization.A twostep technique was used to create the polymeric nanofluids.First, a predetermined number of NPs (0, 0.02, 0.03, 0.04, 0.05, 0.1, 0.2, 0.5, 1.0 weight percent) were dispersed in DIW and ultrasonically homogenized to produce a stable and homogeneous dispersion.The HPAM powder was then gently blended into the matching aqueous NPs dispersion.The sample was then allowed to cool to room temperature.The use of NP as an addition for HPAM reduced thermal degradation and chemical degradation of the aqueous polymer molecules due to their shielding properties.Al 2 O 3 PNF outperformed SiO 2 PNF and individual HPAM solutions in both rheological and oil displacement investigations, owing to their exceptional physicochemical properties and high thermal conductivity.Furthermore, the Al 2 O 3 PNF reduced the capillary force of trapped residual oil by changing the wettability of an oil-soaked surface to a water-soaked surface.Finally, in normal reservoir conditions, 0.1 weight percent Al 2 O 3 PNF enhanced oil recovery efficiency from sandstone cores [37].

Synthesis of carbon nanotubes/SiO 2 nanomaterials
Carbon-based nanomaterials are well known for their de-emulsifying properties.This is due to their ability to form strong bonds with the oil and adsorbing on its surface because of the π−π and p−π bond formations.A nanomaterial was formed using this property by transplanting nano-SiO2 over the surface of oxidized carbon nanotubes (Ox-CNTs).For the synthesis of this particular nanomaterial, materials like CNTs, Tetraethoxysilane (TEOS), sodium chloride (NaCl), ammonia solution (NH 3 •H 2 O), Nitric acid (HNO 3 ) and concentrated sulfuric acid (H 2 SO 4 ) were utilized.Oxidized CNTs were prepared by subjecting CNTs to oxidation in the presence of nitric acid and sulphuric acid mixture.This mixture was dispersed evenly using ultrasonication and later heated at 80 degree celsius.It was then cooled to ambient temperature, filtered, washed, and dried to obtain Ox-CNTs.For grafting SiO 2 over CNTs, the solvothermal method is utilized.In this method, the precursors are solubilized in a solvent at high temperatures where chemical reactions occur, then crystallized to give desired nanostructures.Similarly, Ox-CNTs were dispersed in ethanol, water, and TEOS.To further adjust the pH level, an ammonia solution was also added.This solution is heated at 110 degree celsius; after the product is formed, the mixture is cooled to room temperature, washed, and dried and finally, it is vacuum freeze-dried.An analysis to find out the chemical composition of the prepared nanomaterial was performed using energy-dispersive x-ray (EDX).During this process, distinct S, O, and C peaks were obtained, confirming the perfect grafting of SiO 2 on the CNTs.These nanomaterials are environment-friendly and have high interfacial activity and wettability.These properties allow it to be absorbed quickly and easily on the oil-water interface.Which, in turn, improves the coalescence of water droplets [38].

Synthesis of MgO nanoparticles
Various studies have suggested the use of Magnesium oxide nanoparticles as fuel additives.Fuel additives are substances or chemicals that enhance their octane number when added to the fuel.Octane number directly indicates the combustion characteristics or, more precisely, the anti-knocking properties of the fuel.Due to the high specific surface area and high oil-dispersion properties of MgO nanoparticles, they can be used as fuel additives in heavy fuel oils.The first step in the synthesis is to precipitate magnesium cations in the form of Mg(OH) 2 .The precursors here are magnesium nitrate and NaOH.A mixture of magnesium nitrate in water is prepared, and NaOH is added to it.Upon stirring for 2 h, we obtain our required precipitate of Mg(OH)2.The precipitate is then washed and dried to remove any impurities.After this, calcination is done at 500 °C to obtain MgO nanoparticles.
Capping agents are substances that are added to control the growth of nanoparticles and prevent their agglomeration.They provide stability to the nanoparticles during their synthesis.[39] In MgO nanoparticles synthesis, the capping agent used is oleic acid.These capping agents are added to the solution of MgO nanoparticles and kerosene.Mixed with the capping agents, this solution is heated up to 100-200 °C.

Synthesis of carbon quantum dots
Carbon Quantum Dots, or CQDs, are used as tracers in many oil and petroleum industries.CQDs are potential tracers that can be used and help determine the presence of any pollutants in crude oil.The raw material for the manufacturing of CQD is Mortiño (Vaccinium Meridionale Swartz).Mortiño is a fruit that looks like a berry and has high nutritional value.At first, Mortiño was washed with Chlorine to remove any dirt or impurities.Then the juice of the fruit was taken out as an extract.The concentration of this extract was brought up to the desired value by filtering the juice with Whatman filter paper and then using a 200 W microwave for around 15 min After going through the microwave heating, the desirable concentration was achieved, which was 4 M of natural citric acid.Now this concentrated extract is homogenized by means of a magnetic stirrer for uniform distribution of the pulps throughout the juice.A sample of 2 ml of the extract was taken, and 0.5 ml of pure ethylenediamine was added.This pure ethylenediamine serves as a Nitrogen donor.The mixture was thoroughly stirred for 30 s.A brown-colored homogeneous mixture is obtained.Subsequently, the mixture is irradiated using a domestic microwave oven of 300 W for about 5-6 min This results in the formation of a brown-colored hot gel-like solution.This solution is then dispersed into a 5 ml water bath at 80 °C.Ultimately, the solid CQDs are filtered from the solution.This Carbon Quantum Dots fabrication method using Mortiño fruit was done in the Colombian oil field reservoir [12].The experimental setup of this method is depicted in figure 3.

Mesoporous silica nanoparticles
Nonionic surfactants/mesoporous silica complexes can be used as nanocarriers for surfactant-controlled release in improved oil recovery to reduce surfactant losses [40].Good control of mesoporous silica nanoparticles' morphology, particle size, uniformity, and dispersity (MSNs) is increasingly important in various fields.Several studies have been conducted on synthesizing mesoporous silicas, and have concluded that mesostructured surfactant-silica nanocomposites spontaneously assemble through interaction matching of the organic and inorganic components.Cai et al [41] first synthesized silica nanoparticles.The synthesis of MSNs can be achieved by various adjustments of synthesis conditions, including the pH of the reaction mixture, the characteristics of surfactants or copolymers used, and the concentrations and sources of silica.The wellcontrolled particle size of the MSNs would allow good control in particle-cell interactions and precise quantitative dose in carrying cargos.Moeller et al used the base triethanolamine (TEA) as a substitute [42].The greater the amount of TEA used, the smaller the particle size of the produced [43].MSNs.Rao et al [44] synthesized the monodisperse uniform-sized silica nanoparticles by hydrolysis of TEOS in an ethanol medium with ammonium hydroxide.First, ethanol was taken and kept in a sonication bath.After 10 min, a known volume of TEOS was added while sonicating, and after 20 min, 28% ammonium hydroxide was added as a catalyst to promote the condensation reaction.Sonication was continued for a further 60 min to get a white turbid suspension.All the above experiments were conducted at room temperature [44].

Synthesis of zeolite nanoparticles
Nano zeolite crystals can be synthesized using various methods like hydrothermal crystallization, confined space, ultrasonic, microwave, seeding, and microreactor.Out of all these methods, hydrothermal crystallization is the most used method for synthesizing zeolite nanocrystals as the crystallization process is very easy to control.These crystals are prepared on nucleation of clear solutions with a precursor gel under hydrothermal conditions.To attain desired nucleation, factors like hydrothermal treatment temperature, polymerization process in the course of preparing the initial precursor gel, concentration and type of structure-directing agents (SDAs), mass of metal cation in the colloidal solution of precursor, etc, have to be controlled.In general, zeolites are produced in amorphous form and then converted to crystalline form by varying the size.Basically, the zeolite nuclei are formed in the center of the colloidal solution.Then they gradually grow and expand outwards till the entire amorphous form of the zeolites gets converted into crystalline form.These are then heated to high temperatures to obtain bigger cubic crystals of the zeolite.In recent times, tiny EMT-type zeolite was synthesized from a sodium-rich precursor system that was template-free under low-temperature hydrothermal conditions and by having the control on polymerization process in the course of preparing the initial suspension,resulted in decreased crystal growth [5].

Synthesis of zirconia nanoparticles
Zirconia nanoparticles are catalysts in thermal decomposition, aqueous precipitation, sol-gel, and hydrothermal synthesis.Given that thermal cracking is an example of thermal decomposition and it is a known fact that it is employed in converting low-grade crude oil to a higher one, synthesizing of zirconia (ZnO 2 ) has become important [45].Initially, yellow powder and zirconia are mixed with sodium hydroxide aqueous solution.This mixture is then stirred for 3 h, and transferred to a high-pressure reactor where it is kept at 150 °C for around 85 h.After this hydrothermal treatment of zirconia, we obtain a product in a sol-gel state.This semi-solid medium is then rinsed in dil.HCl and water to eliminate OH -ions.After that, it is dried for 6 h at 110 °C.The dried product is then dispersed into acrylonitrile with the help of an ultrasonic device.X-ray diffraction (XRD) patterns were used to determine the particles' size and the crystalline phase.Changes in the shape and form and aggregate size distributions were analyzed using a scanning electron microscope (SEM) and a transmission electron microscope (TEM).X-ray fluorescence (XRF) analysis was carried out to govern the composition of ZnO 2 before the hydrothermal treatment.A particle size of 15-30 nm can be obtained using this process.Differences between the size of nanoparticles formed by conventional and hydrothermal methods can be seen in figure 4 [7].

Synthesis of graphene oxide nanosheets (GONs)
Because of its peculiar two-dimensional structure and exceptional physical and chemical capabilities, graphene and its derivatives have recently gained popularity in the oil and gas industry.Its exceptional optical, electrical, thermal, and mechanical properties make it an excellent candidate for use in oil and gas exploration, drilling, production, and transportation [46].
Graphene oxide (GO) has been found to be useful in chemically enhanced oil recovery because of its surfactant-like features, such as increasing wettability, emulsifying, and lowering interfacial tension.Graphene oxide is utilized to produce nanosheets that increase the viscosity of the aqueous solution, reduce the oil-water interfacial tension, and change the oil-wet carbonate rocks into water-wet [47].These nanosheets are synthesized by using the traditional modified Hummers' method and through the oxidation of natural graphite flakes.To initiate the process, 50 ml of concentrated sulfuric acid was added to a 500 ml volumetric beaker containing 2 g of graphite and agitated for 1 h at 80 °C to expand graphite carbon sheets.After cooling at ambient temperature, 2 g of sodium nitrate was added to the beaker in an ice bath (510 °C) with constant stirring.Then, 10 g of potassium permanganate was progressively added to the suspension.After reaching a green uniform viscous liquid, the ice bath was withdrawn, and the mixture was agitated at 40 °C for 1.5 h.Within 15 min, 160 ml of deionized (DI) water was added to the beaker.Exfoliation was completed by adding 400 ml of DI water and 5 ml of hydrogen peroxide.The yellow suspension was filtered and rinsed with 10% HCl and DI water until it achieved a neutral pH (6).The GO slurry was then redistributed in DI water and centrifuged at 10 000 rpm to remove the unreacted/ unexfoliated graphite residue.Large sheets of GO were obtained by sonicating the solution in an ultrasonic bath for 1 h.Finally, a probe sonicator was used to transform huge sheets of GO into tiny sheets of GO.The results showed that increasing the dosage of GONs to 800 ppm could modify the viscosity of DI water to 1.6 cSt.After the addition of NaCl, GONs suspensions became increasingly viscous.However, the viscosity augmentation was inconsistent since when the salt content reached 40 000 or 60 000 ppm, the viscosity fluctuated, reaching high points of 3 and 3.2 cSt, respectively.

Conclusion
Nanotechnology originated in the early 1980s, it has gained importance in the previous two decades.Nanomaterials are used in various industries but have recently acquired prominence in the oil and petroleum business.If the entire oil and petroleum industry is categorized into three parts, upstream, midstream, and downstream, it is evident from the literature survey that nanomaterials have a huge role to play in all these sectors.Unlike bulk materials, nanomaterials changed our entire perspective of dealing with things.As the materials' size is reduced to 1 nm and 100 nm, size-related inhibitions are annihilated.Nanomaterials like carbon quantum dots are being used as a tracer in the oil and petroleum industry to detect the presence of pollutants and toxic agents in crude oil.Since it is very small, it doesn't show any noticeable change in the physiochemical properties of the product.With their salient features like high thermal conductivity, large surface area, and pollution resistance, nanomaterials have its implementation in drilling operation, where it helps to clean the wellbore's bottom, discard cuttings, keep up wellbore stability by controlling formation pressure, cool and lubricate the drill bit and prevent fluid inflow.To control oil spills due to the corrosion of the oil containers, Shchukin et al have discovered a novel nanomaterial known as a halloysite/polyelectrolyte anti-corrosion nanocontainer.So, nanomaterials are used as an anticorrosive in the oil and petroleum industry [13].In the midstream process, flooding, nanomaterials are used for EOR.Nanoparticles are added to the injection fluid to alter the fluid characteristics and rock wettability, decreasing interfacial tension, improving sand consolidation, advancing drag reduction, enhancing the ability of movement of capillary-trapped oil and countering the challenges faced during conventional oil recovery.Nanomaterials are used as demulsifiers and catalysts in downstream processes.Since a large amount of water is used in oil extraction, water, and oil form an emulsion.It is important to separate oil and water before treating the crude because it can cause fouling and scaling inside the plant equipment.Since conventional demulsifiers are very toxic and complexe to manufacture, industry experts have devised a novel idea: using nanomaterials as demulsifiers, which are less toxic and eco-friendly than conventional ones.The other important use of nanomaterials in downstream processes is their catalytic property.Nanocatalysts are used to increase the API gravity value of low-grade crude oil in the thermal cracking process.This process is very economical and doesn't cause much harm to the environment.It is also used to sweeten the crude by helping remove sulfur from the crude using the hydro desulphurization process (HDS).

Figure 1 .
Figure 1.Nanomaterials as a helpful additive in the oil & petroleum industry.

Figure 2 .
Figure 2. Venn diagram depicting the different applications in the oil and petroleum industries where nanoparticles are used.

Figure 3 .
Figure 3. Experimental setup for fabricating CQDs using Mortiño fruit in Colombian oil field reservoir.

Figure 4 .
Figure 4. Difference between the size of nanoparticles formed by conventional and hydrothermal methods.

Table 1 .
Improvement in parameters using nanomaterials.