Article

Reducing the Viscosity of Crude Oil by Pulsed Electric or Magnetic Field

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Abstract

A method with pulsed electric or magnetic field to reduce the viscosity of crude oil is developed. Specifically, for paraffin-base crude oil, a magnetic field pulse can effectively reduce its viscosity for several hours, while, for asphalt-base crude oil or mixed-base crude oil, an electric field pulse can do the same. The method does not change the temperature of the crude oil; instead, it temporary aggregates paraffin particles or asphaltene particles inside the crude oil into large ones. This particle aggregation changes the rheological property of the crude oil and leads to the viscosity reduction. While this viscosity reduction is not permanent, it is suitable for many important applications, such as oil transport via deepwater pipelines, since it lasts for several hours and is repeatable.

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... Applying a high-voltage electric field to waxy oils can effectively improve the cold flowability, with the viscosity and yield stress reduced significantly Huang et al., 2021a;2021b;Li et al., 2019;Ma et al., 2017Ma et al., , 2019Tao and Tang, 2014;Tao and Xu, 2006). In 2006, Tao and Xu (2006) first proposed a method with which the viscosity of the tested oil was reduced by more than 80% by exposing the oil to an electric field parallel to its flow direction. ...
... Applying a high-voltage electric field to waxy oils can effectively improve the cold flowability, with the viscosity and yield stress reduced significantly Huang et al., 2021a;2021b;Li et al., 2019;Ma et al., 2017Ma et al., , 2019Tao and Tang, 2014;Tao and Xu, 2006). In 2006, Tao and Xu (2006) first proposed a method with which the viscosity of the tested oil was reduced by more than 80% by exposing the oil to an electric field parallel to its flow direction. found that viscosity reduction can also be achieved by imposing an electric field perpendicular to the flow direction of crude oil. ...
... Up to now, there are mainly three viewpoints about the mechanism of the electrorheological effect of waxy oil, i.e., alignment of suspended particles along the streamline (Tao and Tang, 2014;Tao and Xu, 2006), wax particle aggregation Ma et al., 2017;Xie et al., 2020), and interfacial polarization . However, the first two views cannot explain the electrorheological behaviors observed in waxy oil gels and substantial viscosity reduction Huang et al., 2021b;Li et al., 2019). ...
Article
Applying an electric field to waxy oil may significantly improve its cold flowability. Our previous study has demonstrated that the accumulation of asphaltenes and resins on the surface of wax particles, i.e., interfacial polarization of wax particles, is the essential mechanism of this electrorheological phenomenon. The influence of asphaltenes concentration on the performance of the electrical treatment has been studied. In this paper, the influence of the concentration of resins, the most abundant non-hydrocarbon component in crude oil, on electrically-treated waxy oil's viscosity and impedance was investigated for the first time by using model oils containing resins in the concentration range of 0.05 wt% - 5.00 wt%. It is found that the effect of resins concentration on viscosity and impedance is not monotonous, with both the viscosity reduction and impedance increment induced by the electric field decreased first and then increased with increasing resins concentration at a given amount of precipitated wax. Increasing the polarity of resins would alleviate the viscosity reduction and impedance increment. This work further demonstrates that resins accumulation on the wax particles surface does occur.
... The viscosity of oil decreases at higher temperatures and as a result of electrochemically enhanced reactions that facilitate conversion of heavier hydrocarbons to lighter ones [1]. Recent studies on the viscosity reduction of paraffin, waxy base and asphaltic base crude oil samples showed that the dependence on the electric treatment is more complex and also depends on the oil composition and time of exposure to electric field [11,12,18,[22][23][24][25]. For example, the oil viscosity decreased due to the radiation of 500 W electromagnetic waves and has become lower by 18.9 % than the initial value after cooling to the room temperature [11]. ...
... For example, the oil viscosity decreased due to the radiation of 500 W electromagnetic waves and has become lower by 18.9 % than the initial value after cooling to the room temperature [11]. On the other hand, kinetic viscosity of asphaltic-base crude oil sample decreased by about 15% after applying DC for 8 s or AC of 100 Hz but returned to its original value after 8 h [23]. ...
... The viscosity of paraffin-base crude oil is reduced under the action of a magnetic field pulse, while the viscosity of the asphalt-base crude oil is reduced under the action of electric field pulse. This is because the asphalt is much less sensitive to the magnetic field than paraffin [23]. For a different type of paraffin-base oil, however, the viscosity is reduced substantially in a couple of seconds after the electric field was applied [18]. ...
Article
Electro-enhanced oil recovery (EEOR) methods have the smallest carbon footprint, among which the electric current impulses method is the most economic. Its performance requires minimal surface facilities, no auxiliary equipment, downhole tools or hazardous materials. Stopping oil production or pulling the tubing out of the well for placing the downhole tools are not required either. The period of treatment session is short (12–24 h). The electricity consumption of 150–200 kW is lower than for any other methods. Prior to the abandonment of an oil field in Oman, treatment with the electric current impulses was applied to marginal wells to clean up the near borehole zone and improve well production characteristics. 7 wells were treated in pairs as cathode and anode in two successive electrical treatments, which were carried out with a difference of 4 months. In the period after the second electrical treatment, only five wells were in operation. Two of them, wells 5 and 12 were treated in both electrical treatments. The results of electrical treatments were thoroughly analysed due to the overlap of simultaneous operations that could mask the effect of electrical treatment. The incremental oil production compared to the forecast was evaluated using reservoir simulation and decline curve analysis. In wells after the second electrical treatment, the increase in oil production rate (OPR) by 36% was in Well 5 and by 25% in Well 1. There was no noticeable effect in Well 12, probably because it was located at the very edge of the reservoir structure. The effect of electrical treatment was also observed in untreated nearby wells. An increase of 11% in OPR was observed in Well 23 and 64% in Well 7. The effect of the electrical treatment was also observed in the form of heavy oil and wax flowing in slugs from three treated wells, which increased the total consumption of demulsifier from 12 to 20 L per day. It has been demonstrated that this method has great potential for cleaning the near wellbore space and increasing oil production.
... Effect of Electric Pulse Method. It was found by Tao and Xu (2006) that by the application of an electric pulse method, the viscosity of asphaltene-rich crude oil can effectively be reduced. The pulsing led to temporary aggregation of the asphaltene particles in the crude oil which contributed to the crude oil viscosity reduction. ...
... The pulsing led to temporary aggregation of the asphaltene particles in the crude oil which contributed to the crude oil viscosity reduction. 132 4.1.6. Streaming Potentials. ...
... 151 The application of an electric field may lead to asphaltene aggregation and/or precipitation, which may contribute to changes of the rheological properties of the crude oil and oil− water interface. 132 The magnitude of the electric field and type of electrodes was also found to play an important role during the separation of asphaltene-stabilized emulsions. Mohammadian et al. (2018) developed an electrical demulsification device where the crude oil/water (O/W) emulsion was placed between the two electrodes, and a direct current was applied to the system. ...
Article
Full-text available
Asphaltenes are regarded as troublesome components of crude oils as their precipitation and deposition inside production wells and downstream infrastructure often result in a reduction of production capacity and, in critical cases, production shut-in. It has been shown that asphaltene deposition on conductive surfaces can be controlled by the application of an electric field. The electric field has been used to either inhibit or accelerate asphaltene deposition. This paper reviews asphaltene behavior in an electric field. It describes the structure and electric properties of asphaltenes as well as their electrokinetic behavior. State-of-the-art asphaltene electrodeposition and separation from both model and crude oils using electric fields are also discussed. The influence of parameters such as asphaltene chemistry, crude oil composition, pH, electric field strength, and flow conditions on the asphaltene electrodeposition process is addressed, and the effect of asphaltene interactions with themselves and other crude oil components is evaluated. A comprehensive literature survey reported the electrodeposition on both positive and negative electrodes, which suggests the complexity of the process. It has been shown that asphaltene charges can be tailored by changing the process parameters. Because of the high energy efficiency and relatively simple process, asphaltene electrodeposition is currently a key solution for removal of asphaltenes from crude oils. This review also highlights the main challenges and knowledge gaps associated with the asphaltene electrodeposition process.
... Over the last decades, the non-conventional magnetic and electric technologies have shown to be effective in reducing viscosity and flow turbulence (mainly when using waxy crude oils) [18], showing lower energetic and economic costs. Several studies have concluded that the magnetic field may reduce viscosity and modify wax crystallization mechanisms of waxy crude oils without affecting their thermodynamic equilibrium [19][20][21][22][23]. It has also been reported that magnetic fields influence the resinous-asphaltic fraction [21,24] and can even modify the rheology due to the presence of paramagnetic ions in the water phase [25]. ...
... It has also been reported that magnetic fields influence the resinous-asphaltic fraction [21,24] and can even modify the rheology due to the presence of paramagnetic ions in the water phase [25]. Some researchers have explained that the magnetic/electric fields improve the flow properties by induction of an anisotropic viscosity, which is the result of aggregation phenomena of the colloidal phase [18,20,26,27]. In contrast, other authors have described the influence of magnetic fields as promoters of disaggregation [22,23]. ...
... It should be highlighted that the crude oil samples without NPs did not show any type of rheological alteration under the presence of a magnetic field, contrary to those reported by other researchers [19,20,25]. However, in the presence of magnetic NPs and magnetic fields, both heavy crude oil-ferrofluid models showed a magnetoviscous effect. ...
Article
This study embraces the evaluation of the rheological and magneto-rheological properties of heavy and extra-heavy crude oils by applying nanotechnology and magnetism as technological solutions in reducing viscosity. Mixtures of heavy oils with ferrofluids were used to study the viscous effects induced by the action of external magnetic fields. The rheological evaluation covered rotational and oscillatory tests as a function of time and temperature. In the magneto-rheological characterization, there were analyzed the magnetoviscous effects. The results revealed that the crude oils are viscoelastic materials that follow the Generalized Maxwell Model over a wide range of temperatures (-5 to 60 °C). It was also proved that the synergy between the carrier liquid and the nanoparticles promoted a significant reduction of viscosity (~98–99%) and viscoelasticity, which was directly related to the simultaneous action of the solvent and the asphaltene adsorption onto the nanoparticles surface. Critical concentrations of nanoparticles (0.2 wt% and 0.6 wt%) were proved to promote the maximum decrease in viscosity (additional ~ 0.3–0.5% or 1000-3000 cP) and the elastic storage modulus, which was crucial evidence of their effect on hindering the aggregation mechanisms of asphaltenes. In the heavy oil–ferrofluid mixtures, a magneto-rheological effect was demonstrated. The magnetic field attenuated the initial relaxation processes, leading to an increase in the viscosity and shear stress. The phenomenon was attributed to the formation of magnetic chains, such as that observed in magneto-rheological fluids. These results were supported by Scanning Electron Microscopy, which showed the formation of magnetic-field induced thick columnar assemblies of nanoparticles-asphaltene complexes.
... There are two kinds of theories for describing the influence of the magnetic field in electromagnetic synergistic dehydration: (1) Magnetization theory, it considers that the magnetic field can significantly change density, viscosity, surface tension and other physical properties of a single phase or emulsions [10][11][12][13]. The experimental results show that the viscosity and rheology of crude oil can be changed by the magnetic field [10,[14][15][16][17][18][19]. ...
... There are two kinds of theories for describing the influence of the magnetic field in electromagnetic synergistic dehydration: (1) Magnetization theory, it considers that the magnetic field can significantly change density, viscosity, surface tension and other physical properties of a single phase or emulsions [10][11][12][13]. The experimental results show that the viscosity and rheology of crude oil can be changed by the magnetic field [10,[14][15][16][17][18][19]. (2) Lorentz force theory, it considers that non-conductive dispersed particles can be separated by the synergistic action of an electric field and magnetic field [20], the charged continuous phase is directed by Lorentz force, and the dispersed phase is concentrated and separated by squeezing force caused by the movement of the continuous phase [21,22]. ...
... Moreover, there is not a unified understanding of magnetization theory. Tao et al. [10,23,24] considered that magnetic (or electric) field treatment aggregates asphaltene (or paraffin) particles inside crude oil into larger particles, which reduces the viscosity of crude oil. Loskutova et al. [19] found that the recovery time of paramagnetic and antioxidant properties of magnetized crude oil was the same as that of rheological properties. ...
Article
Electromagnetic synergistic oil-water separation is a promising technology for deep dehydration with higher efficiency, shorter dehydration period and flexible control of field parameters. In this paper, non-conductive silicone oil without colloid and asphaltene was used as the continuous phase. The effect of magnetization and Lorentz force on the continuous phase can be excluded to explore the mechanism of the electric field and magnetic field synergistic dehydration. Firstly, the particle size of droplets was characterized. The results showed that the dispersed phase was uniformly distributed and the average particle size was 18.24 um. Then the dehydration performance of different types of outfields was compared. The experimental results showed that the dehydration performance of AC electric field combined with magnetic field was better than that of single AC electric field. The dehydration performance of AC electric field and magnetic field was better than that of DC electric field and magnetic field. On this basis, the theory of AC polarization-electromagnetic force was proposed. Finally, the influence of magnetic field intensity on dehydration performance was explored, including dehydration depth and dehydration speed, and the optimal magnetic field intensity range in this experiment was obtained, and its value was [0.269, 0.355] T.
... It has been reported that for some waxy crude oils, the viscosity near the pour point can be reduced by more than 80% and the yield stress reduction rate can be up to 90%, while the energy consumption is only 1% of the heating energy consumption for the same viscosity reduction rate. 94−98 In 2006, Tao and Xu 94 reported the possibility of using pulsed electric or magnetic fields to modify the crude oil. The team reported years later that for light waxy crude oil at a pour point of −4°C, WAT of 12.5°C, and density of 855 kg/m 3 , an electric field of 1.6 kV/mm applied at 1°C above the pour point and along the flow direction of the crude oil could achieve 82.1% viscosity reduction. ...
... The essential reason is that the mechanism of viscosity reduction by magnetization of crude oil is still controversial. Tao,94,112 Homayuni,113 and Chen 114 and their co-workers concluded that whether it is pulsed magnetization or permanent magnet magnetization, the magnetic field reduces the viscosity of the system by enhancing the intermolecular dispersion force, leading to the agglomeration of solid particles in the crude oil and increasing the polydispersity of the system. However, Jiang et al. 115 used terahertz time-domain spectroscopy to demonstrate that the treatment with magnetic fields decondensed the solid particles in the crude oil as determined by characterizing the reduction of the extinction coefficient ( Figure 12). ...
... The reaction products are low solubility surface-active carboxylates, analogous to a surfactant [161]. The magnitude of interfacial tension reduction is reported to be proportional to the applied electric potential [162]. The viscous dragging of oil requires coupling of the oil mass with the water through an interface, similar to the diffuse double layer (DDL) of clay that gives rise to electrokinetic potential. ...
... Considering such a process [141] on the four functional group fractions of the crude oil, SARA (i.e., Saturates, Aromatics, Resins, and Asphaltenes), it is expected that the asphaltene and resin content of the oil decrease and the aromatic content increase, as the viscosity of the oil decrease. Reduction in the oil viscosity under applied electric field has been reported in the literature [153,154,161,162]. The less viscous oil has higher mobility in soil or rock formation pores, hence easier to extract. ...
Chapter
The fundamental principles of electrochemical transport and transformations applied to electrokinetic processing of oil contaminated saturated clays and clayey formations are reviewed, and some findings are presented in this chapter. The experimental results of electrically enhanced extraction, and transformation, in clay and clay rich porous media are presented and discussed in the framework of the theoretical electrochemical and electrokinetic concepts. The data supports the hypothesis that Faradaic current passage in the electric double layer of clay particles may drive forth redox reactions on and near clay surfaces. The contribution of electrochemical reactions to electrically enhanced oil recovery was investigated through floor-scale synthetic core specimens. The results of these experiments indicated that electrochemical reactions do take place, which affect the transformation of heavy crude oil into its different components due to the passage of current through the formation. As the lighter components (aromatics) of the oil increase and the heavier components (asphaltenes) decrease, the viscosity of the oil decrease, which in turn increases the mobility of the crude oil within the porous structure of a formation.
... Recently, Tao et al. proposed a novel electric field-based method for the reduction of viscosity of flowing crude oil [6]. They found that the application of a strong electric field along the flow direction can lead to significant viscosity reduction of the flowing oil, with a viscosity reduction of up to 80% achieved and the viscosity remaining below that of the original oil for more than 24 h [7]. ...
... Compared with the apparatus used in the previous work [6,12,18], this device has the advantage of applying the electric field and performing rheological tests simultaneously, eliminating potential experimental artifacts due to non-instantaneous transfer of oil samples from the electric treatment cell to the rheometer [7,12,18,19]. ...
Article
It has been reported that the application of a high-voltage electric field parallel to the oil flow direction or to a quiescent waxy crude oil can reduce the viscosity of the oil. In this work, an electric field perpendicular to the flow direction is applied to a flowing waxy crude oil in a rheometer equipped with in-situ electric field manipulation, and it is observed that viscosity reduction similar to that obtained with electric field parallel to the flow direction can also be achieved. This, therefore, confirms that the treatment efficacy is insensitive to the direction of the electric field compared to the oil flow direction. Moreover, the non-Newtonian characteristics of the treated crude oil become less significant, and more viscosity reduction is achieved at higher electric field strength and lower oil temperature. After the removal of the electric field, the reduced viscosity gradually recovers and the viscosity reduction disappears after about two days. Though it is found that the electric treatment causes an increase in wax crystal size and aggregation of particles to some extent, we think that weakened interaction between wax particles due to electric field exposure should be the primary reason of the viscosity reduction according to the knowledge of suspension rheology and the mechanism of waxy crude oil rheology.
... Based on their observations, thermal conductivity of water lowered by 16%, and its surface tension, decreased by 18% [31]. Other fluids such as blood and paraffin can also be affected by a magnetic field, as well [32][33][34]. Magnetic J o u r n a l P r e -p r o o f 9 treatment of water is environmentally friendly in view of the fact that it reduces the use of harmful chemicals in the environment [35]. ...
... Another mechanism behind the resulted reduction of stability could be related to the rheology change of fluids. Applying a magnetic field to reservoir fluids leads to change in their rheological properties and reduces crude oil viscosity [33,47]. Lower viscosity of crude oil, the continuous phase, results in a faster rate of two emulsion breakage mechanisms, namely creaming and sedimentation, which are prerequisites for the coalescence mechanism. ...
Article
The injection of solid stabilized water-in-crude oil emulsion to displace heavy crude oil is a new EOR method. Although high emulsion stability, which is essential for achieving the maximum process efficiency, can be obtained using nanoparticles, developing an inexpensive and environmentally friendly technique that improves emulsion stability is highly beneficial to this method. Magnetic field and magnetized water technologies have such capabilities. Contact angle reduction on solid surfaces is among the modifications that occur in the properties of water due to the magnetization. Although studies show that using these technologies might be amenable for enhanced oil recovery, there has been no investigation into their use to alter conventional and solid stabilized water-in-crude oil emulsion stability. In this study, the magnetized water, prepared with distilled water, is used in the process of emulsion preparation and the resulting emulsion stability is compared to that prepared with normal water. Our findings show that using magnetized water improves the stability of solid stabilized emulsion made with fumed silica and iron oxide nanoparticles, while it does not impact the stability of conventional emulsions. Lower three-phase contact angle in case of using magnetized water compared to that of normal water implies that the hydrophobic nanoparticles more rigidly stick to the oil-water interface and more energy is required in order to detach them from the interface. This results in more stable solid stabilized emulsion. Results indicate that applying the magnetic field to a prepared conventional emulsion makes it a bit less stable. The reorientation of asphaltene molecules and resulting disturbance of the interface layer, along with the oil viscosity reduction, which accelerates the coalescence of dispersed water droplets, results in less stable emulsions. Although applying the magnetic field to the solid stabilized emulsion, prepared with fumed silica nanoparticles, has no effect on its stability, it significantly reduces the stability of the iron oxide nanoparticle stabilized emulsion. The magnetic force that exists between the magnets and the iron oxide nanoparticles, forcibly separates them from the interface and leads to emulsion breakage. The findings of this study could help in better understanding of the mechanisms involved in the stability of solid stabilized emulsions. Besides, a new field, in which the magnetized water can be successfully applied, is introduced.
... The significance of the impacts of magnetic field exposure on combustion performance is influenced by several aspects, namely type and volume of machine (Jain & Deshmukh, 2012), workload or engine rotation (Faris et al., 2012), duration of exposure (Abdel-Rehim & Attia, 2014), and type of fuel (Abdel-Rehim & Attia, 2014;Tao & Xu, 2006). Although some experiments have proven the impacts of exposure, the fundamental reason that causes the use of fuel exposed to the field ...
... Figure 6, it is also observed that the O 2 emission will decrease when the engine load increases. This result is supported by Tao (2006) who, in his research, found that oil viscosity will decrease as the engine rotates faster. This decrease in viscosity indicates a bond weakening between molecules, which results in an increase of reaction between the HC molecules and O 2 . ...
Article
Full-text available
The impacts of strengthening magnetic field exposure on combustion performance of low-octane fuel have been examined experimentally. The combustion test was carried out using a 2-stroke 49 cc engine where the fuel was magnetized using a low magnetic field (<2 kG). Moreover, the molecular behavior of magnetized fuel was also characterized through spectrum tests using NIR and UV-Vis spectrophotometers. The result of this study indicates an exponential decrease of magnetized fuel consumption against the strengthening of magnetic field exposure. This exponential decrease of consumption can be related to the Arrhenius principle. In addition, the decrease of oxygen in the exhaust gas along with the strengthening of the magnetic field also confirms the increase of combustion reactions. Meanwhile, the increase of magnetized fuel absorption against ultraviolet and near-infrared lights along with the increase of the magnetic field intensity indicates a bond weakening, accompanied by the increase of molecular vibrational energy.
... Moreover, quite a few experimental studies in the literature show a decrease in the viscosity of oil when exposed to electric or magnetic fields [35][36][37][38]. The method of electromagnetic influence on the oil-saturated reservoir shows an increase in the debits of producing wells [39]. ...
Article
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This review paper presents controversial issues on the formation of hydrocarbon deposits. We look into the geological contradictions of the abiogenic and biogenic theories of petroleum origin, indicating the connection between hydrocarbon deposits and disjunctive dislocations, as well as present disputes about the geological period over which hydrocarbon deposits have been formed. We further overviewed the radical chain mechanism of hydrocarbon generation from organic matter as proposed by Prof. Nesterov. It is noted that the petroleum generation process in reservoir conditions occurs almost instantly in the presence of discrete geomagnetic fields and does not require a long geological time. This is explained by spin magnetic effects (spin catalysis, magnetic isotope properties). We briefly highlight the effect of magnetic fields on chemical reactions involving organic compounds and the use of magnetic fields to enhance oil recovery. We also present the leading causes of discrete magnetic fields in the sedimentary cover: Earth’s geomagnetic reversals, generation of ferromagnetic minerals in oil deposits, electromechanical effects of rock friction near faults, and intermixing of reservoir waters with different mineralization (spontaneous ion polarization). Based on the material reported, we conclude that the radical chain mechanism of petroleum generation processes explains some contradictions of the abiogenic and biogenic theories of petroleum origin. Elaborating this research area has excellent prospects for developing new criteria for hydrocarbon prospecting and devising innovative methods to enhance the oil recovery for shale oil production.
... 2. Effectiveness remains to be evaluated. (Elliott and Lira, 1999;Knowles, 1987;Reif, 2009) (Hamida and Babadagli, 2007;Hou et al., 2015;Mullakaev et al., 2015;Roberts et al., 2000;Tao and Tang, 2014;Tao and Xu, 2006) (Binks et al., 2015;Chen et al., 2010;Hennessy et al., 2004;Pedersen and Rønningsen, 2003) Ethylene polymers and copolymers ...
... In the absence of a magnetic field, the fibers form an entangled network with approximately isotropic orientation of the fibers. With a magnetic field applied, the shorter wires lined up relatively well, and formed agglomerates, which led to a reduction in viscosity [48,49]. The longer wires displayed less alignment with the field due to either passive static friction or entanglement or a combination of both. ...
Article
Full-text available
The yield stress of magnetorheological (MR) fluids has been shown to depend on particle morphology, but the exact nature of this contribution is still not fully understood. In this study, MR fluids containing 4 vol. % cobalt particles (spherical particles vs. nanowires) suspended in silicone oil were investigated. The influence of the aspect ratio on the rheological properties of suspensions that contained cobalt nanowires with aspect ratios ranging from 10 to 101 in increments of ~6 is described. The cobalt nanowires were fabricated using alumina template-based electrodeposition, producing wires with 305 ± 66 nm diameters. The shear stress was measured as a function of shear rate for increasing applied magnetic fields. The apparent yield stress and viscosity as a function of changing aspect ratio of the nanowire suspensions were determined. At a saturated magnetic flux density, the yield stress was found to increase linearly up to an aspect ratio of 23 (7.1 μm long wires) at which time the yield stress reached a plateau of 3.7 kPa even as the aspect ratio was further increased. As a comparison, suspensions containing 4 vol. % 1.6 μm spherical cobalt particles only reached a maximum yield stress of 1.6 kPa.
... Downhole, this helps avoid the build-up of wax deposits and agglomeration by polarizing the wax molecules in a flow-direction orientation. Wax crystals' agglomeration is disrupted by magnetic field techniques, which modify the kinetics of precipitated wax and make it more difficult for wax to precipitate and develop into larger crystals [19][20][21]. The MFC method had no effect on the WAT, but it did increase the crude oil's viscosity, according to research. ...
Article
Full-text available
Deposition of wax is considered one of the most significant culprits in transporting petroleum crude oils, particularly at low temperatures. When lowering pressure and temperature during the flow of crude oil, the micelle structure of the crude oil is destabilized, allowing oil viscosity to increase and precipitating paraffin (wax) in the well tubulars and pipeline, which increase the complexity of this culprit. These deposited substances can lead to the plugging of production and flow lines, causing a decline in oil production and, subsequently, bulk economic risks for the oil companies. Hence, various approaches have been commercially employed to prevent or remediate wax deposition. However, further research is still going on to develop more efficient techniques. These techniques can be categorized into chemical, physical, and biological ones and hybridized or combined techniques that apply one or more of these techniques. This review focused on all these technologies and the advantages and disadvantages of these technologies.
... 9,10 At present, the technology of solid breaking by plasma is being widely used in many fields, especially in the fields of rock breaking and oil production. 11,12 Zuo separated minerals by virtue of the selective crushing characteristics of HVEP. 13 Bru observed that the mineral particles presented an obvious sorting after breaking the low-grade cassiterite schist. ...
Article
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The technique of high-voltage electrical pulses (HVEP) is a new method to enhance the permeability of coal seams and improve the efficiency of coalbed methane (CBM) exploitation. This paper is aimed at investigating the crack propagation characteristics of samples of different strengths, proposing the improved procedure of HVEP in field application, and proving that the electrohydraulic effect has a wide use in field application of CBM extraction. In this paper, an experimental system utilizing HVEP in water condition is established, coal samples with different strengths are crushed, and the extended processes of cracks are analyzed. According to the research results, the electrohydraulic effect has a good breakage on the coal; the number of main cracks is 2–3 and the length of the main cracks is about 30 cm in the vertical direction of the hard samples; and the formation of cracks is relevant to the discharge voltage, discharge times, and mechanical parameters of the samples. The results of scanning electron microscopy (SEM) demonstrate that the cracks and pore connectivity of the coal samples are improved obviously, and the permeability results show that the permeability of crushed coal samples is 20% greater than that of the raw coal sample. Meanwhile, the generation process of cracks can be divided into four periods: namely, fatigue damage accumulation, slow development, rapid development, and failure; the rapid development stage is the optimal phase in field application. Moreover, the shock wave produced by HVEP via electrohydraulic effect can crush the samples mainly; furthermore, the energy produced by bubble rupture also has a great influence on the formation of cracks. This study can provide a foundation for the HVEP to improve CBM exploitation.
... Under the electric field, it is revealed that the aggregation of suspended crystal particles into chains should be responsible for the weakness of crystal network (Tao et al. 2014). Similarly, the suspended crystal particles aggregate and lead to the decrease in waxy crude oil viscosity when applying a pulsed magnetic field (Rosensweig 1996;Tao and Xu 2006). However, the modification effect of magnetic field is selective which is not only related to the properties of crude oil, but also depended on the metal ions (Mn 2+ , Sr 2+ , Br − ) and water content in crude oil (Gonçalves et al. 2010;Gonçalves et al. 2011;Shliomis and Morozov 1994). ...
Article
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Yield stress, as the key parameter to characterize the network strength of waxy oil, is important to the petroleum pipeline safety. Reducing the yield stress of waxy oil is of great significance for flow assurance. In this study, the effect of alternating magnetic field (intensity, frequency) on the yield stress of a waxy model oil with nanocomposite pour point depressant (NPPD) is systematically investigated. An optimum magnetic field intensity and frequency is found for the reduction in yield stress. When adding with NPPD, the heterogeneous nucleation of NPPD contributes to the reduction in yield stress for waxy model oil. Interestingly, the magnetic field is helpful for the modification of yield stress at a lower frequency and intensity before the optimal value; however, the modification is found to be weakened when the magnetic field is further increased after the optimal value. Possible explanation is proposed that the aggregation morphology of wax crystal would be altered and results in the release of wrapped oil phase from the network structure under the magnetic field.
... The behavior described for the evaluated samples is typical of this class of fluids, showing a shear-thinning behavior, that is, oil viscosity decreases as the shear increases. Mortazavi-Manesh and Shaw [21,34], Bazyleva et al. [62], Mozaffari et al. [87], Tao and Xu [88], and Taborda et al. [44] found similar results. Clearly, viscosity reductions are detected when adding up to a concentration of 700 mg/L of the material, obtaining the largest viscosity change at 500 mg/L. ...
Article
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The main objective of this study is the synthesis, use, and reuse of magnetic copper ferrite nanospheres (CFNS) for extra-heavy oil viscosity reduction. The CFNS were synthesized using a solvothermal method resulting in mean particle size of 150 nm. Interactions of CFNS with the crude oil were evaluated through asphaltene adsorption isotherms, as well as static and dynamic rheology measurements for two cycles at 25 ◦C. Adsorption and desorption experiments corroborated that most of the asphaltenes adsorbed can be removed for nanoparticle reuse. During the rheology tests, nanoparticles were evaluated in the first cycle at different concentrations from 300 to 1500 mg/L, leading to the highest degree of viscosity reduction of 18% at 500 mg/L. SiO2, nanoparticles were evaluated for comparison issues, obtaining similar results regarding the viscosity reduction. After measurements, the CFNS were removed with a magnet, washed with toluene, and further dried for the second cycle of viscosity reduction. Rheology tests were performed for a second time at a fixed concentration of 500 mg/L, and slight differences were observed regarding the first cycle. Finally, changes in the extra-heavy oil microstructure upon CFNS addition were observed according to the significant decrease in elastic and viscous moduli.
... The conventional method for improving cold flowability of waxy oil is the pour-point-depressants (PPDs) modification [6,7]. Recently, it is reported that applying an electric field to a flowing liquid oil can significantly reduce its viscosity [8]. This viscosity reduction effect can be maintained for several hours after the removal of the electric field, and it is repeatable, i.e., viscosity reduction can be achieved repeatedly by applying the electric field again and again. ...
Article
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The paraffin molecules in crude oil crystalize and precipitate out as the oil cools, resulting in a sharp increase in oil viscosity and further the gelation of the oil. The waxy crude oil gel exhibits complex rheological behaviors, such as viscoelasticity, yield stress, and thixotropy, posing challenges to the flow assurance of pipelines. Previous studies have verified that applying a high-voltage electric field to a flowing liquid oil can significantly reduce its viscosity. In this work, the electrorheological behaviors of waxy crude oil gel are explored by a stress-controlled rheometer equipped with in situ DC electric field manipulation. It is reported for the first time that the gel structure can be significantly weakened upon the application of an electric field for a duration of not less than 10 s, with the yield stress, storage modulus, loss modulus, and apparent viscosity reduced by up to 90%. In addition, the gel structure fracture is observed to transit from brittle-like to ductile-like. A stronger structure weakening effect can be obtained at a higher field strength and lower temperature. The structure weakening effect induced by the electric field can be maintained for a certain period of time after the removal of the electric field, with a recovery of yield stress and moduli less than 10% in 48 h. We hold the view that the electrorheological behaviors of waxy oil should be attributed to the weakened attraction between wax particles induced by the electric field.
... Recently, many studies focus on a dilution method using a different solvent in order to achieve a certain viscosity, Nourozieh et al [15], observed the adding a minimum quantity of n-hexane to Athabasca bitumen under different temperatures and pressures improve its mobility and has a significant effect on viscosity reduction, Popoola et al [16], reported the addition of (0.05 to 5%) from Triethanolamine (TEA) to Niger-Delta heavy crude oil at different temperature (28-65 °C) has significant effect on the reduction of viscosity and pour point, Mortazavi-Maneshand Shaw [17], showed the mixture of (toluene + butanone) addition with a ratio (50/50 vol. %) under different temperatures (-15 to 60 °C) is the best solvent for decreasing the thixotropic effect and viscosity reduction in comparison with toluene and n-heptane alone, Narro et al [18], investigated the impact of light hydrocarbons addition products from waste plastics on viscosity reduction of heavy crude oil, they found the viscosity was reduced 90% by added 20 vol.% of light hydrocarbon at ambient temperature Mozaffari et al. [19], conducted a wide-ranging study on the relationship between the bitumen viscosity and the aggregation of asphaltene, they showed that blend of heavy crude oil with heptane and Hepatol decrease the viscosity that attributed to precipitated of asphaltene aggregation will lead to decrease it content in the mixture, Bassane et al [20], investigated the effect of temperature and condensed gas addition on the viscosity reduction of different types of Brazilian heavy oils has API from (13.7 -21.6), they observed that a high temperature over 20 ° C led to 70 to 77% reduction in viscosity, While, at 32 vol.% addition of condensate gas has a high impact on the viscosity reduction was about 98%, Rahimi et al. [8], study the effect of dilution with light hydrocarbons (5-15 vol.%) on extra heavy crude under irradiated used ultrasonic for (5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)minutes at various temperatures, they found the best reduction in viscosity at 10 minutes. ...
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The transport of heavy crude oil from the head-well to the refinery plants is an attractive factor as its production is currently increasing around the world, this study focuses on the dilution method to reduce the viscosity of heavy oil that will lead improves it flows through transportation pipes using toluene, dimethyl ketone (DMK) and a mixture of (50/50 vol. %) toluene / dimethyl ketone as a dilutes solvents with different weight fraction (0, 5, 10 and 15 wt. %) at 298.15 K. The heavy oil used collected from Amara oil field, south of Iraq, its viscosity was measured by Brookfield viscometer over a range of shear rate (0 - 42s-1), the better the weight fraction of solvents for reducing the viscosity of heavy oil was investigated under different temperatures (298.15, 308.15 and 318.15 K). The results showed dilution of heavy oil samples with toluene, DMK and a mixture of (50/50 vol. %) toluene and DMK reducing the viscosity, moreover the temperature has a great effect on the degree of viscosity reduction in the presence of the diluents, however, the higher DVR was noticed about 87.17 % at 15 wt.% of the mixture (50/50 vol. %) toluene + DMK at 318.15 K and shear rate 42 s-1.
... Recently, Tao et al. [27][28][29][30][31] developed a novel method to reduce the viscosity of waxy oils via application of high-voltage direct current (DC) electric field. They found that by imposing an electric field on the oil for seconds, the viscosity of the oil can be reduced by as much as 80% at temperatures near the pour point. ...
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Wax deposition during crude oil production, transportation, and processing has been a headache since the early days of oil utilization. It may lead to low mobility ratios, blockage of production tubing/pipelines as well as fouling of surface and processing facilities, among others. These snags cause massive financial constraints increasing projects' turnover. Decades of meticulous research have been dedicated to this problem that is worth a review. Thus, this paper reviews the mechanisms, experimentation, thermodynamic and kinetic modeling, prediction, and remediation techniques of wax deposition. An overall assessment suggests that available models are more accurate for single than multi-phase flows while the kind of remediation and deployment depend on the environment and severity level. In severe cases, both chemical and mechanical are synergistically deployed. Moreover, future prospective research areas that require attention are proposed. Generally, this review could be a valuable tool for novice researchers as well as a foundation for further research on this topic.
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Electrorheological (ER) technology is an advanced technology based on ER effects. The most common material in ER technology is an electrorheological fluid (ERF), which is a type of smart soft material. The viscosity of ERF is reversibly adjustable by an applied electric field. A new type of electroresponsive soft material, electrorheological elastomer (ERE), which is a derivative of ERFs, has attracted wide attention due to its advantages of not precipitating and easy packaging. ER materials are widely applied in mechanical engineering due to their reversibly tunable characteristics, fast response, and low energy consumption. In addition to basic ER material fabrication and application, ER technology is also used in energy material preparation, oil transportation, and energy storage. The application of ER technology in the energy field provides a good example of the potential applications of ER technology in other fields. This article systematically summarizes the research status and future development prospects of ER technology in materials, energy, and mechanical engineering from the mechanism to application, combined with the latest research results.
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This paper studies the effect of physical fields (i.e. ultrasonic and constant magnetic fields) on structural and energy properties (viscosity, limiting shear stress, pour point, activation energy of viscous flow) as well as kinetic (antioxidant) properties of highly resinous problematic oil. The results were obtained via viscometry, determining of pour point and voltammetric method of oxygen electroreduction. It was shown that the treatment of studied oil by acoustic and magnetic fields lead to decrease in viscosity and temperature parameters. Combined treatment displays an additional reduction of viscosity and pour point
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Recent studies have shown that the poor flowability of waxy crude oil can be obviously improved by the application of an external electric field. Available studies about this novel technique to treat waxy oils focus on the efficacy of this technique while the sustainability of the efficacy is not well understood. In this work, the impacts of shearing and thermal cycling on the stability of the electric treatment efficacy were investigated. A representative waxy crude treated by electric field was subjected to shearing at different conditions and reheating to an elevated temperature and cooling, then the viscosity and the yield stress were inspected and wax particle microscopic images were observed to examine the impacts of shear and thermal histories on the sustainability of waxy crude oil flowability improvement by electric treatment. The experimental results show that the electric treatment efficacy of waxy crude oil gradually diminishes after the removal of electric field. However, shearing at a high shear rate and for a prolonged duration partially preserves the efficacy of the electric treatment and intensively shearing the electrically treat oil provides some additional flowability improvement. The flowability improvement by electric treatment is weakened by reheating the treated oil to an elevated temperature. When the treated oil is heated above the wax dissolution temperature, the efficacy of the electric treatment is eventually eliminated. The results presented in this work further the understanding of the flowability improvement of waxy crudes by electric treatment.
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Thesis
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As petroleum industry advanced in the last century, it encouraged most of the technological developments carried out in the same period, providing a cost-effective energetic source in almost all of the human social ambits. However, as conventional crude oils have been exploited to satisfy energetic world demands, heavy oil (HO) and extra-heavy oil (EHO) reserves have gained significant importance, representing approximately 70% of total worldwide reserves. Nevertheless, exploiting HO and EHO carries appreciable technological challenges and issues for petroleum industry in distinct processes such as, production, transportation and refining because of the fluids properties such as high salinities, emulsifying tendencies, low API gravity, low gas/oil ratios, high content of heavy components and high viscosities. There is not a direct relation between fluids density and viscosity in crude oils, but it is common to find crude oils with low API gravities having a high viscosity which generates significant issues for transporting, production and oil recovery processes as the common used techniques for treating this problem generates non cost-effective operations. Thus, the main objective of this thesis is to study a novel technique involving ultrasound cavitation usage assisted with NiO/SiO2 nanoparticulated systems for reducing HO viscosity at transportation and reservoir conditions avoiding thermal processes. It is expected that this study can open a broader landscape about the impacts of nanotechnology in the production and transportation operations of heavy oils
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Chapter
The reduction in viscosity of crude oil due to magnetic field and its subsequent recovery after certain time is an important method of paraffin wax deposition control. It is less energy-intensive than the commonly used heating method. Three crude oils with varying wax content were subjected to magnetic fields of strengths 1000, 3000, 6000 and 9000 gauss for one minute. Reduction in viscosity of the samples was recorded instantaneously. Thereafter the viscosity readings were taken at regular intervals of time and the trend for recovery of viscosity to its original value was observed. Investigations were performed with respect to changes in magnetic field on crude oils having different wax content. It was found that more was the initial reduction, slower was the regain of viscosity. A possible mechanism for recovery of viscosity has also been discussed. The knowledge of recovery trend would help the flow assurance engineer to predict the optimum number of pumping stations thereby conserving energy.
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A functional raspberry-like core–shell composite particle consisting of a conducting polyaniline (PANI) core and magnetic zinc ferrite shell is synthesized by Pickering emulsion polymerization. The morphology and chemical structure of the PANI/zinc-ferrite composite are evaluated by scanning electron microscopy, transmission electron microscopy, and Fourier-transform infrared spectroscopy. An electrorheological/magnetorheological fluid consisting of the PANI/zinc-ferrite composite dispersed in silicone oil with a particle concentration of 5 vol % is fabricated. Its rheological characteristics under external electric and magnetic fields are investigated by using a rotational rheometer. Under the electric or magnetic field, the PANI/zinc-ferrite particles form chain-like structures, demonstrating a solid-like state.
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Magnetorheological (MR) fluids, which can rapidly be changed from a liquid state to a solid state and vice versa by a magnetic field, have the potential to revolutionize several industrial sectors. The key issue is to enhance their yield shear stress. This paper reviews the physical mechanism and microstructure of MR fluids. It finds that the weak points of the MR microstructure under a shear force are at the chains' ends. Hence, a general technique, a compression-assisted-aggregation process, is developed to change the induced MR structure to a structure that consists of robust thick columns with strong ends. The scanning electronic micrographic (SEM) images confirm such a structure change. With this approach, MR fluids become super-strong. The enhanced yield stress of MR fluids reaches 800 kPa at a moderate magnetic field.
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Microemulsions have been prepared from benzene and water using emulsifier blends of 5% Tween 20 + 1% Span 20 or 10% Tween 20 + 1% Span 20. The volume concentration of the dispersed phase (ϕ) extended up to 0.406, and the mean particle diameter ranged from 543A–1245A. The steady-state viscosities of these microemulsions, as determined in a capillary viscometer, could not be represented by any equation which merely related viscosity and dispersed phase volume concentration. After allowing for the volume (ϕ8) of benzene solubilized within the micelles of excess emulsifier, the relative viscosity (nrel) data conformed to where k is a hydrodynamic interaction coefficient which depends empirically on mean particle size (Dm) according to . has a higher value (1.95–2.08) than predicted by Taylor's theory, although it is well below the value of 2.5 for solid spheres. Several factors may hinder fluid circulation within the droplets.
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The use of magnetic fluid conditioning (MFC) technology to treat downhole wax deposition in the production of waxy crude oil has sparked considerable controversy. A variety of claims have been made about the success rate of the technology in field applications. The interpretation of results from MFC field treatments is extremely difficult, since field conditions involve a number of uncontrolled parameters, including oil composition and gas content, downhole temperature and pressure, and flow rate. In an effort to examine the influence of a magnetic field on wax precipitation from crude oil, a set of laboratory experiments was performed under controlled conditions. The experiments demonstrated that the application of a magnetic field can have a measurable effect on waxy crude oil. Properties of waxy crude oil samples, such as viscosity and wax out temperature, were measured before and after magnetic treatment. No changes in the wax out temperature were detected. Increases in the viscosity of oil samples following treatment were observed, but only when the temperature at which an experiment was performed was close to the wax out temperature of the sample. However, not all of the experiments performed near the wax out temperature of the oil resulted in measurable magnetic effects. The variability in the experimental results suggests that all of the key factors affecting the magnetic treatment process were not identified or adequately addressed. The results indicate, though, that one key factor is the state of wax saturation in the oil as it is undergoing magnetic treatment. A mechanism that may account for the magnetic effects observed in the experiments is proposed. Some implications of this mechanism on field applications of magnetic technology are presented. Introduction One of the major problems faced in the production of waxy crude oil is wax deposition in producing wells and associated piping and production facilities. A technology that has been proposed for handling wax deposition is magnetic fluid conditioning (MFC). To date, this technology has achieved varying degrees of success in field applications. Attempts to improve the effectiveness of MFC technology have been hindered by a lack of understanding of the mechanisms that may be responsible for the influence of a magnetic field on wax deposition. The scientific literature on magnetic fluid conditioning is contained almost exclusively in Russian and Chinese journals. For the most part, these papers mention some experimental evidence of magnetic treatment effects on waxy crude oils, but provide little supporting details about the experiments. Moreover, the observations are not consistent from paper to paper, and no credible explanation of the mechanisms involved in magnetic treatment is advanced in any of the papers. The patent literature associated with magnetic fluid conditioning technologies is largely US based. Although a handful of patents have been granted in which the treatment of waxy crude oils is identified as an application, a large number (more than 100) of others have listed water treatment (prevention of scaling) as the intended application. The devices for the latter application are generally similar in design to those for the former.
Article
Although the influence of magnetic fields on paraffin deposition is still dimly understood, magnetic devices have been exploited by the petroleum industry to mitigate this problem. In this study, a series of experiments were carried out using a lab-scale magnetic conditioner and two kind of samples: paraffin mixture and crude oil. The investigated parameters were: exposition time, temperature, magnetic field intensity. paraffin type and content in the fluid and the reversibility of the observed alterations. The results indicate that magnetic fields, up to 1 Tesla applied at a temperature close to the Wax Appearance Temperature (WAT), reduce the apparent viscosity of the samples. This effect has been ascribed to changes in the paraffin crystal morphology promoted by the magnetic field. Scanning Electronic Microscopy (SEM) was fundamental to confirm this hypothesis.
Article
A simple equation is presented for predicting the kinematic viscosity of bitumens and heavy oils mixed with diluents. The correlation has been shown to provide accurate viscosity estimates of these mixtures for a wide range of data and requires only the knowledge of the pure bitumen and pure solvent viscosities at any given temperature. The correlation makes use of a viscosity reduction parameter which reduces error significantly when compared to similar equations presented by Chirinos et al. (1983), and Cragoe (1933). For a total of 89 data points, excluding the pure bitumens and diluents values, the correlation yielded an overall average absolute deviation of about 14 percent. The same equation was applied to predict the mass fraction of diluent required to reduce bitumen viscosity to pumping viscosity. Predicted values matched experimental values very well, with an overall average absolute deviation of about 6 percent.
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The pulsed-field structure of an emulsion of monodisperse, magnetizable oil droplets is investigated via optical microscopy. By permitting droplet diffusion in the field-off state, a pulsed field allows minimization of energy through structural rearrangement. For droplets with a magnetic susceptibility of χ = 2.2 and radius a ≥ 0.32 μm, we find that rearrangement into ellipsoidal aggregates occurs in response to a pulsed magnetic field. The ellipsoid ends are composed of chainlike projections at low pulse frequencies and conical spikes at high pulse frequencies. The conical spikes appear to be energetically favored but cannot form at low pulse frequencies due to the large diffusion distance of the droplets in the field-off state. The eccentricity of the ellipsoids is invariant with field strength in strong fields, but in weak fields we find that the ellipsoids become more elongated as the field strength is lowered. This elongation in weak fields coincides with the formation of more dilute aggregates and gives information about the change in surface structure as field strength decreases.
Article
The effect of Brownian motion of particles in a statistically homogeneous suspension is to tend to make uniform the joint probability density functions for the relative positions of particles, in opposition to the tendency of a deforming motion of the suspension to make some particle configurations more common. This smoothing process of Brownian motion can be represented by the action of coupled or interactive steady ‘thermodynamic’ forces on the particles, which have two effects relevant to the bulk stress in the suspension. Firstly, the system of thermodynamic forces on particles makes a direct contribution to the bulk stress; and, secondly, thermodynamic forces change the statistical properties of the relative positions of particles and so affect the bulk stress indirectly. These two effects are analysed for a suspension of rigid spherical particles. In the case of a dilute suspension both the direct and indirect contributions to the bulk stress due to Brownian motion are of order ø2, where ø([double less-than sign] 1) is the volume fraction of the particles, and an explicit expression for this leading approximation is constructed in terms of hydrodynamic interactions between pairs of particles. The differential equation representing the effects of the bulk deforming motion and the Brownian motion on the probability density of the separation vector of particle pairs in a dilute suspension is also investigated, and is solved numerically for the case of relatively strong Brownian motion. The suspension has approximately isotropic structure in this case, regardless of the nature of the bulk flow, and the effective viscosity representing the stress system to order φ2 is found to be $\mu^{*} = \mu(1+2.5\phi + 6.2\phi^2).$ The value of the coefficient of ø2 for steady pure straining motion in the case of weak Brownian motion is known to be 7[cdot B: small middle dot]6, which indicates a small degree of ‘strain thickening’ in the ø2-term.
Article
Electron spin resonance (ESR) studies are reported which have as their objective a better understanding of the structure of native petroleum asphaltenes as contrasted to other asphaltic and carbonaceous substances. The g-values differed from those of the semiquinold systems, but were close to those of aromatic systems. The number of spins per gram of sample, N0, was found to correlate with H/C ratio, oxidation rate, aromaticity, and color intensity. Correlations also appear to exist between population of aromatic carbon atoms per spin and T1, and between vanadium content and T2. The free radicals are believed to be associated with nonlocalized TT systems in the aromatic centers. Several structures are proposed, two of which involve gaps or holes in the clusters. ESR absorption for metal-free porphyrins and phthalocyanine supports these proposals.
Article
The interparticle forces and resulting shear stresses in a magnetorheological fluid are calculated. The field due to a linear chain of particles in a fixed average magnetic induction B ave is determined from a finite element analysis in which the nonlinearity and saturation of the particle magnetization are incorporated. The shear stresses are then computed from the field using Maxwell’s stress tensor. The stresses obtained for all but the lowest magnetic inductions are controlled by the saturation of the magnetization in the contact regions of each particle. Identifying the maximum shear stress as a function of shear strain with the yield stress gives values in agreement with results reported for typical fluids. For high magnetic inductions the yield stress plateaus due to the complete saturation of the particle magnetization; the stress scales as the square of the saturation magnetization in this regime. © 1994 American Institute of Physics.
Article
A critical analysis was made of the extensive experimental data on the relative viscosity of suspensions of uniform spherical particles. By appropriate extrapolation techniques, non-Newtonian, inertial, and nonhomogeneous suspension effects were minimized. As a result, the scatter of the data was reduced from ±75% to ±13% at a volume fraction solids of 0.50. The coefficients of different power series relating relative viscosity and volume fraction solids were determined using a nonlinear least squares procedure. It was shown that a new expression containing three terms of a power series with coefficients determined from previous theoretical analyses and an exponential term with two adjustable constants fit the data as well as a power series with six terms, either three or four of which were adjustable constants with the remaining coefficients being theoretical values.
Article
Einstein's viscosity equation for an infinitely dilute suspension of spheres is extended to apply to a suspension of finite concentration. The argument makes use of a functional equation which must be satisfied if the final viscosity is to be independent of the sequence of stepwise additions of partial volume fractions of the spheres to the suspension. For a monodisperse system the solution of the functional equation is where ηr is the relative viscosity, φ the volume fraction of the suspended spheres, and k is a constant, the self-crowding factor, predicted only approximately by the theory. The solution for a polydisperse system involves a variable factor, λij, which measures the crowding of spheres of radius rj by spheres of radius ri. The variation of λij with is roughly indicated. There is good agreement of the theory with published experimental data.
Article
The induced electrorheological solid has thick columns in the field direction ({ital z} axis), spreading between two electrodes. The ground state is proposed to be a body-centered tetragonal lattice with {bold a}{sub 1}= {radical}6 {ital a}{bold {cflx x}}, {bold a}{sub 2}= {radical}6 {ital a}{bold {cflx y}}, and {bold a}{sub 3}=2{ital a}{bold {cflx z}}, where {ital a} is the radius of dielectric spheres. This bct lattice can be regarded as a compound of chains of class {ital A} and {ital B}, where chains {ital B} are obtained from chains {ital A} by shifting a distance {ital a} in the {ital z} direction.
Article
Suspensions of polarizable particles in nonpolarizable solvents form fibrillated structures in strong electric fields. The resulting increase in viscosity of these "electrorheological" fluids can couple electrical to hydraulic components in a servomechanism. The physical properties of these fluids are unusual owing to the long-range, anisotropic nature of the interparticle forces. Immediately after the electric field is applied, elongated chains or columns of particles form parallel to the field. This structure then coarsens as a result of thermal forces between the columns. In shear flows, fluids show yielding behavior at low stresses followed by shear-thinning behavior at higher stresses.
• Chow R.