Changes in the Properties of Heavy Oil from Yarega Oilfield under the Action of Magnetic Fields and Microwave Radiation

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1 ISSN , Theoretical Foundations of Chemical Engineering, 26, Vol. 5, No. 5, pp Pleiades Publishing, Ltd., 26. Original Russian Text A.A. Boytsova, N.K. Kondrasheva, 26, published in Khimicheskaya Tekhnologiya, 26, Vol. 7, No., pp PETROCHEMISTRY AND PETROLEUM PROCESSING Changes in the Properties of Heavy Oil from Yarega Oilfield under the Action of Magnetic Fields and Microwave Radiation A. A. Boytsova* and N. K. Kondrasheva** St. Petersburg Mining University, St. Petersburg, Russia *cadaga@mail.ru, **natalia_kondrasheva@mail.ru Received August 5, 25 Abstract The paper discusses the effects of ultra-high frequency radiation and constant and variable magnetic fields on the structural mechanical properties of heavy oil from the Yarega oilfield. It has been found that a constant magnetic field reduces the viscosity of the oil by almost two times, and microwave radiation promotes the formation of insoluble structures. Keywords: heavy oil, physical fields, microwaves, magnetic field, rheology, physicochemical properties DOI:.34/S INTRODUCTION The share of high-gravity oil in the total hydrocarbon production is decreasing, which means the increasing use of heavy oils and natural bitumens that are relatively new for the oil refining industry. Russia has the world s third largest heavy hydrocarbon reserves (after Canada and Venezuela) that various experts estimate to be billion tons, which is 3% of the total hydrocarbon reserves in Russia []. The increasing heavy crude production calls for new methods for the preparation and processing. Heavy crudes contain a significant amount of resins, asphaltenes, and heterocompounds, which negatively affects not only the quality of oil products, but also the performance of the equipment. Another distinguishing characteristic of heavy oils is their high viscosity that can reach mpa s [2]. It is necessary to develop a system of procedures to change physicochemical and structural mechanical properties of heavy oil in order to increase the efficiency of processing it. In [3], it is proposed that a combination of several methods should be used to improve the rheological properties of viscous oils and oil products, e.g. the methods that use solvents/reagents and cavitation. Experiments have shown that this approach significantly reduces the viscosity of raw oil. Thus, the addition of 2 wt % xylene to oil and exposure to ultrasonic radiation (. W/cm 2 ) for min decreased the viscosity by 44%. It has been observed that ultrasonic exposure not only reduces the viscosity of heavy oils, but also intensifies the process of producing polymeric materials based on epoxy-phenolic compositions [4]. As a result of ultrasonic exposure, structure formation changes and energy consumption decreases due to the fact that the temperature at which the composition is formed decreases. Another effective method of decreasing the viscosity of oil is via the action of a magnetic field [5, 6]. Oil treatment and transportation technology using magnetic fields and ultrasonic oscillations is described in [5]. This technology increases the time that oil takes to restore its original viscosity compared to the hot oil pumping technique; therefore, transportation costs may be significantly reduced. In [6], the rheological behavior of oils before and after magnetic field treatment was investigated, as well as the processes of the formation of structures in oil disperse systems under the action of a constant magnetic field. It was found that the rheological, spectral, and antioxidative characteristics of oils after magnetic-assisted treatment are related to the content of resin-asphaltene components. EXPERIMENTAL Viscosity anomalies, the formation of structures in heavy oils, and changes in their physicochemical properties under the influence of various physical fields were studied. The object of the study was the heavy high-viscosity oil of the Yarega field (Table ) located in the Timan-Pechora Province, Russia. The high-viscosity oil was subjected to high-frequency electromagnetic radiation and constant and variable magnetic fields. A microwave oven with an output power of 6 W was used as a source of superhigh frequencies (exposure time min). Neodymium magnets (NdFeB) were used as sources of a constant 83

2 832 BOYTSOVA, KONDRASHEVA Table. Main characteristics of oil from Yarega oilfield Characteristic Density at 2 C, kg/m Kinematic viscosity at 4 C, mm 2 /s (cst) Pour point, C 8 Initial boiling, C 22 Yield of light fractions, vol % 3% Sulfur content, wt %.237% Flash point, closed-cup test, C 88 Ash content, wt %.46 Hydrogen sulfide content Methyl mercaptan content Ethyl mercaptan content, wt % Resin content, wt % 2 Asphaltene content, wt % 3. Paraffin content, wt %.5 magnetic field (exposure time 2 min). N N-magnets were perpendicular to the oil flow. The duration of the action of variable magnetic field was two cycles. The main characteristics of the sources are given in Tables 2 and 3. The light fraction was extracted from oil samples in accordance with the requirements of GOST Oil Products: Methods of Determining the Fractional Composition of Oil. One of the characteristic properties of heavy oils is their viscosity. The possibility of piping heavy oil without additional heating depends on the oil viscosity. It was found that the viscosity of heavy oil of the Yarega field significantly decreases at a temperature of 8 C (Fig. ), which improves its transportability. where τ is the shear stress, Pa, and Γ is the instantaneous shear rate, /s. Fluids, the effective viscosity and shear stress of which decrease over time when the shear rate is constant, which is due to the gradual destruction of the spatial structure of oil, are called thixotropic. Fluids that have the properties of both liquid and solid and the viscosity and elasticity of which are two sides of their ability to respond to the applied shear stress are called viscoelastic [7]. The thixotropic properties of the Yarega oil were examined as follows. The shear rate was gradually increased up to 4 /s for 3 s (a forward stroke), then remained constant at the attained value for 3 s (a wait for the complete destruction of the internal structure), and after that the shear rate was gradually reduced to zero for 3 s (a reverse stroke). Thus, the characteristic hysteresis loops were obtained (Fig. 2). The fact that the curve of the forward stroke does not repeat that of the reverse stroke indicates the for- However, the crude oil pipelines that are located in the North cannot be heated to this temperature, especially in winter. The rheological parameters of the oil were studied using a Rheotest RN 4. rotary viscometer that measures shear stress in the material placed between two components of the measuring system of the viscometer at a constant speed of rotation of one component (rotor). Fluids that cannot be described by the Newton law of viscous friction are called non-newtonian ones [7]. The properties of non-newtonian fluids are described by the effective/apparent viscosity. The effective viscosity of oil at different rotary speeds and shear stresses is determined by the formula μ = τ γ ef, Table 2. Characteristics of NdFeB constant magnets Magnet grade Residual magnetic Coercive force Energy output Maximum induction operating Br, T bhc ihc (BxH) max temperature kg T koe ka/m koe ka/m MGOe kj/m 3 C N C Table 3. Characteristics of the source of a variable magnetic field Characterstic Unit of measurement Nominal value Extreme deviation Maximum electric power, no more than kw 2.2 V 22 ±22 Voltage frequency Hz 5 ±.4 Mode of operation Duty ratio 5% at a cycle of 3 min Service life, no less than h THEORETICAL FOUNDATIONS OF CHEMICAL ENGINEERING Vol. 5 No. 5 26

3 Dynamic viscosity, mpa s CHANGES IN THE PROPERTIES OF HEAVY OIL Temperature, C Fig.. Temperature dependence of the dynamic viscosity of Yarega oil. Shear rate, /s Shear stress, Pa Fig. 2. Rheological curves of the forward and back strokes (of hysteresis loop) of the oil from Yarega field at different temperatures, C. (); (2)2; (3) 3; (4) 4; (5) 5; (6) 6; (7) 7; (8) 8. mation of a thixotropic structure. The area of the hysteresis loop within a single measurement cycle characterizes the mechanical energy of thixotropic bonds per unit volume of oil (Fig. 2). Experiments showed that the thixotropic properties of oil from the Yarega field significantly worsen as the temperature increases; they become negligible at temperatures above 6 C. This suggests that oil of the Yarega field is a complex rheological system, the thixotropic properties of which are due to the high content of high-molecular components (resins and asphaltenes). It was found [8] that oil shows deterioration in the thixotropic properties as the temperature increases, whereas its elastic properties remain unchanged. It is insufficient to heat oil with a view to reduce its viscoelastic properties. It is more reasonable to apply physicochemical methods, e.g., those based on using different physical fields. The effects of physical fields on the viscoelastic properties of oil are still poorly studied. Yield of light fractions, % Temperature, C Fig. 3. Dependence of the true boiling point of Yarega oil on external action, i.e. yield of light fractions vs. temperature: () without treatment; (2) microwave-assisted treatment; (3) constant magnetic field; (4) variable magnetic field THEORETICAL FOUNDATIONS OF CHEMICAL ENGINEERING Vol. 5 No. 5 26

4 834 BOYTSOVA, KONDRASHEVA Viscosity, mm 2 /s. Stress, Pa Before Microwave Variable Constant treatment exposure magnetic field magnetic field Fig. 4. Dependence of the kinematic viscosity of Yarega oil on external action Shear rate, /s Fig. 5. Rheological curves of forward and back strokes (hysteresis loop) of the Yarega oil depending on the external action: () variable magnetic field; (2) microwave radiation; (3) constant magnetic field; (4) without external actions RESULTS AND DISCUSSION Our study showed that all the techniques used (ultrahigh-frequency radiation and constant and variable magnetic fields) adversely affect the yield of light fractions from Yarega oil (Fig. 3), while the action of magnetic fields increases the temperature of oil decomposition and the yield of light fractions. It was found that the kinematic viscosity of the oil significantly decreases under the action of a constant magnetic field (Fig. 4). The area of the hysteresis loop (Fig. 5) formed by the flow curves when the shear rate gradually changes during loading and unloading cycles was used as a quantitative characteristic of the thixotropic effect of the external action on oil of the Yarega oilfield. The fact that the rate of oil thixotropic hardening increases as the asphaltene content increases, thereby forming a stable structure, was taken into account. The area of the hysteresis loop is proportional to the energy per unit volume of a sample subjected to shear. It determines the amount of energy required to destroy the thixotropic structure. The study showed that the area of the hysteresis loop does not change much after different treatments. The coefficient of light absorption by oil was determined (Fig. 6) in order to quantify changes in the structure of the oil under the action of physical fields. This characteristic of a sample of the Yarega oil increased under the action of microwave radiation, which suggests the formation of insoluble structures that are atypical of oil. Oils that contain these components will reduce the service life of processing equipment. CONCLUSIONS In summary, the flow properties and, hence, the transportability of heavy high-viscosity oil of the Yarega field improve under the action of a constant magnetic field. Changes in the viscosity of heavy oil Coefficient of light absorption, av. sq., /cm , 3, Wave length, nm Fig. 6. Dependence of the coefficient of light absorption of the Yarega oil on the external action: () microwave radiation; (2) without external action; (3) constant magnetic field; (4) variable magnetic field. THEORETICAL FOUNDATIONS OF CHEMICAL ENGINEERING Vol. 5 No. 5 26

5 CHANGES IN THE PROPERTIES OF HEAVY OIL 835 are independent of the time of the action of the magnetic field. The exposure of heavy oils to microwave radiation is not advisable in view of the fact that insoluble solid structures are formed as a result. It is necessary to continue the research into the integrated use of external actions and solvents in order to improve the flow properties of oil, which is necessary to facilitate the pumping and processing of heavy oil of the Yarega field. ACKNOWLEDGEMENTS This study was supported by the Russian Science Foundation (project no ). REFERENCES. Akhmetov, S.A., Ishmiyarov, M.H., and Verevkin, A.P., Tekhnologiya, ekonomika i avtomatizatsiya protsessov pererabotki nefti i gaza (Technology, Economics, and Automatization of Oil and Gas Processing), Moscow: Khimiya, Ancheyta, J., Modeling of Processes and Reactors for Upgrading of Heavy Petroleum, Boca Raton, Fla.: CRC, Ershov, M.A., Reducing oil viscosity by the hydrodynamic cavitation method, Cand. Sci. (Eng.) Dissertation, Moscow: Moscow State Univ. of Environmental Engineering, Tuzova, S. and Antipov, E., Ultrasonic method of producing epoxy phenol compositions, Khim. Tekhnol., 23, vol. 4, no., pp Kozachok, M.V., Substantiation of the technology of pumping high-paraffin oil from Khariaginskoe oil field with the use of the joint effect of magnetic field and ultrasonic oscillations, Cand. Sci. (Eng.) Dissertation, St. Petersburg, Loskutova, Yu.V., Effect of magnetic field on rheological properties of oils, Cand. Sci. (Eng.) Dissertation, Tomsk: Inst. of Petroleum Chemistry, Rogachev, M.K. and Kondrasheva, N.K., Reologiya nefti i nefteproduktov (Rheology of Oil and Oil Products), Ufa: Ufa State Petroleum Technological Univ., Nikitin, M.N., Gladkov, P.D., and Petukhov, A.V., Rheological properties of heavy high-viscosity oil from Yaregskoye oil field, Zap. Gorn. Inst., 22, vol. 95, pp Translated by B. Shubik THEORETICAL FOUNDATIONS OF CHEMICAL ENGINEERING Vol. 5 No. 5 26