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Reducing viscosity of paraffin base crude oil with electric field for oil production and transportation R. Tao?, H. Tang Department of Physics, Temple University, Philadelphia, PA 19122, USA h i g h l i g h t s ? The reduction of crude oil viscosity is substantial. ? The new technology consumes little electricity. ? The viscosity reduction lasts more than 11 h. ? Important for both off-shore and on-shore oil production and transportation. a r t i c l ei n f o Article history: Received 20 August 2013 Received in revised form 23 October 2013 Accepted 25 October 2013 Available online 6 November 2013 Keywords: Crude oil viscosity Reducing viscosity Electric field a b s t r a c t Reducing the crude oil viscosity is important for the oil production and transportation. The micro– nanotechnology of viscosity reduction associated with electric field is found to be universal, working for all kinds of crude oil, including asphalt base crude oil and paraffin base crude oil. Especially at low temperature, the electric field is extremely efficient: in a couple of seconds after the electric field is applied, the viscosity is reduced substantially, making the flow rate in a pipeline more than double. The technology consumes very little energy and will be very useful for both off-shore and on-shore crude oil production and transportation. ? 2013 Elsevier Ltd. All rights reserved. 1. Introduction The recent reports by Rocky Mountain Oilfield Testing Centre (RMOTC) of US Department of Energy show that the new micro– nanotechnology, reducing viscosity of crude oil with electric field, is energy efficient and feasible on pipelines [1–3]. All these greatly accelerate the technology progress in the energy area and present more challenges for the science research. Currently hydrocarbons remain the leading energy source. While the amount of conventional light crude oil becomes less and less available, more and more heavy crude oil and off-shore crude oil are needed. High viscosity of these oils becomes a critical issue. Not only the heavy crude oil has a high viscosity, the off- shore crude oil also has very high viscosity because the deep water temperature is very low, around 1.5–1.6 ?C. The high viscosity makes the pressure required to pump crude oil via pipeline very high and creates much difficulties in oil extraction, too. The importance of this issue, reducing the crude oil viscosity, called the attention more than 30 years ago. However, the current dominate methods remain heating and dilution of crude oil with gasoline or diesel. The heating method is slow and energy-consum- ing and raises concerns about its environmental impact, too. More- over, for the off-shore crude oil, it is very difficult to utilize the heating or dilution methods. Some people use the drag-reducing agent (DRA), which are additive of polymer chains. DRA suppresses the turbulence, but has little effect on laminar flow. In addition, DRA is expensive and raises concerns at refinery. In 2006, based on the concepts of electrorheology (ER), a new micro–nanotechnology to reduce the viscosity of crude oils by a strong electric field was proposed [4–6]. Comparing to the heating method, this technology consumes much less energy and is very fast and, therefore, much more efficient. Afterwards, the technol- ogy has developed very fast [1–3]. Recently the Keystone project decides to adapt this technology for its pipeline. In 2006, it was also reported that magnetic field might be useful to reduce viscosity of paraffin base crude oil but had almost no ef- fect on asphalt base crude oil [4]. However, recent experiment by a Brazil group, showing that magnetic field has effect for some kind of paraffin base crude oil, but has little effect on other kind of par- affin base crude oil [7]. This is related to the paraffin molecule structure. If the paraffin molecule has ring structure, the paraffin is diamagnetic; then the magnetic field has effect on the crude oil. If the paraffin molecule’s hydrocarbon chain has no ring 0016-2361/$ - see front matter ? 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.fuel.2013.10.056 ?Corresponding author. Tel.: [phone]; fax: [phone]. E-mail addresses: [e-mail], [e-mail] (R. Tao). Fuel 118 (2014) 69–72 Contents lists available at ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel
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structure, the paraffin is not sensitive to magnetic field; then the magnetic field cannot reduce the crude oil’s viscosity. The electric field has found to be effective in reducing the viscosity of asphalt base crude oil [4]. The work by the Brazil group raises an important question: Is the electric field also effective enough to reduce the viscosity of paraffin base crude oil? This issue is very important as paraffin base crude oil is one of the most important kinds of crude oil. Paraffin base crude oil has two critical temperatures: (1) the wax-appearing temperature (WAT); (2) the pour point, which is a temperature lower than the WAT. When the oil’s temperature is above the WAT, paraffin is in molecule format, the viscosity is usually low. When the oil’s temperature is going below the WAT, more and more paraffin crystallizes into nanoscale particles and the oil’s viscosity increases sharply. When the temperature further goes down and more and more paraffin wax is crystallized, the crude oil will reach its pour point, below which the crude oil stops flowing. At a temperature slightly above the pour point, the crude oil will have very high viscosity. It is thus clear that to reduce the viscosity of paraffin base crude oil at low temperature is critically needed. In this paper, we will report our finding that the micro– nanotechnology associated with electric field is universal, working for all kinds of crude oil, including asphalt base crude oil and paraffin base crude oil. Especially at low temperature, the electric field is extremely efficient in reducing the crude oil viscosity. Our test shows that in a couple of seconds after the electric field is applied, the viscosity is reduced substantially, making the flow rate in a pipeline more than double. The technology also consumes very little energy. After one treatment, the viscosity reduction effect lasts more than 11 h. All these findings prove that the technology will be very useful for both off-shore and on-shore crude oil production and transportation. 2. Methods Crude oil is a mixture of many different molecules. Gasoline, kerosene, and diesel, the liquid made of small hydrocarbon mole- cules, have very low viscosity. If we treat the rest large molecules, paraffin particles, and asphalt particles etc. as suspended particles in such low viscosity base liquid made of gasoline, kerosene, and diesel, crude oil is a liquid suspension. These suspended particles are typically of nanoscale. The theory about liquid suspensions thus provides the physics basis for our new method to reduce vis- cosity of crude oil. Einstein first studied a dilute liquid suspension of non-interact- ing uniform spheres in a base liquid of viscosity g0and found the effective viscosity g as follows [8–10], g ¼ g0ð1 þ 2:5/Þ; where the small parameter / is the volume faction of the suspended particles. Following Einstein’s work, Krieger–Dougherty introduced the intrinsic viscosity [g] for particles of different shapes and general- ized it for all volume fractions [11], ð1Þ g=g0¼ ð1 ? /=/mÞ?½g?/m; where /mis the maximum value fraction allowed for packing the suspended particles. When / is unchanged, the most widely used method to reduce viscosity g is to reduce g0, such as raising the temperature. On the other hand, Eq. (2) suggests that there is another method: if we change the rheology of the suspension to increase the value of /mand lower intrinsic viscosity [g], we will reduce the viscosity g. The physics is clear: the effective viscosity depends on how much freedom the suspended particles have in ð2Þ the suspension. A high /mand low [g] mean high freedom for the suspended particles, which leads to lower dissipation of energy and lower viscosity [4]. The following three mechanisms contribute to the viscosity reduction [4,5]: (1) Aggregate the nanoscale particles into short chains with their shapes streamlined along the flow direction. (2) Increase the polydispersity to increase /m. (3) Increase the average size of suspended particles. Our technology is illustrated in Fig. 1. The crude oil flows from left to right along a pipe. Initially the nanoscale particles are ran- domly distributed and the viscosity is high. When the oil passes a strong local electric field, the suspended particles are polarized by the electric field. The induced dipolar interaction forces the nanoscale particles to aggregate into micrometer-size short chains. They have high polydispersity and large size. In addition, the most important is that they are of streamline shape with low [g] along the flow direction as the electric field is parallel to the flow direction. It is also important to note that after formation of short-chains along the field direction, similar to the flow of nematic liquid crys- tal with its molecular alignment parallel to the flow direction, the viscosity is minimized along the field direction, while the viscosity along the directions perpendicular to the field is actually increased [12]. This fact is very important and very useful as it does not only improve the flow along the field direction, but suppresses the turbulence inside the pipeline. Fig. 1. As the crude oil flow passes a strong local electric field, the suspended particles aggregate along the field direction, and the viscosity along the flow direction is reduced. Fig. 2. The viscosity of untreated crude oil versus temperature. 70 R. Tao, H. Tang/Fuel 118 (2014) 69–72
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3. Results The sample of API 34 crude oil was provided by Rocky Mountain Oilfield Testing Center, US Department of Energy. The oil has quite low viscosity at room temperature. However, as the temperature goes down, the viscosity goes up very fast. With a Brookfield rotational viscometer, we measured its viscosity at various temperatures. As shown in Fig. 2, around 20 ?C, the crude oil has viscosity about 16cp. However, at 0 ?C, the viscosity is about 128cp and at ?3 ?C, the viscosity is 260cp. The wax appearing tem- perature (WAT) is around 12.5 ?C, where the slop of curve turns much steeper: the viscosity increases much faster when the tem- perature goes below the WAT. The pour point of the oil sample is found around ?4 ?C. Therefore, as the temperature below ?3 ?C, slightly above the pour point, the viscosity increases dramatically. Our experiment set up is illustrated in Fig. 3, which is placed in a refrigerator with the temperature controlled. The oil reservoir is at the top. As the crude oil flows down, it passes two capacitors made of three mesh electrodes. When a high voltage is applied on the capacitors, a strong local electric field parallel to the flow direction is applied to the oil. The capillary tube at the bottom en- ables us to find the oil viscosity from the oil flow rate. Once the experiment starts, the microbalance records the collected oil mass in the beaker as a function of time. Hence we can easily find the flow rate, which is the curve’s slope. The difference in the flow rates when the electric field is on and off indicates the viscosity reduction effect. Let the crude oil flow rate be Q. The average flow velocity v ¼ Q=ðpR2q0Þ; where R = 0.056 cm is the radius of the capillary tube and q0= 0.92 g/cm3is the oil density at 0 ?C. The Reynolds number is Re = 2Rvq0/g. If we use the flow rate, then ð3Þ Re ¼ 2Q=ðpRgÞ: ð4Þ For our experiment, the Reynolds number is very small. Therefore, the flow is always laminar. The flow velocity along the tube axis direction and is a function of r, uðrÞ ¼ 2QðR2? r2Þ=ðpR4q0Þð5Þ The highest shear rate is at the tube wall, _ c ¼ jð@u=@rÞjjr¼R¼ 4Q=ðpR3q0Þ: ð6Þ The crude oil viscosity can be determined from the flow rate, g ¼ R2q0g½1 þ h=l ?v2=ð2glÞ?=ð8vÞ; where g = 9.8 m/s2is the gravity acceleration, l = 20 cm is the length of capillary tube, h is the height of crude oil above the capillary tube, which is about 14 cm at the beginning and slowly decreases as the crude oil flows down. Shown in Fig. 4 is the typical curve, collected crude oil mass ver- sus time. The temperature was ?3.1 ?C. Because of the high viscos- ity at low temperature and the small capillary tube, the oil flow rate without electric field was quite small, 2.08 mg/s. From this baseline we know that the oil viscosity was about 261.3cp. Once we applied the electric field 1.6 kV/mm, the flow rate was surging up after the untreated oil in the capillary tube flew out. The stable flow rate under the electric field applied was 11.66 mg/s, increased more than 460.6%. Hence the reduced viscosity along the flow direction was about 46.7cp, down by 82.1%. The current was about 0.63 lA, indicating that it only requires about 0.1025 kW h elec- tricity to treat one barrel crude oil. Once the electric field is turned off, the flow rate returns to the baseline after the treated oil inside the capacitor and capillary tube flows out (Fig. 4). At ?1.4 ?C, the flow rate was 3.633 mg/s without electric field applied, responding to a viscosity of 149.9cp. With electric field 1.6KV/mm applied, the flow rate increased to 9.71 mg/s, increased by 167%. The viscosity was reduced by 62.2% to 56.7cp. At 1.5 ?C, deep ocean water temperature, the flow rate without electric field applied is 4.95 mg/s, corresponding to a viscosity of 105.4cp. An electric field of 1.6 KV/mm increases the flow rate by 104% to 10.1 mg/s. This implies that the viscosity is reduced to 53.9cp, down by 48.9%. The current is about 2.0 lA. ð7Þ Fig. 3. The device to test our crude oil sample. Fig. 4. The collected oil mass versus time at ?3.1 ?C. The curve’s slope is the flow rate. After we apply the electric field 1.6 kV/mm, the flow rate is surging up. Once the electric field is turned off, the flow rate returns to the original value after the treated oil flows out. R. Tao, H. Tang/Fuel 118 (2014) 69–72 71
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We used two temperature sensors to monitor the temperature of crude oil inside the reservoir and the temperature of crude oil flowing out of the capillary tube. The results confirm that the temperature of crude oil does not change during the viscosity reduction process. It is clear that when the temperature is below 0 ?C, the viscosity reduction effect is more effective and it consumes less electricity than that above 0 ?C. We believe that this is related to a fact that our crude oil sample has some water contents. When the temper- ature is above 0 ?C, water contents increase the current between the electrodes. However, when the temperature is below 0 ?C, water contents crystallize into tiny ice particles. The current is thus much smaller. In addition, the suspended ice particles also aggre- gate into streamline chains along the field direction; therefore, the viscosity reduction effect is getting stronger. Naturally, there is a question: How long can the viscosity reduc- tion hold after one treatment? As stated before, the viscosity reduction is the result of the aggregation of suspended particles. The viscosity reduction disappears when the aggregated short chains are dissembled. At recent field test on pipeline, we have found that the viscosity reduction actually lasts about 11 h [3]. In our lab, we used a rotational viscometer to determine how long the viscosity reduction effect lasts. While rotational viscometers are convenient and handy, we must point out first that rotational viscometers are not the best to measure such viscosity. As shown in Fig. 1, the treated crude oil has the suspended particles aggregated into short chains along the flow direction. Therefore, the viscosity is anisotropic. Along the flow direction, the viscosity is the minimum. In the other directions, the viscosity is higher than that along the flow direction. Our capillary tube is excellent to determine such vis- cosity as we can generate electric field parallel to the capillary tube. On the other hand, there is no way to produce electric field along the rotational direction of the viscometer spindle. Therefore, when the spindle starts to rotate, the short chains are initially not along the rotational direction. Under the shear force, the short chains are driven to tilt and align in the rota- tional direction. Once this process is completed, the viscometer will find a low viscosity reading. On the other hand, because some short chains are broken during this driving process, the viscosity measured by the rotational viscometer should be higher than that determined by our capillary tube. Our experi- ment confirms this analysis. At ?3.1 ?C, we collected the electric field treated crude oil sample in a cup, then keep it in the refrigerator at ?3.1 ?C. The rotational viscometer confirmed that the untreated oil at ?3.1 ?C had viscosity 261.3cp. As stated before, from the capillary tube, the treated crude oil had viscosity 46.7cp. However, immediately after the treatment, our rotational viscometer measured the vis- cosity 121.1cp, showing a reduction of 53.7%, but is higher than that measured by capillary tube. Twelve hours after the electric field treatment, we used the rotational viscometer to measure the saved treated sample and found the viscosity was up to 151.2cp, still 42.1% lower than that of the untreated oil. Twenty- four hours after the electric field treatment, we used the rotational viscometer to measure the saved treated sample and found that the viscosity was up to 172.4cp, remaining 34% lower than that of the untreated crude oil. From these tests, we are convinced that the viscosity reduction effect lasts longer than 24 h at ?3.1 ?C. Of course, the viscosity reduction process is repeatable. Once the short chains are broken, reapplication of the electric field will bring the viscosity down again. 4. Conclusions In summary, the basic science associated with the present mi- cro–nanotechnology is proved to be universal, working for all kinds of crude oil, including asphalt base crude oil and paraffin base crude oil. In addition to the present US crude oil sample, we have tested many other crude oil samples from all over the world. Elec- tric field is found to be very effective in reducing all their viscosi- ties. Especially at low temperature, the electric field is extremely efficient. The technology consumes very little energy. For example, at ?3.1 ?C, we only need 0.1025 kW h electricity to treat one barrel crude oil and reduce its viscosity by 82.1%. At the deep water tem- perature, we only need 0.325 kW h electricity to treat one barrel crude oil and reduce its viscosity by 48.9%. It has no doubt that this micro–nanotechnology will play very important role in the future crude oil production and transportation, including off-shore crude oil production and transportation. Acknowledgement This work was supported in part by STWA. References [1] www.rmotc.doe.gov/PDFs/STWA%20Test%20Report%20-%20FINAL.pdf; October 19, 2011. [2] www.rmotc.doe.gov/PDFs/TS19_51141_Final%20Report.pdf; April 4, 2012. [3] http://www.rmotc.doe.gov/PDFs/STWA%20Test%20Report%20- %20Final%20May%202012.pdf. [4] Tao R, Xu X. Reducing the viscosity of crude oil by pulsed electric or magnetic field. Energy Fuels 2006;20:2046–51. [5] Tao R. Electrorheology for efficient energy production and conservation. J Intell Mater Syst Struct 2011;22:1667–71. [6] Tang H, Huang K, Tao R. Electrorheology improves transportation of crude oil. J Intell Mater Syst Struct 2011;22:1673–6. [7] Goncalves JL et al. Study of the factors responsible for the rheology change of a brazilian crude oil under magnetic fields. Energy Fuels 2011;25:3537–43. [8] Einstein A. On the movement of small particles suspended in stationary liquids required by the molecular-kinetic theory of heat. Ann Physik 1905;17:549–60. [9] Einstein A. A new determination of molecular dimensions. A Ann Physik 1906;19:289–306. [10] Einstein A. On the theory of brownian motion. Ann Physik 1906;19:371–81. [11] Krieger IM, Dougherty TJ. A mechanism for non-newtonian flow in suspensions of rigid spheres. Trans Soc Rheol 1959;3:137–52. [12] Miesowicz M. The three coefficients of viscosity of anisotropic liquids. Nature 1946;158:27. 72 R. Tao, H. Tang/Fuel 118 (2014) 69–72
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