Energy Fuels 2011, 25, 482–486 Published on Web 11/02/2010
: DOI:10.1021/ef1009428
)
Effects of Electrical and Radio-Frequency Electromagnetic Heating on the Mass-Transfer Process during Miscible Injection for Heavy-Oil Recovery† Liana Kovaleva,‡ Alfred Davletbaev,§ Tayfun Babadagli, and Zoya Stepanova*,§ ‡ Department of Applied Physics, Bashkir State University, Ufa 450074, Russia, Department of Design Engineering and Control, RN-UfaNIPIneft, Rosneft, Ufa 450103, Russia, and Department of Civil and Environmental Engineering, University of Alberta, Edmonton, Alberta T6G 2W2, Canada
)
§
Received July 24, 2010. Revised Manuscript Received September 29, 2010
This paper deals with the effect of radio-frequency electromagnetic (RF-EM) fields and electrical heating on the mass- and heat-transfer processes in a multi-component hydrocarbon system flowing in porous media. The more specific objective was to determine the major differences between the RF-EM effects and electric heating and eventually to propose the application conditions toward their field-scale applications. Critical parameters, including the viscosity reduction, that affect the recovery of heavy oil under the influence of these heating options with the emphasis on resolving the asphaltene precipitation problem were clarified. It was observed that the EM field influence on the residual oil recovery factor was more critical, and a greater recovery was obtained from the RF-EM case. This was attributed to the fact that the RF-EM field influences polar components of the oil, desorpting these components from the surface of the rock and adding to the production, as indicated by the scanning atomic force microscopy images. This critical role of the RF field on the adsorptive process during the displacement of high-viscosity oils eventually resulted in less asphaltene precipitation and pore plugging. performance were also presented,8-12 as well as the field tests in Russia, Canada, and the United States.13,16-19 Field tests
Introduction Electrical and electromagnetic heating can be considered as an alternative to conventional thermal methods for heavy-oil and bitumen recovery. The results of experimental studies on the radio-frequency electromagnetic (RF-EM) field irradiation and electrical heating are presented in several papers.1-7 Theoretical approaches for the estimation of heavy-oil recovery
(9) Islam, M. R.; Wadadar S. S.; Banzal, A. Enhanced oil recovery of Ugnu tar sands of Alaska using electromagnetic heating with horizontal wells. Proceedings of the International Arctic Technology Conference; Anchorage, AK, May 29-31, 1991; SPE Paper 22177. (10) Kovalyova, L. A.; Khaydar, A. M. Physical and rheological properties of petroleum fluids under the radio-frequency electromagnetic field effect and perspectives of technological solutions. Appl. Surf. Sci. J. 2004, 238 (1-4), 475–479. (11) Davletbaev, A. Ya.; Kovaleva, L. A.; Nasyrov, N. M. Numerical simulation of injection of a solvent into a production well under electromagnetic action. Fluid Dyn. 2008, 43 (4), 583–589. (12) Davletbaev, A. Ya.; Kovaleva, L. A.; Nasyrov, N. M. An investigation of the processes of heat and mass transfer in a miltilayer medium under conditions of injection of a miscible agent with simultaneous electromagnetic stimulation. High Temp. 2009, 47 (4), 574–579. (13) Sierra, R.; Tripathy, B.; Bridges, J. E.; Farouq Ali, S. M. Promising progress in field application of reservoir electrical heating methods. SPE Tech. Pap. 69709; Society of Petroleum Engineers (SPE): Richardson, TX, 2001. (14) Sayakhov, F. L.; Bulgakov, R. T.; Dyblenko, V. P.; Deshura, V. S.; Bykov, M. T. Neftepromysl. Delo 1980, 1, 5–8. (15) Sayakhov, F. L. An investigation of thermal and hydrodynamic processes in multi-phase media affected by a radio-frequency electromagnetic field as applied to oil recovery. Dissertation of the Doctor of Physical and Mathematical Sciences, Lomonosov Moscow State University, Moscow, Russia, 1984; p469. (16) Davletbaev, A.; Kovaleva, L.; Babadagli, T.; Minnigalimov, R. Heavy oil and bitumen recovery using radiofrequency electromagnetic irradiation and electrical heating: Theoretical analysis and field scale observations. Proceedings of the Canadian Unconventional Resources and International Petroleum Conference; Calgary, Alberta, Canada, Oct 19-21, 2010; CSUG/SPE Paper 136611. (17) Hu, Y.; Jha, K. N.; Chakma, A. Heavy-oil recovery from thin pay zones by electromagnetic heating. Energy Sources 1999, 21, 63–73. (18) Maggard, J. B.; Wattenbarger, R. A. Factors affecting the efficiency of electrical resistance heating patterns. Proceedings of the United Nations Institute for Training and Research (UNITAR)/United Nations Development Programme (UNDP) 5th International Conference on Heavy Oil and Tar Sands; Caracas, Venezuela, Aug 4-9, 1991. (19) Rangel-German, E. R.; Schembre, J.; Sandberg, C.; Kovscek, A. R. Electrical-heating-assisted recovery for heavy oil. J. Pet. Sci. Eng. 2004, 45, 213–231.
† Presented at the 11th International Conference on Petroleum Phase Behavior and Fouling. *To whom correspondence should be addressed. E-mail: stepanovazy@ ufanipi.ru. (1) Hascakir, B.; Babadagli, T.; Akin, S. Experimental and numerical modeling of heavy-oil recovery by electrical heating. Proceedings of the 2008 SPE International Thermal Operations and Heavy-Oil Symposium; Calgary, Alberta, Canada, Oct 20-23, 2008; SPE Paper 117669. (2) Hascakir, B.; Babadagli, T.; Akin, S. Experimental and numerical simulation of oil recovery from oil shales by electrical heating. Energy Fuels 2008, 22 (6), 3976–3985. (3) Nigmatulin, R. I.; Sayakhov, F. L.; Kovaleva, L. A. Cross transport phenomena in disperse systems interacting with a high-frequency electromagnetic field. Dokl. Phys. 2001, 46 (3), 215–218. (4) Ovalles, C.; Fonseca, A.; Lara, A.; Alvarado, V.; Urrecheaga, K.; Ranson, A.; Mendoza, H. Opportunities of downhole dielectric heating in Venezuela: Three case studies involving medium, heavy and extraheavy crude oil reservoirs. Proceedings of the International Thermal Operations and Heavy Oil Symposium and International Horizontal Well Technology Conference; Calgary, Alberta, Canada, 2002. (5) Chakma, A.; Jha, K. N. Heavy-oil recovery from thin pay zones by electromagnetic heating. Proceedings of the 67th Annual Technical Conference and Exhibition of the Society of Petroleum Engineers; Washington, D.C., Oct 4-7, 1992; SPE Paper 24817. (6) Kasevich, R. S.; Price, S. L.; Faust, D. L.; Fontaine, M. F. Pilot testing of a radio frequency heating system for enhanced oil recovery from diatomaceous earth. Proceedings of the 69th Annual Technical Conference and Exhibition; New Orleans, LA, Sept 25-28, 1994; SPE Paper 28619. (7) Amba, S. A.; Chilingar, G. V.; Beeson, C. M. Use of direct eletrical current for increasing the flow rate of reservoir fluids during petroleum recovery. JCPT64-01-02, 1964. (8) Sahni, A.; Kumar, M.; Knapp, R. B.; Livermore, L. Electromagnetic heating methods for heavy oil reservoirs. Proceedings of the 2000 Society of Petroleum Engineers (SPE)/American Association of Petroleum Geologists (AAPG) Western Regional Meeting; Long Beach, CA, 2000.
r 2010 American Chemical Society
482
pubs.acs.org/EF
Energy Fuels 2011, 25, 482–486
: DOI:10.1021/ef1009428
Kovaleva et al.
14-16
objective of the three series of experiments was two-folds: (1) a comparison of the results of RF-EM and electric heating (under identical conditions; i.e., the temperature in the models and the injection pressure of the solvent were the same), which enabled us to identify the “non-thermal” effect of EM field impact on the diffusion mixing of oil and solvent and desorption effects, and (2) a comparison of the injection of the solvent in electric heating and injection of “cold” solvent, to assess the influences of the temperature on diffusion processes. Laboratory experiments on sand pack tubes were carried out to clarify the effects of the RF-EM field on the process of asphaltene-resin substance adsorption during the displacement of high-viscosity oil. Three different types of experiments were carried out: (1) solvent (kerosene) flooding under the RF-EM field, (2) solvent (kerosene) flooding under electrical heating, and (3) cold solvent (kerosene) flooding. In all experiments, utmost attention was paid to maintain identical physical characteristics of the model and heating conditions (temperatures). A detailed description of a similar experiment is given in ref 27. In particular, the paper27 discusses the procedure to maintain the same temperature of heating oil, which is measured at the output of the model, conditions to maintain a constant pressure injection of the solvent, etc. To prepare the sand pack models, polyvinyl chloride pipes of 0.5 m in length and 22.5 mm in inner diameter were filled with silica sand. Before preparation, the sand was washed with a 10% hydrochloric acid solution and then dried in a dewatering box under 100 °C to avoid any possible nonuniformities during packing. Dry sand was placed into the pipe placed vertically, the inner surface of which was peeled, de-oiled, and covered with glue in advance. The glue was an epoxy (resin) and was applied for sticking sands onto the internal surface of the pipe to prevent the slipping of injected fluid through the gap between the sandpack column and the pipe. The lower end of the pipe was peeled with sandpaper and also covered with epoxy. Then, it was wrapped with a nylon micromesh, and a metal connector was attached. During sand filling, uniform distribution of sands in the pipe was achieved by tapping against the side face of the pipe with a metal object. For the same purpose, a smaller diameter (20 mm) pipe was put into the upper end of the model. A compact and even packing of the filler was achieved because of the additional weight on the column. After the completion of packing, an inlet connector was put on the upper end. The addition of oil into the sand pack was carried out by oil injection from column 3 (Figure 1) using a pump; no initial water exists in the models. The next stage of the experiment was the displacement of oil by a mixing agent (solvent). The displacement setup is shown in Figure 1. The source of RF-EM radiation (1) is a generator with a wattage of 6 kW and an operating frequency of 81.36 MHz. The sand pack was placed between the coats of the generator. An oil collection bottle (5) and a thermocouple (7) located at the outlet of the model were connected to a voltmeter (8). Two series of experiments on models with different granulometric composition of formation were carried out. A pressure drop of 1-2 atm was maintained during the displacement. The pressure was controlled with a manometer
in Russia showed that RF-EM is highly effective with fields having less than 30% water encroachment because the EM field in the RF range has almost no effect on the water because the resonance effect for water is in the microwave range. However, a large water content (>30%) has certain impacts and created technical difficulties in the oil reservoir,16 and the RF-EM technique was not recommended. In certain circumstances, such as deep, tight, or heterogeneous sand/ carbonate reservoirs or oil shales, it is the only solution because steam injection is not applicable as a result of injectivity problems or high clay content. The main target in heavy-oil recovery through thermal or solvent injection techniques is to reduce the viscosity of reservoir oil and the asphaltene deposition not only from additional oil recovery but also by reducing the precipitation effects. This phenomenon, under thermal or solvent injection, is controlled by the molecular structure of the oil and the surface activity. Oils of different deposits vary greatly in their compositional analysis and physical-chemical properties, but all oils, to a greater or lesser extent, possess surface activity.20,21 Oil filtration in porous media is known to be accompanied by some fadeout.22 The asphaltene precipitation process is explained by the formation of a film-type oil, whose viscosity is higher than that of the original oil, on the surface of pore channels.23 The thickness in some cases is comparable to the radius of pore channels, resulting in a decreasing cross-section of pore channels, and thereby, their permeability. The base of the film-type oil is adsorptive layers of asphaltene-resin substances, which are polar components changing the molecular structure of the solid surface; these present the basis for the formation of an oil boundary layer. To struggle with the asphaltene-resin deposits, suggested applications include chemical reagents or heating. RF-EM is one of the effective heating techniques. RF-EM decreases the viscosity of the oil24 and expands the deliverability of channels in the porous medium because of “non-thermal” effects. The EM field changes the dipole-dipole interaction and causes the action of ponderomotive forces and thermoelastic stresses. The objective of this work is to study the effects of RF-EM on the adsorptive process under dynamic conditions (i.e., displacement of oil), experimentally, and to clarify the optimal application conditions of RF-EM to remove the adsorbed polar components of oil, i.e., heavy ends, such as asphaltenes. The results will provide a path toward the field-scale application of this new technology, which involves the combined effects of injection of the solvent and RF-EM irradiation simultaneously.25,26 Heavy-Oil Displacement Experiments Experimental Design and Procedure. This paper deals with three series of experiments on identical physical models. The (20) Safieva, P. Z. Physics and Oil Chemistry; Nedra: Moscow, Russia, 1998. (21) Babalyan, G. A. Physical-Chemical Processes in Oil Production; Nedra: Moscow, Russia, 1977. (22) Marhasin, I. L. The Physical and Chemical Mechanics of an Oil Layer Petroleum Reservoir; Nedra: Moscow, Russia, 1977. (23) Gimatudinov, S. K. Physics of Oil and Gas Reservoir; Nedra: Moscow, Russia, 1971. (24) Sayakhov F. L., Fatykhov M. A. Radio-Frequency Electromagnetic Hydrodynamics; Bashkir State University: Ufa, Russia, 1990. (25) Sayakhov, F. L.; Kovaleva, L. A.; et al. Method for thermal treatment of hydrocarbon pool. Soviet Union (SU) Patent 1,723,314, 1992. (26) Sayakhov, F. L.; Kovaleva, L. A.; et al. Method for mineral recovery. Soviet Union (SU) Patent 1,824,983, 1996.
(27) Sayakhov, F. L.; Kovaleva, L. A.; Fatichov, M. A.; Chismatullina, F.S. Analysis of influencing of a RF EM field on diffusion processes in saturated porous mediums. Electron. Process. Stuffs 1975, 1, 59–61.
483
Energy Fuels 2011, 25, 482–486
: DOI:10.1021/ef1009428
Kovaleva et al.
Figure 3. Amount of oil left from the initial oil content of the samples for two series of experiments.
Figure 1. Schematic representation of the experimental setup.
Figure 4. Dynamics of solvent concentration changes at the outlet of the layer of the model.
Figure 2. Dependence of oil recovery (K) on the relative volume of solvent injected.
(12) set on the hydraulic press. The solvent was poured into column (3), which was washed with kerosene beforehand. With the faucet (9) closed and the faucet (10) opened, the hydraulic press was filled with the solvent from the basin (11). Then, the faucet (10) was blocked, and the faucet (9) was opened. During this process, the necessary pressure was created with the help of the press. At the moment of agent delivery, the faucet (8) was opened and the pump-in pressure was maintained with the help of the press. The concentration of solvent at the output of the model was determined by the photocolorimetry method. Results and Discussion. Figure 2 shows the dependence of oil recovery on the volume of solvent injected. Figure 3 demonstrates the percentage of oil left in the sample for two series of experiments. Although the same temperatures were applied, the amount of oil left in the samples for the RF-EM case is less than that of the electrical heating case. This confirms the effect of additional stripping of the EM field on polar oil components. This effect can also be observed in Figure 4. This figure clearly indicates that the effect of RF-EM is observed much earlier than that of electrical heating. However, the progress of solvent is not as fast as in the case of electrical heating. Additional experimental evidence and mathematical modeling studies also demonstrated that the main reason for this is the additional desorption of heavy components (paraffinasphaltene-resinous substances, etc.) in the RF-EM case. This process reduces the recovery (or flow) rate for the RF-EM impact compared to the electrical heating case, even though both experiments showed very close temperatures in the system.
In other words, the front of oil recovery with the RF effect falls behind the front with electrical heating during the displacement, and this can be explained with increasing viscosity of the mixture of solvent and oil because of increasing stripped asphaltene-resin substances. Experimental Analysis of the Adsorption Process in Porous Media under Static Conditions Experimental Design. A study of RF-EM effects on the process of asphaltene-resin adsorption was carried out through experiments using a porous medium model saturated with oil. For comparison, the experiments were repeated for thermal heating. The model is a silica-sand- (with 0.2 and 0.6 mm fractions) and silica-gel-filled 1 cm diameter plastic tube with small holes at the bottom to drive off oil on a centrifuge. It was saturated with high viscosity oil. The oil used in the experiments is from the Varandei field, with 970 cP viscosity. Two series of experiments were performed for two different silica sand sizes. The experimental procedure is as follows: Step 1: After the sample was saturated with oil, the model was settled for 24 h. All polar components are considered to be adsorbed on the surface of the sands. Next, the model was put into a centrifuge to extract all moveable oil out of it. Step 2: The sample was exposed to a RF-EM field or thermal heating to observe their effects on the oil left as a film on the surface. The same temperature was applied in both cases. The highest temperatures applied for the 0.2 and 0.6 mm sample cases were about 70 and 57 °C, respectively. Figure 5 shows the temperature values applied for all cases. 484
Energy Fuels 2011, 25, 482–486
: DOI:10.1021/ef1009428
Kovaleva et al.
Figure 6. Dependence of desorbed oil on different types of sand samples under RF-EM and thermal heating (numbers on the top of the bars indicate the amount of stripped oil, %).
more pronounced in the case of the 0.2 mm size silica yielding 100% recovery of the adsorbed oil. The very strong adsorptive silica gel case, which showed no separation of film-type oil by RF-EM heating alone (without solvent extraction), gave 56% recovery when the solvent was used. The least adsorbed oil removal was obtained for the largest sand size (0.6 mm). It is interesting to note that the largest sand size (0.6 mm) yielded higher oil recovery compared to the other case (Figure 5); the adsorptive-film-type oil removal in that case was remarkably lower (28.4 and 25% for RF-EM and thermal heating cases, respectively, as seen in Figure 6). It should also be mentioned that the amount of adsorptive oil in the case of the 0.6 mm silica sand was significantly smaller, because a great portion of it was in a free condition and separated in the centrifuge (step 1).
Figure 5. Dependence of oil produced after RF-EM and thermal heating on the heating temperature for silica sand of different sizes: (a) 0.2 mm and (b) 0.6 mm.
After heating, the samples were exposed to the same centrifugal process and the amount of oil was measured. Step 3: At the final stage, full extraction of adsorptive oil was achieved through the injection of solvent (CCl4-perchloromethane or carbon tetrachloride) and then by a centrifugal process. The amount of oil and solvent from the sample was determined using a colorimetric spectrophotometer. Results and Discussion. The experiments described above were carried out using two different sizes of silica sand (0.2 and 0.6 mm fractions) and silica gel. At step 1, no free oil separation from the silica sand with a 0.2 mm diameter occurred. However, 0.21 mL of free oil was separated from the model with the 0.6 mm fraction silica sand. Figure 5 shows the dependence of the amount of film-type oil removed from the samples on the heating type and sand size (step 2). For the 0.2 mm silica sand case, the amount of film-type oil separated from the sample after exposure to RF-EM was 2 times greater than that of thermal heating (Figure 5a). Thus, under RF-EM, additional ponderomotive forces became effective in addition to the thermal effect. These effects change oil structure and accelerate oil extraction from the samples. In the case of the 0.6 mm silica sand sample, the difference in oil extraction obtained from RF-EM and electrical heating is insignificant (Figure 5b). Also, the amount of oil produced from the 0.6 mm silica sand sample, having less specific surface area, exceeds the amount of oil produced from the sample with the 0.2 mm silica sand sample with the larger specific surface. In the samples with silica gel, which has very high adsorption capacity, it was observed that separation of film-like oil under RF-EM or thermal heating was impossible. Figure 6 compares the effects of RF-EM and thermal heating on the adsorptive oil after full solvent extraction (step 3). The RF-EM field resulted in higher amounts of adsorbed oil removal than the thermal heating cases. This is
Changes in Asphaltene Structure under RF-EM Field It was observed through the analysis presented above that the RF-EM effect on heavy oil extraction is more pronounced in comparison to the other methods used in this study. This, then, requires further analysis on the effects of RF-EM heating on the asphaltene structure, because it is one of the most critical aspects of the adsorptive-desorptive process. More specifically, one needs to clarify the effects of RF-EM on polar oil components that control the adsorptive-desorptive process during the extraction of heavy oil. The study of asphaltene molecular structure changes was carried out with the use of scanning atomic force microscopy (AFM). Under optimal conditions, the equipment can give pictures showing the molecular resolution of LangmuirBlodgett (LB) films. To prepare LB films, asphaltenes extracted from oils on Mortuk (oil 1) and Meshalkinskoye (oil 2) deposits were used. To support developing an asphaltene monolayer, mica was used as a substrate. The LB film developing process is described in ref 3. Figures 7 and 8 show the images of asphaltene particles obtained through the AFM before and after RF-EM field exposure for two different oil types (resolution 5 5 μm). The images taken after the RF-EM treatment differ significantly from the original one. In the original pictures (before the RFEM exposure), the packed structure of asphaltenes on a supporter can be observed. In the first case (Figure 7), a homogeneous layer structure is seen, whereas in the second oil type (Figure 8), some peaks are observed that are due to the development of a polymolecular asphaltene layer on the supporter. After exposure to the RF-EM field, aggregate structures and orientation of particles are seen. Polar particles were oriented 485
Energy Fuels 2011, 25, 482–486
: DOI:10.1021/ef1009428
Kovaleva et al.
changes under the field influence. It was observed that the orientation of asphaltenes in the direction of the field action and their higher interaction with each other than with a surface leads to the formation of oriented “hills” on the surfaces. The critical role of the RF field on the adsorptive process during the displacement of high-viscosity oils is that it results in less asphaltene precipitation and pore plugging compared to that of thermal heating. (3) The size of sand particles significantly affects the oil recovery during the heating process. For the 0.2 mm silica sand case, the amount of film-type oil separated from the sample after exposure to RFEM was 2 times greater than that of thermal heating. Hence, under RF-EM, additional ponderomotive forces became effective in addition to the thermal effect. These effects change the oil structure and accelerate oil extraction from the samples. In the case of the 0.6 mm silica sand sample, the difference in oil extraction obtained from RF-EM and electrical heating is insignificant. The amount of oil produced from the 0.6 mm silica sand sample, having less specific surface area, exceeds the amount of oil produced from the sample with the 0.2 mm silica sand sample with the larger specific surface. (4) The efficiency of the RF-EM field mainly depends upon the frequency of radiation and the effects of frequency fluctuations on polar components of oil (resonant interaction), i.e., electrophysical parameters of oil, and the main condition for selecting optimal field-scale operating conditions is the correct choice of the frequency of the EM field. (5) This paper presents the preliminary (and promising) results of laboratory experiments, which will be useful in selecting the optimal frequency of RF-EM fields. Experimental data can be used in field-scale numerical modeling for selecting the optimal volume of the solvent to be injected and to determine the heated radius around the wellbore and temperature distribution for different frequencies.
Figure 7. AFM pictures of asphaltenes (oil 1): (a) before and (b) after RF-EM effects (resolution 5 5 μm).
Figure 8. AFM pictures of asphaltenes (oil 2): (a) before and (b) after RF-EM effects (resolution 5 5 μm).
in the direction of the field effect, and their location on the supporter is more oriented in comparison to their locations in the original image (before the RF-EM). Conclusions (1) After RF-EM influence on the oil-saturated samples, the quantity of the received oil is more than under electrical (and thermal) processing in all stages at identical temperatures of heating of the media. It confirms the additional “nonthermal” action of the field. (2) The obtained results of the visualization structure of asphaltenes before and after the treatment of a RF-EM field showed that it considerably
Acknowledgment. This study was supported by the Russian Foundation for Basic Research (Grant 08-01-97032).
486
