ARTICLE pubs.acs.org/EF
Analysis of Microscopic Displacement Mechanisms of Alkaline Flooding for Enhanced Heavy-Oil Recovery Haihua Pei,† Guicai Zhang,*,†,‡ Jijiang Ge,† Luchao Jin,† and Xiaoling Liu† †
College of Petroleum Engineering, and ‡State Key Laboratory of Heavy Oil Process, China University of Petroleum, Qingdao 266555, People’s Republic of China ABSTRACT: In this study, the microscopic displacement mechanisms of alkaline flooding for enhanced heavy-oil recovery are investigated using a micromodel. It has been observed that alkaline flooding exhibits a better sweep efficiency than waterflooding, and the serious viscous fingering is significantly reduced. The main microscopic mechanisms of alkaline flooding for enhanced heavy-oil recovery are that the alkaline solution penetrates in crude oil and water drops are, subsequently, formed inside the oil phase, which can improve the mobility ratio and, thus, lead to the improvement of sweep efficiency. The higher the alkaline concentration, the more easily the alkaline solution penetrates in the oil phase. Therefore, a greater improvement in sweep efficiency can be obtained using a higher concentration of alkali. The primary mechanism of the formation of the water drop inside the oil phase during alkaline flooding is related to the interfacial interaction between alkali and heavy oil, which not only results in the drastic reduction of oil water interfacial tension but also leads to the non-uniform enrichment of in situ surfactants activated by alkali.
1. INTRODUCTION With depleting light-oil resources and rising oil prices, successful recovery of heavy-oil resources becomes more and more important. Enhanced heavy-oil recovery is more difficult because of its complicated composition and high viscosity. However, heavy oil usually contains a high content of organic acids that can react with alkali to form in situ surfactants, which may help to improve oil recovery.1 Therefore, much attention has been paid to investigate the effect of injecting alkali into heavy-oil reservoirs in recent years.2 In general, it has been shown that alkaline flooding indeed improves oil recovery compared to waterflooding, but different views on the mechanisms for alkaline flooding to improve heavy-oil recovery are proposed.3 5 Jenning et al.6 performed a caustic flooding coreflooding test using a heavy oil with a viscosity of 187 mPa s at the reservoir temperature. The results showed that oil recovery could be significantly improved by caustic flooding with 0.1 wt % NaOH. The improvements consisted of greater incremental oil recovery before water breakthrough and a lower producing water/oil ratio during the flooding, but the ultimate residual oil saturation or microscopic conformance in the core was not significantly affected by the caustic injection. It was proposed that the mechanism of this process included in situ formation of oil-inwater (O/W) emulsions that tended to plug growing water fingers and channels, diverting flow to an initial unswept area. However, Cooke et al.7 proposed a different alkaline flooding in 1974, in which the alkaline solution should be saline rather than fresh. When the proper alkaline solution and acidic oil flow simultaneously in a porous medium, a viscous oil-external emulsion is formed. The flow properties of this type of emulsion permit a high, non-uniform pressure gradient to be generated across the narrow region in the vicinity of the emulsion front. The pressure gradient is sufficient to overcome the reduced capillary force and displace the oil from the pore space. The displacement efficiency can be much improved over ordinary waterflooding efficiency. This mechanism is quite different from the mechanism of emulsification and entrapment, in which O/W emulsions could be entrapped by pore throats too small for the oil emulsion droplets to penetrate. Cooke et al.7 r 2011 American Chemical Society
suggested this method mainly improved the sweep efficiency rather than reduced the residual oil saturation. However, its significance to develop the heavy-oil reservoir was largely ignored. More recently, Dong et al.8 performed a micromodel study of alkaline flooding for heavy oil. The proposed recovery mechanism was that the W/O emulsion formed in the injection of alkaline solution could block the high permeability zone, leading to an increase in the pressure drop and a high tertiary oil recovery. However, during the flooding, the penetration of alkaline solution in the oil phase could occur without adding a high concentration salt to alkaline solution, which was greatly different from what Cooke et al.7 had mentioned previously. Besides, it was observed that oil could contact the wall of the micromodel, where water-in-oil (W/O) emulsions formed. This wettability alteration from water-wet to oil-wet might also facilitate plugging some pores and improving sweep efficiency. With regard to the design of the displacement agent in chemical flooding for heavy oil, alkaline solution has gained more and more attention. Dong et al. and Ma et al.9,10 conducted alkaline flooding with 0.3 wt % Na2CO3 + 0.6 wt % NaOH on Brintnell heavy oil (1266 mPa s at 22 °C), and tertiary oil recovery of 29.9% initial oil in place (IOIP) was obtained, which was 4.2% higher than that of the best alkali surfactant combination formula. A later study by Zhang et al.11 showed that a greater improvement in oil recovery could be achieved using a higher concentration of alkali. It was also observed that there was always a rapid buildup of the pressure drop during alkaline injection. Therefore, the in situ generated W/O emulsion and the increased resistance to water flow during alkaline flooding have been recognized as the dominant mechanism.8,11,12 Accordingly, some numerical simulations of alkaline flooding for heavy oil were conducted on the basis of the formation of W/O emulsion.13,14 Through micromodel tests, Ding et al.15 proposed that the penetration of alkaline solutions in crude oil and the formation of water drops inside the oil phase were the main mechanism to Received: April 16, 2011 Revised: September 1, 2011 Published: September 04, 2011 4423
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Table 1. Basic Properties of the Heavy-Oil Sample oil sample
viscosity at 55 °C (mPa s)
density at 55 °C (g/cm3)
acid number (mg of KOH/g)
resin (wt %)
normal heptane asphaltene (wt %)
Zhuangxi
325
0.9302
0.80
19.7
0.835
Table 2. Analysis of the Formation Brine Sample ion content (mg/L) K+ + Na+
Ca2+
Mg2+
SO42
CO32
HCO3
Cl
total salinity (mg/L)
pH value
1751.0
103.0
11.1
47.4
23.7
602.2
2501.0
5039
8.35
Figure 1. Schematic of the microscopic oil displacement experimental apparatus.
improve sweep efficiency during alkaline flooding, while W/O emulsion was just the byproduct of alkaline penetration other than the basic reason for enhanced oil recovery by alkaline flooding. However, until now, the mechanism of the penetration of alkaline solution in heavy oil and the formation of water drops inside the oil phase in porous media has been still unclear. The purpose of this study is to analyze the microscopic displacement mechanisms of alkaline flooding for enhanced heavy-oil recovery, especially to elucidate the microscopic mechanism of the formation of water drops inside the oil phase in the alkaline-flooding process.
2. EXPERIMENTAL SECTION 2.1. Fluids and Chemicals. Oil and formation brine were collected from the Zhuangxi 106 heavy-oil reservoir in the Shengli oilfield, China. To remove the solids and water, this heavy oil was centrifuged at 10 000 rpm at 55 °C for 4 h. The viscosity, density, and acid number of the oil are analyzed and listed in Table 1, while the analysis of the formation brine is shown in Table 2. It can be seen that the salinity of the formation brine is relatively low and the concentrations of Ca2+ and Mg2+ in brine are also low. All of the solutions used in the experiments were prepared with NaCl solution with the concentration of 5000 mg/L. The alkaline agents used in this study were sodium carbonate (Na2CO3) and sodium hydroxide (NaOH). To observe the phenomena easily during the microscopic flooding, 0.05 wt % eosin was added to color the injected brine in the micromodel test.
2.2. Interfacial Tension (IFT) Measurements. The oil water IFTs were measured at 55 °C using a Texas model 500 spinning drop tensiometer. With an image-capture device and image-acquisition software equipped, this instrument could automatically measure and record the dynamic IFT. It usually took from 15 min to 2 h for the IFT between each oil drop and alkaline solution to reach a stable value (i.e., equilibrium IFT). 2.3. Microscopic Flooding Test. To investigate the interfacial interaction between alkali and heavy oil, the alkali/oil equilibrated tests were carried out. The systems were equilibrated by taking two-thirds of alkaline aqueous solution and one-third of oil by volume in a 100 mL separatory funnel maintained at 55 °C. After the solutions were shaken vigorously for about 30 min using a mechanical shaker, they were allowed to stand for about 3 weeks until clear mirror-like interfaces were obtained and the oil and aqueous phases became optically clear. The equilibrated oil and aqueous phases were then separated from the top and bottom of the funnel, respectively, for various physicochemical measurements. The glass-etched micromodel was used to investigate the displacement mechanisms of alkaline flooding. The micromodel was made by etching a two-dimensional network of pores and throats on glass plates through a photochemical method. The pore network used in this study was patterned after the pore structure of reservoir core. The transparent nature of the micromodel allows for the pore-scale multiphase displacement to be visually observed. Figure 1 shows the schematic of the microscopic oil displacement experimental apparatus. The procedure of the micromodel test was described as follows: after being vacuumed, the micromodel was saturated with brine, and then the 4424
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Figure 2. Glass-etched micromodel saturated with water and oil. brine was displaced by crude oil until no more water was produced. Because the viscosity of the crude oil was higher than the resident water, almost all of the water present in the micromodel was displaced. After heavy oil saturated, the model was aged for 24 h. Then, brine or alkaline solution was injected into the micromodel at a constant flow rate of 0.003 mL/min. Using a video recorder and camera apparatus, the microscopic flooding test can be visualized during the different stages of fluid injection. The water and oil distribution after saturation is shown in Figure 2. The sweep efficiency and recovery efficiency of the microscopic displacement test are determined using the image analysis technique.
Figure 3. Dynamic IFT curves of the fresh compound alkali/heavy oil system.
3. RESULTS AND DISCUSSION 3.1. IFT Behavior of Oil/Alkaline Systems. According to the results of emulsification tests, a mixture of Na2CO3 and NaOH with a mass ratio of 1:1 was selected as the chemical formula for alkaline flooding. It exhibited a good emulsifying capability for the Zhuangxi heavy oil. For convenience, this chemical formula is termed compound alkali in the following sections of this paper. The dynamic IFTs between the fresh oil and the compound alkali with different concentrations are given in Figure 3. It indicates that, when the alkaline concentration is low, the dynamic IFT is larger than 1.000 mN/m; however, for 0.4 wt % compound alkali, the dynamic IFT decreases to about 0.001 mN/m first and then increases with time. When the concentration of alkali ranges from 0.6 to 1.0 wt %, the dynamic IFT shows little change with time and the equilibrium value is about 0.010 0.100 mN/m. The reason may be that, above a certain concentration, the alkaline solution can provide enough OH at the oil/water interface; thus, there will be enough in situ surfactants to decrease the IFT. On the basis of the above results, 0.6 1.0 wt % of the compound alkali can be selected to mobilize the residual oil in the reservoir. To understand the change of alkaline solution after being equilibrated with heavy oil, pH values of the fresh alkaline solution and the equilibrated solution were measured (see Figure 4). It can be observed that the pH value of the equilibrated alkaline solution is obviously lower than that of the fresh alkaline solution with the same original concentration of alkali. This result indicates that some OH in the alkaline solution has been consumed by the interfacial interaction. To further investigate the effects of the interfacial interaction between alkali and heavy oil on the IFT, the IFTs of the fresh compound alkali/heavy oil and equilibrated compound alkali/ heavy oil were measured, and the results are as shown in Figure 5 (the original concentration of compound alkali was 1.0 wt %). For the fresh alkali solution and fresh oil system, the IFT decreases rapidly at the beginning, then increases, and finally, stabilizes at about 0.070 mN/m. While for the equilibrated compound alkali
Figure 4. pH values of the fresh alkaline solutions and the equilibrated solutions.
Figure 5. Dynamic IFT curves with different alkali/oil systems.
and the equilibrated oil system, no dynamic effect is observed and the equilibrium value is 3.000 mN/m. It implies that there is no interfacial interaction occurring at the interface between the 4425
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Energy & Fuels equilibrated compound alkali and the equilibrated oil. However, for the fresh alkali/equilibrated oil system and the equilibrated alkali/fresh oil system, there is still an interfacial interaction existing at the interface according to their dynamic IFT behaviors. However, the IFT of the equilibrated alkali/fresh oil system is lower than that of the fresh alkali/equilibrated oil system. This is most likely resulting from the consumption of the petroleum acids in the alkali/heavy oil equilibrated test. Therefore, the interfacial interaction between alkali and the petroleum acids in the heavy oil has a great effect on the IFT. 3.2. Microscopic Displacement Mechanisms of Waterflooding. To understand how alkaline flooding can improve heavy-oil recovery, it is necessary to examine the distribution of residual oil after waterflooding. Therefore, a microscopic displacement test was conducted with 0.5 wt % NaCl as the displacement agent, and the microscopic images of oil distribution during the waterflooding process are shown in Figure 6. It can be seen that water mainly penetrates along the pore walls (see Figure 6a) or advances from the center of the pore (see Figure 6b) at the beginning of waterflooding. Along the diagonal direction of the micromodel, water breaks through in a short time and a large amount of oil on both sides of the main diagonal line is unswept. After that, little oil can be recovered by the extended waterflooding and a relatively high oil saturation remains in the micromodel at the end of the test, as shown Figure 6d. 3.3. Microscopic Displacement Mechanisms of Alkaline Flooding. A micromodel test with 0.6 wt % compound alkali as the displacement agent was carried out, and the images of alkaline flooding at different stages are shown in Figure 7. It is observed that the injected alkaline solution penetrates in the crude oil and creates some water columns coated with a thin oil film at the beginning of alkaline injection (see panels a and b of Figure 7). After entering into pore space, the front of the water column is divided into small discontinuous water drops inside the oil phase (see panels c and d of Figure 7), which can be regarded as the precursors of W/O emulsion. Because of the Jamin effect and high viscosity of these dispersed systems, the viscous fingering effect is significantly reduced and the area behind the displacement front becomes relatively uniform (see Figure 7e). Figure 7f shows the micromodel when the alkaline solution front reached its outlet, displaying a relatively uniform oil saturation distribution over the entire micromodel. Therefore, we can conclude that it is the penetration of alkaline solutions in the crude oil and, subsequently, the formation of water drops inside the oil phase that damp viscous fingering, slow water channeling, and thus, improve sweep efficiency. This mechanism is believed to be especially effective for heavy oil, where the sweep efficiency of waterflooding is usually poor. As described above, the penetration of alkaline solutions in crude oil and the formation of water drops inside the oil phase are major mechanisms for alkaline flooding to improve heavy-oil recovery. On the basis of these mechanisms, we can explain many interesting phenomena presented in other published literature. For example, Bryan et al.13,16,17 investigated the nature of the emulsions formed during chemical flooding for heavy oil using low-field nuclear magnetic resonance (NMR). It was discovered that W/O emulsions mainly occurred in the inlet of the core, no matter whether O/W or W/O emulsions would be formed when the displacing system mixed with heavy oil in the emulsification test. Such a finding is difficult to be interpreted according to the theory in the colloid and surface chemistry. However, on the basis of the above observations in this study, it is easy to elucidate the
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Figure 6. Microscopic images (magnification: a and b, 3.0 times; c and d, 1.5 times) of oil distribution during the waterflooding process.
Figure 7. Formation of water drops inside the oil phase during alkaline flooding (image magnification: a d, 3.0 times; e and f, 1.5 times).
occurrence of W/O emulsions in the inlet of the core in experiments. These W/O emulsions may be water drops inside the oil phase generated by alkaline solution penetrating in the crude oil. 4426
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Figure 9. Effects of the alkaline concentration on the sweep efficiency and recovery efficiency at breakthrough of alkaline solution.
Figure 8. Microscopic images (magnification: 1.5 times) of alkaline flooding when alkaline solution breaks through.
Because there are oil films coating the water drops, they may be considered as W/O emulsions according to the NMR analysis. In 2006, Dong et al.8 observed the penetration of alkaline solution in crude oil and the occurrence of discontinuous water ganglia by micromodel tests. They proposed that in situ W/O emulsions acted as the main mechanism of enhanced oil recovery. However, on the basis of the micromodel study in this paper, it should be concluded that W/O emulsion is just a byproduct from the penetration of alkali in the oil phase, which usually occurred at the later stage of alkaline flooding. It can be seen from Figure 7 that the formation of W/O emulsion undergoes three stages: water column, small water drop, and W/O emulsion. All of these dispersed systems can improve sweep efficiency by high viscosity and the Jamin effect. To examine the effectiveness of the alkaline concentration in creating the water drops inside the oil phase during the alkalineflooding process, microscopic displacement tests with different concentrations of compound alkali were conducted. Figure 8 shows the microscopic images of the whole micromodel when the alkaline solution breaks through. Figure 8a is taken after the waterflooding, showing that some water channels (red in color) are created along the diagonal direction of the micromodel. The oil is largely bypassed because of viscous fingering caused by the
adverse mobility ratio between oil and water. The poor sweep efficiency of the waterflooding leaves most of the micromodel area untouched. When the alkaline solution is injected, as shown in panels b f of Figure 8, the severe viscous fingering occurring in waterflooding disappears. This is because the injected alkaline solution can penetrate in the oil phase and create lots of water drops inside the oil phase. As a result, the mobility ratio can be improved and, thus, leads to improved sweep efficiency. Additionally, it is also observed that the alkaline solution with a higher concentration can penetrate in the oil phase more easily and create more water drops inside the oil phase during the displacement. This behavior makes both the sweep efficiency and the tertiary oil recovery increase with the concentration of alkali, as shown in Figure 9. This is consistent with the results of the sandpack flood test conducted by Zhang et al.11 and Ding et al.,15 in which the highest incremental oil recovery is obtained and the highest pressure drop is built up when a high concentration of alkaline solution is injected. 3.4. Mechanisms of the Formation of Water Drops inside the Oil Phase. As mentioned above, the formation of water drops inside the oil phase during the alkaline-flooding process undergoes two stages. The first stage is the occurrence of water columns resulting from the penetration of alkaline solution in the crude oil in the pore. The second stage is that these water columns can be divided into small discontinuous water droplets moving forward. Both stages are related to the interfacial interaction between alkali and heavy oil, which not only results in the drastic reduction of oil water IFT but also leads to the nonuniform enrichment of in situ surfactants activated by alkali. The reduction of IFT promotes the penetration of alkaline solution in the crude oil, while the non-uniform enrichment of surfactants makes it possible that water columns can be divided into small discontinuous water droplets at the points where the surfactant concentration is low and the IFT is relatively high. To prove the above inference, 1.0 wt % compound alkali and heavy oil were mixed and equilibrated at first and then micromodel tests for the fresh alkali/fresh oil, the fresh alkali/equilibrated oil, the equilibrated alkali/fresh oil, and the equilibrated alkali/equilibrated oil systems were carried out. Figure 10 shows the microscopic images of these microscopic displacement tests. It can be observed that there are water drops appearing for the fresh alkali/ fresh oil, the fresh alkali/equilibrated oil, and the equilibrated 4427
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Figure 10. Four kinds of microscopic displacement tests (magnification: 3.0 times).
alkali/fresh oil systems (see panels a c of Figure 10); however, the equilibrated alkali cannot penetrate in the equilibrated oil, and the water column does not appear, as shown in Figure 10d. For the equilibrated alkali/equilibrated oil system, the IFT has no dynamic effect and the equilibrium value is 3.000 mN/m (see Figure 5), which implies that there is no reaction occurring at the oil/water interfaces in the equilibrated alkali/equilibrated oil system. Thus, such displacement is similar to that of waterflooding. While for the other three systems, the IFT has an obvious dynamic effect and the minimum IFT is lower than 0.100 mN/m, which indicates that the interaction between alkali and organic acids in heavy oil occurs at the oil/water interface. Therefore, it is concluded that the interfacial reaction at the oil/alkaline solution interface and low IFT of oil/water seems to be necessary to lead to the penetration in the oil phase by alkaline solution. Furthermore, it is also observed from the images of the fresh alkali/equilibrated oil system (see Figure 10b) that the oil film outside the water drops is thinner compared to that of the equilibrated alkali/fresh oil system (see Figure 10c). This is because most organic acids in the fresh oil have been neutralized by 1.0 wt % compound alkali in the equilibrated test, and thus, the interfacial reaction between the fresh alkali and equilibrated oil during microscopic displacement is weakened. While for the equilibrated alkali/fresh oil systems, it can be seen from the pH value of the equilibrated alkali that the alkalinity of 1.0 wt % equilibrated alkali is still strong (see Figure 4). In addition, the equilibrated alkaline solution contains a small amount of in situ surfactants generated by the reaction of alkali and organic acids in heavy oil, which can weaken the non-uniform enrichment of in situ surfactants at the oil/water interface during the micromodel tests for the equilibrated alkali/fresh oil system. As a result, the division of the water column is less obvious compared to that of the fresh alkali/fresh oil system (see Figure 10a). To prove the speculation that the non-uniform enrichment of the surfactant is the dominant reason for the water column being divided into small discontinuous water droplets, a microscopic displacement with 1.0 wt % compound alkali plus 0.1 wt % petroleum sulfonate was performed. Figure 11 shows that there is a water column appearing during the flooding, but this water column cannot be divided into small discontinuous water droplets moving forward. This phenomenon can be attributed
Figure 11. Microscopic displacement of 1.0 wt % composite alkali plus 0.1 wt % petroleum sulfonate (magnification: a c, 3.0 times; d, 1.5 times).
to the high concentration of preformed surfactants in the water phase. Because of the adsorption of petroleum sulfonate at the oil/water interface, the non-uniform distribution of in situ surfactants is weakened. Thus, for the displacement with 1.0 wt % compound alkali plus 0.1 wt % petroleum sulfonate, distribution of surfactants at the interface is more uniform than that of the in situ surfactants in alkaline flooding.
4. CONCLUSION (1) The microscopic mechanisms of alkaline flooding for enhanced heavy-oil recovery include the penetration of alkaline solutions into the crude oil and, subsequently, the formation of water drops inside the oil phase that tends to damp the tendency toward viscous fingering, slow water channeling, and thus, improve sweep efficiency. (2) The formation of the water drop inside the oil phase during alkaline flooding is related to the interfacial interaction between alkali and heavy oil. The reduction of IFT leads to the penetration of alkaline solution into heavy oil, and the non-uniform enrichment of in situ surfactants generated by the interface interaction at the oil/water interface results in the water column being divided into small discontinuous water drops in the oil phase. ’ AUTHOR INFORMATION Corresponding Author
*Telephone: +8653286981178. E-mail:
[email protected]. com.
’ ACKNOWLEDGMENT Financial support by the National Natural Science Foundation of China (Grant 51104170), the Fok Ying Tung Education Foundation for Young Teachers in the Higher Education Institutions of China (Grant 114016), and the New Century Excellent Talents Awards Program from the Ministry of Education of China (Grant NECT-07-0846) is gratefully acknowledged. 4428
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’ REFERENCES (1) Johnson, C. E. J. Pet. Technol. 1976, 28, 85–92. (2) Liu, Q.; Dong, M.; Ma, S.; Tu, Y. Colloids Surf., A 2007, 293, 63–71. (3) McAuliffe, C. D. J. Pet. Technol. 1973, 25, 727–733. (4) Dranchuk, P. M.; Scott, J. D.; Flock, D. L. J. Can. Pet. Technol. 1974, 13, 27–36. (5) Farouq Ali, S. M.; Figueroa, J. M.; Azuaje, E. A. J. Can. Pet. Technol. 1979, 18, 53–59. (6) Jennings, H. Y.; Jojnson, C. E.; McAuliffe, C. D. J. Pet. Techol. 1974, 26, 1344–1352. (7) Cooke, C. E.; Williams, R. E.; Kolodzie, P. A. J. Pet. Techol. 1974, 26, 1365–1374. (8) Dong, M.; Liu, Q.; Li, A. Proceedings of the International Symposium of the Society of Core Analysts; Calgary, Alberta, Canada, Sept 10 12, 2007; SCA 2007-47. (9) Dong, M.; Ma, S.; Liu, Q. Fuel 2009, 88, 1049–1056. (10) Ma, S.; Dong, M.; Li, Z.; Shirif, E. J. Pet. Sci. Eng. 2007, 55, 294–300. (11) Zhang, H.; Dong, M.; Zhao, S. Energy Fuels 2010, 24, 1829–1836. (12) Bryan, J.; Kantzas, A. Proceedings of the 2007 Society of Petroleum Engineers (SPE) Annual Technical Conference and Exhibition; Anaheim, CA, Nov 11 14, 2007; SPE 110738. (13) Arhuoma, M.; Yang, D.; Dong, M. Energy Fuels 2009, 23, 5995–6002. (14) Wang, J.; Dong, M.; Arhuoma, M. J. Can. Pet. Technol. 2010, 49, 51–58. (15) Ding, B.; Zhang, G.; Ge, J. Energy Fuels 2010, 24, 6346–6352. (16) Bryan, J.; Kantzas, A. Proceedings of the Society of Petroleum Engineers (SPE)/Department of Energy (DOE) 16th Symposium on Improved Oil Recovery; Tulsa, OK, April 19 23, 2008; SPE/DOE 113993. (17) Bryan, J.; Kantzas, A. Proceedings of the 2008 Society of Petroleum Engineers (SPE) International Thermal Operations and Heavy Oil Symposium; Calgary, Alberta, Canada, Oct 20 23, 2008; SPE 117649.
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