Foam by Sodium Dodecyl Sulfate and Hydrophobic Nanoparticl

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Experimental study of the stabilization of CO2 foam by SDS and hydrophobic nanoparticles Songyan Li, Zhaomin Li, and Peng Wang Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.5b04443 • Publication Date (Web): 07 Jan 2016 Downloaded from http://pubs.acs.org on January 18, 2016

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Industrial & Engineering Chemistry Research

Experimental study of the stabilization of CO2 foam by SDS and hydrophobic nanoparticles Songyan Li*, Zhaomin Li*, Peng Wang College of Petroleum Engineering, China University of Petroleum (East China), 266580, China ABSTRACT: CO2 foam can control CO2 mobility and improve sweep efficiency in reservoirs; however, CO2 foam stabilized solely by surfactants is not stable. Nanoparticles can improve the performance of CO2 foam. The synergistic effect of SiO2 nanoparticles and sodium dodecyl sulfate (SDS) on CO2 foam stability was studied in this paper. The experimental results show that the synergistic effect requires an SDS/SiO2 concentration ratio of 0.1 to 0.4. The strength of the effect increases as the SDS/SiO2 concentration ratio increases from 0.1 to 0.17 but then decreases as the ratio further increases from 0.17 to 0.4; thus, a ratio of 0.17 provides the best performance for CO2 foam. The mechanisms of the synergistic effect of SDS and SiO2 include modulating the position of nanoparticle adsorption on the CO2 and liquid interface, improving the interfacial properties of the CO2 foam and reducing its liquid discharge and coarsening. SiO2 nanoparticles can also improve the CO2 foam performance under high temperatures and pressures. The visual flooding experiment reveals that the addition of SiO2 nanoparticles can improve the stability of CO2 foam in porous media, and shows good tolerance of crude oil. SDS/SiO2 foam can increase the pressure differences of the flow in sandpacks after water flooding, and improve the oil recoveries markedly. As the SDS/SiO2 concentration ratio increases, the pressure differences and enhanced oil recovery first increase and then decrease. The best CO2 foam flooding performance is achieved at an SDS/SiO2 concentration ratio of 0.17, which is related to the CO2 foam stability. The experimental results provide theoretical support for improving CO2 foam flooding under reservoir conditions.

1. Introduction CO2 flooding is an important technology for enhanced oil recovery (EOR) in tertiary oil recovery.1-3 In response to increasing requirements for reducing CO2 emissions, CO2 flooding has been widely used in the exploitation of crude oil. Because of the low viscosity and low density of CO2, gas channeling and gravity segregation usually occur under reservoir conditions, resulting in a low sweep efficiency.4-5 To solve this problem, CO2 foam produced by a surfactant solution is widely used to control CO2 mobility.6-8 However, CO2 foam stabilized solely by surfactant has some undesirable properties. For example, CO2 foam is unstable when in contact with crude oil, and the surfactant easily decomposes under the high temperatures and high salt contents of oil reservoirs. CO2 foam has many advantages over N2 foam, but its stability must be improved. With the recent advances in nanotechnology, the application of nanoparticles to stabilize foams has gradually attracted attention. Surface-modified nanoparticles (such as nano silica) can be used as a stabilizer for CO2 foam. Such nanoparticles have the following advantages over surfactants. 1

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(1) They can stabilize foam even under high temperatures and high salt concentrations because of the characteristics of these solid particles, which is important for the application of CO2 foam in reservoir conditions.9-13 (2) The surfactant adsorbs strongly during foam formation, whereas the nanoparticles can migrate in the porous media and are therefore less prone to adsorption during the formation.14-15 (3) The solvent role of CO2 toward the nonpolar end of the surfactant is usually weak because the CO2 molecule lacks a permanent dipole moment and the Van der Waals force is weak. The surfactant is inclined to be in the water phase instead of entering the interface between the CO2 and water, resulting in poor stability of the CO2 foam.16 Meanwhile, surface-modified nanoparticles have affinity both for CO2 and water, improving the binding force of CO2 and water.17 (4) The solubility of CO2 in water is very high (for example, the solubility of CO2 in beverages is 50 times higher than that of N2), which increases gas diffusion between bubble films and causes poor stability.4 Nanoparticles adsorbed on the interface CO2 and water can reduce the contact area between the gas bubble and liquid film, thereby reducing the gas diffusion. The properties mentioned above illustrate that nanoparticles are highly suitable for stabilizing CO2 foam under reservoir conditions. Many researchers have investigated nanoparticle-stabilized foams. Meinders and Vliet reported that the enhanced dilational elasticity caused by the nanoparticles inhibited bubble coarsening.18 The adsorbed nanoparticles also hinder the water flow at the bubble surface and thus slow film thinning.19,

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Ravera et al. studied the dispersion of silica nanoparticles with the cationic

surfactant hexadecyltrimethylammonium bromide (CTAB).21 The nanoparticle surface changed from hydrophilic to hydrophobic upon CTAB adsorption, and its hydrophobicity increased with the CTAB concentration.22 Zhang et al. and Yazhgur et al. found that the dispersion became opaque at high CTAB concentration, indicating nanoparticle aggregation, and the interface property of dispersion was dominated by the surfactant alone.23, 24 Binks et al. also confirmed that surfactant and silica nanoparticles could generate stable air foam at proper surfactant concentrations.25 Binks and Horozov also demonstrated that nanoparticle-stabilized foams can survive for weeks or more, even under extremely harsh conditions.26 Ahuali et al. obtained a very stable nano-sized emulsion with an average diameter of 400 nm by combining silica particle and sodium dodecyl sulfate (SDS). The SDS molecules adsorbed on the surface of the silica nanoparticles and formed a supercharged structure.27 Sun et al. evaluated the performance of N2 foam stabilized by SiO2 nanoparticles and SDS and its EOR effectiveness, finding that the SiO2-stabilized N2 foam had significantly improved EOR performance due to its high stability .28, 29

Several researchers confirmed that CO2 mobility in porous media can be controlled much 2


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better by nanoparticles in indoor experiments and that the resistance factor of CO2 foam could be increased several-fold under the same experimental conditions by adding nanoparticles.30-32 Their experimental results also show that CO2 foam stabilized by nanoparticles and surfactant can further improve the oil recovery by 35.8%-48.7% after water flooding. However, they did not optimize the nanoparticle and surfactant concentrations in CO2 foam, and their CO2 foam did not achieve its optimal performance. Although many results have been reported for the emulsion, N2 foam and air foam stabilized by nanoparticles and surfactant, very few studies have investigated nanoparticle-stabilized CO2 foam.14-16 Only several researchers have studied the flow and mobility control of nanoparticle-stabilized CO2 foams in porous media, and many theoretical problems remain open. In this paper, the performance of CO2 foam stabilized by hydrophobic nanoparticles and surfactant was studied experimentally, the nanoparticle and surfactant concentrations were optimized, and the mechanism and influencing factors for the stability of CO2 foam in the bulk phase and in porous media were discussed. The results are meaningful for the application of CO2 foam flooding for EOR.

2. Experimental methods 2.1. Apparatus A balance (Model PL2002, Mettler Toledo, Switzerland, full scale of 2100 g, accuracy of 0.01 g) was used to determine the weight of the materials. Foams were prepared using a Warning blender (GJ-3S, Qingdao Senxin Machinery Equipment Co., Ltd., China). A viscometer (DV-II+Pro, Brookfield, America, accuracy of ±1%, reproducibility of ±0.2%) was used to measure the viscosities of the fluids. The performances of foams were assessed using a commercial instrument (FoamScan HT, Teclis, France, full scale of 0.8 MPa and 120 °C) able to monitor the foam volume, foam stability, and liquid content in bubbles using image analysis and conductivity measurements.33, 34 The surface tension and interfacial viscoelastic modulus were determined by a drop shape tensiometer (Tracker-H, Teclis, France, full scale of 20 MPa and 200 °C).35 The experimental apparatus for sandpack flooding has been shown in previous studies.28, 29 Microscopic models built of toughened glass were used in the visual flooding experiments. The porous media area of the microscopic model is approximately 40 mm × 40 mm. The depth and width of the flow channel are approximately 60 µm and 80 µm, respectively. The microscopic model was placed in a holder with a pressure of less than 20 MPa and temperature less than 100°C. The video of the foam flow was recorded by a digital microscopic imaging system. 3



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2.2. Materials SDS purchased from Sigma (USA) with a purity greater than 99.0% was used as the surfactant for the CO2 foam in the experiments. SDS is a common anionic surfactant with a simple molecular structure and is mainly used as a detergent in the textile industry. Deionized water served as the liquid phase in all the experiments. CO2 and N2 were supplied by Tianyuan Inc. (China), with a purity of 99.99 wt%. All glassware was cleaned with a surfactant-free cleaning agent. The crude oil used in the sandpack flooding experiment was collected from Shengli Oil Field in China, with a viscosity of 95 mPa.s at 50°C. Partially hydrophobic SiO2 nanoparticles of the type H18 was supplied by Germany Wacker Chemical Co., Ltd., at purities greater than 99.8%. The nanoparticle diameters are 20 nm. The contact angles of SiO2 nanoparticles with water are 122.22 °. 2.3. Experimental methods (1) Foam evaluation experiment Foam generation under normal pressure. First, SDS solutions and SDS/SiO2 dispersions with different concentrations were prepared according to the experimental scheme. Foams were generated by the Waring blender method.36 Then, 100 ml of the solution or dispersion was placed in a stirring cup. The cup was then covered with a sealing cover and injected with CO2 gas for 3 min to displace the air. The solution or dispersion was stirred for 3 min at 8000 r/min. After the stirring time elapsed, the foam was poured into a graduated cylinder. The initial volume of the foam was recorded as an indication of the foaming capability. The time required for 50 ml of liquid to separate was also recorded as the half-life, an indicator of the foam stability. These values were measured three times per sample, and the average value was taken as the final result. Foam generation under high pressure. The foam was generated in a visual blender under high temperature and high pressure.37 First, the air-tightness of the experimental equipment was tested, and 50 ml of SDS solution or SDS/SiO2 dispersion was injected into the blender using a syringe. Next, liquid CO2 was injected into the blender, and the pressure was adjusted to the desired value. The temperature was set to the desired value for 2 h to allow the contents to achieve phase equilibrium. The solution or dispersion was then stirred for 3 min at 1000 r/min. The foam volume and half-life were recorded to evaluate the foam properties under high pressure and high temperature. (2) Surface tension and interfacial viscoelastic modulus The interfacial tension and interfacial viscoelastic modulus of the SDS solution or SDS/SiO2 dispersion with CO2 was tested by the pendant drop method using a Tracker H tensiometer. First, the CO2 was injected into the sample tube. During the measurement, a pendant drop of the 4


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solution or dispersion was formed at the end of a stainless steel needle attached to a gas-tight syringe. The oscillation frequency was 0.1 Hz, and the amplitude was 1 µm3. The drop shape, drop volume and area were recorded by the CCD camera and analyzed by commercial drop image software. Details about the tensiometer and pendent drop method can be found elsewhere.38 (3) Flooding experiment Sandpack flooding experiments for CO2 foam at different concentration ratios were performed in the laboratory. The experimental procedures are as follows. Each sandpack model was packed with silica sand with the same particle-diameter distribution to ensure sandpacks with similar permeabilities and porosities. The sandpack was evacuated for more than 4 hours before being saturated with water, and the pore volumes and permeabilities were tested. The sandpack was then displaced with crude oil at a rate of 0.25 ml/min until water production ceased. The backpressure of the sandpack was 10.0 MPa. The initial oil saturation and irreducible water saturation were calculated. Water flooding was performed until oil production ceased, after which then SDS/SiO2 foam was injected for 1 porous volume (PV) of the sandpacks. The post-water-flooding was then conducted. The pressure differences and oil recovery were recorded. The experimental procedures for the visual flooding are similar to those of the sandpack flooding. The only difference was that the flow rate of the crude oil was 0.05 mL/min for oil saturation because the flow area of the microscopic model was small. The video of the foam flow through the microscopic model was recorded by a digital microscopic imaging system.

3. Results and discussion 3.1. CO2 foam stabilized by SDS The foaming capability and stability of CO2 foams with different SDS concentrations are shown in Figure 1. The foam volume and half-life of CO2 foam increase gradually with the SDS concentration. When the SDS concentration exceeds 0.1 wt%, these values almost plateau. The longest half-life for CO2 foam under normal pressure and room temperature of 22 °C is approximately 4.7 min, whereas the corresponding value for N2 foam under the same experimental conditions is 11.2 min. This difference is likely due to the weak Van der Waals force in the case of CO2 due to the molecule’s lack of a permanent dipole moment. The surfactant thus prefers the liquid phase over the interface of CO2 and liquid, resulting in poor stability.12

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Figure 1. Foam volume and half-life of CO2 foams with different SDS concentrations.

Foam is a dispersion system with high surface energy, making it thermodynamically unstable. The surfactant can reduce the surface tension and surface energy, improving the foam stability. The interfacial viscoelastic modulus indicates the strength of the bubble film. A higher viscoelastic modulus can improve the deformation resistance and stability of the foam. The interfacial viscoelastic modulus of surface layer determines its capability to resist external disturbances and to avoid the bubble coarsening and rupture.28, 29 The interface properties are shown in Figure 2. It can be seen that with increasing SDS concentration, the surface tension of the SDS solution with CO2 decreases rapidly. When the concentration reaches 0.1 wt%, the decrease is not obvious. The interfacial viscoelastic modulus first increases and then decreases with increasing SDS concentration and peaks at a concentration of 0.1 wt%. An increase in the surfactant bulk concentration can affect the interfacial viscoelastic modulus in two aspects. One is to increase the surfactant concentration on the interface, which would cause higher interfacial tension gradient of the interface deforming, and an increase of the interfacial viscoelastic modulus. The effect of an increase of the interfacial viscoelastic modulus may play a dominant role at low surfactant concentration (when the SDS concentration is less than 0.1% in the experiment). When the surfactant concentration increases up to the critical micelle concentration (CMC), the absorption of the surfactant on the interface is almost saturated, and the interfacial viscoelastic modulus reaches a maximum value of 10.25 mN/m shown in Figure 2. The other effect of the rising surfactant bulk concentration is to increase the diffusing capability of the surfactant molecules from the bulk phase to a new interface, which can decrease the interfacial tension gradient and the interfacial viscoelastic modulus. The increase in the surfactant bulk concentration above CMC can only increase the diffusion of the surfactant molecules from the bulk phase to the interface, making the interfacial viscoelastic modulus decrease remarkably 6


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(when the SDS concentration is greater than 0.1% in the experiment).39

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Figure 2. Interfacial properties for different SDS concentrations.

3.2. CO2 foam stabilized by SDS and nanoparticles The experimental results above show that the stabilities of CO2 foam stabilized solely by SDS were poor. Therefore, combination of SDS and SiO2 nanoparticles was used in the following experiments. The effect of the SDS/SiO2 concentration ratio on the stability of CO2 foam was studied in the laboratory, and the results are shown in Figure 3. The concentration ratio is defined here as the ratio of the SDS and SiO2 concentrations in the dispersion in units of wt%/wt%. The performance of the SDS/SiO2 foam was compared with that of the SDS-only foam with the same SDS concentration. It can be seen in Figure 3 that the stabilities of SDS/SiO2 foams with different concentrations of SiO2 are consistent with the change in the SDS/SiO2 concentration ratio, and the optimal performance is achieved at an SDS/SiO2 concentration ratio of 0.17. The shapes of the curves in Figure 3 can be divided into three regions. In region A, the half-life and foam volume both increase obviously with increasing concentration ratio. In region B, the half-life and foam volume both decrease gradually from the peak values. In region C, the half-life and foam volume remain almost stable. Comparing the properties of the SDS/SiO2 foam with those of the SDS-only foam, SiO2 can significantly increase the foam half-life when the SDS/SiO2 concentration ratio is between 0.10 and 0.40. When the concentration ratio exceeds this range, the effect of SiO2 is not obvious. It can be concluded that SiO2 nanoparticles produce a synergistic effect with SDS when the concentration ratio is between 0.10-0.40, which can improve the foaming capability and foam stability. The synergistic effect of SDS and SiO2 for CO2 foam stability can be analyzed from the following four aspects. 7



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(b) SDS/SiO2 concentration ratio of 0.17 Figure 3. Properties of CO2 foams with different concentration.

(1) Modulating the nanoparticle’s adsorbing position at the CO2 and liquid interface Reducing the surface charge of the nanoparticles can promote their adsorption at the interface of the liquid and CO2 by decreasing the electrical barrier between the nanoparticles and the interface.40, 41 Abdel-Fattah and El-Genk reported that the adsorption of particles at the air–water interface was mainly controlled by particle–interface and particle–particle interactions.42 We tested the Zeta potential for the H18 nanoparticle with different SDS/SiO2 concentration ratio. The results reveal that the H18 nanoparticles were positively charged, and the potential was approximately 32 mV. The Zeta potential decreased with increasing SDS/SiO2 concentration ratio, reaching zero at a concentration ratio of 0.17 and then continuing to decrease, taking negative values. The hydrophobic end of SDS can adsorb on the surface of SiO2, improving hydrophobicity of the nanoparticle. The more SDS is absorbed on the surface, the weaker the 8


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hydrophobicity is. The position of the nanoparticle in the foam system has an important effect on the stability of CO2 foam. The nanoparticles can only affect the foam stability when adsorbed on the interface of CO2 and liquid. The contact angle for the H18 nanoparticles is 122.22°; thus, the nanoparticles are mostly in the gas phase when the SDS concentration is relatively low. In region A, with increasing SDS/SiO2 concentration ratio, the hydrophobicity of the nanoparticles decreases, the nanoparticles move from the gas phase to the liquid phase, and the stability of the CO2 foam increases. When the concentration ratio reaches 0.17, the nanoparticle achieves the best hydrophobic property, and these particles can adsorb onto the best positions of the interface. The distribution of SiO2 nanoparticles in the foam system is shown in Figure 4 for a nanoparticle concentration of 1.5 wt% and SDS/SiO2 concentration ratio of 0.17. The SiO2 nanoparticles were dried by fluorescein isothiocyanate (FITC), which is a staining material that fluoresces green under the laser scanning confocal microscope. Figure 4 shows that the concentration of nanoparticles is relatively low in the bulk phase but high on the interface of liquid and CO2. The nanoparticles played an effective role in stabilizing CO2 foam.

Figure 4. Distribution of SiO2 nanoparticles in CO2 foam. The depth normal to the plane of the paper is 80.0 µm.

In region B, the hydrophobicity of the nanoparticles decreases further with increasing SDS/SiO2 concentration ratio, and the nanoparticles are more inclined to be in the liquid phase. When the concentration ratio reaches 0.40, the nanoparticles become more hydrophilic and are mostly in the liquid phase. The nanoparticles cannot play an effective role in stabilizing the CO2 foam, and the foam is mainly stabilized by SDS. With increasing concentration ratio, the nanoparticles are gradually transported from the gas phase into the liquid phase, as shown in Figure 5.

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(a) 0.05

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Figure 5. Positions of the SiO2 nanoparticles relative to the interface. The SDS/SiO2 concentration ratios of (a), (b) and (c) are 0.05, 0.17 and 0.67, respectively. The hydrophobic nanoparticles are transported from the gas phase to the liquid phase due to SDS adsorption on the surface of nanoparticles. The SDS/SiO2 concentration ratios of 0.17 is best for stabilizing CO2 foam.

In addition, the adsorption position of the nanoparticles at the interface can also be studied by observing the foam structure and liquid separated from the foam, as shown in Figure 6. When the nanoparticles are more hydrophobic, most of the nanoparticles will be present at the interface or in the gas phase, and the water separated from the foam will be clear, as shown in Figure 6(a). When the nanoparticles are less hydrophobic, most of the nanoparticles will be in the liquid phase, and the separated liquid from foam will be opaque, as shown in Figure 6(d). As shown in Figure 6, the liquid separated from CO2 foam gradually becomes opaque with the increase of the concentration ratio, which indicates that the nanoparticles transition from hydrophobic to hydrophilic, and the adsorption position changes from the gas phase to the liquid phase.

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Figure 6. The separated liquid from CO2 foam under different SDS/SiO2 concentration ratios. The SDS/SiO2 concentration ratios in (a), (b), (c) and (d) are 0.10, 0.17, 0.30 and 0.45, respectively. The separated liquid from CO2 foam gradually becomes opaque.

The solvent role of CO2 with the nonpolar end of the surfactant is usually weak because the CO2 molecule lacks a permanent dipole moment, making the Van der Waals force weak. The 10


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surfactant is more inclined to be in the liquid phase than on the interface CO2 and liquid, and the stability of the CO2 foam is poor.12 The adsorption SDS of SiO2 nanoparticles at an appropriate concentration ratio provides the SiO2 with affinity for both CO2 and liquid, improving the stability of the CO2 foam.14 The SiO2 nanoparticles can avoid the shortcomings of surfactants for CO2 foam stabilization, which is more efficient for oil reservoir applications. (2) Improving the interfacial properties of CO2 foam The interfacial viscoelastic modulus of the bubble film affects the stability of CO2 foam, as it represents the resistance to film deformation. The higher the value of this modulus is, the stronger the liquid film is. The interfacial tension and interfacial viscoelastic modulus at a SiO2 concentration of 1.5 wt% were tested, and the results are shown in Figure 7. It can be seen from Figure 7 that the interfacial tension initially decreases rapidly as the concentration ratio increases. When the concentration ratio reaches 0.17, the interfacial tension begins to decreases slowly. The interfacial viscoelastic modulus first increases and then decreases, and peaking at a concentration ratio of 0.17. The SDS/SiO2 dispersion has an almost same interfacial tension and much higher viscoelastic modulus than the SDS-only solution, as shown in Figure 2. 80

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Figure 7. Interface properties of the SDS/SiO2 nanoparticle dispersion at a SiO2 concentration of 1.5 wt%.

The surface tension of the nanoparticle dispersion under different concentrations with CO2 was measured, and the results are shown in Figure 8. The red dashed line in Figure 8 shows the surface tension of distilled water and CO2. The surface tension changes little with the nanoparticle concentration. It can be concluded that the nanoparticles have no effect on reducing the surface tension, which is consistent with the results of other related studies.43, 44

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The experimental results shown in Figure 8 reveal that the adsorption of nanoparticles alone at the interface does not reduce the surface tension. However, the SDS/SiO2 system can not only reduce the interfacial tension (at high SDS/SiO2 concentration ratio) but also improve the film strength due to its advantageous synergistic effect. The results indicate that an SDS/SiO2 concentration ratio of 0.17 has the best synergistic stability performance for CO2 foam, as the interfacial tension of the system is relatively low and the viscoelastic modulus is maximal. (3) Reducing liquid discharge of CO2 foam Due to the density difference between gas and liquid in foam, it is difficult to avoid liquid discharge by gravity, which is one of the reasons for the instability of the foam system. The increase of the bulk viscosity can reduce the liquid discharge, which can enhance the foam stability. The viscosities of SiO2 nanoparticle dispersions were tested, and the results are presented in Figure 9. As shown in Figure 9, the viscosities of all the dispersions peak at a concentration ratio of 0.17. SDS has a solubilization effect for SiO2 nanoparticles. When the concentration ratio is less than 0.17, as the concentration ratio increases, the nanoparticle surface becomes more hydrophilic, and more nanoparticles can disperse in the liquid phase. As a result, the viscosity of the dispersion increases. When the concentration ratio exceeds 0.17, the viscosity of the dispersion decreases with further increase of the concentration ratio. For the same concentration ratio, the viscosity of the dispersion increases with the concentration of SiO2 nanoparticles. In particular, when the concentration of SiO2 nanoparticles increases from 1.5 wt% to 2.0 wt%, the viscosity of the SDS/SiO2 dispersion increases sharply. Figure 3 shows that a SiO2 concentration of 2.0 wt% yields a much higher half-life than the other 12


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concentrations studied. This result is most likely due to the obvious increase of the viscosity of the SDS/SiO2 dispersion. Figure 3 also shows that increasing the bulk phase viscosity can greatly reduce the foam volume. 15

Concentration ratio 0.067 Concentration ratio 0.17 Concentration ratio 0.33 Concentration ratio 0.50 Concentration ratio 0.67

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To more clearly observe the process of liquid discharge from CO2 foam, the structure of SDS/SiO2 foam with SiO2 and SDS concentrations of 1.5 wt% and 0.25 wt%, respectively, was compared with that of SDS foam with an SDS concentration of 0.25 wt% using the FoamScan. The structures of the foams at different times are shown in Figure 10. The liquid films both gradually thin over time. The thinning of the SDS/SiO2 foam is much greater than that of SDS foam at the same point in time, which indicates that the SiO2 nanoparticles can stabilize CO2 foam partly by reducing the liquid discharge. SDS/SiO2 foam

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Figure 10. Structural changes of the SDS/SiO2 foam and SDS foam with time under normal pressure and room temperature (22 °C).

(4) Decreasing the coarsening of CO2 foam The coarsening, or Ostwald ripening, process is caused by Laplace pressure between interconnected large and small bubbles. The gas diffuses from the small bubble to the large bubble, making the large bubble even larger and the small bubble even smaller. This phenomenon is one of causes of foam instability. The higher solubility of CO2 in water makes CO2 foam less stable than N2 foam.45 Figure 11 shows the principle for decreasing the coarsening of CO2 foam with nanoparticles. As the adsorption of SiO2 nanoparticles on the interface of CO2 and liquid increases, the contact area between the CO2 gas and liquid film decreases gradually, reducing the gas diffusion. This is why the stability of the foam increases with the concentration ratio from 0 to 0.17, as shown in Figure 3.

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CO 2

Figure 11. Reduction of the coarsening of CO2 foam using nanoparticles.

3.3. Effects of temperature and pressure on the performance of SDS/SiO2 foam (1) Effect of temperature The oil reservoir is a high-temperature environment in which traditional surfactants may decompose, affecting the properties of the CO2 foam. SiO2 nanoparticles have good temperature tolerance, which is helpful for stabilizing CO2 foam under high temperatures. The foam performances under high temperatures were researched to study the effect of temperature on the SDS/SiO2 foam and SDS foam. The SDS solution or SDS/SiO2 dispersion was first placed in an oven for 1 h at the desired temperature, and then the liquid was processed in a blender to generate foam. The foam volume and half-life were then measured. In this 14


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experiment, the SDS concentration for the SDS foam was 0.25 wt%, and the concentrations of SDS and SiO2 for the SDS/SiO2 foam were 0.25 wt% and 1.5 wt%, respectively. The experimental results for the foam volume and half-life are shown in Figure 12 and Figure 13, respectively. As the temperature increases, for both foams, the foam volume first increases and then decreases, and the half-life gradually decreases. The effect of temperature on the half-life is more obvious, mainly for the three following reasons. 500 475

Foam volume (ml)

450 425

SDS foam SDS/SiO2 foam

400 375 350 325 300 10

20

30

40

50

60

70

80

90

Temperature (℃)

Figure 12. Effect of temperature on the foam volume of CO2 foams. 80 70 60

Half-life (min)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


50 40

SDS foam SDS/SiO2 foam

30 20 10 0 10

20

30

40

50

60

70

80

90

Temperature (℃)

Figure 13. Effect of temperature on the half-life of CO2 foams.

a) The increasing temperature changes the interfacial properties. The interfacial properties of the SDS/SiO2 dispersion were measured, and the results are shown in Figure 14. As the temperature increases, the surface tension increases, and the interfacial viscoelastic modulus gradually decreases. This behavior is observed because the SiO2 nanoparticles and surfactant have higher kinetic energies at higher temperatures, which discourages their adsorption at the 15



interface. Increasing interfacial tension and decreasing interfacial viscoelastic modulus result in the instability of CO2 foam.


55

20


50

16

45

12

40 8 35 4


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30 0 20

30

40

50

60

70

80

Temperature (℃)

Figure 14. Interface properties with different temperatures.

b) The increasing temperature decreases the viscosity of the dispersion. With increasing temperature, the viscosity of the SDS/SiO2 dispersion decreases, which accelerates the liquid discharge and reduces the stability of CO2 foam. c) The increasing temperature accelerates the water evaporation of the bubble film and gas diffusion between the bubbles, increasing the instability of CO2 foam. (2) Effect of pressure When the pressure is greater than 7.28 MPa, and temperature is greater than 31.2 °C, CO2 is in a supercritical state. Under this supercritical state, the CO2 is similar to a liquid in terms of density and similar to a gas in terms of viscosity and diffusion. Pressure is an important factor affecting the stability of CO2 foam. The foam-generating experiments were conducted at 22 °C and 40 °C. The experimental results are shown in Figure 15. It can be seen from Figure 15 that the foam volume and half-life at the studied two temperatures both increase with increasing pressure. This increase is sharpest from 4 MPa to 6 MPa at 22 °C and from 6 MPa to 8 MPa at 40 °C. Figure 16 shows the foam morphology under different pressures. We can note that the foam volume and foam density both increase gradually with the pressure. When the pressure is higher than 8 MPa, the CO2 foam resembles ice cream and is very stable and fine.

16


15

200

12

160

9

120

6

80 half-life at 22 ℃ half-life at 40 ℃ foam volume at 22 ℃ foam volume at 40 ℃

3

0 0

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Foam volume (ml)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Half-life (h)

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40

0 14

Pressure (MPa)

Figure 15. CO2 foam properties at different pressures.

(a) 2 MPa (b) 4 MPa (c) 6 MPa (d) 8 MPa (e) 10 MPa (f) 12 MPa Figure 16. Photographs of the foam under different pressures at 40 ºC.

To further analyze the influence of pressure on CO2 foam, the CO2 density under different pressures is given in Figure 17, and the interfacial properties for different pressures at 22 °C and 40 °C were measured (Figure 18). At 22 °C, below 6.8 MPa, CO2 is in gas state, and the density increases slowly with the pressure, as shown in Figure 17. When the pressure reaches 6.8 MPa, the CO2 changes from a gas to a liquid, and the density increases rapidly. The higher temperature studied, 40 °C, is above the supercritical temperature, and the density increases quickly from 6 MPa to 8 MPa. The interface properties are related to the state properties, as displayed in Figure 18. The interfacial tension decreases and viscoelastic modulus increases dramatically over the pressure range of the state change, which is one of the reasons for the improvement of the foam properties in this range. Another reason is that the CO2 density increases with pressure, which decreases the fluid discharge for the CO2 foam. The half-life of SDS/SiO2 foam under high pressure (10 MPa) is 10 times that under normal pressure, which illustrates that higher pressure 17



during formation is beneficial for CO2 foam stability.

3

Density of CO2 (kg/m )

1000

800

600

22℃ 40℃

400

200

0 0

2

4

6

8

10

12

14

Pressure (MPa)

Figure 17. Density of CO2 as a function of pressure.


25

30 25

20 interfacial tension at 22 ℃ interfacial tension at 40 ℃ viscoelastic modulus at 22 ℃ viscoelastic modulus at 40 ℃

15

20 15

10 10 5

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0 16

Pressure (MPa)

Figure 18. Interfacial properties of the SDS/SiO2 dispersion at different pressures.

3.4. CO2 foam flow in porous media through visual flooding experiment A series of visual flooding experiments under different temperatures were conducted to study the difference between the SDS/SiO2 foam and SDS foam. The experimental results are shown in Figure 19. It illustrates that the higher temperature decreases the stability of the SDS/SiO2 foam and SDS foam, which is almost the same rule as the bulk foam shown in Figure 10. Under the temperature of 80 °C, the quality of SDS foam is obviously unstable with very large bubbles and uneven diameter distribution, however, SDS/SiO2 foam is still good enough. It reveals that the addition of SiO2 nanoparticles can improve the quality of CO2 foam in porous media.

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SDS/SiO2 foam

SDS foam

22°C

80°C

Figure 19. Structural of the SDS/SiO2 foam and SDS foam in porous media under pressure of 8.0 MPa and different temperatures.

The process of visual flooding experiment by SDS/SiO2 foam is shown in Figure 20. During water flooding, water bypassed the crude oil on the pore walls because of the unfavorable mobility ratio between the oil and water (Figure 20a). Some of the oil was still stranded in the throat because of capillary force. During the flooding process, water mainly flowed along the main stream line, and the sweep efficiency was relative low once water breakthrough occurred. Only a small percentage of crude oil could be recovered by water flooding, and oil saturation was still high in the micromodel at the end of the water flooding. During SDS/SiO2 foam flooding, many bubbles were formed (Figure 20b), thereby reducing the mobility of gas and preventing gas breakthrough. As a surfactant, SDS in the liquid could lower the oil/water interfacial tension and form O/W emulsions (Figure 20b and Figure 20c). The oil was easily stripped from the surface of the rock. The SDS/SiO2 foam is very stable even contacting with crude oil, which shows good oil tolerance. At the end of foam injection (Figure 20d) about 80% of the crude oil is recovered.

(a)

(b) 19



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(c)

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(d)

Figure 20. The four images depict the visual flooding experiment of SDS/SiO2 foam. Image (a) shows the end of water flooding, Images (b), (c), (d) show SDS/SiO2 foam flooding at 0.5 PV, 1.0 PV and 2.0 PV. The black area in the images is crude oil, the small white areas are CO2 bubbles, and the red area is water which is dried by eosin. The flow direction in the visual model is from left to right, and the water and foam was injected from the left of the model.

3.5. Sandpack flooding experiments using SDS/SiO2 foam The stability of the CO2 foam was enhanced by the addition of SiO2 nanoparticles. A series of sandpack flooding experiments were conducted to study the relationship between the stability of SDS/SiO2 foam and oil recovery efficiency. The experimental parameters are shown in Table 1. Table 1. Parameters of the sandpack flooding experiments. No.

Porosity (%)

Permeability (10-3 µm2)

1 2 3 4 5 6

37.75 37.87 36.55 36.87 35.61 36.98

2114 1987 1967 2058 2019 2011

Initial oil saturation (%) 87.68 88.57 89.27 88.16 86.78 88.32

SiO2 concentration (wt%) 1.5 1.5 1.5 1.5 1.5 1.5

SDS/SiO2 concentration ratio (wt%/wt%) 0.020 0.067 0.170 0.330 0.670 1.000

Temperature (°C)

Backpressure (MPa)

50 50 50 50 50 50

8 8 8 8 8 8

The pressure differences for water flooding and foam flooding are shown in Figure 21. In Figure 21, the pressure differences of the sandpacks increased rapidly during water flooding. It is due to the relative permeabilities of water phase and oil phase in porous media. At the beginning of the water injection, the initial oil saturation is as high as 88%, the relative permeability of water phase is very low, and the pressure difference is very high. When the injected volume of water reached approximately 0.5 PV, the injected water broke through, and the pressure differences decreased rapidly and then leveled off. This behavior is a result of the high viscosity ratio of oil and water, which causes viscous fingering and water channeling. After the water breakthrough, most the post-injected water travels through the water channel, resulting in low sweep efficiency and low oil recovery efficiency in porous media.46-48 When the SDS/SiO2 foam 20


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was injected into the sandpacks, the pressure differences increased quickly for the second time, which indicated good property of profile control. The reason is that the viscosity of the SDS/SiO2 foam is much higher than the water, and the flow resistance for the foam in the porous media is much higher. The flow channels during water flooding could be plugged because of the high viscosity, and swept volume could be increased. During the post water flooding, the pressure differences decreased gradually. As the SDS/SiO2 concentration ratio increased, the pressure differences first increased and then decreased, which is related to the CO2 foam stability shown in Figure 3. The greatest pressure difference is observed at an SDS/SiO2 concentration ratio of 0.17. During SDS/SiO2 foam flow in the sandpack, there were some nanoparticles left in the porous media. We tested the permeability of the sandpack after the post water flooding, and fount that it was about 92% of the original value. The nanoparticles left in the porous media did not cause damage to the sandpack.

Pressure difference (MPa)

2.0 Concentration ratio 0.020 Concentration ratio 0.067 Concentration ratio 0.170 Concentration ratio 0.330 Concentration ratio 0.670 Concentration ratio 1.000

1.6

1.2

0.8

0.4

0.0 0

1

2

3

4

5

6

7

Injected volume (PV)

Figure 21. Pressure differences as a function of injection volume. 90 Concentration ratio 0.020 Concentration ratio 0.067 Concentration ratio 0.170 Concentration ratio 0.330 Concentration ratio 0.670 Concentration ratio 1.000

80

Oil recovery efficiency (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


70 60 50 40 30 20 10 0 0

1

2

3

4

5

Injected volume (PV)

21


6

7


Figure 22. Oil recovery efficiency as a function of injection volume. 100 90

Oil recovery efficiency (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

post water flooding foam flooding water flooding

80 70 60 50 40 30 20 10 0

0.0

0.2

0.4

0.6

0.8

1.0


Figure 23. Oil recovery efficiency as a function of the SDS/SiO2 concentration ratio.

The oil recovery efficiencies for water flooding and foam flooding are shown in Figure 22 and Figure 23. It can be noted from Figure 22 that the oil recovery efficiencies for water flooding are almost the same, at approximately 35%. As the CO2 foam and post water injection increased, the oil recoveries improved obviously because the high viscosity of SDS/SiO2 foam increases the sweep efficiency and the surfactant in the foam decreases the oil and water interfacial tension and increases the oil displacement efficiency.46-48 Figure 23 shows that the oil recovery efficiencies first increase and then decrease with increasing SDS/SiO2 concentration ratio, which is related to the stability of the SDS/SiO2 foam. The foams with greater stability have higher viscosity, which have better effect for mobility control in foam flooding and post water flooding. When the concentration ratio of SDS/SiO2 is 0.02, the enhanced oil recovery for CO2 foam flooding and post water flooding is only 9%, which is due to the poor stability of the CO2 foam. The enhanced oil recovery peaks at 39% for a concentration ratio of 0.17 and then decreases when the concentration ratio increases further. The foam with the highest oil recovery has the best foam stability. The sandpack flooding results reveal that CO2 foam strengthened by SiO2 is much more efficient for EOR. The findings in this study are very useful for improving enhanced oil recovery technology.

4. Conclusions (1) SiO2 nanoparticles have a synergetic effect with SDS for stabilizing CO2 foam when the SDS/SiO2 concentration ratio is between 0.10-0.40. The strength of the effect increases as the SDS/SiO2 concentration ratio increases from 0.1 to 0.17 but then decreases as the ratio further increases from 0.17 to 0.4. The optimal stability for CO2 foam is achieved at an SDS/SiO2 22


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concentration ratio of 0.17. (2) The synergistic effect of SDS/SiO2 for CO2 foam stability can be analyzed by modulating the nanoparticle’s adsorbing position at the CO2 and water interface, improving the interfacial properties, reducing the liquid discharge, and decreasing the coarsening of the CO2 foam. With increasing temperature, the foam volume and half-life of the CO2 foams decrease gradually, and the SDS/SiO2 foam far outperforms the SDS foam under high temperatures. Higher pressures in the formation can obviously improve the CO2 foam properties. (3) The visual flooding experiment reveals that the addition of SiO2 nanoparticles can improve the stability of CO2 foam in porous media, and shows good tolerance of crude oil. SDS/SiO2 foam can increase the pressure differences of the flow in sandpacks after water flooding, and improve the oil recoveries markedly. As the SDS/SiO2 concentration ratio increases, the pressure differences and enhanced oil recovery first increase and then decrease, which is related to the CO2 foam stability. The best performance for CO2 foam flooding is achieved at an SDS/SiO2 concentration ratio of 0.17.

Author Information Corresponding Author *E-mail: [email protected] for Songyan Li, and [email protected] for Zhaomin Li. Notes The authors declare no competing financial interest.

Acknowledgements This project was financially supported by the National Key Basic Research Program of China (No. 2015CB250904), the National Natural Science Foundation of China (No. 51304229 and No. 51274228) , the Fundamental Research Funds for the Central Universities (No. 14CX02043A and No. 14CX02185A), and the Specialized Research Fund for the Doctoral Program of Higher Education of China (No. 20120133110008). The authors sincerely thank colleagues in the Foam Research Center in China University of Petroleum (East China) for assistance with the experimental research.

References (1) Nguyen, N. M. Systematic study of foam for improving sweep efficiency in chemical enhanced oil recovery. The University of Texas at Austin, 2010. (2) Li, R. F.; Yan, W.; Liu, S.; Hirasaki, G.; Miller, C. A. Foam mobility control for surfactant enhanced oil 23



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

recovery. SPE J. 2010, 15(4), 934−948. (3) Seyedeh, H. T.; Rahim, M.; Pacelli, L. J. Foam assisted CO2-EOR: concepts, challenges and applications. Presented at the SPE Enhanced Oil Recovery Conference, Kuala Lumpur, Malaysia, July 2-4, 2013; SPE 165280. (4) Hanssen, J. E.; Dalland, M. Increased oil tolerance of polymer-enhanced foams: deep chemistry or just “simple” displacement effects. Presented at the SPE/DOE Improved Oil Recovery Symposium, Tulsa, Oklahoma, April 3-5, 2000; SPE 59282. (5) Martin, D. F.; Taber, J. J. Carbon dioxide flooding. J. Pet. Technol. 1992, 44 (4), 396−400. (6) Lee, H. O.; Heller, J. P. Laboratory measurements of CO2-foam mobility. SPE Reserv. Eng. 1990, 5(2), 193−197. (7) Tsau, J. S.; Grigg, R. B. CO2-foam Floods: foam properties and mobility-reduction effectiveness. J. Pet. Technol. 1998, 50(1), 69−70. (8) Kim, J.; Dong, Y.; Rossen, W. R. Steady-state flow behavior of CO2 foam. SPE J. 2005, 10(4), 405−415. (9) Hunter, T. N.; Pugh, R. J.; Franks, G. V. The role of particles in stabilizing foams and emulsions. Adv. Colloid Interfac. Sci. 2008, 137, 57−81. (10) Kruglyakov, P. M.; Elaneva, S. I.; Vilkova, N. G. About mechanism of foam stabilization by solid particles. Adv. Colloid Interfac. Sci. 2011, 165(2), 108−116. (11) Horozov, T. S. Foams and foam films stabilized by solid particles. Curr. Opin. Colloid Interfac. Sci. 2008, 13, 134−140. (12) Zhang, S.Y. Foams stabilized by laponite/surfactants and HMHEC/surfactants. Shandong University, 2008. (13) Wang, T. F.; Wang, J. X.; Han, L.; Wang, J. H.; Zhu, Y. Study on the stabilizing effect of aluminum hydroxide nanoparticals on foams. J. Xian Shiyou U. 2012, 27(5), 78−81 (14) Yu, J.; Mo, D.; Liu, N.; Robert, L. The application of nanoparticle-stabilized CO2 foam for oil recovery. Presented at the SPE International Symposium on Oilfield Chemistry, Woodlands, Texas, USA, April 8-10, 2013; SPE 164074. (15) Hariz, T. R. Nanoparticle-stabilized CO2 foams for potential mobility control applications. The University of Texas at Austin, 2012. (16) Xing, D.; Wei, B.; McLendon, J.; Enick, R. M., McNulty, S.; Trickett, K.; Mohamed, A.; Cummings, S.; Eastoe, J.; Rogers, S.; Crandall, D.; Tennant, B.; McLendon, T.; Romanov, V.; Soong, Y. CO2-soluble, nonionic, water-soluble surfactants that stabilize CO2-in-brine foams. SPE J. 2012, 17(4), 1172−1185. (17) Sun, Y. Q.; Gao, T. The optimum wetting angle for the stabilization of liquid-metal foams by ceramic particles: experimental simulations. Metall. Mater. Trans. A 2002, 33(10), 3285−3292. (18) Meinders, M .B. J.; Vliet, T. V. The role of interfacial rheological properties on Ostwald ripening in emulsions. Adv. Colloid Interface Sci. 2004, 108, 119−126. (19) Kam, S. I.; Rossen, W. R. Anomalous capillary pressure, stress, and stability of solids-coated bubbles. J. Colloid Interface Sci. 1999, 213, 329−339. (20) Du, Z. P.; Bilbao-Montoya, M. P.; Binks, B. P.; Dickinson, E.; Ettelaie, R.; Murray, B. S. Outstanding stability of particle-stabilized bubbles. Langmuir 2003, 19, 3106−3108. (21) Ravera, F.; Ferrari, M.; Liggieri, L.; Loglio, G.; Santini, E.; Zanobini, A. Liquid–liquid interfacial 24


Page 24 of 27

Page 25 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


properties of mixed nanoparticle–surfactant systems. Colloids Surf. A 2008, 323, 99−108. (22) Santini, E.; Krägel, J.; Ravera, F.; Liggieri, L.; Miller, R. Study of the monolayer structure and wettability properties of silica nanoparticles and CTAB using the Langmuir trough technique. Colloids Surf. A 2011, 382, 186−191. (23) Zhang, S. Y.; Lan, Q.; Liu, Q.; Xu, J.; Sun, D. J. Aqueous foams stabilized by Laponite and CTAB. Colloids Surf. A 2008, 317, 406−413. (24) Yazhgur, P. A.; Noskov, B. A.; Liggieri, L.; Lin, S. Y.; Loglio, G.; Miller, R.; Ravera, F. Dynamic properties of mixed nanoparticle/surfactant adsorption layers, Soft Matter 2013, 9, 3305-−3314. (25) Binks, B. P.; Kirkland, M.; Rodrigues J. A. Origin of stabilization of aqueous foams in nanoparticlesurfactant mixtures. Soft Matter 2008, 4, 2373−2382. (26) Binks, B. P.; Horozov, T. S. Aqueous foams stabilized solely by silica nanoparticles. Angew. Chem. Int. Ed. 2005, 44 (24), 3722−3725. (27) Ahualli, S.; Iglesias, G. R.; Wachter, W.; Dulle, M.; Minami, D.; Glatter, O. Adsorption of anionic and cationic surfactants on anionic colloids: supercharging and destabilization. Langmuir 2011, 27, 9182−9192. (28) Sun, Q.; Li, Z.; Wang, J.; Li, S.; Li, B.; Jiang, L.; Wang, H.; Lü, Q.; Zhang, C.; Liu, W. Aqueous foam stabilized by partially hydrophobic nanoparticles in the presence of surfactant. Colloids Surf. A 2015, 471, 54−64. (29) Sun, Q.; Li, Z.; Wang, J.; Li, S.; Jiang, L.; Wang, J.; Wang, P. Utilization of surfactant-stabilized foam for enhanced oil recovery by adding nanoparticles. Energy Fuels 2014, 28 (4), 2384−2394. (30) Espinosa, D.; Caldelas, F.; Johnston, K.; Bryant, S. L.; Huh, C. Nanoparticle-stabilized supercritical CO2 foams for potential mobility control applications. Presented at the SPE Improved Oil Recovery Symposium, Tulsa, Oklahoma, USA, April 24-28, 2010; SPE 129925. (31) Mo, D.; Yu, J.; Liu, N.; Lee, R. L. Study of the effect of different factors on nanoparticle-stabilized CO2 foam for mobility control. Presented at the SPE Annual Technical Conference and Exhibition, San Antonio, Texas, USA, October 8-10, 2012; SPE 159282. (32) Mo, D.; Yu, J.; Liu, N.; Lee R. The application of nanoparticle-stabilized CO2 foam for oil recovery. Presented at the SPE International Symposium on Oilfield Chemistry, Woodlands, Texas, USA, April 8-10, 2013; SPE 164074. (33) Martine, M. J.; Ruiz-Henestrosa, V. M. P.; Sánchez, C. C.; Patino, J. M. R.; Pilosof, A. M. R. Interfacial and foaming interactions between casein glycomacropeptide (CMP) and propylene glycol alginate. Colloids Surf. B 2012, 95, 214−221. (34) Boos, J.; Drenckhan, W.; Stubenrauch, C. Protocol for studying aqueous foams stabilized by surfactant mixtures. J. Surf. Deterg. 2013, 16, 1−12. (35) Ravera, F.; Santini, E.; Loglio, G.; Ferrari, M.; Liggieri, L. Effect of nanoparticles on the interfacial properties of liquid/liquid and liquid/air surface layers. J. Phys. Chem. B 2006, 110, 19543−19551. (36) Zhao, X. D.; Li, J. F.; Yang, G. The synthesis and the study of foam properties for N Alkylp Aminopropionate Zwitterionic surfactant. China Surfactant Deterg. Cosmetics 1998, 28(6), 9−13. (37) Li, S.; Liu, J.; Li, Z.; Li, B.; Wang, P.; Liu, W.; Wang, J.; Zhang, C. An experiment on CO2 emulsion stability at reservoir conditions. Acta Petrolei Sinica 2015, 36(5), 584−592 25



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(38) Cao, X. L.; Li, Y.; Jiang, S. X.; Sun, H. Q.; Cagna, A.; Dou, L. X. A study of dilational rheological properties of polymers at interfaces. J. Colloid Interface Sci. 2004, 270, 295−298. (39) Wang, Y.; Zhang, L.; Sun, T.; Zhao, S.; Yu, J. A study of interfacial dilational properties of two different structure demulsiﬁers at oil-water interfaces. J. Colloid Interface Sci. 2004, 270, 163−170. (40) Williams, D. F.; Berg, J. C. The aggregation of colloidal particles at the air–water interface. J. Colloid Interface Sci. 1992, 152, 218−229. (41) Abdel-Fattah, A. I.; El-Genk M. S. Sorption of hydrophobic, negatively charged microspheres onto a stagnant air/water interface. J. Colloid Interface Sci. 1998, 202, 417−429. (42) Abdel-Fattah, A. I.; El-Genk, M. S. On colloidal particle sorption onto a stagnant air–water interface. Adv. Colloid Interface Sci. 1998, 78, 237−266. (43) Okubo, T. Surface tension of structured colloidal suspensions of polystyrene and silica spheres at the air-water interface. J. Colloid Interface Sci. 1995, 171(1), 55−62. (44) Vignati, E.; Piazza, R.; Lockhart, T. P. Pickering emulsions: interfacial tension, colloidal layer morphology, and trapped-particle motion. Langmuir 2003, 19(17), 6650−6656. (45) Li, Z.; Wang, P.; Li, S.; Sun, Q.; Li, Y. Advances of researches on improving the stability of CO2 foams by nanoparticles. J. Southwest Petrol. U. 2014, 36(4), 155−161. (46) Yin, G.; Grigg, R. B.; Svec, Y. Oil recovery and surfactant adsorption during CO2-foam flooding. Presented at the Offshore Technology Conference, Houston, Texas, USA, May 4-7, 2009; SPE 19787. (47) Shrivastava, V. K.; Coombe, D. A.; Singhal, A. K.; Belgrave, J. D. M. Numerical simulation of foam flooding for sweep improvement abstract. J. Can. Petrol. Technol. 1999, 38(13), 13−24. (48) Hou, Q.; Li, J.; Weng, R.; Luo, Y.; Zhu, Y.; Jian, G. Recent progress and effects analysis of foam flooding field tests in China. Presented at the SPE Enhanced Oil Recovery Conference, Kuala Lumpur, Malaysia, July 2-4, 2013; SPE 165211.

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For Table of Contents Only

The hydrophobic nanoparticles are transported from the gas phase to the liquid phase due to SDS adsorption.

27


Foam by Sodium Dodecyl Sulfate and Hydrophobic Nanoparticl

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