Preparation method and application of a novel carbon nanocomposite system oil displacement agent

Abstract

The present invention relates to a novel carbon nanocomposite system oil displacement agent preparation method and application. The preparation method comprises the following steps: (i) a carbon nanoparticle preparation method; (ii) a modified carbon nanoparticle preparation method; (iii) a carbon nanocomposite system oil displacement agent preparation method; and an application method of a novel carbon nanocomposite system oil displacement agent, wherein the oil displacement agent is obtained by diluting the carbon nanocomposite system with formation produced water, and the carbon nanoparticles and surfactant compound system in the oil displacement agent account for 0.05wt%-3wt% of the total mass of the oil displacement agent. The carbon nanoparticles prepared by ultrasonic method in the present application are smaller in size (<10nm) and have uniform particle size distribution; the modified carbon nanoparticles are amphiphilic, and the carbon nanocomposite system oil displacement agent has good effects in physical simulation imbibition and oil displacement experiments under simulated water conditions, and can improve the crude oil recovery rate in chemical flooding and subsequent water flooding stages.

Description

Technical Field

[0001] The invention relates to the technical field of nano materials and oil displacement agents for improving oil recovery, and in particular to a preparation method and application of a novel carbon nano composite system oil displacement agent. Background Art

[0002] Most of the proven oil reservoirs in my country have entered the late stage of development and are in the "double high" stage of high water content and high recovery rate. The efficiency of using traditional oil recovery technology has gradually decreased. The development of low-permeability, heterogeneous and other types of oil reservoirs and the research and development of new high-efficiency, low-cost oil recovery agents have become the hot spots and application needs of oil development. Among them, nanomaterial oil recovery agents have been widely studied and applied by scholars and engineers due to their unique properties brought by their small size. Since nano oil recovery agents still face many problems in actual applications, such as complex preparation methods, poor temperature and salt stability, and difficult to predict reservoir matching, the development of new nano oil recovery agents is of great significance to improving crude oil recovery and the economic benefits of oil field production. Summary of the invention

[0003] Based on the problems existing in the prior art, the first aspect of the present invention provides a method for preparing carbon nanoparticles. This preparation method uses ultrasonic method instead of hydrothermal method, the operation method is simple and convenient, the reaction conditions are easy to control, and the particle size distribution of the synthesized carbon nanoparticles is more uniform. The second aspect of the present invention provides a composite oil displacement system based on ionic surfactant-assisted dispersion of carbon nanoparticles. The composite oil displacement system is prepared by compounding PEG-modified carbon nanoparticles with anionic surfactants, has temperature resistance (70°C) and salt resistance (10wt% NaCl solution) and can effectively enhance the stability of the emulsion, reduce interfacial tension, and improve wettability. The third aspect of the present invention is to provide an application method of a carbon nanocomposite system oil displacement agent, which has an effective production-increasing effect and can further improve the crude oil recovery rate in the chemical flooding stage and the subsequent water flooding stage on the basis of water flooding.

[0004] The technical solution provided by the present invention is: a method for preparing a novel carbon nanocomposite system oil displacement agent comprises the following steps:

[0005] (I) The preparation method of carbon nanoparticles is as follows: deionized water is used as solvent, carbon source and sodium hydroxide with a concentration of 0.5-3 mol / L are used as solutes, and a brown-black product solution is obtained by ultrasonic reaction at room temperature of 25°C for 6 hours, and the pH value is adjusted to 7 with hydrochloric acid, and then the solution is dehydrated and impurized with ethanol and anhydrous magnesium sulfate, and then the carbon nanoparticles are obtained by centrifugal filtration; the centrifugal parameters are 3000-10000RPM and the centrifugation is 10min-30min; the carbon nanoparticles include a carbon skeleton and functional groups connected to the carbon skeleton by chemical bonds, and the functional groups include one or more of -OH, -CHO, and -COOH;

[0006] (II) The preparation method of modified carbon nanoparticles is:

[0007] The carbon nanoparticles prepared in step (i) are prepared into a carbon nanoparticle dispersion with a concentration of 0.5 wt% to 5 wt% and mixed evenly with a polyethylene glycol solution with a concentration of 5 to 30 wt%, and then subjected to a thermal reaction in a polytetrafluoroethylene autoclave using 36 wt% hydrochloric acid as a catalyst, and then placed in a 120° C. thermostat for reaction for 72 hours and then taken out to obtain modified carbon nanoparticles;

[0008] (III) The preparation method of the carbon nanocomposite system oil displacement agent comprises: compounding the modified carbon nanoparticles with a mass concentration of 0.05wt% and the anionic surfactant with a mass concentration of 0.1-3%, and ultrasonically dispersing the compounded carbon nanoparticles for 10-30 minutes to obtain the carbon nanocomposite system oil displacement agent.

[0009] The carbon source described in the above step (i) is specifically glucose, and the average particle size of the carbon nanoparticles is 2-10 nm; the volume ratio of the deionized water to the sodium hydroxide water is (20-100): (20-100), the molar ratio of glucose to sodium hydroxide is 1:1; the volume mass ratio of ethanol to anhydrous magnesium sulfate is (50-300) ml: (10-100) g.

[0010] The polyethylene glycol described in the above step (ii) is specifically PEG-200 or PEG-400, and the volume ratio of the carbon nanoparticle dispersion, the polyethylene glycol solution and the hydrochloric acid is: (25-100): (10-50): 0.03.

[0011] The anionic surfactant described in the above step (iii) is specifically a petroleum sulfonate surfactant or sodium dodecylbenzene sulfonate or other sulfonate surfactants whose alkyl groups are C12-20. The composite mass ratio of the modified carbon nanoparticles described in step (iii) to the anionic surfactant is 2: (1-2).

[0012] The invention discloses an application of a novel carbon nanocomposite system oil displacement agent, wherein the oil displacement agent is obtained by diluting the carbon nanocomposite system with formation produced water, and the modified carbon nanoparticles and surfactant compound system in the oil displacement agent account for 0.05wt%-3wt% of the total mass of the oil displacement agent.

[0013] The carbon nanocomposite system can be stably dispersed without precipitation under high temperature and high salt conditions.

[0014] The carbon nanocomposite system can withstand a high temperature of 70° C. and a high salt solution with a concentration of 10 wt % NaCl.

[0015] The carbon nanocomposite system can promote the improvement of crude oil recovery rate from multiple angles, including emulsifying crude oil, reducing interfacial tension, and improving the wettability of reservoir rocks.

[0016] The carbon nanocomposite system oil displacement agent can enhance the spontaneous imbibition of crude oil during the oil recovery process and can improve the crude oil recovery rate in the chemical flooding and subsequent water flooding stages of the oil recovery experiment.

[0017] The beneficial effects of the present invention are as follows: 1. The carbon nanoparticles prepared by the ultrasonic method are smaller in size (<10nm) and have a uniform particle size distribution. 2. The prepared carbon nanocomposite system has good stability. 3. The modified carbon nanoparticles in the carbon nanocomposite system are amphiphilic and can be used as a carrier of a surfactant to adsorb surfactant molecules, thereby increasing the oil-water interfacial activity of the surfactant, effectively emulsifying crude oil, reducing interfacial tension, and improving the wettability of reservoir rocks. 4. The carbon nanocomposite system oil displacement agent has good effects in physical simulation imbibition and oil displacement experiments under simulated water conditions, and can increase the crude oil recovery rate in chemical flooding and subsequent water flooding stages. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a particle size distribution diagram of carbon nanoparticles prepared in the present invention;

[0019] Figure 2 is an infrared spectrum of the carbon nanoparticles prepared in the present invention;

[0020] Figure 3 is an infrared spectrum of modified carbon nanoparticles in the carbon nanocomposite system prepared in the present invention;

[0021] Figure 4 It is the dispersion stability diagram of modified carbon nanoparticles. From left to right, the temperature conditions are 50, 60, and 70 °C;

[0022] Figure 5 It is the agglomeration precipitation diagram of modified carbon nanoparticles under the temperature condition of 70°C;

[0023] Figure 6 Is 50×10 -3 μm 2 Core imbibition recovery curve;

[0024] Figure 7 It is 20×10 -3 μm 2 Core imbibition recovery curve;

[0025] Figure 8 This is a curve showing the effect of petroleum sulfonate surfactant concentration on the interfacial tension of carbon nanocomposite system;

[0026] Fig. 9 Carbon nanoparticles UV spectrum of

[0027] Fig.10 yes 10wt% injected throughout the process NaCl Pressure and recovery of brine flooding (50×10 -3 μm 2 Core) curve graph;

[0028] Fig.11 yes Changes in recovery factor after injection of different agents (50×10 -3 μm 2 Core) graph;

[0029] Fig.12 yes Pressure changes after injection of different agents (50×10 -3 μm 2 Core) graph;

[0030] Fig.13 yes The recovery factor changes after injecting different agents (20×10 -3 μm 2 Core) graph;

[0031] Fig.14 yes Pressure changes after injection of different agents (20×10 -3 μm 2 Core) graph. DETAILED DESCRIPTION

[0032] The present invention is further described in detail below in conjunction with specific embodiments, and the examples provided are only for illustrating the present invention, rather than for limiting the scope of the present invention. The examples provided below can be used as a guide for further improvements by those of ordinary skill in the art, and do not constitute a limitation of the present invention in any way.

[0033] The experimental methods in the following examples, unless otherwise specified, are all conventional methods, and are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. The materials, reagents, etc. used in the following examples, unless otherwise specified, can all be obtained from commercial channels.

[0034] The surfactants used in the following examples are all commercially available in the art.

[0035] Example 1: Preparation of carbon nanoparticles: The preparation method specifically includes the following steps:

[0036] (1) Dilute 20g of anhydrous glucose in 50mL of water and stir to form a transparent solution, then add 50mL of 1mol / L sodium hydroxide aqueous solution and stir evenly. Ultrasonicate the mixed solution at room temperature of 25℃ for 6h. After the ultrasound, use hydrochloric acid to adjust the mixed solution to pH=7. By ultrasonic method, fluorescent spherical carbon nanoparticles were synthesized using glucose as the carbon source. Since ultrasound can alternately generate low-pressure and high-pressure beams in the solution, tiny air bubbles are generated in the solution. This energy promotes the reaction between glucose and sodium hydroxide, resulting in the polymerization and carbonization of glucose to form carbon nanoparticles.

[0037] (2) Use the hanging drop method to add 100 ml of anhydrous ethanol dropwise into the mixed solution and continue stirring. Then add 30 g of anhydrous magnesium sulfate and stir for 20 min. Let it stand for 24 h to remove impurities such as water and water-soluble inorganic salts.

[0038] (3) The obtained solution was centrifuged for 20 min to remove precipitated impurities and the supernatant was placed in a constant temperature drying oven at 80° C. and dried for 72 h to obtain carbon nanoparticles. The speed of the centrifuge was 6000 RPM.

[0039] (4) The particle size of the synthesized carbon nanoparticles was tested using a Malvern laser particle size analyzer (Zetasizer Nano). The test environment temperature was 25°C, and a 0.05% carbon nanoparticle aqueous dispersion was used as the sample. The sample pH was 6.5-8.5. The particle size distribution diagram of the test is shown in Figure 2. Figure 1 As shown, the carbon nanoparticle size is <10nm, and the particle size distribution is uniform. The maximum frequency range of the particle size distribution is 1.5-2.3nm, and the standard deviation of the experimental results is <2. Compared with other nanoparticles synthesized in the laboratory using hydrothermal method with glucose as the carbon source, the carbon nanoparticles synthesized by ultrasonic method have a more stable particle size distribution, which is because the reaction conditions of ultrasonic method are more constant and the reaction materials are mixed more evenly.

[0040] (5) Infrared spectrum detection of the obtained carbon nanoparticles. Figure 2 is the infrared spectrum of the unmodified carbon nanoparticles obtained in Example 1. Figure 2 It can be seen that a large number of hydrophilic groups are distributed on the surface of the unmodified carbon nanoparticles, mainly including -OH, -CHO, and -COOH. Therefore, the unmodified carbon nanoparticles have strong hydrophilicity.

[0041] (6) The synthesized carbon nanoparticles were analyzed by UV and Fourier transform infrared (FT-IR) spectroscopy. The results of UV spectroscopy are as follows: Fig. 9 As shown. Fig. 9It can be seen that the narrow peak of 250-300nm represents the π absorption of aromatic substances, which is similar to the absorption peak of polycyclic aromatic hydrocarbons, and the red shift of π-π* transition is caused by the extended conjugation in the CDs structure. It is confirmed that glucose reacts under ultrasonic conditions to carbonize and form carbon nanoparticles CDs.

[0042] Example 2: Preparation of modified carbon nanoparticles, the preparation method specifically comprises the following steps:

[0043] (1) Take 0.25 g of the carbon nanoparticles synthesized in Example 1, add 25 ml of deionized water and ultrasonically disperse for 20 min, and dilute with deionized water to a carbon nanoparticle aqueous dispersion with a mass percentage concentration of 1%. Then add 25 ml of a 10 wt% PEG-200 deionized water solution and mix well. Use a constant temperature heating stirrer to stir the two solutions together at 80 ° C for 10 min.

[0044] (2) After stirring, add 0.03 mL of concentrated hydrochloric acid (36 wt%) as a catalyst. Place the mixed solution in a polytetrafluoroethylene autoclave, put it in a 120°C thermostat for 72 hours, and then take it out to obtain an aqueous solution of carbon nanoparticles after PEG surface passivation modification. After drying, grind it into powder, rinse it with anhydrous ethanol three times to remove impurities, and then dry it again to obtain the modified carbon nanoparticle g-CDs particle powder.

[0045] (3) Infrared spectrum detection of modified carbon nanoparticles. Figure 3 is the infrared spectrum of modified carbon nanoparticles. Figure 3 It can be seen that the characteristic peak of carboxyl group is shifted, and carboxylic acid ester is generated. The surface of the modified particles has ester, alcohol and long carbon chain as lipophilic groups, which has a certain degree of amphiphilicity. It can better cooperate with lipophilic surfactant agents to improve oil displacement performance.

[0046] (4) The modified carbon nanoparticle solution was compounded with a petroleum sulfonate surfactant in different mass ratios, and then ultrasonically dispersed for 20 minutes to obtain a series of carbon nanocomposite oil displacement agents with different concentrations. The effect curve of different petroleum sulfonate surfactant concentrations on the interfacial tension of the carbon nanocomposite system is shown in Figure 8 .Depend on Figure 8It can be seen that when the petroleum sulfonate surfactant is at a low concentration (0.01wt%-0.1wt%), the interfacial tension will gradually decrease over time and eventually reach the minimum interfacial tension. When the concentration of the petroleum sulfonate surfactant is 0.2wt%, the interfacial tension of the composite system first drops to an ultra-low level (IFT<0.01 mN / m) within 20 minutes, and then the interfacial tension increases. This is because the reduction in interfacial tension is related to the adsorption of the composite system at the oil-water interface. When the concentration of the petroleum sulfonate surfactant (PS) is greater than the critical micelle concentration (CMC), the excess PS participates in the formation of micelles, resulting in a decrease in the concentration of PS active monomers, and the excess micelles cannot reach the oil-water interface, so the interfacial tension rebounds. The optimal mass ratio of modified carbon nanoparticles to petroleum sulfonate surfactants in the carbon nanocomposite system is 2: (1-2).

[0047] Example 3: This example uses the observation method to evaluate the stability of the carbon nanocomposite system oil displacement agent.

[0048] Three portions of 0.1 wt % modified carbon nanoparticle dispersions were prepared using saline (10 wt % NaCl solution), and the dispersions were placed at different temperatures (50°C, 60°C, 70°C) for 10 days to observe whether precipitation occurred. Figure 4 The appearance of the carbon nanocomposite system oil displacement agent after being left at different temperatures for 10 days. It can be observed that there is no precipitation or agglomeration after the carbon nanocomposite system oil displacement agent is left at 50-70℃ for 10 days, while the carbon nanoparticles show obvious agglomeration in the solution when the temperature is higher than 60℃. Figure 5 ). This shows that carbon nanoparticles can be used as carriers of PS surfactants, and their temperature and salt resistance are enhanced after being wrapped by surfactant molecules.

[0049] Example 4: This example uses a volumetric imbibition experiment to evaluate the imbibition oil recovery performance of the system.

[0050] The experiment was conducted using artificial cores, and the specific parameters of the cores after pretreatment are shown in Table 1. 10wt% NaCl brine was used to prepare modified carbon nanoparticles with a mass concentration of 0.05wt%, petroleum sulfonate surfactants with a mass concentration of 0.05wt%, and carbon nanocomposite system solutions as imbibition fluids. The concentration of modified carbon nanoparticles in the carbon nanocomposite system solution was 0.05wt%, and the concentration of petroleum sulfonate surfactants was 0.05wt%. The experimental cores were immersed in imbibition bottles filled with different imbibition fluids and placed vertically in a constant temperature box at 60°C. The detection equipment connected to the metering tube records the oil discharge from the core every 4 hours. By measuring the volume of crude oil discharged from the imbibition bottle through imbibition, the imbibition recovery rate of different imbibition fluids was calculated, and the imbibition oil displacement curve was drawn. The results are shown in Figure 6 and Figure 7shown.

[0051] serial number <![CDATA[Permeability (10 -3 μm 2 )]]> Oil saturation (%) Porosity (%) Chemicals 1 50 71.90 21.06 Simulated formation water 2 50 72.59 23.57 Modified carbon nanoparticles 3 50 71.87 23.94 Petroleum sulfonate 4 50 72.40 22.80 Carbon nanocomposite system 5 20 59.34 18.62 Simulated formation water 6 20 58.70 19.08 Modified carbon nanoparticles 7 20 59.21 18.90 Petroleum sulfonate 8 20 59.32 18.75 Carbon nanocomposite system

[0052] from Figure 6 (50×10 -3 μm 2 It can be observed from the core that: after about 96 hours, the imbibition recovery rate of each system reached the maximum value, and the imbibition recovery rate of the carbon nanocomposite system reached 43%, which was significantly better than the other two agents. Figure 7 (20×10 -3 μm 2 Core) and Figure 6 In comparison, the imbibition recovery rate was significantly reduced due to the decrease in permeability, but the carbon nanocomposite system still achieved a relatively significant increase in imbibition recovery rate. After 240 h, the recovery rate of brine reached 23.40%, and the others were 27.33% (0.05wt% g-CDs), 37.60% (0.05wt% PS surfactant), and 40.86% (0.05wt% carbon nanocomposite system). This is because these two agents can greatly reduce the oil-water interfacial tension and promote spontaneous oil imbibition. Combining the imbibition results under two permeabilities, it can be seen that the recovery rate of the core soaked in the carbon nanocomposite system is significantly higher than that of other methods, and the recovery rate change curve with time is steeper than that of the surfactant. This shows that the carbon nanocomposite system can promote the imbibition process more quickly and effectively. Because the carbon nanocomposite system can effectively reduce the oil-water interfacial tension, it can enable more crude oil to participate in the seepage process in the porous medium, turn more residual oil into movable oil, and increase the degree of crude oil recovery at the imbibition equilibrium, thereby effectively improving the permeability recovery rate of low permeability cores.

[0053] Example 5: Comparative displacement experiment:

[0054] The oil displacement effect of modified carbon nanoparticles g-CDs and their carbon nanocomposite system was tested. The oil production increment of g-CDs and carbon nanocomposite system was compared with 10wt% NaCl water flooding as the control group. The recovery factor and pressure curve of the water flooding control group are shown in Figure 2. Fig.10 shown. Fig.10 The recovery rate and pressure of 2PV full-time brine injection. It can be seen that when the water drive is 0PV-0.6PV, the pressure increases with the increase of the recovery rate. After exceeding 0.6PV, the pressure continues to decrease and finally stabilizes to about 0.13Mpa, and the recovery rate stops increasing. This is because water can enter the pores of the core in the initial injection and displace the crude oil in the water. After a period of injection, the crude oil in the original pores is displaced, and the displacement fluid breaks through the original pores to form a dominant channel. This leads to a drop in pressure. Due to the difference in rheological properties between oil and water, the flow rate of water in the pores is faster than that of oil, so the remaining oil cannot be effectively mobilized, and the recovery rate is no longer improved.

[0055] Fig.11 and Fig.12 50×10 -3 μm 2 Recovery factor and pressure change curves during displacement process. Fig.11 It can be seen that after the recovery rate of injecting 1PV brine stabilizes and no longer increases, injecting the agent will obtain additional recovery rate improvement. Fig.12 It can be observed that there is a phenomenon of pressure reduction during the oil recovery process when the PS surfactant is injected alone. After the pressure drop phenomenon occurs, a significant increase in recovery can be observed. This is because the surfactant reduces the interfacial tension between oil and water, making the oil and water phases more miscible to form an emulsion with similar fluidity, thereby improving the fluidity of crude oil in the formation pores. In contrast, the g-CDs monomer will cause a certain degree of pressure increase during the oil recovery process, but it will also increase the oil recovery rate to a certain extent. This can be explained by the aggregation phenomenon of carbon nanoparticles, that is, small particles of carbon nanomaterials gather at the entrance of the pore throat during the displacement process, blocking the flow of the displacement fluid. As a result, the displacement pressure increases and the displacement fluid flow rate slows down. When the pressure rises to a certain level, a breakthrough is formed, accompanied by an increase in crude oil recovery.

[0056] Comparing the two chemical agents, g-CDs and PS, the pressure curve of the carbon nanocomposite system is between the two ( Fig.12 ). This is because the carbon nanofluid composite system has improved hydrophilicity and dispersibility compared to g-CDs, making it easier for it to reach the oil-water interface instead of being adsorbed on the rock surface.

[0057] Fig.13 and Fig.14 20×10 -3 μm 2 Recovery factor and pressure change curve during core flooding. Fig.13 It can be seen that the ability of PS to improve oil recovery has significantly decreased in the face of lower permeability environments, while the carbon nanocomposite system still has good performance in improving oil recovery. This may be because the amount of crude oil that can be displaced in a low permeability environment is less, and the advantages of surfactants in reducing interfacial tension and oil-water mobility ratio cannot be brought into play. The carbon nanocomposite system has a better ability to improve rock wettability, thus improving the recovery rate under low permeability conditions.

[0058] The final recovery factors of the two cores with different permeabilities are shown in Table 2. It can be seen that when the permeability is 50×10 -3 μm 2 , 20×10 -3 μm 2 In the core flooding experiment, the carbon nanocomposite system can effectively improve the recovery rate of tertiary oil recovery.

[0059] Table 2 Core data and corresponding chemical flooding recovery improvement

[0060] serial number Permeability Recovery rate Chemicals Recovery enhancement 1 50 48.20% — — 2 50 49.50% CDs 6.12% 3 50 48.90% PS 8.81% 4 50 49.21% Carbon nanocomposite system 13.67% 5 20 30.80% — — 6 20 30.35% CDs 6.43% 7 20 30.06% PS 7.2% 8 20 30.15% Carbon nanocomposite system 14.2%

Claims

1. A method for preparing a novel carbon nanocomposite system oil displacement agent, comprising the following steps: (I) The preparation method of carbon nanoparticles is as follows: deionized water is used as solvent, carbon source and sodium hydroxide with a concentration of 0.5 to 3 mol / L are used as solutes, and a brown-black product solution is obtained by ultrasonic reaction at room temperature of 25°C for 6 hours, and the pH value is adjusted to 7 with hydrochloric acid, and then the solution is dehydrated and impurized with ethanol and anhydrous magnesium sulfate, and then the carbon nanoparticles are obtained by centrifugal filtration; the centrifugal parameters are 3000 to 10000 RPM, and the centrifugation is 10 min to 30 min; the carbon nanoparticles include a carbon skeleton and functional groups connected to the carbon skeleton by chemical bonds, and the functional groups include one or more of -OH, -CHO, and -COOH; the average particle size of the carbon nanoparticles is 2 to 10 nm; the volume ratio of deionized water to sodium hydroxide water is (20-100): (20-100), and the molar ratio of glucose to sodium hydroxide is 1:1; the volume mass ratio of ethanol to anhydrous magnesium sulfate is (50-300) ml: (10 to 100) g; (II) The preparation method of modified carbon nanoparticles is: The carbon nanoparticles prepared in step (i) are prepared into a carbon nanoparticle dispersion with a concentration of 0.5wt% to 5wt% and a polyethylene glycol solution with a concentration of 5 to 30wt% are uniformly mixed, and then a thermal reaction is carried out in a polytetrafluoroethylene high-pressure reactor using 36wt% hydrochloric acid as a catalyst, and the mixture is placed in a 120°C constant temperature box for reaction for 72 hours and then taken out to obtain modified carbon nanoparticles; the volume ratio of the carbon nanoparticle dispersion, the polyethylene glycol solution and the hydrochloric acid is: (25 to 100): (10 to 50): 0.03; (III) The preparation method of the carbon nanocomposite system oil displacement agent comprises: compounding the modified carbon nanoparticles with a mass concentration of 0.05wt% and the anionic surfactant with a mass concentration of 0.1-3%, and ultrasonically dispersing the compounded carbon nanoparticles for 10-30min to obtain the carbon nanocomposite system oil displacement agent; the compounding mass ratio of the modified carbon nanoparticles to the anionic surfactant is 2:(1-2).

2. The method for preparing the novel carbon nanocomposite system oil displacement agent according to claim 1, characterized in that: The carbon source described in step (a) is specifically glucose.

3. The method for preparing the novel carbon nanocomposite system oil displacement agent according to claim 1, characterized in that: The polyethylene glycol described in step (ii) is specifically PEG-200 or PEG-400.

4. The method for preparing the novel carbon nanocomposite system oil displacement agent according to claim 1, characterized in that: The anionic surfactant described in step (iii) is specifically a petroleum sulfonate surfactant or sodium dodecylbenzene sulfonate or other sulfonate surfactants whose alkyl group is C12-20 alkyl sodium sulfonate.

5. Use of the novel carbon nanocomposite system oil displacing agent as claimed in claim 1, wherein the oil displacing agent is obtained by diluting the carbon nanocomposite system with produced water from the formation, and the modified carbon nanoparticles and surfactant complex system in the oil displacing agent account for 0.05wt%-3wt% of the total mass of the oil displacing agent.

6. The use of the novel carbon nanocomposite system oil displacement agent according to claim 5, characterized in that: The carbon nanocomposite system can be stably dispersed without precipitation under high temperature and high salt conditions.

7. The use of the novel carbon nanocomposite system oil displacement agent according to claim 6, characterized in that: The carbon nanocomposite system can withstand a high temperature of 70°C and a high salt solution with a concentration of 10wt% NaCl.

8. The use of the novel carbon nanocomposite system oil displacement agent according to claim 7, characterized in that: The carbon nanocomposite system can promote the improvement of crude oil recovery rate from multiple angles such as emulsifying crude oil, reducing interfacial tension and improving the wettability of reservoir rocks; the carbon nanocomposite system oil displacement agent can enhance the spontaneous imbibition of crude oil during the oil recovery process and can improve the crude oil recovery rate in the chemical flooding and subsequent water flooding stages of the oil recovery experiment.

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