Oil-soluble amphiphilic silica nanoparticles for co2-flooded heavy oil development and preparation method and application thereof

Abstract

This invention relates to oil-soluble amphiphilic silica nanoparticles for CO2 injection development of heavy oil, their preparation method, and applications, belonging to the field of oilfield chemistry technology. The invention uses hydrophilic silica nanoparticles as raw materials, grafting a silane coupling agent onto the silica surface to obtain oil-soluble amphiphilic nanoparticles. Further grafting with a silane coupling agent successfully yields oil-soluble amphiphilic silica nanoparticles for CO2 injection development of heavy oil. These nanoparticles possess excellent oil solubility and interfacial activity with the heavy oil-CO2 interface. They can dissolve in heavy oil and adsorb onto the heavy oil-CO2 interface, reducing interfacial tension. They also exhibit good thermal and chemical stability, making them suitable for CO2 injection development in high-temperature, high-pressure heavy oil reservoirs, with significant potential for improving heavy oil recovery.

Description

Technical Field

[0001] This invention relates to an oil-soluble amphiphilic silica nanoparticle for CO2 injection in the development of heavy oil, its preparation method and application, belonging to the field of oilfield chemical technology. Background Technology

[0002] CO2 injection has become a highly promising green and low-carbon development technology for heavy oil. Injected CO2 is soluble in heavy oil, expanding its volume, reducing its viscosity, and replenishing reservoir pressure, thereby improving oil recovery and enabling underground CO2 storage. However, due to the significant differences in properties between heavy oil and CO2, a large interfacial tension exists between them, resulting in poor CO2 dissolution in heavy oil. Therefore, reducing the interfacial tension between heavy oil and CO2 is crucial to improving the effectiveness of CO2 injection in heavy oil development.

[0003] Nanomaterials refer to ultrafine materials with crystal or particle sizes ranging from 1 to 100 nm. Compared to traditional chemical agents, they are more effective, economical, and environmentally friendly, and have become a research hotspot in the oil and gas development field. Among them, hydrophilic silica nanoparticles are the most widely used, and can be used in waterflooding development processes to reduce the interfacial tension between oil and water systems, thereby improving the waterflooding effect. Inspired by the above research, if silica nanoparticles can be introduced into the CO2 injection process for heavy oil development to reduce the interfacial tension between heavy oil and CO2, it is expected to break through the bottleneck of traditional CO2 injection technology for heavy oil development.

[0004] However, most existing silica nanoparticles are hydrophilic silica nanoparticles with oleophobic surfaces. They are usually dispersed in water and act in oil-water systems. However, the CO2 injection process for developing heavy oil is a heavy oil-CO2 system. Existing hydrophilic silica nanoparticles are difficult to disperse in heavy oil, do not have the interfacial activity of heavy oil-CO2, and cannot play a role. Therefore, they are difficult to apply to the CO2 injection process for developing heavy oil effectively.

[0005] Patent document CN107416844A discloses a nano-silica dispersion with amphiphilic properties and a two-particle structure, and its preparation method. The preparation method includes: using nano-silica alcohol sol as a raw material, adding a silane coupling agent containing lipophilic groups to prepare an lipophilic-modified nano-silica alcohol sol, denoted as the first reaction solution; using nano-silica alcohol sol as a raw material, adding a silane coupling agent containing hydrophilic groups to prepare a hydrophilic-modified nano-silica alcohol sol, denoted as the second reaction solution; adding 3-aminopropyltriethoxysilane to the first reaction solution, stirring, and mixing with the second reaction solution to obtain a nano-silica dispersion with amphiphilic properties and a two-particle structure. This nano-silica dispersion uses a route of separate modification followed by connection, which ensures the independence of the modification, but the preparation method is complex, and the resulting two-particle structure has a large particle size, making it prone to retention and blockage at the pore throat. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides an oil-soluble amphiphilic silica nanoparticle for CO2 injection development of heavy oil, along with its preparation method and application, providing an effective chemical agent for the efficient CO2 injection development of heavy oil reservoirs.

[0007] This invention is achieved through the following technical solution:

[0008] A method for preparing oil-soluble amphiphilic silica nanoparticles for CO2 injection in the development of heavy oil includes the following steps:

[0009] (1) Add hydrophilic silica nanoparticles to a mixed solution of distilled water and ethanol, and disperse by ultrasonication to obtain a hydrophilic silica nanoparticle dispersion. Add silane coupling agent a to the hydrophilic silica nanoparticle dispersion, stir at constant temperature, and react fully to obtain an oleophilic nanoparticle solution.

[0010] (2) Add silane coupling agent b to the lipophilic nanoparticle solution, stir at a constant temperature, and after the reaction is complete, an oil-soluble amphiphilic nanoparticle solution is obtained.

[0011] (3) Add vinyl acetate and reducing agent to the oil-soluble amphiphilic nanoparticle solution, stir evenly, then add oxidant, purge with nitrogen, heat and stir to react, and obtain oil-soluble amphiphilic nanoparticle solution grafted with CO2 groups.

[0012] (4) The solution of oil-soluble amphiphilic nanoparticles grafted with CO2 groups was ultrasonically cleaned, centrifuged, washed to remove excess reactants, and vacuum dried to obtain oil-soluble amphiphilic silica nanoparticles for CO2 injection to develop heavy oil.

[0013] According to a preferred embodiment of the present invention, in step (1), the volume ratio of distilled water to ethanol in the mixed solution of distilled water and ethanol is (130~180):(30~80).

[0014] According to a preferred embodiment of the present invention, in step (1), the mass-to-volume ratio of hydrophilic silica nanoparticles to the mixed solution is (0.1-0.3):(160-260), in g / mL.

[0015] The addition of ethanol helps reduce the electrostatic attraction on the surface of hydrophilic silica nanoparticles, while also facilitating the interaction of water molecules with the surface of the hydrophilic silica nanoparticles to form a hydration layer, preventing particle aggregation and precipitation that could affect reaction efficiency. Furthermore, as an organic solvent, ethanol facilitates the subsequent addition and dissolution of the silane coupling agent, ensuring the complete progress of the reaction.

[0016] According to a preferred embodiment of the present invention, in step (1), the ultrasonic dispersion time is 20-40 min, the ultrasonic power is 20-900 W, the ultrasonic frequency is 20-25 kHz, and after ultrasonic dispersion, the particles are cooled to a temperature of 20-25 °C. Ultrasonic dispersion can prevent the hydrophilic silica nanoparticles from agglomerating and achieve uniform dispersion.

[0017] According to a preferred embodiment of the present invention, in step (1), the silane coupling agent a is selected from hexadecyltrimethoxysilane, dodecyltrimethoxysilane, or octyltrimethoxysilane, and the amount of silane coupling agent a is 2 to 3 times the mass of the hydrophilic silica nanoparticles. Silane coupling agent a provides lipophilic groups to the hydrophilic silica nanoparticles.

[0018] According to a preferred embodiment of the present invention, in step (1), the constant temperature stirring temperature is 50~80℃ and the reaction time is 3~6h.

[0019] According to a preferred embodiment of the present invention, in step (2), the silane coupling agent b is γ-methacryloyloxypropyltrimethoxysilane, and the amount of silane coupling agent b is 1.5 to 2.5 times the mass of the hydrophilic silica nanoparticles. The silane coupling agent b provides CO2-loving groups to the lipophilic silica nanoparticles.

[0020] According to a preferred embodiment of the present invention, in step (2), the constant temperature stirring temperature is 50~80℃ and the reaction time is 3~6h.

[0021] According to a preferred embodiment of the present invention, in step (3), the amount of vinyl acetate used is 0.5 to 1 times the mass of the hydrophilic silica nanoparticles.

[0022] According to a preferred embodiment of the present invention, in step (3), the reducing agent is sodium bisulfite, and the mass ratio of the amount of reducing agent added to the mass of hydrophilic silica nanoparticles is (0.1~0.3):(0.1~0.8). The addition of the reducing agent inhibits the polymerization reaction of vinyl acetate itself.

[0023] According to a preferred embodiment of the present invention, in step (3), the oxidant is potassium persulfate, and the mass ratio of the amount of reducing agent added to the mass of hydrophilic silica nanoparticles is (0.05~0.2):(0.1~0.8).

[0024] According to a preferred embodiment of the present invention, in step (3), the nitrogen gas is introduced for 20-40 minutes to remove oxygen from the air during the reaction process and create an inert atmosphere.

[0025] According to a preferred embodiment of the present invention, in step (3), the temperature of the heated and stirred reaction is 50~80℃ and the reaction time is 3~6h.

[0026] According to a preferred embodiment of the present invention, in step (4), centrifugation is performed by using a high-speed centrifuge to centrifuge the oil-soluble amphiphilic nanoparticle solution to fully separate the oil-soluble amphiphilic nanoparticles from the unreacted substances.

[0027] According to a preferred embodiment of the present invention, in step (4), the speed of the high-speed centrifuge is set to 10,000~15,000 rpm and the centrifugation time is 20~50 min.

[0028] According to a preferred embodiment of the present invention, in step (4), the washing is performed by washing the oil-soluble amphiphilic nanoparticles with a mixed solution of water and ethanol, wherein the volume ratio of water to ethanol in the mixed solution is 1:1.

[0029] According to a preferred embodiment of the present invention, in step (4), the vacuum drying temperature is 50~80℃ and the vacuum drying time is 23~26h.

[0030] An oil-soluble amphiphilic silica nanoparticle for CO2 injection into heavy oil was prepared using the method described above.

[0031] According to a preferred embodiment of the present invention, the particle size of the oil-soluble amphiphilic silica nanoparticles is 20-30 nm.

[0032] The above-mentioned application of oil-soluble amphiphilic silica nanoparticles for CO2 injection in heavy oil development is used for CO2 injection extraction of high-temperature and high-pressure heavy oil reservoirs to improve the recovery rate of heavy oil. The high temperature is 100~300 ℃ and the pressure is 20~70 MPa.

[0033] The oil-soluble amphiphilic silica nanoparticles of the present invention have excellent oil solubility and heavy oil-CO2 interfacial activity. They can dissolve in heavy oil and adsorb onto the heavy oil-CO2 interface, thereby reducing interfacial tension. They can be used in the CO2 injection development process of high-temperature and high-pressure heavy oil reservoirs and have great potential to improve heavy oil recovery.

[0034] Technical features and advantages of the present invention:

[0035] 1. This invention uses hydrophilic silica nanoparticles as raw materials, grafts silane coupling agents onto the silica surface to obtain oil-soluble amphiphilic nanoparticles, and then grafts silane coupling agents to finally obtain oil-soluble amphiphilic silica nanoparticles for CO2 injection development of heavy oil.

[0036] 2. The oil-soluble amphiphilic silica nanoparticles of the present invention have excellent oil solubility and heavy oil-CO2 interfacial activity. They can dissolve in heavy oil and adsorb onto the heavy oil-CO2 interface, thereby reducing interfacial tension. They also have good thermal and chemical stability and can be used in the CO2 injection development process of high-temperature and high-pressure heavy oil reservoirs, with great potential to improve heavy oil recovery. Attached Figure Description

[0037] Figure 1 This is a diagram illustrating the synthesis mechanism of oil-soluble amphiphilic silica nanoparticles in Example 1.

[0038] Figure 2 This is a photograph of the oil-soluble amphiphilic silica nanoparticles prepared in Example 1.

[0039] Figure 3 This is a TEM image of the oil-soluble amphiphilic silica nanoparticles prepared in Example 1.

[0040] Figure 4 The images show the infrared spectra of the hydrophilic silica nanoparticles and the oil-soluble amphiphilic silica nanoparticles used in Example 1.

[0041] Figure 5 Thermogravimetric analysis curves of hydrophilic silica nanoparticles and oil-soluble amphiphilic silica nanoparticles from Example 1 are shown.

[0042] Figure 6 The diagram shows the dispersion of the hydrophilic silica nanoparticles and oil-soluble amphiphilic silica nanoparticles in mineral oil and distilled water in Example 1.

[0043] Figure 7 The wetting angle is the angle of water droplets on the surface of the raw material hydrophilic silica nanoparticles and the oil-soluble amphiphilic silica nanoparticle coating prepared in Example 1.

[0044] Figure 8 The interfacial tension diagram of heavy oil and CO2 after adding oil-soluble amphiphilic silica nanoparticles prepared in Example 1. Detailed Implementation

[0045] The present invention will be further described below with reference to embodiments, which will help to understand the present invention, but does not limit the scope of the present invention.

[0046] Example 1

[0047] A method for preparing oil-soluble amphiphilic silica nanoparticles for heavy oil production using CO2 injection is described, and the synthesis mechanism is shown in the diagram below. Figure 1 As shown.

[0048] The preparation method and steps are as follows:

[0049] (1) 0.2 g of hydrophilic silica nanoparticles (particle size 25 nm) were dispersed in a mixed solution of distilled water and ethanol under continuous stirring. The mixed solution contained 150 mL of distilled water and 50 mL of ethanol. The mixed solution was ultrasonically dispersed using an ultrasonic disperser for 40 min at a power of 900 W and a frequency of 25 kHz. The solution was then cooled to 25 °C to obtain a hydrophilic silica nanoparticle dispersion. 0.578 g of hexadecyltrimethoxysilane was added to the hydrophilic silica nanoparticle dispersion and placed in a three-hole flask. The mixture was stirred at 70 °C for 4 h to allow the reaction to proceed. After cooling to room temperature, a lipophilic silica nanoparticle solution was obtained.

[0050] (2) Add 0.412g of silane coupling agent γ-methacryloxypropyltrimethoxysilane to the lipophilic silica nanoparticle solution, place it in a three-hole flask, stir at 70°C for 4h to react fully, and cool to room temperature to obtain an oil-soluble amphiphilic nanoparticle solution.

[0051] (3) Add 0.143 g of vinyl acetate to the oil-soluble amphiphilic nanoparticle solution and stir until homogeneous. Then, add 0.1 g of sodium bisulfite and stir until homogeneous. Add 0.05 g of potassium persulfate as an oxidant. Purge the reaction flask with nitrogen for 30 min to remove oxygen from the air during the reaction. Heat to 75 °C and stir for 5 h to obtain an oil-soluble amphiphilic nanoparticle solution grafted with CO2 groups.

[0052] (4) The oil-soluble amphiphilic nanoparticle solution grafted with CO2 groups obtained in step (3) was cleaned using an ultrasonic cleaner, and then centrifuged using a high-speed centrifuge at 12,000 rpm for 30 min, repeated three times to fully separate the oil-soluble amphiphilic nanoparticles from the unreacted material. The oil-soluble amphiphilic nanoparticles were then washed with a 1:1 mixture of water and ethanol to remove excess reactants. The oil-soluble amphiphilic nanoparticles were then vacuum-dried in a 70℃ constant temperature oven for 24 h. After drying, the oil-soluble amphiphilic nanoparticles were crushed into powder to obtain oil-soluble amphiphilic silica nanoparticles for CO2 injection development of heavy oil.

[0053] The actual image of the prepared oil-soluble amphiphilic silica nanoparticles is shown below. Figure 2 As shown.

[0054] TEM images of the prepared oil-soluble amphiphilic silica nanoparticles, such as... Figure 3 As shown. By Figure 3 It is known that the particle size of oil-soluble amphiphilic silica nanoparticles is 20~30 nm.

[0055] Example 2

[0056] The preparation method of oil-soluble amphiphilic silica nanoparticles for heavy oil using CO2 injection is as follows:

[0057] (1) 0.2 g of hydrophilic silica nanoparticles (particle size 25 nm) were dispersed in a mixed solution of distilled water and ethanol under continuous stirring. The mixed solution contained 150 mL of distilled water and 50 mL of ethanol. The mixed solution was ultrasonically dispersed using an ultrasonic disperser for 40 min at a power of 900 W and a frequency of 25 kHz. The solution was then cooled to 25 °C to obtain a hydrophilic silica nanoparticle dispersion. 0.5 g of dodecyltrimethoxysilane was added to the hydrophilic silica nanoparticle dispersion and placed in a three-hole flask. The mixture was stirred at 65 °C for 5 h to allow for complete reaction. After cooling to room temperature, a lipophilic silica nanoparticle solution was obtained.

[0058] (2) Add 0.32g of silane coupling agent γ-methacryloxypropyltrimethoxysilane to the lipophilic silica nanoparticle solution, place it in a three-hole flask, stir at 65℃ for 5h to allow the reaction to proceed, and cool to room temperature to obtain an oil-soluble amphiphilic nanoparticle solution.

[0059] (3) Add 0.102 g of vinyl acetate to the oil-soluble amphiphilic nanoparticle solution and stir until homogeneous. Then, add 0.2 g of sodium bisulfite and stir thoroughly. Finally, add 0.08 g of potassium persulfate as an oxidant. Purge the reaction flask with nitrogen for 30 min to remove oxygen from the air during the reaction. Heat to 60 °C and stir for 5 h to obtain an oil-soluble amphiphilic nanoparticle solution grafted with CO2 groups.

[0060] (4) The oil-soluble amphiphilic nanoparticle solution grafted with CO2 groups obtained in step (3) was cleaned using an ultrasonic cleaner, and then centrifuged using a high-speed centrifuge at 12,000 rpm for 30 min, repeated three times to fully separate the oil-soluble amphiphilic nanoparticles from the unreacted material. The oil-soluble amphiphilic nanoparticles were then washed with a 1:1 mixture of water and ethanol to remove excess reactants. The oil-soluble amphiphilic nanoparticles were then vacuum-dried in a 70 ℃ constant temperature oven for 24 h. After drying, the oil-soluble amphiphilic nanoparticles were crushed into powder to obtain oil-soluble amphiphilic silica nanoparticles for CO2 injection development of heavy oil.

[0061] Example 3

[0062] The preparation method of oil-soluble amphiphilic silica nanoparticles for heavy oil using CO2 injection is as follows:

[0063] (1) 0.2 g of hydrophilic silica nanoparticles (particle size 25 nm) were dispersed in a mixed solution of distilled water and ethanol under continuous stirring. The mixed solution contained 150 mL of distilled water and 50 mL of ethanol. The mixed solution was ultrasonically dispersed using an ultrasonic disperser for 40 min at a power of 900 W and a frequency of 25 kHz. The solution was then cooled to 25 °C to obtain a hydrophilic silica nanoparticle dispersion. 0.58 g of octyltrimethoxysilane was added to the hydrophilic silica nanoparticle dispersion and placed in a three-hole flask. The mixture was stirred at 75 °C for 3.5 h to allow for complete reaction. After cooling to room temperature, a lipophilic silica nanoparticle solution was obtained.

[0064] (2) Add 0.50 g of silane coupling agent γ-methacryloxypropyltrimethoxysilane to the lipophilic silica nanoparticle solution, place it in a three-hole flask, stir at 75°C for 3.5 h to react fully, and cool to room temperature to obtain an oil-soluble amphiphilic nanoparticle solution.

[0065] (3) Add 0.199 g of vinyl acetate to the oil-soluble amphiphilic nanoparticle solution and stir until homogeneous. Then, add 0.3 g of sodium bisulfite and stir thoroughly. Finally, add 0.1 g of potassium persulfate as an oxidant. Purge the reaction flask with nitrogen for 30 min to remove oxygen from the air during the reaction. Heat to 75 °C and stir for 5 h to obtain an oil-soluble amphiphilic nanoparticle solution grafted with CO2 groups.

[0066] (4) The oil-soluble amphiphilic nanoparticle solution grafted with CO2 groups obtained in step (3) was cleaned using an ultrasonic cleaner, and then centrifuged using a high-speed centrifuge at 12,000 rpm for 30 min, repeated three times to fully separate the oil-soluble amphiphilic nanoparticles from the unreacted material. The oil-soluble amphiphilic nanoparticles were then washed with a 1:1 mixture of water and ethanol to remove excess reactants. The oil-soluble amphiphilic nanoparticles were then vacuum-dried in a 70 ℃ constant temperature oven for 24 h. After drying, the oil-soluble amphiphilic nanoparticles were crushed into powder to obtain oil-soluble amphiphilic silica nanoparticles for CO2 injection development of heavy oil.

[0067] Experimental example:

[0068] The properties of the oil-soluble amphiphilic silica nanoparticles for heavy oil development using CO2 injection, prepared in Example 1, were verified using infrared spectroscopy, thermogravimetric analysis, wettability and interfacial tension testing. The test results are as follows: Figures 4-8 As shown.

[0069] 1. The infrared spectra of the raw material hydrophilic silica nanoparticles and the oil-soluble amphiphilic silica nanoparticles for CO2 injection development of heavy oil prepared in Example 1 are shown below. Figure 4 As shown. By Figure 4 It can be known that 3299 cm -1 The absorption peak at 1109 cm⁻¹ is due to the stretching vibration of -OH groups on the surface of the hydrophilic silica nanoparticles. -1 795 cm -1 The absorption peak at 474 cm⁻¹ corresponds to the tensile vibration of Si-O-Si. -1 The absorption peak appearing at [value missing] is due to the bending vibration of the Si-O bond; these characteristics are inherent to hydrophilic silica nanoparticles. Five new absorption peaks appeared in the infrared spectrum of oil-soluble amphiphilic silica nanoparticles. Among them, the peak at 2918 cm⁻¹ is [value missing]. -1 The saturated CH stretching vibration peak appearing at 2851 cm⁻¹ is the -CH₃ of the alkyl chain. -1 The unsaturated CH stretching vibration peak at 1466 cm⁻¹ corresponds to the -CH₂ of the alkyl chain. -1 The CH bending vibration peaks appearing at this point are the CH atoms on -CH3 and -CH2. Since hexadecyltrimethoxysilane possesses -CH3, -CH2, and CH atoms, the peak at 2918 cm⁻¹ is... -1 2851 cm -1 1466 cm -1 The emergence of new absorption peaks proves that lipophilic groups have been successfully grafted onto the surface of the oil-soluble amphiphilic silica nanoparticles. Furthermore, at 1732 cm⁻¹... -1 Stretching vibrations of the carbonyl group (C=O) were observed at 897 cm⁻¹. -1 CO bending vibrations were observed. Since γ-methacryloxypropyltrimethoxysilane possesses C=O and CO bonds, it proves that γ-methacryloxypropyltrimethoxysilane has been successfully grafted onto the surface of nanoparticles, and CO-loving groups have been grafted onto the surface of oil-soluble amphiphilic silica nanoparticles.

[0070] 2. Thermogravimetric analysis curves of the raw material hydrophilic silica nanoparticles and the oil-soluble amphiphilic silica nanoparticles for CO2 injection development prepared in Example 1 are shown in the figure below. Figure 5 As shown. By Figure 5It can be seen that when the temperature rises from 30℃ to 330℃, the mass of oil-soluble amphiphilic silica nanoparticles decreases to some extent. This is because the surface of oil-soluble amphiphilic silica nanoparticles is hydrophilic and has a certain amount of adsorbed water, which evaporates upon heating. Simultaneously, the silanol groups on the surface of the hydrophilic silica nanoparticles decompose upon heating, thus causing a certain degree of mass decrease. Since the amphiphilic silica nanoparticles have undergone surface modification, the amount of adsorbed water and silanol groups on their surface decreases, therefore, the mass decrease of oil-soluble amphiphilic silica nanoparticles at this stage is less than that of hydrophilic silica nanoparticles. When the temperature rises from 330℃ to 700℃, the mass of oil-soluble amphiphilic silica nanoparticles decreases significantly compared to hydrophilic nanoparticles. This is mainly because the surface of the oil-soluble amphiphilic silica nanoparticles has been modified by grafting organic chains. Due to the thermal decomposition of these organic chains, the mass of the oil-soluble amphiphilic silica nanoparticles decreases significantly. This indicates that the oil-soluble amphiphilic silica nanoparticles have successfully grafted lipophilic groups. Furthermore, the significant decrease in mass of oil-soluble amphiphilic silica nanoparticles at certain temperatures indicates that these nanoparticles have a high decomposition temperature and good thermal stability.

[0071] 3. The dispersion diagram of the hydrophilic silica nanoparticles and the oil-soluble amphiphilic silica nanoparticles for CO2 injection development prepared in Example 1 in mineral oil and distilled water is shown in the figure. Figure 6 As shown. By Figure 6 It is known that hydrophilic silica nanoparticles disperse well in distilled water, but are difficult to disperse in mineral oil, resulting in precipitation. In contrast, the oil-soluble amphiphilic silica nanoparticles prepared in Example 1 disperse well in mineral oil but are difficult to disperse in distilled water, floating on the surface. This demonstrates that the oil-soluble amphiphilic silica nanoparticles have been successfully grafted with lipophilic groups, significantly reducing hydrophilicity and exhibiting excellent oil-soluble properties.

[0072] 4. The wetting angle of water droplets on the surface of the hydrophilic silica nanoparticles and the oil-soluble amphiphilic silica nanoparticles for heavy oil development prepared in Example 1 is as follows: Figure 7 As shown. By Figure 7 It can be seen that the contact angle of water droplets on hydrophilic silica nanoparticles is 8°, indicating that the hydrophilic silica nanoparticles have strong water solubility. This is mainly due to the large number of hydroxyl groups (-OH) on the surface of the hydrophilic silica nanoparticles, which form a strong interaction with water molecules and have strong hydrophilicity. The contact angle of water droplets on the oil-soluble amphiphilic silica nanoparticle coating prepared in Example 1 is 140°, indicating that the oil-soluble amphiphilic silica nanoparticles have strong oil solubility, and that the surface of the oil-soluble amphiphilic silica nanoparticles has been grafted with lipophilic groups.

[0073] 5. The interfacial tension between heavy oil without any additives and heavy oil with CO2 after adding the oil-soluble amphiphilic silica nanoparticles prepared in Example 1 is as follows: Figure 8 As shown. By Figure 8 It can be seen that the interfacial tension between heavy oil and CO2 is 9.27 mN·m. -1 After adding oil-soluble amphiphilic silica nanoparticles, the interfacial tension between heavy oil and CO2 decreased to 5.99 mN·m. -1 The oil-soluble amphiphilic silica nanoparticles prepared in Example 1 demonstrate their ability to reduce interfacial tension. This is primarily because the oil-soluble amphiphilic silica nanoparticles are grafted with both lipophilic and CO2-philic groups, giving them interfacial activity at the heavy oil-CO2 interface. These nanoparticles can spontaneously adsorb onto the heavy oil-CO2 interface, reducing the free energy at the heavy oil-CO2 interface and thus lowering the interfacial tension, demonstrating significant potential for improving heavy oil recovery.

Claims

1. A method for preparing oil-soluble amphiphilic silica nanoparticles for CO2 injection development of heavy oil, characterized in that, The steps include the following: (1) Add hydrophilic silica nanoparticles to a mixed solution of distilled water and ethanol, and disperse by ultrasonication to obtain a hydrophilic silica nanoparticle dispersion. Add silane coupling agent a to the hydrophilic silica nanoparticle dispersion, stir at a constant temperature, and react fully to obtain an oleophilic nanoparticle solution. Silane coupling agent a is selected from hexadecyltrimethoxysilane, dodecyltrimethoxysilane or octyltrimethoxysilane. The amount of silane coupling agent a is 2 to 3 times the mass of the hydrophilic silica nanoparticles. The constant temperature stirring temperature is 50 to 80°C, and the reaction time is 3 to 6 hours. (2) Add silane coupling agent b to the lipophilic nanoparticle solution, stir at a constant temperature, and after the reaction is complete, an oil-soluble amphiphilic nanoparticle solution is obtained; silane coupling agent b is γ-methacryloyloxypropyltrimethoxysilane, the amount of silane coupling agent b is 1.5 to 2.5 times the mass of hydrophilic silica nanoparticles, the constant temperature stirring temperature is 50 to 80℃, and the reaction time is 3 to 6 hours; (3) Add vinyl acetate and reducing agent to the oil-soluble amphiphilic nanoparticle solution, stir evenly, then add oxidant, purge with nitrogen, heat and stir to react, and obtain oil-soluble amphiphilic nanoparticle solution grafted with CO2 groups; the amount of vinyl acetate is 0.5 to 1 times the mass of hydrophilic silica nanoparticles. (4) The solution of oil-soluble amphiphilic nanoparticles grafted with CO2 groups was ultrasonically cleaned, centrifuged, washed to remove excess reactants, and vacuum dried to obtain oil-soluble amphiphilic silica nanoparticles for CO2 injection to develop heavy oil.

2. The preparation method according to claim 1, characterized in that, In step (1), the volume ratio of distilled water to ethanol in the mixed solution of distilled water and ethanol is (130~180):(30~80), the mass-volume ratio of hydrophilic silica nanoparticles to the mixed solution is (0.1-0.3):(160-260), the unit is g / mL, the ultrasonic dispersion time is 20~40min, the ultrasonic power is 20~900W, the ultrasonic frequency is 20~25kHz, and after ultrasonic dispersion, the solution is cooled to a temperature of 20~25℃.

3. The preparation method according to claim 1, characterized in that, In step (3), the reducing agent is sodium bisulfite, and the mass ratio of the amount of reducing agent added to the mass of hydrophilic silica nanoparticles is (0.1~0.3):(0.1~0.8).

4. The preparation method according to claim 1, characterized in that, In step (3), the oxidant is potassium persulfate, and the mass ratio of the amount of oxidant added to the hydrophilic silica nanoparticles is (0.05~0.2):(0.1~0.8). The nitrogen gas is passed for 20~40 min, the temperature for stirring is 50~80℃, and the reaction time is 3~6 h.

5. The preparation method according to claim 1, characterized in that, In step (4), centrifugation is performed by centrifuging the oil-soluble amphiphilic nanoparticle solution with a high-speed centrifuge to fully separate the oil-soluble amphiphilic nanoparticles from the unreacted substances. The speed of the high-speed centrifuge is set to 10,000~15,000 rpm and the centrifugation time is 20~50 min. Washing is performed by washing the oil-soluble amphiphilic nanoparticles with a mixed solution of water and ethanol. The volume ratio of water to ethanol in the mixed solution is 1:

1. The vacuum drying temperature is 50~80℃ and the vacuum drying time is 23~26 h.

6. A type of oil-soluble amphiphilic silica nanoparticles for developing heavy oil using CO2 injection, characterized in that, It is prepared by the method described in any one of claims 1-5.

7. The oil-soluble amphiphilic silica nanoparticles for developing heavy oil using CO2 injection as described in claim 6, characterized in that, The oil-soluble amphiphilic silica nanoparticles have a particle size of 20-30 nm.

8. The application of the oil-soluble amphiphilic silica nanoparticles for developing heavy oil using CO2 injection as described in claim 6, characterized in that, It is used for CO2 injection in high-temperature and high-pressure heavy oil reservoirs to improve the recovery rate of heavy oil. The high temperature is 100~300 ℃ and the pressure is 20~70MPa.

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