High-temperature and high-salt resistant modified nano oil displacement agent and preparation method thereof

Abstract

The application relates to the technical field of oil development, and discloses a modified nano oil displacement agent with high temperature resistance and high salt resistance and a preparation method thereof. The oil displacement agent comprises the following raw materials in parts by weight: 10-15 parts of a nano oil displacement enhancer, 2-4 parts of molybdenum disulfide nanosheets, 3-5 parts of modified nanosilica, 12-20 parts of a surfactant, 40-50 parts of a solvent and 2-3 parts of a stabilizer. The nano oil displacement agent improves the adaptability of the oil displacement agent in a high-temperature and high-salt environment through the synergistic effect of the components, ensures the oil displacement efficiency and the oil displacement durability, and improves the recovery rate of crude oil after use due to the excellent oil displacement efficiency and durability.

Description

Technical Field

[0001] This invention relates to the field of petroleum development technology, specifically to a modified nano-oil displacement agent resistant to high temperature and high salt and its preparation method. Background Technology

[0002] With the continuous depletion of conventional oil and gas resources, the development of extremely complex reservoirs, such as those with high temperatures and high salinity, has become a significant challenge for the global petroleum industry. These reservoirs are typically buried at great depths, with formation temperatures exceeding 110°C, salinity reaching tens to hundreds of thousands of milligrams per liter, and are rich in polyvalent ions such as calcium and magnesium. Under these harsh conditions, traditional polymer flooding agents (such as partially hydrolyzed polyacrylamide) are prone to amide group hydrolysis and main chain degradation, leading to a significant decrease in solution viscosity and loss of flow control capabilities. Conventional surfactants may also become ineffective due to cloud point effects or precipitation with high-valent ions, failing to effectively reduce oil-water interfacial tension or alter rock wettability.

[0003] Furthermore, existing nano-displacement materials mostly employ single nanoparticles (such as nano-silica) or simple polymer coatings, which suffer from problems such as limited functionality, insufficient synergy between temperature and salt resistance, and easy aggregation and pore throat blockage. These limitations make it difficult to meet the comprehensive technical requirements of deep, high-temperature, and high-salinity oil reservoirs for "temperature resistance, salt resistance, long-term stability, and efficient oil washing." Therefore, it is necessary to develop an oil displacement agent with good stability and high oil displacement efficiency under high-temperature and high-salinity conditions to improve oil washing efficiency. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a modified nano-oil displacement agent resistant to high temperature and high salt, and its preparation method.

[0005] The objective of this invention can be achieved through the following technical solutions: A high-temperature and high-salt resistant modified nano-oil displacement agent comprises the following raw materials in parts by weight: 10-15 parts of nano-oil displacement enhancer, 2-4 parts of molybdenum disulfide nanosheets, 3-5 parts of modified nano-silica, 12-20 parts of surfactant, 40-50 parts of solvent, and 2-3 parts of stabilizer. Furthermore, the modified silica is nano-silica grafted with a silane coupling agent; Furthermore, the surfactant is a nonionic surfactant; Furthermore, the solvent is an aqueous solution of ethanol, and the volume ratio of ethanol to water is 1:6-8; Furthermore, the stabilizer is polyethylene glycol-4000; Furthermore, the nano-oil displacement enhancer is prepared by grafting a mixture of sodium 2-acrylamido-2-methylpropanesulfonate, acrylic acid, and acrylamide imidazole quaternary ammonium salt as shell monomers onto the surface of SP@ZnO@SC nanomaterials via free radical polymerization; the SP@ZnO@SC nanomaterials are synthesized on the surface of SP@ZnO nanomaterials using KH570 and dimethyldimethoxysilane as raw materials; the SP@ZnO nanomaterials are prepared by in-situ loading ZnO onto the surface of nano-sepiolite powder; Furthermore, the acrylamide imidazole quaternary ammonium salt is prepared by reacting 1-chlorohexane with intermediate product 1, wherein intermediate product 1 is prepared by reacting 2-imidazol-1-ylethylamine with acryloyl chloride; Specifically, the nano-oil displacement enhancer is prepared by the following steps: Step A1: Disperse nano-sepiolite powder (SP) in deionized water by ultrasonication for 30 min, then add a mixture of zinc acetate dihydrate and tetrabutylammonium bromide dissolved in ethanol, heat and reflux and stir for 1 h, then add 100 mg / mL potassium hydroxide ethanol solution and stir for 12 h, centrifuge, wash and dry to obtain SP@ZnO nanomaterials. Furthermore, in step A1, the ratio of SP, deionized water, zinc acetate dihydrate, tetrabutylammonium bromide, ethanol, and potassium hydroxide ethanol solution is 0.2g:20mL:2-3g:3-4.5g:50mL:3.5-4.5mL; Step A2: Add SP@ZnO nanomaterials to ethanol and ultrasonically disperse for 15 min. Then add a mixture of KH570 (γ-methacryloyloxypropyltrimethoxysilane) and dimethyldimethoxysilane and stir for 5-10 min. Add deionized water and stir until homogeneous. Then heat to 30-40℃ and stir for 3-5 h. Filter, wash and dry to obtain SP@ZnO@SC nanomaterials (organosilicon-coated SP@ZnO nanomaterials). Furthermore, in step A2, the ratio of SP@ZnO nanomaterials, ethanol, KH570, dimethyldimethoxysilane, and deionized water is 1g:50mL:0.5-1.2mL:0.8-2mL:5-10mL; Step A3: Add hexadecyltrimethylammonium bromide and OP-10 (dodecylphenol polyoxyethylene ether) to deionized water and heat and stir to dissolve. Then add SP@ZnO@SC nanomaterials and ultrasonically disperse for 30 min. Then adjust the pH of the system to 8-10 with 3wt% sodium hydroxide aqueous solution and heat to 80℃. Then add the shell monomer mixture dropwise and finish the addition within 2 h. At the same time, add 10wt% potassium persulfate aqueous solution dropwise at a constant flow rate within 2 h. Continue the reaction for 2-3 h, cool to room temperature, add ethanol and stir to break the emulsion. After filtration, washing and drying, the nano oil displacement enhancer is obtained. Further, in step A3, the ratio of hexadecyltrimethylammonium bromide, OP-10, deionized water, SP@ZnO@SC nanomaterials, shell monomer mixture, potassium persulfate aqueous solution, and ethanol is 0.6-0.8g:0.1-0.3g:100mL:2-3g:12-20g:7.5-12mL:50-80mL; Further, the shell monomer mixture in step A3 is a mixture of sodium 2-acrylamido-2-methylpropanesulfonate, acrylic acid and acrylamide imidazole quaternary ammonium salt, and the mass ratio of the three is 8-12g:3-6g:1-2g; Further, the acrylamide imidazole quaternary ammonium salt described in step A3 is prepared by the following steps: Step A31: Add 2-imidazol-1-ylethylamine to N,N-dimethylacetamide and stir until homogeneous. Then place the mixture in an ice-water bath, add triethylamine and stir until homogeneous. Add acryloyl chloride in three batches and stir until homogeneous. Then transfer the mixture to an oil bath, heat it to 65°C and stir for 5-6 hours. After the reaction is complete, pour the mixture into distilled water to precipitate the product. Filter, wash and dry to obtain intermediate product 1. Further, in step A31, the molar ratio of 2-imidazol-1-ylethylamine, acryloyl chloride, and triethylamine is 1.1-1.2:1:1-1.5; Step A32: Add 1-chlorohexane and intermediate 1 to acetone and stir until homogeneous. Then heat to 60°C and reflux for 48 hours. Remove the solvent by rotary evaporation, add methanol and stir until homogeneous. Ethyl acetate precipitates out and is dried under vacuum to obtain acrylamide imidazole quaternary ammonium salt. Furthermore, in step A32, the molar ratio of 1-chlorohexane to intermediate 1 is 1:1-1.1.

[0006] A method for preparing a high-temperature and high-salt resistant modified nano-oil displacement agent includes the following steps: Weigh the raw materials according to the weight parts, mix and stir the nano oil displacement enhancer, molybdenum disulfide nanosheets, modified nano silica, surfactant, solvent and stabilizer evenly, and then disperse them by ultrasonication to obtain a modified nano oil displacement agent that is resistant to high temperature and high salt.

[0007] The beneficial effects of this invention are: The oil displacement agent of this invention is prepared by using nano-oil displacement enhancers, molybdenum disulfide nanosheets and modified nano-silica as the main raw materials, and adding surfactants, solvents and stabilizers. Through the synergistic effect between the components, the nano-oil displacement agent improves the adaptability of the oil displacement agent in high temperature and high salinity environments, ensuring oil displacement efficiency and oil displacement persistence. The excellent oil displacement efficiency and persistence improve the recovery rate of crude oil after use.

[0008] The modified nano-displacement agent of this invention incorporates a nano-displacement enhancer, molybdenum disulfide nanosheets, and modified nano-silica as nano-displacement components. The molybdenum disulfide nanosheets, with their self-lubricating properties, act like "nano-ball bearings" to reduce frictional resistance between oil-rock and oil-water, facilitating the smooth migration of crude oil within micro- and nano-pores. Their flexible, sheet-like structure acts like "tiles," creating a more effective physical barrier against water flow in the formation, forcing water flow to change direction and driving crude oil from more dead zones. The modified nano-silica and the sepiolite fibers in the nano-displacement enhancer form a "particle-fiber" composite network, filling even smaller pores that the fiber network cannot reach, thus enhancing the overall displacement effect.

[0009] The nano-oil displacement enhancer uses nano-sepiolite as a base, with zinc oxide loaded in situ on its surface and coated with organosilicon segments. Then, a free radical polymer is used to graft a copolymer containing sulfonate groups and imidazole quaternary ammonium salt structures. The nano-sepiolite, acting as a temperature- and salt-resistant framework, disperses rapidly in the matrix and interweaves to form a "haystack" network structure. This network significantly increases the viscosity of the displacement fluid, improves the mobility ratio, and suppresses viscous fingering, thereby effectively expanding the swept volume of the displacement fluid. The nano-zinc oxide loaded on the sepiolite surface can penetrate micropores inaccessible to traditional chemical agents, "prying" and peeling the oil film from the rock surface through "structural separation pressure." Simultaneously, it can adsorb at the oil-water interface, significantly reducing interfacial tension and the contact angle of oil droplets on the rock, changing the rock surface wettability from oleophilic to hydrophilic, making oil droplets easier to detach. The coating of organosilicon segments on the surface of nanoparticles forms a hydrophobic "armor," shielding hydrophilic groups that may affect performance. This significantly enhances the overall chemical stability of the nanocomposite material, including its temperature and salt resistance, protecting the active ingredients and ensuring a long-lasting oil displacement effect. The strongly anionic sulfonate groups introduced into the outermost copolymer endow the oil displacement agent with crucial salt resistance—even in an electrolyte environment, the sulfonate group maintains its activity, ensuring stable interfacial tension. Simultaneously, it contributes to interfacial activity, synergistically reducing interfacial tension with ZnO. Meanwhile, the imidazole quaternary ammonium salt groups can firmly adsorb onto negatively charged rock surfaces, achieving wetting reversal and aiding in the stripping of oil films. Furthermore, it provides multiple oil layer protection functions, including clay stabilization, corrosion inhibition, and bactericidal effects. Detailed Implementation

[0010] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0011] The modified nano-silica in the following examples was prepared using the following steps: 1g of nano-silica was ultrasonically dispersed in a mixture of 30mL ethanol and 5mL deionized water. Then, 0.5mL of KH550 (γ-aminopropyltriethoxysilane) was added, and the mixture was heated to 45℃ and stirred overnight. After filtration, washing, and drying, modified nano-silica was obtained.

[0012] Example 1: The nano-oil displacement enhancer was prepared by the following steps: Step A1: Disperse 0.2g of nano sepiolite powder (SP) in 20mL of deionized water by ultrasonication for 30min, then add a mixture of 2g of zinc acetate dihydrate and 3g of tetrabutylammonium bromide dissolved in 50mL of ethanol, heat and reflux and stir for 1h, then add 3.5mL of 100mg / mL potassium hydroxide ethanol solution and stir for 12h, centrifuge, wash and dry to obtain SP@ZnO nanomaterials; Step A2: Add 1g of SP@ZnO nanomaterial to 50mL of ethanol and sonicate for 15min. Then add a mixture of 0.5mL of KH570 and 0.8mL of dimethyldimethoxysilane and stir for 5min. Then add 5mL of deionized water and stir evenly. Then heat to 30℃ and stir for 3h. Filter, wash and dry to obtain SP@ZnO@SC nanomaterial. Step A3: Add 0.6g hexadecyltrimethylammonium bromide and 0.1g OP-10 to 100mL of deionized water and heat and stir to dissolve. Then add 2g SP@ZnO@SC nanomaterials and ultrasonically disperse for 30min. Then adjust the pH of the system to 8 with 3wt% sodium hydroxide aqueous solution and heat to 80℃. Then add 12g shell monomer mixture dropwise and finish the addition within 2h. At the same time, add 7.5mL of 10wt% potassium persulfate aqueous solution dropwise at a constant flow rate within 2h. Continue the reaction for another 2h, cool to room temperature, add 50mL of ethanol and stir to break the emulsion. After filtration, washing and drying, the nano oil displacement enhancer is obtained. Preferably, the shell monomer mixture in step A3 is a mixture of sodium 2-acrylamido-2-methylpropanesulfonate, acrylic acid and acrylamide imidazole quaternary ammonium salt, and the mass ratio of the three is 12g:3g:1g; Preferably, the acrylamide imidazole quaternary ammonium salt in step A3 is prepared by the following steps: Step A31: Add 0.11 mol of 2-imidazol-1-ylethylamine to 100 mL of N,N-dimethylacetamide and stir until homogeneous. Then place the mixture in an ice-water bath and add 0.1 mol of triethylamine and stir until homogeneous. Add 0.1 mol of acryloyl chloride in three batches and stir until homogeneous. Then transfer the mixture to an oil bath and heat it to 65 °C and stir for 5 h. After the reaction is complete, pour the mixture into 50 mL of distilled water to precipitate the product. Filter, wash, and dry to obtain intermediate product 1. Step A32: Add 0.1 mol of 1-chlorohexane and 0.1 mol of intermediate product 1 to 100 mL of acetone and stir until homogeneous. Then, heat to 60 °C and reflux for 48 h. Remove the solvent by rotary evaporation, add 30 mL of methanol and stir until homogeneous. 50 mL of ethyl acetate precipitates out and is dried under vacuum to obtain acrylamide imidazole quaternary ammonium salt.

[0013] Example 2: The nano-oil displacement enhancer was prepared by the following steps: Step A1: Disperse 0.2g of nano sepiolite powder (SP) in 20mL of deionized water by ultrasonication for 30min, then add a mixture of 2.5g of zinc acetate dihydrate and 3.8g of tetrabutylammonium bromide dissolved in 50mL of ethanol, heat and reflux and stir for 1h, then add 4mL of 100mg / mL potassium hydroxide ethanol solution and stir for 12h, centrifuge, wash and dry to obtain SP@ZnO nanomaterials; Step A2: Add 1g of SP@ZnO nanomaterial to 50mL of ethanol and sonicate for 15min. Then add a mixture of 0.9mL of KH570 and 1.5mL of dimethyldimethoxysilane and stir for 10min. Then add 7.5mL of deionized water and stir evenly. Then heat to 35℃ and stir for 4h. Filter, wash and dry to obtain SP@ZnO@SC nanomaterial. Step A3: Add 0.7g hexadecyltrimethylammonium bromide and 0.2g OP-10 to 100mL of deionized water and heat and stir to dissolve. Then add 2.5g SP@ZnO@SC nanomaterials and ultrasonically disperse for 30min. Then adjust the pH of the system to 9 with 3wt% sodium hydroxide aqueous solution and heat to 80℃. Then add 16g shell monomer mixture dropwise and finish the addition within 2h. At the same time, add 10mL of 10wt% potassium persulfate aqueous solution at a constant flow rate within 2h. Continue the reaction for another 2.5h, cool to room temperature, add 70mL of ethanol and stir to break the emulsion. After filtration, washing and drying, the nano oil displacement enhancer is obtained. Preferably, the shell monomer mixture in step A3 is a mixture of sodium 2-acrylamido-2-methylpropanesulfonate, acrylic acid, and acrylamide imidazole quaternary ammonium salt, and the mass ratio of the three is 10g:4.5g:1.5g; Preferably, the acrylamide imidazole quaternary ammonium salt in step A3 is prepared by the following steps: Step A31: Add 0.115 mol of 2-imidazol-1-ylethylamine to 100 mL of N,N-dimethylacetamide and stir until homogeneous. Then place the mixture in an ice-water bath and add 0.1 mol of triethylamine and stir until homogeneous. Add 0.13 mol of acryloyl chloride in three batches and stir until homogeneous. Then transfer the mixture to an oil bath and heat it to 65 °C and stir for 5.5 h. After the reaction is complete, pour the mixture into 50 mL of distilled water to precipitate the product. Filter, wash, and dry to obtain intermediate product 1. Step A32: Add 0.1 mol of 1-chlorohexane and 0.105 mol of intermediate product 1 to 100 mL of acetone and stir until homogeneous. Then, heat to 60 °C and reflux for 48 h. Remove the solvent by rotary evaporation, add 30 mL of methanol and stir until homogeneous. 50 mL of ethyl acetate precipitates out and is dried under vacuum to obtain acrylamide imidazole quaternary ammonium salt.

[0014] Example 3: The nano-oil displacement enhancer was prepared by the following steps: Step A1: Disperse 0.2g of nano sepiolite powder (SP) in 20mL of deionized water by ultrasonication for 30min, then add a mixture of 3g of zinc acetate dihydrate and 4.5g of tetrabutylammonium bromide dissolved in 50mL of ethanol, heat and reflux and stir for 1h, then add 4.5mL of 100mg / mL potassium hydroxide ethanol solution and stir for 12h, centrifuge, wash and dry to obtain SP@ZnO nanomaterials; Step A2: Add 1g of SP@ZnO nanomaterial to 50mL of ethanol and sonicate for 15min. Then add a mixture of 1.2mL of KH570 and 2mL of dimethyldimethoxysilane and stir for 10min. Then add 10mL of deionized water and stir evenly. Then heat to 40℃ and stir for 5h. Filter, wash and dry to obtain SP@ZnO@SC nanomaterial. Step A3: Add 0.8g hexadecyltrimethylammonium bromide and 0.3g OP-10 to 100mL of deionized water and heat and stir to dissolve. Then add 3g SP@ZnO@SC nanomaterials and ultrasonically disperse for 30min. Then adjust the pH of the system to 10 with 3wt% sodium hydroxide aqueous solution and heat to 80℃. Then add 20g shell monomer mixture dropwise and finish the addition within 2h. At the same time, add 12mL of 10wt% potassium persulfate aqueous solution at a constant flow pump over 2h. Continue the reaction for 3h, cool to room temperature, add 80mL of ethanol and stir to break the emulsion. After filtration, washing and drying, the nano oil displacement enhancer is obtained. Preferably, the shell monomer mixture in step A3 is a mixture of sodium 2-acrylamido-2-methylpropanesulfonate, acrylic acid and acrylamide imidazole quaternary ammonium salt, and the mass ratio of the three is 8g:6g:2g; Preferably, the acrylamide imidazole quaternary ammonium salt in step A3 is prepared by the following steps: Step A31: Add 0.12 mol of 2-imidazol-1-ylethylamine to 100 mL of N,N-dimethylacetamide and stir until homogeneous. Then place the mixture in an ice-water bath and add 0.1 mol of triethylamine and stir until homogeneous. Add 0.15 mol of acryloyl chloride in three batches and stir until homogeneous. Then transfer the mixture to an oil bath and heat it to 65 °C and stir for 6 h. After the reaction is complete, pour the mixture into 50 mL of distilled water to precipitate the product. Filter, wash, and dry to obtain intermediate product 1. Step A32: Add 0.1 mol of 1-chlorohexane and 0.11 mol of intermediate product 1 to 100 mL of acetone and stir until homogeneous. Then, heat to 60 °C and reflux for 48 h. Remove the solvent by rotary evaporation, add 30 mL of methanol and stir until homogeneous. 50 mL of ethyl acetate precipitates out and is dried under vacuum to obtain acrylamide imidazole quaternary ammonium salt.

[0015] Example 4: A method for preparing a high-temperature and high-salt resistant modified nano-oil displacement agent includes the following steps: Example 1 prepared 10 parts of nano-oil displacement enhancer, 2 parts of molybdenum disulfide nanosheets, 3 parts of modified nano-silica, 12 parts of fatty alcohol polyoxyethylene ether, 40 parts of ethanol aqueous solution (volume ratio of ethanol to water is 1:8), and 2 parts of polyethylene glycol-4000. Weigh the raw materials according to the weight parts, mix and stir the nano-oil displacement enhancer prepared in Example 1, molybdenum disulfide nanosheets, modified nano-silica, surfactant, solvent and stabilizer evenly, and then disperse by ultrasonication to obtain a modified nano-oil displacement agent that is resistant to high temperature and high salt.

[0016] Example 5: A method for preparing a high-temperature and high-salt resistant modified nano-oil displacement agent includes the following steps: Example 2 prepared 12 parts of nano-oil displacement enhancer, 3 parts of molybdenum disulfide nanosheets, 4 parts of modified nano-silica, 16 parts of alkylphenol polyoxyethylene ether, 45 parts of ethanol aqueous solution (volume ratio of ethanol to water is 1:7), and 2.5 parts of polyethylene glycol-4000. Weigh the raw materials according to the weight parts, mix and stir the nano-oil displacement enhancer prepared in Example 2, molybdenum disulfide nanosheets, modified nano-silica, surfactant, solvent and stabilizer evenly, and then disperse by ultrasonication to obtain a modified nano-oil displacement agent that is resistant to high temperature and high salt.

[0017] Example 6: A method for preparing a high-temperature and high-salt resistant modified nano-oil displacement agent includes the following steps: Example 3 prepared 15 parts of nano-oil displacement enhancer, 4 parts of molybdenum disulfide nanosheets, 5 parts of modified nano-silica, 20 parts of fatty alcohol polyoxyethylene ether, 50 parts of ethanol aqueous solution (volume ratio of ethanol to water is 1:6), and 3 parts of polyethylene glycol-4000. Weigh the raw materials according to the weight parts, mix and stir the nano-oil displacement enhancer prepared in Example 3, molybdenum disulfide nanosheets, modified nano-silica, surfactant, solvent and stabilizer evenly, and then disperse by ultrasonication to obtain a modified nano-oil displacement agent that is resistant to high temperature and high salt.

[0018] Comparative Example 1: This comparative example is a modified nano-oil displacement agent. The difference between this example and Example 6 is that nano-sepiolite powder is used instead of the nano-oil displacement enhancer prepared in Example 3.

[0019] Comparative Example 2: This comparative example is a modified nano-oil displacement agent. The difference between this example and Example 6 is that the SP@ZnO nanomaterial prepared in Example 3 is used instead of the nano-oil displacement enhancer prepared in Example 3. All other aspects are the same.

[0020] Comparative Example 3: This comparative example is a modified nano-oil displacement agent. The difference between this example and Example 6 is that the SP@ZnO@SC nanomaterial prepared in Example 3 is used instead of the nano-oil displacement enhancer prepared in Example 3. All other aspects are the same.

[0021] Performance testing: (1) High temperature and salt resistance test: Prepare a 5wt% sodium chloride aqueous solution, and use the 5wt% sodium chloride aqueous solution to prepare a 3wt% sample solution of the modified nano oil displacement agents prepared in Examples 4-6 and Comparative Examples 1-3; seal the prepared sample solution, put it in a 90℃ oven for aging for 3 days, and then test the viscosity retention rate (viscosity retention rate ≥80% is excellent, ≥70% is good, ≥60% is qualified) and interfacial tension (the lower the value, the better the salt resistance and dispersion stability, when the interfacial tension drops to 10). -3 At the mN / m level, the salt resistance is significantly better than that at 10. -2 The test results for (mN / m level) and dispersion stability (observing whether the sample exhibits precipitation, stratification, or flocculation after aging) are shown in Table 1. Table 1: Performance Test Results (2) The modified nano-oil displacement agents prepared in Examples 4-6 and Comparative Examples 1-3 were mixed with water to prepare a 3wt% modified nano-oil displacement agent system for testing: Wettability test: Oil droplets with a crude oil density of 0.91 tons per cubic meter and a viscosity (at room temperature) of 1100 mPa·s were selected. Rock slices were made from core samples (porosity 27%) from a heavy oil well. The rock slices were soaked in a modified nano-oil displacement agent system with water added for 24 hours. The contact angle between the oil droplets and the rock slices was then measured by a contact angle measurement experiment. Interfacial tension test: Measured using a fully automatic rotating drop ultra-low interfacial tension meter TX-500C at a temperature of 80℃ and a rotation speed of 5000 rpm. The modified nano-oil displacement agent system was used as the aqueous phase, and the oil droplets used in the test were used as the oil phase. Oil recovery test: Oil displacement experiments were conducted using a core displacement device to simulate reservoir conditions. Multiple artificial heterogeneous core samples were taken, and the basic parameters of the core samples were measured and recorded. The experimental temperature was 90℃. The core samples were displaced with water at a rate of 0.01 mL / min until the water content of the outlet liquid exceeded 98%. The water displacement recovery rate was recorded as 17.9%. After the water displacement was completed, the prepared modified nano-displacement agent system was injected, and the total recovery rate of the core samples was recorded.

[0022] The test results are shown in Table 2: Table 2: Performance Test Results As can be seen from Tables 1 and 2, the modified nano-displacement agent prepared by this invention has excellent high temperature and salt resistance and dispersion stability, as well as good wettability and low interfacial tension. When used as an oil displacement agent in crude oil extraction, it has a high recovery rate.

[0023] The above content is merely an example and illustration of the concept of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described or use similar methods to replace them, as long as they do not deviate from the scope defined by the inventive concept, they should all fall within the protection scope of the present invention.

Claims

1. A modified nano-oil displacement agent resistant to high temperature and high salt, characterized in that, The raw materials include the following parts by weight: 10-15 parts of nano-oil displacement enhancer, 2-4 parts of molybdenum disulfide nanosheets, 3-5 parts of modified nano-silica, 12-20 parts of surfactant, 40-50 parts of solvent, and 2-3 parts of stabilizer. The nano-oil displacement enhancer is prepared by grafting a mixture of sodium 2-acrylamido-2-methylpropanesulfonate, acrylic acid, and acrylamide imidazole quaternary ammonium salt as shell monomers onto the surface of SP@ZnO@SC nanomaterials via free radical polymerization. The SP@ZnO@SC nanomaterials are synthesized on the surface of SP@ZnO nanomaterials using KH570 and dimethyldimethoxysilane as raw materials. The SP@ZnO nanomaterials are prepared by in-situ loading ZnO onto the surface of nano-sepiolite powder. The acrylamide imidazole quaternary ammonium salt is prepared by reacting 1-chlorohexane with intermediate product 1, which is prepared by reacting 2-imidazol-1-ylethylamine with acryloyl chloride.

2. The high-temperature and high-salt resistant modified nano-oil displacement agent according to claim 1, characterized in that, The nano-oil displacement enhancer is prepared by the following steps: Step A1: Disperse nano-sepiolite powder in deionized water by ultrasonication for 30 min, then add a mixture of zinc acetate dihydrate and tetrabutylammonium bromide dissolved in ethanol, heat and reflux and stir for 1 h, then add 100 mg / mL potassium hydroxide ethanol solution and stir for 12 h, centrifuge, wash and dry to obtain SP@ZnO nanomaterials. Step A2: Add SP@ZnO nanomaterials to ethanol and ultrasonically disperse for 15 min. Then add a mixture of KH570 and dimethyldimethoxysilane and stir for 5-10 min. Add deionized water and stir until homogeneous. Then heat to 30-40℃ and stir for 3-5 h. Filter, wash and dry to obtain SP@ZnO@SC nanomaterials. Step A3: Add hexadecyltrimethylammonium bromide and OP-10 to deionized water, heat and stir to dissolve, then add SP@ZnO@SC nanomaterials and ultrasonically disperse for 30 min. Then adjust the pH of the system to 8-10 with 3wt% sodium hydroxide aqueous solution and heat to 80℃. Then add the shell monomer mixture dropwise and finish the addition within 2 h. At the same time, add 10wt% potassium persulfate aqueous solution dropwise at a constant flow rate within 2 h. Continue the reaction for 2-3 h, cool to room temperature, add ethanol and stir to break the emulsion, then filter, wash and dry to obtain the nano oil displacement enhancer.

3. The high-temperature and high-salt resistant modified nano-oil displacement agent according to claim 2, characterized in that, In step A1, the ratio of SP, deionized water, zinc acetate dihydrate, tetrabutylammonium bromide, ethanol, and potassium hydroxide ethanol solution is 0.2g:20mL:2-3g:3-4.5g:50mL:3.5-4.5mL.

4. The high-temperature and high-salt resistant modified nano-oil displacement agent according to claim 2, characterized in that, In step A2, the ratio of SP@ZnO nanomaterials, ethanol, KH570, dimethyldimethoxysilane and deionized water is 1g:50mL:0.5-1.2mL:0.8-2mL:5-10mL.

5. The high-temperature and high-salt resistant modified nano-oil displacement agent according to claim 2, characterized in that, In step A3, the ratio of hexadecyltrimethylammonium bromide, OP-10, deionized water, SP@ZnO@SC nanomaterials, shell monomer mixture, potassium persulfate aqueous solution, and ethanol is 0.6-0.8g:0.1-0.3g:100mL:2-3g:12-20g:7.5-12mL:50-80mL. The shell monomer mixture is a mixture of sodium 2-acrylamido-2-methylpropanesulfonate, acrylic acid, and acrylamide imidazole quaternary ammonium salt, and the mass ratio of the three is 8-12g:3-6g:1-2g.

6. The high-temperature and high-salt resistant modified nano-oil displacement agent according to claim 2, characterized in that, The acrylamide imidazole quaternary ammonium salt described in step A3 is prepared by the following steps: Step A31: Add 2-imidazol-1-ylethylamine to N,N-dimethylacetamide and stir until homogeneous. Then place the mixture in an ice-water bath, add triethylamine and stir until homogeneous. Add acryloyl chloride in three batches and stir until homogeneous. Then transfer the mixture to an oil bath, heat it to 65°C and stir for 5-6 hours. After the reaction is complete, pour the mixture into distilled water to precipitate the product. Filter, wash and dry to obtain intermediate product 1. Step A32: Add 1-chlorohexane and intermediate 1 to acetone and stir until homogeneous. Then, heat to 60°C and reflux for 48 hours. Remove the solvent by rotary evaporation, add methanol and stir until homogeneous. Ethyl acetate precipitates out and is dried under vacuum to obtain acrylamide imidazole quaternary ammonium salt.

7. The high-temperature and high-salt resistant modified nano-oil displacement agent according to claim 6, characterized in that, In step A31, the molar ratio of 2-imidazol-1-ylethylamine, acryloyl chloride, and triethylamine is 1.1-1.2:1:1-1.

5.

8. The high-temperature and high-salt resistant modified nano-oil displacement agent according to claim 6, characterized in that, In step A32, the molar ratio of 1-chlorohexane to intermediate 1 is 1:1-1.

1.

9. The high-temperature and high-salt resistant modified nano-oil displacement agent according to claim 1, characterized in that, The modified nano-silica is nano-silica grafted with a silane coupling agent, the surfactant is a nonionic surfactant, the solvent is an aqueous ethanol solution with a volume ratio of ethanol to water of 1:6-8, and the stabilizer is polyethylene glycol-4000.

10. A method for preparing the high-temperature and high-salt resistant modified nano-oil displacement agent according to any one of claims 1-9, characterized in that, Includes the following steps: Weigh the raw materials according to the weight parts, mix and stir the nano oil displacement enhancer, molybdenum disulfide nanosheets, modified nano silica, surfactant, solvent and stabilizer evenly, and then disperse them by ultrasonication to obtain a modified nano oil displacement agent that is resistant to high temperature and high salt.

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