Block copolymer modified silica nanoparticles, their preparation methods and applications

Abstract

This invention relates to the field of enhanced oil recovery technology in oilfields, and discloses block copolymers and block copolymer-modified silica nanoparticles, their preparation methods, and applications. The block copolymer contains structural unit A as shown in Formula I, structural unit B as shown in Formula II or III, and structural unit C as shown in Formula IV, wherein R1, R3, R5, and R6 are each independently hydrogen or methyl; R2 is C1-C2. 12 The components are: R4, R5, and R6. R7 is a straight-chain or branched alkyl or phenyl group; R8 is a C1-C5 straight-chain or branched alkylene group; R9 is an integer from 1 to 10. In this invention, the -NCO group in the structural unit C of the block copolymer reacts with the amino group in the surface-modified silica nanoparticles via an addition reaction to form the -NHCONH- phase, resulting in block copolymer-modified silica nanoparticles, which are ultimately used in oil displacement agents. These block copolymer-modified silica nanoparticles possess amphiphilicity, stability, and solvent responsiveness, and can reduce oil-water interfacial tension, thereby improving oil recovery.

Description

Technical Field

[0001] This invention relates to the field of enhanced oil recovery technology, specifically to block copolymers and block copolymer-modified silica nanoparticles, their preparation methods, and applications. Background Technology

[0002] Improving the recovery rate of low-permeability reservoirs and achieving economical and efficient development of low-permeability oilfields has become a crucial direction for oilfield development technology research both domestically and internationally. Therefore, existing tertiary oil recovery technologies are no longer sufficient to meet the increasingly deteriorating quality of current oil and gas resources. There is an urgent need to develop new technologies to enhance oil recovery rates, relying on technological innovation to solve new problems in oilfield development and meet the production and technological needs of oilfields.

[0003] In recent years, theoretical breakthroughs and technological innovations in nanotechnology have provided new avenues for the development of new technologies for enhanced oil recovery (EOR). An increasing number of research teams are applying the surface effects of nanomaterials to EOR technologies. Silica nanoparticles, due to their low cost, environmental friendliness, good formation compatibility, high surface activity, high hydroxyl content, and ease of surface modification, have become the preferred nanomaterial for oil displacement. Most of these methods employ selective surface modification, preparing amphiphilic silica nanoparticles by modifying the surface of the same nanoparticle. Since both hydrophilic and lipophilic modifications are performed on the same silica particle, the two modifications may influence each other. The hydrophilicity and lipophilicity of the silica particles cannot be controlled independently, affecting the optimization of their amphiphilic properties. CN107416844B prepared bispherical amphiphilic silica nanoparticles with a particle size less than 100 nm by chemically coupling hydrophilic and lipophilic silica nanoparticles. Although the hydrophilicity and lipophilicity can be controlled separately, they are prone to stagnation and blockage during migration in porous reservoir media. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems of existing technologies, such as the difficulty in precisely controlling the hydrophilic and oleophilic properties of nano-silica, structural instability, and insignificant reduction of oil-water interfacial tension, as well as low recovery rates in low-permeability reservoirs. This invention provides block copolymers and block copolymer-modified silica nanoparticles, their preparation methods, and applications. These block copolymer-modified silica nanoparticles are obtained by an addition reaction between block copolymers containing -NCO structural units and surface-modified silica nanoparticles containing amino groups. The linking group is -NHCONH-, exhibiting amphiphilicity, stability, and solvent responsiveness. They can reduce oil-water interfacial tension and possess oil displacement functions such as automatic oil discovery in reservoirs, oil droplet capture and aggregation, and intelligent expansion of swept volume, significantly improving crude oil recovery rates.

[0005] To achieve the above objectives, a first aspect of the present invention provides a block copolymer, wherein the block copolymer contains structural unit A of Formula I, structural unit B of Formula II or III, and structural unit C of Formula IV.

[0006]

[0007] In this configuration, R1, R3, R5, and R6 are each independently hydrogen or methyl; R2 is C1-C. 12 R4 is a straight-chain or branched alkyl or phenyl group; R5 is a C1-C5 straight-chain or branched alkylene group; R7 is... x, y, and z are integers from 1 to 10.

[0008] A second aspect of the present invention provides a method for preparing a block copolymer, wherein the preparation method includes the following steps:

[0009] (1) Under a nitrogen atmosphere and in the presence of a first initiator, a chain transfer agent and an organic solvent, the monomer shown in formula (1) and the monomer or methacryloyl isocyanate shown in formula (2) are subjected to a first polymerization reaction to obtain a first polymerization product.

[0010] (2) Under a nitrogen atmosphere and in the presence of a second initiator, the first polymerization product is subjected to a second polymerization reaction with the monomer shown in formula (3) to obtain the block copolymer;

[0011]

[0012] In this configuration, R1, R3, and R6 are each independently hydrogen or methyl; R2 is C1-C. 12 R4 is a straight-chain or branched alkyl or phenyl group; R5 is a C1-C5 straight-chain or branched alkylene group; R7 is... x, y, and z are integers from 1 to 10.

[0013] A third aspect of the present invention provides block copolymer modified silica nanoparticles, wherein the modified silica nanoparticles comprise: a core from surface-modified silica nanoparticles, a coating layer from a block copolymer, and a linking group connecting the core and the coating layer, wherein the block copolymer contains structural unit A of Formula I, structural unit B of Formula II or III, and structural unit C of Formula IV.

[0014] The linking group is -NHCONH-, which is obtained by the addition reaction of -NCO contained in the structural unit B with the amino group contained in the surface-modified silica nanoparticles;

[0015]

[0016] In this configuration, R1, R3, R5, and R6 are each independently hydrogen or methyl; R2 is C1-C. 12 R4 is a straight-chain or branched alkyl or phenyl group; R5 is a C1-C5 straight-chain or branched alkylene group; R7 is... x, y, and z are integers from 1 to 10.

[0017] A fourth aspect of the present invention provides a method for preparing block copolymer-modified silica nanoparticles, wherein the preparation method includes the following steps:

[0018] Block copolymers are reacted with silane coupling agents to modify silica nanoparticles to obtain block copolymer-modified silica nanoparticles; wherein the block copolymer is the block copolymer described above or the block copolymer prepared by the above preparation method.

[0019] The mass ratio of the block copolymer to the silane coupling agent modified silica nanoparticles is 0.3-10:1.

[0020] The fifth aspect of the present invention provides block copolymer modified silica nanoparticles prepared by the method of the fourth aspect described above.

[0021] The sixth aspect of the present invention provides the application of the block copolymer modified silica nanoparticles described in the third and / or fifth aspects above in enhancing oil recovery.

[0022] The seventh aspect of the present invention provides an oil displacement agent, wherein the oil displacement agent comprises: 99.5%-99.9% by weight of water and 0.1%-0.5% by weight of the block copolymer modified silica nanoparticles described in the third and / or fifth aspects.

[0023] The eighth aspect of the present invention provides the application of the oil displacement agent described in the seventh aspect in enhancing oil recovery.

[0024] The beneficial technical effects achieved by the present invention through the above technical solution are as follows:

[0025] (1) The present invention obtains block copolymer modified silica nanoparticles with -NHCONH- linkage group by adding a block copolymer containing -NCO structural units to surface-modified silica nanoparticles containing amino groups. The block copolymer modified silica nanoparticles have a stable structure.

[0026] (2) The block copolymer modified silica nanoparticles prepared by the present invention have a triblock copolymer with hydrophilic and oleophilic segments at both ends connected to the surface of silica nanoparticles through the middle segment. It has a spontaneous conformational transformation function for water / oil solvents, which can significantly reduce the interfacial tension between oil and water, thereby improving capillary action, improving the oil washing efficiency of the oil displacement system and the ability to emulsify crude oil.

[0027] (3) The oil displacement agent provided by the present invention can further improve the recovery rate on the basis of water flooding, and has significant application value in tertiary oil recovery in low-permeability reservoirs and further improving the recovery rate after chemical flooding. Attached Figure Description

[0028] Figure 1 The images show the Fourier Transform Infrared (FTIR) spectra of silica nanoparticles before and after modification with the block copolymer in Example 1.

[0029] Figure 2 The image shows the Fourier Transform Infrared (FTIR) spectra of silica nanoparticles before and after modification with block copolymer in Comparative Example 1. Detailed Implementation

[0030] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0031] A first aspect of the present invention provides a block copolymer, wherein the block copolymer contains structural unit A of formula I, structural unit B of formula II or III, and structural unit C of formula IV.

[0032]

[0033] In this configuration, R1, R3, R5, and R6 are each independently hydrogen or methyl; R2 is C1-C. 12 R4 is a straight-chain or branched alkyl or phenyl group; R5 is a C1-C5 straight-chain or branched alkylene group; R7 is... x, y, and z are integers from 1 to 10.

[0034] In some embodiments, R2 is a C1-C8 straight-chain or branched alkyl or phenyl group, preferably methyl or ethyl; R4 is a C1-C3 straight-chain or branched alkylene group, preferably methylene or ethylene; x, y and z are integers from 1 to 6, and x, y and z are preferably 1 or 2.

[0035] In some embodiments, the molar ratio of structural unit A, structural unit B and structural unit C is 1:0.02-3:0.05-20.

[0036] In some embodiments, the block copolymer has a weight-average molecular weight of 15,000-160,000 g / mol, preferably 20,000-60,000 g / mol.

[0037] A second aspect of the present invention provides a method for preparing a block copolymer, wherein the preparation method includes the following steps:

[0038] (1) Under a nitrogen atmosphere and in the presence of a first initiator, a chain transfer agent and an organic solvent, the monomer shown in formula (1) and the monomer or methacryloyl isocyanate shown in formula (2) are subjected to a first polymerization reaction to obtain a first polymerization product.

[0039] (2) Under a nitrogen atmosphere and in the presence of a second initiator, the first polymerization product is subjected to a second polymerization reaction with the monomer shown in formula (3) to obtain the block copolymer;

[0040]

[0041] In this configuration, R1, R3, and R6 are each independently hydrogen or methyl; R2 is C1-C. 12 R4 is a straight-chain or branched alkyl or phenyl group; R5 is a C1-C5 straight-chain or branched alkylene group; R7 is... x, y, and z are integers from 1 to 10.

[0042] In some embodiments, the molar ratio of the monomers shown in formula (1), formula (2), and formula (3) is 1:0.05-0.5:0.05-50.

[0043] In some embodiments, in step (1), the conditions for the first polymerization reaction include: a reaction temperature of 60-80°C and a reaction time of 3-24h.

[0044] In some embodiments, the first initiator is an azo initiator, preferably one of azobisisobutyronitrile, azobisisoheptanenitrile, and dimethyl azobisisobutyrate.

[0045] In some embodiments, the chain transfer agent is benzyl dithiobenzoate or cumyl dithiobenzoate.

[0046] In some embodiments, R2 is a C1-C8 straight-chain or branched alkyl or phenyl group, preferably methyl or ethyl; R4 is a C1-C3 straight-chain or branched alkylene group, preferably methyl or ethyl; x, y and z are integers from 1 to 6, and x, y and z are preferably 1 or 2.

[0047] In some embodiments, the monomer represented by formula (1) is selected from methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, tert-butyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, isooctyl methacrylate, 2-ethylhexyl acrylate, or styrene.

[0048] In some embodiments, the monomer represented by formula (2) is ethyl isocyanate methacrylate or ethyl isocyanate acrylate.

[0049] In some embodiments, the monomer represented by formula (3) is selected from methoxyethyl methacrylate, dimethylaminoethyl methacrylate, dimethylaminoethyl acrylate, poly(ethylene glycol) methacrylate, poly(ethylene glycol) acrylate, hydroxyethyl methacrylate, hydroxyethyl acrylate, hydroxypropyl methacrylate, hydroxypropyl acrylate, 4-hydroxybutyl 2-methacrylate, 4-hydroxybutyl acrylate, or 2-methoxyethyl 2-acrylate.

[0050] In some embodiments, the organic solvent is benzene.

[0051] In some embodiments, the molar ratio of the initiator, chain transfer agent and monomer shown in formula (1) is 1:1-5:50-500.

[0052] In some embodiments, the volume ratio of the monomer shown in formula (1) to the monomer shown in formula (2) is 1:0.06-0.46.

[0053] In some embodiments, step (1) further includes: dissolving the first polymerization product in tetrahydrofuran, then adding it to the first precipitant to precipitate it, repeating this process 3-6 times, filtering it, and drying it at 30-50°C for 36-48 hours.

[0054] In some embodiments, the first precipitant is a mixed solution of toluene and petroleum ether in a volume ratio of 1:1-4.

[0055] In some embodiments, in step (2), the conditions for the second polymerization reaction include: a reaction temperature of 60-80°C and a reaction time of 5-24h.

[0056] In some embodiments, the second initiator is an azo initiator, preferably one of azobisisobutyronitrile, azobisisoheptanenitrile, and dimethyl azobisisobutyrate.

[0057] In some embodiments, the molar ratio of the first polymer product, the monomer of formula (3), and the second initiator is 1:10-1000:0.5-1.0.

[0058] In some embodiments, step (2) further includes: dissolving the block copolymer in tetrahydrofuran, then adding it to a second precipitant for precipitation, repeating this process 3-6 times, filtering the solution, and drying it at 30-50°C for 36-48 hours.

[0059] In some embodiments, the second precipitant is a mixed solution of toluene and petroleum ether in a volume ratio of 1:5-10.

[0060] A third aspect of the present invention provides block copolymer modified silica nanoparticles, wherein the modified silica nanoparticles comprise: a core from surface-modified silica nanoparticles, a coating layer from a block copolymer, and a linking group connecting the core and the coating layer, wherein the block copolymer contains structural unit A of Formula I, structural unit B of Formula II or III, and structural unit C of Formula IV.

[0061] The linking group is -NHCONH-, which is obtained by the addition reaction of -NCO contained in the structural unit B with the amino group contained in the surface-modified silica nanoparticles;

[0062]

[0063] In this configuration, R1, R3, R5, and R6 are each independently hydrogen or methyl; R2 is C1-C. 12 R4 is a straight-chain or branched alkyl or phenyl group; R5 is a C1-C5 straight-chain or branched alkylene group; R7 is... x, y, and z are integers from 1 to 10.

[0064] In some embodiments, R2 is a C1-C8 straight-chain or branched alkyl or phenyl group, preferably methyl or ethyl; R4 is a C1-C3 straight-chain or branched alkylene group, preferably methylene or ethylene; x, y and z are integers from 1 to 6, and x, y and z are preferably 1 or 2.

[0065] In some embodiments, the molar ratio of structural unit A, structural unit B and structural unit C is 1:0.02-0.3:0.05-20.

[0066] In some embodiments, the content of the silica nanoparticles is 15-85 wt%, preferably 35-75 wt%, based on the total weight of the block copolymer-modified silica nanoparticles.

[0067] In some embodiments, the average particle size of the silica nanoparticles is 20-80 nm.

[0068] A fourth aspect of the present invention provides a method for preparing block copolymer-modified silica nanoparticles, wherein the preparation method includes the following steps:

[0069] Block copolymers are reacted with silane coupling agents to modify silica nanoparticles to obtain block copolymer-modified silica nanoparticles; wherein the block copolymer is the block copolymer described above or the block copolymer prepared by the above preparation method.

[0070] The mass ratio of the block copolymer to the silane coupling agent modified silica nanoparticles is 0.3-10:1.

[0071] In some embodiments, the reaction conditions include: ultrasonically dispersing the block copolymer and the silane coupling agent modified silica nanoparticles in toluene; reacting at 20-30°C for 4-12 hours using a reflux method; separating the precipitate, washing it, and drying it at 60-100°C for 12-36 hours to obtain block copolymer modified silica nanoparticles.

[0072] In some embodiments, the silane coupling agent is selected from 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldiethoxysilane, anilinemethyltrimethoxysilane, or anilinemethyltriethoxysilane.

[0073] In some embodiments, the preparation method of the silane coupling agent modified silica nanoparticles includes: mixing anhydrous ethanol, deionized water, ammonia and tetraethyl orthosilicate for a first reaction, then adding a silane coupling agent for a second reaction for 2-5 hours to obtain the silane coupling agent modified silica nanoparticles.

[0074] In some embodiments, the molar ratio of anhydrous ethanol, deionized water, ammonia to tetraethyl orthosilicate is 25-80:2-5:0.25-3.9:1; and the molar ratio of tetraethyl orthosilicate to silane coupling agent is 1:0.01-0.2.

[0075] In some embodiments, the conditions for the first reaction are: under stirring, a reaction time of 12-24 hours and a reaction temperature of 20-30°C; and the conditions for the second reaction are: under stirring, a reaction time of 2-5 hours and a reaction temperature of 60-70°C.

[0076] In some embodiments, the preparation method further includes: washing the silane coupling agent modified silica nanoparticles in a dispersant, filtering them, and drying them at 70-90°C for 12-24 hours, wherein the dispersant is deionized water and / or ethanol.

[0077] The fifth aspect of the present invention provides block copolymer modified silica nanoparticles prepared by the method of the fourth aspect described above.

[0078] The sixth aspect of the present invention provides the application of the block copolymer modified silica nanoparticles described in the third and / or fifth aspects above in enhancing oil recovery.

[0079] The seventh aspect of the present invention provides an oil displacement agent, wherein the oil displacement agent comprises: 99.5%-99.9% by weight of water and 0.1%-0.5% by weight of the block copolymer modified silica nanoparticles described in the third and / or fifth aspects.

[0080] Compared with commercially available nano-displacement agents, oil displacement agents containing block copolymer modified silica nanoparticles prepared in this invention can significantly reduce oil / water interfacial tension, thereby improving crude oil recovery.

[0081] The eighth aspect of the present invention provides the application of the oil displacement agent described in the seventh aspect in enhancing oil recovery.

[0082] The present invention will be described in detail below through embodiments. However, the scope of protection of the present invention is not limited to the following description.

[0083] Unless otherwise specified in the following examples and comparative examples, all conditions were performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments used, unless otherwise specified, are all commercially available products.

[0084] Test on performance in reducing water / crude oil interfacial tension, the test method refers to standard SY / T 5370-2018:

[0085] The test oil was a simulated oil made from crude oil and aviation kerosene from a certain block of Daqing Oilfield, and the test water was deep-treated wastewater from the same block after being filtered through a filter membrane with a pore size of 0.45μm.

[0086] A certain mass of the test sample was added to on-site water of the corresponding mass concentration, ultrasonically dispersed for 30 min, and mechanically stirred for 30 min before use. The testing instrument was a TEXAS-500 rotating drop interfacial tensiometer. The main testing steps are as follows: the constant temperature system was started, and the temperature was controlled between 45±0.2℃; the nano-oil displacement system sample was filled into the measuring tube; simulated oil was drawn into the measuring tube using a micro-syringe to form a suitable droplet, and there should be no air bubbles in the measuring tube; the interfacial tensiometer was started, and the rotation speed was set to 4500 RPM; throughout the measurement process, the oil droplet was kept in the middle of the capillary tube as much as possible, and the experimental data was recorded every 15 min; the entire measurement time was 2 h.

[0087] The procedure for oil displacement experiments follows the standard SY / T 6424-2014, and the main steps are as follows:

[0088] 1. Vacuum a 4.5cm×4.5cm×30cm Bailey core with a square cross-section for more than 4 hours, and then saturate the core with filtered on-site water.

[0089] 2. Heat the core to the formation temperature of 45°C, use the prepared simulated oil to drive the water, and stop when the water volume in the outlet graduated tube no longer changes. Measure the cumulative saturated oil volume to obtain the bound water saturation.

[0090] 3. After the core is saturated with oil, it is aged in a constant temperature chamber at 45℃ for 12 hours. Then, the saturated oil process is changed to a water drive process. When the water content reaches more than 98% during the continuous water drive 0.5 times pore volume (0.5PV) stage, the water drive is stopped.

[0091] 4. Switch to the nano-displacement agent injection process, continuously inject 0.3 PV of nano-displacement system slug at a rate of 0.3 mL / min, and record the oil production and water production at each stage;

[0092] 5. Continue with subsequent water drive until the water content of the produced fluid at the outlet reaches 98% or more for 0.5 PV consecutively. Then, end the experiment and calculate the stage recovery rate and total recovery rate.

[0093] Example 1

[0094] (1) Preparation of block copolymers

[0095] 0.05 g of azobisisobutyronitrile, 0.1 g of isopropylbenzene dithiobenzoate and 2.0 g of ethyl methacrylate (as shown in formula (1), where R1 is methyl and R2 is ethyl) were added to 10 mL of benzene and reacted for 1.5 h under a nitrogen atmosphere at a temperature of 65 °C. Then 1.2 g of isocyanate methyl methacrylate (as shown in formula (2), where R3 is methyl and R4 is ethylene) was added and reacted for another 1.5 h under a nitrogen atmosphere. The product was dissolved and diluted with tetrahydrofuran and slowly added dropwise to the first precipitant (toluene and petroleum ether in a volume ratio of 1:1) in an ice bath to precipitate. This process was repeated 3 times and then the product was dried under vacuum to obtain the first polymer product.

[0096] 1.5g of the first polymerization product and 9.1g of dimethylaminoethyl acrylate (as shown in formula (3), where R6 is hydrogen and R7 is hydrogen) were added. x = 2) and 0.02 g of azobisisobutyronitrile (AIO) were added to 15 mL of benzene. The reaction was carried out under a nitrogen atmosphere for 5 h at 65 °C. The product was dissolved and diluted with tetrahydrofuran and slowly added dropwise to a second precipitant (toluene and petroleum ether, volume ratio 1:5) in an ice bath to precipitate. This process was repeated three times. The product was then vacuum dried to obtain a block copolymer, whose structural unit A (as shown in Formula I, R1 is methyl, R2 is ethyl), structural unit B (as shown in Formula II, R3 is methyl, R4 is ethylidene), and structural unit C (as shown in Formula IV, R6 is hydrogen, R7 is...) are... The molar ratio of x (2) is 1:0.29:3.9.

[0097] (2) Preparation of surface-modified silica nanoparticles

[0098] 200g ethanol, 5g deionized water and 10g ammonia (25wt%) were mixed and stirred for 15min. Then 15g tetraethyl orthosilicate was added and the mixture was stirred at room temperature for 12h. The temperature was raised to 65℃ and 1g 3-aminopropyltriethoxysilane was added dropwise. The mixture was stirred for another 2h. The solid product was collected by centrifugation, dispersed and washed three times with ethanol and deionized water, and then vacuum dried at 80℃ for 12h to obtain surface-modified silica nanoparticles.

[0099] (3) Preparation of block copolymer modified silica nanoparticles

[0100] 1.5 g of block copolymer and 0.5 g of surface-modified silica nanoparticles were ultrasonically dispersed in 20 mL of tetrahydrofuran solvent and refluxed at room temperature for 4 h. The solid product was separated by centrifugation, washed three times with tetrahydrofuran, and then vacuum dried at 80 °C for 24 h to obtain block copolymer modified silica nanoparticles 1.

[0101] Example 2

[0102] Block copolymer modified silica nanoparticles were prepared according to the method of Example 1, except that the monomer shown in formula (2) was replaced with methacryloyl isocyanate, and block copolymer modified silica nanoparticles 2 were obtained.

[0103] Example 3

[0104] Block copolymer-modified silica nanoparticles were prepared according to the method of Example 1, except that the molar ratio of ethyl methacrylate, isocyanate ethyl methacrylate and dimethylaminoethyl methacrylate was 1:0.25:0.33, thus obtaining block copolymer-modified silica nanoparticles 3.

[0105] Example 4

[0106] Block copolymer-modified silica nanoparticles were prepared according to the method of Example 1, except that the molar ratio of ethyl methacrylate, isocyanate ethyl methacrylate and dimethylaminoethyl methacrylate was 1:0.03:0.67, thus obtaining block copolymer-modified silica nanoparticles 4.

[0107] Example 5

[0108] Block copolymer-modified silica nanoparticles were prepared according to the method of Example 1, except that the chain transfer agent was benzyl dithiobenzoate, and block copolymer-modified silica nanoparticles 5 were obtained.

[0109] Comparative Example 1

[0110] Block copolymer-modified silica nanoparticles were prepared according to the method in Example 1, except that no silane coupling agent was used to modify the silica nanoparticles. The specific steps are as follows:

[0111] (1) Block copolymers were prepared according to the method of Example 1;

[0112] (2) 1.2g of block copolymer and 0.4g of silica nanoparticles were ultrasonically dispersed in 20mL of tetrahydrofuran solvent and refluxed at room temperature for 5h. The solid product was separated by centrifugation, washed 3 times with tetrahydrofuran, and then vacuum dried at 80℃ for 24h to obtain block copolymer modified silica nanoparticles D1.

[0113] Comparative Example 2

[0114] Block copolymer-modified silica nanoparticles were prepared according to the method of Example 1, except that structural unit B was derived from glycidyl methacrylate, resulting in block copolymer-modified silica nanoparticles D2.

[0115] Comparative Example 3

[0116] Commercially available nano oil displacement agent D3

[0117] Test case

[0118] The performance of block copolymer modified silica nanoparticles 1-5, D1, D2 and D3 in reducing the interfacial tension between water and crude oil was tested, and the results are shown in Table 1.

[0119] An oil displacement agent system was prepared using block copolymer modified silica nanoparticles 1-5, D1, D2 and D3, and core oil displacement experiments were conducted. The results are shown in Table 2.

[0120] Table 1

[0121]

[0122]

[0123] Table 2

[0124]

[0125] As can be seen from the results in Table 1, the interfacial tension of Examples 1-5 of the present invention is significantly reduced, and the interfacial tension of Examples 1-3 can reach 10 when the mass concentration is higher than 0.3%. -2 The mN / m level indicates that the block copolymer modified silica nanoparticles provided by this invention have good performance in reducing oil-water interfacial tension.

[0126] As can be seen from the results in Table 2, the core permeability of Examples 1-5 and Comparative Examples 1-2 is less than or equal to 50 mD, which are natural Bailey cores in the low permeability range. The waterflood recovery rate fluctuates within ±2%, which is within the normal range. Examples 1-5 of the present invention significantly improve the recovery rate of nano-flooding on the basis of waterflooding, and the total recovery rate is also significantly improved. Moreover, the nano-flooding recovery rate of Examples 1-3 can be increased by more than 8 percentage points on the basis of waterflooding. Compared with commercially available nano-flooding agents, the block copolymer modified silica nanoparticles provided by the present invention can significantly improve the crude oil recovery rate.

[0127] Figure 1 By comparing the infrared spectra of Example 1 with those of silica nanoparticles not modified with the block copolymer of the present invention, it can be clearly seen that Example 1 has a higher infrared spectrum in the 1600-1850 cm⁻¹ range. -1 The characteristic peak of the carbon-oxygen double bond stretching vibration indicates that the block copolymer and silica nanoparticles in Example 1 are connected through -NHCONH- to obtain block copolymer modified silica nanoparticles.

[0128] Figure 2 By comparing the infrared spectra of Comparative Example 1 and silica nanoparticles, it can be seen that there are no obvious changes in characteristic peaks, indicating that the silica nanoparticles of D1 have not undergone block copolymer modification.

[0129] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A block copolymer-modified silica nanoparticle, characterized in that, The modified silica nanoparticles comprise: a core from surface-modified silica nanoparticles, a coating layer from a block copolymer, and a linking group connecting the core and the coating layer, wherein the block copolymer contains structural unit A of Formula I, structural unit B of Formula II or III, and structural unit C of Formula IV. The linking group is -NHCONH-, which is obtained by the addition reaction of -NCO contained in the structural unit B with the amino group contained in the surface-modified silica nanoparticles; Formula I, Formula II, Formula III, Formula IV, In this configuration, R1, R3, R5, and R6 are each independently hydrogen or methyl; R2 is C1-C. 12 R4 is a straight-chain or branched alkyl or phenyl group; R5 is a C1-C5 straight-chain or branched alkylene group; R7 is... , or x, y, and z are each independent integers from 1 to 10.

2. The block copolymer-modified silica nanoparticles according to claim 1, wherein, R2 is a C1-C8 straight-chain or branched alkyl or phenyl group; R4 is a C1-C3 straight-chain or branched alkylene group; x, y and z are each independent integers from 1 to 6; Wherein, the molar ratio of structural unit A, structural unit B and structural unit C is 1:0.02-0.3:0.05-20; And / or, based on the total weight of the block copolymer-modified silica nanoparticles, the content of the silica nanoparticles is 15-85 wt%; And / or, the average particle size of the silica nanoparticles is 20-80 nm.

3. The block copolymer-modified silica nanoparticles according to claim 2, wherein, R2 is methyl or ethyl; R4 is methylene or ethylene; x, y, and z are each independently 1 or 2; And / or, based on the total weight of the block copolymer-modified silica nanoparticles, the content of the silica nanoparticles is 35-75 wt%.

4. A method for preparing block copolymer-modified silica nanoparticles, characterized in that, The preparation method includes the following steps: Block copolymers are reacted with silane coupling agents to modify silica nanoparticles, resulting in block copolymer-modified silica nanoparticles; wherein the block copolymers contain structural unit A of Formula I, structural unit B of Formula II or III, and structural unit C of Formula IV. Formula I, Formula II, Formula III, Formula IV, In this configuration, R1, R3, R5, and R6 are each independently hydrogen or methyl; R2 is C1-C. 12 R4 is a straight-chain or branched alkyl or phenyl group; R5 is a C1-C5 straight-chain or branched alkylene group; R7 is... , or x, y, and z are each independent integers from 1 to 10; The block copolymer-modified silica nanoparticles comprise: a core from the surface-modified silica nanoparticles, a coating layer from the block copolymer, and a linking group connecting the core and the coating layer. The linking group is -NHCONH-, obtained by an addition reaction between -NCO contained in structural unit B and amino groups contained in the surface-modified silica nanoparticles.

5. The preparation method according to claim 4, wherein, The mass ratio of the block copolymer to the silane coupling agent-modified silica nanoparticles is 0.3-10:

1.

6. The preparation method according to claim 4, wherein, R2 is a C1-C8 straight-chain or branched alkyl or phenyl group; R4 is a C1-C3 straight-chain or branched alkylene group; x, y and z are each independent integers from 1 to 6.

7. The preparation method according to claim 6, wherein, R2 is methyl or ethyl; R4 is methylene or ethylene; x, y, and z are each independently 1 or 2; And / or, the molar ratio of structural unit A, structural unit B and structural unit C is 1:0.02-0.3:0.05-20; And / or, the weight-average molecular weight of the block copolymer is 15,000-160,000 g / mol.

8. The preparation method according to claim 7, wherein, The block copolymer has a weight-average molecular weight of 20,000-60,000 g / mol.

9. The preparation method according to any one of claims 4-8, wherein, The method for preparing the block copolymer includes the following steps: (1) Under a nitrogen atmosphere and in the presence of a first initiator, a chain transfer agent and an organic solvent, the monomer shown in formula (1) and the monomer or methacryloyl isocyanate shown in formula (2) are subjected to a first polymerization reaction to obtain a first polymerization product; (2) Under a nitrogen atmosphere and in the presence of a second initiator, the first polymerization product is subjected to a second polymerization reaction with the monomer shown in formula (3) to obtain the block copolymer; Equation (1), Equation (2) Equation (3), In this configuration, R1, R3, and R6 are each independently hydrogen or methyl; R2 is C1-C. 12 R4 is a straight-chain or branched alkyl or phenyl group; R5 is a C1-C5 straight-chain or branched alkylene group; R7 is... , or x, y, and z are each independent integers from 1 to 10.

10. The preparation method according to claim 9, wherein, The molar ratio of the monomers shown in formula (1), formula (2), and formula (3) is 1:0.05-0.5:0.05-50.

11. The preparation method according to claim 9, wherein, In step (1), the conditions for the first polymerization reaction include: a reaction temperature of 60-80℃ and a reaction time of 3-24 h.

12. The preparation method according to claim 11, wherein, The first initiator is an azo initiator; And / or, the chain transfer agent is benzyl dithiobenzoate or cumyl dithiobenzoate; And / or, R2 is a C1-C8 straight-chain or branched alkyl or phenyl group; R4 is a C1-C3 straight-chain or branched alkylene group; x, y and z are each independently an integer from 1 to 6; And / or, the monomer shown in formula (1) is selected from methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, tert-butyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate or 2-ethylhexyl acrylate. And / or, the monomer shown in formula (2) is ethyl isocyanate methacrylate or ethyl isocyanate acrylate; And / or, the monomers shown in formula (3) are selected from dimethylaminoethyl methacrylate, dimethylaminoethyl acrylate, poly(ethylene glycol) methacrylate, poly(ethylene glycol) acrylate, hydroxyethyl methacrylate or hydroxyethyl acrylate; And / or, the organic solvent is benzene; And / or, the molar ratio of the initiator, chain transfer agent and monomer shown in formula (1) is 1:1-5:50-500; And / or, the volume ratio of the monomer shown in formula (1) to the monomer shown in formula (2) is 1:0.06-0.

46.

13. The preparation method according to claim 12, wherein, The first initiator is one of azobisisobutyronitrile, azobisisoheptanenitrile, and dimethyl azobisisobutyrate; And / or, R2 is methyl or ethyl; R4 is methylene or ethylene; x, y and z are each independently 1 or 2.

14. The preparation method according to claim 10, wherein, In step (1), the conditions for the first polymerization reaction include: a reaction temperature of 60-80℃ and a reaction time of 3-24 h.

15. The preparation method according to claim 14, wherein, The first initiator is an azo initiator; And / or, the chain transfer agent is benzyl dithiobenzoate or cumyl dithiobenzoate; And / or, R2 is a C1-C8 straight-chain or branched alkyl or phenyl group; R4 is a C1-C3 straight-chain or branched alkylene group; x, y and z are each independently an integer from 1 to 6; And / or, the monomer shown in formula (1) is selected from methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, tert-butyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate or 2-ethylhexyl acrylate. And / or, the monomer shown in formula (2) is ethyl isocyanate methacrylate or ethyl isocyanate acrylate; And / or, the monomers shown in formula (3) are selected from dimethylaminoethyl methacrylate, dimethylaminoethyl acrylate, poly(ethylene glycol) methacrylate, poly(ethylene glycol) acrylate, hydroxyethyl methacrylate or hydroxyethyl acrylate; And / or, the organic solvent is benzene; And / or, the molar ratio of the initiator, chain transfer agent and monomer shown in formula (1) is 1:1-5:50-500; And / or, the volume ratio of the monomer shown in formula (1) to the monomer shown in formula (2) is 1:0.06-0.

46.

16. The preparation method according to claim 15, wherein, The first initiator is one of azobisisobutyronitrile, azobisisoheptanenitrile, and dimethyl azobisisobutyrate; And / or, R2 is methyl or ethyl; R4 is methylene or ethylene; x, y and z are each independently 1 or 2.

17. The preparation method according to claim 9, wherein, Step (1) also includes: dissolving the first polymerization product in tetrahydrofuran, then adding it to the first precipitant to precipitate it, repeating this process 3-6 times, filtering it, and drying it at 30-50℃ for 36-48 h.

18. The preparation method according to claim 17, wherein, The first precipitant is a mixed solution of toluene and petroleum ether in a volume ratio of 1:1-4.

19. The preparation method according to any one of claims 10-16, wherein, Step (1) also includes: dissolving the first polymerization product in tetrahydrofuran, then adding it to the first precipitant to precipitate it, repeating this process 3-6 times, filtering it, and drying it at 30-50℃ for 36-48 h.

20. The preparation method according to claim 19, wherein, The first precipitant is a mixed solution of toluene and petroleum ether in a volume ratio of 1:1-4.

21. The preparation method according to claim 9, wherein, In step (2), the conditions for the second polymerization reaction include: a reaction temperature of 60-80℃ and a reaction time of 5-24 h.

22. The preparation method according to claim 21, wherein, The second initiator is an azo initiator; And / or, the molar ratio of the first polymerization product, the monomer of formula (3) and the second initiator is 1:10-1000:0.5-1.0; And / or, step (2) further includes: dissolving the block copolymer in tetrahydrofuran, then adding it to a second precipitant for precipitation, repeating this process 3-6 times, filtering it, and drying it at 30-50°C for 36-48 hours; And / or, the second precipitant is a mixed solution of toluene and petroleum ether in a volume ratio of 1:5-10.

23. The preparation method according to claim 22, wherein, The second initiator is one of azobisisobutyronitrile, azobisisoheptanenitrile, and dimethyl azobisisobutyrate.

24. The preparation method according to any one of claims 10-16, 18, and 20, wherein, In step (2), the conditions for the second polymerization reaction include: a reaction temperature of 60-80℃ and a reaction time of 5-24 h.

25. The preparation method according to claim 24, wherein, The second initiator is an azo initiator; And / or, the molar ratio of the first polymerization product, the monomer of formula (3) and the second initiator is 1:10-1000:0.5-1.0; And / or, step (2) further includes: dissolving the block copolymer in tetrahydrofuran, then adding it to a second precipitant for precipitation, repeating this process 3-6 times, filtering it, and drying it at 30-50°C for 36-48 hours; And / or, the second precipitant is a mixed solution of toluene and petroleum ether in a volume ratio of 1:5-10.

26. The preparation method according to claim 17, wherein, In step (2), the conditions for the second polymerization reaction include: a reaction temperature of 60-80℃ and a reaction time of 5-24 h.

27. The preparation method according to claim 26, wherein, The second initiator is an azo initiator; And / or, the molar ratio of the first polymerization product, the monomer of formula (3) and the second initiator is 1:10-1000:0.5-1.0; And / or, step (2) further includes: dissolving the block copolymer in tetrahydrofuran, then adding it to a second precipitant for precipitation, repeating this process 3-6 times, filtering it, and drying it at 30-50°C for 36-48 hours; And / or, the second precipitant is a mixed solution of toluene and petroleum ether in a volume ratio of 1:5-10.

28. The preparation method according to claim 19, wherein, In step (2), the conditions for the second polymerization reaction include: a reaction temperature of 60-80℃ and a reaction time of 5-24 h.

29. The preparation method according to claim 28, wherein, The second initiator is an azo initiator; And / or, the molar ratio of the first polymerization product, the monomer of formula (3) and the second initiator is 1:10-1000:0.5-1.0; And / or, step (2) further includes: dissolving the block copolymer in tetrahydrofuran, then adding it to a second precipitant for precipitation, repeating this process 3-6 times, filtering it, and drying it at 30-50°C for 36-48 hours; And / or, the second precipitant is a mixed solution of toluene and petroleum ether in a volume ratio of 1:5-10.

30. The preparation method according to claim 9, wherein, The reaction conditions include: ultrasonically dispersing the block copolymer and the silane coupling agent modified silica nanoparticles in tetrahydrofuran; reacting at 20-30℃ for 4-12 h using a reflux method; separating the precipitate, washing, and drying at 60-100℃ for 12-36 h to obtain block copolymer modified silica nanoparticles.

31. The preparation method according to claim 30, wherein, The silane coupling agent is selected from 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldiethoxysilane, anilinemethyltrimethoxysilane, or anilinemethyltriethoxysilane. And / or, the preparation method of the silane coupling agent modified silica nanoparticles includes: mixing anhydrous ethanol, deionized water, ammonia and tetraethyl orthosilicate for a first reaction, then adding a silane coupling agent for a second reaction for 2-5 h to obtain the silane coupling agent modified silica nanoparticles. And / or, the molar ratio of the anhydrous ethanol, deionized water, ammonia water to tetraethyl orthosilicate is 25-80∶2-5∶0.25-3.9∶1; And / or, the molar ratio of the tetraethyl orthosilicate to the silane coupling agent is 1:0.01-0.2; And / or, the conditions for the first reaction are: under stirring, reaction time of 12-24 h; reaction temperature of 20-30℃; And / or, the conditions for the second reaction are: under stirring, reaction time of 2-5 h; reaction temperature of 60-70℃; And / or, the preparation method further includes: washing the silane coupling agent modified silica nanoparticles in a dispersant, filtering them, and drying them at 70-90℃ for 12-24h, wherein the dispersant is deionized water and / or ethanol.

32. The preparation method according to any one of claims 10-16, 18, 20, 22-23 and 25-27, wherein, The reaction conditions include: ultrasonically dispersing the block copolymer and the silane coupling agent modified silica nanoparticles in tetrahydrofuran; reacting at 20-30℃ for 4-12 h using a reflux method; separating the precipitate, washing, and drying at 60-100℃ for 12-36 h to obtain block copolymer modified silica nanoparticles.

33. The preparation method according to claim 32, wherein, The silane coupling agent is selected from 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldiethoxysilane, anilinemethyltrimethoxysilane, or anilinemethyltriethoxysilane. And / or, the preparation method of the silane coupling agent modified silica nanoparticles includes: mixing anhydrous ethanol, deionized water, ammonia and tetraethyl orthosilicate for a first reaction, then adding a silane coupling agent for a second reaction for 2-5 h to obtain the silane coupling agent modified silica nanoparticles. And / or, the molar ratio of the anhydrous ethanol, deionized water, ammonia water to tetraethyl orthosilicate is 25-80∶2-5∶0.25-3.9∶1; And / or, the molar ratio of the tetraethyl orthosilicate to the silane coupling agent is 1:0.01-0.2; And / or, the conditions for the first reaction are: under stirring, reaction time of 12-24 h; reaction temperature of 20-30℃; And / or, the conditions for the second reaction are: under stirring, reaction time of 2-5 h; reaction temperature of 60-70℃; And / or, the preparation method further includes: washing the silane coupling agent modified silica nanoparticles in a dispersant, filtering them, and drying them at 70-90℃ for 12-24h, wherein the dispersant is deionized water and / or ethanol.

34. The preparation method according to claim 17, wherein, The reaction conditions include: ultrasonically dispersing the block copolymer and the silane coupling agent modified silica nanoparticles in tetrahydrofuran; reacting at 20-30℃ for 4-12 h using a reflux method; separating the precipitate, washing, and drying at 60-100℃ for 12-36 h to obtain block copolymer modified silica nanoparticles.

35. The preparation method according to claim 34, wherein, The silane coupling agent is selected from 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldiethoxysilane, anilinemethyltrimethoxysilane, or anilinemethyltriethoxysilane. And / or, the preparation method of the silane coupling agent modified silica nanoparticles includes: mixing anhydrous ethanol, deionized water, ammonia and tetraethyl orthosilicate for a first reaction, then adding a silane coupling agent for a second reaction for 2-5 h to obtain the silane coupling agent modified silica nanoparticles. And / or, the molar ratio of the anhydrous ethanol, deionized water, ammonia water to tetraethyl orthosilicate is 25-80∶2-5∶0.25-3.9∶1; And / or, the molar ratio of the tetraethyl orthosilicate to the silane coupling agent is 1:0.01-0.2; And / or, the conditions for the first reaction are: under stirring, reaction time of 12-24 h; reaction temperature of 20-30℃; And / or, the conditions for the second reaction are: under stirring, reaction time of 2-5 h; reaction temperature of 60-70℃; And / or, the preparation method further includes: washing the silane coupling agent modified silica nanoparticles in a dispersant, filtering them, and drying them at 70-90℃ for 12-24h, wherein the dispersant is deionized water and / or ethanol.

36. The preparation method according to claim 19, wherein, The reaction conditions include: ultrasonically dispersing the block copolymer and the silane coupling agent modified silica nanoparticles in tetrahydrofuran; reacting at 20-30℃ for 4-12 h using a reflux method; separating the precipitate, washing, and drying at 60-100℃ for 12-36 h to obtain block copolymer modified silica nanoparticles.

37. The preparation method according to claim 36, wherein, The silane coupling agent is selected from 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldiethoxysilane, anilinemethyltrimethoxysilane, or anilinemethyltriethoxysilane. And / or, the preparation method of the silane coupling agent modified silica nanoparticles includes: mixing anhydrous ethanol, deionized water, ammonia and tetraethyl orthosilicate for a first reaction, then adding a silane coupling agent for a second reaction for 2-5 h to obtain the silane coupling agent modified silica nanoparticles. And / or, the molar ratio of the anhydrous ethanol, deionized water, ammonia water to tetraethyl orthosilicate is 25-80∶2-5∶0.25-3.9∶1; And / or, the molar ratio of the tetraethyl orthosilicate to the silane coupling agent is 1:0.01-0.2; And / or, the conditions for the first reaction are: under stirring, reaction time of 12-24 h; reaction temperature of 20-30℃; And / or, the conditions for the second reaction are: under stirring, reaction time of 2-5 h; reaction temperature of 60-70℃; And / or, the preparation method further includes: washing the silane coupling agent modified silica nanoparticles in a dispersant, filtering them, and drying them at 70-90℃ for 12-24h, wherein the dispersant is deionized water and / or ethanol.

38. The preparation method according to claim 21, wherein, The reaction conditions include: ultrasonically dispersing the block copolymer and the silane coupling agent modified silica nanoparticles in tetrahydrofuran; reacting at 20-30℃ for 4-12 h using a reflux method; separating the precipitate, washing, and drying at 60-100℃ for 12-36 h to obtain block copolymer modified silica nanoparticles.

39. The preparation method according to claim 38, wherein, The silane coupling agent is selected from 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldiethoxysilane, anilinemethyltrimethoxysilane, or anilinemethyltriethoxysilane. And / or, the preparation method of the silane coupling agent modified silica nanoparticles includes: mixing anhydrous ethanol, deionized water, ammonia and tetraethyl orthosilicate for a first reaction, then adding a silane coupling agent for a second reaction for 2-5 h to obtain the silane coupling agent modified silica nanoparticles. And / or, the molar ratio of the anhydrous ethanol, deionized water, ammonia water to tetraethyl orthosilicate is 25-80∶2-5∶0.25-3.9∶1; And / or, the molar ratio of the tetraethyl orthosilicate to the silane coupling agent is 1:0.01-0.2; And / or, the conditions for the first reaction are: under stirring, reaction time of 12-24 h; reaction temperature of 20-30℃; And / or, the conditions for the second reaction are: under stirring, reaction time of 2-5 h; reaction temperature of 60-70℃; And / or, the preparation method further includes: washing the silane coupling agent modified silica nanoparticles in a dispersant, filtering them, and drying them at 70-90℃ for 12-24h, wherein the dispersant is deionized water and / or ethanol.

40. The preparation method according to claim 24, wherein, The reaction conditions include: ultrasonically dispersing the block copolymer and the silane coupling agent modified silica nanoparticles in tetrahydrofuran; reacting at 20-30℃ for 4-12 h using a reflux method; separating the precipitate, washing, and drying at 60-100℃ for 12-36 h to obtain block copolymer modified silica nanoparticles.

41. The preparation method according to claim 40, wherein, The silane coupling agent is selected from 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldiethoxysilane, anilinemethyltrimethoxysilane, or anilinemethyltriethoxysilane. And / or, the preparation method of the silane coupling agent modified silica nanoparticles includes: mixing anhydrous ethanol, deionized water, ammonia and tetraethyl orthosilicate for a first reaction, then adding a silane coupling agent for a second reaction for 2-5 h to obtain the silane coupling agent modified silica nanoparticles. And / or, the molar ratio of the anhydrous ethanol, deionized water, ammonia water to tetraethyl orthosilicate is 25-80∶2-5∶0.25-3.9∶1; And / or, the molar ratio of the tetraethyl orthosilicate to the silane coupling agent is 1:0.01-0.2; And / or, the conditions for the first reaction are: under stirring, reaction time of 12-24 h; reaction temperature of 20-30℃; And / or, the conditions for the second reaction are: under stirring, reaction time of 2-5 h; reaction temperature of 60-70℃; And / or, the preparation method further includes: washing the silane coupling agent modified silica nanoparticles in a dispersant, filtering them, and drying them at 70-90℃ for 12-24h, wherein the dispersant is deionized water and / or ethanol.

42. Block copolymer modified silica nanoparticles prepared by the preparation method according to any one of claims 4-41.

43. The application of the block copolymer modified silica nanoparticles according to any one of claims 1-3 and 42 in enhancing oil recovery.

44. An oil displacement agent, characterized in that, The oil displacement agent comprises: 99.5%-99.9% by mass of water and 0.1%-0.5% by mass of the block copolymer modified silica nanoparticles as described in any one of claims 1-3 and 42.

45. The application of the oil displacement agent according to claim 44 in enhancing oil recovery.

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