Environment-friendly oil-phase-free clean nano-microsphere and preparation method thereof

Abstract

The invention belongs to the technical field of oilfield chemistry, and particularly provides an environment-friendly oil-phase-free clean nano-microsphere and a preparation method of the environment-friendly oil-phase-free clean nano-microsphere. The nano microsphere is prepared from the following raw materials: 60 to 90 parts of an oil-free phase solvent, 50 to 70 parts of acrylamide, 25 to 35 parts of an anionic unsaturated monomer, 9 to 15 parts of a functional monomer, 3 to 7 parts of a cosolvent, 1 to 2 parts of modified nano silicon dioxide, 0.2 to 0.4 part of an initiator, 0.005 to 0.02 part of a cross-linking agent and 300 to 400 parts of distilled water. The nano-microsphere disclosed by the invention is good in expansion performance, excellent in high temperature resistance and salt resistance, excellent in deep profile control and displacement capacity, free of an oil-phase solvent, environment-friendly and pollution-free, and important support is provided for green transformation of oilfield exploitation.

Description

Technical Field

[0001] The present invention belongs to the technical field of oilfield chemistry, and particularly relates to an environmentally friendly oil-free clean nano-microsphere and a preparation method thereof. Background Art

[0002] In the context of the global energy structure's transformation towards low carbon, the efficient exploration and development of unconventional oil and gas resources such as deep and ultra-deep reservoirs are of great significance. The reservoir geological conditions of such resources are extremely complex, usually having high-temperature, high-pressure, and high-salt environments, and developing a large number of nano-scale to micro-scale fractures. During the drilling process, fractures will not only affect the oilfield recovery rate but also cause problems such as wellbore collapse and caving, seriously affecting the drilling efficiency and safety.

[0003] To solve these problems, nano-sealing agents for drilling fluids have emerged as the times require. Polyacrylamide microspheres exhibit excellent sealing performance due to their characteristics of swelling in water and not swelling in oil, and can effectively change the flow direction of injected water, improve the sweep coefficient of injected water, and thus enhance the oil recovery rate. It can be seen that the application of polyacrylamide microspheres for profile control and displacement has become a new type of deep profile control and plugging technology in the oilfield exploitation field. However, polyacrylamide microspheres are mostly prepared by inverse suspension polymerization and inverse (micro) emulsion polymerization methods. Inverse suspension polymerization requires dispersing raw materials in an oil-soluble medium, and the thermodynamic stability of the polymerization system is poor; in the process of inverse (micro) emulsion polymerization, emulsifiers are needed to disperse polymerization monomers in the oil-phase medium. Inevitably, both raw materials will contain oil-phase solvents, which will cause formation pollution and harm the environment.

[0004] Chinese patent document CN 109735311 B discloses an environmentally friendly sealing agent for drilling fluids and a preparation method thereof. The sealing agent includes the following raw materials: modified starch, lignocellulose, antioxidant, nano-calcium carbonate, and dispersant. The obtained sealing agent is environmentally friendly and has good sealing effect, but the particle size distribution of this invention is not explored, and it may not be able to effectively seal and profile control smaller nano-scale fractures. Chinese patent document CN 113527577 B discloses a preparation method and application of hyperbranched polyacrylamide nano-microspheres for profile control in low-porosity and low-permeability oil reservoirs. The nano-microspheres contain the following raw materials: benzene hexacarboxylic acid, diallylamine, acrylamide, anionic unsaturated monomer, N,N'-methylenebisacrylamide, deionized water, EDC·HCl, complexing agent, stabilizer, crosslinking agent, oxidant, emulsifier, oil-soluble solvent, and a reducing agent solution with a mass concentration of 5%. The nano-microspheres of this invention can expand under high-temperature and high-salt conditions. However, the use of a large amount of oil-soluble solvents causes greater harm to the environment.

[0005] Therefore, there is an urgent need to develop an oil-free, salt-resistant, high-temperature-resistant nano-microsphere with deep profile control and displacement ability, so as to achieve the purpose of improving the oilfield exploitation efficiency. Summary of the Invention

[0006] Aiming at the existing technical problems, the purpose of the present invention is to provide an environmentally friendly oil-phase-free clean nano-microsphere and its preparation method. The nano-microsphere of the present invention has good swelling performance, excellent high-temperature resistance and salt resistance, has excellent deep profile control and displacement ability, and does not contain oil-phase solvents, is environmentally friendly and pollution-free, providing important support for the green transformation of oilfield exploitation.

[0007] In order to achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0008] On the one hand, the present invention provides an environmentally friendly oil-phase-free clean nano-microsphere. By weight, the nano-microsphere comprises the following raw materials: 60-90 parts of oil-phase-free solvent, 50-70 parts of acrylamide, 25-35 parts of anionic unsaturated monomer, 9-15 parts of functional monomer, 3-7 parts of cosolvent, 1-2 parts of modified nano-silica, 0.2-0.4 parts of initiator, 0.005-0.02 parts of crosslinking agent, and 300-400 parts of distilled water.

[0009] The reaction mechanism and function of the present invention are as follows:

[0010] 1. The present invention uses polyethylene glycol solvents and polyol solvents as oil-phase-free solvents, which not only improve the density and viscosity of the system, but also have good fluidity, can enter the deep formation for profile control and displacement, and improve the oilfield exploitation efficiency; at the same time, the preparation method of the present invention overcomes the deficiencies of using oil-phase organic solvents in inverse suspension polymerization and inverse (micro) emulsion polymerization, is conducive to reducing environmental hazards, conforms to the concept of sustainable development, and provides important support for the green transformation of oilfield exploitation.

[0011] 2. In addition to acrylamide, the present invention also introduces anionic unsaturated monomers and functional monomers to improve the high-temperature resistance, salt resistance and shear resistance of polyacrylamide microspheres. On the one hand, the sulfonic acid groups on the anionic unsaturated monomers endow the nano-microspheres with good salt resistance and high-temperature resistance, and are conducive to the formation of the cross-linked structure of the nano-microspheres. On the other hand, the present invention prepares functional monomers by selecting and regulating the ratio of specific monomers. Using diacetone acrylamide as the main monomer and introducing N-acryloylmorpholine monomer, the morpholine group is a six-membered ring structure with high thermal stability and chemical stability, and its ring structure and hydrophilic properties provide good high-temperature resistance and salt resistance for the polymer; introducing β-(acryloyloxy) propionic acid will cause the functional monomer to ionize in a high-salt environment, and these ionized groups will undergo ion exchange or electrostatic interaction with salts in aqueous solution, thereby enhancing the salt resistance of the polymer; and the addition of a small amount of mercaptoethylenediamine helps to effectively regulate the molecular weight of the polymer during the polymerization process, and the resulting functional monomer exhibits excellent high-temperature resistance and salt resistance.

[0012] 3. Nano-silica is prone to agglomeration, making it difficult to be evenly distributed in the plugging agent and affecting the plugging effect. In the present invention, 2-(chloromethyl)allyltrimethoxysilane and 1-(3-aminophenyl)pyrrolidin-2-one are used to modify nano-silica jointly. Through the reaction, the double bonds grafted on its surface will crosslink with the monomers in the polymerization system, enabling it to be evenly dispersed in the polymerization system. Furthermore, it can better interact with the pores and fractures of the formation to form a dense plugging layer. At the same time, the high temperature resistance of the nano-microspheres is also improved, which helps the nano-microspheres to enter the deep formation for profile control and displacement. In addition, during the modification process, the chlorine group on 2-(chloromethyl)allyltrimethoxysilane and the amino group on 1-(3-aminophenyl)pyrrolidin-2-one will react to generate a quaternary ammonium salt structure. This not only improves the antibacterial property of the nano-microspheres, but also helps to reduce the surface tension and enhance the oil displacement effect, thereby increasing the oil recovery rate of the oilfield.

[0013] In some embodiments, the oil-free phase solvent is a composition of polyethylene glycol solvents and polyol solvents.

[0014] Preferably, the mass ratio of the polyethylene glycol solvents to the polyol solvents is (20 - 25):1.

[0015] More preferably, the polyethylene glycol solvent is any one or more of polyethylene glycol 200, polyethylene glycol 400, polyethylene glycol 600, and polyethylene glycol 800.

[0016] More preferably, the polyol solvent is any one or more of 1,4-butanediol, propylene glycol, and glycerol.

[0017] More preferably, the oil-free phase solvent is polyethylene glycol 400 and 1,4-butanediol, and the mass ratio of the two is 22:1.

[0018] In some embodiments, the anionic unsaturated monomer is 2-acrylamido-2-methylpropanesulfonic acid.

[0019] In some embodiments, the preparation method of the functional monomer comprises the following steps:

[0020] Mix diacetone acrylamide, N-acryloylmorpholine, β-(acryloyloxy)propionic acid, mercaptoethylenediamine, and distilled water, add an initiator, pre-polymerize at 10 - 20 °C for 2 - 4 h, raise the temperature to 40 - 75 °C and react for 6 - 10 h, dialyze, and dry to obtain the functional monomer.

[0021] In some embodiments, the mass ratio of diacetone acrylamide, N-acryloylmorpholine, and β-(acryloyloxy)propionic acid is 10:(2.5 - 5):(1 - 2).

[0022] Preferably, the mass ratio of the diacetone acrylamide to the mercaptoethylenediamine is 10:(0.1 - 0.2).

[0023] In some embodiments, the co-solvent is any one or more of N,N-dimethylformamide, methanol, and propylene glycol methyl ether.

[0024] In some embodiments, the method for preparing the modified nano-silica comprises the following steps:

[0025] Q1. Mix nano-silica, 2-(chloromethyl)allyltrimethoxysilane, and distilled water, heat to 70 - 85 °C and react for 5 - 8 h, wash, and dry to obtain a product;

[0026] Q2. Mix the product obtained in step Q1 with 1-(3-aminophenyl)pyrrolidin-2-one, heat to 80 - 90 °C and react for 6 - 10 h, extract with acetonitrile, wash, and dry to obtain the modified nano-silica.

[0027] In some embodiments, the mass ratio of the nano-silica to the 2-(chloromethyl)allyltrimethoxysilane in step Q1 is 1:(0.4 - 0.6).

[0028] Preferably, the mass ratio of the nano-silica to the distilled water in step Q1 is 1:(8 - 10).

[0029] In some embodiments, the mass ratio of the product to the 1-(3-aminophenyl)pyrrolidin-2-one in step Q2 is 1:(0.6 - 1).

[0030] In some embodiments, the initiator is azodiisobutylamidine hydrochloride.

[0031] In some embodiments, the crosslinking agent is N,N-methylenebisacrylamide.

[0032] On the other hand, the present invention provides a method for preparing an environmentally friendly oil-free phase cleaning nano-microsphere, comprising the following steps:

[0033] S1. Mix an oil-free phase solvent and a part of distilled water, add the modified nano-silica and the crosslinking agent and mix, and stir under an inert gas to obtain a mixed solution;

[0034] S2. Mix acrylamide, anionic unsaturated monomer, functional monomer, co-solvent and the remaining part of distilled water, adjust the pH value to neutral, add to the mixed solution obtained in step S1, heat to 50 - 60 °C, dropwise add the initiator, and react under an inert gas for 1.5 - 3 h to obtain nano-microspheres.

[0035] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0036] 1. The nano - microspheres of the present invention have good swelling performance, excellent high - temperature resistance and salt resistance, possess excellent deep - profile control and displacement ability, and do not contain oil - phase solvents, being environmentally friendly and pollution - free, providing important support for the green transformation of oil - field exploitation.

[0037] 2. The present invention uses polyethylene glycol solvents and polyol solvents as oil - free solvents, which not only improve the density and viscosity of the system, enhance the fluidity, but also reduce the environmental hazards.

[0038] 3. The functional monomers of the present invention exhibit good high - temperature resistance, salt resistance and shear resistance, are suitable for oil - field displacement agents, and the entire preparation process uses aqueous solution polymerization, avoiding the use of organic solvents and meeting the requirements of green chemistry.

[0039] 4. The present invention modifies nano - silica with 2 - (chloromethyl) allyltrimethoxysilane and 1 - (3 - aminophenyl) pyrrolidin - 2 - one together, enabling it to be uniformly dispersed in the plugging agent and improving the plugging effect; at the same time, the modified nano - microspheres have enhanced high - temperature resistance, and the reaction between chlorine groups and amino groups generates a quaternary ammonium salt structure, endowing the microspheres with antibacterial properties and the characteristic of reducing surface tension, thereby improving the oil - displacement effect and enhancing the oil - field recovery rate. Detailed implementation manners

[0040] The following will illustrate the present invention in combination with specific implementation schemes. It should be noted that the following examples are examples of the present invention, only used to illustrate the present invention, rather than to limit the present invention. Without departing from the main idea or scope of the present invention, other combinations and various improvements within the concept of the present invention can be made.

[0041] Prepare each nano - microsphere according to the ratio of each raw material and the preparation method specified in the following examples and comparative examples.

[0042] For the convenience of those skilled in the art to implement the present invention, the manufacturers of some raw materials in the examples and comparative examples are described as follows:

[0043] Polyethylene glycol 400: Purchased from Shandong Baihua Chemical Co., Ltd.;

[0044] Nano - silica: particle size 50nm;

[0045] Other raw materials, without special instructions, can be purchased from the market.

[0046] Preparation Example 1

[0047] The preparation method of functional monomer A includes the following steps:

[0048] Mix 1000 g of diacetone acrylamide, 375 g of N - acryloyl morpholine, 150 g of β - (acryloyloxy) propionic acid, 22.8 g of mercaptoethylenediamine, and 6 L of distilled water. Add 15 g of potassium persulfate, pre - polymerize at 15°C for 3 h, raise the temperature to 65°C and react for 8 h, perform dialysis treatment for 48 h, change the distilled water every 12 h, and freeze - dry at a pre - freezing temperature of - 40°C for 24 h to obtain functional monomer A.

[0049] Preparation Example 2

[0050] The preparation method of functional monomer B is the same as that of Preparation Example 1, except that the addition amount of N - acryloyl morpholine is 230 g.

[0051] Preparation Example 3

[0052] The preparation method of functional monomer C is the same as that of Preparation Example 1, except that the addition amount of β - (acryloyloxy) propionic acid is 80 g.

[0053] Preparation Example 4

[0054] The preparation method of modified nano - silica A comprises the following steps:

[0055] Q1. Mix 200 g of nano - silica, 100 g of 2 - (chloromethyl) allyltrimethoxysilane, and 1800 g of distilled water, stir evenly, heat to 80°C and react for 7 h, and dry at 100°C for 4 h to obtain a product;

[0056] Q2. Mix 100 g of the product obtained in step Q1 and 80 g of 1 - (3 - aminophenyl) pyrrolidin - 2 - one, stir evenly, heat to 85°C and react for 8 h, extract with acetonitrile for 24 h, wash twice with distilled water, and dry at 100°C to constant weight to obtain modified nano - silica A.

[0057] Preparation Example 5

[0058] The preparation method of modified nano - silica B is the same as that of Preparation Example 4, except that the addition amount of 2 - (chloromethyl) allyltrimethoxysilane in step Q1 is 160 g.

[0059] Preparation Example 6

[0060] The preparation method of modified nano - silica C is the same as that of Preparation Example 4, except that the addition amount of 1 - (3 - aminophenyl) pyrrolidin - 2 - one in step Q2 is 58 g.

[0061] Example 1

[0062] An environmentally friendly oil-free cleaning nano-microsphere. By weight, the nano-microsphere comprises the following raw materials: 75 parts of an oil-free solvent, 60 parts of acrylamide, 30 parts of 2-acrylamido-2-methylpropanesulfonic acid, 12 parts of functional monomer A, 5 parts of propylene glycol methyl ether, 1.5 parts of modified nano-silica A, 0.3 part of azobisisobutyramidine hydrochloride, 0.0125 part of N,N'-methylenebisacrylamide, and 350 parts of distilled water; wherein, the oil-free solvent is polyethylene glycol 400 and 1,4-butanediol, and the mass ratio of the two is 22:1.

[0063] The preparation method of the nano-microsphere in this example comprises the following steps:

[0064] S1. Mix the oil-free solvent and 150 parts of distilled water, add modified nano-silica A and N,N'-methylenebisacrylamide, and stir evenly under nitrogen to obtain a mixed solution;

[0065] S2. Mix acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, functional monomer A, propylene glycol methyl ether with 200 parts of distilled water, adjust the pH value to neutral, add it to the mixed solution obtained in step S1, heat to 55 °C, dropwise add azobisisobutyramidine hydrochloride, and react for 2.5 h under nitrogen to obtain nano-microspheres.

[0066] Example 2

[0067] An environmentally friendly oil-free cleaning nano-microsphere. By weight, the nano-microsphere comprises the following raw materials: 60 parts of an oil-free solvent, 50 parts of acrylamide, 25 parts of 2-acrylamido-2-methylpropanesulfonic acid, 9 parts of functional monomer A, 3 parts of propylene glycol methyl ether, 1 part of modified nano-silica A, 0.2 part of azobisisobutyramidine hydrochloride, 0.005 part of N,N'-methylenebisacrylamide, and 300 parts of distilled water; wherein, the oil-free solvent is polyethylene glycol 400 and 1,4-butanediol, and the mass ratio of the two is 22:1.

[0068] The preparation method of the nano-microsphere in this example comprises the following steps:

[0069] S1. Mix the oil-free solvent and 100 parts of distilled water, add modified nano-silica A and N,N'-methylenebisacrylamide, and stir evenly under nitrogen to obtain a mixed solution;

[0070] S2. Mix acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, functional monomer A, propylene glycol methyl ether with 200 parts of distilled water, adjust the pH value to neutral, add it to the mixed solution obtained in step S1, heat to 60 °C, dropwise add azobisisobutyramidine hydrochloride, and react for 1.5 h under nitrogen to obtain nano-microspheres.

[0071] Example 3

[0072] An environmentally friendly oil-free cleaning nano microsphere. By weight, the nano microsphere comprises the following raw materials: 90 parts of an oil-free solvent, 70 parts of acrylamide, 35 parts of 2-acrylamido-2-methylpropane sulfonic acid, 15 parts of functional monomer A, 7 parts of propylene glycol methyl ether, 2 parts of modified nano-silica A, 0.4 part of azodiisobutyramidine hydrochloride, 0.02 part of N,N'-methylenebisacrylamide, and 400 parts of distilled water; wherein, the oil-free solvent is polyethylene glycol 400 and 1,4-butanediol, and the mass ratio of the two is 22:1.

[0073] The preparation method of the nano microsphere of this embodiment comprises the following steps:

[0074] S1. Mix the oil-free solvent and 150 parts of distilled water, add the modified nano-silica A and N,N'-methylenebisacrylamide and mix them, and stir evenly under nitrogen to obtain a mixed solution;

[0075] S2. Mix acrylamide, 2-acrylamido-2-methylpropane sulfonic acid, functional monomer A, propylene glycol methyl ether with 250 parts of distilled water, adjust the pH value to neutral, add it to the mixed solution obtained in step S1, heat to 50 °C, dropwise add azodiisobutyramidine hydrochloride, and react for 3 h under nitrogen to obtain the nano microsphere.

[0076] Example 4

[0077] An environmentally friendly oil-free cleaning nano microsphere and its preparation method. The specific implementation manner is the same as that of Example 1, except that an equal amount of functional monomer B is used to replace functional monomer A.

[0078] Example 5

[0079] An environmentally friendly oil-free cleaning nano microsphere and its preparation method. The specific implementation manner is the same as that of Example 1, except that an equal amount of functional monomer C is used to replace functional monomer A.

[0080] Example 6

[0081] An environmentally friendly oil-free cleaning nano microsphere and its preparation method. The specific implementation manner is the same as that of Example 1, except that an equal amount of modified nano-silica B is used to replace modified nano-silica A.

[0082] Example 7

[0083] An environmentally friendly oil-free cleaning nano microsphere and its preparation method. The specific implementation manner is the same as that of Example 1, except that an equal amount of modified nano-silica C is used to replace modified nano-silica A.

[0084] Comparative Example 1

[0085] An environmentally friendly oil-free cleaning nano microsphere and its preparation method. The specific implementation manner is the same as that of Example 1, except that commercially available nano-silica of equal amount is used to replace the modified nano-silica A.

[0086] Effect evaluation:

[0087] The nano microspheres prepared in the above Examples 1-7 and Comparative Example 1 were tested and analyzed. The specific results are shown in Tables 1-2.

[0088] Performance test:

[0089] (1) Swelling performance test:

[0090] The nano microspheres of Examples 1-3 were dispersed in sodium chloride brine to prepare an aqueous dispersion solution with a salinity of 3000 mg / L. After stirring evenly, it was placed in an incubator at 70 °C and left standing for 0 days, 6 days, 12 days, and 20 days. After taking out, the particle size was detected using a laser particle size analyzer. The specific results are shown in Table 1;

[0091] (2) High temperature resistance performance test:

[0092] The nano microspheres of Examples 1-7 and Comparative Example 1 were dispersed in sodium chloride brine to prepare an aqueous dispersion solution with a salinity of 3000 mg / L. After stirring evenly, it was placed in an incubator at 70 °C and 140 °C and left standing for 20 days. After taking out, the particle size was detected using a laser particle size analyzer. The specific results are shown in Table 2;

[0093] (3) Salt tolerance performance test:

[0094] The nano microspheres of Examples 1-7 and Comparative Example 1 were dispersed in sodium chloride brine to prepare aqueous dispersion solutions with salinities of 3000 mg / L and 30000 mg / L. After stirring evenly, it was placed in an incubator at 70 °C and left standing for 20 days. After taking out, the particle size was detected using a laser particle size analyzer. The specific results are shown in Table 2.

[0095] Table 1

[0096]

[0097] As can be seen from Table 1, the swelling performance of Examples 1-3 is good, with excellent plugging performance, and the particle size expands relatively slowly in the early stage, which is beneficial for the nano microspheres to enter the deep formation, so as to carry out deep profile control and plugging and improve the oilfield recovery rate.

[0098] Table 2

[0099]

[0100] From the results in Table 1, it can be seen that the nano-microspheres prepared in Examples 1-3 have good high-temperature resistance and salt resistance.

[0101] Compared with Example 1, in Examples 4-5, when preparing the functional monomer, the mass ratios of diacetone acrylamide, N-acryloylmorpholine, and β-(acryloyloxy) propionic acid were changed. In Example 4, the morpholine group decreased and the rigid structure weakened, resulting in a decrease in the high-temperature resistance and salt resistance of the nano-microspheres; in Example 5, the carboxylic acid group decreased and the ionization effect decreased, thereby causing a decrease in the salt resistance of the nano-microspheres.

[0102] Compared with Example 1, when preparing the modified nano-silica, in Example 6, the mass ratio of nano-silica and 2-(chloromethyl) allyltrimethoxysilane was changed, and the crosslinking density of the nano-silica and the polymer system increased. Although the high-temperature resistance of the nano-microspheres was improved to a certain extent, the overall swelling effect of the nano-microspheres became worse; in Example 7, the mass ratio of the product and 1-(3-aminophenyl) pyrrolidin-2-one was changed, and the quaternary ammonium salt structure decreased, affecting the surface tension of the nano-silica, and further affecting the high-temperature resistance and salt resistance of the nano-microspheres;

[0103] Compared with Example 1, in Comparative Example 1, the same amount of commercially available nano-silica was used, which affected the dispersion uniformity of the nano-silica, and further affected the high-temperature resistance and salt resistance of the nano-microspheres.

[0104] As mentioned above, it is only a preferred embodiment of the present invention, and does not impose any form of limitation on this application. Although this application is disclosed with preferred embodiments as above, it is not used to limit this application. Any person skilled in the art, within the scope of the technical solution of this application, making some changes or modifications using the disclosed technical content is equivalent to equivalent implementation cases. However, as long as it does not depart from the technical solution content of the present invention, any simple modification, equivalent change, and modification made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution.

Claims

1. An environmentally friendly oil-free cleaning nano microsphere, characterized in that By weight, the nano-microspheres comprise the following raw materials: 60 - 90 parts of oil-free phase solvent, 50 - 70 parts of acrylamide, 25 - 35 parts of anionic unsaturated monomer, 9 - 15 parts of functional monomer, 3 - 7 parts of co-solvent, 1 - 2 parts of modified nano-silica, 0.2 - 0.4 parts of initiator, 0.005 - 0.02 parts of cross-linking agent, and 300 - 400 parts of distilled water.

2. The environmentally friendly oil-free cleaning nano microspheres according to claim 1, characterized in that, The oil-free phase solvent is a composition of polyethylene glycol solvents and polyol solvents.

3. The environmentally friendly oil-free cleaning nano microsphere according to claim 1, wherein, The anionic unsaturated monomer is 2-acrylamido-2-methylpropanesulfonic acid.

4. The environmentally friendly oil-free cleaning nano microsphere according to claim 1, characterized in that The preparation method of the functional monomer comprises the following steps: Mix diacetone acrylamide, N-acryloylmorpholine, β-(acryloyloxy)propionic acid, mercaptoethylenediamine, and distilled water, add an initiator, pre-polymerize at 10 - 20 °C for 2 - 4 h, raise the temperature to 40 - 75 °C and react for 6 - 10 h, dialyze, and dry to obtain the functional monomer.

5. The environmentally friendly oil-free cleaning nano microsphere according to claim 4, characterized in that The mass ratio of diacetone acrylamide, N-acryloylmorpholine, and β-(acryloyloxy)propionic acid is 10:(2.5 - 5):(1 - 2).

6. The environmentally friendly oil-free cleaning nano microsphere according to claim 1, characterized in that, The co-solvent is any one or more of N,N-dimethylformamide, methanol, and propylene glycol methyl ether.

7. An environmentally friendly oil-free cleaning nano microsphere according to claim 1, characterized in that The preparation method of the modified nano-silica is characterized by comprising the following steps: Q1. Mix nano-silica, 2-(chloromethyl)allyltrimethoxysilane, and distilled water, heat to 70 - 85 °C and react for 5 - 8 h, wash, and dry to obtain a product; Q2. Mix the product obtained in step Q1 with 1-(3-aminophenyl)pyrrolidin-2-one, heat to 80 - 90 °C and react for 6 - 10 h, extract with acetonitrile, wash, and dry to obtain the modified nano-silica.

8. An environmentally friendly oil-free cleaning nano microsphere according to claim 7, characterized in that, In step Q1, the mass ratio of nano-silica to 2-(chloromethyl)allyltrimethoxysilane is 1:(0.4 - 0.6).

9. An environmentally friendly oil-free cleaning nano microsphere according to claim 7, characterized in that, In step Q2, the mass ratio of the product to 1-(3-aminophenyl)pyrrolidin-2-one is 1:(0.6 - 1).

10. A method for preparing the environmentally friendly oil-free cleaning nano microspheres according to any one of claims 1-9, characterized in that, Comprises the following steps: S1. Mix the oil-free phase solvent and a part of distilled water, add the modified nano-silica and the cross-linking agent, and stir under an inert gas to obtain a mixed solution; S2. Mix acrylamide, anionic unsaturated monomer, functional monomer, co-solvent, and the remaining part of distilled water, adjust the pH value to neutral, add it to the mixed solution obtained in step S1, heat to 50 - 60 °C, dropwise add the initiator, and react under an inert gas for 1.5 - 3 h to obtain the nano-microspheres.

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