Nano imbibition agent suitable for shale oil reservoir and preparation method of nano imbibition agent

Abstract

The invention provides a nano imbibition agent suitable for shale oil reservoirs and a preparation method of the nano imbibition agent. The nano imbibition agent is prepared from the following substances in percentage by mass: 0.02 to 0.1 percent of surface in-situ polymerization modified nanoparticles, 0.3 to 0.5 percent of I-type surfactant, 0.2 to 0.3 percent of II-type surfactant, 0.5 percent of clay stabilizer and the balance of water. According to the method, the oil film on the rock surface is stripped in a manner of cooperation of the surface in-situ polymerization modified nanoparticles and the surfactant, surfactant molecules are spontaneously arranged on an oil-water-solid three-phase interface, and the oil-water interface tension and the adsorption energy of the oil film on the rock surface are remarkably reduced, so that the wettability of the rock surface is improved. After the nanoparticles are arranged on the oil-water-solid three-phase interface, the free energy of the interface is further reduced, and the redundant nanoparticles are distributed in a wedge-shaped area between an oil film and the rock surface to generate additional osmotic pressure from outside to inside to form another force-diffusion force, so that the oil film is promoted to be stripped, and the oil washing efficiency is obviously improved compared with that of a pure surfactant.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas field development technology research, and specifically relates to a nano-imbibition agent suitable for shale oil reservoirs and a preparation method thereof. Background Art

[0002] As one of the important alternative energy sources in my country, shale oil is of great significance for its large-scale and effective development. In the process of studying the shale oil imbibition system, it was found that nanomaterials and nano-like particles have received widespread attention due to their excellent performance. They exert good wettability improvement performance through intermolecular forces and their own surface effects. However, due to their extremely high specific surface area, nanomaterials cause the particles to aggregate and become larger, showing extremely poor dispersion stability, which hinders their migration in the porous media of the reservoir, greatly limiting their further application. Therefore, the ultra-high dispersion stability of nanoparticles in ultra-low permeability oil and gas reservoirs is critical for the effective imbibition effect.

[0003] Conventional methods are mostly to increase the dispersibility of nanoparticles by grafting chemical functional groups on the surface of nanoparticles to increase the electrostatic repulsion effect, but the improvement effect is not outstanding. Qin Wenlong et al. (CN113527601A) grafted polymers onto the surface of nanoparticles and invented a high-temperature and high-salt resistant nano oil-displacing agent and its preparation method. The nano oil-displacing agent is a core-shell structure nanomaterial formed by initiating the polymerization of monomer AMPS on the surface of ferroferric oxide nanoparticles after amino modification. The invention solves the problem of poor dispersion stability of traditional nano oil-displacing agents under high temperature and high salt conditions. Compared with before modification, amino-modified nano Fe3O4 has stronger dispersion stability. Under 120°C, it can be stable in API saline for 19 days. At the same time, it can resist CaCl2 up to 70,000 mg / L and NaCl up to 200,000 mg / L at room temperature. However, although the nanofluid has good wettability improvement performance, the effect of reducing interfacial tension is not obvious. Low interfacial tension can significantly reduce the desorption energy of the oil film and thus increase the oil washing efficiency. Meeting these two points at the same time is the key to improving the infiltration effect. Surfactants can significantly reduce the interfacial tension between oil and water. Wu Wenwei et al. (CN114410286A) invented and disclosed a heat-resistant and salt-resistant nano-imbibition oil-displacing agent and its preparation method and application. The active nanomaterial is prepared by initiating polymerization of double-bond-modified flaky nanomaterials with hydrophilic monomers and hydrophobic monomers to prepare surface amphiphilic nanomaterials, and then compounding heat-resistant anionic surfactants and salt-resistant nonionic surfactants to prepare nano-imbibition oil-displacing agents. The application effect was studied using the core of the Chang 6 block. The results showed that the nano-imbibition oil-displacing agent has good heat and salt resistance and can reduce interfacial tension by up to 10 -4mN / m, and the imbibition efficiency obtained by the synergistic effect of functionalized nanoparticles and surfactants is significantly higher than that of pure nanoparticle fluids and pure surfactant fluids. It can be seen that nanoparticle composite surfactants can further improve the imbibition replacement performance, and the imbibition replacement rate is as high as 39.19%. However, the application of this invention in high-mineralization and high-temperature reservoirs such as shale is obviously limited. Summary of the invention

[0004] The purpose of the present invention is to provide a nano-imbibition agent suitable for shale oil reservoirs, so as to overcome the above-mentioned technical problems existing in the prior art.

[0005] Another object of the present invention is to provide a method for preparing a nano-imbibing agent suitable for shale oil reservoirs, wherein surface in-situ polymerization-modified nanoparticles are obtained through polymerization reaction, and the nanoparticles maintain a good stretch state in a high temperature and high salt environment while having a high electrostatic effect and a steric hindrance effect to maintain excellent dispersion stability.

[0006] To this end, the technical solution provided by the present invention is as follows: A nano-imbibition agent suitable for shale oil reservoirs is composed of the following substances in percentage by mass: 0.02-0.1% of surface in-situ polymerization-modified nano-particles, 0.3-0.5% of type I surfactant, 0.2-0.3% of type II surfactant, 0.5% of clay stabilizer, and the balance of water. The surface in-situ polymerized modified nanoparticles are obtained by polymerization reaction of amino modified nanosilica particles, temperature resistant monomers and salt resistant monomers, the mass sum of the temperature resistant monomers and the salt resistant monomers is 15-20% of the mass of the amino modified nanosilica particles, and the molar ratio of the temperature resistant monomers to the salt resistant monomers is 1:3-1:5.

[0007] The type I surfactant is one of the anionic surfactants heavy alkyl benzene sodium sulfonate and petroleum sulfonate.

[0008] The type II surfactant is one of the amphoteric betaine surfactants erucamidopropyl betaine, erucamidopropyl hydroxysulfonyl betaine and oleamidopropyl hydroxysulfonyl betaine.

[0009] The clay stabilizer is an inorganic salt NaCl or KCl.

[0010] The salt-resistant monomer is a sulfonic acid unsaturated double bond monomer, and the temperature-resistant monomer is a monomer with an unsaturated double bond of a cyclic functional group.

[0011] A method for preparing a nano-imbibing agent suitable for shale oil reservoirs comprises the following steps: uniformly dispersing a formulated amount of surface in-situ polymerized modified nanoparticles in an aqueous solution under ultrasonic stirring conditions at room temperature, then sequentially adding a formulated amount of a type I surfactant, a type II surfactant, and a clay stabilizer, and mechanically stirring the mixture until uniform.

[0012] The preparation process of the surface in-situ polymerization modified nanoparticles comprises the following steps: Step 1) adding water into a reaction container, filling with nitrogen to deoxygenate, adding a formulated amount of amino-modified nano-silicon dioxide particles, and uniformly dispersing them under ultrasonic and mechanical stirring conditions to obtain a nano-dispersed fluid; Step 2) adding a formulated amount of temperature-resistant monomer and salt-resistant monomer to the nano-dispersed fluid, and mechanically stirring until they are uniformly dissolved to obtain a mixed solution; Step 3) dissolving the initiator in water and then adding dropwise to the mixed solution, stirring and reacting at a constant temperature of 40-60° C. for 6-10 hours; wherein the mass of the initiator is 10-20% of the mass of the temperature-resistant monomer and the salt-resistant monomer, and the mass of the amino-modified nano-silica particles is 0.1-1% of the total mass of the water used to dissolve the initiator and the water added in step 1); Step 4) After the reaction is completed, cool to room temperature, use a high-speed centrifuge at a speed of 18000 rpm to separate the solid and liquid, wash with water three times, and then vacuum dry in an oven at 50°C to constant weight to obtain the product.

[0013] The amino-modified nano-silicon dioxide particles are one of industrial-grade spherical gas-phase nano-silicon dioxide and amorphous silica sol, and have an average particle size of 10-20 nm.

[0014] The initiator is one of ammonium persulfate, sodium persulfate and potassium persulfate.

[0015] The beneficial effects of the present invention are: The present invention uses surface in-situ polymerization modified nanoparticles and surfactants to peel off the oil film on the rock surface. The surfactant molecules are spontaneously arranged at the oil-water-solid three-phase interface, significantly reducing the oil-water interfacial tension and the adsorption energy of the oil film on the rock surface, thereby improving the wettability of the rock surface. After the nanoparticles are arranged at the oil-water-solid three-phase interface, the interfacial free energy is further reduced. The excess nanoparticles are distributed in the wedge-shaped area between the oil film and the rock surface to generate additional osmotic pressure from the outside to the inside to form another force - diffusion force, which promotes the peeling of the oil film, so that the oil washing efficiency is significantly increased compared with pure surfactants.

[0016] The present invention grafts salt-resistant monomers and cyclic temperature-resistant monomers on the surface of nanoparticles, so that the surface polymer molecules maintain a good stretch state in a high-temperature and high-salt environment, and at the same time cause the nanoparticles to have high electrostatic effect and steric hindrance effect to maintain excellent dispersion stability, which significantly broadens the application scope of nanoparticles as imbibing agents in complex oil and gas storage environments. This invention is of great value to the post-pressure increase of shale oil and gas reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1This is a schematic diagram of the principle of ultra-high dispersion and stability of surface in-situ polymerization-modified nanoparticles of the present invention; Figure 2 It is a schematic diagram of the oil film stripping mechanism of the present invention. DETAILED DESCRIPTION

[0018] The following describes the implementation of the present invention through specific embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification.

[0019] The exemplary embodiments of the present invention are now described with reference to the accompanying drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. These embodiments are provided to disclose the present invention in detail and completely and to fully convey the scope of the present invention to those skilled in the art. The terms used in the exemplary embodiments shown in the accompanying drawings are not intended to limit the present invention.

[0020] Unless otherwise specified, the terms (including technical terms) used herein have the commonly understood meanings to those skilled in the art. In addition, it is understood that the terms defined in commonly used dictionaries should be understood to have the same meanings as those in the context of the relevant fields, and should not be understood as idealized or overly formal meanings.

[0021] Example 1 The present embodiment provides a nano-imbibition agent suitable for shale oil reservoirs, which is composed of the following substances in percentage by mass: 0.02-0.1% surface in-situ polymerization-modified nanoparticles, 0.3-0.5% Class I surfactant, 0.2-0.3% Class II surfactant, 0.5% clay stabilizer, and the balance is water. The surface in-situ polymerized modified nanoparticles are obtained by polymerization reaction of amino modified nanosilica particles, temperature resistant monomers and salt resistant monomers, the mass sum of the temperature resistant monomers and the salt resistant monomers is 15-20% of the mass of the amino modified nanosilica particles, and the molar ratio of the temperature resistant monomers to the salt resistant monomers is 1:3-1:5.

[0022] The type I surfactant is one of the anionic surfactants heavy alkyl benzene sodium sulfonate and petroleum sulfonate.

[0023] The type II surfactant is one of the amphoteric betaine surfactants erucamidopropyl betaine, erucamidopropyl hydroxysulfonyl betaine and oleamidopropyl hydroxysulfonyl betaine.

[0024] The clay stabilizer is an inorganic salt NaCl or KCl.

[0025] The salt-resistant monomer is a sulfonic acid unsaturated double bond monomer, and the temperature-resistant monomer is a monomer with an unsaturated double bond of a cyclic functional group.

[0026] Example 2 Based on Example 1, this example provides a nano-imbibition agent suitable for shale oil reservoirs, which is composed of the following substances in percentage by mass: 0.1% surface in-situ polymerization modified nanoparticles, 0.3% Class I surfactant, 0.2% Class II surfactant, 0.5% clay stabilizer, and the balance is water. In this embodiment, the type I surfactant is sodium heavy alkyl benzene sulfonate, and the type II surfactant is erucamidopropyl betaine.

[0027] Nano-permeating agent preparation process: The surface in-situ polymerized modified nanoparticles are uniformly dispersed in an aqueous solution under ultrasonic stirring at room temperature, and then the Class I surfactant, Class II surfactant and clay stabilizer are added in sequence, and mechanical stirring is performed until uniform to obtain the product.

[0028] The preparation process of surface in-situ polymerization modified nanoparticles is as follows: Step 1) Add 90 ml of water into a reaction container, fill with nitrogen to deoxygenate for 30 minutes, then add amino-modified nano-silicon dioxide particles and evenly disperse them under ultrasonic and mechanical stirring conditions to obtain a nano-dispersed fluid; Step 2) adding the temperature-resistant monomer and the salt-resistant monomer to the nano-dispersed fluid, and mechanically stirring until they are uniformly dissolved to obtain a mixed solution; Step 3) dissolving the initiator in 10 ml of water and adding dropwise to the mixed solution, stirring and reacting at a constant temperature of 60°C for 6 hours; Step 4) After the reaction is completed, cool to room temperature, use a high-speed centrifuge at a speed of 18000 rpm to separate the solid and liquid, wash with water three times, and then vacuum dry in an oven at 50°C to constant weight to obtain the product.

[0029] Among them, the mass of the amino-modified nano-silica particles is 1% of the total mass of the water (10 ml) used to dissolve the initiator and the water (90 ml) in step 1); the amount of the temperature-resistant monomer (2-acrylamide-2-methylpropanesulfonic acid, AMPS) and the salt-resistant monomer (N-vinyl-2-pyrrolidone, NVP) added is 20% of the mass of the amino-modified nano-silica particles, and the molar ratio of the temperature-resistant monomer to the salt-resistant monomer is 1:4; the mass of the initiator is 10% of the sum of the mass of the temperature-resistant monomer and the salt-resistant monomer.

[0030] Experimental preparation process of amino-modified nano-silica particles: Ultrasonic dispersion of 1wt.% nano-silica in an aqueous solution containing 80wt.% ethanol; dropwise addition of 20wt.% ammonia water to adjust the solution pH to 10; temperature raised to 45°C, and during stirring, 10ml of 1.1% aminopropyltrimethoxysilane ethanol solution was dropwise added to the mixed solution, and the reaction was maintained for 18h. Finally, separation was performed using a high-speed centrifuge at 18000rpm and washed three times with deionized water for later use.

[0031] Comparative Example 1-1. Without adding the surface in-situ polymerized modified nanoparticles, 0.2wt.% erucamidopropyl betaine, 0.3% sodium heavy alkylbenzene sulfonate, and 0.5% KCl were directly added to water in sequence to prepare the absorbing agent.

[0032] 1-2. Without adding surfactant, 0.1% surface in-situ polymerization modified nanoparticles were directly stirred with water by ultrasonic stirring to prepare a nano-water dispersion as a nano-permeating agent.

[0033] Example 3 Based on Example 1, this example provides a nano-imbibition agent suitable for shale oil reservoirs, which is composed of the following substances in percentage by mass: 0.05% surface in-situ polymerization modified nanoparticles, 0.3% Class I surfactant, 0.2% Class II surfactant, 0.5% clay stabilizer, and the balance is water. In this embodiment, the type I surfactant is sodium heavy alkyl benzene sulfonate, and the type II surfactant is erucamidopropyl hydroxysulfobetaine.

[0034] The preparation process of the nano-permeating agent is the same as that of Example 2.

[0035] Comparative Example 2-1. Without adding the surface in-situ polymerized modified nanoparticles, 0.2wt.% erucamidopropyl hydroxysulfobetaine, 0.3% sodium heavy alkylbenzene sulfonate, and 0.5% KCl were directly added to water in sequence to prepare the nano-permeating agent.

[0036] 2-2. Without adding surfactant, 0.05% surface in-situ polymerization modified nanoparticles were directly stirred with water by ultrasonic stirring to prepare a nano-water dispersion as a nano-permeating agent.

[0037] Example 4 Based on Example 1, this example provides a nano-imbibition agent suitable for shale oil reservoirs, which is composed of the following substances in percentage by mass: 0.02% surface in-situ polymerization modified nanoparticles, 0.5% Class I surfactant, 0.3% Class II surfactant, 0.5% clay stabilizer, and the balance is water. In this embodiment, the type I surfactant is petroleum sulfonate, and the type II surfactant is oleamidopropyl hydroxysulfobetaine.

[0038] The preparation process of the nano-permeating agent is the same as that of Example 2.

[0039] Comparative Example 3-1. Without adding the surface in-situ polymerized modified nanoparticles, 0.3% oleamidopropyl hydroxysulfobetaine, 0.5% petroleum sulfonate, and 0.5% KCl were directly added to water in sequence to prepare an imbibition oil displacement agent.

[0040] 3-2. Without adding surfactant, 0.02% surface in-situ polymerization modified nanoparticles were directly stirred with water by ultrasonic stirring to prepare a nano-water dispersion as a nano-infiltration oil displacement agent.

[0041] Example 5 Based on Example 1, this example provides a nano-imbibition agent suitable for shale oil reservoirs, which is composed of the following substances in percentage by mass: 0.02% surface in-situ polymerization modified nanoparticles, 0.4% Class I surfactant, 0.25% Class II surfactant, 0.5% clay stabilizer, and the balance is water. In this embodiment, the type I surfactant is petroleum sulfonate, and the type II surfactant is erucamidopropyl hydroxysulfobetaine.

[0042] The preparation process of the nano-permeating agent is the same as that of Example 2.

[0043] Comparative Example 4-1. Without adding the surface in-situ polymerized modified nanoparticles, 0.25 wt.% erucamidopropyl hydroxysulfobetaine, 0.4 wt.% petroleum sulfonate, and 0.5 wt.% KCl were directly added to water in sequence to prepare the absorbing agent.

[0044] 4-2. Without adding a surfactant, 0.02 wt.% of the surface in-situ polymerized modified nanoparticles were directly stirred with water by ultrasonic stirring to prepare a nano-water dispersion as a nano-permeating agent.

[0045] The performance of the nano-permeating agents prepared in Examples 2-5 and the comparative examples was tested, and the results are shown in Table 1.

[0046] 1. Interfacial tension test The interfacial tension was measured by a rotating drop interfacial tension meter at room temperature. The oil phase was crude oil from the Longdong Chang 7 shale reservoir, and the water phase was simulated formation water. The rotation speed was 5000 rpm.

[0047] 2. Wetting Angle Test Quartz glass sheets were used for wettability measurement. First, the quartz glass sheet was immersed in silicone oil, sealed and stored in an oven at a formation temperature of 67.5°C for one week; then the excess oil droplets on the surface were wiped off, and the water contact angle was measured using a contact angle meter and the data was recorded; then the quartz glass sheet was immersed in the corresponding wettability improving liquid, sealed and stored in an oven, and placed at the same temperature for one week; then the water contact angle was measured and the data was recorded.

[0048] 3. Determination and calculation process of imbibition replacement rate The static imbibition method was used to determine the imbibition replacement rate of the imbibition agent.

[0049] First, the natural core was saturated with crude oil using the axial loading method and the crude oil volume (V1) was recorded. Then, the imbibition agent was added to the imbibition bottle, and then the 5 cm × 2.5 cm × 2.5 cm natural core saturated with crude oil was immersed in the imbibition liquid. The imbibition bottle was left to stand and the liquid level of the imbibition liquid was in the middle range of the measuring scale. It was sealed and placed in an oven for 30 days at a temperature of 67.5 ° C. The volume of crude oil displaced was read and recorded every other day. The final stable crude oil volume was the maximum crude oil volume displaced by the imbibition agent (V2). The imbibition replacement rate R of the imbibition agent is the ratio of the maximum replacement volume of crude oil to the initial saturation volume, and the calculation formula is as follows: The natural core of this embodiment adopts Longdong Chang 7 shale.

[0050] Table 1 Performance test Example 6 In order to further illustrate the preparation process of surface in situ polymerization modified nanoparticles, based on the preparation method of surface in situ polymerization modified nanoparticles in Example 2, this example prepares surface in situ polymerization modified nanoparticles by changing the amount of amino-modified nano-silica and the amount of monomer added, and performs performance tests respectively.

[0051] The surface in-situ polymerization modified nanoparticles prepared in Example 2 are recorded as surface in-situ polymerization modified nanoparticles A, and the others are named accordingly.

[0052] Surface in situ polymerization modified nanoparticles B: The mass percentage of the amino-modified nano-silica particles in Example 2 was changed from 1% to 0.1%, and the other mass percentages remained unchanged.

[0053] Surface in situ polymerization modified nanoparticles C: The mass percentage of the amino-modified nano-silica particles in Example 2 was changed from 1% to 0.5%, and the other mass percentages remained unchanged.

[0054] Surface in situ polymerization modified nanoparticles D: The amount of the temperature-resistant monomer and the salt-resistant monomer added in Example 2 was changed from 20% of the mass of the amino-modified nano-silica particles to 15%, and the other contents remained unchanged.

[0055] Surface in situ polymerization modified nanoparticles E: The amount of the temperature-resistant monomer and the salt-resistant monomer added in Example 2 was changed from 20% to 17% of the mass of the amino-modified nano-silica particles, and the other contents remained unchanged.

[0056] Surface in situ polymerization modified nanoparticles F: The molar ratio of the temperature-resistant monomer to the salt-resistant monomer in Example 2 was changed from 1:4 to 1:3, while the other parameters remained unchanged.

[0057] Surface in situ polymerization modified nanoparticles G: The molar ratio of the temperature-resistant monomer to the salt-resistant monomer in Example 2 was changed from 1:4 to 1:5, while the other components remained unchanged.

[0058] Comparative Example 1 Aminated nano-silica modified by polymerization of salt-resistant monomer 2-acrylamide-2-methylpropanesulfonic acid was used as a nano-permeating agent and uniformly dispersed in deionized water by ultrasonic stirring to prepare an aqueous dispersion for testing.

[0059] Performance Testing: High temperature and high salt resistance Resistance to high temperature and high salt means that the polymer-modified nanoparticles prepared in a high temperature and high salt environment still have good dispersion stability.

[0060] Add inorganic salt NaCl or CaCl2 to 1wt% nanoparticle dispersion, increase temperature and salt concentration, and use laser particle size analyzer to measure particle size under each experimental condition. If particle size increases significantly, it means that nanodispersed fluid does not have good dispersion stability under temperature and salt concentration conditions. The results are shown in Table 2.

[0061] Among them, the dispersion stability evaluation experimental process: The 1% polymerized nanodispersed fluid was placed in the environment required for the experiment, and samples were taken out every other day and diluted to the required concentration of 0.001% for Malvern laser particle size analyzer for particle size measurement and the median particle size value was taken.

[0062] Table 2 Nanodispersion stability results As can be seen from Table 2, compared with the amino-modified nano-silica before AMPS polymerization, the dispersion stability of the nanoparticles has been significantly improved after the surface modification of the amino-modified nano-silica with salt-resistant monomers and temperature-resistant monomers. At a temperature of 130°C, a NaCl concentration of 180,000 mg / L, and a CaCl2 concentration of 40,000 mg / L, the average particle size did not increase significantly after one week of stabilization, showing excellent temperature and salt resistance. It can be seen that for complex and tight oil and gas reservoirs such as shale oil, the surface polymerization-modified nanoparticles can be fully and evenly laid on the pore wall and effectively strip the oil film to improve wettability, thereby increasing capillary force and increasing crude oil production.

[0063] The surface in-situ polymerization modified nanoparticles graft strong electrolyte monomers and cyclic temperature-resistant monomers on the surface of the nanoparticles, so that the surface polymer molecules maintain a good stretch state in a high temperature and high salt environment, and at the same time, the nanoparticles have a high electrostatic effect and a steric hindrance effect to maintain excellent dispersion stability, as shown in the schematic diagram Figure 1 At the same time, nanoparticles and surfactants are used to peel off the oil film on the rock surface. The specific principle and process can be found in Figure 2 As shown. Surfactant molecules spontaneously arrange at the oil-water-solid three-phase interface, significantly reducing the oil-water interfacial tension and the adsorption energy of the oil film on the rock surface, thereby improving the wettability of the rock surface. After the nanoparticles are arranged at the oil-water-solid three-phase interface, the interfacial free energy is further reduced. The excess nanoparticles are distributed in the wedge-shaped area between the oil film and the rock surface, generating additional osmotic pressure from the outside to the inside, forming another force - diffusion force, which promotes the peeling of the oil film, making the oil washing efficiency significantly higher than that of pure surfactants.

[0064] The above examples are merely illustrative of the present invention and do not constitute a limitation on the protection scope of the present invention. All designs that are the same or similar to the present invention fall within the protection scope of the present invention.

Claims

1. A nano-imbibing agent suitable for shale oil reservoirs, characterized in that: The invention is composed of the following substances in the following mass percentages: 0.02-0.1% of surface in-situ polymerization-modified nanoparticles, 0.3-0.5% of type I surfactant, 0.2-0.3% of type II surfactant, 0.5% of clay stabilizer, and the balance of water.

2. A nano-imbibing agent suitable for shale oil reservoirs according to claim 1, characterized in that: The surface in-situ polymerized modified nanoparticles are obtained by polymerization reaction of amino modified nanosilica particles, temperature resistant monomers and salt resistant monomers, the mass sum of the temperature resistant monomers and the salt resistant monomers is 15-20% of the mass of the amino modified nanosilica particles, and the molar ratio of the temperature resistant monomers to the salt resistant monomers is 1:3-1:

5.

3. The nano-imbibing agent suitable for shale oil reservoirs according to claim 1, characterized in that: The type I surfactant is one of the anionic surfactants heavy alkyl benzene sodium sulfonate and petroleum sulfonate.

4. The nano-imbibing agent suitable for shale oil reservoirs according to claim 1, characterized in that: The type II surfactant is one of the amphoteric betaine surfactants erucamidopropyl betaine, erucamidopropyl hydroxysulfonyl betaine and oleamidopropyl hydroxysulfonyl betaine.

5. The nano-imbibing agent suitable for shale oil reservoirs according to claim 1, characterized in that: The clay stabilizer is an inorganic salt NaCl or KCl.

6. The nano-imbibing agent suitable for shale oil reservoirs according to claim 2, characterized in that: The salt-resistant monomer is a sulfonic acid unsaturated double bond monomer, and the temperature-resistant monomer is a monomer with an unsaturated double bond of a cyclic functional group.

7. The method for preparing a nano-imbibing agent suitable for shale oil reservoirs according to claim 2, characterized in that: The surface in-situ polymerized modified nanoparticles are uniformly dispersed in an aqueous solution under ultrasonic stirring at room temperature, and then the Class I surfactant, Class II surfactant and clay stabilizer are added in sequence, and mechanical stirring is performed until uniform to obtain the product.

8. The method for preparing a nano-imbibing agent suitable for shale oil reservoirs according to claim 7, characterized in that: The preparation process of the surface in-situ polymerization modified nanoparticles comprises the following steps: Step 1) adding water into a reaction container, filling with nitrogen to deoxygenate, adding a formulated amount of amino-modified nano-silicon dioxide particles, and uniformly dispersing them under ultrasonic and mechanical stirring conditions to obtain a nano-dispersed fluid; Step 2) adding a formulated amount of temperature-resistant monomer and salt-resistant monomer to the nano-dispersed fluid, and mechanically stirring until they are uniformly dissolved to obtain a mixed solution; Step 3) dissolving the initiator in water and then adding dropwise to the mixed solution, stirring and reacting at a constant temperature of 40-60° C. for 6-10 hours; wherein the mass of the initiator is 10-20% of the mass of the temperature-resistant monomer and the salt-resistant monomer, and the mass of the amino-modified nano-silica particles is 0.1-1% of the total mass of the water used to dissolve the initiator and the water added in step 1); Step 4) After the reaction is completed, cool to room temperature, use a high-speed centrifuge at a speed of 18000 rpm to separate the solid and liquid, wash with water three times, and then vacuum dry in an oven at 50°C to constant weight to obtain the product.

9. The method for preparing a nano-imbibing agent suitable for shale oil reservoirs according to claim 8, characterized in that: The amino-modified nano-silicon dioxide particles are one of industrial-grade spherical gas-phase nano-silicon dioxide and amorphous silica sol, and have an average particle size of 10-20 nm.

10. The method for preparing a nano-imbibing agent suitable for shale oil reservoirs according to claim 8, characterized in that: The initiator is one of ammonium persulfate, sodium persulfate and potassium persulfate.

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