Nano oil-displacing agent for shale oil as well as preparation method and application of nano oil-displacing agent

Abstract

The invention relates to the technical field of oilfield chemistry, and relates to a shale oil nanometer oil displacement agent, which comprises the following raw materials by mass: 5-35% of an acrylamide monomer; 2%-20% of a surfactant monomer; the use amount of the initiator accounts for 0.08%-1.0% of the total amount of the two monomers; and the balance of deionized water. The invention also discloses a preparation method of the polymer. The polymer is prepared from an acrylamide monomer, a surfactant monomer and an initiator through a free radical polymerization reaction, the acrylamide monomer is acrylamide; the surfactant monomer is lauryl sodium sulfate. The invention further discloses application of the nano oil displacement agent, and the nano oil displacement agent and fracturing fluid are mixed and then added into shale oil in the fracturing process. In the shale oil imbibition process, the nano oil-displacing agent system reduces the interfacial tension adhesion work and improves the wettability and the oil-water mobility ratio, so that shale oil is easy to peel off from the inner wall of a reservoir, residual oil in large, medium and small holes is comprehensively used, spontaneous imbibition is enhanced, and the recovery efficiency is improved.

Description

Technical Field

[0001] This invention relates to the field of oilfield chemical technology, specifically to a nano-displacement agent for shale oil, its preparation method, and its application. Background Technology

[0002] With the gradual depletion of conventional oil and gas resources, unconventional oil and gas, such as shale oil and shale gas, have become the focus of exploration and development both domestically and internationally. my country is rich in shale oil resources, mainly terrestrial shale oil. In recent years, shale oil exploration and development have been achieved in the Triassic Yanchang Formation of the Ordos Basin, the Permian Lucaogou Formation of the Jimsar Depression of the Junggar Basin, and the Cretaceous Qingshankou Formation of the Songliao Basin, and preliminary technologies for the effective utilization of shale oil reserves have been established. my country's shale oil is characterized by complex geological conditions, low formation pressure coefficients, and high crude oil viscosity. While significant progress has been made using the horizontal well volumetric fracturing depletion development model, it faces challenges such as rapid post-fracturing production decline, low recovery rates, and low cumulative production, making it difficult to achieve large-scale, cost-effective shale oil development. Therefore, technological innovation to improve the cumulative production and recovery rate of shale oil per well is a crucial means to ensure the development of my country's shale oil and gas industry.

[0003] To address the issues of rapid production decline and low cumulative production, a high-intensity volumetric fracturing technology featuring "long horizontal sections, large fluid volumes, and large sand volumes" has been developed. The fluid used is a slickwater and guar gum fracturing fluid system, with surfactants added to reduce the expansion of shale upon contact with water. This alters the wettability of the rock, improves fluid absorption in pores and fractures, enhances crude oil fluidity, and achieves the goal of increasing the permeability of shale reservoirs. The cumulative production has also increased compared to conventional fracturing.

[0004] A search revealed that patent document CN115895630A provides an adsorption oil displacement agent and its preparation method, coupled adsorption fracturing fluid and its application. The preparation method of the adsorption oil displacement agent includes preparing nano-silica sol and mixing it with other components to obtain the adsorption oil displacement agent.

[0005] Patent document CN114891040A discloses a nanoemulsion permeation oil displacement agent, a molybdenum-containing gemini surfactant and its preparation method, which involves performing a chain reaction of a tertiary amine and dichloroethyl ether to obtain a chain-chain tertiary amine; mixing the chain-chain tertiary amine, isopropanol and molybdenum dioxide dichlorodioxide, and reacting at 80℃~90℃ for 4h~5h to obtain a nanoemulsion.

[0006] The two nano-displacement agent systems mentioned above are only single surfactant systems. When mixed with shale oil, they are prone to emulsification, which increases the viscosity of the system and fails to achieve the purpose of viscosity reduction. Furthermore, the increased viscosity will lead to poor flow of crude oil in the pores and gaps, resulting in the inability to extract the oil and causing the overall recovery rate of shale oil blocks to be low. Summary of the Invention

[0007] The purpose of this invention is to provide a nano-displacement agent for shale oil, its preparation method, and its application, which solves the problem that existing displacement agent systems are prone to emulsification when mixed with shale oil, leading to an increase in system viscosity.

[0008] This invention is achieved through the following technical solution:

[0009] This invention discloses a nano-displacement agent for shale oil, the structural formula of which is:

[0010]

[0011] Where M is Na or K, w:x:y:z=(2-8):(1-5):(0-5):(0-5);

[0012] The particle size of the nano-displacement agent is in the nanometer range.

[0013] Furthermore, by mass percentage, the nano-oil displacement agent comprises the following raw materials:

[0014] Acrylamide monomers 5%-35%; surfactant monomers 2%-20%;

[0015] An initiator, wherein the amount of the initiator is 0.08%-1.0% of the total amount of the two monomers;

[0016] The remainder is deionized water.

[0017] Furthermore, when the concentration of the aqueous solution formed by the nano-oil displacement agent is 0.1%-2%, the oil-water interfacial tension is 0.08-0.20 mN·m. -1 The viscosity reduction rate is 82%–92%, the wetting contact angle is 25°–54°, and the permeation efficiency is 22%–30%.

[0018] Furthermore, when the aqueous solution formed by the nano-oil displacement agent has a concentration of 2%, the oil-water interfacial tension reaches 0.08 mN·m. -1 It achieves a viscosity reduction rate of 92%, a wetting contact angle of 25°, and a penetration efficiency of 30%.

[0019] The present invention also discloses a method for preparing the nano-displacement agent for shale oil, wherein the nano-displacement agent is obtained by free radical polymerization of acrylamide monomers, surfactant monomers and initiators;

[0020] Acrylamide monomers include acrylamide; surfactant monomers include sodium dodecyl sulfate.

[0021] Furthermore, acrylamide monomers also include N-dodecylacrylamide and / or methacrylamide;

[0022] Surfactant monomers also include sodium vinyl sulfonate and / or alkylphenol polyoxyethylene ether.

[0023] Furthermore, the initiator is a mixture of persulfates and sulfites;

[0024] The mass ratio of persulfates to sulfites is 1:(0.5-0.6).

[0025] Furthermore, the following processes are included:

[0026] Acrylamide monomers and surfactant monomers were mixed, added to deionized water, and dissolved evenly to obtain a blend system.

[0027] The blend system was heated in a water bath and nitrogen gas was introduced. Then an initiator was added to start the reaction. After the reaction, a pale yellow, transparent, viscous liquid was obtained.

[0028] After washing, drying, and grinding the pale yellow, transparent, viscous liquid, a nano-oil displacement agent was obtained.

[0029] Furthermore, the reaction is initiated by adding an initiator, with a specific reaction temperature of 45-75℃ and a reaction time of 3-5 hours.

[0030] The present invention also discloses the application of the nano-displacement agent for shale oil, wherein the nano-displacement agent is mixed with fracturing fluid and added to the shale oil together during the fracturing process.

[0031] Compared with the prior art, the present invention has the following beneficial technical effects:

[0032] This invention discloses a nano-displacement agent for shale oil. Its structural formula reveals that the nano-displacement agent possesses amide groups, sulfonic acid groups, and surfactant groups. The amide groups serve as the polymer backbone, while the surfactant groups enable high surface / interfacial activity and improved wettability, effectively reducing adhesion work and achieving emulsification and viscosity reduction while enhancing the percolation and displacement effect. The amide and sulfonic acid groups also enhance the affinity between the displacement agent and the polar components of shale oil, further improving its viscosity-reducing performance. The nano-displacement agent provided by this invention has a nano-sized particle size, allowing it to penetrate into the micro-nano pores of shale oil reservoirs and mobilize deep crude oil. During shale oil percolation, the nano-displacement agent system effectively reduces interfacial tension adhesion work, improves wettability and oil-water mobility ratio, making it easier for shale oil to detach from the reservoir wall, comprehensively utilizing residual oil in large, medium, and small pores, enhancing spontaneous percolation, and improving oil recovery.

[0033] Furthermore, the nano-displacement agent comprises the following raw materials: 5%-35% acrylamide monomers; 2%-20% surfactant monomers. By optimizing the ratio of acrylamide monomers to surfactants, polymers with specific structural units and polymerization degrees are obtained, further improving their comprehensive oil displacement performance. The nano-displacement agent provided by this invention can provide an appropriately low interfacial tension by adjusting the surfactant monomer ratio, with the surfactant monomer accounting for 2%-20% of the total raw material content. This reduces the oil-water interfacial tension initiation pressure, increases capillary force, and enhances the percolation oil displacement power. Simultaneously, the nano-percolation oil displacement agent has hydrophobic long chains, which can form a bilayer with hydrophilic groups facing outward and hydrophobic groups facing inward on the rock surface. This alters the oil wettability caused by the self-generation and self-storage of shale reservoirs, thereby reducing the adhesion work of shale oil and utilizing the residual oil in the large, medium, and small pores of the shale reservoir, thus strengthening the spontaneous percolation oil displacement effect.

[0034] Furthermore, when the concentration of the aqueous solution formed by the nano-oil displacement agent and the aqueous phase is 2%, the oil-water interfacial tension reaches 0.08 mN·m. -1 It achieves a viscosity reduction rate of 92%, a wetting contact angle of 25°, and an adsorption efficiency of 30%. It exhibits good compatibility with the on-site slickwater system and can effectively improve the adsorption recovery rate during fracturing and well shut-in processes in shale oil reservoirs.

[0035] This invention also discloses a method for preparing the nano-displacement agent for shale oil, which is copolymerized from acrylamide monomer and surfactant monomer. Specifically, hydrophobic long-chain functional groups are grafted onto the polyacrylamide backbone. The preparation process is simple and economically efficient. The displacement agent is a polymer surfactant, which, compared with surfactants, can effectively avoid the adsorption effect caused by charge interaction between the polymer and the formation core. The polymer and surfactant in the displacement agent molecule are bonded by chemical bonds, which are much stronger than the intermolecular forces in the polymer-surfactant blend system, thus avoiding chromatographic separation problems.

[0036] Furthermore, acrylamide monomers also include N-dodecylacrylamide and / or methacrylamide, which can increase the number of amide groups in the oil displacement agent molecule, strengthen its affinity with shale oil polar molecules, and improve viscosity reduction performance;

[0037] Surfactant monomers also include sodium vinyl sulfonate and / or alkylphenol polyoxyethylene ether, which can reduce the interfacial tension between oil and water, improve wettability to enhance the permeation effect, and also generate a steric hindrance effect through hydrophobic long chains, effectively reducing the viscosity of shale oil.

[0038] This invention also discloses the application of the nano-displacement agent for shale oil. Adding the nano-displacement agent of this invention together with fracturing fluid to shale oil can effectively reduce the oil-water interfacial tension, improve wettability, achieve the purpose of efficient viscosity reduction, and transport it into the nanopores of the reservoir in all directions, thereby improving the spontaneous permeation efficiency of shale oil. Attached Figure Description

[0039] Figure 1 Particle size distribution of shale oil nano-displacement agents at different concentrations;

[0040] Figure 2 The interfacial tension between nano-displacement agents of different concentrations and shale oil in a certain region;

[0041] Figure 3 To reduce the contact angle between core samples and deionized water for different concentrations of nano-displacement agents;

[0042] Figure 4 The viscosity reduction rate of shale oil in a certain area by different concentrations of nano-displacement agents;

[0043] Figure 5 The spontaneous adsorption recovery rate of different concentrations of nano-displacement agents in shale reservoirs. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of the present invention clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention; that is, the described embodiments are only a part of the embodiments of the present invention, and not all of them.

[0045] The components described and illustrated in the accompanying drawings and embodiments of this invention can be arranged and designed in various different configurations. Therefore, the detailed description of the embodiments of the invention provided in the following drawings is not intended to limit the scope of the claimed invention, but merely to illustrate one selected embodiment of the invention. All other embodiments obtained by those skilled in the art based on the accompanying drawings and embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0046] It should be noted that the terms “comprising,” “including,” or any other variations are intended to cover non-exclusive inclusion, such that a process, element, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to the process, element, method, article, or apparatus.

[0047] This invention discloses a nano-displacement agent for shale oil, with the following structural formula:

[0048]

[0049] Where M is Na or K, w:x:y:z=(2-8):(1-5):(0-5):(0-5);

[0050] The particle size of the nano-displacement agent is in the nanometer range.

[0051] The structural formula reveals that this nano-displacement agent possesses amide, sulfonic acid, and surfactant groups. The amide groups serve as the polymer backbone, while the surfactant groups enable high surface / interfacial activity and improved wettability, effectively reducing adhesion work and enhancing the permeation and displacement effect while simultaneously achieving emulsification and viscosity reduction. The amide and sulfonic acid groups also enhance the affinity between the agent and the polar components of shale oil, further improving its viscosity-reducing performance.

[0052] The preparation method of the nano-displacement agent for shale oil includes the following steps:

[0053] Acrylamide monomers and surfactant monomers were mixed, added to deionized water, and dissolved evenly to obtain a blend system.

[0054] The blend system was heated in a water bath and nitrogen gas was introduced. Then an initiator was added to start the reaction. After the reaction, a pale yellow, transparent, viscous liquid was obtained.

[0055] After washing, drying, and grinding the pale yellow, transparent, viscous liquid, a nano-oil displacement agent was obtained.

[0056] The nano-oil displacement agent comprises the following raw materials by mass percentage:

[0057] Acrylamide monomers 5%-35%; surfactant monomers 2%-20%;

[0058] An initiator, wherein the amount of the initiator is 0.08%-1.0% of the total amount of the two monomers;

[0059] The remainder is deionized water.

[0060] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0061] Example 1

[0062] Preparation of the nano-oil displacement agent system SD-1:

[0063] (1) Add 5g of acrylamide and 10g of sodium dodecyl sulfate to a three-necked flask, then add 84.9g of deionized water to dissolve them, and stir mechanically with a stirrer until homogeneous.

[0064] (2) After fixing the three-necked flask, place it in a 55°C water bath and heat it. Set the stirrer speed to 400 rpm and stir from the top of the three-necked flask. Adjust the air flow meter to a certain flow rate and introduce nitrogen into the side of the three-necked flask.

[0065] (3) Add 0.07g sodium persulfate and 0.03g sodium sulfite to the other mouth of the three-necked flask to initiate the reaction. After reacting for 4 hours, cool to room temperature to obtain a pale yellow transparent viscous liquid.

[0066] (4) Pour the pale yellow, transparent, viscous liquid into a beaker, wash it with an appropriate amount of ethanol, dry it, grind it, and the final product, nano oil displacement agent, is obtained, which is denoted as SD-1.

[0067] The nano-oil displacement agent prepared in this embodiment has the following structural formula:

[0068]

[0069] Where M is Na, and w:x = 7:3.

[0070] Example 2

[0071] By changing the monomer mass (10g acrylamide, 8g methacrylamide, and 5g sodium dodecyl sulfate), adding 76.88g of deionized water, and changing the initiator to 0.08g sodium persulfate and 0.04g sodium sulfite, and following the same steps as in Example 1, nano-oil displacement agent SD-2 was prepared.

[0072] The nano-oil displacement agent prepared in this embodiment has the following structural formula:

[0073]

[0074] Where M is Na, and w:x:y = 7:1:4.5.

[0075] Example 3

[0076] By changing the monomer mass (15g acrylamide, 10g N-dodecylacrylamide, 5g methacrylamide, 5g sodium dodecyl sulfate, and 5g sodium vinyl sulfonate), changing the initiator to 0.15g sodium persulfate and 0.09g sodium sulfite, and adding 59.76g of deionized water, and following the same procedures as in Example 1, nano-oil displacement agent SD-3 was prepared.

[0077] The nano-oil displacement agent prepared in this embodiment has the following structural formula:

[0078]

[0079] Where M is Na, and w:x:y:z = 5.3:1:1.5:1.

[0080] Example 4

[0081] By changing the monomer mass (20g acrylamide, 15g N-dodecylacrylamide, 10g sodium dodecyl sulfate, 5g sodium vinyl sulfonate, 5g alkylphenol polyoxyethylene ether), and changing the initiator to 0.23g sodium persulfate and 0.12g sodium sulfite, and following the same steps as in Example 1, the nano-oil displacement agent SD-4 was prepared.

[0082] The nano-oil displacement agent prepared in this embodiment has the following structural formula:

[0083]

[0084] Where M is Na, and w:x:z = 4.7:1:1.

[0085] Sodium dodecyl sulfate in the above embodiments can also be replaced with potassium dodecyl sulfate.

[0086] The mass percentages of the two monomers in Examples 1-4 above are shown in Table 1 below:

[0087] Table 1

[0088]

[0089] By converting the raw materials in Examples 1-4 into molar ratios, we can obtain the subscripts in the structural formulas of the nano-oil displacement agents obtained in each example, as shown in Table 2.

[0090] Table 2

[0091]

[0092] Performance evaluation of nano-oil displacement agents in Examples 1-4:

[0093] Preparation of nano-oil displacement agent solution: Weigh 2g of nano-oil displacement agent SD-4 from Example 4, place it in a 200mL beaker, add deionized water, and prepare nano-oil displacement agent solutions of different mass concentrations.

[0094] Six different concentrations of nano-displacement agent solutions were prepared, namely 0.1 wt%, 0.25 wt%, 0.5 wt%, 0.75 wt%, 1 wt%, and 2 wt%. Shale oil from a certain area was analyzed, and the results are as follows:

[0095] (1) Particle size distribution of nano-oil displacement agent solution

[0096] The nano-oil displacement agent prepared by this invention can be dispersed into a nanoemulsion, such as... Figure 1 As shown, the solution particle size is 2-6 nm, which can utilize the residual oil in the reservoir micropores and improve the oil recovery rate.

[0097] (2) Interfacial tension of nano-oil displacement agent solution

[0098] The interfacial tension between shale oil and nano-displacement agent in this area was measured using an SVT-20 interfacial tensiometer. When the concentration of the nano-displacement agent solution was 0.1%, the interfacial tension was 0.2 mN·m. -1 It has achieved a low interfacial tension, exhibiting strong emulsifying and viscosity-reducing properties as well as strong spontaneous absorption properties; when the concentration of the nano-oil displacement agent solution is 2%, the interfacial tension is as low as 0.07 mN·m. -1 (like Figure 2 As shown in the figure, this can increase the driving force of percolation and improve the spontaneous percolation efficiency.

[0099] (3) Improvement of wettability of nano-oil displacement agent solution

[0100] The ability of nano-displacement agent solutions to improve wettability is an important indicator for evaluating their application effect in oilfield development.

[0101] Nano-displacement agents can adsorb onto rock surfaces and alter the wettability of the rocks, transforming them from oleophilic or hydrophilic to neutral or more favorable for crude oil extraction. This transformation helps reduce the adhesion between crude oil and the rock surface, making it easier to displace the crude oil.

[0102] The surfactants and other components in nano-displacement agents can significantly reduce the interfacial tension between oil and water, making it easier for oil droplets to disperse in the aqueous phase and form an emulsion, thereby improving the fluidity of crude oil.

[0103] The contact angle between deionized water and core thin sections was measured using a JY-82C-N2 contact angle meter, and the contact angle was 97°. The contact angles of core thin sections soaked in different concentrations of nano-displacement agents were then measured. When the nano-displacement agent solution concentration was 0.1%, the contact angle was 54°; when the concentration was 2%, the contact angle was 25°, a decrease of 72° (e.g., ...). Figure 3 As shown in the figure, it can effectively improve the wettability of the core.

[0104] (4) Viscosity-reducing ability of nano-oil displacement agent solution

[0105] The viscosity reduction rate of shale oil in this region with different concentrations of nano-displacement agent was determined using a Hacker rheometer. When the concentration of the nano-displacement agent solution was 0.1%, the viscosity reduction rate was 82%; when the concentration was 2%, the viscosity reduction rate could reach over 90% (e.g., ...). Figure 4 As shown in the figure, the viscosity reduction effect is significant.

[0106] (5) Adhesion work reduction ability of nano-oil displacement agent solution

[0107] The reduction rate of adhesion work of the nano-displacement agent was calculated based on the interfacial tension and contact angle of oil and water before and after wetting. The higher the reduction rate of adhesion work, the stronger the ability of the nano-displacement agent to strip shale oil from the rock surface. The reduction rate of adhesion work of different concentrations of nano-displacement agents can reach over 93%.

[0108] (6) Spontaneous adsorption recovery rate of nano-displacement agent solution

[0109] The oil recovery rates of different concentrations of nano-displacement agent solutions and core samples were measured using a percolation balance, such as... Figure 5 As shown, when the concentration of the nano-displacement agent solution is 0.1%, the oil recovery rate is 22%; when the concentration of the nano-displacement agent solution is 2%, the oil recovery rate is as high as 30%.

[0110] The nano-oil displacement agents prepared in Examples 1-4 were all formulated into 2% nano-oil displacement agent solutions, and their performance was evaluated. The results are shown in Table 3. When the nano-oil displacement agent concentration was 2%, the oil-water interfacial tension was ≥0.07 mN·m. -1 Viscosity reduction rate ≥92%, wetting contact angle ≥25°, and permeation efficiency ≥25%.

[0111] Table 3 Performance test results for different solution systems

[0112]

[0113] In summary, the nano-displacement agent for shale oil of the present invention can be compounded with fracturing fluid and water, and has the characteristics of low interfacial tension, good wettability, and excellent viscosity reduction effect. It is beneficial to reduce crude oil viscosity and improve the spontaneous permeation efficiency of shale reservoirs, improve the oil-water mobility ratio in the formation, and fully utilize residual oil in large, medium and small pores. It solves the problem of ineffective utilization of nanopores in shale oil, improves the recovery rate of the entire reservoir, meets the technical requirements for enhanced oil recovery of shale oil, and achieves the goal of cost reduction and efficiency improvement.

[0114] Nano-displacement agents exhibit significant viscosity-reducing capabilities, thanks to their unique nanomaterials and formulation composition. These agents not only improve reservoir permeability but also significantly reduce crude oil viscosity by decreasing water-oil interfacial tension and enhancing oil-water interaction forces. Therefore, nano-displacement agents hold broad application prospects and significant economic value in oilfield development.

[0115] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A nano-displacement agent for shale oil, characterized in that, The nano-oil displacement agent has the following structural formula: Where M is Na or K, w:x:y:z=(2-8):(1-5):(0-5):(0-5); The particle size of the nano-displacement agent is in the nanometer range.

2. The nano-displacement agent for shale oil according to claim 1, characterized in that, The nano-oil displacement agent comprises the following raw materials by weight percentage: Acrylamide monomers 5%-35%; surfactant monomers 2%-20%; An initiator, wherein the amount of the initiator is 0.08%-1.0% of the total amount of the two monomers; The remainder is deionized water.

3. The nano-displacement agent for shale oil according to claim 1, characterized in that, When the aqueous solution formed by the nano-oil displacement agent has a concentration of 0.1%-2%, the oil-water interfacial tension is 0.08-0.20 mN·m. -1 The viscosity reduction rate is 82%–92%, the wetting contact angle is 25°–54°, and the permeation efficiency is 22%–30%.

4. The nano-displacement agent for shale oil according to claim 3, characterized in that, When the aqueous solution formed by the nano-oil displacement agent has a concentration of 2%, the oil-water interfacial tension reaches 0.08 mN·m. -1 It achieves a viscosity reduction rate of 92%, a wetting contact angle of 25°, and a penetration efficiency of 30%.

5. The method for preparing the nano-displacement agent for shale oil according to any one of claims 1-4, characterized in that, The nano-oil displacement agent is obtained by free radical polymerization of acrylamide monomers, surfactant monomers and initiators. Acrylamide monomers include acrylamide; surfactant monomers include sodium dodecyl sulfate.

6. The method for preparing the nano-displacement agent for shale oil according to claim 5, characterized in that, Acrylamide monomers also include N-dodecylacrylamide and / or methacrylamide; Surfactant monomers also include sodium vinyl sulfonate and / or alkylphenol polyoxyethylene ether.

7. The method for preparing the nano-displacement agent for shale oil according to claim 5, characterized in that, The initiator is a mixture of persulfates and sulfites; The mass ratio of persulfates to sulfites is 1:(0.5-0.6).

8. The method for preparing the nano-displacement agent for shale oil according to claim 5, characterized in that, Includes the following processes: Acrylamide monomers and surfactant monomers were mixed, added to deionized water, and dissolved evenly to obtain a blend system. The blend system was heated in a water bath and nitrogen gas was introduced. Then an initiator was added to start the reaction. After the reaction, a pale yellow, transparent, viscous liquid was obtained. After washing, drying, and grinding the pale yellow, transparent, viscous liquid, a nano-oil displacement agent was obtained.

9. The method for preparing the nano-displacement agent for shale oil according to claim 8, characterized in that, The reaction begins with the addition of an initiator, specifically at a temperature of 45-75°C and a reaction time of 3-5 hours.

10. The application of the nano-displacement agent for shale oil according to any one of claims 1-4, characterized in that, The nano-displacement agent and fracturing fluid are mixed and then added to the shale oil during the fracturing process.

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