Preparation method of emulsion polymer for oil displacement

Abstract

The application relates to the technical field of oil and gas field development, and discloses a preparation method of an emulsion polymer for oil displacement, which comprises the following preparation steps: glycidyl methacrylate, carboxymethyl-beta-cyclodextrin and water-soluble cellulose are mixed and reacted to obtain modified water-soluble cellulose; acrylamide, methyl methacrylate, styrene, hydroxyethyl acrylate and deionized water are mixed and uniformly stirred, a pH regulator is added, and a monomer solution is obtained; the modified water-soluble cellulose and a composite material are added into the monomer solution, uniformly stirred, an initiator is added, and stirring reaction is carried out to obtain an emulsion polymer. The water-soluble cellulose can significantly improve the viscosity of the acrylamide-based emulsion polymer and improve the oil recovery rate; the glycidyl methacrylate and the carboxymethyl-beta-cyclodextrin are grafted on the water-soluble cellulose, the water-soluble cellulose is endowed with a cavity structure, and it is beneficial to forming more stable acrylamide-based emulsion polymers.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of oil and gas field development, in particular to a preparation method of an emulsion polymer for oil displacement. BACKGROUND

[0002] According to different oil field development stages, oil exploitation is generally divided into three stages: the first stage is primary oil recovery by using oil layer energy, the oil recovery efficiency of the stage is generally only about 15%; the second stage is secondary oil recovery by injecting water and gas into the oil layer to supplement the oil layer energy so as to achieve the purpose of exploitation, the oil recovery rate is 30-40%; the third stage is tertiary oil recovery by using new technologies such as physics, chemistry and biology, in order to efficiently recover residual oil in the formation, it is urgent to develop a tertiary oil recovery method suitable for special geological conditions in China;

[0003] Polyacrylamide is a water-soluble polymer, has good water solubility and high chemical activity, is easy to obtain branched or network structure modified products by grafting or crosslinking, and is widely applied to oil field exploitation operations such as drilling, well completion, well cementing, fracturing and enhanced oil recovery, but the salt resistance of polyacrylamide is poor, the carboxyl groups in the polyacrylamide molecules are easy to be neutralized in salt water, the polyacrylamide molecules are in a curled state, the solution viscosity is reduced, the oil recovery rate is affected, and the mechanical strength and high temperature resistance of the polyacrylamide are poor. SUMMARY

[0004] The application provides a preparation method of an emulsion polymer for oil displacement, and solves the problems of poor salt resistance, mechanical strength and high temperature resistance of polyacrylamide.

[0005] The technical scheme of the application is as follows:

[0006] A preparation method of an emulsion polymer for oil displacement, comprising the following preparation steps:

[0007] S1. Glycidyl methacrylate, carboxymethyl-beta-cyclodextrin and water-soluble cellulose are mixed and reacted to obtain modified water-soluble cellulose;

[0008] S2. Acrylamide, methyl methacrylate, styrene, hydroxyethyl acrylate and deionized water are mixed and stirred uniformly, a pH regulator is added to adjust the pH to 2-3, and a monomer solution is obtained;

[0009] S3. The modified water-soluble cellulose and the composite material are added to the monomer solution and stirred uniformly, an initiator is added, and stirring reaction is carried out at 85-90 DEG C for 20-30 min to obtain an emulsion polymer;

[0010] The composite material is obtained by mixing and reacting graphene oxide, a reducing agent and modified montmorillonite, and then modifying the surface of konjac glucomannan;

[0011] The modified montmorillonite is obtained by intercalating montmorillonite with cationic quaternary ammonium salt and then reacting the intercalated montmorillonite with glucose and sodium dodecylsulfonate.

[0012] Furthermore, the water-soluble cellulose is selected from any one of carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose and hydroxypropyl methyl cellulose.

[0013] Furthermore, the initiator is selected from any one of azobisisobutylamidine hydrochloride, azobisisobutylimidazoline hydrochloride, azobisisoheptanonitrile, and azobisisobutyronitrile.

[0014] Furthermore, the pH adjuster is selected from any one of hydrochloric acid, phosphoric acid, acetic acid, sulfuric acid, sodium hydroxide and potassium hydroxide.

[0015] Furthermore, in step S2, the mass ratio of acrylamide, methyl methacrylate, styrene, hydroxyethyl acrylate and deionized water is (60-80):(10-15):(10-12):(3-5):(180-200).

[0016] Furthermore, in step S3, the mass ratio of the modified water-soluble cellulose, the composite material, the monomer solution and the initiator is (8-10):(5-6):(150-170):(1-2).

[0017] Furthermore, in step S1, the modified water-soluble cellulose is prepared by the following steps:

[0018] A1. Tetrabutylammonium bromide, carboxymethyl-β-cyclodextrin, and 2,6-di-tert-butyl-p-cresol were added to dimethyl sulfoxide and stirred uniformly. Glycidyl methacrylate was added and stirred at 60-70°C for 2-3 hours. Acetic acid was added to adjust the pH to terminate the reaction. The light yellow liquid was separated and collected, and then freeze-dried to obtain modified carboxymethyl-β-cyclodextrin.

[0019] A2. Add water-soluble cellulose to ethanol and stir evenly. Add sodium hydroxide solution and stir evenly. Add modified carboxymethyl-β-cyclodextrin and stir at 70-80°C for 30-40 minutes. Cool to room temperature and freeze-dry to obtain modified water-soluble cellulose.

[0020] Furthermore, in the above-mentioned reaction process A1, in the organic solvent dimethyl sulfoxide, tetrabutylammonium bromide is used as a catalyst, 2,6-di-tert-butyl-p-cresol is used as an inhibitor, and the carboxyl group of carboxymethyl-β-cyclodextrin can undergo a ring-opening reaction with the epoxy group of glycidyl methacrylate, so that glycidyl methacrylate is grafted onto the carboxymethyl-β-cyclodextrin to obtain modified carboxymethyl-β-cyclodextrin.

[0021] Further, in the above A2 reaction process, the lipid group contained in the modified carboxymethyl-β-cyclodextrin and the hydroxyl group produced by ring opening can be combined with the oxygen-containing functional groups on the water-soluble cellulose through a chemical bond, so that the modified carboxymethyl-β-cyclodextrin is grafted on the water-soluble cellulose to obtain modified water-soluble cellulose.

[0022] Further, in step A1, the amount ratio of tetrabutylammonium bromide, carboxymethyl-β-cyclodextrin, 2,6-di-tert-butyl-p-cresol, dimethyl sulfoxide and glycidyl methacrylate is (0.03-0.07) g:(1-2) g:(0.03-0.05) g:(45-55) mL:(2-4) g.

[0023] Further, in step A2, the amount ratio of water-soluble cellulose, ethanol, sodium hydroxide solution and modified carboxymethyl-β-cyclodextrin is (2.1-2.5) g:(90-110) mL:(0.4-0.6) g:(0.6-0.8) g.

[0024] Further, the composite material is prepared by the following steps:

[0025] B1. Glucose and sodium dodecyl sulfonate are added to deionized water, stirred uniformly, and cationic quaternary ammonium salt intercalated montmorillonite is added, stirred at 500-600 r / min for 20-30 min, then reacted at 170-190℃ for 7-9 h, cooled to room temperature, and the product is taken out, washed and dried to obtain modified montmorillonite;

[0026] B2. Graphene oxide is added to deionized water, stirred uniformly, and modified montmorillonite is added, ultrasonically treated at 40-60 KHz for 20-30 min, a reducing agent is added, stirred uniformly, and a gel is formed by stirring and reacting at 90-100℃ for 1-2 h, and the gel is freeze-dried to obtain composite graphene aerogel;

[0027] B3. The composite graphene aerogel and konjac glucomannan are added to ethanol, stirred uniformly, and a sodium hydroxide solution is added, stirred at 55-65℃ for 20-30 min, then heated to 80-90℃, and stirred until the ethanol evaporates, and the solid is collected, washed and dried to obtain the composite material.

[0028] Further, in the above B1 reaction process, glucose and sodium dodecyl sulfonate can act on the cationic quaternary ammonium salt intercalated montmorillonite layer or surface, and glucose acts as a carbon source and sodium dodecyl sulfonate acts as a surfactant, after hydrothermal reaction, glucose reacts with sodium dodecyl sulfonate to realize in-situ synthesis of amphiphilic nanocarbon dots in the cationic quaternary ammonium salt intercalated montmorillonite layer or surface, and modified montmorillonite is obtained.

[0029] Furthermore, during the above-mentioned B2 reaction process, the modified montmorillonite sheet structure can be distributed between the graphene oxide layers, and ascorbic acid is used as a reducing agent, so that the graphene oxide sheets are overlapped with each other through π-π conjugation to form an aerogel structure with a three-dimensional network porous structure with graphene oxide as the skeleton, so that the modified montmorillonite is evenly distributed in the porous structure of the aerogel structure, thereby obtaining a composite graphene aerogel.

[0030] Furthermore, during the above-mentioned B3 reaction process, the konjac glucomannan molecular chain contains a large number of hydroxyl structures and has excellent adhesion, and the composite graphene aerogel has porous adsorption properties, so that the konjac glucomannan is deposited on the surface of the composite graphene aerogel to obtain a composite material.

[0031] Furthermore, in step B1, the ratio of glucose, sodium dodecyl sulfate, deionized water and cationic quaternary ammonium salt intercalated montmorillonite is (4-6) g: (0.3-0.7) g: (80-120) mL: (8.1-8.5) g.

[0032] Furthermore, in step B2, the ratio of the graphene oxide, deionized water, modified montmorillonite and reducing agent is (1.1-1.3) g: (90-110) mL: (0.5-0.7) g: (0.8-1) g.

[0033] Furthermore, in step B3, the ratio of the composite graphene aerogel, konjac glucomannan, ethanol and sodium hydroxide solution is (5-6) g: (1.6-1.8) g: (70-90) mL: (4-6) mL.

[0034] Furthermore, the graphene oxide has a particle size of 0.5-1 μm.

[0035] Furthermore, the reducing agent is ascorbic acid.

[0036] Furthermore, the cationic quaternary ammonium salt intercalated montmorillonite is specifically prepared by the following steps:

[0037] Add cationic quaternary ammonium salt to deionized water, stir evenly, add montmorillonite, stir at 55-65° C. for 1-3 hours, heat to 65-75° C., age, centrifuge, wash, and dry to obtain cationic quaternary ammonium salt intercalated montmorillonite.

[0038] Furthermore, during the above reaction process, the cationic functional groups contained in the cationic quaternary ammonium salt can undergo ion exchange reactions with the cations between the montmorillonite layers, so that the cationic quaternary ammonium salt is intercalated into the montmorillonite layers to expand the interlayer spacing of the montmorillonite, which is beneficial for adsorbing metal salt ions in oil wells, improving the salt resistance of the acrylamide-based emulsion polymer, and expanding the interlayer spacing of the montmorillonite, which is beneficial for the synthesis of amphiphilic nanocarbon dots between the montmorillonite layers or on the surface.

[0039] Furthermore, the usage ratio of the cationic quaternary ammonium salt, deionized water and montmorillonite is (8.2-8.4) g:(90-110) mL:(5-6) g.

[0040] Furthermore, the cationic quaternary ammonium salt is cetyltrimethylammonium bromide.

[0041] Furthermore, the montmorillonite is sodium montmorillonite, and the particle size is 0.2-0.4 μm.

[0042] The present invention has the following beneficial effects:

[0043] (1) In the technical solution of the present invention, the cationic quaternary ammonium salt intercalated montmorillonite has a large interlayer spacing, which is conducive to the adsorption of metal salt ions in oil wells, improving the salt resistance of acrylamide-based emulsion polymers, and is conducive to the synthesis of amphiphilic nanocarbon dots between montmorillonite layers or on the surface; amphiphilic nanocarbon dots are synthesized in situ between the cationic quaternary ammonium salt intercalated montmorillonite layers or on the surface. On the one hand, the cationic quaternary ammonium salt intercalated montmorillonite acts as a carrier of nanocarbon dots and can load more nanocarbon dots, thereby avoiding the aggregation of nanocarbon dots when added to the emulsion polymer. In addition, the hydroxyl and sulfonate groups on the surface of the nanocarbon dots can further chelate cationic ions in the oil field. The modified montmorillonite can prevent the polyacrylamide emulsion polymer from being firmly adsorbed by the metal salt ions between the montmorillonite layers in a high shear stress field, and release them into the polyacrylamide emulsion polymer to neutralize the carboxyl anions of the polyacrylamide molecular chain, resulting in a decrease in the viscosity of the polyacrylamide emulsion polymer. On the other hand, the hydrophobic chains carried by the nano-carbon dots on the montmorillonite surface can change the wettability between the rock pore wall and the crude oil, making it easier for the oil droplets to be carried away by the water flow, thereby improving the efficiency of water flooding. In addition, the modified montmorillonite also has excellent high temperature resistance, which can be grafted into polyacrylamide to improve the high temperature resistance of the polyacrylamide emulsion polymer.

[0044] (2) In the technical solution of the present invention, the modified montmorillonite is uniformly distributed in the three-dimensional network porous aerogel with graphene oxide as the skeleton to form a composite graphene aerogel. On the one hand, the aerogel forming the three-dimensional network porous structure has excellent high temperature resistance, which improves the high temperature resistance of the acrylamide-based emulsion polymer and avoids the thermal oxidation degradation of the acrylamide-based emulsion polymer at high temperature. On the other hand, the modified montmorillonite gives the graphene oxide aerogel excellent salt resistance, and the large specific surface area and pore structure of the aerogel provide a large capacity for metal salt ions, thereby enhancing the salt resistance of the acrylamide-based emulsion polymer.

[0045] (3) In the technical solution of the present invention, konjac glucomannan is deposited on the surface of the composite graphene aerogel. On the one hand, konjac glucomannan can improve the drilling efficiency of the acrylamide-based emulsion polymer, and has the ability to exchange cations, can adsorb and chelate metal salt ions, and further enhance the salt resistance of the acrylamide-based emulsion polymer. On the other hand, konjac glucomannan can copolymerize with the emulsion polymer raw material under the action of the initiator, so that the composite material is embedded in the acrylamide-based emulsion polymer. Konjac glucomannan has a strong hydrogen bond effect with the acrylamide-based emulsion polymer, which increases the cross-linking density of the acrylamide-based emulsion polymer and enhances the viscosity of the acrylamide-based emulsion polymer, thereby slowing down the flow rate of the injected water, so that the injected water can be more evenly distributed in the oil layer, and improving the oil recovery rate.

[0046] (4) In the technical solution of the present invention, water-soluble cellulose has advantages that general surfactants do not have, such as thickening performance, which can significantly increase the viscosity of acrylamide emulsion polymers and improve crude oil recovery. Glycidyl methacrylate and carboxymethyl-β-cyclodextrin are grafted onto water-soluble cellulose. On the one hand, a cavity structure is given to the water-soluble cellulose, which weakens the hydrogen bonding between cellulose molecules and forms a more stable acrylamide emulsion polymer. The double bonds contained in the modified water-soluble cellulose can copolymerize with the emulsion polymer raw materials, so that the modified water-soluble cellulose and acrylamide emulsion polymer form a stable system, thereby improving the viscosity of the acrylamide emulsion polymer. On the other hand, the cavity structure of carboxymethyl-β-cyclodextrin can adsorb metal salt ions, further weakening the shielding effect of metal salt ions on acrylamide emulsion polymers. In addition, the double bonds contained in the modified water-soluble cellulose can also copolymerize with konjac glucomannan in the composite material, thereby forming a cross-linked structure in the acrylamide emulsion polymer, thereby improving the mechanical strength, salt resistance and high temperature resistance of the acrylamide emulsion polymer. DETAILED DESCRIPTION

[0047] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0048] The raw materials used in the examples of the present invention are as follows, and all reagents used are of analytical grade.

[0049] Wherein, the initiator is azobisisobutylamidine hydrochloride.

[0050] The pH regulator is selected from hydrochloric acid with a concentration of 1 mol / L.

[0051] The water-soluble cellulose is selected from carboxymethyl cellulose with a weight average molecular weight of 2.5×10 5 , viscosity 700 mPa·s, purchased from Shanghai MacLean Biochemical Technology Co., Ltd.

[0052] The particle size of graphene oxide is 0.8 μm.

[0053] The reducing agent is ascorbic acid.

[0054] The montmorillonite is sodium montmorillonite with a particle size of 0.3 μm, and the cationic quaternary ammonium salt is hexadecyltrimethylammonium bromide.

[0055] Cationic quaternary ammonium salt intercalated montmorillonite is specifically prepared by the following steps:

[0056] 8.3 g of hexadecyltrimethylammonium bromide was added to 100 mL of deionized water and stirred evenly. 5.5 g of montmorillonite was added and stirred at 60°C for 2 h. The mixture was heated to 70°C and aged for 12 h. The mixture was centrifuged at 4000 r / min for 10 min to collect the solid. The solid was washed three times with deionized water and dried in an oven at 80°C for 10 min to obtain cationic quaternary ammonium salt intercalated montmorillonite. Example

[0057] A method for preparing an emulsion polymer for oil displacement comprises the following steps:

[0058] S1. mixing glycidyl methacrylate, carboxymethyl-β-cyclodextrin and water-soluble cellulose to obtain modified water-soluble cellulose;

[0059] S2 acrylamide, methyl methacrylate, styrene, hydroxyethyl acrylate and deionized water were mixed and stirred, and hydrochloric acid was added at a concentration of 1 mol / L to adjust the pH to 2 to obtain a monomer solution;

[0060] S3. The modified water-soluble cellulose and the composite material were added to the monomer solution, stirred evenly, an initiator was added, nitrogen was introduced, and the reaction was stirred at 85 ° C for 20 min to obtain an emulsion polymer;

[0061] Wherein, in step S2, the mass ratio of acrylamide, methyl methacrylate, styrene, hydroxyethyl acrylate and deionized water is 60:10:10:3:180;

[0062] In step S3, the mass ratio of the modified water-soluble cellulose, the composite material, the monomer solution and the initiator is 8:5:150:1.

[0063] The modified water-soluble cellulose is specifically prepared by the following steps:

[0064] A1. 0.03 g of tetrabutylammonium bromide, 1 g of carboxymethyl-β-cyclodextrin, and 0.03 g of 2,6-di-tert-butyl-p-cresol were added to 45 mL of dimethyl sulfoxide and stirred. 2 g of glycidyl methacrylate was added and stirred at 60°C for 2 h. Acetic acid was added to adjust the pH to 7 to terminate the reaction. The pale yellow liquid was separated and collected by thin-layer chromatography (ethyl acetate as the developing solvent). The pale yellow liquid was freeze-dried at -12°C for 1 h to obtain modified carboxymethyl-β-cyclodextrin.

[0065] A2. Add 2.1 g of water-soluble cellulose to 90 mL of ethanol and stir. Add 0.4 g of 36% sodium hydroxide solution and stir. Add 0.6 g of modified carboxymethyl-β-cyclodextrin and react at 70°C with stirring for 30 minutes. Cool to room temperature and freeze-dry at -12°C for 1 hour to obtain modified water-soluble cellulose.

[0066] The composite material is specifically prepared by the following steps:

[0067] B1. 4 g of glucose and 0.3 g of sodium dodecyl sulfate were added to 80 mL of deionized water and stirred. 8.1 g of cationic quaternary ammonium salt-intercalated montmorillonite was added and stirred at 500 rpm for 20 min. The mixture was reacted at 170 ° C for 7 h, cooled to room temperature, and the product was removed. The product was washed three times with deionized water and dried in an oven at 70 ° C for 15 min to obtain modified montmorillonite.

[0068] B2. 1.1 g of graphene oxide was added to 90 mL of deionized water and stirred. 0.5 g of modified montmorillonite was added and ultrasonicated at 40 kHz for 20 min. 0.8 g of ascorbic acid was added and stirred. The mixture was stirred at 90 ° C for 1 h to form a gel. The gel was freeze-dried at -20 ° C for 24 h to obtain a composite graphene aerogel.

[0069] B3. Add 5 g of composite graphene aerogel and 1.6 g of konjac glucomannan to 70 mL of ethanol and stir evenly. Add 4 mL of 50% sodium hydroxide solution and stir at 55°C for 20 min. Raise the temperature to 80°C and stir until the ethanol evaporates. Collect the solid, wash it three times with deionized water, and dry it in an oven at 70°C for 10 min to obtain a composite material. Example

[0070] A method for preparing an emulsion polymer for oil displacement comprises the following steps:

[0071] S1. mixing glycidyl methacrylate, carboxymethyl-β-cyclodextrin and water-soluble cellulose to obtain modified water-soluble cellulose;

[0072] S2 acrylamide, methyl methacrylate, styrene, hydroxyethyl acrylate and deionized water were mixed and stirred, and hydrochloric acid was added at a concentration of 1 mol / L to adjust the pH to 2.5 to obtain a monomer solution;

[0073] S3. The modified water-soluble cellulose and the composite material were added to the monomer solution, stirred evenly, an initiator was added, nitrogen was introduced, and the reaction was stirred at 87 ° C for 25 min to obtain an emulsion polymer;

[0074] Wherein, in step S2, the mass ratio of acrylamide, methyl methacrylate, styrene, hydroxyethyl acrylate and deionized water is 70:13:11:4:190;

[0075] In step S3, the mass ratio of the modified water-soluble cellulose, the composite material, the monomer solution and the initiator is 9:5.5:160:1.5.

[0076] The modified water-soluble cellulose is specifically prepared by the following steps:

[0077] A1. Add 0.05 g of tetrabutylammonium bromide, 1.5 g of carboxymethyl-β-cyclodextrin, and 0.04 g of 2,6-di-tert-butyl-p-cresol to 50 mL of dimethyl sulfoxide (DMSO) and stir until uniform. Then add 3 g of glycidyl methacrylate and stir at 65°C for 2.5 h. Acetic acid is added to adjust the pH to 7 to terminate the reaction. The resulting pale yellow liquid is separated by thin-layer chromatography (ethyl acetate as the developing solvent) and freeze-dried at -12°C for 1 h to obtain modified carboxymethyl-β-cyclodextrin.

[0078] A2. Add 2.3 g of water-soluble cellulose to 100 mL of ethanol and stir. Add 0.5 g of 36% sodium hydroxide solution and stir. Add 0.7 g of modified carboxymethyl-β-cyclodextrin and react at 75°C with stirring for 35 minutes. Cool to room temperature and freeze-dry at -12°C for 1 hour to obtain modified water-soluble cellulose.

[0079] The composite material is specifically prepared by the following steps:

[0080] B1. 5 g of glucose and 0.5 g of sodium dodecyl sulfate were added to 100 mL of deionized water and stirred. 8.3 g of cationic quaternary ammonium salt-intercalated montmorillonite was added and stirred at 550 rpm for 25 min. The mixture was reacted at 180°C for 8 h, cooled to room temperature, and the product was removed. The product was washed three times with deionized water and dried in an oven at 70°C for 15 min to obtain modified montmorillonite.

[0081] B2. 1.2 g of graphene oxide was added to 100 mL of deionized water and stirred. 0.6 g of modified montmorillonite was added and ultrasonicated at 50 kHz for 25 min. 0.9 g of ascorbic acid was added and stirred. The mixture was stirred at 95 ° C for 1.5 h to form a gel. The gel was freeze-dried at -20 ° C for 24 h to obtain a composite graphene aerogel.

[0082] B3. Add 5.6 g of composite graphene aerogel and 1.7 g of konjac glucomannan to 80 mL of ethanol and stir evenly. Add 5 mL of 50% sodium hydroxide solution and stir at 60°C for 25 min. Raise the temperature to 85°C and stir until the ethanol evaporates. Collect the solid, wash it three times with deionized water, and dry it in an oven at 70°C for 10 min to obtain a composite material. Example

[0083] A method for preparing an emulsion polymer for oil displacement comprises the following steps:

[0084] S1. mixing glycidyl methacrylate, carboxymethyl-β-cyclodextrin and water-soluble cellulose to obtain modified water-soluble cellulose;

[0085] S2 acrylamide, methyl methacrylate, styrene, hydroxyethyl acrylate and deionized water were mixed and stirred, and hydrochloric acid was added at a concentration of 1 mol / L to adjust the pH to 3 to obtain a monomer solution;

[0086] S3. The modified water-soluble cellulose and the composite material were added to the monomer solution, stirred evenly, an initiator was added, nitrogen was introduced, and the reaction was stirred at 90 ° C for 30 min to obtain an emulsion polymer;

[0087] Wherein, in step S2, the mass ratio of acrylamide, methyl methacrylate, styrene, hydroxyethyl acrylate and deionized water is 80:15:12:5:200;

[0088] In step S3, the mass ratio of the modified water-soluble cellulose, the composite material, the monomer solution and the initiator is 10:6:170:2.

[0089] The modified water-soluble cellulose is specifically prepared by the following steps:

[0090] A1. 0.07 g of tetrabutylammonium bromide, 2 g of carboxymethyl-β-cyclodextrin, and 0.05 g of 2,6-di-tert-butyl-p-cresol were added to 55 mL of dimethyl sulfoxide and stirred. 4 g of glycidyl methacrylate was added and stirred at 70°C for 3 h. Acetic acid was added to adjust the pH to 7 to terminate the reaction. The pale yellow liquid was separated and collected by thin-layer chromatography (ethyl acetate as the developing solvent). The pale yellow liquid was freeze-dried at -12°C for 1 h to obtain modified carboxymethyl-β-cyclodextrin.

[0091] A2. 2.5 g water-soluble cellulose was added to 110 mL ethanol, stirred uniformly, 0.6 g of 36% mass fraction sodium hydroxide solution was added, stirred uniformly, 0.8 g modified carboxymethyl-β-cyclodextrin was added, stirred and reacted at 80°C for 40 min, cooled to room temperature, and freeze-dried at -12°C for 1 h to obtain modified water-soluble cellulose.

[0092] The composite material was specifically prepared by the following steps:

[0093] B1. 6 g of glucose and 0.7 g of sodium dodecyl sulfonate were added to 120 mL of deionized water, stirred uniformly, 8.5 g of cationic quaternary ammonium salt intercalated montmorillonite was added, stirred at 600 r / min for 30 min, then reacted at 190°C for 9 h, cooled to room temperature, and the product was taken out, washed with deionized water for 3 times, and dried in an oven at 70°C for 15 min to obtain modified montmorillonite;

[0094] B2. 1.3 g of graphene oxide was added to 110 mL of deionized water, stirred uniformly, 0.7 g of modified montmorillonite was added, ultrasonically treated at 60 KHz for 30 min, 1 g of ascorbic acid was added, stirred uniformly, and stirred and reacted at 100°C for 2 h to form a gel, and the gel was freeze-dried at -20°C for 24 h to obtain a composite graphene aerogel;

[0095] B3. 6 g of composite graphene aerogel and 1.8 g of konjac glucomannan were added to 90 mL of ethanol, stirred uniformly, 6 mL of 50% mass fraction sodium hydroxide solution was added, stirred at 65°C for 30 min, the temperature was increased to 90°C, and stirring was performed until the ethanol was volatilized, the solid was collected, washed with deionized water for 3 times, and dried in an oven at 70°C for 10 min to obtain a composite material.

[0096] Comparative Example 1

[0097] A preparation method of an emulsion polymer for oil displacement, comprising the following preparation steps:

[0098] S1. Glycerol methacrylate, carboxymethyl-β-cyclodextrin and water-soluble cellulose were mixed and reacted to obtain modified water-soluble cellulose;

[0099] S2. Acrylamide, methyl methacrylate, styrene, hydroxyethyl acrylate and deionized water were mixed and stirred uniformly, 1 mol / L hydrochloric acid was added to adjust the pH to 3 to obtain a monomer solution;

[0100] S3. The modified water-soluble cellulose and the composite material were added to the monomer solution, stirred uniformly, an initiator was added, nitrogen was introduced, and stirring was performed at 90°C for 30 min to obtain an emulsion polymer;

[0101] Wherein, in step S2, the mass ratio of acrylamide, methyl methacrylate, styrene, hydroxyethyl acrylate and deionized water is 80:15:12:5:200;

[0102] In step S3, the mass ratio of the modified water-soluble cellulose, the composite material, the monomer solution and the initiator is 10:6:170:2.

[0103] The modified water-soluble cellulose is specifically prepared by the following steps:

[0104] A1. 0.07 g of tetrabutylammonium bromide, 2 g of carboxymethyl-β-cyclodextrin, and 0.05 g of 2,6-di-tert-butyl-p-cresol were added to 55 mL of dimethyl sulfoxide and stirred. 4 g of glycidyl methacrylate was added and stirred at 70°C for 3 h. Acetic acid was added to adjust the pH to 7 to terminate the reaction. The pale yellow liquid was separated and collected by thin-layer chromatography (ethyl acetate as the developing solvent). The pale yellow liquid was freeze-dried at -12°C for 1 h to obtain modified carboxymethyl-β-cyclodextrin.

[0105] A2. Add 2.5 g of water-soluble cellulose to 110 mL of ethanol and stir. Add 0.6 g of 36% sodium hydroxide solution and stir. Add 0.8 g of modified carboxymethyl-β-cyclodextrin and react at 80°C with stirring for 40 minutes. Cool to room temperature and freeze-dry at -12°C for 1 hour to obtain modified water-soluble cellulose.

[0106] The composite material is specifically prepared by the following steps:

[0107] B1. 6 g of glucose and 0.7 g of sodium dodecyl sulfate were added to 120 mL of deionized water and stirred. 8.5 g of sodium montmorillonite was added and stirred at 600 rpm for 30 min. The mixture was reacted at 190°C for 9 h, cooled to room temperature, and the product was removed. The product was washed three times with deionized water and dried in an oven at 70°C for 15 min to obtain modified montmorillonite.

[0108] B2. 1.3 g of graphene oxide was added to 110 mL of deionized water and stirred. 0.7 g of modified montmorillonite was added and ultrasonicated at 60 kHz for 30 min. 1 g of ascorbic acid was added and stirred. The mixture was stirred at 100 ° C for 2 h to form a gel. The gel was freeze-dried at -20 ° C for 24 h to obtain a composite graphene aerogel.

[0109] B3. Add 6 g of composite graphene aerogel and 1.8 g of konjac glucomannan to 90 mL of ethanol and stir evenly. Add 6 mL of 50% sodium hydroxide solution and stir at 65°C for 30 min. Raise the temperature to 90°C and stir until the ethanol evaporates. Collect the solid, wash it three times with deionized water, and dry it in an oven at 70°C for 10 min to obtain a composite material.

[0110] Comparative Example 2

[0111] A method for preparing an emulsion polymer for oil displacement comprises the following steps:

[0112] S1. mixing glycidyl methacrylate, carboxymethyl-β-cyclodextrin and water-soluble cellulose to obtain modified water-soluble cellulose;

[0113] S2 acrylamide, methyl methacrylate, styrene, hydroxyethyl acrylate and deionized water were mixed and stirred, and hydrochloric acid was added at a concentration of 1 mol / L to adjust the pH to 3 to obtain a monomer solution;

[0114] S3. The modified water-soluble cellulose and the composite material were added to the monomer solution, stirred evenly, an initiator was added, nitrogen was introduced, and the reaction was stirred at 90 ° C for 30 min to obtain an emulsion polymer;

[0115] Wherein, in step S2, the mass ratio of acrylamide, methyl methacrylate, styrene, hydroxyethyl acrylate and deionized water is 80:15:12:5:200;

[0116] In step S3, the mass ratio of the modified water-soluble cellulose, the composite material, the monomer solution and the initiator is 10:6:170:2.

[0117] The modified water-soluble cellulose is specifically prepared by the following steps:

[0118] A1. 0.07 g of tetrabutylammonium bromide, 2 g of carboxymethyl-β-cyclodextrin, and 0.05 g of 2,6-di-tert-butyl-p-cresol were added to 55 mL of dimethyl sulfoxide and stirred. 4 g of glycidyl methacrylate was added and stirred at 70°C for 3 h. Acetic acid was added to adjust the pH to 7 to terminate the reaction. The pale yellow liquid was separated and collected by thin-layer chromatography (ethyl acetate as the developing solvent). The pale yellow liquid was freeze-dried at -12°C for 1 h to obtain modified carboxymethyl-β-cyclodextrin.

[0119] A2. Add 2.5 g of water-soluble cellulose to 110 mL of ethanol and stir. Add 0.6 g of 36% sodium hydroxide solution and stir. Add 0.8 g of modified carboxymethyl-β-cyclodextrin and react at 80°C with stirring for 40 minutes. Cool to room temperature and freeze-dry at -12°C for 1 hour to obtain modified water-soluble cellulose.

[0120] The composite material is specifically prepared by the following steps:

[0121] B1. 1.3 g of graphene oxide was added to 110 mL of deionized water and stirred. 0.7 g of cationic quaternary ammonium salt-intercalated montmorillonite was added and ultrasonicated at 60 kHz for 30 min. 1 g of ascorbic acid was added and stirred. The mixture was stirred at 100 ° C for 2 h to form a gel. The gel was freeze-dried at -20 ° C for 24 h to obtain a composite graphene aerogel.

[0122] B2. Add 6 g of composite graphene aerogel and 1.8 g of konjac glucomannan to 90 mL of ethanol and stir evenly. Add 6 mL of 50% sodium hydroxide solution and stir at 65°C for 30 min. Raise the temperature to 90°C and stir until the ethanol evaporates. Collect the solid, wash it three times with deionized water, and dry it in an oven at 70°C for 10 min to obtain the composite material.

[0123] Comparative Example 3

[0124] A method for preparing an emulsion polymer for oil displacement comprises the following steps:

[0125] S1. mixing glycidyl methacrylate, carboxymethyl-β-cyclodextrin and water-soluble cellulose to obtain modified water-soluble cellulose;

[0126] S2 acrylamide, methyl methacrylate, styrene, hydroxyethyl acrylate and deionized water were mixed and stirred, and hydrochloric acid was added at a concentration of 1 mol / L to adjust the pH to 3 to obtain a monomer solution;

[0127] S3. The modified water-soluble cellulose and the composite material were added to the monomer solution, stirred evenly, an initiator was added, nitrogen was introduced, and the reaction was stirred at 90 ° C for 30 min to obtain an emulsion polymer;

[0128] Wherein, in step S2, the mass ratio of acrylamide, methyl methacrylate, styrene, hydroxyethyl acrylate and deionized water is 80:15:12:5:200;

[0129] In step S3, the mass ratio of the modified water-soluble cellulose, the composite material, the monomer solution and the initiator is 10:6:170:2.

[0130] The modified water-soluble cellulose is specifically prepared by the following steps:

[0131] A1. 0.07 g of tetrabutylammonium bromide, 2 g of carboxymethyl-β-cyclodextrin, and 0.05 g of 2,6-di-tert-butyl-p-cresol were added to 55 mL of dimethyl sulfoxide and stirred. 4 g of glycidyl methacrylate was added and stirred at 70°C for 3 h. Acetic acid was added to adjust the pH to 7 to terminate the reaction. The pale yellow liquid was separated and collected by thin-layer chromatography (ethyl acetate as the developing solvent). The pale yellow liquid was freeze-dried at -12°C for 1 h to obtain modified carboxymethyl-β-cyclodextrin.

[0132] A2. Add 2.5 g of water-soluble cellulose to 110 mL of ethanol and stir. Add 0.6 g of 36% sodium hydroxide solution and stir. Add 0.8 g of modified carboxymethyl-β-cyclodextrin and react at 80°C with stirring for 40 minutes. Cool to room temperature and freeze-dry at -12°C for 1 hour to obtain modified water-soluble cellulose.

[0133] The composite material is specifically prepared by the following steps:

[0134] B1. 6 g of glucose and 0.7 g of sodium dodecyl sulfate were added to 120 mL of deionized water and stirred. 8.5 g of cationic quaternary ammonium salt-intercalated montmorillonite was added and stirred at 600 rpm for 30 min. The mixture was reacted at 190 ° C for 9 h, cooled to room temperature, and the product was removed. The product was washed three times with deionized water and dried in an oven at 70 ° C for 15 min to obtain modified montmorillonite.

[0135] B2. Add 6 g of modified montmorillonite and 1.8 g of konjac glucomannan to 90 mL of ethanol and stir evenly. Add 6 mL of 50% sodium hydroxide solution and stir at 65°C for 30 min. Then raise the temperature to 90°C and stir until the ethanol evaporates. Collect the solid, wash it three times with deionized water, and dry it in an oven at 70°C for 10 min to obtain a composite material.

[0136] Comparative Example 4

[0137] A method for preparing an emulsion polymer for oil displacement comprises the following steps:

[0138] S1. mixing glycidyl methacrylate, carboxymethyl-β-cyclodextrin and water-soluble cellulose to obtain modified water-soluble cellulose;

[0139] S2 acrylamide, methyl methacrylate, styrene, hydroxyethyl acrylate and deionized water were mixed and stirred, and hydrochloric acid was added at a concentration of 1 mol / L to adjust the pH to 3 to obtain a monomer solution;

[0140] S3. The modified water-soluble cellulose and the composite material were added to the monomer solution, stirred evenly, an initiator was added, nitrogen was introduced, and the reaction was stirred at 90 ° C for 30 min to obtain an emulsion polymer;

[0141] Wherein, in step S2, the mass ratio of acrylamide, methyl methacrylate, styrene, hydroxyethyl acrylate and deionized water is 80:15:12:5:200;

[0142] In step S3, the mass ratio of the modified water-soluble cellulose, the composite material, the monomer solution and the initiator is 10:6:170:2.

[0143] The modified water-soluble cellulose is specifically prepared by the following steps:

[0144] A1. 0.07 g of tetrabutylammonium bromide, 2 g of carboxymethyl-β-cyclodextrin, and 0.05 g of 2,6-di-tert-butyl-p-cresol were added to 55 mL of dimethyl sulfoxide and stirred. 4 g of glycidyl methacrylate was added and stirred at 70°C for 3 h. Acetic acid was added to adjust the pH to 7 to terminate the reaction. The pale yellow liquid was separated and collected by thin-layer chromatography (ethyl acetate as the developing solvent). The pale yellow liquid was freeze-dried at -12°C for 1 h to obtain modified carboxymethyl-β-cyclodextrin.

[0145] A2. Add 2.5 g of water-soluble cellulose to 110 mL of ethanol and stir. Add 0.6 g of 36% sodium hydroxide solution and stir. Add 0.8 g of modified carboxymethyl-β-cyclodextrin and react at 80°C with stirring for 40 minutes. Cool to room temperature and freeze-dry at -12°C for 1 hour to obtain modified water-soluble cellulose.

[0146] The composite material is specifically prepared by the following steps:

[0147] B1. 6 g of glucose and 0.7 g of sodium dodecyl sulfate were added to 120 mL of deionized water and stirred. 8.5 g of cationic quaternary ammonium salt-intercalated montmorillonite was added and stirred at 600 rpm for 30 min. The mixture was reacted at 190 ° C for 9 h, cooled to room temperature, and the product was removed. The product was washed three times with deionized water and dried in an oven at 70 ° C for 15 min to obtain modified montmorillonite.

[0148] B2. Add 1.3 g of graphene oxide to 110 mL of deionized water and stir well. Then add 0.7 g of modified montmorillonite and ultrasonicate at 60 kHz for 30 min. Then add 1 g of ascorbic acid and stir well. Stir and react at 100°C for 2 h to form a gel. The gel is freeze-dried at -20°C for 24 h to obtain a composite material.

[0149] Comparative Example 5

[0150] A method for preparing an emulsion polymer for oil displacement comprises the following steps:

[0151] S1. mixing glycidyl methacrylate, carboxymethyl-β-cyclodextrin and water-soluble cellulose to obtain modified water-soluble cellulose;

[0152] S2 acrylamide, methyl methacrylate, styrene, hydroxyethyl acrylate and deionized water were mixed and stirred, and hydrochloric acid was added at a concentration of 1 mol / L to adjust the pH to 3 to obtain a monomer solution;

[0153] S3. The modified water-soluble cellulose and the composite material were added to the monomer solution, stirred evenly, an initiator was added, nitrogen was introduced, and the reaction was stirred at 90 ° C for 30 min to obtain an emulsion polymer;

[0154] Wherein, in step S2, the mass ratio of acrylamide, methyl methacrylate, styrene, hydroxyethyl acrylate and deionized water is 80:15:12:5:200;

[0155] In step S3, the mass ratio of the modified water-soluble cellulose, the composite material, the monomer solution and the initiator is 10:6:170:2.

[0156] The modified water-soluble cellulose is specifically prepared by the following steps:

[0157] Add 2.5 g of water-soluble cellulose to 110 mL of ethanol and stir evenly. Add 0.6 g of 36% sodium hydroxide solution and stir evenly. Add 0.8 g of carboxymethyl-β-cyclodextrin and stir at 80 ° C for 40 minutes. Cool to room temperature and freeze-dry at -12 ° C for 1 hour to obtain modified water-soluble cellulose.

[0158] The composite material is specifically prepared by the following steps:

[0159] B1. 6 g of glucose and 0.7 g of sodium dodecyl sulfate were added to 120 mL of deionized water and stirred. 8.5 g of cationic quaternary ammonium salt-intercalated montmorillonite was added and stirred at 600 rpm for 30 min. The mixture was reacted at 190 ° C for 9 h, cooled to room temperature, and the product was removed. The product was washed three times with deionized water and dried in an oven at 70 ° C for 15 min to obtain modified montmorillonite.

[0160] B2. 1.3 g of graphene oxide was added to 110 mL of deionized water and stirred. 0.7 g of modified montmorillonite was added and ultrasonicated at 60 kHz for 30 min. 1 g of ascorbic acid was added and stirred. The mixture was stirred at 100 ° C for 2 h to form a gel. The gel was freeze-dried at -20 ° C for 24 h to obtain a composite graphene aerogel.

[0161] B3. Add 6 g of composite graphene aerogel and 1.8 g of konjac glucomannan to 90 mL of ethanol and stir evenly. Add 6 mL of 50% sodium hydroxide solution and stir at 65°C for 30 min. Raise the temperature to 90°C and stir until the ethanol evaporates. Collect the solid, wash it three times with deionized water, and dry it in an oven at 70°C for 10 min to obtain a composite material.

[0162] Comparative Example 6

[0163] A method for preparing an emulsion polymer for oil displacement comprises the following steps:

[0164] S1. mixing glycidyl methacrylate, carboxymethyl-β-cyclodextrin and water-soluble cellulose to obtain modified water-soluble cellulose;

[0165] S2 acrylamide, methyl methacrylate, styrene, hydroxyethyl acrylate and deionized water were mixed and stirred, and hydrochloric acid was added at a concentration of 1 mol / L to adjust the pH to 3 to obtain a monomer solution;

[0166] S3. The modified water-soluble cellulose and the composite material were added to the monomer solution, stirred evenly, an initiator was added, nitrogen was introduced, and the reaction was stirred at 90 ° C for 30 min to obtain an emulsion polymer;

[0167] Wherein, in step S2, the mass ratio of acrylamide, methyl methacrylate, styrene, hydroxyethyl acrylate and deionized water is 80:15:12:5:200;

[0168] In step S3, the mass ratio of the modified water-soluble cellulose, the composite material, the monomer solution and the initiator is 10:6:170:2.

[0169] The modified water-soluble cellulose is specifically prepared by the following steps:

[0170] Add 2.5 g of water-soluble cellulose to 110 mL of ethanol and stir evenly. Add 0.6 g of 36% sodium hydroxide solution and stir evenly. Add 0.8 g of glycidyl methacrylate and stir at 80 °C for 40 min. Cool to room temperature and freeze-dry at -12 °C for 1 h to obtain modified water-soluble cellulose.

[0171] The composite material is specifically prepared by the following steps:

[0172] B1. 6 g of glucose and 0.7 g of sodium dodecyl sulfate were added to 120 mL of deionized water and stirred. 8.5 g of cationic quaternary ammonium salt-intercalated montmorillonite was added and stirred at 600 rpm for 30 min. The mixture was reacted at 190 ° C for 9 h, cooled to room temperature, and the product was removed. The product was washed three times with deionized water and dried in an oven at 70 ° C for 15 min to obtain modified montmorillonite.

[0173] B2. 1.3 g of graphene oxide was added to 110 mL of deionized water and stirred. 0.7 g of modified montmorillonite was added and ultrasonicated at 60 kHz for 30 min. 1 g of ascorbic acid was added and stirred. The mixture was stirred at 100 ° C for 2 h to form a gel. The gel was freeze-dried at -20 ° C for 24 h to obtain a composite graphene aerogel.

[0174] B3. Add 6g of composite graphene aerogel and 1.8g of konjac glucomannan to 90mL of ethanol, stir evenly, add 6mL of 50% sodium hydroxide solution, stir at 65℃ for 30min, heat to 90℃, stir until the ethanol evaporates, collect the solid, wash the solid with deionized water three times, and dry in an oven at 70℃ for 10min to obtain a composite material.

[0175] The properties of the emulsion polymers prepared in Examples 1-3 and Comparative Examples 1-6 were tested.

[0176] Prepare high-mineralization simulated formation water containing 177 mg / L Mg 2+ , 700mg / L of Ca 2+ , 11668mg / L K + and Na + , 20323 mg / L Cl - , its total mineralization is 32868 mg / L,

[0177] Viscosity test: The prepared emulsion polymer was dissolved in prepared high-mineralization simulated formation water at a concentration of 0.15%. After the emulsion polymer solution was prepared, the apparent viscosity of the emulsion polymer solution at 25°C was measured using a DV-III ULTRA rotational viscometer, which was recorded as the initial apparent viscosity (n1).

[0178] Thermal stability test: The emulsion after apparent viscosity measurement was heat aged in a 90°C oven for 90 days, and the apparent viscosity of the emulsion polymer was measured;

[0179] Surface tension measurement: The prepared emulsion polymer was prepared into a solution with deionized water at a concentration of 0.15%, and the surface tension of the solution was measured using a DCAT 21 surface tension meter (Data Physics, Germany).

[0180] Oil displacement performance test: the end face of the artificial core (core length 8.5 cm, inner diameter 2.3 cm) was ground flat and dried at 85℃; the simulated oil sample: crude oil and neutral kerosene in a weight ratio of 1:0.9 (crude oil and neutral kerosene from Shengli Oilfield); the simulated formation water is the high salinity simulated formation water prepared above;

[0181] After the artificial core was saturated with the high salinity simulated formation water prepared above and the bound water was established with the simulated oil sample, the prepared oil displacement agent containing the emulsion polymer was used for displacement, and when the water content of the effluent reached 96%, the calculated oil recovery rate (%) was calculated;

[0182] Emulsion polymer oil displacement agent: the concentration of the emulsion polymer prepared above was 1000 mg / L, sodium dodecyl diphenyl ether sulfonate 300 mg / L, and sodium hydroxide solution 1000 mg / L;

[0183] The test results are shown in Table 1 below.

[0184] Table 1 Performance test of emulsion polymers prepared in Examples 1-3 and Comparative Examples 1-6

[0185] project Apparent viscosity at 25℃ (mPa·s) Apparent viscosity at 90℃ (mPa·s) Surface tension mN / s Recovery rate / % Example 1 42.3 21.9 71.5 59.6 Example 2 43.6 23.3 72.5 60.3 Example 3 41.5 20.5 71.1 59.1 Comparative Example 1 36.6 14.1 63.2 32.6 Comparative Example 2 35.2 11.3 62.4 29.7 Comparative Example 3 37.9 11.9 63.2 28.2 Comparative Example 4 38.9 16.1 60.8 30.2 Comparative Example 5 35.8 12.2 59.1 30.1 Comparative Example 6 39.6 26.5 64.8 33.9

[0186] As can be seen from the data in Table 1, the emulsion polymers prepared in Examples 1-3 have excellent mechanical strength, salt resistance and high temperature resistance.

[0187] In Comparative Example 1, the apparent viscosity and recovery rate of the emulsion polymer into which the composite material prepared by replacing the cationic quaternary ammonium salt intercalated montmorillonite with sodium-based montmorillonite was added decreased, proving that the cationic quaternary ammonium salt intercalated montmorillonite has a large interlayer spacing, is beneficial to adsorbing metal salt ions in the oil well, improves the salt resistance of the acrylamide-based emulsion polymer, and is beneficial to the in-situ synthesis of amphiphilic nanocarbon dots in the interlayer or surface of the montmorillonite, thereby improving the efficiency of water flooding.

[0188] In Comparative Example 2, the apparent viscosity and recovery rate of the emulsion polymer into which the composite material prepared by replacing the modified montmorillonite with the cationic quaternary ammonium salt intercalated montmorillonite was added decreased, proving that the in-situ synthesis of amphiphilic nanocarbon dots in the interlayer or surface of the cationic quaternary ammonium salt intercalated montmorillonite can further chelate cationic groups in the oil field, improve the salt resistance of the acrylamide-based emulsion polymer, and the nanocarbon dots are on the surface of the montmorillonite, the hydrophobic chains carried thereby can change the wettability between the rock pore wall and the crude oil, so that the oil droplets are more easily carried away by the water flow, thereby improving the efficiency of water flooding. In addition, the modified montmorillonite also has excellent high temperature resistance.

[0189] In Comparative Example 3, the composite graphene aerogel is replaced with a composite material prepared by modified montmorillonite and added to the emulsion polymer. Its apparent viscosity and recovery rate decrease, proving that the modified montmorillonite is uniformly distributed in the three-dimensional network porous aerogel with graphene oxide as the skeleton, and has excellent high temperature resistance. The large specific surface area and pore structure of the aerogel provide a larger capacity for metal salt ions, thereby enhancing the salt resistance of the acrylamide-based emulsion polymer.

[0190] In Comparative Example 4, the composite material prepared without adding konjac glucomannan was added to the emulsion polymer, and its apparent viscosity and recovery rate decreased, which proved that konjac glucomannan can improve the drilling efficiency of the acrylamide-based emulsion polymer and enhance the salt tolerance of the acrylamide-based emulsion polymer. In addition, under the action of the initiator, konjac glucomannan can copolymerize with the emulsion polymer raw material, so that the composite material is embedded in the acrylamide-based emulsion polymer, thereby increasing the crosslinking density of the acrylamide-based emulsion polymer and enhancing the viscosity of the acrylamide-based emulsion polymer.

[0191] In Comparative Example 5, modified water-soluble cellulose prepared by replacing modified carboxymethyl-β-cyclodextrin with carboxymethyl-β-cyclodextrin was added to the emulsion polymer, and its apparent viscosity and recovery rate decreased, proving that glycidyl methacrylate was grafted on the water-soluble cellulose, and the double bonds contained therein could copolymerize with the emulsion polymer raw material, so that the modified water-soluble cellulose and the acrylamide-based emulsion polymer formed a stable system, and could also copolymerize with the konjac glucomannan in the composite material, thereby forming a cross-linked structure in the acrylamide-based emulsion polymer, thereby improving the mechanical strength, salt resistance and high temperature resistance of the acrylamide-based emulsion polymer.

[0192] In Comparative Example 6, modified water-soluble cellulose prepared by replacing modified carboxymethyl-β-cyclodextrin with glycidyl methacrylate was added to the emulsion polymer, and its apparent viscosity and recovery rate decreased, proving that carboxymethyl-β-cyclodextrin was grafted onto the water-soluble cellulose, giving the water-soluble cellulose a cavity structure, weakening the hydrogen bonding between cellulose molecules, and forming a more stable acrylamide-based emulsion polymer. The cavity structure can adsorb metal salt ions, further weakening the shielding effect of metal salt ions on the acrylamide-based emulsion polymer.

[0193] Throughout the specification, references to terms such as "one embodiment," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0194] The above contents are merely examples and explanations of the present invention. Those skilled in the art may make various modifications or additions to the described specific embodiments or replace them in similar ways. As long as they do not deviate from the invention or exceed the scope defined by the claims, they should all fall within the scope of protection of the present invention.

Claims

1. A method for preparing an emulsion polymer for oil displacement, characterized in that: The method comprises the following preparation steps: S1. mixing glycidyl methacrylate, carboxymethyl-β-cyclodextrin and water-soluble cellulose to obtain modified water-soluble cellulose; S2 acrylamide, methyl methacrylate, styrene, hydroxyethyl acrylate and deionized water were mixed and stirred, and a pH adjuster was added to adjust the pH to 2-3 to obtain a monomer solution; S3. The modified water-soluble cellulose and the composite material are added to the monomer solution, stirred evenly, an initiator is added, and the reaction is stirred at 85-90 ° C for 20-30min to obtain an emulsion polymer; The composite material is obtained by mixing graphene oxide, a reducing agent and modified montmorillonite, and then surface-modifying the composite material with konjac glucomannan. The modified montmorillonite is obtained by intercalating montmorillonite with cationic quaternary ammonium salt and then reacting the intercalated montmorillonite with glucose and sodium dodecyl sulfate.

2. The method for preparing an oil displacement emulsion polymer according to claim 1, wherein In step S1, the modified water-soluble cellulose is specifically prepared by the following steps: A1. Tetrabutylammonium bromide, carboxymethyl-β-cyclodextrin, and 2,6-di-tert-butyl-p-cresol were added to dimethyl sulfoxide and stirred uniformly. Glycidyl methacrylate was added and stirred at 60-70°C for 2-3 hours. Acetic acid was added to adjust the pH to terminate the reaction. The light yellow liquid was separated and collected, and then freeze-dried to obtain modified carboxymethyl-β-cyclodextrin. A2. Add water-soluble cellulose to ethanol and stir evenly. Add sodium hydroxide solution and stir evenly. Add modified carboxymethyl-β-cyclodextrin and stir at 70-80°C for 30-40 minutes. Cool to room temperature and freeze-dry to obtain modified water-soluble cellulose.

3. The method for preparing an oil displacement emulsion polymer according to claim 2, wherein In step A1, the amount ratio of tetrabutylammonium bromide, carboxymethyl-β-cyclodextrin, 2,6-di-tert-butyl-p-cresol, dimethyl sulfoxide and glycidyl methacrylate is (0.03-0.07) g:(1-2) g:(0.03-0.05) g:(45-55) mL:(2-4) g.

4. The method for preparing an oil displacement emulsion polymer according to claim 2, wherein In step A2, the ratio of the water-soluble cellulose, ethanol, sodium hydroxide solution and modified carboxymethyl-β-cyclodextrin is (2.1-2.5) g: (90-110) mL: (0.4-0.6) g: (0.6-0.8) g.

5. The method for preparing an oil displacement emulsion polymer according to claim 1, wherein In step S2, the mass ratio of acrylamide, methyl methacrylate, styrene, hydroxyethyl acrylate and deionized water is (60-80):(10-15):(10-12):(3-5):(180-200).

6. The method for preparing an oil displacement emulsion polymer according to claim 1, wherein In step S3, the mass ratio of the modified water-soluble cellulose, the composite material, the monomer solution and the initiator is (8-10):(5-6):(150-170):(1-2).

7. The method for preparing an oil displacement emulsion polymer according to claim 1, wherein In step S3, the composite material is specifically prepared by the following steps: B1. Glucose and sodium dodecyl sulfate were added to deionized water, stirred evenly, and a cationic quaternary ammonium salt intercalated montmorillonite was added. After stirring at 500-600 r / min for 20-30 min, the reaction was incubated at 170-190 ° C for 7-9 h, cooled to room temperature, and the product was removed. The product was washed and dried to obtain a modified montmorillonite. B2. Graphene oxide was added to deionized water and stirred, modified montmorillonite was added, ultrasonicated at 40-60 kHz for 20-30 min, a reducing agent was added, stirred, and stirred at 90-100 ° C for 1-2 h to form a gel. The gel was freeze-dried to obtain a composite graphene aerogel; B3. Add the composite graphene aerogel and konjac glucomannan to ethanol, stir evenly, add sodium hydroxide solution, stir at 55-65°C for 20-30 minutes, raise the temperature to 80-90°C, stir until the ethanol evaporates, collect the solid, wash the solid, and dry it to obtain a composite material.

8. The method for preparing an oil displacement emulsion polymer according to claim 7, wherein: In step B1, the ratio of glucose, sodium dodecyl sulfate, deionized water and cationic quaternary ammonium salt intercalated montmorillonite is (4-6) g: (0.3-0.7) g: (80-120) mL: (8.1-8.5) g.

9. The method for preparing an oil displacement emulsion polymer according to claim 7, wherein: In step B2, the ratio of the graphene oxide, deionized water, modified montmorillonite and reducing agent is (1.1-1.3) g: (90-110) mL: (0.5-0.7) g: (0.8-1) g.

10. The method for preparing an oil displacement emulsion polymer according to claim 7, wherein: In step B3, the ratio of the composite graphene aerogel, konjac glucomannan, ethanol and sodium hydroxide solution is (5-6) g: (1.6-1.8) g: (70-90) mL: (4-6) mL.