Preparation method of emulsion polymer for oil displacement

Abstract

The invention relates to the technical field of oil-gas field development, and discloses a preparation method of an emulsion polymer for oil displacement, which comprises the following preparation steps: mixing glycidyl methacrylate, carboxymethyl-beta-cyclodextrin and water-soluble cellulose for reaction to obtain modified water-soluble cellulose; the preparation method comprises the following steps: mixing acrylamide, methyl methacrylate, styrene, hydroxyethyl acrylate and deionized water, uniformly stirring, and adding a pH regulator to obtain a monomer solution; adding the modified water-soluble cellulose and the composite material into a monomer solution, uniformly stirring, adding an initiator, and stirring for reaction to obtain an emulsion polymer. The water-soluble cellulose can obviously improve the viscosity of the acrylamide-based emulsion polymer and improve the crude oil recovery ratio; glycidyl methacrylate and carboxymethyl-beta-cyclodextrin are grafted on water-soluble cellulose, so that the water-soluble cellulose is endowed with a cavity structure, and formation of a more stable acrylamide-based emulsion polymer is facilitated.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas field development, and specifically provides a preparation method of an emulsion polymer for oil displacement. Background Art

[0002] According to the different stages of oilfield development, oil extraction is generally divided into three stages: primary oil recovery, which utilizes the energy of the oil reservoir to extract oil, and the oil recovery efficiency at this stage is generally only about 15%; secondary oil recovery, which injects water and gas into the oil reservoir to supplement the energy of the oil reservoir to achieve the purpose of extraction, and the oil recovery rate is 30 - 40%; tertiary oil recovery, which is the stage of extracting crude oil through new technologies such as physics, chemistry, and biology. In order to efficiently extract the residual oil in the formation, it is urgent to develop a tertiary oil recovery method suitable for the special geological conditions in China; Polyacrylamide is a water-soluble polymer, with good water solubility and high chemical activity. It is easy to obtain various modified products with branched or network structures through grafting or cross-linking, and is widely used in oilfield exploitation operations such as drilling, well completion, cementing, fracturing, and enhanced oil recovery. However, polyacrylamide has poor salt tolerance. In salt water, the carboxylic acid groups in the polyacrylamide molecules are easily neutralized, and the polyacrylamide molecules are in a curled state, resulting in a decrease in the solution viscosity, affecting the oil recovery rate, and the mechanical strength and high-temperature resistance of polyacrylamide are also poor. Summary of the Invention

[0003] The present invention provides a preparation method of an emulsion polymer for oil displacement, which solves the problems of poor salt tolerance, mechanical strength, and high-temperature resistance of polyacrylamide.

[0004] The technical solution of the present invention: A preparation method of an emulsion polymer for oil displacement, comprising the following preparation steps: S1. Mix glycidyl methacrylate, carboxymethyl-β-cyclodextrin, and water-soluble cellulose to react to obtain modified water-soluble cellulose; S2. Mix acrylamide, methyl methacrylate, styrene, 2-hydroxyethyl acrylate, and deionized water, stir evenly, add a pH regulator to adjust the pH to 2 - 3 to obtain a monomer solution; S3. Add the modified water-soluble cellulose and the composite material to the monomer solution, stir evenly, add an initiator, and stir and react at 85 - 90 °C for 20 - 30 min to obtain an emulsion polymer; The composite material is obtained by mixing graphene oxide, a reducing agent, and modified montmorillonite, and then subjecting it to surface modification with konjac glucomannan; The modified montmorillonite is obtained by intercalating montmorillonite with a cationic quaternary ammonium salt and then mixing and reacting it with glucose and sodium dodecyl sulfate.

[0005] Further, the water-soluble cellulose is selected from any one of carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, and hydroxypropyl methyl cellulose.

[0006] Further, the initiator is selected from any one of azobisamidinium hydrochloride, azobisisobutyramidine hydrochloride, azodiisobutyronitrile, and azobisisobutyronitrile.

[0007] Further, the pH regulator is selected from any one of hydrochloric acid, phosphoric acid, acetic acid, sulfuric acid, sodium hydroxide, and potassium hydroxide.

[0008] Further, in step S2, the mass ratio of acrylamide, methyl methacrylate, styrene, 2-hydroxyethyl acrylate, and deionized water is (60 - 80):(10 - 15):(10 - 12):(3 - 5):(180 - 200).

[0009] Further, 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).

[0010] Further, in step S1, the modified water-soluble cellulose is specifically prepared by the following steps: A1. Add tetrabutylammonium bromide, carboxymethyl-β-cyclodextrin, and 2,6-di-tert-butyl-p-cresol to dimethyl sulfoxide, stir evenly, add glycidyl methacrylate, stir and react at 60 - 70 °C for 2 - 3 h, add acetic acid to adjust the pH to terminate the reaction, separate and collect the light yellow liquid, and freeze-dry the light yellow liquid to obtain modified carboxymethyl-β-cyclodextrin; A2. Add the water-soluble cellulose to ethanol, stir evenly, add sodium hydroxide solution, stir evenly, add the modified carboxymethyl-β-cyclodextrin, stir and react at 70 - 80 °C for 30 - 40 min, cool to room temperature, and freeze-dry to obtain the modified water-soluble cellulose.

[0011] Further, in the above A1 reaction process, in the organic solvent dimethyl sulfoxide, tetrabutylammonium bromide acts as a catalyst, 2,6-di-tert-butyl-p-cresol acts 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 carboxymethyl-β-cyclodextrin to obtain modified carboxymethyl-β-cyclodextrin.

[0012] Further, in the above A2 reaction process, the lipid group and the hydroxyl group generated by ring-opening in the modified carboxymethyl-β-cyclodextrin can be combined with the oxygen-containing functional groups on the water-soluble cellulose through chemical bonds, so that the modified carboxymethyl-β-cyclodextrin is grafted onto the water-soluble cellulose to obtain the modified water-soluble cellulose.

[0013] Further, in step A1, the dosage 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.

[0014] Further, in step A2, the dosage 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.

[0015] Further, the composite material is specifically prepared by the following steps: B1. Add glucose and sodium dodecyl sulfonate into deionized water, stir evenly, add cationic quaternary ammonium salt intercalated montmorillonite, stir at 500 - 600 r / min for 20 - 30 min, then react at 170 - 190 °C for 7 - 9 h, cool to room temperature, take out the product, wash and dry the product to obtain modified montmorillonite; B2. Add graphene oxide into deionized water, stir evenly, add modified montmorillonite, ultrasonically treat at 40 - 60 KHz for 20 - 30 min, add a reducing agent, stir evenly, stir and react at 90 - 100 °C for 1 - 2 h to form a gel-like substance, and freeze-dry the gel to obtain a composite graphene aerogel; B3. Add the composite graphene aerogel and konjac glucomannan into ethanol, stir evenly, add sodium hydroxide solution, stir at 55 - 65 °C for 20 - 30 min, raise the temperature to 80 - 90 °C, stir until the ethanol evaporates, collect the solid, wash and dry the solid to obtain the composite material.

[0016] Further, during the reaction process of B1 above, glucose and sodium dodecyl sulfonate can act on the interlayer or surface of the cationic quaternary ammonium salt intercalated montmorillonite, and glucose serves as a carbon source and sodium dodecyl sulfonate serves as a surfactant. After the hydrothermal reaction, glucose reacts with sodium dodecyl sulfonate to realize the in-situ synthesis of amphiphilic carbon dots between the interlayers or on the surface of the cationic quaternary ammonium salt intercalated montmorillonite, and modified montmorillonite is obtained.

[0017] Further, during the reaction process of B2 above, the lamellar structure of the modified montmorillonite can be distributed between the layers of graphene oxide, and ascorbic acid serves as a reducing agent, enabling the graphene oxide sheets to form a three-dimensional network porous structure aerogel structure with a graphene oxide framework through π-π conjugation, and making the modified montmorillonite evenly distributed in the porous structure aerogel structure to obtain the composite graphene aerogel.

[0018] Further, in the above B3 reaction process, the konjac glucomannan molecular chain contains a large number of hydroxyl groups, which 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.

[0019] Further, in step B1, the dosage 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.

[0020] Further, in step B2, the dosage ratio of 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.

[0021] Further, in step B3, the dosage 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.

[0022] Further, the particle size of graphene oxide is 0.5 - 1 μm.

[0023] Further, the reducing agent is ascorbic acid.

[0024] Further, the cationic quaternary ammonium salt intercalated montmorillonite is specifically prepared by the following steps: Add the cationic quaternary ammonium salt to deionized water, stir evenly, add montmorillonite, stir at 55 - 65 °C for 1 - 3 h, raise the temperature to 65 - 75 °C, after aging, centrifuge, wash, and dry to obtain the cationic quaternary ammonium salt intercalated montmorillonite.

[0025] Further, during the above reaction process, the cationic functional groups contained in the cationic quaternary ammonium salt can undergo an ion exchange reaction with the cations between the montmorillonite layers, so that the cationic quaternary ammonium salt is intercalated into the montmorillonite layers to expand the layer spacing of the montmorillonite, which is beneficial to adsorbing metal salt ions in oil wells, improving the salt tolerance of acrylamide-based emulsion polymers, and expanding the layer spacing of the montmorillonite, which is beneficial to synthesizing amphiphilic carbon dots between or on the surface of the montmorillonite layers.

[0026] Further, the dosage ratio of the cationic quaternary ammonium salt, deionized water and montmorillonite is (8.2 - 8.4) g : (90 - 110) mL : (5 - 6) g.

[0027] Further, the cationic quaternary ammonium salt is cetyltrimethylammonium bromide.

[0028] Further, the montmorillonite is sodium-based montmorillonite, and the particle size is 0.2 - 0.4 μm.

[0029] The present invention has the following beneficial effects: (1) In the technical solution of the present invention, the cationic quaternary ammonium salt intercalated montmorillonite has a large interlayer spacing, which is beneficial to adsorb metal salt ions in oil wells, improve the salt tolerance of acrylamide-based emulsion polymers, and is also beneficial to synthesize amphiphilic carbon dots between or on the surface of montmorillonite layers; in-situ synthesis of amphiphilic carbon dots between or on the surface of cationic quaternary ammonium salt intercalated montmorillonite, on the one hand, the cationic quaternary ammonium salt intercalated montmorillonite, as a carrier of carbon dots, can load more carbon dots, avoid the aggregation of carbon dots when added to the emulsion polymer, and the hydroxyl and sulfonic acid groups on the surface of the carbon dots can further chelate the cationic groups in the oil field, avoiding the metal salt ions adsorbed between the montmorillonite layers in the polyacrylamide emulsion polymer from being unstable under high shear stress fields and releasing into the polyacrylamide emulsion polymer to neutralize the carboxyl anions of the polyacrylamide molecular chains, resulting in a decrease in the viscosity of the polyacrylamide emulsion polymer. On the other hand, the hydrophobic chains carried by the carbon dots on the surface of the montmorillonite can change the wettability between the rock pore wall and the crude oil, making the oil droplets easier 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 performance, grafted into polyacrylamide, to improve the high-temperature resistance performance of the polyacrylamide emulsion polymer.

[0030] (2) In the technical solution of the present invention, the modified montmorillonite is uniformly distributed in a three-dimensional network porous aerogel with graphene oxide as the skeleton to form a composite graphene aerogel. On the one hand, the aerogel with a three-dimensional network porous structure has excellent high-temperature resistance performance, improving the high-temperature resistance performance of acrylamide-based emulsion polymers and avoiding the thermal-oxidative degradation of acrylamide-based emulsion polymers at high temperatures. On the other hand, the modified montmorillonite endows the graphene oxide aerogel with excellent salt resistance performance, and the large specific surface area and pore structure of the aerogel provide a large capacity for metal salt ions, enhancing the salt tolerance performance of acrylamide-based emulsion polymers.

[0031] (3) In the technical solution of the present invention, depositing konjac glucomannan on the surface of the composite graphene aerogel, on the one hand, konjac glucomannan can improve the drilling efficiency of acrylamide-based emulsion polymers, and has the ability to exchange cations, can adsorb and chelate metal salt ions, further enhancing and improving the salt tolerance performance of acrylamide-based emulsion polymers. On the other hand, under the action of initiators, konjac glucomannan can copolymerize with the raw materials of the emulsion polymer, enabling the composite material to be embedded in the acrylamide-based emulsion polymer, and konjac glucomannan has a strong hydrogen bond interaction with the acrylamide-based emulsion polymer, increasing the crosslinking density of the acrylamide-based emulsion polymer and enhancing the viscosity of the acrylamide-based emulsion polymer, thereby slowing down the flow rate of the injected water, enabling the injected water to be more evenly distributed in the oil reservoir, and improving the oil recovery rate.

[0032] (4) In the technical solution of the present invention, water-soluble cellulose has advantages that general surfactants do not have, such as viscosity-increasing performance, which can significantly increase the viscosity of acrylamide-based emulsion polymers, improve the oil recovery rate. Glycidyl methacrylate and carboxymethyl-β-cyclodextrin are grafted onto water-soluble cellulose. On the one hand, it endows water-soluble cellulose with a cavity structure, weakens the hydrogen bond interaction between cellulose molecules, forms a more stable acrylamide-based emulsion polymer, and the double bonds contained in the modified water-soluble cellulose can copolymerize with the raw materials of the emulsion polymer, making the modified water-soluble cellulose and the acrylamide-based emulsion polymer form a stable system, increasing the viscosity of the acrylamide-based 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 the acrylamide-based emulsion polymer. 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-based emulsion polymer, improving the mechanical strength, salt tolerance and high-temperature resistance of the acrylamide-based emulsion polymer. Detailed implementation mode

[0033] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0034] The raw materials used in the embodiments of the present invention are as follows, and all the reagents used are of analytical grade.

[0035] Among them, the initiator is azodiisobutyramidine hydrochloride.

[0036] The pH regulator is selected from hydrochloric acid with a concentration of 1 mol / L.

[0037] The water-soluble cellulose is selected from carboxymethyl cellulose with a weight average molecular weight of 2.5×10 5 , and the viscosity is 700 mPa·s, purchased from Shanghai Macklin Biochemical Technology Co., Ltd.

[0038] The particle size of graphene oxide is 0.8 μm.

[0039] The reducing agent is ascorbic acid.

[0040] The montmorillonite is sodium-based montmorillonite with a particle size of 0.3 μm, and the cationic quaternary ammonium salt is cetyltrimethylammonium bromide.

[0041] The cationic quaternary ammonium salt intercalated montmorillonite is specifically prepared by the following steps: 8.3 g of cetyltrimethylammonium bromide was added to 100 mL of deionized water, stirred evenly, 5.5 g of montmorillonite was added, stirred at 60 °C for 2 h, heated to 70 °C, aged for 12 h, centrifuged at a rate of 4000 r / min for 10 min, the solid was collected, the solid was washed 3 times with deionized water, and dried in an oven at 80 °C for 10 min to obtain cationic quaternary ammonium salt intercalated montmorillonite. Example

[0042] A preparation method of an emulsion polymer for enhanced oil recovery, comprising the following preparation steps: S1. Glycidyl methacrylate, carboxymethyl-β-cyclodextrin and water-soluble cellulose were mixed and reacted to obtain modified water-soluble cellulose; S2. Acrylamide, methyl methacrylate, styrene, 2-hydroxyethyl acrylate and deionized water were mixed, stirred evenly, and the pH was adjusted to 2 with 1 mol / L hydrochloric acid to obtain a monomer solution; 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 mixture was stirred and reacted at 85 °C for 20 min to obtain an emulsion polymer; Among them, in step S2, the mass ratio of acrylamide, methyl methacrylate, styrene, 2-hydroxyethyl acrylate and deionized water is 60:10:10:3:180; 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.

[0043] The modified water-soluble cellulose was specifically prepared by the following steps: 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, stirred evenly, 2 g of glycidyl methacrylate was added, stirred and reacted at 60 °C for 2 h, acetic acid was added to adjust the pH to 7 to terminate the reaction, and the light yellow liquid was separated and collected by thin layer chromatography (ethyl acetate as the developing agent), and the light yellow liquid was freeze-dried at -12 °C for 1 h to obtain modified carboxymethyl-β-cyclodextrin; A2. 2.1 g of water-soluble cellulose was added to 90 mL of ethanol, stirred evenly, 0.4 g of a 36% sodium hydroxide solution was added, stirred evenly, 0.6 g of modified carboxymethyl-β-cyclodextrin was added, stirred and reacted at 70 °C for 30 min, cooled to room temperature, and freeze-dried at -12 °C for 1 h to obtain modified water-soluble cellulose.

[0044] The composite material was specifically prepared by the following steps: B1. Add 4 g of glucose and 0.3 g of sodium dodecyl sulfonate to 80 mL of deionized water, stir evenly, add 8.1 g of cationic quaternary ammonium salt intercalated montmorillonite, stir at 500 r / min for 20 min, react at 170 °C for 7 h, cool to room temperature, take out the product, wash the product 3 times with deionized water, and dry it in an oven at 70 °C for 15 min to obtain modified montmorillonite; B2. Add 1.1 g of graphene oxide to 90 mL of deionized water, stir evenly, add 0.5 g of modified montmorillonite, ultrasonically treat it at 40 KHz for 20 min, add 0.8 g of ascorbic acid, stir evenly, stir and react at 90 °C for 1 h to form a gel, and freeze-dry the gel at -20 °C for 24 h to obtain composite graphene aerogel; B3. Add 5 g of composite graphene aerogel and 1.6 g of konjac glucomannan to 70 mL of ethanol, stir evenly, add 4 mL of sodium hydroxide solution with a mass fraction of 50%, stir at 55 °C for 20 min, raise the temperature to 80 °C, stir until the ethanol evaporates, collect the solid, wash the solid 3 times with deionized water, and dry it in an oven at 70 °C for 10 min to obtain the composite material. Example

[0045] A preparation method of an emulsion polymer for enhanced oil recovery, comprising the following preparation steps: S1. React glycidyl methacrylate, carboxymethyl-β-cyclodextrin and water-soluble cellulose to obtain modified water-soluble cellulose; S2. Mix acrylamide, methyl methacrylate, styrene, 2-hydroxyethyl acrylate and deionized water, stir evenly, add hydrochloric acid with a concentration of 1 mol / L to adjust the pH to 2.5 to obtain a monomer solution; S3. Add the modified water-soluble cellulose and the composite material to the monomer solution, stir evenly, add an initiator, introduce nitrogen, and stir and react at 87 °C for 25 min to obtain an emulsion polymer; Among them, in step S2, the mass ratio of acrylamide, methyl methacrylate, styrene, 2-hydroxyethyl acrylate and deionized water is 70:13:11:4:190; 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.

[0046] The modified water-soluble cellulose is specifically prepared by the following steps: 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, stir evenly, add 3 g of glycidyl methacrylate, stir and react at 65 °C for 2.5 h, add acetic acid to adjust the pH to 7 to terminate the reaction, separate and collect the light yellow liquid by thin-layer chromatography (ethyl acetate as the developing agent), and freeze-dry the light yellow liquid at -12 °C for 1 h to obtain modified carboxymethyl-β-cyclodextrin; A2. Add 2.3 g of water-soluble cellulose to 100 mL of ethanol, stir evenly, add 0.5 g of sodium hydroxide solution with a mass fraction of 36%, stir evenly, add 0.7 g of modified carboxymethyl-β-cyclodextrin, stir and react at 75 °C for 35 min, cool to room temperature, and freeze-dry at -12 °C for 1 h to obtain modified water-soluble cellulose.

[0047] The composite material is specifically prepared by the following steps: B1. Add 5 g of glucose and 0.5 g of sodium dodecyl sulfonate to 100 mL of deionized water, stir evenly, add 8.3 g of cationic quaternary ammonium salt intercalated montmorillonite, stir at 550 r / min for 25 min, then react at 180 °C for 8 h, cool to room temperature, take out the product, wash the product 3 times with deionized water, and dry it in an oven at 70 °C for 15 min to obtain modified montmorillonite; B2. Add 1.2 g of graphene oxide to 100 mL of deionized water, stir evenly, add 0.6 g of modified montmorillonite, ultrasonically treat at 50 KHz for 25 min, add 0.9 g of ascorbic acid, stir evenly, stir and react at 95 °C for 1.5 h to form a gel, and freeze-dry the gel at -20 °C for 24 h to obtain a composite graphene aerogel; B3. Add 5.6 g of composite graphene aerogel and 1.7 g of konjac glucomannan to 80 mL of ethanol, stir evenly, add 5 mL of sodium hydroxide solution with a mass fraction of 50%, stir at 60 °C for 25 min, raise the temperature to 85 °C, stir until the ethanol evaporates, collect the solid, wash the solid 3 times with deionized water, and dry it in an oven at 70 °C for 10 min to obtain the composite material. Example

[0048] A preparation method of an emulsion polymer for enhanced oil recovery includes the following preparation steps: S1. Mix and react glycidyl methacrylate, carboxymethyl-β-cyclodextrin, and water-soluble cellulose to obtain modified water-soluble cellulose; S2. Mix acrylamide, methyl methacrylate, styrene, 2-hydroxyethyl acrylate, and deionized water, stir evenly, add hydrochloric acid with a concentration of 1 mol / L to adjust the pH to 3 to obtain a monomer solution; S3. Add the modified water-soluble cellulose and the composite material to the monomer solution, stir evenly, add the initiator, introduce nitrogen, and stir and react at 90 °C for 30 min to obtain an emulsion polymer; Among them, in step S2, the mass ratio of acrylamide, methyl methacrylate, styrene, 2-hydroxyethyl acrylate and deionized water is 80:15:12:5:200; 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.

[0049] The modified water-soluble cellulose is specifically prepared by the following steps: A1. Add 0.07 g of tetrabutylammonium bromide, 2 g of carboxymethyl-β-cyclodextrin and 0.05 g of 2,6-di-tert-butyl-p-cresol to 55 mL of dimethyl sulfoxide, stir evenly, add 4 g of glycidyl methacrylate, and stir and react at 70 °C for 3 h. Add acetic acid to adjust the pH to 7 to terminate the reaction. Separate and collect the light yellow liquid by thin layer chromatography (ethyl acetate as the developing agent). The light yellow liquid is freeze-dried at -12 °C for 1 h to obtain modified carboxymethyl-β-cyclodextrin; A2. Add 2.5 g of water-soluble cellulose to 110 mL of ethanol, stir evenly, add 0.6 g of a 36% sodium hydroxide solution, stir evenly, add 0.8 g of modified carboxymethyl-β-cyclodextrin, stir and react 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.

[0050] The composite material is specifically prepared by the following steps: B1. Add 6 g of glucose and 0.7 g of sodium dodecyl sulfonate to 120 mL of deionized water, stir evenly, add 8.5 g of cationic quaternary ammonium salt intercalated montmorillonite, stir at 600 r / min for 30 min, then react at 190 °C for 9 h, cool to room temperature, take out the product, wash the product 3 times with deionized water, and dry it in an oven at 70 °C for 15 min to obtain modified montmorillonite; B2. Add 1.3 g of graphene oxide to 110 mL of deionized water, stir evenly, add 0.7 g of modified montmorillonite, ultrasonically treat it at 60 KHz for 30 min, add 1 g of ascorbic acid, stir evenly, 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 graphene aerogel; B3. Add 6 g of composite graphene aerogel and 1.8 g of konjac glucomannan to 90 mL of ethanol, stir evenly, add 6 mL of sodium hydroxide solution with a mass fraction of 50%, stir at 65 °C for 30 min, heat up to 90 °C, stir until the ethanol volatilizes, collect the solid, wash the solid 3 times with deionized water, and dry it in an oven at 70 °C for 10 min to obtain the composite material.

[0051] Comparative Example 1 A preparation method of an emulsion polymer for enhanced oil recovery, comprising the following preparation steps: S1. React glycidyl methacrylate, carboxymethyl-β-cyclodextrin and water-soluble cellulose to obtain modified water-soluble cellulose; S2. Mix acrylamide, methyl methacrylate, styrene, 2-hydroxyethyl acrylate and deionized water, stir evenly, add hydrochloric acid with a concentration of 1 mol / L to adjust the pH to 3 to obtain a monomer solution; S3. Add the modified water-soluble cellulose and the composite material to the monomer solution, stir evenly, add an initiator, introduce nitrogen, and stir and react at 90 °C for 30 min to obtain an emulsion polymer; Among them, in step S2, the mass ratio of acrylamide, methyl methacrylate, styrene, 2-hydroxyethyl acrylate and deionized water is 80:15:12:5:200; 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.

[0052] The modified water-soluble cellulose is specifically prepared by the following steps: A1. Add 0.07 g of tetrabutylammonium bromide, 2 g of carboxymethyl-β-cyclodextrin and 0.05 g of 2,6-di-tert-butyl-p-cresol to 55 mL of dimethyl sulfoxide, stir evenly, add 4 g of glycidyl methacrylate, stir and react at 70 °C for 3 h, add acetic acid to adjust the pH to 7 to terminate the reaction, separate and collect the light yellow liquid by thin layer chromatography (ethyl acetate as the developing agent), and freeze-dry the light yellow liquid at -12 °C for 1 h to obtain modified carboxymethyl-β-cyclodextrin; A2. Add 2.5 g of water-soluble cellulose to 110 mL of ethanol, stir evenly, add 0.6 g of sodium hydroxide solution with a mass fraction of 36%, stir evenly, add 0.8 g of modified carboxymethyl-β-cyclodextrin, stir and react 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.

[0053] The composite material is specifically prepared by the following steps: B1. Add 6 g of glucose and 0.7 g of sodium dodecyl sulfonate to 120 mL of deionized water, stir evenly, add 8.5 g of sodium montmorillonite, stir at 600 r / min for 30 min, react at 190 °C for 9 h, cool to room temperature, take out the product, wash the product 3 times with deionized water, and dry it in an oven at 70 °C for 15 min to obtain modified montmorillonite; B2. Add 1.3 g of graphene oxide to 110 mL of deionized water, stir evenly, add 0.7 g of modified montmorillonite, ultrasonically treat it at 60 KHz for 30 min, add 1 g of ascorbic acid, stir evenly, stir and react at 100 °C for 2 h to form a gel, and freeze-dry the gel at -20 °C for 24 h to obtain composite graphene aerogel; B3. Add 6 g of composite graphene aerogel and 1.8 g of konjac glucomannan to 90 mL of ethanol, stir evenly, add 6 mL of sodium hydroxide solution with a mass fraction of 50%, stir at 65 °C for 30 min, raise the temperature to 90 °C, stir until the ethanol evaporates, collect the solid, wash the solid 3 times with deionized water, and dry it in an oven at 70 °C for 10 min to obtain the composite material.

[0054] Comparative Example 2 A preparation method of an emulsion polymer for oil displacement, comprising the following preparation steps: S1. React glycidyl methacrylate, carboxymethyl-β-cyclodextrin and water-soluble cellulose to obtain modified water-soluble cellulose; S2. Mix acrylamide, methyl methacrylate, styrene, 2-hydroxyethyl acrylate and deionized water, stir evenly, add hydrochloric acid with a concentration of 1 mol / L to adjust the pH to 3 to obtain a monomer solution; S3. Add the modified water-soluble cellulose and the composite material to the monomer solution, stir evenly, add an initiator, introduce nitrogen, and stir and react at 90 °C for 30 min to obtain an emulsion polymer; Among them, in step S2, the mass ratio of acrylamide, methyl methacrylate, styrene, 2-hydroxyethyl acrylate and deionized water is 80:15:12:5:200; 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.

[0055] The modified water-soluble cellulose is specifically prepared by the following steps: A1. Add 0.07 g of tetrabutylammonium bromide, 2 g of carboxymethyl-β-cyclodextrin, and 0.05 g of 2,6-di-tert-butyl-p-cresol to 55 mL of dimethyl sulfoxide, stir evenly, add 4 g of glycidyl methacrylate, stir and react at 70 °C for 3 h, add acetic acid to adjust the pH to 7 to terminate the reaction, separate and collect the light yellow liquid by thin-layer chromatography (ethyl acetate as the developing agent), and freeze-dry the light yellow liquid at -12 °C for 1 h to obtain modified carboxymethyl-β-cyclodextrin; A2. Add 2.5 g of water-soluble cellulose to 110 mL of ethanol, stir evenly, add 0.6 g of a sodium hydroxide solution with a mass fraction of 36%, stir evenly, add 0.8 g of modified carboxymethyl-β-cyclodextrin, stir and react 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.

[0056] The composite material is specifically prepared by the following steps: B1. Add 1.3 g of graphene oxide to 110 mL of deionized water, stir evenly, add 0.7 g of cationic quaternary ammonium salt intercalated montmorillonite, ultrasonically treat at 60 KHz for 30 min, add 1 g of ascorbic acid, stir evenly, stir and react at 100 °C for 2 h to form a gel, and freeze-dry the gel at -20 °C for 24 h to obtain a composite graphene aerogel; B2. Add 6 g of the composite graphene aerogel and 1.8 g of konjac glucomannan to 90 mL of ethanol, stir evenly, add 6 mL of a sodium hydroxide solution with a mass fraction of 50%, stir at 65 °C for 30 min, raise the temperature to 90 °C, stir until the ethanol evaporates, collect the solid, wash the solid 3 times with deionized water, and dry it in an oven at 70 °C for 10 min to obtain the composite material.

[0057] Comparative Example 3 A preparation method of an emulsion polymer for enhanced oil recovery includes the following preparation steps: S1. Mix and react glycidyl methacrylate, carboxymethyl-β-cyclodextrin, and water-soluble cellulose to obtain modified water-soluble cellulose; S2. Mix acrylamide, methyl methacrylate, styrene, 2-hydroxyethyl acrylate, and deionized water, stir evenly, add hydrochloric acid with a concentration of 1 mol / L to adjust the pH to 3 to obtain a monomer solution; S3. Add the modified water-soluble cellulose and the composite material to the monomer solution, stir evenly, add an initiator, introduce nitrogen, and stir and react at 90 °C for 30 min to obtain an emulsion polymer; Among them, in step S2, the mass ratio of acrylamide, methyl methacrylate, styrene, 2-hydroxyethyl acrylate, and deionized water is 80:15:12:5:200; 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.

[0058] The modified water-soluble cellulose is specifically prepared by the following steps: A1. Add 0.07 g of tetrabutylammonium bromide, 2 g of carboxymethyl-β-cyclodextrin and 0.05 g of 2,6-di-tert-butyl-p-cresol to 55 mL of dimethyl sulfoxide, stir evenly, add 4 g of glycidyl methacrylate, stir and react at 70 °C for 3 h, add acetic acid to adjust the pH to 7 to terminate the reaction, separate and collect the light yellow liquid by thin-layer chromatography (ethyl acetate as the developing agent), and freeze-dry the light yellow liquid at -12 °C for 1 h to obtain modified carboxymethyl-β-cyclodextrin; A2. Add 2.5 g of water-soluble cellulose to 110 mL of ethanol, stir evenly, add 0.6 g of sodium hydroxide solution with a mass fraction of 36%, stir evenly, add 0.8 g of modified carboxymethyl-β-cyclodextrin, stir and react 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.

[0059] The composite material is specifically prepared by the following steps: B1. Add 6 g of glucose and 0.7 g of sodium dodecyl sulfonate to 120 mL of deionized water, stir evenly, add 8.5 g of cationic quaternary ammonium salt intercalated montmorillonite, stir at 600 r / min for 30 min, then react at 190 °C for 9 h, cool to room temperature, take out the product, wash the product 3 times with deionized water, and dry it in an oven at 70 °C for 15 min to obtain modified montmorillonite; B2. Add 6 g of modified montmorillonite and 1.8 g of konjac glucomannan to 90 mL of ethanol, stir evenly, add 6 mL of sodium hydroxide solution with a mass fraction of 50%, stir at 65 °C for 30 min, raise the temperature to 90 °C, stir until the ethanol evaporates, collect the solid, wash the solid 3 times with deionized water, and dry it in an oven at 70 °C for 10 min to obtain the composite material.

[0060] Comparative Example 4 A preparation method of an emulsion polymer for oil displacement includes the following preparation steps: S1. Mix and react glycidyl methacrylate, carboxymethyl-β-cyclodextrin and water-soluble cellulose to obtain modified water-soluble cellulose; S2. Mix acrylamide, methyl methacrylate, styrene, 2-hydroxyethyl acrylate and deionized water, stir evenly, add hydrochloric acid with a concentration of 1 mol / L to adjust the pH to 3 to obtain a monomer solution; S3. Add the modified water-soluble cellulose and the composite material into the monomer solution, stir evenly, add the initiator, introduce nitrogen, and stir and react at 90 °C for 30 min to obtain the emulsion polymer; Among them, in step S2, the mass ratio of acrylamide, methyl methacrylate, styrene, 2-hydroxyethyl acrylate and deionized water is 80:15:12:5:200; 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.

[0061] The modified water-soluble cellulose is specifically prepared by the following steps: A1. Add 0.07 g of tetrabutylammonium bromide, 2 g of carboxymethyl-β-cyclodextrin and 0.05 g of 2,6-di-tert-butyl-p-cresol into 55 mL of dimethyl sulfoxide, stir evenly, add 4 g of glycidyl methacrylate, stir and react at 70 °C for 3 h, add acetic acid to adjust the pH to 7 to terminate the reaction, separate and collect the light yellow liquid by thin layer chromatography (ethyl acetate as the developing agent), and freeze-dry the light yellow liquid at -12 °C for 1 h to obtain the modified carboxymethyl-β-cyclodextrin; A2. Add 2.5 g of water-soluble cellulose into 110 mL of ethanol, stir evenly, add 0.6 g of sodium hydroxide solution with a mass fraction of 36%, stir evenly, add 0.8 g of modified carboxymethyl-β-cyclodextrin, stir and react at 80 °C for 40 min, cool to room temperature, and freeze-dry at -12 °C for 1 h to obtain the modified water-soluble cellulose.

[0062] The composite material is specifically prepared by the following steps: B1. Add 6 g of glucose and 0.7 g of sodium dodecyl sulfonate into 120 mL of deionized water, stir evenly, add 8.5 g of cationic quaternary ammonium salt intercalated montmorillonite, stir at 600 r / min for 30 min, then react at 190 °C for 9 h, cool to room temperature, take out the product, wash the product 3 times with deionized water, and dry it in an oven at 70 °C for 15 min to obtain the modified montmorillonite; B2. Add 1.3 g of graphene oxide into 110 mL of deionized water, stir evenly, add 0.7 g of modified montmorillonite, ultrasonically treat it at 60 KHz for 30 min, add 1 g of ascorbic acid, stir evenly, stir and react at 100 °C for 2 h to form a gel, and freeze-dry the gel at -20 °C for 24 h to obtain the composite material.

[0063] Comparative Example 5 A preparation method of an emulsion polymer for enhanced oil recovery, comprising the following preparation steps: S1. Mix and react glycidyl methacrylate, carboxymethyl-β-cyclodextrin and water-soluble cellulose to obtain modified water-soluble cellulose; S2. Mix acrylamide, methyl methacrylate, styrene, 2-hydroxyethyl acrylate and deionized water, stir evenly, add hydrochloric acid with a concentration of 1 mol / L to adjust the pH to 3 to obtain a monomer solution; S3. Add the modified water-soluble cellulose and the composite material to the monomer solution, stir evenly, add an initiator, introduce nitrogen, and stir and react at 90 °C for 30 min to obtain an emulsion polymer; Among them, in step S2, the mass ratio of acrylamide, methyl methacrylate, styrene, 2-hydroxyethyl acrylate and deionized water is 80:15:12:5:200; 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.

[0064] The modified water-soluble cellulose is specifically prepared by the following steps: Add 2.5 g of water-soluble cellulose to 110 mL of ethanol, stir evenly, add 0.6 g of sodium hydroxide solution with a mass fraction of 36%, stir evenly, add 0.8 g of carboxymethyl-β-cyclodextrin, stir and react at 80 °C for 40 min, cool to room temperature, and freeze-dry at -12 °C for 1 h to obtain the modified water-soluble cellulose.

[0065] The composite material is specifically prepared by the following steps: B1. Add 6 g of glucose and 0.7 g of sodium dodecyl sulfonate to 120 mL of deionized water, stir evenly, add 8.5 g of cationic quaternary ammonium salt intercalated montmorillonite, stir at 600 r / min for 30 min, then react at 190 °C for 9 h, cool to room temperature, take out the product, wash the product 3 times with deionized water, and dry in an oven at 70 °C for 15 min to obtain modified montmorillonite; B2. Add 1.3 g of graphene oxide to 110 mL of deionized water, stir evenly, add 0.7 g of modified montmorillonite, ultrasonically treat at 60 KHz for 30 min, add 1 g of ascorbic acid, stir evenly, stir and react at 100 °C for 2 h to form a gel, and freeze-dry the gel at -20 °C for 24 h to obtain a composite graphene aerogel; B3. Add 6 g of the composite graphene aerogel and 1.8 g of konjac glucomannan to 90 mL of ethanol, stir evenly, add 6 mL of sodium hydroxide solution with a mass fraction of 50%, stir at 65 °C for 30 min, raise the temperature to 90 °C, stir until the ethanol evaporates, collect the solid, wash the solid 3 times with deionized water, and dry in an oven at 70 °C for 10 min to obtain the composite material.

[0066] Comparative Example 6 A preparation method of an emulsion polymer for enhanced oil recovery, comprising the following preparation steps: S1. Mix glycidyl methacrylate, carboxymethyl-β-cyclodextrin, and water-soluble cellulose for reaction to obtain modified water-soluble cellulose; S2. Mix acrylamide, methyl methacrylate, styrene, 2-hydroxyethyl acrylate, and deionized water, stir evenly, add hydrochloric acid with a concentration of 1 mol / L to adjust the pH to 3 to obtain a monomer solution; S3. Add the modified water-soluble cellulose and the composite material to the monomer solution, stir evenly, add an initiator, introduce nitrogen, and stir and react at 90 °C for 30 min to obtain an emulsion polymer; Among them, in step S2, the mass ratio of acrylamide, methyl methacrylate, styrene, 2-hydroxyethyl acrylate, and deionized water is 80:15:12:5:200; 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.

[0067] The modified water-soluble cellulose is specifically prepared by the following steps: Add 2.5 g of water-soluble cellulose to 110 mL of ethanol, stir evenly, add 0.6 g of sodium hydroxide solution with a mass fraction of 36%, stir evenly, add 0.8 g of glycidyl methacrylate, stir and react 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.

[0068] The composite material is specifically prepared by the following steps: B1. Add 6 g of glucose and 0.7 g of sodium dodecyl sulfate to 120 mL of deionized water, stir evenly, add 8.5 g of cationic quaternary ammonium salt intercalated montmorillonite, stir at 600 r / min for 30 min, then react at 190 °C for 9 h, cool to room temperature, take out the product, wash the product 3 times with deionized water, and dry in an oven at 70 °C for 15 min to obtain modified montmorillonite; B2. Add 1.3 g of graphene oxide to 110 mL of deionized water, stir evenly, add 0.7 g of modified montmorillonite, ultrasonically treat at 60 KHz for 30 min, add 1 g of ascorbic acid, stir evenly, stir and react at 100 °C for 2 h to form a gel, and freeze-dry the gel at -20 °C for 24 h to obtain a composite graphene aerogel; B3. Add 6 g of the composite graphene aerogel and 1.8 g of konjac glucomannan to 90 mL of ethanol, stir evenly, add 6 mL of sodium hydroxide solution with a mass fraction of 50%, stir at 65 °C for 30 min, raise the temperature to 90 °C, stir until the ethanol evaporates, collect the solid, wash the solid 3 times with deionized water, and dry in an oven at 70 °C for 10 min to obtain the composite material The emulsion polymers prepared in Examples 1-3 and Comparative Examples 1-6 were subjected to performance testing.

[0069] Prepare a high salinity simulated formation water containing 177 mg / L of Mg 2+ 、700 mg / L of Ca 2+ 、11668 mg / L of K + and Na + 、20323 mg / L of Cl - , with a total salinity of 32868 mg / L. Viscosity test: Dissolve the above-prepared emulsion polymer in the prepared high salinity simulated formation water at a concentration of 0.15%. After preparing the emulsion polymer into a solution, use a DV-III ULTRA rotational viscometer to measure the apparent viscosity value of the emulsion polymer solution at 25 °C, denoted as the initial apparent viscosity (n 1 ); Thermal stability test: Heat-age the emulsion after measuring the apparent viscosity in an oven at 90 °C for 90 d, and take out the emulsion polymer to measure the apparent viscosity; Surface tension measurement: Use deionized water to prepare a solution of the above-prepared emulsion polymer at a concentration of 0.15%, and use a DCAT 21 type surface tension measuring instrument (Data physics, Germany) to measure the surface tension of the solution.

[0070] Oil displacement performance test: Grind the end face of an artificial core (core length 8.5 cm, inner diameter 2.3 cm) and dry it at 85 °C; Simulated oil sample: The weight ratio of crude oil to neutral kerosene is 1:0.9 (crude oil and neutral kerosene are from Shengli Oilfield); The simulated formation water is the above-prepared high salinity simulated formation water; After saturating the artificial core with the above-prepared high salinity simulated formation water and establishing irreducible water with the simulated oil sample, displace it with a displacing agent containing the above-prepared emulsion polymer. When the water cut of the effluent reaches 96%, calculate the crude oil recovery rate (%); Emulsion polymer displacing agent: The concentration of the above-prepared emulsion polymer is 1000 mg / L, sodium dodecyl diphenyl ether sulfonate is 300 mg / L, and sodium hydroxide solution is 1000 mg / L; The test results are shown in Table 1 below.

[0071] Table 1 Performance testing of emulsion polymers prepared in Examples 1-3 and Comparative Examples 1-6 Project Apparent viscosity at 25°C (mPa·s) Apparent viscosity at 90°C (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 As can be seen from the data in Table 1, the emulsion polymers prepared in Examples 1-3 have excellent mechanical strength, salt tolerance and high temperature resistance.

[0072] In Comparative Example 1, the composite material prepared by replacing the cationic quaternary ammonium salt intercalated montmorillonite with sodium-based montmorillonite was added to the emulsion polymer, and its apparent viscosity and recovery rate decreased. This proved that the cationic quaternary ammonium salt intercalated montmorillonite had a larger interlayer spacing, which was beneficial to adsorb metal salt ions in the oil well, improve the salt tolerance of the acrylamide-based emulsion polymer, and was also beneficial to synthesize amphiphilic carbon dots between or on the surface of the montmorillonite layers, thereby improving the efficiency of water flooding.

[0073] In Comparative Example 2, the composite material prepared by replacing the modified montmorillonite with the cationic quaternary ammonium salt intercalated montmorillonite was added to the emulsion polymer, and its apparent viscosity and recovery rate decreased. This proved that in-situ synthesis of amphiphilic carbon dots between or on the surface of the cationic quaternary ammonium salt intercalated montmorillonite could further chelate the cationic groups in the oil field, improve the salt tolerance of the acrylamide-based emulsion polymer, and the carbon dots on the surface of the montmorillonite carried hydrophobic chains that could change the wettability between the rock pore wall and the crude oil, making the oil droplets easier to be carried away by the water flow, thereby improving the efficiency of water flooding. In addition, the modified montmorillonite also had excellent high-temperature resistance.

[0074] In Comparative Example 3, the composite material prepared by replacing the composite graphene aerogel with the modified montmorillonite was added to the emulsion polymer, and its apparent viscosity and recovery rate decreased. This proved that the modified montmorillonite was evenly distributed in the three-dimensional network porous aerogel with graphene oxide as the skeleton, had excellent high-temperature resistance, and the large specific surface area and pore structure of the aerogel provided a large capacity for metal salt ions, enhancing the salt tolerance of the acrylamide-based emulsion polymer.

[0075] 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. This proved that konjac glucomannan could improve the drilling efficiency of the acrylamide-based emulsion polymer, enhance the salt tolerance of the acrylamide-based emulsion polymer, and in addition, under the action of the initiator, konjac glucomannan could copolymerize with the raw materials of the emulsion polymer, making the composite material embedded in the acrylamide-based emulsion polymer, increasing the crosslinking density of the acrylamide-based emulsion polymer, and enhancing the viscosity of the acrylamide-based emulsion polymer.

[0076] In Comparative Example 5, the modified water-soluble cellulose prepared by replacing the modified carboxymethyl-β-cyclodextrin with carboxymethyl-β-cyclodextrin was added to the emulsion polymer, and its apparent viscosity and recovery rate decreased. This proved that glycidyl methacrylate was grafted onto the water-soluble cellulose, and the double bonds contained could copolymerize with the raw materials of the emulsion polymer, making the modified water-soluble cellulose form a stable system with the acrylamide-based emulsion polymer, and could also copolymerize with the konjac glucomannan in the composite material, thereby forming a crosslinked structure in the acrylamide-based emulsion polymer, improving the mechanical strength, salt tolerance and high-temperature resistance of the acrylamide-based emulsion polymer.

[0077] Comparative Example 6 The modified water-soluble cellulose prepared by replacing the modified carboxymethyl-β-cyclodextrin with glycidyl methacrylate was added to the emulsion polymer. Its apparent viscosity and recovery rate decreased, which proved that carboxymethyl-β-cyclodextrin was grafted onto the water-soluble cellulose, endowing the water-soluble cellulose with a cavity structure, weakening the hydrogen bond interaction between cellulose molecules, forming a more stable acrylamide-based emulsion polymer, and the cavity structure could adsorb metal salt ions, further weakening the shielding effect of metal salt ions on the acrylamide-based emulsion polymer.

[0078] In the description of the specification, the description with reference to terms such as "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0079] The above content is only an example and illustration of the present invention. Those skilled in the art of this technology can make various modifications or supplements to the described specific embodiments or use similar ways to replace them. As long as they do not deviate from the invention or exceed the scope defined by the claims of this patent, they should all belong to the protection scope 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 20-30 min 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 with glucose and sodium dodecyl sulfate.

2. The method for preparing an emulsion polymer for oil displacement according to claim 1, characterized in that: 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 are added to dimethyl sulfoxide, stirred evenly, glycidyl methacrylate is added, stirred and reacted at 60-70° C. for 2-3 hours, acetic acid is added to adjust the pH to terminate the reaction, and a light yellow liquid is separated and collected, and the light yellow liquid is freeze-dried to obtain modified carboxymethyl-β-cyclodextrin; A2. Add water-soluble cellulose to ethanol, stir evenly, add sodium hydroxide solution, stir evenly, add modified carboxymethyl-β-cyclodextrin, stir and react 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, characterized in that: 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, characterized in that: In step A2, the amount 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 emulsion polymer for oil displacement according to claim 1, characterized in that: 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 emulsion polymer for oil displacement according to claim 1, characterized in that: 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, characterized in that: 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 cationic quaternary ammonium salt intercalated montmorillonite was added. After stirring at 500-600 r / min for 20-30 min, the mixture was reacted at 170-190 ° C for 7-9 h, cooled to room temperature, and the product was taken out. The product was washed and dried to obtain modified montmorillonite; B2. Add graphene oxide to deionized water, stir evenly, add modified montmorillonite, ultrasonically treat at 40-60KHz for 20-30min, add a reducing agent, stir evenly, react with stirring at 90-100°C for 1-2h to form a gel, and freeze-dry the gel 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 20-30min, heat to 80-90°C, stir until ethanol evaporates, collect solids, wash the solids, and dry them to obtain a composite material.

8. The method for preparing an emulsion polymer for oil displacement according to claim 7, characterized in that: 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 emulsion polymer for oil displacement according to claim 7, characterized in that: 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 emulsion polymer for oil displacement according to claim 7, characterized in that: 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.