Self-thickening polyacrylamide as well as preparation method and application thereof

Abstract

The invention belongs to the field of oilfield chemistry, and relates to self-thickening polyacrylamide as well as a preparation method and application thereof. The preparation method of the self-thickening polyacrylamide comprises the following steps: dissolving acrylamide, 2-acrylamide-2-phenyl ethanesulfonic acid, hydroxyl-N-allylaniline, N-hydroxymethyl acrylamide and a cosolvent in deionized water, and adjusting the pH value to obtain a homopolymerization solution; cooling the homopolymerization solution, introducing nitrogen, adding an initiator, introducing nitrogen again, carrying out a polymerization reaction, and after the reaction is completed, carrying out heating and heat preservation, and carrying out an aging reaction, so as to obtain a polyacrylamide rubber block; and cutting, granulating, drying, crushing and screening the polyacrylamide gel block to obtain the self-thickening polyacrylamide. The self-thickening polyacrylamide disclosed by the invention contains hydroxyl-N-allylaniline and N-hydroxymethyl acrylamide monomers, gel is generated along with time extension under the oil reservoir condition, the profile control effect is improved, and the problems of phase separation and chromatographic effect caused by migration velocity difference of a conventional gel system are avoided.

Description

Technical Field

[0001] The invention belongs to the technical field of oilfield chemistry, and in particular relates to a self-thickening polyacrylamide and a preparation method and application thereof. Background Art

[0002] Polyacrylamide is widely used in many fields, especially in the field of oil field exploitation. With the development of oil field exploitation, most oil fields have entered the tertiary oil recovery stage. The polyacrylamide used in the tertiary oil recovery stage needs to have high viscosity characteristics, low degradation rate at high temperature and high mineralization, and be able to maintain high viscosity for a long time.

[0003] Most of the polyacrylamide used in oil fields on the market have been improved by changing the polymerization process to a post-hydrolysis polymerization process, that is, adding a hydrolyzing agent to hydrolyze the polyacrylamide twice to increase the molecular weight, so that the molecular weight reaches more than 30 million, to ensure that under high temperature and high salt geological conditions, as the polyacrylamide molecules degrade, they can still maintain a certain viscosity. In addition, some products add about 5% of monomer units containing sulfonic acid groups during the post-hydrolysis process for polymerization. Because the sulfonic acid group has an inhibitory effect on the polymerization reaction, after the secondary hydrolysis, the molecular weight of the polyacrylamide is still not too high, and most of them are between 18 million and 25 million. And because of the secondary hydrolysis, its solubility is poor and the dissolution time is long, which is difficult to meet the requirements of oil field use. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides a self-thickening polyacrylamide and a preparation method and application thereof.

[0005] Specifically, the present invention is achieved through the following technical solutions:

[0006] A method for preparing a self-thickening polyacrylamide comprises:

[0007] (1) dissolving acrylamide, 2-acrylamide-2-phenylethanesulfonic acid, hydroxy-N-allylaniline, N-hydroxymethyl acrylamide, and a cosolvent in deionized water, and adjusting the pH value with an alkali to obtain a homopolymer solution;

[0008] (2) adding the homopolymerization solution to a polymerization kettle, cooling it, introducing nitrogen, adding an initiator, and introducing nitrogen for a period of time to carry out a polymerization reaction. After the reaction is completed, the temperature is raised, the temperature is kept, and an aging reaction is carried out to obtain a polyacrylamide gel block;

[0009] (3) Cutting, granulating, drying, crushing and screening the polyacrylamide block to obtain self-thickening polyacrylamide.

[0010] The preparation method of the self-thickening polyacrylamide comprises, by weight percentage, 5-20% of acrylamide, 1-10% of 2-acrylamide-2-phenylethanesulfonic acid, 1-5% of hydroxy-N-allylaniline, 1-10% of N-hydroxymethyl acrylamide, 0.1-0.5% of the cosolvent and the balance of deionized water.

[0011] The preparation method of the self-thickening polyacrylamide comprises, by weight percentage, 10-15% of acrylamide, 2-5% of 2-acrylamide-2-phenylethanesulfonic acid, 2-5% of hydroxy-N-allylaniline, 1-2.5% of N-hydroxymethyl acrylamide, 0.1-0.3% of the cosolvent and the balance of deionized water.

[0012] In the above-mentioned method for preparing self-thickening polyacrylamide, the co-solvent is thiourea or urea.

[0013] In the above-mentioned method for preparing self-thickening polyacrylamide, the alkali is sodium hydroxide or sodium carbonate solution.

[0014] In the above-mentioned method for preparing self-thickening polyacrylamide, the pH of the homopolymerization solution is 6.5-7.5.

[0015] In the above-mentioned method for preparing the self-thickening polyacrylamide, the homopolymerization solution is added into a polymerization kettle and cooled to 0-5°C.

[0016] In the above-mentioned method for preparing self-thickening polyacrylamide, the mass of the initiator accounts for 0.02-0.1% of the mass of the homopolymerization solution.

[0017] In the above-mentioned method for preparing self-thickening polyacrylamide, the initiator is an azo compound, a persulfide, or a redox system composed of a persulfide and a reducing agent, sodium bisulfite.

[0018] In the above-mentioned preparation method of self-thickening polyacrylamide, the polymerization reaction temperature is below 5°C, and the polymerization reaction time is 2-4 hours; the heating rate is gradually increased to 40-60°C within 1-3 hours, and the insulation temperature is 40-60°C; the aging reaction time is 4-6 hours.

[0019] A self-thickening polyacrylamide is prepared by the above-mentioned preparation method.

[0020] The above self-thickening polyacrylamide is used in the preparation of oil field production and displacement system.

[0021] Compared with the prior art, the self-thickening polyacrylamide of the present invention has the following beneficial effects:

[0022] (1) The self-thickening polyacrylamide of the present invention contains cross-linkable hydroxy-N-allylaniline and N-hydroxymethyl acrylamide monomers, which can generate gels over time under reservoir conditions, thereby improving the profile control effect and avoiding the problems of phase separation and chromatographic effect caused by differences in migration velocities in conventional gel systems;

[0023] (2) The preparation method of the self-thickening polyacrylamide of the present invention has a simple process and can be produced by the current production line, with low equipment investment and production cost;

[0024] (3) The self-thickening polyacrylamide of the present invention can initiate polymerization at low temperature, and the reaction process is stable. Compared with the existing common high molecular weight polyacrylamide, it has the characteristics of good temperature and salt resistance, high viscosity retention rate, long viscosity retention time, and good solubility and quick solubility;

[0025] (4) The self-thickening polyacrylamide of the present invention has the characteristics of low energy consumption in product production, stable quality, high viscosity, self-thickening, slow viscosity reduction under high temperature and high mineralization environment, fast dissolution rate, good solubility, etc., which meets the use requirements of oil field exploitation. DETAILED DESCRIPTION

[0026] In order to fully understand the purpose, features and effects of the present invention, the present invention is described in detail through the following specific embodiments. Except for the following contents, the process method of the present invention adopts conventional methods or devices in the art. Unless otherwise specified, the following terms have the meanings commonly understood by those skilled in the art.

[0027] When a numerical range is disclosed herein, the above range is considered to be continuous and includes the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise indicated, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0028] Specifically, the method for preparing the self-thickening polyacrylamide provided by the present invention comprises:

[0029] (1) dissolving acrylamide, 2-acrylamide-2-phenylethanesulfonic acid, hydroxy-N-allylaniline, N-hydroxymethyl acrylamide, and a cosolvent in deionized water, and adjusting the pH value with an alkali to obtain a homopolymer solution;

[0030] (2) adding the homopolymerization solution to a polymerization kettle, cooling it, introducing nitrogen, adding an initiator, and introducing nitrogen for a period of time to carry out a polymerization reaction. After the reaction is completed, the temperature is raised, the temperature is kept, and an aging reaction is carried out to obtain a polyacrylamide gel block;

[0031] (3) Cutting, granulating, drying, crushing and screening the polyacrylamide block to obtain self-thickening polyacrylamide.

[0032] In the preparation method of the self-thickening polyacrylamide of the present invention, the introduction of 2-acrylamide-2-phenylethanesulfonic acid and hydroxy-N-allylaniline improves the temperature resistance and salt resistance and hydrophobicity of the polyacrylamide, and the initial viscosity is low, and no blockage will be formed near the well. Under reservoir conditions, as time goes by, 2-acrylamide-2-phenylethanesulfonic acid and hydroxy-N-allylaniline can react with N-hydroxymethyl acrylamide to form a gel, thereby improving the profile control effect.

[0033] The invention can effectively improve the temperature and salt resistance of polyacrylamide by introducing the monomer 2-acrylamide-2-phenylethanesulfonic acid containing a benzene ring and a sulfonic acid group, and at the same time introduce the monomer hydroxy-N-allylaniline containing a benzene ring hydrophobic group and the monomer N-hydroxymethyl acrylamide containing a hydroxymethyl group, so that the hydration layer is weakened and the viscosity is reduced, and the self-thickening polyacrylamide further reacts at a certain temperature to form a body gel, and the viscosity is increased.

[0034] In some preferred embodiments, by weight percentage, the acrylamide is 5-20%, the 2-acrylamide-2-phenylethanesulfonic acid is 1-10%, the hydroxy-N-allylaniline is 1-5%, the N-hydroxymethyl acrylamide is 1-10%, the cosolvent is 0.1-0.5% and the balance is deionized water.

[0035] According to the ratio of the present invention, the polymerization process is stable, and it is not easy to cause violent polymerization. The prepared self-thickening polyacrylamide product has low initial viscosity, high viscosity retention rate and good self-thickening performance; when the ratio of each monomer is lower than the range of the present invention, the strength of the jelly generated by the self-thickening polyacrylamide reaction is low, and it is difficult to achieve the effect of profile adjustment; when the ratio of each monomer is higher than the range of the present invention, the polymerization reaction is difficult to control, and the initial viscosity of the product is high. .

[0036] Further preferably, by weight percentage, the acrylamide is 10-15%, the 2-acrylamide-2-phenylethanesulfonic acid is 2-5%, the hydroxy-N-allylaniline is 2-5%, the N-hydroxymethyl acrylamide is 1-2.5%, the cosolvent is 0.1-0.3% and the balance is deionized water.

[0037] In some preferred embodiments, acrylamide is an industrial product with a CAS number of 79-06-1 and a content of greater than or equal to 99%; N-hydroxymethyl acrylamide is an industrial product with a CAS number of 924-42-5 and a content of greater than or equal to 99.5%; 2-acrylamide-2-phenylethanesulfonic acid and hydroxy-N-allylaniline are laboratory self-synthesized products.

[0038] Among them, 2-acrylamide-2-phenylethanesulfonic acid can be synthesized according to the existing method, and can also be synthesized according to the following method: adding concentrated sulfuric acid as a sulfonating agent to acrylonitrile at 0°C, and then adding styrene, the molar ratio of concentrated sulfuric acid to styrene to acrylonitrile is 1:1:3.5, and after the addition is completed, keeping warm at 0°C for 1.5 hours and keeping warm at 40°C for 2 hours, washing, separating and drying the product to obtain 2-acrylamide-2-phenylethanesulfonic acid.

[0039] Among them, hydroxy-N-allyl aniline can be synthesized according to the existing method, and can also be synthesized according to the following method: hydroxyaniline and potassium carbonate are evenly mixed in a dimethylformamide solvent, 3-bromo-1-propylene (the molar ratio of hydroxyaniline, potassium carbonate and 3-bromo-1-propylene is 2:2:1) is added dropwise, heated at 80° C. and stirred for 16 hours, and then the mixture is cooled to room temperature, water is added and then extracted with ethyl acetate, and the product is washed, separated and dried to obtain hydroxy-N-allyl aniline.

[0040] In some preferred embodiments, the hydroxy-N-allyl aniline may be: o-hydroxy-N-allyl aniline, m-hydroxy-N-allyl aniline, p-hydroxy-N-allyl aniline, or a mixture of the two or more thereof.

[0041] In order to help each monomer to dissolve better in deionized water, the present invention introduces a co-solvent. Preferably, the co-solvent is thiourea or urea.

[0042] In some preferred embodiments, the present invention uses sodium hydroxide or sodium carbonate solution to adjust the pH of the homopolymerization solution to 6.5-7.5.

[0043] Since acrylamide, N-hydroxymethyl acrylamide, 2-acrylamide-2-phenylethanesulfonic acid, and hydroxy-N-allylaniline monomers are added together during batching, the pH value of the solution is adjusted to 6.5-7.5. In this medium, acrylamide hardly undergoes hydrolysis reaction, so it is easier to accurately produce a polyacrylamide product with a lower degree of hydrolysis and excellent solubility.

[0044] In some preferred embodiments, step (2) comprises: adding the homopolymerization solution into a polymerization kettle, cooling it to 0-5°C, introducing nitrogen for 20-60 minutes, adding an initiator accounting for 0.02-0.1% of the mass of the homopolymerization solution under nitrogen protection, continuing to introduce nitrogen for 10-60 minutes, controlling the temperature below 5°C to carry out polymerization reaction for 2-4 hours, gradually raising the temperature of the system to 40-60°C within 1-3 hours after the reaction is completed, and heat-insulating and aging the reaction at 40-60°C for 4-6 hours to obtain a polyacrylamide gel block.

[0045] In step (2), the initiator decomposes to generate primary free radicals, which attack acrylamide, N-hydroxymethyl acrylamide, 2-acrylamide-2-phenylethanesulfonic acid, and hydroxy-N-allylaniline monomers to generate monomer free radicals. The monomer free radicals continue to react with the remaining monomers to form new free radicals by opening the double bonds, thereby achieving chain growth and generating high molecular weight self-thickening polyacrylamide.

[0046] In some preferred embodiments, the initiator is an azo compound, a persulfide, or a redox system consisting of a persulfide and a reducing agent, sodium bisulfite.

[0047] Further preferably, the azo compound is azobisisoheptanenitrile or 4,4'-azobis(cyanovaleric acid); the persulfide is sodium persulfate, ammonium persulfate or potassium persulfate; the persulfide or the redox system composed of the persulfide and the reducing agent sodium bisulfite includes ammonium persulfate and sodium bisulfite, or potassium persulfate and sodium bisulfite, and the mass ratio of the two is 1.5:1-2.5:1.

[0048] On the other hand, the present invention also provides a self-thickening polyacrylamide, which is prepared by the above-mentioned preparation method.

[0049] The self-thickening polyacrylamide prepared according to the method of the present invention has the following characteristics: low initial viscosity, when the polymer concentration is 20000 mg / L, its viscosity does not exceed 20 mPa·s; the viscosity increases more than 10 times after cross-linking; good temperature resistance, the upper limit of which can reach 150°C; good salt resistance, under the condition of 100,000 mineralization degrees, the influence on the system is not significant.

[0050] In another aspect, the present invention also provides the use of self-thickening polyacrylamide in the preparation of oilfield production and displacement system.

[0051] The self-thickening polyacrylamide of the present invention has the characteristics of low energy consumption in product production, stable quality, high viscosity, self-thickening, slow viscosity reduction under high temperature and high mineralization environment, fast dissolution speed, good solubility, etc., and meets the use requirements of oil field exploitation.

[0052] Example

[0053] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples. The experimental methods in the following examples without specifying specific conditions are carried out according to conventional methods and conditions. In the present invention, the devices or equipment used are conventional devices or equipment known in the art and can be purchased.

[0054] Example 1

[0055] (1) A 1L enameled synthesis reactor was added with 788g of deionized water, 150g of acrylamide, 25g of 2-acrylamide-2-phenylethanesulfonic acid, 25g of hydroxy-N-allylaniline, 10g of N-hydroxymethyl acrylamide, and 2g of urea, and the mixture was stirred thoroughly until the mixture was completely dissolved. Then, the pH was adjusted to 7.0 with 10% sodium hydroxide to obtain a homopolymer solution.

[0056] (2) The homopolymer solution mixed in (1) was added to a polymerization kettle and cooled to 3°C. After passing high-purity nitrogen for 30 minutes, 0.3 g of ammonium persulfate and 0.2 g of sodium bisulfite were added. After passing high-purity nitrogen for 10 minutes, the temperature was controlled at 3°C ​​and the polymerization reaction was carried out for 3 hours. The temperature was then kept at 50°C and aged for 5 hours to obtain a transparent and elastic polyacrylamide block.

[0057] (3) taking out the rubber block, cutting, granulating, drying, crushing and screening it to obtain self-thickening polyacrylamide.

[0058] Evaluation of product self-thickening performance:

[0059] Deionized water was used to prepare polymer solutions of different concentrations and placed in a constant temperature oven. The experimental results are as follows:

[0060]

[0061] The polymer takes more than 5 days to completely gel, and its viscosity increases more than 10 times after gelation.

[0062] A 10,000 mg / L polymer solution was prepared with sodium chloride saline with a mineralization degree of 100,000 mg / L and placed in an oven at 150°C. After 6 months, there was no obvious change in the gel state.

[0063] It can be seen that the product of the present invention has good temperature resistance, which can reach 150°C; good salt resistance, and 100,000 mineralization has little effect on the system. Compared with the existing common high molecular weight polyacrylamide, it has the characteristics of good temperature and salt resistance, high viscosity retention rate, long viscosity retention time, and good solubility and quick solubility.

[0064] Example 2

[0065] (1) A 1L enameled synthesis reactor was added with 773g of deionized water, 150g of acrylamide, 25g of 2-acrylamide-2-phenylethanesulfonic acid, 25g of hydroxy-N-allylaniline, 25g of N-hydroxymethyl acrylamide, and 2g of urea, and the mixture was stirred thoroughly until the mixture was completely dissolved. Then, the pH was adjusted to 7.0 with 10% sodium hydroxide to obtain a homopolymer solution.

[0066] (2) The homopolymer solution mixed in (1) was added to a polymerization kettle and cooled to 3°C. After passing high-purity nitrogen for 30 minutes, 0.3 g of ammonium persulfate and 0.2 g of sodium bisulfite were added. After passing high-purity nitrogen for 10 minutes, the temperature was controlled at 3°C ​​and the polymerization reaction was carried out for 4 hours. The temperature was then kept at 60°C and aged for 6 hours to obtain a transparent and elastic polyacrylamide block.

[0067] (3) taking out the rubber block, cutting, granulating, drying, crushing and screening it to obtain self-thickening polyacrylamide.

[0068] Evaluation of product self-thickening performance:

[0069] Deionized water was used to prepare polymer solutions of different concentrations and placed in a constant temperature oven. The experimental results are as follows:

[0070]

[0071] The polymer takes more than 6 days to completely gel, and its viscosity increases more than 10 times after gelation.

[0072] A 10,000 mg / L polymer solution was prepared with sodium chloride saline with a mineralization degree of 100,000 mg / L and placed in an oven at 150°C. The gelling time was 24 hours and there was no obvious change in the gel state after being placed for 6 months.

[0073] It can be seen that the product of the present invention has good temperature resistance, which can reach 150°C; good salt resistance, and 100,000 mineralization has little effect on the system. Compared with the existing common high molecular weight polyacrylamide, it has the characteristics of good temperature and salt resistance, high viscosity retention rate, long viscosity retention time, and good solubility and quick solubility.

[0074] Comparative Example 1

[0075] (1) A 1L enameled synthesis reactor was added with 788g of deionized water, 185g of acrylamide, 25g of 2-acrylamide-2-phenylethanesulfonic acid, and 2g of urea, and the mixture was stirred thoroughly until the mixture was completely dissolved. Then, the pH was adjusted to 7.0 with 10% sodium hydroxide to obtain a homopolymer solution.

[0076] (2) The homopolymer solution mixed in (1) was added to a polymerization kettle and cooled to 3°C. After passing high-purity nitrogen for 30 minutes, 0.3 g of ammonium persulfate and 0.2 g of sodium bisulfite were added. After passing high-purity nitrogen for 10 minutes, the temperature was controlled at 3°C ​​and the polymerization reaction was carried out for 3 hours. The temperature was then kept at 50°C and aged for 5 hours to obtain a transparent and elastic polyacrylamide block.

[0077] (3) taking out the rubber block, cutting, granulating, drying, crushing and screening it to obtain self-thickening polyacrylamide.

[0078] Evaluation of product self-thickening performance:

[0079] A 20,000 mg / L polymer solution prepared with deionized water was placed in a constant temperature oven at 70°C. The initial viscosity was 25.6 mPa·s. After 30 days, it still did not gel and the viscosity decreased to 20.3 mPa·s.

[0080] A 10,000 mg / L polymer solution was prepared with sodium chloride saline with a mineralization degree of 100,000 mg / L and placed in an oven at 150°C. After 6 months, it still did not form a gel.

[0081] It can be seen that without introducing hydroxy-N-allylaniline and N-hydroxymethyl acrylamide monomers, the prepared polymer has a higher initial viscosity, does not have self-thickening ability, and has lower thermal stability.

[0082] Comparative Example 2

[0083] (1) A 1L enameled synthesis reactor was added with 788g of deionized water, 175g of acrylamide, 25g of hydroxy-N-allylaniline, 10g of N-hydroxymethyl acrylamide, and 2g of urea, and the mixture was stirred thoroughly until the mixture was completely dissolved. Then, the pH was adjusted to 7.0 with 10% sodium hydroxide to obtain a homopolymer solution.

[0084] (2) The homopolymer solution mixed in (1) was added to a polymerization kettle and cooled to 3°C. After passing high-purity nitrogen for 30 minutes, 0.3 g of ammonium persulfate and 0.2 g of sodium bisulfite were added. After passing high-purity nitrogen for 10 minutes, the temperature was controlled at 3°C ​​and the polymerization reaction was carried out for 3 hours. The temperature was then kept at 50°C and aged for 5 hours to obtain a transparent and elastic polyacrylamide block.

[0085] (3) taking out the rubber block, cutting, granulating, drying, crushing and screening it to obtain self-thickening polyacrylamide.

[0086] Evaluation of product self-thickening performance:

[0087] Deionized water was used to prepare polymer solutions of different concentrations and placed in a constant temperature oven. The experimental results are as follows:

[0088]

[0089] The polymer takes more than 5 days to completely gel, and its viscosity increases more than 10 times after gelation.

[0090] A 10,000 mg / L polymer solution was prepared with sodium chloride saline with a mineralization degree of 100,000 mg / L and placed in an oven at 150°C. The initial viscosity after gelation was 4,680 mPa·s, and the viscosity of the frozen gel decreased to 3,010 mPa·s after 6 months.

[0091] It can be seen that the polymer prepared by introducing hydroxy-N-allylaniline and N-hydroxymethyl acrylamide monomers but not introducing 2-acrylamide-2-phenylethanesulfonic acid monomer has self-thickening ability, but its temperature and salt resistance stability is reduced.

[0092] The present invention has been disclosed above with preferred embodiments, but those skilled in the art should understand that these embodiments are only used to describe the present invention and should not be understood as limiting the scope of the present invention. It should be noted that all changes and substitutions equivalent to these embodiments should be deemed to be included in the scope of the claims of the present invention. Therefore, the scope of protection of the present invention should be based on the scope defined in the claims.

Claims

1. A method for preparing a self-thickening polyacrylamide, characterized in that: include: (1) dissolving acrylamide, 2-acrylamide-2-phenylethanesulfonic acid, hydroxy-N-allylaniline, N-hydroxymethyl acrylamide, and a cosolvent in deionized water, and adjusting the pH value with an alkali to obtain a homopolymer solution; (2) adding the homopolymerization solution to a polymerization kettle, cooling it, introducing nitrogen, adding an initiator, and introducing nitrogen for a period of time to carry out a polymerization reaction. After the reaction is completed, the temperature is raised, the temperature is kept, and an aging reaction is carried out to obtain a polyacrylamide gel block; (3) Cutting, granulating, drying, crushing and screening the polyacrylamide block to obtain self-thickening polyacrylamide.

2. The preparation method according to claim 1, characterized in that: By weight percentage, the acrylamide is 5-20%, the 2-acrylamide-2-phenylethanesulfonic acid is 1-10%, the hydroxy-N-allylaniline is 1-5%, the N-hydroxymethyl acrylamide is 1-10%, the cosolvent is 0.1-0.5% and the balance is deionized water.

3. The preparation method according to claim 1, characterized in that: By weight percentage, the acrylamide is 10-15%, the 2-acrylamide-2-phenylethanesulfonic acid is 2-5%, the hydroxy-N-allylaniline is 2-5%, the N-hydroxymethyl acrylamide is 1-2.5%, the cosolvent is 0.1-0.3% and the balance is deionized water.

4. The preparation method according to claim 1, characterized in that: The co-solvent is thiourea or urea.

5. The preparation method according to claim 1, characterized in that: The alkali is sodium hydroxide or sodium carbonate solution.

6. The preparation method according to claim 1, characterized in that: The pH of the homopolymerization solution is 6.5-7.

5.

7. The preparation method according to claim 1, characterized in that: The homopolymerization solution was added into a polymerization kettle and cooled to 0-5°C.

8. The preparation method according to claim 1, characterized in that: The mass of the initiator accounts for 0.02-0.1% of the mass of the homopolymerization solution.

9. The preparation method according to claim 1, characterized in that: The initiator is an azo compound, persulfide or a redox system consisting of persulfide and a reducing agent, sodium bisulfite.

10. The preparation method according to claim 1, characterized in that: The polymerization reaction temperature is below 5°C, and the polymerization reaction duration is 2-4 hours; the heating rate is gradually increased to 40-60°C within 1-3 hours, and the insulation temperature is 40-60°C; the aging reaction duration is 4-6 hours.

11. A self-thickening polyacrylamide, characterized in that: The preparation method is described in any one of claims 1 to 10.

12. Use of the self-thickening polyacrylamide according to claim 11 in the preparation of an oilfield production and displacement system.

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