A method for synthesizing a polymer for viscoelastic fracturing fluid

Abstract

The present invention belongs to the technical field of fracturing fluids, and particularly relates to a method for synthesizing a polymer for viscoelastic fracturing fluid. The present invention uses 2-ethylhexyl methacrylate, methacrylic acid, acrylamide, and sodium methallylsulfonate as polymerization monomers, and synthesizes a polymer for viscoelastic fracturing fluid through inverse emulsion polymerization. Groups with surfactant functions such as carboxyl groups, sulfonic acid groups, amide groups, and long-chain ester groups are introduced into the polymer, improving the drag reduction, temperature resistance, and sand-carrying capacity of the polymer for viscoelastic fracturing fluid; the relative molecular mass of the polymer for viscoelastic fracturing fluid is controlled by controlling the dosage of the emulsifier, and during the polymerization process, the obtained polymer is dispersed evenly through high-speed stirring, with stable performance, further improving the friction reduction performance of the polymer.

Description

Technical Field

[0001] The present invention belongs to the technical field of fracturing fluids, and particularly relates to a method for synthesizing a polymer for viscoelastic fracturing fluids. Background Art

[0002] The hydraulic fracturing technology is one of the important technical means applied to the stimulation of low-permeability and extra-low-permeability oil and gas wells and the injection enhancement of injection wells. Among them, the water-based gel fracturing fluid is applied to major oil and gas fields in China due to its advantages such as high viscosity, low friction resistance, and strong sand suspension performance. The hydraulic fracturing fluid is a surfactant with a relatively high viscosity itself and has a certain viscoelasticity. The process of oil reservoir hydraulic fracturing is to use a high-pressure and large-displacement pump on the ground. Based on the principle of liquid pressure transmission, a fracturing fluid with a certain viscosity is injected into the oil reservoir at a pressure greater than the absorption capacity of the oil reservoir, and the pressure in the wellbore is gradually increased, so as to build up a high pressure at the bottom of the well. When this pressure is greater than the in-situ stress near the wellbore and the tensile strength of the formation rock, fractures are generated in the formation near the bottom of the well: continue to inject the sand-carrying fluid with proppants, the fractures extend forward and are filled with proppants, and after shutting in the well, the fractures close on the proppants, so as to form a sand-filled fracture with a certain geometric size and high conductivity in the formation near the bottom of the well, achieving the purpose of increasing production and injection. However, the frictional resistance of the viscoelastic fracturing fluid in the pipeline is very large, and most of the pump pressure during construction is consumed in overcoming the pipeline friction resistance. The pressure actually acting on the pay zone to fracture the pay zone is not large, so it is difficult to increase the displacement, and it is difficult for the fractures to extend forward to achieve the purpose of forming a fracture network. The addition of a friction reducer can effectively reduce the friction resistance of the fracturing fluid and reduce energy consumption.

[0003] At present, the friction reducers used in domestic oil and gas fields during exploitation mainly include two types: highly flexible polymer friction reducers and viscoelastic surfactant friction reducers. The viscoelastic surfactant friction reducers mainly include quaternary ammonium salt cationic surfactants, betaine zwitterionic surfactants, etc. With the large-scale exploitation of deep oil and gas fields, the thermal stability and temperature resistance of the friction reducer need to be further improved.

[0004] The Chinese patent application document with the publication number CN115851252A discloses a drag reducer for seawater-based fracturing fluid prepared with active water, which is polymerized from non-ionic monomers, two or one of 2-acrylamido-2-methylpropanesulfonic acid and sodium acrylate, anionic monomers containing carboxylic acid groups, and active water under a redox-azo composite initiation system. By introducing sulfonic acid groups and carboxylic acid groups, the salt resistance is improved. Active water polymerization is adopted to overcome the cage effect formed between monomers and between monomers and initiators when using ordinary pure water for polymerization, reduce the reaction activation energy, reduce the dosage of initiators, and improve the polymer molecular weight and the uniform regularity of each group of chain segments. However, due to the relatively small molecular weight of this drag reducer, during use, as time prolongs, the viscosity decreases, resulting in the need for further improvement in the drag reduction effect. In addition, due to its relatively small molecular weight, its heat resistance is poor. Under high-temperature conditions, the drag reducer molecules will decompose, resulting in a decrease in both high-temperature viscosity and high-temperature drag reduction performance. Summary of the Invention

[0005] In order to solve the technical problems of poor thermal stability, poor heat resistance, and low drag reduction rate of polymers for viscoelastic fracturing fluids in related technologies, the object of the present invention is to provide a method for synthesizing a polymer for viscoelastic fracturing fluid.

[0006] In order to achieve the above object, the technical solution of the present invention is as follows:

[0007] A method for synthesizing a polymer for viscoelastic fracturing fluid includes the following steps:

[0008] S1: Add an emulsifier and 2-ethylhexyl methacrylate to a high-temperature and high-pressure reaction kettle to form a uniform oil phase;

[0009] S2: Add monomers to water to form an aqueous solution, and adjust the pH value of the solution to neutral to obtain an aqueous phase;

[0010] S3: Under stirring conditions, slowly add the aqueous phase prepared in step S2 to the oil phase prepared in step S1, continue stirring, introduce nitrogen to remove oxygen, and then dropwise add an initiator and a polymerization stabilizer for polymerization reaction. After the reaction ends, continue stirring for 4 - 4.5 h to obtain a polymer for viscoelastic fracturing fluid;

[0011] The monomers are composed of methacrylic acid, acrylamide, and sodium methallylsulfonate in a mass ratio of 4 - 7:13 - 16:10 - 13.

[0012] The present invention uses 2-ethylhexyl methacrylate, methacrylic acid, acrylamide, and sodium methallylsulfonate as polymerization monomers, and synthesizes a polymer for viscoelastic fracturing fluid through inverse emulsion polymerization. Groups with surfactant functions such as carboxyl groups, sulfonic acid groups, amide groups, and long-chain ester groups are introduced into the polymer. During the process of entering the formation, with the degradation effects such as mechanical shear, thermochemical pyrolysis, and microbial reactions, the drag reducer polymer is dispersed into molecular fragments with surface-active functions, improving the oil displacement effect after the fracturing fluid enters the well. At the same time, the coordinated action of these molecular side chains can improve the drag reduction and temperature resistance properties of the polymer. In addition, the side chains of the polymer prepared in the present invention are divided into long side chains and short side chains, which can form a spatial network structure in the fracturing fluid and effectively improve the sand-carrying capacity of the fracturing fluid.

[0013] Further, the monomers are composed of methacrylic acid, acrylamide, and sodium methallylsulfonate in a mass ratio of 6:14:11.

[0014] Further, the monomers are composed of methacrylic acid, acrylamide, and sodium methallylsulfonate in a mass ratio of 5:14:12.

[0015] Further, in step S1, the emulsifier is composed of sorbitan monolaurate, sodium oleate, and glycerol in a mass ratio of 1-3:5-8:100, and the mass fraction of the emulsifier is 8-12 parts.

[0016] During the research process of the present invention, it was found that when the amount of the emulsifier is relatively low, the relative molecular mass of the polymer is relatively high, but the emulsion is unstable and prone to delamination; when the amount of the emulsifier is relatively high, the stability of the emulsion is significantly improved, but the relative molecular mass of the polymer is reduced to a certain extent, resulting in a decrease in the friction reduction performance of the polymer. This is because the emulsifier has a certain chain transfer effect, resulting in a reduction in the relative molecular mass of the polymer.

[0017] Further, in step S1, the mass fraction of 2-ethylhexyl methacrylate is 10-13 parts.

[0018] Further, in step S2, the mass fraction of the monomers is 40-45 parts.

[0019] Further, in step S3, the rotation speed of the stirring is 800-1000 rpm.

[0020] During the monomer polymerization process of the present invention, a stable microemulsion dispersion is formed in the reaction system through high-speed stirring, effectively reducing the size of the monomer droplets. Under the action of the polymerization stabilizer, it is ensured that the polymerization reaction occurs in the droplets, making the obtained polymer evenly dispersed and having stable properties, effectively improving the friction reduction performance of the polymer.

[0021] Further, the time for continuous stirring in step S3 is 20 - 30 min. This step can fully emulsify the oil phase and water phase in the reaction system.

[0022] Further, the initiator in step S3 includes initiator I and initiator II; the initiator I is an aqueous solution of sodium persulfate, and the mass percentage of the aqueous solution of sodium persulfate is 15% - 20%; the initiator II is an aqueous solution of sodium bisulfite, and the mass percentage of the aqueous solution of sodium bisulfite is 10% - 14%; the mass parts of the initiator I are 8 - 10 parts, and the mass parts of the initiator II are 12 - 14 parts.

[0023] Further, the polymerization stabilizer in step S3 is one of sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, and sodium dioctyl sulfosuccinate, and the mass parts of the polymerization stabilizer are 3 - 7 parts.

[0024] The polymerization stabilizer added during the polymerization process of the present invention can wrap around the monomers, weakening the interaction between the monomers. At the same time, the polymerization stabilizer has a certain dispersing effect, which can greatly improve the solubility of the monomers and polymers, ensuring that the polymerization reaction occurs in the droplets.

[0025] Compared with the prior art, the polymer synthesis method for viscoelastic fracturing fluid provided by the present invention has the following technical advantages:

[0026] (1) The present invention uses 2-ethylhexyl methacrylate, methacrylic acid, acrylamide, and sodium methallylsulfonate as polymerization monomers, and synthesizes a polymer for viscoelastic fracturing fluid through inverse emulsion polymerization, effectively improving the drag reduction, temperature resistance, and sand-carrying capacity of the polymer for viscoelastic fracturing fluid;

[0027] (2) The present invention further controls the relative molecular mass of the polymer for viscoelastic fracturing fluid by controlling the dosage of the emulsifier, and makes the obtained polymer disperse evenly and have stable performance through high-speed stirring during the polymerization process, effectively improving the friction reduction performance of the polymer;

[0028] (3) The polymer for viscoelastic fracturing fluid prepared by the present invention can not only reduce friction but also has a high sand-carrying capacity and good compatibility;

[0029] (4) The polymer for viscoelastic fracturing fluid prepared by the present invention can stretch freely in the fluid, inhibiting the energy loss caused by the molecular collision of fluid molecules in the turbulent region, achieving the purpose of drag reduction. Detailed implementation mode

[0030] The following will be further described in conjunction with specific embodiments, but the present invention is not limited to the following embodiments. Those skilled in the art can make various modifications according to the basic idea of the present invention, but as long as they do not depart from the basic idea of the present invention, they are within the scope of the present invention.

[0031] Example 1

[0032] A method for synthesizing a polymer for viscoelastic fracturing fluid, comprising the following steps:

[0033] S1: Add 8 g of emulsifier and 10 g of 2-ethylhexyl methacrylate to a high-temperature and high-pressure reactor to form a uniform oil phase; the emulsifier is composed of sorbitan monolaurate, sodium oleate and glycerol in a mass ratio of 1:5:100;

[0034] S2: Add 45 g of monomers to water to form an aqueous solution, and add a 10% NaOH solution by mass percentage to adjust the pH value of the solution to neutral to obtain an aqueous phase; the monomers are composed of methacrylic acid, acrylamide and sodium methallyl sulfonate in a mass ratio of 4:13:10;

[0035] S3: Under the stirring condition of a rotation speed of 800 rpm, slowly add the aqueous phase prepared in step S2 to the oil phase prepared in step S1, continue stirring for 20 min, introduce nitrogen to remove oxygen, and then dropwise add 8 g of an aqueous solution of sodium persulfate with a mass percentage of 15%, 12 g of an aqueous solution of sodium bisulfite with a mass percentage of 10% and 3 g of sodium dodecyl sulfate for polymerization reaction. After the reaction is completed, continue stirring for 4 h to obtain a polymer for viscoelastic fracturing fluid.

[0036] Example 2

[0037] A method for synthesizing a polymer for viscoelastic fracturing fluid, comprising the following steps:

[0038] S1: Add 12 g of emulsifier and 13 g of 2-ethylhexyl methacrylate to a high-temperature and high-pressure reactor to form a uniform oil phase; the emulsifier is composed of sorbitan monolaurate, sodium oleate and glycerol in a mass ratio of 3:8:100;

[0039] S2: Add 40 g of monomers to water to form an aqueous solution, and add a 10% NaOH solution by mass percentage to adjust the pH value of the solution to neutral to obtain an aqueous phase; the monomers are composed of methacrylic acid, acrylamide and sodium methallyl sulfonate in a mass ratio of 7:16:13;

[0040] S3: Under the stirring condition at a rotational speed of 1000 rpm, slowly add the aqueous phase prepared in step S2 into the oil phase prepared in step S1, continue stirring for 30 min, introduce nitrogen to remove oxygen, then dropwise add 10 g of an aqueous solution of sodium persulfate with a mass percentage of 20%, 14 g of an aqueous solution of sodium bisulfite with a mass percentage of 14%, and 7 parts of sodium dodecylbenzenesulfonate for polymerization reaction. After the reaction ends, continue stirring for 4.5 h to obtain the polymer for viscoelastic fracturing fluid.

[0041] Example 3

[0042] A method for synthesizing a polymer for viscoelastic fracturing fluid, comprising the following steps:

[0043] S1: Add 9 g of emulsifier and 12 g of 2-ethylhexyl methacrylate into a high-temperature and high-pressure reaction kettle to form a uniform oil phase; the emulsifier is composed of sorbitan monolaurate, sodium oleate and glycerol according to a mass ratio of 2:7:100;

[0044] S2: Add 43 g of monomers into water to form an aqueous solution, add a NaOH solution with a mass percentage of 10% to adjust the pH value of the solution to neutral to obtain an aqueous phase; the monomers are composed of methacrylic acid, acrylamide and sodium methallylsulfonate according to a mass ratio of 6:14:11;

[0045] S3: Under the stirring condition at a rotational speed of 900 rpm, slowly add the aqueous phase prepared in step S2 into the oil phase prepared in step S1, continue stirring for 25 min, introduce nitrogen to remove oxygen, then dropwise add 9 g of an aqueous solution of sodium persulfate with a mass percentage of 16%, 13 g of an aqueous solution of sodium bisulfite with a mass percentage of 12%, and 5 g of sodium dioctyl sulfosuccinate for polymerization reaction. After the reaction ends, continue stirring for 4.3 h to obtain the polymer for viscoelastic fracturing fluid.

[0046] Example 4

[0047] A method for synthesizing a polymer for viscoelastic fracturing fluid, comprising the following steps:

[0048] S1: Add 11 g of emulsifier and 10 g of 2-ethylhexyl methacrylate into a high-temperature and high-pressure reaction kettle to form a uniform oil phase; the emulsifier is composed of sorbitan monolaurate, sodium oleate and glycerol according to a mass ratio of 3:7:100;

[0049] S2: Add 44 g of monomers into water to form an aqueous solution, add a NaOH solution with a mass percentage of 10% to adjust the pH value of the solution to neutral to obtain an aqueous phase; the monomers are composed of methacrylic acid, acrylamide and sodium methallylsulfonate according to a mass ratio of 5:14:12;

[0050] S3: Under the stirring condition at a rotational speed of 900 rpm, slowly add the aqueous phase prepared in step S2 into the oil phase prepared in step S1, continue stirring for 25 min, introduce nitrogen for deoxidation, then dropwise add 9 g of an aqueous solution of sodium persulfate with a mass percentage of 16%, 13 g of an aqueous solution of sodium bisulfite with a mass percentage of 12%, and 5 g of sodium dioctyl sulfosuccinate for polymerization reaction. After the reaction is completed, continue stirring for 4.3 h to obtain the polymer for viscoelastic fracturing fluid.

[0051] Comparative Example 1

[0052] The synthesis method of the polymer for viscoelastic fracturing fluid in this comparative example is similar to that in Example 3. The difference between this comparative example and Example 3 is that 2-ethylhexyl methacrylate was not added in step S1 of this comparative example.

[0053] Comparative Example 2

[0054] The synthesis method of the polymer for viscoelastic fracturing fluid in this comparative example is similar to that in Example 3. The difference between this comparative example and Example 3 is that in step S2 of this comparative example, the monomer used is an equal amount of methacrylic acid instead of sodium methallyl sulfonate.

[0055] Comparative Example 3

[0056] The synthesis method of the polymer for viscoelastic fracturing fluid in this comparative example is similar to that in Example 3. The difference between this comparative example and Example 3 is that in step S2 of this comparative example, the monomer is composed of methacrylic acid, acrylamide, and sodium methallyl sulfonate in a mass ratio of 9:2:1.

[0057] Comparative Example 4

[0058] The synthesis method of the polymer for viscoelastic fracturing fluid in this comparative example is similar to that in Example 4. The difference between this comparative example and Example 4 is that the dosage of the emulsifier in step S1 of this comparative example is 2 g.

[0059] Comparative Example 5

[0060] The synthesis method of the polymer for viscoelastic fracturing fluid in this comparative example is similar to that in Example 4. The difference between this comparative example and Example 4 is that the dosage of the emulsifier in step S1 of this comparative example is 20 g.

[0061] Comparative Example 6

[0062] The synthesis method of the polymer for viscoelastic fracturing fluid in this comparative example is similar to that in Example 4. The difference between this comparative example and Example 4 is that the rotational speed of the high-speed stirring in step S3 of this comparative example is 200 rpm.

[0063] Comparative Example 7

[0064] The method for synthesizing the polymer used in the viscoelastic fracturing fluid in this comparative example is similar to that in Example 4. The difference between this comparative example and Example 4 is that no polymerization stabilizer was added in step S3 of this comparative example.

[0065] Test Example

[0066] Friction reduction performance test: The polymers of the viscoelastic fracturing fluids prepared in Examples 1 - 4 and Comparative Examples 1 - 7 were used to prepare fracturing fluids respectively according to the following method: (1) Measure 500 mL of tap water and 500 mL of a 12% mass percentage NaCl solution respectively, pour them into a beaker, and add the polymer for viscoelastic fracturing fluid (the mass percentage of the polymer for viscoelastic fracturing fluid is 3%) under stirring, and stir evenly for standby.

[0067] According to the provisions of 7.13.1 in SY / T 6376 - 2008, the friction reduction performance test was carried out on the fracturing fluids of the polymers for viscoelastic fracturing fluids prepared in Examples 1 - 4 and Comparative Examples 1 - 7. Specifically: (1) Fill clear water (12% mass percentage NaCl solution) into the base liquid tank of a multifunctional flow loop instrument or similar product, and measure the stable pressure difference when the clear water (12% mass percentage NaCl solution) passes through the pipeline; (2) Fill the prepared active drag reduction agent solution into the friction meter, and measure the stable pressure difference when the active drag reduction agent solution flows through the pipeline; (3) Calculate the drag reduction rate of the polymer for viscoelastic fracturing fluid according to the following formula: where η is the drag reduction rate of the fracturing fluid for clear water (12% mass percentage NaCl solution), expressed as a percentage; △P1 is the stable pressure difference when the clear water (12% mass percentage NaCl solution) flows through the pipeline, with the unit of pascal (Pa); △P2 is the stable pressure difference when the fracturing fluid flows through the pipeline, with the unit of pascal (Pa). The test results are shown in Table 1.

[0068]

[0069] Viscosity test: Use a rotary viscometer of model NDJ - 1 to conduct viscosity tests on the polymers for viscoelastic fracturing fluids prepared in Examples 1 - 4 and Comparative Examples 1 - 3 at normal temperature and 300 °C, and measure the viscosities of the polymers after 20 min and 1800 min respectively. The test results are shown in Table 2.

[0070] Table 1 Friction reduction performance test results

[0071]

[0072] As can be seen from Table 1, the drag reduction rate of the polymer for viscoelastic fracturing fluid prepared by using the polymer synthesis method for viscoelastic fracturing fluid provided by the present invention is 78.2% - 83.5% after being prepared with fresh water, and the drag reduction rate is 74.1% - 79.6% after being prepared with a 12% NaCl solution by mass percentage. This fully shows that the polymer for viscoelastic fracturing fluid synthesized by using the polymer synthesis method for viscoelastic fracturing fluid provided by the present invention has good friction reduction performance, and can effectively improve the drag reduction rate when applied to viscoelastic fracturing fluid. Among them, the polymer prepared in Example 4 has the best friction reduction performance and is the best embodiment of the present invention.

[0073] Compared with Example 4, in Comparative Example 1, 2-ethylhexyl methacrylate was not added in step S1, and in Comparative Example 2, the monomer in step S2 was replaced with an equal amount of methacrylic acid instead of sodium methallyl sulfonate, but the drag reduction rate of the polymer for viscoelastic fracturing fluid prepared was reduced. This shows that introducing ester-based long side chains and sulfonic acid groups into the molecular side chain of the polymer in the present invention can effectively improve the friction reduction performance of the polymer; in Comparative Example 3, the mass ratio of the monomers of methacrylic acid, acrylamide, and sodium methallyl sulfonate in step S2 was changed, but the drag reduction rate of the polymer for viscoelastic fracturing fluid prepared was reduced. This shows that the mass ratio of the monomers provided by the present invention has been optimized; in Comparative Example 4, the amount of emulsifier in step S1 was reduced, and in Comparative Example 5, the amount of emulsifier in step S1 was increased, but the drag reduction rate of the polymer for viscoelastic fracturing fluid prepared was reduced to varying degrees. This shows that the amount of emulsifier can regulate the relative molecular mass of the polymer, thereby affecting the friction reduction performance of the polymer; in Comparative Example 6, the rotation speed of the high-speed stirring in step S3 was reduced, but the friction reduction performance of the polymer for viscoelastic fracturing fluid prepared was slightly reduced. This shows that using high-speed stirring during the polymerization process can ensure that the polymerization reaction occurs in the droplets and improve the polymer performance; in Comparative Example 7, no polymerization stabilizer was added in step S3, but the drag reduction rate of the polymer for viscoelastic fracturing fluid prepared was reduced. This shows that the polymerization stabilizer and the high-speed stirring during the polymerization process play a synergistic role to effectively ensure that the polymerization reaction occurs in the droplets and improve the polymer performance.

[0074] Table 2 Viscosity Test Results

[0075]

[0076] As can be seen from Table 2, the polymer for viscoelastic fracturing fluid prepared by the present invention has a viscosity of 3.29 - 3.51 mPa·S after 20 min at room temperature and a viscosity of 3.17 - 3.45 mPa·S after 1800 min; the viscosity after 20 min at 300 °C is 2.79 - 3.08 mPa·S, and the viscosity after 1800 min is 2.06 - 2.64 mPa·S. This fully shows that the polymer for viscoelastic fracturing fluid prepared by the present invention has good thermal properties and temperature resistance. The polymers for viscoelastic fracturing fluid prepared in Comparative Examples 1 - 3 have deteriorated viscosities both at room temperature and at 300 °C. This shows that introducing groups with surfactant functions such as carboxyl groups, sulfonic acid groups, amide groups, and long-chain ester groups into the polymer in the present invention can improve the temperature resistance of the polymer.

[0077] The above embodiments are merely illustrative of the present invention and do not limit the present invention. Those skilled in the art shall not modify the above embodiments without departing from the spirit and scope of the present invention. All equivalent modifications or changes completed by those with ordinary knowledge in the technical field without departing from the technical idea of the present invention still fall within the protection scope of the present invention.

Claims

1. A method for synthesizing a polymer for viscoelastic fracturing fluid, characterized in that: The following steps are involved: S1: adding emulsifier and 2-ethylhexyl methacrylate into a high temperature and high pressure reactor to form a uniform oil phase; S2: adding the monomer to water to form an aqueous solution, adjusting the pH value of the solution to neutral, and obtaining an aqueous phase; S3: slowly adding the water phase obtained in step S2 to the oil phase obtained in step S1 under stirring conditions at a rotation speed of 800-1000 rpm, continuing stirring, introducing nitrogen to deoxygenate, and then dropping an initiator and a polymerization stabilizer to carry out a polymerization reaction. After the reaction is completed, stirring is continued for 4-4.5 hours to obtain a polymer for a viscoelastic fracturing fluid; The monomer is composed of methacrylic acid, acrylamide and sodium methacrylic sulfonate in a mass ratio of 4-7:13-16:10-13; The emulsifier in step S1 is composed of sorbitan monolaurate, sodium oleate and glycerol in a mass ratio of 1-3:5-8:100; In step S1, the mass fraction of 2-ethylhexyl methacrylate is 10-13 parts, and the mass fraction of the emulsifier is 8-12 parts; The polymerization stabilizer in step S3 is one of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate and dioctyl sodium sulfosuccinate, and the mass fraction of the polymerization stabilizer is 3-7 parts.

2. The method for synthesizing a polymer for viscoelastic fracturing fluid according to claim 1, characterized in that: The monomers are composed of methacrylic acid, acrylamide and sodium methacrylic acid sulfonate in a mass ratio of 6:14:

11.

3. The method for synthesizing a polymer for viscoelastic fracturing fluid according to claim 1, characterized in that: The monomers are composed of methacrylic acid, acrylamide and sodium methacrylic acid sulfonate in a mass ratio of 5:14:

12.

4. The method for synthesizing a polymer for viscoelastic fracturing fluid according to claim 1, characterized in that: The mass fraction of the monomer in step S2 is 40-45 parts.

5. The method for synthesizing a polymer for viscoelastic fracturing fluid according to claim 1, characterized in that: The stirring time in step S3 is 20-30 minutes.

6. The method for synthesizing a polymer for viscoelastic fracturing fluid according to claim 1, characterized in that: The initiator in step S3 includes initiator I and initiator II; the initiator I is a sodium persulfate aqueous solution, and the mass percentage of the sodium persulfate aqueous solution is 15%-20%; the initiator II is a sodium bisulfite aqueous solution, and the mass percentage of the sodium bisulfite aqueous solution is 10%-14%; the mass fraction of the initiator I is 8-10 parts, and the mass fraction of the initiator II is 12-14 parts.

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