Synthesis method of polymer for viscoelastic fracturing fluid

Abstract

The invention belongs to the technical field of fracturing fluids, and particularly relates to a synthesis method of a polymer for a viscoelastic fracturing fluid. Methacrylic acid-2-ethylhexyl acrylate, methacrylic acid, acrylamide and sodium methallyl sulfonate are adopted as polymeric monomers, a polymer for the viscoelastic fracturing fluid is synthesized through an inverse emulsion polymerization method, carboxyl, a sulfonic acid group, an amide group, a long-chain ester group and other groups with surfactant functions are introduced into the polymer, and the viscoelastic fracturing fluid is prepared. The resistance reduction, temperature resistance and sand carrying capacity of the polymer for the viscoelastic fracturing fluid are improved; the relative molecular mass of the polymer for the viscoelastic fracturing fluid is controlled by controlling the dosage of the emulsifier, and the obtained polymer is uniformly dispersed and stable in performance through high-speed stirring in the polymerization process, so that the friction resistance reduction performance of the polymer is further improved.

Description

Technical Field

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

[0002] Hydraulic fracturing technology is one of the important technical means used to increase the production of low-permeability and extra-low-permeability oil and gas wells and increase the injection of water injection wells. Among them, water-based gel fracturing fluid is used in major oil and gas fields in my country due to its advantages such as high viscosity, low friction and strong sand suspension performance. Hydraulic fracturing fluid is a surfactant with high viscosity and certain viscoelasticity. The process of hydraulic fracturing of oil layers is to use a high-pressure and large-displacement pump on the ground, and use the principle of liquid pressure transmission to inject fracturing fluid with a certain viscosity into the oil layer at a pressure greater than the absorption capacity of the oil layer, and gradually increase the pressure in the wellbore, thereby creating high pressure at the bottom of the well. When this pressure is greater than the ground stress near the well wall and the tensile strength of the formation rock, cracks will be generated in the formation near the bottom of the well: continue to inject sand-carrying fluid with proppant, the cracks will extend forward and be filled with proppant, and the cracks will close on the proppant after the well is shut down, thereby forming sand-filled cracks with certain geometric dimensions and high conductivity in the formation near the bottom of the well, achieving the purpose of increasing production and injection. However, the friction resistance of viscoelastic fracturing fluid in the pipeline is very large, and most of the pump pressure during construction is consumed to overcome the friction resistance of the pipeline. The actual pressure acting on the production layer to open the production layer is not large, so it is difficult to increase the displacement and the cracks are difficult to extend forward to achieve the purpose of forming a fracture network. The addition of resistance reducing agent can effectively reduce the friction resistance of fracturing fluid and reduce energy consumption.

[0003] At present, the drag reducing agents used in the exploitation process of domestic oil and gas fields mainly include high-flexibility polymer drag reducing agents and viscoelastic surfactant drag reducing agents. Viscoelastic surfactant drag reducing agents 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 drag reducing agents need to be further improved.

[0004] The Chinese patent application document with application publication number CN115851252A discloses a drag reducing agent for seawater-based fracturing fluid prepared with active water, which is polymerized under a redox-azo composite initiation system by nonionic monomers, two or one of 2-acrylamide-2-methylpropane sulfonic acid and sodium propylene sulfonate, anionic monomers containing carboxylic acid groups and active water. Salt resistance is improved by introducing sulfonic acid groups and carboxylic acid groups, and active water polymerization is adopted to overcome the cage shielding effect formed between each monomer and between monomer and initiator when ordinary pure water is used for polymerization, reduce reaction activation energy, reduce initiator dosage, and improve polymer molecular weight and uniform regularity of each group of chain segment. However, due to the small relative molecular weight of this drag reducing agent, in use, as time goes on, viscosity decreases, causing the drag reducing effect to be further improved, in addition, due to its small relative molecular weight, causing its temperature resistance to be poor, under high temperature conditions, the drag reducing agent molecule can decompose, causing high temperature viscosity and high temperature drag reducing performance to all decrease. Summary of the invention

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

[0006] In order to achieve the above object, the technical solution of the present invention is as follows: A method for synthesizing a polymer for viscoelastic fracturing fluid comprises the following steps: 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: under stirring conditions, slowly adding the water phase obtained in step S2 to the oil phase obtained in step S1, continuing stirring, introducing nitrogen to deoxygenate, and then dropwise adding 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 viscoelastic fracturing fluid; The monomers are composed of methacrylic acid, acrylamide and sodium methacrylic sulfonate in a mass ratio of 4-7:13-16:10-13.

[0007] The present invention adopts 2-ethylhexyl methacrylate, methacrylic acid, acrylamide and sodium methacrylic acid sulfonate as polymerization monomers, and synthesizes a polymer for viscoelastic fracturing fluid by reverse emulsion polymerization. Groups with surfactant functions such as carboxyl, sulfonic acid group, amide group and long-chain ester group are introduced into the polymer. During the process of entering the formation, with the degradation effects of mechanical shearing, thermochemical pyrolysis, microbial reaction, etc., the drag reducing agent polymer is dispersed into molecular fragments with surface active functions, which improves the oil displacement effect of the fracturing fluid after entering the well. At the same time, the coordination of these molecular side chains can improve the drag reduction and temperature resistance of the polymer. In addition, the side chains of the polymer prepared by 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 can effectively improve the sand carrying capacity of the fracturing fluid.

[0008] Furthermore, the monomer is composed of methacrylic acid, acrylamide and sodium methacrylic acid sulfonate in a mass ratio of 6:14:11.

[0009] Furthermore, the monomer is composed of methacrylic acid, acrylamide and sodium methacrylic acid sulfonate in a mass ratio of 5:14:12.

[0010] Furthermore, the emulsifier in step S1 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.

[0011] During the research process of the present invention, it was found that when the amount of emulsifier used was low, the relative molecular mass of the polymer was high, but the emulsion was unstable and easy to stratify; when the amount of emulsifier used was high, the stability of the emulsion was significantly improved, but the relative molecular mass of the polymer was 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, which causes the relative molecular mass of the polymer to decrease.

[0012] Furthermore, the mass fraction of 2-ethylhexyl methacrylate in step S1 is 10-13 parts.

[0013] Furthermore, the mass fraction of the monomer in step S2 is 40-45 parts.

[0014] Furthermore, the stirring speed in step S3 is 800-1000 rpm.

[0015] In the process of monomer polymerization, the present invention forms a stable microemulsion dispersion through high-speed stirring to effectively reduce the size of monomer droplets. Under the action of a polymerization stabilizer, the polymerization reaction is ensured to occur in the droplets, so that the obtained polymer is evenly dispersed and has stable performance, thereby effectively improving the friction reduction performance of the polymer.

[0016] Furthermore, the stirring time in step S3 is 20-30 minutes. This step can fully emulsify the oil phase and the water phase in the reaction system.

[0017] Furthermore, 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.

[0018] Furthermore, 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.

[0019] The polymerization stabilizer added in the polymerization process of the present invention can be wrapped around the monomers to weaken 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 and ensure that the polymerization reaction occurs in the droplets.

[0020] Compared with the prior art, the method for synthesizing a polymer for viscoelastic fracturing fluid provided by the present invention has the following technical advantages: (1) The present invention uses 2-ethylhexyl methacrylate, methacrylic acid, acrylamide and sodium methacrylic acid sulfonate as polymerization monomers, and synthesizes a viscoelastic fracturing fluid polymer by an inverse emulsion polymerization method, thereby effectively improving the resistance reduction, temperature resistance and sand carrying capacity of the viscoelastic fracturing fluid polymer; (2) The present invention further controls the relative molecular weight of the polymer used in the viscoelastic fracturing fluid by controlling the amount of the emulsifier, and makes the obtained polymer evenly dispersed and stable in performance by high-speed stirring during the polymerization process, thereby effectively improving the friction reduction performance of the polymer; (3) The viscoelastic fracturing fluid polymer prepared by the present invention can reduce friction and has a high sand carrying capacity and good compatibility; (4) The viscoelastic fracturing fluid polymer prepared by the present invention can stretch freely in the fluid, inhibiting the energy loss caused by molecular collisions of fluid molecules in the turbulent zone, thereby achieving the purpose of reducing resistance. DETAILED DESCRIPTION

[0021] 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 based on the basic idea of ​​the present invention, but as long as they do not deviate from the basic idea of ​​the present invention, they are all within the scope of the present invention.

[0022] Example 1 A method for synthesizing a polymer for viscoelastic fracturing fluid comprises the following steps: S1: adding 8 g of emulsifier and 10 g of 2-ethylhexyl methacrylate into 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; S2: adding 45 g of monomer into water to form an aqueous solution, adding 10% by mass of NaOH solution to adjust the pH value of the solution to neutral, to obtain an aqueous phase; the monomer is composed of methacrylic acid, acrylamide and sodium methacrylic acid sulfonate in a mass ratio of 4:13:10; S3: Under the stirring condition of a rotation speed of 800 rpm, the water phase obtained in step S2 is slowly added to the oil phase obtained in step S1, and the stirring is continued for 20 minutes. Nitrogen is introduced for deoxygenation, and then 8g of a 15% by mass sodium persulfate aqueous solution, 12g of a 10% by mass sodium bisulfite aqueous solution and 3g of sodium dodecyl sulfate are added dropwise to carry out a polymerization reaction. After the reaction is completed, stirring is continued for 4 hours to obtain a polymer for viscoelastic fracturing fluid.

[0023] Example 2 A method for synthesizing a polymer for viscoelastic fracturing fluid comprises the following steps: S1: adding 12 g of emulsifier and 13 g of 2-ethylhexyl methacrylate into 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; S2: adding 40 g of monomer into water to form an aqueous solution, adding 10% by mass of NaOH solution to adjust the pH value of the solution to neutral, to obtain an aqueous phase; the monomer is composed of methacrylic acid, acrylamide and sodium methacrylic acid sulfonate in a mass ratio of 7:16:13; S3: Under the stirring condition of a rotation speed of 1000 rpm, the water phase obtained in step S2 is slowly added to the oil phase obtained in step S1, and stirring is continued for 30 minutes. Nitrogen is introduced for deoxygenation, and then 10g of a 20% by mass sodium persulfate aqueous solution, 14g of a 14% by mass sodium bisulfite aqueous solution and 7 parts of sodium dodecylbenzene sulfonate are dropwise added to carry out polymerization reaction. After the reaction is completed, stirring is continued for 4.5 hours to obtain a polymer for viscoelastic fracturing fluid.

[0024] Example 3 A method for synthesizing a polymer for viscoelastic fracturing fluid comprises the following steps: S1: adding 9 g of emulsifier and 12 g of 2-ethylhexyl methacrylate into 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 2:7:100; S2: 43 g of monomers are added into water to form an aqueous solution, and a 10% by mass NaOH solution is added 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 methacrylic acid sulfonate in a mass ratio of 6:14:11; S3: Under the stirring condition of a rotation speed of 900 rpm, the water phase obtained in step S2 is slowly added to the oil phase obtained in step S1, and the stirring is continued for 25 minutes. Nitrogen is introduced for deoxygenation, and then 9g of a 16% by mass sodium persulfate aqueous solution, 13g of a 12% by mass sodium bisulfite aqueous solution and 5g of dioctyl sodium sulfosuccinate are dropwise added to carry out a polymerization reaction. After the reaction is completed, stirring is continued for 4.3 hours to obtain a polymer for viscoelastic fracturing fluid.

[0025] Example 4 A method for synthesizing a polymer for viscoelastic fracturing fluid comprises the following steps: S1: adding 11 g of emulsifier and 10 g of 2-ethylhexyl methacrylate into 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 3:7:100; S2: 44 g of monomers are added into water to form an aqueous solution, and a 10% by mass NaOH solution is added 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 methacrylic acid sulfonate in a mass ratio of 5:14:12; S3: Under the stirring condition of a rotation speed of 900 rpm, the water phase obtained in step S2 is slowly added to the oil phase obtained in step S1, and the stirring is continued for 25 minutes. Nitrogen is introduced for deoxygenation, and then 9g of a 16% by mass sodium persulfate aqueous solution, 13g of a 12% by mass sodium bisulfite aqueous solution and 5g of dioctyl sodium sulfosuccinate are dropwise added to carry out a polymerization reaction. After the reaction is completed, stirring is continued for 4.3 hours to obtain a polymer for viscoelastic fracturing fluid.

[0026] Comparative Example 1 The method for synthesizing 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 is not added in step S1 of this comparative example.

[0027] Comparative Example 2 The synthetic 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 the monomer in step S2 of this comparative example uses an equal amount of methacrylic acid instead of sodium methacrylic acid sulfonate.

[0028] Comparative Example 3 The synthetic method of the viscoelastic fracturing fluid polymer in this comparative example is similar to that in Example 3. The difference between this comparative example and Example 3 is that the monomer in step S2 of this comparative example is composed of methacrylic acid, acrylamide and sodium methacrylic acid sulfonate in a mass ratio of 9:2:1.

[0029] Comparative Example 4 The synthetic 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 amount of the emulsifier used in step S1 of this comparative example is 2 g.

[0030] Comparative Example 5 The synthetic 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 amount of the emulsifier used in step S1 of this comparative example is 20 g.

[0031] Comparative Example 6 The synthetic 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 rotation speed of the high-speed stirring in step S3 of this comparative example is 200 rpm.

[0032] Comparative Example 7 The method for synthesizing 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 no polymer stabilizer is added in step S3 of this comparative example.

[0033] Test example Friction reduction performance test: The viscoelastic fracturing fluid polymers prepared in Examples 1 to 4 and Comparative Examples 1 to 7 were respectively used to prepare fracturing fluids according to the following methods: (1) 500 mL of tap water and 500 mL of 12% by mass NaCl solution were respectively measured and poured into a beaker, and the viscoelastic fracturing fluid polymer (the mass percentage of the viscoelastic fracturing fluid polymer is 3%) was added under stirring, and the mixture was stirred evenly and set aside.

[0034] According to the provisions of 7.13.1 of SY / T 6376-2008, the viscoelastic fracturing fluid polymer fracturing fluid prepared in Examples 1 to 4 and Comparative Examples 1 to 7 was tested for friction reduction performance, specifically: (1) clean water (12% by mass NaCl solution) was placed in a multifunctional flow loop instrument or a base fluid tank of a similar product, and the stable pressure difference when the clean water (12% by mass NaCl solution) passed through the pipeline was measured; (2) the prepared active drag reducing agent was dissolved in a flask; The fluid was loaded into the friction meter to measure the stable pressure difference when the active drag reducing agent solution flows through the pipeline; (3) the drag reduction rate of the viscoelastic fracturing fluid polymer was calculated according to the following formula: where η is the drag reduction rate of the fracturing fluid to clean water (12% by mass NaCl solution), expressed as a percentage; △P1 is the stable pressure difference when clean water (12% by mass NaCl solution) flows through the pipeline, in Pascals (Pa); △P2 is the stable pressure difference when the fracturing fluid flows through the pipeline, in Pascals (Pa). The test results are shown in Table 1.

[0035]

[0036] Viscosity test: The viscosities of the viscoelastic fracturing fluid polymers prepared in Examples 1 to 4 and Comparative Examples 1 to 3 were tested at room temperature and 300° C. using an NDJ-1 rotational viscometer. The viscosities of the polymers were tested after 20 min and 1800 min, respectively. The test results are shown in Table 2.

[0037] Table 1 Friction reduction performance test results

[0038] As can be seen from Table 1, the drag reduction rate of the viscoelastic fracturing fluid polymer prepared by the viscoelastic fracturing fluid polymer synthesis method provided by the present invention is 78.2%-83.5% after being prepared with clean water, and the drag reduction rate after being prepared with a 12% by mass NaCl solution is 74.1%-79.6%, which fully demonstrates that the viscoelastic fracturing fluid polymer synthesized by the viscoelastic fracturing fluid polymer synthesis method provided by the present invention has good friction reduction performance, and can be effectively improved by being applied to viscoelastic fracturing fluid. Among them, the friction reduction performance of the polymer prepared in Example 4 is the best, which is the best embodiment of the present invention.

[0039] Compared with Example 4, in step S1 of comparative example 1, 2-ethylhexyl methacrylate is not added, and in step S2 of comparative example 2, an equal amount of methacrylic acid is used instead of sodium methacrylic acid sulfonate in the monomer, but the drag reduction rate of the obtained viscoelastic fracturing fluid polymer is reduced, which indicates that the introduction of ester long side chains and sulfonic acid groups into the molecular side chains of the polymer of the present invention can effectively improve the friction reduction performance of the polymer; in comparative example 3, the mass ratio of methacrylic acid, acrylamide and sodium methacrylic acid in the monomer of step S2 is changed, but the drag reduction rate of the obtained viscoelastic fracturing fluid polymer is reduced, which indicates that the mass ratio of the monomers provided by the present invention has been optimized; comparative example 4 reduces the amount of emulsifier used in step S1, and comparative example 5 increases the amount of emulsifier used in step S1. The amount of emulsifier is increased, but the drag reduction rate of the obtained viscoelastic fracturing fluid polymer is reduced to varying degrees, which shows that the amount of emulsifier can regulate the relative molecular weight 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 is reduced, but the friction reduction performance of the obtained viscoelastic fracturing fluid polymer is slightly reduced, which shows that the use of high-speed stirring in the polymerization process can ensure that the polymerization reaction occurs in the droplets, thereby improving the polymer performance; in Comparative Example 7, no polymerization stabilizer is added in step S3, but the drag reduction rate of the obtained viscoelastic fracturing fluid polymer is reduced, which shows that the polymerization stabilizer and the high-speed stirring in the polymerization process play a synergistic role, effectively ensuring that the polymerization reaction occurs in the droplets, thereby improving the polymer performance.

[0040] Table 2 Viscosity test results

[0041] As shown in Table 2, the viscosity of the viscoelastic fracturing fluid polymer prepared by the present invention is 3.29-3.51 mPa·S after 20 minutes at room temperature, and 3.17-3.45 mPa·S after 1800 minutes; the viscosity is 2.79-3.08 mPa·S after 20 minutes at 300°C, and 2.06-2.64 mPa·S after 1800 minutes, which fully demonstrates that the viscoelastic fracturing fluid polymer prepared by the present invention has good thermal properties and temperature resistance. The viscosities of the viscoelastic fracturing fluid polymers prepared by Comparative Examples 1 to Comparative Examples 3 are deteriorated at both room temperature and 300°C, which demonstrates that the present invention introduces groups with surfactant functions such as carboxyl groups, sulfonic acid groups, amide groups and long-chain ester groups into the polymer, which can improve the temperature resistance of the polymer.

[0042] The above embodiments are merely illustrative of the present invention, and are not intended to limit the present invention. Those skilled in the art should not modify the above embodiments without violating the spirit and scope of the present invention. All equivalent modifications or changes made by those with ordinary knowledge in the relevant technical field without departing from the technical concept of the present invention still fall within the scope of protection 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: under stirring conditions, slowly adding the water phase obtained in step S2 to the oil phase obtained in step S1, continuing stirring, introducing nitrogen to deoxygenate, and then dropwise adding 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 viscoelastic fracturing fluid; The monomers are composed of methacrylic acid, acrylamide and sodium methacrylic sulfonate in a mass ratio of 4-7:13-16:10-13.

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 emulsifier in step S1 is composed of sorbitan monolaurate, sodium oleate and glycerol in a mass ratio of 1-3:5-8:

100.

5. The method for synthesizing a polymer for viscoelastic fracturing fluid according to claim 1, characterized in that: 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.

6. 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.

7. The method for synthesizing a polymer for viscoelastic fracturing fluid according to claim 1, characterized in that: The stirring speed in step S3 is 800-1000 rpm.

8. 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.

9. 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.

10. The method for synthesizing a polymer for viscoelastic fracturing fluid according to claim 1, characterized in that: 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.

Images