Salt-tolerant polyacrylamide drag reducer and preparation method thereof

Abstract

The invention relates to the technical field of drag reducer preparation, in particular to a salt-tolerant polyacrylamide drag reducer and a preparation method thereof.The preparation method comprises the following steps that S1, alkyl naphthalene sulfonate and hexadecyl sulfopropyl betaine are compounded to obtain a surfactant; the preparation method comprises the following steps: sequentially adding a surfactant, sodium allyloxy hydroxypropyl sulfonate, acrylamide and acrylic acid into deionized water to obtain a water phase; s2, uniformly stirring and mixing white oil, coconut oil, Tween 80 and Span 80 to obtain an oil phase; s3, slowly dropwise adding the water phase into the oil phase under violent stirring to prepare a water-in-oil inverse emulsion base solution; and then removing oxygen, slowly adding a potassium peroxodisulfate slow-release agent solution, and reacting to obtain the salt-tolerant polyacrylamide drag reducer. The prepared drag reducer is good in salt resistance effect, uniform in molecular chain segment and high in drag reduction efficiency.

Description

Technical Field

[0001] This invention relates to the field of drag-reducing agent preparation technology, specifically a method for preparing a salt-resistant polyacrylamide drag-reducing agent. Background Technology

[0002] Polyacrylamide (PAM) possesses excellent thickening and rheological properties, making it widely used as a drag-reducing agent in fracturing fluids. The drag-reducing performance of polymers in aqueous solutions is mainly related to their molecular weight, flexibility, chain structure, and solubility. Higher molecular weight, greater molecular flexibility, fewer side groups, stronger water solubility, and greater extension in water result in better drag reduction. With the continuous vertical exploration and development of oil and gas fields, deeper burial depths and higher temperatures place higher demands on the temperature resistance of fracturing fluids in deep well reservoirs. When using traditional drag-reducing agents, such as the most commonly used polyacrylamide, their molecular chains react with calcium-containing... 2+ Mg 2+ When ions are in a salt solution, they automatically coil, making it difficult for them to stretch and hydrate to form a linear polymer fluid. This results in a reduction in fluid dynamics volume and a decrease in solution viscosity, thus affecting the performance. Furthermore, during the preparation of drag-reducing agents, the polymerization of acrylamide generates a large amount of heat, which, if not properly controlled, can easily lead to explosive polymerization. This results in uneven molecular chain segments in the prepared drag-reducing agent, reducing its drag-reducing effect. Slowly adding the initiator dropwise, if not properly controlled, can also cause the aforementioned problems.

[0003] Therefore, in response to the problems raised in the background art, those skilled in the art propose a salt-resistant polyacrylamide drag-reducing agent and its preparation method. Summary of the Invention

[0004] The purpose of this invention is to provide a salt-resistant polyacrylamide drag-reducing agent and its preparation method, so as to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for preparing a salt-resistant polyacrylamide drag-reducing agent, the method comprising the following steps:

[0007] S1. Alkyl naphthalene sulfonate and hexadecyl sulfopropyl betaine are compounded at a mass ratio of 1:(15-20) to obtain a surfactant. During stirring, 3-8 parts of surfactant, 2-5 parts of sodium allyl hydroxypropyl sulfonate, 50-80 parts of acrylamide, and 15-30 parts of acrylic acid are added sequentially to 200 parts of deionized water. After thorough stirring and dissolution, an aqueous phase is obtained.

[0008] S2. Mix the white oil, coconut oil, Tween 80, and Span 80 until well combined to obtain the oil phase;

[0009] S3. Under vigorous stirring, the aqueous phase is slowly added dropwise to the oil phase at 30°C, with a mass ratio of aqueous phase to oil phase of 1:(1.5-2), to prepare a water-in-oil reverse emulsion base liquid; then, nitrogen gas is introduced into the reverse emulsion base liquid and stirred at high speed to remove oxygen, and the temperature is kept constant at 30°C. After stirring for 30 minutes, potassium persulfate slow-release agent solution is slowly added. After the potassium persulfate slow-release agent solution is completely added, the reaction is catalytically initiated at 30°C for 8-15 hours to obtain a salt-resistant polyacrylamide drag-reducing agent;

[0010] The method for preparing the potassium persulfate slow-release agent in the potassium sulfate slow-release agent solution includes the following steps:

[0011] S101. Sodium hexadecyl sulfate and potassium persulfate are added to deionized water to obtain solution A;

[0012] S102. Span 80 and pyrrole monomer are added to a mixed solution of isopropanol, glycerol and butanol to obtain solution B.

[0013] S103. Polyethylene glycol, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide salt and N,N-dicyclohexylcarbodiimide were added to deionized water and stirred for 4-6 hours to obtain solution C.

[0014] S104. Add solution A obtained in step S101 to solution B and stir continuously for 0.5-1h. Add acetic acid dropwise to adjust the pH to 2, continue stirring for 2-3h, then add solution C to solution B to obtain the reaction solution, and continue stirring continuously for 15-25h.

[0015] S105. The precipitate in the reaction solution obtained in step S104 is filtered and separated. The separated product is washed with sufficient anhydrous ethanol and then vacuum dried at 40°C for 10 hours to obtain potassium persulfate slow-release agent.

[0016] Furthermore, in step S1, the mass ratio of alkylnaphthalene sulfonate to hexadecyl sulfopropyl betaine is 1:(15-20); the alkylnaphthalene sulfonate is sodium diisobutylnaphthalene sulfonate or sodium methylene dinaphthalene disulfonate.

[0017] Furthermore, in step S2, the mass ratio of white oil, coconut oil, Tween 80, and Span 80 is (15-20):(10-15):(4.5-5.5):(0.3-0.5).

[0018] Furthermore, in step S3, the mass ratio between the potassium persulfate slow-release agent solution and the oil phase is 1:(10-20); the mass fraction of potassium persulfate slow-release agent in the potassium persulfate slow-release agent solution is 3-5%.

[0019] Furthermore, in step S101, the mass ratio of sodium hexadecyl sulfate, potassium persulfate, and deionized water is 1:(20-30):(50-70).

[0020] Furthermore, in step S102, the mass ratio of Span 80, pyrrole monomer, isopropanol, glycerol and butanol is 1:(35-40):(180-220):(30-35):(40-50), and the mass ratio of pyrrole monomer in step S102 to potassium persulfate in step S101 is (1.5-2):1.

[0021] Furthermore, in step S103, the mass ratio of polyethylene glycol, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide salt, N,N-dicyclohexylcarbodiimide, ethanol, and deionized water is 1:(4-6):(2-4):(30-40), and the mass ratio of polyethylene glycol in step S103 to pyrrole monomer in step S102 is 1:(20-30).

[0022] A salt-resistant polyacrylamide drag-reducing agent is prepared by the above-described method for preparing salt-resistant polyacrylamide drag-reducing agents.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] 1. By using a compounded surfactant as an aqueous solvent, the stability and temperature resistance of the drag-reducing agent of the present invention are effectively improved; by using sodium allyl hydroxypropyl sulfonate to participate in the polymerization reaction of acrylamide and acrylic acid, the salt resistance of the drag-reducing agent of the present invention is effectively improved.

[0025] 2. This invention creatively applies the concept of potassium persulfate slow release to the preparation of drag-reducing agents. By using polypyrrole to coat potassium persulfate as a potassium persulfate slow release agent, the potassium persulfate slow release agent can controllably release persulfate ions in the aqueous phase, effectively controlling the polymerization between sodium allyl hydroxypropyl sulfonate, acrylamide and acrylic acid, preventing the polymer from undergoing explosive polymerization, and the drag-reducing agent product has uniform polymerization and excellent drag reduction effect.

[0026] 3. In this invention, polypyrrole is first synthesized. After a period of time, polyethylene glycol activated by 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide salt and N,N-dicyclohexylcarbodiimide is added. Polyethylene glycol modifies polypyrrole, which enhances the compatibility of potassium persulfate slow-release agent with the aqueous phase and improves the slow-release effect. Attached Figure Description

[0027] Figure 1 This is a process flow diagram for preparing the salt-resistant polyacrylamide drag-reducing agent in this invention;

[0028] Figure 2This is a process flow diagram for preparing potassium persulfate slow-release agent in this invention. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Please see Figures 1-2 The present invention provides:

[0031] Example 1

[0032] A method for preparing a salt-resistant polyacrylamide drag-reducing agent, the method comprising the following steps:

[0033] S1. 0.2g of sodium diisobutylnaphthalenesulfonate and 3.4g of hexadecyl sulfopropyl betaine were compounded to obtain a surfactant; during stirring, 3.6g of surfactant, 2.7g of sodium allyl oxyhydroxypropyl sulfonate, 54g of acrylamide and 7.2g of acrylic acid were added to 180g of deionized water in sequence, and after being stirred and dissolved, an aqueous phase was obtained.

[0034] S2. Mix 213.6g of white oil, 160.2g of coconut oil, 66.8g of Tween 80 and 5.3g of Span 80 until homogeneous to obtain the oil phase;

[0035] S3. Under vigorous stirring, the aqueous phase is slowly added dropwise to the oil phase at 30°C to prepare a water-in-oil reverse emulsion base liquid; then, nitrogen gas is introduced into the reverse emulsion base liquid and stirred at high speed to remove oxygen. After stirring at a constant temperature of 30°C for 30 minutes, 30g of potassium persulfate slow-release agent solution is slowly added. The mass fraction of potassium persulfate slow-release agent in the potassium persulfate slow-release agent solution is 4%. After the potassium persulfate slow-release agent solution is completely added, the reaction is catalytically initiated at 30°C for 11 hours to obtain a salt-resistant polyacrylamide drag-reducing agent.

[0036] The preparation method of the potassium persulfate slow-release agent in the above potassium sulfate slow-release agent solution includes the following steps:

[0037] S101. Add 0.08g of sodium hexadecyl sulfate and 2g of potassium persulfate to 4.8g of deionized water to obtain solution A;

[0038] S102. Add 0.08g Span 80 and 3.2g pyrrole monomer to a mixed solution of 24g isopropanol, 2.56g glycerol and 3.6g butanol to obtain solution B;

[0039] S103. Add 0.13g polyethylene glycol, 0.65g 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide salt and 0.38g N,N-dicyclohexylcarbodiimide to 4.5g deionized water and stir for 5h to obtain solution C;

[0040] S104. Add solution A obtained in step S101 to solution B and stir continuously for 0.8 h. Add acetic acid dropwise to adjust the pH to 2, continue stirring for 2.5 h, then add solution C to solution B to obtain the reaction solution, and continue stirring continuously for 18 h.

[0041] S105. The precipitate in the reaction solution obtained in step S104 is filtered and separated. The separated product is washed with sufficient anhydrous ethanol and then vacuum dried at 40°C for 10 hours to obtain potassium persulfate slow-release agent.

[0042] Example 2

[0043] A method for preparing a salt-resistant polyacrylamide drag-reducing agent, comprising the following steps:

[0044] S1. 0.2g of sodium methylene dinaphthalene disulfonate and 3g of hexadecyl sulfopropyl betaine were compounded to obtain a surfactant; during stirring, 3.2g of surfactant, 2.13g of sodium allyl oxyhydroxypropyl sulfonate, 53.3g of acrylamide and 16g of acrylic acid were added to 213.2g of water in sequence, and after being stirred and dissolved, an aqueous phase was obtained.

[0045] S2. Mix 217.3g of white oil, 144.9g of coconut oil, 65.2g of Tween 80, and 4.35g of Span 80 until homogeneous to obtain the oil phase;

[0046] S3. Under vigorous stirring, the aqueous phase is slowly added dropwise to the oil phase at 30°C to prepare a water-in-oil reverse emulsion base solution. Then, nitrogen gas is introduced into the reverse emulsion base solution and stirred at high speed to remove oxygen. After stirring at a constant temperature of 30°C for 30 minutes, 43g of potassium persulfate slow-release agent solution is slowly added. The mass fraction of potassium persulfate slow-release agent in the solution is 3%. After the potassium persulfate slow-release agent solution is completely added, the reaction is catalytically initiated at 30°C for 8 hours to obtain a salt-resistant polyacrylamide drag-reducing agent.

[0047] The preparation method of the potassium persulfate slow-release agent in the above potassium sulfate slow-release agent solution includes the following steps:

[0048] S101. Add 0.075g sodium hexadecyl sulfate and 1.5g potassium persulfate to 3.75g deionized water to obtain solution A;

[0049] S102. Add 0.064g Span 80 and 2.25g pyrrole monomer to a mixed solution of 11.52g isopropanol, 1.92g glycerol and 2.56g butanol to obtain solution B;

[0050] S103. Add 0.1125g polyethylene glycol, 0.4g 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide salt and 0.225g N,N-dicyclohexylcarbodiimide to deionized water and stir for 4h to obtain solution C;

[0051] S104. Add solution A obtained in step S101 to solution B and stir continuously for 0.5 h. Add acetic acid dropwise to adjust the pH to 2, continue stirring for 2 h, then add solution C to solution B to obtain the reaction solution, and continue stirring continuously for 15 h.

[0052] S105. The precipitate in the reaction solution obtained in step S104 is filtered and separated. The separated product is washed with sufficient anhydrous ethanol and then vacuum dried at 40°C for 10 hours to obtain potassium persulfate slow-release agent.

[0053] Example 3

[0054] A method for preparing a salt-resistant polyacrylamide drag-reducing agent, the method comprising the following steps:

[0055] S1. 0.2g of sodium diisobutylnaphthalenesulfonate and 4g of hexadecyl sulfopropyl betaine were compounded to obtain a surfactant; during stirring, 4.2g of surfactant, 2.625g of sodium allyl oxyhydroxypropyl sulfonate, 42g of acrylamide and 15.75g of acrylic acid were added sequentially to 105g of deionized water, and after thorough stirring and dissolution, an aqueous phase was obtained.

[0056] S2. Mix 149g white oil, 111.7g coconut oil, 40.9g Tween 80 and 2.27g Span 80 until homogeneous to obtain the oil phase;

[0057] S3. Under vigorous stirring, the aqueous phase is slowly added dropwise to the oil phase at 30°C to prepare a water-in-oil reverse emulsion base liquid; then, nitrogen gas is introduced into the reverse emulsion base liquid and stirred at high speed to remove oxygen. After stirring at a constant temperature of 30°C for 30 minutes, 17g of potassium persulfate slow-release agent solution is slowly added. The mass fraction of potassium persulfate slow-release agent in the potassium persulfate slow-release agent solution is 5%. After the potassium persulfate slow-release agent solution is completely added, the reaction is catalytically initiated at 30°C for 15 hours to obtain a salt-resistant polyacrylamide drag-reducing agent.

[0058] The preparation method of the potassium persulfate slow-release agent in the above potassium sulfate slow-release agent solution includes the following steps:

[0059] S101. Add 0.05g sodium hexadecyl sulfate and 1.5g potassium persulfate to 3.5g deionized water to obtain solution A;

[0060] S102. Add 0.075g Span 80 and 3g pyrrole monomer to a mixed solution of 16.5g isopropanol, 2.625g glycerol and 3.75g butanol to obtain solution B;

[0061] S103. Add 0.1g polyethylene glycol, 0.6g 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide salt and 0.4g N,N-dicyclohexylcarbodiimide to 0.4g deionized water and stir for 6h to obtain solution C;

[0062] S104. Add solution A obtained in step S101 to solution B and stir continuously for 1 hour. Add acetic acid dropwise to adjust the pH to 2 and continue stirring for 3 hours. Then add solution C to solution B to obtain the reaction solution and continue stirring continuously for 25 hours.

[0063] S105. The precipitate in the reaction solution obtained in step S104 is filtered and separated. The separated product is washed with sufficient anhydrous ethanol and then vacuum dried at 40°C for 10 hours to obtain potassium persulfate slow-release agent.

[0064] Example 4

[0065] A method for preparing a salt-resistant polyacrylamide drag-reducing agent, the method comprising the following steps:

[0066] S1. 0.2g of sodium diisobutylnaphthalenesulfonate and 3.6g of hexadecyl sulfopropyl betaine were compounded to obtain a surfactant; during stirring, 3.8g of surfactant, 2.5g of sodium allyl oxyhydroxypropyl sulfonate, 34.5g of acrylamide and 15g of acrylic acid were added sequentially to 126g of deionized water and stirred thoroughly to dissolve, thus obtaining an aqueous phase;

[0067] S2. Mix 147.4g of white oil, 129g of coconut oil, 46.1g of Tween 80, and 4.6g of Span 80 until homogeneous to obtain the oil phase;

[0068] S3. Under vigorous stirring, the aqueous phase is slowly added dropwise to the oil phase at 30°C to prepare a water-in-oil reverse emulsion base liquid. Then, nitrogen gas is introduced into the reverse emulsion base liquid and stirred at high speed to remove oxygen. After stirring at a constant temperature of 30°C for 30 minutes, 22g of potassium persulfate slow-release agent solution is slowly added. The mass fraction of potassium persulfate slow-release agent in the potassium persulfate slow-release agent solution is 4%. After the potassium persulfate slow-release agent solution is completely added, the reaction is catalytically initiated at 30°C for 9 hours to obtain a salt-resistant polyacrylamide drag-reducing agent.

[0069] The preparation method of the potassium persulfate slow-release agent in the above potassium sulfate slow-release agent solution includes the following steps:

[0070] S101. Add 0.06g of sodium hexadecyl sulfate and 1.5g of potassium persulfate to 38g of deionized water to obtain solution A;

[0071] S102, 0.08g Span 80 and 2.8g pyrrole monomer were added to a mixed solution of 16.5g isopropanol, 2.5g glycerol and 3.6g butanol to obtain solution B;

[0072] S103. Add 0.12g polyethylene glycol, 0.58g 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide salt and 0.34g N,N-dicyclohexylcarbodiimide to deionized water and stir for 5.5h to obtain solution C;

[0073] S104. Add solution A obtained in step S101 to solution B and stir continuously for 0.7 h. Add acetic acid dropwise to adjust the pH to 2, continue stirring for 2.5 h, then add solution C to solution B to obtain the reaction solution, and continue stirring continuously for 22 h.

[0074] S105. The precipitate in the reaction solution obtained in step S104 is filtered and separated. The separated product is washed with sufficient anhydrous ethanol and then vacuum dried at 40°C for 10 hours to obtain potassium persulfate slow-release agent.

[0075] Comparative Example 1

[0076] The difference between Comparative Example 1 and Example 1 is that the addition of sodium allyl hydroxypropyl sulfonate in step S1 was omitted, while the remaining steps are exactly the same as in Example 1.

[0077] Comparative Example 2

[0078] The difference between Comparative Example 2 and Example 1 is that sodium diisobutylnaphthalenesulfonate was replaced with an equal mass of hexadecyl sulfopropyl betaine, while the rest of the steps were exactly the same as in Example 1.

[0079] Comparative Example 3

[0080] The difference between Comparative Example 3 and Example 1 is that hexadecyl sulfopropyl betaine was replaced with an equal mass of sodium diisobutylnaphthalene sulfonate, while the rest of the steps were exactly the same as in Example 1.

[0081] Comparative Example 4

[0082] The difference between Comparative Example 4 and Example 1 is that the addition of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide salt and N,N-dicyclohexylcarbodiimide in step S103 was omitted, while the remaining steps were exactly the same as in Example 1.

[0083] Comparative Example 5

[0084] The difference between Comparative Example 5 and Example 1 is that the potassium persulfate slow-release agent solution is replaced with potassium persulfate solution, while the rest of the steps are exactly the same as in Example 1.

[0085] The kinematic viscosity and drag reduction rate of the salt-resistant polyacrylamide drag-reducing agents obtained in Examples 1-4 and Comparative Examples 1-5 were tested, as were the kinematic viscosity and drag reduction rate of the salt-resistant polyacrylamide drag-reducing agents after being stored at 90°C for 60 days. The method for determining kinematic viscosity and drag reduction rate was as follows: First, a brine solution with a sodium chloride content of 80,000 ppm and a calcium chloride content of 20,000 ppm was prepared; then, 0.30 g of the salt-resistant polyacrylamide drag-reducing agent was accurately weighed and dissolved in 300 g of the prepared brine solution. The solution was stirred at 3000 rpm for 3 min using a high-frequency stirrer, and the kinematic viscosity η (unit: mm) was measured using a Polkidus viscometer (0.8 mm inner diameter). 2 / s); Finally, the drag reduction rate of the salt-resistant polyacrylamide drag-reducing agent in the above-prepared brine was tested using a JZL-I type drag reduction rate tester. During the test, the mass fraction of the salt-resistant polyacrylamide drag-reducing agent in the brine was 0.5‰, and the test time was 60 minutes; The required amount of brine was added to the storage tank of the pipe flow friction tester, the circulation was started, and the speed of the power pump was slowly adjusted to fill the entire test pipeline with test liquid. The discharge rate was adjusted to the set flow rate (ensuring that the liquid reaches a turbulent state), and the pressure difference at this flow rate was read. When the pressure difference change within 1 minute was < ±1%, At this time, the pressure difference is recorded as the frictional pressure difference of the brine (ΔP1); under the same procedure and conditions, the frictional pressure difference (ΔP2) of a brine solution containing 0.5‰ salt-resistant polyacrylamide drag-reducing agent by mass flowing through the pipeline is tested, wherein the salt-resistant polyacrylamide drag-reducing agent is stirred in the brine fluid for no less than 20s after being added; the drag reduction rate at the corresponding time of 60min is recorded as the 60min drag reduction rate. At the beginning of the drag reduction rate test, the highest drag reduction rate measured is the initial drag reduction rate. The drag reduction rate results are shown in Table 1 below. The drag reduction rate calculation formula is:

[0086] DR=(△P1-△P2) / △P1×100

[0087] The drag reduction rate of DR-salt-resistant polyacrylamide drag reducer, expressed as a percentage;

[0088] △P1—Frictional pressure difference when brine flows through the pipeline, in Pascals (Pa);

[0089] △P2—The frictional pressure difference when a salt solution containing salt-resistant polyacrylamide drag-reducing agent flows through a pipeline, in Pa.

[0090] Table 1: Drag Reduction Rate Test Table of Drag Reduction Agents Prepared in Examples 1-4 and Comparative Examples 1-5

[0091]

[0092] The data in the table above clearly show that the sodium allyl hydroxypropyl sulfonate added in this invention, after participating in the polymerization reaction of polyacrylamide, improves the stability and salt resistance of the drag-reducing agent. The compounded surfactants alkyl naphthalene sulfonate and hexadecyl sulfopropyl betaine effectively improve the temperature resistance of the drag-reducing agent and reduce the rate of decrease in drag reduction rate after 60 minutes, thus improving the performance of the drag-reducing agent. Furthermore, the table shows that by adding materials capable of slow-release potassium persulfate, the drag-reducing agent prepared in this invention has a better drag-reducing effect than the direct addition of potassium persulfate. By activating polyethylene glycol with 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide salt and N,N-dicyclohexylcarbodiimide glycol, polyethylene glycol is better linked to polypyrrole, making it easier for the potassium persulfate slow-release agent to combine with water, thereby improving the drag-reducing effect of the prepared drag-reducing agent.

[0093] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a salt-resistant polyacrylamide drag-reducing agent, characterized in that, The preparation method includes the following steps: S1. Alkyl naphthalene sulfonate and hexadecyl sulfopropyl betaine are compounded at a mass ratio of 1:(15-20) to obtain a surfactant. During stirring, 3-8 parts of surfactant, 2-5 parts of sodium allyl hydroxypropyl sulfonate, 50-80 parts of acrylamide, and 15-30 parts of acrylic acid are added sequentially to 200 parts of deionized water. After thorough stirring and dissolution, an aqueous phase is obtained. S2. Mix the white oil, coconut oil, Tween 80, and Span 80 until well combined to obtain the oil phase; S3. Under vigorous stirring, the aqueous phase is slowly added dropwise to the oil phase at 30°C, with a mass ratio of aqueous phase to oil phase of 1:(1.5-2), to prepare a water-in-oil reverse emulsion base liquid; then, nitrogen gas is introduced into the reverse emulsion base liquid and stirred at high speed to remove oxygen, and the temperature is kept constant at 30°C. After stirring for 30 minutes, potassium persulfate slow-release agent solution is slowly added. After the potassium persulfate slow-release agent solution is completely added, the reaction is catalytically initiated at 30°C for 8-15 hours to obtain a salt-resistant polyacrylamide drag-reducing agent; The method for preparing the potassium persulfate slow-release agent in the potassium sulfate slow-release agent solution includes the following steps: S101. Sodium hexadecyl sulfate and potassium persulfate are added to deionized water to obtain solution A; S102. Span 80 and pyrrole monomer are added to a mixed solution of isopropanol, glycerol and butanol to obtain solution B. S103. Polyethylene glycol, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide salt and N,N-dicyclohexylcarbodiimide were added to deionized water and stirred for 4-6 hours to obtain solution C. S104. Add solution A obtained in step S101 to solution B and stir continuously for 0.5-1h. Add acetic acid dropwise to adjust the pH to 2, continue stirring for 2-3h, then add solution C to solution B to obtain the reaction solution, and continue stirring continuously for 15-25h. S105. The precipitate in the reaction solution obtained in step S104 is filtered and separated. The separated product is washed with sufficient anhydrous ethanol and then vacuum dried at 40°C for 10 hours to obtain potassium persulfate slow-release agent.

2. The salt-resistant polyacrylamide drag-reducing agent according to claim 1, characterized in that, In step S1, the mass ratio of alkylnaphthalene sulfonate to hexadecyl sulfopropyl betaine is 1:(15-20); the alkylnaphthalene sulfonate is sodium diisobutylnaphthalene sulfonate or sodium methylene dinaphthalene disulfonate.

3. The salt-resistant polyacrylamide drag-reducing agent according to claim 1, characterized in that, In step S2, the mass ratio of white oil, coconut oil, Tween 80, and Span 80 is (15-20):(10-15):(4.5-5.5):(0.3-0.5).

4. The salt-resistant polyacrylamide drag-reducing agent according to claim 1, characterized in that, In step S3, the mass ratio between the potassium persulfate slow-release agent solution and the oil phase is 1:(10-20); the mass fraction of potassium persulfate slow-release agent in the potassium persulfate slow-release agent solution is 3-5%.

5. The salt-resistant polyacrylamide drag-reducing agent according to claim 1, characterized in that, In step S101, the mass ratio of sodium hexadecyl sulfate, potassium persulfate, and deionized water is 1:(20-30):(50-70).

6. The salt-resistant polyacrylamide drag-reducing agent according to claim 1, characterized in that, In step S102, the mass ratio of Span 80, pyrrole monomer, isopropanol, glycerol and butanol is 1:(35-40):(180-220):(30-35):(40-50), and the mass ratio of pyrrole monomer in step S102 to potassium persulfate in step S101 is (1.5-2):

1.

7. The salt-resistant polyacrylamide drag-reducing agent according to claim 1, characterized in that, In step S103, the mass ratio of polyethylene glycol, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide salt, N,N-dicyclohexylcarbodiimide, ethanol, and deionized water is 1:(4-6):(2-4):(30-40), and the mass ratio of polyethylene glycol in step S103 to pyrrole monomer in step S102 is 1:(20-30).

8. A salt-resistant polyacrylamide drag-reducing agent, characterized in that, The salt-resistant polyacrylamide drag-reducing agent is prepared by the method described in any one of claims 1-7.

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