Polyacrylamide fracturing resistance reducing agent and preparation method thereof

Abstract

The invention belongs to the technical field of preparation of polyacrylamide resistance reducing agents, and particularly relates to a polyacrylamide resistance reducing agent for fracturing and a preparation method of the polyacrylamide resistance reducing agent. The preparation method comprises the following steps: adopting raw materials of an acrylamide monomer, a temperature-resistant and salt-resistant monomer and a tail hydrophobic monomer, performing template polymerization to prepare polyacrylamide core microspheres, performing water-oil phase polymerization coating to form a crude product, and finally performing modification with a cationic silane coupling agent to obtain the resistance reducing agent. Through the design of the porous core and the twin-tailed hydrophobic monomer, the resistance reducing agent has excellent thermal stability and salt resistance in a high-salt environment.

Description

Technical Field

[0001] This invention belongs to the field of polyacrylamide drag-reducing agent preparation technology, specifically relating to a polyacrylamide drag-reducing agent for fracturing and its preparation method. Background Technology

[0002] In oil and gas extraction, hydraulic fracturing is a key technology for modifying low-permeability oil and gas reservoirs and increasing oil and gas production. During fracturing operations, fracturing fluid needs to be rapidly pumped into the formation under high pressure. The frictional resistance generated by the fluid flowing in the pipeline consumes a large amount of energy, affecting the fracturing effect. Therefore, adding drag-reducing agents to the fracturing fluid to reduce fluid flow resistance is one of the core requirements of hydraulic fracturing technology. Polyacrylamide polymers are among the most widely used drag-reducing agents for fracturing due to their good water solubility, thickening, and drag-reducing properties. However, they are prone to hydrolysis at high temperatures, leading to a significant decrease in drag-reducing efficiency. Furthermore, in high-salt formation environments, the molecular chains coil, losing their thickening and drag-reducing properties.

[0003] Chinese Patent CN104559998B discloses a slickwater for shale gas fracturing and its preparation method. The slickwater is composed of an emulsion drag reducer, clay stabilizer, drainage aid, potassium chloride, bactericide, and water. The emulsion drag reducer is an anionic polyacrylamide copolymer. The prepared slickwater has low adsorption to shale gas reservoirs, significantly reducing reservoir damage caused by polymer adsorption on rocks. Chinese Patent CN115947891B discloses a temperature- and salt-resistant, fast-dissolving polyacrylamide and its preparation method. This method modifies polyacrylamide by introducing a benzene-ring-containing rigid temperature- and salt-resistant monomer and a fluorine-containing cationic hydrophobic monomer onto acrylamide monomer and sodium acrylate monomer, initiating polymerization to obtain the temperature- and salt-resistant, fast-dissolving polyacrylamide. Through low- to medium-molecular-weight structure design, low hydrophobic monomer content, introduction of strong hydrophilic carboxyl groups and sulfonic acid groups, and rapid dissolution technology, the polymer meets the requirements for online rapid dissolution in fracturing fluids.

[0004] However, existing drag-reducing agents have poor structural uniformity and are difficult to form a stable spatial network structure, resulting in insufficient adaptability in complex formation environments. Therefore, developing a polyacrylamide-based drag-reducing agent for fracturing that combines excellent temperature and salt resistance, high drag reduction rate and good stability has become a research hotspot in the current oil extraction field. Summary of the Invention

[0005] To solve at least one of the above-mentioned technical problems, the present invention provides a method for preparing a polyacrylamide-based drag-reducing agent for fracturing, comprising the following steps: S1. Polyacrylamide core microspheres are prepared by template polymerization using acrylamide monomer, temperature-resistant and salt-resistant monomer, twin-tailed hydrophobic monomer, cationic stabilizer, initiator A, and crosslinking agent A as raw materials. The reaction temperature of the template polymerization stage is 40-50℃, and the reaction time is 6-8h. The mass ratio of acrylamide monomer, temperature-resistant and salt-resistant monomer, twin-tailed hydrophobic monomer, cationic stabilizer, initiator A, and crosslinking agent A is 10-18:3-8:2-5:0.3-0.8:0.1-0.5:0.05-0.15. S2. The raw materials, including polyacrylamide core microspheres, emulsifier, and crosslinking accelerator, are mixed with deionized water and sheared and emulsified at a speed of 6000-8000 r / min for 10-15 min to obtain an aqueous dispersion; the mass ratio of polyacrylamide core microspheres, emulsifier, and crosslinking accelerator is 8-15:0.8-1.2:0.2-0.5. S3. Using N,N-dimethylacrylamide, N-vinylpyrrolidone, initiator B, and crosslinking agent B as raw materials, an oil phase is obtained by mixing with ethyl acetate. Under an inert atmosphere, the crude drag reducer is obtained by water-oil phase polymerization and coating. The polymerization reaction temperature is 60-65℃, and the polymerization reaction time is 4-6h. The mass ratio of ethyl acetate, N,N-dimethylacrylamide, N-vinylpyrrolidone, initiator B, and crosslinking agent B is 55-70:6-12:4-8:0.1-0.4:0.03-0.06. S4. Disperse the crude drag-reducing agent in deionized water, then add a cationic silane coupling agent, and obtain the drag-reducing agent by ultrasonic dispersion, filtration, and drying; the mass ratio of deionized water, crude drag-reducing agent, and cationic silane coupling agent is 180-300:38-48:3-8.

[0006] Furthermore, the preparation method of the twinned hydrophobic monomer is as follows: A1. Add brominated long-chain alkyl and long-chain alkylamine to acetonitrile, raise the temperature to increase the reaction temperature until it is complete, then add dichloromethane and sodium hydroxide solution. After filtration, recrystallization and drying, white crystals are obtained. A2. White crystals were added to dichloromethane, and methacryloyl chloride was added dropwise under ice bath conditions. The reaction was carried out under an inert atmosphere. After the reaction was completed, the twinned hydrophobic monomer was obtained by separation, washing, and rotary evaporation.

[0007] Furthermore, in step A1, the number of carbon atoms in the brominated long-chain alkyl group is 8-16, and the number of carbon atoms in the long-chain alkylamine is 8-16.

[0008] Further, step S1 specifically involves: adding a template agent to deionized water, stirring and dispersing it, then adding acrylamide monomer, temperature-resistant and salt-resistant monomer, twin-tailed hydrophobic monomer and cationic stabilizer, ultrasonically dispersing it, adding initiator A and crosslinking agent A under an inert atmosphere, raising the temperature to 40-50℃, stirring and reacting at a constant temperature for 6-8 hours, washing away the template agent after the reaction, and obtaining polyacrylamide core microspheres after washing, filtering and drying.

[0009] Furthermore, the initiator A is obtained by mixing ammonium persulfate and sodium amine bisulfite in a mass ratio of 1-2:1; the crosslinking agent is N,N'-methylenebisacrylamide.

[0010] Further, step S2 specifically involves adding polyacrylamide core microspheres, emulsifier, and crosslinking accelerator to deionized water, mixing them evenly, adding a pH buffer, adjusting the pH of the system to 7.0, and obtaining an aqueous dispersion after high-speed shear emulsification.

[0011] Further, step S3 specifically involves: adding N,N-dimethylacrylamide, N-vinylpyrrolidone, initiator B, and crosslinking agent B to ethyl acetate, stirring until a homogeneous oil phase is obtained, raising the temperature to 50-60°C, and adding the oil phase dropwise to the aqueous dispersion under an inert atmosphere. After the dropwise addition is complete, raising the temperature to 60-65°C, maintaining the reaction temperature for 4-6 hours, and then naturally cooling to room temperature. Adding a demulsifier, stirring until homogeneous, and then centrifuging, washing, and drying to obtain the crude drag-reducing agent.

[0012] Further, step S4 specifically involves: dispersing the crude drag-reducing agent in deionized water, then adding a cationic silane coupling agent, ultrasonically dispersing the mixture, raising the temperature to 40-50°C, reacting for 2-4 hours, filtering, and drying to obtain the drag-reducing agent.

[0013] The present invention also provides a polyacrylamide-based drag reducer for fracturing, which is prepared by the preparation method of a polyacrylamide-based drag reducer for fracturing described in any of the above technical solutions.

[0014] The present invention has the following beneficial effects: This invention utilizes a porous silica template method to prepare porous polyacrylamide core microspheres, whose three-dimensional porous structure provides a certain degree of spatial constraint. Simultaneously, the addition of temperature- and salt-resistant monomers imparts excellent thermal stability to the polymer. Twin-tailed hydrophobic monomers participate in polymerization through double bonds, introducing long, double-hydrophobic chains into the molecular chain. Utilizing the spatial constraint of the porous structure, the hydrophobic chains more readily form a regular associative network structure. The addition of a cationic stabilizer enhances the enrichment of monomers on the porous silica surface, while the use of crosslinking agent A promotes further crosslinking of the molecular chains to form a three-dimensional network structure, preventing structural collapse of the core microspheres during subsequent processes. Oil-phase monomers form a coating layer on the porous core surface and pore walls, significantly improving interlayer bonding strength and reducing direct contact between the core and the external high-temperature, high-salt environment, avoiding molecular chain curling, breakage, and interlayer delamination. Further modification with a cationic silane coupling agent strengthens the crosslinked network structure between molecular chains, improving the thermal stability of the drag-reducing agent and its salt resistance in high-salt environments. Detailed Implementation

[0015] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0016] To improve the temperature and salt resistance of polyacrylamide drag-reducing agents, this invention provides a method for preparing a polyacrylamide-based drag-reducing agent for fracturing, comprising the following steps: S1. Polyacrylamide core microspheres are prepared by template polymerization using raw materials including acrylamide monomer, temperature-resistant and salt-resistant monomer, twin-tailed hydrophobic monomer, cationic stabilizer, initiator A, and crosslinking agent A. S2. An aqueous dispersion is obtained by mixing polyacrylamide core microspheres, emulsifier, crosslinking accelerator and deionized water. S3. Using N,N-dimethylacrylamide, N-vinylpyrrolidone, initiator B, and crosslinking agent B as raw materials, an oil phase is obtained by mixing with ethyl acetate; the oil phase is added to an aqueous dispersion, and after heating and reaction, a demulsifier is added; after centrifugation, washing, and drying, a crude drag reducer is obtained. S4. Disperse the crude drag-reducing agent in deionized water, add a cationic silane coupling agent, heat the reaction, and then filter and dry to obtain the drag-reducing agent.

[0017] The preparation method of the twinned hydrophobic monomer is as follows: A1. Add brominated long-chain alkyl and long-chain alkylamine to acetonitrile, raise the temperature to 75-85℃, react for 6-8h, then add dichloromethane and 2mol / L NaOH solution, filter, recrystallize twice with dichloromethane, and dry in a vacuum drying oven at 50-60℃ for 2-4h to obtain white crystals. A2. Add white crystals to dichloromethane, and slowly add methacryloyl chloride dropwise under ice bath conditions at a rate of 0.5-1 mL / min. Stir rapidly and react for 5-6 hours under nitrogen protection. After the reaction is complete, separate the contents, wash, and rotary evaporate to obtain the twinned hydrophobic monomer.

[0018] In step A1, the mass ratio of acetonitrile, brominated long-chain alkyl group, long-chain alkylamine, dichloromethane, and sodium hydroxide solution is 50-80:10-15:10-16:30-50:15-25; the brominated long-chain alkyl group has 8-16 carbon atoms, preferably bromododecane; the long-chain alkylamine has 8-16 carbon atoms, preferably dodecylamine. In step A2, the mass ratio of dichloromethane, white crystals, and methacryloyl chloride is 40-60:8-12:4-8; the rotary evaporation conditions are: temperature 50-60℃.

[0019] In step A1, the brominated long-chain alkyl group reacts with the long-chain alkylamine to form a double-chain structure, endowing the monomer with strong hydrophobic properties. In step A2, the ice bath condition effectively suppresses side reactions such as hydrolysis and self-polymerization of methacryloyl chloride, while nitrogen gas isolates oxygen, preventing the formation of oxidation byproducts. The acyl chloride group in methacryloyl chloride reacts with the active sites on the double-chain structure obtained in step A1, introducing an acryloyl group containing a carbon-carbon double bond into the double-chain structure, resulting in a twin-tailed hydrophobic monomer with both double hydrophobic chains and double bonds. The double hydrophobic chains of this monomer can form stronger hydrophobic association between polymer molecules, significantly improving the shear resistance and salt resistance of drag-reducing agents compared to the single hydrophobic chain monomers commonly used in the prior art.

[0020] Specifically, step S1 involves adding a template agent to deionized water, ultrasonically dispersing it, then adding acrylamide monomer, temperature-resistant and salt-resistant monomer, twin-tailed hydrophobic monomer, and cationic stabilizer. Stirring is continued for 20-30 minutes. Under a nitrogen atmosphere, initiator A and crosslinking agent A are added, and the temperature is raised to 40-50°C. The mixture is stirred at a constant temperature for 6-8 hours. After the reaction, a 5-10% hydrochloric acid solution is added, and the template agent is washed away by stirring at room temperature for 2-3 hours. The mixture is then repeatedly washed with deionized water until the filtrate is neutral. After filtration, the filtrate is vacuum-dried at 60-80°C for 4-6 hours to obtain polyacrylamide core microspheres.

[0021] In this step, the mass ratio of deionized water, template agent, acrylamide monomer, temperature- and salt-resistant monomer, twinned hydrophobic monomer, cationic stabilizer, initiator A, and crosslinking agent A is 100:1-3:10-18:3-8:2-5:0.3-0.8:0.1-0.5:0.05-0.15; wherein the template agent is porous silica (purity ≥99.9%, pore size ≥200nm, particle size ≤20μm, sphericity ≥90%); and the temperature- and salt-resistant monomer is 2-acrylamide. The reagent is selected from one or a mixture of two of 2-acrylamido-2-methylpropanesulfonic acid, sodium propylene sulfonate, and sodium methpropylene sulfonate, preferably 2-acrylamido-2-methylpropanesulfonic acid; the cationic stabilizer is selected from one of polydiallyl dimethylammonium chloride, methacryloyloxyethyltrimethylammonium chloride, and methyltriethylammonium chloride, preferably polydiallyl dimethylammonium chloride; the initiator A is obtained by mixing ammonium persulfate and sodium bisulfite in a mass ratio of 1-2:1; the crosslinking agent A is N,N'-methylenebisacrylamide.

[0022] In this step, a porous silica template polymerization method is employed. The high specific surface area and unique three-dimensional porous structure of porous silica form a stable suspension system in the aqueous phase, providing spatial confinement for monomer polymerization and preventing intermolecular entanglement and aggregation of long-chain hydrophobic polymer segments. The sulfonic acid groups in the temperature- and salt-resistant monomer 2-acrylamido-2-methylpropanesulfonic acid endow the polymer with excellent thermal stability. Furthermore, in high-salt environments, 2-acrylamido-2-methylpropanesulfonic acid effectively maintains the polymer's solubility and viscosity, preventing inactivation due to salt. Copolymerization with acrylamide significantly increases solution viscosity and enhances drag reduction. The twinned hydrophobic monomer participates in polymerization through double bonds, introducing long, double hydrophobic chains into the molecular chain. The spatial confinement of the porous structure facilitates the formation of a regular associative network structure of the hydrophobic chains. The cationic stabilizer further enhances monomer enrichment on the porous silica surface through charge adsorption, improving the polymerization rate and product structural stability. The free radicals generated by initiator A can initiate free radical polymerization of monomers inside the pores and on the surface. Crosslinking agent A further crosslinks the molecular chains to form a porous three-dimensional network structure, giving the core microspheres both stable morphology and mechanical strength, and preventing structural collapse in subsequent processes.

[0023] Specifically, step S2 involves adding polyacrylamide core microspheres, emulsifier, and crosslinking accelerator to deionized water, mixing them thoroughly, adding a pH buffer to adjust the pH of the system to 7.0, and then shearing and emulsifying the mixture at a speed of 6000-8000 r / min for 10-15 min to obtain an aqueous dispersion.

[0024] In this step, the mass ratio of deionized water, polyacrylamide core microspheres, emulsifier, and crosslinking accelerator is 100:8-15:0.8-1.2:0.2-0.5; wherein the emulsifier is obtained by mixing Span-80 and Tween-80 at a mass ratio of 1:2-3; the crosslinking accelerator is one of triethanolamine and diethylamine, preferably triethanolamine; and the pH buffer is a disodium hydrogen phosphate-citric acid buffer system.

[0025] In this step, the addition of emulsifiers can significantly reduce the interfacial tension between water and oil, thereby improving the stability of the emulsion. Crosslinking promoters enter the porous structure of the core through diffusion, and during the subsequent polymerization of oil phase monomers, they act on the surface of the core and the inner wall of the pores to promote the crosslinking reaction, thereby improving the bonding strength between the coating layer and the core. pH buffers maintain the system in a neutral state, ensuring the stability of the emulsion during subsequent reactions.

[0026] Specifically, step S3 involves adding N,N-dimethylacrylamide, N-vinylpyrrolidone, initiator B, and crosslinking agent B to ethyl acetate and stirring until a homogeneous oil phase is obtained. The temperature is then raised to 50-60°C, and the oil phase is added dropwise to the aqueous dispersion under an inert atmosphere. After the addition is complete, the temperature is raised to 60-65°C, and the reaction is maintained at this temperature for 4-6 hours. The mixture is then naturally cooled to room temperature, and a demulsifier is added. After stirring for 20-30 minutes, the mixture is placed in a centrifuge and centrifuged at 6000-8000 r / min for 15-20 minutes. The precipitate is collected, washed 3-4 times with an ethanol-water mixture, and then vacuum dried at 60-70°C for 4-6 hours to obtain the crude drag-reducing agent.

[0027] In this step, the mass ratio of ethyl acetate, N,N-dimethylacrylamide, N-vinylpyrrolidone, initiator B, and crosslinking agent B is 55-70:6-12:4-8:0.1-0.4:0.03-0.06; initiator B is one of azobisisobutyronitrile, azobisisoheptanenitrile, and azobisisovaleratenitrile, preferably azobisisobutyronitrile; crosslinking agent B is one of trimethylolpropane triacrylate and p-divinylbenzene, preferably trimethylolpropane triacrylate; the demulsifier is polyoxyethylene alkyl ether, and the amount added is 0.5-1% of the total mass of the water and oil phases; the washing solvent is anhydrous ethanol and deionized water mixed at a volume ratio of 1:2.

[0028] In this step, initiator B decomposes to generate free radicals that initiate the free radical polymerization of N,N-dimethylacrylamide and N-vinylpyrrolidone, while crosslinking agent B initiates crosslinking of the polymer molecular chains. Due to the porous structure of the core, some oil-phase monomers can penetrate into the pores and polymerize with the pore walls, forming a coating layer on both the pore walls and the surface of the core microspheres, rather than simply surface coating, significantly improving the interlayer bonding strength. In this structure, the porous core improves water solubility and dispersibility, while the dense coating layer reduces direct contact between the core and the external high-temperature, high-salt environment, delaying core hydrolysis and shrinkage. Simultaneously, the strong interlayer bonding and the dense structure of the coating layer jointly enhance the overall shear stability.

[0029] Specifically, step S4 involves dispersing the crude drag-reducing agent in deionized water, then adding a cationic silane coupling agent, ultrasonically dispersing the mixture, raising the temperature to 40-50°C, reacting for 2-4 hours, filtering, and drying to obtain the drag-reducing agent.

[0030] In this step, the mass ratio of deionized water, crude drag-reducing agent, and cationic silane coupling agent is 180-300:38-48:3-8; the cationic silane coupling agent is one of 3-aminopropyltriethoxysilane and N-(β-aminoethyl-γ-aminopropyl)methyldimethoxysilane, preferably 3-aminopropyltriethoxysilane; the ultrasonic dispersion power is 300-400W, and the time is 15-20min; the drying conditions are vacuum drying at 60-70℃ for 4-6h.

[0031] In this step, cationic groups can interact with polar groups in the polymer molecular chain, further strengthening the cross-linked network structure between molecular chains and improving the salt resistance of the drag-reducing agent in high-salt environments. Furthermore, due to the extremely high bond energy of the silicon-oxygen bond, the thermal and chemical stability of the drag-reducing agent can be improved, preventing molecular chain breakage at high temperatures.

[0032] Preparation Example 1 The preparation method of the twinned hydrophobic monomer is as follows: A1. Add 10 parts by weight of bromododecane and 10 parts by weight of dodecylamine to 50 parts by weight of acetonitrile, raise the temperature to 75℃, react for 6 hours, then add 30 parts by weight of dichloromethane and 15 parts by weight of 2 mol / L NaOH solution, filter, recrystallize twice with dichloromethane, and dry in a vacuum drying oven at 50℃ for 2 hours to obtain white crystals. A2. Add 8 parts by weight of white crystals to 40 parts by weight of dichloromethane. Under ice bath conditions, slowly add 4 parts by weight of methacryloyl chloride at a dropping rate of 0.5 mL / min. Stir rapidly and react for 5 hours under nitrogen protection. After the reaction is complete, separate the lower liquid, wash with distilled water until neutral, and then rotary evaporate at 50 °C to obtain the twinned hydrophobic monomer.

[0033] Preparation Example 2 This preparation example differs from Preparation Example 1 in the following ways: In step A1, 12 parts by weight of bromododecane and 14 parts by weight of dodecylamine were added to 65 parts by weight of acetonitrile. The temperature was raised to 80°C, and after reacting for 8 hours, 45 parts by weight of dichloromethane and 21 parts by weight of NaOH solution were added. In step A2, 10 parts by weight of white crystals were added to 50 parts by weight of dichloromethane. Under ice bath conditions, 6 parts by weight of methacryloyl chloride were slowly added dropwise at a dropping rate of 0.5 mL / min with rapid stirring. Under nitrogen protection, the reaction was carried out for 6 hours. After the reaction was completed, the lower liquid was separated, washed with distilled water until neutral, and then rotary evaporated at 50°C to obtain the twinned hydrophobic monomer.

[0034] Preparation Example 3 This preparation example differs from Preparation Example 1 in the following ways: In step A1, 15 parts by weight of bromododecane and 16 parts by weight of dodecylamine were added to 80 parts by weight of acetonitrile. The temperature was raised to 85°C, and after reacting for 8 hours, 50 parts by weight of dichloromethane and 25 parts by weight of NaOH solution were added. In step A2, 12 parts by weight of white crystals were added to 60 parts by weight of dichloromethane. Under ice bath conditions, 8 parts by weight of methacryloyl chloride were slowly added dropwise at a dropping rate of 1 mL / min.

[0035] Example 1

[0036] A method for preparing a polyacrylamide-based drag-reducing agent for fracturing includes the following steps: S1. Add 1 part by weight of porous silica template agent to 100 parts by weight of deionized water, and ultrasonically disperse at 200W for 15 min. Then add 10 parts by weight of acrylamide, 3 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid, 2 parts by weight of the twin-tailed hydrophobic monomer obtained in Preparation Example 2, and 0.3 parts by weight of polydiallyldimethylammonium chloride. Continue stirring for 20 min. Under a nitrogen atmosphere, add 0.05 parts by weight of a mixture of sodium persulfate and 0.05 parts by weight of sodium bisulfite and 0.05 parts by weight of N,N'-methylenebisacrylamide. Raise the temperature to 40°C and stir at a constant temperature for 6 h. After the reaction is completed, add 50 parts by weight of 5% hydrochloric acid solution and stir at room temperature for 2 h to wash away the template agent. Then wash repeatedly with deionized water until the filtrate is neutral. After filtration, place it in a vacuum dryer at 60°C for 4 h to obtain polyacrylamide core microspheres. S2. Add 8 parts by weight of polyacrylamide core microspheres, 0.3 parts by weight of Span-80 and 0.6 parts by weight of Tween-80 mixture and 0.2 parts by weight of triethanolamine to 100 parts by weight of deionized water. After mixing evenly, add disodium hydrogen phosphate-citric acid buffer to adjust the pH of the system to 7.0. Shear emulsify at 6000 r / min for 10 min to obtain an aqueous dispersion. S3. Add 6 parts by weight of N,N-dimethylacrylamide, 4 parts by weight of N-vinylpyrrolidone, 0.1 parts by weight of azobisisobutyronitrile, and 0.03 parts by weight of trimethylolpropane triacrylate to 55 parts by weight of ethyl acetate. After stirring evenly, an oil phase is obtained. The temperature is raised to 50°C, and the oil phase is added dropwise to the aqueous dispersion under a nitrogen atmosphere. After the addition is completed, the temperature is raised to 60°C, and the reaction is maintained at this temperature for 4 hours. Then, the mixture is naturally cooled to room temperature. Polyoxyethylene alkyl ether is added to the mixture at a rate of 0.5% of the total mass of the oil and water phases. After stirring for 20 minutes, the mixture is placed in a centrifuge and centrifuged at 6000 r / min for 15 minutes. The precipitate is collected and washed three times with an ethanol-water mixture, which is obtained by mixing anhydrous ethanol and deionized water at a volume ratio of 1:2. Then, the mixture is vacuum dried at 60°C for 4 hours to obtain the crude drag reducer. S4. Disperse 38 parts by weight of crude drag-reducing agent in 180 parts by weight of deionized water, then add 3 parts by weight of 3-aminopropyltriethoxysilane, ultrasonically disperse at 200W power for 15 minutes, raise the temperature to 40℃, react for 2 hours, filter, and dry in a vacuum drying oven at 60℃ for 4 hours to obtain drag-reducing agent.

[0037] Example 2

[0038] This embodiment differs from Embodiment 1 in the following ways: In step S1, 2 parts by weight of porous silica template agent were added to 100 parts by weight of deionized water. After ultrasonic dispersion, 14 parts by weight of acrylamide, 5 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid, 3 parts by weight of the twin-tailed hydrophobic monomer obtained in Preparation Example 2, and 0.5 parts by weight of polydiallyl dimethyl ammonium chloride were added. The mixture was stirred for 25 min. Then, 0.15 parts by weight of a mixture of sodium persulfate and 0.1 parts by weight of sodium bisulfite and 0.08 parts by weight of N,N'-methylenebisacrylamide were added. The temperature was raised to 45°C and the reaction was stirred at a constant temperature for 7 h. After the reaction was completed, 55 parts by weight of 5% hydrochloric acid solution were added. The template agent was washed away by stirring at room temperature for 3 h. Then, the mixture was repeatedly washed with deionized water until the filtrate was neutral. After filtration, the mixture was placed at 80°C and vacuum dried for 6 h to obtain polyacrylamide core microspheres.

[0039] In step S2, 10 parts by weight of polyacrylamide core microspheres, 0.4 parts by weight of a mixture of Span-80 and 0.8 parts by weight of Tween-80 and 0.3 parts by weight of triethanolamine are added to 100 parts by weight of deionized water, and the mixture is sheared and emulsified at a speed of 8000 r / min for 15 min to obtain an aqueous dispersion.

[0040] In step S3, 8 parts by weight of N,N-dimethylacrylamide, 5 parts by weight of N-vinylpyrrolidone, 0.2 parts by weight of azobisisobutyronitrile, and 0.04 parts by weight of trimethylolpropane triacrylate were added to 60 parts by weight of ethyl acetate. After stirring evenly, an oil phase was obtained. The temperature was raised to 55°C, and the oil phase was added dropwise to the aqueous dispersion under a nitrogen atmosphere. After the addition was completed, the temperature was raised to 60°C, and the reaction was maintained at this temperature for 4 hours. Then, the mixture was naturally cooled to room temperature. A demulsifier, polyoxyethylene alkyl ether, was added at 1% of the total mass of the oil and water phases. After stirring for 30 minutes, the mixture was placed in a centrifuge and centrifuged at 8000 r / min for 20 minutes. The precipitate was collected, washed, and then vacuum dried at 60°C for 6 hours to obtain the crude drag reducer.

[0041] In step S4, 42 parts by weight of crude drag-reducing agent are dispersed in 220 parts by weight of deionized water, and then 4.5 parts by weight of 3-aminopropyltriethoxysilane are added. After ultrasonic dispersion, the temperature is raised to 50°C and reacted for 4 hours. After filtration, the mixture is placed in a vacuum drying oven at 60°C and dried for 6 hours to obtain the drag-reducing agent.

[0042] Example 3

[0043] This embodiment differs from Embodiment 1 in the following ways: In step S1, 2.5 parts by weight of porous silica template agent were added to 100 parts by weight of deionized water. After ultrasonic dispersion, 16 parts by weight of acrylamide, 6.5 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid, 4 parts by weight of the twin-tailed hydrophobic monomer obtained in Preparation Example 2, and 0.6 parts by weight of polydiallyldimethylammonium chloride were added. The mixture was stirred for 25 min. Then, a mixture of 0.2 parts by weight of sodium persulfate and 0.2 parts by weight of sodium bisulfite and 0.12 parts by weight of N,N'-methylenebisacrylamide were added. The temperature was raised to 50°C and the reaction was stirred at a constant temperature for 8 h. After the reaction was completed, 68 parts by weight of 5% hydrochloric acid solution were added. The template agent was washed away by stirring at room temperature for 3 h. Then, the mixture was repeatedly washed with deionized water until the filtrate was neutral. After filtration, the mixture was placed in a vacuum dryer at 80°C for 6 h to obtain polyacrylamide core microspheres.

[0044] In step S2, 12 parts by weight of polyacrylamide core microspheres, 0.4 parts by weight of a mixture of Span-80 and 0.8 parts by weight of Tween-80 and 0.4 parts by weight of triethanolamine are added to 100 parts by weight of deionized water, and the mixture is sheared and emulsified at a speed of 8000 r / min for 15 min to obtain an aqueous dispersion.

[0045] In step S3, 10 parts by weight of N,N-dimethylacrylamide, 6 parts by weight of N-vinylpyrrolidone, 0.3 parts by weight of azobisisobutyronitrile, and 0.05 parts by weight of trimethylolpropane triacrylate were added to 65 parts by weight of ethyl acetate. After stirring evenly, an oil phase was obtained. The temperature was raised to 60°C, and the oil phase was added dropwise to the aqueous dispersion under a nitrogen atmosphere. After the addition was completed, the temperature was raised to 65°C, and the reaction was maintained at this temperature for 6 hours. Then, the mixture was naturally cooled to room temperature. A demulsifier, polyoxyethylene alkyl ether, was added at 1% of the total mass of the oil and water phases. After stirring for 30 minutes, the mixture was placed in a centrifuge and centrifuged at 8000 r / min for 20 minutes. The precipitate was collected, washed, and then vacuum dried at 70°C for 6 hours to obtain the crude drag reducer.

[0046] In step S4, 45 parts by weight of crude drag-reducing agent are dispersed in 260 parts by weight of deionized water, and then 6 parts by weight of 3-aminopropyltriethoxysilane are added. After ultrasonic dispersion, the temperature is raised to 50°C and reacted for 4 hours. After filtration, the mixture is placed in a vacuum drying oven at 70°C and dried for 6 hours to obtain the drag-reducing agent.

[0047] Example 4

[0048] This embodiment differs from Embodiment 1 in the following ways: In step S1, 3 parts by weight of porous silica template agent were added to 100 parts by weight of deionized water. After ultrasonic dispersion, 18 parts by weight of acrylamide, 8 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid, 5 parts by weight of the twin-tailed hydrophobic monomer obtained in Preparation Example 2, and 0.8 parts by weight of polydiallyldimethylammonium chloride were added. The mixture was stirred for 25 min. Then, 0.25 parts by weight of a mixture of sodium persulfate and sodium bisulfite and 0.15 parts by weight of N,N'-methylenebisacrylamide were added. The temperature was raised to 50°C and the reaction was stirred at a constant temperature for 8 h. After the reaction was completed, 72 parts by weight of 5% hydrochloric acid solution were added. The template agent was washed away by stirring at room temperature for 3 h. Then, the mixture was repeatedly washed with deionized water until the filtrate was neutral. After filtration, the mixture was placed in a vacuum dryer at 80°C for 6 h to obtain polyacrylamide core microspheres.

[0049] In step S2, 15 parts by weight of polyacrylamide core microspheres, 0.4 parts by weight of a mixture of Span-80 and 0.8 parts by weight of Tween-80 and 0.5 parts by weight of triethanolamine are added to 100 parts by weight of deionized water, and the mixture is sheared and emulsified at a speed of 8000 r / min for 15 min to obtain an aqueous dispersion.

[0050] In step S3, 12 parts by weight of N,N-dimethylacrylamide, 8 parts by weight of N-vinylpyrrolidone, 0.4 parts by weight of azobisisobutyronitrile, and 0.06 parts by weight of trimethylolpropane triacrylate were added to 70 parts by weight of ethyl acetate. After stirring evenly, an oil phase was obtained. The temperature was raised to 60°C, and the oil phase was added dropwise to the aqueous dispersion under a nitrogen atmosphere. After the addition was completed, the temperature was raised to 65°C, and the reaction was maintained at this temperature for 6 hours. Then, the mixture was naturally cooled to room temperature. A demulsifier, polyoxyethylene alkyl ether, was added at 1% of the total mass of the oil and water phases. After stirring for 30 minutes, the mixture was placed in a centrifuge and centrifuged at 8000 r / min for 20 minutes. The precipitate was collected, washed, and then vacuum dried at 70°C for 6 hours to obtain the crude drag reducer.

[0051] In step S4, 48 parts by weight of crude drag-reducing agent are dispersed in 300 parts by weight of deionized water, and then 8 parts by weight of 3-aminopropyltriethoxysilane are added. After ultrasonic dispersion, the temperature is raised to 50°C and reacted for 4 hours. After filtration, the mixture is placed in a vacuum drying oven at 70°C and dried for 6 hours to obtain the drag-reducing agent.

[0052] Comparative Example 1 Compared with Example 2, this comparative example replaces the twin-tailed hydrophobic monomer with the single-chain hydrophobic monomer N-dodecylacrylamide, and the rest is the same as in Example 2.

[0053] Comparative Example 2 Compared with Example 2, this comparative example does not contain the added coelenterate hydrophobic monomer, and the rest is the same as in Example 2.

[0054] Comparative Example 3 Compared with Example 2, this comparative example does not contain any temperature- and salt-resistant monomers, but otherwise follows the same procedure as Example 2.

[0055] Comparative Example 4 Compared with Example 2, this comparative example does not contain the added coelenterate hydrophobic monomer and temperature- and salt-resistant monomer, while the rest is the same as in Example 2.

[0056] Comparative Example 5 Compared with Example 2, this comparative example uses PEG-2000 template agent instead of porous silica template agent. The template agent is then removed by washing with deionized water. The rest is the same as in Example 2.

[0057] Comparative Example 6 Compared with Example 2, this comparative example does not add porous silica template agent and directly carries out monomer polymerization, while the rest is the same as in Example 2.

[0058] Comparative Example 7 Compared with Example 2, this comparative example directly uses the crude drag-reducing agent as the final product without modifying it with a cationic silane coupling agent; the rest is the same as in Example 2.

[0059] Related tests The drag-reducing agents prepared in each example and comparative example were added to deionized water to prepare a series of solutions with a mass fraction of 0.3%. The apparent viscosity of the solutions was tested using a Brookfield DV2T viscometer at temperatures ranging from 25 to 120°C and a shear rate of 170 s⁻¹. -1 The measurement time was 3600 s. The test results are shown in Table 1.

[0060] Table 1 Apparent viscosity of temperature drop inhibitors

[0061] As can be seen from the above test data, the apparent viscosity of the drag-reducing agents prepared in Examples 1 to 4 at 25°C is higher than that of the drag-reducing agents prepared in Comparative Examples 1 to 7, and the apparent viscosity can still reach above 44.1 mPa·s at a high temperature of 120°C, showing excellent temperature resistance.

[0062] Drag reduction rate test: The drag reduction rate under distilled water and simulated brine was tested using a HAMZ-IV fracturing fluid friction tester. The distilled water formulation was: 0.12% drag reducer + 0.25% clay stabilizer (stabilizer CT8-5) + 0.15% flow aid (flow aid CT5-12) + distilled water. The simulated brine formulation was: 0.12% drag reducer + 0.25% clay stabilizer (stabilizer CT8-5) + 0.15% flow aid (flow aid CT5-12) + brine (6g calcium chloride + 1.6g magnesium chloride + 3g sodium sulfate + 9.4g sodium chloride dissolved in 1L distilled water). The test results are shown in Table 2.

[0063] Table 2. Results of drag reduction test

[0064] The test results above show that the drag-reducing agents prepared in Examples 1 to 4 have higher drag-reduction rates compared to the comparative examples. A comparison of the test results of Comparative Example 1 (single hydrophobic chain) and Example 2 reveals that the twin-tailed hydrophobic chain exhibits stronger association than the single hydrophobic chain, enhancing the salt resistance of the drag-reducing agent. A comparison of the test results of Comparative Example 2 (without twin-tailed hydrophobic monomer) shows that the lack of a hydrophobic monomer makes the drag-reducing agent prone to uneven dispersion in salt water environments, resulting in decreased drag-reduction performance. A comparison of the test results of Comparative Example 3 (without heat-resistant and salt-resistant monomer), Comparative Example 4 (without twin-tailed hydrophobic monomer and heat-resistant and salt-resistant monomer), and Example 2 shows that the heat-resistant and salt-resistant monomer can improve the drag-reducing agent's performance in high-salt environments. The stability under various environmental conditions is crucial, but without the twin-tailed hydrophobic monomer drag-reducing agent, there is no stability due to hydrophobic association. A comparison of the test results of Comparative Example 5 (using PEG-2000 template agent) and Comparative Example 6 (without template agent) reveals that PEG-2000 is a linear template, resulting in poorly regular pore structures, while porous silica templates can form three-dimensional porous structures, which are more conducive to material dispersion. Without a template agent, the monomer polymerization forms a relatively dense structure, significantly reducing the performance of the drag-reducing agent. A comparison of the test results of Comparative Example 7 (without coupling agent modification) shows that cationic silane coupling agents can further strengthen the cross-linking between molecular chains and improve the salt resistance of the drag-reducing agent.

[0065] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0066] Although embodiments of this application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a polyacrylamide-based drag-reducing agent for fracturing, characterized in that, Includes the following steps: S1. Polyacrylamide core microspheres are prepared by template polymerization using acrylamide monomer, temperature-resistant and salt-resistant monomer, twin-tailed hydrophobic monomer, cationic stabilizer, initiator A, and crosslinking agent A as raw materials. The reaction temperature of the template polymerization stage is 40-50℃, and the reaction time is 6-8h. The mass ratio of acrylamide monomer, temperature-resistant and salt-resistant monomer, twin-tailed hydrophobic monomer, cationic stabilizer, initiator A, and crosslinking agent A is 10-18:3-8:2-5:0.3-0.8:0.1-0.5:0.05-0.

15. S2. The raw materials, including polyacrylamide core microspheres, emulsifier, and crosslinking accelerator, are mixed with deionized water and sheared and emulsified at a speed of 6000-8000 r / min for 10-15 min to obtain an aqueous dispersion; the mass ratio of polyacrylamide core microspheres, emulsifier, and crosslinking accelerator is 8-15:0.8-1.2:0.2-0.

5. S3. Using N,N-dimethylacrylamide, N-vinylpyrrolidone, initiator B, and crosslinking agent B as raw materials, an oil phase is obtained by mixing with ethyl acetate. Under an inert atmosphere, the crude drag reducer is obtained by water-oil phase polymerization and coating. The polymerization reaction temperature is 60-65℃, and the polymerization reaction time is 4-6h. The mass ratio of ethyl acetate, N,N-dimethylacrylamide, N-vinylpyrrolidone, initiator B, and crosslinking agent B is 55-70:6-12:4-8:0.1-0.4:0.03-0.

06. S4. Disperse the crude drag-reducing agent in deionized water, then add a cationic silane coupling agent, and obtain the drag-reducing agent by ultrasonic dispersion, filtration, and drying; the mass ratio of deionized water, crude drag-reducing agent, and cationic silane coupling agent is 180-300:38-48:3-8.

2. The method for preparing a polyacrylamide-based drag-reducing agent for fracturing according to claim 1, characterized in that, The preparation method of the twinned hydrophobic monomer is as follows: A1. Add brominated long-chain alkyl and long-chain alkylamine to acetonitrile, raise the temperature to increase the temperature after the reaction is complete, add dichloromethane and sodium hydroxide solution, filter, recrystallize and dry to obtain white crystals; A2. White crystals were added to dichloromethane, and methacryloyl chloride was added dropwise under ice bath conditions. The reaction was carried out under an inert atmosphere. After the reaction was completed, the twinned hydrophobic monomer was obtained by separation, washing, and rotary evaporation.

3. The method for preparing a polyacrylamide-based drag reducer for fracturing according to claim 2, characterized in that, In step A1, the number of carbon atoms in the brominated long-chain alkyl group is 8-16, and the number of carbon atoms in the long-chain alkylamine is 8-16.

4. The method for preparing a polyacrylamide-based drag-reducing agent for fracturing according to claim 1, characterized in that, Step S1 is as follows: Add template agent to deionized water, stir and disperse, then add acrylamide monomer, temperature-resistant and salt-resistant monomer, twin-tailed hydrophobic monomer and cationic stabilizer. After ultrasonic dispersion, add initiator A and crosslinking agent A under an inert atmosphere, raise the temperature to 40-50℃, and stir at a constant temperature for 6-8 hours. After the reaction is completed, wash off the template agent, and obtain polyacrylamide core microspheres by washing, filtering and drying.

5. The method for preparing a polyacrylamide-based drag reducer for fracturing according to claim 4, characterized in that, The initiator A is obtained by mixing ammonium persulfate and sodium amine bisulfite in a mass ratio of 1-2:1; the crosslinking agent is N,N'-methylenebisacrylamide.

6. The method for preparing a polyacrylamide-based drag-reducing agent for fracturing according to claim 1, characterized in that, Step S2 specifically involves adding polyacrylamide core microspheres, emulsifier, and crosslinking accelerator to deionized water, mixing them evenly, adding a pH buffer, adjusting the pH of the system to 7.0, and obtaining an aqueous dispersion after high-speed shear emulsification.

7. The method for preparing a polyacrylamide-based drag-reducing agent for fracturing according to claim 1, characterized in that, Step S3 is as follows: N,N-dimethylacrylamide, N-vinylpyrrolidone, initiator B, and crosslinking agent B are added to ethyl acetate and stirred until homogeneous to obtain an oil phase. The temperature is raised to 50-60℃, and the oil phase is added dropwise to the aqueous dispersion under an inert atmosphere. After the addition is complete, the temperature is raised to 60-65℃, and the reaction is maintained at this temperature for 4-6 hours. The mixture is then naturally cooled to room temperature. A demulsifier is added to the mixture, and after stirring until homogeneous, it is centrifuged, washed, and dried to obtain a crude drag-reducing agent.

8. The method for preparing a polyacrylamide-based drag reducer for fracturing according to claim 1, characterized in that, Step S4 specifically involves dispersing the crude drag-reducing agent in deionized water, then adding a cationic silane coupling agent, ultrasonically dispersing the mixture, raising the temperature to 40-50°C, reacting for 2-4 hours, filtering, and drying to obtain the drag-reducing agent.

9. A polyacrylamide-based drag reducer for fracturing, characterized in that, It is prepared by the method for preparing a polyacrylamide-based drag reducer for fracturing as described in any one of claims 1-8.

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