Preparation and application method of a salt-resistant, multifunctional, and highly efficient drag-reducing agent

Abstract

This invention relates to the field of fracturing additives for oil and gas fields, and discloses a method for preparing and applying a salt-resistant, multifunctional, and highly efficient drag-reducing agent. Acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, methacryloyloxyethyltrimethylammonium chloride, and a betaine-type amphoteric monomer are mixed in a specific ratio. After pH adjustment, a redox-azo composite initiation system is used for low-temperature polymerization. The resulting colloid is granulated, dried, ground, and sieved to obtain the finished product. This invention combines excellent salt resistance, drag reduction, anti-swelling, and drainage-aiding properties. It requires no additional additives, dissolves quickly, and is suitable for fracturing scenarios such as offshore oil fields and deep, high-saltification reservoirs. It simplifies the fluid preparation process, reduces operating costs, and meets the needs of continuous fracturing operations.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas field fracturing additives technology, and in particular to the preparation and application method of a salt-resistant, multifunctional, and highly efficient drag-reducing agent. Background Technology

[0002] Fracturing, as a core technology for enhancing the production of low-permeability and ultra-low-permeability oil and gas reservoirs, is widely used throughout the entire process of stabilizing production in conventional oil and gas fields, developing unconventional oil and gas resources, and improving production in old oil and gas wells. Its effectiveness directly determines the production and recovery rate of oil and gas wells. Drag-reducing agents, as core additives in fracturing fluid systems, primarily reduce the frictional resistance of fluids during pipeline pumping, thereby reducing energy consumption in fracturing operations and improving safety and efficiency. As global oil and gas exploration moves towards deeper, offshore, and unconventional reservoirs, reservoir geological conditions are becoming increasingly complex. The sources of water for fracturing fluid preparation are diverse, and salinity fluctuates greatly. Simultaneously, the demand for cost reduction and efficiency improvement from operators continues to rise. The industry is placing higher demands on the salt resistance, functional integration, dissolution rate, and application cost of drag-reducing agents.

[0003] Currently, the mainstream fracturing drag reducers in the industry are mainly divided into two categories. The first category is conventional polyacrylamide drag reducers, which use acrylamide homopolymer or copolymer of acrylamide and a small amount of anionic monomers as the active ingredient. Its working principle is to reduce friction by disrupting the turbulent structure through the directional arrangement of long-chain polymers in the solution. This type of drag reducer has a mature production process and low raw material cost. It is widely used in fracturing operations of continental reservoirs with abundant freshwater resources and a solution salinity of less than 50,000 mg / L. The drag reduction rate can reach about 60% with the conventional addition amount. However, the anionic groups in the molecular chains of this type of drag reducer are easily neutralized by metal cations such as calcium and magnesium in highly salinized water, causing the molecular chains to coil and the solution viscosity to drop sharply. In environments with salinity higher than 100,000 mg / L, the drag reduction rate is less than 30%, making it unsuitable for applications involving highly salinized water. In addition, this type of drag reducer has a single function, requiring the addition of multiple additives such as anti-swelling agents and flow aids during fracturing operations. This makes the preparation process complex and the preparation cycle long. Furthermore, the combination of multiple additives can easily lead to compatibility issues, resulting in fluctuations in the performance of the fracturing fluid and increasing the overall cost of fracturing operations.

[0004] The second category is modified salt-resistant polyacrylamide drag reducers, prepared by introducing salt-resistant functional monomers such as 2-acrylamide-2-methylpropanesulfonic acid into the molecular chain. These agents can improve salt resistance to a certain extent and are suitable for solution environments with mineralization up to 150,000 mg / L. They are currently being gradually promoted and applied in fracturing operations in some high-mineralization reservoirs. However, this type of drag reducer only improves salt resistance and does not solve the problem of limited functionality. Furthermore, the molecular structure control during polymerization is difficult, the product dissolves slowly, requiring large-capacity stirring devices for prolonged stirring and dissolution. The solution preparation efficiency is insufficient to meet the needs of continuous fracturing operations. Additionally, some products introduce excessively high levels of hydrophobic monomers to improve salt resistance, leading to decreased product dispersibility in water and a tendency for "fish-eye" agglomeration, affecting the stability of the drag reduction effect. Moreover, the high cost of raw materials and production energy consumption limit their large-scale application.

[0005] With the continuous expansion of the development scale of high-mineralization reservoirs in deep and offshore areas, existing drag-reducing agents can no longer meet the comprehensive requirements of high salt resistance, multi-functional integration, rapid dissolution, and low cost. The industry urgently needs to develop a new type of high-efficiency drag-reducing agent that integrates drag reduction, salt resistance, anti-swelling, and drainage functions to simplify the fracturing fluid preparation process, reduce the overall cost of fracturing operations, and adapt to the fracturing operation requirements of complex reservoirs. Summary of the Invention

[0006] To address the shortcomings of existing drag-reducing agents, such as poor salt resistance, limited functionality, and complex preparation processes, this invention provides a method for preparing and applying a salt-resistant, multifunctional, and highly efficient drag-reducing agent.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a salt-resistant, multifunctional, and highly efficient drag-reducing agent includes the following steps: S1. Mix 2-acrylamido-2-methylpropanesulfonic acid, acrylamide, quaternized cationic monomer, fluorinated long-chain hydrophobic associating monomer, and polyether side-chain modified monomer in a mass ratio of 45-55:25-35:10-15:3-8:2-5. Add simulated oilfield prepared water with a mineralization of 500-1000 mg / L and stir to dissolve, to obtain a monomer mixed solution with a total mass fraction of 20%-30%. Adjust the pH of the mixed solution to 6.5-7.5 using a 20% sodium hydroxide solution. During the process, control the solution temperature to not exceed 30℃ to avoid monomer self-polymerization. S2. High-purity nitrogen gas is introduced into the monomer mixture solution after pH adjustment and deoxygenated at a constant rate for 15-20 minutes, with the nitrogen flow rate controlled at 0.5-0.8 L / min. After the dissolved oxygen content of the solution drops below 0.5 mg / L, 0.05%-0.1% of the total monomer mass of initiator ammonium persulfate, 0.02%-0.05% of the accelerator tetramethylethylenediamine, and 0.01%-0.03% of the chain transfer agent isopropanol are added sequentially. After stirring for 30 seconds, stirring is stopped and the reaction vessel is sealed. The reaction is carried out under adiabatic polymerization at a constant temperature water bath of 40-50℃ for 6-8 hours. External vibrations are avoided during the reaction to ensure uniform growth of polymer molecular chains. S3. After the polymerization reaction is completed, the obtained gel-like polymer is taken out and granulated into gel particles with a diameter of 3-5mm using a spiral granulator. 0.2%-0.5% of polyethylene glycol dispersant is sprayed into the gel particles and stirred for 5 minutes to make the surface of the gel particles uniformly coated with dispersant to avoid the gel particles sticking together and clumping during the subsequent drying process. S4. Place the coated particles in a fluidized bed dryer and dry them for 2-3 hours under hot air circulation at 80-90℃. Control the moisture content of the dried product to be within the range of 8%-10%. Take a sample every 30 minutes during the drying process to test the moisture content. Stop drying immediately after the preset range is reached and transfer the product to a cooler to cool to room temperature. S5. The cooled and dried product is put into an ultra-fine pulverizer for pulverization. The pulverized product is then screened through an 80-100 mesh vibrating screen. The material that passes through the screen is the salt-resistant multifunctional high-efficiency drag-reducing agent powder product. The coarse particles remaining on the screen are returned to the pulverizer for re-pulverization. The final product yield is not less than 95%.

[0008] Preferably, the quaternized cationic monomer in S1 is any one of methacryloyloxyethyltrimethylammonium chloride or dimethyl diallyl ammonium chloride, with a monomer cationicity of not less than 90% and a sodium chloride content of not more than 0.5%, to ensure the adsorption and binding capacity of the polymer with the formation clay and improve the anti-swelling effect; the fluorinated long-chain hydrophobic associating monomer in S1 is any one of dodecafluoroheptyl methacrylate or perfluorooctyl ethyl acrylate, with a monomer fluorine content of not less than 60%, which can form a dynamic physical cross-linking network in the solution through hydrophobic association, increase the hydrodynamic volume of the polymer, and improve the solution viscosity retention rate in high mineralization environments.

[0009] Preferably, the polyether side chain modified monomer in S1 is methoxy polyethylene glycol acrylate with a number average molecular weight of 800-1200. By introducing flexible polyether long side chains into the polymer backbone, the steric hindrance effect of the side chains is used to shield the charge neutralization effect of metal cations on the anionic groups of the polymer backbone under high mineralization environment, thereby further improving the salt resistance of the polymer. At the same time, the polyether side chains reduce the surface tension of the solution and endow the product with the function of promoting excretion.

[0010] Preferably, the ammonium persulfate and tetramethylethylenediamine used in S2 form a redox initiation system, which can continuously release free radicals to initiate monomer polymerization under medium and low temperature conditions, avoiding the molecular chain breakage problem caused by high temperature. Combined with the chain transfer agent isopropanol to regulate the molecular weight distribution of the polymer, the molecular weight of the product is controlled in the range of 8 million to 12 million, and the molecular weight distribution coefficient is less than 2.0, ensuring that the product has both excellent solubility and drag reduction properties.

[0011] Preferably, it includes the following steps: S1. The prepared drag-reducing agent powder is continuously added to the conveying pipeline of fracturing fluid preparation water through a dry powder feeder. The fluid in the pipeline is automatically mixed and dissolved by the turbulence of the fluid. The mixing time in the pipeline is 3-5 minutes. No additional stirring and dissolving device is required. The fracturing fluid base fluid with a mass fraction of 0.05%-0.2% is prepared. The salinity of the fracturing fluid preparation water is not higher than 200,000 mg / L. S2. The prepared fracturing fluid base is transported to an online viscosity testing device, and the viscosity of the base fluid is tested at 170s. -1 The apparent viscosity at the shear rate is used to determine the liquid preparation is qualified when the apparent viscosity reaches 5-10 mPa·s. If the viscosity is lower than the preset value, the feeding rate of the dry powder feeder will be automatically adjusted to ensure the stability of the base liquid performance. S3. Add proppant and crosslinking agent sequentially to qualified fracturing fluid base fluid. After uniform mixing online using a static mixer, pump directly into the well for fracturing operations. No additional anti-swelling agent or flow-out aid is required during the fluid preparation process. The proppant is quartz sand or ceramsite, added at a mass concentration of 100-500 kg / m³. 3 The crosslinking agent is an organoboron crosslinking agent, and the amount added is 0.1%-0.3% of the mass of the fracturing fluid base fluid; S4. After the fracturing operation is completed, close the wellhead and let the well sit for 24-48 hours. After the fracturing fluid has fully broken down, open the well for flowback. No additional flowback aid is needed during the flowback process. The surface tension of the flowback fluid is reduced by the fluorine surface-active groups and polyether side chains contained in the drag reducer itself. The flowback rate is not less than 75%. S5. Collect the backflow liquid, filter it to remove solid impurities, and reuse it directly as water for preparing the solution. The difference between the amount of drag-reducing agent added during the repeated preparation process and the amount added during the first preparation should not exceed 10%, and the drag reduction rate retention rate should not be less than 90%.

[0012] Preferably, the dry powder feeder used in S1 has a loss-in-weight metering function with a metering accuracy of not less than ±0.5%. It can automatically adjust the feeding amount according to the real-time flow rate of the water used for liquid preparation in the pipeline, ensuring the stability of the drag-reducing agent concentration and avoiding the concentration fluctuation problem caused by manual feeding. At the same time, it realizes a continuous liquid preparation mode of adding and using the drug simultaneously, and the liquid preparation efficiency is more than 3 times higher than that of traditional stirring liquid preparation.

[0013] Preferably, during the pumping process, the fracturing fluid in S3 reduces turbulent frictional resistance through the directional arrangement of molecular chains, with a resistance reduction rate of not less than 75%. At the same time, the quaternized cationic groups in the polymer can be adsorbed on the surface of the formation clay particles, inhibiting clay hydration and swelling through charge neutralization and molecular chain coating, with an anti-swelling rate of not less than 85%. No additional clay stabilizer is required, effectively reducing the overall cost of fracturing fluid.

[0014] Preferably, the surface tension of the fracturing fluid in S4 after gel breaking is not higher than 28 mN / m, and the interfacial tension is not lower than 1×10⁻⁶ m / m. - 2 mN / m effectively reduces capillary resistance, improves flowback efficiency, avoids damage to the formation caused by fracturing fluid residue, and is suitable for fracturing operations in oil and gas reservoirs with different permeability.

[0015] The present invention has the following beneficial effects: This invention enhances the salt resistance of drag-reducing agents by introducing salt-tolerant functional monomers and zwitterionic structures into the polymer molecular chain. Even in high-salinity liquid preparation environments, the molecular chain remains extended, effectively reducing turbulent friction. This solves the problem of conventional polyacrylamide drag-reducing agents experiencing molecular chain curling and a sharp drop in drag-reducing efficiency under high-salinity conditions. Simultaneously, this molecular structure can adsorb onto the surface of clay particles through charge interaction, inhibiting clay hydration and swelling. It also possesses surface-active properties that reduce liquid surface tension. This eliminates the need for additional anti-swelling agents and drainage aids to meet the performance requirements of fracturing fluids, reducing the need for additive compounding and avoiding performance fluctuations in fracturing fluids caused by poor compatibility of multiple additives.

[0016] This invention improves the dissolution rate and dispersibility of drag-reducing agent products by optimizing the polymerization reaction process and post-processing steps. During on-site solution preparation, rapid and uniform dispersion and dissolution are achieved without prolonged vigorous stirring, meeting the rapid solution preparation requirements of continuous fracturing operations. It eliminates the need for additional large-capacity stirring equipment, reducing equipment investment and energy consumption for on-site solution preparation. This invention overcomes the shortcomings of existing modified salt-resistant drag-reducing agents, such as slow dissolution rate, tendency to agglomerate ("fish-eye"), and low solution preparation efficiency. Simultaneously, the high raw material conversion rate and mild reaction conditions during preparation effectively reduce production energy consumption and overall costs, improving the product's cost-effectiveness.

[0017] This invention's drag-reducing agent is adaptable to various operational scenarios, including high-salinity deep reservoirs, offshore oil and gas fields, and repeated fracturing of old wells. It can meet the conventional fracturing requirements for freshwater-based fluid preparation, and can also be directly prepared using high-salinity water sources such as flowback fluid and formation water, eliminating the need for pre-desalination of the preparation water and reducing freshwater resource consumption and flowback fluid treatment costs. Its multi-functional integrated characteristics simplify the fracturing fluid preparation process, shorten the preparation cycle, and reduce on-site construction labor costs and operational complexity. It has broad application value in unconventional oil and gas development and deep oil and gas reservoir production enhancement, and can meet the current industry development needs for cost reduction and efficiency improvement in oil and gas extraction. Attached Figure Description

[0018] Figure 1 This is a flowchart illustrating the preparation process of a salt-resistant, multifunctional, and highly efficient drag-reducing agent proposed in this invention. Figure 2 A flowchart illustrating the on-site application steps of a salt-resistant, multifunctional, and highly efficient drag-reducing agent; Figure 3 This is a bar chart comparing the core performance of the embodiments of the present invention with existing comparative examples; Figure 4 This is a line graph showing the change in resistivity under different mineralization environments, as proposed in this invention. Figure 5 This is a radar chart showing the overall performance of the drag-reducing agent proposed in this invention. Detailed Implementation

[0019] The following will refer to the appendices in the embodiments of the present invention. Figure 1-5 The technical solutions in the embodiments of the present invention are clearly and completely described herein. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] Example 1 S1. Monomer Mixing: Weigh out 35 parts by weight of acrylamide, 15 parts by weight of 2-acrylamide-2-methylpropanesulfonic acid, 8 parts by weight of methacryloyloxyethyltrimethylammonium chloride, 5 parts by weight of carboxyethyl betaine, and 42 parts by weight of deionized water. Place them in a stirred reactor and stir until all monomers are completely dissolved. Adjust the pH of the system to 7.5 with a 20% sodium hydroxide solution to obtain a homogeneous and transparent monomer mixed solution. S2. Polymerization reaction: High-purity nitrogen gas is continuously introduced into the monomer mixture solution to remove oxygen for 25 minutes, so that the dissolved oxygen content in the system is less than 1 mg / L. Then, 0.05 parts of azobisisobutyramidine hydrochloride and 0.03 parts of sodium bisulfite are added. The nitrogen gas passage is closed, the reaction vessel is sealed, the temperature of the reaction system is controlled at 50℃, and the reaction is maintained at this temperature for 5 hours. After the reaction is completed, a transparent elastic colloidal polymer product is obtained. S3. Granulation and Drying: The colloidal polymer is transferred to a granulator for shearing and granulation to obtain polymer particles with a particle size of 3-4 mm. The particles are then fed into a hot air dryer, with the drying temperature set at 90℃ and the drying time at 2.5 hours. The moisture content of the dried product is 7.2%. S4. Post-processing: The dried polymer particles are fed into a grinder for grinding. The ground product is passed through a 150-mesh standard sieve. The undersize components are collected to obtain the salt-resistant, multifunctional, and highly efficient drag-reducing agent.

[0021] Performance Verification: The prepared drag-reducing agent was applied to simulated high-salinity water with a salinity of 200,000 mg / L at an addition rate of 0.2%. After stirring for 3 minutes, it was completely dissolved. The drag reduction rate was 72%, the swelling prevention rate was 88%, and the surface tension was 26 mN / m, which meets the performance requirements for fracturing in high-salinity reservoirs. The zwitterionic structure introduced in this embodiment works synergistically with the salt-resistant monomer to ensure the extended state of the molecular chain in a high-salinity environment, effectively solving the defect of poor salt resistance in existing drag-reducing agents. At the same time, its multifunctional properties avoid the addition of additional additives and simplify the solution preparation process.

[0022] Core Implementation Example 2 Preparation process S1. Monomer Mixing: Weigh out 28 parts by weight of acrylamide, 18 parts by weight of 2-acrylamide-2-methylpropanesulfonic acid, 10 parts by weight of methacryloyloxyethyltrimethylammonium chloride, 6 parts by weight of sulfopropyl betaine, and 46 parts by weight of deionized water. After stirring and mixing evenly, adjust the pH value to 7.2 with sodium hydroxide to obtain a monomer mixed solution. S2. Polymerization reaction: Nitrogen gas was introduced into the monomer mixture solution to remove oxygen for 22 minutes, and 0.06 parts of azobisisobutyramidine hydrochloride and 0.04 parts of sodium bisulfite were added. The reaction temperature was controlled at 45℃ and the reaction was maintained for 4.5 hours to obtain a colloidal polymer product. S3. Granulation and Drying: The colloidal product is sheared and granulated to obtain particles of 2-3 mm, and then dried with hot air at 85°C for 2.8 hours, controlling the moisture content of the product to 8.5%. S4. Post-processing: Grind the dried granules and pass them through a 120-mesh sieve to obtain the drag-reducing agent product.

[0023] Performance Verification: The drag-reducing agent was added to fracturing flowback fluid with a salinity of 180,000 mg / L at a dosage of 0.15%. After stirring for 4 minutes, it was completely dissolved. The drag reduction rate was 70%, the anti-swelling rate was 85%, and the surface tension was 27 mN / m. It can be directly used in fracturing operations without additional treatment of the flowback fluid, thus reducing the disposal cost of the flowback fluid. The product of this embodiment is suitable for flowback fluid preparation scenarios, solving the problem that existing drag-reducing agents cannot be used in high-salinity flowback fluids, and reducing the consumption of freshwater resources.

[0024] Core Implementation Example 3 Preparation process S1. Monomer Mixing: Weigh out 42 parts by weight of acrylamide, 12 parts by weight of 2-acrylamide-2-methylpropanesulfonic acid, 6 parts by weight of methacryloyloxyethyltrimethylammonium chloride, 4 parts by weight of carboxyethyl betaine, and 38 parts by weight of deionized water. Adjust the pH value to 7.8 to obtain a monomer mixed solution. S2. Polymerization reaction: Nitrogen gas was introduced to remove oxygen for 28 minutes, then 0.04 parts of azobisisobutyramidine hydrochloride and 0.02 parts of sodium bisulfite were added. The reaction temperature was controlled at 55℃ and the reaction was carried out for 5.5 hours to obtain a colloidal product. S3. Granulation and drying: Granulation yields 4-5 mm particles, which are then dried at 95℃ for 2.2 hours, resulting in a product moisture content of 6.8%. S4. Post-processing: After grinding, pass through a 180-mesh sieve to obtain the drag-reducing agent product.

[0025] Performance Verification: The drag-reducing agent was applied to formation water with a salinity of 150,000 mg / L at a dosage of 0.1%. After stirring for 3 minutes, it completely dissolved, achieving a drag reduction rate of 68%, an anti-swelling rate of 86%, and a surface tension of 26.5 mN / m, meeting the requirements for deep reservoir fracturing. This embodiment demonstrates rapid product dissolution without prolonged stirring, adapting to the rapid solution preparation needs of continuous fracturing operations and overcoming the shortcomings of existing modified drag-reducing agents, such as slow dissolution and low solution preparation efficiency.

[0026] Comparative Example Using existing conventional modified salt-resistant polyacrylamide drag-reducing agent as a comparative example, its preparation method is as follows: weigh 45 parts of acrylamide, 15 parts of 2-acrylamide-2-methylpropanesulfonic acid, and 40 parts of deionized water according to the mass ratio, adjust the pH value to 7.5, remove oxygen by nitrogen purging, add potassium persulfate-sodium sulfite initiator, react at 60℃ for 6 hours, granulate, dry and grind to obtain the finished product.

[0027] The comparative product was applied to a fracturing fluid with a salinity of 200,000 mg / L at a dosage of 0.2%. It required stirring for 15 minutes to completely dissolve. Tests showed a drag reduction rate of 52%, an anti-swelling rate of 42%, and a surface tension of 38 mN / m. Additional anti-swelling agents and flow aids were needed to meet the performance requirements of the fracturing fluid. The performance verification results of the comparative example highlight the shortcomings of existing drag-reducing agents, such as poor salt tolerance, limited functionality, and slow dissolution rate.

[0028] Application Scenario Examples Scenario 1: Fracturing operations in high-mineralization offshore reservoirs In offshore oil and gas field development, only highly salinized seawater (approximately 35,000 mg / L) can be used for fracturing fluid preparation. Furthermore, limited space at sea prevents the installation of large-scale mixing equipment, necessitating high preparation efficiency. When the drag-reducing agent of this invention is applied to this scenario, it is directly added to seawater at a dosage of 0.15%. Using existing small-scale mixing equipment at the work site, it dissolves completely in 3 minutes without the need for additional additives. The resulting fracturing fluid exhibits a drag reduction rate of 70% and an anti-swelling rate of 86%, meeting the performance requirements for offshore fracturing operations. In this scenario, the drag-reducing agent's high salt tolerance ensures effective drag reduction under seawater preparation, its rapid dissolution adapts to the limited operating conditions at sea, and its multifunctional properties reduce the transportation and storage costs of additives, effectively solving the problems of complex and costly fracturing fluid preparation in offshore operations.

[0029] Scenario 2: Repeated fracturing operations on old wells Repeated fracturing operations in old wells typically require the preparation of fracturing flowback fluid, which has a salinity of approximately 180,000 mg / L. Simultaneously, it is crucial to minimize the preparation cycle and reduce the impact on oil and gas production. When the drag-reducing agent of this invention is applied to this scenario, it is directly added to simply filtered flowback fluid at a dosage of 0.2%. Stirring for 4 minutes yields a qualified fracturing fluid with a drag reduction rate of 69% and an anti-swelling rate of 84%. No additional anti-swelling agents or flowback aids are required, and the preparation cycle is shortened by more than 70% compared to existing technologies. In this scenario, the high salt tolerance of the drag-reducing agent allows for the direct use of the flowback fluid without desalination. Its multifunctional characteristics simplify the preparation process, effectively solving the problems of low preparation efficiency and high flowback fluid treatment costs associated with repeated fracturing operations in old wells.

[0030] Core data tables and explanations Table 1. Comparison of performance parameters between the embodiments of the present invention and the comparative examples. This table presents the differences in core performance parameters between the three embodiments of the present invention and the comparative examples of existing technologies. The drag reduction rate and anti-swelling rate of the embodiments of the present invention are significantly higher than those of the comparative examples, while the surface tension is lower, and the dissolution time is only about one-fifth that of the comparative examples. It meets the performance requirements of fracturing fluids without the need for additional additives. This comparative result verifies that the present invention achieves multifunctional integration through molecular structure optimization, effectively solving the defects of existing drag reducers such as poor salt resistance, single function, and slow dissolution rate. Examples 1-3 all exhibit excellent comprehensive performance under different monomer ratios, indicating that the technical solution of the present invention has good stability and adaptability to different production adjustment needs.

[0031] Table 2 Comparison of drag reduction rates under different mineralization environments The table shows the drag reduction rate changes of Example 1 and the comparative example under different mineralization environments. As the mineralization increases, the drag reduction rate of the example of this invention only decreases slightly, while the drag reduction rate of the comparative example declines significantly. Even at an extremely high mineralization environment of 250,000 mg / L, the example still maintains a drag reduction rate of 69%, higher than the 45% of the comparative example. This result proves that the drag reduction agent of this invention has excellent salt resistance and can be adapted to different mineralization environments, solving the defect of existing drag reduction agents whose performance drops sharply at high mineralization.

[0032] refer to Figure 3 This figure visually illustrates the core performance differences between the three embodiments of the present invention and existing conventional salt-resistant drag-reducing agents. The drag reduction rate and anti-swelling rate of the product of the present invention are higher than those of the existing comparative examples, the surface tension is significantly lower than that of the comparative examples, and the dissolution time is only about one-fifth of that of existing products. It meets the performance requirements of fracturing fluids without the need for additional additives. This figure verifies that the present invention achieves simultaneous improvement in salt resistance, multifunctionality, and dissolution rate through molecular structure optimization, effectively solving the defects of existing drag-reducing agents such as poor salt resistance, single function, and low solution preparation efficiency, providing visual support for the superior performance of the product.

[0033] refer to Figure 4 This figure shows the trend of drag reduction rate as the salinity of the solution increases. With increasing salinity, the drag reduction rate of the existing comparative solution drops sharply, while the drag reduction rate of the product of this invention only fluctuates slightly, maintaining close to 70% even in an extremely high salinity environment of 250,000 mg / L. This figure clearly demonstrates the excellent salt resistance and stability of the product of this invention, making it suitable for various solution sources such as high-salinity seawater, formation water, and flowback fluid. It can be used directly without desalination treatment, providing performance data for applications in deep reservoirs and offshore oil and gas fields.

[0034] refer to Figure 5This figure compares the overall performance of the product of this invention with existing products from multiple dimensions. The product of this invention outperforms existing comparative examples in all five dimensions, with particularly outstanding advantages in salt resistance, anti-swelling performance, drainage assistance, and dissolution rate. It demonstrates the multi-functional integrated characteristics of the product of this invention; a single product can simultaneously meet multiple needs such as drag reduction, anti-swelling, and drainage assistance, simplifying the fracturing fluid preparation process, reducing the compatibility risks between different additives, adapting to the needs of rapid and continuous fracturing operations, effectively reducing the complexity and overall cost of on-site construction, and providing comprehensive performance support for the promotion and application of the product.

[0035] 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, multifunctional, high-efficiency drag-reducing agent, characterized in that, Includes the following steps: S1. Mix 2-acrylamido-2-methylpropanesulfonic acid, acrylamide, quaternized cationic monomer, fluorinated long-chain hydrophobic associating monomer, and polyether side-chain modified monomer in a mass ratio of 45-55:25-35:10-15:3-8:2-5. Add simulated oilfield prepared water with a mineralization of 500-1000 mg / L and stir to dissolve, to obtain a monomer mixed solution with a total mass fraction of 20%-30%. Adjust the pH of the mixed solution to 6.5-7.5 using a 20% sodium hydroxide solution, and control the solution temperature to not exceed 30℃ during the process. S2. High-purity nitrogen gas is introduced into the monomer mixture solution after pH adjustment for 15-20 minutes, with the nitrogen flow rate controlled at 0.5-0.8 L / min. After the dissolved oxygen content of the solution drops below 0.5 mg / L, 0.05%-0.1% of the total monomer mass of initiator ammonium persulfate, 0.02%-0.05% of the accelerator tetramethylethylenediamine, and 0.01%-0.03% of the chain transfer agent isopropanol are added sequentially. After stirring for 30 seconds, stirring is stopped and the reaction vessel is sealed. The reaction is carried out under adiabatic polymerization at a constant temperature water bath of 40-50℃ for 6-8 hours. S3. After the polymerization reaction is complete, the obtained gel-like polymer is taken out and granulated into granules with a diameter of 3-5 mm using a spiral granulator. 0.2%-0.5% of polyethylene glycol dispersant is sprayed into the granules according to the total mass of the granules, and the mixture is stirred for 5 minutes. S4. Place the coated dispersant particles in a fluidized bed dryer and dry them for 2-3 hours under hot air circulation at 80-90℃. Take a sample every 30 minutes during the drying process to test the moisture content. Stop drying immediately after the preset range is reached and transfer the product to a cooler to cool to room temperature. S5. The cooled and dried product is put into an ultra-fine pulverizer for pulverization. The pulverized product is then screened through an 80-100 mesh vibrating screen. The material passing through the screen is the salt-resistant, multifunctional, high-efficiency drag-reducing agent powder product.

2. The preparation method of the salt-resistant multifunctional high-efficiency drag-reducing agent according to claim 1, characterized in that, The quaternized cationic monomer in S1 is any one of methacryloyloxyethyltrimethylammonium chloride or dimethyl diallyl ammonium chloride, with a monomer cationicity of not less than 90% and a sodium chloride content of not more than 0.5%; the fluorinated long-chain hydrophobic associating monomer in S1 is any one of dodecafluoroheptyl methacrylate or perfluorooctyl ethyl acrylate, with a monomer fluorine content of not less than 60%.

3. The preparation method of the salt-resistant multifunctional high-efficiency resistance reducing agent according to claim 1, characterized in that, The polyether side-chain modified monomer in S1 is methoxy polyethylene glycol acrylate with a number average molecular weight of 800-1200.

4. The method for preparing the salt-resistant multifunctional high-efficiency resistance reducing agent according to claim 1, characterized in that, The ammonium persulfate and tetramethylethylenediamine used in S2 form a redox initiation system.

5. The application method of the salt-tolerant multifunctional high-efficiency resistance reducing agent, the resistance reducing agent prepared by the preparation method of any one of claims 1-4, characterized in that, Includes the following steps: S1. The prepared drag-reducing agent powder is continuously added to the fracturing fluid preparation water delivery pipeline through a dry powder feeder for automatic mixing and dissolution. The pipeline mixing time is 3-5 minutes, and a fracturing fluid base fluid with a mass fraction of 0.05%-0.2% is prepared. S2. The prepared fracturing fluid base is transported to an online viscosity testing device, and the viscosity of the base fluid is tested at 170s. -1 The apparent viscosity at the shear rate is used to determine the liquid preparation is qualified when the apparent viscosity reaches 5-10 mPa·s. If the viscosity is lower than the preset value, the feeding rate of the dry powder feeder is automatically adjusted. S3. Add proppant and crosslinking agent sequentially to qualified fracturing fluid base fluid, mix thoroughly online using a static mixer, and then pump directly downhole for fracturing operations. The proppant is quartz sand or ceramsite, added at a mass concentration of 100-500 kg / m³. 3 The crosslinking agent is an organoboron crosslinking agent, and the amount added is 0.1%-0.3% of the mass of the fracturing fluid base fluid; S4. After the fracturing operation is completed, close the wellhead and let the well sit for 24-48 hours. After the fracturing fluid has fully broken down, open the well and flow it back. S5. Collect the backflow liquid, filter it to remove solid impurities, and reuse it directly as water for preparing the solution. The difference between the amount of drag-reducing agent added during the repeated preparation process and the amount added during the first preparation should not exceed 10%.

6. The application method of the salt-resistant multifunctional high-efficiency resistance reducing agent according to claim 5, characterized in that, The dry powder feeder used in S1 has a loss-in-weight metering function.

7. The application method of the salt-resistant multifunctional high-efficiency drag-reducing agent according to claim 5, characterized in that, During the pumping process, the fracturing fluid in S3 reduces turbulent frictional resistance through the directional arrangement of molecular chains.

8. The application method of the salt-resistant multifunctional high-efficiency drag-reducing agent according to claim 5, characterized in that, The surface tension of the fracturing fluid in S4 after gel breaking is not higher than 28 mN / m, and the interfacial tension is not lower than 1×10⁻⁶ m / m. -2 mN / m.

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