A quick-dissolving salt-resistant friction-reducing powder for fracturing fluid, a preparation method thereof and application thereof

Abstract

The present application belongs to the technical field of oil field chemical additives, and particularly relates to a kind of instant anti-salt resistance and resistance reduction powder for fracturing fluid and a preparation method and application thereof.The instant anti-salt resistance and resistance reduction powder for fracturing fluid provided by the present application is prepared from raw materials including mixed monomers, redox initiator system, template agent and dry powder flow aid agent.The mixed monomers include acrylamide, methacryloyloxyethyl trimethylammonium chloride, 2-acrylamido-2-methylpropanesulfonic acid sodium and N-vinyl caprolactam.The instant anti-salt resistance and resistance reduction powder for fracturing fluid provided by the present application has higher adaptability to swelling time and powder mixing equipment, is moisture-proof, has efficient salt resistance and stable resistance reduction performance, and can effectively improve the delivery efficiency of fracturing fluid and proppant.

Description

Technical Field

[0001] This invention belongs to the field of oilfield chemical additives technology, specifically relating to a fast-dissolving salt-resistant drag-reducing powder for fracturing fluid, its preparation method, and its application. Background Technology

[0002] In shale gas fracturing operations, drag-reducing agents are the core additives in slickwater fracturing fluids, used to reduce pipeline friction resistance and enable high-volume, low-pump-pressure operations. Currently, the main types used in the field are emulsion-based and quick-dissolving powder-based agents. Emulsion-based agents dissolve quickly but are expensive and have poor storage stability; quick-dissolving powder-based drag-reducing agents have lower overall fracturing costs and are convenient to store and transport, but they generally suffer from technical bottlenecks such as hygroscopicity, mismatch between dissolution rate and preparation equipment, and a sharp decline in drag-reducing efficiency in high-salinity fracturing fluids (such as flowback fluid preparation).

[0003] Indoor experiments showed that most powders had weak moisture resistance, and some drag-reducing powders exhibited problems such as difficulty in dispersing and excessive fish-eyes after only 1-2 minutes of contact with air. Currently, online mixing equipment for quick-dissolving powders used in the field is mainly divided into fully enclosed and open mixing equipment. Taking the main shale gas blocks such as Jiaoshi, Hongxing, and Fuxing as examples, open equipment is mostly used for on-site fracturing fluid preparation. During the preparation process, the drag-reducing powder inevitably comes into contact with air, and the powder in the conveyor after construction also suffers from moisture absorption and clumping. Most quick-dissolving powders on the market exhibit varying degrees of clumping, difficulty in dispersion, and high viscosity during on-site fluid preparation, leading to uneven on-site fluid preparation, failure to meet design specifications due to high viscosity, and even clumping of the pump head by the powder, causing fracturing truck shutdowns.

[0004] During on-site construction, the online powder mixing equipment first mixes a small amount of water with the fast-dissolving powder drag reducer to prepare a concentrated fracturing fluid. This concentrated fracturing fluid then enters the sand mixing truck, where it is further mixed with the remaining water, formulation additives, and proppant to form a standard injection fluid, which is then pumped into the wellbore. To ensure smooth operation, it is necessary to avoid pumping difficulties due to excessive viscosity of the concentrated fluid during transport to the sand mixing truck; it is also necessary to prevent excessively rapid viscosity increase, which would prevent sufficient secondary mixing with the water and proppant in the sand mixing truck. Simultaneously, the injection fluid must reach the designed viscosity after being pumped into the wellbore to meet fracturing requirements. Therefore, the concentrated fluid must be in a "dispersed but not swollen" state before entering the sand mixing truck, and must achieve complete swelling after entering the wellbore. This places strict requirements on the swelling time of the fast-dissolving powder.

[0005] Currently, well farm development models in blocks such as Jiaoshi and Hongxing require cost reduction and efficiency improvement. To reduce the cost of transporting and treating backflow, most well sites use backflow for direct fluid preparation. However, the drag reduction rate of readily soluble powders on the market is ≤60% in 30,000-50,000 ppm backflow, which greatly reduces the performance of fracturing fluid and further affects the fracturing effect.

[0006] Existing technologies for improving powder performance mostly focus on compounding monomer formulations (such as introducing AMPS monomers) or using co-precipitation methods for powder preparation. However, these methods often only improve the powder from a single dimension of chemical structure, neglecting the decisive influence of the physical morphology of powder particles (such as particle size and porosity) on the dissolution rate. Powder moisture protection mainly relies on physical isolation through multi-layer composite packaging bags (such as inner aluminum foil moisture-proof layers and built-in desiccant strips) or airtight moisture-proof storage containers to reduce the risk of moisture absorption during storage and transportation. This makes it difficult for current conventional products to simultaneously achieve the triple demanding goals of "controlled swelling time," "moisture protection," and "high salt tolerance."

[0007] Therefore, developing a fast-dissolving powder drag reducer that is highly compatible with powder mixing equipment (swelling time ≤ 120 seconds), has excellent moisture resistance and salt resistance (drag reduction rate retention ≥ 90% in high-mineralized brine) is of great significance for improving fracturing construction efficiency and reducing overall costs. Summary of the Invention

[0008] Therefore, the technical problem to be solved by the present invention is to provide a fast-dissolving salt-resistant drag-reducing powder for fracturing fluid, its preparation method and application. The fast-dissolving salt-resistant drag-reducing powder for fracturing fluid provided by the present invention has high compatibility with powder mixing equipment, good moisture-proof effect, and can maintain excellent drag-reducing effect in high salinity environment, effectively improving the delivery efficiency of fracturing fluid and proppant.

[0009] This invention provides a fast-dissolving, salt-resistant, drag-reducing powder for fracturing fluids, the raw materials for which include mixed monomers, a redox initiator system, a template agent, and a dry powder flow aid;

[0010] The mixed monomers include acrylamide, methacryloyloxyethyltrimethylammonium chloride, sodium 2-acrylamido-2-methylpropanesulfonate, and N-vinylcaprolactam.

[0011] Preferably, the molar ratio of acrylamide, methacryloyloxyethyltrimethylammonium chloride, sodium 2-acrylamido-2-methylpropanesulfonate and N-vinylcaprolactam is 1:(0.001-0.05):(0.001-0.15):(0.001-0.10).

[0012] Preferably, the template agent is selected from at least one of PEG-200, PEG-400, PEG-600 and polyvinylpyrrolidone, and the mass of the template agent is 5% to 10% of the total mass of the mixed monomers.

[0013] Preferably, the redox initiator system is composed of ammonium persulfate and sodium bisulfite, wherein the molar ratio of ammonium persulfate to sodium bisulfite is 1.8:1 to 2.2:1.

[0014] Preferably, the dry powder flow aid is a mixture of polyethylene glycol stearate and other additives in a mass ratio of 1.5:1 to 2:1. The other additives are selected from at least one of fumed silica, precipitated silica, hydrophobic fumed silica, microcrystalline cellulose, and magnesium stearate, and are preferably fumed silica.

[0015] Preferably, the particle size of the quick-dissolving salt-resistant drag-reducing powder is 80-120 mesh.

[0016] This invention also provides a method for preparing the above-mentioned fast-dissolving salt-resistant drag-reducing powder for fracturing fluid, comprising the following steps:

[0017] A) A mixed monomer aqueous solution is mixed with a redox initiator system to carry out a copolymerization reaction, and the polymerized product is obtained;

[0018] B) The polymerization reactant is mixed and stirred with a template agent to obtain a polymer colloid containing an in-situ dispersed template agent;

[0019] C) The polymer colloid containing the in-situ dispersing template agent is sequentially precipitated, washed, and spray-dried to obtain a primary dry powder;

[0020] D) After the primary dry powder is pulverized and sieved, it is mixed with a dry powder flow aid to obtain a fast-dissolving salt-resistant drag-reducing powder.

[0021] Preferably, the copolymerization reaction is carried out under a protective atmosphere, and the temperature of the copolymerization reaction is 10-20°C, and the time is 3-5 hours.

[0022] The spray drying process conditions are as follows: centrifugal atomization is used, the atomizing disc speed is 12000-18000 rpm, the atomization pressure is 0.4-0.8MPa, the inlet air temperature is controlled at 110-130℃, and the outlet air temperature is controlled at 65-75℃.

[0023] Preferably, the mass of the dry powder flow aid accounts for 0.8% to 1.5% of the mass of the primary dried powder.

[0024] The present invention also provides a high-saltification fracturing fluid, comprising the above-mentioned fast-dissolving salt-resistant drag-reducing powder for fracturing fluid, or comprising the fast-dissolving salt-resistant drag-reducing powder for fracturing fluid prepared by the above preparation method.

[0025] Compared with existing technologies, this invention provides a fast-dissolving, salt-resistant, and drag-reducing powder for fracturing fluids. The raw materials for preparation include mixed monomers, a redox initiator system, a template agent, and a dry powder flow aid. The mixed monomers include acrylamide, methacryloyloxyethyltrimethylammonium chloride, sodium 2-acrylamido-2-methylpropanesulfonate, and N-vinylcaprolactam. The fast-dissolving, salt-resistant, and drag-reducing powder for fracturing fluids provided by this invention has higher compatibility with powder mixing equipment in terms of swelling time, moisture resistance, high salt resistance, and stable drag-reducing performance, effectively improving the delivery efficiency of fracturing fluids and proppant. Detailed Implementation

[0026] This invention provides a fast-dissolving, salt-resistant, drag-reducing powder for fracturing fluids, the raw materials for which include mixed monomers, a redox initiator system, a template agent, and a dry powder flow aid;

[0027] The mixed monomers include acrylamide (AM), methacryloyloxyethyltrimethylammonium chloride (DMC), sodium 2-acrylamido-2-methylpropanesulfonate (AMPS), and N-vinylcaprolactam (NVCL).

[0028] The raw materials for preparing the fast-dissolving salt-resistant drag-reducing powder for fracturing fluid provided by the present invention include mixed monomers. In the mixed monomers, the molar ratio of acrylamide, methacryloyloxyethyltrimethylammonium chloride, sodium 2-acrylamido-2-methylpropanesulfonate, and N-vinylcaprolactam is 1:(0.001~0.05):(0.001~0.15):(0.001~0.10), which can be any value between 1:0.02:0.08:0.05, 1:0.001:0.001:0.001, 1:0.05:0.15:0.10, or 1:(0.001~0.05):(0.001~0.15):(0.001~0.10).

[0029] AMPS, an anionic monomer, provides strong hydrophilicity and sulfonic acid groups, significantly enhancing the polymer's solubility and salt resistance, which helps the drag-reducing agent maintain its effectiveness under high mineralization conditions. DMC, a cationic monomer, introduces positively charged groups, which can form an electrostatic synergistic effect with AMPS, optimizing the aggregation state and swelling behavior of the polymer molecular chain. This not only improves the moisture-proof stability of the powder during storage and transportation but also enables controllable swelling time. Simultaneously, it synergistically enhances the salt resistance and interfacial lubrication and friction-reducing efficiency of the drag-reducing agent in high mineralization environments. Through charge regulation and structural synergy, the two work together to optimize the comprehensive performance of the drag-reducing agent, including its temperature and salt resistance, controllable swelling, moisture resistance of the powder, and core drag-reducing efficiency.

[0030] The raw materials for preparing the fast-dissolving salt-resistant drag-reducing powder for fracturing fluid provided by the present invention also include a redox initiator system composed of ammonium persulfate and sodium bisulfite, wherein the molar ratio of ammonium persulfate and sodium bisulfite is 1.8:1 to 2.2:1, and can be any value between 1.8:1, 1.9:1, 2.0:1, 2.1:1, 2.2:1, or 1.8:1 to 2.2:1.

[0031] The random copolymer molecular chain generated by this invention is as follows:

[0032] -[CH2-CH(CONH2)] x -[CH2-CH(CONH-C(CH3)2-CH2SO3-Na + )] y -[CH2-C(CH3)(COOCH2CH2N + (CH3)3Cl - )] z -[CH2-CH(N-C5H 10 O)] w -

[0033] The copolymer backbone is formed by random copolymerization of acrylamide (AM), sodium 2-acrylamido-2-methylpropanesulfonate (AMPS), methacryloyloxyethyltrimethylammonium chloride (DMC), and N-vinylcaprolactam (NVCL). The molecular chain contains strong anionic sulfonic acid groups, quaternary ammonium cationic groups, and hydrophobic lactam rings, which endows the product with excellent salt resistance, rapid dissolution performance, and good moisture-proof stability of powder.

[0034] The raw materials for preparing the fast-dissolving, salt-resistant, drag-reducing powder for fracturing fluid provided by this invention also include a template agent, which is selected from substances having a similar hydrophilic-hydrophobic balance and nonionic surface activity. Preferably, the template agent is selected from at least one of PEG-200, PEG-400, PEG-600, and polyvinylpyrrolidone. In this invention, polyethylene glycol-400 acts as both a dispersant and a template agent. PEG-200 and PEG-600 can adjust the chain length to affect the dispersibility of the polymer colloid and the template pore size; polyvinylpyrrolidone (PVP) has good water solubility and film-forming properties, which is beneficial for forming a uniform porous structure. The mass of the template agent is 5% to 10% of the total mass of the mixed monomers, and can be any value between 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, or 5% to 10%.

[0035] The raw materials for preparing the fast-dissolving, salt-resistant, drag-reducing powder for fracturing fluid provided by this invention also include a dry powder flow aid, the mass of which is 0.8% to 1.5% of the mass of the generated powder. The dry powder flow aid is a mixture of polyethylene stearate and other additives at a mass ratio of 1.5:1 to 2:1. The mass ratio of polyethylene stearate to other additives can be any value between 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2.0:1, or 1.5:1 to 2:1. Polyethylene stearate, as a nonionic surfactant, is a key component for achieving moisture-proof powder: its hydrophobic long-chain alkyl groups can form a continuous hydrophobic protective film on the surface of powder particles, effectively blocking the intrusion of environmental moisture and inhibiting the powder from absorbing moisture and clumping at the source; at the same time, the hydrophilic polyethylene glycol segments can quickly hydrate and expand after contact with water, ensuring that the moisture-proof effect does not affect the on-site quick-dissolving performance, and can also regulate the polymer swelling kinetics through the steric hindrance effect, and synergistically enhance the salt resistance stability in high-salt environments.

[0036] The other additives in the dry powder flow aid are selected from one of fumed silica, precipitated silica, hydrophobic fumed silica, microcrystalline cellulose, and magnesium stearate, preferably fumed silica. Fumed silica can form a dual-layer moisture-proof synergistic system with polyethylene stearate through the physical barrier effect of nanoparticles: on the one hand, it further enhances the powder's resistance to moisture absorption; on the other hand, it improves powder flowability by utilizing its nano-ball effect, preventing agglomeration during storage and transportation, and improving the dispersion uniformity of the product during mixing.

[0037] To ensure product performance, the key parameters of the selected fumed silica should be controlled as follows: specific surface area: 150~400 m² 2 / g; Average particle size: 5~30 nm; Purity: SiO2 content ≥99.8%; Surface properties: hydrophilic to adapt to hydration dispersion in high-salt environments.

[0038] In this invention, the particle size of the rapidly dissolving, salt-resistant, and drag-reducing powder is 80-120 mesh. The 80-120 mesh powder further ensures an optimal balance between rapid dissolution and effective drag reduction. This particle size range is limited based on comprehensive engineering considerations: powders with excessively fine particles (e.g., <120 mesh) have too large a specific surface area, swell instantly upon contact with water, and easily form "fish-eye" shaped agglomerates at the dosing port, hindering uniform dispersion in the solution preparation system and being incompatible with the fluid dynamics conditions of high-speed mixing equipment on-site; while powders with excessively coarse particles (e.g., <80 mesh) have significantly slower dissolution rates, and the internal effective components cannot fully hydrate and expand in a high-mineralization environment, leading to a decrease in salt resistance and drag-reduction efficiency. Therefore, this invention preferably uses a particle size distribution of 80-120 mesh to achieve optimal dispersion and hydration dynamics of the powder in salt water while ensuring a swelling time of 60-120 seconds.

[0039] This invention also provides a method for preparing the above-mentioned fast-dissolving salt-resistant drag-reducing powder for fracturing fluid, comprising the following steps:

[0040] A) A mixed monomer aqueous solution is mixed with a redox initiator system to carry out a copolymerization reaction, and the polymerized product is obtained;

[0041] B) The polymerization reactant is mixed and stirred with a template agent to obtain a polymer colloid containing an in-situ dispersed template agent;

[0042] C) The polymer colloid containing the in-situ dispersing template agent is sequentially precipitated, washed, and spray-dried to obtain a primary dry powder;

[0043] D) After the primary dry powder is pulverized and sieved, it is mixed with a dry powder flow aid to obtain a fast-dissolving salt-resistant drag-reducing powder.

[0044] Specifically, the present invention first prepares a mixed monomer aqueous solution. Specifically, at 10~20°C, acrylamide (AM), methacryloyloxyethyltrimethylammonium chloride (DMC), sodium 2-acrylamido-2-methylpropanesulfonate (AMPS) and N-vinylcaprolactam (NVCL) are dissolved in deionized water, stirred until completely dissolved, and nitrogen gas is continuously introduced to remove dissolved oxygen, forming a monomer mixture.

[0045] Next, a redox initiator system is added to the monomer mixture to carry out a copolymerization reaction and obtain the polymer.

[0046] The copolymerization reaction is carried out under a protective atmosphere, preferably a nitrogen atmosphere. The temperature of the copolymerization reaction is 10~20℃, which can be 10, 15, 18, 20℃, or any value between 10~20℃, and the time is 3~5 hours, which can be 3, 4, 5, or any value between 3~5 hours.

[0047] After the reaction is complete, a template agent is added to the polymer reactants and stirred to disperse them evenly, thus obtaining a polymer colloid containing an in-situ dispersed template agent.

[0048] Next, the polymer colloid containing the in-situ dispersing template agent was injected into 2 to 6 times its volume of organic solvent under stirring speed of 800 to 1200 rpm for precipitation. After standing and aging for 20 to 40 minutes, solid-liquid separation was performed, and the mixture was washed with organic solvent to obtain a wet gel precursor.

[0049] The organic solvent is selected from those that are miscible with water and have a precipitating effect on the polymer, and can be anhydrous ethanol, acetone, isopropanol, or methanol. The volume ratio of the organic solvent to the polymer colloid is 2:1 to 6:1 to ensure complete precipitation and facilitate subsequent separation. The volume ratio of the organic solvent to the polymer colloid can be 2:1, 3:1, 4:1, 5:1, 6:1, or any value between 2:1 and 6:1.

[0050] Then, the wet gel precursor is redispersed in water to form a dispersion with a solid content of 8% to 12%, and then dried using a spray drying process. The spray drying process conditions are as follows: centrifugal atomization is used, the atomizing disc speed is 12000 to 18000 rpm, the atomization pressure is 0.4 to 0.8 MPa, the inlet air temperature is controlled at 110 to 130℃, and the outlet air temperature is controlled at 65 to 75℃ to obtain a primary dried powder.

[0051] The primary dry powder is pulverized and sieved, collecting the powder that passes through an 80-mesh sieve but is retained on a 120-mesh sieve. Then, a dry powder flow aid, accounting for 0.8% to 1.5% of its total mass, is dry-mixed into the powder to obtain the fast-dissolving salt-resistant drag-reducing powder for fracturing fluid. The dry powder flow aid accounts for 0.5% to 1.0% of the mass of the primary dry powder, and can be any value between 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, or 0.5% to 1.0%.

[0052] This invention provides a fast-dissolving, salt-resistant, drag-reducing powder for fracturing fluid, or a fast-dissolving, salt-resistant, drag-reducing powder for fracturing fluid prepared by the above preparation method.

[0053] The present invention has the following beneficial effects:

[0054] 1. Breakthrough improvements in solubility, moisture resistance, and salt tolerance.

[0055] The product's swelling time is 60-120 seconds, enabling "instantaneous dispersion and controlled-speed viscosity increase." This completely solves the technical bottlenecks of conventional powdered drag reducers, such as dissolving too quickly or too slowly, incompatibility with on-site liquid preparation equipment, high viscosity clumping, and easy agglomeration forming "fish eyes," thus greatly improving on-site liquid preparation efficiency.

[0056] Under 24-hour constant temperature and humidity (25℃ / 60%RH) testing, the moisture absorption rate is less than 1.3%, and the powder remains loose and does not clump. In 50,000 ppm saline solution, its drag reduction rate is maintained at ≥90%. In particular, it exhibits strong adaptability to environments with high calcium and magnesium ions and high monovalent salt ions, with performance degradation far lower than conventional products, ensuring reliability and effectiveness under harsh formation conditions.

[0057] 2. Enhance solution preparation quality and improve operational efficiency.

[0058] This product further enhances its compatibility with on-site mixing equipment by precisely controlling the swelling time: the powder is evenly dispersed and does not clump during the liquid preparation process, and the timing of the stickiness is just right. This effectively reduces viscosity friction during transportation and reduces pumping pressure loss, while ensuring that the powder is fully hydrated without clumping or waste, thereby improving powder utilization efficiency. It improves the quality of liquid preparation while reducing overall costs and improving the overall efficiency of fracturing operations.

[0059] 3. Overall costs are significantly reduced, resulting in outstanding economic benefits.

[0060] By streamlining equipment investment (reducing liquid tanks, agitators, etc.), lowering warehousing and logistics costs (powder storage and transportation are far more convenient and economical than liquids), saving labor costs, and reducing operational time losses due to liquid preparation waiting and performance instability, the application of this invention can effectively reduce the overall cost of oil and gas production enhancement, fracturing and other operations from multiple dimensions, and improve overall operational efficiency and economy.

[0061] To further understand the present invention, the following embodiments illustrate the fast-dissolving salt-resistant drag-reducing powder for fracturing fluid, its preparation method, and its application. The scope of protection of the present invention is not limited by the following embodiments.

[0062] Example 1

[0063] This embodiment provides a fast-dissolving, salt-resistant, drag-reducing powder for fracturing fluids, the preparation method of which is as follows:

[0064] (1) Monomer premixing and deoxygenation: In a fully automated continuous reactor, add 800g of deionized water, start stirring and control the temperature to 10℃. Add 284.0g (4.0mol) of acrylamide (AM), 13.7g (0.08mol, molar ratio 0.02) of methacryloyloxyethyltrimethylammonium chloride (DMC, 75% aqueous solution), 69.4g (0.32mol, molar ratio 0.08) of sodium 2-acrylamido-2-methylpropanesulfonate (AMPS), and 22.5g (0.20mol, molar ratio 0.05) of N-vinylcaprolactam (NVCL). Continue stirring until all monomers are completely dissolved to form a clear solution. Continuously purge the solution with high-purity nitrogen gas and bubble to remove oxygen for 60 minutes.

[0065] (2) Copolymerization reaction and introduction of template agent: The monomer mixture obtained in step (1) was kept at a constant temperature of 10°C. Under nitrogen protection, ammonium persulfate solution (0.76 g ammonium persulfate dissolved in 10 g deionized water) and sodium bisulfite solution (0.33 g sodium bisulfite dissolved in 10 g deionized water) were added sequentially, with a molar ratio of 2.0:1. The system thickened rapidly, and the reaction was continued for 4 hours at 10°C under a nitrogen atmosphere to obtain a viscous polymer colloid. After the reaction was completed, 38.9 g polyethylene glycol-400 (approximately 8.0% of the total monomer mass of 389 g) was added to the colloid, and the mixture was stirred at 20°C for 60 minutes to ensure uniform dispersion in the colloid.

[0066] (3) Precipitation to form a porous precursor: The polymer colloid containing the template agent obtained in step (2) was slowly injected into 5 times its volume (about 6.5 L) of industrial anhydrous ethanol under high-speed stirring (1000 rpm). After the addition was complete, stirring was stopped and the mixture was allowed to stand for 30 minutes to age. Then, vacuum filtration was performed using a Buchner funnel, and the filter cake was washed three times with 1 L of fresh anhydrous ethanol to obtain a wet gel precursor.

[0067] (4) Spray drying: The wet gel precursor obtained in step (3) is transferred to a dispersion tank, and an appropriate amount of deionized water is added. Under stirring, an aqueous dispersion with a solid content of 10% is prepared. A centrifugal spray drying tower (atomizing disc speed 18000 rpm) is used for drying. The process parameters are set as follows: feed rate 30 mL / min, inlet air temperature 125℃, outlet air temperature 70℃, and atomization pressure 0.45 MPa. The primary dried powder is collected from the bottom of the drying tower and the cyclone separator.

[0068] (5) Crushing and sieving: After the primary powder obtained in step (4) is initially crushed by a universal pulverizer, 0.6% polyethylene stearate and 0.3% fumed silica by mass are dry-mixed into the powder. The powder is then passed through 80-mesh and 120-mesh standard inspection sieves in sequence. The powder that can pass through the 80-mesh sieve and is retained on the 120-mesh sieve is collected to obtain the target drag-reducing powder product with a particle size distribution of 80-120 mesh.

[0069] (6) Performance testing:

[0070] a) Swelling Time Test: Accurately weigh 0.50 g (accurate to 0.01 g) of sample powder. Measure 495 mL of room temperature (25℃) water into a 1 L beaker, place it on a magnetic stirrer, turn on the stirrer and adjust the speed to 800-1000 rpm. Pour the powder evenly and quickly into the center of the vortex, and start timing simultaneously. Observe the solution state for 30 seconds. Stop timing when the solution becomes a uniform, transparent, viscous colloid, and there are no visible undissolved particles or "fish eyes" on the beaker wall and stir bar surface. Record this as the swelling time. Repeat three times and take the average value.

[0071] b) Moisture absorption rate test

[0072] Set the temperature of the constant temperature and humidity incubator to 25℃ and the humidity to 60%. Prepare three petri dishes, clean and dry them, and weigh them (accurate to 0.01g). Use an electronic balance to weigh 4g of instant powder drag-reducing agent (accurate to 0.01g) into each petri dish and spread it evenly to a thickness of less than 2mm. Place the three groups of samples in the constant temperature and humidity incubator and test their mass and calculate their moisture absorption rate after 1h, 2h, 4h, 8h, and 24h.

[0073] Moisture absorption rate = (Total mass of watch glass and powder after moisture absorption - Mass of powder before moisture absorption - Mass of watch glass) / Mass of powder before moisture absorption × 100%

[0074] c) Test of resistivity retention rate when high mineralization decreases

[0075] Preparation of simulated salt solution: Sample solutions were prepared using deionized water and simulated salt water with a mineralization of 50,000 mg / L (formulation: NaCl 45 g / L + CaCl2 3.5 g / L + MgCl2·6H2O 1.5 g / L), and their drag reduction rate was tested.

[0076] Drag reduction retention rate test: Using the same drag reduction testing device, the drag reduction rate of 0.1% sample was tested. The test procedure was carried out in accordance with NB / T 14003.1-2015 "Shale gas fracturing fluid Part 1: Slickwater performance indicators and evaluation methods". The drag reduction retention rate was calculated based on the test results.

[0077] Resistivity retention rate = (Resistivity in brine / Resistivity in clear water) × 100%

[0078] Example 2

[0079] A fast-dissolving, salt-resistant, drag-reducing powder for fracturing fluids, the specific preparation steps of which include:

[0080] (1) Monomer premixing and deoxygenation: The operation is the same as in Example 1, but the set temperature of the fully automatic continuous reactor is changed to 20°C, and the molar ratio of monomers is AM:DMC:AMPS:NVCL = 1:0.001:0.001:0.001. That is, AM 284.0 g (4.0 mol), DMC (75%) 0.68 g (0.004 mol), AMPS 0.87 g (0.004 mol), NVCL 0.45 g (0.004 mol).

[0081] (2) Copolymerization reaction and introduction of template agent: polymerization temperature 20℃, reaction time 3 hours. The amount of polyethylene glycol-400 added is 5.0% of the total mass of monomers.

[0082] (3) Precipitation to form a porous precursor: The standing aging time is 20 minutes.

[0083] (4) Spray drying: The solid content of the dispersion liquid is 8%, the air inlet temperature is 110℃, and the air outlet temperature is 65℃.

[0084] (5) Crushing and sieving: Same as in Example 1.

[0085] (6) Performance testing: Tested according to the method in Example 1.

[0086] Example 3

[0087] A fast-dissolving, salt-resistant, drag-reducing powder for fracturing fluids, the specific preparation steps of which include:

[0088] (1) Monomer premixing and deoxygenation: The operation is the same as in Example 1, but the molar ratio of monomers is changed to AM:DMC:AMPS:NVCL = 1:0.05:0.15:0.10. That is, AM 284.0 g (4.0 mol), DMC (75%) 34.2 g (0.20 mol), AMPS 130.1 g (0.60 mol), NVCL 45.0 g (0.40 mol).

[0089] (2) Copolymerization reaction and introduction of template agent: polymerization temperature 10℃, reaction time 5 hours. The amount of polyethylene glycol-400 added is 10.0% of the total mass of monomers.

[0090] (3) Precipitation to form a porous precursor: The standing aging time is 40 minutes.

[0091] (4) Spray drying: the solid content of the dispersion liquid is 12%, the air inlet temperature is 130℃, the air outlet temperature is 75℃, and the atomization pressure is 0.48MPa.

[0092] (5) Crushing and sieving: Same as in Example 1.

[0093] (6) Performance testing: Tested according to the method in Example 1.

[0094] Example 4

[0095] Steps (1) to (3) are the same as in Example 1.

[0096] (4) Spray drying: Centrifugal atomization is used, and the speed of the atomizing disc is adjusted to 15,000 rpm.

[0097] (5) Crushing and sieving: Same as in Example 1.

[0098] (6) Performance testing: Tested according to the method in Example 1.

[0099] Example 5

[0100] A fast-dissolving, salt-resistant, drag-reducing powder for fracturing fluids, the specific preparation steps of which include:

[0101] (1) to (5) Steps: Prepare drag-reducing powder with a particle size of 80-120 mesh by following steps (1) to (5) of Example 1.

[0102] (2) Dry mixing glidant: Place 100 g of the powder obtained in step (1) into a V-type mixer, add 1% polyethylene stearate and 0.5% fumed silica (Aerosil 200, accounting for 1.5% of the total powder mass), and mix for 30 minutes until uniform.

[0103] (3) Performance test: Test according to the method in Example 1.

[0104] Comparative Example 1

[0105] A drag-reducing powder, the specific preparation steps of which include:

[0106] (1) Monomer premixing and deoxygenation: The operation is the same as in Example 1, but the molar ratio of monomers is changed to AM:DMC:AMPS:NVCL = 1:0.08:0.08:0.05. The molar ratio of DMC is 0.08.

[0107] Steps (2) to (6): The subsequent polymerization, precipitation, drying, sieving and performance testing steps are exactly the same as in Example 1.

[0108] Comparative Example 2

[0109] A drag-reducing powder, the specific preparation steps of which include:

[0110] (1) Monomer premixing and deoxygenation: The operation is the same as in Example 1, but the molar ratio of monomers is changed to AM:DMC:AMPS:NVCL = 1:0.02:0.18:0.05. Among them, the molar ratio of AMPS is 0.18.

[0111] Steps (2) to (6): The subsequent steps are exactly the same as in Example 1.

[0112] Comparative Example 3

[0113] A drag-reducing powder, the specific preparation steps of which include:

[0114] (1) to (2) Steps: Same as steps (1) to (2) of Example 1, but after the reaction in step (2) is completed, only 7.8g of polyethylene glycol-400 (2.0% of the total mass of monomers of about 389g) is added.

[0115] (2) Subsequent steps: sedimentation, spray drying, pulverization and sieving are the same as in Example 1.

[0116] (3) Performance test: Test according to the method in Example 1.

[0117] Comparative Example 4

[0118] A drag-reducing powder, the specific preparation steps of which include:

[0119] Steps (1) to (3): Same as steps (1) to (3) in Example 1.

[0120] (2) Spray drying: The dispersion is spray dried, but the inlet air temperature is set to 155°C and the outlet air temperature is set to 85°C.

[0121] (3) Subsequent steps: Same as in Example 1.

[0122] Comparative Example 5

[0123] A drag-reducing powder, the specific preparation steps of which include:

[0124] (1) Monomer premixing and deoxygenation: Same as in Example 1.

[0125] (2) Copolymerization reaction and introduction of template agent: The molar ratio of initiator ammonium persulfate to sodium bisulfite was adjusted to 2.5:1.

[0126] (3) Subsequent steps: Same as in Example 1.

[0127] Comparative Example 6

[0128] A drag-reducing powder, the specific preparation steps of which include:

[0129] Steps (1) to (4) are the same as in Example 1.

[0130] (5) Crushing and sieving: After the primary powder obtained in step (4) is initially crushed by a universal pulverizer, 0.6% polyethylene stearate and 0.3% fumed silica by mass are dry-mixed into the powder. The powder is then passed through a 120-mesh standard inspection sieve. The powder that can pass through the 120-mesh sieve is collected to obtain the target drag-reducing powder product with a particle size <120 mesh.

[0131] (3) Subsequent steps: Same as in Example 1.

[0132] Comparative Example 7

[0133] A drag-reducing powder, the specific preparation steps of which include:

[0134] Steps (1) to (4) are the same as in Example 1.

[0135] (5) Crushing and sieving: After the primary powder obtained in step (4) is initially crushed by a universal pulverizer, 0.9% of fumed silica by mass is dry-mixed into the powder. The powder is then passed through 80-mesh and 120-mesh standard inspection sieves in sequence. Powder that can pass through the 80-mesh sieve and is retained on the 120-mesh sieve is collected to obtain the target drag-reducing powder product with a particle size distribution of 80-120 mesh.

[0136] (6) Subsequent steps: Same as in Example 1.

[0137] Table 1 Key performance test results of each embodiment and comparative example

[0138]

[0139] The core advantage of this invention lies not only in its ability to achieve rapid online mixing, but more importantly, in the precise control of swelling time: the complete swelling time is controlled within 60-120 seconds, while the system is sufficiently dispersed but not yet fully thickened at 30 seconds. This characteristic brings engineering advantages: after the concentrated solution is prepared on-site, the system experiences less resistance during transport to the sand mixing truck, facilitating thorough mixing with the mixing water and proppant, effectively avoiding clumping and "fisheye" phenomena; upon entering the wellbore, the system rapidly swells, quickly reaching the viscosity required for sand carrying, thus achieving efficient sand carrying. Furthermore, the product of this invention has a moisture absorption rate of only 0.986%–1.208% at 60% humidity over 24 hours. This low moisture absorption characteristic makes it perfectly compatible with the powder drag-reducing agent mixing equipment commonly used in current main blocks. Even if on-site shutdowns occur due to unforeseen circumstances such as malfunctions, the product is not prone to moisture absorption and clumping, significantly reducing the construction risks associated with common problems such as fisheye and clumping during the mixing process.

[0140] As shown in Table 1, the comparative examples, due to exceeding the mixing ratio range, exhibited problems such as uneven dissolution, decreased drag reduction, or structural instability. In particular, although Comparative Example 6 had a drag reduction rate >70%, its swelling time was too short (56 s), easily leading to premature swelling, uneven dispersion, and pump blockage during on-site solution preparation. This, in turn, demonstrates the engineering applicability of the present invention in terms of particle size control and dissolution kinetics. Therefore, the present invention, through monomer compatibility, template control, particle size optimization, and additive modification, achieves sustained and stable drag reduction performance in high-salt environments while ensuring rapid dissolution, possessing significant practical and process matching advantages.

[0141] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A fast-dissolving, salt-resistant, drag-reducing powder for fracturing fluid, characterized in that, The raw materials for preparation include mixed monomers, redox initiator system, template agent, and dry powder flow aid; The mixed monomers include acrylamide, methacryloyloxyethyltrimethylammonium chloride, sodium 2-acrylamido-2-methylpropanesulfonate, and N-vinylcaprolactam.

2. The fast-dissolving, salt-resistant, drag-reducing powder for fracturing fluid according to claim 1, characterized in that, The molar ratio of acrylamide, methacryloyloxyethyltrimethylammonium chloride, sodium 2-acrylamido-2-methylpropanesulfonate and N-vinylcaprolactam is 1:(0.001-0.05):(0.001-0.15):(0.001-0.10).

3. The fast-dissolving, salt-resistant, drag-reducing powder for fracturing fluid according to claim 1, characterized in that, The template agent is selected from at least one of PEG-200, PEG-400, PEG-600 and polyvinylpyrrolidone, and the mass of the template agent is 5% to 10% of the total mass of the mixed monomers.

4. The fast-dissolving, salt-resistant, drag-reducing powder for fracturing fluid according to claim 1, characterized in that, The redox initiator system is composed of ammonium persulfate and sodium bisulfite, wherein the molar ratio of ammonium persulfate to sodium bisulfite is 1.8:1 to 2.2:

1.

5. The fast-dissolving, salt-resistant, drag-reducing powder for fracturing fluid according to claim 1, characterized in that, The dry powder flow aid is a mixture of polyethylene stearate and other additives in a mass ratio of 1.5:1 to 2:

1. The other additives are selected from at least one of fumed silica, precipitated silica, hydrophobic fumed silica, microcrystalline cellulose, and magnesium stearate, preferably fumed silica.

6. The fast-dissolving, salt-resistant, drag-reducing powder for fracturing fluid according to claim 1, characterized in that, The particle size of the fast-dissolving salt-resistant drag-reducing powder is 80~120 mesh.

7. A method for preparing a fast-dissolving, salt-resistant, drag-reducing powder for fracturing fluid as described in any one of claims 1 to 6, characterized in that, Includes the following steps: A) A mixed monomer aqueous solution is mixed with a redox initiator system to carry out a copolymerization reaction, and the polymerized product is obtained; B) The polymerization reactant is mixed and stirred with a template agent to obtain a polymer colloid containing an in-situ dispersed template agent; C) The polymer colloid containing the in-situ dispersing template agent is sequentially precipitated, washed, and spray-dried to obtain a primary dry powder; D) After the primary dry powder is pulverized and sieved, it is mixed with a dry powder flow aid to obtain a fast-dissolving salt-resistant drag-reducing powder.

8. The preparation method according to claim 7, characterized in that, The copolymerization reaction is carried out under a protective atmosphere, at a temperature of 10-20°C, for 3-5 hours. The spray drying process conditions are as follows: centrifugal atomization is used, the atomizing disc speed is 12000-18000 rpm, the atomization pressure is 0.4-0.8MPa, the inlet air temperature is controlled at 110-130℃, and the outlet air temperature is controlled at 65-75℃.

9. The preparation method according to claim 7, characterized in that, The mass of the dry powder flow aid accounts for 0.8% to 1.5% of the mass of the primary dried powder.

10. A high-salinity fracturing fluid, characterized in that, It includes the fast-dissolving salt-resistant drag-reducing powder for fracturing fluid as described in any one of claims 1 to 6, or the fast-dissolving salt-resistant drag-reducing powder for fracturing fluid prepared by the preparation method described in any one of claims 7 to 9.

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