Drag reducer for shear-resistant high-temperature-resistant salt-resistant fracturing fluid as well as preparation method and application of drag reducer

Abstract

The invention discloses a shear-resistant high-temperature-resistant salt-resistant drag reducer for a fracturing fluid, which is prepared from the following components: 14 to 19.5 percent of acrylamide, 3.5 to 4.8 percent of 2-acrylamide-2-methylpropanesulfonic acid, 3.5 to 4.8 percent of sodium p-styrenesulfonate, 1.5 to 2.5 percent of hexadecyl dimethyl allyl ammonium chloride, 1.5 to 2.5 percent of acryloylmorpholine, 0.05 to 0.14 percent of cosolvent urea, 0.025 to 0.07 percent of chelating agent ethylene diamine tetraacetic acid tetrasodium salt, 0.05 to 0.18 percent of initiator azobis (isobutylamidine hydrochloride) and the balance of water. And the balance of water. The invention further discloses a preparation method and application of the drag reducer for the shear-resistant high-temperature-resistant salt-resistant fracturing fluid. The drag reducer for the shear-resistant, high-temperature-resistant and salt-resistant fracturing fluid provided by the invention solves the problem that the drag reduction capability of the existing drag reducer is reduced under the conditions of high temperature, high salinity and on-site high shear rate.

Description

Technical Field

[0001] This invention belongs to the field of fracturing and stimulation technology for old oil and gas reservoirs, specifically relating to drag-reducing agents for shear-resistant, high-temperature-resistant, and salt-resistant fracturing fluids. This invention also relates to the preparation method and application of the aforementioned drag-reducing agents for shear-resistant, high-temperature-resistant, and salt-resistant fracturing fluids. Background Technology

[0002] Tight oil and gas, along with other low-permeability / ultra-low-permeability and low-grade resources, are important alternative energy sources, with very abundant reserves, accounting for over 60%. Shale oil and gas are unconventional natural gas resources with enormous potential in recent years and have become a hot area for global oil and gas exploration and development.

[0003] For the initial and subsequent repeated stimulation of shale oil and gas reservoirs, slickwater fracturing technology is the main technique used both domestically and internationally. Drag reducers are the most important additives in slickwater fracturing fluids and are key components of the slickwater fracturing fluid system. In the slickwater system, they can significantly reduce friction, effectively alleviate the high-pressure requirements of fracturing equipment, increase the net pressure on the reservoir rock, and improve fracturing performance. However, in current field operations, high-salinity groundwater is often used for fluid preparation, and the high formation temperature leads to a significant decline in the performance of conventional slickwater drag reducers. Furthermore, slickwater fracturing involves large fluid volumes, with shear rates within the tubing reaching 1000-3000 s⁻¹. Ordinary drag reducers have poor shear resistance, and their molecular chains are prone to breakage. Therefore, developing a shear-resistant, high-temperature-resistant, and salt-resistant drag reducer is essential.

[0004] Chinese invention patent CN108865101A, filed on June 22, 2018, entitled "A drag-reducing agent for high-temperature and high-mineralization slickwater fracturing fluid and its preparation method," discloses a drag-reducing agent for high-temperature and high-mineralization slickwater fracturing fluid and its preparation method. This drag-reducing agent can exhibit good drag-reducing effects at 130℃, 150,000 mineralization, and 170 s⁻¹ shear rate. Chinese invention patent CN114835105A, filed on May 20, 2022, entitled "A method for preparing carbon dots with high-temperature and salt resistance and drag-reducing properties, its products, and applications," discloses a method for preparing carbon dots with high-temperature and salt resistance and drag-reducing properties, its products, and applications. This drag-reducing agent can effectively reduce drag under conditions of 90℃, 20 wt% NaCl, and 3 wt% CaCl₂. Chinese invention patent CN105777984A, filed on May 16, 2016, entitled "A Temperature- and Salt-Resistant Brine Pipeline Drag Reduction Agent and Its Preparation Method," discloses a temperature- and salt-resistant brine pipeline drag reduction agent and its preparation method. The drag reduction agent described achieves a drag reduction rate of 45.3% in simulated brine at 25°C, a flow rate of 960 L / h, a salt content of 150 g / L, and an agent dosage of 20 ppm. However, none of the aforementioned drag reduction agents have demonstrated effective drag reduction capabilities at higher temperatures, higher salt concentrations, or higher shear rates. Summary of the Invention

[0005] The purpose of this invention is to provide a drag-reducing agent for shear-resistant, high-temperature and salt-resistant fracturing fluids, which solves the problem that the drag-reducing ability of existing drag-reducing agents decreases under high temperature, high salinity and high shear rate conditions in the field.

[0006] The second objective of this invention is to provide a method for preparing the above-mentioned drag-reducing agent for shear-resistant, high-temperature resistant, and salt-resistant fracturing fluid.

[0007] A third objective of this invention is to provide the application of the above-mentioned drag-reducing agent for shear-resistant, high-temperature-resistant, and salt-resistant fracturing fluids.

[0008] The first technical solution adopted in this invention is a drag-reducing agent for shear-resistant, high-temperature resistant, and salt-resistant fracturing fluid, comprising the following components: 14-19.5% acrylamide, 3.5-4.8% 2-acrylamido-2-methylpropanesulfonic acid, 3.5-4.8% sodium styrene sulfonate, 1.5-2.5% hexadecyl dimethyl allyl ammonium chloride, 1.5-2.5% acryloylmorpholine, 0.05-0.14% urea as a co-solvent, 0.025-0.07% tetrasodium ethylenediaminetetraacetate as a chelating agent, 0.05-0.18% azobisisobutyramidine hydrochloride as an initiator, with the balance being water.

[0009] The second technical solution adopted in this invention is a method for preparing a drag-reducing agent for shear-resistant, high-temperature-resistant, and salt-resistant fracturing fluid, the specific steps of which are as follows: S1. Weigh out acrylamide, 2-acrylamide-2-methylpropanesulfonic acid, sodium styrene sulfonate, hexadecyl dimethyl allyl ammonium chloride, acryloylmorpholine, cosolvent urea, chelating agent tetrasodium ethylenediaminetetraacetate, initiator azobisisobutyramidine hydrochloride, and the remainder is deionized water. S2. Add acrylamide, 2-acrylamide-2-methylpropanesulfonic acid, and sodium styrene sulfonate to deionized water. Stir until fully dispersed for the first time, adjust the pH, add acrylomorpholine, and stir until fully dispersed for the second time to obtain a dispersion solution. S3. Transfer the dispersion to a container and reflux it. Under a nitrogen atmosphere, add hexadecyl dimethyl allyl ammonium chloride, co-solvent urea and initiator azobisisobutyramidine hydrochloride in sequence to obtain the reflux solution. S4. After cooling the reflux liquid to 50°C, add tetrasodium ethylenediaminetetraacetate and stir to react, obtaining a gel-like liquid. S5. Cool the gel-like liquid to room temperature and dilute to dissolve. Add anhydrous acetone to obtain a precipitate. Soak the precipitate in acetone and purify it. Vacuum dry and pulverize to obtain a drag-reducing agent for shear-resistant, high-temperature resistant, and salt-resistant fracturing fluid.

[0010] The invention is further characterized by: S1 contains, by mass percentage, 14-19.5% acrylamide, 3.5-4.8% 2-acrylamido-2-methylpropanesulfonic acid, 3.5-4.8% sodium styrene sulfonate, 1.5-2.5% hexadecyl dimethyl allyl ammonium chloride, 1.5-2.5% acryloylmorpholine, 0.05-0.14% urea as a cosolvent, 0.025-0.07% tetrasodium ethylenediaminetetraacetate as a chelating agent, 0.05-0.18% azobisisobutyramidine hydrochloride as an initiator, and the remainder is deionized water.

[0011] In S2, the solution pH is adjusted to 7-8 using a pH adjuster before adding acrylomorpholine.

[0012] The specific method for S3 is as follows: the dispersion solution is transferred to a container for reflux and stirring is maintained at a stirring speed of 500 rpm-1500 rpm. Nitrogen gas is purged for 15 min, hexadecyl dimethyl allyl ammonium chloride is added, the temperature is raised to 70°C, urea as a cosolvent and azobisisobutyramidine hydrochloride are added, nitrogen gas is purged for another 35 min, and the reaction is carried out for 4-6 h to obtain the reflux solution.

[0013] The stirring rate in S4 is 500 rpm-1500 rpm, and the stirring reaction time in S4 is 2-2.5 h.

[0014] The specific steps of S5 are as follows: The gel-like liquid was cooled to room temperature, diluted and dissolved with water, and then anhydrous acetone was added to precipitate it. The precipitate was soaked in acetone for 24-30 hours, and then purified by reflux extraction with ethanol for 12 hours to obtain the purified product.

[0015] The third technical solution adopted in this invention is the application of a drag-reducing agent for shear-resistant, high-temperature-resistant, and salt-resistant fracturing fluid in slickwater fracturing fluid.

[0016] The beneficial effects of this invention are: (1) The drag-reducing agent for shear-resistant, high-temperature and salt-resistant fracturing fluid of the present invention is a high-temperature resistant, salt-resistant and shear-resistant polymer made from acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, sodium styrene sulfonate, hexadecyl dimethyl allyl ammonium chloride, acryloylmorpholine, urea and tetrasodium ethylenediaminetetraacetate. It has good dispersion and drag-reducing properties under high temperature and high salt conditions. (2) The drag reducer polymer chain of the shear-resistant, high-temperature and salt-resistant fracturing fluid of the present invention contains amide groups, sulfonic acid groups and other groups with strong hydrophilicity, which can form strong hydrogen bonds with water, increasing the water solubility of the copolymer and improving the stability of the drag reducer in slickwater fracturing fluid; the presence of aromatic rings improves the high temperature resistance and salt resistance of the molecule. Therefore, the drag reducer can adapt to the complex working conditions in the oilfield, disperse quickly in salt water, and play a good drag reduction role at high temperature. (3) The long alkyl hydrophobic chain of the drag-reducing agent for shear-resistant, high-temperature and salt-resistant fracturing fluid of the present invention can form a strong and tough hydrophobic association structure in slickwater fracturing fluid, which improves the shear resistance of the drag-reducing agent polymer and further enhances the temperature and salt resistance of the drag-reducing agent. (4) The preparation method of the drag-reducing agent for shear-resistant, high-temperature and salt-resistant fracturing fluid of the present invention is to wash with acetone and extract with ethanol, so that the drag-reducing agent for shear-resistant, high-temperature and salt-resistant fracturing fluid prepared has fewer impurities and the amount of drag-reducing agent is small. Depending on different construction conditions, the drag-reducing agent can play an excellent drag-reducing role with an addition of 0.05%-0.1% of the fracturing fluid mass. Detailed Implementation

[0017] The present invention will now be described in detail with reference to specific embodiments.

[0018] A drag-reducing agent for shear-resistant, high-temperature, and salt-resistant fracturing fluid comprises the following components: 14-19.5% acrylamide, 3.5-4.8% 2-acrylamido-2-methylpropanesulfonic acid, 3.5-4.8% sodium styrene sulfonate, 1.5-2.5% hexadecyl dimethyl allyl ammonium chloride, 1.5-2.5% acryloylmorpholine, 0.05-0.14% urea as a co-solvent, 0.025-0.07% tetrasodium ethylenediaminetetraacetate as a chelating agent, 0.05-0.18% azobisisobutyramidine hydrochloride as an initiator, with the balance being water.

[0019] The preparation method of drag-reducing agent for shear-resistant, high-temperature-resistant, and salt-resistant fracturing fluid is as follows: S1. Weigh out the following components by mass percentage: 14-19.5% acrylamide, 3.5-4.8% 2-acrylamido-2-methylpropanesulfonic acid, 3.5-4.8% sodium styrene sulfonate, 1.5-2.5% hexadecyl dimethyl allyl ammonium chloride, 1.5-2.5% acryloylmorpholine, 0.05-0.14% urea (co-solvent), 0.025-0.07% tetrasodium ethylenediaminetetraacetate (chelating agent), 0.05-0.18% azobisisobutyramidine hydrochloride (initiator), with the remainder being deionized water. S2. Add acrylamide, 2-acrylamide-2-methylpropanesulfonic acid, and sodium styrene sulfonate to deionized water. Stir for the first time until fully dispersed. Adjust the pH of the solution to 7-8 with a pH adjuster, then add acrylomorpholine. Stir for the second time until fully dispersed to obtain a dispersion solution. S3. Transfer the dispersion to a three-necked flask and reflux it. Keep stirring at a speed of 500-1500 rpm and purge with nitrogen for 15 min. Add hexadecyl dimethyl allyl ammonium chloride, heat to 70°C, add urea as a cosolvent and azobisisobutyramidine hydrochloride as an initiator, and continue purging with nitrogen for 35 min. React for 4-6 h to obtain the reflux solution.

[0020] S4. After cooling the reflux liquid to 50℃, add tetrasodium ethylenediaminetetraacetate and stir the reaction at a stirring speed of 500rpm-1500rpm for 2~2.5h to obtain a pale yellow gel-like liquid. S5. Cool the gel-like liquid to room temperature, dilute and dissolve the gel-like liquid with water, add anhydrous acetone to precipitate, obtain the precipitate, soak the precipitate in anhydrous acetone for 24-30 hours, then reflux and purify with ethanol for 12 hours, vacuum dry for 3 days, and pulverize to obtain a light yellow powder, which is the shear-resistant, high-temperature resistant, and salt-resistant drag-reducing agent for fracturing fluid.

[0021] According to the present invention, the above-mentioned drag-reducing agent for shear-resistant, high-temperature and salt-resistant fracturing fluid can achieve excellent drag reduction effect when applied in slickwater fracturing fluid at an addition of 0.05%-0.1% by mass of fracturing fluid.

[0022] Example 1 The preparation method of drag-reducing agent for shear-resistant, high-temperature-resistant, and salt-resistant fracturing fluid is as follows: S1. Weigh 20g acrylamide, 5g 2-acrylamide-2-methylpropanesulfonic acid, and 5g sodium styrene sulfonate, add them to 75g deionized water, stir until fully dispersed, add pH adjuster to adjust pH to 7-8, then add 2.5g acrylomorpholine in proportion, stir until fully dispersed, and obtain dispersion; S2. Transfer the dispersion to a three-necked flask and reflux it. Keep stirring at a speed of 500 rpm and purge with nitrogen for 15 min. Add 2.5 g of hexadecyl dimethyl allyl ammonium chloride according to the ratio. Heat to 70 °C and add 0.14 g of cosolvent urea and 0.14 g of initiator azobisisobutyramidine hydrochloride. Continue to purge with nitrogen for 35 min and react for 4 h. S3. Cool the above solution to 50°C, add 0.07g of tetrasodium ethylenediaminetetraacetate, keep stirring at a stirring rate of 500rpm, and continue the reaction for 2h to obtain a pale yellow gel-like liquid. S4. After the above gel liquid cools to room temperature, dilute and dissolve it with water, precipitate it with anhydrous acetone to obtain a precipitate, soak the precipitate in acetone for 30 hours and then reflux and purify it with ethanol for 12 hours to obtain the purified product. S5. After purification, the purified product obtained in S4 is vacuum dried for 3 days. The light yellow powder obtained after pulverization is the drag-reducing agent for shear-resistant, high-temperature and salt-resistant fracturing fluid.

[0023] Weigh 1g of drag reducer by mass percentage, and slowly add it to 1000g of water under stirring conditions. After stirring and dissolving for 3-5 minutes, add 2g of drainage aid YD-3078 and 2g of anti-swelling agent HJZ-302 and stir to mix. Let stand for 5 minutes to obtain shear-resistant, high-temperature resistant, and high-salt slickwater fracturing fluid.

[0024] According to the construction design, the on-site mixing truck sequentially draws in the drainage aid, anti-swelling agent, and drag-reducing agent for shear-resistant, high-temperature, and salt-resistant fracturing fluid in appropriate proportions, mixes them thoroughly on the mixing truck, and then transfers them to the storage tank. During construction, the sand mixing truck draws in the above liquids, adds proppant, mixes them, and then injects them into the formation through the fracturing truck. The entire process can be carried out while mixing the fluids.

[0025] Example 2 The preparation method of drag-reducing agent for shear-resistant, high-temperature-resistant, and salt-resistant fracturing fluid is as follows: S1. Weigh 16g acrylamide, 4g 2-acrylamide-2-methylpropanesulfonic acid, and 4g sodium styrene sulfonate, add them to 82g deionized water, stir until fully dispersed, add pH adjuster to adjust pH to 7-8, then add 1.8g acrylomorpholine in proportion, stir until fully dispersed, and obtain dispersion; S2. Transfer the dispersion to a three-necked flask and reflux it. Keep stirring at a speed of 1500 rpm and purge with nitrogen for 15 min. Add 2 g of hexadecyl dimethyl allyl ammonium chloride according to the ratio, heat to 70 °C, add 0.14 g of cosolvent urea and 0.2 g of initiator azobisisobutyramidine hydrochloride, continue to purge with nitrogen for 35 min, and react for 6 h. S3. Cool the above solution to 50°C, add 0.03g of tetrasodium ethylenediaminetetraacetate, keep stirring at a stirring rate of 1500rpm, and continue the reaction for 2h to obtain a pale yellow gel-like liquid. S4. After the above gel liquid cools to room temperature, dilute and dissolve it with water, precipitate it with anhydrous acetone to obtain a precipitate, soak the precipitate in acetone for 30 hours and then reflux and purify it with ethanol for 12 hours to obtain the purified product. S5. After purification, the purified product obtained in S4 is vacuum dried for 3 days. The light yellow powder obtained after pulverization is the drag reducer for shear-resistant, high-temperature and salt-resistant fracturing fluid.

[0026] Example 3 The preparation method of drag-reducing agent for shear-resistant, high-temperature-resistant, and salt-resistant fracturing fluid is as follows: S1. Weigh 21g acrylamide, 4.5g 2-acrylamide-2-methylpropanesulfonic acid, and 4.5g sodium styrene sulfonate, add them to 76g deionized water, stir until fully dispersed, add pH adjuster to adjust pH to 7-8, then add 1.7g acrylomorpholine in proportion, stir until fully dispersed, and obtain dispersion; S2. Transfer the dispersion to a three-necked flask and reflux it. Keep stirring at a speed of 1000 rpm and purge with nitrogen for 15 min. Add 1.7 g of hexadecyl dimethyl allyl ammonium chloride according to the ratio. Heat to 70 °C, add 0.05 g of cosolvent urea and 0.07 g of initiator azobisisobutyramidine hydrochloride, and continue to purge with nitrogen for 35 min. React for 5 h. S3. Cool the above solution to 50°C, add 0.05g of tetrasodium ethylenediaminetetraacetate, keep stirring at a stirring speed of 1000rpm, and continue the reaction for 2.5h to obtain a pale yellow gel-like liquid. S4. After the above gel liquid cools to room temperature, dilute and dissolve it with water, precipitate it with anhydrous acetone to obtain a precipitate, soak the precipitate in acetone for 30 hours and then reflux and purify it with ethanol for 12 hours to obtain the purified product. S5. After purification, the purified product obtained in S4 is vacuum dried for 3 days. The light yellow powder obtained after pulverization is the drag reducer for shear-resistant, high-temperature and salt-resistant fracturing fluid.

[0027] Example 4 The preparation method of the drag-reducing agent for shear-resistant, high-temperature and salt-resistant fracturing fluid is the same as that in Example 1, except that the mass of the substances weighed is different. Specifically, 18g of acrylamide, 5g of 2-acrylamido-2-methylpropanesulfonic acid, 5g of sodium styrene sulfonate, 75g of deionized water, 2g of acryloylmorpholine, 2g of hexadecyl dimethyl allyl ammonium chloride, 0.1g of co-solvent urea, 0.14g of initiator azobisisobutyramidine hydrochloride, and 0.05g of tetrasodium ethylenediaminetetraacetate are weighed. The remaining process conditions and steps are the same as in Example 1. The resulting light yellow powder is the drag-reducing agent for shear-resistant, high-temperature and salt-resistant fracturing fluid.

[0028] The drag-reducing agent for shear-resistant, high-temperature-resistant, and salt-resistant fracturing fluid prepared in Example 1 was subjected to performance testing, as detailed below: Test 1 Take 2g of the shear-resistant, high-temperature, and salt-resistant drag-reducing agent for fracturing fluid prepared in Example 1, and slowly add it to 1000g of a 30wt% NaCl aqueous solution under stirring, stirring thoroughly until completely dissolved. Using a HAAKE MARS III rheometer, the above solution is sheared at 150°C and a shear rate of 1000 s⁻¹ for 30 min. The apparent viscosity of the solution decreases from 46.85 mPa·s before shearing to 35.76 mPa·s after shearing, with a retention rate of 76.3%. This indicates that under high temperature, high salt, and high shear rate conditions, the shear-resistant, high-temperature, and salt-resistant drag-reducing agent for fracturing fluid prepared in this example can still maintain good dispersion in water and effectively maintain the viscosity of the solution.

[0029] Test 2 Take 2g of the shear-resistant, high-temperature-resistant, and salt-resistant drag-reducing agent for fracturing fluid prepared in Example 1, and slowly add it to 1000g of 30wt% NaCl aqueous solution under stirring, stirring thoroughly until completely dissolved. According to NB / T 14003.1—2015 "Shale Gas Fracturing Fluids Part 1: Slickwater Performance Indicators and Evaluation Methods", fill a multi-functional flow loop apparatus or a similar product's base fluid tank with clean water, and measure the stable pressure difference as the clean water flows through the pipeline. The drag reduction rate of the slickwater system base fluid can be calculated from the pressure difference. Tests were conducted at 150℃ in a straight pipe with a diameter of 10mm and a length of 2m, using different flow rates. The drag reduction rates are shown in Table 1 below. Table 1. Resistance reduction test

[0030] It can be seen that under the conditions of 150℃ and 30wt% NaCl, the drag-reducing agent can maintain a drag reduction rate of more than 67%, and can still maintain excellent drag reduction effect under high flow rate. This demonstrates the temperature resistance, salt resistance and shear resistance of the shear-resistant, high-temperature and salt-resistant fracturing fluid drag-reducing agent described in this invention, which can meet the needs of complex working conditions in oilfields.

Claims

1. A drag-reducing agent for shear-resistant, high-temperature-resistant, and salt-resistant fracturing fluids, characterized in that, It comprises the following components: 14-19.5% acrylamide, 3.5-4.8% 2-acrylamido-2-methylpropanesulfonic acid, 3.5-4.8% sodium styrene sulfonate, 1.5-2.5% hexadecyl dimethyl allyl ammonium chloride, 1.5-2.5% acryloylmorpholine, 0.05-0.14% urea as a cosolvent, 0.025-0.07% tetrasodium ethylenediaminetetraacetate as a chelating agent, 0.05-0.18% azobisisobutyramidine hydrochloride as an initiator, and the balance being water.

2. A method for preparing a drag-reducing agent for shear-resistant, high-temperature-resistant, and salt-resistant fracturing fluid, characterized in that, The specific steps are as follows: S1. Weigh out acrylamide, 2-acrylamide-2-methylpropanesulfonic acid, sodium styrene sulfonate, hexadecyl dimethyl allyl ammonium chloride, acryloylmorpholine, cosolvent urea, chelating agent tetrasodium ethylenediaminetetraacetate, initiator azobisisobutyramidine hydrochloride, and the remainder is deionized water. S2. Add acrylamide, 2-acrylamide-2-methylpropanesulfonic acid, and sodium styrene sulfonate to deionized water. Stir until fully dispersed for the first time, adjust the pH, add acrylomorpholine, and stir until fully dispersed for the second time to obtain a dispersion solution. S3. Transfer the dispersion to a container and reflux it. Under a nitrogen atmosphere, add hexadecyl dimethyl allyl ammonium chloride, co-solvent urea and initiator azobisisobutyramidine hydrochloride in sequence to obtain the reflux solution. S4. After cooling the reflux liquid to 50°C, add tetrasodium ethylenediaminetetraacetate and stir to react, obtaining a gel-like liquid. S5. Cool the gel-like liquid to room temperature and dilute to dissolve. Add anhydrous acetone to obtain a precipitate. Soak the precipitate in acetone and purify it. Vacuum dry and pulverize to obtain a drag-reducing agent for shear-resistant, high-temperature resistant, and salt-resistant fracturing fluid.

3. The preparation method of the drag-reducing agent for shear-resistant, high-temperature resistant, and salt-resistant fracturing fluid as described in claim 2, characterized in that, The S1 component, by mass percentage, comprises 14-19.5% acrylamide, 3.5-4.8% 2-acrylamido-2-methylpropanesulfonic acid, 3.5-4.8% sodium styrene sulfonate, 1.5-2.5% hexadecyl dimethyl allyl ammonium chloride, 1.5-2.5% acryloylmorpholine, 0.05-0.14% urea as a cosolvent, 0.025-0.07% tetrasodium ethylenediaminetetraacetate as a chelating agent, 0.05-0.18% azobisisobutyramidine hydrochloride as an initiator, with the remainder being deionized water.

4. The preparation method of the drag-reducing agent for shear-resistant, high-temperature resistant, and salt-resistant fracturing fluid as described in claim 2, characterized in that, In step S2, the solution pH is adjusted to 7-8 using a pH adjuster before acrylomorpholine is added.

5. The preparation method of the drag-reducing agent for shear-resistant, high-temperature resistant, and salt-resistant fracturing fluid according to claim 2, characterized in that, The specific method of S3 is as follows: the dispersion solution is transferred to a container for reflux and condensation, and stirring is maintained at a stirring rate of 500 rpm-1500 rpm. Nitrogen gas is purged for 15 min, hexadecyl dimethyl allyl ammonium chloride is added, the temperature is raised to 70°C, urea as a cosolvent and azobisisobutyramidine hydrochloride are added, nitrogen gas is purged for another 35 min, and the reaction is carried out for 4-6 h to obtain the reflux liquid.

6. The preparation method of the drag-reducing agent for shear-resistant, high-temperature resistant, and salt-resistant fracturing fluid according to claim 2, characterized in that, The stirring rate in S4 is 500 rpm to 1500 rpm, and the stirring reaction time in S4 is 2 to 2.5 h.

7. The preparation method of the drag-reducing agent for shear-resistant, high-temperature resistant, and salt-resistant fracturing fluid according to claim 2, characterized in that, The specific steps of S5 are as follows: The gel-like liquid was cooled to room temperature, diluted and dissolved with water, and then anhydrous acetone was added to precipitate it. The precipitate was soaked in acetone for 24-30 hours, and then purified by reflux extraction with ethanol for 12 hours to obtain the purified product.

8. The application of the drag-reducing agent for shear-resistant, high-temperature resistant, and salt-resistant fracturing fluid according to any one of claims 1 to 7 in slickwater fracturing fluid.

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