A polyamide drag reducer and a method of making the same

Abstract

The application discloses a kind of polyamide drag reduction agent and preparation method thereof, specifically related to high polymer functional material technical field, the drag reduction agent is the polyamide copolymer containing amide bond, by diacid, diamine, compound containing polyether chain segment and end-capping agent are prepared by polycondensation reaction, weight average molecular weight is 50,000~1,500,000 Da.Its preparation method includes: diacid and diamine are precondensation polymerization to obtain amino-terminated polyamide prepolymer;Melt polycondensation is carried out by adding compound containing polyether chain segment;End-capping agent is added to carry out end-capping reaction;Post-processing is obtained.The drag reduction agent of the application has good temperature resistance, salt resistance, shear recovery resistance, fast solubility and biodegradability, and can be used for water-based fracturing fluid or drag reduction in oil and gas pipeline transportation.

Description

Technical Field

[0001] This invention relates to the field of polymer functional materials technology, and more specifically, to a polyamide drag-reducing agent and its preparation method. Background Technology

[0002] Drag reducers are a class of polymeric compounds that can significantly reduce the frictional resistance of fluid turbulence, and are widely used in shale gas fracturing slickwater and oil and gas pipeline transportation. Polyacrylamide and its derivatives are currently the most widely used water-soluble drag reducers, exhibiting excellent drag reduction performance in clean water. However, as the development of deep shale oil and gas resources progresses towards extreme conditions such as high temperature, high salinity, and high shear, existing polyacrylamide-based drag reducers have revealed the following technical shortcomings:

[0003] 1. Insufficient temperature resistance: The temperature of deep shale gas reservoirs can reach above 120℃. Polyacrylamide is prone to thermal oxidation degradation under high temperature conditions, and the molecular chain breakage leads to a significant decrease in drag reduction performance.

[0004] 2. Poor salt resistance: Salt ions in high-mineralization backflow solutions compress polymer molecular chains through the polyelectrolyte effect, leading to molecular chain shrinkage, aggregation, or even precipitation, resulting in a significant decrease in drag reduction rate;

[0005] 3. Poor shear resistance: The main chain of polyacrylamide has a C-C bond structure, which is prone to irreversible mechanical degradation in a strong shear field, and the drag reduction performance continues to decrease with the shearing process.

[0006] 4. There is a contradiction between dissolution rate and drag reduction efficiency: Powdered polyacrylamide has a slow dissolution rate, which makes it difficult to meet the process requirements of on-site mixing in shale gas fracturing; although emulsion products dissolve faster, they require the addition of phase inversion agents and have poor storage stability.

[0007] 5. Insufficient environmental friendliness: Polyacrylamide drag reducers have limited biodegradability, and their residue problem in reservoirs has not been effectively solved.

[0008] To address the aforementioned issues, existing research primarily focuses on copolymerization modification of polyacrylamide, such as introducing temperature- and salt-resistant monomers like 2-acrylamido-2-methylpropanesulfonic acid, or optimizing it through nanocomposites and hydrophobic association. However, these modification schemes are still based on the polyacrylamide CC backbone, and core issues such as high-temperature thermal stability and resistance to irreversible shear degradation have not been fundamentally resolved.

[0009] Therefore, developing a novel drag-reducing agent that combines good temperature resistance, salt resistance, shear resistance, rapid solubility, and biodegradability is of great practical significance. Summary of the Invention

[0010] To achieve the above objectives, the present invention provides the following technical solution:

[0011] On one hand, the present invention provides a polyamide drag-reducing agent, wherein the drag-reducing agent is a polyamide copolymer containing amide bonds, and the polyamide copolymer is prepared by polycondensation reaction of raw materials containing the following monomers:

[0012] (a) At least one dicarboxylic acid;

[0013] (b) at least one diamine;

[0014] (c) A compound containing polyether segments, wherein the compound containing polyether segments is selected from at least one of polyether diamine and monomethoxy polyethylene glycol, wherein the polyether diamine is embedded in the main chain of the polyamide copolymer through its two end amino groups, and the monomethoxy polyethylene glycol is attached to the main chain of the polyamide copolymer as a side chain through its terminal hydroxyl groups;

[0015] (d) End-capping agent, wherein the end-capping agent is selected from long-chain monocarboxylic acids of C8 to C24;

[0016] The polyamide copolymer has a weight-average molecular weight of 50,000 to 1,500,000 Da.

[0017] Preferably, the dicarboxylic acid is selected from at least one of aliphatic dicarboxylic acids of C4 to C20, alicyclic dicarboxylic acids of C5 to C12, and aromatic dicarboxylic acids of C6 to C14.

[0018] Preferably, the dicarboxylic acid is at least one selected from adipic acid, sebacic acid, dodecanoic acid, and hydrogenated dimer acid.

[0019] Preferably, the diamine is selected from at least one of C2-C12 aliphatic diamines and diamines containing tertiary amine groups.

[0020] Preferably, the diamine is hexamethylenediamine.

[0021] Preferably, the polyether diamine has a molecular weight of 230 to 2000 Da.

[0022] Preferably, the capping agent is at least one selected from stearic acid, oleic acid, and docosanoic acid.

[0023] On the other hand, the present invention also provides a method for preparing a polyamide drag-reducing agent, which includes the following steps:

[0024] S1. Pre-condensation reaction: Under inert gas protection, a dicarboxylic acid and a diamine are mixed at a molar ratio of 1:1.01 to 1.03 and reacted at 180 to 240°C and 0.5 to 2.0 MPa for 2 to 6 hours to obtain an amino-terminated polyamide prepolymer.

[0025] S2, Melt polycondensation: Add a compound containing polyether segments to the prepolymer obtained in step S1, and react for 3 to 8 hours at 200 to 260°C and a vacuum degree ≤100Pa to obtain a polyamide-polyether copolymer;

[0026] S3, End-capping reaction: Add an end-capping agent to the copolymer obtained in step S2 and react at 180-220°C for 1-3 hours;

[0027] S4. Post-processing: Dissolve, filter, dry and pulverize the product obtained in step S3 to obtain the polyamide drag reducer.

[0028] Preferably, the amount of the compound containing polyether segments added in step S2 is 5 to 30 wt% of the amount of the prepolymer obtained in step S1.

[0029] Preferably, the amount of end-capping agent added in step S3 is based on the total molar amount of terminal amino groups in the terminal amino polyamide prepolymer obtained in step S1, and the molar amount of carboxyl groups contained in the end-capping agent is 50% to 300% of the total molar amount of terminal amino groups.

[0030] The technical effects and advantages of this invention are as follows:

[0031] 1. This invention provides a polyamide drag reducer, which is copolymerized by introducing polyether segments into the polyamide molecular chain. Without changing the thermal stability of the polyamide backbone, the resulting polyamide copolymer is endowed with good water solubility. At the same time, long-chain alkyl end-capping groups are grafted onto the molecular chain ends. By utilizing the synergistic effect of the hydrophobic association of the long-chain alkyl groups and the hydrogen bonding between the polyamide molecular chains, the drag reducer can maintain the extended molecular chain conformation in a high-saltification brine environment, and has excellent temperature resistance and salt resistance.

[0032] 2. The polyamide drag reducer of this invention utilizes the intermolecular hydrogen bond network formed by amide bonds in its molecular structure, which enables the molecular chain to achieve conformational recovery through the reformation of hydrogen bonds after high-speed shearing, thereby effectively reducing the irreversible loss of drag reduction performance caused by shearing. At the same time, the introduction of polyether segments increases the hydrophilicity of the polymer, giving the product the characteristic of rapid dissolution, which meets the requirements for on-site online mixing in shale gas fracturing.

[0033] 3. The molecular chain of the polyamide drag reducer of the present invention contains amide bonds. These chemical bonds can be gradually hydrolyzed by amidases secreted by microorganisms in the natural environment. The degradation products are small molecule organic acids and amine compounds, which can be further mineralized by microorganisms into carbon dioxide and water. It has good environmental biodegradability, which reduces the residual risk of drag reducers in reservoirs and their potential impact on the ecological environment. Attached Figure Description

[0034] Figure 1 This is a flowchart of the preparation method of the present invention. Detailed Implementation

[0035] The present invention will be described in detail below with reference to specific embodiments. These embodiments are for illustrative purposes only and should not be construed as limiting the scope of the invention.

[0036] Example 1

[0037] This embodiment provides a polyamide drag-reducing agent, with the following specific raw materials:

[0038] Sebacic acid, CAS No. 111-20-6: 202.3g, i.e. 1.0mol;

[0039] Hexamethylenediamine, CAS No. 124-09-4: 118.6g, i.e. 1.02mol;

[0040] Polyether diamine, using Huntsman's JEFFAMINE® D-1000 product, with an average molecular weight of approximately 1000, is used in an amount of 60g;

[0041] Dodecanoic acid, CAS No. 112-85-6: 16.8g, i.e. 0.05mol;

[0042] Deionized water: 180mL.

[0043] This embodiment also provides a method for preparing a polyamide drag-reducing agent, as shown in the attached figure. Figure 1 As shown, the specific steps of the preparation method in this embodiment are as follows:

[0044] S1, Pre-condensation reaction

[0045] 202.3 g of sebacic acid and 118.6 g of hexamethylenediamine were added to a 2 L stainless steel reactor, along with 180 mL of deionized water. The air inside the reactor was replaced three times with high-purity nitrogen gas (99.999% purity). Under nitrogen protection, the temperature was raised to 215 °C, and the reaction pressure was controlled at 1.2 MPa. The reaction was maintained at this temperature for 4 hours. After the reaction was completed, the atmosphere was slowly vented to atmospheric pressure to obtain an amino-terminated polyamide prepolymer.

[0046] S2, Melt polycondensation:

[0047] Add 60g of polyether diamine to the prepolymer obtained in step S1, heat to 245°C, start the vacuum system, and evacuate to a vacuum degree not exceeding 50Pa. Melt polycondensation reaction is carried out at 245°C and a vacuum degree not exceeding 50Pa for 5 hours to obtain polyamide-polyether copolymer. In this embodiment, polyether diamine is embedded in the main chain of polyamide copolymer by reacting with the end groups of polyamide prepolymer through its two end amino groups.

[0048] S3, End-capping reaction:

[0049] Add 16.8 g of docosanoic acid to the copolymer obtained in step S2, and continue the reaction at 210 °C for 2 h to end-cap the copolymer, and obtain the crude product of end-capped polyamide-polyether copolymer.

[0050] S4. Post-processing:

[0051] After cooling the crude product obtained in step S3 to room temperature, it is dissolved in a mixed solvent of ethanol and isopropanol with a volume ratio of 1:1. The mixture is stirred until completely dissolved, filtered to remove insoluble matter, and the solvent is recovered by vacuum distillation of the filtrate. The resulting solid product is dried in a vacuum drying oven at 80°C for 14 hours to constant weight, and then pulverized through a 120-mesh sieve to obtain the polyamide drag reducer.

[0052] In this embodiment, the weight-average molecular weight of the product was determined by gel permeation chromatography, specifically using polystyrene as a standard and hexafluoroisopropanol as the mobile phase. The weight-average molecular weight (Mw) of the drag-reducing agent in Example 1 was determined to be 3.85 × 10⁻⁶. 5 The molecular weight distribution index (PDI) of Da was 2.1. The amine value was determined by potentiometric titration, yielding 8.2 mg KOH / g. The melting point was determined by differential scanning calorimetry (DSC) at a heating rate of 10 °C / min under nitrogen atmosphere, yielding a value of 185 °C.

[0053] Example 2

[0054] This embodiment provides a polyamide drag-reducing agent, with the following specific raw materials:

[0055] Dodecanoic acid, CAS No. 693-23-2: 230.3g, i.e. 1.0mol;

[0056] Hexamethylenediamine, CAS No. 124-09-4: 118.6g, i.e. 1.02mol;

[0057] Polyether diamine, using Huntsman's JEFFAMINE® D-400 product, with an average molecular weight of approximately 400, is used in an amount of 60g;

[0058] Oleic acid, CAS No. 112-80-1: 14.1g, i.e. 0.05mol;

[0059] Deionized water: 150mL.

[0060] This embodiment also provides a method for preparing a polyamide drag-reducing agent, the specific steps of which are as follows:

[0061] S1, Pre-condensation reaction:

[0062] 230.3 g of dodecanoic acid and 118.6 g of hexamethylenediamine were added to a 2 L stainless steel reactor, along with 150 mL of deionized water. The air inside the reactor was purged three times with high-purity nitrogen (99.999% purity). Under nitrogen protection, the temperature was raised to 210 °C, and the reaction pressure was controlled at 1.0 MPa. The reaction was maintained at this temperature for 3.5 h. After the reaction was completed, the atmosphere was slowly vented to atmospheric pressure to obtain an amino-terminated polyamide prepolymer.

[0063] S2, Melt polycondensation:

[0064] Add 60g of polyether diamine to the prepolymer obtained in step S1, heat to 235°C, start the vacuum system, and evacuate to a vacuum degree not exceeding 50Pa. Melt polycondensation reaction is carried out at 235°C and a vacuum degree not exceeding 50Pa for 6 hours to obtain polyamide-polyether copolymer. In this embodiment, polyether diamine is embedded in the main chain of polyamide copolymer by reacting with the end groups of polyamide prepolymer through its two end amino groups.

[0065] S3, End-capping reaction:

[0066] 14.1 g of oleic acid was added to the copolymer obtained in step S2, and the reaction was continued at 200 °C for 2.5 h to end-cap the copolymer, thus obtaining the crude product of end-capped polyamide-polyether copolymer.

[0067] S4. Post-processing:

[0068] The post-processing steps are the same as step S4 in Example 1, to obtain a polyamide drag reducer.

[0069] This embodiment was characterized using the same method as Example 1, and the weight-average molecular weight Mw of the drag-reducing agent in Example 2 was measured to be 2.56 × 10⁻⁶. 5 Da has a molecular weight distribution index (PDI) of 2.3, an amine value of 6.5 mg KOH / g, and a melting point of 152℃.

[0070] Example 3

[0071] This embodiment provides a polyamide drag-reducing agent, with the following specific raw materials:

[0072] Hydrogenated dimer acid, CAS No. 68783-41-5, average molecular weight approximately 570: 570g, i.e. 1.0mol;

[0073] Hexamethylenediamine, CAS No. 124-09-4: 118.6g, i.e. 1.02mol;

[0074] Monomethoxy polyethylene glycol, abbreviated as mPEG, has an average molecular weight of 2000 and a dosage of 100g.

[0075] Stearic acid, CAS No. 57-11-4: 14.2g, i.e. 0.05mol;

[0076] Deionized water: 250mL.

[0077] This embodiment also provides a method for preparing a polyamide drag-reducing agent, the specific steps of which are as follows:

[0078] S1, Pre-condensation reaction:

[0079] 570 g of hydrogenated dimer acid and 118.6 g of hexamethylenediamine were added to a 3 L stainless steel reactor, along with 250 mL of deionized water. The air inside the reactor was replaced three times with high-purity nitrogen gas (99.999% purity). Under nitrogen protection, the temperature was raised to 230 °C, and the reaction pressure was controlled at 1.5 MPa. The reaction was maintained at this temperature for 5 hours. After the reaction was completed, the atmosphere was slowly vented to atmospheric pressure to obtain an amino-terminated polyamide prepolymer.

[0080] S2, Melt polycondensation:

[0081] 100g of monomethoxy polyethylene glycol with an average molecular weight of 2000 was added to the prepolymer obtained in step S1. The temperature was raised to 250°C, the vacuum system was started, and the vacuum was drawn to a vacuum degree of no more than 50Pa. The melt polycondensation reaction was carried out at 250°C and a vacuum degree of no more than 50Pa for 6 hours to obtain a polyamide-polyether copolymer. In this embodiment, the monomethoxy polyethylene glycol reacts with the terminal carboxyl group of the polyamide prepolymer through its terminal hydroxyl group and is connected to the main chain of the polyamide copolymer in the form of a side chain.

[0082] S3, End-capping reaction:

[0083] Add 14.2 g of stearic acid to the copolymer obtained in step S2, and continue the reaction at 220 °C for 2 h to end-cap the copolymer, thereby obtaining the crude product of end-capped polyamide-polyether copolymer.

[0084] S4. Post-processing: The post-processing steps are the same as step S4 in Example 1, to obtain a polyamide drag reducer.

[0085] The drag-reducing agent of Example 3 was characterized using the same method as in Example 1, and its weight-average molecular weight Mw was determined to be 5.12 × 10⁻⁶. 5 Da has a molecular weight distribution index (PDI) of 2.4, an amine value of 4.8 mg KOH / g, and a melting point of 98℃.

[0086] Comparative Example 1

[0087] Comparative Example 1 used a commercially available anionic polyacrylamide drag reducer with a weight-average molecular weight of approximately 8.0 × 10⁻⁶. 6 Da has a degree of hydrolysis of 25%.

[0088] Comparative Example 2

[0089] Comparative Example 2 used a commercially available heat-resistant polyacrylamide drag-reducing agent, which is a copolymer of acrylamide and 2-acrylamido-2-methylpropanesulfonic acid, with a weight-average molecular weight of approximately 6.0 × 10⁻⁶. 6 Da.

[0090] The performance tests for Examples 1-3 and Comparative Examples 1-2 will be conducted as follows:

[0091] 1. Drag Reduction Performance Test: Evaluation was conducted using a pipeline circulation drag reduction test device. This device consists of a storage tank, centrifugal pump, turbine flow meter, differential pressure transmitter, test pipe section, and data acquisition system. The test pipe section has an inner diameter of 10 mm and a length of 5 m. The sample to be tested was prepared as an aqueous solution of a specified concentration. The flow rate was adjusted to achieve a Reynolds number Re of 50,000 within the test pipe section, and the pressure drop across the test pipe section was recorded. The pressure drop of blank water with the same solvent composition as the test sample under the same conditions but without drag-reducing agents. Based on this, the drag reduction ratio DR% is calculated using the following formula:

[0092]

[0093] Each test was repeated three times, and the arithmetic mean was taken.

[0094] 2. Temperature resistance test: Prepare a 200ppm aqueous solution for the sample to be tested, and age it in constant temperature oil baths at 80℃, 100℃ and 120℃ for 24h respectively. After cooling to 25℃, test the drag reduction rate according to the above drag reduction performance test method, and calculate the drag reduction rate retention rate according to the following formula: drag reduction rate retention rate = drag reduction rate after aging / drag reduction rate before aging × 100%.

[0095] 3. Dissolution rate test: Under constant temperature of 25℃, the sample to be tested was added to water in the form of 200-mesh powder and magnetically stirred at 300 rpm. The change in transmittance of the solution was continuously monitored using a UV-Vis spectrophotometer. The time when the transmittance no longer changed was recorded as the complete dissolution time. Each group was repeated three times and the average value was taken.

[0096] 4. Biodegradability test: Referring to GB / T 19276.1-2003 "Determination of final aerobic biodegradation capacity of materials in aqueous culture medium by measuring oxygen demand in a closed respiration meter", the biodegradation rate was tested for 28 days in a simulated soil microbial environment using the carbon dioxide release method.

[0097] The test results are shown in Table 1 below:

[0098] Table 1: Drag reduction rate of each sample at different concentrations (25℃, Re=50000)

[0099] 50ppm drag reduction % 100ppm drag reduction % 200ppm drag reduction % Example 1 52.6 62.3 71.8 Example 2 48.9 58.7 68.2 Example 3 55.3 65.1 74.5 Comparative Example 1 46.8 55.6 68.3 Comparative Example 2 48.5 57.2 70.1

[0100] As shown in Table 1, under normal temperature conditions, the drag reduction rate of Example 3 at a concentration of 200 ppm reached 74.5%, which is better than the 68.3% of Comparative Example 1 and the 70.1% of Comparative Example 2. This indicates that the drag reduction performance of the polyamide drag reducer of the present invention in clean water has reached or partially surpassed that of existing polyacrylamide products, and has a good foundation for industrial application.

[0101] Table 2: Drag reduction retention rate of each sample after high-temperature aging (200ppm, Re=50000)

[0102] 80℃ aging for 24 hours retention rate % % retention rate after 24 hours of aging at 100℃ 120℃ aging for 24 hours retention rate % Example 1 94.2 89.6 84.3 Example 2 92.8 87.1 81.5 Example 3 95.5 91.3 86.7 Comparative Example 1 62.4 38.7 21.5 Comparative Example 2 78.6 55.2 35.8

[0103] As shown in Table 2, after aging at 120°C for 24 hours, the drag reduction rate of Examples 1 to 3 still reached 81.5% to 86.7%, while that of Comparative Example 1 was only 21.5% and that of Comparative Example 2 was only 35.8%. This indicates that the temperature resistance of the polyamide drag reduction agent of the present invention is significantly better than that of the prior art.

[0104] Table 3: Drag reduction rate of each sample at different salinity (200ppm, 25℃, Re=50000)

[0105] Clear water drag reduction rate % Mineralization 5000 mg / L, drag reduction % Mineralization 10000 mg / L, drag reduction % Mineralization 20000 mg / L, drag reduction % Example 1 71.8 69.2 65.8 60.3 Example 2 68.2 65.5 61.2 55.8 Example 3 74.5 72.1 68.9 64.2 Comparative Example 1 68.3 52.4 38.6 25.7 Comparative Example 2 70.1 58.7 45.2 32.4

[0106] As shown in Table 3, under high salt conditions with a mineralization of 20,000 mg / L, the drag reduction rate of Example 3 still reached 64.2%, while that of Comparative Example 1 was only 25.7% and that of Comparative Example 2 was only 32.4%. This indicates that the hydrophobic association of the long-chain alkyl end-capping agent and the hydrogen bonding between polyamide molecular chains synergistically resisted the electrostatic compression effect of salt ions on the molecular chains.

[0107] Table 4: Drag reduction recovery rate of each sample after high shear cycling (200ppm, shear rate 10000s⁻¹, 25℃, Re=50000)

[0108] Recovery rate after 1 cycle % Recovery rate after 3 cycles % Recovery rate after 5 cycles % Recovery rate after 10 cycles % Example 1 96.5 92.3 87.6 81.2 Example 2 95.8 90.5 85.1 78.5 Example 3 97.2 93.8 89.4 83.6 Comparative Example 1 78.4 58.2 42.5 28.6 Comparative Example 2 82.1 65.4 50.3 35.2

[0109] As shown in Table 4, after 10 high-shear cycles, the drag reduction recovery rate of Example 3 still reached 83.6%, while that of Comparative Example 1 was only 28.6% and that of Comparative Example 2 was only 35.2%, indicating that the hydrogen bond network between polyamide molecular chains has reversible self-repairing ability of breaking and recombination.

[0110] Table 5: Complete dissolution time of each sample in water (25℃, 300rpm, 200-mesh powder)

[0111] Complete dissolution time (min) Example 1 4.2 Example 2 3.8 Example 3 4.5 Comparative Example 1 22.0 Comparative Example 2 18.5

[0112] As shown in Table 5, the dissolution time of the drag-reducing agent of the present invention does not exceed 5 minutes, which meets the process requirements of on-site online mixing in shale gas fracturing, i.e., not exceeding 10 minutes, while Comparative Example 1 and Comparative Example 2 require 22 minutes and 18.5 minutes, respectively.

[0113] Table 6: Biodegradation rate of each sample after 28 days

[0114] 28-day biodegradation rate % Example 1 62.5 Example 2 58.3 Example 3 67.1 Comparative Example 1 15.8 Comparative Example 2 12.3

[0115] As shown in Table 6, the 28-day biodegradation rate of the polyamide drag reducer of the present invention is not less than 58%, while that of Comparative Example 1 and Comparative Example 2 is only 15.8% and 12.3%, respectively, indicating that the drag reducer of the present invention has good environmental friendliness.

[0116] In summary, this invention provides thermal stability and hydrogen bond self-healing capability through the polyamide backbone, water solubility and flexibility through the polyether segments, hydrophobic association and salt resistance through long-chain alkyl end capping, and biodegradability through amide bonds, achieving a synergistic unity of temperature resistance, salt resistance, shear resistance, rapid solubility and biodegradability in a single molecular structure.

[0117] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A polyamide-based drag reducer, characterized in that: The drag-reducing agent is a polyamide copolymer containing amide bonds, which is prepared by polycondensation reaction of raw materials containing the following monomers: (a) At least one dicarboxylic acid; (b) at least one diamine; (c) A compound containing polyether segments, wherein the compound containing polyether segments is selected from at least one of polyether diamine and monomethoxy polyethylene glycol, wherein the polyether diamine is embedded in the main chain of the polyamide copolymer through its two end amino groups, and the monomethoxy polyethylene glycol is attached to the main chain of the polyamide copolymer as a side chain through its terminal hydroxyl groups; (d) End-capping agent, wherein the end-capping agent is selected from long-chain monocarboxylic acids of C8 to C24; The polyamide copolymer has a weight-average molecular weight of 50,000 to 1,500,000 Da.

2. The polyamide drag reducer according to claim 1, characterized in that: The dicarboxylic acid is selected from at least one of the following: aliphatic dicarboxylic acids of C4 to C20, alicyclic dicarboxylic acids of C5 to C12, and aromatic dicarboxylic acids of C6 to C14.

3. The polyamide drag reducer according to claim 1, characterized in that: The dicarboxylic acid is at least one of adipic acid, sebacic acid, dodecanoic acid, and hydrogenated dimer acid.

4. The polyamide drag reducer according to claim 1, characterized in that: The diamine is selected from at least one of C2-C12 aliphatic diamines and diamines containing tertiary amine groups.

5. The polyamide drag reducer according to claim 1, characterized in that: The diamine is hexamethylenediamine.

6. The polyamide drag reducer according to claim 1, characterized in that: The molecular weight of the polyether diamine is 230–2000 Da.

7. The polyamide drag reducer according to claim 1, characterized in that: The capping agent is at least one of stearic acid, oleic acid, and docosanoic acid.

8. A method for preparing a polyamide drag-reducing agent, used to prepare the polyamide drag-reducing agent according to any one of claims 1-7, characterized in that: Includes the following steps: S1. Pre-condensation reaction: Under inert gas protection, a dicarboxylic acid and a diamine are mixed at a molar ratio of 1:1.01 to 1.03 and reacted at 180 to 240°C and 0.5 to 2.0 MPa for 2 to 6 hours to obtain an amino-terminated polyamide prepolymer. S2, Melt polycondensation: Add a compound containing polyether segments to the prepolymer obtained in step S1, and react for 3 to 8 hours at 200 to 260°C and a vacuum degree ≤100Pa to obtain a polyamide-polyether copolymer; S3, End-capping reaction: Add an end-capping agent to the copolymer obtained in step S2 and react at 180-220°C for 1-3 hours; S4. Post-processing: Dissolve, filter, dry and pulverize the product obtained in step S3 to obtain the polyamide drag reducer.

9. The preparation method according to claim 8, characterized in that: The amount of the compound containing polyether segments added in step S2 is 5 to 30 wt% of the amount of the prepolymer obtained in step S1.

10. The preparation method according to claim 8, characterized in that: The amount of capping agent added in step S3 is based on the total molar amount of terminal amino groups in the terminal amino polyamide prepolymer obtained in step S1, and the molar amount of carboxyl groups contained in the capping agent is 50% to 300% of the total molar amount of terminal amino groups.

Images