Water treatment agent for oilfield reinjection water and preparation method thereof

Abstract

This invention relates to the field of water treatment technology and discloses a water treatment agent for oilfield reinjection water and its preparation method. The invention obtains the water treatment agent for oilfield reinjection water by copolymerizing quinoline modified with sulfonic acid imidazoline quaternary ammonium salt, chitosan modified with Mannich base, acrylic acid, and sodium hypophosphite. Quaternization modification of imidazoline improves its water solubility and corrosion inhibition properties. The quaternary ammonium salt imidazoline can be adsorbed on metal surfaces, reducing the corrosion rate and acting as a surfactant to wet and disperse, accelerating the scale removal rate. The sulfonic acid group improves temperature resistance, prevents gel formation, and its strong hydrophilicity allows the molecular chain to fully extend in water, improving scale inhibition performance. Introducing Mannich base into chitosan improves its acid solubility and temperature resistance. The conjugation effect of the aromatic ring strengthens the coordination chelation effect of chitosan, improving the corrosion inhibition effect. Multiple functional groups exert a synergistic effect, further enhancing the corrosion and scale inhibition effects.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, specifically to a water treatment agent for oilfield reinjection water and its preparation method. Background Technology

[0002] Water injection is a crucial measure for replenishing reservoir energy and enhancing oil recovery during oil extraction. To improve water recycling efficiency, produced water from high-salinity formations is typically reinjected into the formation to replenish formation pressure and maintain production. With the application of stratified water injection technology, formation scaling, wellbore scaling, pipeline corrosion, and sucker rod breakage frequently occur, affecting normal oil production. The most common approach to addressing corrosion and scaling problems caused by water injection in oilfields is to add corrosion inhibitors and scale inhibitors to the injection system. However, these methods generally suffer from unsatisfactory results. Currently used corrosion and scale inhibitors are applied in excessive amounts, resulting in low inhibition rates. Furthermore, the high temperature of the reinjected wastewater in oilfields also affects the activity of these inhibitors, leading to a decline in their performance. The literature "Synthesis of Modified Polyepoxysuccinic Acid and Study on its Scale Inhibition and Corrosion Inhibition Mechanism" synthesized modified polyepoxysuccinic acid using thiourea and polyepoxysuccinic acid, and found that it has a good corrosion inhibition effect; however, as a scale inhibitor, polyepoxysuccinic acid has limited dispersibility and poor scale inhibition effect, which limits its application. Summary of the Invention

[0003] (a) Technical problems to be solved

[0004] To address the shortcomings of existing technologies, this invention provides an oilfield reinjection water treatment agent and its preparation method. The oilfield reinjection water treatment agent prepared by this invention exhibits excellent high-temperature resistance and corrosion and scale inhibition effects.

[0005] (II) Technical Solution

[0006] To achieve the above objectives, the present invention provides the following technical solution: an oilfield reinjection water treatment agent, comprising the following weight components: 15-20 parts by weight of sulfonated imidazoline quaternary ammonium salt modified quinoline, 12-18 parts by weight of Mannich base modified chitosan, 3-7 parts by weight of acrylic acid, and 2-5 parts by weight of sodium hypophosphite.

[0007] Preferably, the method for preparing the sulfonyl imidazoline quaternary ammonium salt-modified quinoline includes the following steps:

[0008] (1) Add 3-7g of sodium bisulfite sulfonating agent to deionized water, heat to 72-78℃ while stirring, add 9-13g of 2-chloro-3,4-epoxy-1-butene dropwise, and after the addition is complete, raise the temperature to 80-85℃ and react for 2-3h. After the reaction is complete, cool in an ice bath, filter the crystals that precipitate after cooling, recrystallize to obtain sodium alkenyl sulfonate.

[0009] (2) Add sodium alkenyl sulfonate and 2-imidazoline to acetone solvent, stir to dissolve, heat to 60-65℃, reflux at 200-400 rpm for 4-6 h, filter, wash and dry by rotary evaporation to obtain sulfonyl imidazoline quaternary ammonium salt.

[0010] (3) Add 12-16g of 2-quinoline carboxylic acid and 8-10g of sulfonated imidazoline quaternary ammonium salt to dichloromethane solvent, stir to dissolve, add 0.05-0.08g of N,N'-dicyclohexylcarbodiimide dehydrating agent, react at 24-30℃ for 3-5h, after the reaction is completed, filter, and dry by rotary evaporation to obtain sulfonated imidazoline quaternary ammonium salt modified quinoline;

[0011] Preferably, the method for preparing the Mannich base-modified chitosan includes the following steps:

[0012] S1. Add 4-8g of N-vinylpyrrolidone, 12-18g of formaldehyde solution, and 0.02-0.04g of p-diphenol reducing agent to the reactor. Purge with nitrogen for 20-40min to remove oxygen. Heat to 85-90℃ and add 6-12g of 4-methylaminobenzoic acid. Heat to 130-140℃ and react for 6-9h. After the reaction is complete, wash and dry to obtain an alkenyl Mannich base.

[0013] S2. Add 14-18g of chitosan to a 0.8%-1.2% acetic acid solution, stir to dissolve, add 0.04-0.08g of 1-hydroxybenzotriazole initiator and 3-6g of alkenyl Mannich base, heat to the reaction temperature, react for 6-10h, after the reaction is completed, dialyze and freeze dry to obtain Mannich base modified chitosan.

[0014] Preferably, the dropping time of 2-chloro-3,4-epoxy-1-butene in step (1) is controlled at 40-60 min.

[0015] Preferably, in step (2), the mass ratio of sodium alkenyl sulfonate and 2-imidazoline is 1:1-1.4.

[0016] Preferably, the formaldehyde solution in S1 has a mass fraction of 38%-42%.

[0017] Preferably, the reaction temperature in S2 is 70-80℃.

[0018] Preferably, the preparation method of the oilfield reinjection water treatment agent is as follows: sulfonated imidazoline quaternary ammonium salt modified quinoline, Mannich base modified chitosan, acrylic acid, and sodium hypophosphite are added to deionized water. After stirring and mixing at 60-68℃, the temperature is raised to 80-90℃, and 0.2-0.5 parts by weight of ammonium persulfate initiator are added. The reaction is maintained at this temperature for 3-4 hours. After the reaction is completed, the mixture is settled in ethanol, filtered, and vacuum dried to obtain the oilfield reinjection water treatment agent.

[0019] (III) Beneficial Technical Effects

[0020] This invention obtains an oilfield reinjection water treatment agent by copolymerizing quinoline modified with sulfonated imidazoline quaternary ammonium salt, chitosan modified with Mannich base, acrylic acid, and sodium hypophosphite under an ammonium persulfate initiator.

[0021] The epoxy group in 2-chloro-3,4-epoxy-1-butene undergoes a ring-opening addition reaction with sodium bisulfite to yield sodium alkenyl sulfonate, introducing a hydroxyl group. The chlorine in sodium alkenyl sulfonate undergoes a quaternization reaction with 2-imidazoline to yield a sulfonyl imidazoline quaternary ammonium salt. The hydroxyl group in the sulfonyl imidazoline quaternary ammonium salt undergoes an esterification reaction with the carboxyl group in 2-quinoline carboxylic acid to yield a sulfonyl imidazoline quaternary ammonium salt modified quinoline. N-vinylpyrrolidone, formaldehyde, and 4-methylaminobenzoic acid undergo a Mannich reaction to yield an alkenyl Mannich base containing a carboxyl group. The carboxyl group in the alkenyl Mannich base undergoes an amidation reaction with the amino group in chitosan to yield Mannich base modified chitosan.

[0022] The carboxyl groups in the water treatment agents for oilfield reinjection water have a strong complexing ability for calcium, magnesium, and iron ions, not only dispersing and coagulating but also disrupting the regular arrangement of scale-forming crystal structures, thus inhibiting scale formation. In quinoline modified with sulfonic acid imidazoline quaternary ammonium salt, the water solubility and corrosion inhibition properties of imidazoline are improved through quaternization. Quaternary ammonium imidazoline can adsorb onto metal surfaces, forming a dense protective layer that effectively reduces the metal corrosion rate. It can also act as a surfactant, providing wetting and dispersing effects, making it easier for the water treatment agent to penetrate the scale layer and accelerate the scale removal rate. Introducing sulfonic acid groups, which are more acidic than carboxyl groups, not only increases the temperature resistance of the water treatment agent but also prevents the carboxyl groups from forming gels with scale-forming cations. Furthermore, the strong hydrophilicity of sulfonic acid groups allows the molecular chains to fully extend in water, increasing permeability and thus improving scale inhibition performance. Ester groups possess both lattice distortion and microcrystal dispersion properties, exhibiting good complexing effects on scale-forming cations, thereby achieving… It exhibits scale prevention and inhibition, and demonstrates good thermal stability at high temperatures, enhancing the high-temperature resistance of the water treatment agent. Quinoline, a nitrogen-containing bicyclic compound, has a high electron density, which can reduce the enrichment of anions on the metal surface and improve the corrosion inhibition effect. In Mannich base-modified chitosan, the chitosan molecule contains a large number of active groups such as hydroxyl and amino groups, and after dissolving in water, the molecular chain can carry a positive charge, which can generate a strong binding force with metal atoms, forming a protective film, reducing the active corrosion sites on the metal surface, and thus having scale inhibition and corrosion inhibition effects. By introducing Mannich base into the chitosan molecule, the acid solubility and temperature resistance of chitosan are improved. The conjugation effect of the aromatic ring in the Mannich base strengthens the coordination chelation between chitosan molecules and metals, thereby enhancing the corrosion inhibition effect. By modifying quinoline with sulfonic acid imidazoline quaternary ammonium salt, Mannich base-modified chitosan, acrylic acid, and sodium hypophosphite to form a copolymer, multiple functional groups exert a synergistic effect, further enhancing the corrosion inhibition and scale inhibition effect of the water treatment agent for oilfield reinjection water. Detailed Implementation

[0023] Example 1

[0024] (1) Add 3g of sodium bisulfite sulfonating agent to deionized water, heat to 72°C while stirring, add 9g of 2-chloro-3,4-epoxy-1-butene dropwise, control the dropwise addition time to 40min, after the dropwise addition is completed, raise the temperature to 80°C and react for 2h. After the reaction is completed, cool in an ice bath, filter the crystals that precipitate after cooling, recrystallize to obtain sodium alkenyl sulfonate.

[0025] (2) Add sodium alkenyl sulfonate and 2-imidazoline to acetone solvent, stir to dissolve, wherein the mass ratio of sodium alkenyl sulfonate and 2-imidazoline is 1:1, heat to 60℃, reflux at 200rpm for 4h, after the reaction is completed, filter, wash and dry by rotary evaporation to obtain sulfonyl imidazoline quaternary ammonium salt.

[0026] (3) Add 12g of 2-quinoline carboxylic acid and 8g of sulfonyl imidazoline quaternary ammonium salt to dichloromethane solvent, stir to dissolve, add 0.05g of N,N'-dicyclohexylcarbodiimide dehydrating agent, react at 24℃ for 3h, after the reaction is completed, filter, and dry by rotary evaporation to obtain sulfonyl imidazoline quaternary ammonium salt modified quinoline;

[0027] (4) Add 4g of N-vinylpyrrolidone, 12g of formaldehyde solution with a mass fraction of 38%, and 0.02g of p-diphenol reducing agent to the reactor. Purge with nitrogen for 20min to remove oxygen. Heat to 85℃ and add 6g of 4-methylaminobenzoic acid. Heat to 130℃ and react for 6h. After the reaction is complete, wash and dry to obtain alkenyl Mannich base.

[0028] (5) Add 14g of chitosan to a 0.8% acetic acid solution, stir to dissolve, add 0.04g of 1-hydroxybenzotriazole initiator and 3g of alkenyl Mannich base, heat to 70℃, react for 6h, after the reaction is completed, dialyze and freeze dry to obtain Mannich base modified chitosan.

[0029] (6) Add 15 parts by weight of sulfonated imidazoline quaternary ammonium salt modified quinoline, 12 parts by weight of Mannich base modified chitosan, 3 parts by weight of acrylic acid, and 2 parts by weight of sodium hypophosphite to deionized water. Stir and mix at 60°C, then heat to 80°C. Add 0.2 parts by weight of ammonium persulfate initiator and keep the reaction at this temperature for 3 hours. After the reaction is complete, precipitate in ethanol, filter, and vacuum dry to obtain the water treatment agent for oilfield reinjection water.

[0030] Example 2

[0031] (1) Add 7g of sodium bisulfite sulfonating agent to deionized water, heat to 78°C while stirring, add 13g of 2-chloro-3,4-epoxy-1-butene dropwise, control the dropwise addition time to 60min, after the dropwise addition is completed, raise the temperature to 85°C and react for 3h. After the reaction is completed, cool in an ice bath, filter the crystals that precipitate after cooling, recrystallize to obtain sodium alkenyl sulfonate.

[0032] (2) Add sodium alkenyl sulfonate and 2-imidazoline to acetone solvent, stir to dissolve, wherein the mass ratio of sodium alkenyl sulfonate and 2-imidazoline is 1:1.4, heat to 65℃, reflux at 400rpm for 6h, after the reaction is completed, filter, wash and dry by rotary evaporation to obtain sulfonyl imidazoline quaternary ammonium salt.

[0033] (3) Add 16g of 2-quinoline carboxylic acid and 10g of sulfonated imidazoline quaternary ammonium salt to dichloromethane solvent, stir to dissolve, add 0.08g of N,N'-dicyclohexylcarbodiimide dehydrating agent, react at 30℃ for 5h, after the reaction is completed, filter, and dry by rotary evaporation to obtain sulfonated imidazoline quaternary ammonium salt modified quinoline;

[0034] (4) Add 8g of N-vinylpyrrolidone, 12-18g of 42% formaldehyde solution and 0.04g of p-diphenol reducing agent to the reactor, purge with nitrogen for 40min to remove oxygen, raise the temperature to 90℃, add 12g of 4-methylaminobenzoic acid, raise the temperature to 140℃ and react for 9h. After the reaction is completed, wash and dry to obtain alkenyl Mannich base;

[0035] (5) Add 18g of chitosan to a 1.2% acetic acid solution, stir to dissolve, add 0.08g of 1-hydroxybenzotriazole initiator and 6g of alkenyl Mannich base, heat to 80℃, react for 10h, after the reaction is completed, dialyze and freeze dry to obtain Mannich base modified chitosan.

[0036] (6) Add 20 parts by weight of sulfonated imidazoline quaternary ammonium salt modified quinoline, 18 parts by weight of Mannich base modified chitosan, 7 parts by weight of acrylic acid, and 5 parts by weight of sodium hypophosphite to deionized water. Stir and mix at 68°C, then heat to 90°C. Add 0.5 parts by weight of ammonium persulfate initiator and keep the reaction at this temperature for 4 hours. After the reaction is complete, precipitate in ethanol, filter, and vacuum dry to obtain the oilfield reinjection water treatment agent.

[0037] Example 3

[0038] (1) Add 5g of sodium bisulfite sulfonating agent to deionized water, heat to 75°C while stirring, add 11g of 2-chloro-3,4-epoxy-1-butene dropwise, control the dropwise addition time to 50min, after the dropwise addition is completed, raise the temperature to 82°C and react for 2.5h. After the reaction is completed, cool in an ice bath, filter the crystals that precipitate after cooling, recrystallize to obtain sodium alkenyl sulfonate;

[0039] (2) Add sodium alkenyl sulfonate and 2-imidazoline to acetone solvent, stir to dissolve, wherein the mass ratio of sodium alkenyl sulfonate and 2-imidazoline is 1:1.2, heat to 62℃, reflux at 300rpm for 5h, after the reaction is completed, filter, wash and dry by rotary evaporation to obtain sulfonyl imidazoline quaternary ammonium salt.

[0040] (3) Add 14g of 2-quinoline carboxylic acid and 9g of sulfonated imidazoline quaternary ammonium salt to dichloromethane solvent, stir to dissolve, add 0.06g of N,N'-dicyclohexylcarbodiimide dehydrating agent, react at 27℃ for 4h, after the reaction is completed, filter, and dry by rotary evaporation to obtain sulfonated imidazoline quaternary ammonium salt modified quinoline;

[0041] (4) Add 6g of N-vinylpyrrolidone, 15g of 40% formaldehyde solution, and 0.03g of p-diphenol reducing agent to the reactor, purge with nitrogen for 30min to remove oxygen, raise the temperature to 88℃, add 9g of 4-methylaminobenzoic acid, raise the temperature to 135℃ and react for 7.5h. After the reaction is completed, wash and dry to obtain alkenyl Mannich base;

[0042] (5) Add 16g of chitosan to a 1% acetic acid solution, stir to dissolve, add 0.06g of 1-hydroxybenzotriazole initiator and 4.5g of alkenyl Mannich base, heat to 75℃, react for 8h, after the reaction is completed, dialyze and freeze dry to obtain Mannich base modified chitosan.

[0043] (6) Add 17 parts by weight of sulfonated imidazoline quaternary ammonium salt modified quinoline, 15 parts by weight of Mannich base modified chitosan, 5 parts by weight of acrylic acid, and 3 parts by weight of sodium hypophosphite to deionized water. Stir and mix at 64°C, then heat to 85°C. Add 0.3 parts by weight of ammonium persulfate initiator and keep the reaction at this temperature for 3.5 hours. After the reaction is complete, precipitate in ethanol, filter, and vacuum dry to obtain the water treatment agent for oilfield reinjection water.

[0044] Example 4

[0045] (1) Add 3g of sodium bisulfite sulfonating agent to deionized water, heat to 72°C while stirring, add 9g of 2-chloro-3,4-epoxy-1-butene dropwise, control the dropwise addition time to 40min, after the dropwise addition is completed, raise the temperature to 80°C and react for 2h. After the reaction is completed, cool in an ice bath, filter the crystals that precipitate after cooling, recrystallize to obtain sodium alkenyl sulfonate.

[0046] (2) Add sodium alkenyl sulfonate and 2-imidazoline to acetone solvent, stir to dissolve, wherein the mass ratio of sodium alkenyl sulfonate and 2-imidazoline is 1:1, heat to 60℃, reflux at 200rpm for 4h, after the reaction is completed, filter, wash and dry by rotary evaporation to obtain sulfonyl imidazoline quaternary ammonium salt.

[0047] (3) Add 16g of 2-quinoline carboxylic acid and 10g of sulfonated imidazoline quaternary ammonium salt to dichloromethane solvent, stir to dissolve, add 0.08g of N,N'-dicyclohexylcarbodiimide dehydrating agent, react at 30℃ for 5h, after the reaction is completed, filter, and dry by rotary evaporation to obtain sulfonated imidazoline quaternary ammonium salt modified quinoline;

[0048] (4) Add 8g of N-vinylpyrrolidone, 12-18g of 42% formaldehyde solution and 0.04g of p-diphenol reducing agent to the reactor, purge with nitrogen for 40min to remove oxygen, raise the temperature to 90℃, add 12g of 4-methylaminobenzoic acid, raise the temperature to 140℃ and react for 9h. After the reaction is completed, wash and dry to obtain alkenyl Mannich base;

[0049] (5) Add 16g of chitosan to a 1% acetic acid solution, stir to dissolve, add 0.06g of 1-hydroxybenzotriazole initiator and 4.5g of alkenyl Mannich base, heat to 75℃, react for 8h, after the reaction is completed, dialyze and freeze dry to obtain Mannich base modified chitosan.

[0050] (6) Add 17 parts by weight of sulfonated imidazoline quaternary ammonium salt modified quinoline, 15 parts by weight of Mannich base modified chitosan, 5 parts by weight of acrylic acid, and 3 parts by weight of sodium hypophosphite to deionized water. Stir and mix at 64°C, then heat to 85°C. Add 0.3 parts by weight of ammonium persulfate initiator and keep the reaction at this temperature for 3.5 hours. After the reaction is complete, precipitate in ethanol, filter, and vacuum dry to obtain the water treatment agent for oilfield reinjection water.

[0051] Example 5

[0052] (1) Add 7g of sodium bisulfite sulfonating agent to deionized water, heat to 78°C while stirring, add 13g of 2-chloro-3,4-epoxy-1-butene dropwise, control the dropwise addition time to 60min, after the dropwise addition is completed, raise the temperature to 85°C and react for 3h. After the reaction is completed, cool in an ice bath, filter the crystals that precipitate after cooling, recrystallize to obtain sodium alkenyl sulfonate.

[0053] (2) Add sodium alkenyl sulfonate and 2-imidazoline to acetone solvent, stir to dissolve, wherein the mass ratio of sodium alkenyl sulfonate and 2-imidazoline is 1:1.4, heat to 65℃, reflux at 400rpm for 6h, after the reaction is completed, filter, wash and dry by rotary evaporation to obtain sulfonyl imidazoline quaternary ammonium salt.

[0054] (3) Add 14g of 2-quinoline carboxylic acid and 9g of sulfonated imidazoline quaternary ammonium salt to dichloromethane solvent, stir to dissolve, add 0.06g of N,N'-dicyclohexylcarbodiimide dehydrating agent, react at 27℃ for 4h, after the reaction is completed, filter, and dry by rotary evaporation to obtain sulfonated imidazoline quaternary ammonium salt modified quinoline;

[0055] (4) Add 6g of N-vinylpyrrolidone, 15g of 40% formaldehyde solution, and 0.03g of p-diphenol reducing agent to the reactor, purge with nitrogen for 30min to remove oxygen, raise the temperature to 88℃, add 9g of 4-methylaminobenzoic acid, raise the temperature to 135℃ and react for 7.5h. After the reaction is completed, wash and dry to obtain alkenyl Mannich base;

[0056] (5) Add 14g of chitosan to a 0.8% acetic acid solution, stir to dissolve, add 0.04g of 1-hydroxybenzotriazole initiator and 3g of alkenyl Mannich base, heat to 70℃, react for 6h, after the reaction is completed, dialyze and freeze dry to obtain Mannich base modified chitosan.

[0057] (6) Add 15 parts by weight of sulfonated imidazoline quaternary ammonium salt modified quinoline, 12 parts by weight of Mannich base modified chitosan, 3 parts by weight of acrylic acid, and 2 parts by weight of sodium hypophosphite to deionized water. Stir and mix at 60°C, then heat to 80°C. Add 0.2 parts by weight of ammonium persulfate initiator and keep the reaction at this temperature for 3 hours. After the reaction is complete, precipitate in ethanol, filter, and vacuum dry to obtain the water treatment agent for oilfield reinjection water.

[0058] Comparative Example 1

[0059] The difference between this comparative example and Example 5 is that quinoline was not modified with sulfonated imidazoline quaternary ammonium salt in step (6).

[0060] Comparative Example 2

[0061] The difference between this comparative example and Example 5 is that Mannich base-modified chitosan was not added in step (6).

[0062] Static scale inhibition tests were conducted according to the national standard GB / T16632-2008 "Determination of Scale Inhibition Performance of Water Treatment Agents - Calcium Carbonate Deposition Method" to test the scale inhibition performance of water treatment agents used in oilfield reinjection water. Simulated solution Ca2+... + and HCO3 - The concentrations were 250 mg / L and 750 mg / L, respectively. The dosage of the water treatment agent added to the oilfield reinjection water was 8 mg / L. The samples were kept at a constant temperature for 24 hours at different temperatures, cooled and filtered, and then subjected to complexometric titration with EDTA standard solution to calculate the scale inhibition rate. The test results are shown in Table 1.

[0063] Table 1: Scale inhibition performance test.

[0064]

[0065] As shown in Table 1, Examples 1-5 of the present invention have better scale inhibition performance compared with Comparative Examples 1-2, and the scale inhibition rate remains above 90% as the temperature increases, demonstrating better high-temperature resistance.

[0066] A 50mm × 10mm × 2mm carbon steel sheet was sanded smooth, washed with deionized water and ethanol, vacuum dried, and then weighed. Ca was prepared according to GB / T18175-2014. 2+ =200.4 mg / L, Mg 2+ =48.62mg / L, Cl - =399.1 mg / L, HCO3 2- A simulated solution with a concentration of 122.0 mg / L was used to immerse carbon steel sheets. The amount of water treatment agent added to the oilfield reinjection water was 20 mg / L. The solution was kept at a constant temperature for 24 hours at different temperatures. The carbon steel sheets were then removed, washed with deionized water and ethanol, vacuum dried, and weighed. The corrosion inhibition rate was calculated. The test results are shown in Table 2.

[0067] Table 2: Corrosion Inhibition Performance Test.

[0068]

[0069]

[0070] As shown in Table 2, Examples 1-5 of the present invention have better corrosion inhibition performance and high temperature resistance compared with Comparative Examples 1-2.

[0071] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A water treatment agent for oilfield reinjection water, characterized in that, It includes the following components by weight: 15-20 parts by weight of sulfonated imidazoline quaternary ammonium salt modified quinoline, 12-18 parts by weight of Mannich base modified chitosan, 3-7 parts by weight of acrylic acid, and 2-5 parts by weight of sodium hypophosphite. The method for preparing the sulfonated imidazoline quaternary ammonium salt-modified quinoline includes the following steps: (1) Add 3-7g of sodium bisulfite sulfonating agent to deionized water, heat to 72-78℃ while stirring, add 9-13g of 2-chloro-3,4-epoxy-1-butene dropwise, and after the addition is complete, raise the temperature to 80-85℃ and react for 2-3h. After the reaction is complete, cool in an ice bath, filter the crystals that precipitate after cooling, recrystallize to obtain sodium alkenyl sulfonate. (2) Add sodium alkenyl sulfonate and 2-imidazoline to acetone solvent, stir to dissolve, heat to 60-65℃, reflux at 200-400rpm for 4-6h, filter after reaction, wash and dry by rotary evaporation to obtain sulfonyl imidazoline quaternary ammonium salt. (3) Add 12-16g of 2-quinoline carboxylic acid and 8-10g of sulfonic acid imidazoline quaternary ammonium salt to dichloromethane solvent, stir to dissolve, add 0.05-0.08g of N,N'-dicyclohexylcarbodiimide dehydrating agent, react at 24-30℃ for 3-5h, after the reaction is completed, filter, and dry by rotary evaporation to obtain sulfonic acid imidazoline quaternary ammonium salt modified quinoline; The method for preparing Mannich base-modified chitosan includes the following steps: S1. Add 4-8g of N-vinylpyrrolidone, 12-18g of formaldehyde solution, and 0.02-0.04g of p-diphenol reducing agent to the reactor. Purge with nitrogen for 20-40min to remove oxygen. Heat to 85-90℃ and add 6-12g of 4-methylaminobenzoic acid. Heat to 130-140℃ and react for 6-9h. After the reaction is complete, wash and dry to obtain an alkenyl Mannich base. S2. Add 14-18g of chitosan to a 0.8%-1.2% acetic acid solution, stir to dissolve, add 0.04-0.08g of 1-hydroxybenzotriazole initiator and 3-6g of alkenyl Mannich base, heat to the reaction temperature, react for 6-10h, after the reaction is completed, dialyze and freeze dry to obtain Mannich base modified chitosan; The preparation method of the oilfield reinjection water treatment agent is as follows: sulfonated imidazoline quaternary ammonium salt modified quinoline, Mannich base modified chitosan, acrylic acid, and sodium hypophosphite are added to deionized water. After stirring and mixing at 60-68℃, the temperature is raised to 80-90℃, and 0.2-0.5 parts by weight of ammonium persulfate initiator are added. The reaction is maintained at this temperature for 3-4 hours. After the reaction is completed, the mixture is settled in ethanol, filtered, and vacuum dried to obtain the oilfield reinjection water treatment agent.

2. The oilfield reinjection water treatment agent according to claim 1, characterized in that, In step (1), the dropping time of 2-chloro-3,4-epoxy-1-butene is controlled at 40-60 min.

3. The oilfield reinjection water treatment agent according to claim 1, characterized in that, In step (2), the mass ratio of sodium alkenyl sulfonate and 2-imidazoline is 1:1-1.

4.

4. The oilfield reinjection water treatment agent according to claim 1, characterized in that, The formaldehyde solution in S1 has a mass fraction of 38%-42%.

5. The water treatment agent for oilfield reinjection water according to claim 1, characterized in that, The reaction temperature in S2 is 70-80℃.

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