Oilfield produced water treatment agent and preparation method thereof

Abstract

The application belongs to the technical field of water treatment agent preparation, and particularly relates to an oilfield produced water treatment agent and a preparation method thereof.The oilfield produced water treatment agent comprises the following raw materials: hydrophobic modified cationic polyacrylamide copolymer, modified sepiolite, trimethylolpropane polyoxypropylene polyoxyethylene ether, ethylene glycol monobutyl ether, tetrasodium glutamate diacetate, phosphonyl butane tricarboxylic acid, oleic acid imidazoline, dibromocyanoacetamide, first deionized water and second deionized water.The oilfield produced water treatment agent has excellent oil removal rate, solid suspended substance removal rate, COD removal rate and scale and corrosion inhibition performance due to the synergistic effect among the raw materials.

Description

Technical Field

[0001] This invention belongs to the field of water treatment agent preparation technology, specifically relating to an oilfield produced water treatment agent and its preparation method. Background Technology

[0002] As oilfields enter the mid-to-late stages of development, large amounts of water are extracted along with crude oil, resulting in high water content in the produced fluid. Produced water is the water separated from the oil well's produced fluid during crude oil extraction after three-phase separation of oil, gas, and water. Its water quality characteristics are closely related to the properties of the crude oil, geological conditions of the formation, and extraction processes. The main pollutants in produced water include residues of various chemical treatment agents added during drilling and extraction, crude oil components, suspended solids, and inorganic salts. It has high chemical oxygen demand (COD) and mineralization, and its composition is complex. Its main hazards include corrosion of pipelines and equipment and reservoir blockage after reinjection. Untreated produced water has a relatively high oil content, with the oil phase mainly existing in the form of floating oil, dispersed oil, emulsified oil, and dissolved oil. High mineralization is a major factor restricting the reinjection and utilization of produced water. The dissolved inorganic salts in the water are mainly composed of Na+. + K + Ca 2+ Mg 2+ Fe 2+ / Fe 3+ The plasma composition typically ranges from 30,000 to 50,000 mg / L in total mineralization. Dissolved organic matter in the water mainly includes hydrocarbons, phenols, surfactants, and various polymers, while suspended solids primarily consist of sand, clay minerals, and corrosion products. Furthermore, sulfate-reducing bacteria, saprophytic bacteria, and iron bacteria are commonly found in oilfield produced water. Reinjecting substandard produced water into the formation can easily clog rock pores and throats, reducing reservoir permeability and injection efficiency, increasing extraction costs, and directly discharging it would severely impact the ecological environment and waste water resources.

[0003] Currently, the main methods for treating oilfield produced water include physical, chemical, and biological methods, with chemical treatment being widely used due to its simplicity and adaptability. Processes such as flocculation sedimentation, adsorption filtration, and corrosion and scale inhibition all rely on the matching of highly efficient treatment agents. However, existing oilfield produced water treatment agents generally suffer from problems such as limited functionality, poor synergistic effects in compound formulations, large dosage requirements, and limited effectiveness in treating high-salinity oily wastewater. Therefore, it is necessary to develop a new type of oilfield produced water treatment agent. Summary of the Invention

[0004] The purpose of this invention is to provide an oilfield produced water treatment agent, which has excellent oil removal rate, solid suspended matter removal rate, COD removal rate, and scale and corrosion inhibition performance. In addition, this invention also provides its preparation method.

[0005] The oilfield produced water treatment agent of this invention, by weight, is composed of the following raw materials: 15-17 parts of hydrophobically modified cationic polyacrylamide copolymer, 8-10 parts of modified sepiolite, 10-12 parts of trimethylolpropane polyoxypropylene polyoxyethylene ether, 5-6 parts of ethylene glycol monobutyl ether, 2.5-3.5 parts of tetrasodium diacetate of glutamic acid, 3.0-3.5 parts of phosphonobutane tricarboxylic acid, 2-3 parts of imidazoline oleate, and 1.5-2 parts of dibromocyanacetamide. The first deionized water consists of 300-340 parts, and the second deionized water consists of 200-250 parts. The preparation method of the hydrophobic modified cationic polyacrylamide copolymer consists of the following steps: ① preparation of monomer solution; ② initiation of polymerization; ③ post-treatment. The preparation method of the modified sepiolite consists of the following steps: (a) preparation of pretreated sepiolite; (b) preparation of epoxy sepiolite wet filter cake; (c) preparation of modified sepiolite by epoxy ring-opening grafting of β-cyclodextrin.

[0006] The preparation method of the hydrophobically modified cationic polyacrylamide copolymer comprises the following steps: ① Preparation of monomer solution: Add deionized water to the reaction vessel, then add sodium chloride, disodium ethylenediaminetetraacetate and urea in sequence and stir to dissolve. Finally, add acrylamide, acryloyloxyethyl dimethyl benzyl ammonium chloride and acryloyloxyethyl dimethyl dodecyl ammonium chloride in one go and stir until completely clear. Heat to 54-56℃ and bubble high-purity nitrogen gas to remove oxygen for 30-35 minutes to prepare monomer solution; ② Initiating polymerization: Azobisisobutyramidine hydrochloride is dissolved in deoxygenated deionized water at 0℃ to prepare an initiator solution. High-purity nitrogen gas is bubbled through the reaction vessel containing the monomer solution to remove oxygen for 30-35 minutes. Then, the initiator solution is added to the monomer solution at once, the reaction vessel is sealed, and the reaction is carried out at a constant temperature of 54-56℃ for 5.5-6 hours. ③ Post-treatment: Cool the reaction solution from step ② to room temperature, pour the reaction solution into acetone at 0℃, the volume of acetone being 6-7 times the volume of the reaction solution, stir continuously for 40-45 minutes, filter, and then wash twice with acetone, the volume of acetone used for each wash being 2-3 times the volume of the filter cake, and finally vacuum dry at 45-50℃ for 31-32 hours, pass through a 40-mesh sieve to prepare the hydrophobic modified cationic polyacrylamide copolymer.

[0007] In step ①, the mass ratio of acrylamide, acryloyloxyethyl dimethyl benzyl ammonium chloride, and acryloyloxyethyl dimethyl dodecyl ammonium chloride is 8:2.5:2.

[0008] In step ①, the mass of sodium chloride accounts for 3.2% of the total mass of acrylamide, acryloyloxyethyl dimethyl benzyl ammonium chloride, and acryloyloxyethyl dimethyl dodecyl ammonium chloride.

[0009] In step ①, the mass ratio of sodium chloride, disodium ethylenediaminetetraacetate, and urea is 2:0.1:1.

[0010] In step ①, the mass of deionized water is 3.2 times the sum of the masses of acrylamide, acryloyloxyethyl dimethyl benzyl ammonium chloride, and acryloyloxyethyl dimethyl dodecyl ammonium chloride.

[0011] In step ②, the stirring speed during the isothermal reaction is 300 r / min.

[0012] In step ②, the mass ratio of azobisisobutyramidine hydrochloride to deoxygenated deionized water in the initiator solution is 0.28:20.

[0013] The preparation method of modified sepiolite consists of the following steps: (a) Preparation of pretreated sepiolite: sepiolite powder was added to hydrochloric acid and ultrasonically dispersed for 30-35 min to form a suspension slurry. The suspension slurry was then kept at 53℃ for 3.5 h. After the reaction was completed, it was naturally cooled to room temperature. Finally, the filter cake was filtered, washed with deionized water, dried, crushed and sieved to obtain pretreated sepiolite. (b) Preparation of epoxy sepiolite wet filter cake: Add acetic acid to a mixed solvent of anhydrous ethanol and deionized water to adjust the pH of the system to 4.5. Add γ-glycidyl etheroxypropyltrimethoxysilane dropwise under stirring. Stir and hydrolyze at 45°C for 40 min to obtain hydrolysate. Then add pretreated sepiolite to the hydrolysate, heat to 70-75°C, and stir at 350 r / min for 5 h. After the reaction is completed, filter and separate. Wash the filter cake 2-3 times with anhydrous ethanol to prepare epoxy sepiolite wet filter cake. (c) Preparation of modified sepiolite by epoxy ring-opening grafting of β-cyclodextrin: β-cyclodextrin was added to a mixed solvent of anhydrous ethanol and deionized water and heated under reflux at 80°C for 55-60 min to disperse and dissolve it. The dispersion was transferred to a reaction vessel, and the epoxy sepiolite wet filter cake prepared in step (b) was added and stirred evenly. Then, sodium hydroxide was added to the system to adjust the pH value of the system to 10.0. Under nitrogen protection, the temperature was maintained at 80°C and the reaction was stirred at 400 r / min for 7 h. After the reaction was completed, the mixture was filtered and finally post-treated to prepare modified sepiolite.

[0014] In step (a), the mass-to-volume ratio of sepiolite powder to hydrochloric acid is 1:20, with units of g / mL.

[0015] In step (a), the concentration of hydrochloric acid is 2.5 mol / L.

[0016] The process of washing the filter cake with deionized water, drying, pulverizing and sieving in step (a) specifically involves washing the filter cake with deionized water 5-6 times, drying at a temperature of 65-70℃ for 7.5-8 hours, and pulverizing it through a 200-mesh sieve.

[0017] In step (b), the volume ratio of anhydrous ethanol to deionized water is 8:2.

[0018] In step (b), the mass-to-volume ratio of pretreated sepiolite to hydrolysate is 1:15, with units of g / mL.

[0019] In step (b), the mass of γ-glycidyl etheroxypropyltrimethoxysilane is 12% of the mass of sepiolite pretreated in step (a).

[0020] In step (c), the volume ratio of anhydrous ethanol to deionized water is 8:2.

[0021] In step (c), the mass-to-volume ratio of the mixed solvent of β-cyclodextrin, anhydrous ethanol, and deionized water is 1:18, in g / mL.

[0022] In step (c), the concentration of sodium hydroxide is 1 mol / L.

[0023] In step (c), the mass of β-cyclodextrin is 25% of the mass of sepiolite pretreated in step (a).

[0024] The post-treatment described in step (c) involves washing twice with ethanol at 55-60℃, washing with deionized water until no blue color develops when iodine solution is added to the filtrate, and finally vacuum drying the filter cake at 75℃ to constant weight, pulverizing it through a 200-mesh sieve to prepare modified sepiolite.

[0025] The preparation method of the oilfield produced water treatment agent of the present invention consists of the following steps: (1) Add ethylene glycol monobutyl ether to an atmospheric pressure reactor equipped with a stirrer, start stirring at 20-25°C, and then add trimethylolpropane polyoxypropylene polyoxyethylene ether and oleic acid imidazoline in sequence and stir for 20-30 min to mix evenly to prepare the first mixture; (2) Add the hydrophobic modified cationic polyacrylamide copolymer to the first deionized water and stir for 80-85 min until completely dissolved to prepare a hydrophobic modified cationic polyacrylamide aqueous solution; (3) Modified sepiolite was added to the second deionized water and ultrasonically dispersed to prepare a modified sepiolite suspension. (4) Add hydrophobic modified cationic polyacrylamide aqueous solution to the first mixture under stirring. After the addition is complete, continue stirring for 30-40 min to form a uniform emulsion dispersion system. Then add the modified sepiolite suspension in batches. After the addition is complete, raise the temperature to 40-45℃ and keep stirring for 55-60 min to obtain the second mixture. (5) Cool the second mixture to 30-35℃, add tetrasodium diacetate of glutamic acid to the second mixture and stir for 12-15 min to mix evenly, then add phosphonobutane tricarboxylic acid and stir for 20-25 min to mix evenly, then stop heating and let the system cool naturally to 25-30℃, then add dibromocyanate acetamide and stir for 15-20 min to mix evenly, continue stirring and maturing for 30-35 min, and finally filter. The resulting filtrate is the oilfield produced water treatment agent.

[0026] Wherein: the stirring speed in step (1) is 250 r / min.

[0027] In step (2), the stirring speed is 250 r / min and the stirring temperature is 20-25℃.

[0028] In step (3), the ultrasonic dispersion power is 300W, the ultrasonic mode is intermittent mode, that is, working for 2 seconds and then pausing for 1 second, and the total ultrasonic dispersion time is 15-20 minutes.

[0029] In step (4), the stirring speed is 250 r / min and the stirring temperature is 20-25℃.

[0030] In step (4), the hydrophobic modified cationic polyacrylamide aqueous solution is added within 8-10 minutes.

[0031] In step (4), the modified sepiolite suspension is divided into three equal parts, and one part is added every 8-10 minutes.

[0032] In step (5), the stirring speed is 250 r / min.

[0033] The filtration described in step (5) is performed using a 100-mesh filter.

[0034] Compared with the prior art, the present invention has the following advantages: (1) The oilfield produced water treatment agent of the present invention is mainly composed of hydrophobically modified cationic polyacrylamide copolymer, modified sepiolite and trimethylolpropane polyoxypropylene polyoxyethylene ether. Among them, trimethylolpropane polyoxypropylene polyoxyethylene ether reduces the interfacial tension between oil and water and weakens the strength of the emulsion film; modified sepiolite selectively captures pollutants through electrostatic attraction and host-guest inclusion; hydrophobically modified cationic polyacrylamide copolymer plays a role in long-chain polymer bridging to form dense flocs and achieve rapid oil-water separation; tetrasodium diacetate of glutamic acid, phosphonobutane tricarboxylic acid, imidazoline oleate and dibromocyanoacetamide respectively achieve chelation stability, scale inhibition, corrosion inhibition and antibacterial protection; ethylene glycol monobutyl ether improves the miscibility of each additive. Thus, the synergistic effect between the raw materials ensures that the prepared water treatment agent has good performance.

[0035] (2) The oilfield produced water treatment agent of the present invention, wherein the hydrophobically modified cationic polyacrylamide copolymer is copolymerized by free radical aqueous solution method, using azobisisobutyramidine hydrochloride as initiator, and at 54-56℃, three monomers, acrylamide, acryloyloxyethyl dimethyl benzyl ammonium chloride and acryloyloxyethyl dimethyl dodecyl ammonium chloride, undergo random copolymerization. Acrylamide constitutes the polymer backbone, and the two quaternary ammonium salt monomers respectively introduce cationic groups and hydrophobic long-chain alkyl side chains, thereby preparing a ternary copolymer with both high charge density and hydrophobic association properties. When this copolymer is used to treat oilfield produced water, the cationic quaternary ammonium groups on the molecular chain compress the electric double layer on the surface of colloidal particles and emulsified oil droplets in the water through charge neutralization, eliminating their stability; the polymer backbone connects the destabilized particles and oil droplets into coarse flocs through adsorption bridging, accelerating sedimentation or floating separation; the C of the side chain 12 Hydrophobic long chains bind to hydrophobic regions on the surface of oil droplets through hydrophobic interactions, causing interfacial displacement / perturbation at the oil-water interface and reducing the mechanical strength and elasticity of the interfacial film. Therefore, hydrophobically modified cationic polyacrylamide copolymers exert their effects on oilfield produced water through a triple mechanism of charge neutralization, adsorption bridging, and hydrophobic demulsification.

[0036] (3) The oilfield produced water treatment agent of the present invention, wherein the modified sepiolite is first acid-activated with hydrochloric acid to dissolve exchangeable magnesium ions in the crystal lattice, clear the pores and introduce a large number of silanol groups on the surface; then, γ-glycidoxypropyltrimethoxysilane is hydrolyzed under weakly acidic conditions, and its silanol condenses with the silanol groups on the sepiolite surface to form Si-O-Si covalent bonds, thus covalently grafting epoxy groups onto the sepiolite surface; finally, under alkaline conditions, the hydroxyl groups of β-cyclodextrin nucleophilically attack the epoxy groups to open the ring, thus achieving covalent bonding between β-cyclodextrin and the sepiolite surface. When this modified sepiolite is used for oilfield produced water treatment, the high specific surface area and pore structure generated by acid activation provide physical adsorption sites, the residual charge on the surface generates electrostatic attraction, and the grafted β-cyclodextrin has a hydrophobic cavity, which can selectively capture pollutants such as emulsified oil droplets and aromatic organic matter in the water through host-guest inclusion. In addition, modified sepiolite can also be embedded in flocs as a floc skeleton to improve floc density and settling performance, thereby achieving efficient oil-water separation.

[0037] (4) The preparation method of the oilfield produced water treatment agent described in this invention is simple and the parameters are reasonable. The oilfield produced water treatment agent prepared by this method has excellent oil removal rate, solid suspended matter removal rate, COD removal rate and scale and corrosion inhibition performance. Detailed Implementation

[0038] Example 1 The oilfield produced water treatment agent described in Example 1 is composed of the following raw materials by mass: 16 parts of hydrophobically modified cationic polyacrylamide copolymer, 9 parts of modified sepiolite, 11 parts of trimethylolpropane polyoxypropylene polyoxyethylene ether, 5.5 parts of ethylene glycol monobutyl ether, 3.0 parts of tetrasodium diacetate of glutamic acid, 3.3 parts of phosphonobutane tricarboxylic acid, 2.5 parts of oleic acid imidazoline, 1.7 parts of dibromocyanoacetamide, 320 parts of first deionized water, and 225 parts of second deionized water. The preparation method of the hydrophobically modified cationic polyacrylamide copolymer consists of the following steps: ① preparation of monomer solution; ② initiation of polymerization; ③ post-treatment. The preparation method of the modified sepiolite consists of the following steps: (a) preparation of pretreated sepiolite; (b) preparation of epoxy sepiolite wet filter cake; (c) preparation of modified sepiolite by epoxy ring-opening grafting of β-cyclodextrin.

[0039] The preparation method of the hydrophobically modified cationic polyacrylamide copolymer comprises the following steps: ① Preparation of monomer solution: Add deionized water to the reaction vessel, then add sodium chloride, disodium ethylenediaminetetraacetate and urea in sequence and stir to dissolve. Finally, add acrylamide, acryloyloxyethyl dimethyl benzyl ammonium chloride and acryloyloxyethyl dimethyl dodecyl ammonium chloride all at once and stir until completely clear. Heat to 55°C and bubble high-purity nitrogen gas to remove oxygen for 33 min to prepare monomer solution. ② Initiation of polymerization: Azobisisobutyramidine hydrochloride was dissolved in deoxygenated deionized water at 0℃ to prepare an initiator solution. High-purity nitrogen gas was bubbled through the reaction vessel containing the monomer solution to remove oxygen for 33 min. Then the initiator solution was added to the monomer solution at one time, the reaction vessel was sealed, and the reaction was carried out at a constant temperature of 55℃ for 5.7 h. ③ Post-treatment: Cool the reaction solution from step ② to room temperature, pour the reaction solution into acetone at 0℃, the volume of acetone being 6.5 times the volume of the reaction solution, stir continuously for 43 min, filter, and then wash twice with acetone, the volume of acetone used for each wash being 2.5 times the volume of the filter cake, and finally vacuum dry at 47℃ for 31.5 h, pass through a 40-mesh sieve to prepare the hydrophobic modified cationic polyacrylamide copolymer.

[0040] In step ①, the mass ratio of acrylamide, acryloyloxyethyl dimethyl benzyl ammonium chloride, and acryloyloxyethyl dimethyl dodecyl ammonium chloride is 8:2.5:2.

[0041] In step ①, the mass of sodium chloride accounts for 3.2% of the total mass of acrylamide, acryloyloxyethyl dimethyl benzyl ammonium chloride, and acryloyloxyethyl dimethyl dodecyl ammonium chloride.

[0042] In step ①, the mass ratio of sodium chloride, disodium ethylenediaminetetraacetate, and urea is 2:0.1:1.

[0043] In step ①, the mass of deionized water is 3.2 times the sum of the masses of acrylamide, acryloyloxyethyl dimethyl benzyl ammonium chloride, and acryloyloxyethyl dimethyl dodecyl ammonium chloride.

[0044] In step ②, the stirring speed during the isothermal reaction is 300 r / min.

[0045] In step ②, the mass ratio of azobisisobutyramidine hydrochloride to deoxygenated deionized water in the initiator solution is 0.28:20.

[0046] The preparation method of modified sepiolite consists of the following steps: (a) Preparation of pretreated sepiolite: sepiolite powder was added to hydrochloric acid and ultrasonically dispersed for 33 min to form a suspension slurry. The suspension slurry was then kept at 53℃ for 3.5 h. After the reaction was completed, it was naturally cooled to room temperature. Finally, the filter cake was filtered, washed with deionized water, dried, crushed and sieved to prepare pretreated sepiolite. (b) Preparation of epoxy sepiolite wet filter cake: Acetic acid was added to a mixed solvent of anhydrous ethanol and deionized water to adjust the pH of the system to 4.5. γ-glycidyl etheroxypropyltrimethoxysilane was added dropwise under stirring. The mixture was stirred and hydrolyzed at 45°C for 40 min to obtain a hydrolysate. Pretreated sepiolite was then added to the hydrolysate. The temperature was raised to 73°C and the mixture was stirred at 350 r / min for 5 h. After the reaction was completed, the mixture was separated by filtration. The filter cake was washed three times with anhydrous ethanol to obtain epoxy sepiolite wet filter cake. (c) Preparation of modified sepiolite by epoxy ring-opening grafting with β-cyclodextrin: β-cyclodextrin was added to a mixed solvent of anhydrous ethanol and deionized water and heated to reflux at 80°C for 57 min to disperse and dissolve it. The above dispersion was transferred to a reaction vessel, and the epoxy sepiolite wet filter cake prepared in step (b) was added and stirred evenly. Then, sodium hydroxide was added to the system to adjust the pH value of the system to 10.0. Under nitrogen protection, the temperature was maintained at 80°C and the reaction was stirred at 400 r / min for 7 h. After the reaction was completed, the mixture was filtered and finally post-processed to prepare modified sepiolite.

[0047] In step (a), the mass-to-volume ratio of sepiolite powder to hydrochloric acid is 1:20, with units of g / mL.

[0048] In step (a), the concentration of hydrochloric acid is 2.5 mol / L.

[0049] The process of washing the filter cake with deionized water, drying, pulverizing and sieving in step (a) specifically involves washing the filter cake with deionized water 6 times, drying it at a temperature of 67°C for 7.7 hours, and pulverizing it through a 200-mesh sieve.

[0050] In step (b), the volume ratio of anhydrous ethanol to deionized water is 8:2.

[0051] In step (b), the mass-to-volume ratio of pretreated sepiolite to hydrolysate is 1:15, with units of g / mL.

[0052] In step (b), the mass of γ-glycidyl etheroxypropyltrimethoxysilane is 12% of the mass of sepiolite pretreated in step (a).

[0053] In step (c), the volume ratio of anhydrous ethanol to deionized water is 8:2.

[0054] In step (c), the mass-to-volume ratio of the mixed solvent of β-cyclodextrin, anhydrous ethanol, and deionized water is 1:18, in g / mL.

[0055] In step (c), the concentration of sodium hydroxide is 1 mol / L.

[0056] In step (c), the mass of β-cyclodextrin is 25% of the mass of sepiolite pretreated in step (a).

[0057] The post-treatment described in step (c) involves washing twice with ethanol at 57°C, washing with deionized water until no blue color develops when iodine solution is added to the filtrate, and finally vacuum drying the filter cake at 75°C to constant weight, pulverizing it through a 200-mesh sieve to prepare modified sepiolite.

[0058] The preparation method of the oilfield produced water treatment agent described in Example 1 consists of the following steps: (1) Add ethylene glycol monobutyl ether to an atmospheric pressure reactor equipped with a stirrer, start stirring at 23°C, and then add trimethylolpropane polyoxypropylene polyoxyethylene ether and oleic acid imidazoline in sequence and stir for 27 min to mix evenly to prepare the first mixture. (2) Add hydrophobic modified cationic polyacrylamide copolymer to the first deionized water and stir for 83 min until completely dissolved to prepare hydrophobic modified cationic polyacrylamide aqueous solution; (3) Modified sepiolite was added to the second deionized water and ultrasonically dispersed to prepare a modified sepiolite suspension. (4) Add hydrophobic modified cationic polyacrylamide aqueous solution to the first mixture under stirring. After the addition is complete, continue stirring for 35 min to form a uniform emulsion dispersion system. Then add the modified sepiolite suspension in batches. After the addition is complete, heat to 43℃ and stir for 57 min to obtain the second mixture. (5) Cool the second mixture to 33°C, add tetrasodium diacetate of glutamic acid to the second mixture and stir for 13 min to mix evenly, then add phosphonobutane tricarboxylic acid and stir for 22 min to mix evenly, then stop heating and let the system cool naturally to 27°C, then add dibromocyanate acetamide and stir for 17 min to mix evenly, continue stirring and maturing for 33 min, and finally filter. The resulting filtrate is the oilfield produced water treatment agent.

[0059] Wherein: the stirring speed in step (1) is 250 r / min.

[0060] In step (2), the stirring speed is 250 r / min and the stirring temperature is 23℃.

[0061] In step (3), the ultrasonic dispersion power is 300W, the ultrasonic mode is intermittent mode, that is, working for 2 seconds and intermittent for 1 second, and the total ultrasonic dispersion time is 17 minutes.

[0062] In step (4), the stirring speed is 250 r / min and the stirring temperature is 23℃.

[0063] In step (4), the hydrophobic modified cationic polyacrylamide aqueous solution is added within 9 minutes.

[0064] In step (4), the modified sepiolite suspension is divided into three equal parts, and one part is added every 9 minutes.

[0065] In step (5), the stirring speed is 250 r / min.

[0066] The filtration described in step (5) is performed using a 100-mesh filter.

[0067] Example 2 The oilfield produced water treatment agent described in Example 2 is composed of the following raw materials by mass: 15 parts of hydrophobically modified cationic polyacrylamide copolymer, 10 parts of modified sepiolite, 10 parts of trimethylolpropane polyoxypropylene polyoxyethylene ether, 5 parts of ethylene glycol monobutyl ether, 3.5 parts of tetrasodium diacetate of glutamic acid, 3.0 parts of phosphonobutane tricarboxylic acid, 3 parts of imidazoline oleate, 1.5 parts of dibromocyanoacetamide, 300 parts of first deionized water, and 250 parts of second deionized water. The preparation method of the hydrophobically modified cationic polyacrylamide copolymer consists of the following steps: ① preparation of monomer solution; ② initiation of polymerization; ③ post-treatment. The preparation method of the modified sepiolite consists of the following steps: (a) preparation of pretreated sepiolite; (b) preparation of epoxy sepiolite wet filter cake; (c) preparation of modified sepiolite by epoxy ring-opening grafting of β-cyclodextrin.

[0068] The preparation method of the hydrophobically modified cationic polyacrylamide copolymer comprises the following steps: ① Preparation of monomer solution: Add deionized water to the reaction vessel, then add sodium chloride, disodium ethylenediaminetetraacetate and urea in sequence and stir to dissolve. Finally, add acrylamide, acryloyloxyethyl dimethyl benzyl ammonium chloride and acryloyloxyethyl dimethyl dodecyl ammonium chloride all at once and stir until completely clear. Heat to 54°C and bubble high-purity nitrogen gas to remove oxygen for 30 min to prepare monomer solution. ② Initiating polymerization: Azobisisobutyramidine hydrochloride was dissolved in deoxygenated deionized water at 0℃ to prepare an initiator solution. High-purity nitrogen gas was bubbled through the reaction vessel containing the monomer solution for 35 minutes to remove oxygen. Then the initiator solution was added to the monomer solution at one time, the reaction vessel was sealed, and the reaction was carried out at a constant temperature of 54℃ for 6 hours. ③ Post-treatment: Cool the reaction solution from step ② to room temperature, pour the reaction solution into acetone at 0℃, the volume of acetone being 6 times the volume of the reaction solution, stir continuously for 40 min, filter, and then wash twice with acetone, the volume of acetone used for each wash being 2 times the volume of the filter cake, and finally vacuum dry at 45℃ for 32 h, pass through a 40-mesh sieve to prepare the hydrophobic modified cationic polyacrylamide copolymer.

[0069] In step ①, the mass ratio of acrylamide, acryloyloxyethyl dimethyl benzyl ammonium chloride, and acryloyloxyethyl dimethyl dodecyl ammonium chloride is 8:2.5:2.

[0070] In step ①, the mass of sodium chloride accounts for 3.2% of the total mass of acrylamide, acryloyloxyethyl dimethyl benzyl ammonium chloride, and acryloyloxyethyl dimethyl dodecyl ammonium chloride.

[0071] In step ①, the mass ratio of sodium chloride, disodium ethylenediaminetetraacetate, and urea is 2:0.1:1.

[0072] In step ①, the mass of deionized water is 3.2 times the sum of the masses of acrylamide, acryloyloxyethyl dimethyl benzyl ammonium chloride, and acryloyloxyethyl dimethyl dodecyl ammonium chloride.

[0073] In step ②, the stirring speed during the isothermal reaction is 300 r / min.

[0074] In step ②, the mass ratio of azobisisobutyramidine hydrochloride to deoxygenated deionized water in the initiator solution is 0.28:20.

[0075] The preparation method of modified sepiolite consists of the following steps: (a) Preparation of pretreated sepiolite: sepiolite powder was added to hydrochloric acid and ultrasonically dispersed for 35 min to form a suspension slurry. The suspension slurry was then kept at 53℃ for 3.5 h. After the reaction was completed, it was naturally cooled to room temperature. Finally, the filter cake was filtered, washed with deionized water, dried, crushed and sieved to obtain pretreated sepiolite. (b) Preparation of epoxy sepiolite wet filter cake: Acetic acid was added to a mixed solvent of anhydrous ethanol and deionized water to adjust the pH of the system to 4.5. γ-glycidyl etheroxypropyltrimethoxysilane was added dropwise under stirring. The mixture was stirred and hydrolyzed at 45°C for 40 min to obtain a hydrolysate. Pretreated sepiolite was then added to the hydrolysate. The temperature was raised to 75°C and the mixture was stirred at 350 r / min for 5 h. After the reaction was completed, the mixture was separated by filtration. The filter cake was washed three times with anhydrous ethanol to obtain epoxy sepiolite wet filter cake. (c) Preparation of modified sepiolite by epoxy ring-opening grafting with β-cyclodextrin: β-cyclodextrin was added to a mixed solvent of anhydrous ethanol and deionized water and heated under reflux at 80°C for 55 min to disperse and dissolve it. The dispersion was transferred to a reaction vessel, and the epoxy sepiolite wet filter cake prepared in step (b) was added and stirred evenly. Then, sodium hydroxide was added to the system to adjust the pH value of the system to 10.0. Under nitrogen protection, the temperature was maintained at 80°C and the reaction was stirred at 400 r / min for 7 h. After the reaction was completed, the mixture was filtered and finally post-processed to prepare modified sepiolite.

[0076] In step (a), the mass-to-volume ratio of sepiolite powder to hydrochloric acid is 1:20, with units of g / mL.

[0077] In step (a), the concentration of hydrochloric acid is 2.5 mol / L.

[0078] The process of washing the filter cake with deionized water, drying, pulverizing and sieving in step (a) specifically involves washing the filter cake with deionized water 6 times, drying it at a temperature of 70°C for 7.5 hours, and pulverizing it through a 200-mesh sieve.

[0079] In step (b), the volume ratio of anhydrous ethanol to deionized water is 8:2.

[0080] In step (b), the mass-to-volume ratio of pretreated sepiolite to hydrolysate is 1:15, with units of g / mL.

[0081] In step (b), the mass of γ-glycidyl etheroxypropyltrimethoxysilane is 12% of the mass of sepiolite pretreated in step (a).

[0082] In step (c), the volume ratio of anhydrous ethanol to deionized water is 8:2.

[0083] In step (c), the mass-to-volume ratio of the mixed solvent of β-cyclodextrin, anhydrous ethanol, and deionized water is 1:18, in g / mL.

[0084] In step (c), the concentration of sodium hydroxide is 1 mol / L.

[0085] In step (c), the mass of β-cyclodextrin is 25% of the mass of sepiolite pretreated in step (a).

[0086] The post-treatment described in step (c) involves washing twice with ethanol at 60°C, washing with deionized water until no blue color develops when iodine solution is added to the filtrate, and finally vacuum drying the filter cake at 75°C to constant weight, pulverizing it through a 200-mesh sieve to prepare modified sepiolite.

[0087] The preparation method of the oilfield produced water treatment agent described in Example 2 consists of the following steps: (1) Add ethylene glycol monobutyl ether to an atmospheric pressure reactor equipped with a stirrer, start stirring at 20°C, and then add trimethylolpropane polyoxypropylene polyoxyethylene ether and oleic acid imidazoline in sequence and stir for 30 min to mix evenly to prepare the first mixture. (2) Add hydrophobic modified cationic polyacrylamide copolymer to the first deionized water and stir for 80 min until completely dissolved to prepare hydrophobic modified cationic polyacrylamide aqueous solution; (3) Modified sepiolite was added to the second deionized water and ultrasonically dispersed to prepare a modified sepiolite suspension. (4) Add hydrophobic modified cationic polyacrylamide aqueous solution to the first mixture under stirring. After the addition is complete, continue stirring for 30 min to form a uniform emulsion dispersion system. Then add the modified sepiolite suspension in batches. After the addition is complete, heat to 40℃ and stir for 60 min to obtain the second mixture. (5) Cool the second mixture to 30°C, add tetrasodium diacetate of glutamic acid to the second mixture and stir for 15 minutes to mix evenly, then add phosphonobutane tricarboxylic acid and stir for 20 minutes to mix evenly, then stop heating and let the system cool naturally to 25°C, then add dibromocyanate acetamide and stir for 20 minutes to mix evenly, continue stirring and maturing for 30 minutes, and finally filter. The resulting filtrate is the oilfield produced water treatment agent.

[0088] Wherein: the stirring speed in step (1) is 250 r / min.

[0089] In step (2), the stirring speed is 250 r / min and the stirring temperature is 20℃.

[0090] In step (3), the ultrasonic dispersion power is 300W, the ultrasonic mode is intermittent mode, that is, working for 2 seconds and then intermittent for 1 second, and the total ultrasonic dispersion time is 20 minutes.

[0091] In step (4), the stirring speed is 250 r / min and the stirring temperature is 20℃.

[0092] In step (4), the hydrophobic modified cationic polyacrylamide aqueous solution is added within 8 minutes.

[0093] In step (4), the modified sepiolite suspension is divided into three equal parts, and one part is added every 10 minutes.

[0094] In step (5), the stirring speed is 250 r / min.

[0095] The filtration described in step (5) is performed using a 100-mesh filter.

[0096] Example 3 The oilfield produced water treatment agent described in Example 3 is composed of the following raw materials by mass: 17 parts of hydrophobic modified cationic polyacrylamide copolymer, 8 parts of modified sepiolite, 12 parts of trimethylolpropane polyoxypropylene polyoxyethylene ether, 6 parts of ethylene glycol monobutyl ether, 2.5 parts of tetrasodium diacetate of glutamic acid, 3.5 parts of phosphonobutane tricarboxylic acid, 2 parts of oleic acid imidazoline, 2 parts of dibromocyanoacetamide, 340 parts of first deionized water, and 200 parts of second deionized water. The preparation method of the hydrophobic modified cationic polyacrylamide copolymer consists of the following steps: ① preparation of monomer solution; ② initiation of polymerization; ③ post-treatment. The preparation method of the modified sepiolite consists of the following steps: (a) preparation of pretreated sepiolite; (b) preparation of epoxy sepiolite wet filter cake; (c) preparation of modified sepiolite by epoxy ring-opening grafting of β-cyclodextrin.

[0097] The preparation method of the hydrophobically modified cationic polyacrylamide copolymer comprises the following steps: ① Preparation of monomer solution: Add deionized water to the reaction vessel, then add sodium chloride, disodium ethylenediaminetetraacetate and urea in sequence and stir to dissolve. Finally, add acrylamide, acryloyloxyethyl dimethyl benzyl ammonium chloride and acryloyloxyethyl dimethyl dodecyl ammonium chloride all at once and stir until completely clear. Heat to 56°C and bubble high-purity nitrogen gas to remove oxygen for 35 min to prepare monomer solution. ② Initiation of polymerization: Azobisisobutyramidine hydrochloride was dissolved in deoxygenated deionized water at 0℃ to prepare an initiator solution. High-purity nitrogen gas was bubbled through the reaction vessel containing the monomer solution to remove oxygen for 30 min. Then the initiator solution was added to the monomer solution at one time, the reaction vessel was sealed, and the reaction was carried out at a constant temperature of 56℃ for 5.5 h. ③ Post-treatment: Cool the reaction solution from step ② to room temperature, pour the reaction solution into acetone at 0℃, the volume of acetone being 7 times the volume of the reaction solution, stir continuously for 45 min, filter, and then wash twice with acetone, the volume of acetone used for each wash being 3 times the volume of the filter cake, and finally vacuum dry at 50℃ for 31 h, pass through a 40-mesh sieve to prepare the hydrophobic modified cationic polyacrylamide copolymer.

[0098] In step ①, the mass ratio of acrylamide, acryloyloxyethyl dimethyl benzyl ammonium chloride, and acryloyloxyethyl dimethyl dodecyl ammonium chloride is 8:2.5:2.

[0099] In step ①, the mass of sodium chloride accounts for 3.2% of the total mass of acrylamide, acryloyloxyethyl dimethyl benzyl ammonium chloride, and acryloyloxyethyl dimethyl dodecyl ammonium chloride.

[0100] In step ①, the mass ratio of sodium chloride, disodium ethylenediaminetetraacetate, and urea is 2:0.1:1.

[0101] In step ①, the mass of deionized water is 3.2 times the sum of the masses of acrylamide, acryloyloxyethyl dimethyl benzyl ammonium chloride, and acryloyloxyethyl dimethyl dodecyl ammonium chloride.

[0102] In step ②, the stirring speed during the isothermal reaction is 300 r / min.

[0103] In step ②, the mass ratio of azobisisobutyramidine hydrochloride to deoxygenated deionized water in the initiator solution is 0.28:20.

[0104] The preparation method of modified sepiolite consists of the following steps: (a) Preparation of pretreated sepiolite: sepiolite powder was added to hydrochloric acid and ultrasonically dispersed for 30 min to form a suspension slurry. The suspension slurry was then kept at 53℃ for 3.5 h. After the reaction was completed, it was naturally cooled to room temperature. Finally, the filter cake was filtered, washed with deionized water, dried, crushed and sieved to obtain pretreated sepiolite. (b) Preparation of epoxy sepiolite wet filter cake: Acetic acid was added to a mixed solvent of anhydrous ethanol and deionized water to adjust the pH of the system to 4.5. γ-glycidyl etheroxypropyltrimethoxysilane was added dropwise under stirring. The mixture was stirred and hydrolyzed at 45°C for 40 min to obtain a hydrolysate. Pretreated sepiolite was then added to the hydrolysate. The temperature was raised to 70°C and the mixture was stirred at 350 r / min for 5 h. After the reaction was completed, the mixture was separated by filtration. The filter cake was washed twice with anhydrous ethanol to obtain epoxy sepiolite wet filter cake. (c) Preparation of modified sepiolite by epoxy ring-opening grafting with β-cyclodextrin: β-cyclodextrin was added to a mixed solvent of anhydrous ethanol and deionized water and heated to reflux at 80°C for 60 min to disperse and dissolve it. The above dispersion was transferred to a reaction vessel, and the epoxy sepiolite wet filter cake prepared in step (b) was added and stirred evenly. Then, sodium hydroxide was added to the system to adjust the pH value of the system to 10.0. Under nitrogen protection, the temperature was maintained at 80°C and the reaction was stirred at 400 r / min for 7 h. After the reaction was completed, the mixture was filtered and finally post-processed to prepare modified sepiolite.

[0105] In step (a), the mass-to-volume ratio of sepiolite powder to hydrochloric acid is 1:20, with units of g / mL.

[0106] In step (a), the concentration of hydrochloric acid is 2.5 mol / L.

[0107] The process of washing the filter cake with deionized water, drying, pulverizing and sieving in step (a) specifically involves washing the filter cake with deionized water 5 times, drying it at a temperature of 65°C for 8 hours, and pulverizing it through a 200-mesh sieve.

[0108] In step (b), the volume ratio of anhydrous ethanol to deionized water is 8:2.

[0109] In step (b), the mass-to-volume ratio of pretreated sepiolite to hydrolysate is 1:15, with units of g / mL.

[0110] In step (b), the mass of γ-glycidyl etheroxypropyltrimethoxysilane is 12% of the mass of sepiolite pretreated in step (a).

[0111] In step (c), the volume ratio of anhydrous ethanol to deionized water is 8:2.

[0112] In step (c), the mass-to-volume ratio of the mixed solvent of β-cyclodextrin, anhydrous ethanol, and deionized water is 1:18, in g / mL.

[0113] In step (c), the concentration of sodium hydroxide is 1 mol / L.

[0114] In step (c), the mass of β-cyclodextrin is 25% of the mass of sepiolite pretreated in step (a).

[0115] The post-treatment described in step (c) involves washing twice with ethanol at 55°C, washing with deionized water until no blue color develops when iodine solution is added to the filtrate, and finally vacuum drying the filter cake at 75°C to constant weight, pulverizing it through a 200-mesh sieve to prepare modified sepiolite.

[0116] The preparation method of the oilfield produced water treatment agent described in Example 3 consists of the following steps: (1) Add ethylene glycol monobutyl ether to an atmospheric pressure reactor equipped with a stirrer, start stirring at 25°C, and then add trimethylolpropane polyoxypropylene polyoxyethylene ether and oleic acid imidazoline in sequence and stir for 20 min to mix evenly to prepare the first mixture; (2) Add the hydrophobic modified cationic polyacrylamide copolymer to the first deionized water and stir for 85 min until completely dissolved to prepare a hydrophobic modified cationic polyacrylamide aqueous solution; (3) Modified sepiolite was added to the second deionized water and ultrasonically dispersed to prepare a modified sepiolite suspension. (4) Add hydrophobic modified cationic polyacrylamide aqueous solution to the first mixture under stirring. After the addition is complete, continue stirring for 40 min to form a uniform emulsion dispersion system. Then add the modified sepiolite suspension in batches. After the addition is complete, heat to 45℃ and stir for 55 min to obtain the second mixture. (5) Cool the second mixture to 35°C, add tetrasodium diacetate of glutamic acid to the second mixture and stir for 12 min to mix evenly, then add phosphonobutane tricarboxylic acid and stir for 25 min to mix evenly, then stop heating and let the system cool naturally to 30°C, then add dibromocyanate acetamide and stir for 15 min to mix evenly, continue stirring and aging for 35 min, and finally filter. The resulting filtrate is the oilfield produced water treatment agent.

[0117] Wherein: the stirring speed in step (1) is 250 r / min.

[0118] In step (2), the stirring speed is 250 r / min and the stirring temperature is 25℃.

[0119] In step (3), the ultrasonic dispersion power is 300W, the ultrasonic mode is intermittent mode, that is, working for 2 seconds and intermittent for 1 second, and the total ultrasonic dispersion time is 15 minutes.

[0120] In step (4), the stirring speed is 250 r / min and the stirring temperature is 25℃.

[0121] In step (4), the hydrophobic modified cationic polyacrylamide aqueous solution is added within 10 minutes.

[0122] In step (4), the modified sepiolite suspension is divided into three equal parts, and one part is added every 8 minutes.

[0123] In step (5), the stirring speed is 250 r / min.

[0124] The filtration described in step (5) is performed using a 100-mesh filter.

[0125] Comparative Example 1 The preparation method of the oilfield produced water treatment agent described in Comparative Example 1 is the same as that in Example 1, the only difference being the composition of the raw materials. The oilfield produced water treatment agent described in Comparative Example 1, by mass parts, consists of the following raw materials: 9 parts modified sepiolite, 11 parts trimethylolpropane polyoxypropylene polyoxyethylene ether, 5.5 parts ethylene glycol monobutyl ether, 3.0 parts tetrasodium diacetate of glutamic acid, 3.3 parts phosphonobutane tricarboxylic acid, 2.5 parts imidazoline oleate, 1.7 parts dibromocyanoacetamide, 320 parts first deionized water, and 225 parts second deionized water. The preparation method of the modified sepiolite is the same as that in Example 1.

[0126] Comparative Example 2 The preparation method of the oilfield produced water treatment agent described in Comparative Example 2 is the same as that in Example 1, the only difference being the composition of the raw materials. The oilfield produced water treatment agent described in Comparative Example 2, by mass parts, consists of the following raw materials: 16 parts of hydrophobically modified cationic polyacrylamide copolymer, 11 parts of trimethylolpropane polyoxypropylene polyoxyethylene ether, 5.5 parts of ethylene glycol monobutyl ether, 3.0 parts of tetrasodium diacetate of glutamic acid, 3.3 parts of phosphonobutane tricarboxylic acid, 2.5 parts of imidazoline oleate, 1.7 parts of dibromocyanoacetamide, 320 parts of first deionized water, and 225 parts of second deionized water. The preparation method of the hydrophobically modified cationic polyacrylamide copolymer is the same as that in Example 1.

[0127] Comparative Example 3 The preparation method of the oilfield produced water treatment agent described in Comparative Example 3 is the same as that in Example 1, the only difference being the composition of the raw materials. The oilfield produced water treatment agent described in Comparative Example 3, by mass parts, consists of the following raw materials: 16 parts of hydrophobically modified cationic polyacrylamide copolymer, 9 parts of modified sepiolite, 5.5 parts of ethylene glycol monobutyl ether, 3.0 parts of tetrasodium diacetate of glutamic acid, 3.3 parts of phosphonobutane tricarboxylic acid, 2.5 parts of imidazoline oleate, 1.7 parts of dibromocyanacetamide, 320 parts of first deionized water, and 225 parts of second deionized water. The preparation methods of the hydrophobically modified cationic polyacrylamide copolymer and the modified sepiolite are the same as in Example 1.

[0128] The performance of the oilfield produced water treatment agents prepared in Examples 1-3 and Comparative Examples 1-3 was tested. The oilfield produced water quality was as follows: total salinity 40859 mg / L, suspended solids content 215 mg / L, and oil content 908 mg / L. The agents were added to the oilfield produced water samples to be treated at a dosage of 120 mg / L. After stirring for 3 hours to allow sufficient reaction, the oil removal rate, suspended solids removal rate, and COD removal rate were tested. Corrosion inhibition performance was tested according to SY / T5273-2014 "Performance Indicators and Evaluation Methods for Corrosion Inhibitors for Oilfield Produced Water Treatment". The experimental conditions were: temperature 55℃, time 120 h, test piece: Q235 steel, rotation speed 100 r / min. The scale inhibition performance of calcium carbonate was tested according to SY / T 5673-93 "Performance Evaluation Method for Scale Inhibitors for Oilfield Use". The test temperature was 70℃, and the time was 25 h. The test results are shown in Table 1.

[0129] Table 1. Test results of oilfield produced water treatment reagents

[0130] As shown in Table 1, the performance of the oilfield produced water treatment agents prepared in Examples 1-3 is significantly better than that in Comparative Examples 1-3. The performance of the oilfield produced water treatment agents in Comparative Examples 1-3 is greatly reduced due to the absence of any one of the hydrophobic modified cationic polyacrylamide copolymer, modified sepiolite, and trimethylolpropane polyoxypropylene polyoxyethylene ether in the raw materials.

[0131] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A chemical agent for treating produced water in oilfields, characterized in that: The mixture, by mass fraction, comprises the following raw materials: 15-17 parts of hydrophobically modified cationic polyacrylamide copolymer, 8-10 parts of modified sepiolite, 10-12 parts of trimethylolpropane polyoxypropylene polyoxyethylene ether, 5-6 parts of ethylene glycol monobutyl ether, 2.5-3.5 parts of tetrasodium diacetate of glutamic acid, 3.0-3.5 parts of phosphonobutane tricarboxylic acid, 2-3 parts of imidazoline oleate, 1.5-2 parts of dibromocyanoacetamide, 300-340 parts of first deionized water, and 200-250 parts of second deionized water. The preparation method of the hydrophobically modified cationic polyacrylamide copolymer consists of the following steps: ① preparation of monomer solution; ② initiation of polymerization; ③ post-treatment. The preparation method of the modified sepiolite consists of the following steps: (a) preparation of pretreated sepiolite; (b) preparation of epoxy sepiolite wet filter cake; (c) preparation of modified sepiolite by epoxy ring-opening grafting with β-cyclodextrin.

2. The oilfield produced water treatment agent according to claim 1, characterized in that: The preparation method of the hydrophobically modified cationic polyacrylamide copolymer comprises the following steps: ① Preparation of monomer solution: Add deionized water to the reaction vessel, then add sodium chloride, disodium ethylenediaminetetraacetate and urea in sequence and stir to dissolve. Finally, add acrylamide, acryloyloxyethyl dimethyl benzyl ammonium chloride and acryloyloxyethyl dimethyl dodecyl ammonium chloride in one go and stir until completely clear. Heat to 54-56℃ and bubble high-purity nitrogen gas to remove oxygen for 30-35 minutes to prepare monomer solution; ② Initiating polymerization: Azobisisobutyramidine hydrochloride is dissolved in deoxygenated deionized water at 0℃ to prepare an initiator solution. High-purity nitrogen gas is bubbled through the reaction vessel containing the monomer solution to remove oxygen for 30-35 minutes. Then, the initiator solution is added to the monomer solution at once, the reaction vessel is sealed, and the reaction is carried out at a constant temperature of 54-56℃ for 5.5-6 hours. ③ Post-treatment: Cool the reaction solution from step ② to room temperature, pour the reaction solution into acetone at 0℃, the volume of acetone being 6-7 times the volume of the reaction solution, stir continuously for 40-45 minutes, filter, and then wash twice with acetone, the volume of acetone used for each wash being 2-3 times the volume of the filter cake, and finally vacuum dry at 45-50℃ for 31-32 hours, pass through a 40-mesh sieve to prepare the hydrophobic modified cationic polyacrylamide copolymer.

3. The oilfield produced water treatment agent according to claim 2, characterized in that: In step ①, the mass ratio of acrylamide, acryloyloxyethyl dimethyl benzyl ammonium chloride, and acryloyloxyethyl dimethyl dodecyl ammonium chloride is 8: 2.5:

2. In step ①, the mass of sodium chloride accounts for 3.2% of the total mass of acrylamide, acryloyloxyethyl dimethyl benzyl ammonium chloride, and acryloyloxyethyl dimethyl dodecyl ammonium chloride. In step ①, the mass ratio of sodium chloride, disodium ethylenediaminetetraacetate, and urea is 2:0.1:

1. In step ①, the mass of deionized water is 3.2 times the sum of the masses of acrylamide, acryloyloxyethyl dimethyl benzyl ammonium chloride, and acryloyloxyethyl dimethyl dodecyl ammonium chloride.

4. The oilfield produced water treatment agent according to claim 2, characterized in that: In step ②, the stirring speed during the isothermal reaction is 300 r / min; In step ②, the mass ratio of azobisisobutyramidine hydrochloride to deoxygenated deionized water in the initiator solution is 0.28:

20.

5. The oilfield produced water treatment agent according to claim 1, characterized in that: The preparation method of modified sepiolite consists of the following steps: (a) Preparation of pretreated sepiolite: sepiolite powder was added to hydrochloric acid and ultrasonically dispersed for 30-35 min to form a suspension slurry. The suspension slurry was then kept at 53℃ for 3.5 h. After the reaction was completed, it was naturally cooled to room temperature. Finally, the filter cake was filtered, washed with deionized water, dried, crushed and sieved to obtain pretreated sepiolite. (b) Preparation of epoxy sepiolite wet filter cake: Add acetic acid to a mixed solvent of anhydrous ethanol and deionized water to adjust the pH of the system to 4.

5. Add γ-glycidyl etheroxypropyltrimethoxysilane dropwise under stirring. Stir and hydrolyze at 45°C for 40 min to obtain hydrolysate. Then add pretreated sepiolite to the hydrolysate, heat to 70-75°C, and stir at 350 r / min for 5 h. After the reaction is completed, filter and separate. Wash the filter cake 2-3 times with anhydrous ethanol to prepare epoxy sepiolite wet filter cake. (c) Preparation of modified sepiolite by epoxy ring-opening grafting of β-cyclodextrin: β-cyclodextrin was added to a mixed solvent of anhydrous ethanol and deionized water and heated under reflux at 80°C for 55-60 min to disperse and dissolve it. The dispersion was transferred to a reaction vessel, and the epoxy sepiolite wet filter cake prepared in step (b) was added and stirred evenly. Then, sodium hydroxide was added to the system to adjust the pH value of the system to 10.

0. Under nitrogen protection, the temperature was maintained at 80°C and the reaction was stirred at 400 r / min for 7 h. After the reaction was completed, the mixture was filtered and finally post-treated to prepare modified sepiolite.

6. The oilfield produced water treatment agent according to claim 5, characterized in that: In step (a), the mass-to-volume ratio of sepiolite powder to hydrochloric acid is 1:20, with units of g / mL. In step (a), the concentration of hydrochloric acid is 2.5 mol / L; The process of washing the filter cake with deionized water, drying, pulverizing and sieving in step (a) specifically involves washing the filter cake with deionized water 5-6 times, drying at a temperature of 65-70℃ for 7.5-8 hours, and pulverizing it through a 200-mesh sieve.

7. The oilfield produced water treatment agent according to claim 5, characterized in that: In step (b), the volume ratio of anhydrous ethanol to deionized water is 8:2; In step (b), the mass-to-volume ratio of pretreated sepiolite to hydrolysate is 1:15, in g / mL. In step (b), the mass of γ-glycidyl etheroxypropyltrimethoxysilane is 12% of the mass of sepiolite pretreated in step (a).

8. The oilfield produced water treatment agent according to claim 5, characterized in that: In step (c), the volume ratio of anhydrous ethanol to deionized water is 8:2; In step (c), the mass-to-volume ratio of the mixed solvent of β-cyclodextrin, anhydrous ethanol, and deionized water is 1:18, with units of g / mL. In step (c), the concentration of sodium hydroxide is 1 mol / L; In step (c), the mass of β-cyclodextrin is 25% of the mass of the pretreated sepiolite in step (a); The post-treatment described in step (c) involves washing twice with ethanol at 55-60℃, washing with deionized water until no blue color develops when iodine solution is added to the filtrate, and finally vacuum drying the filter cake at 75℃ to constant weight, pulverizing it through a 200-mesh sieve to prepare modified sepiolite.

9. A method for preparing the oilfield produced water treatment agent according to claim 1, characterized in that: It consists of the following steps: (1) Add ethylene glycol monobutyl ether to an atmospheric pressure reactor equipped with a stirrer, start stirring at 20-25°C, and then add trimethylolpropane polyoxypropylene polyoxyethylene ether and oleic acid imidazoline in sequence and stir for 20-30 min to mix evenly to prepare the first mixture; (2) Add the hydrophobic modified cationic polyacrylamide copolymer to the first deionized water and stir for 80-85 min until completely dissolved to prepare a hydrophobic modified cationic polyacrylamide aqueous solution; (3) Modified sepiolite was added to the second deionized water and ultrasonically dispersed to prepare a modified sepiolite suspension. (4) Add hydrophobic modified cationic polyacrylamide aqueous solution to the first mixture under stirring. After the addition is complete, continue stirring for 30-40 min to form a uniform emulsion dispersion system. Then add the modified sepiolite suspension in batches. After the addition is complete, heat to 40-45℃ and stir for 55-60 min to obtain the second mixture. (5) Cool the second mixture to 30-35℃, add tetrasodium diacetate of glutamic acid to the second mixture and stir for 12-15 min to mix evenly, then add phosphonobutane tricarboxylic acid and stir for 20-25 min to mix evenly, then stop heating and let the system cool naturally to 25-30℃, then add dibromocyanate acetamide and stir for 15-20 min to mix evenly, continue stirring and maturing for 30-35 min, and finally filter. The resulting filtrate is the oilfield produced water treatment agent.

10. The method for preparing the oilfield produced water treatment agent according to claim 9, characterized in that: The stirring speed in step (1) is 250 r / min; In step (2), the stirring speed is 250 r / min and the stirring temperature is 20-25℃; In step (3), the ultrasonic dispersion power is 300W, the ultrasonic mode is intermittent mode, that is, working for 2 seconds and then pausing for 1 second, and the total ultrasonic dispersion time is 15-20 minutes. In step (4), the stirring speed is 250 r / min and the stirring temperature is 20-25℃; In step (4), the hydrophobic modified cationic polyacrylamide aqueous solution is added within 8-10 minutes; In step (4), the modified sepiolite suspension is divided into three equal parts, and one part is added every 8-10 minutes. The stirring speed in step (5) is 250 r / min; The filtration described in step (5) is performed using a 100-mesh filter.

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