High temperature resistant workover fluid and method of making same

Abstract

This application relates to the field of well workover fluid technology, specifically to a high-temperature resistant well workover fluid and its preparation method. The high-temperature resistant well workover fluid comprises the following raw materials: deionized water, modified anti-settling enhancer, temperature-resistant polymer thickener, heat stabilizer, viscosity stabilizer, bactericide, density regulator, and plugging agent. The preparation method of the high-temperature resistant well workover fluid is as follows: Density regulator and plugging agent are added sequentially to deionized water and stirred evenly; then the modified anti-settling enhancer and temperature-resistant polymer thickener are added and stirred evenly; next, the heat stabilizer and viscosity stabilizer are added, and the mixture is stirred at a constant temperature. After cooling to room temperature, the bactericide is added, stirred evenly, and allowed to stand for aging to obtain the high-temperature resistant well workover fluid. This high-temperature resistant well workover fluid exhibits outstanding high-temperature stability. After standing at 210℃ for 7 days, the density remains stable, and the parameters of plastic viscosity, dynamic shear force, and initial / final shear are reasonable, with no significant sedimentation, effectively improving the stability of the well workover fluid at high temperatures.

Description

Technical Field

[0001] This application relates to the field of well workover fluid technology, and more specifically, to a high-temperature resistant well workover fluid and its preparation method. Background Technology

[0002] As oil and gas field drilling and development continues to advance into ultra-deep areas, the increasing well depth leads to a significant rise in downhole temperature, which can reach nearly 210°C. In addition, wells often face complex operating environments such as brine intrusion and oil and gas intrusion, which places more stringent requirements on the high-temperature stability of workover fluids.

[0003] As a key component in well workover and completion operations for oil and gas wells, the performance of workover fluids directly impacts operational efficiency and downhole safety. Currently, for ultra-deep and ultra-high-temperature wells, conventional water-based workover fluids often struggle to address the issue of high-temperature stability, failing to construct a stable, uniformly dispersed colloidal structure of ultra-fine weighted particles at high temperatures, thus failing to meet the operational requirements under high-temperature conditions. While most oil-based workover fluid systems used in the industry can achieve high-temperature resistance, they suffer from drawbacks such as significantly increased operating costs and prominent safety and environmental risks. Therefore, developing a workover fluid with excellent high-temperature resistance, safety, environmental friendliness, and controllable costs to meet the workover needs of ultra-deep and ultra-high-temperature oil and gas wells has become an urgent technical challenge in the field of workover fluid technology. Summary of the Invention

[0004] To address the technical problems mentioned in the background section, this application provides a high-temperature resistant well workover fluid and its preparation method.

[0005] Firstly, this application provides a high-temperature resistant well workover fluid, employing the following technical solution:

[0006] A high-temperature resistant well workover fluid, by weight, comprises the following components: 100-120 parts deionized water, 1.5-3 parts modified anti-settling enhancer, 0.5-2 parts heat-resistant polymer thickener, 0.3-1.5 parts heat stabilizer, 1-5 parts viscosity stabilizer, 0.1-0.8 parts bactericide, 8-12 parts density adjuster, and 2-6 parts plugging agent.

[0007] Preferably, the preparation method of the modified anti-settling enhancer includes the following preparation steps:

[0008] The nano-reinforcing agent was added to an ethanol aqueous solution and dispersed by ultrasound. The pH was then adjusted to 4.0-5.5 to obtain a nano-powder dispersion. The composite coupling agent was added to the ethanol aqueous solution and hydrolyzed at a constant temperature of 40-50℃ to obtain a hydrolyzed composite coupling agent solution. The hydrolyzed composite coupling agent solution was added dropwise to the nano-powder dispersion. After the addition was complete, the temperature was raised to 75-85℃ and the reaction was stirred for 3-5 hours. After the reaction was completed, the mixture was centrifuged, washed, and dried to obtain the modified anti-settling reinforcing agent.

[0009] Preferably, the nano-reinforcing agent is one or more of nano-silica, nano-magnesium oxide, and sodium montmorillonite; the composite coupling agent is composed of phenyltriethoxysilane and aminopropyltriethoxysilane in a mass ratio of 10-15:4-8.

[0010] Preferably, the preparation method of the heat-resistant polymer thickener includes the following preparation steps:

[0011] Step 1: Add acrylamide, 2-acrylamido-2-methylpropanesulfonic acid and N-vinylpyrrolidone to deionized water, adjust the pH of the system to 7.0-8.5, add redox initiator under nitrogen protection, control the reaction start temperature to 5-10℃, and carry out the closed isothermal polymerization reaction for 4-6 hours. Then raise the temperature to 40-50℃ and keep it warm for 2-3 hours. After the reaction is completed, crush, dry and sieve to obtain ternary random copolymer.

[0012] Step 2: Mix the ternary random copolymer and the heat-resistant modified starch derivative, and stir evenly to obtain the heat-resistant polymer thickener.

[0013] Preferably, in step 1, the mass ratio of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone, redox initiator and deionized water is 65-75:20-28:3-7:0.1-0.15:350-450.

[0014] Preferably, in step 2, the mass ratio of the ternary random copolymer to the heat-resistant modified starch derivative is 85-90:10-15.

[0015] Preferably, the heat-resistant modified starch derivative in step 2 is one or more of hydroxypropyl distarch phosphate, acetylated distarch phosphate, and phosphorylated distarch phosphate.

[0016] Preferably, the heat stabilizer is composed of zinc oxide and diethylenetriaminepentamethylphosphonic acid in a mass ratio of 2-4:1-1.2.

[0017] Preferably, the viscosity stabilizer is one or more of organobentonite, attapulgite, and polyanionic cellulose.

[0018] Preferably, the bactericide is one or more of glutaraldehyde, isothiazolinone, and dodecyl dimethyl benzyl ammonium chloride.

[0019] Preferably, the density regulator is one or more of barite powder, limestone powder, and iron ore powder.

[0020] Preferably, the sealing agent is one or more of diatomaceous earth, asbestos wool, expanded graphite, and nano-calcium carbonate.

[0021] Secondly, this application also provides a method for preparing a high-temperature resistant well workover fluid, employing the following technical solution:

[0022] A method for preparing a high-temperature resistant well workover fluid includes the following preparation steps:

[0023] Add density regulator and plugging agent to deionized water in sequence and stir until uniformly dispersed. Then add modified anti-settling enhancer and ultrasonically disperse. Add heat-resistant polymer thickener and stir for 30-40 minutes. Add heat stabilizer and viscosity stabilizer, heat to 40-50℃, stir at constant temperature for 1-2 hours, cool to room temperature, add bactericide, stir for 10-15 minutes until uniformly mixed, and let stand for 30-60 minutes to mature. The high-temperature resistant well workover fluid is then obtained.

[0024] In summary, this application has the following beneficial effects:

[0025] This application modifies nano-reinforcing agents using a composite coupling agent of phenyltriethoxysilane and aminopropyltriethoxysilane. By precisely controlling the parameters of ultrasonic dispersion, hydrolysis, and grafting reactions, the functional groups of the two coupling agents achieve synergistic effects. The aminopropyl group of aminopropyltriethoxysilane possesses strong polarity and high reactivity, enabling it to undergo an efficient grafting reaction with the hydroxyl groups on the surface of the nano-reinforcing agent, forming stable chemical bonds and firmly anchoring it to the surface of the nano-reinforcing agent. This enhances the bonding strength between the coupling agent and the nano-reinforcing agent, while also strengthening the interfacial bonding with polar components in the workover fluid. The phenyl group of phenyltriethoxysilane exhibits excellent temperature resistance, forming a hydrophobic protective layer on the surface of the nanoparticles, inhibiting particle aggregation at high temperatures. The combination of these two agents effectively solves the problems of insufficient dispersibility and inadequate temperature resistance when modifying single coupling agents, allowing the nano-reinforcing agent to remain uniformly dispersed even at high temperatures, significantly improving the structural integrity and anti-settling ability of the workover fluid.

[0026] This application prepares a heat-resistant polymer thickener by constructing a ternary copolymer system of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and N-vinylpyrrolidone. Strict control of the polymerization and compounding processes ensures the precise synergistic effect of the three monomers: the amide group of acrylamide provides strong adsorption, forming a spatial network structure on the particle surface; the sulfonic acid group of 2-acrylamido-2-methylpropanesulfonic acid exhibits excellent temperature and salt resistance, maintaining charge stability at high temperatures and inhibiting molecular chain shrinkage; the pyrrolidone group of N-vinylpyrrolidone is rigid, enhancing the molecular chain's resistance to high-temperature degradation. After ternary copolymerization, compounding with a heat-resistant modified starch derivative further optimizes the thickener's rheological regulation capabilities, enabling it to maintain suitable plastic viscosity and dynamic shear force at 210℃. This solves the technical pain point of high-temperature degradation and thickening failure of thickeners when copolymerization is lacking monomers or without compounding treatment. Through precise matching and synergistic optimization of the preparation process of the modified anti-settling enhancer and the heat-resistant polymer thickener, the workover fluid exhibits no significant sedimentation and high solidification strength after standing at 210℃ for 7 days. This effectively solves the problems of particle agglomeration, thickener degradation, and uncontrolled rheological properties in traditional workover fluids at high temperatures, providing a reliable system with excellent stability, high temperature resistance, and mechanical properties for high-temperature workover operations. Detailed Implementation

[0027] The present application will be further described in detail below with reference to the embodiments.

[0028] Zinc oxide used in the embodiments and comparative examples of this application was purchased from Weifang Aolong Zinc Industry Co., Ltd.; diethylenetriaminepentamethylphosphonic acid was purchased from Hubei Xinjiecheng Chemical Technology Co., Ltd.; organobentonite was purchased from Lingshou County Chengming Mineral Products Processing Plant; barite powder (particle size: 325 mesh) was purchased from Lingshou County Jingfeng New Materials Technology Co., Ltd.; asbestos wool (particle size: 1-6 mm) was purchased from Shijiazhuang Hualang Mineral Products Trading Co., Ltd.; nano silica (particle size: 200 mesh) was purchased from Qinghe County Chaotai Metal Materials Co., Ltd.; 2-acrylamido-2-methylpropanesulfonate The acid was purchased from Hubei Xinghengye Technology Co., Ltd.; phenyltriethoxysilane was purchased from Shandong Baister New Material Co., Ltd.; aminopropyltriethoxysilane was purchased from Hubei Jianghao New Material Technology Co., Ltd.; acetylated distarch phosphate (brand name: JYS15451) was purchased from Wuhan Jiyesheng Chemical Co., Ltd.; attapulgite (density: 2.3 g / cm³) was purchased from Lingshou County Qianlai Mineral Products Business Department; polyanionic cellulose was purchased from Hebei Chaoyan New Material Technology Co., Ltd.; and dodecyl dimethyl benzyl ammonium chloride was purchased from Shanghai Boyun New Material Co., Ltd.

[0029] Examples 1-8 provide a high-temperature resistant well workover fluid and its preparation method.

[0030] Example 1

[0031] A high-temperature resistant well workover fluid, by weight, comprises the following components: 100 parts deionized water, 1.5 parts modified anti-settling enhancer, 0.5 parts heat-resistant polymer thickener, 0.3 parts heat stabilizer, 1 part viscosity stabilizer, 0.1 parts bactericide, 8 parts density regulator, and 2 parts plugging agent. The heat stabilizer is composed of zinc oxide and diethylenetriaminepentamethylphosphonic acid in a mass ratio of 2:1; the viscosity stabilizer is organic bentonite; the bactericide is isothiazolinone; the density regulator is barite powder; and the plugging agent is asbestos wool.

[0032] The preparation method of the modified anti-settling enhancer includes the following preparation steps:

[0033] The mass ratio of nano-reinforcing agent to ethanol aqueous solution was controlled at 2:10. The nano-reinforcing agent was added to a 40% ethanol aqueous solution and ultrasonically dispersed for 10 min at an ultrasonic power of 200 W and an ultrasonic frequency of 40 kHz. The pH was then adjusted to 4.0 with a 5% hydrochloric acid solution to obtain a nano-powder dispersion. The mass ratio of composite coupling agent to ethanol aqueous solution was controlled at 1:10. The composite coupling agent was added to a 40% ethanol aqueous solution and hydrolyzed at a constant temperature of 40℃ for 30 min at a stirring speed of 200 rpm to obtain a hydrolyzed composite coupling agent solution. The hydrolyzed composite coupling agent solution was added dropwise to the nanoparticle dispersion, with the mass ratio of nanoparticle dispersion to hydrolyzed composite coupling agent solution controlled at 100:2. The dropwise addition time was 30 min. After the dropwise addition was completed, the temperature was raised to 75℃, and the reaction was carried out at a stirring speed of 200 rpm for 3 h. After the reaction was completed, the mixture was centrifuged at 5000 rpm for 10 min, washed three times with anhydrous ethanol, and dried at 60℃ for 10 h to obtain the modified anti-settling reinforcing agent. The nano-reinforcing agent was nano-silica, and the composite coupling agent was composed of phenyltriethoxysilane and aminopropyltriethoxysilane in a mass ratio of 10:4.

[0034] The preparation method of the heat-resistant polymer thickener includes the following preparation steps:

[0035] Step 1: Acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and N-vinylpyrrolidone were added to deionized water. The pH of the system was adjusted to 7.0 with a 20% sodium hydroxide solution. Under nitrogen protection, a redox initiator was added. The initial reaction temperature was controlled at 5°C. The reaction was carried out in a sealed, constant-temperature polymerization reaction for 4 hours. The temperature was then raised to 40°C and maintained for 2 hours. After the reaction was completed, the mixture was pulverized, dried at 60°C for 10 hours, and passed through a 100-mesh sieve to obtain a ternary random copolymer. The mass ratio of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone, redox initiator, and deionized water was 65:20:3:0.1:350. The redox initiator was composed of ammonium persulfate and sodium bisulfite in a mass ratio of 1:0.3.

[0036] Step 2: Mix the ternary random copolymer and acetylated distarch phosphate at a mass ratio of 85:10, add to a high-speed mixer, and stir evenly at a stirring speed of 500 rpm to obtain a heat-resistant polymer thickener.

[0037] A method for preparing a high-temperature resistant well workover fluid includes the following preparation steps:

[0038] Density regulator and plugging agent are added sequentially to deionized water and stirred at 200 rpm for 30 minutes until uniformly dispersed. Then, modified anti-settling enhancer is added and ultrasonically dispersed at 200 W and 40 kHz for 10 minutes. Then, heat-resistant polymer thickener is added and stirred at 200 rpm for 30 minutes. Next, heat stabilizer and viscosity stabilizer are added, and the temperature is raised to 40°C. The mixture is stirred at 300 rpm for 1 hour. After cooling to room temperature, bactericide is added and stirred at 400 rpm for 10 minutes until uniformly mixed. The mixture is then allowed to stand for 30 minutes to mature, thus obtaining the high-temperature resistant well workover fluid.

[0039] Example 2

[0040] A high-temperature resistant well workover fluid, by weight, comprises the following components: 110 parts deionized water, 2.3 parts modified anti-settling enhancer, 1 part temperature-resistant polymer thickener, 0.8 parts heat stabilizer, 3 parts viscosity stabilizer, 0.5 parts bactericide, 10 parts density regulator, and 4 parts plugging agent. The heat stabilizer is composed of zinc oxide and diethylenetriaminepentamethylphosphonic acid in a mass ratio of 3:1.1; the viscosity stabilizer is organic bentonite; the bactericide is isothiazolinone; the density regulator is barite powder; and the plugging agent is asbestos wool.

[0041] The preparation method of the modified anti-settling enhancer includes the following preparation steps:

[0042] The mass ratio of nano-reinforcing agent to ethanol aqueous solution was controlled at 2.5:11. The nano-reinforcing agent was added to a 45% (w / w) ethanol aqueous solution and ultrasonically dispersed for 15 min at an ultrasonic power of 250 W and an ultrasonic frequency of 50 kHz. The pH was then adjusted to 4.5 with a 5% (w / w) hydrochloric acid solution to obtain a nano-powder dispersion. The mass ratio of composite coupling agent to ethanol aqueous solution was controlled at 1.5:11. The composite coupling agent was added to a 45% (w / w) ethanol aqueous solution and hydrolyzed at a stirring speed of 250 rpm and a constant temperature of 45℃ for 35 min to obtain a hydrolyzed composite coupling agent solution. The hydrolyzed composite coupling agent solution was added dropwise to the nanoparticle dispersion, with the mass ratio of the nanoparticle dispersion to the hydrolyzed composite coupling agent solution controlled at 110:2.5. The dropwise addition time was 35 min. After the dropwise addition was completed, the temperature was raised to 80℃, and the reaction was carried out by stirring at 300 rpm for 4 h. After the reaction was completed, the mixture was centrifuged at 6500 rpm for 11 min, washed 4 times with anhydrous ethanol, and dried at 70℃ for 11 h to obtain the modified anti-settling reinforcing agent. The nano-reinforcing agent was nano-silica, and the composite coupling agent was composed of phenyltriethoxysilane and aminopropyltriethoxysilane in a mass ratio of 12:6.

[0043] The preparation method of the heat-resistant polymer thickener includes the following preparation steps:

[0044] Step 1: Acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and N-vinylpyrrolidone were added to deionized water. The pH of the system was adjusted to 7.5 with a 20% sodium hydroxide solution. Under nitrogen protection, a redox initiator was added, and the reaction was controlled at an initial temperature of 8°C. The reaction was carried out in a sealed, constant-temperature polymerization reaction for 5 hours, then the temperature was raised to 45°C and maintained for 2.5 hours. After the reaction was completed, the mixture was pulverized, dried at 68°C for 12 hours, and passed through a 200-mesh sieve to obtain a ternary random copolymer. The mass ratio of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone, redox initiator, and deionized water was 70:24:5:0.12:400. The redox initiator was composed of ammonium persulfate and sodium bisulfite in a mass ratio of 1.5:0.4.

[0045] Step 2: Mix the ternary random copolymer and acetylated distarch phosphate at a mass ratio of 88:12, add to a high-speed mixer, and stir evenly at a stirring speed of 750 rpm to obtain a heat-resistant polymer thickener.

[0046] A method for preparing a high-temperature resistant well workover fluid includes the following preparation steps:

[0047] Density regulator and plugging agent are added sequentially to deionized water and stirred at 300 rpm for 35 minutes until uniformly dispersed. Then, modified anti-settling enhancer is added and ultrasonically dispersed at 250 W and 50 kHz for 20 minutes. Then, heat-resistant polymer thickener is added and stirred at 300 rpm for 35 minutes. Next, heat stabilizer and viscosity stabilizer are added, and the temperature is raised to 45°C. The mixture is stirred at 400 rpm for 1.5 hours. After cooling to room temperature, bactericide is added and stirred at 600 rpm for 12 minutes until uniformly mixed. The mixture is then allowed to stand for 45 minutes to mature, thus obtaining the high-temperature resistant well workover fluid.

[0048] Example 3

[0049] A high-temperature resistant well workover fluid, by weight, comprises the following components: 120 parts deionized water, 3 parts modified anti-settling enhancer, 2 parts heat-resistant polymer thickener, 1.5 parts heat stabilizer, 5 parts viscosity stabilizer, 0.8 parts bactericide, 12 parts density regulator, and 6 parts plugging agent. The heat stabilizer is composed of zinc oxide and diethylenetriaminepentamethylphosphonic acid in a mass ratio of 4:1.2; the viscosity stabilizer is organic bentonite; the bactericide is isothiazolinone; the density regulator is barite powder; and the plugging agent is asbestos wool.

[0050] The preparation method of the modified anti-settling enhancer includes the following preparation steps:

[0051] The mass ratio of nano-reinforcing agent to ethanol aqueous solution was controlled at 3:12. The nano-reinforcing agent was added to a 50% ethanol aqueous solution and ultrasonically dispersed for 20 min at an ultrasonic power of 300 W and an ultrasonic frequency of 60 kHz. The pH was then adjusted to 5.5 with a 5% hydrochloric acid solution to obtain a nano-powder dispersion. The mass ratio of composite coupling agent to ethanol aqueous solution was controlled at 2:12. The composite coupling agent was added to a 50% ethanol aqueous solution and hydrolyzed at a constant temperature of 50℃ for 40 min at a stirring speed of 300 rpm to obtain a hydrolyzed composite coupling agent solution. The hydrolyzed composite coupling agent solution was added dropwise to the nanoparticle dispersion, with the mass ratio of nanoparticle dispersion to hydrolyzed composite coupling agent solution controlled at 120:3. The dropwise addition time was 40 min. After the dropwise addition was completed, the temperature was raised to 85℃, and the reaction was carried out at a stirring speed of 400 rpm for 5 h. After the reaction was completed, the mixture was centrifuged at 8000 rpm for 12 min, washed 5 times with anhydrous ethanol, and dried at 80℃ for 12 h to obtain the modified anti-settling reinforcing agent. The nano-reinforcing agent was nano-silica, and the composite coupling agent was composed of phenyltriethoxysilane and aminopropyltriethoxysilane in a mass ratio of 15:8.

[0052] The preparation method of the heat-resistant polymer thickener includes the following preparation steps:

[0053] Step 1: Acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and N-vinylpyrrolidone were added to deionized water. The pH of the system was adjusted to 8.5 with a 20% sodium hydroxide solution. Under nitrogen protection, a redox initiator was added, and the reaction was controlled at an initial temperature of 10°C. The reaction was carried out under sealed constant temperature for 6 hours, then the temperature was raised to 50°C and kept warm for 3 hours. After the reaction was completed, the mixture was pulverized, dried at 75°C for 15 hours, and passed through a 300-mesh sieve to obtain a ternary random copolymer. The mass ratio of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone, redox initiator, and deionized water was 75:28:7:0.15:450. The redox initiator was composed of ammonium persulfate and sodium bisulfite in a mass ratio of 2:0.5.

[0054] Step 2: Mix the ternary random copolymer and acetylated distarch phosphate at a mass ratio of 90:15, add the mixture to a high-speed mixer, and stir at a stirring speed of 800 rpm until homogeneous to obtain a heat-resistant polymer thickener.

[0055] A method for preparing a high-temperature resistant well workover fluid includes the following preparation steps:

[0056] Density regulator and plugging agent are added sequentially to deionized water and stirred at 400 rpm for 40 minutes until uniformly dispersed. Then, modified anti-settling enhancer is added and ultrasonically dispersed at 300 W and 60 kHz for 30 minutes. Then, heat-resistant polymer thickener is added and stirred at 400 rpm for 40 minutes. Next, heat stabilizer and viscosity stabilizer are added, and the temperature is raised to 50°C. The mixture is stirred at 500 rpm for 2 hours. After cooling to room temperature, bactericide is added and stirred at 800 rpm for 15 minutes until uniformly mixed. The mixture is then allowed to stand for 60 minutes to mature, thus obtaining the high-temperature resistant well workover fluid.

[0057] Example 4

[0058] A high-temperature resistant well workover fluid, by weight, comprises the following components: 100 parts deionized water, 1.5 parts modified anti-settling enhancer, 0.5 parts heat-resistant polymer thickener, 0.3 parts heat stabilizer, 1 part viscosity stabilizer, 0.1 parts bactericide, 8 parts density regulator, and 2 parts plugging agent. The heat stabilizer is composed of zinc oxide and diethylenetriaminepentamethylphosphonic acid in a mass ratio of 2:1; the viscosity stabilizer is attapulgite; the bactericide is isothiazolinone; the density regulator is barite powder; and the plugging agent is asbestos wool.

[0059] The preparation method of the modified anti-settling enhancer includes the following preparation steps:

[0060] The mass ratio of nano-reinforcing agent to ethanol aqueous solution was controlled at 2:10. The nano-reinforcing agent was added to a 40% ethanol aqueous solution and ultrasonically dispersed for 10 min at an ultrasonic power of 200 W and an ultrasonic frequency of 40 kHz. The pH was then adjusted to 4.0 with a 5% hydrochloric acid solution to obtain a nano-powder dispersion. The mass ratio of composite coupling agent to ethanol aqueous solution was controlled at 1:10. The composite coupling agent was added to a 40% ethanol aqueous solution and hydrolyzed at a constant temperature of 40℃ for 30 min at a stirring speed of 200 rpm to obtain a hydrolyzed composite coupling agent solution. The hydrolyzed composite coupling agent solution was added dropwise to the nanoparticle dispersion, with the mass ratio of nanoparticle dispersion to hydrolyzed composite coupling agent solution controlled at 100:2. The dropwise addition time was 30 min. After the dropwise addition was completed, the temperature was raised to 75℃, and the reaction was carried out at a stirring speed of 200 rpm for 3 h. After the reaction was completed, the mixture was centrifuged at 5000 rpm for 10 min, washed three times with anhydrous ethanol, and dried at 60℃ for 10 h to obtain the modified anti-settling reinforcing agent. The nano-reinforcing agent was nano-silica, and the composite coupling agent was composed of phenyltriethoxysilane and aminopropyltriethoxysilane in a mass ratio of 10:4.

[0061] The preparation method of the heat-resistant polymer thickener includes the following preparation steps:

[0062] Step 1: Acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and N-vinylpyrrolidone were added to deionized water. The pH of the system was adjusted to 7.0 with a 20% sodium hydroxide solution. Under nitrogen protection, a redox initiator was added. The initial reaction temperature was controlled at 5°C. The reaction was carried out in a sealed, constant-temperature polymerization reaction for 4 hours. The temperature was then raised to 40°C and maintained for 2 hours. After the reaction was completed, the mixture was pulverized, dried at 60°C for 10 hours, and passed through a 100-mesh sieve to obtain a ternary random copolymer. The mass ratio of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone, redox initiator, and deionized water was 65:20:3:0.1:350. The redox initiator was composed of ammonium persulfate and sodium bisulfite in a mass ratio of 1:0.3.

[0063] Step 2: Mix the ternary random copolymer and acetylated distarch phosphate at a mass ratio of 85:10, add to a high-speed mixer, and stir evenly at a stirring speed of 500 rpm to obtain a heat-resistant polymer thickener.

[0064] A method for preparing a high-temperature resistant well workover fluid includes the following preparation steps:

[0065] Density regulator and plugging agent are added sequentially to deionized water and stirred at 200 rpm for 30 minutes until uniformly dispersed. Then, modified anti-settling enhancer is added and ultrasonically dispersed at 200 W and 40 kHz for 10 minutes. Then, heat-resistant polymer thickener is added and stirred at 200 rpm for 30 minutes. Next, heat stabilizer and viscosity stabilizer are added, and the temperature is raised to 40°C. The mixture is stirred at 300 rpm for 1 hour. After cooling to room temperature, bactericide is added and stirred at 400 rpm for 10 minutes until uniformly mixed. The mixture is then allowed to stand for 30 minutes to mature, thus obtaining the high-temperature resistant well workover fluid.

[0066] Example 5

[0067] A high-temperature resistant well workover fluid, by weight, comprises the following components: 100 parts deionized water, 1.5 parts modified anti-settling enhancer, 0.5 parts heat-resistant polymer thickener, 0.3 parts heat stabilizer, 1 part viscosity stabilizer, 0.1 parts bactericide, 8 parts density regulator, and 2 parts plugging agent. The heat stabilizer is composed of zinc oxide and diethylenetriaminepentamethylphosphonic acid in a mass ratio of 2:1; the viscosity stabilizer is polyanionic cellulose; the bactericide is isothiazolinone; the density regulator is barite powder; and the plugging agent is asbestos wool.

[0068] The preparation method of the modified anti-settling enhancer includes the following preparation steps:

[0069] The mass ratio of nano-reinforcing agent to ethanol aqueous solution was controlled at 2:10. The nano-reinforcing agent was added to a 40% ethanol aqueous solution and ultrasonically dispersed for 10 min at an ultrasonic power of 200 W and an ultrasonic frequency of 40 kHz. The pH was then adjusted to 4.0 with a 5% hydrochloric acid solution to obtain a nano-powder dispersion. The mass ratio of composite coupling agent to ethanol aqueous solution was controlled at 1:10. The composite coupling agent was added to a 40% ethanol aqueous solution and hydrolyzed at a constant temperature of 40℃ for 30 min at a stirring speed of 200 rpm to obtain a hydrolyzed composite coupling agent solution. The hydrolyzed composite coupling agent solution was added dropwise to the nanoparticle dispersion, with the mass ratio of nanoparticle dispersion to hydrolyzed composite coupling agent solution controlled at 100:2. The dropwise addition time was 30 min. After the dropwise addition was completed, the temperature was raised to 75℃, and the reaction was carried out at a stirring speed of 200 rpm for 3 h. After the reaction was completed, the mixture was centrifuged at 5000 rpm for 10 min, washed three times with anhydrous ethanol, and dried at 60℃ for 10 h to obtain the modified anti-settling reinforcing agent. The nano-reinforcing agent was nano-silica, and the composite coupling agent was composed of phenyltriethoxysilane and aminopropyltriethoxysilane in a mass ratio of 10:4.

[0070] The preparation method of the heat-resistant polymer thickener includes the following preparation steps:

[0071] Step 1: Acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and N-vinylpyrrolidone were added to deionized water. The pH of the system was adjusted to 7.0 with a 20% sodium hydroxide solution. Under nitrogen protection, a redox initiator was added. The initial reaction temperature was controlled at 5°C. The reaction was carried out in a sealed, constant-temperature polymerization reaction for 4 hours. The temperature was then raised to 40°C and maintained for 2 hours. After the reaction was completed, the mixture was pulverized, dried at 60°C for 10 hours, and passed through a 100-mesh sieve to obtain a ternary random copolymer. The mass ratio of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone, redox initiator, and deionized water was 65:20:3:0.1:350. The redox initiator was composed of ammonium persulfate and sodium bisulfite in a mass ratio of 1:0.3.

[0072] Step 2: Mix the ternary random copolymer and acetylated distarch phosphate at a mass ratio of 85:10, add to a high-speed mixer, and stir evenly at a stirring speed of 500 rpm to obtain a heat-resistant polymer thickener.

[0073] A method for preparing a high-temperature resistant well workover fluid includes the following preparation steps:

[0074] Density regulator and plugging agent are added sequentially to deionized water and stirred at 200 rpm for 30 minutes until uniformly dispersed. Then, modified anti-settling enhancer is added and ultrasonically dispersed at 200 W and 40 kHz for 10 minutes. Then, heat-resistant polymer thickener is added and stirred at 200 rpm for 30 minutes. Next, heat stabilizer and viscosity stabilizer are added, and the temperature is raised to 40°C. The mixture is stirred at 300 rpm for 1 hour. After cooling to room temperature, bactericide is added and stirred at 400 rpm for 10 minutes until uniformly mixed. The mixture is then allowed to stand for 30 minutes to mature, thus obtaining the high-temperature resistant well workover fluid.

[0075] Example 6

[0076] A high-temperature resistant well workover fluid, by weight, comprises the following components: 100 parts deionized water, 1.5 parts modified anti-settling enhancer, 0.5 parts heat-resistant polymer thickener, 0.3 parts heat stabilizer, 1 part viscosity stabilizer, 0.1 parts bactericide, 8 parts density regulator, and 2 parts plugging agent. The heat stabilizer is composed of zinc oxide and diethylenetriaminepentamethylphosphonic acid in a mass ratio of 2:1; the viscosity stabilizer is organic bentonite; the bactericide is glutaraldehyde; the density regulator is barite powder; and the plugging agent is asbestos wool.

[0077] The preparation method of the modified anti-settling enhancer includes the following preparation steps:

[0078] The mass ratio of nano-reinforcing agent to ethanol aqueous solution was controlled at 2:10. The nano-reinforcing agent was added to a 40% ethanol aqueous solution and ultrasonically dispersed for 10 min at an ultrasonic power of 200 W and an ultrasonic frequency of 40 kHz. The pH was then adjusted to 4.0 with a 5% hydrochloric acid solution to obtain a nano-powder dispersion. The mass ratio of composite coupling agent to ethanol aqueous solution was controlled at 1:10. The composite coupling agent was added to a 40% ethanol aqueous solution and hydrolyzed at a constant temperature of 40℃ for 30 min at a stirring speed of 200 rpm to obtain a hydrolyzed composite coupling agent solution. The hydrolyzed composite coupling agent solution was added dropwise to the nanoparticle dispersion, with the mass ratio of nanoparticle dispersion to hydrolyzed composite coupling agent solution controlled at 100:2. The dropwise addition time was 30 min. After the dropwise addition was completed, the temperature was raised to 75℃, and the reaction was carried out at a stirring speed of 200 rpm for 3 h. After the reaction was completed, the mixture was centrifuged at 5000 rpm for 10 min, washed three times with anhydrous ethanol, and dried at 60℃ for 10 h to obtain the modified anti-settling reinforcing agent. The nano-reinforcing agent was nano-silica, and the composite coupling agent was composed of phenyltriethoxysilane and aminopropyltriethoxysilane in a mass ratio of 10:4.

[0079] The preparation method of the heat-resistant polymer thickener includes the following preparation steps:

[0080] Step 1: Acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and N-vinylpyrrolidone were added to deionized water. The pH of the system was adjusted to 7.0 with a 20% sodium hydroxide solution. Under nitrogen protection, a redox initiator was added. The initial reaction temperature was controlled at 5°C. The reaction was carried out in a sealed, constant-temperature polymerization reaction for 4 hours. The temperature was then raised to 40°C and maintained for 2 hours. After the reaction was completed, the mixture was pulverized, dried at 60°C for 10 hours, and passed through a 100-mesh sieve to obtain a ternary random copolymer. The mass ratio of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone, redox initiator, and deionized water was 65:20:3:0.1:350. The redox initiator was composed of ammonium persulfate and sodium bisulfite in a mass ratio of 1:0.3.

[0081] Step 2: Mix the ternary random copolymer and acetylated distarch phosphate at a mass ratio of 85:10, add to a high-speed mixer, and stir evenly at a stirring speed of 500 rpm to obtain a heat-resistant polymer thickener.

[0082] A method for preparing a high-temperature resistant well workover fluid includes the following preparation steps:

[0083] Density regulator and plugging agent are added sequentially to deionized water and stirred at 200 rpm for 30 minutes until uniformly dispersed. Then, modified anti-settling enhancer is added and ultrasonically dispersed at 200 W and 40 kHz for 10 minutes. Then, heat-resistant polymer thickener is added and stirred at 200 rpm for 30 minutes. Next, heat stabilizer and viscosity stabilizer are added, and the temperature is raised to 40°C. The mixture is stirred at 300 rpm for 1 hour. After cooling to room temperature, bactericide is added and stirred at 400 rpm for 10 minutes until uniformly mixed. The mixture is then allowed to stand for 30 minutes to mature, thus obtaining the high-temperature resistant well workover fluid.

[0084] Example 7

[0085] A high-temperature resistant well workover fluid, by weight, comprises the following components: 100 parts deionized water, 1.5 parts modified anti-settling enhancer, 0.5 parts heat-resistant polymer thickener, 0.3 parts heat stabilizer, 1 part viscosity stabilizer, 0.1 parts bactericide, 8 parts density regulator, and 2 parts plugging agent. The heat stabilizer is composed of zinc oxide and diethylenetriaminepentamethylphosphonic acid in a mass ratio of 2:1; the viscosity stabilizer is organobentonite; the bactericide is dodecyl dimethyl benzyl ammonium chloride; the density regulator is barite powder; and the plugging agent is asbestos wool.

[0086] The preparation method of the modified anti-settling enhancer includes the following preparation steps:

[0087] The mass ratio of nano-reinforcing agent to ethanol aqueous solution was controlled at 2:10. The nano-reinforcing agent was added to a 40% ethanol aqueous solution and ultrasonically dispersed for 10 min at an ultrasonic power of 200 W and an ultrasonic frequency of 40 kHz. The pH was then adjusted to 4.0 with a 5% hydrochloric acid solution to obtain a nano-powder dispersion. The mass ratio of composite coupling agent to ethanol aqueous solution was controlled at 1:10. The composite coupling agent was added to a 40% ethanol aqueous solution and hydrolyzed at a constant temperature of 40℃ for 30 min at a stirring speed of 200 rpm to obtain a hydrolyzed composite coupling agent solution. The hydrolyzed composite coupling agent solution was added dropwise to the nanoparticle dispersion, with the mass ratio of nanoparticle dispersion to hydrolyzed composite coupling agent solution controlled at 100:2. The dropwise addition time was 30 min. After the dropwise addition was completed, the temperature was raised to 75℃, and the reaction was carried out at a stirring speed of 200 rpm for 3 h. After the reaction was completed, the mixture was centrifuged at 5000 rpm for 10 min, washed three times with anhydrous ethanol, and dried at 60℃ for 10 h to obtain the modified anti-settling reinforcing agent. The nano-reinforcing agent was nano-silica, and the composite coupling agent was composed of phenyltriethoxysilane and aminopropyltriethoxysilane in a mass ratio of 10:4.

[0088] The preparation method of the heat-resistant polymer thickener includes the following preparation steps:

[0089] Step 1: Acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and N-vinylpyrrolidone were added to deionized water. The pH of the system was adjusted to 7.0 with a 20% sodium hydroxide solution. Under nitrogen protection, a redox initiator was added. The initial reaction temperature was controlled at 5°C. The reaction was carried out in a sealed, constant-temperature polymerization reaction for 4 hours. The temperature was then raised to 40°C and maintained for 2 hours. After the reaction was completed, the mixture was pulverized, dried at 60°C for 10 hours, and passed through a 100-mesh sieve to obtain a ternary random copolymer. The mass ratio of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone, redox initiator, and deionized water was 65:20:3:0.1:350. The redox initiator was composed of ammonium persulfate and sodium bisulfite in a mass ratio of 1:0.3.

[0090] Step 2: Mix the ternary random copolymer and acetylated distarch phosphate at a mass ratio of 85:10, add to a high-speed mixer, and stir evenly at a stirring speed of 500 rpm to obtain a heat-resistant polymer thickener.

[0091] A method for preparing a high-temperature resistant well workover fluid includes the following preparation steps:

[0092] Density regulator and plugging agent are added sequentially to deionized water and stirred at 200 rpm for 30 minutes until uniformly dispersed. Then, modified anti-settling enhancer is added and ultrasonically dispersed at 200 W and 40 kHz for 10 minutes. Then, heat-resistant polymer thickener is added and stirred at 200 rpm for 30 minutes. Next, heat stabilizer and viscosity stabilizer are added, and the temperature is raised to 40°C. The mixture is stirred at 300 rpm for 1 hour. After cooling to room temperature, bactericide is added and stirred at 400 rpm for 10 minutes until uniformly mixed. The mixture is then allowed to stand for 30 minutes to mature, thus obtaining the high-temperature resistant well workover fluid.

[0093] Example 8

[0094] A high-temperature resistant well workover fluid, by weight, comprises the following components: 100 parts deionized water, 1.5 parts modified anti-settling enhancer, 0.5 parts heat-resistant polymer thickener, 0.3 parts heat stabilizer, 1 part viscosity stabilizer, 0.1 parts bactericide, 8 parts density regulator, and 2 parts plugging agent. The heat stabilizer is composed of zinc oxide and diethylenetriaminepentamethylphosphonic acid in a mass ratio of 2:1; the viscosity stabilizer is organobentonite; the bactericide is composed of glutaraldehyde and isothiazolinone in a mass ratio of 1:1; the density regulator is barite powder; and the plugging agent is asbestos wool.

[0095] The preparation method of the modified anti-settling enhancer includes the following preparation steps:

[0096] The mass ratio of nano-reinforcing agent to ethanol aqueous solution was controlled at 2:10. The nano-reinforcing agent was added to a 40% ethanol aqueous solution and ultrasonically dispersed for 10 min at an ultrasonic power of 200 W and an ultrasonic frequency of 40 kHz. The pH was then adjusted to 4.0 with a 5% hydrochloric acid solution to obtain a nano-powder dispersion. The mass ratio of composite coupling agent to ethanol aqueous solution was controlled at 1:10. The composite coupling agent was added to a 40% ethanol aqueous solution and hydrolyzed at a constant temperature of 40℃ for 30 min at a stirring speed of 200 rpm to obtain a hydrolyzed composite coupling agent solution. The hydrolyzed composite coupling agent solution was added dropwise to the nanoparticle dispersion, with the mass ratio of nanoparticle dispersion to hydrolyzed composite coupling agent solution controlled at 100:2. The dropwise addition time was 30 min. After the dropwise addition was completed, the temperature was raised to 75℃, and the reaction was carried out at a stirring speed of 200 rpm for 3 h. After the reaction was completed, the mixture was centrifuged at 5000 rpm for 10 min, washed three times with anhydrous ethanol, and dried at 60℃ for 10 h to obtain the modified anti-settling reinforcing agent. The nano-reinforcing agent was nano-silica, and the composite coupling agent was composed of phenyltriethoxysilane and aminopropyltriethoxysilane in a mass ratio of 10:4.

[0097] The preparation method of the heat-resistant polymer thickener includes the following preparation steps:

[0098] Step 1: Acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and N-vinylpyrrolidone were added to deionized water. The pH of the system was adjusted to 7.0 with a 20% sodium hydroxide solution. Under nitrogen protection, a redox initiator was added. The initial reaction temperature was controlled at 5°C. The reaction was carried out in a sealed, constant-temperature polymerization reaction for 4 hours. The temperature was then raised to 40°C and maintained for 2 hours. After the reaction was completed, the mixture was pulverized, dried at 60°C for 10 hours, and passed through a 100-mesh sieve to obtain a ternary random copolymer. The mass ratio of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone, redox initiator, and deionized water was 65:20:3:0.1:350. The redox initiator was composed of ammonium persulfate and sodium bisulfite in a mass ratio of 1:0.3.

[0099] Step 2: Mix the ternary random copolymer and acetylated distarch phosphate at a mass ratio of 85:10, add to a high-speed mixer, and stir evenly at a stirring speed of 500 rpm to obtain a heat-resistant polymer thickener.

[0100] A method for preparing a high-temperature resistant well workover fluid includes the following preparation steps:

[0101] Density regulator and plugging agent are added sequentially to deionized water and stirred at 200 rpm for 30 minutes until uniformly dispersed. Then, modified anti-settling enhancer is added and ultrasonically dispersed at 200 W and 40 kHz for 10 minutes. Then, heat-resistant polymer thickener is added and stirred at 200 rpm for 30 minutes. Next, heat stabilizer and viscosity stabilizer are added, and the temperature is raised to 40°C. The mixture is stirred at 300 rpm for 1 hour. After cooling to room temperature, bactericide is added and stirred at 400 rpm for 10 minutes until uniformly mixed. The mixture is then allowed to stand for 30 minutes to mature, thus obtaining the high-temperature resistant well workover fluid.

[0102] Comparative Example 1

[0103] A high-temperature resistant well workover fluid, by weight, comprises the following components: 100 parts deionized water, 1.5 parts modified anti-settling enhancer, 0.5 parts heat-resistant polymer thickener, 0.3 parts heat stabilizer, 1 part viscosity stabilizer, 0.1 parts bactericide, 8 parts density regulator, and 2 parts plugging agent. The heat stabilizer is composed of zinc oxide and diethylenetriaminepentamethylphosphonic acid in a mass ratio of 2:1; the viscosity stabilizer is organic bentonite; the bactericide is isothiazolinone; the density regulator is barite powder; and the plugging agent is asbestos wool.

[0104] The preparation method of the modified anti-settling enhancer includes the following preparation steps:

[0105] The mass ratio of nano-reinforcing agent to ethanol aqueous solution was controlled at 2:10. The nano-reinforcing agent was added to a 40% (w / w) ethanol aqueous solution and ultrasonically dispersed for 10 min at an ultrasonic power of 200 W and an ultrasonic frequency of 40 kHz. The pH was then adjusted to 4.0 with a 5% (w / w) hydrochloric acid solution to obtain a nanoparticle dispersion. The mass ratio of coupling agent to ethanol aqueous solution was controlled at 1:10. The coupling agent was added to a 40% (w / w) ethanol aqueous solution and hydrolyzed at a constant temperature of 40℃ for 30 min with a stirring speed of 200 rpm. n, to obtain a hydrolysis coupling agent solution; add the hydrolysis coupling agent solution dropwise to the nanopowder dispersion, controlling the mass ratio of the nanopowder dispersion to the hydrolysis coupling agent solution to be 100:2, the dropwise addition time to be 30 min, after the dropwise addition is completed, raise the temperature to 75℃, stir at a stirring speed of 200 rpm for 3 h, after the reaction is completed, centrifuge at 5000 rpm for 10 min, wash 3 times with anhydrous ethanol, and dry at 60℃ for 10 h to obtain a modified anti-settling reinforcing agent, wherein the nano-reinforcing agent is nano-silica and the coupling agent is aminopropyltriethoxysilane.

[0106] The preparation method of the heat-resistant polymer thickener includes the following preparation steps:

[0107] Step 1: Acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and N-vinylpyrrolidone were added to deionized water. The pH of the system was adjusted to 7.0 with a 20% sodium hydroxide solution. Under nitrogen protection, a redox initiator was added. The initial reaction temperature was controlled at 5°C. The reaction was carried out in a sealed, constant-temperature polymerization reaction for 4 hours. The temperature was then raised to 40°C and maintained for 2 hours. After the reaction was completed, the mixture was pulverized, dried at 60°C for 10 hours, and passed through a 100-mesh sieve to obtain a ternary random copolymer. The mass ratio of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone, redox initiator, and deionized water was 65:20:3:0.1:350. The redox initiator was composed of ammonium persulfate and sodium bisulfite in a mass ratio of 1:0.3.

[0108] Step 2: Mix the ternary random copolymer and acetylated distarch phosphate at a mass ratio of 85:10, add to a high-speed mixer, and stir evenly at a stirring speed of 500 rpm to obtain a heat-resistant polymer thickener.

[0109] A method for preparing a high-temperature resistant well workover fluid includes the following preparation steps:

[0110] Density regulator and plugging agent are added sequentially to deionized water and stirred at 200 rpm for 30 minutes until uniformly dispersed. Then, modified anti-settling enhancer is added and ultrasonically dispersed at 200 W and 40 kHz for 10 minutes. Then, heat-resistant polymer thickener is added and stirred at 200 rpm for 30 minutes. Next, heat stabilizer and viscosity stabilizer are added, and the temperature is raised to 40°C. The mixture is stirred at 300 rpm for 1 hour. After cooling to room temperature, bactericide is added and stirred at 400 rpm for 10 minutes until uniformly mixed. The mixture is then allowed to stand for 30 minutes to mature, thus obtaining the high-temperature resistant well workover fluid.

[0111] Comparative Example 2

[0112] A high-temperature resistant well workover fluid, by weight, comprises the following components: 100 parts deionized water, 1.5 parts modified anti-settling enhancer, 0.5 parts heat-resistant polymer thickener, 0.3 parts heat stabilizer, 1 part viscosity stabilizer, 0.1 parts bactericide, 8 parts density regulator, and 2 parts plugging agent. The heat stabilizer is composed of zinc oxide and diethylenetriaminepentamethylphosphonic acid in a mass ratio of 2:1; the viscosity stabilizer is organic bentonite; the bactericide is isothiazolinone; the density regulator is barite powder; and the plugging agent is asbestos wool.

[0113] The preparation method of the modified anti-settling enhancer includes the following preparation steps:

[0114] The mass ratio of nano-reinforcing agent to ethanol aqueous solution was controlled at 2:10. The nano-reinforcing agent was added to a 40% (w / w) ethanol aqueous solution and ultrasonically dispersed for 10 min at an ultrasonic power of 200 W and an ultrasonic frequency of 40 kHz. The pH was then adjusted to 4.0 with a 5% (w / w) hydrochloric acid solution to obtain a nanoparticle dispersion. The mass ratio of coupling agent to ethanol aqueous solution was controlled at 1:10. The coupling agent was added to a 40% (w / w) ethanol aqueous solution and hydrolyzed at a constant temperature of 40℃ for 30 min with a stirring speed of 200 rpm. n, to obtain a hydrolysis coupling agent solution; add the hydrolysis coupling agent solution dropwise to the nanopowder dispersion, controlling the mass ratio of the nanopowder dispersion to the hydrolysis coupling agent solution to be 100:2, the dropwise addition time to be 30 min, after the dropwise addition is completed, raise the temperature to 75℃, stir at a stirring speed of 200 rpm for 3 h, after the reaction is completed, centrifuge at 5000 rpm for 10 min, wash 3 times with anhydrous ethanol, and dry at 60℃ for 10 h to obtain a modified anti-settling reinforcing agent, wherein the nano-reinforcing agent is nano-silica and the coupling agent is phenyltriethoxysilane.

[0115] The preparation method of the heat-resistant polymer thickener includes the following preparation steps:

[0116] Step 1: Acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and N-vinylpyrrolidone were added to deionized water. The pH of the system was adjusted to 7.0 with a 20% sodium hydroxide solution. Under nitrogen protection, a redox initiator was added. The initial reaction temperature was controlled at 5°C. The reaction was carried out in a sealed, constant-temperature polymerization reaction for 4 hours. The temperature was then raised to 40°C and maintained for 2 hours. After the reaction was completed, the mixture was pulverized, dried at 60°C for 10 hours, and passed through a 100-mesh sieve to obtain a ternary random copolymer. The mass ratio of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone, redox initiator, and deionized water was 65:20:3:0.1:350. The redox initiator was composed of ammonium persulfate and sodium bisulfite in a mass ratio of 1:0.3.

[0117] Step 2: Mix the ternary random copolymer and acetylated distarch phosphate at a mass ratio of 85:10, add to a high-speed mixer, and stir evenly at a stirring speed of 500 rpm to obtain a heat-resistant polymer thickener.

[0118] A method for preparing a high-temperature resistant well workover fluid includes the following preparation steps:

[0119] Density regulator and plugging agent are added sequentially to deionized water and stirred at 200 rpm for 30 minutes until uniformly dispersed. Then, modified anti-settling enhancer is added and ultrasonically dispersed at 200 W and 40 kHz for 10 minutes. Then, heat-resistant polymer thickener is added and stirred at 200 rpm for 30 minutes. Next, heat stabilizer and viscosity stabilizer are added, and the temperature is raised to 40°C. The mixture is stirred at 300 rpm for 1 hour. After cooling to room temperature, bactericide is added and stirred at 400 rpm for 10 minutes until uniformly mixed. The mixture is then allowed to stand for 30 minutes to mature, thus obtaining the high-temperature resistant well workover fluid.

[0120] Comparative Example 3

[0121] A high-temperature resistant well workover fluid, by weight, comprises the following components: 100 parts deionized water, 1.5 parts modified anti-settling enhancer, 0.5 parts heat-resistant polymer thickener, 0.3 parts heat stabilizer, 1 part viscosity stabilizer, 0.1 parts bactericide, 8 parts density regulator, and 2 parts plugging agent. The heat stabilizer is composed of zinc oxide and diethylenetriaminepentamethylphosphonic acid in a mass ratio of 2:1; the viscosity stabilizer is organic bentonite; the bactericide is isothiazolinone; the density regulator is barite powder; and the plugging agent is asbestos wool.

[0122] The preparation method of the modified anti-settling enhancer includes the following preparation steps:

[0123] The mass ratio of nano-reinforcing agent to ethanol aqueous solution was controlled at 2:10. The nano-reinforcing agent was added to a 40% ethanol aqueous solution and ultrasonically dispersed for 10 min at an ultrasonic power of 200 W and an ultrasonic frequency of 40 kHz. The pH was then adjusted to 4.0 with a 5% hydrochloric acid solution to obtain a nano-powder dispersion. The mass ratio of composite coupling agent to ethanol aqueous solution was controlled at 1:10. The composite coupling agent was added to a 40% ethanol aqueous solution and hydrolyzed at a constant temperature of 40℃ for 30 min at a stirring speed of 200 rpm to obtain a hydrolyzed composite coupling agent solution. The hydrolyzed composite coupling agent solution was added dropwise to the nanoparticle dispersion, with the mass ratio of nanoparticle dispersion to hydrolyzed composite coupling agent solution controlled at 100:2. The dropwise addition time was 30 min. After the dropwise addition was completed, the temperature was raised to 75℃, and the reaction was carried out at a stirring speed of 200 rpm for 3 h. After the reaction was completed, the mixture was centrifuged at 5000 rpm for 10 min, washed three times with anhydrous ethanol, and dried at 60℃ for 10 h to obtain the modified anti-settling reinforcing agent. The nano-reinforcing agent was nano-silica, and the composite coupling agent was composed of phenyltriethoxysilane and aminopropyltriethoxysilane in a mass ratio of 10:4.

[0124] The preparation method of the heat-resistant polymer thickener includes the following preparation steps:

[0125] Step 1: Add acrylamide and N-vinylpyrrolidone to deionized water, adjust the pH of the system to 7.0 with 20% sodium hydroxide solution, add redox initiator under nitrogen protection, control the initial reaction temperature to 5℃, and perform a closed-cell isothermal polymerization reaction for 4 hours. Then raise the temperature to 40℃ and keep it warm for 2 hours. After the reaction is completed, pulverize, dry at 60℃ for 10 hours, and pass through a 100-mesh sieve to obtain a binary random copolymer. The mass ratio of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone, redox initiator and deionized water is 65:23:0.1:350. The redox initiator is composed of ammonium persulfate and sodium bisulfite in a mass ratio of 1:0.3.

[0126] Step 2: Mix the binary random copolymer and acetylated distarch phosphate at a mass ratio of 85:10, add the mixture to a high-speed mixer, and stir at a stirring speed of 500 rpm until homogeneous to obtain a heat-resistant polymer thickener.

[0127] A method for preparing a high-temperature resistant well workover fluid includes the following preparation steps:

[0128] Density regulator and plugging agent are added sequentially to deionized water and stirred at 200 rpm for 30 minutes until uniformly dispersed. Then, modified anti-settling enhancer is added and ultrasonically dispersed at 200 W and 40 kHz for 10 minutes. Then, heat-resistant polymer thickener is added and stirred at 200 rpm for 30 minutes. Next, heat stabilizer and viscosity stabilizer are added, and the temperature is raised to 40°C. The mixture is stirred at 300 rpm for 1 hour. After cooling to room temperature, bactericide is added and stirred at 400 rpm for 10 minutes until uniformly mixed. The mixture is then allowed to stand for 30 minutes to mature, thus obtaining the high-temperature resistant well workover fluid.

[0129] Comparative Example 4

[0130] A high-temperature resistant well workover fluid, by weight, comprises the following components: 100 parts deionized water, 1.5 parts modified anti-settling enhancer, 0.5 parts heat-resistant polymer thickener, 0.3 parts heat stabilizer, 1 part viscosity stabilizer, 0.1 parts bactericide, 8 parts density regulator, and 2 parts plugging agent. The heat stabilizer is composed of zinc oxide and diethylenetriaminepentamethylphosphonic acid in a mass ratio of 2:1; the viscosity stabilizer is organic bentonite; the bactericide is isothiazolinone; the density regulator is barite powder; and the plugging agent is asbestos wool.

[0131] The preparation method of the modified anti-settling enhancer includes the following preparation steps:

[0132] The mass ratio of nano-reinforcing agent to ethanol aqueous solution was controlled at 2:10. The nano-reinforcing agent was added to a 40% ethanol aqueous solution and ultrasonically dispersed for 10 min at an ultrasonic power of 200 W and an ultrasonic frequency of 40 kHz. The pH was then adjusted to 4.0 with a 5% hydrochloric acid solution to obtain a nano-powder dispersion. The mass ratio of composite coupling agent to ethanol aqueous solution was controlled at 1:10. The composite coupling agent was added to a 40% ethanol aqueous solution and hydrolyzed at a constant temperature of 40℃ for 30 min at a stirring speed of 200 rpm to obtain a hydrolyzed composite coupling agent solution. The hydrolyzed composite coupling agent solution was added dropwise to the nanoparticle dispersion, with the mass ratio of nanoparticle dispersion to hydrolyzed composite coupling agent solution controlled at 100:2. The dropwise addition time was 30 min. After the dropwise addition was completed, the temperature was raised to 75℃, and the reaction was carried out at a stirring speed of 200 rpm for 3 h. After the reaction was completed, the mixture was centrifuged at 5000 rpm for 10 min, washed three times with anhydrous ethanol, and dried at 60℃ for 10 h to obtain the modified anti-settling reinforcing agent. The nano-reinforcing agent was nano-silica, and the composite coupling agent was composed of phenyltriethoxysilane and aminopropyltriethoxysilane in a mass ratio of 10:4.

[0133] The preparation method of the heat-resistant polymer thickener includes the following preparation steps:

[0134] Acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and N-vinylpyrrolidone were added to deionized water. The pH of the system was adjusted to 7.0 with a 20% sodium hydroxide solution. Under nitrogen protection, a redox initiator was added, and the reaction was carried out at a controlled initial temperature of 5°C for 4 hours. The temperature was then raised to 40°C and maintained for 2 hours. After the reaction was completed, the mixture was pulverized, dried at 60°C for 10 hours, and passed through a 100-mesh sieve to obtain a heat-resistant polymer thickener. The mass ratio of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone, redox initiator, and deionized water was 65:20:3:0.1:350. The redox initiator was composed of ammonium persulfate and sodium bisulfite in a mass ratio of 1:0.3.

[0135] A method for preparing a high-temperature resistant well workover fluid includes the following preparation steps:

[0136] Density regulator and plugging agent are added sequentially to deionized water and stirred at 200 rpm for 30 minutes until uniformly dispersed. Then, modified anti-settling enhancer is added and ultrasonically dispersed at 200 W and 40 kHz for 10 minutes. Then, heat-resistant polymer thickener is added and stirred at 200 rpm for 30 minutes. Next, heat stabilizer and viscosity stabilizer are added, and the temperature is raised to 40°C. The mixture is stirred at 300 rpm for 1 hour. After cooling to room temperature, bactericide is added and stirred at 400 rpm for 10 minutes until uniformly mixed. The mixture is then allowed to stand for 30 minutes to mature, thus obtaining the high-temperature resistant well workover fluid.

[0137] Comparative Example 5

[0138] A high-temperature resistant well workover fluid, by weight, comprises the following components: 100 parts deionized water, 1.5 parts modified anti-settling enhancer, 0.5 parts heat-resistant polymer thickener, 0.3 parts heat stabilizer, 1 part viscosity stabilizer, 0.1 parts bactericide, 8 parts density regulator, and 2 parts plugging agent. The heat stabilizer is zinc oxide, the viscosity stabilizer is organobentonite, the bactericide is isothiazolinone, the density regulator is barite powder, and the plugging agent is asbestos wool.

[0139] The preparation method of the modified anti-settling enhancer includes the following preparation steps:

[0140] The mass ratio of nano-reinforcing agent to ethanol aqueous solution was controlled at 2:10. The nano-reinforcing agent was added to a 40% ethanol aqueous solution and ultrasonically dispersed for 10 min at an ultrasonic power of 200 W and an ultrasonic frequency of 40 kHz. The pH was then adjusted to 4.0 with a 5% hydrochloric acid solution to obtain a nano-powder dispersion. The mass ratio of composite coupling agent to ethanol aqueous solution was controlled at 1:10. The composite coupling agent was added to a 40% ethanol aqueous solution and hydrolyzed at a constant temperature of 40℃ for 30 min at a stirring speed of 200 rpm to obtain a hydrolyzed composite coupling agent solution. The hydrolyzed composite coupling agent solution was added dropwise to the nanoparticle dispersion, with the mass ratio of nanoparticle dispersion to hydrolyzed composite coupling agent solution controlled at 100:2. The dropwise addition time was 30 min. After the dropwise addition was completed, the temperature was raised to 75℃, and the reaction was carried out at a stirring speed of 200 rpm for 3 h. After the reaction was completed, the mixture was centrifuged at 5000 rpm for 10 min, washed three times with anhydrous ethanol, and dried at 60℃ for 10 h to obtain the modified anti-settling reinforcing agent. The nano-reinforcing agent was nano-silica, and the composite coupling agent was composed of phenyltriethoxysilane and aminopropyltriethoxysilane in a mass ratio of 10:4.

[0141] The preparation method of the heat-resistant polymer thickener includes the following preparation steps:

[0142] Step 1: Acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and N-vinylpyrrolidone were added to deionized water. The pH of the system was adjusted to 7.0 with a 20% sodium hydroxide solution. Under nitrogen protection, a redox initiator was added. The initial reaction temperature was controlled at 5°C. The reaction was carried out in a sealed, constant-temperature polymerization reaction for 4 hours. The temperature was then raised to 40°C and maintained for 2 hours. After the reaction was completed, the mixture was pulverized, dried at 60°C for 10 hours, and passed through a 100-mesh sieve to obtain a ternary random copolymer. The mass ratio of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone, redox initiator, and deionized water was 65:20:3:0.1:350. The redox initiator was composed of ammonium persulfate and sodium bisulfite in a mass ratio of 1:0.3.

[0143] Step 2: Mix the ternary random copolymer and acetylated distarch phosphate at a mass ratio of 85:10, add to a high-speed mixer, and stir evenly at a stirring speed of 500 rpm to obtain a heat-resistant polymer thickener.

[0144] A method for preparing a high-temperature resistant well workover fluid includes the following preparation steps:

[0145] Density regulator and plugging agent are added sequentially to deionized water and stirred at 200 rpm for 30 minutes until uniformly dispersed. Then, modified anti-settling enhancer is added and ultrasonically dispersed at 200 W and 40 kHz for 10 minutes. Then, heat-resistant polymer thickener is added and stirred at 200 rpm for 30 minutes. Next, heat stabilizer and viscosity stabilizer are added, and the temperature is raised to 40°C. The mixture is stirred at 300 rpm for 1 hour. After cooling to room temperature, bactericide is added and stirred at 400 rpm for 10 minutes until uniformly mixed. The mixture is then allowed to stand for 30 minutes to mature, thus obtaining the high-temperature resistant well workover fluid.

[0146] Performance testing

[0147] The high-temperature resistant workover fluids prepared in Examples 1-8 and Comparative Examples 1-5 were subjected to heat settling at 210°C for 7 days. The density, plastic viscosity, dynamic shear force, initial / final shear rate, and settling stability of the high-temperature resistant workover fluids were tested according to the national standard GB / T 29170-2012 "Laboratory Testing of Drilling Fluids for Petroleum and Natural Gas Industry". Settling rate = (volume of supernatant fluid / total volume of workover fluid) × 100%.

[0148] The specific test results are shown in Table 1.

[0149] Table 1 Performance parameters of high-temperature resistant workover fluids in Examples 1-8 and Comparative Examples 1-5

[0150] As shown in Table 1, the high-temperature resistant workover fluid prepared in this application exhibits excellent comprehensive performance and outstanding high-temperature stability. After being heated and allowed to stand at 210℃ for 7 days, its density stabilizes at 1.18-1.24 g / cm³. The plastic viscosity, dynamic shear force, and initial / final shear parameters are reasonable, with no significant sedimentation. This effectively improves the viscosity stability and sedimentation resistance of the workover fluid at high temperatures, making it suitable for high-temperature workover conditions, avoiding sedimentation, and ensuring the safety and effectiveness of workover operations. Its application value is significant.

[0151] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A high-temperature resistant well workover fluid, characterized in that, By weight, it includes the following components: 100-120 parts deionized water, 1.5-3 parts modified anti-settling agent, 0.5-2 parts heat-resistant polymer thickener, 0.3-1.5 parts heat stabilizer, 1-5 parts viscosity stabilizer, 0.1-0.8 parts bactericide, 8-12 parts density regulator, and 2-6 parts sealing agent; The preparation method of the heat-resistant polymer thickener includes the following preparation steps: Step 1: Add acrylamide, 2-acrylamido-2-methylpropanesulfonic acid and N-vinylpyrrolidone to deionized water, adjust the pH of the system to 7.0-8.5, add redox initiator under nitrogen protection, control the reaction start temperature to 5-10℃, and carry out the closed isothermal polymerization reaction for 4-6 hours. Then raise the temperature to 40-50℃ and keep it warm for 2-3 hours. After the reaction is completed, crush, dry and sieve to obtain ternary random copolymer. Step 2: Mix the ternary random copolymer and the heat-resistant modified starch derivative, and stir evenly to obtain a heat-resistant polymer thickener; The heat stabilizer is composed of zinc oxide and diethylenetriamine pentamethylphosphonic acid in a mass ratio of 2-4:1-1.2; The preparation method of the modified anti-settling enhancer includes the following preparation steps: The nano-reinforcing agent was added to an ethanol aqueous solution, and after ultrasonic dispersion, the pH was adjusted to 4.0-5.5 to obtain a nano-powder dispersion. The composite coupling agent was added to an ethanol aqueous solution and hydrolyzed at a constant temperature of 40-50℃ to obtain a hydrolyzed composite coupling agent solution. The hydrolyzed composite coupling agent solution was added dropwise to a nanoparticle dispersion. After the addition was complete, the temperature was raised to 75-85℃ and the reaction was stirred for 3-5 hours. After the reaction was completed, the mixture was centrifuged, washed, and dried to obtain a modified anti-settling enhancer. The composite coupling agent was composed of phenyltriethoxysilane and aminopropyltriethoxysilane in a mass ratio of 10-15:4-8. In step 2, the mass ratio of the ternary random copolymer to the heat-resistant modified starch derivative is 85-90:10-15; the heat-resistant modified starch derivative is one or more of hydroxypropyl distarch phosphate, acetylated distarch phosphate, and phosphorylated distarch phosphate.

2. The high-temperature resistant well workover fluid according to claim 1, characterized in that, The nano-reinforcing agent is one or more of nano-silica, nano-magnesium oxide, and sodium-based montmorillonite.

3. The high-temperature resistant well workover fluid according to claim 1, characterized in that, In step 1, the mass ratio of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone, redox initiator, and deionized water is 65-75:20-28:3-7:0.1-0.15:350-450.

4. The high-temperature resistant well workover fluid according to claim 1, characterized in that, The viscosity stabilizer is one or more of organobentonite, attapulgite, and polyanionic cellulose; the bactericide is one or more of glutaraldehyde, isothiazolinone, and dodecyl dimethyl benzyl ammonium chloride.

5. The high-temperature resistant well workover fluid according to claim 1, characterized in that, The density regulator is one or more of barite powder, limestone powder, and iron ore powder; the sealing agent is one or more of diatomaceous earth, asbestos wool, expanded graphite, and nano-calcium carbonate.

6. A method for preparing a high-temperature resistant well workover fluid as described in any one of claims 1-5, characterized in that, The preparation steps include the following: Add density regulator and plugging agent to deionized water in sequence and stir until uniformly dispersed. Then add modified anti-settling enhancer and ultrasonically disperse. Add heat-resistant polymer thickener and stir for 30-40 minutes. Add heat stabilizer and viscosity stabilizer, heat to 40-50℃, stir at constant temperature for 1-2 hours, cool to room temperature, add bactericide, stir for 10-15 minutes until uniformly mixed, and let stand for 30-60 minutes to mature. The high-temperature resistant well workover fluid is then obtained.

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