Plugging agent for rebuilding shaft of low-efficiency horizontal well and preparation method of plugging agent

Abstract

The invention belongs to the technical field of oil exploitation, and discloses a plugging agent for rebuilding a shaft of a low-efficiency horizontal well and a preparation method of the plugging agent, the plugging agent is prepared from the following raw materials in parts by weight: 100 parts of water, 26-31 parts of a composite monomer, 0.35-0.55 part of a functional monomer, 0.012-0.016 part of an initiator, 0.9-1.3 parts of a cross-linking agent and 0.055-0.075 part of a stabilizer; the composite monomer is a mixture of acrylamide and 2-acrylamido-2-methyl-1-propanesulfonic acid, and the composite monomer is a mixture of acrylamide and 2-acrylamido-2-methyl-1-propanesulfonic acid; the functional monomer is a mixture of 1-vinyl imidazole and N-vinyl caprolactam; the initiator is prepared by mixing sodium azodiisobutyramide propanesulfonate and lauroyl peroxide. According to the invention, the azodiisobutyramide sodium propanesulfonate and the lauroyl peroxide are compounded and synergistically realize uniform monomer polymerization and dense gel.

Description

Technical Field

[0001] This invention belongs to the field of petroleum extraction technology, specifically relating to a plugging agent for reconstructing inefficient horizontal wells and its preparation method. Background Technology

[0002] Inefficient horizontal wells in old oilfields, during long-term development, are generally affected by formation pressure fluctuations, fluid scouring, casing corrosion, and reservoir heterogeneity. They commonly face core problems such as wellbore damage and leakage, severe formation water channeling, and water cut exceeding 90%. This results in reservoir utilization rates of less than 30%, an average annual decline in single-well production, and some wells being forced to shut down due to excessive water production, causing significant resource waste and economic losses. Wellbore reconstruction, a key technology for restoring horizontal well productivity, focuses on efficiently sealing the pore channels of old wellbores with chemical plugging agents to cut off water channeling. However, existing plugging agents are difficult to adapt to complex and harsh formation environments and suffer from insufficient initiator performance. Traditional plugging agents often use single oil-soluble or water-soluble initiators (such as ammonium persulfate and azobisisobutyramidine hydrochloride AIBA), which suffer from poor water solubility, uneven dispersion, and mismatch between decomposition temperature and polymerization system. This leads to incomplete monomer polymerization, a wide molecular weight distribution, and pore defects in the gel network, ultimately resulting in low gelation efficiency and weak gel strength. Meanwhile, the crosslinking system is simple, with insufficient shear resistance and strength; the stabilization mechanism is imperfect, resulting in poor temperature and salt resistance; and there is a sharp contradiction between injectability and plugging properties.

[0003] Therefore, developing a wellbore reconstruction plugging agent with strong temperature and salt resistance, good injectability, and high sealing efficiency is of great significance for solving the problem of inefficient horizontal well development. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a plugging agent for reconstructing inefficient horizontal wells and its preparation method. The method involves synthesizing sodium azobisisobutyramide propanesulfonate and compounding it with lauroyl peroxide as an initiator. The resulting plugging agent exhibits high plugging efficiency and good injectability.

[0005] A plugging agent for rebuilding the wellbore inefficient horizontal wells is composed of the following raw materials in parts by weight: 100 parts water, 26-31 parts composite monomer, 0.35-0.55 parts functional monomer, 0.012-0.016 parts initiator, 0.9-1.3 parts crosslinking agent, and 0.055-0.075 parts stabilizer. The composite monomer is a mixture of acrylamide and 2-acrylamido-2-methyl-1-propanesulfonic acid; The functional monomer is a mixture of 1-vinylimidazole and N-vinylcaprolactam; The initiator is prepared by the following method: sodium azobisisobutyramide propanesulfonate and lauroyl peroxide are mixed and added to an aqueous solution of Tween 80 at a mass ratio of (18-22):100. The mixture is stirred and dispersed at 10-20°C for 25-35 min, deoxygenated for 8-12 min, and then sealed and refrigerated.

[0006] Preferably, the stirring and dispersing speed is 1200-1600 rpm.

[0007] Preferably, the sodium azobisisobutyramide propanesulfonate is prepared by the following method: (1) Mix azobisisobutyramidine hydrochloride with methyl acrylate, add it to N,N-dimethylformamide, and react at 40-50℃ for 6-8h to obtain the intermediate azobisisobutyramidine propionate methyl acrylate. (2) Mix the methyl azobisisobutyramide propionate with sodium sulfite, add water, react at 65-75℃ for 7-9h, cool to room temperature, add anhydrous ethanol for recrystallization, let stand and filter, wash the crystals with ethanol, and dry under vacuum to obtain sodium azobisisobutyramide propionate sulfonate.

[0008] Preferably, the molar ratio of azobisisobutyramidine hydrochloride to methyl acrylate is 1:(2-2.2), and the molar ratio of azobisisobutyramamide propionate to sodium sulfite is 1:(2.0-2.1).

[0009] Preferably, the mass ratio of sodium azobisisobutyramide propanesulfonate to lauroyl peroxide is (2-4):1; and the concentration of the Tween 80 aqueous solution is 0.03-0.06wt%.

[0010] Preferably, the mass ratio of acrylamide to 2-acrylamido-2-methyl-1-propanesulfonic acid is 7.2:2.8-8.8:1.2.

[0011] Preferably, the mass ratio of 1-vinylimidazole to N-vinylcaprolactam is (3-5):1.

[0012] Preferably, the crosslinking agent is a mixture of polyethyleneimine and polyethylene glycol diglycidyl ether in a mass ratio of (4-6):1; the number average molecular weight of the polyethyleneimine is 1900-2100 Da, and the molecular weight of the polyethylene glycol diglycidyl ether is 400-600 Da.

[0013] Preferably, the stabilizer is a mixture of sulfonated hydroxyethyl cellulose and povidone K30 in a mass ratio of (2-4):1; the sulfonated hydroxyethyl cellulose has a degree of sulfonation substitution of 3.0 and a viscosity of 12000 mPa·s, and the viscosity corresponds to the viscosity of a 2wt% aqueous solution at 25°C.

[0014] Preferably, the raw materials are composed of the following parts by weight: 100 parts water, 28 parts composite monomer, 0.45 parts functional monomer, 0.014 parts initiator, 1.1 parts crosslinking agent, and 0.065 parts stabilizer; and the composite monomer is a mixture of acrylamide and 2-acrylamido-2-methyl-1-propanesulfonic acid in a mass ratio of 8.2:1.8.

[0015] The method for preparing the plugging agent for rebuilding the wellbore of inefficient horizontal wells includes the following steps: Step 1: Weigh the composite monomer and functional monomer, add them to water, stir to dissolve, and then adjust the pH of the system to 6.5-7.5 with NaOH solution to obtain a mixed monomer solution; Step 2: Deoxygenate the mixed monomer solution for 16-21 min, add the initiator, first heat to 45-50℃ and react for 1-1.5 h, then heat to 55-60℃ and react for 1-1.5 h, cool to room temperature to obtain polymer colloid; Step 3: Add a stabilizer to the polymer adhesive, first ultrasonically disperse for 10-20 minutes, then stir at 380-480 rpm for 30-40 minutes, and finally add a crosslinking agent and continue stirring for 18-24 minutes to obtain the plugging agent.

[0016] Preferably, the deoxygenation in this invention is carried out by introducing nitrogen gas, and the flow rate of nitrogen gas is 1.1-1.6 L / min.

[0017] In this invention, acrylamide (AM) in the composite monomer provides a good crosslinking basis, and the sulfonic acid group of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) can enhance the salt resistance and thermal stability of the polymer. By precisely adjusting the ratio of the two, the optimal balance of the hydrophilicity and hydrophobicity of the molecular chain is achieved, which greatly improves the stability of the plugging agent in a high-mineralization environment. The rigid imidazole ring of 1-vinylimidazole (VIM) in the composite functional monomer forms a synergistic steric hindrance effect with the caprolactam ring of N-vinylcaprolactam (NVC), which inhibits the hydrolysis of amide groups in a dual manner, while enhancing the rigidity and heat resistance of the polymer chain, enabling the plugging agent to adapt to higher temperature formation environments. Among the initiators, sodium azobisisobutyramide propanesulfonate (AIBA-PS) has better water solubility than traditional AIBA, its decomposition temperature is suitable for the reaction range of the system, and it can slowly release free radicals; lauroyl peroxide (LPO), as a long-chain oil-soluble initiator, is combined with AIBA-PS to form a "water-oil biphase precise initiation system", which solves the problems of uneven polymerization and wide molecular weight distribution of traditional initiators leading to weak gel strength. It helps to form a denser polymer network, significantly improves the mechanical properties of the gel, and increases the plugging rate and injection efficiency. In the dual crosslinking agent, polyethyleneimine (PEI) provides nitrogen atom crosslinking sites to form the main crosslinking network, while polyethylene glycol diglycidyl ether (PEGDE) reacts with the active groups on the polymer chain through epoxy groups to form a secondary crosslinking network. The dual crosslinking structure significantly improves gel strength and shear resistance, and avoids structural damage to the plugging agent during injection. In the stabilizer, sulfonated hydroxyethyl cellulose (S-HEC) can both entangle polymer molecular chains to inhibit thermal motion and resist salt ion erosion through electrostatic repulsion. It forms a triple stabilization mechanism of "electrostatic protection-structural entanglement-hydrolysis resistance" with the hydrogen bonding of polyvinylpyrrolidone K30 (PVP K30), which further extends the shelf life of the plugging agent in high temperature and high salt environment.

[0018] Advantages of this invention: (1) This invention innovatively synthesizes a composite initiation system. The synthesized sodium azobisisobutyramide propanesulfonate (AIBA-PS) is combined with lauroyl peroxide (LPO) to form a "water-oil biphase precise initiation system". AIBA-PS has better water solubility than traditional AIBA, and its decomposition temperature is precisely matched with the segmented heating mode, which slowly and stably releases free radicals. LPO has good dispersibility. The two work together to achieve uniform monomer polymerization, narrow molecular weight distribution, and dense and defect-free gel network. Compared with traditional initiators, the gelation time is shortened, the gel strength is improved, and the water separation rate is reduced, which solves the core pain points of "random polymerization, slow gelation, and weak strength". (2) The stabilizer described in this invention has a long chain structure of sulfonated hydroxyethyl cellulose that wraps around the polymer molecular chain to inhibit thermal motion, and sulfonate groups resist salt ion erosion through electrostatic repulsion; PVP K30 inhibits the hydrolysis of amide groups through hydrogen bonding. This mechanism enables the plugging agent to stabilize and gel under high temperature and high salt conditions, thus expanding the applicability of the plugging agent and meeting the needs of extreme formation environments. (3) The preparation process of this invention is simple, the cost is controllable, and it is highly practical. The resulting plugging agent has high sealing efficiency and can effectively block the bottom water flow channel. Attached Figure Description

[0019] Figure 1 The image shows the gelation effect of the plugging agent described in Example 1 under the conditions of 100°C and 96000 mg / L mineralization. Figure 2 The image shows the gelation effect of the plugging agent described in Example 1 under the conditions of 80°C and 64000 mg / L mineralization. Figure 3 The image shows the gelation effect of the plugging agent described in Example 1 under the conditions of 60°C and 32000 mg / L mineralization. Detailed Implementation

[0020] Example 1: A plugging agent for rebuilding the wellbore of an inefficient horizontal well, composed of the following raw materials in parts by weight: 100 parts water, 28 parts composite monomer, 0.45 parts functional monomer, 0.014 parts initiator, 1.1 parts crosslinking agent, and 0.065 parts stabilizer. The composite monomer is a mixture of acrylamide and 2-acrylamido-2-methyl-1-propanesulfonic acid in a mass ratio of 8.2:1.8. The functional monomer is a mixture of 1-vinylimidazole and N-vinylcaprolactam in a mass ratio of 4:1; The crosslinking agent is a mixture of polyethyleneimine and polyethylene glycol diglycidyl ether in a mass ratio of 5:1, wherein the number average molecular weight of the polyethyleneimine is 2000 Da and the molecular weight of the polyethylene glycol diglycidyl ether is 500 Da. The stabilizer is a mixture of sulfonated hydroxyethyl cellulose and povidone K30 in a mass ratio of 3:1; the sulfonated hydroxyethyl cellulose has a degree of sulfonation substitution of 3.0 and a viscosity of 12000 mPa·s; The initiator was prepared by the following method: (1) Azobisisobutyramidine hydrochloride and methyl acrylate were mixed at a molar ratio of 1:2.1 and added to N,N-dimethylformamide. The mixture was amidated at 45°C for 7 h to obtain the intermediate methyl azobisisobutyramamide propionate. (2) The methyl azobisisobutyramide propionate was mixed with sodium sulfite at a molar ratio of 1:2, added to water, and sulfonated at 70°C for 8 hours. After cooling to room temperature, 3 times the volume of anhydrous ethanol was added for recrystallization. After standing and filtering, the crystals were washed twice with ethanol and dried under vacuum at 60°C for 4 hours to obtain sodium azobisisobutyramide propionate sulfonate. (3) The sodium azobisisobutyramide propanesulfonate and lauroyl peroxide are mixed at a mass ratio of 3:1 to obtain a mixture. The mixture is added to a 0.4wt% Tween 80 aqueous solution at a mass ratio of 20:100. The mixture is stirred and dispersed at 1400rpm at 15°C for 30min. Nitrogen gas is introduced at a flow rate of 1.5L / min to remove oxygen for 10min. The mixture is then sealed and refrigerated. The preparation method of the plugging agent for rebuilding the wellbore of inefficient horizontal wells is as follows: Step 1: Weigh the composite monomer and functional monomer, add them to water, stir to dissolve, and then adjust the pH of the system to 7.0 with 30wt% NaOH solution to obtain a mixed monomer solution; Step 2: Nitrogen gas is introduced into the mixed monomer solution at a flow rate of 1.5 L / min to remove oxygen for 18 min. An initiator is added, and the temperature is first raised to 48°C and reacted for 1 h, then raised to 58°C and reacted for 1.5 h. The mixture is then cooled to room temperature to obtain a polymer colloid. Step 3: Add a stabilizer to the polymer adhesive, first ultrasonically disperse it for 15 minutes at an ultrasonic power of 380W, then stir it at a speed of 420rpm for 35 minutes, and finally add a crosslinking agent and continue stirring for 21 minutes to obtain the plugging agent; Performance testing: The plugging agent, under conditions of 100℃ and 96000 mg / L salinity, gelled in 1 day, achieved a gel strength of grade G, and showed no water exudation after 60 days. It achieved a 96.2% plugging rate for 0.5×0.5 mm fractured cores, with a breakthrough pressure of 0.455 MPa. See the gelation effect diagram below. Figure 1 The gel remains intact without cracks.

[0021] Example 2: A plugging agent for rebuilding the wellbore of an inefficient horizontal well, composed of the following raw materials in parts by weight: 100 parts water, 26 parts composite monomer, 0.35 parts functional monomer, 0.012 parts initiator, 0.9 parts crosslinking agent, and 0.055 parts stabilizer. The composite monomer is a mixture of acrylamide and 2-acrylamido-2-methyl-1-propanesulfonic acid in a mass ratio of 7.2:2.8. Everything else is the same as in Example 1; The preparation method of the plugging agent for rebuilding the wellbore of inefficient horizontal wells is as follows: Step 1: Weigh the composite monomer and functional monomer, add them to water, stir to dissolve, and then adjust the pH of the system to 6.5 with 30wt% NaOH solution to obtain a mixed monomer solution; Step 2: Nitrogen gas is introduced into the mixed monomer solution at a flow rate of 1.3 L / min to remove oxygen for 16 min. An initiator is added, and the temperature is first raised to 48°C and reacted for 1 h, then raised to 58°C and reacted for 1.5 h. The mixture is then cooled to room temperature to obtain a polymer colloid. Step 3: Add a stabilizer to the polymer glue, first ultrasonically disperse it for 15 minutes under an ultrasonic power of 380W, then stir it at a speed of 380rpm for 35 minutes, and finally add a crosslinking agent and continue stirring for 18 minutes to obtain the plugging agent; Performance testing: The plugging agent, under conditions of 80℃ and 64000 mg / L salinity, gelled in 1 day, with a gel strength of grade G, and showed no significant water exudation after 60 days; the plugging rate for a 3.0×3.0 mm fracture core was 94.4%, with a breakthrough pressure of 0.063 MPa; see the gelation effect diagram below. Figure 2 The gel remains intact without cracks.

[0022] Example 3: A plugging agent for rebuilding the wellbore of an inefficient horizontal well, composed of the following raw materials in parts by weight: 100 parts water, 31 parts composite monomer, 0.55 parts functional monomer, 0.016 parts initiator, 1.3 parts crosslinking agent, and 0.075 parts stabilizer. The composite monomer is a mixture of acrylamide and 2-acrylamido-2-methyl-1-propanesulfonic acid in a mass ratio of 8.8:1.2. Everything else is the same as in Example 1; The preparation method of the plugging agent for rebuilding the wellbore of the inefficient horizontal well is as follows: Step 1: Weigh the composite monomer and functional monomer, add them to water, stir to dissolve, and then adjust the pH of the system to 7.5 with 30wt% NaOH solution to obtain a mixed monomer solution; Step 2: Nitrogen gas is introduced into the mixed monomer solution at a flow rate of 1.1 L / min to remove oxygen for 21 min. An initiator is added, and the temperature is first raised to 48°C and reacted for 1 h, then raised to 58°C and reacted for 1.5 h. The mixture is then cooled to room temperature to obtain a polymer colloid. Step 3: Add a stabilizer to the polymer adhesive, first ultrasonically disperse it for 15 minutes at an ultrasonic power of 380W, then stir it at a speed of 480rpm for 35 minutes, and finally add a crosslinking agent and continue stirring for 24 minutes to obtain the blockage agent; Performance testing: The plugging agent, under conditions of 60℃ and 32000 mg / L salinity, gelled in 1 day, with a gel strength of grade G, and showed no significant water exudation after 60 days. It achieved a 95.9% plugging rate for a 1.0×0.5 mm fracture core, with a breakthrough pressure of 0.318 MPa. See the gelation effect diagram below. Figure 3 The gel remains intact without cracks.

[0023] Example 4: A plugging agent for rebuilding the wellbore of an inefficient horizontal well, composed of the following raw materials in parts by weight: 100 parts water, 28 parts composite monomer, 0.45 parts functional monomer, 0.014 parts initiator, 1.1 parts crosslinking agent, and 0.065 parts stabilizer. The composite monomer is a mixture of acrylamide and 2-acrylamido-2-methyl-1-propanesulfonic acid in a mass ratio of 8.2:1.8. The functional monomer is a mixture of 1-vinylimidazole and N-vinylcaprolactam in a mass ratio of 3:1; The crosslinking agent is a mixture of polyethyleneimine and polyethylene glycol diglycidyl ether in a mass ratio of 4:1, wherein the number average molecular weight of the polyethyleneimine is 1900 Da and the molecular weight of the polyethylene glycol diglycidyl ether is 400 Da. The stabilizer is a mixture of sulfonated hydroxyethyl cellulose and povidone K30 in a mass ratio of 2:1; the sulfonated hydroxyethyl cellulose has a degree of sulfonation substitution of 3.0 and a viscosity of 12000 mPa·s; The initiator was prepared by the following method: (1) Azobisisobutyramidine hydrochloride and methyl acrylate were mixed at a molar ratio of 1:2.0 and added to N,N-dimethylformamide. The mixture was amidated at 40°C for 8 hours to obtain the intermediate methyl azobisisobutyramamide propionate. (2) The methyl azobisisobutyramide propionate was mixed with sodium sulfite at a molar ratio of 1:2.1, added to water, and sulfonated at 65°C for 9 hours. After cooling to room temperature, 3 times the volume of anhydrous ethanol was added for recrystallization. After standing and filtering, the crystals were washed with ethanol 3 times and dried under vacuum at 60°C for 4 hours to obtain sodium azobisisobutyramide propionate sulfonate. (3) The sodium azobisisobutyramide propanesulfonate and lauroyl peroxide are mixed at a mass ratio of 2:1 to obtain a mixture. The mixture is added to a 0.3wt% Tween 80 aqueous solution at a mass ratio of 18:100. The mixture is stirred and dispersed at 1200rpm at 10℃ for 35min. Nitrogen gas is introduced at a flow rate of 1.6L / min to remove oxygen for 8min. The mixture is then sealed and refrigerated. The preparation method of the plugging agent for rebuilding the wellbore of the inefficient horizontal well is as follows: Step 1: Weigh the composite monomer and functional monomer, add them to water, stir to dissolve, and then adjust the pH of the system to 7.0 with 30wt% NaOH solution to obtain a mixed monomer solution; Step 2: Nitrogen gas is introduced into the mixed monomer solution at a flow rate of 1.6 L / min to remove oxygen for 18 min. An initiator is added, and the temperature is first raised to 45°C and reacted for 1.5 h. Then the temperature is raised to 55°C and reacted for 1 h. The mixture is then cooled to room temperature to obtain a polymer colloid. Step 3: Add a stabilizer to the polymer adhesive, first ultrasonically disperse it for 10 minutes at an ultrasonic power of 380W, then stir it at a speed of 420rpm for 30 minutes, and finally add a crosslinking agent and continue stirring for 21 minutes to obtain the plugging agent.

[0024] Example 5: A plugging agent for rebuilding the wellbore of an inefficient horizontal well, composed of the following raw materials in parts by weight: 100 parts water, 28 parts composite monomer, 0.45 parts functional monomer, 0.014 parts initiator, 1.1 parts crosslinking agent, and 0.065 parts stabilizer. The composite monomer is a mixture of acrylamide and 2-acrylamido-2-methyl-1-propanesulfonic acid in a mass ratio of 8.2:1.8. The functional monomer is a mixture of 1-vinylimidazole and N-vinylcaprolactam in a mass ratio of 5:1; The crosslinking agent is a mixture of polyethyleneimine and polyethylene glycol diglycidyl ether in a mass ratio of 6:1, wherein the number average molecular weight of the polyethyleneimine is 2100 Da and the molecular weight of the polyethylene glycol diglycidyl ether is 600 Da. The stabilizer is a mixture of sulfonated hydroxyethyl cellulose and povidone K30 in a mass ratio of 4:1; the sulfonated hydroxyethyl cellulose has a degree of sulfonation substitution of 3.0 and a viscosity of 12000 mPa·s; The initiator was prepared by the following method: (1) Azobisisobutyramidine hydrochloride and methyl acrylate were mixed at a molar ratio of 1:2.1 and added to N,N-dimethylformamide. The mixture was amidated at 50°C for 6 h to obtain the intermediate methyl azobisisobutyramamide propionate. (2) The methyl azobisisobutyramide propionate was mixed with sodium sulfite at a molar ratio of 1:2, added to water, and sulfonated at 75°C for 7 hours. After cooling to room temperature, 3 times the volume of anhydrous ethanol was added for recrystallization. After standing and filtering, the crystals were washed twice with ethanol and dried under vacuum at 60°C for 4 hours to obtain sodium azobisisobutyramide propionate sulfonate. (3) The sodium azobisisobutyramide propanesulfonate and lauroyl peroxide are mixed at a mass ratio of 4:1 to obtain a mixture. The mixture is added to a 0.6wt% Tween 80 aqueous solution at a mass ratio of 22:100. The mixture is stirred and dispersed at 1600rpm at 20°C for 25min. Nitrogen gas is introduced at a flow rate of 1.5L / min to remove oxygen for 12min. The mixture is then sealed and refrigerated. The preparation method of the plugging agent for rebuilding the wellbore of the inefficient horizontal well is as follows: Step 1: Weigh the composite monomer and functional monomer, add them to water, stir to dissolve, and then adjust the pH of the system to 7.0 with 30wt% NaOH solution to obtain a mixed monomer solution; Step 2: Nitrogen gas is introduced into the mixed monomer solution at a flow rate of 1.5 L / min to remove oxygen for 18 min. An initiator is added, and the temperature is first raised to 50 °C and reacted for 1 h, then raised to 60 °C and reacted for 1.5 h. The mixture is then cooled to room temperature to obtain a polymer colloid. Step 3: Add a stabilizer to the polymer adhesive, first ultrasonically disperse it for 20 minutes at an ultrasonic power of 380W, then stir it at a speed of 420rpm for 40 minutes, and finally add a crosslinking agent and continue stirring for 21 minutes to obtain the plugging agent.

[0025] Comparative Example 1: A conventional polyacrylamide wellbore plugging agent for oil fields, composed of the following raw materials in parts by weight: 100 parts deionized water, 27.5 parts polyacrylamide (PAM), 0.05 parts ammonium persulfate, 1.0 part phenolic crosslinking agent, and 0.05 parts thiourea. Preparation method: (1) Weigh PAM, add it to deionized water, stir at 300 rpm for 2 hours at room temperature until completely dissolved to obtain PAM mother liquor, and adjust the pH to 7.5 with 30% NaOH solution; (2) Add 0.05 parts of thiourea (oxygen scavenger) to the PAM mother liquor, stir for 15 min, then purge with nitrogen for 20 min to remove oxygen (flow rate 1.2 L / min), add ammonium persulfate, heat to 60℃ and react for 3 h to obtain the polymer intermediate system; (3) Cool down to room temperature, add phenolic crosslinking agent, stir at 400 rpm for 20 min, let stand and mature for 4 h to obtain the plugging agent; Performance testing: The gelation performance of the plugging agent under the conditions of 80℃ and 64000 mg / L mineralization is shown in Table 1.

[0026] Comparative Example 2: A conventional azo initiator, azobisisobutyramidine hydrochloride (AIBA), was used instead of the initiator in Example 2, and everything else was the same as in Example 2; The performance of the obtained plugging agent in gelation under the conditions of 80℃ and 64000 mg / L mineralization is shown in Table 1. The resistance coefficient is dimensionless. Table 1 Performance tests of Comparative Examples 1-2 and Example 2 , As shown in Table 1, the gelation time of Example 2 was only 24 hours, which is 50% shorter than that of Comparative Example 1 (48 hours), and the gel strength reached Grade G, while the gel strength of Comparative Example 1 was only Grade D. The difference in gelation efficiency and strength is significant. In the 60-day aging test, the water separation rate of Example 2 was 0% under the conditions of 80℃ and 64000mg / L, and the gel morphology was intact without cracking. The water separation rate of Comparative Example 1 was as high as 15.7%, and it was prone to local collapse. For the 3.0×3.0mm wide fracture core, the plugging rate of Example 2 reached 94.4%, which is 15.9 percentage points higher than that of Comparative Example 1 (78.5%). In the 1mD low-permeability core, the injection efficiency of Example 2 reached 1.4PV / h, which is 75% higher than that of Comparative Example 1 (0.8PV / h), and the resistance coefficient was only 45.2, which is much lower than that of Comparative Example 1 (230.5). There was no blockage during the injection process, which solved the contradiction of "easy blockage or insufficient gel strength" of the existing plugging agent, and greatly improved the efficiency of on-site construction. The gelation time of Comparative Example 2 was 36 hours, which was 50% longer than the 24 hours of Example 2. This was due to the poor water solubility of traditional AIBA and uneven dispersion, resulting in a slow polymerization rate. The water separation rate at 60 days was 12.3%, which was much higher than the 0% of Example 2. This was because the decomposition rate of traditional AIBA fluctuated greatly, the molecular weight distribution of the polymerized product was wide, and the gel structure was loose and prone to water separation. The gel strength was only grade E, which was lower than grade G of Example 2. This was due to insufficient density of the gel network caused by uneven polymerization. The core plugging rate was 82.7%, which was 11.7 percentage points lower than the 94.4% of Example 2. The loose gel could not effectively fill the fracture channels. The injection efficiency was 1.0 PV / h, which was lower than the 1.4 PV / h of Example 2, and the resistance coefficient was 156.8, which was higher than the 45.2 of Example 2. This was because some initiators that were not sufficiently dispersed caused local overpolymerization, which increased the injection resistance. Therefore, the plugging agent provided by this invention has faster gelation, better long-term stability, higher plugging efficiency, and better injectability, perfectly solving the technical problems of "poor dispersion, disordered polymerization, and weak performance" of traditional initiators in horizontal well plugging agent applications.

Claims

1. A plugging agent for rebuilding the wellbore in inefficient horizontal wells, characterized in that: It is composed of the following raw materials in parts by weight: 100 parts water, 26-31 parts composite monomer, 0.35-0.55 parts functional monomer, 0.012-0.016 parts initiator, 0.9-1.3 parts crosslinking agent, and 0.055-0.075 parts stabilizer; The composite monomer is a mixture of acrylamide and 2-acrylamido-2-methyl-1-propanesulfonic acid; The functional monomer is a mixture of 1-vinylimidazole and N-vinylcaprolactam; The initiator is prepared by the following method: sodium azobisisobutyramide propanesulfonate and lauroyl peroxide are mixed and added to an aqueous solution of Tween 80 at a mass ratio of (18-22):

100. The mixture is stirred and dispersed at 10-20°C for 25-35 min, deoxygenated for 8-12 min, and then sealed and refrigerated.

2. The plugging agent for reconstructing inefficient horizontal wells according to claim 1, characterized in that: The sodium azobisisobutyramide propanesulfonate is prepared by the following method: (1) Mix azobisisobutyramidine hydrochloride with methyl acrylate, add it to N,N-dimethylformamide, and react at 40-50℃ for 6-8h to obtain the intermediate azobisisobutyramidine propionate methyl acrylate. (2) Mix the methyl azobisisobutyramide propionate with sodium sulfite, add water, react at 65-75℃ for 7-9h, cool to room temperature, add anhydrous ethanol for recrystallization, let stand and filter, wash the crystals with ethanol, and dry under vacuum to obtain the sodium azobisisobutyramide propionate sulfonate.

3. The plugging agent for reconstructing inefficient horizontal wells according to claim 2, characterized in that: The molar ratio of azobisisobutyramidine hydrochloride to methyl acrylate is 1:(2-2.2), and the molar ratio of azobisisobutyramamide propionate to sodium sulfite is 1:(2.0-2.1).

4. The plugging agent for reconstructing inefficient horizontal wells according to claim 1, characterized in that: The mass ratio of sodium azobisisobutyramide propanesulfonate to lauroyl peroxide is (2-4):1; the concentration of the aqueous solution of Tween 80 is 0.03-0.06wt%.

5. The plugging agent for reconstructing inefficient horizontal wells according to claim 1, characterized in that: The mass ratio of acrylamide to 2-acrylamido-2-methyl-1-propanesulfonic acid is 7.2:2.8-8.8:1.

2.

6. The plugging agent for reconstructing inefficient horizontal wells according to claim 1, characterized in that: The mass ratio of 1-vinylimidazole to N-vinylcaprolactam is (3-5):

1.

7. The plugging agent for reconstructing inefficient horizontal wells according to claim 1, characterized in that: The crosslinking agent is a mixture of polyethyleneimine and polyethylene glycol diglycidyl ether in a mass ratio of (4-6):1; the number average molecular weight of the polyethyleneimine is 1900-2100 Da, and the molecular weight of the polyethylene glycol diglycidyl ether is 400-600 Da.

8. The plugging agent for reconstructing inefficient horizontal wells according to claim 1, characterized in that: The stabilizer is a mixture of sulfonated hydroxyethyl cellulose and polyvinyl ketone K30 in a mass ratio of (2-4):1; the sulfonated hydroxyethyl cellulose has a degree of sulfonation substitution of 3.0 and a viscosity of 12000 mPa·s.

9. A plugging agent for rebuilding the wellbore of an inefficient horizontal well according to claim 1, characterized in that: It is composed of the following raw materials in parts by weight: 100 parts water, 28 parts composite monomer, 0.45 parts functional monomer, 0.014 parts initiator, 1.1 parts crosslinking agent, and 0.065 parts stabilizer; and the composite monomer is a mixture of acrylamide and 2-acrylamido-2-methyl-1-propanesulfonic acid in a mass ratio of 8.2:1.

8.

10. A method for preparing a plugging agent for rebuilding the wellbore in inefficient horizontal wells, characterized in that: The preparation method for a plugging agent used to rebuild an inefficient horizontal well as described in claim 1 includes the following steps: Step 1: Weigh the composite monomer and functional monomer, add them to water, stir to dissolve, and then adjust the pH of the system to 6.5-7.5 with NaOH solution to obtain a mixed monomer solution; Step 2: Deoxygenate the mixed monomer solution for 16-21 min, add the initiator, first heat to 45-50℃ and react for 1-1.5 h, then heat to 55-60℃ and react for 1-1.5 h, cool to room temperature to obtain polymer colloid; Step 3: Add a stabilizer to the polymer adhesive, first ultrasonically disperse for 10-20 minutes, then stir at 380-480 rpm for 30-40 minutes, and finally add a crosslinking agent and continue stirring for 18-24 minutes to obtain the plugging agent.

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