Polyacrylamide-based high-temperature-resistant gel plugging agent and preparation method thereof

Abstract

The invention relates to the technical field of oil exploitation, and discloses a polyacrylamide-based high-temperature-resistant gel plugging agent and a preparation method thereof. Comprising the following operation steps: adding modified polyethyleneimine into deionized water, mixing, adding polyacrylonitrile modified lignin, carrying out ultrasonic dispersion, adding acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, ammonium persulfate and a retarder, mixing, adjusting the pH value to 7-8, and uniformly stirring to obtain the polyacrylamide-based high-temperature-resistant gel plugging agent. According to the scheme, acrylamide is introduced into polyacrylonitrile modified lignin, so that the toughness is improved; the hydroxyl silicone oil and the silane coupling agent are used for modifying polyethyleneimine, so that the dispersity of polyacrylonitrile modified lignin is improved, and the high-temperature resistance is not sacrificed, so that the polyacrylamide-based high-temperature-resistant gel plugging agent is prepared.

Description

Technical Field

[0001] This invention relates to the field of petroleum extraction technology, specifically to a polyacrylamide-based high-temperature resistant gel plugging agent and its preparation method. Background Technology

[0002] In the mid-to-late stages of oil and gas field development, water shut-off and profile control in high-temperature formations are key technologies for enhancing oil recovery. Traditional polyacrylamide-based gel plugging agents are prone to oxidative degradation in high-temperature environments above 80°C due to insufficient molecular chain thermal stability, resulting in short plugging effectiveness and insufficient compressive strength. In existing technologies, although the high-temperature resistance can be improved by introducing rigid monomers or inorganic fillers, there is often a contradiction between dispersibility and toughness, which leads to a decrease in toughness after the plugging agent has solidified.

[0003] In summary, solving the above problems and preparing a polyacrylamide-based high-temperature resistant gel plugging agent is of great significance. Summary of the Invention

[0004] The purpose of this invention is to provide a polyacrylamide-based high-temperature resistant gel plugging agent and its preparation method, so as to solve the problems raised in the prior art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing a polyacrylamide-based high-temperature resistant gel plugging agent includes the following steps: Modified polyethyleneimine was added to deionized water and mixed. Polyacrylonitrile-modified lignin was added and ultrasonically dispersed. Acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, ammonium persulfate and retarder were added and mixed. The pH was adjusted to 7-8 and stirred evenly to obtain polyacrylamide-based high-temperature resistant gel plugging agent.

[0006] In a more optimized form, the raw materials of the polyacrylamide-based high-temperature resistant gel plugging agent include the following components: by mass parts, 4-6 parts modified polyethyleneimine, 5-10 parts polyacrylonitrile-modified lignin, 15-25 parts acrylamide, 10-15 parts 2-acrylamido-2-methylpropanesulfonic acid, 0.3-0.4 parts ammonium persulfate, 0.1-0.2 parts retarder, and 40-50 parts deionized water.

[0007] A more optimized method for preparing the polyacrylonitrile-modified lignin is as follows: (1) Sulfate lignin and 1,1,3,3-tetramethyl-1,3-divinyldisilazane are mixed and melt-extruded to obtain vinylsilylated lignin; (2) Acrylonitrile and initiator are added to dimethyl sulfoxide and mixed. Under nitrogen protection, the mixture is heated to 65-70°C and stirred for 2-3 hours. The mixture is then cooled to 40-50°C, and vinyl silylated lignin and acrylamide are added and mixed. Hydrogen peroxide solution is added, and the mixture is heated to 65-70°C and stirred for 5-6 hours. After post-treatment, polyacrylonitrile-modified lignin is obtained.

[0008] In a more optimized form, the mass ratio of sulfate lignin to 1,1,3,3-tetramethyl-1,3-divinyldisilazane in the vinylsilylated lignin is (4~6):1; The method for preparing sulfate lignin in the scheme is as follows: at 160~180℃ and 0.6~1.0MPa, wood chips (pine wood) are mixed and stirred with sodium hydroxide and sodium sulfide for 2~4 hours. The pH is adjusted to 2~3 with sulfuric acid, precipitate is formed, washed multiple times, dried and ground to obtain sulfate lignin.

[0009] The raw materials for polyacrylonitrile-modified lignin include the following components: by mass, 10-15 parts acrylonitrile, 0.2-0.25 parts initiator, 5-8 parts vinyl silicified lignin, 2-3 parts acrylamide, and 4.2-5 parts hydrogen peroxide solution.

[0010] A more optimized method for preparing the modified polyethyleneimine is as follows: (1) Hydroxy silicone oil is added to anhydrous ethanol and mixed, isophorone diisocyanate and dibutyltin dilaurate are added, and the mixture is stirred at 60~75℃ for 6~8 hours, followed by post-treatment to obtain isocyanate-based silicone oil; (2) Isocyanate-based silicone oil, 3-isocyanate-based propyltriethoxysilane and polyethyleneimine are added to chloroform and mixed, dibutyltin dilaurate is added, and the mixture is stirred at 60~70℃ for 10~15 hours, followed by post-treatment to obtain modified polyethyleneimine.

[0011] In this scheme, under the action of a catalyst, the hydroxyl group (-OH) at the end of the hydroxyl silicone oil molecule reacts with the isocyanate group (-NCO) in the isophorone diisocyanate (IPDI) molecule to form a carbamate bond, ultimately forming an isocyanate-based silicone oil that retains the isocyanate group; the isocyanate-based silicone oil reacts with the -NCO in 3-isocyanate-propyltriethoxysilane and the amino group in the polyethyleneimine molecule to form a urea bond, thus obtaining modified polyethyleneimine.

[0012] In a more optimized form, the molar ratio of the hydroxyl groups in the hydroxyl silicone oil to the isocyanate groups in the isophorone diisocyanate is 1:2~3; the raw material for the modified polyethyleneimine includes the following components: by mass, 10~15 parts isocyanate silicone oil, 8~12 parts 3-isocyanate-propyltriethoxysilane, 30~40 parts polyethyleneimine, and 0.3~0.6 parts dibutyltin dilaurate.

[0013] More preferably, the raw materials for the retarder include one of organophosphonates and citric acid.

[0014] Compared with the prior art, the beneficial effects of the present invention are: In this scheme, acrylamide and 2-acrylamido-2-methylpropanesulfonic acid are used as the matrix structure; under the action of the initiator, cross-linking can be initiated by geothermal energy, and polyacrylamide-based high-temperature resistant gel plugging agent is used; 2-acrylamido-2-methylpropanesulfonic acid is used as a functional comonomer to give the gel high-temperature resistant auxiliary properties; in order to further improve its high-temperature resistance, polyacrylonitrile-modified lignin is added.

[0015] In this process, acrylonitrile is prepolymerized under an AIBN initiator to generate a low molecular weight polyacrylonitrile (prepolymer), followed by the addition of vinyl silylated lignin, acrylamide, and hydrogen peroxide. Polyacrylonitrile-modified lignin is then prepared by initiating the polymerization of the low molecular weight acrylonitrile prepolymer with acrylamide and vinyl silylated lignin using hydrogen peroxide. This lignin forms a dual rigid framework in synergy with the aromatic rings of lignin, hindering the thermal motion of molecular chains at high temperatures and reducing gel network disintegration. Furthermore, the lignin modified with 1,3-divinyl-1,1,3,3-tetramethyldisilazane exhibits increased hydrophobicity and improved dispersibility in water. Poor performance is not conducive to sealing; if a dispersant is added directly, it may affect the high temperature resistance. To solve this problem, the solution adjusts the ratio of hydroxyl silicone oil, 3-isocyanate-propyltriethoxysilane, and polyethyleneimine to obtain a modified polyethyleneimine with certain hydrophilicity. It has a certain dispersing effect on polyacrylonitrile-modified lignin and introduces acrylamide into polyacrylonitrile-modified lignin. Among them, hydroxyl silicone oil and 3-isocyanate-propyltriethoxysilane synergistically balance rigidity with acrylamide; and acrylamide improves toughness while enhancing interfacial compatibility with the polyacrylamide matrix.

[0016] In this method, modified polyethyleneimine is first added to deionized water to form a uniform dispersion system. Then, polyacrylonitrile-modified lignin is added to improve its dispersibility and enhance the high-temperature resistance of the sealing agent. If polyethyleneimine is added directly, although it has good fluidity, the performance of the sealing agent will be significantly reduced after curing due to the formation of a cross-linked network. Furthermore, the amino groups of modified polyethyleneimine, acrylamide, the amide groups of 2-acrylamido-2-methylpropanesulfonic acid, and the cyano groups on polyacrylonitrile-modified lignin form hydrogen bonds or covalent bonds at high temperatures, participating in the cross-linking reaction and forming a three-dimensional network structure. Detailed Implementation

[0017] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0018] In the following specific embodiments, "parts" refers to parts by weight. It should be noted that, in this embodiment, there are no special restrictions on the manufacturers of the raw materials involved in this invention; exemplarily, they include: The CAS number for hydroxyl silicone oil is 58130-04-4, with a molecular weight of 2000; the CAS number for isophorone diisocyanate is 4098-71-9; the CAS number for dibutyltin dilaurate is 77-58-7; the CAS number for 3-isocyanatopropyltriethoxysilane is 24801-88-5; the CAS number for polyethyleneimine is 9002-98-6, with a molecular weight of 1800; the CAS number for acrylonitrile is 107-13-1; the CAS number for azobisisobutyronitrile (initiator) is 78-67-1; the CAS number for acrylamide is 79-06-1; the CAS number for 2-acrylamido-2-methylpropanesulfonic acid is 79-06-1; the CAS number for ammonium persulfate is 7727-54-0; and the CAS number for citric acid is 77-92-9.

[0019] Example 1: A method for preparing a polyacrylamide-based high-temperature resistant gel plugging agent, comprising the following steps: Pre-preparation: The preparation method of polyacrylonitrile modified lignin is as follows: (1) Sulfate lignin and 1,1,3,3-tetramethyl-1,3-divinyldisilazane are mixed, the temperature is set to 120℃, the rotation speed is 120r / min, and the mixture is melt-extruded to obtain vinylsilylated lignin; the mass ratio of sulfate lignin to 1,1,3,3-tetramethyl-1,3-divinyldisilazane is 5:1; (2) 12 parts acrylonitrile and 0.22 parts initiator were added to 60 parts dimethyl sulfoxide and mixed. Under nitrogen protection, the mixture was heated to 65°C and stirred for 2 hours. The mixture was then cooled to 50°C, and 8 parts vinyl silylated lignin and 3 parts acrylamide were added and mixed. 4.6 parts hydrogen peroxide solution (concentration of 30%) was added, and the mixture was heated to 65°C and stirred for 6 hours. The mixture was then cooled to room temperature, and deionized water was added to precipitate the lignin. The lignin was filtered and dried to obtain polyacrylonitrile modified lignin. The preparation method of modified polyethyleneimine is as follows: (1) Hydroxy silicone oil is added to anhydrous ethanol and mixed, isophorone diisocyanate and dibutyltin dilaurate are added, and the mixture is stirred at 70°C for 6 hours. The mixture is precipitated by petroleum ether, and the precipitate is repeatedly dissolved and precipitated 3 times. The mixture is washed and dried to obtain isocyanate-based silicone oil. The molar ratio of the hydroxyl group of the hydroxyl silicone oil to the isocyanate group of the isophorone diisocyanate is 1:2.2. (2) 15 parts of isocyanate-based silicone oil, 8 parts of 3-isocyanate-based propyltriethoxysilane and 32 parts of polyethyleneimine were added to chloroform and mixed. 0.4 parts of dibutyltin dilaurate were added and stirred at 70°C for 10 hours. After cooling to room temperature, ether was added to precipitate the mixture. The mixture was then filtered and dried to obtain modified polyethyleneimine. Four parts of modified polyethyleneimine were added to 40 parts of deionized water and mixed. Five parts of polyacrylonitrile-modified lignin were added and ultrasonically dispersed. Then, 15 parts of acrylamide, 10 parts of 2-acrylamido-2-methylpropanesulfonic acid, 0.4 parts of ammonium persulfate, and 0.13 parts of retarder were added and mixed. The pH was adjusted to 8, and the mixture was stirred evenly to obtain a polyacrylamide-based high-temperature resistant gel plugging agent.

[0020] Example 2, a method for preparing a polyacrylamide-based high-temperature resistant gel plugging agent, comprising the following steps: Pre-preparation: The preparation method of polyacrylonitrile modified lignin is as follows: (1) Sulfate lignin and 1,1,3,3-tetramethyl-1,3-divinyldisilazane are mixed, the temperature is set to 120℃, the rotation speed is 120r / min, and the mixture is melt-extruded to obtain vinylsilylated lignin; the mass ratio of sulfate lignin to 1,1,3,3-tetramethyl-1,3-divinyldisilazane is 5:1; (2) 12 parts acrylonitrile and 0.22 parts initiator were added to 60 parts dimethyl sulfoxide and mixed. Under nitrogen protection, the mixture was heated to 65°C and stirred for 2 hours. The mixture was then cooled to 50°C, and 8 parts vinyl silylated lignin and 3 parts acrylamide were added and mixed. 4.6 parts hydrogen peroxide solution (concentration of 30%) was added, and the mixture was heated to 65°C and stirred for 6 hours. The mixture was then cooled to room temperature, and deionized water was added to precipitate the lignin. The lignin was filtered and dried to obtain polyacrylonitrile modified lignin. The preparation method of modified polyethyleneimine is as follows: (1) Hydroxy silicone oil is added to anhydrous ethanol and mixed, isophorone diisocyanate and dibutyltin dilaurate are added, and the mixture is stirred at 70°C for 6 hours. The mixture is precipitated by petroleum ether, and the precipitate is repeatedly dissolved and precipitated 3 times. The mixture is washed and dried to obtain isocyanate-based silicone oil. The molar ratio of the hydroxyl group of the hydroxyl silicone oil to the isocyanate group of the isophorone diisocyanate is 1:2.2. (2) 15 parts of isocyanate-based silicone oil, 8 parts of 3-isocyanate-based propyltriethoxysilane and 32 parts of polyethyleneimine were added to chloroform and mixed. 0.4 parts of dibutyltin dilaurate were added and stirred at 70°C for 10 hours. After cooling to room temperature, ether was added to precipitate the mixture. The mixture was then filtered and dried to obtain modified polyethyleneimine. Six parts of modified polyethyleneimine were added to 40 parts of deionized water and mixed. Ten parts of polyacrylonitrile-modified lignin were added and ultrasonically dispersed. Then, 25 parts of acrylamide, 15 parts of 2-acrylamido-2-methylpropanesulfonic acid, 0.4 parts of ammonium persulfate, and 0.13 parts of retarder were added and mixed. The pH was adjusted to 8, and the mixture was stirred evenly to obtain a polyacrylamide-based high-temperature resistant gel plugging agent.

[0021] Example 3, a method for preparing a polyacrylamide-based high-temperature resistant gel plugging agent, comprising the following steps: Pre-preparation: The preparation method of polyacrylonitrile modified lignin is as follows: (1) Sulfate lignin and 1,1,3,3-tetramethyl-1,3-divinyldisilazane are mixed, the temperature is set to 120℃, the rotation speed is 120r / min, and the mixture is melt-extruded to obtain vinylsilylated lignin; the mass ratio of sulfate lignin to 1,1,3,3-tetramethyl-1,3-divinyldisilazane is 5:1; (2) 12 parts acrylonitrile and 0.22 parts initiator were added to 60 parts dimethyl sulfoxide and mixed. Under nitrogen protection, the mixture was heated to 65°C and stirred for 2 hours. The mixture was then cooled to 50°C, and 8 parts vinyl silylated lignin and 3 parts acrylamide were added and mixed. 4.6 parts hydrogen peroxide solution (concentration of 30%) was added, and the mixture was heated to 65°C and stirred for 6 hours. The mixture was then cooled to room temperature, and deionized water was added to precipitate the lignin. The lignin was filtered and dried to obtain polyacrylonitrile modified lignin. The preparation method of modified polyethyleneimine is as follows: (1) Hydroxy silicone oil is added to anhydrous ethanol and mixed, isophorone diisocyanate and dibutyltin dilaurate are added, and the mixture is stirred at 70°C for 6 hours. The mixture is precipitated by petroleum ether, and the precipitate is repeatedly dissolved and precipitated 3 times. The mixture is washed and dried to obtain isocyanate-based silicone oil. The molar ratio of the hydroxyl group of the hydroxyl silicone oil to the isocyanate group of the isophorone diisocyanate is 1:2.2. (2) 15 parts of isocyanate-based silicone oil, 8 parts of 3-isocyanate-based propyltriethoxysilane and 32 parts of polyethyleneimine were added to chloroform and mixed. 0.4 parts of dibutyltin dilaurate were added and stirred at 70°C for 10 hours. After cooling to room temperature, ether was added to precipitate the mixture. The mixture was then filtered and dried to obtain modified polyethyleneimine. Six parts of modified polyethyleneimine were added to 40 parts of deionized water and mixed. Seven parts of polyacrylonitrile-modified lignin were added and ultrasonically dispersed. 25 parts of acrylamide, 15 parts of 2-acrylamido-2-methylpropanesulfonic acid, 0.4 parts of ammonium persulfate, and 0.13 parts of retarder were added and mixed. The pH was adjusted to 8, and the mixture was stirred evenly to obtain a polyacrylamide-based high-temperature resistant gel plugging agent.

[0022] Comparative Example 1 is based on Example 2, but without modification of the polyethyleneimine; the remaining operating steps are the same. Pre-preparation: The preparation method of polyacrylonitrile modified lignin is as follows: (1) Sulfate lignin and 1,1,3,3-tetramethyl-1,3-divinyldisilazane are mixed, the temperature is set to 120℃, the rotation speed is 120r / min, and the mixture is melt-extruded to obtain vinylsilylated lignin; the mass ratio of sulfate lignin to 1,1,3,3-tetramethyl-1,3-divinyldisilazane is 5:1; (2) 12 parts acrylonitrile and 0.22 parts initiator were added to 60 parts dimethyl sulfoxide and mixed. Under nitrogen protection, the mixture was heated to 65°C and stirred for 2 hours. The mixture was then cooled to 50°C, and 8 parts vinyl silylated lignin and 3 parts acrylamide were added and mixed. 4.6 parts hydrogen peroxide solution (concentration of 30%) was added, and the mixture was heated to 65°C and stirred for 6 hours. The mixture was then cooled to room temperature, and deionized water was added to precipitate the lignin. The lignin was filtered and dried to obtain polyacrylonitrile modified lignin. Six parts of polyethyleneimine were added to 40 parts of deionized water and mixed. Ten parts of polyacrylonitrile-modified lignin were added and ultrasonically dispersed. Then, 25 parts of acrylamide, 15 parts of 2-acrylamido-2-methylpropanesulfonic acid, 0.4 parts of ammonium persulfate, and 0.13 parts of retarder were added and mixed. The pH was adjusted to 8, and the mixture was stirred evenly to obtain a polyacrylamide-based high-temperature resistant gel plugging agent.

[0023] Comparative Example 2 is based on Example 2, except that the polyacrylonitrile-modified lignin is replaced with lignin; the remaining operating steps are the same. Pre-preparation: The preparation method of modified polyethyleneimine is as follows: (1) Hydroxy silicone oil is added to anhydrous ethanol and mixed, isophorone diisocyanate and dibutyltin dilaurate are added, and the mixture is stirred at 70°C for 6 hours. The mixture is precipitated by petroleum ether, and the precipitate is repeatedly dissolved 3 times. After washing and drying, isocyanate-based silicone oil is obtained. The molar ratio of hydroxyl groups in hydroxy silicone oil to isocyanate groups in isophorone diisocyanate is 1:2.2. (2) 15 parts of isocyanate-based silicone oil, 8 parts of 3-isocyanate-based propyltriethoxysilane and 32 parts of polyethyleneimine were added to chloroform and mixed. 0.4 parts of dibutyltin dilaurate were added and stirred at 70°C for 10 hours. After cooling to room temperature, ether was added to precipitate the mixture. The mixture was then filtered and dried to obtain modified polyethyleneimine. Six parts of modified polyethyleneimine were added to 40 parts of deionized water and mixed. Ten parts of lignin were added and ultrasonically dispersed. Then, 25 parts of acrylamide, 15 parts of 2-acrylamido-2-methylpropanesulfonic acid, 0.4 parts of ammonium persulfate, and 0.13 parts of retarder were added and mixed. The pH was adjusted to 8, and the mixture was stirred evenly to obtain a polyacrylamide-based high-temperature resistant gel plugging agent.

[0024] Comparative Example 3 is based on Example 2, in which the component raw materials of the polyacrylamide-based high-temperature resistant gel plugging agent are directly mixed; the remaining operation steps are the same. Six parts of modified polyethyleneimine, 10 parts of polyacrylonitrile-modified lignin, 25 parts of acrylamide, 15 parts of 2-acrylamido-2-methylpropanesulfonic acid, 0.4 parts of ammonium persulfate, and 0.13 parts of retarder were mixed and added to 40 parts of deionized water. The pH was adjusted to 8, and the mixture was stirred evenly to obtain a polyacrylamide-based high-temperature resistant gel plugging agent.

[0025] Comparative Example 4 was based on Example 2, but without the addition of acrylamide to the polyacrylonitrile-modified lignin; the remaining operating steps were the same. Pre-preparation: The preparation method of polyacrylonitrile modified lignin is as follows: (1) Sulfate lignin and 1,1,3,3-tetramethyl-1,3-divinyldisilazane are mixed, the temperature is set to 120℃, the rotation speed is 120r / min, and the mixture is melt-extruded to obtain vinylsilylated lignin; the mass ratio of sulfate lignin to 1,1,3,3-tetramethyl-1,3-divinyldisilazane is 5:1; (2) 12 parts acrylonitrile and 0.22 parts initiator were added to 60 parts dimethyl sulfoxide and mixed. Under nitrogen protection, the mixture was heated to 65°C and stirred for 2 hours. The mixture was then cooled to 50°C, 8 parts vinyl silylated lignin were added and mixed. 4.6 parts hydrogen peroxide solution (concentration of 30%) was added, and the mixture was heated to 65°C and stirred for 6 hours. The mixture was then cooled to room temperature, deionized water was added to precipitate the lignin, and the mixture was filtered and dried to obtain polyacrylonitrile modified lignin. Six parts of modified polyethyleneimine were added to 40 parts of deionized water and mixed. Ten parts of polyacrylonitrile-modified lignin were added and ultrasonically dispersed. Then, 25 parts of acrylamide, 15 parts of 2-acrylamido-2-methylpropanesulfonic acid, 0.4 parts of ammonium persulfate, and 0.13 parts of retarder were added and mixed. The pH was adjusted to 8, and the mixture was stirred evenly to obtain a polyacrylamide-based high-temperature resistant gel plugging agent.

[0026] Comparative Example 5 is based on Example 2, except that the modified polyethyleneimine is replaced with sodium dodecylbenzenesulfonate; the remaining operating steps are the same. Six parts of sodium dodecylbenzenesulfonate were added to 40 parts of deionized water and mixed. Ten parts of polyacrylonitrile-modified lignin were added and ultrasonically dispersed. Then, 25 parts of acrylamide, 15 parts of 2-acrylamido-2-methylpropanesulfonic acid, 0.4 parts of ammonium persulfate, and 0.13 parts of retarder were added and mixed. The pH was adjusted to 8, and the mixture was stirred evenly to obtain a polyacrylamide-based high-temperature resistant gel plugging agent.

[0027] Testing and Experimentation: A simulated rock core with a diameter d of 25 mm and a length L of 200 mm was prepared; the core was evacuated to remove air from the pores; water was injected into the core at a flow rate of 2 mL / min; the permeability k0 of the core before plugging was calculated according to Darcy's Law; the polyacrylamide-based high-temperature resistant gel plugging agent prepared in Examples 1-3 and Comparative Examples 1-5 was injected into the core model to plug both ends of the core; the core was placed in a 150℃ constant temperature chamber and left to stand for 40 days; water was injected again until the pressure stabilized. Record the pressure gauge reading to obtain the injection pressure difference. Calculate the post-plugging permeability (k') of the core using Darcy's Law formula, and thus calculate the plugging rate (η). Darcy's Law formula: k = QμL / AΔP; Q is the injection rate, μ is the fluid viscosity, A is the cross-sectional area of ​​the core, and ΔP is the injection pressure difference. Calculate the pre-plugging permeability k0 and the post-plugging permeability k' of the core; η = (1-k' / k0) × 100%. A higher plugging rate indicates better plugging performance of the plugging agent at high temperatures. Table 1 Conclusions: Comparative Example 1, based on Example 2, did not modify polyethyleneimine; unmodified polyethyleneimine lacks flexible silica segments, leading to network embrittlement at high temperatures and poor sealing layer density, thus resulting in performance degradation; Comparative Example 2, based on Example 2, did not modify lignin, resulting in reduced high-temperature resistance, thus degrading performance; Comparative Example 3, based on Example 2, directly mixed the components of the polyacrylamide-based high-temperature resistant gel plugging agent; polyacrylonitrile-modified lignin agglomerated, leading to performance degradation; Comparative Example 4, based on Example 2, did not add acrylamide to the polyacrylonitrile-modified lignin; the lack of acrylamide segments reduced the hydrophilicity of lignin and its interfacial compatibility with the matrix, thus degrading performance; Comparative Example 5, based on Example 2, used a conventional dispersant to disperse the polyacrylonitrile-modified lignin; sodium dodecylbenzenesulfonate only played a certain dispersing role and did not participate in crosslinking, failing to form a dense network, thus leading to performance degradation in Comparative Example 5.

[0028] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A method for preparing a polyacrylamide-based high-temperature resistant gel plugging agent, characterized in that: The method comprises the following steps: The modified polyethylene imine is mixed in deionized water, the polyacrylonitrile modified lignin is ultrasonically dispersed, the acrylamide, 2-acrylamido-2-methylpropane sulfonic acid, ammonium persulfate and the retarder are mixed, the pH is adjusted to 7-8, and the mixture is uniformly stirred to obtain the polyacrylamide-based high-temperature-resistant gel plugging agent.

2. The method for preparing a polyacrylamide-based high-temperature resistant gel plugging agent according to claim 1, characterized in that: The raw materials of the polyacrylamide-based high-temperature-resistant gel plugging agent comprise the following components: 4-6 parts of modified polyethylene imine, 5-10 parts of polyacrylonitrile modified lignin, 15-25 parts of acrylamide, 10-15 parts of 2-acrylamido-2-methylpropane sulfonic acid, 0.3-0.4 parts of ammonium persulfate, 0.1-0.2 parts of retarder and 40-50 parts of deionized water.

3. The method for preparing a polyacrylamide-based high-temperature resistant gel plugging agent according to claim 1, characterized in that: The preparation method of the polyacrylonitrile modified lignin is as follows: (1) The sulfite lignin and 1,1,3,3-tetramethyl-1,3-divinyl disilazane are mixed and melt-extruded to obtain the vinyl silicon-modified lignin; (2) The acrylonitrile and initiator are mixed in dimethyl sulfoxide, stirred at 65-70 DEG C for 2-3 hours under nitrogen protection, cooled to 40-50 DEG C, mixed with the vinyl silicon-modified lignin and acrylamide, added with hydrogen peroxide solution, stirred at 65-70 DEG C for 5-6 hours, and post-treated to obtain the polyacrylonitrile modified lignin.

4. The preparation method of a polyacrylamide-based high-temperature resistant gel plugging agent according to claim 3, characterized in that: In the vinyl silicon-modified lignin, the mass ratio of the sulfite lignin to 1,1,3,3-tetramethyl-1,3-divinyl disilazane is (4-6):1; The raw materials of the polyacrylonitrile modified lignin comprise the following components: 10-15 parts of acrylonitrile, 0.2-0.25 parts of initiator, 5-8 parts of vinyl silicon-modified lignin, 2-3 parts of acrylamide and 4.2-5 parts of hydrogen peroxide solution.

5. The method for preparing a polyacrylamide-based high-temperature resistant gel plugging agent according to claim 1, characterized in that: The preparation method of the modified polyethylene imine is as follows: (1) the hydroxyl silicone oil is mixed in anhydrous ethanol, isophorone diisocyanate and dibutyltin dilaurate are added, stirred at 60-75 DEG C for 6-8 hours, and post-treated to obtain the isocyanate group silicone oil; (2) the isocyanate group silicone oil, 3-isocyanate group propyl triethoxysilane and polyethylene imine are mixed in chloroform, dibutyltin dilaurate is added, stirred at 60-70 DEG C for 10-15 hours, and post-treated to obtain the modified polyethylene imine.

6. The method for preparing a polyacrylamide-based high-temperature resistant gel plugging agent according to claim 5, characterized in that: In the isocyanate group silicone oil, the molar ratio of the hydroxyl group of the hydroxyl silicone oil to the isocyanate group of the isophorone diisocyanate is 1:2-3; the raw materials of the modified polyethylene imine comprise the following components: 10-15 parts of isocyanate group silicone oil, 8-12 parts of 3-isocyanate group propyl triethoxysilane, 30-40 parts of polyethylene imine and 0.3-0.6 parts of dibutyltin dilaurate.

7. The method for preparing a polyacrylamide-based high-temperature resistant gel plugging agent according to claim 1, characterized in that: The raw materials of the retarder comprise one of organic phosphonate and citric acid.

8. The polyacrylamide-based high-temperature-resistant gel plugging agent is prepared by the preparation method of the polyacrylamide-based high-temperature-resistant gel plugging agent according to any one of claims 1-7.

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