A method for preparing a pH-sensitive self-crosslinking polyacrylamide emulsion system for deep profile control in high-temperature and high-salinity oil reservoirs.

Abstract

This invention relates to a method for preparing a pH-sensitive self-crosslinking polyacrylamide emulsion system for deep profile control in high-temperature and high-salinity oil reservoirs. The method involves uniformly mixing three functional temperature- and salt-resistant monomers, a pH-sensitive monomer diacetone acrylamide intermediate oxazine sulfate, an aqueous chain transfer agent, a chelating agent, and distilled water. The pH is adjusted to 3-5, and a water-soluble oxidant is added to obtain an aqueous solution. An oil phase is obtained by mixing a solvent oil, a nonionic emulsifier, an ionic emulsifier, and an oil-soluble initiator. The aqueous solution is slowly added while the oil phase is stirred, and the mixture is then subjected to high-speed shear emulsification. Nitrogen blowing removes oxygen, followed by polymerization with a water-soluble reducing agent. A phase-inversion agent is added for phase inversion, and the mixture is thoroughly mixed to obtain a light yellow to milky white semi-transparent emulsion, which is the pH-sensitive self-crosslinking polyacrylamide emulsion for deep profile control in high-temperature and high-salinity oil reservoirs. This emulsion allows for continuous mixing, reduces surface investment, has a low initial viscosity, and good injectability.

Description

Technical Field

[0001] This invention pertains to oilfield enhanced oil recovery technology, specifically involving the preparation of a pH-sensitive self-crosslinking polyacrylamide emulsion system suitable for deep profile control in high-temperature and high-salinity oil reservoirs using pH-sensitive monomers and an environmentally friendly emulsification system. Background Technology

[0002] Gel plugging has become one of the most important and widely implemented technologies in my country's oilfield development. Currently, the most widely used gel plugging agents are mainly polyacrylamide or polysaccharides complexed with high-valence metal ions such as chromium and aluminum, and chemically cross-linked polymers with formaldehyde, phenol, etc. (Polymer Gel Systems for Water Management in High-Temperature Petroleum Reservoirs: A Chemical Review, Daoyi Zhu et al., Energy Fuels, 2017, 31, 13063−13087). However, most existing self-crosslinking polymer gels are prone to decrosslinking, degradation, and hydrolysis under high temperature and high salinity conditions, resulting in polymer gel performance that falls far short of actual construction requirements.

[0003] For example, CN105860946A discloses a low-temperature gel-forming controllable profile adjustment system, whose main components are hydrolyzed polyacrylamide, paraformaldehyde, resorcinol and m-phenylenediamine.

[0004] Publication number CN106634907A discloses a polyethyleneimine-based profile control and water-blocking agent, which comprises hydrolyzed polyacrylamide, crosslinking agent polyethyleneimine, gelling retarder, and stabilizer.

[0005] Publication number CN102816558A discloses a deep profile control and water shut-off agent, the components of which are partially hydrolyzed polyacrylamide, potassium dichromate, sodium sulfite, hexamethylenetetramine, phenol and ammonium chloride.

[0006] The above-mentioned profile control and water shut-off agents have some drawbacks: ordinary hydrolyzed polyacrylamide has a large viscosity shear loss rate after dissolution and injection, which affects its gelation performance and strength; it generally has poor temperature resistance, and the hydrolyzed polyacrylamide molecules will break down at no more than 100 degrees Celsius, resulting in a decrease in viscosity, especially in high-salt formations.

[0007] In recent years, various polymer crosslinking systems with low toxicity and low harm have been developed in large quantities and have achieved certain results. Among them, self-crosslinking systems have gradually become one of the hot topics in the research of new crosslinking polymers because the polymer monomers themselves have both polymerization ability and crosslinking characteristics. Diacetone acrylamide is a new type of self-crosslinking monomer developed in recent years. The monomer structure contains ketone carbonyl and amide groups. It can form weak crosslinked polymer gels through intermolecular forces, which is suitable for gelation at medium and low temperatures. It can also be used with other crosslinking agents to densify and strengthen the polymer network to form a stronger crosslinking network, which is suitable for profile control in deep high-temperature oil reservoirs. Moreover, it is low in toxicity and harmless to the environment (Research progress of modified acrylate emulsion hydraulic sensitive adhesive, Li Wanlin, Liaoning Chemical Industry, 2020, 49(10):1274-1279). However, due to the very active chemical properties of the monomer itself, it is very easy to undergo polymerization and crosslinking reactions under light, heat and other conditions, which restricts its large-scale use (Application of diacetone acrylamide in the modification of polyacrylamide, Zhang Yuping, Applied Chemical Industry, 2006, 35(11):858-860). Based on this, we intend to obtain a relatively stable intermediate oxazine sulfate suitable for transportation and storage by improving the synthesis conditions of the self-crosslinking monomer, and copolymerize it with acrylamide to obtain a pH-sensitive self-crosslinking, environmentally friendly polymer gel. The preparation of the intermediate oxazine sulfate is shown in the formula (Synthesis of N-(1,1-dimethyl-3-oxobutyl)acrylamide, Ran Rong, Journal of Sichuan University, 2001, 33(2): 57-59). The preparation process is as follows: acrylonitrile and acetone are added to the reactor, concentrated sulfuric acid is slowly added dropwise at zero degrees, after the addition is completed, the temperature is naturally raised to 50 degrees, and the reaction is carried out for 3-6 hours. After the reaction is completed, the system is cooled to room temperature, a large amount of acetone and deionized water are added, and the pH value is adjusted to 4.0 with NaOH solution; after standing, light brown flaky crystals are obtained by filtration, and the oxazine sulfate is obtained by recrystallization with acetone.

[0008] To improve the swept volume and oil displacement efficiency of injected water and extract high-permeability oil reserves from low- to medium-permeability reservoirs, chemical agents are typically added to injection wells to seal high-permeability layers to a certain extent. Currently, profile control and water shut-off technologies used in onshore oilfields cannot meet the requirements of offshore platform operations, necessitating in-depth research into profile control and water shut-off technologies suitable for offshore oilfields. Gel-type profile control agents possess excellent flow guidance and rate control properties, playing a dual role in profile control and oil displacement in water-driven reservoirs, and can be used as profile control agents in offshore oilfields. Summary of the Invention

[0009] This invention addresses the problems existing in the above-mentioned oilfields by providing a method for preparing a pH-sensitive self-crosslinking polyacrylamide emulsion system for deep profile control in high-temperature and high-salinity oil reservoirs. This method enables continuous mixing, reduces surface investment, and features low initial viscosity and good injectability.

[0010] The technical solution adopted in this invention is: a method for preparing a pH-sensitive self-crosslinking polyacrylamide emulsion system for deep profile control in high-temperature and high-salinity oil reservoirs, characterized by comprising the following steps:

[0011] S1. Preparation of the aqueous phase: By mass, 50-80 parts of the first nonionic monomer, 1-20 parts of the second functional cationic monomer, 1-20 parts of the third functional temperature- and salt-resistant monomer, and 1-10 parts of the fourth pH-sensitive monomer, diacetone acrylamide intermediate oxazine sulfate, 0.001-0.01 parts of aqueous phase chain transfer agent, 0.01-1 parts of chelating agent, and 10-30 parts of distilled water are mixed evenly. The pH value is then adjusted to 3-5 with sodium hydroxide or ammonia. 0.001-0.005 parts of water-soluble oxidant are added and mixed evenly to obtain the aqueous phase solution.

[0012] S2. Preparation of the oil phase: In the reactor, according to the mass fraction ratio, use 20-40 parts of solvent oil, 1-3 parts of nonionic emulsifier, 1-2 parts of ionic emulsifier, and 0.02-0.05 parts of oil-soluble initiator, and mix evenly to obtain the oil phase;

[0013] S3. Emulsification and homogenization: While stirring the oil phase prepared in the reactor, slowly add the aqueous phase solution to it. After mixing thoroughly, an emulsion is obtained. Use a homogenizer at 18000-20000 rpm / min to perform high-speed shear emulsification on the emulsion for 1-2 minutes, so that the emulsion viscosity reaches the Brookfield viscosity of 800-1200 cps.

[0014] S4. Polymerization reaction: After emulsification, nitrogen blowing is immediately performed to remove oxygen. After sufficient displacement, water-soluble reducing agent is gradually added to start the polymerization reaction. During the polymerization reaction, the stirring speed is always maintained at 500 rpm / min, and the reaction temperature is controlled below 45℃.

[0015] S5. Phase inversion: After the polymerization reaction is completed, 2-5 parts of phase inversion agent are added to carry out phase inversion. After mixing evenly, a light yellow to milky white semi-transparent emulsion is obtained, which is the pH-sensitive self-crosslinking polyacrylamide emulsion for deep profile control of high-temperature and high-salt oil reservoirs.

[0016] Furthermore, the first nonionic monomer is one or more of acrylamide, N,N-dimethylacrylamide, and vinylpyrrolidone;

[0017] Furthermore, the second type of functional cationic monomer is one or a mixture of dimethyl diallyl ammonium chloride and (meth)acryloyloxyethyltrimethyl ammonium chloride;

[0018] Furthermore, the third functional temperature- and salt-resistant monomer is 2-acrylamido-2-methylpropanesulfonic acid, allyl sulfonic acid, styrene sulfonic acid, or a mixture of both.

[0019] Furthermore, the aqueous chain transfer agent is one or more of sodium formate, sodium hypophosphite, isopropanol, and mercaptoacetic acid.

[0020] Further, the chelating agent is a sodium ethylenediaminetetraacetate, a sodium diethylenetriaminepentaacetate, a sodium iminodisuccinate, a sodium tartrate, a sodium citrate, a sodium gluconate, a sodium organic polyphosphate, or a sodium amino acid chelating agent; preferably, it is one or a mixture of biodegradable sodium iminodisuccinate, sodium tartrate, sodium citrate, sodium gluconate, or sodium amino acid chelating agents.

[0021] Furthermore, the water-soluble oxidant is one or more of tert-butyl hydroperoxide, ammonium persulfate, and sodium persulfate.

[0022] Furthermore, the solvent oil may be a blend of two or more of vegetable oils, white oil, liquid paraffin, kerosene, and diesel oil; preferably, environmentally friendly vegetable oils, such as peanut oil, soybean oil, sunflower seed oil, coconut oil, and two or more of castor oil or hydrogenated castor oil, may be selected.

[0023] Furthermore, the ionic emulsifier is a combination of two or more of the following: linear alkylbenzene sulfonate, linear alkyl alcohol polyoxyethylene ether sulfate, α-fatty acid methyl ester sulfonate, sodium lauryl ether sulfate, oleate, and amphoteric emulsifiers disodium cocoamphodiacetate and cocamidopropyl betaine.

[0024] Furthermore, the nonionic emulsifier is one or a mixture of sophorolipids, rhamnolipids, trehaloses, cocoamides, and alkyl glycoside surfactants.

[0025] Furthermore, the oil-soluble initiator is one or two of azobisisobutyronitrile, azobisisoheptanenitrile, and azobisisobutylamidine hydrochloride.

[0026] Furthermore, the water-soluble reducing agent is one or a mixture of sodium metabisulfite, sodium bisulfite, and potassium bisulfite.

[0027] Further, the phase inversion agent is derived from a biodegradable alkyl (phenol) polyoxyethylene ether, selected from at least one of nonylphenol polyoxyethylene ether, octylphenol polyoxyethylene ether, benzylphenol polyoxyethylene ether, phenethylphenol polyoxyethylene ether, isomeric decaol polyoxyethylene ether, isomeric undecaol polyoxyethylene ether, and isomeric tridecaol polyoxyethylene ether; preferably at least one of nonylphenol polyoxyethylene ether, octylphenol polyoxyethylene ether, benzylphenol polyoxyethylene ether, phenethylphenol polyoxyethylene ether, isomeric decaol polyoxyethylene ether, isomeric undecaol polyoxyethylene ether, and isomeric tridecaol polyoxyethylene ether.

[0028] The emulsion of this invention exhibits pH-sensitive controllable crosslinking under underground conditions, achieving deep profile control. The temperature resistance of the profile control system mainly depends on the synergistic effect of the polymer and the crosslinking agent. On the polymer side, a portion of the pH-sensitive diacetone acrylamide intermediate oxazine sulfate monomer is introduced, copolymerized with functional temperature- and salt-resistant monomers and functional cationic monomers to prepare a multi-component copolymer. This improves the temperature and salt resistance of the polymer itself and enhances the synergistic effect with the crosslinking agent, satisfying the compatibility requirements of different crosslinking agents, including organometallic crosslinking agents, phenolic resin crosslinking agents, and polyethyleneimine crosslinking agents. This results in a profile control system with controllable gel strength, ranging from weak to strong gels, thus meeting the adaptability requirements of different reservoir conditions, especially high-temperature and high-salinity reservoirs. The profile control system of this invention preferentially uses polyethyleneimine crosslinking agent, a water-soluble polymer solution with low toxicity. It also uses environmentally friendly sulfonate / sulfate emulsifiers and vegetable oils as solvents. This emulsion system has good emulsifying properties and good interfacial activity, while also possessing oil displacement and plugging effects. Detailed Implementation Example 1

[0029] S1. Preparation of the aqueous phase: By mass, 70 parts of acrylamide, 10 parts of dimethyl diallyl ammonium chloride, 10 parts of 2-acrylamido-2-methylpropanesulfonic acid, 10 parts of pH-sensitive monomer diacetone acrylamide intermediate oxazine sulfate, 0.005 parts of sodium formate, 0.04 parts of diethylenetriaminepentaacetic acid pentasodium salt, 154 parts of deionized water, adjust the pH value to 3.5 with sodium hydroxide, add 1.8 parts of oxidant tert-butyl hydroperoxide, mix well to obtain an aqueous phase solution;

[0030] S2. Preparation of the oil phase: In the reaction vessel, according to the mass fraction ratio, 80 parts of coconut oil, 54 parts of castor oil mixture, 8 parts of sodium sulfate of linear alkyl alcohol polyoxyethylene ether, 4 parts of oleate, 4 parts of α-fatty acid methyl ester sulfonate, and finally 0.25 parts of azo oil-soluble initiator azobisisobutyronitrile, after mixing evenly, a yellow transparent oil phase is obtained.

[0031] S3. Emulsification and homogenization: While stirring the prepared oil phase in the reactor, slowly add the aqueous phase solution to it. After mixing thoroughly, an emulsion is obtained. Use a homogenizer at 18000-20000 rpm / min to perform high-speed shear emulsification on the emulsion for 1-2 minutes, so that the emulsion viscosity reaches the Brookfield viscosity of 800-1000 cps.

[0032] S4. Polymerization reaction: After emulsification, nitrogen purging is immediately performed to remove oxygen. After sufficient displacement, sodium metabisulfite solution, a reducing agent, is gradually added to initiate the polymerization reaction. The stirring speed is maintained at 500 rpm / min throughout the polymerization process. The reaction temperature is controlled below 45℃.

[0033] S5. Phase inversion: After the polymerization reaction is completed, 4 parts of nonylphenol polyoxyethylene ether are added to carry out phase inversion. After mixing evenly, a light yellow to milky white semi-transparent emulsion is obtained, which is the self-crosslinking polyacrylamide emulsion. Example 2

[0034] S1. Preparation of the aqueous phase: By mass, 74 parts of acrylamide, 10 parts of dimethyl diallyl ammonium chloride, 10 parts of sodium 2-acrylamido-2-methylpropanesulfonate, 6 parts of oxazine sulfate (an intermediate of the pH-sensitive monomer diacetone acrylamide), 0.005 parts of sodium formate, 0.04 parts of pentasodium diethylenetriaminepentaacetate, 154 parts of deionized water, the pH value is adjusted to 3.5 with sodium hydroxide, 1.8 parts of tert-butyl hydroperoxide (an oxidant) are added, and the mixture is stirred evenly to obtain the aqueous phase solution.

[0035] S2-S5 are the same as in Example 1. Example 3

[0036] S1. Preparation of the aqueous phase: By mass, 77 parts of acrylamide, 10 parts of dimethyl diallyl ammonium chloride, 10 parts of 2-acrylamido-2-methylpropanesulfonic acid, 3 parts of the pH-sensitive monomer diacetone acrylamide intermediate oxazine sulfate, 0.005 parts of sodium formate, 0.04 parts of diethylenetriaminepentaacetic acid pentasodium salt, 154 parts of deionized water, the pH value is adjusted to 3.5 with sodium hydroxide, 1.8 parts of oxidant tert-butyl hydroperoxide are added, and the mixture is mixed evenly to obtain the aqueous phase solution;

[0037] S2-S5 are the same as in Example 1. Example 4

[0038] S1. Preparation of the aqueous phase: By mass, 70 parts of acrylamide, 10 parts of (meth)acryloyloxyethyltrimethylammonium chloride, 10 parts of 2-acrylamido-2-methylpropanesulfonic acid, 10 parts of pH-sensitive monomer diacetone acrylamide intermediate oxazine sulfate, 0.005 parts of sodium formate, 0.04 parts of diethylenetriaminepentaacetic acid pentasodium salt, 154 parts of deionized water, adjust the pH value to 3.5 with sodium hydroxide, add 1.8 parts of oxidant tert-butyl hydroperoxide, mix well to obtain an aqueous phase solution;

[0039] S2. Preparation of the oil phase: In the reaction vessel, according to the mass fraction ratio, 80 parts of coconut oil, 54 parts of castor oil mixture, 6 parts of cocoamide, 5 parts of oleate, 4 parts of α-fatty acid methyl ester sulfonate, and finally 0.25 parts of azo oil-soluble initiator azobisisobutyronitrile, after mixing evenly, a yellow transparent oil phase is obtained.

[0040] S3. Emulsification and homogenization: While stirring the prepared oil phase in the reactor, slowly add the aqueous phase solution to it. After mixing thoroughly, an emulsion is obtained. Use a homogenizer at 18000-20000 rpm / min to perform high-speed shear emulsification on the emulsion for 1-2 minutes, so that the emulsion viscosity reaches the Brookfield viscosity of 800-1000 cps.

[0041] S4. Polymerization reaction: After emulsification, nitrogen purging is immediately performed to remove oxygen. After sufficient displacement, sodium metabisulfite solution, a reducing agent, is gradually added to initiate the polymerization reaction. The stirring speed is maintained at 500 rpm / min throughout the polymerization process. The reaction temperature is controlled below 45℃.

[0042] S5. Phase inversion: After the polymerization reaction is completed, 4 parts of nonylphenol polyoxyethylene ether are added to carry out phase inversion. After mixing evenly, a light yellow to milky white semi-transparent emulsion is obtained, which is the self-crosslinking polyacrylamide emulsion. Example 5

[0043] S1. Preparation of the aqueous phase: By mass, 70 parts of N,N-dimethylacrylamide, 10 parts of dimethyl diallyl ammonium chloride, 10 parts of allyl sulfonic acid, 10 parts of oxazine sulfate (an intermediate of the pH-sensitive monomer diacetone acrylamide), 0.005 parts of sodium formate, 0.04 parts of pentasodium diethylenetriaminepentaacetate, 154 parts of deionized water, adjust the pH to 3.5 with sodium hydroxide, add 1.8 parts of tert-butyl hydroperoxide as oxidant, and mix thoroughly to obtain an aqueous solution;

[0044] S2. Preparation of the oil phase: In the reaction vessel, according to the mass fraction ratio, 80 parts of coconut oil, 54 parts of castor oil mixture, 6 parts of trehalose, 6 parts of oleate, 4 parts of linear alkylbenzene sulfonate, and finally 0.25 parts of azo oil-soluble initiator azobisisobutyronitrile, after mixing evenly, a yellow transparent oil phase is obtained.

[0045] S3. Emulsification and homogenization: While stirring the prepared oil phase in the reactor, slowly add the aqueous phase solution to it. After mixing thoroughly, an emulsion is obtained. Use a homogenizer at 18000-20000 rpm / min to perform high-speed shear emulsification on the emulsion for 1-2 minutes, so that the emulsion viscosity reaches the Brookfield viscosity of 800-1000 cps.

[0046] S4. Polymerization reaction: After emulsification, nitrogen purging is immediately performed to remove oxygen. After sufficient displacement, sodium metabisulfite solution, a reducing agent, is gradually added to initiate the polymerization reaction. The stirring speed is maintained at 500 rpm / min throughout the polymerization process. The reaction temperature is controlled below 45℃.

[0047] S5. Phase inversion: After the polymerization reaction is completed, 4 parts of nonylphenol polyoxyethylene ether are added to carry out phase inversion. After mixing evenly, a light yellow to milky white semi-transparent emulsion is obtained, which is the self-crosslinking polyacrylamide emulsion. Example 6

[0048] S1. Preparation of the aqueous phase: By mass, 70 parts of acrylamide, 10 parts of (meth)acryloyloxyethyltrimethylammonium chloride, 10 parts of styrene sulfonic acid, 10 parts of pH-sensitive monomer diacetone acrylamide intermediate oxazine sulfate, 0.005 parts of sodium formate, 0.04 parts of diethylenetriaminepentaacetic acid pentasodium salt, 154 parts of deionized water, adjust the pH value to 3.5 with sodium hydroxide, add 1.8 parts of oxidant tert-butyl hydroperoxide, mix well to obtain an aqueous phase solution;

[0049] S2. Preparation of the oil phase: In the reaction vessel, according to the mass fraction ratio, 80 parts of coconut oil, 54 parts of castor oil mixture, 8 parts of sodium sulfate of linear alkyl alcohol polyoxyethylene ether, 4 parts of oleate, 4 parts of α-fatty acid methyl ester sulfonate, and finally 0.25 parts of azo oil-soluble initiator azobisisobutyronitrile, after mixing evenly, a yellow transparent oil phase is obtained.

[0050] S3. Emulsification and homogenization: While stirring the prepared oil phase in the reactor, slowly add the aqueous phase solution to it. After mixing thoroughly, an emulsion is obtained. Use a homogenizer at 18000-20000 rpm / min to perform high-speed shear emulsification on the emulsion for 1-2 minutes, so that the emulsion viscosity reaches the Brookfield viscosity of 800-1000 cps.

[0051] S4. Polymerization reaction: After emulsification, nitrogen purging is immediately performed to remove oxygen. After sufficient displacement, sodium metabisulfite solution, a reducing agent, is gradually added to initiate the polymerization reaction. The stirring speed is maintained at 500 rpm / min throughout the polymerization process. The reaction temperature is controlled below 45℃.

[0052] S5. Phase inversion: After the polymerization reaction is completed, 4 parts of nonylphenol polyoxyethylene ether are added to carry out phase inversion. After mixing evenly, a light yellow to milky white semi-transparent emulsion is obtained, which is the self-crosslinking polyacrylamide emulsion. Comparative Example 1

[0053] S1. Preparation of the aqueous phase: By mass, 70 parts of acrylamide, 10 parts of dimethyl diallyl ammonium chloride, 10 parts of sodium 2-acrylamido-2-methylpropanesulfonate, 0.005 parts of sodium formate, 0.04 parts of pentasodium diethylenetriaminepentaacetate, 154 parts of deionized water, adjust the pH to 3.5 with sodium hydroxide, add 1.8 parts of tert-butyl hydroperoxide as oxidant, and mix well to obtain an aqueous phase solution;

[0054] S2-S5 are the same as in Example 1. Comparative Example 2

[0055] S1. Preparation of the aqueous phase: By mass, 80 parts of acrylamide, 10 parts of (meth)acryloyloxyethyltrimethylammonium chloride, 10 parts of acrylic acid, 0.005 parts of sodium formate, 0.04 parts of pentasodium diethylenetriaminepentaacetate, 154 parts of deionized water, adjust the pH to 3.5 with sodium hydroxide, add 1.8 parts of oxidant tert-butyl hydroperoxide, and mix well to obtain an aqueous phase solution;

[0056] S2-S5 are the same as comparison 1.

[0057] The performance of the embodiments is evaluated below:

[0058] Comparison of temperature and salt resistance of the sample examples:

[0059] The emulsions of the examples and comparative samples were dissolved in simulated water (simulated seawater TDS: 33000 mg / L) and stirred evenly. After aging for different times in an oven at 90 °C, the viscosity of the samples was tested and their temperature and salt resistance was compared, as shown in Table 1.

[0060] Table 1: As shown in Table 1, the comparison between the examples and the comparative examples reveals that the addition of the pH-sensitive monomer diacetone acrylamide intermediate oxazine sulfuric acid and 2-acrylamido-2-methylpropanesulfonic acid can improve the temperature and salt resistance of the polymer and result in a higher viscosity retention rate.

[0061] Performance comparison of crosslinked gels in the examples:

[0062] At room temperature, the above emulsion, simulated water (simulated seawater TDS: 33000 mg / L), crosslinking agent, and pH adjuster were added sequentially to a beaker and stirred until homogeneous to obtain a gelling solution. The gelling solution was poured into an ampoule and sealed. The gelling process was observed in an oven (set at different temperatures: 50, 100, and 120 °C), as shown in Table 2 below.

[0063] Table 2: Under low temperature and low pH conditions, the copolymer is not easily cross-linked and exhibits excellent injectability. After injection into the reservoir, with increasing temperature or adjustment by pH adjusters, self-crosslinking depth profile control systems with different gelation times and intensities can be formed. This is because the gelation time depends on the rate of network structure formation. Under high concentrations of diacetone acrylamide, the solution contains many chain-chain contact points, making intermolecular cross-linking easy to form a network structure, which facilitates gelation and thus reduces the gelation time. Conversely, as the temperature increases, the formation of the network structure is accelerated, and the gelation time also decreases accordingly.

[0064] The results of testing the above-mentioned samples at a high temperature of 120 degrees Celsius, including the viscosity of the polyethyleneimine crosslinking system, the water-blocking rate, and the viscosity retention rate after 30 days at a constant temperature, are shown in Table 3 below.

[0065] Table 3: The results of testing the samples of Example 1 and Comparative Example 1 at a high temperature of 120 degrees Celsius, with different crosslinking systems, gel viscosity, water-blocking rate, and viscosity retention rate after 30 days of constant temperature are shown in Table 4 below.

[0066] Table 4: Based on the gelation, viscosity, water shut-off rate, and 30-day viscosity retention rate under different crosslinking systems at 120 degrees Celsius, as shown in Tables 2, 3, and 4 above, Example 1 is the optimal example. It utilizes three functional monomers: acrylamide, dimethyl diallyl ammonium chloride, and 2-acrylamido-2-methylpropanesulfonic acid, along with the pH-sensitive monomer diacetone acrylamide intermediate oxazine sulfate. These significantly improve the polymer's temperature and salt resistance, as well as its synergistic effect with the crosslinking agent, compared to other examples. Particularly at high temperatures, such as 120 degrees Celsius downhole, the gelation time is reduced by 64% compared to Example 3, and by over 75% compared to the comparative example which does not use the pH-sensitive monomer diacetone acrylamide intermediate oxazine sulfate. Furthermore, when combined with the crosslinking agent phenolic resin, the water shut-off rate increases from 61.3% to 92.1% compared to the comparative example, and the viscosity retention rate after 30 days increases from 71.4% to 95.3%. Example 1 demonstrates the best oil displacement and plugging effects.

Claims

1. A method for preparing a pH-sensitive self-crosslinking polyacrylamide emulsion system for deep profile control in high-temperature and high-salinity oil reservoirs, characterized in that: Includes the following steps: S1. Preparation of the aqueous phase: By mass, 70 parts of acrylamide, 10 parts of dimethyl diallyl ammonium chloride, 10 parts of 2-acrylamido-2-methylpropanesulfonic acid, 10 parts of pH-sensitive monomer diacetone acrylamide intermediate oxazine sulfate, 0.005 parts of sodium formate, 0.04 parts of diethylenetriaminepentaacetic acid pentasodium salt, 154 parts of deionized water, adjust the pH value to 3.5 with sodium hydroxide, add 1.8 parts of oxidant tert-butyl hydroperoxide, mix well to obtain an aqueous phase solution; S2. Preparation of the oil phase: In the reaction vessel, according to the mass fraction ratio, 80 parts of coconut oil, 54 parts of castor oil mixture, 8 parts of sodium sulfate of linear alkyl alcohol polyoxyethylene ether, 4 parts of oleate, 4 parts of α-fatty acid methyl ester sulfonate, and finally 0.25 parts of azo oil-soluble initiator azobisisobutyronitrile, after mixing evenly, a yellow transparent oil phase is obtained. S3. Emulsification and homogenization: While stirring the prepared oil phase in the reactor, slowly add the aqueous phase solution to it. After mixing thoroughly, an emulsion is obtained. Use a homogenizer at 18000-20000 rpm to perform high-speed shear emulsification on the emulsion for 1-2 minutes, so that the emulsion viscosity reaches the Brookfield viscosity of 800-1000 cps. S4. Polymerization reaction: After emulsification, nitrogen purging is immediately performed to remove oxygen. After sufficient replacement, sodium metabisulfite solution is gradually added as a reducing agent to start the polymerization reaction. During the polymerization reaction, the stirring speed is always maintained at 500 rpm and the reaction temperature is controlled below 45℃. S5. Phase inversion: After the polymerization reaction is completed, 4 parts of nonylphenol polyoxyethylene ether are added for phase inversion. After mixing evenly, a light yellow to milky white semi-transparent emulsion is obtained, which is the pH-sensitive self-crosslinking polyacrylamide emulsion.

2. A pH-sensitive self-crosslinking polyacrylamide emulsion gelling application for deep profile control in high-temperature and high-salinity oil reservoirs, comprising an emulsion prepared by the method described in claim 1, simulated seawater TDS: 33000 mg / L, polyethyleneimine crosslinking agent, and pH adjuster.

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