Composite polyacrylamide oil displacement agent and preparation method thereof

Abstract

The invention relates to the technical field of oil exploitation, and particularly discloses a composite polyacrylamide oil displacement agent and a preparation method thereof. The composite polyacrylamide oil-displacing agent comprises a polyacrylamide main chain, a cross-linking agent and a modified functional body, and the modified functional body comprises nano inorganic particles, a functional monomer and an amphiphilic modifier; the preparation method comprises the following steps: S1, pretreating the raw materials; s2, preparing a mixed monomer solution; s3, surface modification of the nanoparticles; s4, carrying out prepolymerization reaction; s5, regulating and controlling the structure of the prepolymer; s6, pre-preparing a cross-linking agent; s7, carrying out a two-stage cross-linking reaction; s8, dynamic aperture monitoring; and S9, carrying out a post-treatment process. According to the oil-displacing agent disclosed by the invention, a system consisting of a polyacrylamide main chain, a cross-linking agent and a modified functional body containing nano inorganic particles, a functional monomer and an amphiphilic modifier is adopted, so that the problem that the network structure of an improved precursor oil agent lacks dynamic regulation capability and is easy to lose efficacy in a complex environment of an oil reservoir is solved.

Description

Technical Field

[0001] The present application relates to the technical field of oil extraction, and in particular to a composite polyacrylamide oil displacement agent and a preparation method thereof. Background Art

[0002] Oil production is generally divided into three phases, depending on the stage of oilfield development. Primary recovery, which exploits reservoir energy to extract oil, typically has an efficiency of only around 15%; secondary recovery, which replenishes reservoir energy by injecting water and gas, achieving recovery, with a recovery rate of 30-40%; and tertiary recovery, which utilizes new physical, chemical, and biological methods to extract crude oil. To efficiently extract residual oil from formations, it is necessary to develop tertiary recovery methods suitable for my country's unique geological conditions. Four major categories of mature tertiary recovery technologies exist: chemical flooding, thermal flooding, microbial flooding, and mixed-phase flooding. Based on an understanding of reservoir geology and residual oil, chemical flooding has become a key method for improving oil recovery in most oilfields in my country.

[0003] With respect to the above-mentioned related technologies, the inventors believe that most oil displacement agents adopt linear or static cross-linked structures, which are prone to failure in complex reservoir environments due to the lack of dynamic adjustment capabilities of the network structure. Summary of the Invention

[0004] In order to solve the problem that the network structure lacks dynamic adjustment ability and is easily ineffective in the complex environment of the oil reservoir, the present application provides a composite polyacrylamide oil-displacing agent and a preparation method thereof.

[0005] In the first aspect, the present application provides a composite polyacrylamide oil-displacing agent, which adopts the following technical solution: A composite polyacrylamide oil-displacing agent comprises a polyacrylamide main chain, a cross-linking agent and a modified functional body, wherein the modified functional body comprises nano-inorganic particles, a functional monomer and an amphiphilic modifier, the cross-linking agent and the polyacrylamide main chain form a dynamic covalent cross-linked network structure, and the modified functional body is uniformly dispersed in the dynamic covalent cross-linked network structure through the dual effects of physical entanglement and chemical grafting; the polyacrylamide main chain is a ternary copolymer of acrylamide, a sulfonic acid monomer and a zwitterionic monomer.

[0006] By adopting the above technical solution, a system consisting of a polyacrylamide main chain, a cross-linking agent and a modified functional body comprising nano-inorganic particles, functional monomers and amphiphilic modifiers is adopted, and the cross-linking agent and the main chain form a dynamic covalent cross-linked network structure, and the modified functional body is uniformly dispersed through the dual effects of physical entanglement and chemical grafting. Therefore, a three-dimensional network with both elasticity and stability is obtained for the oil-displacing agent, thereby improving the problem that most of the precursor oil-displacing agents adopt a linear or static cross-linked structure, which lacks dynamic adjustment ability of the network structure, resulting in easy failure in the complex environment of the reservoir.

[0007] Preferably, the nano inorganic particles are surface carboxylated nano titanium dioxide or nano attapulgite with a particle size of 5-50 nm, with an aminosilane coupling agent grafted on the surface, and the mass proportion of the nano inorganic particles in the oil displacement agent is 0.5-3%.

[0008] By adopting the above technical solution, the temperature resistance and shear resistance of the oil displacement agent are improved and the blockage of the reservoir pores is avoided due to the use of surface carboxylation to enhance compatibility with the main chain, control of particle size to match the reservoir pore size, surface grafting of aminosilane coupling agent to prevent agglomeration, and limiting the mass ratio to form effective filling.

[0009] Preferably, the functional monomer is a composite system of 2-acrylamido-2-methylpropanesulfonic acid and dimethylaminoethyl methacrylate, the molar ratio of 2-acrylamido-2-methylpropanesulfonic acid to dimethylaminoethyl methacrylate is 3:1-5:1, accounting for 10-15 mol% of the total amount of the modified functional body.

[0010] By adopting the above technical solution, a compound system of 2-acrylamido-2-methylpropanesulfonic acid and dimethylaminoethyl methacrylate is used to form a charge balance, the molar ratio of the two is controlled to optimize the stretching state of the molecular chain, and the amount of the modified functional body is limited to avoid excessive cross-linking. Therefore, the salt resistance of the oil displacement agent is improved and the rheological properties of the molecular chain are optimized.

[0011] Preferably, the dynamic covalent cross-linked network structure is composed of imine bonds formed by glutaraldehyde and the main chain amide group, with a cross-linking degree of 1-2.5 mol%. The dynamic covalent cross-linked network structure contains a metal ion coordination structure, and the metal ion is a zirconium ion or a titanium ion, and the coordination concentration is 50-200 ppm.

[0012] By adopting the above technical solution, the viscosity retention rate and injection performance of the oil displacement agent in a high-temperature and high-salt environment are improved by using a dynamic reversible structure of the imine bond to achieve network self-repair, controlling the cross-linking degree to form a moderate three-dimensional network, and introducing a metal ion coordination structure to enhance salt resistance.

[0013] Preferably, the amphiphilic modifier is a polyether surfactant, the polyether surfactant molecule contains both polyoxyethylene segments and long-chain alkyl segments, the amphiphilic modifier accounts for 0.1-1% of the total mass of the oil-displacing agent, and forms a nano-scale micelle dispersed phase in the dynamic covalent cross-linked network structure.

[0014] By adopting the above technical solution, the oil-washing efficiency and shear resistance of the oil-displacing agent are improved by using an amphiphilic structure having both polyoxyethylene chain segments and long-chain alkyl chain segments to reduce the oil-water interfacial tension, controlling their mass proportion to form stable nanomicelles, and forming a micellar dispersed phase in the network to enhance the structural flexibility.

[0015] Preferably, the molecular chain branching degree of the oil-displacing agent is 8-18%, and the network pore size is 20-100 nm.

[0016] By adopting the above technical solution, the viscosity stability of the oil displacement agent in brine is improved and the swept volume of the reservoir is expanded by controlling the branching degree of the molecular chain to inhibit chain curling in a high-salt environment and regulating the network pore size to match the pore size of the reservoir.

[0017] In a second aspect, the present application provides a method for preparing a composite polyacrylamide oil-displacing agent, which adopts the following technical solution: A method for preparing a composite polyacrylamide oil-displacing agent comprises the following steps: S1. Raw material pretreatment: Calcine the inorganic nanoparticles in a muffle furnace at 400-500°C for 2-3 hours. Dissolve the zwitterionic monomer in a 1:2 ethanol-water mixture by volume and sterilize by filtration using a 0.45 μm filter. S2. Preparation of a mixed monomer solution: acrylamide, sulfonic acid monomer, and zwitterionic monomer were added to deionized water in a molar ratio of 8:1.5:0.5, and the pH was adjusted to 7.5-8.2 with sodium carbonate solution. 0.05-0.1 wt% of a chain transfer agent, mercaptoethanol, was added and dissolved under stirring at 300 rpm for 20-30 min to form a mixed monomer solution with a concentration of 20 ± 2 wt%; S3. Nanoparticle Surface Modification: The calcined inorganic nanoparticles and aminosilane coupling agent were added to an ethanol-water mixture at a mass ratio of 10:1 (volume ratio of 1:1). The mixture was magnetically stirred at 60°C for 4 h, followed by ultrasonic dispersion at 400 W for 30 min. The mixture was centrifugally dried and passed through a 200-mesh sieve to obtain surface-modified nanoparticles. S4 prepolymerization reaction: S3 modified nanoparticles were added to the mixed monomer solution of S2, the mass of the modified nanoparticles accounted for 1-2% of the mass of the mixed monomers, an amphiphilic modifier was added, the mass of the amphiphilic modifier accounted for 0.5% of the mass of the solution, nitrogen was introduced for deoxygenation for 30 minutes, potassium persulfate - sodium bisulfite initiator was added, the initiator was used in an amount of 0.3wt% of the total monomer amount, ultrasonic-assisted polymerization was started in a constant temperature water bath at 50 ° C, the ultrasonic power was 350 W, the reaction was continued for 5 hours, and the stirring speed was maintained at 400 rpm; S5. Prepolymer structure control: After the polymerization reaction is completed, 1-2 mL of 10% sodium hydroxide solution is added to the system to adjust the pH to 7-7.5. The prepolymer molecular size is monitored by dynamic light scattering to control the weight-average molecular weight to 5-8 million Da. S6. Crosslinker pre-formulation: glutaraldehyde and deionized water were mixed in a volume ratio of 1:5, zirconium lactate solution was added, the zirconium ion concentration was 200 ppm, and the pH was adjusted to 4-5 with hydrochloric acid to form a crosslinker mixture; S7 two-stage crosslinking reaction: The prepolymer of S5 was heated to 35 ° C, and the crosslinker mixture of S6 was added in an amount of 1% of the prepolymer mass. The reaction was stirred at 300 rpm for 1.5 h, and then the temperature was raised to 60 ° C and the reaction was continued for 1 h, during which nitrogen was continuously introduced; S8. Dynamic pore size monitoring: The network pore size was monitored every 30 min using a dynamic light scattering instrument during the crosslinking process. The final network pore size was controlled to be between 30 and 80 nm by adjusting the crosslinking temperature and time. S9. Post-treatment process: After the cross-linking reaction is completed, the system is cooled to 25°C, 0.5wt% of antioxidant stabilizer and hindered phenols are added, and the mixture is homogenized in a high-pressure homogenizer at 100MPa, and then spray-dried with an inlet temperature of 180°C and an outlet temperature of 80°C. The dried product is ultrafinely ground and passed through a 300-mesh sieve to obtain the composite polyacrylamide oil-displacing agent.

[0018] By adopting the above technical scheme, a composite polyacrylamide oil displacement agent with uniform structure, temperature and salt resistance is prepared by pre-treating raw materials to remove impurities and sterilize, preparing monomers in a specific molar ratio and adjusting the pH, surface modification of nanoparticles to enhance compatibility, ultrasound-assisted polymerization and two-stage cross-linking to control the network structure, dynamic pore size monitoring to match the reservoir pores, and post-processing technology to improve product stability.

[0019] Preferably, the nano inorganic particles in S1 are surface carboxylated nano titanium dioxide, and the heating rate of the muffle furnace during calcination is 5°C / min.

[0020] By adopting the above technical solution, surface carboxylation of nano-titanium dioxide is used to enhance the chemical bonding ability with the main chain and the aqueous phase dispersibility, and the heating rate of the muffle furnace is controlled at 5°C / min to avoid thermal stress fracture of the particles, thereby ensuring the consistency of the particle size and the degree of surface carboxylation. Therefore, the dispersion stability and enhancement effect of the nanoparticles in the oil displacement agent are improved.

[0021] Preferably, the amphiphilic modifier in S4 is a polyoxyethylene-polyoxypropylene block copolymer, which needs to be pre-dissolved in 60° C. deionized water to form a 10 wt% solution before addition.

[0022] By adopting the above technical solution, since a polyoxyethylene-polyoxypropylene block copolymer is used to form an amphiphilic micelle structure to enhance the system compatibility and interfacial activity, and the polyoxyethylene-polyoxypropylene block copolymer is pre-dissolved in 60°C deionized water to form a 10wt% solution to promote full dissolution and avoid micelle agglomeration, the oil-washing efficiency of the oil-displacing agent is improved and the uniform dispersion of the components is ensured.

[0023] Preferably, the feed flow rate of the spray drying in S9 is 5-8 mL / min, and the homogenization pressure of the high-pressure homogenizer is divided into two stages: first homogenization at 60 MPa for one time, and then homogenization at 100 MPa for two times.

[0024] By adopting the above technical solution, the spray drying feed flow rate is controlled at 5-8 mL / min to ensure uniform drying of the material and uniform product particle size, and two-stage high-pressure homogenization is used to avoid nano-micelle agglomeration. Therefore, the fluidity and microstructural uniformity of the oil displacement agent product are improved.

[0025] In summary, this application has the following beneficial effects: 1. Since the present application adopts a system consisting of a polyacrylamide main chain, a cross-linking agent and a modified functional body comprising nano-inorganic particles, functional monomers and amphiphilic modifiers, and the cross-linking agent and the main chain form a dynamic covalent cross-linked network structure, the modified functional body is evenly dispersed through the dual effects of physical entanglement and chemical grafting, thereby allowing the oil-displacing agent to form a three-dimensional network with both elasticity and stability, thereby improving the problem that most of the improved precursor oil-displacing agents adopt a linear or static cross-linked structure, which lacks dynamic adjustment ability of the network structure, resulting in easy failure in the complex environment of the reservoir.

[0026] 2. This application designs the polyacrylamide main chain as a ternary copolymer of acrylamide, sulfonic acid monomer and zwitterionic monomer, and then utilizes the salt resistance of the sulfonic acid group and the charge balance effect of the zwitterion to enhance the stretchability of the molecular chain in salt water, thereby improving the problem that most of the precursor oil main chains adopt a single or binary copolymer structure, which has a strong shielding effect of salt ions on the molecular chain, resulting in insufficient salt resistance.

[0027] 3. The present application forms a synergistic effect with the dynamic covalent cross-linking network by modifying the nano-inorganic particles, functional monomers and amphiphilic modifiers in the functional body, and then improves the comprehensive performance of the oil displacement agent through the physical enhancement of the nanoparticles, the chemical modification of the functional monomers and the interface adjustment of the amphiphilic modifier, thereby improving the problem that most of the precursor oil displacement agents only use a single modified component, and due to the single modification mechanism, they cause insufficient temperature resistance or oil washing efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a flow chart of the method provided in this application. DETAILED DESCRIPTION

[0029] The present application is further described in detail below with reference to the accompanying drawings and examples.

[0030] Technical concept: Oil displacement agent is an important chemical agent used to enhance crude oil recovery in the field of oil extraction. Its core function is to promote the flow of underground crude oil to production wells by improving the physical and chemical properties of fluids in oil reservoirs, thereby improving oil extraction efficiency. Polyacrylamide oil displacement agent is prone to failure in high temperature and high salt environments due to its linear or static cross-linking structure, insufficient network dynamic adjustment ability and limitations of a single modification mechanism. Research has found that by constructing a dynamic covalent cross-linked network in which glutaraldehyde forms an imine bond with the main chain amide group and combines it with the zirconium ion coordination structure, supplemented by a composite functional body of surface carboxylated nano-inorganic particles, AMPS and DMAEMA compound functional monomers and polyether-type amphiphilic modifiers, and utilizing the dual dispersion effect of physical entanglement and chemical grafting, combined with a two-stage cross-linking reaction and dynamic pore size monitoring process to precisely control the network structure, the oil displacement agent can form a three-dimensional network with both elasticity and stability, significantly improving its adaptability and oil displacement efficiency in complex reservoir environments.

[0031] An embodiment of the present application provides a composite polyacrylamide oil-displacing agent, comprising a polyacrylamide main chain, a cross-linking agent, and a modified functional body, wherein the modified functional body comprises nano-inorganic particles, a functional monomer, and an amphiphilic modifier, wherein the cross-linking agent and the polyacrylamide main chain form a dynamic covalent cross-linked network structure, and the modified functional body is uniformly dispersed in the dynamic covalent cross-linked network structure through the dual effects of physical entanglement and chemical grafting; the polyacrylamide main chain is a ternary copolymer of acrylamide, a sulfonic acid monomer, and a zwitterionic monomer.

[0032] Specifically, the polyacrylamide main chain is a ternary copolymer formed by copolymerization of acrylamide, sulfonic acid monomer and zwitterionic monomer, wherein the sulfonic acid monomer can give the molecular chain salt resistance, and the zwitterionic monomer inhibits the curling of the molecular chain in a high-salt environment through the balance of positive and negative charges. The ternary copolymer structure improves the stretchability and stability of the main chain in salt water; the dynamic covalent cross-linked network structure is formed by the cross-linker and the main chain, wherein the dynamic reversibility of the imine bond enables the network to have self-repairing ability at high temperature, and the metal ion coordination structure enhances the salt resistance and stability of the network. The network structure formed by the synergistic effect of the two can effectively maintain the viscosity of the solution; the modified functional body has a composite effect, and the nano-inorganic particles are grafted through the surface aminosilane coupling agent and are uniformly dispersed in the network, which plays a physical reinforcement role and improves the temperature resistance of the oil displacement agent; the functional monomer compound system further optimizes the charge distribution of the molecular chain, increases Strong salt resistance; the amphiphilic modifier forms a nano-scale micellar dispersed phase, which can reduce the oil-water interfacial tension and improve the interfacial activity of the oil displacement agent; thereby, a dual dispersion mechanism of physical entanglement and chemical grafting can be generated, ensuring the stable combination of the modified functional body and the network structure, avoiding the agglomeration of nanoparticles, and improving the uniformity of the overall performance of the oil displacement agent; by adopting a system composed of a polyacrylamide main chain, a cross-linking agent and a modified functional body containing nano-inorganic particles, functional monomers and amphiphilic modifiers, and the cross-linking agent and the main chain form a dynamic covalent bond cross-linked network structure, the modified functional body is uniformly dispersed through the dual effects of physical entanglement and chemical grafting, thereby allowing the oil displacement agent to form a three-dimensional network with both elasticity and stability, thereby improving the problem that most of the precursor oil displacement agents adopt a linear or static cross-linked structure, and the network structure lacks dynamic adjustment ability, resulting in easy failure in the complex environment of the reservoir.

[0033] The nano inorganic particles are surface carboxylated nano titanium dioxide or nano attapulgite with a particle size of 5-50 nm and an aminosilane coupling agent grafted on the surface. The mass proportion of the nano inorganic particles in the oil displacement agent is 0.5-3%.

[0034] Specifically, surface carboxylation treatment can impart polarity to the surface of nano-titanium dioxide or nano-attapulgite, enhance compatibility with the polyacrylamide main chain, and promote its uniform dispersion in the network structure; controlling the particle size at 5-50nm can match the nanoparticle size with the reservoir pore size, avoiding blockage of the reservoir pore throat due to excessive particle size, while ensuring sufficient specific surface area to exert an enhancing effect; the surface-grafted aminosilane coupling agent connects the nanoparticles to the polyacrylamide main chain through chemical bonding to form a chemical grafting structure, preventing the nanoparticles from agglomerating in the solution and improving the shear resistance of the oil displacement agent; by accounting for 0.5-3% by mass, it can ensure that the nanoparticles form effective filling in the network structure, which can not only improve the viscosity stability of the oil displacement agent through physical enhancement, but also avoid abnormal system viscosity or increased costs due to excessive addition.

[0035] The functional monomer is a compound system of 2-acrylamido-2-methylpropanesulfonic acid and dimethylaminoethyl methacrylate, the molar ratio of 2-acrylamido-2-methylpropanesulfonic acid to dimethylaminoethyl methacrylate is 3:1-5:1, and accounts for 10-15 mol% of the total amount of the modified functional body.

[0036] Specifically, 2-acrylamido-2-methylpropanesulfonic acid (AMPS) is a monomer containing a sulfonic acid group. Its strong ionization property can dissociate into sulfonate ions in water, inhibiting the curling of the molecular chain in a high-salt environment through electrostatic repulsion, thereby improving the salt resistance of the oil displacement agent; dimethylaminoethyl methacrylate (DMAEMA) is a monomer containing an amino group. Its amino group carries a positive charge after protonation in water, forming a charge balance with the negative charge of AMPS, reducing the shielding effect of salt ions on the molecular chain and further enhancing the salt resistance; at the same time, the amino group can react with the cross-linking agent to participate in the construction of the network structure, thereby improving the Cross-linking density; through a molar ratio of 3:1-5:1, the ratio of positive and negative charged groups can be optimized, so that the molecular chain can maintain a moderate stretch state in salt water, avoiding excessive electrostatic repulsion between chains due to too high a proportion of AMPS, which affects the viscosity of the solution, or excessive charge neutralization due to too high a proportion of DMAEMA, which loses the salt resistance effect; by accounting for 10-15 mol% of the total amount of the modified functional body, it can ensure that the functional monomer forms an effective chemical modification in the network structure, which can not only regulate the solubility and rheology of the molecular chain through the ionic groups, but also avoid excessive addition leading to runaway polymerization reaction or excessive cross-linking of the network structure.

[0037] The dynamic covalent cross-linked network structure is composed of imine bonds formed by glutaraldehyde and main chain amide groups, with a cross-linking degree of 1-2.5 mol%. The dynamic covalent cross-linked network structure contains a metal ion coordination structure, wherein the metal ion is zirconium ion or titanium ion, and the coordination concentration is 50-200 ppm.

[0038] Specifically, the imine bond cross-linking structure is formed by the reaction of glutaraldehyde and the main chain amide group. Its dynamically reversible properties enable the network to self-repair through the breakage-recombination process of the imine bond when damaged by shear force, thereby maintaining the viscosity stability of the oil displacement agent in the porous medium; the cross-linking density of the network can be controlled by a cross-linking degree of 1-2.5 mol%, so that the system forms a moderate three-dimensional network structure, which can not only effectively improve the viscosity of the solution, but also avoid excessive cross-linking resulting in increased rigidity and decreased fluidity of the molecular chain, which affects the injection performance of the oil displacement agent in the reservoir; the metal ion coordination structure forms coordination bonds with carbonyl, sulfonic acid and other groups on the main chain through zirconium ions or titanium ions, thereby enhancing the network structure's tolerance to high temperature and high salt environments, inhibiting the shielding effect of salt ions on the molecular chain, and improving the stability of the oil displacement agent under harsh reservoir conditions; by ensuring that the metal ions form uniformly distributed coordination nodes in the network through a coordination concentration of 50-200 ppm, the network structure can be strengthened through the strong interaction of the coordination bonds, while avoiding excessive cross-linking of the molecular chains due to excessive concentration, which may trigger gelation or precipitation of the solution.

[0039] The amphiphilic modifier is a polyether surfactant, which contains both polyoxyethylene segments and long-chain alkyl segments in its molecules. The amphiphilic modifier accounts for 0.1-1% of the total mass of the oil displacement agent and forms a nano-scale micelle dispersed phase in the dynamic covalent bond cross-linked network structure.

[0040] Specifically, in the structure of polyether surfactants, the polyoxyethylene chain segment is hydrophilic and can form hydrogen bonds with water molecules, thereby enhancing the solubility of the surfactant in the aqueous phase; the long-chain alkyl chain segment is oleophobic and can interact with crude oil molecules, reducing the oil-water interfacial tension through the amphiphilic structure and improving the oil washing ability of the oil displacement agent; nano-micelles are formed by self-assembly of the nano-micelle dispersed phase in the dynamic covalent bond cross-linked network, and the core-shell structure of the micelles can encapsulate salt-resistant additives or functional monomers to achieve slow release and extend the salt resistance of the oil displacement agent; at the same time, the micelles fill the network pores, enhancing the flexibility of the network structure and improving the shear resistance of the oil displacement agent; by accounting for 0.1-1% by mass, it can ensure that the surfactant forms a stable micelle structure in the system, which can not only improve the crude oil recovery rate through interfacial activity, but also avoid excessive aggregation of micelles due to excessive addition, affecting the rheological properties of the oil displacement agent or causing emulsion stability problems.

[0041] The molecular chain branching degree of the oil-displacing agent is 8-18%, and the network pore diameter is 20-100nm.

[0042] Specifically, a molecular chain branching degree of 8-18% increases the spatial steric hindrance of the molecular chain through the branched structure, inhibits the curling and entanglement of the molecular chain in a high-salt environment, and keeps the chain segments stretched in water, thereby maintaining the viscosity of the solution; moderate branching can also increase the number of reaction sites between the molecular chain and the cross-linker, and optimize the uniformity of the network structure; by matching the network pore size of 20-100nm with the size of 50-150nm of the reservoir rock pores, it is ensured that the network structure of the oil displacement agent can effectively block the high permeability channel, forcing the injected water to turn to the low permeability area and expand the swept volume; at the same time, the appropriate pore size can reduce the seepage resistance of the oil displacement agent in the porous medium, ensuring its injection performance.

[0043] Please see the attached Figure 1 A method for preparing a composite polyacrylamide oil-displacing agent comprises the following steps: S1. Raw material pretreatment: Calcine the inorganic nanoparticles in a muffle furnace at 400-500°C for 2-3 hours. Dissolve the zwitterionic monomer in a 1:2 ethanol-water mixture by volume and sterilize by filtration using a 0.45 μm filter. S2. Preparation of a mixed monomer solution: acrylamide, sulfonic acid monomer, and zwitterionic monomer were added to deionized water in a molar ratio of 8:1.5:0.5, and the pH was adjusted to 7.5-8.2 with sodium carbonate solution. 0.05-0.1 wt% of a chain transfer agent, mercaptoethanol, was added and dissolved under stirring at 300 rpm for 20-30 min to form a mixed monomer solution with a concentration of 20 ± 2 wt%; S3. Nanoparticle Surface Modification: The calcined inorganic nanoparticles and aminosilane coupling agent were added to an ethanol-water mixture at a mass ratio of 10:1 (volume ratio of 1:1). The mixture was magnetically stirred at 60°C for 4 h, followed by ultrasonic dispersion at 400 W for 30 min. The mixture was centrifugally dried and passed through a 200-mesh sieve to obtain surface-modified nanoparticles. S4 prepolymerization reaction: S3 modified nanoparticles were added to the mixed monomer solution of S2, the mass of the modified nanoparticles accounted for 1-2% of the mass of the mixed monomers, an amphiphilic modifier was added, the mass of the amphiphilic modifier accounted for 0.5% of the mass of the solution, nitrogen was introduced for deoxygenation for 30 minutes, potassium persulfate - sodium bisulfite initiator was added, the initiator was used in an amount of 0.3wt% of the total monomer amount, ultrasonic-assisted polymerization was started in a constant temperature water bath at 50 ° C, the ultrasonic power was 350 W, the reaction was continued for 5 hours, and the stirring speed was maintained at 400 rpm; S5. Prepolymer structure control: After the polymerization reaction is completed, 1-2 mL of 10% sodium hydroxide solution is added to the system to adjust the pH to 7-7.5. The prepolymer molecular size is monitored by dynamic light scattering to control the weight-average molecular weight to 5-8 million Da. S6. Crosslinker pre-formulation: glutaraldehyde and deionized water were mixed in a volume ratio of 1:5, zirconium lactate solution was added, the zirconium ion concentration was 200 ppm, and the pH was adjusted to 4-5 with hydrochloric acid to form a crosslinker mixture; S7 two-stage crosslinking reaction: The prepolymer of S5 was heated to 35 ° C, and the crosslinker mixture of S6 was added in an amount of 1% of the prepolymer mass. The reaction was stirred at 300 rpm for 1.5 h, and then the temperature was raised to 60 ° C and the reaction was continued for 1 h, during which nitrogen was continuously introduced; S8. Dynamic pore size monitoring: The network pore size was monitored every 30 min using a dynamic light scattering instrument during the crosslinking process. The final network pore size was controlled to be between 30 and 80 nm by adjusting the crosslinking temperature and time. S9. Post-treatment process: After the cross-linking reaction is completed, the system is cooled to 25°C, 0.5wt% of antioxidant stabilizer and hindered phenols are added, and the mixture is homogenized in a high-pressure homogenizer at 100MPa, and then spray-dried with an inlet temperature of 180°C and an outlet temperature of 80°C. The dried product is ultrafinely ground and passed through a 300-mesh sieve to obtain a composite polyacrylamide oil-displacing agent.

[0044] Specifically, S1 raw material pretreatment: calcining nano-inorganic particles to remove surface adsorbed water and enhance their compatibility with the organic phase; filtering and sterilizing to prevent microbial contamination from affecting the polymerization reaction; S2 mixed monomer solution preparation: preparing terpolymer monomers according to a specific molar ratio, adjusting the pH to a weak alkaline level to promote monomer dissolution, adding a chain transfer agent to control the molecular weight, and forming a uniform and stable reaction system; S3 nanoparticle surface modification: introducing organic functional groups on the surface of nanoparticles through a silane coupling agent, so that it can chemically bond with the polymer main chain, thereby improving dispersion stability and enhancement effect; S4 prepolymerization reaction: initiating monomer polymerization with the assistance of ultrasound, and the ultrasonic cavitation effect promotes the modified nanoparticles and amphiphilic modifiers to be uniformly dispersed in the molecular chain to form a primary network structure; S5 prepolymer structure regulation: through alkali dissolution The pH of the liquid is adjusted and the molecular weight is monitored to ensure that the prepolymer reaches the target size, providing a suitable molecular basis for subsequent cross-linking; S6 cross-linker pre-preparation: glutaraldehyde is mixed with the metal ion solution and the pH is adjusted to form a composite cross-linking system with both imine bonds and coordination bonds, laying the foundation for the dynamic network structure; S7 two-stage cross-linking reaction: the initial cross-linking network is formed in the low-temperature stage, and the high-temperature stage promotes the rearrangement and improvement of the cross-linking bonds. Combined with nitrogen protection to prevent oxidative degradation, it ensures the uniformity of the network structure; S8 dynamic pore size monitoring: real-time control of the cross-linking process to match the final network pore size with the reservoir pores, and optimize the plugging and mobility control capabilities of the oil displacement agent; S9 post-processing process: adding antioxidants to improve aging resistance, high-pressure homogenization to break up agglomerates, spray drying and ultrafine grinding to form a powder product that is easy to store and use.

[0045] The nano-inorganic particles in S1 are surface-carboxylated nano-titanium dioxide, and the heating rate of the muffle furnace during calcination is 5°C / min.

[0046] Specifically, the surface carboxyl-treated nano-titanium dioxide can undergo an esterification reaction with the aminosilane coupling agent through the surface carboxyl group, thereby enhancing the chemical bonding ability of the nanoparticles and the polyacrylamide main chain, while improving their dispersibility in the aqueous phase and avoiding agglomeration; by controlling the heating rate of the muffle furnace at 5°C / min during calcination, the internal lattice of the nano-titanium dioxide can be slowly reconstructed, avoiding thermal stress fracture of the particles due to excessively rapid heating, and ensuring the consistency of the particle size uniformity and the degree of surface carboxylation of the particles after calcination.

[0047] The amphiphilic modifier in S4 is a polyoxyethylene-polyoxypropylene block copolymer, which needs to be pre-dissolved in 60° C. deionized water to form a 10 wt % solution before addition.

[0048] Specifically, the polyoxyethylene-polyoxypropylene block copolymer is an amphiphilic modifier. The polyoxyethylene segment is hydrophilic and the polyoxypropylene segment is hydrophobic, and can self-assemble in an aqueous solution to form a micelle structure. Its hydrophobic environment can wrap functional monomers or nanoparticles, thereby improving the compatibility of the system. At the same time, the structure can reduce the oil-water interfacial tension and enhance the oil washing ability of the oil displacement agent. It is pre-dissolved in 60°C deionized water to form a 10wt% solution. The 60°C water temperature can reduce the hydrogen bonding between the surfactant molecules, promote the full dissolution of the block copolymer, and avoid micelle agglomeration due to too low a water temperature. The 10wt% concentration can ensure that the surfactant forms stable micelles in the solution, and the viscosity is moderate, which is convenient for uniform mixing with the mixed monomer solution, thereby preventing abnormal viscosity of the system due to excessively high concentration.

[0049] The feed flow rate of the spray drying in S9 was 5-8 mL / min, and the homogenization pressure of the high-pressure homogenizer was divided into two stages: first, homogenization at 60 MPa for one time, and then homogenization at 100 MPa for two times.

[0050] Specifically, the feed flow rate of spray drying is 5-8mL / min. By controlling the feed flow rate, the material can be evenly dispersed in the drying tower, ensuring stable heat exchange efficiency and avoiding the formation of lumps due to insufficient drying of droplets due to excessively high flow rate, or the impact of production efficiency due to too low flow rate; this range can ensure uniform particle size distribution of the dried product and improve product fluidity; the high-pressure homogenization pressure is divided into two sections, first homogenizing once at 60MPa, and then homogenizing twice at 100MPa: first, use a lower pressure of 60MPa to preliminarily break up the agglomerates and reduce the particle size of the material; then use a higher pressure of 100MPa to further refine the particles and evenly disperse the nano-micelles and network structure, avoiding secondary agglomeration of nanoparticles or micelles in the composite system, ensuring the microstructural uniformity of the final product, and improving the injection performance and stability of the oil displacement agent in the reservoir.

[0051] Example 1: The nanoparticle content is 1.5%, the cross-linking degree is 1.8 mol%, the functional monomer molar ratio of AMPS:DMAEMA is 4:1, and the amphiphilic modifier content is 0.5%; Example 2: The nanoparticle content is 0.5%, the cross-linking degree is 1.0 mol%, the functional monomer molar ratio of AMPS:DMAEMA is 3:1, and the amphiphilic modifier content is 0.1%; Example 3: The nanoparticle content is 3.0%, the cross-linking degree is 2.5 mol%, the functional monomer molar ratio of AMPS:DMAEMA is 5:1, and the amphiphilic modifier content is 1.0%; Examples 1-3 were prepared in the following manner: S1. Raw material pretreatment: Calcine the inorganic nanoparticles in a muffle furnace at 400-500°C for 2-3 hours. Dissolve the zwitterionic monomer in a 1:2 ethanol-water mixture by volume and sterilize by filtration using a 0.45 μm filter. S2. Preparation of a mixed monomer solution: acrylamide, sulfonic acid monomer, zwitterionic monomer were added to deionized water in a molar ratio of 8:1.5:0.5, the pH was adjusted to 7.5-8.2 with sodium carbonate solution, 0.05-0.1 wt% of a chain transfer agent, mercaptoethanol, was added and dissolved under stirring at 300 rpm for 20-30 min to form a mixed monomer solution with a concentration of 20 ± 2 wt%; S3. Nanoparticle Surface Modification: The calcined inorganic nanoparticles and an aminosilane coupling agent were added to an ethanol-water mixture at a mass ratio of 10:1 (volume ratio of 1:1). The mixture was magnetically stirred at 60°C for 4 h, followed by ultrasonic dispersion at 400 W for 30 min. The mixture was centrifugally dried and passed through a 200-mesh sieve to obtain surface-modified nanoparticles. S4 prepolymerization reaction: S3 modified nanoparticles were added to the mixed monomer solution of S2, the mass of the modified nanoparticles accounted for 1-2% of the mass of the mixed monomers, an amphiphilic modifier was added, the mass of the amphiphilic modifier accounted for 0.5% of the mass of the solution, nitrogen was introduced for deoxygenation for 30 minutes, potassium persulfate - sodium bisulfite initiator was added, the initiator was used in an amount of 0.3wt% of the total monomer amount, ultrasonic-assisted polymerization was started in a constant temperature water bath at 50 ° C, the ultrasonic power was 350 W, the reaction was continued for 5 hours, and the stirring speed was maintained at 400 rpm; S5. Prepolymer structure control: After the polymerization reaction is completed, 1-2 mL of 10% sodium hydroxide solution is added to the system to adjust the pH to 7-7.5. The prepolymer molecular size is monitored by dynamic light scattering to control the weight-average molecular weight to 5-8 million Da. S6 crosslinker preformulation: glutaraldehyde and deionized water were mixed in a volume ratio of 1:5, zirconium lactate solution was added, the zirconium ion concentration was 200ppm, and the pH was adjusted to 4-5 with hydrochloric acid to form a crosslinker mixture; S7 two-stage crosslinking reaction: The prepolymer of S5 was heated to 35 ° C, and the crosslinker mixture of S6 was added in an amount of 1% of the prepolymer mass. The reaction was stirred at 300 rpm for 1.5 h, and then the temperature was raised to 60 ° C and the reaction was continued for 1 h, during which nitrogen was continuously introduced; S8. Dynamic pore size monitoring: The network pore size was monitored every 30 min using a dynamic light scattering instrument during the crosslinking process. The final network pore size was controlled to be between 30 and 80 nm by adjusting the crosslinking temperature and time. S9. Post-treatment process: After the cross-linking reaction is completed, the system is cooled to 25°C, 0.5wt% of antioxidant stabilizer and hindered phenols are added, and the mixture is homogenized in a high-pressure homogenizer at 100MPa, and then spray-dried with an inlet temperature of 180°C and an outlet temperature of 80°C. The dried product is ultrafinely ground and passed through a 300-mesh sieve to obtain a composite polyacrylamide oil-displacing agent.

[0052] The nano-inorganic particles in S1 are surface-carboxylated nano-titanium dioxide, and the heating rate of the muffle furnace during calcination is 5°C / min.

[0053] The amphiphilic modifier in S4 is a polyoxyethylene-polyoxypropylene block copolymer, which needs to be pre-dissolved in 60° C. deionized water to form a 10 wt % solution before addition.

[0054] The feed flow rate of the spray drying in S9 was 5-8 mL / min, and the homogenization pressure of the high-pressure homogenizer was divided into two stages: first, homogenization at 60 MPa for one time, and then homogenization at 100 MPa for two times.

[0055] Comparative Example 1: Formula: same polyacrylamide backbone as in Example 1 + 200ppm zirconium ions, without glutaraldehyde crosslinker; Preparation: The S6-S7 crosslinking step was omitted, and zirconium ions were directly added to the prepolymer. The pH was adjusted to 7.0, and no imine bond network was formed.

[0056] Comparative Example 2: Formula: Linear polyacrylamide with a molecular weight of 8 million Da + chromium triacetate with a cross-linking degree of 2.0 mol%; Preparation: After polymerizing acrylamide and AMPS at a molar ratio of 8:1.5, add Cr 3+ Solution, cross-linked at 60℃ for 2h, without nanoparticles and functional monomers.

[0057] Comparative Example 3: Formula: polyacrylamide backbone + glutaraldehyde with a cross-linking degree of 1.8 mol% + 200 ppm zirconium ions, without nanoparticles, functional monomers and amphiphilic modifiers; Preparation: Omit the steps of adding nanoparticles and amphiphilic modifier in S3-S4, and replace the functional monomer with an equimolar amount of acrylamide.

[0058] Comparative Example 4: Formula: Same as Example 1, nano-titanium dioxide particle size 100nm; Preparation: In S1, the calcination temperature was raised to 600°C at a heating rate of 10°C / min, resulting in particle agglomeration and growth.

[0059] Performance testing methods Temperature and salt resistance test method: refer to SY / T5862-2017, prepare the oil displacement agent into 0.3% aqueous solution, and 5 After aging in ppm NaCl solution for 15 days, the viscosity retention rate was measured using a Brookfield DV-III rotational viscometer at a speed of 60 rpm and a temperature of 30°C.

[0060] Interfacial tension test method: The interfacial tension between the oil displacement agent solution and the simulated crude oil was measured using the hanging drop method using a Krüss DSA100 instrument at a temperature of 60°C and an equilibrium time of 30 minutes.

[0061] Shear resistance test method: at 170s -1 The viscosity ratio before and after shearing was measured after the shear rate was applied for 1 hour to evaluate the shear resistance of the molecular chain.

[0062] Core flooding experimental model: a heterogeneous core with a permeability variation coefficient of 0.7 and a porosity of 25% is injected with 0.3% oil displacement agent solution at 0.5 PV, and the recovery enhancement value is measured.

[0063] Table 1: Comparison of temperature and salt resistance and shear resistance Table 2: Correlation between dynamic network pore size and core plugging performance Group Network aperture (nm) High permeability layer plugging rate (%) Injection pressure fluctuation (%) Example 1 50-60 78 ±3.2 Comparative Example 1 Unregulated Network 45 ±12.5 Comparative Example 2 Static large aperture 32 ±18.7 The key role of dynamic covalent bonds: Comparing Example 1 with Comparative Example 1 without imine bond, the viscosity retention rate increased by 41.4%, proving that the dynamic self-repairing ability of the imine bond significantly enhanced the temperature resistance; Cr 3+ The viscosity retention rate of the cross-linked comparative example 2 is only 42% because the static cross-linking bonds are easily broken under high salt conditions.

[0064] Synergistic effect of modified functional bodies: Compared with the comparative example 3 without modified functional bodies, the interfacial tension of Example 1 is reduced by 77.6% and the recovery rate is increased by 51.1%. This is attributed to the triple synergy of the nanoparticles being able to enhance the network rigidity, the functional monomer being able to achieve the purpose of salt resistance, and the amphiphilic modifier being able to achieve the purpose of reducing the interfacial tension.

[0065] The recovery rate of comparative example 4, in which the nanoparticles have too large a particle size, decreased by 25.8%, indicating that the particle size exceeding 50 nm is prone to clogging pore throats, thus verifying the necessity of particle size control.

[0066] Optimization effect of parameter range: Example 1 has the best performance. When the nanoparticles in Example 3 are increased to 3.0%, the viscosity retention rate does not increase significantly, indicating that 1.5% has reached the optimal filling efficiency. When the crosslinking degree of Example 2 is lower than 1.0 mol%, the network strength is insufficient and the shear resistance is reduced.

[0067] Comparison of the examples with the comparative examples demonstrates that the dynamic covalently cross-linked network and modified functional complex system of the present application significantly enhances the stability, interfacial activity, and reservoir adaptability of oil displacement agents in high-temperature, high-salt environments. The synergistic effect of the dynamic imine bonds and metal coordination bonds imparts self-healing capabilities to the network, while the nanoparticles and functional monomers enhance salt resistance through a dual physical-chemical interaction. The amphiphilic modifier reduces interfacial tension. Together, these three enhance oil recovery by over 10% compared to a static cross-linked system.

[0068] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A composite polyacrylamide oil-displacing agent, characterized in that: The invention comprises a polyacrylamide main chain, a cross-linking agent and a modified functional body, wherein the modified functional body comprises nano-inorganic particles, a functional monomer and an amphiphilic modifier, the cross-linking agent and the polyacrylamide main chain form a dynamic covalent cross-linked network structure, and the modified functional body is uniformly dispersed in the dynamic covalent cross-linked network structure through the dual effects of physical entanglement and chemical grafting; the polyacrylamide main chain is a ternary copolymer of acrylamide, a sulfonic acid monomer and a zwitterionic monomer.

2. A composite polyacrylamide oil-displacing agent according to claim 1, characterized in that: The nano inorganic particles are surface carboxylated nano titanium dioxide or nano attapulgite with a particle size of 5-50 nm and an aminosilane coupling agent grafted on the surface. The mass proportion of the nano inorganic particles in the oil displacement agent is 0.5-3%.

3. A composite polyacrylamide oil-displacing agent according to claim 1, characterized in that: The functional monomer is a compound system of 2-acrylamido-2-methylpropanesulfonic acid and dimethylaminoethyl methacrylate, the molar ratio of 2-acrylamido-2-methylpropanesulfonic acid to dimethylaminoethyl methacrylate is 3:1-5:1, accounting for 10-15 mol% of the total amount of the modified functional body.

4. A composite polyacrylamide oil-displacing agent according to claim 1, characterized in that: The dynamic covalent cross-linked network structure is composed of imine bonds formed by glutaraldehyde and main chain amide groups, with a cross-linking degree of 1-2.5 mol%. The dynamic covalent cross-linked network structure contains a metal ion coordination structure, wherein the metal ion is a zirconium ion or a titanium ion, and the coordination concentration is 50-200 ppm.

5. A composite polyacrylamide oil-displacing agent according to claim 1, characterized in that: The amphiphilic modifier is a polyether surfactant, and the polyether surfactant molecule contains both polyoxyethylene segments and long-chain alkyl segments. The amphiphilic modifier accounts for 0.1-1% of the total mass of the oil-displacing agent and forms a nano-scale micelle dispersed phase in a dynamic covalent bond cross-linked network structure.

6. A composite polyacrylamide oil-displacing agent according to claim 1, characterized in that: The molecular chain branching degree of the oil-displacing agent is 8-18%, and the network pore diameter is 20-100 nm.

7. The method for preparing a composite polyacrylamide oil-displacing agent according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1. Raw material pretreatment: Calcine the inorganic nanoparticles in a muffle furnace at 400-500°C for 2-3 hours. Dissolve the zwitterionic monomer in a 1:2 ethanol-water mixture by volume and sterilize by filtration using a 0.45 μm filter. S2. Preparation of a mixed monomer solution: acrylamide, sulfonic acid monomer, zwitterionic monomer were added to deionized water in a molar ratio of 8:1.5:0.5, the pH was adjusted to 7.5-8.2 with sodium carbonate solution, 0.05-0.1wt% of a chain transfer agent, mercaptoethanol, was added and dissolved under stirring at 300rpm for 20-30min to form a concentration of 20±2wt% of a mixed monomer solution; S3. Nanoparticle Surface Modification: The calcined inorganic nanoparticles and an aminosilane coupling agent were added to an ethanol-water mixture at a mass ratio of 10:1 (volume ratio of 1:1). The mixture was magnetically stirred at 60°C for 4 h, followed by ultrasonic dispersion at 400 W for 30 min. The mixture was centrifugally dried and passed through a 200-mesh sieve to obtain surface-modified nanoparticles. S4 prepolymerization reaction: S3 modified nanoparticles were added to the mixed monomer solution of S2, the mass of the modified nanoparticles accounted for 1-2% of the mass of the mixed monomers, an amphiphilic modifier was added, the mass of the amphiphilic modifier accounted for 0.5% of the mass of the solution, nitrogen was introduced for deoxygenation for 30 minutes, potassium persulfate - sodium bisulfite initiator was added, the amount of initiator was 0.3wt% of the total monomer amount, ultrasonic-assisted polymerization was started in a constant temperature water bath at 50 ° C, the ultrasonic power was 350 W, the reaction was carried out for 5 hours, and the stirring speed was maintained at 400 rpm during the reaction; S5. Prepolymer structure control: After the polymerization reaction is completed, add 1-2 mL of 10% sodium hydroxide solution to the system to adjust the pH to 7-7.

5. Monitor the prepolymer molecular size using dynamic light scattering to control the weight-average molecular weight to 5-8 million Da. S6 crosslinker preformulation: glutaraldehyde and deionized water were mixed in a volume ratio of 1:5, zirconium lactate solution was added, the zirconium ion concentration was 200ppm, and the pH was adjusted to 4-5 with hydrochloric acid to form a crosslinker mixture; S7. Two-stage crosslinking reaction: The prepolymer of S5 was heated to 35°C, and the crosslinker mixture of S6 was added in an amount of 1% of the prepolymer mass. The reaction was stirred at 300 rpm for 1.5 h, and then the temperature was raised to 60°C and the reaction was continued for 1 h, during which nitrogen was continuously introduced; S8. Dynamic pore size monitoring: The network pore size was monitored every 30 min using a dynamic light scattering instrument during the crosslinking process. The final network pore size was controlled to be between 30 and 80 nm by adjusting the crosslinking temperature and time. S9. Post-treatment process: After the cross-linking reaction is completed, the system is cooled to 25°C, 0.5wt% of antioxidant stabilizer and hindered phenols are added, and the mixture is homogenized in a high-pressure homogenizer at 100MPa, and then spray-dried with an inlet temperature of 180°C and an outlet temperature of 80°C. The dried product is ultrafinely ground and passed through a 300-mesh sieve to obtain the composite polyacrylamide oil-displacing agent.

8. The method for preparing a composite polyacrylamide oil-displacing agent according to claim 7, wherein: The nano inorganic particles in S1 are surface carboxylated nano titanium dioxide, and the heating rate of the muffle furnace during calcination is 5° C. / min.

9. The method for preparing a composite polyacrylamide oil-displacing agent according to claim 7, wherein: The amphiphilic modifier in S4 is a polyoxyethylene-polyoxypropylene block copolymer, which needs to be pre-dissolved in 60° C. deionized water to form a 10 wt % solution before addition.

10. The method for preparing a composite polyacrylamide oil-displacing agent according to claim 7, characterized in that: The feed flow rate of the spray drying in S9 is 5-8 mL / min, and the homogenization pressure of the high-pressure homogenizer is divided into two stages: first, homogenization once at 60 MPa, and then homogenization twice at 100 MPa.

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