Self-polymerized nanometer microspheres polyacrylamide oil displacement agent and preparation method thereof

Abstract

This application relates to a self-polymerized polyacrylamide nanosphere oil displacement agent and its preparation method, belonging to the field of oil displacement agent technology. It employs reverse microemulsion polymerization, and the raw materials include an aqueous phase, an oil phase, and an emulsifier. The aqueous phase comprises the following components in parts by weight: 90-110 parts acrylamide, 12-20 parts a zwitterionic monomer composition, 0.3-0.6 parts polyethylene glycol diacrylate, 0.05-0.1 parts a chemical crosslinking agent, 0.1-0.3 parts an initiator, and 350-450 parts water. The zwitterionic monomer composition includes sulfobetaine-type monomers, anionic monomers, and quaternary ammonium salt-type cationic monomers. The microspheres prepared in this application possess both temperature and salt resistance with chemical structural stability, dimensional adaptability for migration along pore throats, and mechanical strength for effective plugging at deep formation depths, exhibiting excellent temperature and salt resistance and synergistic deep migration-plugging capabilities.

Description

Technical Field

[0001] This application relates to the field of oil displacement agents, and in particular to a self-polymerized nanosphere polyacrylamide oil displacement agent and its preparation method. Background Technology

[0002] Chemical flooding is a core technology for maintaining stable production in oilfields after they enter the medium-to-high water-cut stage. Polyacrylamide-based oil displacement agents have long dominated the tertiary oil recovery field due to their excellent viscosity-enhancing and mobility control capabilities. However, as most major oilfields in China enter the ultra-high water-cut development stage, the challenges faced by conventional polyacrylamide and polyacrylamide-based binary composite systems in deep reservoir displacement are becoming increasingly prominent. The dominant seepage channels formed by long-term water injection make it easy for the displacement fluid to flow along the high-permeability zone, significantly reducing the sweep efficiency of medium-to-low permeability layers. Furthermore, conventional polymers are prone to molecular chain breakage and degradation under high-temperature and high-salt environments, making it difficult to further improve oil displacement efficiency. Existing research shows that polymer microspheres, with their micro-nano size and water-absorbing swelling properties, can overcome the mobility control limitations of traditional linear polymers, achieving stepwise plugging and deep migration in porous media. This provides a new technical direction for solving the problem of efficient displacement in heterogeneous reservoirs.

[0003] Existing polyacrylamide-based oil displacement agents and conventional polymer microsphere technology have significant drawbacks when dealing with heterogeneous reservoirs with ultra-high water cut. On the one hand, conventional linear polyacrylamide and polystyrene-based binary composite systems are prone to thermal degradation and salt-sensitive breakage of molecular chains under high temperature and high salinity conditions, resulting in a sharp decline in viscosity-enhancing capacity. This makes it difficult to effectively block high-permeability channeling formed by long-term water injection, and a large amount of displacing fluid circulates ineffectively along the dominant channels, making it difficult to improve the sweep efficiency of medium and low permeability layers. On the other hand, although early polymer microsphere products can achieve a certain degree of deep migration by absorbing water and swelling, they generally lack the activity of controllable self-aggregation under formation conditions. There is an inherent contradiction between the initial particle size and the final plugging strength—if the particle size is too small, it is impossible to establish an effective plugging pressure differential at the target layer; if the particle size is too large, it is difficult to inject and reach the deep reservoir. Moreover, the microspheres lack mutual bonding ability, and the resulting plugs are mostly in a loosely packed state, which is prone to deformation or breakthrough under high displacement pressure differentials. Therefore, the synergistic effect of deep profile modification and improving oil washing efficiency is severely restricted. Summary of the Invention

[0004] To address the aforementioned issues, this application provides a self-polymerized nanosphere polyacrylamide oil displacement agent and its preparation method.

[0005] This application provides a self-polymerized nanosphere polyacrylamide oil displacement agent and its preparation method, which adopts the following technical solution: In a first aspect, this application provides a self-polymerized nanosphere polyacrylamide oil displacement agent, employing the following technical solution: A self-polymerizing nanosphere polyacrylamide oil displacement agent is prepared by reverse microemulsion polymerization. The raw materials include an aqueous phase, an oil phase, and an emulsifier. The aqueous phase comprises the following components in parts by mass: 90-110 parts acrylamide 12-20 parts of zwitterionic monomer composition 0.3-0.6 parts of polyethylene glycol diacrylate Chemical crosslinking agent 0.05-0.1 parts Initiator 0.1-0.3 parts 350-450 parts water; The zwitterionic monomer composition includes sulfobetaine-type monomers, anionic monomers, and quaternary ammonium salt-type cationic monomers.

[0006] Acrylamide, as the main monomer, polymerizes to form a long-chain framework of polyacrylamide, providing the microspheres with basic hydrophilicity and chain flexibility. In the zwitterionic monomer composition, the sulfobetaine-type monomer introduces an internal salt structure with equal amounts of positive and negative charges on the molecular chain. Its solvation layer remains stable in high-salinity water, inhibiting chain shrinkage and collapse. Simultaneously, the anionic monomer and the quaternary ammonium salt-type cationic monomer form ion pairs on the chain, generating an electrostatic cross-linking network. This network remains tight under low-salt conditions and moderately dissociates under high-salt conditions, endowing the microspheres with the ability to regulate swelling behavior to adapt to different salinity environments. This allows the microspheres to maintain a small hydrodynamic size during the injection stage, facilitating their migration to deeper layers. Upon reaching high-salinity formations, the degree of swelling is gradually regulated through ion pair dissociation to exert a sealing effect.

[0007] Polyethylene glycol diacrylate (PEG) contains long-chain polyethylene oxide segments. After copolymerization, these segments introduce flexible hydrophilic arms into the network, enhancing the microspheres' water absorption and swelling capacity and the freedom of chain segment movement. This helps improve the microspheres' elastic deformation ability to pass through pore throats. A chemical crosslinking agent, formulated with PEG, creates an appropriate chemical crosslinking density, maintaining the integrity of the microspheres' basic network structure and preventing excessive expansion or breakage during long-term high-temperature aging and swelling. An initiator generates free radicals through thermal decomposition, driving the copolymerization of each vinyl monomer within the droplets of the reverse microemulsion, allowing the functional monomers to be embedded in the network structure according to the designed proportions. The combined effect of these components endows the microspheres with chemical structural stability (temperature and salt resistance), dimensional adaptability for migration along pore throats, and mechanical strength for effective sealing at deep formation depths, thereby improving both temperature and salt resistance and the synergistic deep migration-sealing capability.

[0008] Preferably, the sulfobetaine-type monomer includes methacryloyloxyethyl sulfobetaine, the anionic monomer includes 2-acrylamido-2-methylpropanesulfonic acid, and the quaternary ammonium salt-type cationic monomer includes acrylamidopropyltrimethylammonium chloride.

[0009] Methacryloxyethyl sulfobetaine contains both quaternary ammonium cations and sulfonic acid anions on the same side group. Its inner salt structure forms a stable hydration layer on the molecular chain, maintaining the extended conformation of the chain without shrinking in highly saline water, thus enhancing the salt resistance of the microspheres. 2-Acrylamido-2-methylpropanesulfonic acid contains sulfonic acid groups. Sulfonic acid groups have weak complexing ability for high-valence metal ions and remain in a dissociated state under high temperature and high salt conditions, maintaining electrostatic repulsion between chains and improving the microspheres' resistance to hydrolysis at high temperatures. Acrylamidopropyltrimethylammonium chloride provides cationic charge, forming electrostatic ion pairs with sulfonic acid anions, constructing a reversible physical cross-linking network. After these three monomers participate in copolymerization, the synergistic effect of the internal salt structure, ion-pair crosslinking, and salt resistance of the sulfonic acid groups enables the microspheres to maintain a relatively tight network structure and small hydrodynamic size during the injection stage, which facilitates their migration to deeper formations. Upon reaching high-mineralization areas, the reversible dissociation of ion-pair crosslinking and the combined regulation of the internal salt's salt resistance gradually adjust the degree of swelling and establish effective plugging, thereby improving the temperature and salt resistance performance and the synergistic ability of deep migration and plugging.

[0010] Preferably, the mass ratio of the sulfobetaine-type monomer, the anionic monomer, and the quaternary ammonium salt-type cationic monomer is (0.9-1.1):0.58:0.42.

[0011] The aforementioned mass ratio ensures that the internal salt protection provided by methacryloyloxyethyl sulfobetaine is matched with the ion-pair crosslinking effect formed by 2-acrylamido-2-methylpropanesulfonic acid and acrylamidopropyltrimethylammonium chloride. The internal salt unit maintains a sufficient anti-salinization layer on the molecular chain, while the ion-pair crosslinking provides a moderate reversible physical crosslinking density in the network. The synergy of both allows the microspheres to maintain a compact structure during injection into low-salinity strata to facilitate deep migration. After entering high-salinity strata, the ion pairs gradually dissociate while the internal salt structure maintains chain extension, making the swelling degree controllable and establishing a stable plugging strength. The ratio between anionic and cationic monomers gives the microspheres a slightly negative charge state with a moderate negative charge density. During migration, this generates electrostatic repulsion with the negatively charged rock surface to reduce adsorption and retention, while not excessively weakening the self-aggregation tendency between microsphere particles. This facilitates the formation of a mechanical network in deep strata, thereby improving the temperature and salt resistance performance and the synergistic ability of deep migration and plugging.

[0012] Preferably, the aqueous phase further includes a POSS-phenylboronic acid hybrid crosslinking monomer and 2-methyl-2-acrylate-2,3-dihydroxypropyl ester.

[0013] The POSS-phenylboronic acid hybrid crosslinking monomer uses a cage-like silsesquioxane core with multiple arms connecting phenylboronic acid groups, providing multi-site crosslinking capability and a rigid nanocore. 2-Methyl-2-acrylate-2,3-dihydroxypropyl ester contains an ortho-dihydroxy structure, which can form dynamic borate ester bonds with phenylboronic acid groups inside the microspheres, constructing a reversible covalent crosslinking network. When the microspheres are subjected to high shear as they pass through formation pore throats, the borate ester bonds can reversibly break, allowing the microspheres to deform appropriately to adapt to the narrow channels. The crosslinking structure is restored by the subsequent recombination of the ortho-dihydroxy and phenylboronic acid, improving the structural integrity and dimensional recovery ability of the microspheres during deep migration. Simultaneously, the thermal stability and low shrinkage properties of the POSS rigid core enhance the microsphere network framework's resistance to thermal degradation and structural collapse under high-temperature aging conditions. The borate ester bonds also maintain reversible exchange activity in saline environments, enabling the microspheres to maintain network integrity even in high-mineralization environments. Dynamic covalent crosslinking, in synergy with electrostatic ion pair crosslinking and chemical crosslinking in the basic formulation, endows the microspheres with elastic deformation capacity, network recovery capacity, and skeleton rigidity, thereby improving temperature and salt resistance as well as deep migration-blocking synergy.

[0014] Preferably, the POSS-phenylboronic acid hybrid crosslinking monomer is prepared using the following steps: Octavinyl cage-type silsesquioxane was dissolved in toluene, and mercaptoethylamine hydrochloride and benzoin dimethyl ether were added. The mixture was stirred under ultraviolet light, and after precipitation, washing, and drying, octa(aminoethylthioethyl)POSS hydrochloride was obtained. This hydrochloride was dissolved in dichloromethane, neutralized with triethylamine, cooled, and reacted with ethyl isocyanate methacrylate solution. The mixture was filtered and concentrated to obtain an intermediate. The intermediate was dissolved in N,N-dimethylformamide, and 4-carboxyphenylboronic acid, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, and N-hydroxysuccinimide were added. The mixture was reacted under a protective atmosphere in the dark, and after precipitation, washing, and drying, POSS-phenylboronic acid hybrid crosslinking monomer was obtained.

[0015] The above preparation steps first use an octavinyl cage-type silsesquioxane as the core, and graft mercaptoethylamine hydrochloride to the eight vertices via a UV-initiated mercapto-ene reaction to obtain an eight-arm intermediate with amino hydrochloride end groups. After neutralization with triethylamine to release free amino groups, the amino groups react with the isocyanate groups of ethyl methacrylate to convert some of the amino groups into urea bonds containing polymerizable double bonds. Then, using the remaining free amino groups as anchor points, an amide bond is formed with the carboxyl group of 4-carboxyphenylboronic acid through a carbodiimide condensation system, attaching the phenylboronic acid group to the POSS core. The resulting hybrid crosslinked monomer has a POSS rigid cage as the core, with polymerizable double bonds and phenylboronic acid recognition sites simultaneously suspended at the ends of multiple arms. The polymerizable double bonds enable it to participate in the reverse microemulsion copolymerization of acrylamide and embed into the network framework, while the phenylboronic acid groups endow it with the ability to dynamically covalently crosslink with ortho-dihydroxy groups. The thermal stability of the POSS core and the inorganic cage structure enhance the microsphere network's resistance to thermal degradation and structural collapse under high-temperature aging. The multi-site cross-linking architecture strengthens the network's integrity and mechanical rigidity. The dynamic covalent bonds, along with the ion-pair cross-linking and chemical cross-linking in the basic formulation, work synergistically to enable the microspheres to have elastic deformation and structural recovery capabilities when passing through formation pores, thereby improving their temperature and salt resistance as well as their deep migration-blocking synergy.

[0016] Preferably, the amount of the POSS-phenylboronic acid hybrid crosslinking monomer added is 4-6 parts.

[0017] The aforementioned dosage range allows the rigid POSS nanocores to form a suitable cross-linking node density within the microsphere network. The multi-site phenylboronic acid groups form dynamic borate ester bonds with the ortho-dihydroxy groups of 2-methyl-2-acrylate-2,3-dihydroxypropyl ester, establishing uniformly distributed reversible covalent cross-linking sites within the network. When the microspheres pass through formation pore throats during injection, excessively high cross-linking density increases the rigidity of the microspheres, making deformation difficult, while excessively low cross-linking density results in insufficient structural recovery after shearing. This limited dosage endows the microspheres with both elastic deformation capacity and structural recovery capacity after passage, improving the efficiency of microsphere migration into deeper formations. The rigid framework and thermal stability of the POSS cage can be evenly distributed in the network at this dosage, which improves the microspheres' resistance to thermal degradation and structural collapse under high temperature aging conditions. The reversibility of the borate ester bond maintains its activity in the high salt environment, so that the dynamic network can still maintain its structural integrity after long-term high temperature and high salt aging. After reaching deep strata, a stable blocking network is established through dynamic covalent bonds and ion pair crosslinking, thereby improving the temperature and salt resistance performance and the deep migration-blocking synergy.

[0018] Preferably, the mass ratio of the POSS-phenylboronic acid hybrid crosslinking monomer to 2-methyl-2-acrylate-2,3-dihydroxypropyl ester is 1:(0.25-0.35).

[0019] The aforementioned ratio ensures a reasonable match between the phenylboronic acid groups at multiple sites on the POSS-phenylboronic acid hybrid crosslinking monomer and the ortho-dihydroxy groups of 2-methyl-2-acrylate-2,3-dihydroxypropyl ester. The phenylboronic acid groups are sufficient while the ortho-dihydroxy groups are relatively limited, resulting in a moderate number of borate ester crosslinking points in the network. This establishes a dynamic covalent network to enhance the mechanical rigidity of the microspheres while avoiding excessive crosslinking that would restrict chain segment movement and reduce elasticity. When the microspheres undergo high shear as they pass through formation pore throats, the borate ester bonds undergo reversible breakage, causing the microspheres to deform appropriately to adapt to the narrow channels. After passage, the phenylboronic acid and ortho-dihydroxy groups recombine to restore the crosslinked structure. This ratio balances the rates of breakage and recombination, allowing the microspheres to maintain structural integrity during transport and recover network strength after passage. Meanwhile, the distribution density of the POSS rigid core and the dynamic cross-linking network at this mass ratio synergistically enhance the microsphere skeleton's resistance to thermal degradation under high-temperature aging conditions. The reversible activity of the dynamic covalent bonds in high-mineralized water is maintained, allowing the microspheres to form a stable blocking network after deep aggregation, thereby improving the temperature and salt resistance performance and the deep migration-blocking synergy.

[0020] Preferably, the aqueous phase further includes dodecafluoroheptyl methacrylate.

[0021] Dodecafluoroheptyl methacrylate (DFHMA) contains long-chain polyfluoroalkyl side groups. After copolymerization, its polyfluorocarbon chains drive hydrophobic association in the aqueous phase, forming reversible hydrophobic physical crosslinking points within the microspheres. These points, along with ion-pair crosslinks, chemical crosslinks, and dynamic covalent crosslinks of borate esters, constitute a multi-layered network. The low surface energy and strong hydrophobic aggregation tendency of the fluorocarbon chains enhance the association strength of the microsphere network in saline water, helping to maintain the structural integrity of the microspheres under high salinity conditions. The rigidity and thermal stability of the polyfluoroalkyl side groups improve the resistance of the microsphere framework to thermal degradation under high-temperature aging. During deep migration, the hydrophobic association crosslinking points can dissociate when subjected to high shear as they pass through pore throats, causing the microspheres to deform appropriately to adapt to the narrow channels. After passing through, the polyfluorocarbon chains re-aggregate to restore the physical crosslinking network. At the same time, the polyfluoroalkyl groups on the surface of the microspheres reduce their adsorption tendency to the rock surface, improving the passage efficiency of the microspheres during migration. This achieves mechanical sealing through the synergistic establishment of multiple networks in deep strata, thereby enhancing the temperature and salt resistance and the synergistic ability of deep migration and sealing.

[0022] Preferably, the amount of dodecafluoroheptyl methacrylate added is 1-3 parts.

[0023] The aforementioned dosage range ensures a moderate density of hydrophobic association points formed by polyfluoroalkyl side chains in the microsphere network. This, together with the dynamic covalent crosslinking provided by the POSS-phenylboronic acid hybrid crosslinking monomer and the ion-pair crosslinking in the basic formulation, constitutes a synergistic multi-layer network. When the dosage of fluorinated monomers is within this range, the hydrophobic aggregation effect of fluorocarbon chains in highly saline water is enhanced, improving the network cohesion and resistance to structural collapse of the microspheres under high-temperature and high-salt aging conditions. Simultaneously, the number of hydrophobic association crosslinking points is not excessive. When the microspheres undergo high shear as they pass through formation pore throats, the hydrophobic associations can undergo reversible dissociation, causing the microspheres to elastically deform to adapt to the narrow channels. After passage, the polyfluorocarbon chains re-aggregate to restore the physical crosslinking network, improving the passage efficiency and structural recovery ability of the microspheres during deep migration. The polyfluoroalkyl side chains endow the microspheres with low surface energy, reducing their tendency to adsorb onto rock pores and throats. Appropriate addition ensures that the surface fluorine content is sufficient to reduce adsorption without weakening the integrity of the microspheres due to phase separation. After reaching deep strata, multiple cross-linked networks work together to establish stable mechanical plugging, thereby improving temperature and salt resistance as well as deep migration-plugging synergy.

[0024] Secondly, this application provides a method for preparing a self-polymerized nanosphere polyacrylamide oil displacement agent, employing the following technical solution: A method for preparing a self-polymerized nanosphere polyacrylamide oil displacement agent includes the following steps: Acrylamide, a zwitterionic monomer composition, polyethylene glycol diacrylate, chemical crosslinking agent, and initiator were dissolved in water, deoxygenated, and prepared as an aqueous phase. Emulsifier was dissolved in white oil, deoxygenated, and prepared as an oil phase. The aqueous phase was added to the oil phase under a protective atmosphere, and pre-emulsified under stirring to form a stable microemulsion. After heating and reacting, the mixture was cooled to room temperature, demulsified, washed, and dried to obtain a self-polymerized polyacrylamide nanosphere oil displacement agent.

[0025] The aforementioned process enables the copolymerization of functional monomers within the confined space of the water-in-oil microemulsion droplets, ensuring a uniform distribution of different reactive monomers along the polymer chain. This allows internal salt units, ion-pair crosslinking units, hydrophilic flexible segments, and chemical crosslinking points to be embedded in the microsphere network in a designed proportion, avoiding compositional drift and structural inhomogeneity between microspheres caused by differences in the reactivity ratios of the components. Confined-space polymerization imparts controllable particle size and a narrow particle size distribution to the microspheres. Controllable particle size allows the hydrodynamic dimensions of the microspheres during the injection stage to match the pore throat size of the formation, facilitating their migration to deeper layers. The microspheres formed by reverse microemulsion polymerization are coated with an emulsifier layer, maintaining an independent particle morphology even after subsequent demulsification and washing, which is beneficial for the uniform dispersion of microspheres in water and prevents premature aggregation. During the polymerization process, each cross-linking system is established simultaneously within the droplet. Ion-pair cross-linking, chemical cross-linking, and chain entanglement form an integrated multi-network structure inside the microsphere, which enables the microsphere to maintain structural stability under high temperature and high salt aging conditions and elastic deformation capacity under pore throat shearing, thereby improving its temperature and salt resistance as well as its deep migration-blocking synergistic ability.

[0026] In summary, this application includes at least one of the following beneficial technical effects: 1. Acrylamide, as the main monomer, polymerizes to form a long-chain backbone, giving the microspheres basic hydrophilicity and chain flexibility. The internal salt structure of the sulfobetaine-type monomer maintains a stable solvation layer in high-salt water to inhibit chain shrinkage. The ion-pair crosslinking network formed by the anionic monomer and the quaternary ammonium salt-type cationic monomer is tight under low-salt conditions and moderately dissociates under high-salt conditions, giving the microspheres the ability to regulate swelling in different salinity environments. This allows them to maintain a small hydrodynamic size during the injection stage and migrate to deeper layers. After reaching high-salt formations, they gradually exert a sealing effect through ion-pair dissociation. The polyoxyethylene flexible arm of polyethylene glycol diacrylate enhances the water absorption, swelling, and elastic deformation capacity of the microspheres. It is compounded with chemical crosslinking agents to construct an appropriate chemical crosslinking density to maintain the integrity of the network structure and prevent excessive expansion or breakage during high-temperature aging. The initiator decomposes free radicals to drive the copolymerization of each monomer in the droplet, so that the functional units are embedded in the network according to the design ratio. The synergistic effect of the components gives the microspheres chemical structural stability with temperature and salt resistance, size adaptability for migration along the pore throat, and mechanical strength to form an effective plug in the deep formation, thereby improving the temperature and salt resistance performance and the synergistic ability of deep migration and plugging.

[0027] 2. The POSS-phenylboronic acid hybrid crosslinking monomer uses a cage-like silsesquioxane as the core and multiple arms connecting phenylboronic acid groups, providing multi-site crosslinking capability and a rigid nanocore. 2-Methyl-2-acrylate-2,3-dihydroxypropyl ester contains an ortho-dihydroxy structure, which can form dynamic borate ester bonds with phenylboronic acid groups inside the microspheres, constructing a reversible covalent crosslinking network. When the microspheres are subjected to high shear as they pass through formation pore throats, the borate ester bonds can reversibly break, allowing the microspheres to deform appropriately to adapt to the narrow channels. The crosslinking structure is restored by the subsequent recombination of the ortho-dihydroxy and phenylboronic acid, improving the structural integrity and dimensional recovery ability of the microspheres during deep migration. Simultaneously, the thermal stability and low shrinkage characteristics of the POSS rigid core enhance the microsphere network framework's resistance to thermal degradation and structural collapse under high-temperature aging conditions. The borate ester bonds also maintain reversible exchange activity in saline environments, enabling the microspheres to maintain network integrity even in high-mineralization environments. Dynamic covalent crosslinking, in synergy with electrostatic ion pair crosslinking and chemical crosslinking in the basic formulation, endows the microspheres with elastic deformation capacity, network recovery capacity, and skeleton rigidity, thereby improving temperature and salt resistance as well as deep migration-blocking synergy.

[0028] 3. Dodecafluoroheptyl methacrylate (DFHMA) contains long-chain polyfluoroalkyl side groups. After copolymerization, its polyfluorocarbon chains drive hydrophobic association in the aqueous phase, forming reversible hydrophobic physical crosslinking points inside the microspheres. These points, along with ion-pair crosslinks, chemical crosslinks, and dynamic covalent crosslinks of borate esters, constitute a multi-layered network. The low surface energy and strong hydrophobic aggregation tendency of the fluorocarbon chains enhance the association strength of the microsphere network in saline water, helping to maintain the structural integrity of the microspheres under high salinity conditions. The rigidity and thermal stability of the polyfluoroalkyl side groups improve the resistance of the microsphere skeleton to thermal degradation under high-temperature aging. During deep migration, the hydrophobic association crosslinking points can dissociate when subjected to high shear as they pass through pore throats, causing the microspheres to deform appropriately to adapt to the narrow channels. After passing through, the polyfluorocarbon chains re-aggregate to restore the physical crosslinking network. At the same time, the polyfluoroalkyl groups on the surface of the microspheres reduce their adsorption tendency to the rock surface, improving the passage efficiency of the microspheres during migration. This achieves mechanical sealing through the synergistic establishment of multiple networks in deep strata, thereby enhancing the temperature and salt resistance and the synergistic ability of deep migration and sealing. Detailed Implementation

[0029] This application discloses a self-polymerized nanosphere polyacrylamide oil displacement agent and its preparation method. Unless otherwise specified, all raw materials used in this application can be obtained from commercially available sources. The following examples provide further detailed description of this application: Raw material description: Octadecyl cage-type silsesquioxane was purchased from Forsmann Technology (Beijing) Co., Ltd.; mercaptoethylamine hydrochloride (CAS No.: 156-57-0); dimethyl benzoate (CAS No.: 24650-42-8); triethylamine (CAS No.: 121-44-8); ethyl isocyanate methacrylate (CAS No.: 30674-80-7); 4-carboxyphenylboronic acid (CAS No.: 14047-29-1); 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride (CAS No.: 25952-53-8); N-hydroxysuccinimide (CAS No.: 6066-82-6); acrylamide (CAS No.: 79-06-1); methacryloyloxyethyl Sulfobetaine (CAS No.: 3637-26-1), 2-acrylamido-2-methylpropanesulfonic acid (CAS No.: 15214-89-8), acrylamide-propyltrimethylammonium chloride (CAS No.: 45021-77-0), N,N'-methylenebisacrylamide (CAS No.: 110-26-9), ammonium persulfate (CAS No.: 7727-54-0), white oil was purchased from Shandong Zhenxiang New Materials Co., Ltd., Span80 and Tween80 were purchased from Greenlink (Jining) Chemical Technology Co., Ltd., 2-methyl-2-acrylate-2,3-dihydroxypropyl ester (CAS No.: 5919-74-4), dodecafluoroheptyl methacrylate (CAS No.: 2261-99-6).

[0030] Preparation Example 1 1 g of octavinylclade silsesquioxane was dissolved in 15 mL of anhydrous toluene. 2.8 g of mercaptoethylamine hydrochloride and 0.03 g of benzoin dimethyl ether were added. The mixture was stirred at 25 °C for 6 h under UV irradiation. After precipitation with diethyl ether and washing with methanol, the solution was dried under vacuum to obtain octa(aminoethylthioethyl)POSS hydrochloride. This hydrochloride was dissolved in 20 mL of anhydrous dichloromethane and neutralized with 1.35 g of triethylamine. A 10 mL solution of dichloromethane containing 1.4 g of ethyl isocyanate methacrylate was added dropwise over 30 min while cooling in an ice bath. The mixture was then reacted at 0 °C for 2 h, and the temperature was increased to 25 °C. The reaction was continued at ℃ for 12 h. Triethylamine hydrochloride was removed by filtration, and the intermediate was concentrated by rotary evaporation. The intermediate was dissolved in 20 mL of anhydrous N,N-dimethylformamide, and 1.4 g of 4-carboxyphenylboronic acid, 1.8 g of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and 1.1 g of N-hydroxysuccinimide were added. The reaction was carried out at 25 °C in the dark for 24 h under a nitrogen atmosphere. The reaction solution was poured into 100 mL of deionized water to precipitate the product. The product was washed thoroughly with methanol and deionized water in sequence, and dried under vacuum to constant weight to obtain the POSS-phenylboronic acid hybrid crosslinking monomer. Example 1

[0031] Weigh the following components in parts by mass: 90 parts acrylamide, 12 parts zwitterionic monomer composition, 0.3 parts polyethylene glycol diacrylate, 0.05 parts chemical crosslinking agent, 0.1 parts initiator, and 350 parts water; the mass ratio of the aqueous phase, oil phase, and emulsifier is 1:1.5:0.15. The zwitterionic monomer composition consists of sulfobetaine-type monomers (methacryloyloxyethyl sulfobetaine), anionic monomers (2-acrylamido-2-methylpropanesulfonic acid), and quaternary ammonium salt-type cationic monomers (acrylamidopropyltrimethylammonium chloride) in a mass ratio of 0.9:0.58:0.42. The chemical crosslinking agent is N,N'-methylenebisacrylamide, the initiator is ammonium persulfate, the oil phase is white oil, and the emulsifier consists of Span80 and Tween80 in a mass ratio of 3:1.

[0032] Acrylamide, a zwitterionic monomer composition, polyethylene glycol diacrylate, chemical crosslinking agent, and initiator were dissolved in deionized water and purified by nitrogen purging for 15 min to prepare an aqueous phase. Emulsifier was dissolved in white oil and purified by nitrogen purging for 20 min to prepare an oil phase. Under a nitrogen protective atmosphere, the aqueous phase was added dropwise to the oil phase, and the addition was completed within 45 min. The mixture was pre-emulsified at a stirring speed of 600 rpm for 30 min to form a stable microemulsion. The mixture was heated to 70 °C and reacted for 7 h. After cooling to room temperature, anhydrous ethanol was added to break the emulsion. The mixture was stirred at 1500 rpm for 15 min, centrifuged, washed with an ethanol-water solution (ethanol and water volume ratio of 1:1), and dried under vacuum at 60 °C to obtain a self-polymerized polyacrylamide nanosphere oil displacement agent. Example 2

[0033] Weigh the following components in parts by mass: 110 parts acrylamide, 20 parts zwitterionic monomer composition, 0.6 parts polyethylene glycol diacrylate, 0.1 parts chemical crosslinking agent, 0.3 parts initiator, and 450 parts water; the mass ratio of the aqueous phase, oil phase, and emulsifier is 1:1.5:0.15. The zwitterionic monomer composition consists of sulfobetaine-type monomers (methacryloyloxyethyl sulfobetaine), anionic monomers (2-acrylamido-2-methylpropanesulfonic acid), and quaternary ammonium salt-type cationic monomers (acrylamidopropyltrimethylammonium chloride) in a mass ratio of 1.1:0.58:0.42. The chemical crosslinking agent is N,N'-methylenebisacrylamide, the initiator is ammonium persulfate, the oil phase is white oil, and the emulsifier consists of Span80 and Tween80 in a mass ratio of 3:1.

[0034] Acrylamide, a zwitterionic monomer composition, polyethylene glycol diacrylate, chemical crosslinking agent, and initiator were dissolved in deionized water and purified by nitrogen purging for 15 min to prepare an aqueous phase. Emulsifier was dissolved in white oil and purified by nitrogen purging for 20 min to prepare an oil phase. Under a nitrogen protective atmosphere, the aqueous phase was added dropwise to the oil phase, and the addition was completed within 45 min. The mixture was pre-emulsified at a stirring speed of 600 rpm for 30 min to form a stable microemulsion. The mixture was heated to 70 °C and reacted for 7 h. After cooling to room temperature, anhydrous ethanol was added to break the emulsion. The mixture was stirred at 1500 rpm for 15 min, centrifuged, washed with an ethanol-water solution (ethanol and water volume ratio of 1:1), and dried under vacuum at 60 °C to obtain a self-polymerized polyacrylamide nanosphere oil displacement agent. Example 3

[0035] Weigh the following components in parts by mass: 100 parts acrylamide, 16 parts zwitterionic monomer composition, 0.45 parts polyethylene glycol diacrylate, 0.075 parts chemical crosslinking agent, 0.2 parts initiator, and 400 parts water; the mass ratio of the aqueous phase, oil phase, and emulsifier is 1:1.5:0.15. The zwitterionic monomer composition consists of sulfobetaine-type monomers (methacryloyloxyethyl sulfobetaine), anionic monomers (2-acrylamido-2-methylpropanesulfonic acid), and quaternary ammonium salt-type cationic monomers (acrylamidopropyltrimethylammonium chloride) in a mass ratio of 1:0.58:0.42. The chemical crosslinking agent is N,N'-methylenebisacrylamide, the initiator is ammonium persulfate, the oil phase is white oil, and the emulsifier consists of Span80 and Tween80 in a mass ratio of 3:1.

[0036] Acrylamide, a zwitterionic monomer composition, polyethylene glycol diacrylate, chemical crosslinking agent, and initiator were dissolved in deionized water and purified by nitrogen purging for 15 min to prepare an aqueous phase. Emulsifier was dissolved in white oil and purified by nitrogen purging for 20 min to prepare an oil phase. Under a nitrogen protective atmosphere, the aqueous phase was added dropwise to the oil phase, and the addition was completed within 45 min. The mixture was pre-emulsified at a stirring speed of 600 rpm for 30 min to form a stable microemulsion. The mixture was heated to 70 °C and reacted for 7 h. After cooling to room temperature, anhydrous ethanol was added to break the emulsion. The mixture was stirred at 1500 rpm for 15 min, centrifuged, washed with an ethanol-water solution (ethanol and water volume ratio of 1:1), and dried under vacuum at 60 °C to obtain a self-polymerized polyacrylamide nanosphere oil displacement agent. Example 4

[0037] Example 4 is based on Example 3. The only difference between Example 4 and Example 3 is that in Example 4, the zwitterionic monomer composition consists of a sulfobetaine-type monomer (methacryloyloxyethyl sulfobetaine), an anionic monomer (2-acrylamido-2-methylpropanesulfonic acid), and a quaternary ammonium salt-type cationic monomer (acrylamidopropyltrimethylammonium chloride) in a mass ratio of 0.8:0.58:0.42. Example 5

[0038] Example 5 is based on Example 3. The only difference between Example 5 and Example 3 is that in Example 5, the zwitterionic monomer composition consists of a sulfobetaine-type monomer (methacryloyloxyethyl sulfobetaine), an anionic monomer (2-acrylamido-2-methylpropanesulfonic acid), and a quaternary ammonium salt-type cationic monomer (acrylamidopropyltrimethylammonium chloride) in a mass ratio of 1.2:0.58:0.42. Example 6

[0039] Example 6 is based on Example 3. The only difference between Example 6 and Example 3 is that the aqueous phase in Example 6 also includes POSS-phenylboronic acid hybrid crosslinking monomer and 2-methyl-2-acrylate-2,3-dihydroxypropyl ester. The amount of POSS-phenylboronic acid hybrid crosslinking monomer added is 4 parts, and the mass ratio of POSS-phenylboronic acid hybrid crosslinking monomer to 2-methyl-2-acrylate-2,3-dihydroxypropyl ester is 1:0.25. Example 7

[0040] Example 7 is based on Example 3. The only difference between Example 7 and Example 3 is that the aqueous phase in Example 7 also includes POSS-phenylboronic acid hybrid crosslinking monomer and 2-methyl-2-acrylate-2,3-dihydroxypropyl ester. The amount of POSS-phenylboronic acid hybrid crosslinking monomer added is 6 parts, and the mass ratio of POSS-phenylboronic acid hybrid crosslinking monomer to 2-methyl-2-acrylate-2,3-dihydroxypropyl ester is 1:0.35. Example 8

[0041] Example 8 is based on Example 3. The only difference between Example 8 and Example 3 is that the aqueous phase in Example 8 also includes POSS-phenylboronic acid hybrid crosslinking monomer and 2-methyl-2-acrylate-2,3-dihydroxypropyl ester. The amount of POSS-phenylboronic acid hybrid crosslinking monomer added is 5 parts, and the mass ratio of POSS-phenylboronic acid hybrid crosslinking monomer to 2-methyl-2-acrylate-2,3-dihydroxypropyl ester is 1:0.3. Example 9

[0042] Example 9 is based on Example 8. The only difference between Example 9 and Example 8 is that the amount of POSS-phenylboronic acid hybrid crosslinking monomer added in Example 9 is 2 parts. Example 10

[0043] Example 10 is based on Example 8. The only difference between Example 10 and Example 8 is that the amount of POSS-phenylboronic acid hybrid crosslinking monomer added in Example 10 is 8 parts. Example 11

[0044] Example 11 is based on Example 8. The only difference between Example 11 and Example 8 is that the mass ratio of POSS-phenylboronic acid hybrid crosslinking monomer and 2-methyl-2-acrylate-2,3-dihydroxypropyl ester in Example 11 is 1:0.15. Example 12

[0045] Example 12 is based on Example 8. The only difference between Example 12 and Example 8 is that in Example 12, the mass ratio of POSS-phenylboronic acid hybrid crosslinking monomer and 2-methyl-2-acrylate-2,3-dihydroxypropyl ester is 1:0.5. Example 13

[0046] Example 13 is based on Example 8. The only difference between Example 13 and Example 8 is that the aqueous phase in Example 13 also includes 1 part of dodecafluoroheptyl methacrylate. Example 14

[0047] Example 14 is based on Example 13. The only difference between Example 14 and Example 13 is that the amount of dodecafluoroheptyl methacrylate added in Example 14 is 3 parts. Example 15

[0048] Example 15 is based on Example 13. The only difference between Example 15 and Example 13 is that the amount of dodecafluoroheptyl methacrylate added in Example 15 is 2 parts. Example 16

[0049] Example 16 is based on Example 13. The only difference between Example 16 and Example 13 is that the amount of dodecafluoroheptyl methacrylate added in Example 16 is 0.5 parts. Example 17

[0050] Example 17 is based on Example 13. The only difference between Example 17 and Example 13 is that the amount of dodecafluoroheptyl methacrylate added in Example 17 is 5 parts.

[0051] Comparative Example 1 Comparative Example 1 is based on Example 3. The only difference between Comparative Example 1 and Example 3 is that the zwitterionic monomer composition in Comparative Example 1 consists of an anionic monomer (2-acrylamido-2-methylpropanesulfonic acid) and a quaternary ammonium salt cationic monomer (acrylamidopropyltrimethylammonium chloride) in a mass ratio of 0.58:0.42. Performance testing experiment

[0052] (1) Using the standard "SY / T5862-2020 Technical Requirements for Polymers for Oil Displacement", the sample was dispersed at a concentration of 2000 mg / L in simulated formation water with a salinity of 80000 mg / L (formulation: NaCl 68.0 g / L, CaCl2·2H2O 4.2 g / L, MgCl2·6H2O 3.8 g / L, Ca²⁺+Mg²⁺ content 2100 mg / L). The sample was sealed in a high-temperature aging tank filled with nitrogen and aged in a constant temperature oven at 120℃ for 30 days. The apparent viscosity before and after aging was measured using a Brookfield rotational viscometer (rotor No. 0, 25℃). The shear rate was 7.34 s⁻¹. The viscosity retention rate was calculated by the ratio of the viscosity after aging to the initial viscosity. The results are recorded in Table 1.

[0053] (2) Using GB / T32668-2016 General Rules for Electrophoresis Method of Zeta Potential Analysis of Colloidal Particles as the standard, the microspheres were dispersed at a concentration of 0.1 g / L in simulated formation water with a mineralization of 50000 mg / L (formulation: NaCl 42.5 g / L, CaCl2·2H2O 2.6 g / L, MgCl2·6H2O 2.4 g / L, Ca²⁺+Mg²⁺ content 1300 mg / L, pH adjusted to 7.5). After magnetic stirring for 30 min, the mixture was ultrasonically dispersed for 5 min at a power of 200 W. The samples were injected directly into the potential sample cell without being filtered through a filter membrane. The Zeta potential was measured by electrophoretic light scattering at 25°C. The voltage was set to 100V during the measurement. If the electrophoretic current exceeded 10mA, the voltage could be appropriately reduced to 50-70V. Each sample was measured three times. The system suitability was verified by calibrating standard polystyrene latex microparticles with known Zeta potential values ​​(-42±3mV, 25°C). The average value was taken after measurement, and the results are recorded in Table 1.

[0054] (3) Using GB / T33061.10-2016 Determination of Dynamic Mechanical Properties of Plastics Part 10: Determination of Complex Shear Viscosity Using Parallel Plate Oscillating Rheometer and SY / T7812-2024 Evaluation Method of Polymer Microspheres for Regulating Drive as standards, the microspheres were dispersed at 2000 mg / L in simulated formation water with a salinity of 50000 mg / L, and aged in a 70℃ constant temperature oven for 72 h to allow for sufficient self-aggregation. After removal, the microspheres were subjected to stress-controlled rotational rheology at 25℃. The strain was scanned using an instrument (40mm parallel flat plate clamp, 1mm plate spacing), with a fixed frequency of 1Hz and a strain range of 0.01% to 100% to determine the strain value in the linear viscoelastic region. The criteria for determining the linear viscoelastic region was that the rate of change of G' was ≤5%. Within the linear viscoelastic region, a strain of 0.1% was taken, and a frequency scan (0.1 to 100 rad / s) was performed. The storage modulus G' at a frequency of 1Hz was taken as the characterization value of the sealing strength. Each sample was tested three times, and the average value was taken after measurement. The results are recorded in Table 1.

[0055] Table 1. Test results of temperature and salt resistance, and deep migration-blocking synergistic ability. Example 1 91.2 -12.4 5620 Example 2 90.5 -14.6 5895 Example 3 91.8 -13.5 6180 Example 4 87.3 -17.1 5210 Example 5 88.0 -9.2 4980 Example 6 93.6 -13.2 8520 Example 7 94.1 -13.8 9010 Example 8 94.5 -13.5 9480 Example 9 92.5 -13.5 7020 Example 10 93.0 -13.5 7780 Example 11 92.0 -13.6 6630 Example 12 92.1 -13.4 6710 Example 13 94.8 -13.5 9650 Example 14 95.1 -13.4 9780 Example 15 95.3 -13.3 9920 Example 16 94.6 -13.5 9520 Example 17 94.2 -13.6 9340 Comparative Example 1 51.5 -25.3 2520 As shown in Table 1, the viscosity retention rate of Examples 1-3 is above 90.5%, the Zeta potential is between -12.4 and -14.6 mV, and the storage modulus G' is above 5620 Pa. This demonstrates that the materials prepared in this application have good temperature and salt resistance, as well as deep migration-blocking synergistic ability.

[0056] As shown in Table 1, the only difference between Examples 4 and 5 and Example 3 is that the synergistic balance between the inner and outer salts was disrupted in Examples 4 and 5, resulting in a decrease in both viscosity retention rate and plugging strength.

[0057] As shown in Table 1, the only difference between Examples 6-12 and Example 3 is that in Examples 6-8, under the optimal amount of POSS crosslinking monomer and the ratio of dihydroxy monomer, the dynamic borate ester bond network and electrostatic assembly work together efficiently, resulting in improved performance; in Examples 9-12, the optimal limiting ratio was destroyed, and the performance improvement effect was reduced.

[0058] As shown in Table 1, the only difference between Examples 13-17 and Example 3 is that in Examples 13-15, fluorinated monomers were introduced according to a defined ratio, and the network structure was enhanced by moderate hydrophobic association. Examples 16 and 17 deviated from the defined ratio. If the dosage was too low, the effect would be insignificant, and if it was too high, the self-aggregation might be weakened due to phase separation, and the performance improvement effect would decrease.

[0059] As shown in Table 1, the only difference between Comparative Example 1 and Example 3 is that: no methacryloyloxyethyl sulfobetaine was added in Comparative Example 1, and the microspheres lost their internal salt protection, resulting in a sharp decrease in temperature and salt resistance; at the same time, the net negative charge was too strong, making it difficult for self-aggregation to occur effectively.

[0060] This specific embodiment is merely an explanation of this application and is not intended to limit it. Based on the above description, those skilled in the art can make various changes and modifications without departing from the technical concept of this application. The technical scope of this application is not limited to the contents of the specification but must be determined according to the scope of the claims.

Claims

1. A self-polymerizing nanosphere polyacrylamide oil displacement agent, characterized in that: The reverse microemulsion polymerization method is used to prepare the raw materials, which include an aqueous phase, an oil phase, and an emulsifier. The aqueous phase comprises the following components in parts by mass: 90-110 parts acrylamide 12-20 parts of zwitterionic monomer composition 0.3-0.6 parts of polyethylene glycol diacrylate Chemical crosslinking agent 0.05-0.1 parts Initiator 0.1-0.3 parts 350-450 parts water; The zwitterionic monomer composition includes sulfobetaine-type monomers, anionic monomers, and quaternary ammonium salt-type cationic monomers.

2. The self-polymerized nanosphere polyacrylamide oil displacement agent according to claim 1, characterized in that: The sulfobetaine-type monomer includes methacryloyloxyethyl sulfobetaine, the anionic monomer includes 2-acrylamido-2-methylpropanesulfonic acid, and the quaternary ammonium salt-type cationic monomer includes acrylamidopropyltrimethylammonium chloride.

3. The self-polymerized nanosphere polyacrylamide oil displacement agent according to claim 2, characterized in that: The mass ratio of the sulfobetaine-type monomer, the anionic monomer, and the quaternary ammonium salt-type cationic monomer is (0.9-1.1):0.58:0.

42.

4. The self-polymerized nanosphere polyacrylamide oil displacement agent according to claim 1, characterized in that: The aqueous phase also includes POSS-phenylboronic acid hybrid crosslinking monomer and 2-methyl-2-acrylate-2,3-dihydroxypropyl ester.

5. The self-polymerized nanosphere polyacrylamide oil displacement agent according to claim 4, characterized in that: The POSS-phenylboronic acid hybrid crosslinking monomer was prepared using the following steps: Octavinyl cage-type silsesquioxane was dissolved in toluene, and mercaptoethylamine hydrochloride and benzoin dimethyl ether were added. The mixture was stirred under ultraviolet light, and after precipitation, washing, and drying, octa(aminoethylthioethyl)POSS hydrochloride was obtained. This hydrochloride was dissolved in dichloromethane, neutralized with triethylamine, cooled, and reacted with ethyl isocyanate methacrylate solution. The mixture was filtered and concentrated to obtain an intermediate. The intermediate was dissolved in N,N-dimethylformamide, and 4-carboxyphenylboronic acid, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, and N-hydroxysuccinimide were added. The mixture was reacted under a protective atmosphere in the dark, and after precipitation, washing, and drying, POSS-phenylboronic acid hybrid crosslinking monomer was obtained.

6. The self-polymerized nanosphere polyacrylamide oil displacement agent according to claim 5, characterized in that: The amount of the POSS-phenylboronic acid hybrid crosslinking monomer added is 4-6 parts.

7. The self-polymerized nanosphere polyacrylamide oil displacement agent according to claim 6, characterized in that: The mass ratio of the POSS-phenylboronic acid hybrid crosslinking monomer to 2-methyl-2-acrylate-2,3-dihydroxypropyl ester is 1:(0.25-0.35).

8. The self-polymerized nanosphere polyacrylamide oil displacement agent according to claim 4, characterized in that: The aqueous phase also includes dodecafluoroheptyl methacrylate.

9. The self-polymerized nanosphere polyacrylamide oil displacement agent according to claim 8, characterized in that: The amount of dodecafluoroheptyl methacrylate added is 1-3 parts.

10. A method for preparing a self-polymerized nanosphere polyacrylamide oil displacement agent as described in any one of claims 1-9, characterized in that: Includes the following steps: Acrylamide, a zwitterionic monomer composition, polyethylene glycol diacrylate, chemical crosslinking agent, and initiator were dissolved in water, deoxygenated, and prepared as an aqueous phase. Emulsifier was dissolved in white oil, deoxygenated, and prepared as an oil phase. The aqueous phase was added to the oil phase under a protective atmosphere, and pre-emulsified under stirring to form a stable microemulsion. After heating and reacting, the mixture was cooled to room temperature, demulsified, washed, and dried to obtain a self-polymerized polyacrylamide nanosphere oil displacement agent.