Intelligent chemical oil displacement agent, preparation method and application thereof

Abstract

This application discloses an intelligent chemical flooding agent, its preparation method, and its application, belonging to the field of petroleum extraction technology. The intelligent chemical flooding agent, by weight, comprises 100 parts of nanocapsules, 2-4 parts of polyether block copolymer, 1-2 parts of stabilizer, 0.5-1 parts of chelating agent, and 0.3-0.8 parts of water-soluble salt-resistant dispersant. The nanocapsules consist of a copolymer shell and an internal functional phase. Based on 100 parts of nanocapsules, the copolymer shell accounts for 60-65 parts, and the internal functional phase accounts for 35-40 parts. By using quaternary monomer copolymerization to form an intelligent responsive shell, it combines excellent temperature and salt resistance with shell mechanical strength, achieving targeted and controlled drug release and avoiding ineffective near-wellbore loss of the agent. The internal functional phase reduces interfacial tension and deep profile control. The compounding of polyether block copolymer, stabilizer, chelating agent, and water-soluble salt-resistant dispersant enhances the system's shear stability, scale inhibition, and salt-resistant dispersion performance, enabling deep reservoir profile control and improving oil recovery in low-permeability, high-temperature, and high-salinity reservoirs.

Description

Technical Field

[0001] This application relates to an intelligent chemical displacement agent, its preparation method and application, belonging to the field of petroleum extraction technology. Background Technology

[0002] Low-permeability reservoirs exhibit complex operating conditions characterized by low permeability, high formation temperature, and high formation water salinity. Not only are the reservoir pore throat sizes small and the reservoir heterogeneity severe, but the formation water environment is also rich in high-valence metal ions such as calcium and magnesium ions. The harsh formation environment places stringent requirements on the temperature resistance, salt resistance, and migration stability of chemical flooding systems. Conventional chemical flooding systems are difficult to adapt to the field conditions, which greatly restricts the potential for improving the crude oil recovery rate of low-permeability and difficult-to-develop reservoirs.

[0003] Chemical flooding is a core enhanced oil recovery technology in the tertiary oil recovery stage. This technology involves injecting functional chemical agents into the formation water to directionally regulate the rheological properties of the displacement fluid, the oil-water interface characteristics, and the three-phase interface relationships between the displacement fluid, crude oil, and rock. This process removes residual oil adsorbed in pores, expands the waterflood sweep volume, and ultimately achieves efficient extraction of difficult-to-access crude oil. Currently, chemical flooding systems used on a large scale in the field are mainly divided into three categories: single polymer flooding, surfactant-polymer binary composite flooding, and alkali-surfactant-polymer ternary composite flooding. The core functional agents include high molecular weight polymers, anionic / nonionic surfactants, inorganic alkalis, and supporting auxiliary agents.

[0004] However, existing traditional chemical flooding systems have inherent technical defects: conventional polymers lack sufficient temperature and salt resistance; in high-temperature and high-salt formation environments, polymer chains are prone to coiling and aggregation, leading to a significant decrease in system viscosity and rapid failure of deep profile modification capabilities; conventional surfactants readily react with formation Ca²⁺. + Mg² + High-valence ions undergo complexation reactions, forming insoluble precipitates and directly losing their interfacial activation, oil washing, and displacement functions. Overall chemical flooding agents have limited effective range within the formation, only improving displacement in the near-wellbore area. They cannot reach deeper reservoirs to achieve vertical and horizontal profile control, making them unsuitable for the field development needs of low-permeability, high-temperature, and high-salinity reservoirs.

[0005] To address the shortcomings of traditional chemical flooding, nanoparticle-based enhanced oil recovery (EOR) technology is increasingly being applied in the field of tertiary oil recovery. Nanoparticles possess unique advantages such as large specific surface area, high surface activity, and size matching the micropores and throats of reservoirs. On the one hand, they can effectively reduce oil-water interfacial tension, reverse rock surface wettability, and efficiently strip adsorbed residual crude oil from reservoir pores. On the other hand, they can adjust the formation seepage field through the pore-throat temporary plugging effect, block high-permeability water flow channels, and expand the swept volume of the displacing fluid. Nanoparticle-based EOR technology has become the mainstream research direction for improving oil recovery in low-permeability reservoirs at present.

[0006] However, under the shearing action of formation fluids and the adsorption effect of rock pore walls, nanoparticles are prone to irreversible adsorption loss and particle agglomeration failure, making it difficult for them to migrate long distances to reach the deep parts of the oil reservoir. At the same time, nanoparticles have poor stability in high-temperature and high-salinity formation environments and are prone to agglomeration and deactivation.

[0007] Therefore, there is a need to provide a smart chemical displacement agent to achieve deep reservoir profile modification and improve the crude oil recovery rate of low-permeability, high-temperature, and high-salinity reservoirs. Summary of the Invention

[0008] To address the aforementioned issues, a smart chemical flooding agent, its preparation method, and its application are provided. This agent utilizes a quaternary monomer copolymer to form a smart responsive shell, combining excellent temperature and salt resistance with shell mechanical strength to achieve targeted and controlled drug release, avoiding ineffective near-wellbore loss. The internal functions work synergistically to reduce interfacial tension and improve deep profile control. The combination of polyether block copolymers, stabilizers, chelating agents, and sodium gluconate significantly enhances the system's shear stability, scale inhibition, and salt dispersion resistance, thereby achieving efficient deep-seated flooding and improving oil recovery in low-permeability, high-temperature, and high-salinity reservoirs.

[0009] According to one aspect of this application, a smart chemical oil displacement agent is provided, comprising, by weight, 100 parts of nanocapsules, 2-4 parts of polyether block copolymer, 1-2 parts of stabilizer, 0.5-1 parts of chelating agent, and 0.3-0.8 parts of water-soluble salt-resistant dispersant; The nanocapsule comprises a copolymer shell and an internal functional phase. Based on 100 parts of the nanocapsule, the copolymer shell accounts for 60-65 parts and the internal functional phase accounts for 35-40 parts. The copolymer shell is obtained by copolymerizing N-isopropylacrylamide, methacryloylethyl sulfobetaine, methacrylic acid, and isooctyl methacrylate. The internal functional phase includes a modified nanocarrier, an acrylamide-styrene copolymer, and a surfactant. The internal functional phase is uniformly dispersed and anchored within the copolymer shell.

[0010] Specifically, this application employs a quaternary monomer copolymer shell, with each monomer cross-linked synergistically through covalent bonds, balancing temperature-sensitive response, salt resistance, anti-ion properties, and shell flexibility. The internal functional phases are synergistically formulated, with modified nanocarriers and surfactants reducing interfacial tension, and acrylamide-styrene copolymers playing a deep profile control role. Polyether block copolymers optimize the system's rheological properties, stabilizers enhance the shear resistance of nanocapsules, chelating agents complex high-valence ions in the formation, and sodium gluconate improves nanocapsule dispersibility while being calcium and magnesium resistant, inhibiting the precipitation of dodecylphosphonic acid and sulfonate surfactants, thus synergistically enhancing the effect when combined with the chelating agent. The synergistic combination of internal and external components adapts to high-temperature, high-salt, low-permeability reservoirs, preventing premature capsule rupture and failure, achieving deep, controllable profile control, and improving oil recovery.

[0011] Optionally, the modified nanocarrier is nano-silica modified with polydopamine and long-chain alkyl acrylate, and the nano-silica has a particle size of 20~80nm.

[0012] Specifically, this application specifies the modification method for nano-silica. Polydopamine modification can provide abundant active sites, enhance the interfacial bonding force between nanoparticles and internal organic components, and improve the overall compatibility of internal functional phases. Long-chain alkyl acrylates impart hydrophobicity to nano-silica and limit the particle size of nano-silica, so that there is no problem of particle clogging of pore throats, and the nano-size effect can be exerted. At the same time, it avoids the agglomeration and adsorption of nanoparticles, ensures the stable dispersion of nanocarriers, and continuously exerts the wettability reversal oil displacement effect.

[0013] Specifically, the long-chain alkyl acrylate is dodecyl acrylate.

[0014] Optionally, the modified nanocarrier is prepared by the following method: nano-silica and dopamine hydrochloride are added to an alkaline buffer solution and mixed evenly to carry out a self-polymerization reaction to obtain a suspension containing polydopamine-modified nano-silica; the suspension containing polydopamine-modified nano-silica is subjected to solid-liquid separation, washing, and drying to obtain a polydopamine-activated nano-silica intermediate; the nano-silica intermediate is dispersed in anhydrous ethanol, a long-chain alkyl acrylate and an initiator are added, and the reaction is carried out under nitrogen purging and heating at 70-80°C for 3-4 hours. After the reaction is completed, the nanocarrier is centrifuged, washed, and dried to obtain the modified nanocarrier.

[0015] Specifically, this application modifies the nanocarrier in two steps. First, dopamine hydrochloride undergoes self-polymerization in alkaline Tris buffer to form a polydopamine active intermediate layer on the surface of nano-silica, and the nano-silica is activated by hydroxyl and amino groups. Subsequently, long-chain alkyl acrylates are grafted and polymerized under the action of an initiator to form covalent bonds with the polydopamine surface active groups, thereby improving the interfacial compatibility between nano-silica and the oil phase components in the cavity and preventing phase separation between nano-silica and polymers and surfactants.

[0016] Optionally, the mass ratio of nano-silica to dopamine hydrochloride is 1:(0.3~0.5); the alkaline buffer is Tris buffer, and the solid content of nano-silica in the Tris buffer is 5~8wt%; the mass ratio of nano-silica intermediate to long-chain alkyl acrylate is 1:(0.25~0.35); the initiator is azobisisobutyronitrile, and the amount of initiator added is 0.3~0.5% of the mass of long-chain alkyl acrylate.

[0017] Specifically, this application specifies the ratio of raw materials and process parameters for carrier modification. A reasonable ratio of silica to dopamine can ensure uniform coating of the activation layer and avoid excessive self-agglomeration of dopamine. Precise control of the amount of long-chain alkyl acrylate can regulate the degree of hydrophobic modification of the nanocarrier and achieve optimal compatibility with the oil phase. Controlling the amount of azobisisobutyronitrile initiator can ensure that the graft polymerization reaction proceeds fully and avoid excessive initiator leading to increased side reactions and particle agglomeration. At the same time, limiting the solid content of the buffer solution ensures the uniformity and stability of the reaction system and improves the batch stability of the modified nanocarrier.

[0018] Optionally, the polyether block copolymer includes a polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer; the stabilizer is a composite stabilizer comprising nano-aluminum magnesium silicate and iron chromium lignin sulfonate in a mass ratio of 1:(0.8~1); the chelating agent is tetrasodium iminodisuccinate; the water-soluble salt-resistant dispersant is sodium gluconate; and the surfactant is a composite surfactant comprising sodium fatty alcohol ether sulfate and long-chain alkyl imidazoline in a mass ratio of 1:(1~1.2).

[0019] Specifically, the combination of nano-aluminum magnesium silicate and iron-chromium lignin sulfonate enhances the shear stability of nanocapsules; chelating agents can complex calcium and magnesium ions in the formation, blocking the reaction between high-valence ions and anionic surfactants; sodium fatty alcohol ether sulfate and long-chain alkyl imidazoline surfactants are combined to further reduce the oil-water interfacial tension through the synergistic effect of anions and cations; sodium gluconate and other adjuvants are combined to inhibit the aggregation of nanocapsules in high-salt environments, comprehensively improving the formation compatibility of the oil displacement system.

[0020] Specifically, the fatty alcohol ether sulfate includes sodium lauryl polyoxyethylene ether-3 sulfate, and the long-chain alkyl imidazoline includes lauryl imidazoline.

[0021] Optionally, the molar ratio of N-isopropylacrylamide, methacryloylethyl sulfobetaine, methacrylic acid, and isooctyl methacrylate is 1:(0.65~0.85):(0.15~0.25):(0.08~0.12); and the mass ratio of the modified nanocarrier, acrylamide-styrene copolymer, and surfactant in the internal functional phase is (8~12):(14~19):(3~5).

[0022] Specifically, N-isopropylacrylamide, as a thermosensitive monomer, provides the system with temperature-responsive properties; methacryloyl ethyl sulfobetaine, as an amphoteric monomer, enhances the system's salt resistance; and isooctyl methacrylate, as a hydrophobic monomer, improves the shell's oil resistance. The four monomers are copolymerized to obtain the capsule shell. By precisely controlling the ratio of the nanocapsule shell to the inner cavity, the balance between the outer shell's protective strength and the inner cavity's drug loading is ensured. By limiting the ratio of the functional phases in the inner cavity, the components work synergistically, avoiding performance antagonism caused by excessive amounts of a single component, thus achieving a balance between the nanocapsule's structural stability and oil displacement performance.

[0023] Optionally, the internal functional phase further includes dodecylphosphonic acid, wherein the amount of dodecylphosphonic acid is 8-10% of the mass of the modified nanocarrier.

[0024] Specifically, dodecylphosphonic acid relies on the phosphonic acid groups on its surface to form coordination bonds with the hydroxyl groups on the surface of modified nano-silica, and is directionally adsorbed on the surface of the nano-carrier. On the one hand, it can block the acrylamide-styrene copolymer macromolecular chains from encapsulating the nano-active sites, thus solving the defect of the polymer shielding the nano-oil displacement activity in the inner cavity. On the other hand, dodecylphosphonic acid can help complex residual high-valence metal ions in the formation, forming a double ion shielding system with the chelating agent, protecting the surfactant from ion precipitation failure, and has good compatibility with the original components in the inner cavity without any antagonistic effect.

[0025] According to another aspect of this application, a method for preparing the above-mentioned intelligent chemical displacement agent is also provided, comprising the following steps: (1) Take N-isopropylacrylamide, methacryloylethyl sulfobetaine, methacrylic acid, and isooctyl methacrylate according to the ratio, add them to a mixed solvent of water and isopropanol, add crosslinking agent and initiator, stir and dissolve under nitrogen atmosphere to obtain aqueous monomer liquid; (2) Weigh the modified nanocarrier, acrylamide-styrene copolymer, surfactant and dodecylphosphonic acid in sequence according to the ratio and add them to the isododecane solvent. Disperse them evenly by ultrasonication to obtain the functional phase dispersion in the oil phase. (3) Under continuous stirring and nitrogen protection, the functional phase dispersion in the oil phase is slowly and uniformly added to the aqueous monomer solution. After the addition is complete, defoamer GP330 is added and high-speed homogenization emulsification is carried out to form an oil-in-water suspension emulsion. (4) High-purity nitrogen gas is continuously introduced into the suspension emulsion to raise the temperature and react in stages. After the reaction is completed, the mixture is cooled to room temperature to obtain a nanocapsule dispersion. (5) Add polyether block copolymer, stabilizer, chelating agent and water-soluble salt-resistant dispersant to the above nanocapsule dispersion in sequence, stir at room temperature, filter to remove agglomerated particles, and finally obtain intelligent chemical oil displacement agent.

[0026] Specifically, this application employs an oil-in-water suspension polymerization process, in which the aqueous phase quaternary monomers are cross-linked and polymerized to form a copolymer shell, while the oil phase encapsulates all internal functional components. The interaction between the oil and water phases is mild, allowing the internal functional phases to be uniformly anchored on the inner wall of the copolymer shell. Furthermore, it is compounded with polyether block copolymers, stabilizers, chelating agents, and water-soluble anti-salt dispersants, without damaging the already formed structure of the nanocapsules. The preparation processes are seamlessly connected, the interfacial bonding between components is strong, and the nanocapsule structure is stable and not prone to leakage.

[0027] Optionally, in step (1), the stirring time is 30-35 min, the crosslinking agent is N,N'-methylenebisacrylamide, and the amount is 0.8-2% of the total mass of the monomer; the initiator is ammonium persulfate, and the amount is 0.3-0.5% of the total mass of the monomer; in step (2), the ultrasonic power is 200-300 W, and the ultrasonic time is 20-25 min; in step (3), the amount of defoamer added is 0.1-0.15% of the total mass of the aqueous phase and the oil phase, the high-speed homogenization emulsification speed is 8000-9000 rpm, and the time is 10-20 min; in step (4), the temperature is first raised to 55-65℃ and the reaction is kept at a constant temperature for 2.5-3.5 h, and then the temperature is raised to 65-70℃ and the reaction is continued for 3-4 h; in step (5), the stirring time is 25-35 min.

[0028] Specifically, this application limits the process parameters of the preparation method to improve the nanocapsule forming rate and structural integrity, and to achieve good batch repeatability.

[0029] Specifically, this application employs segmented heating polymerization, which effectively avoids defects in the copolymer shell caused by rapid polymerization.

[0030] According to another aspect of this application, the application of the above-described intelligent chemical displacement agent or the intelligent chemical displacement agent prepared by the above-described preparation method in oil extraction is also provided.

[0031] The beneficial effects of this application include, but are not limited to: 1. According to the intelligent chemical flooding agent of this application, a nanocapsule shell is prepared by copolymerization of four functional monomers. Each monomer forms a complementary network through covalent cross-linking and intermolecular hydrogen bonds. N-isopropylacrylamide provides temperature-sensitive responsiveness, methacryloyl ethyl sulfobetaine enhances salt resistance and anti-ion ability, and isooctyl methacrylate enhances shell flexibility and oil resistance. This composite shell can stably encapsulate the internal functional phase during formation migration, resist the shearing action of the wellbore and pores, and accurately respond and release after reaching deep high-temperature oil reservoirs, solving the problems of premature gel breaking and ineffective loss of traditional flooding agents near the wellbore.

[0032] 2. According to the intelligent chemical displacement agent of this application, the modified nano-carrier, surfactant, and acrylamide-styrene copolymer in the internal functional phase play a synergistic role in oil displacement and regulation. At the same time, dodecylphosphonic acid is introduced, and the phosphonic acid group coordinates with the hydroxyl groups on the surface of nano-silica to block the hydrophobic polymer from coating the nano-active sites. Dodecylphosphonic acid can also help complex high-valence ions in the formation and form a compatible protective system with the internal surfactant to avoid surfactant failure and precipitation, thus taking into account multiple functions of oil displacement such as wettability reversal, interfacial tension reduction, and deep profile regulation.

[0033] 3. The intelligent chemical oil displacement agent of this application is formulated with four types of additives: polyether block copolymer, stabilizer, chelating agent, and water-soluble salt-resistant dispersant. These additives work synergistically. The polyether block copolymer regulates the rheological properties of the system, while the combination of nano-aluminum magnesium silicate and iron-chromium lignin sulfonate enhances the shear resistance of the nanocapsules. The chelating agent complexes calcium and magnesium ions to inhibit scale formation, and sodium gluconate inhibits nanocapsule aggregation. The polyether block copolymer, stabilizer, chelating agent, and water-soluble salt-resistant dispersant have good compatibility with the nanocapsules and do not damage the shell structure of the nanocapsules, thus significantly improving the dispersibility and long-term stability of the oil displacement agent in high-salt formations.

[0034] 4. According to the preparation method of the intelligent chemical oil displacement agent of this application, the oil displacement agent is prepared into nanocapsules by water-in-oil suspension polymerization process. The process parameters are controllable, the preparation method of the oil displacement agent is simple and easy to operate, and it is easy to promote. Detailed Implementation

[0035] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of skill in the art. The reagents and raw materials used in this invention are readily available through conventional means, and unless otherwise specified, they are used in accordance with conventional methods or product instructions. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to the methods of this invention. The preferred embodiments and materials described in this patent are for illustrative purposes only. The polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymers involved in the following examples and comparative examples have a molecular weight of 5000-10000; the nano-silica has a particle size of 50 nm; and the polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer is poloxamer 184.

[0037] Example 1: Preparation of a smart chemical displacement agent The nanocapsules prepared in this embodiment are based on 100 parts by weight, of which 60 parts are copolymer shell and 40 parts are internal functional phase.

[0038] (1) Take the raw material monomers according to the molar ratio of N-isopropylacrylamide, methacryloylethyl sulfobetaine, methacrylic acid, and isooctyl methacrylate of 1:0.65:0.15:0.08, add them to a mixed solvent of water and isopropanol (the mass ratio of water to isopropanol is 7:1), add a crosslinking agent and an initiator. The crosslinking agent is N,N'-methylenebisacrylamide, and the amount used is 0.8% of the total mass of the monomers; the initiator is ammonium persulfate, and the amount used is 0.3% of the total mass of the monomers. The total mass of all monomers, crosslinking agents, and initiators accounts for 10% of the total mass of the mixed solvent of water and isopropanol. Stir for 30 min under a nitrogen atmosphere to dissolve and obtain an aqueous monomer solution. (2) Weigh the modified nanocarrier, acrylamide-styrene copolymer, composite surfactant (lauryl polyoxyethylene ether-3-sulfate: lauryl imidazoline = 1:1) and dodecylphosphonic acid in sequence according to the ratio and add them to the isododecane solvent. The mass ratio of modified nanocarrier, acrylamide-styrene copolymer and composite surfactant is 8:14:3. The amount of dodecylphosphonic acid is 8% of the mass of modified nanocarrier. The total mass of the solid phase of modified nanocarrier, acrylamide-styrene copolymer, composite surfactant and dodecylphosphonic acid accounts for 15% of the mass of isododecane. Disperse evenly by ultrasonication with an ultrasonic power of 200W and an ultrasonic time of 20min to obtain the functional phase dispersion in the oil phase. (3) Under continuous stirring and nitrogen protection, the functional phase dispersion in the oil phase is slowly and uniformly added to the aqueous monomer solution. After the addition is complete, defoamer GP330 is added and high-speed homogenization emulsification is performed. The amount of defoamer added is 0.1% of the total mass of the aqueous and oil phases. The high-speed homogenization emulsification speed is 8000 rpm and the time is 10 min to form an oil-in-water suspension emulsion. (4) High-purity nitrogen gas was continuously introduced into the suspension emulsion and the temperature was raised to a staged reaction. First, the temperature was raised to 55°C and kept constant for 2.5 hours, and then the temperature was raised to 65°C and the reaction continued for 3 hours. After the reaction was completed, the mixture was cooled to room temperature to obtain a nanocapsule dispersion. (5) Add 2 parts of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer, 1 part of composite stabilizer (the mass ratio of nano-aluminum magnesium silicate to iron chromium lignin sulfonate is 1:0.8), 0.5 parts of chelating agent tetrasodium iminodisuccinate, and 0.3 parts of water-soluble salt-resistant dispersant sodium gluconate to a nanocapsule dispersion containing 100 parts by weight. Stir at room temperature, filter to remove agglomerated particles, and finally obtain the intelligent chemical oil displacement agent.

[0039] in, The modified nanocarrier was prepared by the following method: Nano-silica and dopamine hydrochloride were added to Tris buffer and mixed evenly to carry out a self-polymerization reaction. The mass ratio of nano-silica to dopamine hydrochloride was 1:0.3. The solid content of nano-silica in the Tris buffer was 5 wt%, resulting in a suspension containing polydopamine-modified nano-silica. The suspension containing polydopamine-modified nano-silica was subjected to solid-liquid separation, washing, and drying to obtain a polydopamine-activated nano-silica intermediate. The nano-silica intermediate was dispersed in anhydrous ethanol at a mass ratio of 1:8. Long-chain alkyl acrylate dodecyl acrylate and azobisisobutyronitrile were added at a mass ratio of 1:0.25. The amount of initiator added was 0.3% of the mass of long-chain alkyl acrylate dodecyl acrylate. The reaction was carried out under nitrogen purging and heated at 70°C for 3 h. After the reaction was completed, the nanocarrier was centrifuged, washed, and dried to obtain the modified nanocarrier.

[0040] Example 2: Preparation of a smart chemical displacement agent The nanocapsules prepared in this embodiment are based on 100 parts by weight, of which the copolymer shell accounts for 65 parts and the internal functional phase accounts for 35 parts.

[0041] (1) Take the raw material monomers according to the molar ratio of N-isopropylacrylamide, methacryloylethyl sulfobetaine, methacrylic acid, and isooctyl methacrylate of 1:0.85:0.25:0.12, add them to a mixed solvent of water and isopropanol (the mass ratio of water to isopropanol is 8:1), add a crosslinking agent and an initiator. The crosslinking agent is N,N'-methylenebisacrylamide, and the amount used is 2% of the total mass of the monomers; the initiator is ammonium persulfate, and the amount used is 0.5% of the total mass of the monomers. The total mass of all monomers, crosslinking agents, and initiators accounts for 12% of the total mass of the mixed solvent of water and isopropanol. Stir for 35 min under a nitrogen atmosphere to dissolve and obtain an aqueous monomer solution. (2) Weigh the modified nanocarrier, acrylamide-styrene copolymer, composite surfactant (lauryl polyoxyethylene ether-3-sulfate sodium: lauryl imidazoline = 1:1.2) and dodecylphosphonic acid in sequence according to the ratio and add them to the isododecane solvent. The mass ratio of modified nanocarrier, acrylamide-styrene copolymer and composite surfactant is 12:19:5. The amount of dodecylphosphonic acid is 10% of the mass of modified nanocarrier. The total mass of the solid phase of modified nanocarrier, acrylamide-styrene copolymer, composite surfactant and dodecylphosphonic acid accounts for 20% of the mass of isododecane. Disperse evenly by ultrasonication with an ultrasonic power of 300W and an ultrasonic time of 25min to obtain the functional phase dispersion in the oil phase. (3) Under continuous stirring and nitrogen protection, the functional phase dispersion in the oil phase is slowly and uniformly added to the aqueous phase monomer solution. After the addition is complete, defoamer GP330 is added and high-speed homogenization emulsification is performed. The amount of defoamer added is 0.15% of the total mass of the aqueous and oil phases. The high-speed homogenization emulsification speed is 9000 rpm and the time is 20 min to form an oil-in-water suspension emulsion. (4) High-purity nitrogen gas was continuously introduced into the suspension emulsion and the temperature was raised to staged reaction. First, the temperature was raised to 65°C and kept constant for 3.5 h, and then the temperature was raised to 70°C and the reaction continued for 4 h. After the reaction was completed, the mixture was cooled to room temperature to obtain nanocapsule dispersion. (5) To a nanocapsule dispersion containing 100 parts by weight of nanocapsules, add sequentially 4 parts of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer, 2 parts of composite stabilizer (nano-aluminum magnesium silicate and iron-chromium lignin sulfonate in a mass ratio of 1:1), 1 part of chelating agent tetrasodium iminodisuccinate, and 0.8 parts of water-soluble salt-resistant dispersant sodium gluconate. Stir at room temperature, filter to remove agglomerated particles, and finally obtain the intelligent chemical oil displacement agent. The modified nanocarrier was prepared by the following method: Nano-silica and dopamine hydrochloride were added to Tris buffer and mixed evenly to carry out a self-polymerization reaction. The mass ratio of nano-silica to dopamine hydrochloride was 1:0.5. The solid content of nano-silica in the Tris buffer was 8 wt%, resulting in a suspension containing polydopamine-modified nano-silica. The suspension containing polydopamine-modified nano-silica was subjected to solid-liquid separation, washing, and drying to obtain a polydopamine-activated nano-silica intermediate. The nano-silica intermediate was dispersed in anhydrous ethanol at a mass ratio of 1:10. Long-chain alkyl acrylate dodecyl acrylate and azobisisobutyronitrile were added at a mass ratio of 1:0.35. The amount of initiator added was 0.5% of the mass of long-chain alkyl acrylate dodecyl acrylate. The reaction was carried out under nitrogen purging and heated at 80°C for 4 h. After the reaction was completed, the nanocarrier was centrifuged, washed, and dried to obtain the modified nanocarrier.

[0042] Example 3: Preparation of a smart chemical displacement agent The nanocapsules prepared in this embodiment are based on 100 parts by weight, of which the copolymer shell accounts for 62 parts and the internal functional phase accounts for 38 parts.

[0043] (1) Take the raw material monomers according to the molar ratio of N-isopropylacrylamide, methacryloylethyl sulfobetaine, methacrylic acid, and isooctyl methacrylate of 1:0.75:0.2:0.1, add them to a mixed solvent of water and isopropanol (the mass ratio of water to isopropanol is 7:1), add a crosslinking agent and an initiator. The crosslinking agent is N,N'-methylenebisacrylamide, and the amount used is 1% of the total mass of the monomers; the initiator is ammonium persulfate, and the amount used is 0.4% of the total mass of the monomers. The total mass of all monomers, crosslinking agents, and initiators accounts for 11% of the total mass of the mixed solvent of water and isopropanol. Stir for 32 min under a nitrogen atmosphere to dissolve and obtain an aqueous monomer solution. (2) Weigh the modified nanocarrier, acrylamide-styrene copolymer, composite surfactant (lauryl polyoxyethylene ether-3-sulfate sodium: lauryl imidazoline = 1:1.1) and dodecylphosphonic acid in sequence according to the ratio and add them to the isododecane solvent. The mass ratio of modified nanocarrier, acrylamide-styrene copolymer and composite surfactant is 10:15:4. The amount of dodecylphosphonic acid is 9% of the mass of modified nanocarrier. The total mass of the solid phase of modified nanocarrier, acrylamide-styrene copolymer, composite surfactant and dodecylphosphonic acid accounts for 18% of the mass of isododecane. Disperse evenly by ultrasonication with an ultrasonic power of 250W and an ultrasonic time of 22min to obtain the functional phase dispersion in the oil phase. (3) Under continuous stirring and nitrogen protection, the functional phase dispersion in the oil phase is slowly and uniformly added to the aqueous monomer solution. After the addition is complete, defoamer GP330 is added and high-speed homogenization emulsification is performed. The amount of defoamer added is 0.12% of the total mass of the aqueous and oil phases. The high-speed homogenization emulsification speed is 8500 rpm and the time is 15 min to form an oil-in-water suspension emulsion. (4) High-purity nitrogen gas was continuously introduced into the suspension emulsion and the temperature was raised to staged reaction. First, the temperature was raised to 60°C and kept constant for 3 hours, and then the temperature was raised to 65°C and the reaction continued for 3.5 hours. After the reaction was completed, the mixture was cooled to room temperature to obtain the nanocapsule dispersion. (5) Add 3 parts of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer, 1.5 parts of composite stabilizer (the mass ratio of nano-aluminum magnesium silicate to iron chromium lignin sulfonate is 1:0.9), 0.7 parts of chelating agent tetrasodium iminodisuccinate, and 0.5 parts of water-soluble salt-resistant dispersant sodium gluconate to a nanocapsule dispersion containing 100 parts by weight. Stir at room temperature, filter to remove agglomerated particles, and finally obtain the intelligent chemical oil displacement agent.

[0044] in, The modified nanocarrier was prepared by the following method: Nano-silica and dopamine hydrochloride were added to Tris buffer and mixed evenly to carry out a self-polymerization reaction. The mass ratio of nano-silica to dopamine hydrochloride was 1:0.4. The solid content of nano-silica in the Tris buffer was 6 wt%, resulting in a suspension containing polydopamine-modified nano-silica. The suspension containing polydopamine-modified nano-silica was subjected to solid-liquid separation, washing, and drying to obtain a polydopamine-activated nano-silica intermediate. The nano-silica intermediate was dispersed in anhydrous ethanol at a mass ratio of 1:9. Long-chain alkyl acrylate dodecyl acrylate and azobisisobutyronitrile were added at a mass ratio of 1:0.3. The amount of initiator added was 0.4% of the mass of long-chain alkyl acrylate dodecyl acrylate. The reaction was carried out under nitrogen purging and heated at 75°C for 3.5 h. After the reaction was completed, the nanocarrier was centrifuged, washed, and dried to obtain the modified nanocarrier.

[0045] Example 4 The difference between Example 4 and Example 3 is that the internal functional phase does not include dodecylphosphonic acid, while the rest are the same.

[0046] Example 5 The difference between Example 5 and Example 3 is that the composite surfactant does not include long-chain alkyl imidazoline, but only sodium lauryl ether-3 sulfate is used as the surfactant, while the rest are the same.

[0047] Example 6 The difference between Example 6 and Example 3 is that the composite stabilizer does not include nano-aluminum magnesium silicate, but only iron-chromium lignin sulfonate is used as the stabilizer, while the rest are the same.

[0048] Comparative Example 1 The difference between Comparative Example 1 and Example 3 is that the latter does not include isooctyl methacrylate, while all other aspects are the same.

[0049] Comparative Example 2 The difference between Comparative Example 2 and Example 3 is that unmodified nano-silica was used as the nanocarrier; all other aspects are the same. Comparative Example 3 The difference between Comparative Example 3 and Example 3 is that Comparative Example 3 does not include the polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer, but all other aspects are the same.

[0050] Test case In the following test examples, tests were conducted simulating low-permeability, high-temperature, and high-salinity reservoir conditions: test temperature 68℃; simulated formation water total salinity 15×10⁻⁶. 4The specific preparation method for the mg / L solution is as follows: Dissolve NaCl, KCl, CaCl2, and MgCl2·6H2O in deionized water, with the following composition: NaCl 75.59 g / L, KCl 19.07 g / L, CaCl2 23.54 g / L, and MgCl2·6H2O 71.10 g / L. The oil used in the experiment was simulated crude oil in the field. The permeability of the artificial low-permeability homogeneous core was 5~10 mD. All reagents in the examples and comparative examples were uniformly diluted to the concentration injected in the field to ensure single-variable comparison.

[0051] Experimental Example 1: Oil-Water Interfacial Tension Test A rotating drop ultra-low interfacial tension meter was used, with the test temperature set at 68℃, to test the equilibrium oil-water interfacial tension between each group of oil displacement agents and simulated crude oil. The lower the interfacial tension value, the stronger the agent's ability to strip residual oil from rock pores and improve the oil-water interface properties, resulting in superior oil washing and displacement performance. The test results are shown in Table 1.

[0052] Table 1. Results of oil-water interfacial tension test

[0053] As shown in Table 1, Examples 1-3 can all achieve 10. -3 Ultra-low interfacial tension. In Example 5, the removal of long-chain alkyl imidazoline resulted in the disappearance of the synergistic effect of anionic and cationic surfactants, leading to the largest increase in interfacial tension. In Example 4, the lack of dodecylphosphonic acid resulted in the nano-active sites being masked by the polymer, leading to a decrease in interfacial activity. Comparative Example 1 exhibited shell defects, and Comparative Example 3 lacked polyether additives, resulting in poorer interfacial regulation capabilities.

[0054] Experiment Example 2 Stability Test 50 mL of the oil displacement agent samples prepared in the above examples and comparative examples were measured and placed in sealed pressure-resistant reagent bottles. The samples were kept at a constant temperature of 68°C for 7 days to observe whether the samples showed stratification, flocculation, precipitation, or capsule rupture. The average particle size and particle size distribution index (PDI) of the nanocapsules before and after the static test were detected by a dynamic light scattering instrument. The growth rate of the capsule particle size was calculated. The lower the growth rate of the particle size, the better the long-term stability of the oil displacement agent in the high-temperature and high-salinity formation water environment. The equilibrium interfacial tension was also measured. The test results are shown in Table 2.

[0055] Table 2 Stability Test Results

[0056] Table 2 shows that the particle size growth rate of Examples 1-3 was less than 8%, indicating excellent stability of the high-temperature, high-salt system. Furthermore, after 7 days of constant-temperature aging in simulated high-mineralized formation water at 68℃, the interfacial tension of the three groups of samples only increased slightly, remaining at around 10. -3Within the extremely low interfacial tension range, Example 3 is the optimal embodiment, exhibiting the most stable capsule structure. Examples 4 and 6, lacking dodecylphosphonic acid and magnesium aluminum silicate, show significantly reduced stability, with interfacial tension increasing dramatically to 10. -2 The comparative examples 1 and 3, which lacked the hydrophobic monomer and polyether block copolymer in the outer shell, showed insufficient shell strength and lack of a hydration stabilization network, resulting in severe stratification and agglomeration, a significant increase in particle size, and the most significant increase in interfacial tension. This demonstrates that the components work together to ensure the high-temperature and high-salt stability of the capsules.

[0057] Test Example 3: Quartz Surface Wetting Angle Test The wetting angle of the oil displacement agents prepared in the above examples and comparative examples on the quartz surface was measured according to the provisions of Chapter 5 of SY / T 5153-2007. The test results are shown in Table 3.

[0058] Table 3 Results of Quartz Surface Wetting Angle Test

[0059] Table 3 shows that after treatment in Examples 1-3, the wetting angle decreased to below 45°, successfully transitioning to a favorable wettable state, with Example 3 being the best (35.4°). Examples 4-6 lacked the core functional component, and the wetting angle increased significantly to above 69°; the wetting angles of Comparative Examples 1-3 were above 80°, failing to achieve effective wetting reversal.

[0060] Experimental Example 4 Recovery Rate Test The following are the specific steps for conducting indoor physical simulation displacement tests using a standard core displacement apparatus: (1) The core was saturated with simulated formation water, and the permeability of the water phase in the core was measured; then, simulated crude oil was saturated and aged at 68℃ for 24 hours to restore the state of crude oil in the formation; (2) Water flooding was continued until the water cut at the core outlet reached 98%, and the basic water flooding recovery rate was recorded; (3) 0.5PV of the corresponding group of intelligent chemical flooding agent was injected into the core, and the well was shut in and left to stand for 12 hours to achieve formation adsorption and response release of the agent; (4) Subsequent secondary water flooding was carried out until the water cut at the outlet reached 98% again, and the crude oil recovery rate increase value corresponding to chemical flooding was calculated. The test results are shown in Table 4.

[0061] Table 4 Recovery Rate Test Results

[0062] Table 4 shows that the recovery improvement of Examples 1-3 was much higher than that of the other groups, with Example 3 showing the best overall oil displacement effect. All examples lacking a single functional component showed a significant decrease in oil displacement effect; the three comparative examples lacked the hydrophobic monomer on the outer shell, the modified nanocarrier, and the polyether stabilizer, respectively, resulting in unstable drug transport and ineffective drug release, leading to the lowest recovery improvement.

[0063] The above description is merely an embodiment of this application, and the scope of protection of this application is not limited to these specific embodiments, but is determined by the claims of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the technical concept and principles of this application should be included within the scope of protection of this application.

Claims

1. A smart chemical displacement agent, characterized in that, Based on parts by weight, it includes 100 parts of nanocapsules, 2-4 parts of polyether block copolymer, 1-2 parts of stabilizer, 0.5-1 part of chelating agent, and 0.3-0.8 parts of water-soluble salt-resistant dispersant; The nanocapsule comprises a copolymer shell and an internal functional phase. Based on 100 parts of the nanocapsule, the copolymer shell accounts for 60-65 parts and the internal functional phase accounts for 35-40 parts. The copolymer shell is obtained by copolymerizing N-isopropylacrylamide, methacryloylethyl sulfobetaine, methacrylic acid, and isooctyl methacrylate. The internal functional phase includes a modified nanocarrier, an acrylamide-styrene copolymer, and a surfactant. The internal functional phase is uniformly dispersed and anchored within the copolymer shell.

2. The intelligent chemical displacement agent according to claim 1, characterized in that, The modified nanocarrier is nano-silica modified with polydopamine and long-chain alkyl acrylate, and the particle size of the nano-silica is 20~80nm.

3. The intelligent chemical displacement agent according to claim 2, characterized in that, The modified nanocarrier was prepared by the following method: nano-silica and dopamine hydrochloride were added to an alkaline buffer solution and mixed evenly to carry out a self-polymerization reaction to obtain a suspension containing polydopamine-modified nano-silica; the suspension containing polydopamine-modified nano-silica was subjected to solid-liquid separation, washing, and drying to obtain a polydopamine-activated nano-silica intermediate; the nano-silica intermediate was dispersed in anhydrous ethanol, a long-chain alkyl acrylate and an initiator were added, and the reaction was carried out under nitrogen purging and heating at 70-80°C for 3-4 hours. After the reaction was completed, the nanocarrier was centrifuged, washed, and dried to obtain the modified nanocarrier.

4. The intelligent chemical displacement agent according to claim 3, characterized in that, The mass ratio of nano-silica to dopamine hydrochloride is 1:(0.3~0.5); the alkaline buffer is Tris buffer, and the solid content of nano-silica in the Tris buffer is 5~8wt%; the mass ratio of nano-silica intermediate to long-chain alkyl acrylate is 1:(0.25~0.35); the initiator is azobisisobutyronitrile, and the amount of initiator added is 0.3~0.5% of the mass of long-chain alkyl acrylate.

5. The intelligent chemical displacement agent according to claim 1, characterized in that, The polyether block copolymer includes a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer; the stabilizer is a composite stabilizer comprising nano-aluminum magnesium silicate and iron-chromium lignin sulfonate in a mass ratio of 1:(0.8~1); the chelating agent is tetrasodium iminodisuccinate; the water-soluble salt-resistant dispersant is sodium gluconate; and the surfactant is a composite surfactant comprising sodium fatty alcohol ether sulfate and long-chain alkyl imidazoline in a mass ratio of 1:(1~1.2).

6. The intelligent chemical displacement agent according to claim 1, characterized in that, The molar ratio of N-isopropylacrylamide, methacryloylethyl sulfobetaine, methacrylic acid, and isooctyl methacrylate is 1:(0.65~0.85):(0.15~0.25):(0.08~0.12); in the internal functional phase, the mass ratio of modified nanocarrier, acrylamide-styrene copolymer, and surfactant is (8~12):(14~19):(3~5).

7. The intelligent chemical displacement agent according to claim 1, characterized in that, The internal functional phase also includes dodecylphosphonic acid, and the amount of dodecylphosphonic acid is 8-10% of the mass of the modified nanocarrier.

8. The method for preparing the intelligent chemical displacement agent according to any one of claims 1 to 7, characterized in that, Includes the following steps: (1) Take N-isopropylacrylamide, methacryloylethyl sulfobetaine, methacrylic acid, and isooctyl methacrylate according to the ratio, add them to a mixed solvent of water and isopropanol, add crosslinking agent and initiator, stir and dissolve under nitrogen atmosphere to obtain aqueous monomer liquid; (2) Weigh the modified nanocarrier, acrylamide-styrene copolymer, surfactant and dodecylphosphonic acid in sequence according to the ratio and add them to the isododecane solvent. Disperse them evenly by ultrasonication to obtain the functional phase dispersion in the oil phase. (3) Under continuous stirring and nitrogen protection, the functional phase dispersion in the oil phase is slowly and uniformly added to the aqueous monomer solution. After the addition is complete, defoamer GP330 is added and high-speed homogenization emulsification is carried out to form an oil-in-water suspension emulsion. (4) High-purity nitrogen gas is continuously introduced into the suspension emulsion to raise the temperature and react in stages. After the reaction is completed, the mixture is cooled to room temperature to obtain a nanocapsule dispersion. (5) Add polyether block copolymer, stabilizer, chelating agent and water-soluble salt-resistant dispersant to the above nanocapsule dispersion in sequence, stir at room temperature, filter to remove agglomerated particles, and finally obtain intelligent chemical oil displacement agent.

9. The preparation method of the intelligent chemical displacement agent according to claim 8, characterized in that, In step (1), the stirring time is 30-35 min, the crosslinking agent is N,N'-methylenebisacrylamide, and the amount is 0.8-2% of the total mass of the monomers; the initiator is ammonium persulfate, and the amount is 0.3-0.5% of the total mass of the monomers; in step (2), the ultrasonic power is 200-300W, and the ultrasonic time is 20-25 min; in step (3), the amount of defoamer added is 0.1-0.15% of the total mass of the aqueous phase and the oil phase, the high-speed homogenization emulsification speed is 8000-9000 rpm, and the time is 10-20 min; in step (4), the temperature is first raised to 55-65℃ and the reaction is kept at a constant temperature for 2.5-3.5 h, and then the temperature is raised to 65-70℃ and the reaction is continued for 3-4 h; in step (5), the stirring time is 25-35 min.

10. The application of the intelligent chemical displacement agent according to any one of claims 1 to 7 or the intelligent chemical displacement agent prepared by the preparation method according to any one of claims 8 to 9 in oil extraction.

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