A bifunctional polyelectrolyte nanoparticle material, a preparation method thereof and application thereof in carbon dioxide flooding

Abstract

The application provides a kind of bifunctional polyelectrolyte nanoparticle material and its preparation method and its application in carbon dioxide flooding.The bifunctional polyelectrolyte nanoparticle material is core-shell structure, which is obtained by positive and negative electric adsorption after dissolving anionic CO2 response multi-copolymer and cationic CO2 body swelling gel microsphere material.The application also provides the preparation method of the above-mentioned bifunctional polyelectrolyte nanoparticle material and its application in carbon dioxide flooding.The bifunctional polyelectrolyte nanoparticle material provided by the application can be used for gas channeling large channel plugging, and after the "core-shell" separation of the nanoparticle material, the released inner core body swelling gel microsphere contacts CO2 to occur secondary expansion and efficiently plugs gas channeling channel.

Description

Technical Field

[0001] This invention relates to a bifunctional polyelectrolyte composite nanoparticle material, its preparation method, and its application in carbon dioxide flooding, belonging to the field of CO2 flooding technology. Background Technology

[0002] CO2 flooding is a crucial component of CO2 geological utilization in carbon capture, utilization, and storage (CCUS) technology, and also a key technology for improving oil recovery. Compared to traditional chemical flooding, CO2 flooding increases sweep efficiency, significantly removes residual oil, and effectively utilizes and stores large amounts of CO2. Based on the flooding method, CO2 flooding technology in low-permeability tight oil reservoirs primarily uses miscible CO2 flooding, supplemented by immiscible CO2 flooding. Both technologies involve injecting liquid CO2 into the formation to form supercritical fluid (scCO2) that enters the matrix. However, due to environmental factors and CO2 channeling, some CO2 precipitates from the scCO2 before entering the matrix. This precipitated CO2 not only struggles to enter the micro-nano scale matrix but also forms gas locks within the pores, hindering subsequent fluid entry and significantly impeding the effectiveness of CO2 flooding. Therefore, effectively controlling precipitated CO2 and efficiently blocking gas channeling is a major technical bottleneck restricting the success of CCUS-EOR construction in low-permeability tight oil reservoirs.

[0003] Based on the oil displacement method, low-permeability tight oil reservoirs in CCUS-EOR primarily utilize CO2 miscible flooding technology, supplemented by CO2 immiscible flooding, and also employ alternating slug waterflooding (WAG) technology. After entering the formation in liquid form, most of the CO2 forms a supercritical flow state and enters the matrix to displace the remaining oil. Due to formation environmental factors and gas channeling issues, some CO2 precipitates before entering the matrix, forming gas locks within micro- and nano-pores that block subsequent fluid flow, significantly hindering CO2 oil displacement efficiency.

[0004] To address gas channeling, CN111139051A provides a method for preparing and applying a CO2 foam sealing agent. This method utilizes the released CO2 to form a CO2 foam of a certain strength to block large channels, maintain reservoir pressure, and improve the sweep efficiency of scCO2. Specifically, it utilizes quaternary ammonium salt imidazoline molecules and hydroxyethyl cellulose molecules to form high-strength foam with CO2 to achieve the purpose of sealing large channels. This type of technology aims to use emulsification to form water-based foam after a large amount of CO2 is released, thereby achieving the purpose of sealing. However, after CO2 is released, it is difficult to enter the matrix and form gas locks in the micro-nano-sized pores of the matrix, which has a greater impact on scCO2 oil displacement. Moreover, there is currently no good solution for the gas locks formed by prematurely released CO2 in micro-nano-pores. In addition to using chemical plugging agents to block large channels, current methods to suppress CO2 release mainly involve using chemical methods to thicken the viscosity of injected CO2 and micro-foaming the released CO2 to increase its fluidity.

[0005] Bernard and Hold first proposed in 1967 the use of surfactants to form stable water-based CO2 foam in reservoirs for synergistic oil and gas extraction. For example, CN110317598B and CN114876425B provide two water-soluble surfactants suitable for scCO2 and WAG technologies, respectively. The agents used are wettability improvers such as sodium fatty alcohol polyoxyethylene ether sulfate and sodium α-alkenyl sulfonate, and CO2-loving polymers such as polyvinylpyrrolidone, aiming to further efficiently utilize precipitated CO2 to form foam for oil displacement. However, due to the lack of shear force in the reservoir environment, when a large amount of CO2 has already been precipitated, the remedial formation of CO2-water-based microfoam is unstable, and the particle size of the formed microfoam is uncontrollable. CN104334679B utilizes a nonionic surfactant to form stable oil-based CO2 foam from CO2 precipitated after entering the matrix. This CO2-oil-based foam has a higher effective viscosity in the matrix compared to pure gas, increasing crude oil fluidity. CN111909679B discloses an oil-soluble surfactant that explores its ability to reduce the minimum miscibility pressure between CO2 and crude oil, forming micron-sized foams to improve matrix-based oil displacement efficiency. However, due to insufficient reservoir fluid shear force, the particle size and stability of the formed CO2-oil-based microfoams cannot be guaranteed. Other research focuses on thickening CO2 surfactants, aiming to prevent and reduce the impact of gas channeling and other viscous fingering problems on scCO2 migration by increasing the viscosity of scCO2. Currently, CO2 thickeners are mainly classified into siloxane thickeners, fluoroolefin thickeners, and oxycarbon thickeners. However, their application is economically constrained due to the relatively high required concentration (generally greater than 0.2%).

[0006] In summary, existing chemical methods for controlling gas channeling face three main challenges: ① Thickening scCO2 increases injection pressure, raising construction difficulty and posing safety risks to equipment and personnel; ② Insufficient reservoir shear forces result in uncontrollable foam particle size from precipitated CO2, failing to meet the requirements for matrix entry; ③ Given the temporal and spatial overlap between CO2 precipitation and channeling, controlling the injection of a single chemical agent cannot simultaneously address both issues. Therefore, achieving in-situ control of CO2 precipitation and precise deep channeling prevention is a key step in overcoming these technical bottlenecks, and existing CO2 enhancement and anti-channeling technologies no longer meet this new requirement. Summary of the Invention

[0007] To address the aforementioned technical problems, the present invention aims to provide a bifunctional polyelectrolyte nanoparticle material and its preparation method. This bifunctional polyelectrolyte nanoparticle material can solve the problems of CO2 evolution and gas channeling.

[0008] To achieve the above objectives, the present invention provides a bifunctional polyelectrolyte nanoparticle material, wherein the bifunctional polyelectrolyte nanoparticle material has a core-shell structure and is obtained by dissolving anionic CO2-responsive multi-component copolymer and cationic CO2-swellable gel microsphere material and then adsorbing them through positive and negative charge.

[0009] The anionic CO2-responsive multi-component copolymer is prepared by the RAFT addition polymerization reaction proposed in CN116425931A, specifically through the following steps: a Pluronic block polymer undergoes a reversible addition-fragmentation chain transfer esterification reaction with a chain transfer agent to obtain a RAFT precursor polymer; the RAFT precursor polymer undergoes a primary addition polymerization reaction with a perfluoroacrylate monomer; the product of the primary addition polymerization reaction undergoes a secondary addition polymerization reaction with a propanesulfonic acid-containing monomer to obtain the anionic CO2-responsive multi-component copolymer; the CO2-responsive anionic multi-component copolymer contains one or more functional groups that exhibit negative electrochemical properties upon hydrolysis.

[0010] The cationic CO2-swellable gel microspheres are prepared by a polymerization reaction based on organic solvent impregnation, using two or more polymeric materials to form an interpenetrating network structure through a cross-linking reaction, wherein the polymeric materials include at least one CO2-loving polymeric material.

[0011] According to a specific embodiment of the present invention, preferably, the average molecular weight of the CO2-responsive anionic multi-component copolymer material is 5000 Da-30000 Da.

[0012] According to a specific embodiment of the present invention, preferably, the Pluronic block polymer includes one or more of Pluronic P-123, Pluronic 17R4, Pluronic F-68, Pluronic F-127 and Pluronic L-121.

[0013] According to a specific embodiment of the present invention, preferably, the chain transfer agent comprises 4-cyano-4-thiopropylthiovalerate and / or S-dodecyl-S'-(α,α'-dimethyl-α”-acetic acid) trithiocarbonate;

[0014] According to a specific embodiment of the present invention, preferably, the perfluoroacrylate monomer includes 1H,1H,2H,2H-perfluorodecyl acrylate and / or hexafluorobutyl methacrylate.

[0015] According to a specific embodiment of the present invention, preferably, the propanesulfonic acid-containing monomer includes one of 2-acrylamide-2-methylpropanesulfonic acid (AMPS), oleic acid imidazoline sulfonate, N,N-dimethyl-dithiocarbamate propanesulfonic acid, and sodium 3-chloro-2-hydroxypropanesulfonate.

[0016] According to a specific embodiment of the present invention, preferably, the cationic CO2-swellable gel microspheres are prepared using polymeric materials that include at least CO2-loving polymeric materials and pH-responsive polymeric materials.

[0017] According to a specific embodiment of the present invention, preferably, the CO2-loving polymer material is a polymer material prepared by copolymerization of CO2-loving monomers and hydrophilic monomers, or a polymer material with inherent CO2-loving properties. That is, the CO2-loving polymer is a polymer material prepared by copolymerization of CO2-loving monomers and hydrophilic monomers, or a polymer material with inherent CO2-loving properties is directly used. More preferably, the CO2-loving monomer includes one or more combinations of perfluoroacrylate (TPA), 1H,1H,2H,2H-perfluorodecyl acrylate (FDA), and hexafluorobutyl methacrylate (HFBMA); the hydrophilic monomer includes one or more combinations of 2-acrylamido-2-methylpropanesulfonic acid (AMPS), acrylamide (AM), vinyl alcohol, and vinyl acetate; and the polymer material with inherent CO2-loving properties includes one or more combinations of polydimethylsiloxane (PDMS) and its derivatives.

[0018] According to a specific embodiment of the present invention, preferably, the pH-responsive polymer material is a polymer material capable of undergoing an amine matrix protonation reaction, preferably including linear polyethyleneimine (PEI) and / or branched polyethyleneimine (B-PEI), etc.

[0019] According to a specific embodiment of the present invention, preferably, in the process of preparing cationic CO2 bulked gel microspheres, the crosslinking agent of the crosslinking reaction includes one or more of N,N'-methylenebisacrylamide (MBAA), glutaraldehyde (GA), and 1,4-butanediol diglycidyl ether.

[0020] According to a specific embodiment of the present invention, preferably, in the process of preparing cationic CO2 bulked gel microspheres, the crosslinking reaction includes a crosslinking method of one polymer material and a crosslinking method of two polymer materials.

[0021] According to a specific embodiment of the present invention, the "core" structure CO2 bulk gel microspheres in the bifunctional polyelectrolyte composite nanoparticle material of the present invention contain CO2-loving polymer chains, pH-responsive polymer chains, and crosslinking agent molecules.

[0022] According to a specific embodiment of the present invention, preferably, the average particle size of the bifunctional polyelectrolyte nanoparticle material is about 100 nm to 1.3 μm.

[0023] According to a specific embodiment of the present invention, preferably, the average particle size of the cationic CO2 bulk-swellable gel microsphere material is about 80 nm to 900 nm.

[0024] The bifunctional polyelectrolyte nanoparticle material provided by this invention is a nanoparticle material formed by the positive and negative adsorption of anionic CO2-responsive multi-component copolymers and cationic CO2-swellable microspheres after dissolution. It is mainly used for CO2 precipitation inhibition and deep macroporous channel sealing during CO2 flooding in low-permeability tight oil reservoirs. Considering the temporal and spatial overlap of the two requirements for CO2 precipitation inhibition and channel sealing, the bifunctional polyelectrolyte nanoparticle material provided by this invention is applied to CCUS-EOR technology. It utilizes and regulates the formation of a "core-shell" structure of polyelectrolyte nanoparticles from the oppositely charged CO2-responsive anionic multi-component copolymers and cationic CO2-swellable microspheres. This not only improves the delivery capacity of the two chemical agents but also allows for more precise control over the location and timing of agent action. On one hand, the CO2-responsive multi-component copolymer proposed in CN116425931A, after detaching from the core and outer layer, provides in-situ instantaneous inhibition of CO2 precipitation, controlling the bubble size within the nanometer range and improving its ability to enter the matrix. On the other hand, the released core CO2-swellable microspheres undergo secondary expansion upon contact with CO2, effectively sealing gas channeling channels. Therefore, the synergistic enhancement technology of CO2 bifunctional polyelectrolyte nanoparticles provides a new technical approach for in-situ suppression of CO2 bubble precipitation and deep sealing in reservoirs, and is expected to fundamentally solve the technical problems in existing technologies.

[0025] This invention also provides a method for preparing the above-mentioned bifunctional polyelectrolyte nanoparticle material, which includes the following steps:

[0026] A cationic CO2-swellable gel microsphere dispersion with a mass concentration of 0.02-1% was added dropwise to an anionic CO2-responsive multi-component copolymer dispersion with a mass concentration of 0.02-1%. The nanoparticles were then concentrated and washed by centrifugation to prepare a bifunctional polyelectrolyte nanoparticle dispersion with a mass concentration of 0.04-1.5%.

[0027] The volume ratio of the cationic CO2-swellable gel microsphere dispersion to the anionic CO2-responsive multi-component copolymer dispersion is 10:15.

[0028] In the above preparation method, preferably, the cationic CO2 bulk-swellable gel microsphere material dispersion is prepared using one of the following methods one and two:

[0029] Method 1 (involves monomer polymerization):

[0030] The raw material composition of the cationic CO2 bulk-swellable gel microsphere material dispersion, by weight percentage, includes:

[0031] Aqueous phase, 1-2.5%; solvent oil phase, 25-35%; initiator, 0.008-0.06%; non-solvent oil phase, 64-73%;

[0032] The aqueous phase comprises 0.1-0.35% CO2-loving monomers, 0.3-1.2% hydrophilic monomers, 0.2-0.45% pH-responsive polymers, and 0.015-0.2% crosslinking agents.

[0033] The cationic CO2 bulk-swellable gel microsphere material dispersion was prepared through the following steps:

[0034] A stable microemulsion is formed by emulsifying an aqueous phase, a solvent oil phase, and a non-solvent oil phase. Then, the solvent oil phase is evaporated, and the initiator enters the aqueous phase to carry out a polymerization reaction. After centrifugation, washing, and drying, the cationic CO2-body swollen gel microsphere material is obtained. The cationic CO2-body swollen gel microsphere material dispersion is prepared by adding deionized water, with a preferred mass concentration of 0.01-2%.

[0035] Preferably, the polymerization reaction is carried out under a nitrogen atmosphere at a temperature of 40-80°C;

[0036] Preferably, the solvent oil phase is sulfoxide, and the polymerization reaction temperature is 40-50°C; or, the solvent oil phase is tetrahydrofuran, and the polymerization reaction temperature is 55-70°C; or, the solvent oil phase is acetone, and the polymerization reaction temperature is 70-80°C.

[0037] Method 2 (no monomer polymerization reaction):

[0038] The raw material composition of the cationic CO2 bulk-swellable gel microsphere material dispersion, by weight percentage, includes:

[0039] Aqueous phase, 2-10%; solvent oil phase, 25-35%; non-solvent oil phase, 64-73%; preferably, the solvent oil phase is one or a combination of two or more of thionyl chloride, tetrahydrofuran, and acetone;

[0040] The aqueous phase comprises 0.4-1.6% of a polymer material with CO2 affinity, 0.2-0.45% of a pH-responsive long-chain polymer, and 0.015-0.2% of a crosslinking agent.

[0041] The cationic CO2 bulk-swellable gel microsphere material dispersion was prepared through the following steps:

[0042] A stable microemulsion is formed by emulsifying the aqueous phase, solvent oil phase, and non-solvent oil phase. Then, the solvent oil phase is evaporated, and the microemulsion is obtained by centrifugation, washing, and drying. The cationic CO2 bulk swollen gel microsphere material is then obtained by adding deionized water to prepare a dispersion of the cationic CO2 bulk swollen gel microsphere material, with a preferred mass concentration of 0.01-2%.

[0043] Preferably, the polymerization reaction is carried out under a nitrogen atmosphere at a temperature of 40-55°C;

[0044] According to a specific embodiment of the present invention, preferably, the first method for preparing the bifunctional polyelectrolyte composite nanoparticle material of the present invention includes the following specific steps (step one involves a monomer polymerization reaction):

[0045] Step 1: Based on the organic solvent infiltration reaction, CO2-filled swollen gel microspheres are prepared by cross-linking two or more polymers to form an interpenetrating network structure. Specifically, based on the total mass of the raw materials (including organic solvents) in Step 1 as 100%, the amount of the aqueous phase is 2-10% (the aqueous phase contains 0.1-0.35% CO2-loving monomers, 0.3-1.2% hydrophilic monomers, 0.2-0.45% pH-responsive polymers (pH-responsive long-chain polymers), and the remainder is deionized water); the amount of the cross-linking agent is 0.015-0.2%; the amount of the solvent oil phase is 25-35%; and the amount of the initiator is... The dosage is 0.008-0.06%; the dosage of the non-solvent oil phase is 64-73%; the specific process is as follows: the aqueous phase, solvent oil phase and non-solvent oil phase are emulsified (preferably for about 3 minutes) under stirring (preferably at a speed of 12000 RPM) using an IKEA high-speed homogenizer to form a stable microemulsion. Then, the mixture is stirred at a certain temperature (preferably at a speed of 500 RPM) to allow the solvent oil phase volatile initiator to enter the aqueous phase for polymerization reaction (reaction time is about 3-6 hours). The prepared bulk-swellable gel microspheres are centrifuged, washed and dried, and then poured into deionized water to prepare a cationic CO2 bulk-swellable gel microsphere material dispersion with a mass concentration of 0.01-2%.

[0046] Step 2: Prepare a CO2-responsive multi-component copolymer dispersion with a mass concentration of 0.02-1% using the RAFT addition polymerization method proposed in CN116425931A.

[0047] Step 3: Stir 15 ml of the prepared CO2-responsive multi-component copolymer dispersion (concentration 0.02-1%) (preferably at 800 RPM). Slowly add 10 ml of cationic CO2-swellable gel microsphere material dispersion (concentration 0.01-2%) to the CO2-responsive multi-component copolymer dispersion using a syringe to prepare a CO2 bifunctional polyelectrolyte nanoparticle dispersion. Concentrate and wash the nanoparticles by centrifugation to prepare a CO2 bifunctional polyelectrolyte nanoparticle dispersion with a mass concentration of 0.04-1.5%, which is the dispersion of bifunctional polyelectrolyte composite nanoparticle material.

[0048] On the other hand, the second preparation method of the bifunctional polyelectrolyte composite nanoparticle material of the present invention includes the following specific steps (step one does not involve monomer polymerization reaction):

[0049] Step 1: Based on the organic solvent infiltration reaction, CO2-filled swellable gel microspheres are prepared by cross-linking two or more polymers to form an interpenetrating network structure. Specifically, based on the total mass of the raw materials (including organic solvents) in Step 1 as 100%, the amount of the aqueous phase is 2-10% (the aqueous phase includes: 0.4-1.6% of CO2-loving long-chain polymers, 0.2-0.45% of pH-responsive long-chain polymers, and 0.015-0.2% of cross-linking agents); the amount of the solvent-based oil phase is 25-35%; and the amount of the non-solvent-based oil phase... The dosage is 64-73%; the specific process is as follows: the aqueous phase, solvent oil phase and non-solvent oil phase are emulsified (preferably for about 3 minutes) under stirring (preferably at a speed of 12000 RPM) using an IKEA high-speed homogenizer to form a stable microemulsion. Then, the solvent oil phase is evaporated by stirring at a certain temperature (preferably at a speed of 500 RPM) (for about 3-6 hours). The prepared bulk-swellable gel microspheres are centrifuged, washed and dried, and then poured into deionized water to prepare a cationic CO2 bulk-swellable gel microsphere material dispersion with a mass concentration of 0.01-2%.

[0050] Steps two and three are the same as the first preparation method.

[0051] This invention utilizes CO2-swellable gel microspheres prepared by impregnation of two or more polymers with organic solvents and CO2-responsive multi-component copolymers prepared by the RAFT addition polymerization method proposed in CN116425931A to prepare CO2 bifunctional polyelectrolyte nanoparticles via electro-adsorption. In actual preparation, the specific materials and amounts of each component can be determined within the range provided by this invention according to actual needs, thereby precisely controlling the concentration, charge, and affinity of each component.

[0052] According to a specific embodiment of the present invention, preferably, the CO2 bulked gel microspheres prepared in step one have an initial average particle size of about 80 nm to about 900 nm.

[0053] According to a specific embodiment of the present invention, preferably, relative to the initial average particle size of the CO2-body swollen gel microspheres prepared in step one, the size of the cationic CO2-body swollen gel microspheres after swelling in water can reach about 5 to about 15 times, more preferably about 8 to about 13.5 times, the size of the cationic CO2-body swollen gel microspheres after secondary swelling in CO2 can reach about 1.2 to about 3.5 times, more preferably about 1.5 to about 2.5 times, the average particle size after complete swelling in water.

[0054] According to a specific embodiment of the present invention, preferably, the initial average particle size of the CO2 bifunctional polyelectrolyte nanoparticles prepared in step three is about 100 nm to about 1.3 μm.

[0055] According to a specific embodiment of the present invention, preferably, in step three, the reaction temperature is room temperature, preferably 23-25°C.

[0056] According to a specific embodiment of the present invention, preferably, in step one, the initiator includes one or a combination of several of the following: ammonium persulfate, potassium persulfate, 4,4-azobis(4-cyanopentanoic acid), azobisisobutyronitrile.

[0057] According to a specific embodiment of the present invention, preferably, in step one, the solvent oil phase of the organic solvent impregnation reaction includes one or more of dichloromethane (DCM), tetrahydrofuran (THF), and ethyl acetate (ACE).

[0058] According to a specific embodiment of the present invention, preferably, in step one, the non-solvent oil phase of the organic solvent impregnation reaction includes one or more combinations of cyclohexane (CYH), heptane (HPT), and kerosene.

[0059] According to a specific embodiment of the present invention, preferably, in step one, the 500 RPM stirring reaction is carried out under a nitrogen atmosphere, and the specific temperature is 40-80℃, depending on the selection of the solvent oil phase and its boiling point; preferably, the solvent oil phase is DCM, and the polymerization reaction temperature is 40-50℃; the solvent oil phase is THF, and the polymerization reaction temperature is 55-70℃; the solvent oil phase is ACE, and the polymerization reaction temperature is 70-80℃.

[0060] According to a specific embodiment of the present invention, preferably, in step three, the centrifugation speed during the concentration process is 2000 RPM and the centrifugation time is 3-20 minutes, preferably 3-5 minutes. After centrifugation, the upper solvent layer is removed using a syringe with a needle, and the bottom solid is removed and dried by vacuum filtration at room temperature. The washing process is performed after the concentration process is completed by pouring 15 mL of deionized water into a test tube containing the solid, shaking the test tube for 5 minutes, and then repeating the centrifugation steps of the concentration process, washing repeatedly 2-4 times.

[0061] According to a specific embodiment of the present invention, in step one, an appropriate amount of emulsion stabilizer can be added as needed. Preferably, when adding an emulsion stabilizer, the amount of the emulsion stabilizer is 0.001-0.05% based on the total mass of the raw materials. More preferably, the emulsion stabilizer includes one or a combination of two or more of Triton X-45, Tergitol NP-4, Brij L-4, Brij72, Span60, and Span80.

[0062] This invention also provides the application of the above-mentioned bifunctional polyelectrolyte nanoparticle material in CO2 flooding and storage.

[0063] According to a specific embodiment of the present invention, preferably, the CO2 flooding is supercritical CO2 (scCO2) flooding. CO2 sequestration is achieved by retaining the remaining CO2 in the matrix after the remaining oil in the matrix is ​​displaced, thus achieving the purpose of sequestration. More preferably, the supercritical CO2 flooding includes CO2 miscible flooding or WAG flooding.

[0064] In practical applications, scCO2 containing CO2 bifunctional polyelectrolyte nanoparticles is injected into low-permeability tight oil reservoirs. As the injected scCO2 migrates to areas with underground fractures and gas channeling, it can precisely release two polymeric materials—a CO2-responsive multi-component copolymer and CO2-swellable gel microspheres—through pH-responsive core-shell separation. These materials are used to suppress CO2 release in situ and block deep gas channeling, respectively, ultimately achieving a synergistic effect of CO2 oil displacement and storage. The pH response is achieved through the protonation / deprotonation transformation of the amine functional groups on the CO2-swellable gel microspheres (core structure) in response to pH.

[0065] According to a specific embodiment of the present invention, by enabling the pH-responsive "core-shell" separation of bifunctional polyelectrolyte nanoparticles injected into the reservoir with supercritical CO2 (scCO2), precise and controllable release of anionic CO2-responsive multi-component copolymers and cationic CO2-swellable microspheres can be achieved. In low-permeability tight oil reservoirs where CO2 precipitation and gas channeling occur, the pH typically rises due to scCO2 dilution by formation water. This is precisely the reservoir location where the "core-shell" separation of bifunctional polyelectrolyte composite nanoparticles is needed to release both anionic CO2-responsive multi-component copolymers and cationic CO2-swellable microspheres. This release method further precisely controls the location and timing of the two agents' activation.

[0066] Compared with existing technologies, the beneficial technical effects achieved by the bifunctional polyelectrolyte nanoparticle material provided by this invention include:

[0067] (1) The CO2 bifunctional polyelectrolyte nanoparticles provided by this invention are formed by the positive and negative adsorption of polymer materials, resulting in a core-shell structure. The core is a gel polymer material with an interpenetrating network structure formed by cross-linking CO2-loving polymers and polyethyleneimine, while the outer shell is a CO2-responsive anionic multi-component copolymer material formed by RAFT addition of CO2-loving and anionic polymers using the Pluronic polymer described in CN116425931A. The stable dispersed CO2 bifunctional polyelectrolyte nanoparticles have a size between 100 and 1300 nm and exhibit strong formation transport capacity with scCO2 in low-permeability tight sandstone reservoirs (with negatively charged surfaces).

[0068] (2) The CO2 bifunctional polyelectrolyte nanoparticle material provided by this invention is used for CO2 miscible flooding or WAG flooding. The CO2 bifunctional polyelectrolyte nanoparticle material can enter the formation with scCO2, and exhibits a weakly negatively charged outer surface structure during this process.

[0069] (3) The "core-shell" separation of CO2 bifunctional polyelectrolyte nanoparticles provided by this invention is mainly achieved through the reversible deprotonation reaction of the CN bonds on PEI or the Si-O bonds on PDMS. When the ambient pH changes, both chemical bonds undergo deprotonation, causing the CO2 bulk-swellable gel microspheres to lose their charge, thus separating from the anionic multi-component copolymer shell. This mechanism is referred to as a "pH trigger" in this invention. While improving the delivery capacity of the two chemical agents, this invention precisely achieves in-situ CO2 bubble precipitation suppression and precise sealing of large channels by controlling the activation timing of the multi-component polymer and the bulk-swellable gel microspheres through the "pH trigger."

[0070] (4) The CO2-responsive anionic multi-component copolymer material provided by this invention simultaneously possesses Pluronic polymer chain segment structures, perfluorinated compound chain segment structures, and propanesulfonic acid chain segment structures. Within scCO2 fluid, its hydrophilic, oleophilic, and CO2-friendly properties are all tunable. Furthermore, the CO2-water-based microfoams and CO2-oil-based microfoams formed by this material exhibit excellent stability. These two types of stability further promote the conversion between CO2-water-based and CO2-oil-based microfoams, which is beneficial for in-situ suppression of bubble size during scCO2 precipitation, maintaining it at the nanobubble level, thereby reducing CO2 precipitation and increasing its ability to enter the matrix. Therefore, the CO2-responsive anionic multi-component copolymer material provided by this invention can control CO2 precipitation in relatively harsh reservoir environments. After the remaining oil is completely extracted, the CO2-water-based microfoams decompose in the matrix, encapsulating CO2 within the matrix, further enhancing the effect of CO2 replacing crude oil in the matrix.

[0071] (5) The CO2 bulk-swellable gel microsphere material provided by the present invention can be used to block large gas migration channels. After the CO2 bifunctional polyelectrolyte nanoparticles are separated into a core and a shell, the released core bulk-swellable gel microspheres come into contact with CO2 and undergo secondary expansion, effectively blocking the gas migration channels. Attached Figure Description

[0072] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0073] Figure 1This is a schematic diagram of the structure of the cationic CO2 bulked gel microspheres prepared in Example 1.

[0074] Figure 2 The image shows the FTIR spectrum of cationic CO2 bulked gel microspheres.

[0075] Figure 3 The flowchart for the preparation of CO2-responsive anionic multi-component copolymers in Example 1 is shown.

[0076] Figure 4 This is a scanning electron microscope image of the cationic CO2-swellable gel microspheres prepared in Example 1.

[0077] Figure 5 This is a scanning electron microscope image of the CO2 bifunctional polyelectrolyte nanoparticles prepared in Example 1.

[0078] Figure 6 Transmission electron microscopy image of CO2 bifunctional polyelectrolyte nanoparticles prepared in Example 1. Detailed Implementation

[0079] It should be noted that the term "comprising" and any variations thereof in the specification and claims of this invention are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such processes, methods, products, or devices.

[0080] The "range" disclosed in this invention is given in the form of a lower limit and an upper limit. It can be one or more lower limits and one or more upper limits, respectively. A given range is defined by selecting a lower limit and an upper limit. The selected lower and upper limits define the boundaries of the particular range. All ranges defined in this way are composable, meaning that any lower limit can be combined with any upper limit to form a range. For example, if a range of 40-80 is listed for a specific parameter, it is also expected that ranges of 40-55 and 55-80 can be understood. Furthermore, if the listed minimum range values ​​are 1 and 2, and the listed maximum range values ​​are 3, 4, and 5, then the following ranges can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5.

[0081] In this invention, unless otherwise specified, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this invention, and "0-5" is simply a shortened representation of these numerical combinations.

[0082] In this invention, unless otherwise specified, all embodiments and preferred embodiments mentioned in this invention can be combined with each other to form new technical solutions.

[0083] In this invention, unless otherwise specified, all technical features and preferred features mentioned in this invention can be combined with each other to form new technical solutions.

[0084] In this invention, unless otherwise specified, the term "two kinds" as used in this specification means "at least two kinds".

[0085] In this invention, unless otherwise specified, all steps mentioned herein may be performed sequentially or randomly, but are preferably performed sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0086] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying tables, drawings, and embodiments. The embodiments described below are some, but not all, embodiments of this invention, and are only used to illustrate the invention, and should not be considered as limiting the scope of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0087] Example 1

[0088] This embodiment provides a CO2 bifunctional polyelectrolyte nanoparticle material, which is prepared by a method including the following specific steps:

[0089] Step 1: Disperse 0.2g of PEI polymer and 0.01g of GA crosslinking agent in 2ml of deionized water to prepare an aqueous phase;

[0090] 0.08 g of PDMS polymer was dispersed in 7.5 ml of THF to prepare a solvent oil phase;

[0091] Separately, 17.5 ml of CYH was added to a 50 ml three-necked flask along with the aqueous and solvent oil phases. Nitrogen gas was bubbled through the flask at 12000 RPM for 3 minutes to emulsify and form a stable microemulsion. The mixture was then stirred at 60°C (500 RPM) for 2 hours to allow the organic solvent to evaporate. The resulting bulk-swelling gel microspheres were separated by low-speed centrifugation, washed, and dried. They were then added to deionized water to prepare a 0.05% cationic CO2 bulk-swelling gel microsphere dispersion. The structure of the cationic CO2 bulk-swelling gel microspheres is as follows: Figure 1 As shown.

[0092] Step 2: Prepare a CO2-responsive multi-component copolymer dispersion according to the RAFT addition polymerization method proposed in CN116425931A. The specific steps are as follows (flowchart shown). Figure 3 As shown):

[0093] Take a 50mL three-necked flask, add 2.12g of Pluronic P-123 block polymer, 0.4g of CTPPA and 0.265g of EDAC to 24mL of DCM, stir and disperse thoroughly, and carry out esterification reaction at 65℃ under nitrogen protection. After the reaction is completed, RAFT precursor polymer is prepared and dried for later use.

[0094] In another 100mL three-necked flask, add 3g of RAFT precursor polymer, 9g of FDA, 0.06g of ACPA and 6g of Triton X-45 to 60mL of cycC6 solvent. React at 75℃ and 100rpm for 8 hours (under nitrogen protection). After the reaction is complete, separate and dry the solid obtained for later use.

[0095] 3.5g of the solid prepared above was added to 60mL of cycC6 solvent along with 6g of AMPS, 0.1g of ACPA and 6g of Triton X-45. The mixture was reacted at 75℃ and 100rpm for 10 hours (under nitrogen protection). After the reaction was completed, the solid was separated and dried to obtain the CO2-responsive anionic multi-component copolymer. It was then dissolved in deionized water to prepare a dispersion with a concentration of 0.05%.

[0096] Step 3: Stir 15 ml of the CO2-responsive multi-component copolymer dispersion (0.05%) obtained in Step 2 at 800 RPM. Slowly add 10 ml of the bulk-swelling gel microsphere dispersion (0.05%) obtained in Step 1 to the stirred CO2-responsive multi-component copolymer dispersion using a 20 ml scale syringe. This will prepare a CO2 bifunctional polyelectrolyte nanoparticle dispersion. Concentrate and wash the nanoparticles by repeatedly centrifuging at low speed (300 rpm) for 5 minutes to prepare a CO2 bifunctional polyelectrolyte nanoparticle dispersion with a concentration of 0.12%.

[0097] Example 2

[0098] This embodiment provides a CO2 bifunctional polyelectrolyte nanoparticle material, which is prepared by a method including the following specific steps:

[0099] Step 1: Disperse 0.15g of B-PEI polymer and 0.013g of GA crosslinking agent in 2ml of deionized water to prepare an aqueous phase;

[0100] 0.1 g of PDMS polymer was dispersed in 7.5 ml of THF to prepare a solvent oil phase;

[0101] Another 17.5 ml of CYH was poured into a 50 ml three-necked flask along with the aqueous phase and the solvent oil phase. Nitrogen gas was introduced at 12000 RPM and emulsified for 3 minutes to form a stable microemulsion. Then, the mixture was stirred at 60 °C (500 RPM) to allow the organic solvent to evaporate and react for 2 hours. The resulting bulk-swelling gel microspheres were separated by low-speed centrifugation, washed and dried, and then poured into deionized water to prepare a 0.05% cationic CO2 bulk-swelling gel microsphere dispersion.

[0102] Steps two and three are the same as in Example 1.

[0103] Example 3

[0104] This embodiment provides a CO2 bifunctional polyelectrolyte nanoparticle material, which is prepared by a method including the following specific steps:

[0105] Step 1: Take a 50mL three-necked flask and put 0.08g of TPA monomer, 0.11g of AMPS monomer, 0.2g of AM monomer, 0.015g of MABA crosslinking agent, 0.01g of GA crosslinking agent, 0.001g of ammonium persulfate initiator, 0.0007g of 4,4-azobis(4-cyanopentanoic acid) initiator, 0.001g of Brij L-4 and 2ml of deionized water into the three-necked flask. Pour in 7.5ml of THF and 17.5ml of CYH. Emulsify with nitrogen gas at 12000RPM for 3 minutes to form a stable microemulsion. Then stir at a certain temperature (500RPM) to allow the organic solvent to evaporate and the initiator to enter the aqueous phase for polymerization reaction for 5 hours. The prepared bulk-swellable gel microspheres are separated by low-speed centrifugation, washed and dried, and then poured into deionized water to prepare a cationic CO2 bulk-swellable gel microsphere dispersion with a concentration of 0.05%.

[0106] Step 2: Prepare a CO2-responsive multi-component copolymer dispersion according to the RAFT addition polymerization method proposed in CN116425931A. The specific steps are as follows:

[0107] Take a 50mL three-necked flask, add 2.12g of Pluronic P-123 block polymer, 0.4g of CTPPA and 0.265g of EDAC to 24mL of DCM, stir and disperse thoroughly, and carry out esterification reaction at 65℃ under nitrogen protection. After the reaction is completed, RAFT precursor polymer is prepared and dried for later use.

[0108] In another 100mL three-necked flask, add 3g of the prepared RAFT precursor polymer, 9g of FDA, 0.06g of ACPA and 6g of Triton X-45 to 60mL of cycC6 solvent. React at 75℃ and 100rpm for 8 hours (under nitrogen protection). After the reaction is complete, separate and dry the prepared solid for later use.

[0109] 3.5g of the solid prepared above was added to 60mL of cycC6 solvent along with 6g of AMPS, 0.1g of ACPA and 6g of Triton X-45. The mixture was reacted at 75℃ and 100rpm for 10 hours (under nitrogen protection). After the reaction was completed, the solid was separated and dried to obtain the CO2-responsive anionic multi-component copolymer. It was then dissolved in deionized water to prepare a dispersion with a concentration of 0.05%.

[0110] Step 3: Stir 15 ml of the CO2-responsive multi-component copolymer dispersion (0.05%) prepared in Step 2 at 800 RPM. Slowly add 10 ml of the bulk-swelling gel microsphere dispersion (0.05%) prepared in Step 1 to the stirred CO2-responsive multi-component copolymer dispersion using a 20 ml scale syringe. This will prepare a CO2 bifunctional polyelectrolyte nanoparticle dispersion. Concentrate and wash the nanoparticles by repeatedly centrifuging at low speed (300 rpm) for 5 minutes to prepare a 0.12% CO2 bifunctional polyelectrolyte nanoparticle dispersion.

[0111] Example 4

[0112] This embodiment provides a CO2 bifunctional polyelectrolyte nanoparticle material, which is prepared by a method including the following specific steps:

[0113] Step 1: Take a 50mL three-necked flask and put 0.08g of TPA monomer, 0.11g of AMPS monomer, 0.2g of AM monomer, 0.015g of MABA crosslinking agent, 0.01g of GA crosslinking agent, 0.001g of ammonium persulfate initiator, 0.0007g of 4,4-azobis(4-cyanopentanoic acid) initiator, 0.001g of Brij L-4 and 2ml of deionized water into the three-necked flask. Pour in 7.5ml of THF and 17.5ml of CYH. Emulsify with nitrogen gas at 12000RPM for 3 minutes to form a stable microemulsion. Then stir at a certain temperature (500RPM) to allow the organic solvent to evaporate and the initiator to enter the aqueous phase for polymerization reaction for 5 hours. The prepared bulk-swellable gel microspheres are separated by low-speed centrifugation, washed and dried, and then poured into deionized water to prepare a cationic CO2 bulk-swellable gel microsphere dispersion with a concentration of 0.05%.

[0114] Steps two and three are the same as in Example 3.

[0115] Test Example 1

[0116] In this test example, the cationic CO2 bulk-swellable gel microspheres prepared in Example 1 were first pressed into pellets using KBr, and then their functional groups were analyzed using a Nicolet Nexus 570 infrared spectrometer. The resulting infrared spectra are shown below. Figure 2 As shown. From Figure 2 It can be seen from this that 671cm -1 (Si-O-Si), 893cm -1 (Si-CH), 1112cm -1 (Si-O) and 1274cm -1 The (Si-C) peak is a characteristic vibrational peak of PDMS; 1410-1590 cm⁻¹ -1 The peak is the amino vibration peak on PEI; 2810-2950 cm⁻¹ -1 The peaks are the stretching vibration peaks of CN and CH bonds. Infrared analysis results show that Example 1 of this invention successfully prepared cationic CO2 bulk swollen gel microspheres.

[0117] Test Example 2

[0118] The cationic CO2 bulk-swellable gel microspheres and CO2 bifunctional polyelectrolyte nanoparticles prepared in Examples 1-4 were dried in a negative pressure oven for 24 hours. The particle size of the samples was measured using a Malvern Zetasizer Nano ZS90 dynamic light scattering instrument, and the results are shown in Table 1. The cationic CO2 bulk-swellable gel microspheres prepared in Example 1 were studied using SEM and TEM. Figure 4 ) and CO2 bifunctional polyelectrolyte nanoparticles ( Figure 5 and Figure 6).

[0119] Table 1

[0120]

[0121]

[0122] Test Example 3

[0123] This test aims to determine the particle size of CO2 bulk-swellable gel microspheres and CO2 bifunctional polyelectrolyte nanoparticles in deionized water and 1% NaCl solution, and is conducted in the following manner:

[0124] Under a temperature of 70°C, the bulk-swelling gel microspheres and bifunctional polyelectrolyte nanoparticles provided in Examples 1-4 were dried in a negative pressure oven for 24 hours and then placed in deionized water and 1% NaCl saline for saturation water absorption tests. The particle size of the samples was measured by a dynamic light scattering instrument. The experimental data are shown in Table 2.

[0125] As can be seen from the test results in Table 2, the particle size of the samples provided in Examples 1-4 in deionized water is slightly larger than that in 1% NaCl solution; the particle size of the bifunctional polyelectrolyte nanoparticles in the same example is only half that of the bulk-swellable gel microspheres, indicating that after the formation of the "core-shell" structure, the outer shell polymer restricts the water absorption rate of the core CO2 bulk-swellable gel microspheres in a short time, which helps the particles migrate in the reservoir.

[0126] Table 2

[0127]

[0128] Test Example 4

[0129] This test aims to determine the particle size of CO2 bifunctional polyelectrolyte nanoparticles in deionized water and 1% NaCl solution, and is conducted as follows:

[0130] Take the CO2 bifunctional polyelectrolyte nanoparticles (solid content 0.12%) saturated with deionized water obtained in Example 3 and introduce CO2 into the dispersion for 1 minute. Test the particle size of the nanoparticles before and after introducing CO2 at a temperature of 70°C and calculate the expansion factor after 120 minutes. The results are shown in Table 3.

[0131] The results shown in Table 3 indicate that as the CO2 introduction time increases, the solution pH decreases, causing the core and shell of the CO2 bifunctional polyelectrolyte nanoparticles to separate. The detached core begins to absorb CO2 and undergo secondary expansion. At the same time, as the temperature increases, the nanoparticle size increases more rapidly, indicating that high temperature increases the core and shell separation rate of the CO2 bifunctional polyelectrolyte nanoparticles.

[0132] Table 3

[0133]

[0134] Test Example 5

[0135] Supercritical CO2 enhanced oil recovery experiments were conducted in tight reservoirs using CO2 bifunctional polyelectrolyte nanoparticles prepared in Examples 1-4, and the oil recovery rate was determined. The experimental temperature was 70℃, and the specific experimental procedure is as follows:

[0136] The experiment used 12 cylindrical, dense cores (3.5 cm in diameter and 11 cm in length) with a permeability of ~0.12 mD ± 0.03 mD. The cores were treated with saturated oil. The crude oil used in the experiment had a back pressure of 6.1 MPa at 70℃.

[0137] First, the core sample was subjected to supercritical CO2 flooding until the pressure at both the inlet and outlet ends stabilized (approximately 2.5 PV) and no further crude oil flow occurred. Then, 0.3-1 PV of CO2 bifunctional polyelectrolyte nanoparticles (0.12%) prepared in Examples 1-4 were injected, and the model was sealed and allowed to stand for 24 hours. Finally, supercritical CO2 flooding was reinjected until no more crude oil flowed out. The test results are shown in Table 4.

[0138] As shown in Table 4, the experimental results indicate that the recovery rate of pre-supercritical CO2 flooding reached a maximum of 53.2%. When supercritical CO2 was injected into the CO2 bifunctional polyelectrolyte nanoparticles prepared in Examples 1-4, a small amount of crude oil was recovered (less than 1.51%). This was mainly because the CO2-responsive anionic multi-component copolymer on the surface of the nanoparticles reduced the viscosity and improved the flowability of the remaining oil upon contact with it after entering the core. Simultaneously, the nanoparticles attached to the surface of the core pores reduced surface resistance. After sealing the core for 24 hours, some of the CO2 bifunctional polyelectrolyte nanoparticles underwent shell-core separation, further enhancing the oil displacement capacity. This process achieved a recovery rate of 6.25%. The changes in crude oil recovery rate between the two supercritical CO2 flooding operations demonstrate that the CO2 bifunctional polyelectrolyte nanoparticles proposed in this invention have a good effect on improving CO2 flooding in tight oil reservoirs.

[0139] Table 4

[0140]

[0141] The above description is merely a specific embodiment of the present invention and should not be construed as limiting the scope of the invention. Therefore, any substitution of equivalent components or equivalent changes and modifications made within the scope of protection of this patent should still fall within the scope of this patent. Furthermore, the technical features, technical features and technical inventions, and technical inventions in this invention can be freely combined and used.

Claims

1. A bifunctional polyelectrolyte nanoparticle material, wherein, This bifunctional polyelectrolyte nanoparticle material has a core-shell structure and is obtained by dissolving anionic CO2-responsive multi-component copolymers and cationic CO2-swellable gel microspheres and then adsorbing them through positive and negative charge adsorption. The anionic CO2-responsive multi-component copolymer is prepared through the following steps: a Pluronic block polymer undergoes a reversible addition-fragmentation chain transfer esterification reaction with a chain transfer agent to obtain a RAFT precursor polymer; the RAFT precursor polymer undergoes a primary addition polymerization reaction with a perfluoroacrylate monomer; and the product of the primary addition polymerization reaction undergoes a secondary addition polymerization reaction with a propanesulfonic acid-containing monomer to obtain the anionic CO2-responsive multi-component copolymer; the CO2-responsive anionic multi-component copolymer contains one or more functional groups that exhibit negative electrochemical properties upon hydrolysis. The cationic CO2-swellable gel microspheres are prepared by a polymerization reaction based on organic solvent infiltration, using two or more polymeric materials to form an interpenetrating network structure through a cross-linking reaction, wherein the polymeric materials include at least one CO2-loving polymeric material. The CO2-loving polymer material is a polymer material prepared by copolymerization of CO2-loving monomers and hydrophilic monomers or a polymer material that has CO2-loving properties. The CO2-loving monomer includes one or more of perfluoroacrylate, 1H,1H,2H,2H-perfluorodecyl acrylate, and hexafluorobutyl methacrylate; the hydrophilic monomer includes one or more of 2-acrylamido-2-methylpropanesulfonic acid, acrylamide, vinyl alcohol, and vinyl acetate; the CO2-loving polymer material includes one or more of polydimethylsiloxane and its derivatives.

2. The bifunctional polyelectrolyte nanoparticle material according to claim 1, wherein, The average molecular weight of the CO2-responsive anionic multi-component copolymer material is 5000 Da-30000 Da.

3. The bifunctional polyelectrolyte nanoparticle material according to claim 1, wherein, The Pluronic block polymers include one or more of Pluronic P-123, Pluronic 17R4, Pluronic F-68, Pluronic F-127 and Pluronic L-121.

4. The bifunctional polyelectrolyte nanoparticle material according to claim 2, wherein, The Pluronic block polymers include one or more of Pluronic P-123, Pluronic 17R4, Pluronic F-68, Pluronic F-127 and Pluronic L-121.

5. The bifunctional polyelectrolyte nanoparticle material according to any one of claims 1-4, wherein, The chain transfer agent comprises 4-cyano-4-thiopropylthiovalerate and / or S-dodecyl-S'-(α,α'-dimethyl-α”-acetic acid) trithiocarbonate; The perfluoroacrylate monomers include 1H,1H,2H,2H-perfluorodecyl acrylate and / or hexafluorobutyl methacrylate. The propanesulfonic acid-containing monomers include one of 2-acrylamide-2-methylpropanesulfonic acid, oleic acid imidazoline sulfonate, N,N-dimethyl-dithiocarbamate propanesulfonic acid, and sodium 3-chloro-2-hydroxypropanesulfonate.

6. The bifunctional polyelectrolyte nanoparticle material according to claim 1, wherein, The polymeric materials used to prepare cationic CO2-swellable gel microspheres include at least CO2-loving polymeric materials and pH-responsive polymeric materials. The pH-responsive polymer material is a polymer material capable of undergoing amine matrix protonation reaction.

7. The bifunctional polyelectrolyte nanoparticle material according to claim 6, wherein, The pH-responsive polymeric material includes linear polyethyleneimine and / or branched polyethyleneimine.

8. The bifunctional polyelectrolyte nanoparticle material according to claim 6, wherein, The crosslinking agent for the crosslinking reaction includes one or more of N,N'-methylenebisacrylamide, glutaraldehyde, and 1,4-butanediol diglycidyl ether.

9. The bifunctional polyelectrolyte nanoparticle material according to claim 8, wherein, The cross-linking reaction includes a cross-linking method of one polymer material and a cross-linking method of two polymer materials.

10. The bifunctional polyelectrolyte nanoparticle material according to any one of claims 1-4 and 6-9, wherein, The average particle size of the bifunctional polyelectrolyte nanoparticle material is 100 nm to 1.3 μm; The average particle size of the cationic CO2 bulk-swellable gel microsphere material is 80 nm to 900 nm.

11. The bifunctional polyelectrolyte nanoparticle material according to claim 5, wherein, The average particle size of the bifunctional polyelectrolyte nanoparticle material is 100 nm to 1.3 μm; The average particle size of the cationic CO2 bulk-swellable gel microsphere material is 80 nm to 900 nm.

12. A method for preparing bifunctional polyelectrolyte nanoparticle materials according to any one of claims 1-11, comprising the following steps: A cationic CO2-swellable gel microsphere dispersion with a mass concentration of 0.02-1% was added dropwise to an anionic CO2-responsive multi-component copolymer dispersion with a mass concentration of 0.02-1%. The nanoparticles were then concentrated and washed by centrifugation to prepare a bifunctional polyelectrolyte nanoparticle dispersion with a mass concentration of 0.04-1.5%. The volume ratio of the cationic CO2-swellable gel microsphere dispersion to the anionic CO2-responsive multi-component copolymer dispersion is 10:

15.

13. The preparation method according to claim 12, wherein, The cationic CO2 bulk-swellable gel microsphere material dispersion is prepared using one of the following methods: Method 1 and Method 2. Method 1: The raw material composition of the cationic CO2 bulk-swellable gel microsphere material dispersion, by weight percentage, includes: Aqueous phase, 1-2.5%; solvent oil phase, 25-35%; initiator, 0.008-0.06%; non-solvent oil phase, 64-73%; The aqueous phase comprises 0.1-0.35% CO2-loving monomers, 0.3-1.2% hydrophilic monomers, 0.2-0.45% pH-responsive polymers, and 0.015-0.2% crosslinking agents. The cationic CO2 bulk-swellable gel microsphere material dispersion was prepared through the following steps: A stable microemulsion is formed by emulsifying the aqueous phase, solvent oil phase, and non-solvent oil phase. Then, the solvent oil phase is evaporated, and the initiator enters the aqueous phase to carry out the polymerization reaction. After centrifugation, washing, and drying, the cationic CO2 bulk swollen gel microsphere material is obtained. Deionized water is added to prepare the dispersion of the cationic CO2 bulk swollen gel microsphere material. Method 2: The raw material composition of the cationic CO2 bulk-swellable gel microsphere material dispersion, by weight percentage, includes: Aqueous phase, 2-10%; solvent oil phase, 25-35%; non-solvent oil phase, 64-73%; The aqueous phase comprises 0.4-1.6% of a polymer material with CO2 affinity, 0.2-0.45% of a pH-responsive long-chain polymer, and 0.015-0.2% of a crosslinking agent. The cationic CO2 bulk-swellable gel microsphere material dispersion was prepared through the following steps: A stable microemulsion is formed by emulsifying the aqueous phase, solvent oil phase, and non-solvent oil phase. Then, the solvent oil phase is evaporated, and the microemulsion is obtained by centrifugation, washing, and drying. The cationic CO2 bulk swollen gel microsphere material is then obtained by adding deionized water to prepare a dispersion of the cationic CO2 bulk swollen gel microsphere material.

14. The preparation method according to claim 13, wherein, In Method 1, the mass concentration of the cationic CO2 bulk-swellable gel microsphere material dispersion is 0.01-2%.

15. The preparation method according to claim 13, wherein, In Method 1, the polymerization reaction is carried out under a nitrogen atmosphere at a temperature of 40-80°C.

16. The preparation method according to claim 15, wherein, In Method 1, the solvent oil phase is sulfoxide, and the polymerization reaction temperature is 40-50°C; or, the solvent oil phase is tetrahydrofuran, and the polymerization reaction temperature is 55-70°C; or, the solvent oil phase is acetone, and the polymerization reaction temperature is 70-80°C.

17. The preparation method according to claim 13, wherein, In the second method, the mass concentration of the cationic CO2 bulk-swellable gel microsphere material dispersion is 0.01-2%.

18. The preparation method according to claim 13, wherein, In the second method, the solvent oil phase is one or a combination of two or more of thionyl chloride, tetrahydrofuran, and acetone.

19. The application of the bifunctional polyelectrolyte nanoparticle material according to any one of claims 1-11 in carbon dioxide flooding.

20. The application according to claim 19, wherein, The carbon dioxide flooding is supercritical carbon dioxide flooding.

21. The application according to claim 20, wherein, The supercritical carbon dioxide flooding is a carbon dioxide miscible flooding.

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