Acid-resistant nano-polymer microsphere inclusion plugging system and its preparation method and application

Abstract

The present invention provides an acid-resistant nano-polymer microsphere inclusion plugging system and its preparation method and application. The plugging system of the present invention is prepared by including the following raw materials in parts by mass: 1-5 parts of acid-resistant nano-polymer microspheres, 1-5 parts of acid-resistant low-molecular-weight cyclodextrin polymers, and 80-120 parts of water. The present invention introduces the idea of ​​supramolecular construction, and proposes an inclusion-enhanced plugging system constructed by the host-guest inclusion action of acid-resistant nano-polymer microspheres and cyclodextrin polymers through the design of the surface molecular structure of nano-polymer microspheres and the molecular structure of cyclodextrin polymers. The plugging system of the present invention has strong acid resistance and excellent shear resistance, wherein the nano-polymer microspheres have good dispersibility, good injectability, and are easy to be injected into the formation and migrate to deep; at the same time, they have the characteristics of low concentration and high efficiency, can effectively enter the deep formation and efficiently achieve the plugging of cracks, thereby increasing the swept volume and displacement efficiency of CO2.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and natural gas development, and particularly relates to an acid-resistant nano-polymer microsphere inclusion plugging system and a preparation method and application thereof. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to those skilled in the art.

[0003] Currently, low-permeability reservoirs are a key area for increasing reserves and production in my country. CO2 flooding technology has solved the problem of "no injection and no production" in low-permeability reservoir water injection development, effectively improving the crude oil utilization rate and recovery rate of low-permeability reservoirs. However, due to the presence of fractures and high-permeability channels in low-permeability reservoirs, gas channeling is prone to occur during the development of such reservoirs, seriously affecting the effectiveness of gas injection development in oil fields. Therefore, research on plugging technology suitable for CO2 flooding is of far-reaching significance for the efficient development of low-permeability oil and gas reservoirs.

[0004] In order to solve the problem of CO2 gas channeling, the research and development of acid-resistant gas channeling plugging materials is the key. Polymer microspheres have shown great development prospects in low permeability reservoir channeling plugging. They can be transported in cracks or microcracks to the deep part of the reservoir to achieve deep plugging. However, the acid resistance of the commonly used nano-polymer microspheres is poor, and the effect of the particles in plugging gas is limited. Nano-polymer microspheres are often compounded with polymer solutions during application. The high viscosity of the polymer enhances the suspension and dispersion stability of the nano-polymer microspheres and carries them into the injection well. The commonly used polymer at present is partially hydrolyzed polyacrylamide. The interaction strength between the polymer and the nano-polymer microspheres is low, and the polymer has limited viscosity-increasing ability under the acidic conditions of supercritical CO2. Therefore, the compound system has limited synergistic plugging effect in application. For this reason, the present invention is proposed. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the present invention provides an acid-resistant nano-polymer microsphere inclusion sealing system and its preparation method and application. The present invention introduces the idea of ​​supramolecular construction, and through the design of the molecular structure of the surface of nano-polymer microspheres and the molecular structure of cyclodextrin polymers, proposes an acid-resistant nano-polymer microsphere and cyclodextrin polymer to construct an inclusion enhancement sealing system through host-guest inclusion, which solves the problems of conventional polymer microspheres such as poor deformability, weak suspension stability, poor expansion performance under acidic conditions, poor acid resistance, and limited gas sealing effect of particles. The sealing system of the present invention has strong acid resistance and excellent shear resistance. The nano-polymer microspheres have good dispersibility, good injectability, and are easy to be injected into the formation and migrate to deep depths. At the same time, they have the characteristics of low concentration and high efficiency, can effectively enter the deep formation and efficiently achieve the sealing of cracks, thereby increasing the swept volume and displacement efficiency of CO2.

[0006] The present invention is achieved through the following technical solutions:

[0007] An acid-resistant nano polymer microsphere inclusion plugging system is prepared from the following raw materials in parts by mass: 1-5 parts of acid-resistant nano polymer microspheres, 1-5 parts of acid-resistant low molecular weight cyclodextrin polymer, and 80-120 parts of water.

[0008] Preferably, according to the present invention, the acid-resistant nano-polymer microsphere inclusion plugging system is prepared by including the following raw materials in parts by mass: 2-4 parts of acid-resistant nano-polymer microspheres, 2-4 parts of acid-resistant low molecular weight cyclodextrin polymer, and 90-110 parts of water.

[0009] Preferably, the acid-resistant nano-polymer microsphere inclusion plugging system is prepared by including the following raw materials in parts by mass: 3 parts of acid-resistant nano-polymer microspheres, 3 parts of acid-resistant low molecular weight cyclodextrin polymer, and 100 parts of water.

[0010] Preferably, according to the present invention, the acid-resistant nano-polymer microspheres are prepared by including the following raw materials in parts by weight: 110-150 parts of basic building unit monomers, 1-15 parts of hydrophobic monomers, 1-20 parts of acid-resistant monomers, 0.1-3 parts of nanoparticles, 0.3-6 parts of double cross-linking agent systems, 0.2-3 parts of initiators, 150-200 parts of emulsifiers, 500-550 parts of oil phase solvents, and 100-200 parts of water.

[0011] Preferably, the acid-resistant nanopolymer microspheres are prepared by including the following raw materials in parts by weight: 130-140 parts of basic building unit monomers, 2-4 parts of hydrophobic monomers, 1-2 parts of acid-resistant monomers, 0.4-0.6 parts of nanoparticles, 3-5 parts of double cross-linking agent systems, 0.8-1.2 parts of initiators, 180-185 parts of emulsifiers, 510-520 parts of oil phase solvents, and 155-160 parts of water.

[0012] Preferably, the acid-resistant nanopolymer microspheres are prepared by including the following raw materials in parts by weight: 132 parts of basic building unit monomers, 3 parts of hydrophobic monomers, 1 part of acid-resistant monomers, 0.5 parts of nanoparticles, 4 parts of double cross-linking agent system, 1.125 parts of initiator, 181.2 parts of emulsifier, 518.8 parts of oil phase solvent, and 158.5 parts of water.

[0013] Preferably, the basic building block monomer is acrylamide (AM).

[0014] Preferably, the hydrophobic monomer is hexadecyldimethylallylammonium chloride.

[0015] Preferably, the acid-resistant monomer is diallyldimethylammonium chloride.

[0016] Preferably, the nanoparticles are modified nano-silicon dioxide (SiO2) with carbon-carbon double bonds on the surface. The modified nano-silicon dioxide (SiO2) has the structure shown below and a particle size of 1-10 nm. The preparation method of the modified nano-silicon dioxide with carbon-carbon double bonds on the surface can be based on existing technology.

[0017]

[0018] Preferably, the dual crosslinker system is a combination of a stable crosslinker N,N-methylenebisacrylamide and an unstable crosslinker polyethylene glycol diacrylate, wherein the mass ratio of N,N-methylenebisacrylamide to polyethylene glycol diacrylate is 6:4-9:1, preferably 2:1-4:1.

[0019] Preferably, the initiator is 2,2'-azo(2-methylpropylamidine) dihydrochloride.

[0020] Preferably, the emulsifier is a combination of sorbitan fatty acid ester and polyoxyethylene sorbitan monooleate, wherein the mass ratio of sorbitan fatty acid ester to polyoxyethylene sorbitan monooleate is 2-3:1.

[0021] Preferably, the oil phase solvent is white oil.

[0022] According to the present invention, the particle size of the acid-resistant nano-polymer microspheres is preferably 150-300 nm. Preferably, the particle size of the acid-resistant nano-polymer microspheres is 150-200 nm.

[0023] According to the present invention, the acid-resistant nano-polymer microspheres have the following structure:

[0024]

[0025] According to a preferred embodiment of the present invention, a method for preparing acid-resistant nano-polymer microspheres comprises the following steps:

[0026] (1) fully dispersing the basic building block monomer, hydrophobic monomer, acid-resistant monomer, nanoparticles, and dual cross-linking agent system in water to obtain an aqueous phase;

[0027] (2) dissolving the emulsifier in the oil phase solvent to obtain an oil phase;

[0028] (3) mixing the aqueous phase and the oil phase and emulsifying them to obtain a microemulsion;

[0029] (4) adding an initiator aqueous solution to the microemulsion, reacting, breaking the emulsion by phase inversion, filtering, washing, drying, grinding, granulating, and sieving to obtain acid-resistant nano-polymer microspheres.

[0030] Preferably, in step (3), the aqueous phase is added dropwise to the oil phase at a rate of 1-2 drops per second at room temperature and under stirring conditions of 500-700 r / min.

[0031] Preferably, in step (3), the emulsification speed is 500-700 r / min, and the emulsification time is 20-40 min.

[0032] Preferably, in step (4), the mass concentration of the initiator aqueous solution is 1%-5%; the droplet addition rate is 1-2 drops per second; the droplet addition temperature is 35-50°C; and the droplet addition is carried out under stirring at 300-400 r / min and protective gas protection conditions. Preferably, the protective gas is nitrogen or argon.

[0033] Preferably, in step (4), the reaction temperature is 35-50° C., the reaction time is 3-6 hours, and the reaction is carried out at a stirring rate of 300-400 r / min under protective gas protection. Preferably, the protective gas is nitrogen or argon.

[0034] According to the present invention, the acid-resistant low molecular weight cyclodextrin polymer is preferably prepared by including the following raw materials in parts by weight: 60-80 parts of basic building unit monomer a, 1-10 parts of inclusion monomer, 1-5 parts of acid-resistant monomer a, 1-10 parts of temperature-resistant monomer a, 1-10 parts of raft chain transfer agent, 2-4 parts of initiator system, and 100-200 parts of water.

[0035] Preferably, the acid-resistant low molecular weight cyclodextrin polymer is prepared by including the following raw materials in parts by weight: 70-80 parts of basic building unit monomer a, 3-5 parts of inclusion monomer, 1-2 parts of acid-resistant monomer a, 7-9 parts of temperature-resistant monomer a, 5-7 parts of raft chain transfer agent, 1-3 parts of initiator system, and 140-160 parts of water.

[0036] Further preferably, the acid-resistant low molecular weight cyclodextrin polymer is prepared by including the following raw materials in parts by weight: 75 parts of basic building unit monomer a, 4 parts of inclusion monomer, 1 part of acid-resistant monomer a, 8 parts of temperature-resistant monomer a, 6 parts of raft chain transfer agent, 2 parts of initiator system, and 150 parts of water.

[0037] Preferably, the basic building block monomer a is a combination of acrylamide (AM) and acrylic acid (AA), wherein the mass ratio of acrylamide (AM) to acrylic acid (AA) is 8:1-10:1.

[0038] Preferably, the inclusion monomer is allyl β-cyclodextrin.

[0039] Preferably, the acid-resistant monomer a is diallyldimethylammonium chloride.

[0040] Preferably, the temperature-resistant monomer a is sodium 3-(N-allyl-N-methylamino)propane-1-sulfonate.

[0041] Preferably, the raft chain transfer agent is benzyl dithiobenzoate.

[0042] Preferably, the initiator system is a three-stage initiator or a photoinitiator. Further preferably, the three-stage initiator system is a combination of a low-temperature initiator, a medium-temperature initiator, and a high-temperature initiator; the low-temperature initiator is potassium persulfate and sodium bisulfite, with the mass ratio of potassium persulfate to sodium bisulfite being 1:1; the medium-temperature initiator is 2,2'-azo(2-methylpropylamidine) dihydrochloride; and the high-temperature initiator is cyclohexanone peroxide; the mass ratio of the low-temperature initiator, medium-temperature initiator, and high-temperature initiator is 1:1:1. The photoinitiator is the water-soluble photoinitiator 2,2'-azo(2-methylpropylamidine) dihydrochloride.

[0043] According to the present invention, the acid-resistant low molecular weight cyclodextrin polymer has the structure shown below:

[0044]

[0045] According to a preferred embodiment of the present invention, a method for preparing an acid-resistant low molecular weight cyclodextrin polymer comprises the steps of:

[0046] The basic building unit monomer a, inclusion monomer, acid-resistant monomer a, heat-resistant monomer a, and raft chain transfer agent are fully dispersed in water, and the pH of the system is adjusted to 7; an initiator system is added dropwise, reacted, and then washed, crushed, dried, and granulated to obtain an acid-resistant low-molecular-weight cyclodextrin polymer.

[0047] Preferably, a NaOH aqueous solution with a mass concentration of 10-30% is used to adjust the pH of the system.

[0048] Preferably, when the initiator system is a three-stage initiator, the initiator system is an aqueous solution of the three-stage initiator at a mass concentration of 2%-5%. The reaction conditions are as follows: stirring at 3-8°C under protective gas until the system becomes viscous, and then allowing the reaction to proceed at 3-8°C under protective gas for 1-10 hours. More preferably, the protective gas is nitrogen or argon.

[0049] Preferably, when the initiator system is a photoinitiator, the reaction is carried out under ultraviolet light irradiation and protective gas protection, the reaction temperature is room temperature, and the reaction time is 2-4 hours; further preferably, the protective gas is nitrogen or argon; the ultraviolet light is provided by an ultraviolet high-pressure mercury lamp.

[0050] The preparation method of the acid-resistant nano-polymer microsphere inclusion plugging system comprises the following steps:

[0051] Acid-resistant nano-polymer microspheres are fully dispersed in water, expanded and aged to obtain a microsphere dispersion; acid-resistant low-molecular-weight cyclodextrin polymer is added, fully dispersed, and then aged to obtain an acid-resistant nano-polymer microsphere inclusion blocking system.

[0052] According to the preferred embodiment of the present invention, the expansion reaction temperature is 40-50° C., the expansion reaction time is 2-6 hours, and the expansion reaction is carried out under stirring conditions of 50-200 r / min.

[0053] According to the preferred embodiment of the present invention, during the preparation of the microsphere dispersion, the aging reaction temperature is 40-50° C., and the aging reaction time is 20-30 h.

[0054] Preferably, according to the present invention, after adding the acid-resistant low molecular weight cyclodextrin polymer, stirring is carried out at 40-50° C. and 50-200 r / min for 2-6 hours to fully disperse it.

[0055] According to the preferred embodiment of the present invention, after the acid-resistant low molecular weight cyclodextrin polymer is added, the aging reaction temperature is 40-50° C., and the aging reaction time is 30-70 hours.

[0056] The acid-resistant nano-polymer microsphere inclusion plugging system is used to plug gas channeling channels in CO2 flooding reservoirs.

[0057] The technical features and beneficial effects of the present invention are as follows:

[0058] 1. The acid-resistant nano-polymer microsphere inclusion plugging system provided by the present invention is environmentally friendly, has a wide source of raw materials, and is low in cost.

[0059] 2. The acid-resistant nano-polymer microspheres involved in the present invention have a double cross-linking effect in their molecular structure. The stable cross-linking agent N,N-methylenebisacrylamide and the unstable cross-linking agent polyethylene glycol diacrylate constitute the double cross-linking effect of the polymer microspheres. Polyethylene glycol diacrylate contains ester bonds and is a temperature-sensitive monomer; when the polymer microspheres are in a temperature environment higher than 60°C, the ester bonds in the unstable cross-linking agent will break. Therefore, the double cross-linking structure of the present invention has three effects: first, the polymer microspheres have good injectability; due to the double cross-linking effect, the polymer microspheres are in places with lower temperatures such as ground equipment, wellbores, and near injection wells. The unstable cross-linking agent can play a cross-linking role, making the polymer microspheres have a denser cross-linking structure. At this time, the polymer microspheres have poor water absorption and expansion, small particle size, and have the characteristics of delayed expansion, making them easy to be injected into the formation and migrate to deep places. Second, the polymer microspheres have strong deep plugging properties. Due to the delayed expansion caused by the double cross-linking effect, the polymer microspheres enter the deep formation. After reaching the high-temperature area, the ester bond in the unstable cross-linker breaks, and the polymer microspheres can then absorb water and expand a second time, thereby achieving effective plugging in the deep formation. Third, the acid resistance of the polymer microspheres is improved. The presence of the cationic acid-resistant monomer diallyldimethylammonium chloride in the molecular structure of the acid-resistant nano-polymer microspheres allows the polymer microsphere molecular chain to maintain a stretched configuration in an acidic environment, thus providing acid resistance. The secondary expansion characteristics of the microspheres caused by the unstable cross-linker can, to a certain extent, give the polymer microspheres another level of acid resistance.

[0060] 3. Because the hydrophobic monomer hexadecyldimethylallylammonium chloride is introduced during the synthesis process of the acid-resistant nanopolymer microspheres of the present invention, the hydrophobic monomer in the microspheres after the reaction occurs in three states: ① both ends of the hydrophobic chain and the main chain are completely inside the microsphere; ② both ends of the hydrophobic chain are inside the microsphere, and the main chain is outside the microsphere; ③ one end of the hydrophobic chain is inside the microsphere, and the other end is outside the microsphere. Only the microspheres formed in the third state can undergo supramolecular inclusion complexation with the β-cyclodextrin cavity to form a composite system. Figure 1 (a) is an acid-resistant nanopolymer microsphere with one end of the hydrophobic chain inside the microsphere and the other end outside the microsphere.

[0061] 4. The acid-resistant low molecular weight cyclodextrin polymer involved in the present invention has controllable molecular weight, strong shear resistance, good high temperature resistance and acid resistance. The RAFT chain transfer agent used in the present invention can make the β-cyclodextrin monomer block enter the polymer molecular chain, and can realize controllable preparation of polymers. The RAFT polymerization technology involved in the present invention can make the polymer molecular weight controllable, so the prepared cyclodextrin polymer has a low molecular weight (less than 1 million), and can have an excellent viscosity-increasing effect at low molecular weight. The low molecular weight cyclodextrin polymer prepared by the present invention has good shear resistance under high-speed shear due to the inclusion synergistic effect of β-cyclodextrin. The acid-resistant low molecular weight cyclodextrin polymer of the present invention is as follows Figure 1 (b) It consists primarily of two components: a hydrophilic backbone composed of acrylamide / acrylic acid and a side chain encompassing the β-cyclodextrin cavity. Cyclodextrin is a general term for a series of cyclic oligosaccharides linked by α-1,4-glycosidic bonds, produced by amylose in the presence of cyclodextrin glucosyltransferase (fermented by Bacillus). Each cyclodextrin molecule typically contains 6 to 12 glucopyranose units, with varying numbers of glucose units and spatial dimensions. The most studied are α-CD, β-CD, and γ-CD, which contain 6, 7, and 8 glucose units, respectively. The interior of the cyclodextrin cavity, shielded by C-H bonds, contains numerous hydrophobic groups, giving it a highly hydrophobic character. Therefore, under certain solvent conditions, the hydrophobic nature of the cyclodextrin cavity allows it to form stable host-guest inclusion complexes with small guest molecules that spatially match its structure.

[0062] 5. The acid-resistant nano-polymer microsphere inclusion plugging system of the present invention has the characteristics of low concentration and high efficiency, that is, high viscosity and excellent plugging effect can be achieved at a low concentration. The acid-resistant nano-polymer microspheres of the present invention have a hydrophobic alkyl long-chain guest structure in their molecular structure, and a β-cyclodextrin main structure in the acid-resistant low-molecular-weight cyclodextrin polymer molecular chain; the hydrophobic alkyl long-chain guest structure and the β-cyclodextrin main structure have an inclusion-enhancing supramolecular interaction, which can achieve the purpose of low concentration and high efficiency between the polymer microspheres and the polymer, such as Figure 1 As shown in (c), on the one hand, the inclusion complex between the polymer microspheres and the polymer strengthens the network structure of the polymer itself, which can enhance the viscosity of the polymer. On the other hand, the high viscosity of the polymer can maintain the good dispersion of the polymer microspheres in the dispersion system without aggregation, which is conducive to the migration of the polymer microspheres under the action of formation seepage.

[0063] 6. The acid-resistant nano-polymer microsphere inclusion plugging system involved in the present invention has strong acid resistance, excellent shear resistance, good injectability, and is easy to be injected into the formation and migrate to deep depths; at the same time, it has the characteristics of low concentration and high efficiency, can effectively enter the deep formation and efficiently achieve the plugging of cracks, thereby increasing the swept volume and displacement efficiency of CO2.

[0064] 7. The acid-resistant monomer in the raw material composition and the double-crosslinked structure in the molecular structure design of the acid-resistant nanopolymer microspheres involved in this invention are extremely important. The strong acid resistance and high plugging effect of the acid-resistant nanopolymer microspheres are mainly achieved by these two aspects. The acid-resistant monomer is diallyldimethylammonium chloride, and the molecular structure has polymerizable C=C double bonds at both ends, which participate in the molecular structure through cyclization during the reaction. Its five-membered ring structure and positive charge give it strong acid resistance. On the other hand, the double-crosslinked structure makes the acid-resistant nanopolymer microspheres temperature-sensitive, and can achieve secondary expansion to enhance acid resistance under harsh reservoir conditions.

[0065] 8. The inclusion monomer allyl β-cyclodextrin and the heat-resistant monomer sodium 3-(N-allyl-N-methylamino)propane-1-sulfonate are crucial components of the acid-resistant low-molecular-weight cyclodextrin polymer raw materials of this invention. The cyclodextrin polymer contains an acid-resistant monomer that has the same acid-resistant effect as the acid-resistant nanopolymer microspheres. Therefore, the inclusion monomer and the heat-resistant monomer are more important in improving the polymer's performance. Allyl β-cyclodextrin provides the structural foundation for the supramolecular inclusion interaction between the polymer and the polymer microspheres. Sodium 3-(N-allyl-N-methylamino)propane-1-sulfonate contains a sulfonic acid group, and therefore plays an important role in temperature resistance. Under acidic conditions, the tertiary amine group in sodium 3-(N-allyl-N-methylamino)propane-1-sulfonate is protonated to become an ammonium group, thereby causing the monomer to become a zwitterionic structure under acidic conditions. The hydrogen ions form a double-layer structure of counterions near the sulfonic acid group. The ammonium group has the same effect as the ammonium group in the acid-resistant monomer, which can make the polymer achieve stronger acid resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] Figure 1 Schematic diagram of the structure of the acid-resistant nano-polymer microspheres (a), the acid-resistant low molecular weight cyclodextrin polymer (b) and the acid-resistant nano-polymer microsphere inclusion blocking system (c). DETAILED DESCRIPTION

[0067] The present invention will be further described below in conjunction with specific examples. It should be understood that these examples are intended to illustrate the present invention only and are not intended to limit the scope of the invention. The experimental methods in the following examples, for which specific conditions are not specified, are generally performed under conventional conditions or as recommended by the manufacturer.

[0068] The preparation method for modified nano-silica with carbon-carbon double bonds on its surface is described in the DOI: https: / / doi.org / 10.1016 / j.colsurfa.2018.03.034. The specific preparation steps are as follows: 1g of nano-silica was ultrasonically dispersed in 44mL of a mixture of deionized water and anhydrous ethanol (the volume ratio of deionized water to ethanol was 1:10) for 1 hour. After dispersion, the mixture was placed in a three-necked flask connected to a nitrogen inlet, a reflux condenser, and a stirring device. The water bath temperature was maintained at 50°C and the stirring rate at 500 rpm. To the nano-silica dispersion, 1.03g of the silane coupling agent 3-(methacryloyloxy)propyltrimethoxysilane and 10 drops of 28% aqueous ammonia were added dropwise. The solution was allowed to react for 24 hours, then centrifuged and precipitated. The product was rinsed 3-5 times with anhydrous ethanol and then dried to obtain modified nano-silica with carbon-carbon double bonds on its surface. The particle size is between 1-10nm.

[0069] The polyethylene glycol diacrylate used in the examples has an average molecular weight of 308 and is commercially available.

[0070] Example 1

[0071] A method for preparing an acid-resistant nano-polymer microsphere inclusion plugging system comprises the following steps:

[0072] (1) Preparation of acid-resistant nanopolymer microspheres:

[0073] Preparation method: Accurately weigh 0.1g of diallyldimethylammonium chloride and 0.3g of N,N-methylenebisacrylamide and dissolve them in 15.85g of deionized water, and stir evenly with a magnetic stirrer; weigh 13.2g of acrylamide, 0.1g of polyethylene glycol diacrylate, and 0.3g of hexadecyldimethylallylammonium chloride and dissolve them in the above solution; after each agent is completely dissolved, continue stirring for 5 minutes before dissolving other agents, and finally weigh 0.05g of modified nano-silica with carbon-carbon double bonds on the surface and ultrasonically disperse it evenly; after all agents are evenly dissolved, pass nitrogen for 10 minutes and ultrasonically oscillate for 10 minutes to fully remove oxygen in the aqueous phase, and set aside.

[0074] According to the composition of the microemulsion under the condition of the optimal HLB value of 7.5, 12.7 g of Span80 and 5.42 g of Tween80 were weighed respectively, and dissolved in 51.88 g of white oil in turn using a magnetic stirrer. After nitrogen ultrasonic deoxygenation, the mixture was transferred to a four-necked flask and set aside.

[0075] Connect the synthesis reaction apparatus, control the speed to 600 r / min, and continuously flow nitrogen. Add the aqueous phase to the oil phase at room temperature at a rate of 1-2 drops per second. Stir and emulsify at 600 r / min for 30 minutes until the microemulsion becomes clear and transparent. Reduce the speed to 350 r / min, maintain a constant water bath temperature of 40°C, and add 2.25g of a 5% aqueous solution of the initiator 2,2'-azo(2-methylpropylamidine) dihydrochloride at a rate of 1-2 drops per second. Continue the reaction for 4 hours to obtain an acid-resistant nanopolymer microsphere emulsion.

[0076] Obtain solid microspheres. After the reaction is complete, cool and allow to stand at room temperature. Add anhydrous ethanol to induce phase transition and demulsification, precipitating the precipitate. Filter the precipitate and wash with anhydrous ethanol to thoroughly remove the oil adhering to the surface of the microspheres. Dry the solid in a 50°C drying oven for 24 hours. Grind, granulate, and sieve the solid microspheres to obtain acid-resistant nanopolymer microspheres with an average particle size of 175 nm.

[0077] (2) Preparation of acid-resistant low molecular weight cyclodextrin polymer:

[0078] 6.75g acrylamide, 0.75g acrylic acid, 0.4g allyl β-cyclodextrin, 0.6g benzyl dithiobenzoate, 0.8g sodium 3-(N-allyl-N-methylamino)propane-1-sulfonate, and 0.1g diallyldimethylammonium chloride were weighed and added to 15g of deionized water. The mixture was placed in a 250mL three-necked flask and dissolved under nitrogen flow with constant stirring. The pH of the solution was adjusted to 7 with a 20wt% aqueous solution of NaOH and then transferred to the flask. The three-necked flask was placed in a thermostatic water bath at 40°C with continuous nitrogen flow and high-speed stirring for 2-3 hours. Then, 4g of a 5% aqueous solution of 2,2'-azo(2-methylpropylamidine) dihydrochloride was added dropwise via syringe. The mixture was stirred under nitrogen at room temperature for 0.5h and then irradiated with a high-pressure mercury lamp for 2h. A transparent colloidal product was obtained, which was taken out and cut into small pieces, purified three times with ethanol, and then crushed, vacuum-dried, and granulated to obtain an acid-resistant low-molecular-weight cyclodextrin polymer dry powder.

[0079] (3) Preparation method of acid-resistant nano-polymer microsphere inclusion plugging system:

[0080] First, 0.3 g of acid-resistant nanopolymer microspheres were weighed and slowly dispersed in 100 mL of distilled water. The mixture was then stirred at high speed for 10 minutes to ensure that the microspheres were well dispersed and did not clump. Once the microspheres were evenly dispersed, the stirring speed was reduced and the microspheres were placed in a 45°C water bath at 100 rpm for 4 hours to expand. Stirring was then stopped and the dispersion was aged in a 45°C incubator for 24 hours. Then, 0.3 g of an acid-resistant low-molecular-weight cyclodextrin polymer was weighed and added to the aged dispersion at a ratio of 1:1. The mixture was stirred in a 45°C water bath at 100 rpm for 4 hours to ensure that the low-molecular-weight cyclodextrin polymer completely dissolved in the dispersion. The resulting composite system was then aged in a 45°C incubator for 48 hours to obtain an acid-resistant nanopolymer microsphere inclusion plugging system.

[0081] Example 2

[0082] A method for preparing an acid-resistant nano-polymer microsphere inclusion plugging system is as described in Example 1, except that: in step (1), the mass ratio of the stable cross-linking agent N,N-methylenebisacrylamide to the unstable cross-linking agent polyethylene glycol diacrylate in the acid-resistant nano-polymer microspheres is 4:1, that is, the amount of N,N-methylenebisacrylamide is 0.32g, and the amount of polyethylene glycol diacrylate is 0.08g; the other steps and conditions are the same as in Example 1.

[0083] Example 3

[0084] A method for preparing an acid-resistant nano-polymer microsphere inclusion plugging system is as described in Example 1, except that the synthesis method of the acid-resistant low molecular weight cyclodextrin polymer in step (2) is a three-stage initiation method; the details are as follows:

[0085] Weigh 6.75g acrylamide, 0.75g acrylic acid, 0.4g allyl β-cyclodextrin, 0.6g benzyl dithiobenzoate, 0.8g sodium 3-(N-allyl-N-methylamino)propane-1-sulfonate, and 0.1g diallyldimethylammonium chloride into 15g of deionized water. Place the mixture in a 250mL three-necked flask and dissolve under N2 flow with constant stirring. Adjust the solution to pH 7 with 20wt% aqueous NaOH solution and transfer it to the flask. Place the flask in a thermostatic water bath at 40°C with high-speed stirring for 2-3 hours while continuously flowing N2. Subsequently, 4 g of a 5% aqueous solution of a three-stage initiator (the low-temperature, medium-temperature, and high-temperature initiators were in a 1:1:1 mass ratio, with a 1:1 mass ratio of potassium persulfate to sodium bisulfite in the low-temperature initiator, namely 0.033 g of potassium persulfate, 0.033 g of sodium bisulfite, 0.066 g of 2,2'-azo(2-methylpropylamidine) dihydrochloride, and 0.066 g of cyclohexanone peroxide) was added dropwise via syringe. The mixture was stirred at 5°C under nitrogen until the mixture became viscous. The mixture was then allowed to react at 5°C under nitrogen for 6 hours. The resulting transparent, colloidal product was cut into small pieces and purified three times with ethanol. The resulting dry powder of an acid-resistant, low-molecular-weight cyclodextrin polymer was obtained by pulverization, vacuum drying, and granulation.

[0086] Other steps and conditions are the same as in Example 1.

[0087] Example 4

[0088] A method for preparing an acid-resistant nano-polymer microsphere inclusion blocking system is as described in Example 1, except that the mass ratio of the acid-resistant nano-polymer microspheres to the acid-resistant low molecular weight cyclodextrin polymer is 1:2, that is, the amount of the acid-resistant nano-polymer microspheres is 0.15g, and the amount of the acid-resistant cyclodextrin polymer is 0.3g; the other steps and conditions are the same as in Example 1.

[0089] Example 5

[0090] A method for preparing an acid-resistant nano-polymer microsphere inclusion blocking system is as described in Example 1, except that the mass ratio of the acid-resistant nano-polymer microspheres to the acid-resistant low-molecular-weight cyclodextrin polymer is 2:1, that is, the amount of the acid-resistant low-molecular-weight cyclodextrin polymer is 0.15 g, and the amount of the acid-resistant nano-polymer microspheres is 0.3 g; the other steps and conditions are the same as in Example 1.

[0091] Example 6

[0092] A method for preparing an acid-resistant nano-polymer microsphere inclusion plugging system is as described in Example 1, except that:

[0093] In step (1), the amount of hexadecyldimethylallyl ammonium chloride is 0.4 g, the amount of diallyldimethylammonium chloride is 0.2 g, and the amount of modified nano-silica (SiO2) with carbon-carbon double bonds on the surface is 0.06 g; other steps and conditions are the same as in Example 1.

[0094] Example 7

[0095] A method for preparing an acid-resistant nano-polymer microsphere inclusion plugging system is as described in Example 1, except that:

[0096] In step (2), the amount of diallyldimethylammonium chloride used is 0.2 g, the amount of 3-(N-allyl-N-methylamino)propane-1-sodium sulfonate used is 0.9 g, and the amount of allyl β-cyclodextrin used is 0.5 g; other steps and conditions are the same as in Example 1.

[0097] Comparative Example 1

[0098] A method for preparing a plugging system, as described in Example 1, except that no acid-resistant cyclodextrin polymer is added; the details are as follows:

[0099] The preparation of acid-resistant nanopolymer microspheres is the same as step (1) of Example 1;

[0100] First, 0.3g of acid-resistant nanopolymer microspheres were weighed and slowly dispersed in 100mL of distilled water. The solution was then stirred at high speed for 10 minutes to ensure that the microspheres were well dispersed in the water without clumping. Once the microspheres were evenly dispersed, the stirring speed was reduced and the solution was placed in a 45°C water bath at 100 rpm for four hours to expand. Stirring was then stopped and the dispersion was aged in a 45°C incubator for 24 hours to obtain a plugging system.

[0101] Comparative Example 2

[0102] A method for preparing a plugging system is as described in Example 1, except that the acid-resistant nanopolymer microspheres are replaced by ordinary acid-inresistant nanopolymer microspheres; that is, diallyldimethylammonium chloride is not added in step (1); and the other steps and conditions are the same as in Example 1.

[0103] Comparative Example 3

[0104] A method for preparing a plugging system is as described in Example 1, except that only a single cross-linked structure is used to prepare the acid-resistant nanopolymer microspheres. That is, in step (1), polyethylene glycol diacrylate is not added, and only the cross-linking agent N,N-methylenebisacrylamide is used. The other steps and conditions are the same as in Example 1.

[0105] Comparative Example 4

[0106] A method for preparing a plugging system is as described in Example 1, except that diallyldimethylammonium chloride monomer is not added in step (2); the other steps and conditions are the same as in Example 1.

[0107] Comparative Example 5

[0108] A method for preparing a plugging system is as described in Example 1, except that the temperature-resistant monomer 3-(N-allyl-N-methylamino)propane-1-sodium sulfonate is not added in step (2); the other steps and conditions are the same as in Example 1.

[0109] Comparative Example 6

[0110] A method for preparing a plugging system is as described in Example 1, except that modified nano-silica with carbon-carbon double bonds on its surface is not added in step (1). Other steps and conditions are the same as in Example 1.

[0111] Comparative Example 7

[0112] A method for preparing a plugging system is as described in Example 1, except that no chain transfer agent is added in step (2); the other steps and conditions are the same as in Example 1.

[0113] Test Example 1

[0114] The acid resistance of the plugging systems prepared in the examples and comparative examples was tested. The test method is as follows:

[0115] First, the volumetric method was used to test the expansion of polymer microspheres in water with a pH of 4. 1.0 mL of polymer microspheres was placed in a 40 mL colorimetric tube. 30 mL of water (hydrochloric acid solution) with a pH of 4 was added. The microspheres were allowed to expand at 80°C for 24 hours. The volume of the expanded microspheres was recorded, and the expansion multiple was calculated.

[0116] The viscosities of the plugging systems prepared in the examples and comparative examples at 80°C were measured using a viscometer, as well as those in which the water in the plugging systems was replaced with a hydrochloric acid solution with a pH of 4. This test measures the viscosity of the plugging system (water) and the plugging system (acid). The acid resistance of the plugging system was evaluated by measuring the expansion factor of the polymer microspheres and the viscosity of the composite system.

[0117] The composite system (acid) was injected into water at a constant rate of 0.5 mL / min and the permeability was 100×10 -3 μm 2 In a 10cm long core, we simulated actual formation shear by sampling the system at the production end and testing its viscosity. We then calculated the shear retention rate based on the viscosity values ​​before and after injection to evaluate the shear resistance of the composite system (acid). All of these tests were conducted at 80°C.

[0118] The test results are shown in Table 1.

[0119] Table 1 Acid resistance of acid-resistant nano-polymer microsphere inclusion plugging system

[0120]

[0121] The results of Table 1 show that the performance of the acid-resistant nano polymer microsphere inclusion sealing system (Example 1) prepared under the optimal raw material composition and synthesis conditions is the best. Factors such as the double cross-linked structure, the acid-resistant monomer and the cross-linking agent ratio all affect the expansion performance and acid resistance of the acid-resistant nano polymer microspheres; and the acid-resistant monomer and the heat-resistant monomer also affect the acid resistance of the acid-resistant low molecular weight cyclodextrin polymer. From the shear viscosity retention rate data, it can be clearly seen that the shear resistance of basically all systems is good, and only the shear resistance of the cyclodextrin polymer composite system without chain transfer agent in Comparative Example 7 is the worst; the reason is that when the chain transfer agent is not present, the chain termination reaction of the polymer in the synthesis process is delayed, resulting in a high molecular weight and long molecular chain of the synthesized polymer. Therefore, the long-chain polymer cannot withstand the pore throat shearing effect during the migration process, resulting in the lowest system viscosity retention rate. This also reflects that the addition of the chain transfer agent enables the synthesis process of the cyclodextrin polymer to synthesize a low molecular weight, shear-resistant polymer with better shear resistance.

[0122] Test Example 2

[0123] The CO2 blocking effect and enhanced oil recovery performance of the plugging systems prepared in the examples and comparative examples were tested. The testing method is as follows:

[0124] ① Saturate the core with oil and calculate the original oil saturation of the core;

[0125] ② Add a 0.03mm metal gasket to the middle of the matrix core to make a fracture core model; then place the core in a core holder and set the confining pressure to 15MPa and the back pressure to 7.6MPa;

[0126] ③Carry out CO2 gas drive oil recovery test at a constant flow rate of 0.5 mL / min, collect produced fluid every 1 minute at the core outlet, and calculate the gas drive recovery rate;

[0127] ④ After the production end of the pre-CO2 gas drive stops producing oil, replace it with a different plugging system and inject it at a volume of 0.6 times the core pore volume;

[0128] ⑤ Subsequently, CO2 flooding was performed at a constant flow rate of 0.5 mL / min. Produced fluid was collected at the core outlet every 1 minute until oil production ceased. The final recovery factor was calculated. The injection-production pressure differential was recorded throughout the entire oil flooding and CO2 channeling isolation experiment to calculate the plugging efficiency. All of the above experimental procedures were performed at 80°C. The test results are shown in Table 2.

[0129] Table 2 CO2 blocking performance and enhanced oil recovery effect of acid-resistant nano-polymer microsphere inclusion plugging system

[0130]

[0131]

[0132] The results in Table 2 show that the acid-resistant nano-polymer microsphere inclusion plugging system prepared under optimal conditions achieved a maximum plugging rate of 95.23%, the best effect in improving core heterogeneity, and a subsequent CO2 flooding enhanced oil recovery of up to 16.77%. The data from various examples and comparative examples demonstrate that the successful design of the acid-resistant monomer, dual-crosslinked structure, and inclusion supramolecular interaction introduced into the polymer microsphere and polymer preparation scheme results in an acid-resistant nano-polymer microsphere inclusion plugging system with superior acid resistance, plugging performance, and enhanced oil recovery.

[0133] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art will be able to modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein with equivalents. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. An acid-resistant nano-polymer microsphere inclusion plugging system, characterized in that: The method is prepared by the following raw materials in parts by weight: 1-5 parts of acid-resistant nano-polymer microspheres, 1-5 parts of acid-resistant low molecular weight cyclodextrin polymer, and 80-120 parts of water; The acid-resistant nano polymer microspheres are prepared by comprising the following raw materials in parts by weight: 110-150 parts of basic building block monomers, 1-15 parts of hydrophobic monomers, 1-20 parts of acid-resistant monomers, 0.1-3 parts of nanoparticles, 0.3-6 parts of a double cross-linking agent system, 0.2-3 parts of an initiator, 150-200 parts of an emulsifier, 500-550 parts of an oil phase solvent, and 100-200 parts of water; The basic building block monomer is acrylamide (AM); the hydrophobic monomer is hexadecyldimethylallyl ammonium chloride; the acid-resistant monomer is diallyldimethylammonium chloride; the nanoparticles are modified nano-silica (SiO2) with carbon-carbon double bonds on the surface. The modified nano-silica (SiO2) has the structure shown below and a particle size of 1-10 nm. The dual crosslinker system is a combination of a stable crosslinker N,N-methylenebisacrylamide and an unstable crosslinker polyethylene glycol diacrylate, wherein the mass ratio of N,N-methylenebisacrylamide to polyethylene glycol diacrylate is 6:4-9:1; The emulsifier is a combination of sorbitol fatty acid ester and polyoxyethylene sorbitan monooleate, wherein the mass ratio of sorbitol fatty acid ester to polyoxyethylene sorbitan monooleate is 2-3:1; the oil phase solvent is white oil; The acid-resistant low molecular weight cyclodextrin polymer is prepared by including the following raw materials in parts by weight: 60-80 parts of basic building block monomer a, 1-10 parts of inclusion monomer, 1-5 parts of acid-resistant monomer a, 1-10 parts of temperature-resistant monomer a, 1-10 parts of raft chain transfer agent, 2-4 parts of initiator system, and 100-200 parts of water; The basic building unit monomer a is a combination of acrylamide (AM) and acrylic acid (AA), wherein the mass ratio of acrylamide (AM) to acrylic acid (AA) is 8:1-10:1; the inclusion monomer is allyl β-cyclodextrin; the acid-resistant monomer a is diallyldimethylammonium chloride; the temperature-resistant monomer a is sodium 3-(N-allyl-N-methylamino)propane-1-sulfonate; and the raft chain transfer agent is benzyl dithiobenzoate.

2. The acid-resistant nano-polymer microsphere inclusion plugging system according to claim 1, characterized in that: The acid-resistant nano-polymer microsphere inclusion plugging system is prepared by including the following raw materials in parts by weight: 2-4 parts of acid-resistant nano-polymer microspheres, 2-4 parts of acid-resistant low-molecular-weight cyclodextrin polymer, and 90-110 parts of water.

3. The acid-resistant nano-polymer microsphere inclusion blocking system according to claim 1, characterized in that: The acid-resistant nano-polymer microspheres are prepared by including the following raw materials in parts by weight: 130-140 parts of basic building unit monomers, 2-4 parts of hydrophobic monomers, 1-2 parts of acid-resistant monomers, 0.4-0.6 parts of nanoparticles, 3-5 parts of a double cross-linking agent system, 0.8-1.2 parts of an initiator, 180-185 parts of an emulsifier, 510-520 parts of an oil phase solvent, and 155-160 parts of water.

4. The acid-resistant nano-polymer microsphere inclusion plugging system according to claim 1, characterized in that: The acid-resistant nano-polymer microspheres include one or more of the following conditions: i. The mass ratio of N,N-methylenebisacrylamide to polyethylene glycol diacrylate is 2:1-4:1 ii. The initiator is 2,2'-azo(2-methylpropylamidine) dihydrochloride.

5. The acid-resistant nano-polymer microsphere inclusion plugging system according to claim 1, characterized in that: The method for preparing acid-resistant nano-polymer microspheres comprises the following steps: (1) Fully dispersing the basic building block monomer, hydrophobic monomer, acid-resistant monomer, nanoparticles, and double cross-linking agent system in water to obtain an aqueous phase; (2) dissolving the emulsifier in the oil phase solvent to obtain the oil phase; (3) Mixing the aqueous phase and the oil phase and emulsifying them to obtain a microemulsion; (4) Adding an initiator aqueous solution to the microemulsion, reacting, breaking the emulsion by phase inversion, filtering, washing, drying, grinding, granulating, and sieving to obtain acid-resistant nanopolymer microspheres.

6. The acid-resistant nano-polymer microsphere inclusion plugging system according to claim 5, characterized in that: Include one or more of the following conditions: i. In step (3), the aqueous phase is added dropwise to the oil phase at a rate of 1-2 drops per second at room temperature and 500-700 r / min stirring; ii. In step (3), the emulsification speed is 500-700 r / min and the emulsification time is 20-40 min; iii. In step (4), the mass concentration of the initiator aqueous solution is 1%-5%; the dropping rate is 1-2 drops per second; the dropping temperature is 35-50°C; the dropping is carried out under stirring at 300-400 r / min and protective gas protection conditions; the protective gas is nitrogen or argon; iv. In step (4), the reaction temperature is 35-50° C., the reaction time is 3-6 hours, and the reaction is carried out at a stirring rate of 300-400 r / min under the protection of a protective gas; the protective gas is nitrogen or argon.

7. The acid-resistant nano-polymer microsphere inclusion plugging system according to claim 1, characterized in that: The acid-resistant low molecular weight cyclodextrin polymer is prepared by comprising the following raw materials in parts by weight: 70-80 parts of basic building block monomer a, 3-5 parts of inclusion monomer, 1-2 parts of acid-resistant monomer a, 7-9 parts of temperature-resistant monomer a, 5-7 parts of raft chain transfer agent, 1-3 parts of initiator system, and 140-160 parts of water.

8. The acid-resistant nano-polymer microsphere inclusion plugging system according to claim 1, characterized in that: The initiation system is a three-stage initiator or a photoinitiator; the three-stage initiation system is a combination of a low-temperature initiator, a medium-temperature initiator and a high-temperature initiator; the low-temperature initiator is potassium persulfate and sodium bisulfite, and the mass ratio of potassium persulfate to sodium bisulfite is 1:1; the medium-temperature initiator is 2,2'-azo (2-methylpropyl amidine) dihydrochloride; the high-temperature initiator is cyclohexanone peroxide; the mass ratio of the low-temperature initiator, the medium-temperature initiator and the high-temperature initiator is 1:1:1; the photoinitiator is a water-soluble photoinitiator 2,2'-azo (2-methylpropyl amidine) dihydrochloride.

9. The acid-resistant nano-polymer microsphere inclusion plugging system according to claim 1, characterized in that: The preparation method of an acid-resistant low molecular weight cyclodextrin polymer comprises the following steps: The basic building unit monomer a, inclusion monomer, acid-resistant monomer a, heat-resistant monomer a, and raft chain transfer agent are fully dispersed in water, and the pH of the system is adjusted to 7; an initiator system is added dropwise, reacted, and then washed, crushed, dried, and granulated to obtain an acid-resistant low-molecular-weight cyclodextrin polymer.

10. The acid-resistant nano-polymer microsphere inclusion plugging system according to claim 9, characterized in that: Include one or more of the following conditions: i. Use a 10-30% NaOH aqueous solution to adjust the pH of the system; ii. When the initiating system is a three-stage initiator, the initiating system is an aqueous solution of the three-stage initiator with a mass concentration of 2%-5%. The reaction conditions are as follows: stirring at 3-8°C under protective gas protection until the system becomes viscous, and then standing at 3-8°C under protective gas protection for 1-10 hours; the protective gas is nitrogen or argon; iii. When the initiator system is a photoinitiator, the reaction is carried out under ultraviolet light irradiation and protective gas protection, the reaction temperature is room temperature, and the reaction time is 2-4 hours; the protective gas is nitrogen or argon; the ultraviolet light is provided by an ultraviolet high-pressure mercury lamp.

11. A method for preparing the acid-resistant nano-polymer microsphere inclusion plugging system according to any one of claims 1 to 10, comprising the steps of: Acid-resistant nano-polymer microspheres are fully dispersed in water, expanded and aged to obtain a microsphere dispersion; acid-resistant low-molecular-weight cyclodextrin polymer is added, fully dispersed, and then aged to obtain an acid-resistant nano-polymer microsphere inclusion blocking system.

12. The method for preparing the acid-resistant nano-polymer microsphere inclusion plugging system according to claim 11, characterized in that: Include one or more of the following conditions: i. The expansion reaction temperature is 40-50°C, the expansion reaction time is 2-6 hours, and the expansion reaction is carried out under stirring conditions of 50-200 r / min; ii. During the preparation of the microsphere dispersion, the aging reaction temperature is 40-50°C and the aging reaction time is 20-30h; iii. After adding the acid-resistant low molecular weight cyclodextrin polymer, stir at 40-50°C and 50-200 r / min for 2-6 hours to fully disperse; iv. After adding the acid-resistant low molecular weight cyclodextrin polymer, the aging reaction temperature is 40-50° C. and the aging reaction time is 30-70 hours.

13. Use of the acid-resistant nano-polymer microsphere inclusion plugging system according to any one of claims 1 to 10, characterized in that: Used to seal gas channel in CO2 flooding reservoirs.

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