A polyacid-based heterogeneous supramolecular inclusion synergistic system for CO2 flooding reservoirs, and its preparation method and application

Abstract

The present invention provides a polyacid-based heterogeneous supramolecular inclusion enhancement system for CO2 flooding reservoirs, and its preparation method and application. The supramolecular inclusion enhancement system of the present invention is composed of acid-resistant hydrophobic polymer microspheres, acid-resistant cyclodextrin polymers and polyacids. The hydrophobic cavity structure in the acid-resistant cyclodextrin polymer molecular chain can efficiently identify the hydrophobic groups on the surface of the acid-resistant hydrophobic polymer microspheres, and the acid-resistant hydrophobic polymer microspheres are included through the host-guest inclusion action to form a new aggregate structure. A certain amount of polyacid is then added thereto, and a supramolecular network is constructed through electrostatic interaction to form a supramolecular inclusion enhancement system. The system has shear recovery. When injected under high shear conditions, the supramolecular effect is destroyed, and the viscosity of the system is reduced to improve the injectability; when injected into the underground, the in-situ viscosity increase of the formation after shearing is achieved through self-assembly, and the gas channel is effectively blocked, which is of great significance for improving the CO2 flooding effect.

Description

Technical Field

[0001] The present invention belongs to the technical field of oilfield chemistry, and in particular relates to a CO2 flooding reservoir heterogeneous supramolecular inclusion synergistic system based on polyacids, and a preparation method and application thereof. Background Art

[0002] As most medium- and high-permeability oilfields in my country have reached the middle and late stages of development, recoverable reserves are declining sharply year by year. The need to improve crude oil recovery in low-permeability reservoirs is becoming increasingly prominent. The exploration, development, and utilization of low-permeability reservoirs are crucial for ensuring the sustainable development of my country's oil and gas industry. Currently, waterflooding is the most commonly used development method. However, due to the low porosity, low permeability, and strong heterogeneity of these reservoirs, waterflooding efficiency is generally low. Gas flooding, with its growing popularity and significant success, has become the primary technology for developing these reservoirs.

[0003] CO2 gas is chemically stable, neither combustible nor supportive of combustion. It is a low-density, non-viscous, and highly fluid fluid. Its injection capacity is significantly higher than that of water injection, and its seepage resistance is low, making it easier to establish an effective displacement system than water injection. CO2 can undergo a series of physical and chemical reactions with subsurface fluids, causing crude oil volume expansion, a decrease in crude oil viscosity, and an increase in water viscosity. Under certain conditions, CO2 can be miscible with crude oil, significantly reducing interfacial tension and thereby improving oil displacement sweep efficiency. During oil displacement, some CO2 is stored in the reservoir, achieving CO2 sequestration. CO2 flooding not only significantly increases oil recovery but also addresses geological storage issues, protects the atmospheric environment, and mitigates the greenhouse effect, offering broad application prospects. However, reservoir heterogeneity, fracture characteristics, and CO2 fluid properties make CO2 injection development susceptible to gas channeling. Once gas channeling occurs, the swept volume of the gas decreases significantly, significantly reducing oil displacement efficiency and severely impacting the effectiveness of gas injection development.

[0004] To address the gas channeling problem during CO2 flooding, experts and scholars at home and abroad have proposed a variety of solutions: CO2 self-viscosification, foam plugging, and gel plugging. While these methods have been effective, they also present challenges. CO2 viscosity enhancement is costly and ineffective. While foam has good injection capacity, it suffers from poor stability and struggles to persist in the formation for extended periods. Gel has high viscosity, poor injection capacity, and uncontrollable gelling time. Therefore, for CO2 gas injection development, the development of new gas channeling prevention and control technologies is urgently needed to overcome the shortcomings of existing technologies. This is crucial for preventing and plugging gas channeling and improving gas injection effectiveness. Summary of the Invention

[0005] In response to the deficiencies in the prior art, the present invention provides a polyacid-based heterogeneous supramolecular inclusion enhancement system for CO2 flooding reservoirs, and its preparation method and application. The supramolecular inclusion enhancement system of the present invention is composed of acid-resistant hydrophobic polymer microspheres, acid-resistant cyclodextrin polymers and polyacids. The hydrophobic cavity structure in the molecular chain of the acid-resistant cyclodextrin polymer can efficiently identify the hydrophobic groups on the surface of the acid-resistant hydrophobic polymer microspheres, and the acid-resistant hydrophobic polymer microspheres are included through the host-guest inclusion action to form a new aggregate structure. A certain amount of polyacid is then added thereto, and a supramolecular network is constructed through electrostatic interaction to form a supramolecular inclusion enhancement system. The system has shear recovery. When injected under high shear conditions, the supramolecular effect is destroyed, and the viscosity of the system is reduced to improve injectability. When injected underground, the in-situ viscosity increase of the formation after shearing is achieved through self-assembly, which effectively realizes the blocking of gas channeling channels, which is of great significance for improving the effect of CO2 flooding.

[0006] The technical solutions of the present invention are as follows:

[0007] A polyacid-based heterogeneous supramolecular inclusion synergistic system for CO2 flooding reservoirs is prepared by including the following components in parts by weight: 1-10 parts of acid-resistant hydrophobic polymer microspheres, 1-5 parts of acid-resistant cyclodextrin polymer, 1-5 parts of polyacid, and 80-120 parts of water.

[0008] According to a preferred embodiment of the present invention, a polyacid-based heterogeneous supramolecular inclusion synergistic system for CO2 flooding reservoirs is prepared by including the following components in parts by mass: 3-5 parts of acid-resistant hydrophobic polymer microspheres, 1-3 parts of acid-resistant cyclodextrin polymer, 2-4 parts of polyacid, and 90-110 parts of water.

[0009] Preferably, the CO2 flooding reservoir heterogeneous supramolecular inclusion synergistic system based on polyacid is prepared by including the following components in parts by weight: 4 parts of acid-resistant hydrophobic polymer microspheres, 2 parts of acid-resistant cyclodextrin polymer, 3 parts of polyacid, and 100 parts of water.

[0010] According to the present invention, the structure of the acid-resistant hydrophobic polymer microspheres is shown as follows:

[0011]

[0012] According to a preferred embodiment of the present invention, a method for preparing acid-resistant hydrophobic polymer microspheres comprises the steps of:

[0013] (1) white oil, Span80, and Tween80 are mixed uniformly to obtain an oil phase;

[0014] (2) Fully dissolving acrylamide (AM), hexadecyldimethylallyl ammonium chloride (C16DMAAC), and dimethyldiallyl ammonium chloride (DMDAAC) in water, adjusting the pH value of the system, adding N,N-methylenebisacrylamide (MBA) and mixing uniformly to obtain an aqueous phase;

[0015] (3) The aqueous phase is added dropwise to the oil phase, and then an aqueous ammonium persulfate solution and an aqueous sodium bisulfite solution are added dropwise in sequence. After reaction, washing, drying, and grinding, the acid-resistant hydrophobic polymer microspheres are obtained.

[0016] Preferably, in step (1), the mass ratio of white oil, Span80, and Tween80 is 35-40:2-3:0.5-1.5, preferably 39:2.7:0.9.

[0017] Preferably, in step (2), the mass ratio of acrylamide (AM), hexadecyldimethylallylammonium chloride (C16DMAAC), dimethyldiallylammonium chloride (DMDAAC), N,N-methylenebisacrylamide (MBA) and water is 5-6:0.1-0.2:0.1-0.2:0.04-0.06:15-30, preferably 5.25:0.105:0.105:0.0546:21.

[0018] Preferably, in step (2), a sodium hydroxide aqueous solution with a mass concentration of 15%-30% is used to adjust the pH value of the system to 7.

[0019] Preferably, in step (3), the aqueous phase is added at a rate of 1-5 drops per second, and the addition is carried out under stirring and under the protection of a protective gas. Further preferably, the protective gas is nitrogen or argon.

[0020] Preferably, in step (3), the mass ratio of acrylamide in the aqueous phase to the mass ratio of the oil phase is 5-6:40-45.

[0021] Preferably, in step (3), the rate of addition of the aqueous ammonium persulfate solution and the aqueous sodium bisulfite solution is 1-5 drops per second, and the addition is carried out under stirring and under the protection of a protective gas. Further preferably, the protective gas is nitrogen or argon.

[0022] Preferably, in step (3), the mass concentrations of the ammonium persulfate aqueous solution and the sodium bisulfite aqueous solution are both 0.02%-0.2%, wherein the mass ratio of ammonium persulfate to sodium bisulfite is 1:1; and the mass ratio of ammonium persulfate to acrylamide in the aqueous phase is 1:475-785.

[0023] Preferably, in step (3), the reaction temperature is 25-40°C, the reaction time is 2-6 hours, and the reaction is carried out under stirring and protective gas. More preferably, the protective gas is nitrogen or argon.

[0024] According to the preferred embodiment of the present invention, the particle size of the acid-resistant hydrophobic polymer microspheres is 60-320 nm.

[0025] According to the present invention, the structure of the acid-resistant cyclodextrin polymer is as follows:

[0026]

[0027] According to a preferred embodiment of the present invention, a method for preparing an acid-resistant cyclodextrin polymer comprises the steps of:

[0028] Acrylamide (AM) and 6-O-allyl-β-cyclodextrin (DPTD) are dissolved in water, and sodium persulfate and sodium bisulfite are added and fully dissolved to obtain solution A; acrylic acid (AA) and azobisisobutylamidine dihydrochloride are mixed, and the pH value is adjusted to 7-8 to obtain solution B; solution A and solution B are mixed, dimethyldiallylammonium chloride, azobisisobutyronitrile, and dibenzoyl peroxide are added, and the mixture is uniformly mixed, reacted, crushed, precipitated, purified, dried, and granulated to obtain an acid-resistant cyclodextrin polymer.

[0029] Preferably, the mass ratio of acrylamide (AM) and 6-O-allyl-β-cyclodextrin (DPTD) is 15-30:1, preferably 18:1; the mass ratio of acrylamide and water is 1:3-8; the mass ratio of acrylamide (AM), sodium persulfate and sodium bisulfite is 3.6:0.0005-0.005:0.001-0.002, preferably 3.6:0.001:0.00151.

[0030] Preferably, the mass ratio of acrylic acid (AA), azobisisobutylamidine dihydrochloride and acrylamide is 1:0.001-0.005:3-4, preferably 1:0.002:3.6.

[0031] Preferably, a NaOH aqueous solution with a mass concentration of 15%-20% is used to adjust the pH.

[0032] Preferably, the mass ratio of dimethyldiallylammonium chloride, azobisisobutyronitrile, dibenzoyl peroxide and acrylamide is 0.1-0.3:0.001-0.005:0.0001-0.001:3-4, preferably 0.2:0.0025:0.0005:3.6.

[0033] Preferably, the reaction temperature is room temperature, the reaction time is 1-4 hours, and the reaction is carried out under static conditions and protective gas. Preferably, the protective gas is nitrogen or argon.

[0034] According to the present invention, preferably, the polyacid is pimelic acid, citric acid, disodium EDTA or sodium polyacrylate.

[0035] The preparation method of the polyacid-based CO2 flooding reservoir heterogeneous supramolecular inclusion synergistic system comprises the following steps:

[0036] Acid-resistant hydrophobic polymer microspheres are fully dispersed in water and subjected to expansion and aging reactions; then, an acid-resistant cyclodextrin polymer is added, fully dispersed, and then subjected to aging reactions; polyacid is added, fully dispersed, and allowed to stand to obtain a polyacid-based CO2 flooding reservoir heterogeneous supramolecular inclusion enhancement system.

[0037] Preferably, according to the present invention, the acid-resistant hydrophobic polymer microspheres are added to water and stirred at room temperature at 100-300 r / min for 5-15 minutes to fully disperse them.

[0038] According to the present invention, preferably, the expansion is carried out by stirring at room temperature and a rotation speed of 80-120 r / min for 3-5 hours.

[0039] According to the present invention, preferably, the aging is performed by static aging at 40-50° C. for 20-30 hours.

[0040] Preferably, according to the present invention, after the acid-resistant cyclodextrin polymer is added, stirring is performed at a speed of 80-120 r / min at room temperature for 2-6 hours to fully disperse it.

[0041] According to the preferred embodiment of the present invention, the aging reaction after adding the acid-resistant cyclodextrin polymer is to stand and age at 40-50° C. for 40-50 hours.

[0042] According to the preferred embodiment of the present invention, after the polyacid is added, stirring is performed at a speed of 80-120 r / min at room temperature for 0.1-1 hour to fully disperse the mixture.

[0043] According to the preferred embodiment of the present invention, the standing temperature is room temperature and the standing time is 1-3 hours.

[0044] The above-mentioned polyacid-based heterogeneous supramolecular inclusion enhancement system for CO2 flooding reservoirs is applied to plug gas channeling in CO2 flooding reservoirs.

[0045] The preparation routes of the acid-resistant hydrophobic polymer microspheres and the acid-resistant cyclodextrin polymer of the present invention are as follows:

[0046] Acid-resistant hydrophobic polymer microspheres:

[0047]

[0048] Acid-resistant cyclodextrin polymer:

[0049]

[0050] The technical features and beneficial effects of the present invention are as follows:

[0051] (1) The supramolecular inclusion synergistic system provided by the present invention has good acid resistance. For traditional microspheres and polymers, under acidic conditions, the hydrolysis of the amide groups in the microspheres is weak, which is not conducive to the expansion of the microspheres; while polymer microspheres mainly rely on water absorption to expand and aggregate to achieve blocking, but under acidic conditions, the structural density is large and the water absorption and expansion capacity is poor; at the same time, traditional polymers are composed of water-soluble polymers plus cross-linking agents, and the water-soluble polymer molecular chains often expose negatively charged anionic groups. In the acidic environment of CO2, its viscosity-increasing effect is poor and the acid resistance is poor. The polymer viscosity decreases, resulting in a poor blocking effect. The present invention introduces an acid-resistant monomer (dimethyldiallyl ammonium chloride (DMDAAC)) into acid-resistant hydrophobic polymer microspheres and acid-resistant cyclodextrin polymers, which enhances the acid resistance and enables them to be used under the acidic conditions of supercritical CO2.

[0052] (2) The components of the supramolecular inclusion synergistic system provided by the present invention interact with each other. The acid-resistant hydrophobic polymer microspheres contain long hydrophobic chains, and the acid-resistant cyclodextrin polymer contains cyclodextrin groups. The hydrophobic cavity structure of cyclodextrin can efficiently recognize the hydrophobic groups on the surface of the polymer microspheres, forming a new aggregate structure through the host-guest inclusion interaction, thereby increasing the fluid dynamics radius and bulk viscosity. Then, by using a polybasic organic acid with an anion and the cationic groups in the acid-resistant hydrophobic polymer microspheres and the acid-resistant cyclodextrin polymer to generate electrostatic interactions to construct a supramolecular network, forming a supramolecular inclusion synergistic system. This system has a stronger thickening effect than traditional polymers.

[0053] (3) The supramolecular inclusion synergistic system provided by the present invention can be used to block gas channeling and can effectively block gas channeling, thereby improving the CO2 flooding effect. Compared with the traditional particle system, the traditional particle system is easily broken through by gas in the formation, because the medium between the particles in the formation is water. In the heterogeneous supramolecular inclusion synergistic system provided by the present invention, the medium between the particles (acid-resistant hydrophobic polymer microspheres) in the formation is a composite system with high viscosity such as cyclodextrin polymer and polyacid. In addition, the cyclodextrin polymer and polyacid can interact with the surface of the particles and act as a cross-linking agent to bond the particles together, thereby effectively blocking the gas channeling. However, this effect is not strong. Under certain strong shearing action, the above effect will be destroyed, thereby reducing the viscosity of the system and improving the injectability. When injected into the ground, the in-situ viscosity increase of the formation after shearing is achieved through self-assembly, which not only solves the problem of poor injectability of the system, but also solves the problem of poor underground gas flooding sealing effect, laying the foundation for the application of low-cost CO2 flooding sealing technology.

[0054] (4) The ratio of the acid-resistant hydrophobic polymer microspheres, acid-resistant cyclodextrin polymer, and polyacid in the present invention needs to be appropriate. If an excessive amount of acid-resistant cyclodextrin polymer is added, the hydrophobic groups in the microspheres will be completely encapsulated, preventing the positively charged hydrophobic groups on the surface of the polymer microspheres from interacting with the polyacid. In addition, if an excessive amount of polyacid is added, the excessive negative charge will cause the hydrophobic chains to move away from each other, destroying the spatial network structure formed by electrostatic interactions.

[0055] (5) In the process of synthesizing the acid-resistant cyclodextrin polymer in the present invention, a three-stage composite initiator system is used, that is, a low-temperature-medium-temperature-high-temperature three-stage composite initiator is used as the initiator system. By matching different initiators, the molecular weight of the product is improved. Among them, the redox agent sodium persulfate / sodium bisulfite as a low-temperature initiator system has the advantages of high decomposition rate and fast initiation reaction; and the azo initiator azobisisobutylamidine dihydrochloride as a medium-temperature initiator can further expand the relative molecular weight of the polymer in the middle stage of the reaction; azobisisobutyronitrile / dibenzoyl peroxide as a high-temperature initiator, continues the two-stage reaction and promotes the reaction to be complete. The composite emulsifier used in the process of synthesizing the acid-resistant hydrophobic polymer microspheres of the present invention has better stability than a single emulsifier. This is because the complex formed by the composite emulsifier molecules at the oil-water interface makes the two-phase interface more concentrated, and the composite emulsifier increases the mixing entropy, which also makes the emulsification effect better. DETAILED DESCRIPTION

[0056] 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.

[0057] Example 1

[0058] A method for preparing a heterogeneous supramolecular inclusion synergistic system for CO2 flooding reservoirs based on polyacids comprises the following steps:

[0059] (1) Synthesis of acid-resistant hydrophobic polymer microspheres

[0060] Weigh 39g of white oil, 2.7g of Span80, and 0.9g of Tween80 into a four-necked flask equipped with a thermometer, stirrer, and reflux apparatus. Stir and mix thoroughly at 600 rpm. Flow nitrogen through the system for at least 30 minutes to remove dissolved oxygen.

[0061] Weigh 0.105 g of dimethyldiallyl ammonium chloride (DMDAAC), 5.25 g of acrylamide (AM), and 0.105 g of hexadecyldimethylallyl ammonium chloride (C16DMAAC) in a beaker and dissolve them in 21 g of deionized water. Stir evenly with a magnetic stirrer. After stirring and dissolving, adjust the pH value of the system to 7 with NaOH (aqueous solution, 20 wt%). Weigh 0.0546 g of N,N-methylenebisacrylamide and add it to the beaker and stir evenly. After each agent is completely dissolved, continue stirring for 5 minutes before dissolving other agents. After all agents are evenly dissolved, pass nitrogen for 15 minutes and ultrasonically oscillate for 15 minutes to fully remove oxygen in the aqueous phase.

[0062] After the oil phase was stirred for 20 minutes, the aqueous phase was added dropwise at a rate of 1-2 drops per second under nitrogen protection under stirring conditions of 600 r / min. After the microemulsion became clear and transparent, the rotation speed was reduced to 350 r / min, and a 0.2% aqueous solution of ammonium persulfate (wherein the mass of ammonium persulfate was 0.01092 g) and a 0.2% aqueous solution of sodium bisulfite (wherein the mass of sodium bisulfite was 0.01092 g) were added to the microemulsion in sequence at a rate of 1-2 drops per second. After the addition was completed, the reaction was continued with stirring at 40° C. under nitrogen protection for 4 hours.

[0063] After the reaction is completed, cool and stand at room temperature; repeatedly wash the microemulsion with anhydrous ethanol for 3-5 times to fully remove the oil phase adhering to the solid surface of the microspheres, and separate the solid and liquid using filter paper; place the solid in a drying oven at 50°C for 24 hours to fully dry, and grind the solid microspheres to obtain acid-resistant hydrophobic polymer microspheres with an average particle size of 82 nm.

[0064] (2) Synthesis of acid-resistant cyclodextrin polymers

[0065] 3.6 g of acrylamide and 0.2 g of 6-O-allyl-β-cyclodextrin were weighed, dissolved in 20 g of deionized water, and placed in a 250 mL three-necked flask. 0.001 g of sodium persulfate and 0.00151 g of sodium bisulfite were added and dissolved under constant stirring under nitrogen flow. 1 g of acrylic acid was weighed, 0.002 g of azobisisobutylamidine dihydrochloride was added, and the pH was adjusted to approximately 7-8 with a 20% aqueous NaOH solution. The mixture was then transferred to the flask. 0.2 g of dimethyldiallylammonium chloride was added, and 0.0025 g of azobisisobutylonitrile and 0.0005 g of dibenzoyl peroxide were added using a syringe and stirred to mix thoroughly. When the reaction system becomes viscous, stirring is stopped and the three-necked flask is sealed and placed for reaction at room temperature under nitrogen protection for 4 hours to obtain a transparent colloidal product. The product is taken out and cut into small pieces, and purified by acetone precipitation three times. After vacuum drying and granulation, acid-resistant cyclodextrin polymer particles are obtained.

[0066] (3) Preparation of heterogeneous supramolecular inclusion enhancement system for CO2 flooding reservoirs based on polyacids

[0067] Weigh 0.4g of acid-resistant hydrophobic polymer microspheres and slowly disperse them in 100mL of distilled water. Then stir at high speed at room temperature (stirring rate 200r / min) for 10 minutes so that the acid-resistant hydrophobic polymer microspheres can be well dispersed in water. When the acid-resistant hydrophobic polymer microspheres are evenly dispersed, reduce the stirring speed and expand at room temperature for 4 hours at a speed of 100r / min. Then stop stirring and put the acid-resistant hydrophobic polymer microsphere dispersion into a 45°C constant temperature box for aging for 24 hours. Then weigh 0.2g of acid-resistant cyclodextrin polymer and add it to the aged acid-resistant hydrophobic polymer microsphere dispersion. Stir at room temperature for 4 hours at a speed of 100r / min so that the acid-resistant cyclodextrin polymer is completely dispersed in the acid-resistant hydrophobic polymer microsphere dispersion. Put the prepared composite system into a 45°C constant temperature box and age for 48 hours. 0.3 g of pimelic acid was weighed and added to the above inclusion system in a ratio of acid-resistant hydrophobic polymer microspheres to polyacid of 1:0.75, and stirred at room temperature for 0.5 h at a speed of 100 r / min. Finally, it was allowed to stand at room temperature for 2 h to obtain a heterogeneous supramolecular inclusion enhancement system for CO2 flooding reservoirs based on polyacid.

[0068] Example 2

[0069] A method for preparing a heterogeneous supramolecular inclusion enhancement system for CO2 flooding reservoirs based on polyacids is as described in Example 1, except that the ratio of acid-resistant hydrophobic polymer microspheres to polyacid is 1:0.5, that is, the amount of pimelic acid used is 0.2 g; the other steps and conditions are the same as in Example 1.

[0070] Example 3

[0071] A method for preparing a heterogeneous supramolecular inclusion enhancement system for CO2 flooding reservoirs based on polyacids is as described in Example 1, except that the ratio of acid-resistant hydrophobic polymer microspheres to polyacid is 1:2, that is, the amount of pimelic acid used is 0.8 g; the other steps and conditions are the same as in Example 1.

[0072] Example 4

[0073] A method for preparing a heterogeneous supramolecular inclusion enhancement system for CO2 flooding reservoirs based on polyacids is as described in Example 1, except that the ratio of acid-resistant hydrophobic polymer microspheres to acid-resistant cyclodextrin polymer is 1:1, that is, the acid-resistant cyclodextrin polymer is 0.4 g; the other steps and conditions are the same as in Example 1.

[0074] Example 5

[0075] A method for preparing a heterogeneous supramolecular inclusion enhancement system for CO2 flooding reservoirs based on polyacids is as described in Example 1, except that: in the preparation of acid-resistant hydrophobic polymer microspheres in step (1), the amount of dimethyldiallylammonium chloride added is 0.2 g; the other steps and conditions are the same as in Example 1.

[0076] Example 6

[0077] A method for preparing a heterogeneous supramolecular inclusion enhancement system for CO2 flooding reservoirs based on polyacids is as described in Example 1, except that: in the preparation of acid-resistant hydrophobic polymer microspheres in step (1), the amount of hexadecyldimethylallyl ammonium chloride added is 0.2 g; the other steps and conditions are the same as in Example 1.

[0078] Example 7

[0079] A method for preparing a heterogeneous supramolecular inclusion enhancement system for CO2 flooding reservoirs based on polyacids is as described in Example 1, except that: in the preparation of the acid-resistant cyclodextrin polymer in step (2), the amount of dimethyldiallylammonium chloride added is 0.3 g; the other steps and conditions are the same as in Example 1.

[0080] Example 8

[0081] A method for preparing a heterogeneous supramolecular inclusion enhancement system for CO2 flooding reservoirs based on polyacids is as described in Example 1, except that: in the preparation of the acid-resistant cyclodextrin polymer in step (2), the amount of 6-O-allyl-β-cyclodextrin added is 0.12 g; the other steps and conditions are the same as in Example 1.

[0082] Comparative Example 1

[0083] A method for preparing a supramolecular inclusion synergistic system is as described in Example 1, except that the acid-resistant cyclodextrin polymer and the polybasic acid pimelic acid are not added; the details are as follows:

[0084] The preparation of acid-resistant hydrophobic polymer microspheres is the same as step (1);

[0085] Omit step (2);

[0086] Step (3) is as follows:

[0087] Weigh 0.4g of acid-resistant hydrophobic polymer microspheres and slowly disperse them in 100mL of distilled water. Then stir at high speed (stirring rate 200r / min) at room temperature for 10 minutes to allow the acid-resistant hydrophobic polymer microspheres to be well dispersed in water. When the acid-resistant hydrophobic polymer microspheres are evenly dispersed, reduce the stirring speed and expand at room temperature for 4 hours at 100r / min. Then stop stirring and place the acid-resistant hydrophobic polymer microsphere dispersion in a 45°C thermostat for 24 hours to obtain a supramolecular inclusion synergistic system.

[0088] Comparative Example 2

[0089] A method for preparing a supramolecular inclusion synergistic system is as described in Example 1, except that in step (3), no polybasic acid, pimelic acid, is added; the specific steps are as follows:

[0090] The preparation of acid-resistant hydrophobic polymer microspheres and acid-resistant cyclodextrin polymer is the same as steps (1) and (2), respectively;

[0091] Step (3) is as follows:

[0092] Weigh 0.4g of acid-resistant hydrophobic polymer microspheres and slowly disperse them in 100mL of distilled water. Then stir at high speed at room temperature (stirring rate 200r / min) for 10 minutes so that the acid-resistant hydrophobic polymer microspheres can be well dispersed in water. When the acid-resistant hydrophobic polymer microspheres are evenly dispersed, reduce the stirring speed and expand at room temperature for 4 hours at 100r / min. Then stop stirring and put the acid-resistant hydrophobic polymer microsphere dispersion into a 45°C constant temperature box for aging for 24 hours. Then weigh 0.2g of acid-resistant cyclodextrin polymer and add it to the aged acid-resistant hydrophobic polymer microsphere dispersion. Stir at room temperature for 4 hours at a speed of 100r / min so that the acid-resistant cyclodextrin polymer is completely dispersed in the acid-resistant hydrophobic polymer microsphere dispersion. Put the prepared composite system into a 45°C constant temperature box for aging for 48 hours to obtain a supramolecular inclusion synergistic system.

[0093] Comparative Example 3

[0094] A method for preparing a supramolecular inclusion synergistic system is as described in Example 1, except that in step (1), the acid-resistant monomer dimethyldiallyl ammonium chloride (DMDAAC) is not added; the other steps and conditions are the same as in Example 1.

[0095] Comparative Example 4

[0096] A method for preparing a supramolecular inclusion synergistic system is as described in Example 1, except that in step (2), the three-stage composite initiation system is changed to an azo reaction system (azobisisobutylamidine dihydrochloride); the details are as follows:

[0097] Step (2) is as follows:

[0098] 3.6g of acrylamide and 0.2g of 6-O-allyl-β-cyclodextrin were weighed, dissolved in 20g of deionized water, and placed in a 250mL three-necked flask. Under nitrogen, the mixture was stirred continuously to dissolve. 1g of acrylic acid was weighed, and 0.002g of azobisisobutylamidine dihydrochloride was added. The pH was adjusted to approximately 7-8 with a 20% aqueous solution of NaOH, and the mixture was then transferred to the flask. 0.2g of dimethyldiallylammonium chloride was added and stirred to mix thoroughly. Stirring was stopped when the reaction system became viscous, and the three-necked flask was sealed and allowed to react at room temperature under nitrogen for 4h. A transparent colloidal product was obtained, which was cut into small pieces and purified by acetone precipitation three times. The product was then vacuum-dried and granulated to obtain acid-resistant cyclodextrin polymer particles.

[0099] Other steps and conditions are the same as in Example 1.

[0100] Comparative Example 5

[0101] A method for preparing a supramolecular inclusion synergistic system is as described in Example 1, except that in step (3), no acid-resistant cyclodextrin polymer is added; the specific steps are as follows:

[0102] The preparation of acid-resistant hydrophobic polymer microspheres is the same as step (1);

[0103] Omit step (2);

[0104] Step (3) is as follows:

[0105] Weigh 0.4g acid-resistant hydrophobic polymer microspheres, slowly disperse them in 100mL distilled water, and then stir at room temperature at high speed (stirring rate 200r / min) for 10 minutes so that the acid-resistant hydrophobic polymer microspheres can be well dispersed in water. When the acid-resistant hydrophobic polymer microspheres are evenly dispersed, reduce the stirring speed, and expand at room temperature for 4 hours at 100r / min. Then stop stirring, and the acid-resistant hydrophobic polymer microsphere dispersion is placed in a 45°C thermostat and aged for 24 hours. According to the ratio of acid-resistant hydrophobic polymer microspheres to polyacids of 1:0.75, weigh 0.3g pimelic acid and add it to the above system, stir at room temperature for 0.5h at a speed of 100r / min, and finally stand at room temperature for 2h to obtain a supramolecular inclusion synergistic system.

[0106] Comparative Example 6

[0107] A method for preparing a supramolecular inclusion synergistic system is as described in Example 1, except that in step (1), hexadecyldimethylallylammonium chloride is replaced by octadecyldimethylallylammonium chloride; the other steps and conditions are the same as in Example 1.

[0108] Comparative Example 7

[0109] A method for preparing a supramolecular inclusion synergistic system is as described in Example 1, except that in step (2), the acid-resistant monomer dimethyldiallyl ammonium chloride (DMDAAC) is not added; the other steps and conditions are the same as in Example 1.

[0110] Test Example 1

[0111] Shear resistance test. The viscosity values ​​of the synergistic systems obtained in the examples and comparative examples before and after shear were tested. The test method is as follows:

[0112] First, the initial viscosity of the sample at 85°C was measured; then the viscosity was measured at 1000s -1 The shear rate was set at 85°C for 3 minutes, and the post-shear viscosity at 85°C was measured. The post-shear viscosity retention of the synergistic system was determined by analyzing the data. The results are shown in Table 1.

[0113] Table 1 Viscosity data of synergistic system

[0114] system Initial viscosity / mPa·s Viscosity after shearing / mPa·s Viscosity retention rate / % Example 1 112 109 97.4 Example 2 101 92 91.1 Example 3 87 72 82.8 Example 4 97 86 88.7 Example 5 109 104 95.4 Example 6 107 101 94.4 Example 7 105 98 93.3 Example 8 103 94 91.3 Comparative Example 2 74 52 70.3 Comparative Example 3 91 76 83.5 Comparative Example 4 82 60 73.2 Comparative Example 5 65 49 75.4 Comparative Example 6 94 81 86.2 Comparative Example 7 89 71 79.8

[0115] Viscosity As can be seen from the data in Table 1, the viscosity retention rate of the synergistic system of the present invention is relatively high, indicating that the supramolecular inclusion synergistic system has relatively high viscosity and shear resistance.

[0116] Test Example 2

[0117] Plugging Performance Test: The plugging performance of the synergistic systems obtained in the examples and comparative examples was tested using the following test method:

[0118] (1) A 0.03 mm wide metal gasket was added to the middle of the matrix core to make a fracture core model; the core was then placed in a core holder, and the confining pressure was set to 15 MPa and the back pressure to 7.6 MPa;

[0119] (2) Adjust the flow rate of the constant speed pump to 0.5 mL min -1 Perform CO2 gas flooding until the pressure stabilizes, record the injection pressure difference on both sides of the core holder, and calculate the permeability;

[0120] (3) 0.5 mL min -1 Inject 0.6 PV of the enhancement system solution into the core at a rate of 100 μm, heat the displacement device to 60-80°C, and shut down the displacement device for 8-12 hours;

[0121] (4) Again at 0.5 mL min -1 The CO2 gas drive was carried out at a rate of 100 nm until the pressure was stable. The injection pressure difference on both sides of the core holder was recorded, and the permeability and thus the plugging rate were calculated.

[0122] The plugging performance of the enhanced systems prepared in the examples and comparative examples was evaluated through indoor core flooding experiments. The results are shown in Table 2.

[0123] Table 2 Data on the plugging effect of the synergistic system

[0124] system <![CDATA[Pre-drive gas permeability / × 10 -3 μm 2 > <![CDATA[Permeability of postposition air drive / ×10 -3 μm 2 > Blockage rate / % Example 1 75.4 0.54 99.28 Example 2 85.8 5.06 94.10 Example 3 75.6 7.12 90.58 Example 4 84.6 6.68 92.10 Example 5 79.9 1.21 98.49 Example 6 81.5 1.90 97.67 Example 7 86.7 2.75 96.82 Example 8 73.3 3.14 95.72 Comparative Example 1 76.9 22.55 70.68 Comparative Example 2 77.2 11.97 84.49 Comparative Example 3 78.2 21.56 72.43 Comparative Example 4 83.6 23.77 71.57 Comparative Example 5 82.8 19.20 76.81 Comparative Example 6 79.7 10.52 86.80 Comparative Example 7 80.7 24.00 70.26

[0125] As shown in Table 2, the supramolecular inclusion synergistic system prepared in the embodiment can be smoothly injected into cracks with a size of 0.03 mm, has good injectability, and has a gas phase blocking rate of almost 90% or more, which can block gas channeling channels. The corresponding microsphere blocking rate is only 70.68%. After adding the acid-resistant cyclodextrin polymer, the blocking rate increases to 84.49%.

[0126] 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. A heterogeneous supramolecular inclusion synergistic system for CO2 flooding reservoirs based on polyacids, characterized in that: The method is prepared by comprising the following components in parts by weight: 1-10 parts of acid-resistant hydrophobic polymer microspheres, 1-5 parts of acid-resistant cyclodextrin polymer, 1-5 parts of polyacid or polyacid salt, and 80-120 parts of water; The preparation method of acid-resistant hydrophobic polymer microspheres comprises the following steps: (1) Mix white oil, Span80, and Tween80 evenly to obtain an oil phase; (2) Fully dissolve acrylamide (AM), hexadecyldimethylallyl ammonium chloride (C16DMAAC), and dimethyldiallyl ammonium chloride (DMDAAC) in water, adjust the pH value of the system, add N,N-methylenebisacrylamide (MBA) and mix well to obtain an aqueous phase; (3) adding the aqueous phase dropwise to the oil phase, and then sequentially adding an aqueous solution of ammonium persulfate and an aqueous solution of sodium bisulfite, reacting, washing, drying, and grinding to obtain acid-resistant hydrophobic polymer microspheres; The preparation method of the acid-resistant cyclodextrin polymer comprises the following steps: Acrylamide (AM) and 6-O-allyl-β-cyclodextrin (DPTD) are dissolved in water, and sodium persulfate and sodium bisulfite are added and fully dissolved to obtain solution A; acrylic acid (AA) and azobisisobutylamidine dihydrochloride are mixed, and the pH value is adjusted to 7-8 to obtain solution B; solutions A and B are mixed, and dimethyldiallylammonium chloride, azobisisobutyronitrile, and dibenzoyl peroxide are added, mixed evenly, reacted, and then crushed, precipitated, purified, dried, and granulated to obtain an acid-resistant cyclodextrin polymer. The polyacid or polyacid salt is pimelic acid, citric acid, disodium edetate or sodium polyacrylate.

2. The polyacid-based heterogeneous supramolecular inclusion synergistic system for CO2 flooding reservoirs according to claim 1, characterized in that: The polyacid-based heterogeneous supramolecular inclusion synergistic system for CO2 flooding reservoirs is prepared by including the following components in parts by weight: 3-5 parts of acid-resistant hydrophobic polymer microspheres, 1-3 parts of acid-resistant cyclodextrin polymer, 2-4 parts of polyacid or polyacid salt, and 90-110 parts of water.

3. The polyacid-based heterogeneous supramolecular inclusion synergistic system for CO2 flooding reservoirs according to claim 1, characterized in that: The method for preparing acid-resistant hydrophobic polymer microspheres includes one or more of the following conditions: i. In step (1), the mass ratio of white oil, Span80, and Tween80 is 35-40:2-3:0.5-1.5; ii. In step (2), the mass ratio of acrylamide (AM), hexadecyldimethylallylammonium chloride (C16DMAAC), dimethyldiallylammonium chloride (DMDAAC), N,N-methylenebisacrylamide (MBA) and water is 5-6:0.1-0.2:0.1-0.2:0.04-0.06:15-30; iii. In step (2), the pH value of the system is adjusted to 7 using a sodium hydroxide aqueous solution with a mass concentration of 15%-30%; iv. In step (3), the aqueous phase is added at a rate of 1-5 drops per second, and the addition is carried out under stirring and under the protection of a protective gas; the protective gas is nitrogen or argon; v. In step (3), the mass ratio of acrylamide in the aqueous phase to the oil phase is 5-6:40-45; vi. In step (3), the dropping rate of the aqueous ammonium persulfate solution and the aqueous sodium bisulfite solution is 1-5 drops per second, and the dropping is carried out under stirring conditions and protective gas protection; the protective gas is nitrogen or argon; vii. In step (3), the mass concentrations of the ammonium persulfate aqueous solution and the sodium bisulfite aqueous solution are both 0.02%-0.2%, wherein the mass ratio of ammonium persulfate to sodium bisulfite is 1:1; the mass ratio of ammonium persulfate to acrylamide in the aqueous phase is 1:475-785; viii. In step (3), the reaction temperature is 25-40°C, the reaction time is 2-6 hours, and the reaction is carried out under stirring and protective gas protection; the protective gas is nitrogen or argon.

4. The polyacid-based heterogeneous supramolecular inclusion synergistic system for CO2 flooding reservoirs according to claim 1, characterized in that: The method for preparing the acid-resistant cyclodextrin polymer includes one or more of the following conditions: i. The mass ratio of acrylamide (AM) to 6-O-allyl-β-cyclodextrin (DPTD) is 15-30:1; the mass ratio of acrylamide to water is 1:3-8; the mass ratio of acrylamide (AM), sodium persulfate, and sodium bisulfite is 3.6:0.0005-0.005:0.001-0.002; ii. the mass ratio of acrylic acid (AA), azobisisobutylamidine dihydrochloride and acrylamide is 1:0.001-0.005:3-4; iii. Use a 15%-20% NaOH aqueous solution to adjust the pH; iv. the mass ratio of dimethyldiallylammonium chloride, azobisisobutyronitrile, dibenzoyl peroxide and acrylamide is 0.1-0.3:0.001-0.005:0.0001-0.001:3-4; v. The reaction temperature is room temperature, the reaction time is 1-4 hours, and the reaction is carried out under static conditions and protective gas protection; the protective gas is nitrogen or argon.

5. The method for preparing the polyacid-based heterogeneous supramolecular inclusion synergistic system for CO2 flooding reservoirs according to any one of claims 1 to 4, comprising the steps of: Acid-resistant hydrophobic polymer microspheres are fully dispersed in water and subjected to expansion and aging reactions; then, an acid-resistant cyclodextrin polymer is added, fully dispersed, and then subjected to aging reactions; polyacid or polyacid salt is added, fully dispersed, and allowed to stand to obtain a polyacid-based CO2 flooding reservoir heterogeneous supramolecular inclusion enhancement system.

6. The method for preparing the polyacid-based heterogeneous supramolecular inclusion synergistic system for CO2 flooding reservoirs according to claim 5, characterized in that: Include one or more of the following conditions: i. Add the acid-resistant hydrophobic polymer microspheres into water and stir at room temperature at 100-300 r / min for 5-15 minutes to fully disperse them; ii. Expansion is carried out by stirring at room temperature and 80-120 r / min for 3-5 hours; iii. Aging is to place the product at 40-50°C for 20-30 hours; iv. After adding the acid-resistant cyclodextrin polymer, stir at room temperature at a speed of 80-120 r / min for 2-6 hours to fully disperse; v. The aging reaction after adding the acid-resistant cyclodextrin polymer is to stand at 40-50°C for 40-50 hours; vi. After adding the polyacid or polyacid salt, stir at room temperature at a speed of 80-120 r / min for 0.1-1 hour to fully disperse; vii. The standing temperature is room temperature and the standing time is 1-3 hours.

7. The use of the polyacid-based heterogeneous supramolecular inclusion synergistic system for CO2 flooding reservoirs according to any one of claims 1 to 4, characterized in that: Used to seal gas channel in CO2 flooding reservoirs.

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