A double-network CO2-responsive gel particle and its application

Abstract

The present invention relates to the technical field of oil and gas field development, and in particular to a double-network CO2-responsive gel particle and its application. In the gel particle, a covalent bond between acrylamide, zwitterions, CO2-responsive monomers (composed of vinyl pyridine and DMAEMA) and a crosslinking agent forms a first-layer network, which mineralizes Ca in water. 2+ , pyridine, SO in zwitterionic monomers 3‑ and coordinated water, Mg 2+ There are coordination bonds between pyridine, carboxyl (partial hydrolysis of amide group) and coordinated water, and the second layer of network is formed under the synergistic effect of π-π bonds between aromatic rings. The toughness of the double network structure enhances the strength of the gel; the introduction of aromatic ring sulfobetaine monomers and water molecules carried by coordination bonds increase the strength of gel particles in mineralized water and show stronger water retention. The introduction of CO2-responsive monomers with different pKa values ​​makes the particles have good CO2 responsiveness, and after the response, they still have the above-mentioned double network structure in mineralized water.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas field development, and specifically relates to a dual-network CO 2 responsive gel particles and their applications. Background Art

[0002] CO 2 flooding can achieve a win-win situation of improving oil reservoir recovery factor and CO 2 storage. Although this technology has been widely developed and applied, the existence of natural fractures in the formation makes CO 2 channeling occur during the CO 2 flooding process, reducing the sweep efficiency of CO

[0003] Conventional gel particles are generally synthesized from acrylamide monomers to form polymers, which are cross-linked with organic or inorganic cross-linking agents, etc. This makes conventional polymer gel particles face two main problems when plugging micro-fractures in formations with high salinity, especially high divalent metal ion content, during the CO 2 flooding process. On the one hand, cations in formation water will shield the negatively charged groups in the polymer, weakening the intermolecular forces of the polymer, resulting in a decrease in the elastic free energy of the system, making it easier to reach a stable state and reducing the water absorption capacity of the particles. To overcome this shortcoming of conventional polymer gel particles, zwitterionic monomers or cationic monomers are introduced during the polymer preparation process to form polyzwitterionic electrolytes, enabling them to exhibit the "anti-polyelectrolyte effect" of volume swelling in salt solutions. However, these gels show typical swelling-weakening phenomena due to the dilution of the network, and the mechanical strength decreases after swelling. On the other hand, the decrease in pH value during the CO 2 flooding process destroys the cross-linked structure of conventional polymer gel particles, resulting in dehydration and gel breaking phenomena. Therefore, CO 2Responsive gel particles have attracted people's attention. These gel particles generally contain cationic groups such as dimethyldiallylammonium chloride (Bobo Zhou, Wanli Kang, Hongbin Yang, Tongyu Zhu, Hongwen Zhang, Xinxin Li, Bauyrzhan Sarsenbekuly, Turtabayev Sarsenbek. Preparation and properties of an acid-resistant preformed particle gel for conformance control[J]. Journal of Petroleum Science and Engineering, 197, 2021, 107964.) or have CO 2 responsive organic amine monomers, such as N,N-dimethylaminoethyl methacrylate (DMAEMA) (Liu Yajie. Preparation and performance enhancement of CO 2 responsive gels[D]. China University of Petroleum (Beijing), 2023.), vinylimidazole (Chen Wuhua, Liu Zhicong, Wang Yefei, Ding Mingchen, Cui Shizhang. A CO 2 responsive salt-tolerant polymer gel particle and its application[P], 2024.), dimethylaminopropyl methacrylamide (DMAPMA) (Meng Mu, Hongyao Yin, Yujun Feng. CO 2 -responsive polyacrylamide microspheres with interpenetrating networks[J]. Journal of Colloid and Interface Science, 497, 2017, 249.), etc., which significantly increase the swelling ratio in an acidic environment. However, the significant increase in the swelling ratio often leads to a decrease in gel strength, especially the increase in the salinity of formation water will reduce the pH value of the system (Reza K. Haghi, Antonin Chapoy, Luís M.C. Peirera, Jinhai Yang, Bahman Tohidi. pH of CO 2 saturated water and CO 2Saturated brines: experimental measurements and modeling[J]. International Journal of Greenhouse Gas Control, 66, 2017, 190.), which further damages the strength of the gel.

[0004] The significant weakening of the swelling ratio or strength limits the use of gel particles in the formation. Especially when exposed to high-pressure conditions in the formation, the reduction in strength makes the gel particles vulnerable to physical damage, thus reducing their plugging efficiency. Therefore, how to prepare a CO-responsive gel particle with enhanced swelling in mineralized water and still maintain a high strength in mineralized water after response is of great significance for CO flooding in high-mineralization microfracture reservoirs. 2 A CO-responsive gel particle, and still maintain a high strength in mineralized water after response, is of great significance for CO flooding in high-mineralization microfracture reservoirs. 2 Drive has important significance. Summary of the Invention

[0005] The purpose of the present invention is to overcome the above-mentioned deficiencies of the prior art and provide a double-network CO-responsive gel particle and its application. Based on acrylamide monomers, zwitterionic monomers and two CO-responsive monomers are introduced. Through the interaction between monomers and divalent metal ions in formation water, the characteristics of enhanced swelling of gel particles in mineralized water, good CO-responsive effect and high strength in high-mineralized water after response are realized. 2 A double-network CO-responsive gel particle and its application. Based on acrylamide monomers, zwitterionic monomers and two CO-responsive monomers are introduced. Through the interaction between monomers and divalent metal ions in formation water, the characteristics of enhanced swelling of gel particles in mineralized water, good CO-responsive effect and high strength in high-mineralized water after response are realized. 2 Response monomer, through the interaction between monomers and divalent metal ions in formation water, realizes the characteristics of enhanced swelling of gel particles in mineralized water, good CO 2 Response effect and still has high strength in high-mineralized water after response.

[0006] To achieve the above technical effects, the present invention uses the following technical solutions:

[0007] A double-network CO 2 Response gel particle, prepared by the following method:

[0008] S1. Put acrylamide, zwitterionic monomer, CO 2 Response monomer and emulsifier into deionized water, stir and mix evenly to obtain the first mixed solution;

[0009] S2. Adjust the pH of the first mixed solution to 7, and introduce N into the first mixed solution under ice bath 2 To discharge air to obtain the second mixed solution;

[0010] S3. Add the initiator and crosslinker to the second mixed solution successively under stirring, adjust the temperature to 30°C - 60°C and keep introducing N 2 And react for 2h - 4h to obtain the reaction product;

[0011] S4. Wash the reaction product prepared in step S3 with absolute ethanol, and then dry, grind and screen to obtain the target product double-network CO2 Responsive gel particles;

[0012] In the preparation method, the feeding percentages of each component are as follows: 15%-20% acrylamide, 5-10% zwitterionic monomer, 5-10% CO 2 responsive monomer, 0.25-1% emulsifier, 0.05%-0.25% crosslinking agent, 0.075%-0.15% initiator, and the balance water.

[0013] Among them, the CO 2 responsive monomer is composed of vinylpyridine and N,N-dimethylaminoethyl methacrylate (DMAEMA) in a mass ratio of (0.5-1):1.

[0014] Preferably, in step S1, deionized water is used as the water.

[0015] Preferably, the zwitterionic monomer is selected from one of 4-(2-sulfoethyl)-1-(4-vinylbenzyl)pyridinium betaine, 3-(1-(4-vinylbenzyl)-1H-imidazol-3-ium)propane-1-sulfonate, or 3-(dimethyl(4-vinylbenzyl)amino)propanesulfonate.

[0016] Preferably, the vinylpyridine is selected from one of 4-vinylpyridine and 2-vinylpyridine; further preferably, the mass ratio of vinylpyridine to DMAEMA is 2:3; more preferably, the vinylpyridine is 4-vinylpyridine.

[0017] Preferably, the emulsifier is one or two of sodium dodecyl sulfate, OP-10, and sodium stearate; further preferably, the emulsifier is a mixture of sodium dodecyl sulfate and OP-10, and their mass ratio is 1:4.

[0018] Preferably, the crosslinking agent is selected from one or a mixture of two of N,N'-methylenebisacrylamide or polyethylene glycol diacrylate; more preferably, when the crosslinking agent is N,N'-methylenebisacrylamide and polyethylene glycol diacrylate, the mass ratio of the two is (1.5-6):1; further preferably, the mass ratio is 4:1.

[0019] Further preferably, the crosslinking agent is N,N'-methylenebisacrylamide.

[0020] Preferably, the initiator is selected from the azo compound 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride or the initiator is composed of sodium bisulfite and ammonium persulfate; further preferably, when the initiator is composed of sodium bisulfite and ammonium persulfate, the molar ratio range of sodium bisulfite to ammonium persulfate is (0.6-1.2):1.

[0021] Preferably, in step S2, the ice bath temperature is 0°C.

[0022] Preferably, in step S3, the stirring speed is 100 rpm - 500 rpm; more preferably, the stirring speed is 200 rpm.

[0023] Preferably, in step S4, the drying temperature is 60°C, the drying time is 48 h, and particles with an initial particle size less than 135 μm are sieved using a sieve.

[0024] Preferably, in the preparation method, the mass percentages of each component charged are: 15% acrylamide, 10% zwitterionic monomer, 10% CO 2 responsive monomer, 0.3% emulsifier, 0.1% crosslinking agent, 0.1% initiator, and the balance water, wherein the CO 2 responsive monomer is composed of 4-vinylpyridine and DMAEMA in a mass ratio of 2:3.

[0025] The double-network CO 2 responsive gel particles provided by the present invention, covalent bonds between acrylamide, zwitterionic monomer, CO 2 responsive monomer, and crosslinking agent in the gel particles form the first three-dimensional network structure, and Ca 2+ ions, pyridyl groups, SO in the zwitterionic monomer 3 - and coordinated water, and between Mg 2+ ions, pyridyl groups, carboxyl groups (produced by partial hydrolysis of amide groups), and coordinated water all have metal coordination bonds. Additionally, π-π stacking interactions between aromatic rings form the second network structure, and the toughness of the double-network structure significantly enhances the strength of the gel; the introduction of the aromatic ring sulfobetaine zwitterionic monomer with an "anti-polyelectrolyte effect" and a large number of water molecules carried by the metal coordination bonds enable the gel particles to exhibit stronger water retention performance while increasing the strength in high salinity water. CO with different pKa values is simultaneously introduced into the gel particles 2 responsive monomers vinylpyridine and DMAEMA. During CO 2 flooding in fractured reservoirs, DMAEMA with a high pKa value is first protonated, significantly increasing the swelling ratio of the gel particles. However, vinylpyridine with a low pKa value, due to its low degree of protonation, can still form coordination bonds with Ca 2+ , Mg 2+ ions, coordinated water, etc. The formation of the double-network structure results in an increase in strength that exceeds the strength loss caused by CO 2 response. Therefore, compared with the performance of gel particles in deionized water, the gel particles in high salinity water exhibit excellent properties of swelling and strength enhancement after CO 2 response.

[0026] The present invention also provides the above-mentioned double-network CO 2 responsive gel particles for plugging microfractures in oil reservoirs.

[0027] Preferably, the application specifically is that at a temperature of 25°C - 120°C, the formation water salinity is 0 - 10%, where the Ca 2+ , Mg 2+ ion content is 0 - 1%, plugging fractures in the oil reservoir with a width of 0.2 mm - 0.5 mm. The double-network CO 2 responsive gel particles are uniformly dispersed in the formation water as a plugging agent and injected into the formation, and the fractures are plugged after aging for 24 h.

[0028] Preferably, the oil reservoir is a low-permeability oil reservoir; more preferably, the oil reservoir is a low-permeability oil reservoir undergoing CO 2 flooding.

[0029] Advantages of the present invention:

[0030] 1. In the double-network CO 2 responsive gel particles of the present invention, covalent bonds among acrylamide, zwitterionic monomer, CO 2 responsive monomer and crosslinking agent form the first three-dimensional network structure. There are metal coordination bonds among Ca 2+ ions, pyridyl groups, SO 3 - in mineralized water, zwitterionic monomer, and coordinated water, and among Mg 2+ ions, pyridyl groups, carboxyl groups (produced by partial hydrolysis of amide groups) and coordinated water. In addition, π-π stacking between aromatic rings forms the second network structure. The toughness of the double-network structure significantly enhances the strength of the gel; the introduction of aromatic ring sulfobetaine zwitterionic monomers with "anti-polyelectrolyte effect" and a large number of water molecules carried by metal coordination bonds enable the gel particles to exhibit stronger water retention performance while increasing the strength in high-salinity water.

[0031] 2. In the double-network CO 2 responsive gel particles provided by the present invention, the CO 2 responsive monomer consists of vinylpyridine and DMAEMA with different pKa values. The pKa values of 4-vinylpyridine, 2-vinylpyridine and DMAEMA are 5.62, 4.98 and 8.18 respectively. After contacting with CO 2 , DMAEMA with a high pKa value is protonated first, and vinylpyridine with a low pKa value is not protonated or has a low degree of protonation, so it can continue to form metal coordination bonds with Ca 2+ , Mg 2+ in mineralized water and coordinated water, etc. The formation of the double-network structure leads to an increase in strength exceeding that of CO2 The intensity loss caused by the response. Therefore, compared with the performance of gel particles in deionized water, the gel particles in high-mineralized water have CO 2 exhibit excellent swelling and strength enhancement performance after the response.

[0032] 3. The gel particles of the present invention have the characteristics of swelling and strengthening in high-mineralized water, good CO 2 response characteristics and still having the characteristic of enhancing the gel strength by metal coordination crosslinking after the response, and can effectively block microfractures during CO 2 flooding in high-mineralized microfracture reservoirs. Detailed implementation manners

[0033] The present invention will be further described below in conjunction with examples and comparative examples.

[0034] The materials and testing equipment used in each example and comparative example are all commonly used commercially available materials and testing equipment. For example, acrylamide is purchased from Puyang Haiyuan Chemical Industry Co., Ltd., 4-vinylpyridine and 2-vinylpyridine are both purchased from Jiangsu Bost Chemical Technology Co., Ltd., DMAEMA is purchased from Jinan Century Tongda Chemical Co., Ltd., and the sources of other materials are not elaborated here. Those skilled in the art can select different manufacturers according to needs.

[0035] The synthesis process of zwitterionic monomer 4-(2-sulfoethyl)-1-(4-vinylbenzyl)pyridinium betaine is as follows:

[0036] 。

[0037] The specific synthesis steps are as follows: In a 250 mL three-necked round-bottom flask equipped with a reflux condenser, thermometer and magnetic stirrer, dissolve 18.72 g of 4-pyridineethanesulfonic acid (0.1 mol) and 4.0 g of NaOH (0.1 mol) in 150 mL of formamide solution, and pass N 2 for 30 min, then slowly add dropwise 15.26 g of p-chloromethylstyrene (0.1 mol), and stir the reaction mixture at room temperature for 72 h. After the reaction is completed, precipitate in acetone and recover the solid, and then recrystallize with absolute ethanol.

[0038] The synthesis process of zwitterionic monomer 3-(1-(4-vinylbenzyl)-1H-imidazol-3-ium) propane-1-sulfonate:

[0039] 。

[0040] The synthesis process of zwitterionic monomer 3-(dimethyl(4-vinylbenzyl)amino)propanesulfonate:

[0041] 。

[0042] Example 1

[0043] A double-network CO 2 responsive gel particle, by mass percentage, includes:

[0044] 15% acrylamide, 10% zwitterionic monomer, 10% CO 2 responsive monomer (where the mass ratio of 4-vinylpyridine to DMAEMA is 2:3), 0.3% emulsifier, 0.1% crosslinker, 0.1% initiator, and the balance water.

[0045] Specifically, in this example, the zwitterionic monomer is 3-(1-(4-vinylbenzyl)-1H-imidazol-3-ium) propane-1-sulfonate, the crosslinker is N,N′-methylenebisacrylamide, the initiator consists of ammonium persulfate and sodium bisulfite in an equal mass ratio, and the water is deionized water.

[0046] The double-network CO 2 responsive gel particle provided in this example is prepared by the following method:

[0047] S1. Put 15 g of acrylamide, 10 g of 3-(1-(4-vinylbenzyl)-1H-imidazol-3-ium) propane-1-sulfonate, 4 g of 4-vinylpyridine, 6 g of DMAEMA, and 0.3 g of emulsifier (0.06 g of sodium dodecyl sulfonate + 0.24 g of OP-10) into 63.5 g of deionized water, stir and mix evenly to obtain a first mixed solution;

[0048] S2. Use a 0.1 mol / L NaHCO 3 solution to adjust the pH of the first mixed solution to 7.0. Under an ice bath at 0 °C, introduce N 2 into the first mixed solution for a total of 30 min to expel air and obtain a second mixed solution;

[0049] S3. Dissolve 0.05 g of potassium persulfate and 0.05 g of sodium bisulfite in 1 g of deionized water to obtain an initiator solution. While stirring and continuously introducing N 2 into the second mixed solution, add the initiator solution, and then add 0.1 g of N,N′-methylenebisacrylamide. Keep introducing N 2 and react at 40 °C with a stirring rate of 200 rpm for 3 h;

[0050] S4. Cut the reaction product obtained in step S3 into pieces, soak it repeatedly 3 times in absolute ethanol, dry it at 60 °C for 48 h, crush it into particles, and use a sieve to screen gel particles with an initial particle size less than 135 μm.

[0051] Use the above gel particles for CO 2During the driving process, the microcracks are blocked, and the crack width is 0.3 mm.

[0052] Example 2

[0053] A double-network CO 2 Responsive gel particles, which are different from those in Example 1 in that the zwitterionic monomer is 3-(dimethyl(4-vinylbenzyl)amino)propanesulfonate, and other components and preparation methods are the same as those in Example 1.

[0054] Example 3

[0055] A double-network CO 2 Responsive gel particles, which are different from those in Example 1 in that the zwitterionic monomer is 4-(2-sulfoethyl)-1-(4-vinylbenzyl)pyridinium betaine, and other components and preparation methods are the same as those in Example 1.

[0056] Example 4

[0057] A double-network CO 2 Responsive gel particles, which are different from those in Example 1 in that the mass ratio of 4-vinylpyridine to DMAEMA is 1:1, and other components and preparation methods are the same as those in Example 1.

[0058] Example 5

[0059] A double-network CO 2 Responsive gel particles, and the mass percentage of each component is as follows:

[0060] 20% acrylamide,

[0061] 7.5% 3-(1-(4-vinylbenzyl)-1H-imidazol-3-ium)propane-1-sulfonate,

[0062] 7.5% mixture of 4-vinylpyridine and DMAEMA, in which the mass ratio of 4-vinylpyridine to DMAEMA is 2:3,

[0063] 0.25% N,N′-methylenebisacrylamide,

[0064] A total mass of 0.075% of ammonium persulfate and sodium bisulfite with equal mass ratio,

[0065] The balance is water;

[0066] During the preparation process, the feeding masses of each component are also replaced accordingly, and the specific preparation method is the same as that in Example 1.

[0067] Example 6

[0068] A double-network CO 2Responsive gel particles, different from those in Example 1, in which the pyridine monomer is 2-vinylpyridine, and other components and preparation methods are the same as those in Example 1.

[0069] Example 7

[0070] A double-network CO 2 Responsive gel particles, different from those in Example 1, in which the crack width is 0.2 mm, and other components and preparation methods are the same as those in Example 1.

[0071] Example 8

[0072] A double-network CO 2 Responsive gel particles, different from those in Example 1, in which the crack width is 0.5 mm, and other components and preparation methods are the same as those in Example 1.

[0073] Example 9

[0074] A double-network CO 2 Application of responsive gel particles in plugging micro-cracks during CO 2 displacement process. In this example, the gel particles are selected from the gel particles provided in Example 1.

[0075] Specifically, at a temperature of 50 °C, the formation water salinity is 10%, in which the content of Ca 2+ , Mg 2+ ions is 1%, plugging a crack with a width of 0.3 mm, uniformly dispersing the double-network CO 2 responsive gel particles in the mineralized water as a plugging agent and injecting it into the formation. After aging for 24 h, the gas channel is plugged, and the plugging rate of the crack is ≥ 90%.

[0076] In this example, the reservoir is a low-permeability reservoir for CO 2 displacement.

[0077] Example 10

[0078] A double-network CO 2 Application of responsive gel particles in plugging micro-cracks during CO 2 displacement process. In this example, the gel particles are selected from the gel particles provided in Example 5.

[0079] Specifically, at a temperature of 120 °C, the formation water salinity is 0.1%, in which the content of Ca 2+ , Mg 2+ ions is 0.02%, plugging a crack with a width of 0.5 mm, uniformly dispersing the double-network CO 2Responsive gel particles are uniformly dispersed in mineralized water and injected into the formation as a plugging agent. After aging for 24 h, the gas channel is plugged, and the plugging rate of the cracks is ≥90%.

[0080] In this embodiment, the reservoir is a low-permeability reservoir for CO 2 flooding.

[0081] Example 11

[0082] An application of a double-network CO 2 responsive gel particle in plugging microcracks during the CO 2 flooding process. In this embodiment, the gel particles are selected from the gel particles provided in Example 6.

[0083] The specific application is as follows: at a temperature of 85 °C, the salinity of formation water is 5.5%, in which the contents of Ca 2+ , Mg 2+ ions are 0.4%. A crack with a width of 0.2 mm is plugged. The double-network CO 2 responsive gel particles are uniformly dispersed in mineralized water and injected into the formation as a plugging agent. After aging for 24 h, the gas channel is plugged, and the plugging rate of the cracks is ≥90%.

[0084] In this embodiment, the reservoir is a low-permeability reservoir for CO 2 flooding.

[0085] Comparative Example 1

[0086] A CO 2 responsive gel particle, which is different from that in Example 1 in that the mass ratio of N,N′-methylenebisacrylamide is 0.025%; the feeding masses of each component in the preparation process are also replaced accordingly, and the specific preparation method is the same as that in Example 1.

[0087] Comparative Example 2

[0088] A CO 2 responsive gel particle, which is different from that in Example 1 in that the dosage of the initiator is 0.2%, and the mass ratio of sodium bisulfite to ammonium persulfate is 1:1. The feeding masses of each component in the preparation process are also replaced accordingly, and the specific preparation method is the same as that in Example 1.

[0089] Comparative Example 3

[0090] A CO 2 responsive gel particle, which is different from that in Example 1 in that the zwitterionic monomer is sulfobetaine methacrylate (SBMA); other components and preparation methods are the same as those in Example 1.

[0091] Comparative Example 4

[0092] A kind of CO 2 responsive gel particles, which are different from those in Example 1 in that the CO 2 responsive monomer is the single 4-vinylpyridine; other components and preparation methods are the same as those in Example 1.

[0093] Comparative Example 5

[0094] A kind of CO 2 responsive gel particles, which are different from those in Example 1 in that the CO 2 responsive monomer is the single DMAEMA; other components and preparation methods are the same as those in Example 1.

[0095] Comparative Example 6

[0096] A kind of CO 2 responsive gel particles, which are different from those in Example 1 in that the CO 2 mass ratio of the responsive monomer is 1% (mass ratio of 4-vinylpyridine and DMAEMA is 2:3), and the feeding masses of each component in the preparation process are also replaced accordingly, and the specific preparation methods are the same as those in Example 1.

[0097] Experimental Example 1:

[0098] 1). Swelling test

[0099] a. Neutral environment

[0100] Put dry gel particles with the same mass M 0 into beakers filled with deionized water and formation water respectively, and let them swell in a 60 °C high-temperature blast drying oven for 24 h until water absorption saturation is reached. Then wipe the gel particles with filter paper and weigh the mass of the swollen gel particles M 1 , and calculate the swelling multiple of the gel particles in the neutral environment according to the following formula SR . Among them, the total salinity of the formation water is 10%, and the sum of the contents of Ca 2+ , Mg 2+ ions is 1%.

[0101] (Ⅰ)

[0102] In formula (Ⅰ), SR is the swelling multiple, dimensionless; M 0 is the mass of the gel particles before swelling, in g; M 1 is the mass of the swollen gel particles, in g.

[0103] b. CO 2 environment

[0104] Put dry gel particles with the same mass M 0 into a high-temperature and high-pressure reactor filled with water of a certain salinity, and introduce CO 2 into the reactor until the pressure reaches about 4 MPa. Then, place the reactor in a high-temperature air blast drying oven at 60 °C and let it expand for 24 h. After taking it out, measure its mass, and calculate the swelling multiple of the gel particles in the water of a certain salinity according to the above formula. 2 in the water of a certain salinity under a CO

[0105] Compare the experimental data under neutral and CO 2 environments, and observe the CO 2 response characteristics of the gel particles; compare the swelling multiples of the gel particles in deionized water and water of a certain salinity to analyze whether the gel particles have the properties of anti-polyelectrolytes.

[0106] 2). Gel strength test

[0107] Use the plate measurement system in the Anton Paar rheometer to measure the elastic modulus of the gel particles after swelling for 24 h under different conditions, so as to analyze whether the gel particles show enhanced strength behavior in the water of a certain salinity. In the experiment, the shear strain is 1%, and the oscillation frequency is 0.1 - 100 Hz.

[0108] 3). Plugging performance test

[0109] Evaluate the channel plugging ability of the gel particles through a physical model with a length of 10 cm, a diameter of 2.5 cm, crack widths of 0.2 mm, 0.3 mm, 0.5 mm respectively, and a matrix permeability of 45 mD. After the gel particle system is dispersed in the above formation water (i.e., the total salinity is 10%, and the sum of the contents of Ca 2+ and Mg 2+ ions is 1%), the concentration is 5000 mg·L -1 . The specific experimental steps are as follows:

[0110] ① Evacuate the core and calculate its porosity;

[0111] ② Connect the pipelines, assemble the experimental device, set the temperature of the constant temperature oven to 60 °C, the confining pressure to 8 MPa, and the back pressure to 4 MPa;

[0112] ③ Inject CO 2 until the pressure is stable, and record the differential pressure after stabilization P 1 ;

[0113] ④ Inject 0.6 PV of the gel particle suspension, and record the pressure change during the injection process.

[0114] ⑤ After aging at 60 °C for 24 h, continue to inject CO2 The gas reaches pressure stability, and the final stable value of the pressure difference is P 2 ;

[0115] ⑥ Evaluate the channel plugging performance of the gel system through the plugging rate F

[0116] (II)

[0117] In formula (II), F is the plugging rate, with the unit of %; P 1 is the initial stable value of the pressure difference, with the unit of MPa; P 2 is the final stable value of the pressure difference, with the unit of MPa.

[0118] The test results are shown in the following table:

[0119] Table 1 Test results of examples and comparative examples

[0120]

[0121] In Table 1, the swelling ratio is a dimensionless parameter, and the unit of strength is Pa. The plugging rates of Examples 1 - 6 and Comparative Examples 1 - 6 were measured in a physical model with a crack width of 0.3 mm, and the plugging rates of Examples 7 and 8 were measured in physical models with crack widths of 0.2 mm and 0.5 mm, respectively.

[0122] From the data in Table 1, it can be seen that the swelling ratio and storage modulus of the gel particles prepared in Example 1 in deionized water under a neutral environment are 30.8 and 1548 Pa, respectively, and the corresponding results in water with salinity are 34.4 and 2142 Pa. Compared with the gel particles in deionized water, the gel particles in water with high salinity have higher strength and stronger water retention performance. This is because in deionized water, there is only a single-layer network structure formed between the monomer and the crosslinking agent MBA, while in saline water, the Ca 2+ ions, pyridyl groups, SO in zwitterionic monomers 3- and coordinated water, and, Mg in saline water 2+Metal coordination bonds can be formed between ions, pyridyl groups, carboxyl groups (produced by partial hydrolysis of amide groups), and coordinated water molecules. At the same time, there are a large number of π-π stacking interactions between zwitterions and pyridines, which can synergistically construct a double-network structure with the network between monomers and cross-linkers, thus significantly enhancing the strength of gel particles. On the other hand, the introduction of zwitterionic monomers results in electrostatic attraction between polymer chain segments. Therefore, the network structure formed by gel particles in deionized water is relatively dense. In formation water, the destruction of ionic bonds in the network and the osmotic pressure difference cause the polymer segments to be in an extended state, and more water molecules are loaded in the network structure. At the same time, metal ions can carry a large number of water molecules through coordination bonds to participate in the reconstruction of the gel multiphase structure, making the gel particles have stronger water retention performance in formation water.

[0123] After CO is introduced into formation water 2 in the gel particles, the CO 2 responsive monomers are protonated, the electrostatic repulsion between polymer chains increases, and the gel particles swell significantly, with the swelling ratio increasing to 48.5. At the same time, it can be seen that the strength of the gel particles after CO 2 response in formation water is 1806 Pa, which is still significantly higher than that in deionized water under neutral conditions. This is because two CO 2 responsive monomers, vinylpyridine and DMAEMA, are introduced into the gel particles. The pKa of 4-vinylpyridine is 5.62, and the pKa of DMAEMA is 8.18. After CO 2 is introduced, DMAEMA with a higher pKa value is protonated first, increasing the swelling ratio of the gel particles. Vinylpyridine with a lower degree of protonation can still form coordination bonds with Ca 2+ , Mg 2+ in formation water and coordinated water molecules, etc., and form a three-dimensional network structure under the action of a large number of π-π bonds between aromatic rings. When the gel strength enhanced by the formation of the second network structure exceeds the strength loss caused by swelling, the overall mechanical properties of the gel will be improved instead, so that the gel particles can still maintain the structural strength while the swelling ratio increases significantly during CO 2 flooding in high salinity reservoirs.

[0124] When the temperature is 60 °C, the salt content in formation water is 10%, the Ca 2+ ion concentration is 1%, and CO 2 flooding is carried out in a core with a fracture width of 0.3 mm, the plugging rate of the gel particles is 99.0%. This indicates that the double-network CO 2 responsive gel particles provided by the present invention have excellent plugging ability for microfractures during CO 2 flooding in a high salt environment.

[0125] Compared with Example 1, the swelling ratio, storage modulus and plugging performance of the gel particles in Example 2 are slightly reduced. Compared with 3-(1-(4-vinylbenzyl)-1H-imidazol-3-ium) propane-1-sulfonate, the 3-(dimethyl(4-vinylbenzyl)amino)propanesulfonate has one less benzene ring with a rigid structure on the chain, resulting in a decrease in the strength of the gel particles. At the same time, the weaker hydration ability of 3-(dimethyl(4-vinylbenzyl)amino)propanesulfonate slightly reduces the swelling ratio of the gel, so the plugging rate decreases.

[0126] Compared with Example 1, the zwitterionic monomer in Example 3 is 4-(2-sulfoethyl)-1-(4-vinylbenzyl)pyridinium betaine. Due to the different hydration abilities of the two monomers, the swelling ratio and plugging effect of the gel particles in Example 3 are slightly reduced.

[0127] Compared with Example 1, in Example 4, the mass ratio of vinylpyridine to dimethylaminoethyl methacrylate is 1:1. With the increase in the mass fraction of vinylpyridine, the coordination effect enhances the strength of the gel particles in the formation water. At the same time, the mass proportion of DMAEMA decreases, and the CO 2 response characteristics of the gel particles are reduced, so the swelling ratio and plugging effect of the gel particles are reduced.

[0128] Compared with Example 1, the concentrations of acrylamide and crosslinking agent in Example 5 increase significantly, the intermolecular crosslinking density increases, the formed network structure is dense, and the elastic modulus increases significantly. However, the significant increase in crosslinking density leads to a decrease in the free space inside the particles, and the swelling ratio of the gel particles decreases. At the same time, the decrease in the mass proportion of the zwitterionic monomer and the CO 2 response monomer reduces the CO 2 responsiveness, anti-polyelectrolyte effect and metal coordination ability of the gel particles, and the plugging performance is reduced.

[0129] Compared with Example 1, the pyridine monomer in Example 6 is 2-vinylpyridine, and its solubility in deionized water is slightly lower than that of 4-vinylpyridine. Therefore, the swelling ratio in deionized water is less than that in Example 1. At the same time, the pKa value of 2-vinylpyridine is lower than that of 4-vinylpyridine. Therefore, in the CO 2 environment, its degree of protonation is low. So, compared with Example 1, the swelling ratio of the gel particles after CO 2 response in formation water decreases, the strength increases, and the plugging performance slightly decreases.

[0130] In Example 1, the crack width of the physical model is 0.3 mm, while in Examples 7 and 8, the crack widths of the physical models are 0.2 mm and 0.5 mm respectively. When the crack width is 0.3 mm, the gel particles have a good match with the crack width, so it has a good plugging effect; when the crack width is 0.2 mm, the crack width may be smaller than the average particle size, so the gel particles are mainly concentrated in the middle and front end of the cracked core, and the plugging performance decreases slightly; when the crack width is 0.5 mm, the crack width may be larger than the average particle size. Although the particles can completely enter the crack and the injection performance is good, the plugging effect decreases.

[0131] Compared with Example 1, in Comparative Example 1, the mass fraction of the crosslinking agent MBA is 0.025%. At this time, the crosslinking agent concentration is too low, the crosslinking degree is incomplete, and a complete three-dimensional network structure cannot be formed. Part of the gel particles dissolve in water, and the gel strength is significantly reduced. After the CO 2 response, the gel network structure is almost completely destroyed, and the plugging rate is only 33.3%.

[0132] Compared with Example 1, in Comparative Example 2, the mass fraction of the initiator is 0.2%, and the mass ratio of sodium bisulfite to ammonium persulfate is 1:1. At this time, the initiator dosage is too large, the initiation rate increases too fast, and the reaction heat in the system is not easy to disperse, resulting in shorter polymer molecular chains, and finally leading to a decrease in both the swelling ratio and elastic modulus of the gel particles.

[0133] Compared with Example 1, the zwitterionic monomer in Comparative Example 3 is SBMA. SBMA has excellent hydrophilicity, so it has stronger water absorption performance in deionized water, and the swelling ratio is 33.1. However, due to its excellent hydrophilicity, its ionic responsiveness is greatly weakened, and there is no anti-polyelectrolyte effect in mineralized water, and the water retention performance even decreases slightly. The introduction of the benzene ring and imidazole structure in the zwitterionic monomer of Example 1 increases the hydrophobicity of the monomer on the one hand and enhances the binding energy between zwitterions on the other hand, so that relatively dense and compact electrostatic cross-linked networks are formed by gel particles in deionized water, which provides enough space for the subsequent swelling of gel particles in mineralized water. Therefore, after the gel particles are dispersed in mineralized water, the counterions free in the mineralized water penetrate into the polymer chains, and their stronger binding energy with zwitterions destroys the dipole interaction inside / between polymer chains, resulting in the polymer chain segments being in an extended conformation in salt water. Therefore, compared with Comparative Example 3, the gel particles in Example 1 have an obvious anti-polyelectrolyte effect in salt water, thus improving their plugging ability for micro-cracks during the CO 2 flooding process in high salinity oil reservoirs.

[0134] Compared with Example 1, in Comparative Example 4, the CO 2 responsive monomer is only 4-vinylpyridine. Its lower pKa value makes it less responsive to CO2 The response degree is low, so CO 2 After the response, the swelling multiple does not increase significantly, and the plugging performance decreases.

[0135] Compared with Example 1, in Comparative Example 5, CO 2 The responsive monomer is only DMAEMA, and its sensitivity to CO 2 The responsiveness causes the swelling multiple of the gel particles to increase significantly after the response. However, the absence of pyridyl groups results in almost no formation of metal coordination bonds in the gel particles. Therefore, the storage modulus of the gel particles decreases significantly after swelling, and the presence of divalent metal ions in the mineralized water further deteriorates the strength and plugging effect of the gel particles.

[0136] Compared with Example 1, in Comparative Example 6, CO 2 The mass fraction of the responsive monomer is 1%. The decrease in the mass fraction of the responsive monomer weakens the CO 2 responsiveness of the gel particles on the one hand, and at the same time reduces the coordination ability between pyridine and other ions. Therefore, when performing CO 2 flooding in high salinity formations, the strength and plugging performance of the gel particles are not ideal.

Claims

1. A double-network CO2-responsive gel particle, characterized in that: Prepared by the following method: S1. Add acrylamide, zwitterionic monomer, CO2 responsive monomer and emulsifier into deionized water, stir and mix to obtain a first mixed solution; S2. The pH of the first mixed solution was adjusted to 7, and N2 was introduced into the first mixed solution under an ice bath to exhaust the air to obtain a second mixed solution; S3. The initiator and the cross-linking agent were successively added to the second mixed solution under stirring, the temperature was adjusted to 30 ℃ -60 ℃ and kept passing N2, and the reaction was carried out for 2h-4h to obtain a reaction product; S4. The reaction product obtained in step S3 is washed with anhydrous ethanol, dried, ground and sieved to obtain the target product, double-network CO2-responsive gel particles; In the preparation method, the percentage of each component is: 15%-20% acrylamide, 5-10% zwitterionic monomer, 5-10% CO2 responsive monomer, 0.25-1% emulsifier, 0.1%-0.25% crosslinker, 0.075%-0.1% initiator and the balance water. The CO2 response monomer is composed of vinyl pyridine and N,N-dimethylaminoethyl methacrylate in a mass ratio of (0.5-1):1; The zwitterionic monomer is selected from 4-(2-sulfoethyl)-1-(4-vinylbenzyl)pyridinium betaine, 3-(1-(4-vinylbenzyl)-1H-imidazol-3-ium)propane-1-sulfonate or 3-(dimethyl(4-vinylbenzyl)amino)propanesulfonate.

2. The double-network CO2-responsive gel particle according to claim 1, characterized in that: The vinyl pyridine is selected from one of 4-vinyl pyridine and 2-vinyl pyridine.

3. The double-network CO2-responsive gel particle according to claim 2, characterized in that: The mass ratio of vinyl pyridine to N,N-dimethylaminoethyl methacrylate is 2:

3.

4. The double-network CO2-responsive gel particle according to claim 1, characterized in that: The emulsifier is one or two of sodium dodecyl sulfate, OP-10 or sodium stearate; The cross-linking agent is selected from one of N,N′-methylenebisacrylamide and polyethylene glycol diacrylate or a mixture of the two; The initiator is selected from azo compound 2,2'-azo[2-(2-imidazoline-2-yl)propane] dihydrochloride, or the initiator is composed of sodium bisulfite and ammonium persulfate.

5. The double-network CO2-responsive gel particle according to claim 4, characterized in that: The emulsifier is a mixture of sodium dodecyl sulfate and OP-10, with a mass ratio of 1:4; The crosslinking agent is selected from N,N′-methylenebisacrylamide and polyethylene glycol diacrylate, and the mass ratio of the two is (1.5-6):1; The initiator consists of sodium bisulfite and ammonium persulfate, and the molar ratio of sodium bisulfite to ammonium persulfate is in the range of (0.6-1.2):

1.

6. The double-network CO2-responsive gel particle according to claim 1, characterized in that: In step S2, the ice bath temperature is 0°C; In step S3, the stirring speed is 100 rpm-500 rpm; In step S4, the drying temperature is 60° C., the drying time is 48 h, and the particles with an initial particle size of less than 135 μm are screened using a sieve.

7. The double-network CO2-responsive gel particle according to claim 1, characterized in that: In the preparation method, the mass percentage of each component is: 15% acrylamide, 10% zwitterionic monomer, 10% CO2 responsive monomer, 0.3% emulsifier, 0.1% cross-linking agent, 0.1% initiator and balance water, wherein the CO2 responsive monomer is composed of 4-vinylpyridine and N,N-dimethylaminoethyl methacrylate in a mass ratio of 2:

3.

8. Use of the double-network CO2 responsive gel particles as described in any one of claims 1 to 7 to plug micro-cracks in oil reservoirs.

9. The use according to claim 8, characterized in that The specific application is that at a temperature of 25℃-120℃, the mineralization of the formation water is 0-10%, and the Ca 2+ Mg 2+ The ion content is 0-1%, and the cracks with a width of 0.2mm-0.5mm in the reservoir are plugged. The double-network CO2 responsive gel particles are evenly dispersed in the formation water and injected into the formation as a plugging agent. The cracks are plugged after aging for 24 hours.

10. The use according to claim 8, characterized in that The oil reservoir is a low permeability oil reservoir for CO2 flooding.

Images