A method for preparing a polymer containing a micro-nano porous structure, a polymer containing a micro-nano porous structure and applications

Abstract

The application provides a preparation method of a polymer containing a micro-nano porous structure, the polymer containing the micro-nano porous structure and application. The preparation method comprises the following steps: introducing inert gas A into an aqueous solution of an alkenyl monomer to remove oxygen, then introducing micro-nano bubbles of gas B, and performing a polymerization reaction to obtain a colloid, and then processing the obtained colloid to obtain the polymer containing the micro-nano porous structure; and the polymerization is initiated by at least one of the following modes: light initiation, thermal initiation, radiation initiation and redox initiation. The micro-nano bubbles can assist free radical polymerization, cost can be saved, the drying time of the polymer can be shortened, energy consumption can be reduced, the porous structure can accelerate the dissolution time of the polymer, and the polymer can be applied to oil reservoir exploitation.

Description

Technical Field

[0001] This invention relates to the field of oilfield development, and more specifically, to a method for preparing a polymer containing a micro / nanoporous structure, the polymer containing a micro / nanoporous structure, and its applications. Background Technology

[0002] Most of China's developed oilfields are already in a stage of high water cut and high recovery rate. In the east, many older oilfields have an overall water cut exceeding 85%, and recoverable reserves have been recovered to over 70%. Polymer flooding mainly involves injecting a polymer solution of a certain scale to increase the viscosity of the injected fluid, thereby adjusting the mobility ratio of the oil and water phases in the reservoir and expanding the swept volume. Partially hydrolyzed polyacrylamide (HPAM) is a major polymer flooding agent in tertiary oil recovery technology and has been widely promoted and applied, playing a crucial role in stabilizing and increasing oilfield production.

[0003] Most acrylamide polymers are solid dry powders obtained through free radical polymerization in aqueous solution initiated by an initiator. The specific process includes polymerization, granulation (hydrolysis), drying, pulverization, and sieving. The presence of water as a solvent during polymerization facilitates the diffusion of polymerization heat and makes the polymerization temperature easy to control. However, the drying process requires a large amount of heat energy to evaporate 60-70% of the water, and an excessively long drying process can cause further cross-linking between polymer chains, affecting polymer properties.

[0004] The aforementioned problems can be mitigated by introducing air bubbles during the polymerization process. There are already patent reports on the production of porous polymers by adding foaming agents. For example, Chinese invention patent CN1542027A uses ammonium bicarbonate as a foaming agent to produce polyacrylamide; Chinese invention patent CN105566539A uses ammonium bicarbonate as a foaming agent and N,N-dimethyldodecylamine oxide or N,N-diethyldodecylamine oxide as a foaming aid to produce polyacrylamide. However, due to limitations in the methods of bubble generation in existing technologies, the introduced bubbles are large in diameter (millimeter-level), unevenly distributed in the polymerization system, and have no significant mass and heat transfer effect, thus having no significant impact on existing polymer production processes.

[0005] In recent years, the technology for efficiently generating micro- and nano-bubbles has received increasing attention. Micro- and nano-bubbles typically refer to bubbles with a diameter of less than 50 μm. Microbubbles with a diameter greater than 1 μm are called microbubbles, and ultramicrobubbles with a diameter less than 1 μm but greater than 1 nm are further called nanobubbles. Compared to traditional large bubbles (coarse bubbles, diameter > 50 mm) and small bubbles (fine bubbles, diameter < 5 mm), micro- and nano-bubbles have smaller diameters and a significant small-size effect. Their mass and heat transfer characteristics and interfacial properties are significantly different from traditional large bubbles, possessing physical and chemical properties not found in traditional bubbles. For example, due to their small size, the total number of micro- and nano-bubbles in water is enormous, greatly increasing the total vapor-liquid contact area, resulting in a large specific surface area and a long residence time in water. Existing patent reports on the application of micro- and nano-bubbles include reports on micro- and nano-bubble generating devices and their application in water treatment, but no reports on the introduction of micro- and nano-bubbles into aqueous solution polymerization processes.

[0006] Therefore, it is necessary to study the introduction of micro- and nano-bubbles into the aqueous solution polymerization process to solve the problems of long subsequent drying time and high energy consumption in the existing aqueous solution polymerization technology. Summary of the Invention

[0007] To address the technical problems existing in the prior art, this invention provides a method for preparing a polymer containing a micro / nanoporous structure, the polymer containing the micro / nanoporous structure, and its applications. This invention utilizes the small size effect of micro / nano bubbles to produce a polymer containing a micro / nanoporous structure, resulting in a shorter drying time and lower energy consumption in subsequent processing.

[0008] This invention utilizes the characteristics of micro- and nano-bubbles. By controlling the introduction time, amount, and size of micro- and nano-bubbles, the micro- and nano-bubble system is uniformly distributed in the polymerization solution during the polymerization process. The small size effect of the micro- and nano-bubbles can enhance efficient heat transfer and reduce the fluctuation of colloidal properties caused by local overheating during polymerization. At the same time, in the drying process, the micro- and nano-bubbles on the surface of the colloid can greatly increase the specific surface area, enhance efficient heat transfer, shorten the drying time, and reduce energy consumption. It also shortens the cooling time of the colloid particles and improves the efficiency of the subsequent crushing and sieving process.

[0009] Meanwhile, when the average diameter of the micro-nano bubbles in this invention is between 50 nanometers and 500 nanometers, their introduction into the alkenyl monomer free radical solution polymerization system will generate a "cavitation" effect, which involves the formation, growth, and collapse of micro-nano bubbles. After cavitation in the system, the micro-nano bubbles generate a large number of hydroxyl radicals, which can be used to initiate the alkenyl monomer free radical solution polymerization. This can partially replace the initiator, shorten the induction period while reducing the cost of the initiator, and play an auxiliary role in free radical polymerization. This can improve polymerization efficiency, save polymerization costs, and at the same time reduce the degradation of polymers at high temperatures due to initiator residues, thereby enhancing the hydrothermal aging stability of the polymer.

[0010] This invention introduces micro- and nano-bubbles into an alkenyl monomer free radical solution polymerization system, ensuring their uniform presence within the system. After initiating the process to thicken the system, the introduction of micro- and nano-bubbles is stopped. Following polymerization, a colloidal post-processing step yields a porous polymer dry powder product containing micro- and nano-bubbles. By selecting a suitable gas source to generate micro- and nano-bubbles of appropriate diameter, the introduced micro- and nano-bubbles are fixed within the system after the reaction system becomes viscous, initiating stable polymerization. Upon completion of polymerization, the resulting colloid exhibits uniform quality. The presence of numerous micro- and nano-bubbles within the colloid block, due to their small size effect, improves the efficiency of each step in the colloid post-processing and reduces energy consumption.

[0011] One objective of this invention is to provide a method for preparing a polymer containing a micro / nanoporous structure, comprising:

[0012] Inert gas A is introduced into an aqueous solution of alkenyl monomer to remove oxygen, followed by the introduction of micro-nano bubbles of gas B, and then a polymerization reaction is initiated to obtain a colloid. After processing the obtained colloid, the polymer containing the micro-nano porous structure is obtained.

[0013] The polymerization can be initiated by at least one of photoinitiation, thermal initiation, radiation initiation, and redox initiation; it can be one of these methods or a mixture of several methods.

[0014] The initiator used in the above polymerization initiation method can be at least one of the initiators commonly used in the art, such as azo initiators, redox initiators, and photoinitiators. The amount of initiator used is the conventional amount, and technicians can select the initiator and the amount of initiator according to the actual situation.

[0015] In this invention, the following is preferred:

[0016] The amount of the azo initiator is 0.0001% to 0.1% of the total mass of the monomer mixture; the amount of the redox initiator is 0.0002% to 0.3% of the total mass of the monomer mixture; the amount of the photoinitiator is 0.0002% to 0.3% of the total mass of the monomer mixture; the azo initiator is a water-soluble azo initiator; the redox initiator includes an oxidant and a reductant, the reductant being at least one of an inorganic reductant and an organic reductant; and the mass ratio of the oxidant to the reductant is (0.1 to 1):1.

[0017] The water-soluble azo initiator is at least one selected from 2,2'-azobis(2-amidinylpropane) dihydrochloride, 2,2'-azobis(2-imidazolinepropane) dihydrochloride, and 4,4'-azobis(4-cyanopentanoic acid); the oxidant is at least one selected from benzoyl peroxide, hydrogen peroxide, tert-butyl hydroperoxide, 2,5-dimethyl-2,5-bis(hydrogen peroxide)hexane, ammonium persulfate, sodium persulfate, and potassium persulfate; the inorganic reducing agent is at least one selected from ferrous sulfate, ferrous ammonium sulfate, cuprous chloride, and ferrous sulfate. At least one of potassium sulfate, sodium sulfite, ammonium bisulfite, potassium bisulfite, sodium thiosulfate, potassium thiosulfate, sodium thiosulfate, sodium dithiosulfate, and sodium bisulfite; the organic reducing agent is at least one of N,N-dimethylethanolamine, N,N'-dimethylpiperazine, N,N,N',N'-tetramethylurea, and N,N,N',N'-tetramethylethylenediamine; the photoinitiator is at least one of 2-hydroxy-2,2-dimethylacetophenone and 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone.

[0018] The alkenyl monomer is at least one of anionic monomers and their alkali metal or ammonium salts, nonionic monomers, and cationic monomers; such as two, three, or more.

[0019] The inert gas A is at least one of nitrogen, argon, and helium;

[0020] The gas B is at least one of nitrogen, argon, helium, and carbon dioxide;

[0021] Inert gas A and gas B can be the same or different; inert gas A and gas B can be one of the above gases or a mixture of the above gases.

[0022] The mass concentration of the alkenyl monomer aqueous solution is 10%–50%; preferably 15%–35%.

[0023] The pH value of the aqueous solution of the alkenyl monomer is 4 to 9; preferably 4 to 6.

[0024] In a preferred embodiment of the present invention,

[0025] The anionic monomer is at least one of acrylic acid, methacrylic acid, maleic anhydride, cinnamic acid, fumaric acid, crotonic acid, aconitic acid, 2-methacrylamidoethanesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, vinyl sulfonic acid, propane sulfonic acid, and styrene sulfonic acid; preferably, the anionic monomer is at least one of acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid. This allows for the preparation of ultra-high molecular weight acrylamide copolymers. The higher the molecular weight of HPAM, the greater the apparent viscosity and the better the oil displacement effect.

[0026] The alkali metal salt is at least one of lithium, potassium or sodium metal salts;

[0027] The nonionic monomer contains a hydrophilic group; preferably, it is at least one of acrylamide, methacrylamide, N-vinylpyrrolidone, N-substituted acrylamide, N,N-dimethylacrylamide, 2-hydroxyethyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl methacrylate, 2-hydroxypropyl acrylate, methoxy polyethylene glycol methacrylate, methoxy polyethylene glycol acrylate, polyethylene glycol acrylate, polyethylene glycol methacrylate, and N-vinylacetamide; preferably, it is at least one of acrylamide, N-vinylpyrrolidone, N-substituted acrylamide, and N,N-dimethylacrylamide. Ultra-high molecular weight acrylamide copolymers can be prepared. The higher the molecular weight of HPAM, the greater the apparent viscosity and the better the oil displacement effect.

[0028] The cationic monomer is at least one of dimethylaminoethyl acrylate and its quaternary ammonium salt, dimethylaminoethyl methacrylate and its quaternary ammonium salt, dimethylaminopropylacrylamide and its quaternary ammonium salt, dimethylaminopropylmethacrylamide and its quaternary ammonium salt, and diallyl dimethylammonium chloride.

[0029] In a preferred embodiment of the present invention,

[0030] The alkenyl monomer also includes at least one of acrylate and hydrophobic monomer; the acrylate and hydrophobic monomer are used in small amounts without affecting the water solubility of the polymer, and the total mass of the acrylate and hydrophobic monomer does not exceed 10% of the total mass of the alkenyl monomer.

[0031] The acrylate is at least one of methacrylate, ethyl methacrylate, and butyl methacrylate; the hydrophobic monomer is at least one of vinyl acetate and vinyl propionate.

[0032] In a preferred embodiment of the present invention,

[0033] The average diameter of the gas B micro-nano bubbles is 20 nanometers to 50 micrometers; preferably 50 nanometers to 20 micrometers.

[0034] The small size effect of micro- and nano-bubbles is well manifested in the range of 20 nanometers to 50 micrometers. Their mass and heat transfer characteristics and interfacial properties are significantly different from those of traditional large bubbles, and they possess physical and chemical properties that traditional bubbles do not have. Micro- and nano-bubbles are uniformly distributed in the polymerization solution during the polymerization process, which can achieve enhanced and efficient heat transfer. On the one hand, it reduces the fluctuation of colloidal properties caused by local overheating during polymerization; on the other hand, in the drying process, the micro- and nano-bubbles on the surface of the colloidal particles can greatly increase the specific surface area, enhance efficient heat transfer, shorten drying time, and reduce energy consumption; and on the other hand, it shortens the cooling time of the colloidal particles and improves the efficiency of subsequent crushing and sieving processes.

[0035] In a preferred embodiment of the present invention,

[0036] The average diameter of the gas B micro-nano bubbles is 50 nanometers to 500 nanometers; preferably 50 nanometers to 200 nanometers.

[0037] When the average diameter of micro-nano bubbles is 50 to 500 nanometers, cavitation begins when these bubbles are introduced into an aqueous solution of alkenyl monomers. The formation, growth, and collapse of micro-nano bubbles in the alkenyl monomer aqueous solution is called "cavitation." This is because micro-nano bubbles are small in size, and the buoyancy they experience in water is much smaller than that experienced by ordinary bubbles in water. They can remain in water for several minutes or even several hours. During the "cavitation" process, when the micro-nano bubbles contract, the charge density of the double layer increases rapidly. When the bubbles collapse, the drastic change of the disappearance of the gas-liquid interface releases the energy stored in the high concentration of positive and negative ions on the interface. This can stimulate the generation of a large number of hydroxyl radicals, thereby initiating free radical solution polymerization of alkenyl monomers. This can play an auxiliary role in free radical polymerization, which can improve polymerization efficiency and save polymerization costs.

[0038] Preferably, the present invention uses the LF-1500 micro-nano bubble generator produced by Shandong Microbubble Environmental Protection Equipment Co., Ltd. to introduce micro-nano bubbles. The diameter of the bubbles is controlled by a rotor flow meter, pressure and generator. When the air intake of the micro-nano bubble generator is controlled at 10-200 mL / min and the inlet pressure is controlled at 0.2-1 MPa, the average diameter of the micro-nano bubbles can be controlled to be 50 nanometers to 20 micrometers.

[0039] In a preferred embodiment of the present invention,

[0040] The initial reaction temperature is -10℃ to 40℃; preferably 0℃ to 25℃.

[0041] The diameter of the inert gas A bubble is 1 mm to 10 mm; the introduction time is 5 min to 60 min; preferably 20 min to 40 min.

[0042] The purpose of introducing inert gas A is to remove oxygen. A regular nitrogen cylinder is used with a pressure reducing valve equipped with a flow meter. The flow rate of the pressure reducing valve is controlled at 2 to 20 L / min, preferably 5 to 15 L / min, which can provide inert gas A with a bubble diameter of 1 mm to 10 mm.

[0043] In a preferred embodiment of the present invention,

[0044] After the system temperature rises by 0.5℃ to 1℃ and the system becomes viscous, stop introducing micro-nano bubbles and continue the reaction for 1 hour to 6 hours; preferably 2 hours to 5 hours.

[0045] The colloid processing method involves granulating, hydrolyzing or not hydrolyzing, drying, pulverizing, and sieving the obtained colloid.

[0046] The colloids of different types of polymers obtained can be granulated and then hydrolyzed or dried directly without hydrolysis, depending on the requirements. For polymers that need to be hydrolyzed, after granulation, alkali is added and reacted at a certain temperature for a period of time to prepare polymers with a certain degree of hydrolysis. For non-hydrolyzed polymers, hydrolysis is not required and they are directly dried after granulation.

[0047] A second objective of this invention is to provide a polymer with a micro / nanoporous structure prepared by the above-mentioned preparation method, preferably an ultra-high molecular weight acrylamide copolymer with a micro / nanoporous structure prepared by the above-mentioned preparation method.

[0048] The present invention preferably uses at least one of acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, acrylamide, N-vinylpyrrolidone, N-substituted acrylamide, and N,N-dimethylacrylamide as raw materials to prepare ultra-high molecular weight acrylamide copolymers with higher apparent viscosity and better oil displacement effect.

[0049] The third objective of this invention is to provide an application of a polymer with a micro-nano porous structure in oil reservoir development, preferably in polymer flooding of high-temperature and high-salinity oil reservoirs, polymer flooding of offshore oil reservoirs, water flooding of heavy oil reservoirs, and fracturing; it can be used as a thickener for polymer flooding of high-temperature and high-salinity oil reservoirs, polymer flooding of offshore oil reservoirs, and water flooding of heavy oil reservoirs, or as a thickener and drag reducer for fracturing.

[0050] The present invention can specifically adopt the following technical solutions:

[0051] A method for preparing a polymer containing a micro / nanoporous structure includes the following steps:

[0052] Weigh one or more of the described alkenyl monomers to prepare an aqueous solution, adjusting the concentration of the aqueous solution to 10%–50%, preferably 15%–35%; the pH value of the aqueous solution is 4–9, preferably 4–6; the system temperature is controlled between -10℃ and 40℃, preferably 0–25℃; and a common bubble inert gas A with a diameter of 1 mm–10 mm is introduced into the system. Oxygen is removed for 5 to 60 minutes, preferably 20 to 40 minutes. Then, gas B micro- and nano-bubbles with an average diameter of 20 nanometers to 50 micrometers, preferably 50 nanometers to 20 micrometers, more preferably 50 nanometers to 500 nanometers, and even more preferably 50 nanometers to 200 nanometers are introduced into the system to ensure that the micro- and nano-bubbles are uniformly present in the system. Polymerization is initiated by conventional methods such as light, heat, radiation, and redox. The system temperature rises by 0.5°C to 1°C. After the system becomes viscous, the introduction of micro- and nano-bubbles is stopped, and the reaction continues for 1 to 6 hours, preferably 2 to 5 hours, to obtain a colloid containing a large number of micro- and nano-bubbles. The obtained colloid is granulated, hydrolyzed or not hydrolyzed, dried, pulverized, and sieved to obtain a polymer dry powder product with a micro- and nano-porous structure.

[0053] The inert gas A, gas B, and alkenyl monomer are as described above.

[0054] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0055] This invention utilizes the small size effect of micro- and nano-bubbles to introduce them into the aqueous solution polymerization process. By introducing micro- and nano-bubbles into the free radical solution polymerization system of alkenyl monomers, porous polymers containing micro- and nano-bubbles are produced. Utilizing their small size effect, they have a significant impact on existing polymer production processes. The process is simple, easy to industrialize, produces a stable polymerization reaction, and yields a colloid with uniform quality and suitable hardness. It can also improve the efficiency of each step in the colloid post-processing and reduce energy consumption.

[0056] The present invention discloses a polymer containing micro / nano porous structures and its preparation method. Compared with the prior art, it has the following advantages and effects in terms of uniform polymerization heat transfer, improved colloid post-processing efficiency, and reduced energy consumption by controlling the introduction time, amount, and size of micro / nano bubbles: 1) The introduced micro / nano bubbles have small diameters and are uniformly distributed in the polymerization solution. Their small size effect can enhance efficient heat transfer and reduce the fluctuation of colloid properties caused by local overheating during polymerization; 2) In the drying process, the micro / nano bubbles on the colloid surface can greatly increase the specific surface area, enhance efficient heat transfer, shorten the drying time, and reduce energy consumption; 3) Similarly, it also shortens the cooling time of the colloid particles and improves the efficiency of the subsequent crushing and sieving process.

[0057] When the average diameter of the micro-nano bubbles in this invention is 50 nanometers to 500 nanometers, they can initiate free radical solution polymerization of alkenyl monomers through cavitation, thus assisting in free radical polymerization, improving polymerization efficiency, and saving polymerization costs. Simultaneously, it can reduce polymer degradation at high temperatures due to initiator residue and enhance the hydrothermal aging stability of the polymer.

[0058] The micro-nano bubbles in this invention form a porous structure in the polymer powder after the colloid is dried, which can significantly improve the solubility of the polymer. Detailed Implementation

[0059] The present invention will now be described in detail with reference to specific embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0060] The raw materials used in the examples and comparative examples were all commercially available.

[0061] Acrylamide was purchased from Jiangxi Changjiu Agricultural Science and Chemical Co., Ltd.

[0062] Sodium 2-acrylamido-2-methylpropanesulfonate was purchased from Weifang Aorui Environmental Protection Technology Co., Ltd.

[0063] 2,2-Azobis(2-amidinylpropane) dihydrochloride was purchased from Sigma-Aldrich.

[0064] N,N-Dimethylacrylamide was purchased from Beijing Ruibolong Technology Development Co., Ltd.

[0065] 2-Hydroxy-4′-(2-hydroxyethoxy)-2-methylphenylacetone was purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0066] Unless otherwise specified, all other reagents can be obtained commercially.

[0067] Test method:

[0068] Residual monomer content test: conducted in accordance with the enterprise standard Q / SH10201572-2017 "Polyacrylamide for Oil Displacement" of Shengli Oilfield Administration Bureau, China Petrochemical Corporation;

[0069] Dissolution rate test: The test was conducted according to standard Q / HNYJ 325-2008 "Detailed Rules for the Implementation of Dissolution Rate Test of Polyacrylamide" in simulated saline with a mineralization of 10000 mg / L and a temperature of 40℃; the specific method is as follows:

[0070] ① In a clean beaker, add 300g of simulated salt water and add 2-3 drops of 1% sodium indigo disulfonate.

[0071] ② Accurately weigh 0.3g of polymer powder (accurate to 0.01g);

[0072] ③ Start stirring and slowly add the weighed polymer powder at a speed of 500 rpm;

[0073] ④ Observe the dissolution status at regular intervals. If the solution color is evenly distributed, it indicates that it has completely dissolved; if there are still bright spots, continue to observe until it is evenly dissolved and the experiment is completed.

[0074] Relative molecular mass test: conducted in accordance with standard Q / HNYJ 307-2007 "Detailed Rules for Testing Intrinsic Viscosity of Polyacrylamide";

[0075] Determination of viscosity retention rate during aging: The viscosity of a 1500 mg / L polymer solution was measured after being placed in simulated brine at 90℃ with a mineralization of 10000 mg / L, a calcium and magnesium ion content of 2000 mg / L, and an oxygen content of less than 0.5 mg / L for a certain number of days. The viscosity retention rate during aging was obtained by comparing the viscosity after aging with the initial viscosity.

[0076] Example 1

[0077] Dissolve 42g of acrylamide and 3g of sodium 2-acrylamido-2-methylpropanesulfonate in 255g of deionized water and adjust the pH to 6.0. Control the initial temperature at 0℃. Puff nitrogen gas at a flow rate of 1mm-10mm into the system for 20min to remove oxygen. Then, introduce nitrogen nanobubbles with an average diameter of 50nm into the system (inlet pressure controlled at 0.8MPa, inlet flow rate controlled at 10mL / min) to ensure uniform bubble distribution. Start timing. Then, add 1.0g of 0.25% (w / w) 2,2-azobis(2-amidinylpropane) to the system. Polymerization was initiated by adding dihydrochloride aqueous solution and redox initiator (1.0 g of 0.1% ammonium persulfate aqueous solution and 3 g of 0.3% sodium bisulfite aqueous solution). When the system temperature rose by 0.5℃, the polymerization induction period ended, the timing was stopped, and the introduction of nitrogen nanobubbles was stopped. The reaction continued for 4 hours. After the polymerization was completed, the obtained colloid was granulated, 4.7 g of sodium hydroxide granules were added and mixed evenly, hydrolyzed at 80℃ for 3 hours, dried at 50℃ until the solid content reached 89%, and then pulverized and sieved to obtain ultra-high molecular weight polymer dry powder with micro-nano porous structure.

[0078] The polymerization induction period was calculated, and the drying time, dissolution time, relative molecular mass, residual monomer content, and viscosity retention rate of the dry powder samples were determined. The data are shown in Table 1.

[0079] Example 2

[0080] Dissolve 70g acrylamide and 5g sodium acrylate in 225g deionized water, adjust the pH to 4.0, and control the initial temperature at 10℃. Blow nitrogen gas at a depth of 1mm-10mm into the system for 30 minutes to remove oxygen. Then, introduce carbon dioxide nanobubbles with an average diameter of 100nm into the system, ensuring uniform bubble distribution (inlet pressure controlled at 0.5MPa, inlet flow rate controlled at 15mL / min). Start timing. Then, add 0.2g of 0.05% (w / w) 2-hydroxy- 1.0 g of 0.25% aqueous solution of 2,2-azobis(2-amidinylpropane) dihydrochloride was used as a photoinitiator. Polymerization was initiated by light irradiation (100W ultraviolet light). After the system temperature rose by 0.5℃, the polymerization induction period ended, the timing was stopped, the introduction of carbon dioxide nanobubbles was stopped, and the reaction continued for 5 hours. After the polymerization was completed, the resulting colloid was granulated, dried at 50℃ until the solid content reached 89%, pulverized and sieved to obtain ultra-high molecular weight polymer dry powder with micro-nano porous structure.

[0081] The polymerization induction period was calculated, and the drying time, dissolution time, relative molecular mass, residual monomer content, and viscosity retention rate of the dry powder samples were determined. The data are shown in Table 1.

[0082] Example 3

[0083] Dissolve 54g of acrylamide, 4g of sodium 2-acrylamido-2-methylpropanesulfonate, and 5g of N,N-dimethylacrylamide in 237g of deionized water, and adjust the pH to 6.0. Control the initial temperature at 20℃, and purge the system with nitrogen gas at a depth of 1mm–10mm for 40 minutes to remove oxygen. Then, introduce helium nanobubbles with an average diameter of 200 nm into the system (inlet pressure controlled at 0.3 MPa, inlet flow rate controlled at 20 mL / min) to ensure uniform distribution of the micro-nanobubbles. Start timing, and then add 0.25% helium gas to the system. 1.5 g of an aqueous solution of 2,2-azobis(2-amidinepropane) dihydrochloride was added to a redox initiator (2.0 g of 0.1% ammonium persulfate aqueous solution and 4 g of 0.3% sodium bisulfite aqueous solution) to initiate polymerization. The system temperature was increased by 0.5℃, the polymerization induction period ended, the timing was stopped, the introduction of helium nanobubbles was stopped, and the reaction continued for 3 hours. After polymerization was completed, the resulting colloid was granulated, dried at 50℃ until the solid content reached 89%, pulverized, and sieved to obtain an ultra-high molecular weight polymer dry powder with a micro-nano porous structure.

[0084] The polymerization induction period was calculated, and the drying time, dissolution time, relative molecular mass, residual monomer content, and viscosity retention rate of the dry powder samples were determined. The data are shown in Table 1.

[0085] Example 4

[0086] Dissolve 41g acrylamide, 2g sodium acrylate, and 2g N-vinylpyrrolidone in 255g deionized water and adjust the pH to 6.0. Control the initial temperature at 25℃. Blow nitrogen gas at a depth of 1mm-10mm into the system for 30 minutes to remove oxygen. Then, introduce nitrogen microbubbles with an average diameter of 0.5μm into the system (inlet pressure controlled at 0.4MPa, inlet flow rate controlled at 80mL / min) to ensure uniform distribution of nitrogen microbubbles in the system. Start timing. Then add 0.25% of 2... 1.8 g of 2-azobis(2-amidinylpropane)dihydrochloride aqueous solution as initiator was added to a redox initiator (2.0 g of 0.1% ammonium persulfate aqueous solution and 3 g of 0.3% sodium bisulfite aqueous solution) to initiate polymerization. After the system temperature was raised by 0.5℃, the polymerization induction period ended, the timing was stopped, the introduction of micron-sized bubbles was stopped, and the reaction continued for 4 hours. After the polymerization was completed, the obtained colloid was granulated, dried at 50℃ until the solid content reached 89%, pulverized, and sieved to obtain an ultra-high molecular weight polymer dry powder with a micro-nano porous structure.

[0087] The polymerization induction period was calculated, and the drying time, dissolution time, relative molecular mass, residual monomer content, and viscosity retention rate of the dry powder samples were determined. The data are shown in Table 1.

[0088] Example 5

[0089] Dissolve 85g acrylamide and 15g sodium acrylate in 200g deionized water, adjust the pH to 6.0, and control the initial temperature at 10℃. Blow nitrogen gas at a depth of 1mm to 10mm into the system for 30 minutes to remove oxygen. Then, introduce nitrogen nanobubbles with an average diameter of 50nm into the system (inlet pressure controlled at 0.8MPa, inlet flow rate controlled at 10mL / min) to ensure uniform bubble distribution. Start timing. Then, add 0.25% (w / w) of 2,2- Polymerization was initiated by adding 1.0 g of azobis(2-amidinepropane) dihydrochloride aqueous solution, 1.0 g of sodium persulfate aqueous solution with a mass concentration of 0.1%, and 3.0 g of sodium bisulfite aqueous solution with a mass concentration of 0.3%. After the system temperature was increased by 0.5℃, the polymerization induction period ended, the timing was stopped, the introduction of nitrogen nanobubbles was stopped, and the reaction continued for 5 hours. After the polymerization was completed, the resulting colloid was granulated, dried at 50℃ until the solid content reached 89%, pulverized, and sieved to obtain ultra-high molecular weight polymer dry powder with micro-nano porous structure.

[0090] The polymerization induction period was calculated, and the drying time, dissolution time, relative molecular mass, residual monomer content, and viscosity retention rate of the dry powder samples were determined. The data are shown in Table 1.

[0091] Example 6

[0092] Dissolve 42g of acrylamide and 3g of sodium 2-acrylamido-2-methylpropanesulfonate in 255g of deionized water, adjust the pH to 6.0, and control the initial temperature at 0℃. Blow nitrogen gas at a flow rate of 1mm–10mm into the system for 20 minutes to remove oxygen. Then, introduce nitrogen nanobubbles with an average diameter of 5μm into the system (inlet pressure controlled at 0.2MPa, inlet flow rate controlled at 90mL / min) to ensure uniform bubble distribution. Start timing. Then, add 1.0g of 0.25% (w / w) 2,2-azobis(2-amidinepropyl) Polymerization was initiated by adding an aqueous solution of alkyl dihydrochloride and a redox initiator (1.0 g of 0.1% ammonium persulfate aqueous solution and 3 g of 0.3% sodium bisulfite aqueous solution). When the system temperature rose by 0.5℃, the polymerization induction period ended, the timing was stopped, the introduction of nitrogen nanobubbles was stopped, and the reaction continued for 4 hours. After the polymerization was completed, the resulting colloid was granulated, 4.7 g of sodium hydroxide granules were added and mixed evenly, hydrolyzed at 80℃ for 3 hours, dried at 50℃ until the solid content reached 89%, and then pulverized and sieved to obtain an ultra-high molecular weight polymer dry powder with a micro-nano porous structure.

[0093] The polymerization induction period was calculated, and the drying time, dissolution time, relative molecular mass, residual monomer content, and viscosity retention rate of the dry powder sample were measured. The data are shown in Table 1.

[0094] Example 7

[0095] Dissolve 42g of acrylamide and 3g of sodium 2-acrylamido-2-methylpropanesulfonate in 255g of deionized water, adjust the pH to 6.0, and control the initial temperature at 0℃. Blow nitrogen gas at a flow rate of 1mm–10mm into the system for 20min to remove oxygen. Then, introduce nitrogen nanobubbles with an average diameter of 20μm into the system (inlet pressure controlled at 0.2MPa, inlet flow rate controlled at 200mL / min) to ensure uniform bubble distribution. Finally, add 1.0g of 0.25% (w / w) 2,2-azobis(2-amidinium) solution to the system. Polymerization was initiated by adding an aqueous solution of propylene dihydrochloride and a redox initiator (1.0 g of 0.1% ammonium persulfate aqueous solution and 3 g of 0.3% sodium bisulfite aqueous solution). After the system temperature rose by 0.5℃, the introduction of nitrogen nanobubbles was stopped, and the reaction continued for 4 hours. After the polymerization was completed, the resulting colloid was granulated, 4.7 g of sodium hydroxide granules were added and mixed evenly, and hydrolyzed at 80℃ for 3 hours. After drying at 50℃ until the solid content reached 89%, the product was pulverized and sieved to obtain a dry powder product of ultra-high molecular weight acrylamide copolymer with micro-nano porous structure.

[0096] The polymerization induction period was calculated, and the drying time, dissolution time, residual monomer content, and viscosity retention rate of the dry powder samples were determined. The data are shown in Table 1.

[0097] Comparative Example 1

[0098] The difference between Comparative Example 1 and Example 1 is that no micro / nano inert gas bubbles are introduced;

[0099] Except for not introducing micro-nano inert gas bubbles into the system, the raw materials, dosages, processes, and preparation methods of Comparative Example 1 are the same as those of Example 1;

[0100] Acrylamide copolymer dry powder product was prepared.

[0101] The polymerization induction period was calculated, and the drying time, dissolution time, residual monomer content, relative molecular mass, and viscosity retention rate of the dry powder product were measured. The data are shown in Table 1.

[0102] Comparative Example 2

[0103] The difference between Comparative Example 2 and Example 1 is that no micro- or nano-sized inert gas bubbles are introduced; the amount of initiator is increased by adding 3.0 g of 0.25% aqueous solution of 2,2-azobis(2-amidinepropane) dihydrochloride and redox initiators (3.0 g of 0.1% aqueous solution of ammonium persulfate and 5 g of 0.3% aqueous solution of sodium bisulfite) to the system to initiate polymerization.

[0104] Apart from the two differences mentioned above, the raw materials, dosages, processes, and preparation methods of Comparative Example 2 are the same as those of Example 1.

[0105] Acrylamide copolymer dry powder product was prepared.

[0106] The polymerization induction period was calculated, and the drying time, dissolution time, residual monomer content, relative molecular mass, and viscosity retention rate of the dry powder product were measured. The data are shown in Table 1.

[0107] Table 1 Performance test results of Examples 1-7 and Comparative Examples 1-2

[0108]

[0109] As shown in Table 1, Examples 1-7 introduced micro-nano bubbles into the system. The average diameter of the micro-nano bubbles was 50 nanometers to 20 micrometers, resulting in polymer dry powder with a micro-nano porous structure. The drying time at 50°C was 9-12 hours, which was significantly shorter than the 48 hours of drying time at 50°C for Comparative Examples 1-2. This demonstrates that introducing micro-nano bubbles into the system can greatly shorten the drying time, which is of great significance for reducing production energy consumption.

[0110] Meanwhile, the dissolution time of Examples 1 to 7, 20 to 30 minutes, is much shorter than that of Comparative Examples 1 and 2, 105 to 110 minutes, demonstrating that the dissolution time of the polymer dry powder obtained after introducing micro-nano bubbles is shorter and the dissolution performance is greatly improved.

[0111] Examples 6 and 7 introduced micron-sized bubbles with average diameters of 5 micrometers and 20 micrometers, respectively. Examples 1 to 5 introduced bubbles with average diameters of 50 to 500 nanometers. It can be seen that the induction period of Examples 1 to 5 is shorter, proving that micro-nano bubbles with an average diameter of 50 to 500 nanometers can replace part of the initiator, reduce the cost of initiator use, effectively avoid the degradation of polymer structure caused by initiator residue at high temperatures, and improve long-term aging stability.

[0112] Compared to Example 1, Comparative Example 1 did not introduce micro / nano bubbles, resulting in a longer induction period, longer drying time, slower dissolution rate, higher residual monomer content, and lower viscosity retention. Comparative Example 2 did not introduce micro / nano bubbles, but increased the amount of initiator, thus achieving a similar induction period and residual monomer content. This demonstrates that the micro / nano bubble initiation effect of Example 1 can replace part of the initiator, reducing the cost of initiator use.

[0113] Compared with Comparative Examples 1-2, the polymers with micro- and nano-porous structures prepared in Examples 1-7 have higher viscosity retention rates and are more suitable for oil reservoir development.

Claims

1. A method for preparing a polymer containing a micro- and nanoporous structure, characterized in that The method includes: Inert gas A is introduced into an aqueous solution of alkenyl monomer to remove oxygen, followed by the introduction of micro-nano bubbles of gas B, and then a polymerization reaction is initiated to obtain a colloid. After processing the obtained colloid, the polymer containing the micro-nano porous structure is obtained. The polymerization initiation method is at least one of photoinitiation, thermal initiation, radiation initiation, and redox initiation; the gas B is at least one of nitrogen, argon, helium, and carbon dioxide; the average diameter of the gas B micro-nano bubbles is 50 nanometers to 20 micrometers. The alkenyl monomer is at least one of anionic monomers and their alkali metal or ammonium salts, nonionic monomers, and cationic monomers. The anionic monomer is at least one selected from acrylic acid, methacrylic acid, maleic anhydride, cinnamic acid, fumaric acid, crotonic acid, aconitic acid, 2-methacrylamidoethanesulfonic acid, 2-acrylamidoethanesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, vinyl sulfonic acid, propane sulfonic acid, and styrene sulfonic acid; the alkali metal salt is at least one selected from lithium, potassium, or sodium metal salts. The nonionic monomer is at least one of acrylamide, methacrylamide, N-vinylpyrrolidone, N-substituted acrylamide, N,N-dimethylacrylamide, 2-hydroxyethyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl methacrylate, 2-hydroxypropyl acrylate, methoxy polyethylene glycol methacrylate, methoxy polyethylene glycol acrylate, polyethylene glycol acrylate, polyethylene glycol methacrylate, and N-vinylacetamide. The cationic monomer is at least one of dimethylaminoethyl acrylate and its quaternary ammonium salt, dimethylaminoethyl methacrylate and its quaternary ammonium salt, dimethylaminopropylacrylamide and its quaternary ammonium salt, dimethylaminopropylmethacrylamide and its quaternary ammonium salt, and diallyl dimethylammonium chloride.

2. The method for preparing the polymer containing micro / nanoporous structures as described in claim 1, characterized in that: The inert gas A is at least one of nitrogen, argon, and helium; and / or, The mass concentration of the alkenyl monomer aqueous solution is 10%~50%; and / or, The pH value of the aqueous solution of alkenyl monomers is 4-9.

3. The method for preparing the polymer containing micro / nanoporous structures as described in claim 2, characterized in that: The mass concentration of the alkenyl monomer aqueous solution is 15%~35%; and / or, The pH value of the aqueous solution of alkenyl monomers is 4-6.

4. The method for preparing the polymer containing micro / nanoporous structures as described in claim 1, characterized in that: The alkenyl monomer further includes at least one of acrylate and hydrophobic monomer; the total mass of acrylate and hydrophobic monomer does not exceed 10% of the total mass of alkenyl monomer; The acrylate is at least one of methacrylate, ethyl methacrylate, and butyl methacrylate; the hydrophobic monomer is at least one of vinyl acetate and vinyl propionate.

5. The method for preparing the polymer containing micro / nanoporous structures as described in claim 1, characterized in that: The average diameter of the gas B micro-nano bubbles is 50 nanometers to 500 nanometers. 6.The method of claim 5, wherein the inert gas B is introduced into the polymerization system at a temperature of -10-40 ℃. The average diameter of the micro-nano bubbles of the inert gas B is 50-200 nm. 7.The method of claim 1, wherein the inert gas A is introduced into the polymerization system at a temperature of 0-25 ℃. The diameter of the bubbles of the inert gas A is 1-10 mm. 8.The method of claim 7, wherein the inert gas A is introduced into the polymerization system at a temperature of 0-25 ℃. The introduction time of the inert gas A is 20-40 min. 9.The method of claim 1, wherein the inert gas B is introduced into the polymerization system at a temperature of -10-40 ℃, and the diameter of the bubbles of the inert gas B is 50-200 nm. The temperature of the system is increased by 0.5-1 ℃, and then the introduction of the micro-nano bubbles is stopped, and the reaction is continued for 1-6 h. The treatment method of the colloid is granulation, hydrolysis or non-hydrolysis, drying, crushing, and screening. 10.The method of claim 9, wherein the temperature of the system is increased by 0.5-1 ℃, and then the introduction of the micro-nano bubbles is stopped, and the reaction is continued for 2-5 h. 11.A polymer containing micro-nano porous structure prepared by the method of any one of claims 1-10. 12.The polymer of claim 11 for use in oil reservoir exploitation. 13.The polymer of claim 12 for use in high-temperature and high-salinity reservoir polymer flooding, offshore oil reservoir polymer flooding, heavy oil reservoir water flooding, and fracturing. ​ ​ ​ ​

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