A supramolecular hydrogel sealing agent constructed by host-guest interaction and its preparation method and application

Abstract

The present invention provides a supramolecular hydrogel sealing agent constructed by host-guest interaction, and its preparation method and application, which belong to the technical field of drilling fluid sealing. The supramolecular hydrogel sealing agent constructed by host-guest interaction of the present invention comprises the following raw materials in percentage by mass: 12-36% copolymerization monomer, 6-10% tannic acid grafted polysaccharide aqueous dispersion, 0.5-1.5% initiator, 0.3-0.6% cross-linking agent, and the balance is water; the total amount of each component is 100%. The raw materials of the present invention are cheap and easy to obtain, the raw material composition is simple, the cost is low, and it is green, safe and environmentally friendly; the preparation method is simple, the conditions are mild, and it is easy to implement. The sealing agent obtained by the present invention has excellent mechanical properties, heat and pressure resistance and outstanding pH degradation ability after cross-linking, can effectively seal the crude oil reservoir to form an integral sealing barrier, and reduce the entry of heavy oil into the wellbore; at the same time, it can effectively realize the degradation of the hydrogel to achieve unsealing.

Description

Technical Field

[0001] The invention relates to a supramolecular hydrogel sealing agent constructed by host-guest interaction, a preparation method and application thereof, and belongs to the technical field of drilling fluid sealing. Background Art

[0002] With the continued growth of global energy demand, the development of conventional oil and gas resources has gradually entered its mid-to-late stages. Resource depletion and increasing extraction difficulties have led to a significant increase in development costs. In this environment, the development of unconventional oil and gas resources (such as heavy oil, shale oil, and oil sands) has become a vital supplement to global energy supply. Heavy oil, a key unconventional oil and gas resource, has global reserves far exceeding those of conventional crude oil, estimated to account for over 70% of the world's total oil reserves, offering enormous development potential. However, compared with conventional crude oil, heavy oil exhibits significant characteristics such as higher viscosity, higher density, and poor fluidity. These characteristics present numerous challenges in its extraction. In particular, when drilling through a heavy oil reservoir, the pressure differential within the wellbore changes, making it highly susceptible to heavy oil intrusion into the drilling fluid system. This intrusive heavy oil can migrate along the wellbore wall, disrupting the rheological properties of the drilling fluid and significantly increasing the risk of downhole complications such as annular blockage and stuck pipe. These issues not only extend drilling cycles and increase operating costs, but also pose a serious threat to the safety and efficiency of drilling operations.

[0003] Faced with the daunting challenge of heavy oil intrusion into the wellbore, researchers at home and abroad have adopted a range of approaches, including heavy slurry push, heating to reduce viscosity, adding heavy oil viscosity reducers, and adding plugging materials. Heavy slurry push, for example, increases the density of the drilling fluid to balance the pressure differential between the wellbore and the formation, but it cannot fundamentally prevent heavy oil intrusion. While heating to reduce viscosity can temporarily reduce the viscosity of heavy oil in the wellbore, it is energy-intensive and difficult to implement in deep wells. Heavy oil viscosity reducers, which chemically modify the rheological properties of heavy oil, can improve its fluidity, but often fail to achieve the desired viscosity reduction effect when the amount of heavy oil intrusion is large. Plugging materials, while effective at filling fractures, cannot effectively remove blockages, hindering subsequent production operations and impacting subsequent heavy oil production. In summary, these existing methods all have limitations and are unable to fully and effectively control the problem of heavy oil intrusion.

[0004] In recent years, supramolecular polymer gels, a novel functional material, have attracted widespread attention in oilfield chemistry due to their unique reversibility and environmental responsiveness. These gels form dynamic cross-linked networks through non-covalent bonds (such as hydrogen bonds and hydrophobic interactions). These gels not only exhibit excellent mechanical properties and adaptability but also enable reversible plugging removal under specific conditions, offering a novel approach to addressing heavy oil isolation. Chinese patent document CN116120905A discloses a supramolecular polymer gel based on multiple hydrogen bonds. By adjusting the pH of the dissolving solution to an acidic value, the ionization of carboxylic acid groups (-COOH) is suppressed, thereby providing more active sites for the formation of multiple hydrogen bonds. This gel system uses an azo initiator to initiate the polymerization of olefinic carboxylic acid-containing monomers under ultraviolet light, forming long polymer chains that are then gelled through physical cross-linking. Compared to traditional chemically cross-linked gels, this system does not require a cross-linker, thus avoiding the difficulty in controlling gelation time. Furthermore, its viscosity changes with shear rate, allowing it to automatically adapt to the plugging pumping process, reducing pumping pressure, adapting to harsh leaking layer pressure environments, and reducing the risk of recurrent leakage. However, this gel material still has certain limitations, especially the inability to achieve reversible plugging and the difficulty in effectively unplugging after plugging, which limits its application in heavy oil reservoir isolation. Therefore, further optimizing the reversibility of the gel material and achieving an effective balance between heavy oil plugging and unplugging will be an important direction for the future research and development of heavy oil reservoir isolation materials. Summary of the Invention

[0005] In response to the deficiencies in the prior art, the present invention provides a supramolecular hydrogel sealing agent constructed by host-guest interaction, and its preparation method and application. The raw materials of the present invention are cheap and easily available, the raw material composition is simple, the cost is low, and it is green, safe and environmentally friendly. The preparation method is simple, the conditions are mild, and it is easy to implement. The sealing agent obtained by the present invention has excellent mechanical properties, heat and pressure resistance and outstanding pH degradation ability after cross-linking, and can effectively seal the crude oil reservoir to form an integral sealing barrier, reducing the entry of heavy oil into the wellbore; at the same time, it can effectively realize the degradation of the hydrogel to achieve unsealing.

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

[0007] A supramolecular hydrogel sealing agent constructed by host-guest interaction, comprising the following raw materials in percentage by weight: 12-36% copolymerization monomer, 6-10% tannic acid grafted polysaccharide aqueous dispersion, 0.5-1.5% initiator, 0.3-0.6% crosslinker, and the balance being water, with the total amount of each component being 100%;

[0008] The copolymerization monomer is a combination of acryloyl cyclodextrin and a double bond-containing monomer; the double bond-containing monomer is one of acrylamide, acrylic acid, methacrylic acid, sodium acrylate, N-isopropylacrylamide, hexadecyldimethylallylammonium chloride or N-hydroxyethylacrylamide;

[0009] The preparation method of acryloyl cyclodextrin comprises the following steps: dissolving cyclodextrin and sodium hydroxide in deionized water, adding acryloyl chloride or methacryloyl chloride, reacting, filtering, precipitating and drying to obtain acryloyl cyclodextrin;

[0010] The preparation method of a tannic acid grafted polysaccharide aqueous dispersion comprises the following steps: fully dispersing a polysaccharide substance in deionized water and adjusting the pH to 8.0; adding tannic acid and reacting to obtain a tannic acid grafted polysaccharide aqueous dispersion; the polysaccharide substance is one or a combination of two or more of cellulose, starch, lignin, xanthan gum, chitosan, guar gum or sodium alginate.

[0011] Preferably, according to the present invention, the supramolecular hydrogel sealing agent comprises the following raw materials in percentage by weight: 16% copolymerization monomer, 8% tannic acid grafted polysaccharide aqueous dispersion, 1% initiator, 0.4% cross-linking agent, and the balance is water, and the total amount of each component is 100%.

[0012] According to a preferred embodiment of the present invention, in the preparation method of acryloyl cyclodextrin, the cyclodextrin is selected from one or a combination of two or more of α-cyclodextrin, β-cyclodextrin or γ-cyclodextrin, preferably β-cyclodextrin.

[0013] According to the preferred preparation method of acryloyl cyclodextrin of the present invention, the mass ratio of cyclodextrin and sodium hydroxide is 1-4:5.84, preferably 2:5.84, the mass ratio of cyclodextrin and deionized water is 1:50-150, preferably 1:100, and the mass ratio of acryloyl chloride or methacryloyl chloride and cyclodextrin is 0.5-2.2:2, preferably 1:1.

[0014] According to a preferred embodiment of the present invention, in the preparation method of acryloyl cyclodextrin, the reaction temperature is 40-60°C, preferably 50°C, the reaction time is 6-12h, preferably 12h, and the reaction is carried out under inert gas protection and stirring conditions. Preferably, the inert gas is nitrogen or argon.

[0015] According to a preferred embodiment of the present invention, in the preparation method of acryloyl cyclodextrin, the filtrate obtained by filtration is purified by precipitation using acetone, the drying temperature is 40-60° C., preferably 40° C., and the drying time is 12-24 h, preferably 24 h.

[0016] According to the present invention, preferably, the mass ratio of acryloyl cyclodextrin to the double bond-containing monomer is 1:2-8, preferably 1:3.

[0017] Preferably, according to the present invention, in the method for preparing the tannic acid grafted polysaccharide aqueous dispersion, the polysaccharide material is cellulose, and the cellulose is selected from nanocellulose fibrils, cellulose nanocrystals or carboxymethyl cellulose.

[0018] According to a preferred embodiment of the present invention, in the method for preparing the tannic acid grafted polysaccharide aqueous dispersion, the mass ratio of the polysaccharide substance to deionized water is 1:20-30, preferably 1:25.

[0019] Preferably, according to the present invention, in the method for preparing the tannic acid-grafted polysaccharide aqueous dispersion, a 0.01 mol / L sodium hydroxide aqueous solution or a 0.01 mol / L HCl aqueous solution is used to adjust the pH to 8.0.

[0020] According to a preferred embodiment of the present invention, in the method for preparing the tannic acid-grafted polysaccharide aqueous dispersion, the mass ratio of the polysaccharide substance to the tannic acid is 3:5-8, preferably 3:7.

[0021] According to a preferred embodiment of the present invention, in the method for preparing the tannic acid grafted polysaccharide aqueous dispersion, the reaction temperature is room temperature, the reaction time is 12-24 hours, preferably 24 hours; and the reaction is carried out under stirring conditions.

[0022] According to the present invention, in the tannic acid-grafted polysaccharide aqueous dispersion, tannic acid can form chemical bonds such as hydrogen bonds with the polysaccharide substance, thereby significantly improving the strength and toughness of the polysaccharide substance.

[0023] According to the present invention, the initiator is preferably selected from one or a combination of two or more of azobisisobutyronitrile, azobisisoheptanenitrile, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone, potassium persulfate, ammonium persulfate, dicumyl peroxide or di-tert-butyl peroxide, preferably potassium persulfate.

[0024] According to the present invention, the crosslinking agent is preferably selected from one or a combination of two or more of dimethyl sulfide, N,N'-methylenebisacrylamide, 2-acrylamide-2-methylpropanesulfonic acid, ethylene oxide, propylene oxide, phenolic resin, formaldehyde, polyethylene glycol diacrylate or boric acid, preferably N,N'-methylenebisacrylamide.

[0025] The preparation method of the supramolecular hydrogel sealing agent constructed by host-guest interaction comprises the following steps: fully dispersing copolymerization monomers, tannic acid grafted polysaccharide aqueous dispersion, initiator and crosslinking agent in water at room temperature.

[0026] The application of the supramolecular hydrogel sealing agent constructed by the above host-guest interaction in the crude oil extraction and drilling process.

[0027] According to a preferred embodiment of the present invention, the application method comprises the following steps: during drilling, injecting a supramolecular hydrogel sealing agent into the formation, where it forms a gel at the formation temperature to seal the crude oil reservoir; and after drilling is completed, injecting an alkaline solution to remove the blockage. Preferably, the alkaline solution is a sodium hydroxide aqueous solution having a mass concentration of 5-15%, and the mass ratio of the alkaline solution to the supramolecular hydrogel sealing agent is 30-60:1.

[0028] According to the present invention, during drilling, the dosage and injection method of the supramolecular hydrogel sealing agent can be based on existing methods; the formation temperature is greater than or equal to 40°C, preferably 40-100°C.

[0029] According to the preferred embodiment of the present invention, the crude oil is heavy oil, which is a crude oil having a viscosity greater than or equal to 1000 mPa·s at 50°C.

[0030] The room temperature in the present invention has a well-known meaning in the art, which refers to 25±5°C.

[0031] The technical features and beneficial effects of the present invention are as follows:

[0032] (1) The present invention obtains a supramolecular hydrogel sealing agent by compounding a copolymerization monomer, a tannic acid grafted polysaccharide aqueous dispersion, a crosslinking agent, and an initiator and dispersing them in water at room temperature. The supramolecular hydrogel sealing agent is in a free-flowing liquid state with suitable viscosity and is easy to pump. After being pumped into the wellbore, the supramolecular hydrogel can be copolymerized and crosslinked to form a gel under the reservoir to form a sealing plug. The sealing plug is applicable to a wide range of formation temperatures. The sealing plug formed by the supramolecular hydrogel has high strength, high pressure bearing capacity, and pH responsiveness, and can isolate the wellbore to prevent heavy oil from invading the wellbore and causing annular blockage or drill bit sticking. At the same time, it can be degraded to achieve unsealing.

[0033] (2) At formation temperature, the copolymerization monomers of the present invention polymerize to form polymers, which in situ form gels with the polysaccharides grafted with tannic acid through supramolecular forces, thus obtaining supramolecular hydrogels based on host-guest interactions. Amide groups and other groups in the polymers obtained by polymerization of the copolymerization monomers of the present invention can form hydrogen bonds with phenolic hydroxyl groups, hydroxyl groups and other groups on the polysaccharides grafted with tannic acid. This hydrogen bonding is an important factor in increasing the crosslinking density of the gel, improving mechanical properties and achieving pH degradation. Under alkaline conditions, OH- will attack the phenolic hydroxyl groups of tannic acid, deprotonating them, destroying the hydrogen bonding between tannic acid and β-cyclodextrin, causing the two to dissociate, and the gel gradually transforming into a sol state.

[0034] (3) Acrylamide polymers can effectively isolate wellbores and prevent heavy oil from invading the wellbore, causing annular blockage or drill bit sticking. However, the molecular weight of acrylamide polymers is small, and the viscosity and mechanical properties are not ideal. The present invention prepares acryloyl cyclodextrin by reacting acryloyl chloride or methacryloyl chloride with cyclodextrin. The chlorine atoms in acryloyl chloride or methacryloyl chloride replace the hydroxyl groups in cyclodextrin to form an ester bond, introducing a polymerizable double bond structure and improving the stability of the structure. Then, the copolymerization reaction with double-bond monomers such as acrylamide in the formation generates a high molecular weight acrylamide-β-cyclodextrin copolymer, which has good properties including retention and mechanical properties. By introducing inclusion units to include tannic acid-grafted polysaccharides, tannic acid can be densely aggregated on the surface of the polysaccharide material in a comb-like form, which is more conducive to the entry of tannic acid into the cavity structure of β-cyclodextrin. The benzene ring of tannic acid can form an inclusion complex in the hydrophobic cavity of β-cyclodextrin, and the phenolic hydroxyl groups of tannic acid, the hydroxyl groups of the polysaccharide material and the hydroxyl groups of β-cyclodextrin form a hydrogen bond structure, forming a stable host-guest structure and a polysaccharide supramolecular hydrogel with pH degradation ability. The above-mentioned host-guest structure is stable under acidic and neutral conditions and dissociates under alkaline conditions, thereby achieving pH degradation ability. In the preparation method of acryloyl cyclodextrin of the present invention, the ratio of cyclodextrin and acryloyl chloride or methacryloyl chloride is relatively important, because if the amount of acryloyl chloride or methacryloyl chloride is low, the grafting rate will be reduced.

[0035] (4) The present invention uses tannic acid grafted polysaccharide as the guest material, which not only reduces environmental pollution, but also increases the elasticity of the gel sealing material, increases the cross-linking density, and improves the mechanical properties, thereby achieving the degradation of the gel under specific conditions. In the preparation method of tannic acid grafted polysaccharide, the ratio of polysaccharide to tannic acid is particularly important. Among them, when the amount of tannic acid is too high, a large number of tannic acid molecules may accumulate excessively on the surface of the polysaccharide material, which may cause the grafted area to be too thick. There is another situation after the tannic acid is excessive. The interaction force between tannic acid molecules will exceed the interaction force between tannic acid and polysaccharide material, so that the tannic acid itself aggregates and cannot be evenly grafted on the surface of the polysaccharide material. When the amount of tannic acid is too low, the surface of the polysaccharide material cannot be fully grafted.

[0036] (5) The specific types of acryloyl cyclodextrin and double bond-containing monomers of the present invention are combined with specific ratios and specific tannic acid grafted polysaccharides, suitable initiators and cross-linking agents to obtain supramolecular hydrogel sealing agents. The supramolecular hydrogel sealing agents obtained by the present invention are gel sealing agents with excellent mechanical properties (high strength, high pressure bearing), heat resistance and outstanding pH degradation ability based on supramolecular interactions (host-guest interactions and hydrogen bond interactions between β-cyclodextrin in the polymer obtained by copolymerization monomer polymerization and hydroxyl groups in the tannic acid grafted polysaccharide). It not only has the advantages of good matching between gel-type leak-proof plugging materials and wellbore, but also increases the heat resistance and pressure resistance of the gel through supramolecular structure design, has unique pH degradation ability, can effectively seal the formation fractures to form an overall sealing barrier, reduce the entry of heavy oil into the wellbore, and can effectively achieve hydrogel degradation and achieve unsealing. The sealing agent of the present invention has heavy oil resistance. In the presence of heavy oil, the sealing agent of the present invention can still be smoothly gelled at the formation temperature, and the obtained gel still maintains high strength and pH degradation ability. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be described in further detail. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0038] The raw materials used in the examples are all conventional raw materials and can be obtained commercially; the methods described are all based on existing technologies unless otherwise specified.

[0039] Example 1

[0040] A nanocellulose supramolecular hydrogel sealing agent comprises the following raw materials in percentage by weight: 4% acryloyl cyclodextrin, 12% acrylamide, 8% tannic acid grafted cellulose aqueous dispersion, 0.4% cross-linking agent (N,N'-methylenebisacrylamide), 1% initiator (potassium persulfate), and the balance water, with the total amount of each component being 100%.

[0041] The acryloylated cyclodextrin is acryloylated β-cyclodextrin, and its preparation method is as follows: β-cyclodextrin and sodium hydroxide are fully dissolved in deionized water, acryloyl chloride is added, and the mixture is stirred at 50°C under a nitrogen atmosphere for 12 hours. The mixture is filtered, the filtrate is collected, and then purified by precipitation with acetone. The resulting precipitate is dried in a vacuum oven at 40°C for 24 hours to obtain a pure white solid, which is acryloylated β-cyclodextrin. The mass ratio of β-cyclodextrin to sodium hydroxide is 2:5.84; the mass ratio of β-cyclodextrin to deionized water is 1:100; and the mass ratio of acryloyl chloride to β-cyclodextrin is 1:1.

[0042] The preparation method for a tannic acid-grafted cellulose aqueous dispersion comprises the following steps: thoroughly dispersing a nanocellulose fibril gel (available from Nanjing Tianlu Nanotechnology Co., Ltd., with a fiber diameter of 3-5 nm, a fiber length of 500-1000 nm, and a solid content of 2 wt%) in deionized water. The pH was adjusted to 8.0 using a 0.01 mol / L sodium hydroxide solution. Tannic acid was added, and the mixture was stirred at room temperature for 24 hours to obtain a tannic acid-grafted cellulose aqueous dispersion. The mass ratio of nanocellulose fibrils to deionized water was 4:100, and the mass ratio of tannic acid to nanocellulose fibrils was 7:3.

[0043] The preparation method of the nanocellulose supramolecular hydrogel sealing agent comprises the steps of: fully dispersing acryloyl cyclodextrin, acrylamide, tannic acid grafted cellulose aqueous dispersion, initiator and crosslinking agent in water at room temperature to obtain the nanocellulose supramolecular hydrogel sealing agent.

[0044] Example 2

[0045] A nanocellulose supramolecular hydrogel sealing agent comprises the following raw materials in percentage by weight: 4% acryloyl cyclodextrin, 8% acrylamide, 8% tannic acid grafted cellulose aqueous dispersion, 0.4% cross-linking agent (N,N'-methylenebisacrylamide), 1% initiator (potassium persulfate), and the balance water; the total amount of each component is 100%.

[0046] The preparation method of the aqueous dispersion of cellulose grafted with acryloyl cyclodextrin and tannic acid is the same as that in Example 1.

[0047] The preparation method of the nanocellulose supramolecular hydrogel sealing agent is the same as that in Example 1.

[0048] Example 3

[0049] A nanocellulose supramolecular hydrogel sealing agent comprises the following raw materials in percentage by weight: 4% acryloyl cyclodextrin, 12% acrylamide, 8% tannic acid grafted cellulose aqueous dispersion, 0.4% cross-linking agent (polyethylene glycol diacrylate, available from Aladdin, with an average molecular weight of approximately 600), 1% initiator (potassium persulfate), and the balance water; the total amount of each component is 100%.

[0050] The preparation method of the aqueous dispersion of cellulose grafted with acryloyl cyclodextrin and tannic acid is the same as that in Example 1.

[0051] The preparation method of the nanocellulose supramolecular hydrogel sealing agent is the same as that in Example 1.

[0052] Example 4

[0053] A nanocellulose supramolecular hydrogel sealing agent has the same raw material composition as in Example 1, except that in the preparation of the tannic acid-grafted polysaccharide aqueous dispersion, the nanocellulose fibril gel is replaced with a cellulose nanocrystal gel (available from Nanjing Tianlu Nanotechnology Co., Ltd., with a fiber diameter of 10-50 nm, a fiber length of 200-500 nm, and a solid content of 8 wt%); the mass ratio of cellulose nanocrystals to deionized water is 4:100, and the mass ratio of tannic acid to cellulose nanocrystals is 7:3; the other preparation steps and conditions are the same as in Example 1.

[0054] The preparation method of the nanocellulose supramolecular hydrogel sealing agent is the same as that in Example 1.

[0055] Example 5

[0056] A nanocellulose supramolecular hydrogel sealing agent comprises the following raw materials in percentage by weight: 4% acryloyl cyclodextrin, 32% acrylamide, 8% tannic acid grafted cellulose aqueous dispersion, 0.4% cross-linking agent (N,N'-methylenebisacrylamide), 1% initiator (potassium persulfate), and the balance water; the total amount of each component is 100%.

[0057] The preparation method of the aqueous dispersion of cellulose grafted with acryloyl cyclodextrin and tannic acid is the same as that in Example 1.

[0058] The preparation method of the nanocellulose supramolecular hydrogel sealing agent is the same as that in Example 1.

[0059] Example 6

[0060] A nanocellulose supramolecular hydrogel sealing agent comprises the following raw materials in percentage by weight: 4% acryloyl cyclodextrin, 12% acrylamide, 6% tannic acid grafted cellulose aqueous dispersion, 0.3% cross-linking agent (N,N'-methylenebisacrylamide), 0.5% initiator (potassium persulfate), and the balance water; the total amount of each component is 100%.

[0061] The preparation method of the aqueous dispersion of cellulose grafted with acryloyl cyclodextrin and tannic acid is the same as that in Example 1.

[0062] The preparation method of the nanocellulose supramolecular hydrogel sealing agent is the same as that in Example 1.

[0063] Example 7

[0064] A nanocellulose supramolecular hydrogel sealing agent comprises the following raw materials in percentage by weight: 4% acryloyl cyclodextrin, 12% acrylamide, 10% tannic acid grafted cellulose aqueous dispersion, 0.6% cross-linking agent (N,N'-methylenebisacrylamide), 1.5% initiator (potassium persulfate), and the balance water; the total amount of each component is 100%.

[0065] The preparation method of the aqueous dispersion of cellulose grafted with acryloyl cyclodextrin and tannic acid is the same as that in Example 1.

[0066] The preparation method of the nanocellulose supramolecular hydrogel sealing agent is the same as that in Example 1.

[0067] Example 8

[0068] A nanocellulose supramolecular hydrogel sealing agent, the raw material composition of which is the same as that described in Example 1, except that acrylamide is replaced by acrylic acid of the same mass.

[0069] The preparation method of the nanocellulose supramolecular hydrogel sealing agent is the same as that in Example 1.

[0070] Example 9

[0071] A nanocellulose supramolecular hydrogel sealing agent, the raw material composition is as described in Example 1, except that in the preparation of acryloyl cyclodextrin, the mass ratio of acryloyl chloride to β-cyclodextrin is 0.5:2, and the other preparation steps and conditions are the same as Example 1.

[0072] The preparation method of the nanocellulose supramolecular hydrogel sealing agent is the same as that in Example 1.

[0073] Example 10

[0074] A nanocellulose supramolecular hydrogel sealing agent, the raw material composition is as described in Example 1, except that in the preparation of acryloyl cyclodextrin, acryloyl chloride is replaced by methacryloyl chloride of the same mass, and the other preparation steps and conditions are the same as in Example 1.

[0075] The preparation method of the nanocellulose supramolecular hydrogel sealing agent is the same as that in Example 1.

[0076] Example 11

[0077] A nanocellulose supramolecular hydrogel sealing agent has the same raw material composition as described in Example 1, except that in the preparation of the tannic acid grafted polysaccharide aqueous dispersion, the polysaccharide material is lignin. Other preparation steps and conditions are the same as those in Example 1.

[0078] The preparation method of the nanocellulose supramolecular hydrogel sealing agent is the same as that in Example 1.

[0079] Example 12

[0080] A hydrogel sealing agent, the raw material composition is as described in Example 1, except that: in the preparation of the tannic acid-grafted polysaccharide aqueous dispersion, the mass ratio of tannic acid to nanocellulose fibrils is 5:3, and the other preparation steps and conditions are the same as in Example 1.

[0081] Comparative Example 1

[0082] A hydrogel sealing agent comprises the following raw materials in percentage by weight: 4% acryloyl cyclodextrin, 12% acrylamide, 8% cellulose aqueous dispersion, 0.4% cross-linking agent (N,N'-methylenebisacrylamide), 1% initiator (potassium persulfate), and the balance water; the total amount of each component is 100%.

[0083] The preparation method of acryloyl cyclodextrin is the same as that in Example 1.

[0084] A cellulose aqueous dispersion was prepared by thoroughly dispersing a nanocellulose fibril gel (available from Nanjing Tianlu Nanotechnology Co., Ltd., with a fiber diameter of 3-5 nm, a fiber length of 500-1000 nm, and a solids content of 2 wt%) in deionized water. The nanocellulose fibril content was the same as in Example 1.

[0085] The preparation method of the above hydrogel sealing agent is the same as that of Example 1.

[0086] Comparative Example 2

[0087] A hydrogel sealing agent, the raw material composition is as described in Example 1, except that the tannic acid grafted polysaccharide aqueous dispersion is omitted, and the omitted component is replaced with the same amount of water.

[0088] The preparation method of the above hydrogel sealing agent is the same as that of Example 1.

[0089] Comparative Example 3

[0090] A hydrogel sealing agent, the raw material composition is the same as that described in Example 1, except that acryloyl cyclodextrin is replaced by acrylamide of the same mass.

[0091] The preparation method of the above hydrogel sealing agent is the same as that of Example 1.

[0092] Test example

[0093] The sealing agents obtained in the examples and comparative examples were subjected to the following tests.

[0094] Test 1, tensile properties test

[0095] The sealant was conditioned at 80°C for 6 hours and then formed into dumbbell-shaped test strips measuring 30 mm long, 5 mm wide, and 2 mm thick. Tensile mechanical properties of the gel were tested using an electronic universal testing machine at a rate of 5 mm / min. The stress-strain values of the sealant samples were recorded during tension. The tensile performance results are shown in Table 1.

[0096] Test 2: Packer compression resistance test

[0097] The packing agent was placed at 80°C for 6 hours and then formed into a cylinder with a base diameter of 20 mm and a height of 10 mm. The gel compression mechanical properties were tested using an electronic universal testing machine. The compression speed was set at 3 mm / min, and the stress-strain values of the sample were recorded during compression. The compression resistance results are shown in Table 1.

[0098] Table 1 Toughness and compression performance test of packing agent

[0099]

[0100] As shown in Table 1, when the acrylamide content used in Example 2 is reduced, the number of monomers participating in the polymerization decreases, which means that the length of the generated polymer chain will become shorter. During the gel formation process, the polymer chain is a key component in building the gel network structure. A reduction in chain length will cause the skeleton of the gel network to become sparse. In addition, as the number of polymer chains decreases, the contact points with the tannic acid-grafted cellulose also decrease accordingly, which will weaken the mutual entanglement and interaction between the polymer and cellulose in the gel system, resulting in a decrease in the mechanical properties of the gel.

[0101] N,N'-methylenebisacrylamide (MBA) is a highly effective crosslinker that forms a dense crosslinked network between polymer chains, thereby enhancing gel strength. The crosslinker polyethylene glycol diacrylate used in Example 3, due to its long polyethylene glycol segments, introduces more flexible segments during the crosslinking process, resulting in a relatively low crosslink density and increased distance between crosslinking points, which in turn reduces gel strength.

[0102] The nanocrystals used in Example 4 have a more regular crystal structure and are relatively uniform in size and shape. They are more evenly dispersed in the gel, but do not form a long-range interwoven network like fibrils, resulting in a decrease in tensile length and compressive strength.

[0103] In Example 5, the amount of acrylamide was increased, and in Examples 6 and 7, the amounts of the tannic acid-grafted cellulose dispersion, the crosslinking agent, and the initiator were changed, resulting in changes in the gel structure formed by the sealing agent and changes in the mechanical properties.

[0104] In Example 8, acrylamide was replaced by acrylic acid, in Example 9, the mass ratio of acryloyl chloride and β-cyclodextrin was adjusted, in Example 10, acryloyl chloride was replaced by methacryloyl chloride of the same mass, in Example 11, the polysaccharide was replaced by lignin, and in Example 12, the mass ratio of tannic acid and nanocellulose fibrils was adjusted. The structure of the resulting gel will change accordingly, thereby affecting its mechanical properties.

[0105] Comparative Example 1 does not use tannic acid grafting. When tannic acid is grafted onto the cellulose surface, it acts as a "bridge" to promote the interaction between cellulose and other gel components (such as grafted β-cyclodextrin and acrylamide polymer). Due to the lack of the "bridge" effect of tannic acid in Comparative Example 1, the interaction between cellulose and other gel components is weakened, and the structural stability and dispersibility of the gel network are affected, thereby reducing the overall strength of the gel.

[0106] In Comparative Example 2, the tannic acid-grafted polysaccharide was replaced with water. After it was replaced with water, the number of structural supports and cross-linking points in the gel was reduced, causing the gel network to become looser.

[0107] Comparative Example 3 is acrylamide. When acryloyl cyclodextrin is replaced by acrylamide, the cross-linking points and structure in the gel network change, and the effective cross-linking points decrease.

[0108] Test 3, rheological properties test of packing agent

[0109] The sealant was placed at 80°C for 6 hours and then formed into circular sheets with a bottom diameter of 30 mm and a height of 3 mm. The rheological properties of the sealant were tested using a HAAKEMARS 60 rheometer. The storage modulus (G') and loss modulus (G") were tested under a constant strain of 1.0%, an oscillation sweep frequency of 1 Hz, and an angular frequency range of 0.01-100 rad·s. -1 , record the storage modulus (G') and loss modulus (G") of the above-mentioned sealing agents. The rheological results (G' and G") at 1 Hz are shown in Figure 3.

[0110] Table 2 Rheological properties of the packing agent

[0111]

[0112] As shown in Table 2, changes in the amount of acrylamide or raw materials, the type of cross-linking agent, the type of polysaccharide, the type of polymerization monomer, the preparation conditions of acryloyl cyclodextrin, and the preparation conditions of tannic acid-grafted polysaccharide aqueous dispersion will all lead to changes in the structure of the resulting gel, thereby affecting the rheological properties of the resulting gel.

[0113] In Comparative Example 1, tannic acid grafting was not used, and the connectivity between cellulose and other structures was reduced, and the elastic modulus decreased. In Comparative Example 2, the tannic acid grafted polysaccharide was replaced with water. Because the gel network lost the structural reinforcement provided by the tannic acid grafted cellulose, the connection and support between the molecular chains became weaker, and the elastic modulus decreased. In Comparative Example 3, the acryloyl cyclodextrin was replaced with acrylamide of the same mass. The special interaction brought by the cyclodextrin structure was lost in the gel network, the interaction between the molecular chains was reduced, and the elastic modulus decreased.

[0114] Test 4, pH degradation ability

[0115] The sealing agent prepared by the method of Example 1 was placed at 80°C for 6 hours to form a gel. To 100g of the gel, 30g of a 5wt% aqueous sodium hydroxide solution was added, and the mixture was allowed to stand for 10 hours to obtain a mixture. The rheological properties of the mixture were tested using a HAAKE MARS 60 rheometer. The storage modulus (G') was tested under the following conditions: 1.0% constant strain, 1Hz oscillation sweep frequency, and an angular frequency range of 0.01-100rad·s. -1 The storage modulus G' of the mixture was recorded. The rheological results (G' at 1 Hz) are shown in Table 3.

[0116] Table 3 pH degradation ability data

[0117]

[0118] As can be seen from the data in Table 3, after alkali treatment, the strength is greatly reduced due to the dissociation of hydrogen bonds, and the gel is basically degraded, indicating that the sealing agent of the present invention has pH degradation ability after gelation and can achieve unblocking after plugging.

[0119] The above description is only a preferred embodiment of the present invention. It should be pointed out that several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A supramolecular hydrogel sealing agent constructed by host-guest interaction, characterized in that: The raw material composition comprises the following weight percentages: 12-36% copolymerization monomer, 6-10% tannic acid grafted polysaccharide aqueous dispersion, 0.5-1.5% initiator, 0.3-0.6% cross-linking agent, and the balance is water; the total amount of each component is 100%; The copolymerization monomer is a combination of acryloyl cyclodextrin and a double bond-containing monomer; the double bond-containing monomer is one of acrylamide, N-isopropylacrylamide or N-hydroxyethylacrylamide; The preparation method of acryloyl cyclodextrin comprises the following steps: dissolving cyclodextrin and sodium hydroxide in deionized water, adding acryloyl chloride or methacryloyl chloride, reacting, filtering, precipitating and drying to obtain acryloyl cyclodextrin; The preparation method of a tannic acid-grafted polysaccharide aqueous dispersion comprises the following steps: fully dispersing a polysaccharide substance in deionized water and adjusting the pH to 8.0; adding tannic acid and reacting to obtain a tannic acid-grafted polysaccharide aqueous dispersion; the polysaccharide substance is one or a combination of two or more of cellulose, starch, lignin, xanthan gum, chitosan, guar gum or sodium alginate; and the mass ratio of the polysaccharide substance to the tannic acid is 3:5-8.

2. The supramolecular hydrogel sealing agent constructed by host-guest interaction according to claim 1, characterized in that: The supramolecular hydrogel sealing agent constructed by host-guest interaction comprises the following raw materials in percentage by weight: 16% copolymerization monomer, 8% tannic acid grafted polysaccharide aqueous dispersion, 1% initiator, 0.4% cross-linking agent, and the balance water; the total amount of each component is 100%.

3. The supramolecular hydrogel sealing agent constructed by host-guest interaction according to claim 1, characterized in that: The preparation method of acryloyl cyclodextrin includes one or more of the following conditions: i. Cyclodextrin is selected from one or a combination of two or more of α-cyclodextrin, β-cyclodextrin or γ-cyclodextrin; ii. The mass ratio of cyclodextrin to sodium hydroxide is 1-4:5.84; the mass ratio of cyclodextrin to deionized water is 1:50-150; the mass ratio of acryloyl chloride or methacryloyl chloride to cyclodextrin is 0.5-2.2:2; iii. The reaction temperature is 40-60°C; the reaction time is 6-12 hours; the reaction is carried out under inert gas protection and stirring; the inert gas is nitrogen or argon.

4. The supramolecular hydrogel sealing agent constructed by host-guest interaction according to claim 1, characterized in that: The mass ratio of the acryloyl cyclodextrin to the double bond-containing monomer is 1:2-8.

5. The supramolecular hydrogel sealing agent constructed by host-guest interaction according to claim 1, characterized in that: The method for preparing the tannic acid grafted polysaccharide aqueous dispersion includes one or more of the following conditions: i. The polysaccharide material is cellulose, and the cellulose is selected from nanocellulose fibrils, cellulose nanocrystals or carboxymethyl cellulose; ii. The mass ratio of polysaccharide to deionized water is 1:20-30; iii. Adjust the pH to 8.0 using a 0.01 mol / L sodium hydroxide aqueous solution or a 0.01 mol / L HCl aqueous solution; iv. The reaction temperature is room temperature and the reaction time is 12-24 hours; the reaction is carried out under stirring conditions.

6. The supramolecular hydrogel sealing agent constructed by host-guest interaction according to claim 1, characterized in that: The initiator is selected from one or a combination of two or more of azobisisobutyronitrile, azobisisoheptanenitrile, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone, potassium persulfate, ammonium persulfate, dicumyl peroxide or di-tert-butyl peroxide.

7. The supramolecular hydrogel sealing agent constructed by host-guest interaction according to claim 1, characterized in that: The cross-linking agent is selected from one or both of N,N'-methylenebisacrylamide and polyethylene glycol diacrylate.

8. The method for preparing the supramolecular hydrogel sealing agent constructed by host-guest interaction according to any one of claims 1 to 7, characterized in that: The method comprises the following steps: fully dispersing copolymerization monomers, tannic acid grafted polysaccharide aqueous dispersion, initiator and cross-linking agent in water at room temperature.

9. Use of the supramolecular hydrogel sealing agent constructed by host-guest interaction according to any one of claims 1 to 7 in the process of crude oil production and drilling.

10. The use according to claim 9, characterized in that The application method comprises the following steps: during drilling, a supramolecular hydrogel sealing agent constructed by host-guest interaction is injected into the formation, and gelled at the formation temperature to seal the crude oil reservoir; after drilling is completed, an alkaline solution is injected for unblocking; the alkaline solution is a sodium hydroxide aqueous solution with a mass concentration of 5-15%, and the mass ratio of the alkaline solution to the supramolecular hydrogel sealing agent is 30-60:1; the crude oil is heavy oil, and the heavy oil is crude oil with a viscosity greater than or equal to 1000 mPa·s at 50°C.

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