A lost circulation material for restoring wellbore integrity

Abstract

The present application relates to the technical field of plugging material, in particular to a plugging agent for restoring wellbore integrity, which is formed by mixing solid components and water in a mass ratio of 1:(3-5) and then forming a gel network through polymerization; the solid components are composed of the following components: a polymer monomer component, a dynamic cross-linking component, a reinforcing and toughening component, and an auxiliary component; the dynamic cross-linking component is composed of graphene oxide, oxidized carboxymethyl chitosan, an aryl boronic acid compound containing an ortho-hydroxyl group, and an amine cross-linking agent; the imine bond formed by the oxidized carboxymethyl chitosan and the amine cross-linking agent, and the borate ester bond formed by the aryl boronic acid compound containing an ortho-hydroxyl group, jointly construct a double dynamic chemical network, which retains the self-repairing characteristics of the dynamic bond, and significantly inhibits high-temperature creep with the physical barrier effect of graphene oxide.

Description

Technical Field

[0001] This invention relates to the field of plugging materials technology, specifically a plugging agent for restoring the integrity of a wellbore. Background Technology

[0002] In the exploration and development of oil, natural gas, and geothermal resources, wellbore integrity is crucial for ensuring operational safety, preventing formation fluid leakage, and protecting the environment. Drilling or workover operations frequently encounter complex situations such as fracture-related losses, cavern-related losses, or high-pressure permeability losses.

[0003] In recent years, polymer gel plugging agents have attracted widespread attention due to their good injectability, controllable gelation time, and excellent sealing performance. Traditional polymer gel plugging agents mainly form a static three-dimensional network structure through chemical cross-linking agents, possessing certain mechanical strength and sealing capabilities. However, static chemical cross-linked networks lack rigid physical support points, making them prone to chain segment slippage and creep under high temperature and pressure environments, and unable to maintain long-term pressure resistance within cracks. Although existing technologies attempt to physically reinforce cracks by adding nanofillers, the interaction between fillers and the polymer matrix is ​​mostly physical blending or non-specific adsorption, resulting in weak interfacial bonding and an inability to form an effective stress transfer network, thus limiting the suppression of high-temperature creep. On the other hand, single dynamic cross-linked networks often face problems of excessively strong bond reversibility and insufficient hydrolytic stability in high-temperature hydrothermal environments, making it difficult to balance high strength and long-term stability. Summary of the Invention

[0004] The purpose of this invention is to provide a plugging agent for restoring wellbore integrity, thereby solving the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a plugging agent for restoring wellbore integrity, wherein the plugging agent is formed by mixing solid components and water in a mass ratio of 1:(3-5) and undergoing a polymerization reaction to form a gel network.

[0006] The solid phase component, by mass percentage, consists of the following components: Monomer content: 51.0%–60.0%; Dynamic cross-linking component: 7.0%–10.0%; Reinforcing and toughening components: 25.0%–36.5%; Additive components: 3.5%–5.5%; The polymer monomer component is composed of 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone, and hydroxyethyl acrylate.

[0007] The dynamic crosslinking component consists of graphene oxide, oxidized carboxymethyl chitosan, an arylboronic acid compound containing ortho-hydroxyl groups, and an amine crosslinking agent. The oxidized carboxymethyl chitosan is a bifunctional modified carboxymethyl chitosan containing both aldehyde groups and cis-vicinal diols, which is obtained by controlling the partial oxidation of carboxymethyl chitosan by sodium periodate. In the gel network, graphene oxide acts as a physical crosslinking point through non-covalent interactions such as hydrogen bonding. The cis-vicinal diol structure retained in the side chain of oxidized carboxymethyl chitosan undergoes a complexation reaction with the arylboronic acid compound containing ortho-hydroxyl groups to form dynamic borate ester bonds. The active aldehyde groups generated by oxidation on the oxidized carboxymethyl chitosan molecular chain undergo a Schiff base condensation reaction with the amine crosslinking agent to form dynamic imine bonds.

[0008] The reinforcing and toughening components consist of modified nano-silica, nano-cellulose crystals, and nitrile rubber powder.

[0009] The additive components consist of an initiator, a retarder, an oxygen scavenger, and a dispersant.

[0010] Preferably, the percentage of each component in the polymer monomer component relative to the total mass of the solid phase component is: 2-Acrylamido-2-methylpropanesulfonic acid: 22.0%~26.0%; N-Vinylpyrrolidone: 16.0%–19.0%; Hydroxyethyl acrylate: 13.0%~15.0%.

[0011] Preferably, the percentage of each component in the dynamic crosslinking component relative to the total mass of the solid phase component is: Graphene oxide: 0.6%–1.0%; Oxidized carboxymethyl chitosan: 2.5%–3.5%; Arylboronic acid compounds containing ortho-hydroxyl groups: 2.0%–3.0%; Amine crosslinking agents: 1.9%–2.5%.

[0012] Preferably, the arylboronic acid compound containing an ortho-hydroxyl group is 2-hydroxyphenylboronic acid or 2,4-dihydroxyphenylboronic acid; The amine crosslinking agent is one or more of ethylenediamine, hexamethylenediamine, and polyethyleneimine.

[0013] Preferably, the percentage of each component in the reinforcing and toughening component relative to the total mass of the solid phase component is: Modified nano-silica: 3.0%–4.5%; Nanocellulose crystals: 4.0%–5.5%; Nitrile rubber powder: 18.0%~26.5%.

[0014] Preferably, the modified nano-silica has an average particle size of 20nm to 50nm, and its surface modifier is a silane coupling agent KH-560 or KH-570; the acrylonitrile content of the nitrile rubber powder is 30% to 45%, and its average particle size is 80 mesh to 120 mesh.

[0015] Preferably, the percentage of each component in the additive component relative to the total mass of the solid phase component is: Initiator: 1.4%–2.2%; Retarder: 0.7%–1.1%; Oxygen scavenger: 0.5%–0.9%; Dispersant: 0.9%–1.3%.

[0016] Preferably, in the auxiliary agent components, the initiator is one or more of ammonium persulfate, potassium persulfate, or azobisisobutyramidine hydrochloride; the retarder is sodium thiosulfate or urea; the oxygen scavenger is sodium sulfite or sodium isoascorbate; and the dispersant is sodium hexametaphosphate or sodium lignin sulfonate.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention uses graphene oxide as a rigid framework to effectively restrict the thermal motion and slippage of polymer chain segments at high temperatures, providing basic compressive strength. It also constructs a dual dynamic chemical network through imine bonds formed by oxidized carboxymethyl chitosan and amine crosslinking agents, and borate ester bonds formed with arylboronic acid containing ortho-hydroxyl groups. While retaining the self-healing properties of dynamic bonds, the physical barrier effect of graphene oxide significantly inhibits high-temperature creep, ensuring that the sealing agent maintains excellent dimensional stability under long-term high-pressure conditions.

[0018] 2. The dynamic cross-linked network constructed in this invention can form a dense and complete sealing layer, effectively blocking fluid seepage. It has excellent sealing ability for cracks of different widths. The sealing agent has excellent mechanical properties, with both high strength and excellent fracture toughness. It can effectively resist high-temperature thermal oxidation degradation and maintain the mechanical integrity of the gel network. Attached Figure Description

[0019] Figure 1 The FTIR spectrum of the plugging agent prepared in Example 1; Figure 2 The XPS full spectrum of the sealing agent prepared in Example 1 is shown. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Example 1: This embodiment provides a plugging agent for restoring wellbore integrity. The plugging agent is formed by mixing solid components and water at a mass ratio of 1:4 and then undergoing a polymerization reaction to form a gel network.

[0022] The solid phase component, by mass percentage, consists of the following components: 55.0% polymeric monomer component, 8.5% dynamic crosslinking component, 32.5% reinforcing and toughening component, and 4.0% additive component. The percentage of each component in the polymeric monomer component relative to the total mass of the solid phase component is as follows: 2-acrylamido-2-methylpropanesulfonic acid 24.0%; N-vinylpyrrolidone 17.0%; hydroxyethyl acrylate 14.0%. The percentage of each component in the dynamic crosslinking component relative to the total mass of the solid phase component is as follows: graphene oxide 0.8%, oxidized carboxymethyl chitosan 3.0%, arylboronic acid compound containing ortho-hydroxyl groups 2.5%, and amine crosslinking agent 2.2%. The arylboronic acid compound containing ortho-hydroxyl groups is 2-hydroxyphenylboronic acid. The percentage of each component in the reinforcing and toughening component relative to the total mass of the solid phase component is as follows: modified nano-silica 3.5%, nano-cellulose crystals 4.5%, and nitrile rubber powder 24.5%. The modified nano-silica has an average particle size of 35 nm, and its surface modifier is silane coupling agent KH-560. The percentage of each component in the additives relative to the total mass of the solid phase is as follows: initiator 1.6%, retarder 0.8%, oxygen scavenger 0.6%, and dispersant 1.0%. Specifically, the initiator is ammonium persulfate; the retarder is sodium thiosulfate; the oxygen scavenger is sodium sulfite; and the dispersant is sodium hexametaphosphate.

[0023] The preparation method of the above-mentioned sealing agent includes the following steps: adding the polymer monomer component, dynamic crosslinking component, reinforcing and toughening component and auxiliary component to a mixer in sequence, mixing at 30 r / min for 40 min to obtain a uniform solid component; weighing deionized water at a solid component to water mass ratio of 1:4, placing it in a preparation tank, turning on the stirrer, and controlling the speed at 300 r / min; slowly adding the solid component to the water, controlling the addition time at 15 min, and continuing to stir for 30 min after the addition is completed to obtain a uniform sealing agent.

[0024] Example 2: This embodiment provides a plugging agent for restoring wellbore integrity. The plugging agent is formed by mixing solid components and water in a mass ratio of 1:3 and then undergoing a polymerization reaction to form a gel network.

[0025] The solid phase component, by mass percentage, consists of the following components: 51.0% polymeric monomer component, 7.0% dynamic crosslinking component, 36.5% reinforcing and toughening component, and 5.5% additive component. The percentage of each component in the polymeric monomer component relative to the total mass of the solid phase component is as follows: 2-acrylamido-2-methylpropanesulfonic acid 22.0%; N-vinylpyrrolidone 16.0%; hydroxyethyl acrylate 13.0%. The percentage of each component in the dynamic crosslinking component relative to the total mass of the solid phase component is as follows: graphene oxide 0.6%, oxidized carboxymethyl chitosan 2.5%, arylboronic acid compound containing ortho-hydroxyl groups 2.0%, and amine crosslinking agent 1.9%. The arylboronic acid compound containing ortho-hydroxyl groups is 2,4-dihydroxyphenylboronic acid. The percentage of each component in the reinforcing and toughening component relative to the total mass of the solid phase component is as follows: modified nano-silica 4.5%, nano-cellulose crystals 5.5%, and nitrile rubber powder 26.5%. The modified nano-silica has an average particle size of 20 nm, and its surface modifier is silane coupling agent KH-560. The percentage of each component in the additives relative to the total mass of the solid phase is as follows: initiator 2.2%, retarder 1.1%, oxygen scavenger 0.9%, and dispersant 1.3%. Specifically, the initiator is potassium persulfate; the retarder is urea; the oxygen scavenger is sodium isoascorbate; and the dispersant is sodium lignosulfonate.

[0026] The preparation method of the above-mentioned sealing agent includes the following steps: adding the polymer monomer component, dynamic crosslinking component, reinforcing and toughening component and auxiliary component to a mixer in sequence, mixing at 20 r / min for 30 min to obtain a uniform solid component; weighing deionized water at a solid component to water mass ratio of 1:3, placing it in a preparation tank, turning on the stirrer, and controlling the speed to 240 r / min; slowly adding the solid component to the water, controlling the addition time to 10 min, and continuing to stir for 20 min after the addition is completed to obtain a uniform sealing agent.

[0027] Example 3: This embodiment provides a plugging agent for restoring wellbore integrity. The plugging agent is formed by mixing solid components and water at a mass ratio of 1:5 and then undergoing a polymerization reaction to form a gel network.

[0028] The solid phase component, by mass percentage, consists of the following components: 60.0% polymeric monomer component, 10.0% dynamic crosslinking component, 25.0% reinforcing and toughening component, and 5.0% additive component. The percentage of each component in the polymeric monomer component relative to the total mass of the solid phase component is as follows: 2-acrylamido-2-methylpropanesulfonic acid 26.0%; N-vinylpyrrolidone 19.0%; hydroxyethyl acrylate 15.0%. The percentage of each component in the dynamic crosslinking component relative to the total mass of the solid phase component is as follows: graphene oxide 1.0%, oxidized carboxymethyl chitosan 3.5%, arylboronic acid compound containing ortho-hydroxyl groups 3.0%, and amine crosslinking agent 2.5%. The arylboronic acid compound containing ortho-hydroxyl groups is 2,4-dihydroxyphenylboronic acid. The percentage of each component in the reinforcing and toughening component relative to the total mass of the solid phase component is as follows: modified nano-silica 3.0%, nano-cellulose crystals 4.0%, and nitrile rubber powder 18.0%. The modified nano-silica has an average particle size of 50 nm, and its surface modifier is silane coupling agent KH-570. The percentage of each component in the additives relative to the total mass of the solid phase is as follows: initiator 2.0%, retarder 1.0%, oxygen scavenger 0.8%, and dispersant 1.2%. Specifically, the initiator is azobisisobutyramidine hydrochloride; the retarder is sodium thiosulfate; the oxygen scavenger is sodium sulfite; and the dispersant is sodium hexametaphosphate.

[0029] The preparation method of the above-mentioned sealing agent includes the following steps: adding the polymer monomer component, dynamic crosslinking component, reinforcing and toughening component and auxiliary component to a mixer in sequence, mixing at 36 r / min for 45 min to obtain a uniform solid component; weighing deionized water at a solid component to water mass ratio of 1:5, placing it in a preparation tank, turning on the stirrer, and controlling the speed at 360 r / min; slowly adding the solid component to the water, controlling the addition time at 20 min, and continuing to stir for 40 min after the addition is completed to obtain a uniform sealing agent.

[0030] Example 4: This embodiment provides a plugging agent for restoring wellbore integrity. The plugging agent is formed by mixing solid components and water at a mass ratio of 1:4.5 and then undergoing a polymerization reaction to form a gel network.

[0031] The solid phase component, by mass percentage, consists of the following components: 57.0% polymeric monomer component, 9.0% dynamic crosslinking component, 30.5% reinforcing and toughening component, and 3.5% additive component. The percentage of each component in the polymeric monomer component relative to the total mass of the solid phase component is as follows: 2-acrylamido-2-methylpropanesulfonic acid 25.0%; N-vinylpyrrolidone 18.0%; hydroxyethyl acrylate 14.0%. The percentage of each component in the dynamic crosslinking component relative to the total mass of the solid phase component is as follows: graphene oxide 0.9%, oxidized carboxymethyl chitosan 3.2%, arylboronic acid compound containing ortho-hydroxyl groups 2.8%, and amine crosslinking agent 2.1%. The arylboronic acid compound containing ortho-hydroxyl groups is 2-hydroxyphenylboronic acid. The percentage of each component in the reinforcing and toughening component relative to the total mass of the solid phase component is as follows: modified nano-silica 3.5%, nano-cellulose crystals 4.5%, and nitrile rubber powder 22.5%. The modified nano-silica has an average particle size of 40 nm, and its surface modifier is silane coupling agent KH-570. The percentage of each component in the additives relative to the total mass of the solid phase is as follows: initiator 1.4%, retarder 0.7%, oxygen scavenger 0.5%, and dispersant 0.9%. Specifically, the initiator is a mixture of ammonium persulfate and potassium persulfate in a 1:2 mass ratio; the retarder is urea; the oxygen scavenger is sodium isoascorbate; and the dispersant is sodium lignosulfonate.

[0032] The preparation method of the above-mentioned sealing agent includes the following steps: adding the polymer monomer component, dynamic crosslinking component, reinforcing and toughening component and auxiliary component to a mixer in sequence, mixing at 32 r / min for 25 min to obtain a uniform solid phase component; weighing deionized water at a solid phase component to water mass ratio of 1:4.5, placing it in a preparation tank, turning on the stirrer, and controlling the speed at 350 r / min; slowly adding the solid phase component to the water, controlling the addition time at 18 min, and continuing to stir for 25 min after the addition is completed to obtain a uniform sealing agent.

[0033] In Examples 1-4, the preparation method of oxidized carboxymethyl chitosan includes the following steps: Carboxymethyl chitosan with a degree of deacetylation of 90% and a degree of substitution of 0.75 is dissolved in deionized water to prepare a 2% (w / w) solution; the pH of the solution is adjusted to 4.5 using 0.5 mol / L dilute hydrochloric acid; sodium periodate is added to the solution in a 15°C constant temperature water bath under light-protected conditions, with a molar ratio of sodium periodate to repeating units of carboxymethyl chitosan of 0.35:1, and the reaction is continuously stirred for 18 hours; ethylene glycol is added to the reaction solution... The molar amount of alcohol was 1.2 times that of sodium periodate. Stirring continued for 30 minutes to completely quench unreacted sodium periodate, terminating the oxidation process and preventing over-oxidation of the product. The quenched product was placed in a dialysis bag with a molecular weight cutoff of 3500 Da and dialyzed against deionized water for 72 hours to remove small molecule impurities, inorganic salts, and quenching byproducts, yielding a dialysate. The dialysate was pre-frozen and freeze-dried for 48 hours to obtain a white flocculent solid, which is oxidized carboxymethyl chitosan with aldehyde and cis-vicinal diol bifunctional groups. The above preparation process precisely controls the molar amount of sodium periodate and the reaction time to regulate the degree of oxidation, causing some sugar rings to open and generate highly reactive dialdehyde structures, while retaining some unreacted cis-vicinal diol structures on the molecular chain, thus obtaining modified carboxymethyl chitosan with aldehyde and vicinal diol bifunctional groups.

[0034] Please see Figure 1 1720cm -1 A distinct C=O stretching vibration peak was observed nearby, which is attributed to the active aldehyde group generated by the oxidation of carboxymethyl chitosan molecular chain with sodium periodate; simultaneously, at 1050 cm⁻¹... -1 ~1100cm -1 The characteristic absorption peaks observed in the region are attributed to the COC / CO stretching vibrations of the sugar ring backbone and the unreacted vicinal diol structure. The simultaneous presence of these two characteristic peaks confirms that oxidized carboxymethyl chitosan successfully retains the aldehyde-vicinal diol bifunctional structure, providing the necessary reaction sites for the subsequent construction of the double crosslinked network; 1350 cm⁻¹ -1 The characteristic absorption peak observed nearby is attributed to the BOC stretching vibration; simultaneously, at 1420 cm⁻¹ -1 Vibrational peaks associated with boron atoms were observed nearby. The appearance of these peaks confirmed that the cis-ortho-diol structure retained on the side chain of oxidized carboxymethyl chitosan reacted with the arylboronic acid compound containing ortho-hydroxyl groups added to the system, successfully forming a dynamic borate ester bond; 1635 cm⁻¹ -1 ~1645cm -1 The characteristic absorption peaks that appeared nearby were attributed to the C=N stretching vibration, indicating that the active aldehyde groups on the oxidized carboxymethyl chitosan molecular chain underwent a Schiff base condensation reaction with the amine crosslinking agent (or the unsubstituted amino group on the backbone) added to the system, and a dynamic imine bond network was successfully constructed.

[0035] Please see Figure 2 The presence of a B1s characteristic peak near the binding energy of 188 eV to 192 eV confirms that the arylboronic acid compound containing ortho-hydroxyl groups has been successfully introduced into the gel network. The presence of an N1s characteristic peak near 400 eV is attributed to the nitrogen in the oxidized carboxymethyl chitosan skeleton and the newly generated imine bond nitrogen, which not only confirms the effective retention of the amino component but also confirms the occurrence of the imine bond crosslinking reaction. The presence of C1s and O1s characteristic peaks near 285 eV and 532 eV, respectively, corresponds to the carbon-oxygen skeleton of the organic gel network composed of oxidized carboxymethyl chitosan, boric acid compounds, and amine crosslinking agents.

[0036] In summary, the XPS and FTIR analysis results corroborate each other, confirming the construction of the dual dynamic cross-linked network from both elemental composition and chemical bond levels.

[0037] Comparative Example 1: The difference from Example 1 is that ordinary polystyrene microspheres are used as non-functional nanofillers to replace graphene oxide.

[0038] Comparative Example 2: The difference from Example 1 is that ordinary polystyrene microspheres are used as non-functional nanofillers to replace oxidized carboxymethyl chitosan.

[0039] Comparative Example 3: The difference from Example 1 is that ordinary polystyrene microspheres are used as non-functional nanofillers to replace 2-hydroxyphenylboronic acid.

[0040] Comparative Example 4: The difference from Example 1 is that ordinary polystyrene microspheres are used as non-functional nanofillers to replace amine crosslinking agents.

[0041] Comparative Example 5: The difference from Example 1 is that phenylboronic acid is used instead of 2-hydroxyphenylboronic acid.

[0042] Test Example 1: Mechanical Property Test Experimental Procedure: The sealing agents prepared in the examples and comparative examples were used as samples. They were injected into a Φ20mm×40mm cylindrical mold, air bubbles were removed, and the molds were sealed. The molds were then placed in a 60℃ water bath for curing for 24 hours. After demolding, the molds were placed in sealed bags and cured at room temperature for 48 hours. Thirty samples were prepared for each group of samples, and the following tests were performed: Room temperature compressive strength test: The test was conducted using a universal testing machine at a temperature of 23±2℃ and a loading rate of 5mm / min. The maximum compressive load F was recorded. max According to the formula: σ=F max / A, calculate the compressive strength, where A is the cross-sectional area of ​​the specimen. 10 specimens are tested in each group, and the arithmetic mean is taken.

[0043] High-temperature aging strength retention rate test: Place the sample in a sealed stainless steel container, add deionized water accounting for 15% of the container volume, and then place the container in a high-temperature oven at 150℃ and 180℃ for 72 hours. After aging, cool to room temperature and test the compressive strength according to the method of room temperature compressive strength test. Calculate the strength retention rate according to the formula: Strength retention rate (%) = Compressive strength after aging / Compressive strength at room temperature × 100%. Test 5 samples in each group and take the arithmetic mean.

[0044] Elastic modulus test: Frequency scanning test was performed using a rheometer. The test conditions were 1% oscillation shear strain amplitude, 60℃ test temperature, and 20mm diameter parallel plate clamp. The storage modulus G' value at a frequency of 10 rad / s was recorded as the result of the elastic modulus test. Ten samples were tested in each group, and the arithmetic mean was taken.

[0045] Fracture toughness test: The single-sided notched beam method was used. The specimen size was 40mm × 10mm × 5mm, the pre-cast notch depth was 2mm, and the loading rate was 1mm / min. The fracture toughness K was calculated. IC (Unit: MPa·m) 1 / 2 Five samples were tested in each group, and the arithmetic mean was taken.

[0046] The test results are shown in Table 1.

[0047] Table 1: Results of Mechanical Property Tests

[0048] As shown in Table 1, the mechanical properties of the embodiments are all superior to those of the comparative examples, specifically as follows: Regarding room temperature compressive strength, the examples showed significantly higher compressive strengths than the comparative examples. In the comparative examples, the compressive strength decreased significantly when any key component was missing (e.g., oxidized carboxymethyl chitosan, or containing ortho-hydroxy arylboronic acid or an amine crosslinking agent). While the compressive strength was slightly higher than the other comparative examples when phenylboronic acid was substituted for ortho-hydroxy arylboronic acid, it was still far lower than that of the examples. This indicates that the dual dynamic network composed of imine bonds and borate ester bonds has a synergistic enhancing effect on the material's mechanical properties, and that the ortho-hydroxy arylboronic acid plays a crucial role in stabilizing the borate ester bonds through intramolecular coordination effects.

[0049] Regarding aging stability, after aging at 150°C and 180°C, the strength retention rates of the examples were significantly higher than those of the comparative examples. In the comparative examples, the strength retention rates after high-temperature aging were significantly reduced when any component of the dual network was missing or when phenylboronic acid was used as a substitute. This indicates that the intramolecular coordination structure formed by arylboronic acid containing ortho-hydroxyl groups effectively inhibits the nucleophilic attack of water molecules on the borate ester bonds, endowing the dual dynamic network with excellent hot water aging stability.

[0050] In terms of elastic modulus and fracture toughness, the energy storage modulus and fracture toughness of the embodiments are significantly better than those of the comparative examples, indicating that the dual network structure composed of imine bonds and borate ester bonds effectively achieves the synergy of rigid support and tough energy dissipation, giving the material good crack resistance.

[0051] In summary, the embodiments successfully constructed a dual dynamic crosslinking system consisting of an imine bond main network and a borate ester bond auxiliary network by introducing bifunctional modified carboxymethyl chitosan containing both aldehyde and cis-ortho-diol groups, and combining it with arylboronic acid compounds containing ortho-hydroxyl groups and amine crosslinking agents. This system provides high-strength mechanical support at room temperature, effectively resists hydrolysis in high-temperature hydrothermal environments through intramolecular coordination effects, and endows the material with excellent toughness and thermal stability through reversible breaking and reconstruction of dynamic bonds, exhibiting significantly better comprehensive mechanical properties than the comparative examples.

[0052] Test Example 2: Hydrolysis Resistance Test Experimental procedure: The sealing agents of Examples 1-4 and Comparative Example 5 were injected into cylindrical molds with a diameter of 20mm×40mm. The air bubbles were removed by slight vibration. After sealing, the molds were placed in a water bath at 60℃ for 24 hours to cure. After demolding, the molds were placed in sealed bags and cured at room temperature for 48 hours to obtain the test samples. Ten samples were prepared for each group of samples.

[0053] Referring to the room temperature compressive strength test method in Test Example 1, 5 samples were randomly selected from each group of 10 samples to determine their room temperature compressive strength, and the arithmetic mean was recorded as the room temperature compressive strength of the samples in that group.

[0054] The remaining samples were placed in high-temperature and high-pressure sealed containers, and sufficient deionized water was added until the samples were completely submerged. The samples were then aged for 24 hours, 72 hours, and 168 hours in high-pressure sealed containers with aging temperatures of 150℃ and 180℃, respectively, with sufficient deionized water added to ensure complete immersion.

[0055] After the aging cycle is completed, the container is removed and allowed to cool naturally to room temperature. The surface moisture is quickly absorbed with filter paper, and the compressive strength of each group of samples after aging under different aging conditions is immediately measured. Five parallel samples are tested under each group of conditions, and their arithmetic mean is taken. The compressive strength retention rate is calculated according to the formula: compressive strength retention rate (%) = compressive strength after aging / compressive strength at room temperature × 100%.

[0056] The test results are shown in Table 2.

[0057] Table 2: Results of Hydrolysis Resistance Test

[0058] As shown in Table 2, the short-term and long-term stability of the examples under high-temperature and high-pressure water conditions is significantly better than that of Comparative Example 5. This indicates that the boronic ester bonds formed by ordinary phenylboronic acid are prone to irreversible hydrolytic breakage in high-temperature water environments, leading to rapid collapse of the network framework. The introduction of the ortho-hydroxyl group in this invention generates significant steric hindrance and electronic effects, effectively suppressing nucleophilic attacks from water molecules. This significantly improves the hydrolysis energy barrier and thermodynamic stability of the boronic ester bonds, verifying the technical necessity of selecting arylboronic acid compounds containing ortho-hydroxyl groups as the specific structural unit in this invention.

[0059] Test Example 3: Sealing Performance Test Experimental Procedure: The sealing agents prepared in Examples 1-4 and Comparative Examples 1-5 were used as samples. A self-made crack simulation module was used, with a crack length of 50 mm, a crack depth of 100 mm, and crack widths of 1 mm, 2 mm, and 3 mm. The samples were injected into the crack simulation module, sealed, and placed in a 60℃ water bath for 24 hours, followed by room temperature curing for 48 hours. After curing, the crack simulation module was connected to a pressurization system, and the nitrogen pressure was gradually increased at a rate of 0.5 MPa / min. The pressure value at which leakage occurred was recorded as the breakthrough pressure (unit: MPa). Five parallel samples were tested under each condition, and the arithmetic mean was taken.

[0060] The test results are shown in Table 3.

[0061] Table 3: Results of the sealing performance test

[0062] As shown in Table 3, under different crack width conditions, the breakthrough pressure of the embodiments was significantly higher than that of the comparative examples, indicating that the high cross-linking density structure formed by the boron oxide graphene sheets, borate ester bonds and imine bonds is crucial to improving the structural integrity and pressure resistance of the sealing layer.

[0063] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A plugging agent for restoring wellbore integrity, characterized in that, The sealing agent is formed by mixing solid components and water in a mass ratio of 1:(3-5) and undergoing a polymerization reaction to form a gel network; The solid phase component, by mass percentage, consists of the following components: Monomer content: 51.0%–60.0%; Dynamic cross-linking component: 7.0%–10.0%; Reinforcing and toughening components: 25.0%–36.5%; Additive components: 3.5%–5.5%; The polymer monomer component is composed of 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone, and hydroxyethyl acrylate; The dynamic crosslinking component consists of graphene oxide, oxidized carboxymethyl chitosan, arylboronic acid compounds containing ortho-hydroxyl groups, and amine crosslinking agents; the oxidized carboxymethyl chitosan is a bifunctional modified carboxymethyl chitosan containing both aldehyde groups and cis-ortho-diols, which is obtained by controlling the partial oxidation of carboxymethyl chitosan by sodium periodate. The reinforcing and toughening components consist of modified nano-silica, nano-cellulose crystals, and nitrile rubber powder. The additive components consist of an initiator, a retarder, an oxygen scavenger, and a dispersant.

2. The plugging agent for restoring wellbore integrity according to claim 1, characterized in that, The percentage of each component in the polymer monomer component relative to the total mass of the solid phase component is as follows: 2-Acrylamido-2-methylpropanesulfonic acid: 22.0%~26.0%; N-Vinylpyrrolidone: 16.0%–19.0%; Hydroxyethyl acrylate: 13.0%~15.0%.

3. The wellbore integrity restoration plugging agent according to claim 1, characterized in that, The percentage of each component in the dynamic crosslinking component relative to the total mass of the solid phase component is as follows: Graphene oxide: 0.6%–1.0%; Oxidized carboxymethyl chitosan: 2.5%–3.5%; Arylboronic acid compounds containing ortho-hydroxyl groups: 2.0%–3.0%; Amine crosslinking agents: 1.9%–2.5%.

4. The plugging agent for restoring wellbore integrity according to claim 1, characterized in that, The arylboronic acid compound containing ortho-hydroxyl groups is 2-hydroxyphenylboronic acid or 2,4-dihydroxyphenylboronic acid; The amine crosslinking agent is one or more of ethylenediamine, hexamethylenediamine, and polyethyleneimine.

5. The plugging agent for restoring wellbore integrity according to claim 1, characterized in that, The percentage of each component in the reinforcing and toughening composition relative to the total mass of the solid phase composition is as follows: Modified nano-silica: 3.0%–4.5%; Nanocellulose crystals: 4.0%–5.5%; Nitrile rubber powder: 18.0%~26.5%.

6. The plugging agent for restoring wellbore integrity according to claim 5, characterized in that, The modified nano-silica has an average particle size of 20nm to 50nm, and its surface modifier is silane coupling agent KH-560 or KH-570; the acrylonitrile content of the nitrile rubber powder is 30% to 45%, and its average particle size is 80 mesh to 120 mesh.

7. The plugging agent for restoring wellbore integrity according to claim 1, characterized in that, The percentage of each component in the additive composition relative to the total mass of the solid phase composition is as follows: Initiator: 1.4%–2.2%; Retarder: 0.7%–1.1%; Oxygen scavenger: 0.5%–0.9%; Dispersant: 0.9%–1.3%.

8. The wellbore integrity restoration plugging agent according to claim 1, characterized in that, In the auxiliary agent components, the initiator is one or more of ammonium persulfate, potassium persulfate, or azobisisobutyramidine hydrochloride; the retarder is sodium thiosulfate or urea; the oxygen scavenger is sodium sulfite or sodium isoascorbate; and the dispersant is sodium hexametaphosphate or sodium lignin sulfonate.

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