A temperature-resistant and salt-resistant biobased degradable cross-linked plugging agent, a preparation method and application thereof

Abstract

The application provides a temperature-resistant and salt-resistant biobased degradable cross-linking plugging agent and a preparation method and application thereof, and belongs to the technical field of plugging material preparation. The preparation method of the temperature-resistant and salt-resistant biobased degradable cross-linking plugging agent comprises the following steps: (1) mixing a sodium alginate aqueous solution and a FeCl2 aqueous solution, adjusting the pH of the system to 9-11 to obtain a mixed solution I; (2) adding acrylamide, 2-acrylamido-2-methylpropanesulfonic acid and polyacrylamide into water, and stirring uniformly to obtain a mixed solution II; (3) adding urotropine, o-diphenol and p-diphenol into water, and stirring uniformly to obtain a mixed solution III; and (4) mixing the mixed solution I, the mixed solution II and the mixed solution III, adding an initiator, and stirring uniformly to obtain the plugging agent. The plugging agent can significantly improve the structural stability of the plugging agent under extreme temperature and salt and strong shearing conditions, and ensure that the plugging agent can be controllably degraded through a specific mechanism after completing the plugging task.

Description

Technical Field

[0001] This invention relates to a temperature- and salt-resistant biodegradable crosslinking plugging agent, its preparation method, and its application, belonging to the field of sealing material preparation technology. Background Technology

[0002] Gel-based plugging agents are important sealing materials in oil extraction, used to effectively seal pores under high-temperature and high-salinity formation conditions. Among them, polymer-based gels are widely used and researched due to their wide range of tunable properties and relatively simple preparation processes. However, these plugging agents generally suffer from drawbacks such as relatively high cost, sensitivity to environmental factors, and insufficient long-term stability. Furthermore, traditional polyacrylamide plugging agents are prone to degradation and lack sufficient strength in high-temperature and high-salinity reservoirs, making it difficult to meet long-term plugging requirements. Therefore, optimizing crosslinking methods (such as introducing slow-release / high-efficiency crosslinking components) or developing biodegradable crosslinking plugging agents that combine excellent shear resistance with environmental friendliness is of great significance for solving the stability problem of gel systems under harsh operating conditions and for their sustainable application.

[0003] Current technologies for biodegradable crosslinking plugging agents in high-temperature and high-salt environments mainly focus on improving temperature and salt resistance, controllable gelation time, mechanical strength, and degradation performance. In recent years, researchers have developed various novel materials and processes. For example, based on chitosan, polylactic acid (PLA), and polyethyleneimine, three-dimensional network structures are achieved through organic or inorganic crosslinking, significantly improving the thermal stability and salt resistance of plugging agents. Some systems can maintain high strength and low water separation rate even at 130–180℃ and salinity as high as 240,000 mg / L. Regarding degradable plugging agents, hydrolyzable or heat-sensitive crosslinking agents are used to enable the plugging agent to spontaneously degrade into a low-viscosity liquid at high temperatures, reducing secondary damage to the reservoir, restoring permeability, and achieving degradation rates of over 90%. Chinese patent document CN111876140A discloses a dual-response self-degrading temporary plugging agent, prepared by polymerization reaction of the following raw materials in parts by weight: 17.7g monomer, 2.5g reinforcing agent, 0.2g dispersant, 0.086g initiator, 7g hydrophobic nanoparticles, and 85g water; wherein the monomer is a mixture of 15g acrylamide, 0.7g polyethylene glycol 600 diacrylate, and 2g methacryloyloxyethyltrimethylammonium chloride; the reinforcing agent is chitosan; and the dispersant is a salt-resistant polymer. Acrylamide, the hydrophobic nanoparticle is hydrophobic nano-TiO2. However, this temporary plugging agent has certain defects in material properties. Hydrophobic nano-TiO2 is difficult to disperse stably for a long time at high doses, and there is a risk of aggregation, sedimentation and clogging of equipment. Its core temperature-responsive degradation mechanism is questionable in the extreme working conditions of deep oil reservoirs. The initial plugging strength and degradation controllability may fail. The cross-linked network designed to pursue complete degradation may not be able to withstand the high pressure of fracturing fluid, and there is a risk of early breakthrough, which brings uncertainty to field application.

[0004] Currently, existing technologies mainly focus on synthetic polymers. While there has been progress in the application of bio-based materials, there is still room for improvement in their degradation performance and environmental friendliness under high temperature and high salinity environments. This is particularly relevant for high temperature (150℃) and ultra-high salinity (2×10⁻⁶) conditions. 5 In extreme reservoir environments (mg / L), existing technologies face core challenges such as poor compatibility of the crosslinking system (especially between the main agent and conventional crosslinking agents) and significant fragmentation and failure of the gel structure under high shear conditions. Therefore, there is an urgent need to design and prepare a novel polymer-based gel plugging agent with environmentally responsive and degradable properties to significantly improve the structural stability (shear resistance / aging ability) of the plugging agent under extreme temperature, salinity, and strong shear conditions, and to ensure that it can be controlled to degrade through a specific mechanism after completing the plugging task. Summary of the Invention

[0005] To address the shortcomings of existing technologies, particularly the poor compatibility of crosslinking systems (especially between the main agent and conventional crosslinking agents) and the susceptibility of gel structures to breakage under high shear conditions, this invention provides a temperature- and salt-resistant biodegradable crosslinking plugging agent, its preparation method, and its applications. The plugging agent of this invention can significantly improve the structural stability (shear resistance / aging ability) of the plugging agent under extreme temperature, salt, and high shear conditions, and ensures that it can be controlled to degrade through a specific mechanism after completing the plugging task.

[0006] The technical solution of the present invention is as follows:

[0007] A method for preparing a temperature- and salt-resistant biodegradable crosslinking plugging agent includes the following steps:

[0008] (1) Mix sodium alginate aqueous solution with FeCl2 aqueous solution, adjust the pH of the system to 9-11, and obtain mixture I;

[0009] (2) Add acrylamide (AM), 2-acrylamido-2-methylpropanesulfonic acid (AMPS) and polyacrylamide (PAM) to water and stir until homogeneous to obtain mixture II;

[0010] (3) Add hexamethylenetetramine, catechol and hydroquinone to water and stir until homogeneous to obtain mixture III;

[0011] (4) Mix mixture I, mixture II and mixture III, add initiator, stir evenly to obtain a temperature- and salt-resistant biodegradable crosslinking plugging agent.

[0012] According to a preferred embodiment of the present invention, the concentration of the sodium alginate aqueous solution in step (1) is 0.02-0.06 g / mL.

[0013] According to a preferred embodiment of the present invention, the concentration of the FeCl2 aqueous solution in step (1) is 0.08-0.3 mmol / mL, which is obtained by dissolving FeCl2·4H2O powder in water.

[0014] According to a preferred embodiment of the present invention, the volume ratio of sodium alginate aqueous solution to FeCl2 aqueous solution in step (1) is 1-1.5:1.

[0015] According to a preferred embodiment of the present invention, in step (1), the pH of the system is adjusted using a NaOH aqueous solution with a concentration of 0.1 mol / L.

[0016] According to a preferred embodiment of the present invention, the polyacrylamide (PAM) in step (2) has a viscosity-average molecular weight of 2 million to 14 million and is a nonionic polyacrylamide.

[0017] According to a preferred embodiment of the present invention, the mass ratio of acrylamide (AM), 2-acrylamido-2-methylpropanesulfonic acid (AMPS) and polyacrylamide (PAM) in step (2) is 1:0.4-0.5:0.5-0.7.

[0018] According to a preferred embodiment of the present invention, the concentration of acrylamide (AM) in the mixture II in step (2) is 0.01-0.03 g / mL.

[0019] According to a preferred embodiment of the present invention, the mass ratio of hexamethylenetetramine, catechol and hydroquinone in step (3) is 1:0.5-0.8:0.3-0.6.

[0020] According to a preferred embodiment of the present invention, the concentration of hexamethylenetetramine in the mixture III in step (3) is 0.01-0.02 g / mL.

[0021] According to a preferred embodiment of the present invention, the mass ratio of sodium alginate in mixture I, acrylamide in mixture II, and hexamethylenetetramine in mixture III in step (4) is 1:3-4:1-2.

[0022] According to a preferred embodiment of the present invention, the initiator in step (4) is potassium persulfate, sodium persulfate or ammonium persulfate; the mass ratio of the initiator to acrylamide is 0.2-0.3:1.

[0023] The present invention also provides a temperature- and salt-resistant biodegradable crosslinking plugging agent, which is prepared by the above preparation method.

[0024] According to the present invention, the above-mentioned temperature- and salt-resistant bio-based degradable crosslinking plugging agent is used in the drilling process to seal the well channel; the specific application method is as follows: the temperature- and salt-resistant bio-based degradable crosslinking plugging agent is added to the formation water to obtain a working fluid, the obtained working fluid is pumped into the target formation, and underground crosslinking occurs in the target formation; the concentration of the temperature- and salt-resistant bio-based degradable crosslinking plugging agent in the working fluid is 4.5-5.5 wt%.

[0025] According to the present invention, the pumping volume of the working fluid can be determined according to the prior art.

[0026] The technical features and beneficial effects of this invention are as follows:

[0027] 1. This invention uses acrylamide (AM), 2-acrylamido-2-methylpropanesulfonic acid (AMPS), and polyacrylamide (PAM) as polymerization raw materials, and phenolic resin (PF) as the main crosslinking agent. Furthermore, it incorporates biomass polysaccharide (sodium alginate SA) and a specific metal compound, FeCl2, to prepare a biodegradable crosslinking plugging agent with a covalent bond, multiple hydrogen bond-metal coordination bond dual-network structure. This plugging agent not only forms a gel system within a specific time period but also degrades under acidic conditions, thereby extending its service life and improving its working efficiency, showing promising application prospects in the field of sealing materials.

[0028] 2. The plugging agent of this invention uses natural high-molecular-weight sodium alginate (SA) and Fe3O4 metal particles obtained by FeCl2 oxidation to form a dynamic network under multiple hydrogen bonds and metal coordination bonds. The dual network structure formed by covalent cross-linking and metal ion cross-linking gives the plugging material good self-healing properties. At the same time, the biomass high-molecular-weight polysaccharide sodium alginate endows the material with good mechanical strength and biodegradability by constructing a dual network structure combining covalent bonds and coordination bonds. In addition, metal ions are selectively used to adjust the performance characteristics of the final product.

[0029] 3. The plugging agent formulation and preparation method provided by the present invention are simple and easy to implement, and the raw materials are readily available and low in cost.

[0030] 4. This invention uses naturally sourced biomass polysaccharides as additives, which not only reduces the environmental impact of synthetic materials, but also improves the biodegradability and biocompatibility of the sealing materials. Attached Figure Description

[0031] Figure 1 SEM images of the gel obtained after gelation of the temperature- and salt-resistant biodegradable crosslinking plugger prepared in Example 1, where a is the overall morphology, b is the cross-sectional view of the gel, and c is the particle morphology.

[0032] Figure 2The infrared spectrum of the gel obtained after gelation of the temperature- and salt-resistant biodegradable crosslinking plugger prepared in Example 1 is shown.

[0033] Figure 3 The UV spectrum of the temperature- and salt-resistant biodegradable crosslinking plugger prepared in Example 1 is shown.

[0034] Figure 4 The figure shows the sealing performance test results of the temperature- and salt-resistant biodegradable crosslinking plugger prepared in Example 1 of Experiment 1. Detailed Implementation

[0035] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited thereto.

[0036] The polyacrylamide (PAM) used in the examples is a nonionic polyacrylamide with a viscosity-average molecular weight of 10 million.

[0037] Example 1

[0038] A method for preparing a temperature- and salt-resistant biodegradable crosslinking plugging agent includes the following steps:

[0039] (1) Add 4g of sodium alginate powder to 100mL of water, stir and dissolve at 60℃, and then cool naturally to room temperature to obtain a 0.04g / mL sodium alginate aqueous solution; dissolve 10mmol of FeCl2·4H2O powder in 100mL of water to obtain a 0.1mol / L FeCl2 aqueous solution; mix 100mL of the obtained sodium alginate aqueous solution and 100mL of FeCl2 aqueous solution, and adjust the pH of the system to 11 using a 0.1mol / L NaOH aqueous solution to obtain mixed solution I.

[0040] (2) Add 14g acrylamide (AM), 6g 2-acrylamido-2-methylpropanesulfonic acid (AMPS) and 8g polyacrylamide (PAM) to 600mL of water and stir until homogeneous to obtain mixture II.

[0041] (3) Under stirring conditions, add 6g hexamethylenetetramine, 4g catechol and 2g hydroquinone to 400mL of water and stir until homogeneous to obtain mixture III.

[0042] (4) Mix all the mixture I obtained in step (1), all the mixture II obtained in step (2) and all the mixture III obtained in step (3), add 3g of initiator potassium persulfate, stir evenly, and obtain a temperature- and salt-resistant biodegradable crosslinking plugging agent.

[0043] The temperature- and salt-resistant biodegradable crosslinking plugger obtained in this embodiment was reacted in a 120°C oven for 2 hours to obtain a gel. The SEM image of the obtained gel is shown below. Figure 1 As shown, by Figure 1 It can be seen that the continuous organic polymer network formed by the AM and AMPS copolymer and the phenolic resin crosslinking agent, sodium alginate and Fe 3+ The introduction of [a specific component] also enhances the stability of the network, resulting in a non-uniform sheet-like, honeycomb-like, or microporous structure. This is the result of the combined effects of multiple cross-linking reactions. This complex topological structure effectively binds water molecules and provides effective resistance to external forces. The infrared spectrum of the resulting gel is shown in the image below. Figure 2 As shown, by Figure 2 It can be seen that at 3400cm -1 The broad absorption peak at 1650 cm⁻¹ is attributed to the stretching vibrations of OH and NH due to intermolecular hydrogen bonding; -1 The characteristic absorption peak at 1550 cm⁻¹ is attributed to the C=O stretching vibration of the amide I band. -1 The coupled peaks of the NH bending vibration and CN stretching vibration of the amide II band at 1040 cm⁻¹ jointly confirm the successful construction of the AM copolymer backbone; -1 and 1200cm -1 The characteristic peaks appearing at 1600 cm⁻¹ correspond to the asymmetric and symmetric stretching vibrations of the sulfonic acid group, respectively, indicating that the AMPS unit has been successfully introduced into the polymer chain; simultaneously, at 1600 cm⁻¹... -1 With 1410cm -1 The absorption peaks appearing at these locations are attributed to sodium alginate carboxylate ions (-COO-). - The asymmetric and symmetric stretching vibrations of Fe provide... 3+ Evidence of ionic crosslinking sites.

[0044] The UV spectrum of the temperature- and salt-resistant biodegradable crosslinking plugger obtained in this embodiment is as follows: Figure 3 As shown, an absorption peak appears at around 235 nm. The 235 nm absorption peak mainly originates from the phenolic resin. The high intensity of the absorption peak indicates that the system has a high degree of conjugation. Conjugated structures can usually enhance intermolecular interactions, and a higher degree of conjugation can improve the thermal stability or mechanical strength of the gel.

[0045] Example 2

[0046] A method for preparing a temperature- and salt-resistant biodegradable crosslinking plugging agent is described in Example 1, except that the mass of sodium alginate powder in step (1) is 3g.

[0047] Example 3

[0048] A method for preparing a temperature- and salt-resistant biodegradable crosslinking plugging agent is described in Example 1, except that the amount of FeCl2·4H2O powder in step (1) is 30 mmol.

[0049] Example 4

[0050] A method for preparing a temperature- and salt-resistant biodegradable crosslinking plugging agent is described in Example 1, except that the mass of sodium alginate powder in step (1) is 5g.

[0051] Example 5

[0052] A method for preparing a temperature- and salt-resistant biodegradable crosslinking plugging agent is as described in Example 1, except that the raw material mass is adjusted in step (3) to be: 8g of hexamethylenetetramine, 6g of catechol, and 4g of hydroquinone.

[0053] Comparative Example 1

[0054] A method for preparing a temperature- and salt-resistant biodegradable crosslinking plug is described in Example 1, except that sodium alginate is not added in step (1), and 100 mL of water is directly mixed with 100 mL of FeCl2 aqueous solution.

[0055] Comparative Example 2

[0056] A method for preparing a temperature- and salt-resistant biodegradable crosslinking plug is described in Example 1, except that FeCl2 is not added in step (1), and 100 mL of sodium alginate aqueous solution is directly mixed with 100 mL of water.

[0057] Comparative Example 3

[0058] A method for preparing a temperature- and salt-resistant biodegradable crosslinking plugging agent is described in Example 1, except that polyacrylamide (PAM) is not added in step (2).

[0059] Comparative Example 4

[0060] A method for preparing a temperature- and salt-resistant biodegradable crosslinking plugging agent is described in Example 1, except that acrylamide (AM) is not added in step (2).

[0061] Comparative Example 5

[0062] A method for preparing a temperature- and salt-resistant biodegradable crosslinking plugging agent is described in Example 1, except that 2-acrylamido-2-methylpropanesulfonic acid (AMPS) is not added in step (2).

[0063] Comparative Example 6

[0064] A method for preparing a temperature- and salt-resistant biodegradable crosslinking plugging agent is as described in Example 1, except that step (3) is omitted, and mixture I and mixture II are directly mixed.

[0065] Comparative Example 7

[0066] A method for preparing a temperature- and salt-resistant biodegradable crosslinking plugging agent is described in Example 1, except that: Mixture III is replaced with an equal volume of N,N'-methylenebisacrylamide (MBA) aqueous solution with a concentration of 0.015 g / mL.

[0067] Experimental Example 1

[0068] The following performance tests were performed on the plugging agents prepared in the examples and comparative examples.

[0069] (1) Anti-aging performance test

[0070] The plugging agents of Examples 1-5 and Comparative Examples 1-7 were reacted in an oven at 120°C for 2 hours to obtain gels. The anti-aging properties of the obtained gels were tested. Tests were conducted at 110°C, 130°C, and 150°C, and the gel collapse time was recorded. The statistical results are shown in Table 1.

[0071] Table 1. Results of Anti-aging Performance Tests

[0072]

[0073] As shown in Table 1, the plugging agents prepared in Examples 1-5 all exhibited certain anti-aging properties under different high-temperature environments, and the higher the temperature, the shorter the anti-aging time. Mixture III determined the temperature stability of the system.

[0074] (2) Salt resistance test

[0075] The plugging agents prepared in the examples and comparative examples were reacted in an oven at 120°C for 2 hours to obtain gels. The salt resistance of the obtained gels was tested, and the specific steps were as follows: the gels were placed in a 1×10⁻⁶ oven at 100°C. 5 mg / L, 2×10 5 mg / L, 4×10 5 The gel was immersed in a NaCl aqueous solution at a concentration of mg / L for 15 days. The residual gel rate was obtained by dividing the mass of the gel after treatment by the mass of the gel before treatment. The statistical results are shown in Table 2.

[0076] Table 2 Statistical Table of Temperature and Salt Resistance Test Results

[0077]

[0078] As can be seen from Table 2, the plugging agents prepared in Examples 1-5 all exhibit certain temperature and salt resistance properties under high-temperature environments with different salt concentrations.

[0079] (3) Shear resistance test

[0080] The plugging agents of Examples 1-5 and Comparative Examples 1-7 were reacted in an oven at 120°C for 2 hours to obtain gels. The shear resistance of the obtained gels was tested, and the specific steps were as follows: Using a rotational rheometer at 25°C, the initial storage modulus of the gel at an angular frequency of 1 rad / s was first tested. Then, the gel was placed in the rheometer and subjected to a 1000s test. -1 The shear rate was continuously applied for 30 minutes, and the storage modulus was tested again under the same conditions. The storage modulus retention rate of the gel was obtained by dividing the storage modulus after shearing by the storage modulus before shearing. The statistical results are shown in Table 3.

[0081] Table 3 Statistical Table of Shear Resistance Tests

[0082]

[0083] As can be seen from Table 3, the plugging agents prepared in Examples 1-5 all have certain shear resistance properties.

[0084] (4) Blocking performance test

[0085] An indoor plugging simulation experiment was conducted on the plugging agent prepared in Example 1. A sand-filled pipe model was used, and the initial permeability was measured after saturation with formation water. The plugging agent was injected at a constant flow rate at 100°C and aged for 72 hours. Subsequently, water flooding was performed, and the change in injection pressure with cumulative injection volume was monitored and recorded in real time. An injection pressure-injection volume curve was plotted, and the breakthrough pressure and plugging rate were calculated based on this curve. The experimental results are as follows: Figure 4 As shown, the pressure gradient after gel solidification can reach 11 MPa, indicating good sealing performance.

[0086] (5) Degradation performance test

[0087] The plugging agents prepared in the examples and comparative examples were reacted in an oven at 120℃ for 2 hours to obtain gels. The degradation performance of the obtained gels was tested, and the specific steps were as follows: the gels were immersed in 10wt% HCl solution and 5wt% ammonium persulfate solution at 100℃ for 7 days, respectively. After that, they were taken out and weighed. The mass loss rate of the gel was obtained by (initial mass - treated mass) / initial mass × 100%. The statistical results are shown in Table 4.

[0088] Table 4. List of Degradation Performance Test Results

[0089]

[0090] As shown in Table 4, the plugging agents of Examples 1-5 exhibited good degradation performance against both acids and oxidants under high-temperature environments with different salt concentrations. In particular, Example 1 showed a mass loss rate of 95.2% in a 10% HCl solution, indicating excellent degradability under acidic conditions. While Comparative Examples 6 and 7 also showed high degradation rates, their initial plugging performance was poor, limiting their practical application value. In summary, the plugging agents prepared in these examples not only maintain stable plugging capabilities in high-temperature and high-salt environments but also demonstrate good environmental responsiveness in the subsequent degradation stage, making them suitable for complex reservoir systems requiring controlled degradation. This plugging agent achieves efficient plugging while triggering a degradation mechanism through environmental stimuli, effectively avoiding long-term damage to the formation. Its excellent comprehensive performance is attributed to the design of the polymer network structure, which combines high strength with degradability. By rationally controlling the crosslinking density and the ratio of degradable units, the synergistic optimization of plugging strength and degradation rate is achieved.

Claims

1. A method for preparing a temperature- and salt-resistant biodegradable crosslinking plugging agent, characterized in that, Includes the following steps: (1) Mix sodium alginate aqueous solution and FeCl2 aqueous solution, and adjust the pH of the system to 9-11 to obtain mixture I; the concentration of sodium alginate aqueous solution is 0.02-0.06 g / mL; the concentration of FeCl2 aqueous solution is 0.08-0.3 mmol / mL; the volume ratio of sodium alginate aqueous solution to FeCl2 aqueous solution is 1-1.5:1; (2) Acrylamide, 2-acrylamido-2-methylpropanesulfonic acid and polyacrylamide are added to water and stirred evenly to obtain mixture II; the mass ratio of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid and polyacrylamide is 1:0.4-0.5:0.5-0.7; the concentration of acrylamide in mixture II is 0.01-0.03 g / mL; (3) Add hexamethylenetetramine, catechol and hydroquinone to water and stir until homogeneous to obtain mixture III; the mass ratio of hexamethylenetetramine, catechol and hydroquinone is 1:0.5-0.8:0.3-0.6; the concentration of hexamethylenetetramine in mixture III is 0.01-0.02 g / mL; (4) Mix mixture I, mixture II and mixture III, add initiator, stir evenly to obtain a temperature and salt resistant biodegradable crosslinking blocker; the mass ratio of sodium alginate in mixture I, acrylamide in mixture II and hexamethylenetetramine in mixture III is 1:3-4:1-2; the initiator is potassium persulfate, sodium persulfate or ammonium persulfate.

2. The preparation method of the temperature- and salt-resistant biodegradable crosslinking plugging agent according to claim 1, characterized in that, In step (1), the pH of the system is adjusted using a 0.1 mol / L NaOH aqueous solution.

3. The preparation method of the temperature- and salt-resistant biodegradable crosslinking plugging agent according to claim 1, characterized in that, The polyacrylamide mentioned in step (2) has a viscosity-average molecular weight of 2 million to 14 million and is a non-ionic polyacrylamide.

4. The preparation method of the temperature- and salt-resistant biodegradable crosslinking plugging agent according to claim 1, characterized in that, The mass ratio of the initiator to acrylamide in step (4) is 0.2-0.3:

1.

5. A temperature- and salt-resistant biodegradable crosslinking plugging agent, characterized in that, It is prepared by the preparation method described in any one of claims 1-4.

6. The application of the temperature- and salt-resistant biodegradable crosslinking plugging agent according to claim 5 in the drilling process, used for sealing boreholes; characterized in that, The specific application method is as follows: add the temperature- and salt-resistant biodegradable crosslinking plugging agent to the formation water to obtain the working solution, pump the obtained working solution into the target formation, and conduct underground crosslinking in the target formation; the concentration of the temperature- and salt-resistant biodegradable crosslinking plugging agent in the working solution is 4.5-5.5 wt%.

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