Composite plugging agent for formation malignant leakage and preparation method thereof

Abstract

The application provides a composite plugging agent for formation malignant leakage and a preparation method thereof, and belongs to the technical field of chemical materials. The composite plugging agent is prepared by compounding an associated polymer gel and etherified phenolic aldehyde resin. The curing time of the composite plugging agent is controlled by temperature, and the composite plugging agent can be cured in 1.5 hours at 140 DEG C. The compressive strength of the cured composite plugging agent can reach 95.7 MPa, and the maximum breakthrough pressure of the cured composite plugging agent can reach 2.8 MPa. The composite plugging agent can effectively plug formation cracks, and the plugging effect is obvious.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of chemical materials, and particularly relates to a composite plugging agent for formation malignant leakage and a preparation method thereof. BACKGROUND

[0002] In the field of oil and gas development and exploration, well leakage has been a technical problem that has plagued the world. Once a well leakage accident occurs, it will seriously delay the construction progress and cause huge losses. With the continuous development and progress of oil and gas resource development technology, permeability leakage and small crack leakage have been well solved, but the prevention technology for malignant leakage has not been developed.

[0003] Gel plugging technology is one of the commonly used and effective technologies for controlling crack malignant well leakage. Through injecting a certain amount of high molecular gel plugging agent into the leakage layer, the cracks are plugged after solidification, which plays a role in isolating drilling fluid and formation fluid and preventing drilling fluid from continuing to leak.

[0004] For example, in the development and evaluation of high-temperature gel-forming degradable polymer gel plugging agent (Guo Yongbin; Yan Bangchuan; Huang Yi, et al., Drilling Fluids and Completion Fluids, 2019, 36(03)), a polymerizable modified gelatin crosslinker was synthesized by quaternary ammonium modification of gelatin with methacrylic anhydride. Based on the thermoplasticity of hot melt adhesive, the initiator was successfully coated in the hot melt adhesive particles, realizing high-temperature slow-release initiation. A high-temperature resistant degradable polymer gel plugging agent P(AM-DGCL) was developed using acrylamide (AM) and self-made crosslinker (DGCL) as raw materials. The structure of the self-made crosslinker was characterized by nuclear magnetic resonance, and the mechanical behavior, plugging capacity and gel breaking performance of the gel were tested. The gelation time at 150℃ is adjustable in 2-13h; P(AM-DGCL) shows excellent mechanical properties, with an elongation at break of 1279% and a tensile strength of 0.0425MPa; due to the gel breaking property of the crosslinker DGCL itself which plays a chemical crosslinking role, the gel breaking rate of P(AM-DGCL) is more than 95% after 16h under the action of high temperature and gel breaker, ensuring the reverse displacement ability after reservoir leakage plugging.

[0005] As disclosed in Chinese patent application CN109796949A, an anti-high-temperature gel plugging agent and a preparation method and application thereof are disclosed. The anti-high-temperature gel plugging agent comprises a vinyl polymer monomer, a solid-phase organic macromolecular crosslinking agent, a first initiator, a particle toughening agent, and a fiber toughening agent. The application also discloses a preparation method of the gel plugging agent, comprising: (I) adding the vinyl polymer monomer, the solid-phase organic macromolecular crosslinking agent, and the particle toughening agent into clean water and stirring at high speed to obtain a mixed solution a; (II) adding the fiber toughening agent into the mixed solution a, stirring at low speed for the first time to disperse uniformly to obtain a mixed solution b; (III) adding the first initiator into the mixed solution b, stirring at low speed for the second time until it is completely dissolved to obtain a mixed solution c; sealing and placing the mixed solution c, and curing to form a gel to obtain a high-strength and high-toughness gel plugging agent. The gel plugging agent has high gel strength and high shear toughness under high-temperature conditions, and has higher pressure-bearing capacity and excellent plugging effect.

[0006] The associated polymer gel has good rheological property, and its shear thinning behavior endows it with rapid and efficient plugging, and has the advantage of rapid plugging in the early stage. The thermosetting phenolic resin is converted from a pumpable liquid into a high-strength solid block under a thermal environment, has the characteristics of inhibiting the formation of a malignant leakage, and is suitable for long-term and high-strength leakage plugging. However, the associated polymer gel generally has low strength, and the resin-based anti-plugging system has poor storage performance and poor dilution resistance. Therefore, it is necessary to develop a composite plugging agent suitable for malignant leakage and a preparation method thereof to solve the problem that the existing plugging agent is difficult to handle the formation of a malignant leakage. SUMMARY

[0007] Based on the deficiencies in the prior art, the purpose of the present application is to provide a composite plugging agent suitable for malignant leakage and a preparation method thereof to solve the problem that the existing plugging agent is difficult to handle the formation of a malignant leakage.

[0008] In order to achieve the above-mentioned purpose, the following technical solutions are adopted in the present application:

[0009] On the one hand, the present application provides a composite plugging agent for the formation of a malignant leakage, which is prepared by compounding an associated polymer gel and an etherified phenolic resin.

[0010] The associated polymer gel is copolymerized from N-dodecyl acrylamide and at least one of acrylamide, acrylic acid, or 2-acrylamido-2-methylpropane sulfonic acid; and the etherified phenolic resin is prepared by reacting phenol and formaldehyde and etherifying with at least one of ethanol, propanol, or butanol.

[0011] Further, in the preferred embodiment of the present application, the associated polymer gel is prepared by aqueous solution polymerization of N-dodecyl acrylamide, acrylamide, acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid in a mass percentage ratio of 2: (54.2-65.0): (25.0-30.0): (3.0-20.0).

[0012] Further, the associated polymer gel further comprises a dispersant and an initiator.

[0013] The dispersant is selected from one of polysorbate-20, polysorbate-80, nonoxynol-10 and ceteareth-10.

[0014] The initiator is 2,2'-azobis(2-methylpropionamidine) dihydrochloride.

[0015] The mass percentage of the dispersant is 0.05-0.08%.

[0016] The 2,2'-azobis(2-methylpropionamidine) dihydrochloride is 0.1-0.5% of the mass of the monomer.

[0017] In another aspect, the present application also provides a preparation method of the associated polymer gel, comprising the following steps:

[0018] The acrylamide, acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid are dissolved in pure water, and the pH is adjusted to obtain a mixed solution; the dispersant and N-dodecyl acrylamide are dispersed in the mixed solution, and 2,2'-azobis(2-methylpropionamidine) dihydrochloride is added after heating to 40-60°C, and the reaction is carried out for 4-6h to obtain the associated polymer gel.

[0019] Further, in the preferred embodiment of the present application, the pH value is adjusted to 6-8.

[0020] Further, in the preferred embodiment of the present application, the etherified phenolic resin is prepared by reaction of phenol and formaldehyde and using normal alcohol etherification.

[0021] The molar ratio of the phenol, formaldehyde and normal alcohol is 1: (1.5-3.0): (0.3-0.6).

[0022] Further, the preparation method of the etherified phenolic resin comprises the following steps:

[0023] NaOH and phenol are mixed at 40-60°C, and then formaldehyde solution is added and heated to 75-80°C, and the reaction is carried out for 4-6h to obtain the phenolic resin; the phenolic resin and normal alcohol are reacted at 100°C for 5-8h to obtain the etherified phenolic resin.

[0024] Further, in the preferred embodiment of the present application, the amount of NaOH added is 5% of the total mass.

[0025] Further, the composite plugging agent is prepared by mixing the aqueous solution of etherified phenolic resin with the associated polymer gel with a mass fraction of 0.5-1.5%.

[0026] The mass concentration of the aqueous solution of etherified phenolic resin is 30-80%.

[0027] Compared with the prior art, the present application has the following advantages:

[0028] The composite water plugging agent suitable for malignant leakage is prepared by compounding the associated polymer gel and the etherified resin, the special composite water plugging agent system has the shear thinning behavior, can meet the requirement of rapid and efficient plugging in the early stage, at the same time, the hydrophobic associated polymer greatly increases the dilution resistance of the composite water plugging agent, and then the etherified phenolic resin plugging agent forms a permanent plugging layer under the action of high temperature in the stratum, which can completely plug the underground site with malignant leakage.

[0029] In addition, the required materials in the present application are generally easy to obtain, the preparation process is simple and mature, and the cost of industrial preparation of the water plugging agent can be reduced, so the present application is a malignant leakage plugging agent worthy of promotion.

[0030] Other advantages, objects and features of the present application will be partly embodied by the following description, and will be partly understood by those skilled in the art through research and practice of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments, and it should be understood that the following drawings only show some embodiments of the present application, and should not be regarded as a limitation to the scope, and for those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0032] Figure 1 It is the infrared spectrum of the associated polymer gel in the embodiment 7 of the present application.

[0033] Figure 2 It is the infrared spectrum of the etherified phenolic resin in the embodiment 7 of the present application.

[0034] Figure 3 It is the time-viscosity curve of the etherified phenolic resin in the embodiment 7 of the present application.

[0035] Figure 4 It is the shear viscosity-shear rate relationship diagram of the composite plugging agent in the embodiment 7 of the present application.

[0036] Figure 5The relationship between the storage modulus (G') and the loss modulus (G") of the composite plugging agent in Example 7 of the present application and the frequency.

[0037] Figure 6 The relationship between the storage modulus (G') and the loss modulus (G") of the composite plugging agent in Example 7 of the present application and the shear stress;

[0038] Figure 7 The compressive strength test of the cured composite plugging agent in Example 7 of the present application; Figure 7 (A) curing at 90℃, Figure 7 (B) curing at 120℃, Figure 7 (C) curing at 140℃.

[0039] Figure 8 The sealing performance test of the cured composite plugging agent in Example 7 of the present application; Figure 8 (A) 1mm wide crack, Figure 8 (B) 2mm wide crack. DETAILED DESCRIPTION

[0040] The principles and features of the present application are described below in conjunction with the embodiments and the accompanying drawings, and the examples are used to explain the present application and are not intended to limit the scope of the present application. If the specific conditions are not specified in the examples, the conventional conditions or the conditions recommended by the manufacturer are used. If the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be purchased on the market.

[0041] The technical solutions of the specific embodiments of the present application are as follows:

[0042] The present embodiment provides a composite plugging agent suitable for malignant leakage, which is a composite system of an associated polymer gel and an etherified phenolic resin. The associated polymer gel is a hydrophobic associated polymer gel comprising N-dodecyl acrylamide, acrylamide, acrylic acid and 2-acrylamido-2-methylpropane sulfonic acid. The etherified phenolic resin is a n-hydrocarbon alcohol modified phenol formaldehyde thermosetting resin.

[0043] The preparation of the associated polymer gel comprises:

[0044] Acrylamide, acrylic acid and 2-acrylamido-2-methylpropane sulfonic acid are dissolved in pure water, the pH is adjusted to 6-8, the dispersant and N-dodecyl acrylamide are dispersed in water, N2 is introduced, after 40min, heating to 40℃-60℃ and adding 2,2'-azobis isobutylamidine dihydrochloride initiator, after 4-6h of reaction, the associated polymer gel is obtained.

[0045] The synthesis route of the associated polymer gel is as follows:

[0046]

[0047] The preparation of the etherified phenolic resin comprises:

[0048] The phenolic resin is prepared by mixing NaOH with a mass concentration of 5% and phenol at 40-60℃, then adding formaldehyde solution and heating to 75-80℃, and reacting for 4-6h; the resin is reacted with n-hydroxy alcohol at 100℃ for 5-8h to obtain the etherified phenolic resin.

[0049] The synthesis route of the etherified phenolic resin is as follows:

[0050]

[0051] The composite plugging agent suitable for malignant leakage is prepared by mixing an aqueous solution of the etherified phenolic resin with an associated polymer gel with a mass fraction of 0.5-1.5%.

[0052] The aqueous solution of the etherified phenolic resin has a mass concentration of 30-80%.

[0053] Example 1:

[0054] The preparation method of the associated polymer gel in this example comprises the following steps:

[0055] Acrylamide, acrylic acid and 2-acrylamido-2-methylpropane sulfonic acid are dissolved in pure water at a mass ratio of 54.2:26.8:17, and the pH is adjusted to 6-8 to obtain a mixed solution; a dispersant polysorbate-80 and N-dodecyl acrylamide with a mass fraction of 2% are dispersed in the mixed solution, N2 is introduced, and after 40min, heating is performed to 55℃ and 2,2'-azobis(2-methylpropionamide) dihydrochloride initiator is added, and after reacting for 4h, the associated polymer gel is obtained.

[0056] The mass concentration of the dispersant polysorbate-80 is 0.05-0.08%.

[0057] Example 2:

[0058] The preparation method of the associated polymer gel in this example comprises the following steps:

[0059] Acrylamide, acrylic acid and 2-acrylamido-2-methylpropane sulfonic acid are dissolved in pure water at a mass ratio of 62:26:11, and the pH is adjusted to 6-8 to obtain a mixed solution; a dispersant polysorbate-80 with a mass fraction of 0.05% and N-dodecyl acrylamide with a mass fraction of 2% are dispersed in the mixed solution, N2 is introduced, and after 40min, heating is performed to 55℃ and 2,2'-azobis(2-methylpropionamide) dihydrochloride initiator is added, and after reacting for 5h, the associated polymer gel is obtained.

[0060] The mass of the 2,2'-azobis (isobutylamidine) dihydrochloride initiator accounts for 0.1-0.5% of the total mass of the monomers.

[0061] Example 3:

[0062] The preparation method of the associated polymer gel in this example includes the following steps:

[0063] Acrylamide, acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid are dissolved in pure water at a mass ratio of 62:26:11, the pH is adjusted to 6-8 to obtain a mixed solution; 0.05% polysorbate-80 and 2% N-dodecyl acrylamide are dispersed in the mixed solution, N2 is introduced, heated to 55°C after 40 min, and 0.2% 2,2'-azobis (isobutylamidine) dihydrochloride initiator is added, which accounts for 0.2% of the total mass of the monomers, and the reaction is carried out for 5h, washed with anhydrous ethanol, dried, and crushed to obtain the associated polymer gel.

[0064] Example 4:

[0065] The preparation method of the etherified phenolic resin in this example includes the following steps:

[0066] 5% NaOH and phenol are mixed at 50°C, then formaldehyde solution is added and the temperature is raised to 75-80°C, the molar ratio of phenol to formaldehyde is 1:1.5, and the phenolic resin is prepared by reacting for 4h; the phenolic resin is reacted with n-butanol at 100°C for 5h to obtain the n-butanol-etherified phenolic resin.

[0067] The molar ratio of n-butanol to phenol is 1:3.2.

[0068] Example 5:

[0069] The preparation method of the etherified phenolic resin in this example includes the following steps:

[0070] 5% NaOH and phenol are mixed at 50°C, then formaldehyde solution is added and the temperature is raised to 75-80°C, the molar ratio of phenol to formaldehyde is 1:2.6, and the phenolic resin is prepared by reacting for 6h; the phenolic resin is reacted with n-propanol at 100°C for 5h to obtain the n-propanol-etherified phenolic resin.

[0071] The molar ratio of n-propanol to phenol is 1:4.

[0072] Example 6:

[0073] The preparation method of the composite plugging agent suitable for malignant leakage in this example includes: mixing an aqueous solution of etherified phenolic resin with an associated polymer gel at a mass ratio of 1:(0.005-0.015) to obtain the composite plugging agent.

[0074] The mass concentration of the aqueous solution of the etherified phenolic resin is 30-80%.

[0075] Example 7:

[0076] 7.1 Preparation of the associated polymer gel

[0077] Acrylamide, acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid are dissolved in pure water at a mass ratio of 54.2:26.8:17, and the pH is adjusted to 6-8 to obtain a mixed solution; 0.05% polysorbate-80 and 2% N-dodecyl acrylamide are dispersed in the mixed solution, and after uniform stirring, high-purity N2 is continuously introduced, and after 40 min, heating to 55°C while adding 0.2% 2,2'-azobis (isobutylamidine) dihydrochloride initiator accounting for the total monomer mass, and reacting for 5 h. After washing with anhydrous ethanol, drying, and crushing, the associated polymer gel is obtained.

[0078] The synthesis route of the associated polymer gel is as follows:

[0079]

[0080] The associated polymer gel is subjected to infrared analysis to determine its chemical formula:

[0081] The purified associated polymer gel is uniformly ground with potassium bromide (KBr), a small amount of finely ground powder is pressed into a tablet for sampling, and the molecular structure of the sample is tested using a Beijing Rayleigh Analytical Instrument Company WQF-520 FTIR Fourier Transform Infrared Spectrometer, and the infrared spectrum analysis chart is shown in Figure 1 .

[0082] 1681 cm -1 The vibration peak corresponding to the amide bond belongs to the signals of acrylamide and N-dodecyl acrylamide; 1309 cm -1 The peak of 1195 cm -1 and 1041 cm -1 all belong to the peaks of the sulfonic acid group, which belong to the signals of 2-acrylamido-2-methylpropanesulfonic acid. In summary, the associated polymer gel with hydrophobic association function is successfully prepared.

[0083] 7.2 Preparation of etherified phenolic resin

[0084] In a three-necked flask equipped with a reflux condenser, a certain amount of phenol was added, then a 5% NaOH solution based on the mass of phenol was added, and stirred at 60°C for 30 min; a certain molar ratio of formaldehyde aqueous solution was added to the three-necked flask, and the temperature was increased to 80°C and stirred for 4 h to obtain a brown red phenolic resin liquid, which was cooled to room temperature and taken out. After the phenolic resin was dehydrated under reduced pressure, a certain amount of n-butanol was added to a three-necked flask equipped with a stirrer, and heated to 100°C in an oil bath for 6 h. Finally, the reaction liquid was distilled under reduced pressure. The molar ratio of phenol to formaldehyde was 1:2.6, and the molar ratio of n-butanol to phenol was 1:4.

[0085]

[0086] (1) The etherified phenolic resin was subjected to infrared analysis to determine its chemical formula, and the infrared spectrum is shown in Figure 2 :

[0087] 3500cm -1 nearby wide and strong peaks are characteristic peaks of phenolic resin, which are the result of the vibration of multiple hydroxyl groups. 2950cm -1 and 2886cm -1 belong to the vibration signals of methylene and methyl groups, which are mainly etherified groups. The peak at 1604cm -1 corresponds to the C=C double bond on the phenol; 1195cm -1 and 1020cm -1 two places are the signals of ether bonds, indicating the presence of ether bonds on the phenolic resin, corresponding to the ether bonds produced by n-butanol etherification. In summary, the etherified phenolic resin is successfully prepared.

[0088] (2) According to GB / T 14074-2017, the storage stability of the etherified phenolic resin was evaluated, and the time- viscosity curve is shown in Figure 3 :

[0089] The initial viscosity of the etherified phenolic resin was 825.8mP·s, and the viscosity reached 200% after continuous storage at 70°C for 30 days, so the storage time of the etherified phenolic resin was 180 days. It can be seen that the etherified phenolic resin has excellent storage stability. Through the applicant's experiment, it is found that the storage stability of the etherified phenolic resin obtained by replacing n-butanol with ethanol, propanol and other alcohols is similar to that obtained by using n-butanol.

[0090] 7.3 Preparation of composite plugging agent

[0091] A certain amount of etherified phenolic resin is added into a beaker, a certain amount of pure water is added for dilution, and then an associated polymer gel is added to the solution of the etherified phenolic resin. Among them, the mass concentration of the etherified phenolic resin aqueous solution is 80%, and the mass ratio of the etherified phenolic resin aqueous solution to the associated polymer gel is 1:(0.005-0.015).

[0092] 7.4 Performance characterization of the composite plugging agent

[0093] The rheological properties of the composite plugging agent at 25°C are evaluated for the plugging capacity of the constructed composite plugging agent before the magnetic layer loss; to confirm the curing properties of the composite plugging agent, the influence of the high-temperature environment of the lost formation on the curing behavior of the composite plugging agent is evaluated; finally, the sealing performance of the composite plugging agent after curing in 1 mm and 2 mm artificial fractures is evaluated.

[0094] 7.4.1 Rheological property characterization of the composite plugging agent

[0095] The test is performed at a test temperature of 25°C using a HAAKE MARSIII rheometer (Thermo Fisher, USA) under the condition of a constant stress τ = 1 Pa and a time t = 10 min, and the test gap is 1 mm. The test results are shown in Figure 4 、 Figure 5 and Figure 6 . The results show that the initial viscosity of the composite plugging agent system with different concentrations is higher than 104 mPa·s, and gradually decreases with the increase of the shear rate. The results show that the plugging system is a typical pseudoplastic fluid with shear thinning properties. When pumping the gel, the apparent viscosity of the gel is low due to incomplete gelation and high shear rate, and the gel is easy to pump. After entering the lost formation, the gel viscosity increases due to the decrease of the shear rate, which is beneficial to the plugging of the lost layer. At the same time, when the vibration frequency is between 0.1-40 Hz, the energy dissipation modulus G" and the storage modulus G' basically increase with the increase of the frequency, and the gel belongs to the linear viscoelastic region. In addition, the yield stress of the composite system before thermal curing can reach 323.6 Pa, indicating that the system has good strength and resistance to water flow impact, and can be used for plugging of the early stage loss. Therefore, the gel has good viscoelasticity in the low frequency band to the high frequency band and from small to large stress scanning.

[0096] 7.4.2 Curing property characterization of the composite plugging agent

[0097] (1) The curing time of the composite plugging agent is determined by the inversion method, and the results are shown in Table 1:

[0098] Table 1 Curing time of the composite plugging agent at different temperatures

[0099]

[0100] The composite plugging agent can start to solidify at 90 DEG C, and the solidification time decreases with the increase of temperature. The solidification time is still 1.5 h at 140 DEG C high temperature, and the sufficient relaxation time is enough to inject the composite plugging agent into the lost circulation section, and then gradually solidify to play the plugging role.

[0101] (2) The compressive strength of the composite plugging agent after high temperature solidification is determined, and the pressure bearing capacity of the composite plugging agent solidification body is determined by using Shimadzu AG-50KNXPLUS universal testing machine (Japan Shimadzu Co., Ltd.), and the results are shown in Figure 7 :

[0102] The strength of the composite plugging agent after solidification at 90 DEG C can reach 15.5 MPa, which can resist the impact of high pressure in the well and lost formation water. With the increase of temperature, the compressive strength also gradually increases, and the composite plugging agent after solidification at 140 DEG C high temperature has strong compressive strength, and the value reaches 95.7 MPa, so higher temperature is more conducive to the solidification of the plugging agent.

[0103] 7.4.3 Plugging performance characterization of the composite plugging agent

[0104] The composite curing agent is solidified in artificial cracks with different widths of 1 mm and 2 mm, and then the breakthrough pressure of the composite plugging agent is determined by using water displacement, and the results are shown in Figure 8 :

[0105] The breakthrough pressure of the plugging agent solidified in the 1 mm slit is 2.8 MPa, and the breakthrough pressure in the 2 mm slit is 2.53 MPa, so the composite plugging agent can effectively plug the cracks and form a composite solidification block, and the strong breakthrough pressure shows that it can effectively avoid the impact of formation water.

[0106] The above only describes the preferred embodiments of the present application, and does not limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A composite plugging agent for severe formation leakage, characterized in that: The composite sealant is prepared by compounding an associative polymer gel and an etherified phenolic resin. The associative polymer gel is prepared by aqueous solution polymerization of N-dodecylacrylamide with acrylamide, acrylic acid, and 2-acrylamido-2-methylpropanesulfonic acid in a mass percentage ratio of 2:(54.2-65.0):(25.0-30.0):(3.0-20.0); the associative polymer gel also includes a dispersant and an initiator. The etherified phenolic resin is prepared by reacting phenol and formaldehyde, and then etherifying it with at least one of ethanol, propanol or butanol.

2. The composite sealant according to claim 1, characterized in that: The dispersant is selected from one of polysorbate-20, polysorbate-80, nonylphenol polyether-10, and cetearyl alcohol polyether-10.

3. The composite sealant according to claim 1, characterized in that: The initiator is 2,2'-azobisisobutylamidine dihydrochloride.

4. The composite sealant according to claim 2, characterized in that: The mass fraction of the dispersant is 0.05-0.08%; the 2,2'-azobisisobutylamidine dihydrochloride is 0.1-0.5% of the monomer mass.

5. The composite sealant according to claim 1, characterized in that: The method for preparing the associative polymer gel includes the following steps: Acrylamide, acrylic acid, and 2-acrylamido-2-methylpropanesulfonic acid were dissolved in pure water, and the pH was adjusted to obtain a mixture. The dispersant and N-dodecylacrylamide were dispersed in the mixture, and after heating to 40-60℃, 2,2'-azobisisobutylamidine dihydrochloride was added. After reacting for 4-6 h, an associative polymer gel was obtained.

6. The composite sealant according to claim 5, characterized in that: The pH value is 6-8.

7. The composite sealant according to claim 1, characterized in that: The etherified phenolic resin is prepared by reacting phenol and formaldehyde and then etherifying it with a n-hydrocarbon alcohol.

8. The composite sealant according to claim 7, characterized in that: The molar ratio of phenol, formaldehyde and n-hydroethanol is 1 : (1.5-3.0) : (0.3-0.6).

9. The composite sealant according to claim 1, characterized in that: The preparation method of the etherified phenolic resin includes the following steps: Phenolic resin is prepared by mixing NaOH and phenol at 40-60℃, adding formaldehyde solution, and then heating to 75-80℃ and reacting for 4-6 h. Phenolic resin is then reacted with n-hydroethanol at 100℃ for 5-8 h to obtain etherified phenolic resin.

10. The composite sealant according to claim 9, characterized in that: The amount of NaOH added is 5% of the total mass.

11. The composite sealant according to claim 1, characterized in that: The composite sealing agent is prepared by mixing an aqueous solution of etherified phenolic resin with an associative polymer gel at a mass fraction of 0.5-1.5%.

12. The composite sealant according to claim 11, characterized in that: The aqueous solution of the etherified phenolic resin has a mass concentration of 30-80%.

13. The use of the composite plugging agent according to any one of claims 1-12 in the preparation of drilling fluid.

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