Composite plugging agent for stratum malignant leakage and preparation method thereof

Abstract

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

Description

Technical Field

[0001] The invention belongs to the technical field of chemical materials, and in particular relates to a composite plugging agent for malignant leakage in formations and a preparation method thereof. Background Art

[0002] In the field of oil and gas development and exploration, the problem of well leakage has always been a technical problem that has troubled 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 fracture leakage have been well solved, but the technology to prevent malignant leakage has not been developed.

[0003] Gel plugging technology is one of the commonly used and effective technologies for controlling malignant lost circulation in fractured wells. This technology injects a certain amount of polymer gel plugging agent into the lost layer, which seals the cracks after solidification, thereby isolating the drilling fluid from the formation fluid and preventing the drilling fluid from continuing to leak.

[0004] Another example is the development and evaluation of the prior art high-temperature gelling and degradable polymer gel plugging agent (Guo Yongbin; Yan Bangchuan; Huang Yi, et al., Drilling Fluids and Completion Fluids. 2019, 36(03)). It is disclosed that gelatin was quaternized with methacrylic anhydride to synthesize a polymerizable modified gelatin crosslinker. Based on the thermoplasticity of the hot melt adhesive, the initiator was successfully encapsulated in the hot melt adhesive particles to achieve high-temperature sustained-release initiation. A high-temperature resistant and degradable polymer gel plugging agent P (AM-DGCL) was developed using acrylamide (AM) and a homemade crosslinker (DGCL) as raw materials. The homemade crosslinker was structurally characterized by nuclear magnetic resonance, and the mechanical behavior, plugging ability and gel breaking performance of the gel were tested. The gelation time at 150℃ is adjustable between 2 and 13h. P(AM-DGCL) exhibits excellent mechanical properties, with an elongation at break of 1279% and a tensile strength of 0.0425MPa. Since the cross-linking agent DGCL, which plays a chemical cross-linking role, is degellable, the gel breaking rate of P(AM-DGCL) gel reaches more than 95% within 16h under the action of high temperature and degelling agent, ensuring the reverse discharge capacity after reservoir leakage plugging.

[0005] For example, Chinese patent application CN109796949A discloses a high-temperature resistant gel plugging agent and its preparation method and application, wherein the high-temperature resistant gel plugging agent includes a vinyl polymerization monomer, a solid-phase organic macromolecular crosslinking agent, a first initiator, a particle toughening agent and a fiber toughening agent. The invention also discloses a preparation method for the above-mentioned gel plugging agent, including: (I) adding a vinyl polymerization monomer, a solid-phase organic macromolecular crosslinking agent and a particle toughening agent to clean water and stirring at high speed to obtain the mixed solution a; (II) adding a fiber toughening agent to the mixed solution a, stirring at a low speed for the first time to disperse evenly, to obtain a mixed solution b; (III) adding a first initiator to the mixed solution b, stirring at a low speed for the second time until it is completely dissolved, to obtain a mixed solution c; sealing the mixed solution c and letting it stand to solidify into a gel, to obtain a high-strength and high-toughness gel plugging agent. The gel plugging agent has both high gelling strength and high shear toughness under high temperature conditions, and has a higher pressure bearing capacity and excellent plugging effect.

[0006] Associative polymer gel has good rheological properties, and its shear-thinning behavior gives it fast and efficient plugging, and has the advantage of rapid early plugging. Thermosetting phenolic resin transforms from a pumpable liquid to a high-strength solid block in a thermal environment, and has the characteristics of inhibiting the vicious leakage of the formation, which is suitable for long-term and high-strength leakage plugging. However, at present, associative polymer gels generally have low strength, and the resin-based anti-plugging system has poor storage resistance and is not resistant to dilution. Therefore, it is necessary to develop a composite plugging agent suitable for vicious leakage and its preparation method to solve the problem that existing plugging agents are difficult to deal with vicious leakage in formations. Summary of the invention

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

[0008] In order to achieve the above objectives, this application is implemented through the following technical solutions:

[0009] On the one hand, the present invention provides a composite plugging agent for malignant leakage in formations, wherein the composite plugging agent is prepared by compounding an associative polymer gel and an etherified phenolic resin.

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

[0011] Furthermore, in a preferred embodiment of the present invention, the associative polymer gel is prepared by aqueous solution polymerization of N-dodecyl acrylamide 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).

[0012] Furthermore, the associative polymer gel also includes a dispersant and an initiator;

[0013] The dispersant is selected from one of polysorbate-20, polysorbate-80, nonylphenol polyether-10 and cetearyl alcohol polyether-10.

[0014] The initiator is 2,2'-azobisisobutylamidine dihydrochloride.

[0015] Wherein, the mass fraction of the dispersant is 0.05-0.08%.

[0016] The 2,2'-azobisisobutylamidine dihydrochloride is 0.1-0.5% of the monomer mass.

[0017] On the other hand, the present invention also provides a method for preparing the above-mentioned associative polymer gel, comprising the following steps:

[0018] Dissolve acrylamide, acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid in pure water, adjust the pH to obtain a mixed solution; disperse a dispersant and N-dodecyl acrylamide in the mixed solution, heat to 40-60°C, add 2,2'-azobisisobutylamidine dihydrochloride, react for 4-6 hours, and obtain an associative polymer gel.

[0019] Furthermore, in a preferred embodiment of the present invention, the pH value is adjusted to 6-8.

[0020] Furthermore, in a preferred embodiment of the present invention, the etherified phenolic resin is prepared by reacting phenol and formaldehyde and etherifying with normal hydrocarbon alcohol.

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

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

[0023] Mix NaOH and phenol at 40-60°C, add formaldehyde solution, heat to 75-80°C, and react for 4-6 hours to obtain phenolic resin; react phenolic resin with normal hydrocarbon alcohol at 100°C for 5-8 hours to obtain etherified phenolic resin.

[0024] Furthermore, in a preferred embodiment of the present invention, the amount of NaOH added is 5% of the total mass.

[0025] Furthermore, the composite plugging agent is prepared by mixing an aqueous solution of etherified phenolic resin with 0.5-1.5% by mass of an associative polymer gel.

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

[0027] Compared with the prior art, the present invention is beneficial in that:

[0028] The composite water plugging agent suitable for vicious leakage of the present invention is prepared by compounding associative polymer gel and etherified resin. The special composite water plugging agent system has shear thinning behavior, which can meet the early stage of rapid and efficient plugging needs. At the same time, the hydrophobic associative polymer greatly increases the dilution resistance of the composite water plugging agent. Subsequently, the etherified phenolic resin plugging agent forms a permanent plugging layer under the action of high temperature of the formation, which can completely plug the underground site of the vicious leakage.

[0029] In addition, the materials required by the present invention are generally available, the preparation process is simple and mature, and the cost of industrial preparation of water plugging agents can be reduced. The present invention is a plugging agent for malignant leakage that is worthy of promotion.

[0030] Other advantages, objectives and features of the present invention will be embodied in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0032] Figure 1 This is the infrared spectrum of the associative polymer gel in Example 7 of the present invention.

[0033] Figure 2 This is the infrared spectrum of the etherified phenolic resin in Example 7 of the present invention.

[0034] Figure 3 This is the time-viscosity curve of the etherified phenolic resin in Example 7 of the present invention.

[0035] Figure 4 This is a graph showing the relationship between shear viscosity and shear rate of the composite plugging agent in Example 7 of the present invention.

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

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

[0038] Figure 7 This is the compressive strength test of the composite plugging agent after curing in Example 7 of the present invention; Figure 7 (A) Curing at 90°C, Figure 7 (B) Curing at 120°C, Figure 7 (C) Cured at 140°C.

[0039] Figure 8 This is a test of the plugging performance of the composite plugging agent after curing in Example 7 of the present invention; Figure 8 (A) 1mm wide crack, Figure 8 (B) Crack with a width of 2 mm. DETAILED DESCRIPTION

[0040] The principles and features of the present invention are described below in conjunction with the examples and drawings. The examples are only used to explain the present invention and are not used to limit the scope of the present invention. If no specific conditions are specified in the embodiments, they are carried out according to normal conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0041] The technical solution of the specific embodiment of the present invention is:

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

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

[0044] Dissolve acrylamide, acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid in pure water, adjust the pH to 6-8, disperse the dispersant and N-dodecyl acrylamide in water, and pass N 2 After 40 minutes, heat to 40°C-60°C and add 2,2'-azobisisobutylamidine dihydrochloride initiator. After reacting for 4-6 hours, an associative polymer gel is obtained.

[0045] The synthetic route of associative polymer gel is as follows:

[0046]

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

[0048] NaOH with a mass concentration of 5% is mixed with phenol at 40-60°C, and then formaldehyde solution is added and the temperature is raised to 75-80°C, and the reaction is carried out for 4-6 hours to obtain phenolic resin; the resin is reacted with normal hydrocarbon alcohol at 100°C for 5-8 hours to obtain etherified phenolic resin.

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

[0050]

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

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

[0053] Embodiment 1:

[0054] The preparation method of the associative polymer gel of this embodiment comprises the following steps:

[0055] Acrylamide, acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid were dissolved in pure water at a mass ratio of 54.2:26.8:17, and the pH was adjusted to 6-8 to obtain a mixed solution; polysorbate-80 as a dispersant and 2% by mass of N-dodecyl acrylamide were dispersed in the mixed solution, and N 2 After 40 minutes, the mixture was heated to 55°C and 2,2'-azobisisobutylamidine dihydrochloride initiator was added. After reacting for 4 hours, an associative polymer gel was obtained.

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

[0057] Embodiment 2:

[0058] The preparation method of the associative polymer gel of this embodiment comprises the following steps:

[0059] Acrylamide, acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid were dissolved in pure water at a mass ratio of 62:26:11, and the pH was adjusted to 6-8 to obtain a mixed solution; 0.05% of the mass fraction of polysorbate-80 and 2% of the mass fraction of N-dodecyl acrylamide were dispersed in the mixed solution, and N 2 After 40 minutes, the mixture was heated to 55°C and 2,2'-azobisisobutylamidine dihydrochloride initiator was added. After 5 hours of reaction, an associative polymer gel was obtained.

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

[0061] Embodiment 3:

[0062] The preparation method of the associative polymer gel of this embodiment comprises the following steps:

[0063] Acrylamide, acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid were dissolved in pure water at a mass ratio of 62:26:11, and the pH was adjusted to 6-8 to obtain a mixed solution; 0.05% polysorbate-80 and 2% N-dodecyl acrylamide were dispersed in the mixed solution, and N 2 After 40 minutes, the mixture was heated to 55°C and 0.2% of the total monomer mass of 2,2'-azobisisobutylamidine dihydrochloride initiator was added. The mixture was reacted for 5 hours, washed with anhydrous ethanol, dried, and crushed to obtain an associative polymer gel.

[0064] Embodiment 4:

[0065] The preparation method of the etherified phenolic resin of the present embodiment comprises the following steps:

[0066] NaOH with a mass concentration of 5% is mixed with phenol at 50°C, and 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 reaction is carried out for 4 hours to obtain phenolic resin; the phenolic resin is reacted with n-butanol at 100°C for 5 hours to obtain n-butanol-etherified phenolic resin.

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

[0068] Embodiment 5:

[0069] The preparation method of the etherified phenolic resin of the present embodiment comprises the following steps:

[0070] NaOH with a mass concentration of 5% is mixed with phenol at 50°C, and 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 reaction is carried out for 6 hours to obtain phenolic resin; the phenolic resin is reacted with n-propanol at 100°C for 5 hours to obtain n-propanol-etherified phenolic resin.

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

[0072] Embodiment 6:

[0073] The preparation method of the composite plugging agent suitable for serious leakage of the present embodiment comprises: mixing an aqueous solution of etherified phenolic resin and an associative 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] Embodiment 7:

[0076] 7.1 Preparation of associative polymer gel

[0077] Acrylamide, acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid were dissolved in pure water at a mass ratio of 54.2:26.8:17, and the pH was adjusted to 6-8 to obtain a mixed solution; 0.05% polysorbate-80 and 2% N-dodecyl acrylamide were dispersed in the mixed solution, and high-purity N 2 After 40 minutes, the mixture was heated to 55°C and 0.2% of the total monomer weight of 2,2'-azobisisobutylamidine dihydrochloride initiator was added and reacted for 5 hours. The mixture was washed with anhydrous ethanol, dried and crushed to obtain an associative polymer gel.

[0078] The synthetic route of associative polymer gel is as follows:

[0079]

[0080] The chemical formula of the associative polymer gel was determined by infrared analysis:

[0081] The purified associative polymer gel was evenly ground with potassium bromide (KBr), and a small amount of the ground powder was pressed into tablets for sample preparation. The molecular structure of the sample was tested using a WQF-520FTIR Fourier transform infrared spectrometer from Beijing Rayleigh Analytical Instruments Co., Ltd., and the infrared spectrum analysis diagram was shown in FIG. Figure 1 .

[0082] 1681cm -1 The vibration peak corresponding to the amide bond belongs to the signal of acrylamide and N-dodecyl acrylamide; 1309cm -1 The peak at 1195 cm corresponds to the ether bond, which belongs to the signal of acrylic acid; -1 and 1041cm -1 All of them are peaks of sulfonic acid groups, which belong to the signal of 2-acrylamide-2-methylpropanesulfonic acid. In summary, the associative polymer gel with hydrophobic associative function was successfully prepared.

[0083] 7.2 Preparation of etherified phenolic resin

[0084] In a three-necked flask equipped with a reflux condenser, add a certain amount of phenol, then add a NaOH solution accounting for 5% of the mass of phenol, and stir at a constant temperature of 60°C for 30 minutes; add a formaldehyde aqueous solution to the three-necked flask according to a certain aldehyde-phenol molar ratio, heat to 80°C and stir for 4 hours to obtain a brown-red phenolic resin liquid, cool to room temperature and take out. Add the phenolic resin after vacuum dehydration and a certain amount of normal hydrocarbon alcohol to a three-necked flask equipped with a stirrer, heat the oil bath to 100°C and react for 6 hours. Finally, the reaction liquid is subjected to vacuum distillation. The molar ratio of phenol to formaldehyde is 1:2.6, and n-butanol accounts for 1:4 of the molar ratio of phenol.

[0085]

[0086] (1) The chemical formula of the etherified phenolic resin was determined by infrared analysis. The infrared spectrum is shown in Figure 2 :

[0087] 3500cm -1 The broad and intense peaks near 2950cm are characteristic peaks of phenolic resins, which are the result of the vibration of multiple hydroxyl groups. -1 and 2886cm -1 The vibration signals of methylene and methyl groups are respectively, which are mainly ether groups. 1604cm -1 The peak at 1195 cm corresponds to the C=C double bond on phenol; -1 and 1020cm -1 The signals of two ether bonds indicate the existence of ether bonds on the phenolic resin, which correspond to the ether bonds produced by the etherification of n-butanol. In summary, the etherified phenolic resin was successfully prepared.

[0088] (2) Evaluate the storage stability of etherified phenolic resin according to GB / T 14074-2017. The time-viscosity curve is shown in Figure 3 :

[0089] The initial viscosity of the etherified phenolic resin is 825.8 mP·s. After continuous storage for 30 days at 70°C, the viscosity reaches 200%. Therefore, the storage time of the etherified phenolic resin is 180 days. It can be seen that the etherified phenolic resin has excellent storage stability. The applicant's experiment shows that the storage stability of the etherified phenolic resin obtained by replacing n-butanol with other alcohols such as ethanol and propanol is very similar to the test results 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 to dilute, and then the associative polymer gel is added into the solution of the etherified phenolic resin, wherein 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 associative polymer gel is 1:(0.005-0.015).

[0092] 7.4 Performance Characterization of Composite Plugging Agent

[0093] The rheological properties of the composite plugging agent at 25°C were evaluated according to its early plugging ability in the leaking magnetic layer. To confirm the curing performance of the composite plugging agent, the influence of the high temperature environment of the leaking formation on the curing behavior of the composite plugging agent was evaluated. Finally, the plugging performance of the composite plugging agent after curing in 1mm and 2mm artificial fractures was evaluated.

[0094] 7.4.1 Characterization of rheological properties of composite plugging agent

[0095] The test was conducted at a test temperature of 25°C using a HAAKE MARSIII rheometer (Thermo Fisher, USA), with a constant stress of τ = 1Pa, a time of t = 10min, and a test gap of 1mm. 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 104mPa·s, and gradually decreases with the increase of 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 and it is easier to pump because it is not completely gelled and the shear rate is high. After entering the leaking formation, the viscosity of the gel increases due to the decrease in shear rate, which is beneficial to plugging the leaking layer. At the same time, when the vibration frequency is between 0.1-40Hz, the energy dissipation modulus G″ and the storage modulus G' basically increase with the increase of frequency, and the gel belongs to the linear viscoelastic region. In addition, the yield stress of the composite system before thermal curing can reach 323.6Pa, indicating that the system has good strength and ability to resist water flow impact, and can be used for plugging early leaks. Therefore, the gel has good viscoelasticity in stress scans from low frequency to high frequency and from small to large.

[0096] 7.4.2 Characterization of curing performance of composite plugging agent

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

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

[0099]

[0100] The composite plugging agent can start to solidify at 90℃, and the solidification time decreases with the increase of temperature. The solidification time at 140℃ is still 1.5h, which is enough relaxation time to inject the composite plugging agent segment into the lost well section, and then gradually solidify to play its plugging role.

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

[0102] The strength of the composite plugging agent after curing at 90°C can reach 15.5MPa, which can withstand the impact of underground high pressure and lost formation water. As the temperature rises, its compressive strength gradually increases. At a high temperature of 140°C, the composite plugging agent has a strong compressive strength after curing, and its value reaches 95.7MPa. It can be seen that higher temperature is more conducive to the curing of the plugging agent.

[0103] 7.4.3 Characterization of the plugging performance of composite plugging agents

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

[0105] The breakthrough pressure of the plugging agent solidified in a 1mm slit is 2.8MPa, while the breakthrough pressure in a 2mm slit is 2.53MPa. It can be seen that the composite plugging agent can effectively seal the cracks and form composite solidified blocks. The stronger breakthrough pressure indicates that it can effectively avoid the impact of formation water.

[0106] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A composite plugging agent for malignant leakage in formations. Features: The composite plugging agent is prepared by compounding associative polymer gel and etherified phenolic resin; The associative polymer gel is obtained by copolymerizing N-dodecyl acrylamide with at least one of acrylamide, acrylic acid or 2-acrylamido-2-methylpropanesulfonic acid; The etherified phenolic resin is prepared by reacting phenol and formaldehyde and etherifying with at least one of ethanol, propanol or butanol.

2. The composite plugging agent according to claim 1, Features: The associative 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).

3. The composite plugging agent according to claim 2, Features: The associative polymer gel also includes a dispersant and an initiator.

4. The composite plugging agent according to claim 3, Features: The dispersant is selected from one of polysorbate-20, polysorbate-80, nonylphenol polyether-10 and cetearyl alcohol polyether-10.

5. The composite plugging agent according to claim 3, Features: The initiator is 2,2'-azobisisobutylamidine dihydrochloride.

6. The composite plugging agent according to claim 3, Features: The mass fraction of the dispersant is 0.05-0.08%; the mass fraction of the 2,2'-azobisisobutylamidine dihydrochloride is 0.1-0.5% of the monomer mass.

7. The composite plugging agent according to claim 1, Features: The method for preparing the associative polymer gel comprises the following steps: Dissolve acrylamide, acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid in pure water, adjust the pH to obtain a mixed solution; disperse a dispersant and N-dodecyl acrylamide in the mixed solution, heat to 40-60°C, add 2,2'-azobisisobutylamidine dihydrochloride, react for 4-6 hours, and obtain an associative polymer gel.

8. The composite plugging agent according to claim 7, Features: The pH value is 6-8.

9. The composite plugging agent according to claim 1, Features: The etherified phenolic resin is prepared by reacting phenol and formaldehyde and etherifying with normal hydrocarbon alcohol.

10. The composite plugging agent according to claim 9, Features: The molar ratio of the phenol, formaldehyde and normal hydrocarbon alcohol is 1:(1.5-3.0):(0.3-0.6).

11. The composite plugging agent according to claim 1, Features: The preparation method of the etherified phenolic resin comprises the following steps: Mix NaOH and phenol at 40-60°C, add formaldehyde solution, heat to 75-80°C, and react for 4-6 hours to obtain phenolic resin; react phenolic resin with normal hydrocarbon alcohol at 100°C for 5-8 hours to obtain etherified phenolic resin.

12. The composite plugging agent according to claim 11, Features: The amount of NaOH added was 5% of the total mass.

13. The composite plugging agent according to claim 1, Features: The composite plugging agent is prepared by mixing an aqueous solution of etherified phenolic resin with an associative polymer gel with a mass fraction of 0.5-1.5%.

14. The composite plugging agent according to claim 13, Features: The mass concentration of the aqueous solution of the etherified phenolic resin is 30-80%.

15. Use of the composite plugging agent according to any one of claims 1 to 14 in preparing drilling fluid.

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