Composite plugging agent and preparation method thereof

Abstract

The invention relates to the technical field of drilling fluid plugging materials, in particular to a composite plugging agent and a preparation method thereof.According to the composite plugging agent, glass fibers and walnut shells serve as raw materials, the walnut shells and the glass fibers are pretreated through the composite plugging agent, and a walnut shell-iron chelate and a glass fiber-tannic acid glue solution are obtained; and mixing the walnut shell-iron chelate with the glass fiber-tannic acid glue solution, standing, and drying to obtain the composite plugging agent. Iron is chelated on the walnut shells, tannic acid is loaded on the glass fibers, then under the complexing action of the tannic acid and the iron, the glass fibers and the walnut shells are stably combined together, and during plugging, the glass fibers and the walnut shells which are stably combined together form a fixed and stable space structure; therefore, a good plugging effect is achieved.

Description

Technical Field

[0001] This invention relates to the field of drilling fluid plugging materials technology, specifically a composite plugging agent and its preparation method. Background Technology

[0002] During drilling, formation fractures develop, resulting in fractures in most oil reservoirs. These fractures provide excellent seepage channels for crude oil extraction, but they also allow excessive formation water to flow into production wells, leading to problems such as high water cut in the produced fluid and low injection water utilization, ultimately resulting in low oilfield recovery. To address these issues, plugging agents are widely used in oil and gas reservoirs. Currently, commonly used plugging agents are composite compositions of solid particles and fibrous gametes.

[0003] Chinese patent document CN108384520A discloses a biodegradable fiber plugging agent for drilling fluid, which contains modified microcrystalline cellulose and modified nano-silica.

[0004] Chinese patent document CN113549432A discloses an environmentally friendly drilling fluid plugging agent based on modified basalt fiber powder and its preparation method. The plugging agent contains basalt fiber powder and nano-silica.

[0005] Both of the above-mentioned plugging agents use a combination of solid particles and fibers to achieve the plugging effect. However, the solid particles and fibers are simply mixed, resulting in a loose and variable structure, which leads to poor plugging effect.

[0006] Therefore, in order to obtain a plugging agent with stable plugging performance, it is necessary to solve the problem of how to achieve tight bonding between solid particles and fibers. Summary of the Invention

[0007] This invention provides a composite sealing agent and its preparation method, which overcomes the shortcomings of the prior art and can effectively solve the problems of loose connection and poor sealing effect of existing composite sealing materials.

[0008] One of the technical solutions of the present invention is achieved through the following measures: a composite plugging agent is prepared according to the following method: The first step is to pretreat the walnut shells to obtain walnut shell-iron chelates; The second step is to pretreat the glass fiber to obtain a glass fiber-tannic acid adhesive. The third step involves mixing the walnut shell-iron chelate with the glass fiber-tannic acid adhesive, allowing it to stand, and then drying it to obtain the composite sealing agent.

[0009] The following are further optimizations and / or improvements to one of the above-mentioned technical solutions: The first step above, the walnut shell pretreatment process, includes: S1, Grind the required amount of walnut shells to obtain walnut shell powder; S2, walnut shell powder is placed in ethanol and dispersed to obtain a dispersion system solution; S3, add the required amounts of sodium hydroxide and 3-chloro-2-hydroxypropyltrimethylammonium chloride to the dispersion system solution, stir and heat, and after reaction, etherified walnut shell powder is obtained; S4. Add the required amount of deionized water to the etherified walnut shell powder and stir to obtain an etherified walnut shell solution. S5, add the required amounts of sodium hydroxide, ethylenediamine, butyraldehyde and carbon disulfide to the etherified walnut shell solution in sequence, stir and heat to carry out the reaction, and obtain chelated walnut shell; S6. The chelated walnut shells were mixed with ferric chloride solution and allowed to stand to obtain walnut shell-iron chelate.

[0010] In step S1 above, the particle size of the walnut shell powder is 0.5 mm to 0.8 mm, and the mass ratio of walnut shell powder to ethanol is 1:10 to 12; or / and, in step S2, dispersion is carried out by ultrasonication; or / and, in step S3, the mass ratio of walnut shell powder, sodium hydroxide, and 3-chloro-2-hydroxypropyltrimethylammonium chloride is 1:0.05 to 0.08:0.14 to 0.16, the heating temperature is 65℃ to 70℃, the reaction time is 4 hours to 4.5 hours, and the solids in the reaction product are filtered out, washed, and dried to obtain etherified walnut shell powder; or / and.

[0011] In step S4 above, the mass ratio of etherified walnut shell powder to deionized water is 1:30 to 34.

[0012] In step S5 above, the mass ratio of etherified walnut shell powder, sodium hydroxide, ethylenediamine, butyraldehyde, and carbon disulfide is 1:0.04 to 0.06:0.1 to 0.12:0.2 to 0.24:0.14 to 0.16, the heating temperature is 80℃ to 85℃, the reaction time is 4 hours to 4.5 hours, and the solids in the reaction product are filtered out, washed, and dried to obtain chelated walnut shells.

[0013] In step S6 above, the concentration of the ferric chloride solution is 20wt% to 25wt%, the mass ratio of chelated walnut shell to ferric chloride solution is 1:6 to 8, the standing time is 22 hours to 24 hours, and the solids in the standing product are filtered out to obtain walnut shell-iron chelate.

[0014] In the second step mentioned above, the glass fiber pretreatment process includes: S12, add the required amount of glass fiber to an aqueous solution of acrylamide to obtain a glass fiber mixed solution; S13, add the required amounts of tannic acid, diethylenetriamine, ammonium disulfate and potassium persulfate to the glass fiber mixed solution in sequence, stir and let stand to obtain glass fiber-tannic acid adhesive solution.

[0015] In step S12 above, the length of the glass fiber is 5 mm to 8 mm, and the mass ratio of glass fiber, deionized water, and acrylamide is 1:16 to 18:0.05 to 0.08; or / and in step S13, the mass ratio of glass fiber, tannic acid, diethylenetriamine, ammonium disulfate, and potassium persulfate is 1:1.2 to 0.16:0.22 to 0.24:0.04 to 0.06:0.04 to 0.06, the stirring time is 30 minutes to 35 minutes, and the standing time is 4 hours to 5 hours.

[0016] In the third step above, the mass ratio of walnut shell-iron chelate to glass fiber-tannic acid adhesive is 1:0.16 to 0.18, the standing time is 48 to 50 hours, and the standing product is dried to obtain the composite sealing agent.

[0017] The second technical solution of the present invention is achieved through the following measures: a method for preparing a composite plugging agent, comprising the following steps: The first step is to pretreat the walnut shells to obtain walnut shell-iron chelates; The second step is to pretreat the glass fiber to obtain a glass fiber-tannic acid adhesive. The third step involves mixing the walnut shell-iron chelate with the glass fiber-tannic acid adhesive, allowing it to stand, and then drying it to obtain the composite sealing agent.

[0018] This invention solves the problems of loose connections and poor sealing effect in existing composite sealing materials by chelating iron on walnut shells and loading tannic acid on glass fibers. Subsequently, the complexation effect of tannic acid and iron makes the glass fibers and walnut shells stably bonded together. During sealing, the stably bonded glass fibers and walnut shells form a fixed and stable spatial structure, thereby achieving a good sealing effect. Detailed Implementation

[0019] This invention is not limited to the following embodiments, and specific implementation methods can be determined according to the technical solutions and actual conditions of this invention. Unless otherwise specified, all chemical reagents and chemical products mentioned in this invention are well-known and commonly used chemical reagents and chemical products in the prior art; unless otherwise specified, all percentages in this invention are mass percentages; unless otherwise specified, all solutions in this invention are aqueous solutions with water as the solvent; room temperature in this invention generally refers to a temperature between 15°C and 25°C, generally defined as 25°C.

[0020] The present invention will be further described below with reference to embodiments: Example 1: This composite plugging agent was prepared according to the following method: The first step is to pretreat the walnut shells to obtain walnut shell-iron chelates; The second step is to pretreat the glass fiber to obtain a glass fiber-tannic acid adhesive. The third step involves mixing the walnut shell-iron chelate with the glass fiber-tannic acid adhesive, allowing it to stand, and then drying it to obtain the composite sealing agent.

[0021] Example 2: As an optimization of the above example, the first step of the walnut shell pretreatment process includes: S1, Grind the required amount of walnut shells to obtain walnut shell powder; S2, walnut shell powder is placed in ethanol and dispersed to obtain a dispersion system solution; S3, add the required amounts of sodium hydroxide and 3-chloro-2-hydroxypropyltrimethylammonium chloride to the dispersion system solution, stir and heat, and after reaction, etherified walnut shell powder is obtained; S4. Add the required amount of deionized water to the etherified walnut shell powder and stir to obtain an etherified walnut shell solution. S5, add the required amounts of sodium hydroxide, ethylenediamine, butyraldehyde and carbon disulfide to the etherified walnut shell solution in sequence, stir and heat to carry out the reaction, and obtain chelated walnut shell; S6. The chelated walnut shells were mixed with ferric chloride solution and allowed to stand to obtain walnut shell-iron chelate.

[0022] Example 3: As an optimization of the above example, in step S1, the particle size of the walnut shell powder is 0.5 mm to 0.8 mm, and the mass ratio of walnut shell powder to ethanol is 1:10 to 12.

[0023] Example 4: As an optimization of the above example, in step S2, ultrasonic dispersion is used.

[0024] Example 5: As an optimization of the above example, in step S3, the mass ratio of walnut shell powder, sodium hydroxide, and 3-chloro-2-hydroxypropyltrimethylammonium chloride is 1:0.05 to 0.08:0.14 to 0.16, the heating temperature is 65°C to 70°C, the reaction time is 4 hours to 4.5 hours, and the solids in the reaction product are filtered out, washed, and dried to obtain etherified walnut shell powder.

[0025] Example 6: As an optimization of the above example, in step S4, the mass ratio of etherified walnut shell powder to deionized water is 1:30 to 34.

[0026] Example 7: As an optimization of the above example, in step S5, the mass ratio of etherified walnut shell powder, sodium hydroxide, ethylenediamine, butyraldehyde, and carbon disulfide is 1:0.04 to 0.06:0.1 to 0.12:0.2 to 0.24:0.14 to 0.16, the heating temperature is 80°C to 85°C, the reaction time is 4 hours to 4.5 hours, and the solids in the reaction product are filtered out, washed, and dried to obtain chelated walnut shells.

[0027] Example 8: As an optimization of the above example, in step S6, the concentration of the ferric chloride solution is 20wt% to 25wt%, the mass ratio of chelated walnut shell to ferric chloride solution is 1:6 to 8, the standing time is 22 hours to 24 hours, and the solids in the standing product are filtered out to obtain walnut shell-iron chelate.

[0028] Example 9: As an optimization of the above embodiment, the glass fiber pretreatment process in the second step includes: S11, add the required amount of acrylamide to deionized water, stir, and obtain an acrylamide aqueous solution; S12, add the required amount of glass fiber to an aqueous solution of acrylamide to obtain a glass fiber mixed solution; S13, add the required amounts of tannic acid, diethylenetriamine, ammonium disulfate and potassium persulfate to the glass fiber mixed solution in sequence, stir and let stand to obtain glass fiber-tannic acid adhesive solution.

[0029] Example 10: As an optimization of the above example, in step S12, the length of the glass fiber is 5 mm to 8 mm, and the mass ratio of glass fiber, deionized water and acrylamide is 1:16 to 18:0.05 to 0.08.

[0030] Example 11: As an optimization of the above example, in step S13, the mass ratio of glass fiber, tannic acid, diethylenetriamine, ammonium disulfide, and potassium persulfate is 1:1.2 to 0.16:0.22 to 0.24:0.04 to 0.06:0.04 to 0.06, the stirring time is 30 to 35 minutes, and the standing time is 4 to 5 hours.

[0031] Example 12: As an optimization of the above example, in the third step, the mass ratio of walnut shell-iron chelate to glass fiber-tannic acid adhesive is 1:0.16 to 0.18, the standing time is 48 hours to 50 hours, and the standing product is dried to obtain a composite sealing agent.

[0032] Example 13: The preparation method of this composite plugging agent is carried out according to the following method: The first step is to pretreat the walnut shells to obtain walnut shell-iron chelates; The second step is to pretreat the glass fiber to obtain a glass fiber-tannic acid adhesive. The third step involves mixing the walnut shell-iron chelate with the glass fiber-tannic acid adhesive, allowing it to stand, and then drying it to obtain the composite sealing agent.

[0033] Example 14: Composite plugging agent sample 1 was prepared according to the following steps: The first step is to prepare walnut shell-iron chelate: S1, grind 10 kg of walnut shells to obtain walnut shell powder with a particle size of 0.6 mm; S2, walnut shell powder is placed in 110 kg of ethanol and dispersed to obtain a dispersion system solution; S3, 0.6 kg of sodium hydroxide and 1.5 kg of 3-chloro-2-hydroxypropyltrimethylammonium chloride were added to the dispersion system solution, stirred, heated to 68°C, and reacted for 4.2 hours to obtain etherified walnut shells; S4. Add 320 kg of deionized water to the etherified walnut shell powder, stir and disperse to obtain an etherified walnut shell solution. S5, 0.5 kg sodium hydroxide, 1.1 kg ethylenediamine, 2.2 kg butyraldehyde and 1.5 kg carbon disulfide were added sequentially to the etherified walnut shell solution, stirred and heated to 82°C, and reacted for 4.2 hours to obtain chelated walnut shells; S6. The chelated walnut shell was mixed with a 22wt% ferric chloride solution at a mass ratio of 1:7 and allowed to stand for 23 hours to obtain a walnut shell-iron chelate.

[0034] The second step is to prepare the glass fiber-tannic acid adhesive: S11, add 0.06 kg of acrylamide to 17 kg of deionized water and stir to obtain an acrylamide aqueous solution; S12, 1 kg of 6 mm glass fiber is added to an aqueous solution of acrylamide to obtain a glass fiber mixed solution; S13. Add 1.2 kg of tannic acid, 0.23 kg of diethylenetriamine, 0.05 kg of ammonium disulfate and 0.05 kg of potassium persulfate to the glass fiber mixed solution in sequence, stir for 32 minutes and let stand for 4.2 hours to obtain glass fiber-tannic acid adhesive solution.

[0035] The third step is to prepare the composite sealing agent: Walnut shell-iron chelate and glass fiber-tannic acid adhesive were mixed at a mass ratio of 1:0.17, allowed to stand at room temperature for 49 hours, and then dried to obtain a composite sealing agent, which was designated as sample 1.

[0036] A plugging drilling fluid was prepared using composite plugging agent sample 1 as raw material to evaluate the performance of the plugging agent. By weight, the raw materials included 100 kg water, 4 kg bentonite, 0.8 kg sodium hydroxide, 2.5 kg sodium carboxymethyl cellulose, 6 kg xanthan gum, 55 kg barite, and 5 kg composite plugging agent sample 1. After mixing and stirring, plugging drilling fluid B1 was obtained.

[0037] Example 15: Composite plugging agent sample 2 was prepared according to the following steps: The first step is to prepare walnut shell-iron chelate: S1, grind 10 kg of walnut shells to obtain walnut shell powder with a particle size of 0.5 mm; S2, walnut shell powder is placed in 100 kg of ethanol and dispersed to obtain a dispersion system solution; S3, 0.5 kg of sodium hydroxide and 1.4 kg of 3-chloro-2-hydroxypropyltrimethylammonium chloride were added to the dispersion system solution, stirred, heated to 65°C, and reacted for 4 hours to obtain etherified walnut shells; S4. Add 300 kg of deionized water to the etherified walnut shell powder, stir and disperse to obtain an etherified walnut shell solution. S5, add 0.4 kg sodium hydroxide, 1 kg ethylenediamine, 2 kg butyraldehyde and 1.4 kg carbon disulfide to the etherified walnut shell solution in sequence, stir, heat to 80°C, and react for 4 hours to obtain chelated walnut shell; S6. The chelated walnut shell was mixed with a 20wt% ferric chloride solution at a mass ratio of 1:6 and allowed to stand for 22 hours to obtain a walnut shell-iron chelate.

[0038] The second step is to prepare the glass fiber-tannic acid adhesive: S11, add 0.05 kg of acrylamide to 16 kg of deionized water and stir to obtain an acrylamide aqueous solution; S12, 1 kg of 5 mm glass fiber is added to an aqueous solution of acrylamide to obtain a glass fiber mixed solution; S13. Add 1.4 kg of tannic acid, 0.22 kg of diethylenetriamine, 0.04 kg of ammonium disulfate and 0.04 kg of potassium persulfate to the glass fiber mixed solution in sequence, stir for 30 minutes and let stand for 4 hours to obtain glass fiber-tannic acid adhesive solution.

[0039] The third step is to prepare the composite sealing agent: Walnut shell-iron chelate and glass fiber-tannic acid adhesive were mixed at a mass ratio of 1:0.16, allowed to stand at room temperature for 48 hours, and then dried to obtain a composite sealing agent, which was designated as sample 2.

[0040] Using composite plugging agent sample 2 as raw material, a plugging drilling fluid was prepared according to the method of Example 8 to obtain plugging drilling fluid B2. This fluid was then used to evaluate the performance of the composite plugging agent.

[0041] Example 16: Composite plugging agent sample 3 was prepared according to the following steps: The first step is to prepare walnut shell-iron chelate: S1, grind 10 kg of walnut shells to obtain walnut shell powder with a particle size of 0.8 mm; S2, walnut shell powder is placed in 120kg ethanol and dispersed to obtain a dispersion system solution; S3, 0.8 kg of sodium hydroxide and 1.6 kg of 3-chloro-2-hydroxypropyltrimethylammonium chloride were added to the dispersion system solution, stirred, heated to 70°C, and reacted for 4.5 hours to obtain etherified walnut shells; S4. Add 340 kg of deionized water to the etherified walnut shell powder, stir and disperse to obtain an etherified walnut shell solution. S5, 0.6 kg sodium hydroxide, 1.2 kg ethylenediamine, 2.4 kg butyraldehyde and 1.6 kg carbon disulfide were added sequentially to the etherified walnut shell solution, stirred and heated to 85°C, and reacted for 4.5 hours to obtain chelated walnut shells; S6. The chelated walnut shell was mixed with a 25wt% ferric chloride solution at a mass ratio of 1:8 and allowed to stand for 24 hours to obtain a walnut shell-iron chelate.

[0042] The second step is to prepare the glass fiber-tannic acid adhesive: S11, add 0.08 kg of acrylamide to 18 kg of deionized water and stir to obtain an acrylamide aqueous solution; S12, 1 kg of 8 mm glass fiber is added to an aqueous solution of acrylamide to obtain a glass fiber mixed solution; S13. Add 1.6 kg of tannic acid, 0.24 kg of diethylenetriamine, 0.06 kg of ammonium disulfide and 0.06 kg of potassium persulfate to the glass fiber mixed solution in sequence, stir for 35 minutes and let stand for 5 hours to obtain glass fiber-tannic acid adhesive solution.

[0043] The third step is to prepare the composite sealing agent: Walnut shell-iron chelate and glass fiber-tannic acid adhesive were mixed at a mass ratio of 1:0.18, allowed to stand at room temperature for 50 hours, and then dried to obtain a composite sealing agent, which was designated as sample 3.

[0044] Using composite plugging agent sample 3 as raw material, a plugging drilling fluid was prepared according to the method in Example 8 to obtain plugging drilling fluid B2. This fluid was used to evaluate the performance of the composite plugging agent.

[0045] Comparative Example 1: Following the preparation method of the sealing drilling fluid in Example 8, the composite sealing agent sample 1 was replaced with a mixture of glass fiber and walnut shell of equal weight, wherein the mass ratio of glass fiber to walnut shell was 1:0.17. After mixing and stirring, sealing drilling fluid D1 was obtained.

[0046] Under normal temperature conditions, the filtration loss of the plugging drilling fluids prepared in Examples 14 to 16 and Comparative Example 1 was tested in half an hour using a high-temperature and high-pressure filtration loss meter. The test conditions were as follows: filter paper with several small pores of 1 micrometer in size was placed at the bottom of the high-temperature and high-pressure filtration loss meter, and the filter paper was 5 millimeters thick. The results are shown in Table 1. As can be seen from Table 1, the composite plugging agent prepared according to the preparation method provided by the present invention has a good plugging effect after being formulated into a plugging drilling fluid, and the filtration loss in half an hour is less than 4 milliliters. However, the plugging agent of Comparative Example 1, because the glass fiber and walnut shell are simply compounded and cannot form a stable structure, has a higher filtration loss in half an hour.

[0047] In summary, this invention achieves a good sealing effect by chelating iron on walnut shells and loading tannic acid onto glass fibers, followed by the complexation of tannic acid and iron, which stably binds the glass fibers and walnut shells together. During sealing, the stably bound glass fibers and walnut shells together form a fixed and stable spatial structure.

[0048] The above technical features constitute various embodiments of the present invention, which have strong adaptability and implementation effect. Unnecessary technical features can be added or removed according to actual needs to meet the needs of different situations.

Claims

1. A composite plugging agent, characterized in that... It was prepared according to the following method: The first step is to pretreat the walnut shells to obtain walnut shell-iron chelates; The second step is to pretreat the glass fiber to obtain a glass fiber-tannic acid adhesive. The third step involves mixing the walnut shell-iron chelate with the glass fiber-tannic acid adhesive, allowing it to stand, and then drying it to obtain the composite sealing agent.

2. The composite plugging agent according to claim 1, characterized in that... The first step, the walnut shell pretreatment process, includes: S1, Grind the required amount of walnut shells to obtain walnut shell powder; S2, walnut shell powder is placed in ethanol and dispersed to obtain a dispersion system solution; S3, add the required amounts of sodium hydroxide and 3-chloro-2-hydroxypropyltrimethylammonium chloride to the dispersion system solution, stir and heat, and after reaction, etherified walnut shell powder is obtained; S4. Add the required amount of deionized water to the etherified walnut shell powder and stir to obtain an etherified walnut shell solution. S5, add the required amounts of sodium hydroxide, ethylenediamine, butyraldehyde and carbon disulfide to the etherified walnut shell solution in sequence, stir and heat to carry out the reaction, and obtain chelated walnut shell; S6. The chelated walnut shells were mixed with ferric chloride solution and allowed to stand to obtain walnut shell-iron chelate.

3. The composite plugging agent according to claim 2, characterized in that... In step S1, the particle size of the walnut shell powder is 0.5 mm to 0.8 mm, and the mass ratio of walnut shell powder to ethanol is 1:10 to 12; or / and, in step S2, dispersion is carried out by ultrasonication; or / and, in step S3, the mass ratio of walnut shell powder, sodium hydroxide, and 3-chloro-2-hydroxypropyltrimethylammonium chloride is 1:0.05 to 0.08:0.14 to 0.16, the heating temperature is 65°C to 70°C, and the reaction time is 4 hours to 4.5 hours.

4. The composite plugging agent according to claim 2 or 3, characterized in that... In step S4, the mass ratio of etherified walnut shell powder to deionized water is 1:30 to 34.

5. The composite plugging agent according to claim 2, 3, or 4, characterized in that... In step S5, the mass ratio of etherified walnut shell powder, sodium hydroxide, ethylenediamine, butyraldehyde, and carbon disulfide is 1:0.04 to 0.06:0.1 to 0.12:0.2 to 0.24:0.14 to 0.16, the heating temperature is 80°C to 85°C, and the reaction time is 4 to 4.5 hours.

6. The composite plugging agent according to claim 2, 3, 4, or 5, characterized in that... In step S6, the concentration of the ferric chloride solution is 20wt% to 25wt%, the mass ratio of chelated walnut shell to ferric chloride solution is 1:6 to 8, and the standing time is 22 hours to 24 hours.

7. The composite plugging agent according to any one of claims 1, 2, 3, 4, 5, or 6, characterized in that... The second step, the glass fiber pretreatment process, includes: S11, add the required amount of acrylamide to deionized water, stir, and obtain an acrylamide aqueous solution; S12, add the required amount of glass fiber to an aqueous solution of acrylamide to obtain a glass fiber mixed solution; S13, add the required amounts of tannic acid, diethylenetriamine, ammonium disulfate and potassium persulfate to the glass fiber mixed solution in sequence, stir and let stand to obtain glass fiber-tannic acid adhesive solution.

8. The composite plugging agent according to claim 7, characterized in that... In step S12, the length of the glass fiber is 5 mm to 8 mm, and the mass ratio of glass fiber, deionized water, and acrylamide is 1:16 to 18:0.05 to 0.08; or / and in step S13, the mass ratio of glass fiber, tannic acid, diethylenetriamine, ammonium disulfate, and potassium persulfate is 1:1.2 to 0.16:0.22 to 0.24:0.04 to 0.06:0.04 to 0.06, the stirring time is 30 minutes to 35 minutes, and the standing time is 4 hours to 5 hours.

9. The composite sealing agent according to any one of claims 1, 2, 3, 4, 5, 6, 7, or 8, characterized in that... In the third step, the mass ratio of walnut shell-iron chelate to glass fiber-tannic acid adhesive is 1:0.16 to 0.18, and the standing time is 48 to 50 hours to obtain a composite sealing agent.

10. A method for preparing a composite plugging agent according to any one of claims 2 to 9, characterized in that... Perform the following steps: The first step is to pretreat the walnut shells to obtain walnut shell-iron chelates; The second step is to pretreat the glass fiber to obtain a glass fiber-tannic acid adhesive. The third step involves mixing the walnut shell-iron chelate with the glass fiber-tannic acid adhesive, allowing it to stand, and then drying it to obtain the composite sealing agent.

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