Composite plugging material with core-shell structure, preparation method thereof and water-based drilling fluid

Abstract

The application discloses a composite plugging material with a core-shell structure, a preparation method thereof and a water-based drilling fluid, and relates to the technical field of oil fields.The preparation method of the composite plugging material comprises the following steps: mixing and melting aromatic compounds prepared by reacting a polyhydroxy aromatic compound with epichlorohydrin, mixing and melting aromatic compounds prepared by sequentially reacting a polybasic alcohol aromatic compound with triphenylphosphine, bromo-trichloromethane, sodium azide and triethyl phosphite, casting, crushing to obtain epoxy resin particles, and coating the epoxy resin particles with a polymer to obtain the composite plugging material, and the composite plugging material is used for preparing the water-based drilling fluid.The plugging material with the core-shell structure prepared in the application has stronger compression resistance than general rigid particle materials, and when reaching a softening point in a high-temperature and high-pressure stratum, the glass state is converted into a high-elasticity state, and the plugging material has elastic deformation capacity, so that the slippage effect between particles can be reduced, a denser plugging layer is formed, and the pressure-bearing capacity is higher.

Description

Technical Field

[0001] This invention relates to the field of oilfield chemical technology, specifically to a core-shell structured composite plugging material and its preparation method, as well as a water-based drilling fluid. Background Technology

[0002] In oil and gas field drilling, well leakage is a frequent and complex problem, especially in areas with well-developed fractures and pores in complex geological structures, where repeated leakage is prone to occur, severely prolonging drilling cycles and increasing drilling costs. Current mainstream plugging technologies mainly use rigid materials such as walnut shells, talc flakes, and quartz sand. These materials lack deformability in practical applications and, when mismatched with the shape of the leakage channel, easily accumulate on the surface, forming a "gate" that cannot achieve long-term sealing. Traditional plugging materials primarily rely on physical bridging and filling mechanisms, resulting in a poorly dense and pressure-bearing sealing layer. When single epoxy resin particles are used as plugging materials, their high cross-linking density and rigid molecular chains after curing result in a lack of elasticity and plastic deformation capabilities, making them prone to slippage in formation fractures, leading to bridging failure and difficulty in forming a stable sealing layer. Currently, there are some methods for preparing resin plugging agents. For example, patent CN116948616B discloses a pressure-bearing epoxy resin plugging material for oil-based drilling fluid. The prepared epoxy resin particles have a compressive strength of 120-190MPa, which is the same principle as the rigid particles bridging and plugging in the cracks. However, it cannot solve the slippage effect of particles in the cracks. Summary of the Invention

[0003] In view of this, the present invention proposes a core-shell structured composite plugging material and its preparation method, as well as a water-based drilling fluid. The core-shell structured composite resin, prepared by encapsulating epoxy resin with thermoplastic resin, is used as the plugging material. The epoxy resin achieves "instant rigid bridging" to quickly control the leakage rate. Furthermore, the thermoplastic resin transforms from a glassy state to a highly elastic state under high temperature, achieving "long-lasting tough sealing". Ultimately, a high-strength, highly dense, and adaptive integrated plugging body is formed, which also has excellent plugging performance, higher economy, and better construction reliability, solving the limitations of traditional simple physical compound plugging materials.

[0004] This invention discloses a method for preparing a composite plugging material with a core-shell structure, comprising the following steps:

[0005] Step S1: The polyhydroxy aromatic compound, tetramethylammonium chloride and water were placed in a three-necked flask and heated to 80°C under nitrogen protection. Then, epichlorohydrin was slowly added dropwise and the mixture was stirred for 1-3 hours. After the reaction was completed, the mixture was cooled to 40°C. The pH was adjusted to 8-10 using a 20% sodium hydroxide solution and the mixture was stirred for another 2-4 hours. After the reaction was completed, 20% acetic acid was added to adjust the pH to neutral. The organic phase was collected by extraction with dichloromethane multiple times. The organic phase was washed multiple times with sodium chloride solution and then n-hexane was added. The precipitate was collected and extracted with tetrahydrofuran to obtain aromatic compound A.

[0006] Step S2: The aromatic compound of dopamine, triphenylphosphine, chloroform, and benzene were refluxed and stirred at 85℃~95℃ for 1.5h~3h. After the reaction was completed, the mixture was cooled to room temperature. Sodium azide, tetrabutylammonium sulfate, and acetonitrile were added sequentially under stirring. The mixture was refluxed and stirred at 80℃~85℃ for 2h~4h. After the reaction was completed, the mixture was transferred to water. The organic phase was collected by multiple extractions with benzene and dried with magnesium sulfate. The organic phase and triethyl phosphite were then added to a beaker. The pH was adjusted to 1~2 with hydrochloric acid and stirred at room temperature for 30min~60min. After the reaction was completed, the pH was adjusted to neutral, the organic phase was collected, and dried to obtain aromatic compound B.

[0007] Step S3: Melt aromatic compounds A and B separately by heating, mix and stir until no bubbles are present, then transfer the mixture to a mold, dry and heat to 80℃~110℃, cure for 10h~12h, cool to room temperature and demold, and crush the demolded product into small particles to obtain epoxy resin particles C.

[0008] Step S4: Dissolve aromatic compound A and monoamino aromatic compound in alkoxy alcohol, and stir the reaction at 120℃~130℃ for 4h~5h under nitrogen protection. After the reaction is completed, cool to room temperature, transfer the reaction solution to anhydrous ethanol and stir until the supernatant is clear. Collect the resulting gel and dry the gel under vacuum at 100℃ for 12h~14h. After cooling to room temperature, collect the product and crush it into thermoplastic particles D.

[0009] Step S5: Adjust the pH of (3-glycidyl ether oxypropyl)trimethoxysilane, anhydrous ethanol and deionized water to 4-5 with acetic acid, stir at room temperature for at least 1 hour to obtain a mixed solution, then spray the mixed solution evenly on the surface of epoxy resin particles C, and vacuum dry at 100℃-120℃ for 0.5-1 hour to obtain the treated epoxy resin particles C.

[0010] Step S6: After heating the thermoplastic particles D to a fluid state, slowly add them to a high-speed mixer containing preheated epoxy resin particles C for mixing. Collect the coated mixture and cool it to room temperature to obtain a composite sealing material with a core-shell structure.

[0011] In one embodiment of the present invention, the polyhydroxy aromatic compound in step S1 is one of 3-[(3-hydroxyphenyl)methyl]phenol, 4-[(3-hydroxyphenyl)methyl]phenol, and 3-hydroxy-α-(3-hydroxyphenyl)benzyl alcohol;

[0012] The polyol aromatic compound mentioned in step S2 is one of [1,1'-biphenyl]-4,4'-diethanol, [1,1'-biphenyl]-2,4'-diethanol, and 3'-(hydroxymethyl)[1,1'-biphenyl]-3-propanol;

[0013] The monoamino aromatic compound mentioned in step S4 is one of 4-ethylaniline, 3-ethylaniline, and 3-methylaniline;

[0014] The alkoxy alcohol mentioned in step S4 is one of 2-isopropoxyethanol, 3-methoxy-1-butanol, and 2-propanediol-1-monoethyl ether;

[0015] The aromatic compound A has a mass fraction of 40% to 50% in the alkoxy alcohol solution.

[0016] In one embodiment of the present invention, the molar ratio of the polyhydroxy aromatic compound to epichlorohydrin in step S1 is 1:1 to 5, and the molar ratio of the polyhydroxy aromatic compound to tetramethylammonium chloride is 1:0.001 to 0.006.

[0017] In one embodiment of the present invention, in step S2, the molar ratio of the primary alcohol aromatic compound to triphenylphosphine, sodium azide, chloroform bromotrichloromethane, and benzene is 1:1:2 to 2.05:1:1, and the molar ratio of the primary alcohol aromatic compound to tetrabutylammonium hydrogen sulfate is 1:0.002 to 0.02.

[0018] The molar ratio of triethyl phosphite to dopamine aromatic compound is 1~2:1.

[0019] In one embodiment of the present invention, the molar ratio of aromatic compound A to aromatic compound B in the mixture in step S3 is 2~3:1;

[0020] The particle size range of the epoxy resin particles C is 6~120 mesh.

[0021] In one embodiment of the present invention, the molar ratio of aromatic compound A to monoamino aromatic compound in step S4 is 1:1 to 1.5.

[0022] In one embodiment of the present invention, the volume ratio of (3-glycidyl ether oxypropyl)trimethoxysilane, anhydrous ethanol, and deionized water in the mixed solution in step S5 is 2:20:1.

[0023] In one embodiment of the present invention, the mass ratio of the thermoplastic particles D to the treated epoxy resin particles C in step S6 is 1:3~4.

[0024] And composite plugging materials with core-shell structures prepared using the above method.

[0025] In addition, the present invention also discloses a water-based drilling fluid, the raw material components of which include the above-mentioned composite plugging material with core-shell structure. By weight, the water-based drilling fluid includes the following components: 100 parts water, 5-7 parts bentonite, 0.4-0.8 parts sodium hydroxide, 3-5 parts sulfomethylphenol resin SMP-3, 2-4 parts emulsified asphalt, 2-4 parts sodium chloride, 2-5 parts potassium chloride, 50-135 parts barite, and the remaining components of the composite plugging material with core-shell structure.

[0026] The core-shell structured composite plugging material is composed of particles with four particle size ranges: 6-10 mesh, 10-18 mesh, 18-35 mesh, and 35-100 mesh. The amount of each of the four particle size ranges is equivalent to 1%-3% of the total weight of the other components, as well as the core-shell structured composite plugging material prepared according to the above method.

[0027] The technical effects of this invention are as follows:

[0028] The core-shell structured plugging material prepared in this invention has a core portion made of thermosetting resin with a compressive strength exceeding 150 MPa, which is stronger than that of ordinary rigid granular materials, and also exhibits good thermal stability and high-temperature resistance. The shell portion is made of thermoplastic resin, which is a rigid particle at room temperature. However, in high-temperature and high-pressure formations, it softens at its temperature and transforms from a glassy state to a highly elastic state, possessing elastic deformation capabilities. This reduces the slippage effect between particles during the plugging process of complex cracks, and the deformation of the shell portion allows the plugging particles to better bridge and seal, forming a denser sealing layer, thereby increasing the pressure-bearing capacity. Attached Figure Description

[0029] Figure 1 This is a SEM image of the core-shell structured composite resin plugging material prepared in Example 2 of the present invention.

[0030] Figure 2 This is an analysis diagram of the glass transition temperature of the plugging material prepared in Example 1 of the present invention;

[0031] Figure 3This is an analysis diagram of the glass transition temperature of the plugging material prepared in Example 2 of the present invention;

[0032] Figure 4 This is an analysis diagram of the glass transition temperature of the plugging material prepared in Example 3 of the present invention. Detailed Implementation

[0033] The present invention will be further described in detail below with reference to the embodiments. However, the implementation of the present invention is not limited thereto. Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods, and the materials and reagents used are commercially available unless otherwise specified.

[0034] Example 1:

[0035] S1. 0.1 mol of 3-[(3-hydroxyphenyl)methyl]phenol, 0.0004 mol of tetramethylammonium chloride, and 50 mL of water were added to a three-necked flask. Nitrogen gas was introduced, and the mixture was heated to 80 °C under nitrogen atmosphere. Then, 0.135 mol of epichlorohydrin was slowly added dropwise to the reaction system using a dropping funnel, and the reaction was stirred for 2 h. After the reaction was complete, the mixture was cooled to 40 °C, and a 20% sodium hydroxide solution was added to adjust the pH to 9. The reaction was continued for 3 h. After the reaction was complete, 20% acetic acid was added to neutralize the mixture, and the organic phase was collected by extraction with dichloromethane multiple times. The organic phase was washed multiple times with sodium chloride solution, and then n-hexane was added to collect the precipitate. The precipitate was extracted with tetrahydrofuran to obtain aromatic compound A.

[0036] S2. 0.1 mol of [1,1'-biphenyl]-4,4'-diethanol, 0.1 mol of triphenylphosphine, 0.1 mol of chloroform, and 0.1 mol of benzene were added to a three-necked flask and stirred under reflux at 90 °C for 2 h. After the reaction was complete, the mixture was cooled to room temperature, and 0.203 mol of sodium azide and 0.0014 mol of tetrabutylammonium hydrogen sulfate were added sequentially, along with 50 mL of acetonitrile as a solvent. The mixture was stirred under reflux at 80 °C for 3 h. After the reaction was complete, the mixture was transferred to water, and the organic phase was collected by multiple extractions with benzene and dried with magnesium sulfate. The organic phase was then added to a beaker with 0.15 mol of triethyl phosphite, and the pH was adjusted to 2 with hydrochloric acid. The mixture was stirred at room temperature for 45 min. After the reaction was complete, the pH was adjusted to 7, the organic phase was collected, and dried to obtain aromatic compound B.

[0037] S3. Heat 0.05 mol of aromatic compound A and 0.02 mol of aromatic compound B to melt, mix and stir until no bubbles are present, then transfer the mixture to a mold, dry and heat to 100°C, and cure for 11 hours. After cooling to room temperature, demold and crush the demolded product into small particles in the range of 6 mesh to 120 mesh to obtain epoxy resin particles C.

[0038] S4. Add 0.05 mol of aromatic compound A, 0.065 mol of 4-ethylaniline and 8.62 mL of 2-isopropoxyethanol (aromatic compound A accounts for 45% of the total mass of the alkoxy alcohol solution) to a three-necked flask. Stir and react at 125 °C for 4 h under nitrogen protection. After the reaction is completed, cool to room temperature and transfer the reaction solution to sufficient anhydrous ethanol. Stir until the supernatant is clear. Pour off all the supernatant and vacuum dry the gel at 100 °C for 13 h. After cooling to room temperature, collect the product and crush it into thermoplastic particles D.

[0039] S5. Add 10 mL of (3-glycidyl ether oxypropyl)trimethoxysilane, 100 mL of anhydrous ethanol and 5 mL of deionized water to an Erlenmeyer flask, adjust the pH to 5 with acetic acid, stir at room temperature for 1 h to obtain a mixed solution, then spray the mixed solution evenly on the surface of epoxy resin particles C, and vacuum dry at 110 °C for 1 h to obtain the treated epoxy resin particles C.

[0040] S6. After heating 3g of thermoplastic granules D to a fluid state, slowly add them to a high-speed mixer containing 9g of preheated epoxy resin granules C for mixing. Collect the coated mixture and cool it to room temperature to obtain a composite sealing material with a core-shell structure.

[0041] Example 2:

[0042] S1. 0.1 mol of 3-hydroxy-α-(3-hydroxyphenyl)benzyl alcohol, 0.0006 mol of tetramethylammonium chloride, and 50 mL of water were added to a three-necked flask. Nitrogen gas was introduced, and the mixture was heated to 80 °C under nitrogen atmosphere. Then, 0.15 mol of epichlorohydrin was slowly added dropwise to the reaction system using a dropping funnel, and the reaction was stirred for 3 h. After the reaction was complete, the mixture was cooled to 40 °C, and a 20% sodium hydroxide solution was added to adjust the pH to 9. The reaction was continued to be stirred for 4 h. After the reaction was complete, 20% acetic acid was added to neutralize the mixture, and the organic phase was collected by extraction with dichloromethane multiple times. The organic phase was washed multiple times with sodium chloride solution, and then n-hexane was added to collect the precipitate. The precipitate was extracted with tetrahydrofuran to obtain aromatic compound A.

[0043] S2. 0.15 mol of 3'-(hydroxymethyl)[1,1'-biphenyl]-3-propanol, 0.15 mol of triphenylphosphine, 0.15 mol of chloroform, and 0.15 mol of benzene were added to a three-necked flask and stirred under reflux at 90 °C for 3 h. After the reaction was complete, the mixture was cooled to room temperature, and 0.3075 mol of sodium azide and 0.003 mol of tetrabutylammonium bisulfate were added sequentially, along with 50 mL of acetonitrile as a solvent. The mixture was stirred under reflux at 85 °C for 4 h. After the reaction was complete, the mixture was transferred to water, and the organic phase was collected by multiple extractions with benzene and dried with magnesium sulfate. The organic phase and 0.3 mol of triethyl phosphite were then added to a beaker, and the pH was adjusted to 2 with hydrochloric acid. The mixture was stirred at room temperature for 50 min. After the reaction was complete, the pH was adjusted to 7, the organic phase was collected, and dried to obtain aromatic compound B.

[0044] S3. Heat 0.06 mol of aromatic compound A and 0.02 mol of aromatic compound B to melt, mix and stir until no bubbles are present, then transfer the mixture to a mold, dry and heat to 110°C, and cure for 12 hours. After cooling to room temperature, demold and crush the demolded product into small particles in the range of 6 mesh to 120 mesh to obtain epoxy resin particles C.

[0045] S4. Add 0.06 mol of aromatic compound A, 0.09 mol of 3-methylaniline and 13.81 mL of 3-methoxy-1-butanol (aromatic compound A accounts for 50% of the total mass of the alkoxy alcohol solution) to a three-necked flask. Stir and react at 130 °C for 5 h under nitrogen protection. After the reaction is completed, cool to room temperature and transfer the reaction solution to anhydrous ethanol. Stir until the supernatant is clear. Pour off all the supernatant and vacuum dry the gel at 100 °C for 14 h. After cooling to room temperature, collect the product and crush it into thermoplastic particles D.

[0046] S5. Add 12 mL of (3-glycidyl ether oxypropyl)trimethoxysilane, 120 mL of anhydrous ethanol and 6 mL of deionized water to an Erlenmeyer flask, adjust the pH to 5 with acetic acid, stir at room temperature for 1 h to obtain a mixed solution, then spray the mixed solution evenly on the surface of epoxy resin particles C, and vacuum dry at 120 °C for 1 h to obtain the treated epoxy resin particles C.

[0047] S6. After heating 3.5g of thermoplastic granules D to a fluid state, slowly add them to a high-speed mixer containing 14g of preheated epoxy resin granules C for mixing. Collect the coated mixture and cool it to room temperature to obtain a core-shell structured composite sealing material. The specific SEM analysis results are as follows: Figure 1 As shown.

[0048] Example 3:

[0049] S1. 0.1 mol of 3-hydroxy-α-(3-hydroxyphenyl)benzyl alcohol, 0.0001 mol of tetramethylammonium chloride, and 50 mL of water were added to a three-necked flask. Nitrogen gas was introduced, and the mixture was heated to 80 °C under nitrogen atmosphere. Then, 0.12 mol of epichlorohydrin was slowly added dropwise to the reaction system using a dropping funnel, and the reaction was stirred for 2 h. After the reaction was complete, the mixture was cooled to 40 °C, and a 20% sodium hydroxide solution was added to adjust the pH to 9. The reaction was continued for 2 h. After the reaction was complete, 20% acetic acid was added to neutralize the solution, and the organic phase was collected by extraction with dichloromethane multiple times. The organic phase was washed multiple times with sodium chloride solution, and then n-hexane was added to collect the precipitate. The precipitate was extracted with tetrahydrofuran to obtain aromatic compound A.

[0050] S2. 0.12 mol [1,1'-biphenyl]-2,4'-diethanol, 0.12 mol triphenylphosphine, 0.12 mol chloroform, and 0.12 mol benzene were added to a three-necked flask and stirred under reflux at 85°C for 1.5 h. After the reaction was complete, the mixture was cooled to room temperature, and 0.24 mol sodium azide and 0.0012 mol tetrabutylammonium bisulfate were added sequentially, along with 50 mL acetonitrile as a solvent. The mixture was stirred under reflux at 80°C for 2 h. After the reaction was complete, the mixture was transferred to water, and the organic phase was collected by multiple extractions with benzene and dried with magnesium sulfate. The organic phase was then added to a beaker with 0.12 mol triethyl phosphite, and the pH was adjusted to 2 with hydrochloric acid. The mixture was stirred at room temperature for 30 min. After the reaction was complete, the pH was adjusted to 7, the organic phase was collected, and dried to obtain aromatic compound B.

[0051] S3. Heat and melt 0.04 mol of aromatic compound A and 0.02 mol of aromatic compound B respectively, mix and stir until no bubbles are present, then transfer the mixture to a mold, dry and heat to 90°C, and cure for 10 hours. After cooling to room temperature, demold and crush the demolded product into small particles in the range of 6 mesh to 120 mesh to obtain epoxy resin particles C.

[0052] S4. Add 0.04 mol of aromatic compound A, 0.044 mol of 3-ethylaniline and 19.8 mL of 2-propanediol-1-monoethyl ether (aromatic compound A accounts for 40% of the total mass of the alkoxy alcohol solution) to a three-necked flask. Stir the mixture at 120 °C for 4 h under nitrogen protection. After the reaction is complete, cool to room temperature and transfer the reaction solution to anhydrous ethanol. Stir until the supernatant is clear. Pour off all the supernatant and vacuum dry the gel at 100 °C for 12 h. After cooling to room temperature, collect the product and crush it into thermoplastic particles D.

[0053] S5. Add 10 mL of (3-glycidyl ether oxypropyl)trimethoxysilane, 100 mL of anhydrous ethanol and 5 mL of deionized water to an Erlenmeyer flask, adjust the pH to 5 with acetic acid, stir at room temperature for 1 h to obtain a mixed solution, then spray the mixed solution evenly on the surface of epoxy resin particles C, and vacuum dry at 100 °C for 0.5 h to obtain the treated epoxy resin particles C.

[0054] S6. After heating 2.5g of thermoplastic granules D to a fluid state, slowly add them to a high-speed mixer containing 7.5g of preheated epoxy resin granules C for mixing. Collect the coated mixture and cool it to room temperature to obtain a composite sealing material with a core-shell structure.

[0055] Example 4:

[0056] Measure 400 mL of water and pour it into a high-speed stirring cup. Place the high-speed stirring cup on a high-speed mixer and stir at 12000 rpm. Weigh 22.0 g of bentonite and slowly add it to the high-speed stirring cup and stir for 10 min. Then, add 2.4 g of sodium hydroxide and stir for 10 min, 16 g of sulfomethylphenol resin SMP-3 and stir for 15 min, 12 g of emulsified asphalt and stir for 10 min, 12 g of NaCl and stir for 10 min, 16 g of KCl and stir for 10 min, and 380 g of ultrafine calcium carbonate and stir for 30 min. Prepare the base slurry by mixing the other components except for the core-shell structure of the composite plugging material.

[0057] Next, composite plugging material particles with core-shell structures and four particle size ranges were added to the base slurry and mixed for 20 minutes to obtain a water-based drilling fluid system. The particle size ranges of the core-shell structured composite resin plugging material are shown in Table 1.

[0058] Table 1. Particle size range of core-shell structured composite resin plugging materials

[0059]

[0060] In this embodiment, the core-shell structured composite resin plugging material that constitutes the water-based drilling fluid system is the product of Example 1. The plugging materials with different particle sizes can be obtained by crushing as needed according to the steps in Example 1. The proportion of particles of different particle sizes relative to the total weight of other components is 3%A+3%B+2%C+1%D.

[0061] Example 5:

[0062] In this embodiment, the base slurry was prepared using the same method and dosage as in Example 4. The product from Example 1 was mixed with the base slurry for 20 minutes to obtain a water-based drilling fluid system. The ratio of particles of different particle sizes of the product to the total weight of other components was 3%A+3%B+2%C+2%D.

[0063] Example 6:

[0064] In this embodiment, the base slurry was prepared using the same method and dosage as in Example 4. The product from Example 2 was mixed with the base slurry for 20 minutes to obtain a water-based drilling fluid system. The proportion of particles of different particle sizes of the product relative to the total weight of other components was 3%A+3%B+2%C+1%D.

[0065] Example 7:

[0066] In this embodiment, the base slurry was prepared using the same method and dosage as in Example 4. The product from Example 2 was mixed with the base slurry for 20 minutes to obtain a water-based drilling fluid system. The ratio of particles of different particle sizes of the product to the total weight of other components was 3%A+3%B+2%C+2%D.

[0067] Example 8:

[0068] In this embodiment, the base slurry was prepared using the same method and dosage as in Example 4. The product from Example 3 was mixed with the base slurry for 20 minutes to obtain a water-based drilling fluid system. The proportion of particles of different particle sizes of the product relative to the total weight of other components was 3%A+3%B+2%C+1%D.

[0069] Example 9:

[0070] In this embodiment, the base slurry was prepared using the same method and dosage as in Example 4. The product from Example 3 was mixed with the base slurry for 20 minutes to obtain a water-based drilling fluid system. The ratio of particles of different particle sizes of the product to the total weight of other components was 3%A+3%B+2%C+2%D.

[0071] Comparative Example 1:

[0072] Comparative experiments were conducted using GZD plugging materials with non-core-shell rigid mineral particles that had undergone particle size screening. Four particle size ranges were used, corresponding to four grades: GZD-A, GZD-B, GZD-C, and GZD-D. The specific particle size ranges are shown in Table 2.

[0073] Table 2. Particle size range of rigid mineral particle GZD plugging material

[0074]

[0075] Four types of rigid mineral particles (GZD plugging material) with different particle sizes were added to a base slurry prepared using the same method and dosage as in Example 4 and mixed for 20 minutes to obtain a water-based drilling fluid system. The proportion of the different particle sizes of the GZD plugging material relative to the total weight of the other components in Example 4 was 3% GZD-A + 3% GZD-B + 2% GZD-C + 1% GZD-D.

[0076] Comparative Example 2:

[0077] Four types of rigid mineral particles (GZD plugging material) with different particle sizes were added to a base slurry prepared using the same method and dosage as in Example 4 and mixed for 20 minutes to obtain a water-based drilling fluid system. The proportion of the different particle sizes of the GZD plugging material relative to the total weight of the other components in Example 4 was 3% GZD-A + 3% GZD-B + 2% GZD-C + 2% GZD-D.

[0078] Performance Evaluation

[0079] I. Testing the glass transition temperature of composite sealing materials

[0080] The composite sealing materials prepared in Examples 1-3 were sampled and their glass transition temperatures were tested. The composite sealing materials in each example were pulverized into a uniform fine powder for later use. A crucible containing the composite sealing material was placed in the test area to test the glass transition temperature. The testing instrument was a HITACHI STA200, the temperature program was set to a temperature scan with a heating rate of 10℃ / min, and nitrogen was used as the test gas atmosphere. The test results for Examples 1-3 are as follows: Figures 2-4 As shown, the glass transition temperatures of each embodiment are also shown in Table 3:

[0081] Table 3 Glass transition temperatures of composite sealing materials

[0082]

[0083] Depend on Figures 2-4 As shown in Table 3, the glass transition temperature of the composite sealing material is between 116 and 138°C. In high-temperature strata, it transforms from a glassy state (hard and brittle, with frozen molecular chains) to a highly elastic state (flexible, with segmented molecular chains). This facilitates the stable "bridging" of the core-shell structured composite resin sealing material in complex cracks, reduces the slippage of sealing particles, and forms a tight-sealed sealing layer.

[0084] II. Compression Resistance Test

[0085] The final products from Examples 1 to 3 were sampled for compressive strength testing, with three sets of samples taken for each material. The compression test followed the ASTM D6641 method for composite material compression testing. Two strain gauges, one longitudinal and one transverse, were attached to each of the front and rear surfaces of the test specimen to obtain the average compressive strain and Poisson's ratio on both surfaces. An Instron 5882 testing machine (range 100 kN) was used with a combined loading compression fixture (CLC) to apply compressive load to the test specimen. The average compressive strength of the three sets of samples was measured, and the specific results are shown in Table 4.

[0086] Table 4. Compressive strength test of composite sealing materials

[0087]

[0088] As can be seen from the data in Table 4, the core-thermosetting resin molecular structure of the composite resin sealing material is rigid and has a high compressive strength, with an average compressive strength of about 170 MPa.

[0089] III. Crack Sealing Performance Test

[0090] Water-based drilling fluid systems from Examples 4 to 9 were used in fracture plugging experiments at 150°C. Based on these experiments, the proportions of different particle sizes in the formulation were adjusted for comparative testing. The simulated core samples used in the plugging experiments had vertical fractures of 10 cm in length and 3 mm to 4 mm in width, and the fractures were wedge-shaped. The experimental results are shown in Tables 3 to 5.

[0091] Table 3. Crack sealing performance test results of Examples 4 and 5

[0092]

[0093] Table 4. Crack sealing performance test results of Examples 6 and 7

[0094]

[0095] Table 5. Crack sealing performance test results of Examples 8 and 9

[0096]

[0097] Based on the results in Tables 3-5, the sealing effect of Example 4 was as follows: the sealing layer was 2.6 cm from the inlet (3 mm) and 6.2 cm from the outlet (4 mm), with a blockage position of 2.6-6.2 cm. The sealing effect of Example 5 was as follows: the sealing layer was 0.9 cm from the inlet (3 mm) and 8.0 cm from the outlet (4 mm), with a blockage position of 0.9-8.0 cm. The sealing effect of Example 6 was as follows: the sealing layer was 1.2 cm from the inlet (3 mm) and 7.4 cm from the outlet (4 mm), with a blockage position of 1.2-7.4 cm. The sealing effect of Example 7 was as follows: the sealing layer was 0.4 cm from the inlet (3 mm) and 8.8 cm from the outlet (4 mm), with a blockage position of 0.4-8.8 cm. cm; The sealing effect of Example 8 is that the sealing layer is 2.9 cm away from the inlet (3 mm) and 6.0 cm away from the outlet (4 mm), and the sealing layer is blocked at a distance of 2.9~6.0 cm; The sealing effect of Example 9 is that the sealing layer is 0.7 cm away from the inlet (3 mm) and 8.1 cm away from the outlet (4 mm), and the sealing layer is blocked at a distance of 0.7~8.1 cm.

[0098] The experimental results above show that the sealing effect of the drilling fluid improves with the increase of the amount of plugging material. When the concentration of plugging particles A and B is increased to 3% by mass relative to the base slurry, the large plugging particles A and B can effectively bridge the fractures. With the increase of small plugging particles C and D, the plugging particles, due to their combination of elastic deformation and rigidity, can better fill the fractures and form a stable sealing layer that can withstand a pressure of 13.5 MPa.

[0099] In addition, comparative examples 1 and 2 were also tested for crack sealing performance using the same performance testing methods described above. The specific results are shown in Table 6.

[0100] Table 6. Crack sealing performance test results of Comparative Examples 1 and 2

[0101]

[0102] As shown in Table 6, the plugging experiment results of Comparative Example 1 indicate that when the pressure increased to 10 MPa, all drilling fluid was lost, and no stable plugging layer was formed. The plugging experiment results of Comparative Example 2 indicate that when the pressure increased to 12 MPa, all drilling fluid was lost, and no stable plugging layer was formed. Examples 4-9 all formed a stable plugging layer at a maximum pressure of 13.5 MPa. In Comparative Examples 1 and 2, before the pressure reached 13.5 MPa, all drilling fluid was lost, and no stable plugging layer was formed. Therefore, it is evident that the core-shell structured composite resin plugging material, compared to uncoated rigid particles, exhibits less drilling fluid loss and superior plugging effect at the same dosage, and can form a stable plugging layer at a pressure of 13.5 MPa.

[0103] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the embodiments of the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be defined by the scope of the claims.

Claims

1. A method for preparing a composite plugging material with a core-shell structure, characterized in that, Includes the following steps: Step S1: The polyhydroxy aromatic compound, tetramethylammonium chloride and water were placed in a three-necked flask and heated to 80°C under nitrogen protection. Then, epichlorohydrin was slowly added dropwise and the mixture was stirred for 1-3 hours. After the reaction was completed, the mixture was cooled to 40°C. The pH was adjusted to 8-10 using a 20% sodium hydroxide solution and the mixture was stirred for another 2-4 hours. After the reaction was completed, 20% acetic acid was added to adjust the pH to neutral. The organic phase was collected by extraction with dichloromethane multiple times. The organic phase was washed multiple times with sodium chloride solution and then n-hexane was added. The precipitate was collected and extracted with tetrahydrofuran to obtain aromatic compound A. Step S2: The aromatic compound of dopamine, triphenylphosphine, chloroform, and benzene were refluxed and stirred at 85℃~95℃ for 1.5h~3h. After the reaction was completed, the mixture was cooled to room temperature. Sodium azide, tetrabutylammonium sulfate, and acetonitrile were added sequentially under stirring. The mixture was refluxed and stirred at 80℃~85℃ for 2h~4h. After the reaction was completed, the mixture was transferred to water. The organic phase was collected by multiple extractions with benzene and dried with magnesium sulfate. The organic phase and triethyl phosphite were then added to a beaker. The pH was adjusted to 1~2 with hydrochloric acid and stirred at room temperature for 30min~60min. After the reaction was completed, the pH was adjusted to neutral, the organic phase was collected, and dried to obtain aromatic compound B. Step S3: Melt aromatic compounds A and B separately by heating, mix and stir until no bubbles are present, then transfer the mixture to a mold, dry and heat to 80℃~110℃, cure for 10h~12h, cool to room temperature and demold, and crush the demolded product into small particles to obtain epoxy resin particles C. Step S4: Dissolve aromatic compound A and monoamino aromatic compound in alkoxy alcohol, and stir the reaction at 120℃~130℃ for 4h~5h under nitrogen protection. After the reaction is completed, cool to room temperature, transfer the reaction solution to anhydrous ethanol and stir until the supernatant is clear. Collect the resulting gel and dry the gel under vacuum at 100℃ for 12h~14h. After cooling to room temperature, collect the product and crush it into thermoplastic particles D. Step S5: Adjust the pH of (3-glycidyl ether oxypropyl)trimethoxysilane, anhydrous ethanol and deionized water to 4-5 with acetic acid, stir at room temperature for at least 1 hour to obtain a mixed solution, then spray the mixed solution evenly on the surface of epoxy resin particles C, and vacuum dry at 100℃-120℃ for 0.5-1 hour to obtain the treated epoxy resin particles C. Step S6: After heating the thermoplastic particles D to a fluid state, slowly add them to a high-speed mixer containing preheated epoxy resin particles C for mixing. Collect the coated mixture and cool it to room temperature to obtain a composite sealing material with a core-shell structure. The polyhydroxy aromatic compound mentioned in step S1 is one of 3-[(3-hydroxyphenyl)methyl]phenol, 4-[(3-hydroxyphenyl)methyl]phenol, and 3-hydroxy-α-(3-hydroxyphenyl)benzyl alcohol; The polyol aromatic compound mentioned in step S2 is one of [1,1'-biphenyl]-4,4'-diethanol, [1,1'-biphenyl]-2,4'-diethanol, and 3'-(hydroxymethyl)[1,1'-biphenyl]-3-propanol; The monoamino aromatic compound mentioned in step S4 is one of 4-ethylaniline, 3-ethylaniline, and 3-methylaniline; The alkoxy alcohol mentioned in step S4 is one of 2-isopropoxyethanol, 3-methoxy-1-butanol, and 2-propanediol-1-monoethyl ether; The aromatic compound A has a mass fraction of 40% to 50% in the alkoxy alcohol solution.

2. The method for preparing a composite plugging material with a core-shell structure according to claim 1, characterized in that: In step S1, the molar ratio of the polyhydroxy aromatic compound to epichlorohydrin is 1:1 to 5, and the molar ratio of the polyhydroxy aromatic compound to tetramethylammonium chloride is 1:0.001 to 0.

006.

3. The method for preparing a composite plugging material with a core-shell structure according to claim 1, characterized in that: In step S2, the molar ratio of the primary alcohol aromatic compound to triphenylphosphine, sodium azide, chloroform bromo, and benzene is 1:1:2 to 2.05:1:1, and the molar ratio of the primary alcohol aromatic compound to tetrabutylammonium hydrogen sulfate is 1:0.002 to 0.

02. The molar ratio of triethyl phosphite to dopamine aromatic compound is 1~2:

1.

4. The method for preparing a composite plugging material with a core-shell structure according to claim 1, characterized in that: In step S3, the molar ratio of aromatic compound A to aromatic compound B in the mixture is 2~3:1; The particle size range of the epoxy resin particles C is 6~120 mesh.

5. The method for preparing a composite plugging material with a core-shell structure according to claim 1, characterized in that: In step S4, the molar ratio of aromatic compound A to monoamino aromatic compound is 1:1 to 1.

5.

6. The method for preparing a composite plugging material with a core-shell structure according to claim 1, characterized in that: In step S5, the volume ratio of (3-glycidyl ether oxypropyl)trimethoxysilane, anhydrous ethanol, and deionized water in the mixed solution is 2:20:

1.

7. The method for preparing a composite plugging material with a core-shell structure according to claim 1, characterized in that: In step S6, the mass ratio of the thermoplastic particles D to the treated epoxy resin particles C is 1:3~4.

8. A composite sealing material with a core-shell structure, characterized in that, Prepared using the method described in any one of claims 1 to 7.

9. A water-based drilling fluid, characterized in that, The raw material components include the core-shell structured composite plugging material as described in claim 8. By weight, the water-based drilling fluid includes the following components: 100 parts water, 5-7 parts bentonite, 0.4-0.8 parts sodium hydroxide, 3-5 parts sulfomethylphenol resin SMP-3, 2-4 parts emulsified asphalt, 2-4 parts sodium chloride, 2-5 parts potassium chloride, 50-135 parts barite, and the remaining components of the core-shell structured composite plugging material. The core-shell structured composite plugging material is composed of particles with four particle size ranges: 6-10 mesh, 10-18 mesh, 18-35 mesh, and 35-100 mesh. The amount of each of the four particle size ranges is equivalent to 1% to 3% of the total weight of the other components.

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