Surface modified nano-SiO2-based core-shell structure gel microsphere and preparation method thereof

Abstract

The invention discloses a core-shell structure gel microsphere based on surface modified nano-SiO2 and a preparation method of the core-shell structure gel microsphere, and belongs to the field of oilfield chemistry. The preparation method of the surface-modified nano-SiO2-based core-shell structure gel microspheres comprises the following steps: sequentially weighing 20-30 parts by weight of tannic acid, 5-10 parts by weight of acrylic acid, 10-20 parts by weight of nano-SiO2, 0.5-1 part by weight of a silane coupling agent and 100-150 parts by weight of water, firstly grafting functional groups on the surface of nano-SiO2 through the silane coupling agent to enhance the compatibility of the nano-SiO2, and then adding the surface-modified nano-SiO2-based core-shell structure gel microspheres into the silane coupling agent to prepare the surface-modified nano-SiO2-based core-shell structure gel microspheres. And preparing the gel microsphere with a core-shell structure by an inverse emulsion polymerization method, the core part is formed by crosslinking tannic acid and acrylic acid, and the shell part is composed of modified nano-SiO2. The gel microspheres prepared by the technical scheme have high strength, high adhesion and high-temperature salt resistance (the temperature resistance can reach 180 DEG C, and the salt resistance can reach 24%), can effectively block microcracks in drilling operation and improve drilling efficiency, are particularly suitable for the problem of well leakage under complex formation conditions, and have remarkable technical advantages.

Description

Technical Field

[0001] The invention discloses a core-shell structure gel microsphere based on surface modified nano-SiO2 and a preparation method thereof, belonging to the field of oilfield chemistry. Background Art

[0002] In the oil drilling process, the problem of lost circulation is one of the main factors affecting drilling efficiency and cost. Lost circulation refers to the leakage of drilling fluid into the surrounding rock formations through leakage channels such as cracks in the well wall or pores in the formation, which causes complex drilling problems and well wall instability, affecting the smooth progress of drilling operations. Especially when drilling into microcracks and fractured formations, the problem of lost circulation becomes more serious, which in turn affects the drilling speed, increases costs and increases risks. Therefore, the research and development of plugging materials with good plugging performance and the ability to effectively cope with complex formation conditions has become a technical problem that needs to be solved urgently in the field of oil drilling.

[0003] Traditional plugging materials, such as granular rigid plugging agents and expandable plugging agents, can reduce the occurrence of well leakage to a certain extent, but most of them have shortcomings such as low plugging efficiency, poor plugging effect, poor adhesion between plugging agents and well walls, and poor high-temperature stability. Under some complex formation conditions, especially high-temperature and high-salt environments, the effect of traditional plugging agents is often not ideal, resulting in the problem of well leakage still not being effectively solved.

[0004] In recent years, core-shell structured gel microspheres, as a new type of plugging material, have gradually become a research hotspot due to their high strength, good expansion and stability. Core-shell structured gel microspheres can expand after encountering water, plugging the microcracks and pores in the formation, thereby improving the plugging efficiency. However, although the existing core-shell gel microspheres can improve the plugging effect in theory, they still face some problems in practical applications. For example, the existing gel microspheres have poor adhesion and cannot effectively adhere to the surface of the fractures in the formation, resulting in poor plugging effect; in addition, their expansion performance and stability in high temperature and high salt environments are often limited, and cannot meet the application requirements of deep wells or complex formations.

[0005] To solve the above problems, the present invention proposes a core-shell structure gel microsphere based on surface modified nano-SiO2. The microsphere strengthens its mechanical strength and stability through the combination of nano-SiO2 and surface modifier, and can maintain its expansibility for a long time under high temperature and high pressure conditions. In addition, by introducing phenolic monomers such as tannic acid and acrylic acid, not only the expansibility of the gel microsphere is improved, but also its adhesion is optimized, ensuring that it can effectively adhere to the cracks in the well wall to form a durable plugging layer. More importantly, the gel microsphere of the present invention still maintains good expansion performance in a high-salt environment, overcoming the problem of reduced expansion of traditional materials in salt water, thereby achieving excellent plugging effect under complex formation conditions. The gel microsphere of the present invention has high strength, good expansibility and high temperature stability, can effectively perform well wall plugging for a long time in complex drilling environments such as high temperature, high salt and high pressure, significantly improves drilling efficiency and reduces operational risks, overcomes the shortcomings of existing plugging materials under complex formation conditions, and has broad application prospects and significant technical advantages. Summary of the invention

[0006] The present invention provides a core-shell structure gel microsphere based on surface modified nano-SiO2 and a preparation method thereof, aiming to solve the problems of poor plugging effect and poor expansion performance of existing drilling fluid plugging materials under high temperature, high salt, micro-cracks and complex formation conditions. The gel microsphere is designed with a precise core-shell structure, combined with high strength, good expansion and excellent adhesion, and can maintain a stable plugging effect in a high temperature and high salt environment while improving the plugging efficiency.

[0007] In order to prepare core-shell structure gel microspheres based on surface modified nano-SiO2, the first aspect of the present invention provides a preparation method, which comprises:

[0008] (1) mixing a silane coupling agent and nano-SiO2 in an aqueous solvent, contacting them in an acidic environment, and performing a first reaction to obtain a surface-modified nano-SiO2 mixed solution, dispersing them to obtain a modified silicon dioxide dispersion, and drying them to obtain modified silicon dioxide;

[0009] (2) contacting the phenolic monomer and the acrylic monomer with an initiator to carry out a second reaction to obtain a pre-gelled mixture;

[0010] (3) contacting the surface-modified silica with an oil phase solvent, uniformly dispersing the silica, and then contacting the surface-modified silica with an oil-soluble surfactant to obtain a modified silica emulsion;

[0011] (4) contacting the pre-gelled mixture with a modified silica emulsion to carry out a third reaction to obtain a modified silica gel microsphere pre-product;

[0012] (5) Cooling the modified silica gel microsphere pre-product, centrifuging it, collecting it, washing it, and drying it to obtain the modified silica gel microspheres.

[0013] The second aspect of the present invention provides core-shell structured gel microspheres based on surface modified nano-SiO2 prepared by the method described in the first aspect, wherein the particle size of the gel microspheres ranges from 10 to 30 μm.

[0014] Through the above technical solution, the present invention can achieve the following excellent effects:

[0015] (1) The core-shell structure gel microspheres based on surface modified nano-SiO2 provided by the present invention provide strong adhesion ability by introducing phenolic hydroxyl groups of tannic acid, which can effectively interact with minerals in the formation, improve the adhesion of the microspheres on the well wall, and thus enhance the durability of the plugging.

[0016] (2) The gel microspheres described in the present invention not only improve the strength of the gel microspheres by surface modification of nano-SiO2, but also enhance their stability under high temperature conditions, so that the gel microspheres can maintain their physical properties and plugging ability at higher temperatures, and are particularly suitable for deep well drilling operations.

[0017] (3) The gel microspheres described in the present invention, by introducing the negative charge characteristics and hydration properties of acrylic monomers, enable the polymer chains to maintain strong swelling and hydration in a saline environment, reduce the effect of salt on the swelling properties of the gel microspheres, and enhance their plugging effect in a high-salt environment. In addition, the introduction of modified silica further improves the stability of the microspheres in saline.

[0018] (4) The mechanical strength of the gel microspheres described in the present invention is significantly improved by the introduction of nano-SiO2, so that the microspheres can withstand greater fracturing stress in complex formation environments and are less likely to break. The microspheres can maintain a good plugging effect for fractures with an opening of 10 to 100 μm. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 The particle size test results of the core-shell structure gel microsphere A1 based on surface modified nano-SiO2 prepared in Example 1 in the test example; Figure 2 The particle size test results of the core-shell structure gel microsphere A2 based on surface modified nano-SiO2 prepared in Example 2 of the test example; Figure 3 The particle size test results of the core-shell structure gel microspheres A3 based on surface modified nano-SiO2 prepared in Example 3 in the test example. DETAILED DESCRIPTION

[0019] The ranges and values ​​of materials written in the present invention are not exactly within the precise ranges. All ranges and values ​​written in the present invention are values ​​included in these ranges or values. For these given numerical ranges, the ranges and the range endpoints can be combined with each other to form a new numerical range. These combined new values ​​should also be regarded as the contents disclosed by the present invention.

[0020] Note that the specific embodiments of the present invention are described in detail below. The specific embodiments described here are only used to illustrate and explain the present invention, and do not limit the present invention.

[0021] The first aspect of the present invention provides a preparation method, which comprises:

[0022] (1) mixing a silane coupling agent and nano-SiO2 in an aqueous solvent, contacting them in an acidic environment, and performing a first reaction to obtain a surface-modified nano-SiO2 mixed solution, dispersing them to obtain a modified silicon dioxide dispersion, and drying them to obtain modified silicon dioxide;

[0023] (2) contacting the phenolic monomer and the acrylic monomer with an initiator to carry out a second reaction to obtain a pre-gelled mixture;

[0024] (3) contacting the surface-modified silica with an oil phase solvent, uniformly dispersing the silica, and then contacting the surface-modified silica with an oil-soluble surfactant to obtain a modified silica emulsion;

[0025] (4) contacting the pre-gelled mixture with a modified silica emulsion to carry out a third reaction to obtain a modified silica gel microsphere pre-product;

[0026] (5) Cooling the modified silica gel microsphere pre-product, centrifuging it, collecting it, washing it, and drying it to obtain the modified silica gel microspheres.

[0027] According to the present invention, in step (1), the silane coupling agent and nano-SiO2 undergo a first reaction in an acidic environment. The silane coupling agent undergoes a hydrolysis reaction in an acidic environment, so that the silane group of the silane coupling agent forms a silicon-oxygen covalent bond with the hydroxyl group on the surface of the nano-SiO2, and at the same time, a strong bonding functional group is introduced to obtain surface-modified nano-SiO2.

[0028] According to the present invention, the silane coupling agent is selected from one of KH570, KH560 and KH550, preferably KH570.

[0029] According to the present invention, the particle size of the nano-SiO2 is selected from 15 μm, 30 μm, and 40 μm, preferably 30 μm nano-SiO2.

[0030] According to the present invention, in step (1), the operation process of the first reaction includes: adding an appropriate amount of aqueous solvent and nano-SiO2 into a reaction container, uniformly dispersing by ultrasonication to obtain a nano-SiO2 dispersion, adjusting the pH to the pH required for the reaction, adding a silane coupling agent, adjusting the temperature to the required temperature for the reaction until the reaction is completed, and drying at an adapted temperature to obtain modified silica.

[0031] According to the present invention, in step (1), in order to obtain the modified nano-SiO2 with the best effect, preferably, the weight ratio of the silane coupling agent: nano-SiO2 is 1:(5-30), preferably 1:(10-20).

[0032] According to the present invention, in step (1), the first reaction conditions include: the dispersion frequency of the surface modified nano-SiO2 mixed liquid is 10-50 Hz, preferably 45 Hz, the pH is 3-7, preferably 4-6, the reaction time is 2-5 h, preferably 2-4 h, the drying temperature is 70-80 ° C, and the time is 6-8 h.

[0033] According to the present invention, in step (2), the phenolic monomer, acrylic monomer and initiator are added to a reaction container to carry out a second reaction, the initiator decomposes under reaction conditions to generate free radicals, and the free radicals initiate a polymerization reaction of the acrylic monomer and the phenolic monomer to form a pregelatinized structure to obtain a pregelatinized mixture.

[0034] According to the present invention, the second reactive phenolic monomer is selected from phenol, p-hydroxybenzoic acid, and tannic acid, preferably tannic acid.

[0035] According to the present invention, the second reactive acrylic monomer is selected from one of acrylic acid, methyl acrylate and butyl acrylate, preferably acrylic acid.

[0036] According to the present invention, the second reaction initiator is selected from potassium persulfate and azobisisobutyronitrile, preferably azobisisobutyronitrile.

[0037] According to the present invention, in step (2), the operation process of the second reaction includes: dissolving the phenolic monomer and the acrylic acid monomer in deionized water, mixing them evenly to obtain a mixture, adding an initiator and continuing to stir until the initiator is fully dissolved to obtain a pre-gelled mixture.

[0038] According to the present invention, in step (2), the weight ratio of initiator: phenolic monomer: acrylic monomer: deionized water to obtain a pre-gelled mixture is 1: (10-40): (5-20): (100-300), preferably 1: (20-30): (5-10): (100-150).

[0039] According to the present invention, in step (3), the operation process is to add the surface-modified silica, oil-soluble surfactant and oil phase solvent into a reaction container, and disperse the mixture evenly by magnetic stirring to obtain a modified silica emulsion.

[0040] According to the present invention, in step (3), the magnetic stirring rate is 400-500 rpm, and the stirring time is 30-60 min.

[0041] According to the present invention, in step (4), the pregelatinized mixture is slowly added to a reaction vessel containing a modified silica emulsion to carry out a third reaction. The pregelatinized mixture forms tiny reverse emulsion droplets with the modified silica emulsion under stirring conditions. The temperature is adjusted to the reaction temperature to start the free radical polymerization reaction. While the phenolic monomer and the acrylic monomer are polymerizing, the modified nano-SiO2 particles are coated in the polymer generated by the reaction to obtain a core-shell structured gel microsphere pre-product based on surface modified nano-SiO2.

[0042] According to the present invention, in the third reaction in step (4), the weight ratio of the modified silica gel microsphere pre-product: the pre-gelled mixture: the modified silica emulsion is (50-100): (100-200), preferably (50-70): (100-120).

[0043] According to the present invention, the conditions of the third reaction include: the stirring method is magnetic stirring, the stirring rate is 200-500 rpm, the temperature is 30-50° C., the reaction time is 2-4 h, and the pH is 4-6.

[0044] According to the present invention, in step (5), the gel microsphere pre-product is cooled to room temperature, the gel microspheres are separated from the emulsion by centrifugation and filtration, the microspheres are washed multiple times with an alcohol reagent to remove residual monomers, surfactants and unreacted substances, and the washed microspheres are placed in an oven to dry until the microspheres are completely dry, thereby obtaining core-shell structured gel microspheres based on surface-modified nano-SiO2.

[0045] According to the present invention, in step (5), the third post-reaction alcohol washing process uses one of anhydrous ethanol and isopropanol, preferably anhydrous ethanol.

[0046] According to the present invention, in step (5), the treatment conditions of the modified silica gel microsphere pre-product include: the cooling method is natural cooling, the centrifugal speed is 3000-6000rpm, the centrifugal time is 10-20min, the drying temperature is 60-80°C, and the time is 6-12h.

[0047] The second aspect of the present invention provides core-shell structured gel microspheres based on surface modified nano-SiO2 prepared by the method described in the first aspect, wherein the particle size of the gel microspheres ranges from 10 to 30 μm and has a good sealing ability for cracks of 20 to 100 μm.

[0048] According to the present invention, the monomer preparation materials are all chemically pure unless otherwise specified, and conventional commercially available products can be used, and the present invention has no special limitation on this.

[0049] The present invention will be described in detail below through examples. Unless otherwise specified in the preparation examples and embodiments of the present invention, other materials used are common commercially available products.

[0050] Example

[0051] In the following examples, the silane coupling agent used is KH570, the nano-SiO2 particle size is 30 μm, the aqueous phase solvent is anhydrous ethanol, the phenolic monomer is tannic acid, the acrylic monomer is acrylic acid, the initiator is azobisisobutyronitrile, the oil phase solvent is cyclohexane, the oil-soluble surfactant is polyvinyl alcohol, and anhydrous ethanol is used in the alcohol washing process.

[0052] Example 1

[0053] (1) Preparation of surface-modified nano-SiO2

[0054] (1-1): Weigh 10 parts of nano-SiO2 (particle size 30 μm) and add them to a reaction container containing 100 parts of anhydrous ethanol. Use ultrasonic equipment to disperse the nano-SiO2 so that the nano-SiO2 is evenly dispersed in the anhydrous ethanol to obtain a nano-SiO2 dispersion.

[0055] (1-2): Add an appropriate amount of acidic solution to the above nano-SiO2 dispersion to adjust the pH of the system to 4. Then, weigh 0.5 parts of silane coupling agent KH570 and add it to the dispersion.

[0056] (1-3): The reaction vessel was placed in an environment with a dispersion frequency set to 45 Hz, and the reaction was carried out for 2 hours. After the reaction was completed, the obtained surface-modified nano-SiO2 mixed solution was transferred to a drying device and dried at 70° C. for 6 hours to obtain modified silicon dioxide.

[0057] (2) Preparation of pre-gelled mixture

[0058] (2-1): Weigh 20 parts of tannic acid and 5 parts of acrylic acid respectively, dissolve them in deionized water, and stir and mix them thoroughly to obtain a mixed solution.

[0059] (2-2): Weigh 0.2 parts of azobisisobutyronitrile initiator, add it to the above mixed solution, and continue stirring until the initiator is completely dissolved to obtain a pre-gelled mixture. At this time, the weight ratio of initiator: phenolic monomer: acrylic monomer: deionized water is 1:20:5:100.

[0060] (3) Preparation of modified silica emulsion

[0061] (3-1): The modified silica obtained in step (1) was added to a reaction vessel containing 50 parts of cyclohexane.

[0062] (3-2): Weigh 5 parts of polyvinyl alcohol as an oil-soluble surfactant and add it to the above reaction container.

[0063] (3-3): Use a magnetic stirring device to stir the mixture in the container. The stirring rate is set to 400 rpm and the stirring time is 30 min to uniformly disperse the mixture to obtain a modified silica emulsion, wherein the weight ratio of modified silica oil phase solution: modified silica: oil-soluble surfactant: oil solvent is 1:1:10:50.

[0064] (4) Preparation of modified silica gel microsphere pre-product

[0065] (4-1): Slowly add the pre-gelled mixture prepared in step (2) into the reaction vessel containing the modified silica emulsion obtained in step (3).

[0066] (4-2): Turn on magnetic stirring at a stirring rate of 200 rpm, control the reaction temperature at 30°C, and maintain the pH of the reaction system at 4.

[0067] (4-3): The reaction was continued for 2 hours to obtain a modified silica gel microsphere pre-product. At this time, the weight ratio of the modified silica gel microsphere pre-product: the pre-gelled mixture: the modified silica emulsion was 50:100:100.

[0068] (5) Preparation of core-shell structured gel microspheres based on surface modified nano-SiO2

[0069] (5-1): The modified silica gel microsphere pre-product obtained in step (4) is taken out from the reaction container and naturally cooled at room temperature.

[0070] (5-2): The cooled pre-product was transferred to a centrifuge, the centrifugal speed was set to 3000 rpm, the centrifugal time was set to 10 min, and the gel microspheres were separated from the emulsion by centrifugal operation.

[0071] (5-3): The separated microspheres are washed multiple times with anhydrous ethanol to remove residual monomers, surfactants and unreacted substances.

[0072] (5-4): The washed microspheres are placed in an oven, the oven temperature is set to 60°C, and the drying time is 6 hours. After drying, core-shell structured gel microspheres A1 based on surface modified nano-SiO2 are obtained.

[0073] Example 2

[0074] (1) Preparation of surface-modified nano-SiO2

[0075] (1-1): Weigh 15 parts of nano-SiO2 (particle size 30 μm) and add them to a reaction container filled with 120 parts of anhydrous ethanol. Use ultrasonic equipment to fully disperse the nano-SiO2 so that the nano-SiO2 is evenly distributed in the anhydrous ethanol, thereby obtaining a nano-SiO2 dispersion.

[0076] (1-2): Add an appropriate amount of acidic solution dropwise to the above nano-SiO2 dispersion to adjust the pH of the system to 5. Then, weigh 0.8 parts of silane coupling agent KH570 and add it to the dispersion.

[0077] (1-3): The reaction vessel was placed in an environment with a dispersion frequency of 45 Hz for a reaction time of 3 hours. After the reaction was completed, the surface-modified nano-SiO2 mixed solution was transferred to a drying device and dried at 75°C for 7 hours to finally obtain modified silica.

[0078] (2) Preparation of pre-gelled mixture

[0079] (2-1): Weigh 25 parts of tannic acid and 8 parts of acrylic acid respectively, dissolve them in deionized water, and stir them thoroughly to mix them evenly to obtain a mixed solution.

[0080] (2-2): Weigh 0.3 parts of azobisisobutyronitrile initiator, add it to the above mixed solution, and continue stirring until the initiator is completely dissolved to obtain a pre-gelled mixture. At this time, the weight ratio of initiator: phenolic monomer: acrylic monomer: deionized water is 1:25:8:120.

[0081] (3) Preparation of modified silica emulsion

[0082] (3-1): The modified silica obtained in step (1) was added into a reaction vessel containing 60 parts of cyclohexane.

[0083] (3-2): Weigh 8 parts of polyvinyl alcohol as an oil-soluble surfactant and add it into the above reaction container.

[0084] (3-3): Use a magnetic stirring device to stir the mixture in the container. The stirring rate is set to 450 rpm and the stirring time is 40 min to uniformly disperse the mixture to obtain a modified silica emulsion, wherein the weight ratio of modified silica oil phase solution: modified silica: oil-soluble surfactant: oil solvent is 1:1.5:15:60.

[0085] (4) Preparation of modified silica gel microsphere pre-product

[0086] (4-1): Slowly add the pre-gelled mixture prepared in step (2) into a reaction vessel containing the modified silica emulsion obtained in step (3).

[0087] (4-2): Turn on magnetic stirring at a stirring rate of 300 rpm, control the reaction temperature at 40°C, and maintain the pH of the reaction system at 5.

[0088] (4-3): The reaction was continued for 3 hours to obtain a modified silica gel microsphere pre-product. At this time, the weight ratio of the modified silica gel microsphere pre-product: the pre-gelled mixture: the modified silica emulsion was 60:110:110.

[0089] (5) Preparation of core-shell structured gel microspheres based on surface modified nano-SiO2

[0090] (5-1): The modified silica gel microsphere pre-product obtained in step (4) is taken out from the reaction container and naturally cooled at room temperature.

[0091] (5-2): The cooled pre-product was transferred to a centrifuge, the centrifugal speed was set to 4000 rpm, the centrifugal time was set to 15 min, and the gel microspheres were separated from the emulsion by centrifugation.

[0092] (5-3): The separated microspheres are washed multiple times with anhydrous ethanol to remove residual monomers, surfactants and unreacted substances.

[0093] (5-4): The washed microspheres are placed in an oven, the oven temperature is set to 70°C, and the drying time is 9 hours. After drying, core-shell structured gel microspheres based on surface modified nano-SiO2 are obtained.

[0094] Example 3

[0095] (1) Preparation of surface-modified nano-SiO2

[0096] (1-1): Weigh 20 parts of nano-SiO2 (particle size 30 μm) and add them to a reaction container filled with 150 parts of anhydrous ethanol. Use ultrasonic equipment to disperse the nano-SiO2 evenly in the anhydrous ethanol to obtain a nano-SiO2 dispersion.

[0097] (1-2): Add an appropriate amount of acidic solution to the above nano-SiO2 dispersion to adjust the pH of the system to 6. Then, weigh 1 part of silane coupling agent KH570 and add it to the dispersion.

[0098] (1-3): The reaction vessel was placed in an environment where the dispersion frequency was set to 45 Hz for reaction, and the reaction time lasted for 4 hours. After the reaction was completed, the obtained surface-modified nano-SiO2 mixed solution was transferred to a drying device and dried at 80° C. for 8 hours to obtain modified silicon dioxide.

[0099] (2) Preparation of pre-gelled mixture

[0100] (2-1): Weigh 30 parts of tannic acid and 10 parts of acrylic acid respectively, dissolve them in deionized water, and stir and mix them thoroughly to obtain a mixed solution.

[0101] (2-2): Weigh 0.4 parts of azobisisobutyronitrile initiator, add it to the above mixed solution, and continue stirring until the initiator is completely dissolved to obtain a pre-gelled mixture. At this time, the weight ratio of initiator: phenolic monomer: acrylic monomer: deionized water is 1:30:10:150.

[0102] (3) Preparation of modified silica emulsion

[0103] (3-1): The modified silica obtained in step (1) was added to a reaction vessel containing 80 parts of cyclohexane.

[0104] (3-2): Weigh 10 parts of polyvinyl alcohol as an oil-soluble surfactant and add it into the above reaction container.

[0105] (3-3): Use a magnetic stirring device to stir the mixture in the container, set the stirring rate to 500 rpm, and the stirring time to 60 min to uniformly disperse the mixture to obtain a modified silica emulsion, wherein the weight ratio of modified silica oil phase solution: modified silica: oil-soluble surfactant: oil solvent is 1:2:20:80.

[0106] (4) Preparation of modified silica gel microsphere pre-product

[0107] (4-1): The pre-gelled mixture prepared in step (2) is slowly added to a reaction vessel containing the modified silica emulsion obtained in step (3).

[0108] (4-2): Turn on magnetic stirring at a stirring rate of 500 rpm, control the reaction temperature at 50°C, and maintain the pH of the reaction system at 6.

[0109] (4-3): The reaction was continued for 4 hours to obtain a modified silica gel microsphere pre-product. At this time, the weight ratio of the modified silica gel microsphere pre-product: the pre-gelled mixture: the modified silica emulsion was 70:120:120.

[0110] (5) Preparation of core-shell structured gel microspheres based on surface modified nano-SiO2

[0111] (5-1): The modified silica gel microsphere pre-product obtained in step (4) is taken out from the reaction container and naturally cooled at room temperature.

[0112] (5-2): The cooled pre-product is transferred to a centrifuge, the centrifugal speed is set to 6000 rpm, the centrifugal time is set to 20 min, and the gel microspheres are separated from the emulsion by centrifugal operation.

[0113] (5-3): The separated microspheres are washed multiple times with anhydrous ethanol to remove residual monomers, surfactants and unreacted substances.

[0114] (5-4): The washed microspheres are placed in an oven, the oven temperature is set to 80°C, and the drying time is 12 h. After drying, core-shell structured gel microspheres A3 based on surface modified nano-SiO2 are obtained.

[0115] Comparative Example

[0116] Comparative Example 1

[0117] (1-1): 15 parts of nano-SiO2 (particle size 30 μm) were directly weighed without surface modification and added to a reaction vessel containing 120 parts of anhydrous ethanol. The subsequent steps (2) to (5) were exactly the same as the corresponding steps in Example 2, i.e., the steps of preparing the pre-gelled mixture, preparing the modified silica emulsion, preparing the modified silica gel microsphere pre-product, and preparing the core-shell structure gel microspheres based on surface-modified nano-SiO2 in Example 2 were followed to obtain Comparative Example B1.

[0118] Comparative Example 2

[0119] (1-1): Weigh 15 parts of nano-SiO2 (particle size 30 μm) and add them to a reaction container filled with 120 parts of anhydrous ethanol. Use ultrasonic equipment to fully disperse the nano-SiO2 so that the nano-SiO2 is evenly distributed in the anhydrous ethanol, thereby obtaining a nano-SiO2 dispersion.

[0120] (1-2): Add an appropriate amount of acidic solution dropwise to the above nano-SiO2 dispersion to adjust the pH of the system to 5. Then, weigh 0.8 parts of silane coupling agent KH570 and add it to the dispersion.

[0121] (1-3): The reaction vessel was placed in an environment with a dispersion frequency of 45 Hz for a reaction time of 3 hours. After the reaction was completed, the surface-modified nano-SiO2 mixed solution was transferred to a drying device and dried at 75°C for 7 hours to obtain modified silicon dioxide.

[0122] (2-1): Weigh only 8 parts of acrylic acid, dissolve it in deionized water, and stir and mix thoroughly to obtain a solution.

[0123] (2-2): Weigh 0.3 parts of azobisisobutyronitrile initiator, add it to the above solution, and continue stirring until the initiator is completely dissolved to obtain a pre-gelled mixture (without tannic acid component at this time).

[0124] (3-1)-(5-4): The subsequent steps are exactly the same as the preparation steps of the modified silica emulsion, the preparation of the modified silica gel microsphere preproduct and the preparation steps of the core-shell structure gel microsphere based on surface modified nano-SiO2 in Example 2 to obtain Comparative Example B2.

[0125] Comparative Example 3

[0126] (1-1)-(1-3): The preparation steps of surface-modified nano-SiO2 are exactly the same as those in Example 2.

[0127] (2-1): Weigh 25 parts of tannic acid, dissolve it in deionized water, and stir thoroughly to obtain a solution.

[0128] (2-2): Weigh 0.3 parts of azobisisobutyronitrile initiator, add it to the above solution, and continue stirring until the initiator is completely dissolved to obtain a pre-gelled mixture (without acrylic acid component at this time).

[0129] (3-1)-(5-4): The subsequent steps are exactly the same as the preparation steps of the modified silica emulsion, the preparation of the modified silica gel microsphere preproduct and the preparation steps of the core-shell structure gel microsphere based on surface modified nano-SiO2 in Example 2 to obtain Comparative Example B3.

[0130] Test Case

[0131] 1. Particle size test

[0132] Take the core-shell structure gel microspheres based on surface modified nano-SiO2 prepared in Examples 1-3 (denoted as A1, A2, A3) and the microspheres prepared in Comparative Examples 1-3 (denoted as B1, B2, B3), and refer to GB / T 19077-2016 "Laser Diffraction Method for Particle Size Analysis" for particle size test. First, an appropriate amount of microsphere sample is dispersed in anhydrous ethanol and stirred at 500rpm for 5 minutes by a magnetic stirrer to preliminarily disperse the sample. Then, use an ultrasonic processor to treat at an ultrasonic frequency of 40kHz for 5-10 minutes to ensure that the sample is evenly dispersed and avoid agglomeration of particles. Finally, the treated sample is injected into a laser particle size analyzer, and its particle size distribution is determined according to the standard operating procedure and the test data is recorded.

[0133] Table 1 Particle size test results

[0134]

[0137] According to the particle size test results ( Figures 1 to 3 , Table 1) shows that the particle size range of the surface-modified nano-SiO2 core-shell structure gel microspheres prepared by Examples A1-A3 is between 10-30 μm, which meets the design requirements, indicating that the particle size distribution of the microspheres can be effectively controlled by using surface-modified nano-SiO2 as a raw material and by appropriate surface modification and structural regulation. However, the microspheres of Comparative Examples B1-B3 are not subjected to corresponding surface modification treatments, resulting in uneven particle size distribution, and the particle size of some microspheres exceeds the design range, verifying the importance of surface modification to the control of microsphere particle size. Through the technical solution of the present invention, the uniformity and controllability of the microsphere particle size can be significantly improved, providing a more stable performance in practical applications.

[0138] 2. Adhesion test (peel test method)

[0139] The core-shell structured gel microspheres based on surface modified nano-SiO2 prepared in Examples 1-3 (denoted as A1, A2, A3) and the microspheres prepared in Comparative Examples 1-3 (denoted as B1, B2, B3) were taken for adhesion test with reference to the relevant standards for adhesion test of surface coatings of some materials (GB / T 9286-1998 "Scratch test for paint and varnish films").

[0140] First, select sandstone slices of uniform specifications and materials, and ultrasonically clean all the rock slices with deionized water and anhydrous ethanol for 15 minutes, and then dry them in an oven at 105°C to constant weight. The A1, A2, A3 microspheres prepared in Examples 1-3 and the B1, B2, B3 microspheres prepared in Comparative Examples 1-3 were respectively formulated into 3% concentration drilling fluid base slurry (drilling fluid base slurry: water + 4% bentonite). Then, the dried rock slices were immersed in different microsphere drilling fluid base slurries (corresponding to Examples 1-3 and Comparative Examples 1-3) one by one, and soaked for 15 minutes to allow the microspheres to fully adhere to the rock surface. Take out the rock slices and dry them in a low-temperature oven at 40°C to ensure that the microspheres are firmly attached to the rock surface. Using a peel tester, one end of a 2cm wide tape with standard viscosity is tightly attached to the rock surface with microspheres attached, and the tape is repeatedly rolled on the tape 3-5 times with a roller to make the tape fully contact and fit tightly with the microspheres. Finally, the tape was peeled off from the rock surface at a constant speed of 1 mm / s, and the force required in the peeling process was recorded by a peeling tester. The test was repeated 3-5 times at different positions of each rock slice, and the average value was taken as the adhesion data of the microspheres on the rock slice. Finally, the average value of the test data of multiple rock slices in each group was taken as the final adhesion data of the microspheres in this group.

[0141] Table 2 Adhesion test data

[0142] Sample No. Applied pressure (N) Adhesion force (N) Test time(s) Test temperature (℃) Test conditions A1 20 15 20 25 40℃ low temperature drying A2 20 16 20 25 40℃ low temperature drying A3 20 15.5 20 25 40℃ low temperature drying B1 20 5 20 25 40℃ low temperature drying B2 20 6 20 25 40℃ low temperature drying B3 20 5.5 20 25 40℃ low temperature drying

[0143] From the test results, the surface modified nano-SiO2 core-shell structure gel microspheres prepared in Examples 1-3 have strong adhesion and can be firmly attached to the rock surface. This shows that the interaction between the microspheres and the rock surface is effectively enhanced by surface modification of nano-SiO2 and reasonable formula design (such as the introduction of ingredients such as tannic acid and acrylic acid). However, the microspheres of Comparative Examples 1-3 have poor adhesion to the rock surface due to the lack of corresponding surface modification treatment or the lack of key ingredients, which verifies the important influence of surface modification and formula composition on the adhesion performance of microspheres.

[0144] 3. Blockage test

[0145] The A1, A2, A3 microspheres prepared in Examples 1-3 and the B1, B2, B3 microspheres prepared in Comparative Examples 1-3 were respectively formulated into water-based drilling fluids (water-based drilling fluids: 4% bentonite + 1% fluid loss reducer + 0.5% lubricant + 2% gel microspheres + barite + water). With reference to the relevant provisions and guidance on the performance testing of drilling fluids under high temperature conditions in SY / T5673-2018 "Specifications for the Calibration of Instruments and Equipment for Drilling Fluid Tests" and SY / T6300-2016 "General Technical Conditions for Oil and Gas Field Drilling and Oil Production Chemicals", the plugging performance of the A1, A2, A3 microspheres prepared in Examples 1-3 and the B1, B2, B3 microspheres prepared in Comparative Examples 1-3 was evaluated.

[0146] (1) Plugging performance test under high temperature resistance:

[0147] The A1, A2, A3 microspheres prepared in Examples 1-3 and the B1, B2, B3 microspheres prepared in Comparative Examples 1-3 were respectively formulated into a water-based drilling fluid with a mass fraction of 2% (water-based drilling fluid: 3%-5% bentonite + 0.5%-1.5% fluid loss reducer + 0.3%-0.8% lubricant + barite + water). In view of the fact that the microspheres can withstand a temperature of 180°C, the drilling fluid was aged at 180°C to more accurately simulate the high-temperature conditions in actual drilling. Artificial cores with different crack widths (10μm, 50μm, 100μm) were selected, and the aged drilling fluid was injected into the artificial core at a flow rate of 0.5mL / min. At the same time, the pressure changes at both ends of the core before and after the injection were recorded, and the plugging rate was calculated.

[0148]

[0149] In order to test the plugging performance of nano-SiO2 gel plugging microspheres under high salt conditions, a high-salt water-based drilling fluid was specially prepared (sodium chloride was added to the above-mentioned water-based drilling fluid formula to a mass fraction of 24%), and the microspheres were prepared into high-salt drilling fluid according to the same steps as above, and the plugging experiment was also carried out after aging at 180°C.

[0150] Table 3 Plugging rate in water-based drilling fluid

[0151]

[0152]

[0153] In the test of the plugging performance of artificial cores with different crack widths, the drilling fluid plugging rate corresponding to the A1 microspheres prepared in Example 1 reached 92% at a crack width of 10 μm, 88% at 50 μm, and 83% at 100 μm; the drilling fluid plugging rate corresponding to the A2 microspheres prepared in Example 2 was 93% at a crack width of 10 μm, 89% at 50 μm, and 85% at 100 μm; the drilling fluid plugging rate corresponding to the A3 microspheres prepared in Example 3 was 91% at a crack width of 10 μm, 87% at 50 μm, and 82% at 100 μm, indicating that the microspheres have a good plugging effect on the drilling fluid under high temperature conditions.

[0154] The drilling fluid plugging rate of the B1 microspheres prepared in Comparative Example 1 is only 40% at a crack width of 10 μm, 30% at 50 μm, and 20% at 100 μm; the drilling fluid plugging rate of the B2 microspheres prepared in Comparative Example 2 is 45% at a crack width of 10 μm, 35% at 50 μm, and 25% at 100 μm; the drilling fluid plugging rate of the B3 microspheres prepared in Comparative Example 3 is 42% at a crack width of 10 μm, 32% at 50 μm, and 22% at 100 μm, and its plugging rate is significantly lower. Among them, Comparative Example 1 does not perform surface modification on nano-SiO2, Comparative Example 2 does not add tannic acid, and Comparative Example 3 does not add acrylic acid. Their plugging performance at high temperature is not as good as that of the embodiment, indicating that the preparation method and formula of the present invention can effectively improve the plugging performance of the microspheres in a high temperature environment.

[0155] Table 4 Plugging rate in high salt water base drilling fluid

[0156]

[0157]

[0158] In a high-temperature and high-salt environment, for artificial cores with different crack widths, the high-salt drilling fluid plugging rate corresponding to the A1 microspheres prepared in Example 1 is 90% at a crack width of 10 μm, 86% at 50 μm, and 81% at 100 μm; the high-salt drilling fluid plugging rate corresponding to the A2 microspheres prepared in Example 2 is 91% at a crack width of 10 μm, 87% at 50 μm, and 82% at 100 μm; the high-salt drilling fluid plugging rate corresponding to the A3 microspheres prepared in Example 3 is 90% at a crack width of 10 μm, 86% at 50 μm, and 80% at 100 μm, and the plugging rate is relatively high.

[0159] The high-salt drilling fluid plugging rate corresponding to the B1 microspheres prepared in Comparative Example 1 is 25% when the crack width is 10μm, 15% when 50μm, and 5% when 100μm; the high-salt drilling fluid plugging rate corresponding to the B2 microspheres prepared in Comparative Example 2 is 30% when the crack width is 10μm, 20% when 50μm, and 10% when 100μm; the high-salt drilling fluid plugging rate corresponding to the B3 microspheres prepared in Comparative Example 3 is 27% when the crack width is 10μm, 17% when 50μm, and 7% when 100μm, and its plugging rate is obviously low. Specifically, B1 did not modify the surface of nano-SiO2, and its corresponding drilling fluid plugging rate dropped significantly in a high-temperature and high-salt environment; B2 did not introduce tannic acid, and the plugging rate of the drilling fluid in a high-temperature and high-salt environment was much lower than that of the embodiment; B3 did not add acrylic acid, resulting in an extremely low plugging rate of the corresponding drilling fluid under high-temperature and high-salt conditions, and almost lost its plugging effect. This shows that the technical solution of the present invention can significantly improve the plugging performance of the microspheres in a high-temperature and high-salt environment, while the microspheres of Comparative Examples 1-3 have not undergone corresponding surface modification treatment or lack key components, and their plugging performance is seriously insufficient in a high-temperature and high-salt environment, and cannot meet the actual application requirements.

Claims

1. A core-shell structure gel microsphere based on surface modified nano-SiO2 and a preparation method thereof, characterized in that: (1) mixing a silane coupling agent and nano-SiO2 in an aqueous solvent, contacting them in an acidic environment, and performing a first reaction to obtain a surface-modified nano-SiO2 mixed solution, dispersing them to obtain a modified silicon dioxide dispersion, and drying them to obtain modified silicon dioxide; (2) contacting the phenolic monomer and the acrylic monomer with an initiator to carry out a second reaction to obtain a pre-gelled mixture; (3) contacting the surface-modified silica with an oil phase solvent, uniformly dispersing the silica, and then contacting the surface-modified silica with an oil-soluble surfactant to obtain a modified silica emulsion; (4) contacting the pre-gelled mixture with a modified silica emulsion to carry out a third reaction to obtain a modified silica gel microsphere pre-product; (5) Cooling the modified silica gel microsphere pre-product, centrifuging it, collecting it, washing it, and drying it to obtain the modified silica gel microspheres.

2. The method according to claim 1, wherein: In step (1), the weight ratio of the surface modified nano-SiO2 mixed solution: silane coupling agent: nano-SiO2 is 1: (5-30), preferably 1: (10-20).

3. The method according to claim 2, wherein: In step (2), the weight ratio of the pre-gelled mixture: initiator: phenolic monomer: acrylic monomer: water is 1: (10-40): (5-20): (100-300), preferably 1: (20-30): (5-10): (100-150).

4. The method according to claim 3, wherein: In step (3), the weight ratio of the modified silica oil phase solution: modified silica: oil-soluble surfactant: oil solvent is 1: (1-10): (10-50), preferably 1: (1-2): (10-20).

5. The method according to claim 4, wherein: In step (4), the weight ratio of the modified silica gel microsphere pre-product: the pre-gelled mixture: the modified silica oil phase solution is (50-100): (100-200), preferably (50-70): (100-120).

6. The method according to any one of claims 1 to 5, wherein: In the first reaction, the silane coupling agent is selected from one of KH570, KH560 and KH550, preferably KH570; Preferably, the particle size of the nano-SiO2 is selected from one of 15 μm, 30 μm, and 40 μm, preferably 30 μm nano-SiO2; Preferably, the aqueous phase solvent is selected from one of anhydrous ethanol, methanol, and ethylene glycol, preferably anhydrous ethanol; Preferably, the second reactive phenolic monomer is selected from phenol, p-hydroxybenzoic acid, and tannic acid, preferably tannic acid; Preferably, the second reactive acrylic monomer is selected from one of acrylic acid, methyl acrylate and butyl acrylate, preferably acrylic acid; Preferably, the second reaction initiator is selected from potassium persulfate and azobisisobutyronitrile, preferably azobisisobutyronitrile; Preferably, the oil phase solvent is selected from one of n-hexane, white oil and cyclohexane, preferably cyclohexane; Preferably, the oil-soluble surfactant is selected from polyvinyl alcohol, octylphenol polyoxyethylene ether, sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, preferably polyvinyl alcohol.

7. The method according to any one of claims 1 to 6, wherein: In step (1), the conditions of the first reaction include: pH 3 to 7, preferably 4 to 6; Preferably, in step (1), the dispersion frequency of the surface-modified nano-SiO2 mixed solution is 10-50 Hz, preferably 45 Hz, and the reaction time is 2-5 h, preferably 2-4 h; Preferably, in step (1), the drying conditions of the modified nano-SiO2 dispersion include: a drying temperature of 70 to 80°C and a drying time of 6 to 8 hours; Preferably, in step (2), the conditions of the second reaction include: stirring mode is magnetic stirring, stirring rate is 200-400 rpm, stirring time is 30-60 min; Preferably, in step (3), the modified silicon dioxide emulsion is prepared under the following conditions: the stirring method is magnetic stirring, the stirring rate is 400 to 500 rpm, and the stirring time is 30 to 60 min; Preferably, in step (4), the conditions of the third reaction include: stirring mode is magnetic stirring, stirring rate is 200-500 rpm, temperature is 30-50° C., reaction time is 2-4 h, pH is 4-6; Preferably, in step (5), the treatment conditions of the modified silica gel microsphere pre-product include: the cooling method is natural cooling, the centrifugal speed is 3000-6000 rpm, the centrifugal time is 10-20 min, the drying temperature is 60-80° C., and the time is 6-12 h.

8. The core-shell structured gel microspheres based on surface modified nano-SiO2 according to claims 1-7, wherein the particle size of the gel microspheres ranges from 10 to 30 μm.

9. The core-shell structure gel microspheres based on surface modified nano-SiO2 and the preparation method thereof according to any one of claims 1 to 8, wherein: The gel microspheres are hydrophilic, and the hydrophilicity of the microspheres can be controlled by adjusting the surface modification ratio of the modified silica.

10. The core-shell structure gel microspheres based on surface modified nano-SiO2 and the preparation method thereof according to any one of claims 1 to 9, wherein: In the core-shell structure of the microsphere, the core is modified nano-SiO2 and the shell is a polymer composite material.

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