Multifunctional microsphere for coal mine area as well as preparation method and application of multifunctional microsphere

Abstract

The invention belongs to the technical field of coal mine area operation, and particularly relates to a multifunctional microsphere for a coal mine area and a preparation method and application thereof. The multifunctional microsphere for the coal mine area comprises the following raw materials in parts by weight: 10-50 parts of a polymer monomer with a polar group, 5-15 parts of a polymer emulsifier with a polar group and 0.02-0.5 part of an initiator. The multifunctional microsphere has the beneficial effects that the multifunctional microsphere can effectively solve the problems of energy consumption increase and ore sand flowback difficulty caused by working fluid viscosity increase in mining of a coal mine area, can effectively reduce stratum filtration, improves the working fluid use efficiency, can fill stratum cracks, strengthens a well wall, and improves the mining efficiency of the coal mine area. And the safety risk in the mining process is reduced.

Description

Technical Field

[0001] This invention belongs to the field of coal mining operation technology, specifically relating to a multifunctional microsphere for coal mining areas, its preparation method, and its application. Background Technology

[0002] In coal mining operations, especially in the roof area, the high strength and large fracture distance of the hard roof, coupled with intense mine pressure, pose a significant challenge to roof control. Particularly under the mining conditions of extra-thick coal seams, the extensive disturbance caused by mining leads to the fracture and instability of the hard roof in large spaces, resulting in more complex and intense mine pressure manifestations in the stope. Research indicates that the fracture and instability of the high-level, thick, hard rock strata is the main factor causing strong mine pressure in extra-thick coal seams with hard roofs, but existing underground pre-fracturing technologies cannot effectively control this. Furthermore, traditional fracturing fluids and water-blocking agents suffer from problems such as high filtration loss, slow sealing speed, and high viscosity, leading to low mining efficiency and increased costs. To address these issues, research has innovatively proposed a segmented hydraulic fracturing technology using long directional boreholes in coal mines and developed corresponding equipment, achieving efficient gas extraction from fractured and soft coal seams and effective control of the hard roof. In addition, studies have revealed the propagation morphology of hydraulic fractures and the stress-strain evolution law of specimens throughout the entire fracturing process through large true triaxial in-situ hydraulic fracturing tests, and established a theoretical model and selection criteria for determining the fracturing location.

[0003] However, existing technologies still have some limitations in terms of working materials. For example, the viscosity reduction and filtration loss reduction effects of fracturing fluids are not ideal, the plugging efficiency of water shut-off agents is not high, and the adaptability and stability to the environment need to be improved. Summary of the Invention

[0004] This application provides a multifunctional microsphere for coal mining areas that can significantly reduce the viscosity of working fluids in coal mining areas, reduce formation filtration loss, quickly seal formation fractures, improve fracturing, and enhance the safety of coal mining, as well as its preparation method and application.

[0005] The first aspect of this application provides a multifunctional microsphere for use in coal mining areas, comprising the following raw materials in parts by weight: 10-50 parts of polymer monomers having polar groups, 5-15 parts of polymer emulsifiers having polar groups, and 0.02-0.5 parts of initiator.

[0006] According to some embodiments of the multifunctional microspheres for coal mining areas described in this application, the raw materials include the following parts by weight: 20-40 parts of polymer monomers having polar groups, 5-10 parts of polymer emulsifiers having polar groups, and 0.02-0.3 parts of initiator.

[0007] According to some embodiments of the multifunctional microspheres for coal mining areas described in this application, the polymer monomers having polar groups include at least two of styrene, chloromethylstyrene, acrylic acid, acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and sodium styrenesulfonate.

[0008] According to some embodiments of the multifunctional microspheres for coal mining areas described in this application, the polymer emulsifier with polar groups includes at least one of hydroxypropyl methylcellulose acetate succinate, polyvinylpyrrolidone, Span, Tween, and xanthan gum.

[0009] According to some embodiments of the multifunctional microspheres for coal mining areas described in this application, the initiator includes at least one of 2,2'-azobisisobutyronitrile, azobisisoheptanenitrile, potassium persulfate, dimethyl azobisisobutyrate, and Trigonox-421.

[0010] According to some embodiments of the multifunctional microspheres for coal mining areas described in this application, the polymer monomers having polar groups include styrene and sodium styrene sulfonate.

[0011] According to some embodiments of the multifunctional microspheres for coal mining areas described in this application, the polymer monomers having polar groups include styrene and sodium styrene sulfonate in a molar ratio of (1-4):1.

[0012] According to some embodiments of the multifunctional microspheres for coal mining areas described in this application, the particle size of the multifunctional microspheres for coal mining areas is 2.6-3.9 μm.

[0013] The second aspect of this application provides a method for preparing the multifunctional microspheres for coal mining areas described in the first aspect of this application, comprising the following steps:

[0014] (1) A reaction solution is obtained by mixing a polymer monomer with polar groups, a polymer emulsifier with polar groups, an initiator and a solvent;

[0015] (2) The reaction solution is centrifuged to obtain centrifuged precipitate, and the centrifuged precipitate is washed and dried in sequence to obtain the multifunctional microspheres for coal mining areas.

[0016] According to some embodiments of the preparation method of multifunctional microspheres for coal mining areas described in this application, the solvent includes at least two of water, ethanol, ethylene glycol, glycerol, and dimethyl sulfoxide.

[0017] According to some embodiments of the preparation method of multifunctional microspheres for coal mining areas described in this application, the mass ratio of the polymer monomer with polar groups to the solvent is (30-50):190.

[0018] According to some embodiments of the preparation method of multifunctional microspheres for coal mining areas described in this application, the mixing temperature is 70-90℃ and the mixing time is 2-7h.

[0019] According to some embodiments of the preparation method of multifunctional microspheres for coal mining areas described in this application, the solvent includes water and ethanol.

[0020] According to some embodiments of the preparation method of multifunctional microspheres for coal mining areas described in this application, the solvent includes water and ethanol in a volume ratio of 1:(6-9).

[0021] According to some embodiments of the preparation method of multifunctional microspheres for coal mining areas described in this application, the centrifugal separation speed is 5000-12000 rpm.

[0022] According to some embodiments of the preparation method of multifunctional microspheres for coal mining areas described in this application, the washing is performed using an inert gas saturated solvent; preferably, the inert gas saturated solvent includes nitrogen-saturated deionized water.

[0023] According to some embodiments of the preparation method of multifunctional microspheres for coal mining areas described in this application, the drying temperature is 55-65℃ and the drying time is 3-5h.

[0024] The third aspect of this application provides the application of the multifunctional microspheres for coal mining areas described in the first aspect of this application or the multifunctional microspheres for coal mining areas prepared by the preparation method described in the second aspect of this application in reducing the viscosity of working fluids in coal mining areas, reducing the filtration loss of formations in coal mining areas, and sealing formation fractures.

[0025] The beneficial effects of this application include: the multifunctional microspheres described in this application can effectively reduce the increase in energy consumption and the difficulty in ore return caused by the increased viscosity of the working fluid during coal mining, and can effectively reduce formation filtration loss, improve the efficiency of working fluid use, and at the same time, fill formation cracks, strengthen the well wall, and reduce safety risks during the mining process. Attached Figure Description

[0026] Figure 1 This is an electron microscope image of the multifunctional microspheres for coal mining areas described in Embodiment 1 of this application. Detailed Implementation

[0027] The embodiments of the present invention are described in detail below. These embodiments are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0028] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0029] This application provides a multifunctional microsphere for coal mining areas, comprising the following raw materials in parts by weight: 10-50 parts of polymer monomers with polar groups, 5-15 parts of polymer emulsifiers with polar groups, and 0.02-0.5 parts of initiator. By selecting monomers containing multiple polar groups, the polymer microspheres, due to their large specific surface area and reactive functional groups, can be effectively endowed with various properties. Utilizing the numerous polar groups on their surface, the microspheres, through adsorption or substitution, disrupt the bridging structure of clay particles, thereby reducing the viscosity of the working fluid. Simultaneously, due to their spherical structure, smooth surface, and charged nature, rolling friction can further reduce the viscosity of the working fluid during flow. Furthermore, the numerous polar groups on the surface of the microspheres allow them to adsorb or chemically interact with clay, synergistically improving the density and stability of the sludge cake, thus reducing filtration loss.

[0030] In some embodiments of this application, the raw materials include the following parts by weight: 20-40 parts of polymer monomers with polar groups, 5-10 parts of polymer emulsifiers with polar groups, and 0.02-0.3 parts of initiator. Within this range, the prepared microspheres have a suitable average particle size and good dispersion stability in water.

[0031] In some embodiments of this application, the polymer monomer having polar groups includes at least two of styrene, chloromethylstyrene, acrylic acid, acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and sodium styrenesulfonate.

[0032] In some embodiments of this application, the polymer emulsifier with polar groups includes at least one selected from hydroxypropyl methylcellulose acetate succinate, polyvinylpyrrolidone, Span, Tween, and xanthan gum. The polar groups of these emulsifiers are anchored in the aqueous phase through hydrophilic interactions, while the hydrophobic chains are adsorbed onto the surface of monomer droplets or polymer particles, forming a stable interfacial layer. This adsorption reduces interfacial tension and prevents droplet / particle aggregation.

[0033] In some embodiments of this application, the initiator includes at least one of 2,2'-azobisisobutyronitrile, azobisisoheptanenitrile, potassium persulfate, dimethyl azobisisobutyrate, and Trigonox-421.

[0034] In some embodiments of this application, the polymer monomer having polar groups includes styrene and sodium styrene sulfonate.

[0035] In some embodiments of this application, the polymer monomers having polar groups include styrene and sodium styrene sulfonate in a molar ratio of (1-4):1. For example, 1:1, 2:1, 3:1, 4:1, etc.

[0036] In some embodiments of this application, the particle size of the multifunctional microspheres used in coal mining areas is 2.6-3.9 μm, such as 2.6 μm, 2.8 μm, 3.2 μm, 3.5 μm, and 3.9 μm. When the particle size of the multifunctional microspheres is within this range, the microspheres exhibit significant volume changes when affected by external environmental factors such as temperature and mineralization, thus better matching formation fractures.

[0037] This application also provides a method for preparing the multifunctional microspheres for coal mining areas described in the first aspect of this application, comprising the following steps:

[0038] (1) A reaction solution is obtained by mixing a polymer monomer with polar groups, a polymer emulsifier with polar groups, an initiator and a solvent;

[0039] (2) The reaction solution is centrifuged to obtain centrifuged precipitate, and the centrifuged precipitate is washed and dried in sequence to obtain the multifunctional microspheres for coal mining areas.

[0040] In some embodiments of this application, the solvent includes at least two of water, ethanol, ethylene glycol, glycerol, and dimethyl sulfoxide. The mixed solvent can effectively dissolve the corresponding polymer monomers, initiators, and emulsifiers, etc. Simultaneously, the solvents are mutually soluble, which can effectively improve the polymerization kinetics, increase the reaction rate, and enhance the degree of reaction during the reaction.

[0041] In some embodiments of this application, the mass ratio of the polymer monomer with polar groups to the solvent is (30-50):190; for example, 30:190, 35:190, 40:190, 45:190, 50:190, etc.

[0042] In some embodiments of this application, the mixing temperature is 70-90°C, such as 70°C, 78°C, 83°C, 88°C, 90°C, etc., and the mixing time is 2-7 hours, such as 2 hours, 4 hours, 5 hours, 7 hours, etc.

[0043] In some embodiments of this application, the solvent includes water and ethanol.

[0044] In some embodiments of this application, the solvent includes water and ethanol in a volume ratio of 1:(6-9), such as 1:6, 1:8, 1:9, etc.

[0045] In some embodiments of this application, the centrifugal separation speed is 5000-12000 rpm, such as 5000 rpm, 8000 rpm, 8600 rpm, 9500 rpm, 10000 rpm, 11000 rpm, 12000 rpm, etc.

[0046] In some embodiments of this application, the washing is performed using an inert gas saturated solvent; preferably, the inert gas saturated solvent includes nitrogen-saturated deionized water.

[0047] In some embodiments of this application, the drying temperature is 55-65°C, such as 55°C, 58°C, 62°C, 65°C, etc., and the drying time is 3-5 hours, such as 3 hours, 4 hours, 5 hours, etc.

[0048] This application also provides an application of the multifunctional microspheres for coal mining areas described in the first aspect of this application or the preparation method described in the second aspect of this application in reducing the viscosity of working fluids in coal mining areas, reducing formation filtration loss in coal mining areas, and sealing formation fractures. The multifunctional microspheres described in this application can effectively reduce the increased energy consumption and difficulties in ore return caused by the increased viscosity of working fluids during coal mining, and can effectively reduce formation filtration loss, improve the efficiency of working fluid use, and simultaneously fill formation fractures, strengthen the wellbore, and reduce safety risks during the mining process.

[0049] The technical solution of this application will be further described below with reference to specific embodiments.

[0050] Example 1

[0051] A method for preparing multifunctional microspheres for coal mining areas includes the following steps:

[0052] S1. Take 10g of styrene, 10g of chloromethylstyrene and 10g of 2-acrylamido-2-methylpropanesulfonic acid, which are polymer monomers with polar groups, and dissolve them in 130g of anhydrous ethanol and 10g of deionized water as a co-solvent. The dissolution temperature is 35℃ and the stirring rate is 400rpm. Stir for 15min to obtain a homogeneous polymer solution.

[0053] S2. Take 3g of polyvinylpyrrolidone, a polymer emulsifier with polar groups, and dissolve it in 30g of anhydrous ethanol and 10g of deionized water as a co-solvent. Stir for 15min at a dissolution temperature of 40℃ and a stirring rate of 1200rpm, and then sonicate to remove bubbles for 15min to obtain a stable polymer emulsion.

[0054] S3. Dissolve 0.5g of initiator 2,2'-azobisisobutyronitrile in a co-solvent of 6.25g of anhydrous ethanol and 3.75g of deionized water at a dissolution temperature of 30℃ and a stirring rate of 500rpm for 10min to obtain an initiator solution.

[0055] S4. Mix the solution obtained in step S1 with the solution obtained in step S2 at a mixing temperature of 40°C and a stirring rate of 1000 rpm, and purge with nitrogen for 0.5 h. Then, when adding the solution obtained in step S3 dropwise to the mixture of S1 and S2, the volume ratio of the initiator solution added to the volume of the mixture is 1:20. The stirring rate is 700 rpm, the reaction temperature is 85°C, and the reaction time is 5 h. The reaction is completed by producing a multifunctional microsphere reaction solution.

[0056] S5. The reaction solution from S4 was centrifuged at 6000 rpm at room temperature to obtain a centrifuged precipitate. The precipitate was washed three times with nitrogen-saturated deionized water, and then dried under vacuum at 60°C for 4 hours. Multifunctional microspheres for coal mining areas with a particle size of 3.2 μm were obtained.

[0057] Example 2

[0058] The only difference between the preparation method of the multifunctional microspheres for coal mining areas described in Example 2 and Example 1 is that the polymer monomer with polar groups used in the preparation process of the multifunctional microspheres for coal mining areas described in Example 2 is a mixture of 15g styrene and 15g sodium styrene sulfonate.

[0059] Example 3

[0060] The only difference between the preparation method of the multifunctional microspheres for coal mining areas described in Example 3 and Example 1 is that the polymer monomer with polar groups used in the preparation process of the multifunctional microspheres for coal mining areas described in Example 3 is a mixture of 20g styrene and 10g sodium styrene sulfonate.

[0061] Example 4

[0062] The only difference between the preparation method of the multifunctional microspheres for coal mining areas described in Example 4 and Example 1 is that the polymer monomer with polar groups used in the preparation process of the multifunctional microspheres for coal mining areas described in Example 4 is a mixture of 22.5g styrene and 7.5g sodium styrene sulfonate.

[0063] Example 5

[0064] The only difference between the preparation method of the multifunctional microspheres for coal mining areas described in Example 5 and Example 1 is that the polymer monomer with polar groups used in the preparation process of the multifunctional microspheres for coal mining areas described in Example 5 is a mixture of 24g styrene and 6g sodium styrene sulfonate.

[0065] Example 6

[0066] The only difference between the preparation method of the multifunctional microspheres for coal mining areas described in Example 6 and Example 2 is that the volume ratio of water to ethanol in the reaction solution during the preparation of the multifunctional microspheres for coal mining areas described in Example 6 is 1:6.

[0067] Example 7

[0068] The only difference between the preparation method of the multifunctional microspheres for coal mining areas described in Example 7 and Example 2 is that the volume ratio of water to ethanol in the reaction solution during the preparation of the multifunctional microspheres for coal mining areas described in Example 7 is 1:8.

[0069] Example 8

[0070] The only difference between the preparation method of the multifunctional microspheres for coal mining areas described in Example 8 and Example 2 is that the volume ratio of water to ethanol in the reaction solution during the preparation of the multifunctional microspheres for coal mining areas described in Example 8 is 1:9.

[0071] Example 9

[0072] The only difference between the preparation method of the multifunctional microspheres for coal mining areas described in Example 9 and Example 2 is that the mass ratio of the polymer monomer with polar groups to the initiator in the preparation process of the multifunctional microspheres for coal mining areas described in Example 9 is 100:0.5.

[0073] Example 10

[0074] The only difference between the preparation method of the multifunctional microspheres for coal mining areas described in Example 10 and Example 2 is that the mass ratio of the polymer monomer with polar groups to the initiator in the preparation process of the multifunctional microspheres for coal mining areas described in Example 10 is 100:1.

[0075] Example 11

[0076] The only difference between the preparation method of the multifunctional microspheres for coal mining areas described in Example 11 and Example 2 is that the mass ratio of the polymer monomer with polar groups to the initiator in the preparation process of the multifunctional microspheres for coal mining areas described in Example 11 is 100:2.

[0077] Example 12

[0078] The only difference between the preparation method of the multifunctional microspheres for coal mining areas described in Example 12 and Example 2 is that the solvent used is a mixture of ethanol and ethylene glycol with a volume ratio of 3:1.

[0079] Comparative Example 1

[0080] The only difference between the preparation method of the multifunctional microspheres for coal mining areas described in Comparative Example 1 and Example 2 is that the polymer monomer with polar groups used in the preparation process of the multifunctional microspheres for coal mining areas described in Comparative Example 1 is 30g of styrene.

[0081] Comparative Example 2

[0082] The only difference between the preparation method of the multifunctional microspheres for coal mining areas described in Comparative Example 2 and Example 2 is that the polymer monomer with polar groups used in the preparation process of the multifunctional microspheres for coal mining areas described in Comparative Example 2 is 30g of sodium styrene sulfonate.

[0083] Comparative Example 3

[0084] The only difference between the preparation method of the multifunctional microspheres for coal mining areas described in Comparative Example 3 and Example 2 is that the solvent used in the preparation process of the multifunctional microspheres for coal mining areas described in Comparative Example 3 is ethanol.

[0085] Performance study of the multifunctional microspheres for coal mining areas described in Examples 1-12 and Comparative Examples 1-3 of this application:

[0086] 1. Electron microscope image of the multifunctional microspheres for coal mining areas described in Embodiment 1 of this application, as shown below. Figure 1 As shown.

[0087] from Figure 1 It can be seen that the multifunctional microspheres for coal mining areas described in this application are micron-sized spheres with relatively uniform dimensions.

[0088] 2. The multifunctional microspheres for coal mining areas described in Examples 1-12 of this application were added to the working fluid for coal mining areas (the amount of multifunctional microspheres added was 1% of the mass of the working fluid). The apparent viscosity values ​​of the working fluid before and after the addition of the multifunctional microspheres were tested (the samples of each example or comparative example were tested five times and the average value was taken). The results are shown in Table 1.

[0089] Table 1

[0090]

[0091] Note: Apparent viscosity test method:

[0092] Pour the above-prepared liquid to be measured into the beaker supporting the six-speed rotational viscometer respectively until it reaches the graduation line. Use a ZNN-D type six-speed rotational viscometer to record the readings of the liquid to be measured at a rotational speed of 600 r / min respectively. Measure and calculate the apparent viscosity (AV) of the liquid to be measured. Wherein:

[0093] AV = 1 / 2 × φ600 (1 - 1)

[0094] In the formula, φ600 is the reading when the rotational speed of the six-speed rotational viscometer is 600 r / min, and the unit of AV is mPa·s.

[0095] It can be seen from Table 1 that by comparing Example 1 and Example 2, it can be seen that when the polymer monomers with polar groups are styrene and sodium styrene sulfonate, the working fluid prepared from the multifunctional microspheres has a lower apparent viscosity, and when the mass ratio of styrene to sodium styrene sulfonate is 1:1, the effect is optimal.

[0096] By comparing Example 2 and Examples 6 - 8, it can be seen that the volume ratio of water to ethanol in the reaction solution during the preparation of the multifunctional microspheres is the key factor affecting the performance of the multifunctional microspheres. When the volume ratio of water to ethanol is 1:(6 - 7), the working fluid prepared from the multifunctional microspheres has a lower apparent viscosity.

[0097] By comparing Example 2 and Examples 9 - 11, it can be seen that the mass ratio of the polymer monomer with polar groups to the initiator during the preparation of the multifunctional microspheres is the key factor affecting the performance of the multifunctional microspheres. When the mass ratio of the polymer monomer with polar groups to the initiator is 100:(1.6 - 2), the working fluid prepared from the multifunctional microspheres has a lower apparent viscosity.

[0098] 3. Add the multifunctional microspheres described in Examples 1 - 12 of this application to the simulated formation base slurry respectively (the addition amount of the multifunctional microspheres is 1% of the mass of the base slurry), and test the filtration loss amount before and after the addition (each example and comparative sample are tested five times, and the average value is taken). The results are shown in Table 2

[0099] Table 2

[0100]

[0101] Remarks: Filtration loss measurement method:

[0102] Use a ZN type mud filtration loss measuring instrument to measure the filtration loss amount (FL) of the base slurry before and after adding the multifunctional microspheres respectively. Measure the strength of the filtration loss reduction effect of the prepared microspheres through the size of the filtration loss amount. Set the test pressure to 0.69 MPa, start timing when the first drop of filtrate drips, and record the filtration loss amount after 30 min (the unit of the filtration loss amount is mL).

[0103] As can be seen from Table 2, comparing Example 1 and Example 2, it can be seen that when the polymer monomers with polar groups are styrene and sodium styrene sulfonate, the slurry prepared from the multifunctional microspheres has a lower filtration loss, and the effect is optimal when the mass ratio of styrene to sodium styrene sulfonate is 1:1.

[0104] Comparing Examples 2 and 6-8, it can be seen that the volume ratio of water to ethanol in the reaction solution during the preparation of multifunctional microspheres is a key factor affecting the performance of multifunctional microspheres. When the volume ratio of water to ethanol is 1:(6-7), the base slurry for preparing multifunctional microspheres has a lower filtration loss.

[0105] Comparing Examples 2 and 9-11, it can be seen that the mass ratio of the polymer monomer with polar groups to the initiator during the preparation of multifunctional microspheres is a key factor affecting the performance of multifunctional microspheres. When the mass ratio of the polymer monomer with polar groups to the initiator is 100:1.6, the slurry prepared from the multifunctional microspheres has a lower filtration loss.

[0106] 4. The multifunctional microspheres used in coal mining areas described in Examples 1-12 and Comparative Examples 1-2 of this application were respectively formulated into aqueous dispersions with a mass fraction of 2%, and their sealing performance on simulated formation fracture cores (fracture width of 1 mm) was tested. (Each example and comparative example sample was tested five times, and the average value was taken.)

[0107] Blocking performance testing methods:

[0108] A fractured core plunger (fracture width 1 mm) was used to simulate the fracture structure of a lost formation. The microsphere plugging performance was determined using a DQ-IV type multifunctional automatic core displacement device. A core was placed inside a core holder, maintaining a confining pressure of 30 MPa. A tail pressure device was connected to the outlet end of the holder. First, an 8% KCl solution was injected using a constant flow pump (protective pressure 30 MPa) in constant flow mode. The pressure difference between the inlet and outlet ends of the core holder was observed over time, and the pressure change over time at stable conditions was recorded. Under the same conditions, an aqueous dispersion of the aforementioned multifunctional microspheres was injected, and the pressure difference was observed over time. The pressure change over time was recorded. The plugging performance of the microspheres was measured by the size of their maximum stable pressure relative to the 8% KCl solution. Specific test results are shown in Table 3.

[0109] Table 3

[0110]

[0111] As can be seen from Table 3, comparing Example 1 and Example 2, it can be seen that the dispersion prepared from the multifunctional microspheres obtained when the polymer monomers with polar groups are styrene and sodium styrene sulfonate have better blocking performance, and the effect is optimal when the mass ratio of styrene to sodium styrene sulfonate is 1:1.

[0112] Comparing Examples 2 and 6-8, it can be seen that the volume ratio of water to ethanol in the reaction solution during the preparation of multifunctional microspheres is a key factor affecting the performance of multifunctional microspheres. When the volume ratio of water to ethanol is 1:(6-7), the dispersion of multifunctional microspheres prepared has better blocking performance.

[0113] Comparing Examples 2 and 9-11, it can be seen that the mass ratio of the polymer monomer with polar groups to the initiator during the preparation of multifunctional microspheres is a key factor affecting the performance of multifunctional microspheres. When the mass ratio of the polymer monomer with polar groups to the initiator is 100:1.6 (Example 2), the dispersion of multifunctional microspheres prepared has better blocking performance.

[0114] As can be seen from Tables 1-3, when styrene or sodium styrene sulfonate is used alone as the polymer monomer with polar groups, the working fluid prepared from the multifunctional microspheres has a low apparent viscosity but poor sealing performance.

[0115] Although the above embodiments have been shown and described, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any changes, modifications, substitutions and variations made to the above embodiments by those skilled in the art are within the protection scope of the present invention.

Claims

1. A multifunctional microsphere for use in coal mining areas, characterized in that, The raw materials include the following parts by weight: 10-50 parts of polymer monomers with polar groups, 5-15 parts of polymer emulsifiers with polar groups, and 0.02-0.5 parts of initiator.

2. The multifunctional microspheres for coal mining areas according to claim 1, characterized in that, The raw materials include the following parts by weight: 20-40 parts of polymer monomers with polar groups, 5-10 parts of polymer emulsifiers with polar groups, and 0.02-0.3 parts of initiator.

3. The multifunctional microspheres for coal mining areas according to claim 1, characterized in that, The polymer monomers having polar groups include at least two of styrene, chloromethylstyrene, acrylic acid, acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and sodium styrenesulfonate; And / or, the polymer emulsifier having polar groups includes at least one of hydroxypropyl methylcellulose acetate succinate, polyvinylpyrrolidone, Span, Tween, and xanthan gum; And / or, the initiator includes at least one of 2,2'-azobisisobutyronitrile, azobisisoheptanenitrile, potassium persulfate, dimethyl azobisisobutyrate, and Trigonox-421.

4. The multifunctional microspheres for coal mining areas according to claim 1, characterized in that, The polymer monomers having polar groups include styrene and sodium styrene sulfonate; Preferably, the polymer monomers having polar groups include styrene and sodium styrene sulfonate in a molar ratio of (1-4):

1.

5. The multifunctional microspheres for coal mining areas according to claim 1, characterized in that, The particle size of the multifunctional microspheres used in the coal mining area is 2.6-3.9 μm.

6. The method for preparing multifunctional microspheres for coal mining areas according to any one of claims 1-5, characterized in that, Includes the following steps: (1) A reaction solution is obtained by mixing a polymer monomer with polar groups, a polymer emulsifier with polar groups, an initiator and a solvent; (2) The reaction solution is centrifuged to obtain centrifuged precipitate, and the centrifuged precipitate is washed and dried in sequence to obtain the multifunctional microspheres for coal mining areas.

7. The method for preparing multifunctional microspheres for coal mining areas according to claim 6, characterized in that, The solvent includes at least two of water, ethanol, ethylene glycol, glycerol, and dimethyl sulfoxide; And / or, the mass ratio of the polymer monomer having polar groups to the solvent is (30-50):190; And / or, the mixing temperature is 70-90°C, and the mixing time is 2-7 hours.

8. The method for preparing multifunctional microspheres for coal mining areas according to claim 6, characterized in that, The solvents include water and ethanol; Preferably, the solvent comprises water and ethanol in a volume ratio of 1:(6-9).

9. The method for preparing multifunctional microspheres for coal mining areas according to claim 6, characterized in that, The centrifugal separation speed is 5000-12000 rpm; And / or, the washing is performed using an inert gas saturated solvent; preferably, the inert gas saturated solvent includes nitrogen-saturated deionized water; And / or, the drying temperature is 55-65℃, and the drying time is 3-5h.

10. The application of the multifunctional microspheres for coal mining areas as described in any one of claims 1-5 or the multifunctional microspheres for coal mining areas prepared by the preparation method described in any one of claims 6-9 in reducing the viscosity of working fluids in coal mining areas, reducing the filtration loss of formations in coal mining areas, and sealing formation fractures.

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