Microspherical plugging agent and preparation method thereof

Abstract

The invention provides a microsphere type blocking agent and a preparation method thereof, the preparation method comprises the following steps: S1, adding modified starch into water, adjusting the pH value of the modified starch, then carrying out gelatinization reaction, and then adding acrylamide to obtain a water phase; wherein the mass ratio of the modified starch to the acrylamide is (10-20): (5-15); s2, adding an emulsifier into an organic solvent, and heating and emulsifying to obtain an oil phase; s3, adding a cross-linking agent and an initiator into the water phase, then dropwise adding the oil phase, and carrying out polymerization reaction to obtain a reaction solution; wherein the volume ratio of the water phase to the oil phase is 1: (3-5); and S4, carrying out post-treatment on the reaction liquid to obtain the microsphere type blocking agent. The acrylamide monomer is introduced into the modified starch, so that the polymerized microspheres have the rigid characteristic of starch macromolecules and the flexible variable characteristic of acrylamide, and are in rigid-flexible succession, thereby improving the deepening and plugging performance of the starch microspheres.

Description

Technical Field

[0001] The present invention relates to the technical field of enhanced oil and gas production, and particularly relates to a microsphere plugging agent and a preparation method thereof. Background Art

[0002] In the middle and late stages of oilfield development, due to the existence of formation heterogeneity, the water flooding advance is uneven both horizontally and vertically during the water flooding development process. Coupled with clay swelling, particle migration and sand production caused by long-term water flow scouring, it further leads to the deterioration of heterogeneity. Large pore channels or even extra-large pore channels are formed in some oil layer parts, causing premature water flooding in the high-permeability layers between injection and production wells, reducing the sweep efficiency of the injected water to the low-permeability layers, resulting in the increase of water cut in surrounding oil wells and even water flooding, making it impossible to produce the oil in some low-permeability layers. Therefore, in the middle and late stages of oilfield water flooding development, the water shutoff of oil wells and profile control of injection wells that can plug high-permeability formations and increase the sweep area have become important measures to improve oil recovery. In addition, with the continuous deepening of oilfield water flooding development, the downhole conditions deteriorate year by year, and many traditional packer operations can no longer be achieved. In this case, the advantages of chemical profile control and plugging become more and more obvious.

[0003] Starch is a hydrophilic and semi-rigid natural polymer formed by the polymerization of glucose molecules. Modified starch is based on the inherent characteristics of natural starch, and new functional groups are introduced into the starch molecules by physical, chemical or enzymatic treatment methods to change its properties and make it more suitable for application in the petrochemical field.

[0004] Polyacrylamide is a water-soluble linear polymer. Under appropriate conditions, it can be polymerized into a three-dimensional network structure. However, due to the linear characteristics of the molecule itself, the polymer of polyacrylamide has the ability to change the molecular chain conformation, that is, a flexible structure. Summary of the Invention

[0005] The inventors found in the research that: the flexible structure of polyacrylamide has both advantages and disadvantages in the application of profile control and displacement. Flexibility means that the molecule can deform and can enter the deep part of the oil layer to achieve deep profile control and displacement, but at the same time, it also leads to weak plugging performance and insufficient molecular rigidity, which is easy to shear and reduce viscosity.

[0006] To overcome the deficiencies of the crosslinked polymer profile control and plugging technology of polyacrylamide, the purpose of the present invention is to provide a microsphere plugging agent and a preparation method thereof.

[0007] To achieve the above object, the present invention provides a preparation method of a microsphere plugging agent, which includes the following steps:

[0008] S1. Aqueous phase preparation: Add modified starch to water, adjust its pH value and then carry out gelatinization reaction, and then add acrylamide to obtain the aqueous phase; wherein, the mass ratio of modified starch to acrylamide is 10 - 20:5 - 15;

[0009] S2. Oil phase preparation: Add an emulsifier to an organic solvent, heat and emulsify to obtain the oil phase;

[0010] S3. Synthesis: Add a crosslinking agent and an initiator to the aqueous phase, then drop in the oil phase and carry out a polymerization reaction to obtain a reaction solution; wherein, the volume ratio of the aqueous phase to the oil phase is 1:3 - 5;

[0011] S4. Product treatment: Carry out post-treatment on the reaction solution to obtain a microsphere-type plugging agent.

[0012] As Figure 1 shown, in the present invention, the flexible polyacrylamide monomer and the semi-rigid modified starch undergo graft copolymerization under the action of an initiator, and the copolymerized polymer starch microspheres have both flexibility and rigidity, thus having good penetration and plugging performance.

[0013] The present invention adopts the inverse emulsion method. By introducing acrylamide monomer into the gelatinized modified starch solution, adding an initiator and a crosslinking agent, and mixing with the oil phase under the action of an emulsifier to form an emulsion, at a certain polymerization reaction temperature, the starch macromolecules and acrylamide monomers undergo copolymerization through the crosslinking agent. After treating the reactants by spray drying method, acrylamide-grafted starch microspheres are obtained.

[0014] Adopting the inverse emulsion method and controlling the emulsion type in the synthesis reaction to be an inverse emulsion, powdery or latex-like microsphere-type plugging agent products can be obtained, and the solid content of the products is relatively high, improving the solubility of the microsphere-type plugging agent and overcoming the disadvantages of low solid content in the solution polymerization method and poor solubility of the suspension polymerization products.

[0015] In the present invention, the volume ratio (W / O) of the aqueous phase to the oil phase affects the dispersion of the aqueous phase. The present invention preferably selects the volume ratio of the aqueous phase to the oil phase to be 1:3 - 5. If the volume ratio of the aqueous phase to the oil phase is too large, the dispersed droplets of the aqueous phase in the emulsion increase, resulting in an increase in the particle size of the synthesized microspheres, and easily causing phenomena such as precipitation and uneven stirring; if the volume ratio of the aqueous phase to the oil phase is too small, the output of the microspheres will decrease accordingly, and at the same time, too low addition amount of the aqueous phase is also not conducive to forming a stable emulsion, affecting the synthesis of the microspheres.

[0016] The microsphere-type plugging agent (starch microspheres) of the present invention has the advantages of controllable particle size, good uniformity, good temperature and salt resistance, wide raw material sources, environmental friendliness, etc.

[0017] According to the specific embodiments of the present invention, preferably, the modified starch is etherified starch.

[0018] The modified starch used in the present invention is an etherified starch, which introduces a non-ionic and water-soluble hydroxyalkyl group onto its active group, enhancing the swelling property of the original starch and reducing the turbidity of the starch paste. As the degree of substitution increases, the gelatinization temperature decreases. When the degree of substitution reaches a certain value, cold water solubility can be achieved, and a uniform starch paste that is not prone to sedimentation can be formed, meeting the requirements of on-site applications.

[0019] According to a specific embodiment of the present invention, preferably, in S1, after adding the modified starch to water, its pH value is adjusted to 7.5 - 8.0.

[0020] According to a specific embodiment of the present invention, preferably, the temperature of the gelatinization reaction is 75 - 85 °C, and the reaction time is 30 - 40 min. The gelatinization reaction is more preferably carried out at a constant temperature.

[0021] According to a specific embodiment of the present invention, preferably, in S1, the content of the modified starch in the aqueous phase is 1 - 2 g / 20 mL.

[0022] According to a specific embodiment of the present invention, preferably, in S2, the organic solvent is a combination of cyclohexane and chloroform, and the volume ratio of cyclohexane to chloroform is 3 - 5:1.

[0023] In the synthesis of starch microspheres by the inverse emulsion method, the present invention selects cyclohexane as the oil phase and incorporates a certain volume of chloroform with relatively strong polarity to dissolve the emulsifier.

[0024] According to a specific embodiment of the present invention, preferably, in S2, the HLB value of the emulsifier is 4.7 - 5.73.

[0025] According to a specific embodiment of the present invention, preferably, the emulsifier is a combination of Span60 and Tween60, and the mass ratio of Span60 to Tween60 is 8 - 10:1.

[0026] According to a specific embodiment of the present invention, preferably, in S2, the content of the emulsifier in the oil phase is 1 - 2 g / 100 mL.

[0027] According to a specific embodiment of the present invention, preferably, in S3, the dosage of the crosslinking agent is 4 - 10% of the mass of the modified starch.

[0028] According to a specific embodiment of the present invention, preferably, in S3, the crosslinking agent is N,N'-methylenebisacrylamide.

[0029] According to a specific embodiment of the present invention, preferably, in S3, the dosage of the initiator is 0.5 - 0.8% of the mass of the modified starch.

[0030] According to a specific embodiment of the present invention, preferably, in S3, the initiator is ammonium persulfate.

[0031] According to a specific embodiment of the present invention, preferably, in S3, the temperature of the polymerization reaction is 60 - 65 °C and the time is 2 - 3 h.

[0032] In the present invention, as the reaction temperature increases, the hydrogen bonds and intermolecular forces between the molecular chain segments in the starch granules are continuously weakened, and the surface molecular chains can freely stretch into the aqueous solution, increasing the active sites for the cross-linking reaction. A higher temperature is also beneficial to the diffusion of the initiator and cross-linking agent and the acceleration of the free radical generation rate. However, too high a temperature will also increase the homopolymerization rate of the cross-linking agent, resulting in a decrease in the yield and cross-linking degree.

[0033] According to a specific embodiment of the present invention, preferably, the stirring process in the polymerization reaction includes: first, high-speed stirring at 800 - 900 r / min for 5 - 8 min, and then continuous low-speed stirring at 500 - 600 r / min.

[0034] According to a specific embodiment of the present invention, preferably, in S4, the post-treatment process of the reaction solution includes: adding an inert solvent to the reaction solution, fully stirring and standing, then discarding the separated clear liquid, and then adding a volatile solvent, heating at 50 - 55 °C to quickly remove the solvent to obtain the microsphere-type plugging agent.

[0035] The present invention adopts the spray drying method, that is, dispersing the reaction solution containing starch microspheres in an inert solvent, then introducing a volatile solvent, and heating at 50 - 55 °C to quickly (within 20 - 30 min) remove the solvent, reducing the damage to the surface morphology of the starch microspheres caused by rapid dehydration.

[0036] According to a specific embodiment of the present invention, preferably, the inert solvent is ethanol.

[0037] According to a specific embodiment of the present invention, preferably, the volatile solvent is acetone.

[0038] According to a specific embodiment of the present invention, preferably, the preparation method of the above microsphere-type plugging agent specifically includes the following steps:

[0039] (1) Preparation of the aqueous phase

[0040] Weigh 1 - 2.0 g of modified starch, add an appropriate amount of deionized water, adjust the pH value to 8, and gelatinize in a constant temperature water bath at 80 °C for 0.5 h; weigh 0.5 - 1.5 g of acrylamide (AM) and add it to the gelatinized solution, and adjust the volume of the solution to 20 mL to obtain the aqueous phase;

[0041] (2) Preparation of the oil phase

[0042] Measure 80 mL of cyclohexane and 20 mL of chloroform, add 1 - 2 g of a compound emulsifier composed of Span60 and Tween60 (mass ratio 9:1), install an electric stirrer and a condensing reflux device, heat and stir in a constant temperature water bath at 60 °C to dissolve the emulsifier to obtain the oil phase;

[0043] (3) Synthesis reaction

[0044] Weigh an appropriate amount of cross - linker N,N’ - methylenebisacrylamide (MBAA) (4% - 10% of the starch mass) into the aqueous phase, stir magnetically to dissolve it, then weigh ammonium persulfate (APS) (0.5 - 0.8% of the modified starch mass) into the aqueous phase. After dissolution, quickly drop the aqueous phase into the oil phase and finish dropping within 5 min. First, stir at a high speed of 900 r / min for 5 min, then change to 600 r / min, and carry out a polymerization reaction in a constant temperature water bath at 60 °C for 2 - 3 h to obtain the reaction solution; At the beginning of the reaction (after high - speed stirring) and at the end of the reaction, use a dropper to take a small amount of the emulsion and drop it into the aqueous phase and the oil phase respectively to check whether the emulsion type is a reverse emulsion (water - in - oil type); (4) Product treatment

[0045] Use the spray - drying method to treat the reaction solution. The specific method is as follows: After the reaction is completed, pour the product into a beaker, add 30 mL of absolute ethanol, stir magnetically for 0.5 h, discard the upper clear liquid, then add an appropriate amount of acetone, dry at room temperature, and collect the white powder, which is the microsphere - type plugging agent (starch microspheres). The product needs to be stored sealed and dried at room temperature.

[0046] The present invention also provides a microsphere - type plugging agent, which is obtained by the preparation method of the above - mentioned microsphere - type plugging agent.

[0047] According to the specific embodiments of the present invention, preferably, the particle size of the microsphere - type plugging agent is 50 - 150 μm.

[0048] The acrylamide - grafted starch microspheres prepared by the present invention have a certain particle size distribution. The present invention can obtain starch microspheres with different particle sizes and strengths through parameters such as the ratio of the aqueous phase to the oil phase, stirring speed, and the amount of cross - linker used. The specific parameters can be adjusted according to the actual situation on site. The synthesized product is a white powder, which can be dissolved in water by stirring, and the aqueous solution is a white emulsion.

[0049] The technical solution provided by the present invention has the following beneficial effects:

[0050] The present invention uses modified starch and acrylamide as the main raw materials. Before the reaction, physical and chemical dispersion of the modified starch is carried out, and the synthesis adopts the inverse emulsion method. Under the action of an initiator and a crosslinking agent, a microsphere-type water plugging agent is copolymerized, that is, an acrylamide-grafted starch microsphere. Since the present invention introduces acrylamide monomers, the polymerized microspheres have both the rigid characteristics of starch macromolecules and the flexible variable characteristics of acrylamide, with rigidity following flexibility, thereby enhancing the penetration and plugging performance of the starch microspheres; in addition, after the starch microspheres absorb water and swell, they can further penetrate deep into the oil reservoir to achieve deep water plugging and profile control of the oil reservoir. Description of the Drawings

[0051] Figure 1 It is the crosslinking reaction formula of the modified starch and acrylamide of the present invention, where AGU is the glucose monomer and AM is the acrylamide monomer;

[0052] Figure 2 It is the infrared spectrum of the etherified starch in Example 1;

[0053] Figure 3 It is the infrared spectrum of the microsphere-type plugging agent in Example 1;

[0054] Figure 4 It is the microscopic image of the microsphere-type plugging agent in Example 1 in water;

[0055] Figure 5 It is the microscopic image of the microsphere-type plugging agent in Example 1 in salt water;

[0056] Figure 6 It is the plugging curve of the microsphere-type plugging agent solution filling the sand tube in Experimental Example 1, where P1, P2, and P3 are three consecutive pressure measurement points from the injection end backward. Detailed Description of the Invention

[0057] In order to have a clearer understanding of the technical features, objectives, and beneficial effects of the present invention, the technical solutions of the present invention are described in detail below, but it should not be construed as a limitation on the scope of implementation of the present invention.

[0058] The experimental reagents used in the specific implementation of the present invention include: etherified starch, acrylamide, cyclohexane, chloroform, deionized water, N,N'-methylenebisacrylamide (MBAA), Span60, Tween60, ammonium persulfate (APS); the main experimental instruments are a constant temperature water bath, a digital display electric stirrer, a constant temperature drying oven, an analytical balance, an infrared spectrometer, etc.

[0059] Example 1

[0060] This example provides a preparation method of a microsphere-type plugging agent, which is as follows:

[0061] (1) Preparation of aqueous phase: Weigh 1.0 g of etherified starch, add an appropriate amount of deionized water, adjust the pH value to 8, and gelatinize it in a constant temperature water bath at 80 °C for 0.5 h; weigh 1.5 g of acrylamide and add it to the gelatinized solution, and adjust the volume of the solution to 20 mL to obtain the aqueous phase;

[0062] (2) Preparation of oil phase: Measure 80 mL of cyclohexane and 20 mL of chloroform, add 1.0 g of a compound emulsifier composed of Span60 and Tween60 (mass ratio 9:1), install an electric stirrer and a condensing reflux device, and heat and stir in a constant temperature water bath at 60 °C to dissolve the emulsifier to obtain the oil phase;

[0063] (3) Synthesis reaction: Weigh 0.05 g of crosslinking agent MBAA into the aqueous phase, stir it magnetically to dissolve it, then weigh 0.005 g of initiator APS into the aqueous phase, and quickly add the aqueous phase dropwise to the oil phase after dissolution, and finish dropping within 5 min; first stir at a high speed of 900 r / min for 5 min, and then change to a constant temperature water bath at 60 °C and react at 600 r / min for 2 h; at the beginning and end of the reaction, use a dropper to take a small amount of emulsion and drop it into the aqueous phase and the oil phase respectively to check the emulsion type and ensure it is a reverse emulsion;

[0064] (4) Product treatment: Use spray drying method to treat the starch microspheres. The specific method is as follows: After the reaction, pour the product into a beaker, add 30 mL of absolute ethanol, stir magnetically for 0.5 h, discard the upper clear liquid, then add an appropriate amount of acetone, heat to 50 °C, and the solvent can be quickly removed within 20 min to obtain a white powder, that is, the microsphere-type plugging agent (starch microspheres).

[0065] This microsphere-type plugging agent is soluble in water and the aqueous solution is a white emulsion. Infrared spectrum detection was carried out on the etherified starch and microsphere-type plugging agent samples, and the results are shown in Figure 2 and Figure 3 respectively. By comparison, it can be found that strong and broad -OH stretching vibration absorption bands appear at 3400 cm -1 for both spectra, but the wave number of the etherified starch before the reaction is about 23, and the wave number of the sample after the reaction (microsphere-type plugging agent) is about 15. The wave number decreases significantly after the crosslinking reaction, indicating that some hydroxyl groups of the starch have undergone crosslinking reactions; in the figure, 1654 cm -1 is the bending vibration peak of amide N-H, and 1290 cm -1 is the stretching vibration peak of tertiary amine C-N. It can be seen that Figure 3 the infrared spectrum of the microsphere-type plugging agent sample shown has obvious bending vibration peaks of amide N-H and stretching vibration peaks of tertiary amine C-N, indicating that crosslinking reactions have occurred among the etherified starch, acrylamide and MBAA.

[0066] Observe the microsphere-type plugging agent in the aqueous solution with an optical microscope, as shown in Figure 4As shown, it can be found that the microsphere plugging agent is in the shape of spherical particles with a particle size of about 50 - 150 μm.

[0067] When the microsphere plugging agent is dissolved in salt water, as Figure 5 shown, it can be found that, compared with that in an aqueous solution ( Figure 4 ), the swelling ratio of the microsphere plugging agent has a certain increase.

[0068] Example 2

[0069] This example provides a preparation method of a microsphere plugging agent, which is as follows:

[0070] (1) Preparation of the aqueous phase: Weigh 2.0 g of etherified starch, add an appropriate amount of deionized water, adjust the pH value to 8, and gelatinize it in a constant temperature water bath at 80 °C for 0.5 h; weigh 0.5 g of acrylamide and add it to the gelatinized solution, and adjust the volume of the solution to 20 mL to obtain the aqueous phase;

[0071] (2) Preparation of the oil phase: Measure 80 mL of cyclohexane and 20 mL of chloroform, add 1.0 g of a compound emulsifier composed of Span60 and Tween60 (mass ratio 9:1), install an electric stirrer and a condenser reflux device, and heat and stir in a constant temperature water bath at 60 °C to dissolve the emulsifier to obtain the oil phase;

[0072] (3) Synthesis reaction: Weigh 0.15 g of the crosslinking agent MBAA in the aqueous phase, stir magnetically to dissolve it, then weigh 0.01 g of the initiator APS in the aqueous phase, and quickly add the aqueous phase dropwise to the oil phase after dissolution, and finish dropping within 5 min. First, keep stirring at a high speed of 900 r / min for 5 min, and then change to a constant temperature water bath at 60 °C and react at 600 r / min for 2 h; at the beginning and end of the reaction, take a small amount of the emulsion with a dropper and drop it into the aqueous phase and the oil phase respectively to check the emulsion type and ensure it is a reverse-phase emulsion;

[0073] (4) Product treatment: Use the spray drying method to treat the starch microspheres. The specific method is as follows: After the reaction, pour the product into a beaker, add 30 mL of absolute ethanol, stir magnetically for 0.5 h, discard the upper clear liquid, then add an appropriate amount of acetone, heat to 50 °C, and the solvent can be quickly removed within 20 min to obtain a white powder, that is, the microsphere plugging agent (starch microspheres).

[0074] The microsphere plugging agent is soluble in water, and the aqueous solution is a white emulsion.

[0075] Example 3

[0076] This example provides a preparation method of a microsphere plugging agent, which is as follows:

[0077] (1) Preparation of aqueous phase: Weigh 1.5 g of etherified starch, add appropriate amount of deionized water, adjust the pH value to 8, and gelatinize in a constant temperature water bath at 80°C for 0.5 h; weigh 1.0 g of acrylamide and add it to the gelatinized solution, adjust the solution volume to 20 mL, and obtain an aqueous phase;

[0078] (2) Preparation of oil phase: 80 mL of cyclohexane and 20 mL of chloroform were weighed, 1.5 g of a composite emulsifier consisting of Span 60 and Tween 60 (mass ratio 9:1) was added, an electric stirring and condensation reflux device was installed, and the mixture was heated and stirred in a constant temperature water bath at 60°C to dissolve the emulsifier to obtain an oil phase;

[0079] (3) Synthesis reaction: weigh 0.15 g of the cross-linking agent MBAA into the water phase, stir it magnetically to dissolve it, then weigh 0.01 g of the initiator APS into the water phase, and after dissolution, quickly add the water phase dropwise to the oil phase, and complete the addition within 5 min. First, maintain high-speed stirring at 900 r / min for 5 min, then change to 600 r / min and react in a constant temperature water bath at 60°C for 3 h; at the beginning and end of the reaction, use a dropper to take a small amount of the emulsion and drop it into the water phase and oil phase respectively, check the emulsion type to ensure that it is an inverse emulsion;

[0080] (5) Product treatment: The starch microspheres were treated by powder spray drying method. The specific method was as follows: after the reaction was completed, the product was poured into a beaker, 30 mL of anhydrous ethanol was added, and magnetic stirring was performed for 0.5 h. The upper clear liquid was discarded, and an appropriate amount of acetone was added. The mixture was dried at room temperature, and the white powder was collected to obtain a microsphere plugging agent (starch microspheres).

[0081] Experimental example

[0082] A physical model experiment was used to evaluate the plugging performance of the microsphere plugging agent in Example 1.

[0083] The microsphere plugging agent of Example 1 was prepared into a microsphere plugging agent solution with a plugging agent concentration of 1000ppm and a mineralization degree of 4000, and after being fully stirred, it was placed in a 45°C thermostat to swell for use. Quartz sand of different mesh sizes was selected to fill a 100cm filled sand pipe, which was placed in a 45°C thermostat, and the filled sand pipe was flushed with formation water at a certain flow rate for 48 hours to simulate the formation of long-term water injection development, and the permeability of the sand pipe was measured to be 1.5D. The microsphere solution was squeezed into the sand pipe at a flow rate of 0.4L / min, and the pressure changes at each pressure measuring point of the sand pipe were recorded.

[0084] The experimental results are as follows Figure 6As shown in the figure, for the microsphere plugging agent solution with a concentration of 1000 ppm, as the injection volume increases, the pressure at each pressure measurement point in the sand tube fluctuates upward. When the injection volume reaches 4.0 Vp, the pressures at the three pressure measurement points (P1, P2, P3) along the flow line direction increase from 6.8 KPa, 5.7 KPa, and 5.6 KPa to 29.8 KPa, 17.3 KPa, and 10.5 KPa respectively. After injecting the microsphere plugging agent and then switching to injecting formation water, the pressure drops slightly. The results show that the starch microsphere solution with a concentration of 1000 ppm can penetrate into the packed sand tube with a permeability of 1.5 D and form a good plugging effect on the sand tube.

Claims

1. A preparation method of a microsphere plugging agent, which comprises the following steps: S1. Aqueous phase preparation: Add modified starch into water, adjust its pH value and then carry out a gelatinization reaction, and then add acrylamide to obtain an aqueous phase; among them, The mass ratio of modified starch to acrylamide is 10 - 20:5 - 15; S2. Preparation of the oil phase: Add an emulsifier to an organic solvent, heat and emulsify to obtain the oil phase; S3. Synthesis: Add a crosslinking agent and an initiator to the water phase, then dropwise add the oil phase and carry out a polymerization reaction to obtain a reaction solution; wherein, the volume ratio of the water phase to the oil phase is 1:3 - 5; S4. Product treatment: Post-treat the reaction solution to obtain the microsphere plugging agent; Preferably, the modified starch is etherified starch.

2. The preparation method of the microsphere-shaped plugging agent according to claim 1, wherein, In S1, after the modified starch is added to water, its pH value is adjusted to 7.5 - 8.

0.

3. The preparation method of the microsphere-shaped plugging agent according to claim 1, wherein, In S1, the temperature of the gelatinization reaction is 75 - 85 °C and the time is 30 - 40 min.

4. The preparation method of the microsphere-shaped plugging agent according to claim 1, wherein, In S1, the content of the modified starch in the water phase is 1 - 2 g / 20 mL.

5. The preparation method of the microsphere type plugging agent according to claim 1, wherein, In S2, the organic solvent is a combination of cyclohexane and chloroform, and the volume ratio of cyclohexane to chloroform is 3 - 5:

1.

6. The preparation method of the microsphere-type plugging agent according to claim 1, wherein, In S2, the HLB value of the emulsifier is 4.7 - 5.73; Preferably, the emulsifier is a combination of Span60 and Tween60, and the mass ratio of Span60 to Tween60 is 8 - 10:

1.

7. The preparation method of the microsphere-type plugging agent according to claim 1, wherein, In S2, the content of the emulsifier in the oil phase is 1 - 2 g / 100 mL.

8. The preparation method of the microsphere-shaped plugging agent according to claim 1, wherein, In S3, the dosage of the crosslinking agent is 4 - 10% of the mass of the modified starch.

9. The preparation method of the microsphere-shaped plugging agent according to claim 1, wherein, In S3, the crosslinking agent is N,N'-methylenebisacrylamide.

10. The preparation method of the microsphere-type plugging agent according to claim 1, wherein, In S3, the dosage of the initiator is 0.5 - 0.8% of the mass of the modified starch.

11. The preparation method of the microsphere-shaped plugging agent according to claim 1, wherein, In S3, the initiator is ammonium persulfate.

12. The preparation method of the microsphere-type plugging agent according to claim 1, wherein, In S3, the temperature of the polymerization reaction is 60 - 65 °C and the time is 2 - 3 h; Preferably, the stirring process in the polymerization reaction includes: first, high-speed stirring at 800 - 900 r / min for 5 - 8 min, and then continuous low-speed stirring at 500 - 600 r / min.

13. The preparation method of the microsphere-shaped plugging agent according to claim 1, wherein, In S4, the post-treatment process of the reaction solution includes: adding an inert solvent to the reaction solution, fully stirring and standing, then discarding the separated clear liquid, and then adding a volatile solvent, heating at 50 - 55 °C to remove the solvent to obtain the microsphere plugging agent.

14. The preparation method of the microsphere-shaped plugging agent according to claim 13, wherein, The inert solvent is ethanol; Preferably, the volatile solvent is acetone.

15. A microsphere plugging agent obtained by the preparation method of the microsphere plugging agent according to any one of claims 1 - 14.

16. The microsphere-shaped plugging agent according to claim 15, wherein, The particle size of the microsphere plugging agent is 50 - 150 μm.

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