阅读说明：本技术 一种耐盐型聚合物微球封堵剂及其制备方法 (Salt-tolerant polymer microsphere plugging agent and preparation method thereof ) 是由 赖小娟 冯雪婷 王磊 王淇 韩宁 杨莛鋆 焦想 于 2021-01-29 设计创作，主要内容包括：本发明公开了一种耐盐型聚合物微球封堵剂及其制备方法,该聚合物微球封堵剂由白油、气相二氧化硅、丙烯酰胺单体、丙烯酸、失水山梨醇脂肪酸酯、N,N-亚甲基双丙烯酰胺、过硫酸铵、亚硫酸氢钠、亲水基表面活性剂、水等原料制备而成；本发明采用反相乳液聚合法合成了具有超低界面张力的耐盐型聚合物微球,制备的聚合物微球封堵剂是一种具有超低界面张力的新型聚合物微球,其界面张力可达到4.3×10～(-3)mN/m,耐盐性可达到50000mg/L矿化度,改善了现有聚合物微球界面张力低、耐盐性较差的问题。(The invention discloses a salt-tolerant polymer microsphere plugging agent and a preparation method thereof, wherein the polymer microsphere plugging agent is prepared from white oil and gas phase IISilicon oxide, acrylamide monomer, acrylic acid, sorbitan fatty acid ester, N-methylene bisacrylamide, ammonium persulfate, sodium bisulfite, hydrophilic group surfactant, water and the like; the invention adopts an inverse emulsion polymerization method to synthesize salt-tolerant polymer microspheres with ultralow interfacial tension, and the prepared polymer microsphere plugging agent is a novel polymer microsphere with ultralow interfacial tension, and the interfacial tension can reach 4.3 multiplied by 10 ‑3 mN/m, the salinity tolerance can reach 50000mg/L, and the problems of low interfacial tension and poor salinity tolerance of the existing polymer microspheres are improved.)

1. A salt-tolerant polymer microsphere plugging agent is characterized in that: the material is prepared from the following raw materials in percentage by weight:

20-40 wt% of white oil, 0.5-2 wt% of fumed silica, 10-25 wt% of acrylamide monomer, 5-15 wt% of acrylic acid, 5-15 wt% of sorbitan fatty acid ester, 0.03-0.08 wt% of N, N-methylene bisacrylamide, 0.01-0.05 wt% of ammonium persulfate, 0.01-0.08 wt% of sodium bisulfite, 10-25 wt% of hydrophilic group surfactant and the balance of water.

2. The plugging agent of claim 1, wherein: the hydrophilic surfactant is one or a mixture of more than two of Tween-80, TX-10, OP-10 and SAS 60.

3. The plugging agent of claim 1, wherein: the sorbitan fatty acid ester is one or a mixture of more than two of Span-40, Span-60 and Span-80.

4. The plugging agent of claim 1, wherein: the water is tap water or deionized water.

5. A preparation method of a salt-tolerant polymer microsphere plugging agent is characterized by comprising the following steps: the method comprises the following steps:

under the condition of room temperature, adding white oil, fumed silica, sorbitan fatty acid ester and hydrophilic surfactant, and uniformly stirring to prepare a solution A;

adding acrylamide monomer, acrylic acid and N, N-methylene bisacrylamide into water, stirring to completely dissolve the acrylamide monomer, adding alkali liquor for neutralization, then adding sodium bisulfite, stirring to completely dissolve the sodium bisulfite to prepare solution B; the mass ratio of the solution A to the solution B is (1-4): 1;

and adding the solution B into the solution A, fully emulsifying, heating to 60-70 ℃, starting condensation reflux, dropwise adding ammonium persulfate, continuously stirring until the reaction is complete after dropwise addition, cooling to room temperature, and discharging after cooling to obtain the polymer microsphere plugging agent.

6. The preparation method of the salt-tolerant polymeric microsphere plugging agent according to claim 5, wherein the preparation method comprises the following steps: the concrete dosage of the raw materials by weight percentage is as follows:

20-40 wt% of white oil, 0.5-2 wt% of fumed silica, 10-25 wt% of acrylamide monomer, 5-15 wt% of acrylic acid, 5-15 wt% of sorbitan fatty acid ester, 0.03-0.08 wt% of N, N-methylene bisacrylamide, 0.01-0.05 wt% of ammonium persulfate, 0.01-0.08 wt% of sodium bisulfite, 10-25 wt% of hydrophilic group surfactant and the balance of water.

7. The salt-tolerant polymeric microsphere plugging agent and the preparation method thereof according to claim 5, wherein the salt-tolerant polymeric microsphere plugging agent is characterized in that: the ammonium persulfate initiator is dropwise added in batches by using an aqueous solution with the mass concentration of 10%, and the dropwise adding time is 45-60 min; and after the ammonium persulfate is dropwise added, continuously stirring at the rotating speed of 200-300 r/min, and continuously reacting for 6-7 h.

8. The salt-tolerant polymeric microsphere plugging agent and the preparation method thereof according to claim 5, wherein the salt-tolerant polymeric microsphere plugging agent is characterized in that: and the alkali liquor is neutralized by using a sodium hydroxide aqueous solution, and the neutralization degree is 50-80%.

9. The salt-tolerant polymeric microsphere plugging agent and the preparation method thereof according to claim 5, wherein the salt-tolerant polymeric microsphere plugging agent is characterized in that: the emulsifying condition is that the stirring speed is 500-600 r/min, and the time is 20-30 min.

10. The salt-tolerant polymeric microsphere plugging agent and the preparation method thereof according to claim 5, wherein the salt-tolerant polymeric microsphere plugging agent is characterized in that: the stirring speed is 200-300 r/min.

Technical Field

The invention belongs to the technical field of oilfield exploitation chemicals, and particularly relates to a salt-tolerant polymer microsphere plugging agent with ultralow interfacial tension and a preparation method thereof.

Background

The polyacrylamide microsphere is a water-absorbent resin with wide application, is applied to deep profile control and water shutoff of an oil field, mainly aims at deep profile control of the oil field with strong heterogeneity, high water content and large pore canal development, and is a new technology developed for improving the water flooding development effect.

In the prior art, Chinese patent CN1888374A discloses a high-temperature and high-salt resistant water plugging method, a three-segment plug injection water plugging method is adopted, and a plugging agent is added into a first segment plug, which accounts for 10-20% of the total injection amount; after the plugging agent is injected for 0.5-1.5 hours, closing the well and waiting for coagulation, so that the oil layer is temporarily plugged before the plugging agent is gelled; a second slug which is injected subsequently, wherein the second slug is characterized by low viscosity, easy injection, and capable of forming high viscoelasticity gel at the formation temperature, the applicable temperature range is 90-280 ℃, and the second slug accounts for 70-80% of the total injection amount;

the third slug is cement and serves as a sealing agent, the strength of the main plugging slug is improved and accounts for 10-20% of the total injection amount, but the third slug can generate gel in an oil layer and can reduce the relative permeability of an oil phase.

The polyacrylamide microsphere water shutoff agent prepared by Chinese patent CN103073679A comprises weighed raw materials of acrylamide, an anti-salt monomer, N-methylene diacryloyl, Span-80, potassium persulfate, cyclohexane and deionized water; stirring and mixing the dispersing agent and cyclohexane in the polymerized monomer; initiating and polymerizing to form the water shutoff agent. Cyclohexane is selected as a continuous phase, so that the cost is high, the continuous phase is layered after standing, the stability is poor, and the salinity tolerance is only 30000 mg/L.

The prior relevant documents and patents do not find the salt-tolerant polymer microsphere plugging agent with ultralow interfacial tension and the preparation method thereof.

Disclosure of Invention

In order to overcome the defects of interfacial tension and salt resistance of the plugging agent in the prior art, the invention provides a salt-tolerant polymer microsphere plugging agent and a preparation method thereof.

In order to achieve the purpose, the invention adopts the following technical scheme:

a salt-tolerant polymer microsphere plugging agent is prepared from the following raw materials in percentage by weight:

20-40 wt% of white oil, 0.5-2 wt% of fumed silica, 10-25 wt% of acrylamide monomer, 5-15 wt% of acrylic acid, 5-15 wt% of sorbitan fatty acid ester, 0.03-0.08 wt% of N, N-methylene bisacrylamide, 0.01-0.05 wt% of ammonium persulfate, 0.01-0.08 wt% of sodium bisulfite, 10-25 wt% of hydrophilic group surfactant and the balance of water.

As a further improvement of the invention, the hydrophilic surfactant is one or a mixture of more than two of Tween-80, TX-10, OP-10 and SAS 60.

As a further improvement of the invention, the sorbitan fatty acid ester is one or a mixture of more than two of Span-40, Span-60 and Span-80.

As a further improvement of the invention, the water is tap water or deionized water.

As a further improvement of the invention, the white oil is technical grade.

A preparation method of a salt-tolerant polymer microsphere plugging agent comprises the following steps:

1) weighing the raw materials according to the weight ratio for later use;

2) under the condition of room temperature, adding white oil, fumed silica, sorbitan fatty acid ester and hydrophilic surfactant into a container provided with a stirrer, a thermometer and a reflux condensing device, and uniformly stirring to prepare a solution A;

3) adding the weighed acrylamide monomer, acrylic acid and N, N-methylene bisacrylamide into water, stirring to completely dissolve the acrylamide monomer, adding alkali liquor for neutralization, then adding sodium bisulfite, and stirring to completely dissolve the sodium bisulfite to prepare a solution B; the mass ratio of the solution A to the solution B is (1-4): 1;

4) and adding the solution B into the solution A, fully emulsifying, heating to 60-70 ℃, starting condensation reflux, dropwise adding ammonium persulfate, continuously stirring until the reaction is complete after dropwise addition, cooling to room temperature, and discharging after cooling to obtain the polymer microsphere plugging agent.

As a further improvement of the invention, the alkali liquor in the step 3) is neutralized by sodium hydroxide aqueous solution, and the neutralization degree is 50-80%.

As a further improvement of the invention, in the step 4), the ammonium persulfate initiator is dropwise added in batches by using an aqueous solution with the mass concentration of 10%, and the dropwise adding time is 45-60 min.

As a further improvement of the invention, in the step 4), the emulsification condition is that the stirring speed is 500-600 r/min, and the time is 20-30 min.

As a further improvement of the invention, in the step 4), after the ammonium persulfate is dripped, the stirring speed is continuously 200-300 r/min, and the continuous reaction time is 6-7 h.

As a further improvement of the invention, the rotating speed in the step 2) is 200-300 r/min.

Compared with the prior art, the invention has the following advantages:

the polymer microsphere plugging agent takes acrylamide and acrylic acid as comonomers, N, N-methylene bisacrylamide as a cross-linking agent, ammonium persulfate and sodium bisulfite as redox initiators, white oil as a continuous phase and a loss reduction agentThe sorbitan fatty acid ester and the hydrophilic surfactant are used as composite emulsifier, the polymer microsphere with ultralow interfacial tension is synthesized by adopting an inverse emulsion polymerization method, and analysis shows that the plugging agent is a salt-tolerant polymer microsphere with ultralow interfacial tension, and the interfacial tension can reach 4.3 multiplied by 10^-3mN/m, the salinity tolerance can reach 50000mg/L, and the problems of low interfacial tension and small salinity tolerance of the existing polymer microspheres are improved.

The polymer microsphere water shutoff agent prepared by the invention has the advantages of simple construction, good stability, ultralow interfacial tension and higher salt tolerance, and can simultaneously achieve the effects of shutoff and oil displacement.

Furthermore, the sorbitan fatty acid ester and the hydrophilic surfactant are used as the composite emulsifier in the formula, so that the emulsifying effect is improved, the speed is increased, and the stability of the emulsion is improved.

Furthermore, the water used in the formula of the invention is tap water or deionized water, both the reaction effect and the yield can be ensured, particularly the use of tap water effectively simulates the actual production condition, and the applicability of the polymer microsphere plugging agent of the invention is improved.

Further, the mass ratio of the solution A to the solution B adopted in the preparation method is (1-4): 1, the requirement of oil-in-water in the inverse emulsion polymerization reaction is ensured.

Further, the ammonium persulfate initiator is added in batches by using an aqueous solution with the concentration of 10% to prevent over violent reaction, ensure full reaction and high yield.

Description of the drawings:

FIG. 1 is a graph of interfacial tension of polymeric microspheres from example 1;

FIG. 2 is a graph of interfacial tension of the polymeric microspheres of example 2;

FIG. 3 is a graph of interfacial tension of the polymeric microspheres of example 3;

FIG. 4 is a graph of interfacial tension of the polymeric microspheres of example 4;

FIG. 5 is a graph of interfacial tension of the polymeric microspheres of example 5;

FIG. 6 salt tolerance analysis plot of polymeric microspheres of example 5;

FIG. 7 stability analysis of the polymeric microspheres of example 5 after 15 days of storage;

FIG. 8 Transmission electron micrograph of polymeric microspheres of example 5.

FIG. 9 is a reaction schematic diagram of a salt-tolerant polymeric microsphere plugging agent of the present invention.

Detailed Description

As shown in fig. 9, a preparation method of a salt-tolerant polymeric microsphere plugging agent comprises the following steps:

1) weighing the raw materials according to the weight ratio for later use;

2) under the condition of room temperature, adding white oil, fumed silica, sorbitan fatty acid ester and hydrophilic surfactant into a container provided with a stirrer, a thermometer and a reflux condensing device, uniformly stirring, and preparing a solution A at the stirring speed of 200-300 r/min;

3) and adding the weighed acrylamide monomer, acrylic acid and N, N-methylene bisacrylamide into water, stirring to completely dissolve the acrylamide monomer, the acrylic acid and the N, N-methylene bisacrylamide, and adding a sodium hydroxide aqueous solution to neutralize, wherein the neutralization degree is 50-80%. Then adding sodium bisulfite, stirring to completely dissolve the sodium bisulfite to prepare solution B; the mass ratio of the solution A to the solution B is (1-4): 1;

4) adding the solution B into the solution A, wherein the emulsifying and stirring speed is 500-600 r/min, the time is 20-30 min, then heating to 60-70 ℃, starting condensation reflux, dropwise adding 10% ammonium persulfate aqueous solution in batches, and the dropwise adding time is 45-60 min and 45-60 min; and (3) continuing stirring after the dropwise adding is finished, wherein the stirring speed is 200-300 r/min until the reaction is completed for 6-7 h. Then cooling to room temperature, and discharging after cooling to obtain the polymer microsphere plugging agent.

20-40 wt% of white oil, 0.5-2 wt% of fumed silica, 10-25 wt% of acrylamide monomer, 5-15 wt% of acrylic acid, 5-15 wt% of sorbitan fatty acid ester, 0.03-0.08 wt% of N, N-methylene bisacrylamide, 0.01-0.05 wt% of ammonium persulfate, 0.01-0.08 wt% of sodium bisulfite, 10-25 wt% of hydrophilic group surfactant and the balance of water.

Wherein, the hydrophilic surfactant can be one or more than two of Tween-80, TX-10, OP-10 and SAS 60; the sorbitan fatty acid ester can be one or more selected from Span-40, Span-60 and Span-80; the water is tap water or deionized water; the white oil is technical grade.

In the calculation of the neutralization degree, y is (M × 71)/(40 × M × c), where y is the neutralization degree, M is the mass of sodium hydroxide, 40 is the relative molecular mass of sodium hydroxide, M is the mass of acrylic acid, c is the concentration of acrylic acid, and 71 is the relative molecular mass of acrylic acid.

The present invention will be further described with reference to specific examples.

Example 1

The weight ratio of the raw materials is as follows: 40 wt% of white oil, 0.5 wt% of fumed silica, 20 wt% of acrylamide monomer, 5 wt% of acrylic acid, 5 wt% of Span-60, 0.03 wt% of N, N-methylene bisacrylamide, 0.01 wt% of ammonium persulfate, 0.015 wt% of sodium bisulfite, 10 wt% of Tween-80 and the balance of distilled water. Putting white oil, fumed silica, Span-60 and Tween-80 into a reactor provided with a stirrer, a reflux condenser and a thermometer, and uniformly stirring at the rotating speed of 200r/min to prepare a solution A; dissolving monomer acrylamide with water in a beaker, adding acrylic acid and N, N-methylene bisacrylamide, uniformly stirring on a magnetic stirrer, adding a sodium hydroxide aqueous solution for neutralization after complete dissolution, wherein the neutralization degree is 50%, adding sodium bisulfite until complete dissolution to prepare a solution B, slowly adding the solution B into the solution A, emulsifying and stirring at the rotation speed of 500r/min for 20min, heating to 60 ℃ after emulsification, preparing a 10 wt% aqueous solution of ammonium persulfate, slowly adding the aqueous solution in batches, completing dropwise addition within 1h, continuing stirring and reacting at the rotation speed of 200r/min for 6h after finishing the initiator dropwise addition, and cooling and discharging. The obtained polymer microspheres are not layered after being placed for 7 days, and the interfacial tension diagram is shown in figure 1, when the mineralization degree is 30000mg/L and the concentration of the microspheres is 0.5 percent, the interfacial tension is 8.6 multiplied by 10^-1mN/m。

Example 2

The weight ratio of the raw materials is as follows: 20 wt% of white oil, 1.1 wt% of fumed silica, 25 wt% of acrylamide monomer, 10 wt% of acrylic acid, Span-10 wt% of 40, 0.08 wt% of N, N-methylene-bisacrylamide, 0.05 wt% of ammonium persulfate, 0.08 wt% of sodium bisulfite, 25 wt% of OP-10 and the balance of tap water. Putting white oil, fumed silica, Span-40 and OP-10 into a reactor provided with a stirrer, a reflux condenser and a thermometer, and uniformly stirring at the rotating speed of 300r/min to prepare a solution A; dissolving monomer acrylamide with water in a beaker, adding acrylic acid and N, N-methylene bisacrylamide, uniformly stirring on a magnetic stirrer, adding a sodium hydroxide aqueous solution for neutralization after complete dissolution, wherein the neutralization degree is 60%, adding sodium bisulfite until complete dissolution, preparing a solution B, slowly adding the solution B into the solution A, emulsifying and stirring at the rotation speed of 600r/min for 25min, heating to 65 ℃ after emulsification, preparing 10 wt% aqueous solution from ammonium persulfate, slowly adding the aqueous solution in batches, continuously stirring and reacting at the rotation speed of 300r/min for 6h after finishing dropping of an initiator, and cooling and discharging. The obtained polymer microspheres are not layered after being placed for 24 hours, the interfacial tension diagram is shown in figure 2, and when the mineralization degree is 30000mg/L and the concentration of the microspheres is 0.5 percent, the interfacial tension is 7.2 multiplied by 10^-1mN/m。

Example 3

The weight ratio of the raw materials is as follows: 38 wt% of white oil, 1.6 wt% of fumed silica, 15 wt% of acrylamide monomer, 15 wt% of acrylic acid, 8 wt% of Span-80, 0.04 wt% of N, N-methylene bisacrylamide, 0.02 wt% of ammonium persulfate, 0.05 wt% of sodium bisulfite, 12 wt% of TX-10 and the balance of tap water. Putting white oil, fumed silica, Span-80 and TX-10 into a reactor provided with a stirrer, a reflux condenser and a thermometer, and uniformly stirring at the rotating speed of 200r/min to prepare a solution A; dissolving monomer acrylamide with water in a beaker, adding acrylic acid and N, N-methylene bisacrylamide, uniformly stirring on a magnetic stirrer, adding a sodium hydroxide aqueous solution for neutralization after completely dissolving, wherein the neutralization degree is 65%, adding sodium bisulfite until completely dissolving to prepare a solution B, slowly adding the solution B into the solution A, emulsifying at the rotation speed of 500r/min for 30min, heating to 65 ℃ after emulsification, preparing an ammonium persulfate aqueous solution with the weight percent of 10%, slowly adding the ammonium persulfate in batches, completing dropwise addition within 45min, and completing the dropwise addition at the speed of 20% after finishing the initiator dropwise additionContinuously stirring and reacting for 7h at the rotating speed of 0r/min, cooling and discharging. The obtained polymer microspheres are not layered after being placed for 30 days, and the interfacial tension graph of the polymer microspheres is shown in figure 3, and when the mineralization degree is 30000mg/L and the concentration of the microspheres is 0.5 percent, the interfacial tension of the polymer microspheres is 8.1 multiplied by 10^-2mN/m。

Example 4

The weight ratio of the raw materials is as follows: 30 wt% of white oil, 2 wt% of fumed silica, 10 wt% of acrylamide monomer, 12 wt% of acrylic acid, 15 wt% of Span-60, 0.04 wt% of N, N-methylene bisacrylamide, 0.015 wt% of ammonium persulfate, 0.03 wt% of sodium bisulfite, 9 wt% of TX-10, 3 wt% of Tween-80 and the balance of tap water. Putting white oil, fumed silica, Span-60, TX-10 and Tween-80 into a reactor provided with a stirrer, a reflux condenser and a thermometer, and uniformly stirring at the rotating speed of 200r/min to prepare a solution A; dissolving monomer acrylamide with water in a beaker, adding acrylic acid and N, N-methylene bisacrylamide, uniformly stirring on a magnetic stirrer, adding a sodium hydroxide aqueous solution for neutralization after complete dissolution, adding sodium bisulfite until complete dissolution to prepare a solution B, slowly adding the solution B into the solution A, emulsifying at the rotation speed of 600r/min for 30min, heating to 70 ℃ after emulsification, preparing a 10 wt% aqueous solution of ammonium persulfate, slowly adding the ammonium persulfate in batches, continuously stirring at the rotation speed of 300r/min for reaction for 7h after finishing dropping of an initiator, and cooling and discharging. The obtained polymer microspheres are not layered after being placed for 30 days, and the interfacial tension graph of the polymer microspheres is shown in figure 4, and when the mineralization degree is 30000mg/L and the concentration of the microspheres is 0.5 percent, the interfacial tension of the polymer microspheres is 2.9 multiplied by 10^-2mN/m。

Example 5

The weight ratio of the raw materials is as follows: 30 wt% of white oil, 1.9 wt% of fumed silica, 18 wt% of acrylamide monomer, 5 wt% of acrylic acid, 4 wt% of Span-60, 3 wt% of Span-80, 0.04 wt% of N, N-methylene bisacrylamide, 0.05 wt% of ammonium persulfate, 0.03 wt% of sodium bisulfite, 9 wt% of OP-10, 3 wt% of SAS60, and the balance of tap water. Putting white oil, fumed silica, Span-60, Span-80, OP-10 and SAS60 into a reactor provided with a stirrer, a reflux condenser and a thermometer, and uniformly stirring at the rotating speed of 300r/min to prepare solution A; dissolving monomer acrylamide with water in a beaker, adding acrylic acid and N, N-methylene bisacrylamide, uniformly stirring on a magnetic stirrer, adding a sodium hydroxide aqueous solution for neutralization after complete dissolution, wherein the neutralization degree is 75%, adding sodium bisulfite until complete dissolution to prepare a solution B, slowly adding the solution B into the solution A, emulsifying at the rotation speed of 600r/min for 30min, heating to 70 ℃ after emulsification, preparing an aqueous solution of 10 wt% of ammonium persulfate, slowly adding the aqueous solution in batches, completing dropwise addition within 1h, continuing to react for 6h after finishing the initiator dropwise addition, and cooling and discharging.

The polymer microspheres obtained in the example are placed for 30 days without delamination, and the interfacial tension diagram is shown in FIG. 5, wherein the interfacial tension is 4.3X 10 when the mineralization degree is 30000mg/L and the concentration of the microspheres is 0.5 percent^-3mN/m. From FIG. 6, it can be seen that at a mineralization degree of 50000mg/L, it still has an ultra-low interfacial tension, indicating that it has a very good salt tolerance; FIG. 7 is a stability test chart of the polymer microsphere after being placed for 15 days, and by observing the light scattering rate of the polymer microsphere, it can be seen that compared with the first baseline, the rest curves are basically overlapped with the first baseline, and the microsphere with large particle size gradually sinks along with the extension of the test time, so that the light scattering rate is increased at 1mm of the bottom of the bottle, and the overall stability is good; as can be seen from the transmission electron micrograph of the polymer microsphere in FIG. 8, the shape of the latex particles of the microsphere is a regular spherical structure and the particle size distribution is relatively uniform.

Example 6

1) Weighing the raw materials according to the weight ratio for later use;

2) under the condition of room temperature, adding white oil, fumed silica, sorbitan fatty acid ester and hydrophilic surfactant into a container provided with a stirrer, a thermometer and a reflux condensing device, uniformly stirring, and stirring at the speed of 200r/min to prepare a solution A;

3) adding weighed acrylamide monomer, acrylic acid and N, N-methylene bisacrylamide into water, stirring to completely dissolve the acrylamide monomer, the acrylic acid and the N, N-methylene bisacrylamide, and adding sodium hydroxide aqueous solution to neutralize until the neutralization degree is 50%. Then adding sodium bisulfite, stirring to completely dissolve the sodium bisulfite to prepare solution B; the mass ratio of the solution A to the solution B is 1: 1;

4) adding the solution B into the solution A, wherein the emulsifying and stirring speed is 500-600 r/min, the time is 20-30 min, then heating to 60 ℃, starting condensation reflux, dropwise adding 10% ammonium persulfate aqueous solution in batches, and the dropwise adding time is 45min and 45 min; and after the dropwise addition is finished, stirring is continuously carried out, wherein the stirring speed is 200r/min until the reaction is completed for 6 hours. Then cooling to room temperature, and discharging after cooling to obtain the polymer microsphere plugging agent.

The oil-based coating comprises, by weight, 20% of white oil, 0.5% of fumed silica, 10% of acrylamide monomer, 5% of acrylic acid, 15% of sorbitan fatty acid ester, 0.08% of N, N-methylene bisacrylamide, 0.05% of ammonium persulfate, 0.08% of sodium bisulfite, 25% of hydrophilic group surfactant and the balance of water.

Example 7

1) Weighing the raw materials according to the weight ratio for later use;

2) under the condition of room temperature, adding white oil, fumed silica, sorbitan fatty acid ester and hydrophilic surfactant into a container provided with a stirrer, a thermometer and a reflux condensing device, and uniformly stirring at the stirring speed of 300r/min to prepare a solution A;

3) adding weighed acrylamide monomer, acrylic acid and N, N-methylene bisacrylamide into water, stirring to completely dissolve the acrylamide monomer, the acrylic acid and the N, N-methylene bisacrylamide, and adding sodium hydroxide aqueous solution to neutralize until the neutralization degree is 80%. Then adding sodium bisulfite, stirring to completely dissolve the sodium bisulfite to prepare solution B; the mass ratio of the solution A to the solution B is 4: 1;

4) adding the solution B into the solution A, emulsifying and stirring at the speed of 600r/min for 30min, then heating to 60-70 ℃, starting condensation reflux, dropwise adding 10% ammonium persulfate aqueous solution in batches for 60min and 60 min; and after the dropwise addition is finished, stirring is continuously carried out, wherein the stirring speed is 300r/min until the reaction is complete for 7 h. Then cooling to room temperature, and discharging after cooling to obtain the polymer microsphere plugging agent.

The water-based paint comprises, by weight, 40% of white oil, 2% of fumed silica, 25% of acrylamide monomer, 5% of acrylic acid, 5% of sorbitan fatty acid ester, 0.03% of N, N-methylene bisacrylamide, 0.01% of ammonium persulfate, 0.01% of sodium bisulfite, 10% of hydrophilic group surfactant and the balance of water.

Compared with the prior art, the polymer microsphere has dual effects of plugging and oil displacement, the plugging rate can reach more than 75 percent, the oil displacement efficiency can reach more than 90 percent, and the lowest interfacial tension is 4.3 multiplied by 10^-3mN/m, the salt tolerance is 50000mg/L mineralization at most, the salt tolerance of the common polymer microsphere can only reach 30000mg/L mineralization, and the oil displacement effect is not achieved.

Although particular embodiments of the invention have been described and illustrated in detail above, it should be noted that various changes and modifications could be made to the above embodiments without departing from the scope of the appended claims.