A Stability Evaluation Method for the Shape Memory Leak Stopping Performance of a Unidirectional Shape Memory Polymer

Abstract

The present invention provides a method for evaluating the stability of the shape memory plugging performance of a unidirectional shape memory polymer. In the present invention, the shape memory recovery rate, fixation rate and pressure-bearing multiple of the shape memory polymer plugging particles at different times are evaluated by testing the changes in particle size and pressure-bearing strength after the shape is fixed and standing for different times; then the average recovery rate, recovery rate stability, average fixation rate, fixation rate stability, average pressure-bearing multiple and pressure-bearing stability are accurately obtained by calculation; finally, the shape memory plugging performance of the shape memory polymer plugging material is comprehensively evaluated through the shape memory plugging performance evaluation index. The principle of the evaluation method of the present invention is reliable, the data is accurate, true and effective, and it has a wide applicability. It can truly reflect the shape memory plugging stability performance of the shape memory polymer plugging material, and provide theoretical support for the subsequent research and development of the shape memory polymer plugging material.

Description

Technical Field

[0001] The present invention relates to a method for evaluating the stability of shape memory plugging performance of a unidirectional shape memory polymer, and belongs to the technical field of oil and gas drilling. Background Art

[0002] In oil and gas exploration and development, the fundamental goal of plugging is to seal the leakage layer to ensure the smooth progress of subsequent oil and gas development work. Traditional inert bridging plugging materials have a poor match with the crack size, and phenomena such as "sealing the door" and "re-leakage" are likely to occur. For swelling-type plugging materials, since their swelling speed is not easy to control, premature or late swelling will reduce the plugging success rate. Although delayed swelling plugging materials can slow down their swelling speed, their strength after swelling is reduced, which limits their further application. Unidirectional thermally induced shape memory polymers can return to their original shape above the glass transition temperature, have variable shapes and high strength, and have good compatibility with drilling fluids. They have been successfully applied in the field of drilling fluid plugging and can effectively solve the above problems. Unidirectional thermally induced shape memory polymer plugging materials have been widely studied in the field of drilling fluid plugging, and most of them are epoxy resin-based shape memory materials. However, their shape memory performance is often measured by the ratio of the difference between the fixed angle and the recovery angle to the fixed angle at different temperatures, and the evaluation of the long-term stability of the plugging layer under high temperature and high pressure conditions is not clear. Therefore, it is necessary to develop a simple, convenient and accurate method for evaluating the stability of the shape memory plugging performance of shape memory plugging materials, so as to truly reflect the shape memory plugging stability of shape memory plugging materials. For this reason, the present invention is proposed. Summary of the Invention

[0003] Aiming at the deficiencies of the existing technology, the present invention provides a method for evaluating the stability of the shape memory plugging performance of a unidirectional shape memory polymer. The present invention comprehensively evaluates from the change relationship of the particle size and pressure-bearing strength of the shape memory plugging material before and after shape memory with time. The method is simple to operate, convenient to calculate, true and effective, can truly reflect the shape memory plugging and its stability of the shape memory plugging material, realizes the stability evaluation of the shape memory plugging performance of the shape memory polymer plugging material, and provides technical support for the subsequent research of the shape memory polymer plugging material.

[0004] The technical solution of the present invention is as follows:

[0005] A method for evaluating the stability of the shape memory plugging performance of a unidirectional shape memory polymer, comprising the steps of:

[0006] (1) Prepare a shape memory polymer; test the glass transition temperature Tg (unit: °C) of the material, dry and crush it into particles, then place it at Tg + 20 °C to release the stress inside the particles, and then cool it to room temperature, and measure the particle size, denoted as R 初(Unit: mm);

[0007] (2) Prepare shape memory polymer particles according to the method in step (1), and then prepare a drilling fluid base slurry containing the shape memory polymer particles; adopt a simulated fracture plugging test to measure its bearing pressure strength τ1 (unit: MPa) at Tg;

[0008] (3) Prepare shape memory polymer particles with a particle size of R 初 using a hot pressing machine to compress them at Tg + 20 °C, and then measure their particle size, denoted as R 固 (Unit: mm);

[0009] (4) Prepare shape memory polymer particles according to the method in step (3), and then prepare a drilling fluid base slurry containing the shape memory polymer particles; after forming a plugging layer by adopting a simulated fracture plugging test, measure the bearing pressure strength τ 2i (Unit: MPa) at different static times, and measure the particle size of the corresponding formed plugging layer, denoted as R 回i (Unit: mm), where i is a non-zero natural number from 1, 2, 3... n;

[0010] (5) Calculate the shape recovery rate α 回复率i , shape fixation rate β 固定率i and bearing pressure multiple γ i of the shape memory polymer plugging material at different static times by using formulas a, b, and c;

[0011] Shape recovery rate:

[0012] Shape fixation rate:

[0013] Bearing pressure multiple:

[0014] (6) According to the shape recovery rate α 回复率i , shape fixation rate β 固定率i and bearing pressure multiple γ i calculated in step (5) at different static times, calculate the average recovery rate α, recovery rate stability α 稳定性 , average fixation rate β, fixation rate stability β 稳定性 , average bearing pressure multiple γ and bearing pressure stability γ 稳定性 by using formulas d - i;

[0015] Average recovery rate:

[0016] Recovery rate stability:

[0017] Average fixation rate:

[0018] Fixation rate stability:

[0019] Average value of pressure-bearing multiple:

[0020] Pressure-bearing stability:

[0021] (7) The average value of the recovery rate α, the stability of the recovery rate α stability, the average value of the fixation rate β, the stability of the fixation rate β 固定率 and the average value of the pressure-bearing multiple γ and the pressure-bearing stability γ 稳定性 are used to evaluate the stability of the shape memory plugging performance of the shape memory polymer plugging material, and the evaluation indexes are shown in the following table:

[0022] α / ％ β / ％ γ / % <![CDATA[α 稳定性 / %]]> <![CDATA[β 稳定性 / %]]> <![CDATA[γ 稳定性 / %]]> Stability α≤100 40≤β ≥200％ <![CDATA[0≤α 稳定性 > <![CDATA[0≤β 稳定性 > <![CDATA[0≤γ 稳定性 > Extremely strong 90≤α 30≤β ≥180 <![CDATA[1≤β 稳定性 > <![CDATA[0.4 ≤ β 稳定性 > <![CDATA[1≤γ 稳定性 > Stronger 70≤α 20≤β ≥150 <![CDATA[3≤α 稳定性 > <![CDATA[0.6≤β 稳定性 > <![CDATA[2≤γ 稳定性 > Strong 50≤α 10≤β ≥130 <![CDATA[5≤α 稳定性 > <![CDATA[0.8 ≤ β 稳定性 > <![CDATA[3≤γ 稳定性 > Medium 0≤α 0≤β ≥0 <![CDATA[7≤α 稳定性 > <![CDATA[1≤β 稳定性 > <![CDATA[4≤γ 稳定性 > Weak

[0023] According to the specific implementation scheme of the present invention, preferably, in step (1), the preparation of the shape memory polymer plugging system varies according to different shape memory polymer synthetic materials, and its glass transition temperature Tg also changes accordingly.

[0024] According to the specific implementation scheme of the present invention, preferably, in step (1), Tg is obtained by testing the thermal decomposition trend of the synthesized shape memory polymer with a differential scanning calorimeter, and the particle size is determined by a particle size analyzer.

[0025] According to the specific implementation scheme of the present invention, preferably, in step (2), the drilling fluid base slurry is prepared by selecting the evaluation soil for drilling fluid tests and preparing a 4% bentonite base slurry. The specific method is as follows: Take 4 parts of bentonite, slowly add it to 100 parts of distilled water, stir for 2 h, and then stand for 24 h to obtain the bentonite base slurry.

[0026] According to the specific implementation scheme of the present invention, preferably, in step (3), the test sample is prepared by dispersing the shape memory polymer particles in the base slurry, and the concentration range is 1% - 30%, and the optimal concentration is 3% - 25%.

[0027] According to the specific implementation scheme of the present invention, preferably, in step (2), according to actual needs, different-sized fracture models can be used to simulate different fractured formations.

[0028] According to the specific implementation scheme of the present invention, preferably, in step (2), the particle size of the shape memory polymer particles is about one-third of the size of the fracture model.

[0029] According to a specific embodiment of the present invention, preferably, in step (2), the test method for the pressure-bearing strength τ1 is as follows: Place the drilling fluid base slurry containing shape memory polymer particles in a high-temperature and high-pressure dynamic and static leak-off instrument. At the test temperature, it migrates through the fracture model. When no plugging layer is formed, the outlet leak-off volume is relatively large; as the particles migrate, the leak-off volume gradually decreases until it becomes constant; slowly increase the pressure of the high-temperature and high-pressure dynamic and static plugging instrument until a large amount of leak-off suddenly occurs, and the corresponding pressure is the pressure-bearing strength τ1.

[0030] According to a specific embodiment of the present invention, preferably, in step (3), when using a hot press to compress, the compression pressure and time are 20 MPa and 30 min respectively.

[0031] According to a specific embodiment of the present invention, preferably, in step (4), the test method for the pressure-bearing strength τ 2i is as follows: Place the drilling fluid base slurry containing shape memory polymer particles in a high-temperature and high-pressure dynamic and static leak-off instrument. At the test temperature, it migrates through the fracture model. Increase the pressure to 1 / 10 of τ1. When the leak-off volume first increases and then decreases to a constant value, a plugging layer is formed; after standing for different times, gradually increase the pressure until a large amount of leak-off suddenly occurs, and the corresponding pressure is the pressure-bearing strength τ 2i , and measure the particle size of the corresponding formed plugging layer, denoted as R 回i , where i is a non-zero natural number from 1, 2, 3... n.

[0032] Beneficial effects:

[0033] (1) The present invention provides a method for evaluating the stability of the shape memory plugging performance of a shape memory polymer plugging material. The present invention evaluates the shape memory recovery rate, fixation rate, and pressure-bearing multiple of shape memory polymer plugging particles at different times by testing the changes in particle size and pressure-bearing strength after the shape is fixed and standing for different times; then accurately calculates the average recovery rate, recovery rate stability, average fixation rate, fixation rate stability, average pressure-bearing multiple, and pressure-bearing stability; finally, comprehensively evaluates the shape memory plugging performance of the shape memory polymer plugging material through shape memory plugging performance evaluation indicators. The evaluation method of the present invention is simple to operate and convenient to calculate, can be tested and evaluated in the laboratory, and does not require a large amount of complex work by operators; its principle is reliable, the data is accurate, true and effective, and it has a wide applicability, and can truly reflect the shape memory plugging stability of the shape memory polymer plugging material, providing theoretical support for the subsequent research and development of the shape memory polymer plugging material.

[0034] (2) The present invention comprehensively evaluates the shape memory plugging stability of the shape memory polymer plugging material using six indicators: the average recovery rate, the stability of the recovery rate, the average fixation rate, the stability of the fixation rate, the average pressure-bearing multiple, and the pressure-bearing stability. It can fully evaluate the stability of the shape memory plugging of the shape memory polymer plugging material from multiple perspectives, ensuring the authenticity and effectiveness of the evaluation results. Through a large number of experimental explorations, the present invention obtains the evaluation indicators for the shape memory plugging performance, and the evaluation results of the indicators are accurate, enabling an intuitive evaluation of the stability of the shape memory plugging of the shape memory polymer plugging material. Detailed implementation mode

[0035] The present invention will be further described below through specific embodiments, but it is not limited thereto.

[0036] The raw materials used in the embodiments are all conventional raw materials and can be obtained commercially; the methods, unless otherwise specified, are all conventional methods and existing technologies.

[0037] Embodiment 1

[0038] A method for evaluating the stability of shape memory plugging of a shape memory polymer plugging material comprises the following steps:

[0039] (1) Prepare a shape memory polymer: Mix 100 parts of epoxy resin with 15 parts of 4,4'-diaminodiphenylmethane evenly at 60°C, pour it into a mold, cure it at 80°C for 2 h, and then cure it at 150°C for 2 h to obtain a shape memory polymer. The glass transition temperature Tg of this material is measured to be 80°C. Crush it into particles, place it at 100°C to release the stress inside the particles, and then cool it to room temperature. Measure the particle size to be 0.32 mm, denoted as R 初 ;

[0040] (2) Prepare shape memory polymer particles according to the method in step (1), and then prepare a drilling fluid base slurry containing the shape memory polymer particles, that is: take 4 parts of bentonite, slowly add it to 100 parts of distilled water, stir for 2 h, and then let it stand for 24 h to obtain a bentonite base slurry. Finally, take 15 parts of shape memory polymer particles and mix them evenly with 100 parts of the bentonite base slurry; conduct a high-temperature and high-pressure displacement experiment using a steel crack model with a crack width of 1 mm, and measure its pressure-bearing strength τ1 at 80°C respectively. The test method is to put the drilling fluid base slurry containing the shape memory polymer particles into a high-temperature and high-pressure dynamic and static leak-off instrument. At the test temperature, it migrates through the crack model. When no plugging layer is formed, the outlet leak-off volume is large; as the particles migrate, the leak-off volume gradually decreases until it remains unchanged; slowly increase the pressure of the leak-off instrument until a large amount of leak-off suddenly occurs, and the corresponding pressure is the pressure-bearing strength. Therefore, τ1 is 3.1 MPa;

[0041] (3) Prepare particles with a particle size of R according to step (1)初 Shape memory polymer particles. After compressing them for 30 minutes at 100 °C and 20 MPa using a hot press molding machine, their particle size is measured to be 0.18 mm, denoted as R 固 ;

[0042] (4) Prepare shape memory polymer particles according to the method in step (3), and then prepare a drilling fluid base slurry containing the shape memory polymer particles, that is: take 4 parts of bentonite, slowly add it to 100 parts of distilled water, stir for 2 hours, then let it stand for 24 hours to obtain a bentonite base slurry. Finally, take 15 parts of shape memory polymer particles and mix them evenly with 100 parts of the bentonite base slurry; conduct a high-temperature and high-pressure displacement experiment using a steel crack model with a crack width of 1 mm to test its pressure-bearing strength τ 2i The test method is as follows: Put the drilling fluid base slurry containing the shape memory polymer particles into a high-temperature and high-pressure dynamic and static leak-off instrument. At the test temperature, let it migrate through the crack model, increase the pressure by 1 / 10 of τ1. When the leakage volume first increases and then decreases to a constant value, a sealing layer is formed; after standing for 0 h, 2 h, 4 h, 6 h, and 8 h, gradually increase the pressure until the pressure corresponding to a sudden large amount of leakage occurs, which is the pressure-bearing strength τ 2i All are 7.8 MPa, and measure the particle size R of the corresponding formed sealing layer 回i All are 0.31 mm, where i is 1, 2, 3, 4, and 5;

[0043] (5) Calculate the shape recovery rate α of the shape memory polymer plugging material at different standing times using formulas a, b, and c 回复率 i, shape fixation rate β 固定率 i, and pressure-bearing multiple γ i ;

[0044] Shape recovery rate:

[0045] Shape fixation rate:

[0046] Pressure-bearing multiple:

[0047] (6) According to the shape recovery rate α calculated in step (5) at different standing times 回复率 i, shape fixation rate β 固定率 i, and pressure-bearing multiple γ i , use formulas d - i to calculate the average recovery rate α, recovery rate stability α 稳定性 , average fixation rate β, fixation rate stability β 稳定性 , average pressure-bearing multiple γ, and pressure-bearing stability γ 稳定性 ;

[0048] Average recovery rate:

[0049] Reply rate stability:

[0050] Average value of fixation rate:

[0051] Fixation rate stability: Average value of pressure-bearing multiple:

[0052] Pressure-bearing stability:

[0053] (7) The average value of reply rate α, reply rate stability α stability, average value of fixation rate β, fixation rate stability β 固定率 calculated according to step (6), average value of pressure-bearing multiple γ and pressure-bearing stability γ 稳定性 are used to evaluate the shape memory plugging performance stability of the shape memory polymer plugging material, and the evaluation indexes are shown in the following table:

[0054] α / ％ β / ％ γ / % <![CDATA[α 稳定性 / %]]> <![CDATA[β 稳定性 / %]]> <![CDATA[γ 稳定性 / %]]> Stability α≤100 40≤β ≥200％ <![CDATA[0 ≤ α 稳定性 > <![CDATA[0≤β 稳定性 > <![CDATA[0≤γ 稳定性 > Extremely strong 90≤α 30≤β ≥180 <![CDATA[1≤α 稳定性 > <![CDATA[0.4≤β 稳定性 > <![CDATA[1≤γ 稳定性 > Stronger 70≤α 20≤β ≥150 <![CDATA[3≤α 稳定性 > <![CDATA[0.6 ≤ β 稳定性 > <![CDATA[2≤γ 稳定性 > Strong 50≤α 10≤β ≥130 <![CDATA[5≤α 稳定性 > <![CDATA[0.8 ≤ β 稳定性 > <![CDATA[3≤γ 稳定性 > Medium 0≤α 0≤β ≥0 <![CDATA[7≤α 稳定性 > <![CDATA[1≤β 稳定性 > <![CDATA[4≤γ 稳定性 > Weak

[0055] It can be seen from the above calculation results and evaluation indexes that the shape memory plugging stability of the shape memory polymer plugging material involved in this embodiment is extremely strong.

[0056] Example 2

[0057] A method for evaluating the stability of the shape memory plugging performance of a shape memory polymer plugging material, the steps are as follows:

[0058] (1) Prepare a shape memory polymer; mix 100 parts of epoxy resin with 20 parts of 4,4'-diaminodiphenylmethane evenly at 60 °C, pour it into a mold and cure it at 80 °C for 2 h, then cure it at 150 °C for 2 h to obtain a shape memory polymer. The glass transition temperature Tg of this material is measured to be 100 °C, it is crushed into particles, and then the stress in the particles is released at 120 °C, and then cooled to room temperature, and the particle size is measured to be 0.32 mm, denoted as R 初 ;

[0059] (2) Prepare shape memory polymer particles according to the method in step (1), and then prepare a drilling fluid base slurry containing the shape memory polymer particles, that is: take 4 parts of bentonite, slowly add it to 100 parts of distilled water, stir for 2 h, and then stand for 24 h to obtain a bentonite base slurry. Finally, take 15 parts of shape memory polymer particles and mix them evenly with 100 parts of the bentonite base slurry; conduct a high-temperature and high-pressure displacement experiment using a steel crack model with a slit width of 1 mm, and measure its bearing pressure strength τ1 at 80 °C. The test method is to place the drilling fluid base slurry containing the shape memory polymer particles in a high-temperature and high-pressure dynamic and static leak-off instrument, and at the test temperature, migrate through the crack model. When no plugging layer is formed, the outlet leak-off volume is relatively large; as the particles migrate, the leak-off volume gradually decreases until it remains unchanged; slowly increase the pressure of the leak-off instrument until a large amount of leak-off suddenly occurs, and the corresponding pressure is the bearing pressure strength. Therefore, τ1 is 3.3 MPa;

[0060] (3) Prepare shape memory polymer particles with a particle size of R according to the method in step (1) 初 using a hot press molding machine to compress them at 100 °C and 20 MPa for 30 min, and then measure its particle size to be 0.28 mm, denoted as R 固 .

[0061] (4) Prepare shape memory polymer particles according to the method in step (3), and then prepare a drilling fluid base slurry containing the shape memory polymer particles, that is: take 4 parts of bentonite, slowly add it to 100 parts of distilled water, stir for 2 h, and then stand for 24 h to obtain a bentonite base slurry. Finally, take 15 parts of shape memory polymer particles and mix them evenly with 100 parts of the bentonite base slurry; conduct a high-temperature and high-pressure displacement experiment using a steel crack model with a slit width of 1 mm, and measure its bearing pressure strength τ 2i at different standing times. The test method is as follows:

[0062] Place the drilling fluid base slurry containing the shape memory polymer particles in a high-temperature and high-pressure dynamic and static leak-off instrument, and at the test temperature, migrate through the crack model. Increase the pressure to 1 / 10 of τ1. When the leak-off volume first increases and then decreases to a constant value, a plugging layer is formed; after standing for 0 h, 2 h, 4 h, 6 h, and 8 h, gradually increase the pressure until a large amount of leak-off suddenly occurs, and the corresponding pressure is the bearing pressure strength τ 2i are 3.4 MPa, 3.3 MPa, 2.8 MPa, 2.8 MPa, and 2.8 MPa respectively, and measure the particle size R 回i of the corresponding formed plugging layer to be 0.29 mm, 0.29 mm, 0.28 mm, 0.28 mm, and 0.28 mm respectively, where i is 1, 2, 3, 4, and 5;

[0063] (5) Use the formula to calculate the shape recovery rate α 回复率 i and shape fixation rate β of the shape memory polymer plugging material at different standing times固定率 i and bearing pressure multiple γ i ;

[0064] Shape recovery rate:

[0065] Shape fixing rate:

[0066] Bearing pressure multiple:

[0067] (6) Shape recovery rate α at different static times calculated according to step (5) 回复率 i, shape fixing rate β 固定率 i and bearing pressure multiple γ i , use the formula to calculate the average recovery rate α, recovery rate stability α 稳定性 , average fixing rate β, fixing rate stability β 稳定性 , average bearing pressure multiple γ and bearing pressure stability γ 稳定性 ;

[0068] Average recovery rate:

[0069] Recovery rate stability:

[0070] Average fixing rate:

[0071] Fixing rate stability:

[0072] Average bearing pressure multiple:

[0073] Bearing pressure stability:

[0074] (7) According to the average recovery rate α, recovery rate stability α stability, average fixing rate β, fixing rate stability β 固定率 calculated in step (6), average bearing pressure multiple γ and bearing pressure stability γ 稳定性 evaluate the shape memory plugging performance stability of the shape memory polymer plugging material, and the evaluation indexes are shown in the following table:

[0075]

[0076]

[0077] It can be seen from the above calculation results and evaluation indexes that the shape memory polymer plugging material involved in this embodiment has weak shape memory plugging stability.

Claims

1. A method for evaluating the stability of the shape memory plugging performance of a unidirectional shape memory polymer, which comprises the following steps: (1) Prepare a shape memory polymer; test the glass transition temperature Tg of the material, crush it into particles after drying, then place it at Tg + 20 °C to release the stress inside the particles, and then cool it to room temperature to measure the particle size, denoted as R 初 ; (2) Prepare shape memory polymer particles according to the method in step (1), and then prepare a drilling fluid base slurry containing the shape memory polymer particles; adopt a simulated fracture plugging test to measure its pressure-bearing strength τ1 at Tg; (3) Produce shape memory polymer particles with a particle size of R according to step (1). 初 After compressing them with a hot press at Tg + 20°C, measure their particle size, denoted as R 固 ; (4) Prepare shape memory polymer particles according to the method in step (3), and then prepare a drilling fluid base slurry containing the shape memory polymer particles; perform a simulated fracture plugging test. After forming a plugging layer, test the bearing pressure strength τ at different standing times 2i , and measure the particle size of the corresponding formed plugging layer, denoted as R 回i , where i is a non-zero natural number from 1, 2, 3... n; (5) Calculate the shape recovery rate α, shape fixation rate β 回复率i and pressure-bearing multiple γ 固定率i of the shape memory polymer plugging material at different standing times by using formulas a, b, and c i ; 回复率i , shape fixation rate β 固定率i and pressure-bearing multiple γ i ; Shape recovery rate: Shape fixation rate: Pressure-bearing multiple: (6) Shape recovery rate α at different standing times calculated according to step (5) 回复率i , shape fixation rate β 固定率i and pressure-bearing multiple γ i , use formula d-i to calculate the average recovery rate α, recovery rate stability α 稳定性 , average fixation rate β, fixation rate stability β 稳定性 , average pressure-bearing multiple γ and pressure-bearing stability γ 稳定性 ; Average response rate: Reply rate stability: Average fixation rate: Fixed rate stability: Average bearing pressure multiple: Bearing stability: (7) The average value of the recovery rate α, the stability of the recovery rate α_stability, the average value of the fixation rate β, the stability of the fixation rate β_stability 固定率 , the average value of the pressure-bearing multiple γ and the pressure-bearing stability γ_stability 稳定性 Evaluate the stability of the shape memory plugging performance of the shape memory polymer plugging material, and the evaluation indexes are shown in the following table: 。 2. The method according to claim 1, wherein In step (2), the drilling fluid base slurry is a bentonite base slurry.

3. The method according to claim 2, wherein The preparation process of the bentonite base slurry is as follows: Take 4 parts of bentonite, slowly add it to 100 parts of distilled water, stir for 2 h, and then stand for 24 h to obtain the bentonite base slurry.

4. The method according to claim 1, wherein In step (3), the test sample, namely the drilling fluid base slurry containing the shape memory polymer particles, is prepared by dispersing the shape memory polymer particles in the base slurry, and the concentration range is 1%-30%.

5. The method according to claim 4, wherein, The concentration is 3%-25%.

6. The method according to claim 1, wherein In step (2), according to actual needs, fracture models of different sizes are used to simulate different fractured formations.

7. The method according to claim 1, wherein In step (2), the particle size of the shape memory polymer particles is one-third of the size of the fracture model.

8. The method according to claim 1, wherein, In step (2), the method for measuring the pressure-bearing strength τ1 is as follows: Place the drilling fluid base slurry containing the shape memory polymer particles in a high-temperature and high-pressure dynamic and static leak-off instrument. At the test temperature, it migrates through the fracture model. When no plugging layer is formed, the outlet leak-off volume is relatively large; as the particles migrate, the leak-off volume gradually decreases until it becomes constant; slowly increase the pressure of the high-temperature and high-pressure dynamic and static plugging instrument until a large amount of leak-off suddenly occurs, and the corresponding pressure is the pressure-bearing strength τ1.

9. The method according to claim 1, wherein In step (3), when using a hot press to compress, the compression pressure and time are 20 MPa and 30 min respectively.

10. The method according to claim 1, wherein In step (4), the bearing strength τ 2i is tested as follows: Place the drilling fluid base slurry containing shape memory polymer particles in a high-temperature and high-pressure dynamic and static leak-off instrument. At the test temperature, let it migrate through the fracture model. Increase the pressure by 1 / 10 of τ1. When the leak-off volume first increases and then decreases to a constant value, a plugging layer is formed. After standing for different times, gradually increase the pressure until the pressure corresponding to a sudden large amount of leak-off is the bearing strength τ 2i , and measure the particle size of the corresponding formed plugging layer, denoted as R 回i , where i is a non-zero natural number from 1, 2, 3... n.

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