A temperature-sensitive polymer, a preparation method thereof and application of the temperature-sensitive polymer in low-temperature rheological adjustment of a drilling fluid

Abstract

The application provides a temperature-sensitive polymer, a preparation method thereof and application of the temperature-sensitive polymer in low-temperature rheological adjustment of a drilling fluid. The temperature-sensitive polymer is obtained through reaction of N,N-dimethyl acrylamide and N,N-diethyl acrylamide under the action of a chain transfer agent and an initiator. The preparation method of the temperature-sensitive polymer comprises the following steps: N,N-dimethyl acrylamide and N,N-diethyl acrylamide, a chain transfer agent and an initiator are dissolved in a first solvent, a protective gas is used for protection, the reaction liquid is placed in a constant-temperature environment of 70 DEG C to 80 DEG C for 1 h to 5 h, then the reaction liquid is cooled and quenched, the reaction liquid is dropped into a second solvent, and the temperature-sensitive polymer is obtained. The temperature-sensitive polymer is applied to low-temperature rheological adjustment of a water-based drilling fluid, and has good low-temperature rheological adjustment performance.

Description

Technical Field

[0001] This invention belongs to the field of rheological modification of water-based drilling fluids, specifically relating to a temperature-sensitive polymer, its preparation method, and its application in low-temperature rheological modification. Background Technology

[0002] As drilling depth increases, temperature gradually rises from the surface to the deeper formations. However, deep-sea drilling differs from shallow water or land drilling; the seabed temperature gradually decreases with increasing depth. Temperature variations can lead to uncontrolled rheological properties of drilling fluids, posing potential hazards to drilling operations. Experimental experience shows that the rheological properties of water-based drilling fluids are difficult to accurately control within the 4-65℃ range, especially below 4℃. Under low-temperature conditions, the viscosity and shear force of water-based drilling fluids increase significantly, resulting in excessively high equivalent circulating density and an increased risk of well leakage.

[0003] Temperature-sensitive materials are a novel and complex material system containing a certain proportion of hydrophilic and hydrophobic groups in their structure. Changes in temperature can affect the intramolecular and intermolecular interactions between these groups and water. Due to their unique environmental response mechanism, they have become widely used materials in aerospace, medical, and textile industries. In recent years, with the continuous deepening of research on temperature-sensitive polymers and the actual needs of various engineering development processes, their application scope has gradually expanded to the oil drilling and production industry (drilling, extraction, and oilfield pollution treatment).

[0004] Thermosensitive polymers can also react with sulfonated styrene polymers, followed by a series of contact reactions to obtain intelligent polymer flow modifiers, slightly increasing the temperature regulation range. However, the synthesis steps are too cumbersome, hindering widespread application. Graft copolymerization of thermosensitive polymer monomers with SiO2 prepares amphiphilic thermosensitive nano-SiO2 hybrid materials. The modified organobentonite exhibits strong suspension stability and maintains good fluidity at 150℃. A novel drilling fluid is prepared by compounding modified bentonite and nano-silica, showing relatively stable rheological properties at high temperatures, but requiring improvement at low temperatures. Copolymerization of alkenylamides and alkenyl sulfonic acids can also generate an intelligent thermosensitive polymer flow modifier, significantly increasing the temperature regulation range and exhibiting good constant rheological properties. However, the synthesis steps are cumbersome and complex, making widespread application difficult.

[0005] Therefore, current intelligent regulation of water-based drilling fluid rheology still faces challenges such as a limited temperature range for regulation and complex and cumbersome synthesis steps, which hinder large-scale promotion and application. Summary of the Invention

[0006] To address the aforementioned problems, the present invention aims to provide a temperature-sensitive polymer, its preparation method, and its application in low-temperature rheological regulation. This temperature-sensitive polymer is used for low-temperature rheological regulation of water-based drilling fluids and exhibits excellent low-temperature rheological control performance.

[0007] To achieve the above objectives, the present invention provides a thermosensitive polymer, which is obtained by reactive polymerization of N,N-dimethylacrylamide and N,N-diethylacrylamide in a monomer molar ratio of (90:10)-(10:90) under the action of a chain transfer agent and an initiator.

[0008] According to a specific embodiment of the present invention, the above reaction is a reversible addition-fragmentation chain transfer radical polymerization (RAFT) reaction.

[0009] According to a specific embodiment of the present invention, preferably, the chain transfer agent is a dithioester derivative chain transfer agent; and the initiator is a water-soluble azo initiator.

[0010] According to a specific embodiment of the present invention, preferably, the chain transfer agent is one or a combination of two or more of 2-(dodecyltrithiocarbonate)-2-methylpropionic acid (DDMAT), dithiobenzoate and trithiocarbonate; more preferably, the chain transfer agent is 2-(dodecyltrithiocarbonate)-2-methylpropionic acid.

[0011] According to a specific embodiment of the present invention, preferably, the initiator is azobisisobutyronitrile and / or azobisisopropylimidazoline; more preferably, the initiator is azobisisobutyronitrile.

[0012] According to a specific embodiment of the present invention, preferably, the molar ratio of the initiator to the chain transfer agent is 1:3.

[0013] According to a specific embodiment of the present invention, preferably, the monomer molar ratio of N,N-dimethylacrylamide to N,N-diethylacrylamide is (90:10)-(60:40), more preferably 90:10, 75:25 or 60:40.

[0014] According to a specific embodiment of the present invention, the number-average molecular weight (M) of the above-mentioned temperature-sensitive polymer is... n The weight-average molecular weight (M) is between 1046 and 1231 Da. w (Between 1108 and 1922 Da)

[0015] The present invention also provides a method for preparing the above-mentioned temperature-sensitive polymer, which includes the following steps:

[0016] N,N-dimethylacrylamide, N,N-diethylacrylamide, chain transfer agent, and initiator were dissolved in a first solvent. Under protective gas, the reaction solution was placed at a constant temperature of 70℃-80℃ for 1-5 hours. The reaction was then cooled at a low temperature and quenched. The reaction solution was then added dropwise to a second solvent to obtain the thermosensitive polymer.

[0017] According to a specific embodiment of the present invention, preferably, in the above preparation method, the first solvent includes one or more of ethyl acetate, isopropanol, tetrahydrofuran, and dimethyl sulfoxide.

[0018] According to a specific embodiment of the present invention, preferably, in the above preparation method, the second solvent includes one or more of n-hexane, aqueous methanol solution, and diethyl ether.

[0019] According to a specific embodiment of the present invention, preferably, the molar amount of the chain transfer agent is 0.45%-0.75% of the total amount of the two monomers N,N-dimethylacrylamide and N,N-diethylacrylamide, more preferably 0.45%, 0.60% or 0.75%.

[0020] According to a specific embodiment of the present invention, preferably, the temperature of the isothermal reaction is 80°C.

[0021] According to a specific embodiment of the present invention, preferably, the isothermal reaction time is 1 hour.

[0022] According to a specific embodiment of the present invention, preferably, the method for preparing the thermosensitive polymer further includes a purification step of the thermosensitive polymer:

[0023] The temperature-sensitive polymer was dissolved in a good solvent, and the resulting solution was added dropwise to an excess of a poor solvent. After centrifugation and precipitation, the precipitate was obtained. The above steps were repeated three times.

[0024] According to a specific embodiment of the present invention, preferably, in the above purification step, the good solvent is one or a combination of two or more of ethyl acetate, isopropanol, tetrahydrofuran and dimethyl sulfoxide, more preferably ethyl acetate.

[0025] According to a specific embodiment of the present invention, preferably, in the above purification step, the undesirable solvent is one or a combination of two or more of n-hexane, methanol aqueous solution and diethyl ether, more preferably n-hexane.

[0026] According to a specific embodiment of the present invention, preferably, a pretreatment step is further included before polymer synthesis:

[0027] The initiator was added to the third solvent, heated to dissolve, and then hot filtered at 20-60°C. The filtrate was cooled at 0-5°C and then filtered to obtain crystals.

[0028] According to a specific embodiment of the present invention, preferably, in the above pretreatment step, the third solvent is one or a combination of two or more of ethanol, carbon tetrachloride and acetone.

[0029] According to a specific embodiment of the present invention, preferably, in the above pretreatment step, the initiator is added to ethanol, heated to dissolve, and then hot filtered at 40°C, with the filtrate cooled to 0°C.

[0030] According to a specific embodiment of the present invention, preferably, a pretreatment step of N,N-dimethylacrylamide and N,N-diethylacrylamide is included before the synthesis of the polymer: excess alumina powder is added to N,N-dimethylacrylamide and N,N-diethylacrylamide respectively, and the mixture is stirred thoroughly for 20 min-30 min. The insoluble matter is removed by filtration, and the resulting filtrates are pretreated N,N-dimethylacrylamide and N,N-diethylacrylamide respectively.

[0031] According to a specific embodiment of the present invention, preferably, in the purification step of the temperature-sensitive polymer, the volume ratio of the unsuitable solvent to the good solvent is greater than 8:1, and more preferably 10:1 or greater.

[0032] According to a specific embodiment of the present invention, the above preparation method can be carried out according to the following specific steps:

[0033] (1) Reagent pretreatment:

[0034] Add 5g of initiator azobisisobutyronitrile (AIBN) to 50mL of ethanol, heat to 40℃, stir to dissolve the initiator, perform hot filtration at 40℃ to remove insoluble matter, and place the filtrate in a refrigerator for deep cooling and crystallization.

[0035] Take 50g of N,N-dimethylacrylamide (DMAAm) and N,N-diethylacrylamide (DEAAm) respectively and place them in 250mL beakers. Add excess alumina powder to both to remove the polymerization inhibitor impurities in the raw materials. After stirring thoroughly for 30min, filter the solid-liquid mixture to remove the solid matter. The resulting filtrates are pretreated N,N-dimethylacrylamide (DMAAm) and N,N-diethylacrylamide (DEAAm), respectively. Store the filtrates in reagent bottles in a refrigerator.

[0036] (2) Synthesis of copolymers:

[0037] Ethyl acetate (22.63 g), DMAAm (1982.00 mg, 20.00 mmol), DEAAm (2543.60 mg, 20.00 mmol), chain transfer agent (DDMAT (72.93 mg, 0.20 mmol), AIBN (0.013 mg, 0.08 mmol)) were added to a 250 mL reaction flask and dissolved by magnetic stirring. The system was evacuated and purged with nitrogen for 30 min. The reaction flask was then placed in an 80 °C oil bath for constant temperature reaction. After the reaction had proceeded for 1 h, the reaction flask was quickly placed in ice water to quench the reaction. The reaction solution was then dropped into n-hexane for precipitation and centrifugation. The solid obtained was the synthesized product.

[0038] (3) Purification of the synthesized product:

[0039] The obtained solid product was placed in a 100 mL beaker, and sufficient ethyl acetate was added (to fully dissolve the solid product). The mixture was stirred until there was no solid phase in the liquid phase. The ethyl acetate liquid containing the product was then added dropwise to an excess of n-hexane solution (the amount of n-hexane was more than 10 times the amount of ethyl acetate) to obtain a solid-liquid mixture. The solid-liquid mixture was then transferred to centrifuge tubes in portions and centrifuged to precipitate the product. The precipitate was collected, and the purification process was repeated three times.

[0040] (4) Drying and pulverizing the product:

[0041] The purified solid product was placed in a 50 mL beaker and placed in a 50 °C constant temperature oven for 48 h to obtain a dried solid product (irregular block solid). The dried product was ground into a uniform powder in a mortar and then transferred to a sealed bag for storage in a refrigerator.

[0042] The present invention also provides the application of the above-mentioned temperature-sensitive polymer in the low-temperature rheological regulation of drilling fluid; preferably, the drilling fluid is a water-based drilling fluid.

[0043] The present invention also provides a water-based drilling fluid comprising the above-mentioned thermosensitive polymer, wherein the water-based drilling fluid comprises, based on the mass of water as 100%, the water-based drilling fluid having the following composition: 2-6% bentonite slurry, 0.1-0.5% potassium polyacrylate (KPAM), 1-5% sulfonyl phenolic resin-I (SD-101), 1-5% sulfonyl lignite (SD-201) and 0.1-2.0% thermosensitive polymer;

[0044] Preferably, the water-based drilling fluid has the following composition: 4% bentonite slurry, 0.3% potassium polyacrylate (KPAM), 3% sulfonyl phenolic resin-I (SD-101), 3% sulfonyl lignite (SD-201) and 0.3% thermosensitive polymer;

[0045] The thermosensitive polymer is the thermosensitive polymer provided by the present invention.

[0046] In the aforementioned water-based drilling fluid, the remainder is water.

[0047] This invention uses DEAAm and DMAAm as polymerizing monomers and polymerizes them under certain conditions through solution RAFT reaction with the help of chain transfer agents and initiators to synthesize a series of random copolymers with different monomer combinations. All polymers have good low-temperature rheological control properties. Attached Figure Description

[0048] Figure 1 Temperature-transmittance curves for DEAAm / DMAAm 90 / 10 random copolymers;

[0049] Figure 2 Temperature-transmittance curves for DEAAm / DMAAm 75 / 25 random copolymers;

[0050] Figure 3 Temperature-transmittance curves for DEAAm / DMAAm 60 / 40 random copolymers;

[0051] Figure 4 To investigate the effect of polymers on the rheological properties of drilling fluids, ① represents drilling fluid without polymer addition; ②, ③, and ④ represent drilling fluids with polymers added at DEAAm / DMAAm molar ratios of 90 / 10, 75 / 25, and 60 / 40, respectively.

[0052] Figure 5 The image shows the FT-IR infrared spectrum of the synthesized product in Example 1. Detailed Implementation

[0053] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0054] Example 1

[0055] This embodiment provides a thermosensitive polymer (DEAAm / DMAAm molar ratio of 90 / 10), which is prepared by the following steps:

[0056] (1) Reagent pretreatment:

[0057] Add 5g of initiator azobisisobutyronitrile (AIBN) to 50mL of ethanol, heat to 40℃, stir to dissolve the initiator, immediately perform hot filtration to remove insoluble matter, and place the filtrate in a refrigerator for deep cooling crystallization.

[0058] Take 50g of N,N-dimethylacrylamide (DMAAm) and N,N-diethylacrylamide (DEAAm) respectively and place them in 250mL beakers. Add excess alumina powder to both to remove the polymerization inhibitor impurities in the raw materials. After stirring thoroughly for 30min, filter the solid-liquid mixture to remove the solid matter. The resulting filtrates are pretreated N,N-dimethylacrylamide (DMAAm) and N,N-diethylacrylamide (DEAAm), respectively. Store the filtrates in a reagent bottle in a refrigerator.

[0059] (2) Synthesis of copolymers:

[0060] Ethyl acetate (12.44 g), DMAAm (198.30 mg, 2.00 mmol), DEAAm (2289.20 mg, 18.00 mmol), DDMAT (32.80 mg, 0.09 mmol), and AIBN (4.90 mg, 0.03 mmol) were added to a 250 mL reaction flask and dissolved by magnetic stirring. After evacuating the system and circulating nitrogen for 30 min, the reaction flask was placed in an 80 °C oil bath for constant temperature reaction. After the reaction had proceeded for 1 h, the reaction flask was quickly placed in ice water to quench the reaction. The reaction solution was then dropped into n-hexane for precipitation and centrifugation. The solid obtained was the synthesized product.

[0061] (3) Purification of the synthesized product:

[0062] The obtained solid product was placed in a 100 mL beaker, and sufficient ethyl acetate was added (enough to fully dissolve the solid product). The mixture was stirred until there was no solid phase in the liquid phase. The ethyl acetate liquid containing the dissolved product was then added dropwise to an excess of n-hexane solution (the amount of n-hexane was more than 10 times the amount of ethyl acetate) to obtain a solid-liquid mixture. The solid-liquid mixture was then transferred to centrifuge tubes in portions and centrifuged to precipitate the product. The precipitate was collected. The purification process was repeated three times.

[0063] (4) Drying and pulverizing the product:

[0064] The purified solid product was placed in a 50 mL beaker and placed in a 50 °C constant temperature oven for 48 h to obtain a dried solid product (irregular block solid). The dried product was ground into a uniform powder in a mortar and then transferred to a sealed bag for storage in a refrigerator.

[0065] The temperature-transmittance curve of the DEAAm / DMAAm 90 / 10 random copolymer obtained in this embodiment is as follows: Figure 1 As shown.

[0066] Figure 5 The image shows the FT-IR infrared spectrum of the synthesized product in Example 1, where 3541.17 cm⁻¹ -1The absorption peak at 2973.81 cm⁻¹ is the NH bond stretching vibration peak. -1 The absorption peak at 2933.61 cm⁻¹ is the -CH₃ stretching vibration peak. -1 The absorption peak is at 1452.68 cm⁻¹, corresponding to the -CH₂- stretching vibration. -1 The absorption peaks at 1380.49 and 1363.20 cm⁻¹ are in-plane bending vibration absorption peaks of CH. -1 The absorption peak is at -C(CH3)2, 1310.69 cm⁻¹. -1 The peak at this location is the absorption peak of the CN stretching vibration in amide.

[0067] Based on the above analysis, it can be determined that a polymerization reaction occurred in the system, and the target product was synthesized.

[0068] Example 2

[0069] This embodiment provides a thermosensitive polymer (DEAAm / DMAAm molar ratio of 75 / 25), which is prepared by the following steps:

[0070] (1) The pretreatment of the reagents is the same as in Example 1;

[0071] (2) Synthesis of copolymers:

[0072] Ethyl acetate (12.02 g), DMAAm (495.70 mg, 5.00 mmol), DEAAm (1907.70 mg, 15.00 mmol), DDMAT (54.70 mg, 0.15 mmol), and AIBN (8.20 mg, 0.05 mmol) were added to a 250 mL reaction flask and dissolved by magnetic stirring. The system was evacuated and purged with nitrogen for 30 min. The reaction flask was then placed in an 80 °C oil bath for constant temperature reaction. After the reaction had proceeded for 3 h, the reaction flask was quickly placed in ice water to quench the reaction. The reaction solution was then dropped into n-hexane for precipitation and centrifugation. The solid obtained was the synthesized product.

[0073] (3) The purification of the synthesized product is the same as in Example 1;

[0074] (4) The drying and pulverization of the product are the same as in Example 1.

[0075] The temperature-transmittance curve of the DEAAm / DMAAm 75 / 25 random copolymer obtained in this embodiment is as follows: Figure 2 As shown.

[0076] Example 3

[0077] This embodiment provides a thermosensitive polymer (DEAAm / DMAAm molar ratio of 60 / 40), which is prepared by the following steps:

[0078] (1) The pretreatment of the reagents is the same as in Example 1;

[0079] (2) Synthesis of copolymers:

[0080] Ethyl acetate (11.60 g), DMAAm (793.00 mg, 8.00 mmol), DEAAm (1526.20 mg, 12.00 mmol), DDMAT (43.80 mg, 0.12 mmol), and AIBN (6.60 mg, 0.04 mmol) were added to a 250 mL reaction flask and dissolved by magnetic stirring. The system was evacuated and purged with nitrogen for 30 min. The reaction flask was then placed in an 80 °C oil bath for constant temperature reaction. After the reaction had proceeded for 5 h, the reaction flask was quickly placed in ice water to quench the reaction. The reaction solution was then dropped into n-hexane for precipitation and centrifugation. The solid obtained was the synthesized product.

[0081] (3) The purification of the synthesized product is the same as in Example 1;

[0082] (4) The drying and pulverization of the product are the same as in Example 1.

[0083] The temperature-transmittance curve of the DEAAm / DMAAm 60 / 40 random copolymer obtained in this embodiment is as follows: Figure 3 As shown.

[0084] The results of the effects of the polymers on the rheological properties of drilling fluids in Examples 1-3 are as follows: Figure 4 As shown, ① is drilling fluid without added polymer; ②, ③, and ④ are drilling fluids with added polymers at a DEAAm / DMAAm molar ratio of 90 / 10, 75 / 25, and 60 / 40, respectively.

[0085] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0086] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0087] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. The application of a temperature-sensitive polymer in the low-temperature rheological property regulation of water-based drilling fluids; wherein, This thermosensitive polymer is obtained by reacting N,N-dimethylacrylamide and N,N-diethylacrylamide in a monomer molar ratio of (90:10)-(60:40) with a chain transfer agent and an initiator. The chain transfer agent is added in a molar amount of 0.45%-0.75% of the total molar amount of the two monomers, N,N-dimethylacrylamide and N,N-diethylacrylamide. The number-average molecular weight of the thermosensitive polymer is between 1046 and 1231 Da, and the weight-average molecular weight is between 1108 and 1922 Da. The chain transfer agent is one or a combination of two or more of 2-(dodecyltrithiocarbonyl)-2-methylpropionic acid, dithiobenzoate and trithiocarbonate.

2. The application according to claim 1, wherein, The initiator is a water-soluble azo initiator.

3. The application according to claim 1, wherein, The chain transfer agent is 2-(dodecyltrithiocarbonate)-2-methylpropionic acid.

4. The application according to claim 1, wherein, The initiator is azobisisobutyronitrile and / or azobisisopropylimidazoline.

5. The application according to claim 1, wherein, The initiator is azobisisobutyronitrile.

6. The application according to claim 1, wherein, The molar ratio of the initiator to the chain transfer agent is 1:

3.

7. The application according to claim 1, wherein, The monomer molar ratio of N,N-dimethylacrylamide to N,N-diethylacrylamide is 90:10, 75:25, or 60:

40.

8. The application according to claim 1, wherein, The method for preparing the temperature-sensitive polymer includes the following steps: N,N-dimethylacrylamide, N,N-diethylacrylamide, chain transfer agent, and initiator were dissolved in a first solvent. Under protective gas, the reaction solution was placed at a constant temperature of 70℃-80℃ for 1-5 hours. The reaction was then quenched by cooling at a low temperature. The reaction solution was then added dropwise to a second solvent to obtain the thermosensitive polymer.

9. The application according to claim 8, wherein, The first solvent includes one or a combination of two or more of ethyl acetate, isopropanol, tetrahydrofuran, and dimethyl sulfoxide.

10. The application according to claim 8, wherein, The second solvent includes one or more of n-hexane, aqueous methanol, and diethyl ether.

11. The application according to claim 8, wherein, The chain transfer agent is added in a molar amount of 0.45%, 0.60%, or 0.75% of the total molar amount of the two monomers, N,N-dimethylacrylamide and N,N-diethylacrylamide.

12. The application according to claim 8, wherein, The temperature of the isothermal reaction is 80°C.

13. The application according to claim 8, wherein, The isothermal reaction time is 1 hour.

14. The application according to claim 8, wherein, The preparation method further includes a purification step of the thermosensitive polymer: The temperature-sensitive polymer was dissolved in a good solvent, and the resulting solution was added dropwise to an excess of a poor solvent. After centrifugation and precipitation, the precipitate was obtained. The above steps were repeated three times.

15. The application according to claim 14, wherein, The good solvent is one or a combination of two or more of ethyl acetate, isopropanol, tetrahydrofuran, and dimethyl sulfoxide.

16. The application according to claim 14, wherein, The good solvent is ethyl acetate.

17. The application according to claim 14, wherein, The unsuitable solvent is one or a combination of two or more of n-hexane, methanol aqueous solution, and diethyl ether.

18. The application according to claim 14, wherein, The unsuitable solvent is n-hexane.

19. The application according to claim 8, wherein, A pretreatment step is also included before polymer synthesis: The initiator was added to the third solvent, heated to dissolve, and then hot filtered at 20℃-60℃. The filtrate was cooled at 0℃-5℃ and then filtered to obtain crystals.

20. The application according to claim 19, wherein, The third solvent is one or a combination of two or more of ethanol, carbon tetrachloride, and acetone.

21. The application according to claim 19, wherein, The pretreatment step specifically involves adding the initiator to ethanol, heating to dissolve it, and then hot filtering at 40°C. The filtrate is cooled to 0°C.

22. The application according to claim 8 or 19, wherein, The synthesis of the polymer also includes pretreatment steps with N,N-dimethylacrylamide and N,N-diethylacrylamide: Excess alumina powder was added to N,N-dimethylacrylamide and N,N-diethylacrylamide respectively. After stirring thoroughly for 20-30 minutes, the insoluble matter was removed by filtration. The resulting filtrates were pretreated N,N-dimethylacrylamide and N,N-diethylacrylamide, respectively.

23. The application according to claim 16, wherein, In the purification step, the volume ratio of the poor solvent to the good solvent is greater than 8:

1.

24. The application according to claim 16, wherein, In the purification step, the volume ratio of the poor solvent to the good solvent is 10:1 or higher.

25. A water-based drilling fluid, wherein, Based on the mass of water (100%), the water-based drilling fluid has the following composition: 2-6% bentonite slurry, 0.1-0.5% potassium polyacrylate, 1-5% sulfomethylphenol resin-I, 1-5% sulfomethyl lignite, and 0.1-2.0% thermosensitive polymer. The thermosensitive polymer is obtained by reacting N,N-dimethylacrylamide and N,N-diethylacrylamide in a monomer molar ratio of (90:10)-(60:40) under the action of a chain transfer agent and an initiator. The chain transfer agent is added in a molar amount of 0.45%-0.75% of the total molar amount of the two monomers, N,N-dimethylacrylamide and N,N-diethylacrylamide. The number-average molecular weight of the thermosensitive polymer is between 1046 and 1231 Da, and the weight-average molecular weight is between 1108 and 1922 Da. The chain transfer agent is one or a combination of two or more of 2-(dodecyltrithiocarbonyl)-2-methylpropionic acid, dithiobenzoate and trithiocarbonate.

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