A zwitterionic crosslinking agent, copolymer flow modifier, preparation method and application

Abstract

This invention provides an amphoteric crosslinking agent, a copolymer flow modifier, its preparation method, and its application. The invention prepares a multi-carboxyl amphoteric crosslinking agent, which is obtained by polymerizing an enamide monomer, a sulfonic acid monomer, an alkyl methacrylate, and the amphoteric crosslinking agent. The copolymer flow modifier provided by this invention is a hydrophobic crosslinking type high-temperature resistant flow modifier with a temperature resistance up to 240℃, a NaCl salt concentration resistance up to 15%, and a viscosity retention rate of over 80%. It exhibits excellent rheological properties after high-temperature aging and has broad application prospects in the field of high-temperature water-based drilling fluids.

Description

Technical Field

[0001] This invention belongs to the field of drilling fluid technology in the petroleum industry, and relates to an amphoteric crosslinking agent, a copolymer flow pattern regulator, its preparation method, and its application. Background Technology

[0002] As oil exploration and development continues to expand into deeper and ultra-deep formations, drilling processes frequently encounter complex formations such as high-temperature zones, salt-gypsum layers, and high-pressure brine layers, placing higher demands on drilling fluid systems for resistance to ultra-high temperatures, salt content, and wellbore cleanliness. Flow modifiers, as important drilling fluid treatment agents, not only have a viscosity-increasing effect but also adjust the dynamic and static shear stress, viscoelasticity, filtration loss, and improve mud cake quality, thus significantly impacting wellbore stability and reservoir protection. Flow modifiers in drilling fluids primarily achieve their effects by interacting with clay particles through van der Waals forces, hydrogen bonding, electrostatic forces, and intermolecular hydrophilic and hydrophobic interactions, forming a three-dimensional network structure to increase the viscosity and improve shear stress of the drilling fluid.

[0003] Commonly used drilling fluid flow modifiers include various types such as those modified from natural plant gums (e.g., high-viscosity anionic cellulose, hydroxyethyl cellulose, etc.), modified organic polysaccharide derivatives (e.g., xanthan gum), and synthetic polymers (mainly acrylamide polymers). While these flow modifiers have advantages in certain aspects, they all exhibit significant high-temperature degradation at higher temperatures, resulting in low viscosity retention. This can lead to insufficient cuttings carrying capacity and barite settling under high-temperature conditions, easily generating cuttings beds during drilling, increasing friction, and causing downhole complications such as pressure buildup and stuck pipe. Conventional flow modifiers generally suffer from insufficient temperature resistance, salt tolerance, or insignificant viscosity-enhancing effects, necessitating reliance on imported flow modifiers in high-temperature well sections. Currently, synthetic polymer flow modifiers have achieved breakthroughs in high-temperature resistance. Existing technologies have reported on improving the temperature resistance of flow pattern regulators. For example, Chinese patent ZL201510509849.6 describes a flow pattern regulator that uses N,N-dimethylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, acrylamide, and acrylic acid to copolymerize and crosslink under the action of a crosslinking agent, forming a three-dimensional network molecular structure. The solution prepared at high temperature (120℃) and high salt (saturated brine) has high viscosity and good compatibility with other treatment agents, but its temperature and salt resistance needs further improvement. Chinese patent ZL202010859019.7 describes a high-temperature resistant polymer flow pattern regulator prepared by emulsion polymerization using 2-acrylamido-2-methylpropanesulfonic acid, alkenylpyridine, and divinylbenzene as raw materials. This product has a temperature resistance of up to 160℃, is not prone to foaming, and has strong salt and calcium resistance, but its temperature resistance cannot meet the technical requirements of ultra-high temperature formations. Chinese patent ZL202210765467.X develops a high-temperature resistant branched polymer flow modifier with a branched structure containing abundant anionic and cationic functional groups, exhibiting an anti-polyelectrolyte effect. It has excellent thickening properties, high temperature resistance, and salt contamination resistance, with a temperature resistance of up to 220℃ and a viscosity retention rate of over 85%. However, the polymer monomer structure is complex and the synthesis process is cumbersome. Therefore, for drilling fluid technical requirements in complex formations such as deep and ultra-deep formations and salt-gypsum layers, there is an urgent need to develop a new type of high-temperature resistant flow modifier. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide an amphoteric crosslinking agent, a copolymer flow modifier, its preparation method, and its application. The present invention provides a crosslinked, high-temperature resistant copolymer flow modifier possessing both amphoteric and hydrophobic groups, overcoming the difficulties of insufficient high-temperature and salt resistance and complex preparation processes in existing technologies.

[0005] To achieve this objective, the present invention adopts the following technical solution:

[0006] On one hand, the present invention provides a zwitterionic crosslinking agent having the following structure:

[0007]

[0008] The zwitterionic crosslinking agent of the present invention has carbon-carbon double bond groups that can undergo polymerization, and has anionic strong hydration groups (carboxyl groups) that can enhance hydration ability. It can also chemically crosslink the polymer molecules, strengthen the three-dimensional network structure of the polymer molecules, enhance the temperature resistance of the polymer, and improve the salt resistance of the polymer because an internal salt structure can be formed in the molecule.

[0009] On the other hand, the present invention provides a method for preparing the zwitterionic crosslinking agent as described above, the method comprising the following steps:

[0010] Disodium ethylenediaminetetraacetate reacts with 4-vinylbenzyl chloride to obtain the zwitterionic crosslinking agent.

[0011] Preferably, the molar ratio of disodium ethylenediaminetetraacetate to 4-vinylbenzyl chloride is 1:(2 to 2.2), for example, 1:2, 1:2.1 or 1:2.2.

[0012] Preferably, the reaction temperature is 60-80℃, for example 60℃, 63℃, 65℃, 68℃, 70℃, 75℃, 78℃ or 80℃, and the reaction time is 8-12h, for example 8h, 9h, 10h, 11h or 12h.

[0013] Preferably, the reaction is carried out in a solvent.

[0014] Preferably, the solvent is selected from N,N-dimethylformamide (DMF).

[0015] On the other hand, the present invention provides a copolymer flow modifier, which is a copolymer obtained by polymerization reaction of acrylamide monomers, sulfonic acid monomers, alkyl methacrylates and zwitterionic crosslinking agents.

[0016] The acrylamide monomers include N,N-dimethylacrylamide and / or N,N-diethylacrylamide.

[0017] Preferably, the sulfonic acid monomer is 2-acrylamido-2-methylpropanesulfonic acid.

[0018] Preferably, the mass ratio of the acrylamide monomer, sulfonic acid monomer, alkyl methacrylate, and zwitterionic crosslinker is (30-50):(40-60):(10-15):(5-10). For example, within this ratio range, the proportion of the acrylamide monomer (30-50) can be listed as 30, 32, 34, 38, 40, 42, 45, 48, or 50, the proportion of the sulfonic acid monomer (40-60) can be listed as 40, 42, 44, 46, 48, 50, 52, 55, 58, or 60, the proportion of the alkyl methacrylate (10-15) can be listed as 10, 11, 12, 13, 14, or 15, and the proportion of the zwitterionic crosslinker (5-10) can be listed as 5, 6, 7, 8, 9, or 10.

[0019] Preferably, the alkyl methacrylate is selected from one or a combination of at least two of dodecyl methacrylate, hexadecyl methacrylate, or octadecyl methacrylate.

[0020] Preferably, the polymerization reaction is carried out under the initiation of an initiator.

[0021] Preferably, the initiator is selected from any one or a combination of at least two azo initiators.

[0022] Preferably, the initiator is selected from any one or a combination of at least two of azobisisobutyronitrile (AIBN), 2,2'-azobisisobutyramidine dihydrochloride (AIBI), or azobisisobutyramidazolinium hydrochloride (Va-044).

[0023] Preferably, the amount of the initiator is 0.2% to 0.5% of the total weight of N,N-dimethylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, alkyl methacrylate and zwitterionic crosslinking agent, for example 0.2%, 0.3%, 0.4% or 0.5%.

[0024] On the other hand, the present invention provides a method for preparing the copolymer flow modifier as described above, the method comprising the following steps:

[0025] (1) Mix the solution of sulfonic acid monomers with acrylamide monomers.

[0026] (2) Add alkyl methacrylate, zwitterionic crosslinker and initiator to the mixture in step (1) and react to obtain the copolymer flow modifier.

[0027] Preferably, the solution of the sulfonic acid monomer is an aqueous solution of the sulfonic acid monomer.

[0028] Preferably, before mixing in step (1), the pH of the sulfonic acid monomer solution is adjusted to neutral.

[0029] Preferably, the pH adjustment is performed using a sodium hydroxide solution.

[0030] Preferably, the mixing in step (1) further includes the addition of a surfactant.

[0031] Preferably, the surfactant is sodium dodecylbenzenesulfonate.

[0032] Preferably, the amount of surfactant added is 3-5% of the total amount of solvent in the sulfonic acid monomer solution, for example, 3%, 3.5%, 4%, 4.5% or 5%.

[0033] Preferably, after adding alkyl methacrylate, zwitterionic crosslinking agent and initiator in step (2), the temperature is raised to 30-40°C, and the mixture is continuously stirred to dissolve and disperse it evenly. Then, nitrogen gas is introduced to remove oxygen, and the temperature is raised to 50-70°C (e.g., 50°C, 55°C, 58°C, 60°C, 65°C, 68°C or 70°C), and the mixture is reacted under nitrogen protection for 4-8 hours (e.g., 4 hours, 5 hours, 6 hours, 7 hours or 8 hours).

[0034] On the other hand, the present invention provides a drilling fluid comprising the copolymer flow modifier described above;

[0035] Preferably, the mass percentage of the copolymer flow modifier in the drilling fluid is ≤4%. For example, it can be 0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.6%, 2.8%, 3%, 3.2%, 3.4%, 3.6%, 3.8%, 4%, etc.

[0036] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] The zwitterionic crosslinking agent of the present invention has carbon-carbon double bond groups that can undergo polymerization, and has anionic strong hydration groups (carboxyl groups) that can enhance hydration ability. It can also chemically crosslink the polymer molecules, strengthen the three-dimensional network structure of the polymer molecules, enhance the temperature resistance of the polymer, and improve the salt resistance of the polymer because an internal salt structure can be formed in the molecule.

[0039] The flow pattern regulator of this invention incorporates anionic strong hydration groups (carboxyl and sulfonic acid groups) into its molecular structure, enhancing the polymer's hydration ability and endowing it with excellent adhesive protection under high temperature and high salt conditions. The introduction of zwitterionic crosslinking agents, on the one hand, crosslinks two linear polymer molecules through chemical bonds, strengthening the three-dimensional network structure of the polymer molecules and enhancing the polymer's temperature resistance; on the other hand, the introduction of zwitterionic groups, due to the formation of an internal salt structure within the molecule, improves the polymer's salt resistance. The introduction of long-chain hydrophobic monomers, due to hydrophobic association and steric hindrance effects in the molecular structure, allows the polymer solution to maintain a good hydraulic diameter under high temperature and high salt conditions, resulting in a high viscosity retention rate. The copolymer flow pattern regulator provided by this invention is a hydrophobically crosslinked, high-temperature resistant flow pattern regulator with a temperature resistance up to 240℃, resistance to NaCl salt concentrations up to 15%, and a viscosity retention rate of over 80%. It exhibits excellent rheological properties after high-temperature aging and has broad application prospects in the field of high-temperature water-based drilling fluids. Detailed Implementation

[0040] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0041] Example 1

[0042] (1) Preparation of zwitterionic crosslinking agent

[0043]

[0044] 0.1 mol of disodium ethylenediaminetetraacetate (Na2EDTA) was added to 80 mL of dimethylformamide (DMF) solution. After thorough stirring, the solution was poured into a three-necked reaction flask, and 0.2 mol of 4-vinylbenzyl chloride was added. The mixture was heated to 60 °C and reacted for 8 h. After the reaction was completed, the mixture was allowed to cool at room temperature. Deionized water was added to wash away the DMF. The product was extracted three times with acetone. After removing the solvent by rotary evaporation, the dry solid obtained was the zwitterionic crosslinking agent.

[0045] (2) Preparation of flow pattern regulator

[0046] Weigh 40g of 2-acrylamido-2-methylpropanesulfonic acid (AMPS) and dissolve it in 200mL of deionized water. After complete dissolution, adjust the pH of the solution to neutral with NaOH. Add 30g of N,N-dimethylacrylamide and pour the solution into a three-necked reaction flask. Add 6g of sodium dodecylbenzenesulfonate (SDS) and stir slowly until dissolved and homogeneous. Then add 10g of dodecyl methacrylate, 5g of zwitterionic crosslinking agent, and 0.17g of azobisisobutyronitrile (AIBN) sequentially. Heat to 35℃ and stir continuously until dissolved and dispersed evenly. Seal the three-necked reaction flask and purge with N2 for 30min to remove oxygen. Then heat the constant temperature water bath to 50℃ and react under N2 protection for 6h to obtain a white gel-like substance. Remove the product, precipitate it with acetone, and then soak it three times each in a 7 / 3 (v / v) acetone / water mixture and acetone. Dry it under vacuum at 60℃ to obtain the copolymer flow modifier sample.

[0047] Example 2

[0048] The difference from Example 1 is that the amounts of substances added in step (2) are as follows: 60g 2-acrylamido-2-methylpropanesulfonic acid (AMPS), 50g N,N-dimethylacrylamide, 15g dodecyl methacrylate, 10g zwitterionic crosslinking agent and 0.27g azobisisobutyronitrile (AIBN). Except for the different amounts of substances, all other operations are the same as in Example 1.

[0049] Example 3

[0050] The difference from Example 1 is that the amounts of substances added in step (2) are as follows: 50g 2-acrylamido-2-methylpropanesulfonic acid (AMPS), 40g N,N-dimethylacrylamide, 12g dodecyl methacrylate, 8g zwitterionic crosslinking agent and 0.22g azobisisobutyronitrile (AIBN). Except for the different amounts of substances, the other operations are the same as in Example 1.

[0051] Example 4

[0052] The difference from Example 1 is that the amounts of substances added in step (2) are as follows: 55g 2-acrylamido-2-methylpropanesulfonic acid (AMPS), 45g N,N-dimethylacrylamide, 14g dodecyl methacrylate, 6g zwitterionic crosslinking agent and 0.24g azobisisobutyronitrile (AIBN). Except for the different amounts of substances, the other operations are the same as in Example 1.

[0053] Example 5

[0054] The difference from Example 1 is that the amounts of substances added in step (2) are as follows: 48g 2-acrylamido-2-methylpropanesulfonic acid (AMPS), 35g N,N-dimethylacrylamide, 13g dodecyl methacrylate, 5g zwitterionic crosslinking agent and 0.21g azobisisobutyronitrile (AIBN). Except for the different amounts of substances, the other operations are the same as in Example 1.

[0055] Example 6

[0056] The difference from Example 1 is that in step (2), the constant temperature water bath is heated to 60°C and reacted for 8 hours under N2 protection.

[0057] Example 7

[0058] The difference from Example 1 is that 10g of dodecyl methacrylate in step (2) is replaced with 10g of hexadecyl acrylate.

[0059] Example 8

[0060] The difference from Example 1 is that 10g of dodecyl methacrylate in step (2) is replaced with 10g of octadecyl acrylate.

[0061] Example 9

[0062] The difference from Example 1 is that 0.17g of azobisisobutyronitrile in step (2) is replaced with 0.17g of 2,2'-azobisisobutyramidine dihydrochloride (AIBI).

[0063] Example 10

[0064] The difference from Example 1 is that 0.17g of azobisisobutyronitrile in step (2) is replaced with 0.17g of azobisisobutyronitrile hydrochloride (Va-044).

[0065] Comparative Example 1

[0066] The difference from Example 1 is that the amount of zwitterionic crosslinking agent added in the preparation of the flow pattern regulator is 0.

[0067] Comparative Example 2

[0068] The difference from Example 1 is that the amount of oil-soluble monomer alkyl methacrylate added in step (2) is 0.

[0069] Comparative Example 3

[0070] The flow pattern regulator product Driscal-D from abroad was used for comparison.

[0071] Comparative Example 4

[0072] The difference from Example 1 is that the amount of 2-acrylamido-2-methylpropanesulfonic acid added in step (2) is 0.

[0073] Application performance testing and results

[0074] The performance evaluation of hydrophobic crosslinking high-temperature flow pattern modifiers is mainly characterized by the following two aspects: first, the viscosity retention rate of the flow pattern modifier at high temperatures; and second, the viscosity retention rate of the flow pattern modifier at different salt concentrations.

[0075] 1. Evaluation of the temperature resistance performance of flow pattern regulators

[0076] (1) Preparation of 4% bentonite-based slurry: Add 16g bentonite and 0.56g anhydrous sodium carbonate to 400mL water, stir at 8000r / min for 20min, and let stand at room temperature for 24h for hydration.

[0077] (2) Sample slurry preparation: Take 400 mL of 4% bentonite-based slurry, add 4 g (1%) of the flow modifier prepared in the examples and comparative examples respectively, stir at 10000 r / min for 20 min, place the above drilling fluid sample in a roller heating furnace, set the aging temperature to 240℃, and the aging time to 16 h.

[0078] (3) The apparent viscosity (AV) of the prepared drilling fluid was tested in accordance with the national standard GB / T 29170-2012 Laboratory Test of Drilling Fluid for Petroleum and Natural Gas Industry. The viscosity retention rate (η) was calculated according to the formula. The experimental results are shown in Table 1.

[0079] η = AV2 / AV1 × 100%

[0080] in:

[0081] η—viscosity retention rate, %;

[0082] AV1—Viscosity before hot rolling, mPa·s;

[0083] AV2—Viscosity after hot rolling, mPa·s;

[0084] Table 1: Changes in apparent viscosity of different flow modifiers before and after hot rolling

[0085]

[0086]

[0087]

[0088] As can be seen from the test results in Table 1, the hydrophobic crosslinking flow modifiers prepared in Examples 1-10, by changing the type of hydrophobic monomer, the type of initiator, and the reaction conditions, maintained good high-temperature rheological properties and a viscosity retention rate of >80% after curing in 4 wt.% bentonite-based slurry at 240°C for 16 h. This indicates that the simultaneous introduction of hydrophobic monomers, strong hydration sulfonic acid groups, and zwitterionic crosslinking agents into the polymer molecular structure enhances the polymer's resistance to ultra-high temperatures through strengthening the rigid molecular structure, intermolecular hydrogen bonding, and hydrophobic association. In contrast, the flow modifier prepared in Comparative Example 1 did not introduce zwitterionic crosslinking agents during the preparation process, and the polymer molecules did not form a three-dimensional network structure connected by chemical bonds. Compared with the polymer with added crosslinking agents, its viscosity-enhancing and shear-lifting properties were weakened. Meanwhile, due to the lack of zwitterionic groups, the polymer is more sensitive to salt concentration. Under high temperature and high complex salt conditions, the polymer double layer is significantly compressed, reducing the polymer's salt resistance. Comparative Example 2, without the addition of alkyl methacrylate, lacks long-chain alkyl groups in its copolymer. Due to the lack of hydrophobic association and steric hindrance, the polymer molecular chains are more prone to decomposition and spatial coiling at high temperatures, resulting in a significant decrease in viscosity and a marked reduction in the product's temperature resistance. Comparative Example 3, using Driscal-D sample slurry, showed a viscosity retention rate of 62% after hot rolling at 240℃ for 16 hours, which is lower than the viscosity retention rate of the hydrophobic crosslinking flow modifier developed in this invention. Comparative Example 4, without the addition of 2-acrylamido-2-methylpropanesulfonic acid, showed a significant decrease in polymer temperature resistance, with a viscosity retention rate of only 45.9% after hot rolling at 240℃.

[0089] 2. Evaluation of the salt resistance of flow pattern regulators

[0090] (1) Preparation of 4% bentonite-based slurry: Add 16g bentonite and 0.56g anhydrous sodium carbonate to 400mL water, stir at 8000r / min for 20min, and let stand at room temperature for 24h for hydration.

[0091] (2) Sample slurry preparation: Take 5 cups of 400mL 4% bentonite-based slurry, add 4g (1%) of the flow pattern regulator prepared in Example 1, stir at 10000r / min for 20min, then add 5%, 10%, 15%, 20%, and 30% sodium chloride in sequence, stir at 10000r / min for 20min, place the above drilling fluid sample in a roller heating furnace, set the aging temperature to 240℃, and the aging time to 16h.

[0092] (3) The apparent viscosity (AV) of the prepared drilling fluid was tested in accordance with the national standard GB / T 29170-2012 Laboratory Test of Drilling Fluid for Petroleum and Natural Gas Industry. The viscosity retention rate (η) was calculated according to the formula. The experimental results are shown in Table 2.

[0093] η = AV2 / AV1 × 100%

[0094] in:

[0095] η—viscosity retention rate, %;

[0096] AV1—Viscosity before hot rolling, mPa·s;

[0097] AV2—Viscosity after hot rolling, mPa·s;

[0098] Table 2. Changes in apparent viscosity before and after hot rolling under different salt dosages for the flow pattern regulator in Example 1.

[0099]

[0100] The high-temperature flow modifier for drilling fluid prepared in Example 1 was used in a 4 wt.% bentonite-based slurry with different concentrations of sodium chloride. After aging at 240°C for 16 hours, the viscosity retention gradually decreased. When 15% NaCl was added, the viscosity retention reached 72.22%, exhibiting good salt resistance. Due to the presence of strong hydration groups, sulfonic acid groups, and zwitterionic groups between polymer molecules, coupled with crosslinking, steric hindrance, and hydrophobic association, a large polymer hydraulic diameter is maintained in high-salt solutions, resulting in high viscosity retention. As the salt concentration increases, the polymer hydration double layer is further compressed, the molecular chains coil, and the viscosity gradually decreases until an equilibrium value is reached.

[0101] Based on the above embodiments, this invention develops a hydrophobic crosslinking high-temperature flow modifier, resistant to temperatures up to 240℃ and resistant to 15% NaCl. By simultaneously introducing strong hydration groups, zwitterionic crosslinking agents, and long-chain hydrophobic groups into the molecular structure, the polymer's high-temperature and salt resistance is enhanced, which can meet the technical requirements for rheological regulation of drilling fluids in complex formations of ultra-deep wells.

[0102] The applicant declares that the present invention illustrates the zwitterionic crosslinking agent, copolymer flow modifier, preparation method, and application of the present invention through the above embodiments. However, the present invention is not limited to the above embodiments, that is, it does not mean that the present invention must rely on the above embodiments to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A zwitterionic crosslinking agent, characterized in that, The zwitterionic crosslinking agent has the following structure: 。 2. A method for preparing the zwitterionic crosslinking agent as described in claim 1, characterized in that, The preparation method includes the following steps: Disodium ethylenediaminetetraacetate reacts with 4-vinylbenzyl chloride to obtain the zwitterionic crosslinking agent.

3. The preparation method according to claim 2, characterized in that, The molar ratio of disodium ethylenediaminetetraacetate to 4-vinylbenzyl chloride is 1:(2~2.2).

4. The preparation method according to claim 2, characterized in that, The reaction temperature is 60-80℃, and the reaction time is 8-12h.

5. The preparation method according to claim 2, characterized in that, The reaction is carried out in a solvent.

6. The preparation method according to claim 5, characterized in that, The solvent is selected from N,N-dimethylformamide.

7. A copolymer flow pattern modifier, characterized in that, The copolymer flow modifier is a copolymer obtained by polymerization of acrylamide monomers, sulfonic acid monomers, alkyl methacrylates and the zwitterionic crosslinking agent as described in claim 1.

8. The copolymer flow pattern modifier according to claim 7, characterized in that, The acrylamide monomers include N,N-dimethylacrylamide and / or N,N-diethylacrylamide.

9. The copolymer flow pattern modifier according to claim 7, characterized in that, The sulfonic acid monomer is 2-acrylamido-2-methylpropanesulfonic acid.

10. The copolymer flow pattern modifier according to claim 7, characterized in that, The mass ratio of the acrylamide monomer, sulfonic acid monomer, alkyl methacrylate and the zwitterionic crosslinker as described in claim 1 is (30~50):(40~60):(10~15):(5~10).

11. The copolymer flow pattern modifier according to claim 7, characterized in that, The alkyl methacrylate is selected from one or a combination of at least two of dodecyl methacrylate, hexadecyl methacrylate, or octadecyl methacrylate.

12. The copolymer flow pattern modifier according to claim 7, characterized in that, The polymerization reaction is initiated by an initiator.

13. The copolymer flow pattern modifier according to claim 12, characterized in that, The initiator is selected from any one or a combination of at least two azo initiators.

14. The copolymer flow pattern modifier according to claim 12, characterized in that, The initiator is selected from any one or a combination of at least two of azobisisobutyronitrile, 2,2'-azobisisobutyramidine dihydrochloride, or azobisisobutyramidazolin hydrochloride.

15. The copolymer flow pattern modifier according to claim 12, characterized in that, The acrylamide monomer is N,N-dimethylacrylamide, the sulfonic acid monomer is 2-acrylamido-2-methylpropanesulfonic acid, and the amount of the initiator is 0.2% to 0.5% of the total weight of N,N-dimethylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, alkyl methacrylate, and the zwitterionic crosslinking agent as described in claim 1.

16. A method for preparing a copolymer flow modifier as described in any one of claims 7-15, characterized in that, The preparation method includes the following steps: (1) Mix the solution of sulfonic acid monomers with acrylamide monomers. (2) Add alkyl methacrylate, zwitterionic crosslinking agent and initiator as described in claim 1 to the mixture in step (1), and react to obtain the copolymer flow modifier.

17. The preparation method according to claim 16, characterized in that, The solution of the sulfonic acid monomer is an aqueous solution of the sulfonic acid monomer.

18. The preparation method according to claim 16, characterized in that, Before mixing in step (1), adjust the pH of the sulfonic acid monomer solution to neutral.

19. The preparation method according to claim 18, characterized in that, The pH adjustment was performed using a sodium hydroxide solution.

20. The preparation method according to claim 16, characterized in that, The mixing in step (1) also includes the addition of a surfactant.

21. The preparation method according to claim 20, characterized in that, The surfactant is sodium dodecylbenzenesulfonate.

22. The preparation method according to claim 20, characterized in that, The amount of surfactant added is 3% to 5% of the total solvent in the sulfonic acid monomer solution.

23. The preparation method according to claim 16, characterized in that, After adding alkyl methacrylate, zwitterionic crosslinking agent and initiator as described in step (2), the temperature is raised to 30-40°C and continuously stirred to dissolve and disperse evenly. Then, nitrogen gas is introduced to remove oxygen, and the temperature is raised to 50-70°C. The reaction is carried out under nitrogen protection for 4-8 hours.

24. A drilling fluid, characterized in that, The drilling fluid includes a copolymer flow modifier as described in any one of claims 7-15.

25. The drilling fluid according to claim 24, characterized in that, The mass percentage of copolymer flow modifier in the drilling fluid is ≤4%.

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