Zwitterionic cross-linking agent, copolymer flow pattern regulator, and preparation method and application of zwitterionic cross-linking agent and copolymer flow pattern regulator

Abstract

The invention provides a zwitterionic cross-linking agent, a copolymer flow pattern regulator and a preparation method and application of the zwitterionic cross-linking agent and the copolymer flow pattern regulator. The preparation method comprises the following steps: preparing a polycarboxyl zwitterionic cross-linking agent, and carrying out polymerization reaction on an acrylamide monomer, a sulfonic monomer, alkyl methacrylate and the zwitterionic cross-linking agent to obtain the copolymer flow pattern regulator. The copolymer flow pattern conditioning agent provided by the invention is a hydrophobic cross-linked high-temperature-resistant flow pattern conditioning agent, the temperature resistance can reach 240 DEG C, the NaCl salt resistant concentration is up to 15%, the viscosity retention rate is 80% or above, and the copolymer flow pattern conditioning agent has excellent rheological property after high-temperature aging and has wide application prospects in the field of high-temperature-resistant water-based drilling fluids.

Description

Technical Field

[0001] The invention belongs to the technical field of drilling fluid in the petroleum industry and relates to a zwitterionic crosslinking agent, a copolymer flow pattern regulator, and a preparation method and application thereof. Background Art

[0002] As oil exploration and development continues to expand to deep and ultra-deep layers, complex formations such as high temperature, salt-gypsum layers, and high-pressure salt water layers are often encountered during drilling, which puts higher requirements on the drilling fluid system's resistance to ultra-high temperature, salt resistance, and wellbore cleaning. As an important drilling fluid treatment agent, flow pattern regulators not only have the effect of increasing viscosity, but also have the functions of adjusting the dynamic shear force, static shear force, viscoelasticity, filtration loss, and improving the quality of mud cakes, thus having an important impact on wellbore stability and oil layer protection. Flow pattern regulators in drilling fluids mainly interact with the treatment agent molecules and clay particles through van der Waals forces, hydrogen bonds, electrostatic forces, and intermolecular hydrophilic and hydrophobic forces to form a three-dimensional network structure, so as to achieve the effect of increasing viscosity and improving shearing of drilling fluids.

[0003] Common drilling fluid flow pattern regulators include modified natural plant gums (such as high-viscosity polyanionic cellulose, hydroxyethyl cellulose, etc.), modified organic polysaccharide derivatives (such as xanthan gum) and synthetic polymers (mainly acrylamide polymers). Although these flow pattern regulators have their own advantages in some aspects, they will produce obvious high-temperature degradation at higher temperatures, and the viscosity retention rate is low, which can easily lead to problems such as insufficient cuttings carrying capacity and barite sedimentation of drilling fluids under high temperature conditions. Cuttings beds are easily generated during drilling, and friction resistance increases during drilling, resulting in downhole complexities such as support pressure and blockage. Most conventional flow pattern regulators have problems such as insufficient temperature resistance and salt resistance or unclear viscosity-increasing effects. In high-temperature well sections, they mainly rely on imported flow pattern regulator products. At present, synthetic polymer flow pattern regulators have made breakthroughs in high temperature resistance. There are reports on improving the temperature resistance of flow pattern regulators in the prior art, such as Chinese patent ZL201510509849.6, which uses N,N-dimethylacrylamide, 2-acrylamide-2-methylpropanesulfonic acid, acrylamide and acrylic acid under the action of a cross-linking agent to form a flow pattern regulator with a spatial network structure molecule while copolymerizing and cross-linking. The solution prepared under high temperature (120°C) and high salt (saturated brine) has a high viscosity and good compatibility with other treatment agents. The temperature and salt resistance needs to be further improved; Chinese patent ZL202010859019.7 uses 2-acrylamide-2-methylpropanesulfonic acid, vinylpyridine, divinylbenzene, etc. as raw materials to prepare a high temperature resistant polymer flow pattern regulator through an emulsion polymerization method. The product is temperature-resistant up to 160°C, not easy to foam, and has strong resistance to salt and calcium, 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 pattern regulator with a branched structure, rich in anionic and cationic functional groups, exhibiting an anti-polyelectrolyte effect, excellent viscosity-increasing, high-temperature resistance and salt pollution resistance, temperature resistance of up to 220°C, and viscosity retention of more than 85%, but the polymer monomer structure is complex and the synthesis process is cumbersome; therefore, in view of the technical requirements of drilling fluids in complex formations such as deep, ultra-deep layers and salt-gypsum layers, it is urgent to develop a new type of high-temperature resistant flow pattern regulator. Summary of the invention

[0004] In view of the deficiencies of the prior art, the purpose of the present invention is to provide a zwitterionic crosslinking agent, a copolymer flow pattern regulator, and a preparation method and application thereof. The present invention provides a crosslinked high temperature resistant copolymer flow pattern regulator having both zwitterionic groups and hydrophobic groups, which overcomes the problems of insufficient high temperature and salt resistance and complex preparation process of the prior art.

[0005] To achieve this object, the present invention adopts the following technical solutions:

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

[0007]

[0008] The zwitterionic crosslinking agent of the present invention has a carbon-carbon double bond group available for polymerization, has an anionic strong hydration group (carboxyl group), can enhance the hydration ability, can also chemically crosslink the pre-written polymer molecules, strengthen the three-dimensional network structure of the polymer molecules, enhance the temperature resistance of the polymer, and because an internal salt structure can be formed in the molecule, the salt resistance of the polymer is improved.

[0009] On the other hand, the present invention provides a method for preparing the zwitterionic crosslinking agent as described above, the preparation 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:(2-2.2), for example 1:2, 1:2.1 or 1:2.2.

[0012] Preferably, the reaction temperature is 60-80°C, for example 60°C, 63°C, 65°C, 68°C, 70°C, 75°C, 78°C or 80°C, 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 pattern regulator, wherein the copolymer flow pattern regulator is a copolymer obtained by polymerization reaction of acrylamide monomers, sulfonic acid monomers, alkyl methacrylate and zwitterionic crosslinking agent.

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

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

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

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

[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 of azo initiators.

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

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

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

[0025] (1) mixing a solution of a sulfonic acid monomer with an acrylamide monomer,

[0026] (2) adding alkyl methacrylate, zwitterionic crosslinking agent and initiator to the mixed solution of step (1), reacting to obtain the copolymer flow pattern regulator.

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

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

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

[0030] Preferably, the mixing in step (1) further comprises adding a surfactant.

[0031] Preferably, the surfactant is sodium dodecylbenzene sulfonate.

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

[0033] Preferably, after adding the alkyl methacrylate, zwitterionic crosslinking agent and initiator in step (2), the temperature is raised to 30-40°C, and stirred continuously to dissolve and disperse them evenly, and then nitrogen is introduced to deoxygenate, and then the temperature is raised to 50-70°C (for example, 50°C, 55°C, 58°C, 60°C, 65°C, 68°C or 70°C), and the reaction is carried out under nitrogen protection for 4-8h (for example, 4h, 5h, 6h, 7h or 8h).

[0034] In another aspect, the present invention provides a drilling fluid, the drilling fluid comprising the copolymer flow pattern regulator as described above;

[0035] Preferably, the mass percentage of the copolymer flow pattern regulator in the drilling fluid is ≤4%, for example, 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 the present invention not only includes the point values ​​listed above, but also includes any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists 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 a carbon-carbon double bond group available for polymerization, has an anionic strong hydration group (carboxyl group), can enhance the hydration ability, can also chemically crosslink the pre-written polymer molecules, strengthen the three-dimensional network structure of the polymer molecules, enhance the temperature resistance of the polymer, and because an internal salt structure can be formed in the molecule, the salt resistance of the polymer is improved.

[0039] The molecular structure of the flow pattern regulator of the present invention introduces anionic strong hydration groups (carboxyl and sulfonic acid groups) to enhance the hydration ability of the polymer and give it excellent glue protection ability 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, strengthens the three-dimensional network structure of the polymer molecules, and enhances the temperature resistance of the polymer; on the other hand, by introducing zwitterionic groups, the salt resistance of the polymer is improved due to the formation of an internal salt structure in the molecule; the introduction of long-chain hydrophobic monomers, due to the hydrophobic association and steric hindrance effect in the molecular structure, the polymer solution can maintain a good hydraulic diameter under high temperature and high salt conditions, so the polymer molecule viscosity retention rate is high. The copolymer flow pattern regulator provided by the present invention is a hydrophobic cross-linked high temperature resistant flow pattern regulator, with a temperature resistance of up to 240°C, a resistance to NaCl salt concentration of up to 15%, a viscosity retention rate of more than 80%, excellent rheological properties after high temperature aging, and has broad application prospects in the field of high temperature resistant water-based drilling fluids. DETAILED DESCRIPTION

[0040] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0041] Example 1

[0042] (1) Preparation of zwitterionic crosslinking agents

[0043]

[0044] 0.1 mol of disodium ethylenediaminetetraacetate (Na2EDTA) was added to 80 mL of dimethylformamide (DMF) solution, and the mixture was poured into a three-necked reaction bottle after being stirred thoroughly. 0.2 mol of 4-vinylbenzyl chloride was added, and the mixture was heated to 60°C for reaction for 8 h. After the reaction was completed, the mixture was allowed to stand and cool at room temperature, and deionized water was added to wash the mixture to remove DMF. The product was extracted with acetone for 3 times, and the solvent was removed by rotary evaporation to obtain a dry solid, which was the zwitterionic crosslinker.

[0045] (2) Preparation of flow pattern regulator

[0046] Weigh 40g of 2-acrylamide-2-methylpropanesulfonic acid (AMPS), prepare an aqueous solution with 200mL of deionized water, wait for it to completely dissolve, adjust the pH value of the solution to neutral with NaOH, add 30g of N,N-dimethylacrylamide, then pour it into a three-necked reaction bottle, add 6g of sodium dodecylbenzenesulfonate (SDS), and stir slowly to dissolve it evenly, add 10g of dodecyl methacrylate, 5g of zwitterionic crosslinker and 0.17g of azobisisobutyronitrile (AIBN) in sequence, heat to 35℃, and stir continuously to dissolve and disperse it evenly. Seal the three-necked reaction bottle, pass N2 to deoxygenate for 30min, heat the constant temperature water bath to 50℃, react for 6h under N2 protection, and obtain a white colloid. Take out the product, precipitate it with acetone, and soak it three times with a mixed solvent of acetone / water (7 / 3, v / v) and acetone, and dry it in vacuum at 60℃ to obtain a copolymer flow regulator sample.

[0047] Example 2

[0048] The difference from Example 1 is that the amounts of substances added in step (2) are as follows: 60 g 2-acrylamido-2-methylpropanesulfonic acid (AMPS), 50 g N,N-dimethylacrylamide, 15 g dodecyl methacrylate, 10 g zwitterionic crosslinker and 0.27 g azobisisobutyronitrile (AIBN). Except for the different amounts of substances, 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: 50 g 2-acrylamido-2-methylpropanesulfonic acid (AMPS), 40 g N,N-dimethylacrylamide, 12 g dodecyl methacrylate, 8 g zwitterionic crosslinking agent and 0.22 g azobisisobutyronitrile (AIBN). Except for the different amounts of substances, 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: 55 g of 2-acrylamido-2-methylpropanesulfonic acid (AMPS), 45 g of N,N-dimethylacrylamide, 14 g of dodecyl methacrylate, 6 g of zwitterionic crosslinking agent and 0.24 g of azobisisobutyronitrile (AIBN). Except for the different amounts of substances, 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: 48 g 2-acrylamido-2-methylpropanesulfonic acid (AMPS), 35 g N,N-dimethylacrylamide, 13 g dodecyl methacrylate, 5 g zwitterionic crosslinking agent and 0.21 g azobisisobutyronitrile (AIBN). Except for the different amounts of substances, 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 the reaction is carried out under N 2 protection for 8 h.

[0057] Example 7

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

[0059] Example 8

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

[0061] Example 9

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

[0063] Example 10

[0064] The difference from Example 1 is that 0.17 g of azobisisobutyronitrile in step (2) is replaced by 0.17 g of azobisisobutylimidazoline 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 foreign flow pattern regulator product Driscal-D was used for comparison.

[0071] Comparative Example 4

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

[0073] Application performance testing and results

[0074] The performance evaluation of hydrophobic cross-linked high temperature resistant flow pattern regulator is mainly characterized by the following two aspects: one is the viscosity retention rate of the flow pattern regulator at high temperature; the other is to test the viscosity retention rate of the flow pattern regulator at different salt concentrations.

[0075] 1. Evaluation of temperature resistance of flow pattern regulator

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

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

[0078] (3) The apparent viscosity (AV) of the prepared drilling fluid was tested with reference to the national standard GB / T 29170-2012 Laboratory Test of Drilling Fluids in the 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 type regulators before and after hot rolling

[0085]

[0086]

[0087]

[0088] From the test results in Table 1, it can be seen that the hydrophobic cross-linked flow type regulator prepared by Examples 1 to 10 by changing the type of hydrophobic monomer, the type of initiator and the reaction conditions maintains good high temperature rheology after curing at 240°C for 16 hours in a 4wt.% bentonite-based slurry, and the viscosity retention rate is >80%. This indicates that the introduction of hydrophobic monomers, strongly hydrated sulfonic acid groups and zwitterionic crosslinkers into the polymer molecular structure simultaneously improves the polymer's ability to resist ultra-high temperatures by strengthening the molecular rigid structure, intermolecular hydrogen bonding, and hydrophobic association. However, the flow type regulator prepared in Comparative Example 1 did not introduce zwitterionic crosslinkers during the preparation process, and the polymer molecules did not form a three-dimensional network structure connected by chemical bonds. Compared with the polymer to which the crosslinker was added, the viscosity-increasing and shear-increasing performance was weakened. At the same time, due to the lack of zwitterionic groups, the polymer is more sensitive to salt concentration, and the polymer double layer is significantly compressed under high temperature and high complex salt conditions, which reduces the polymer's salt resistance. In Comparative Example 2, no alkyl methacrylate is added, and there is no long-chain alkyl group in the copolymer. Due to the lack of hydrophobic association and steric hindrance effect, the polymer molecular chain is more easily decomposed and curled in space at high temperature, and the viscosity effect is significantly reduced, resulting in a significant weakening of the product's temperature resistance. The viscosity retention rate of the sample slurry of Driscal-D in Comparative Example 3 after hot rolling at 240°C for 16h is 62%, and the viscosity retention rate at ultra-high temperature is lower than that of the hydrophobic cross-linked flow type regulator developed by the present invention. Comparative Example 4 does not add 2-acrylamido-2-methylpropanesulfonic acid, and the polymer's temperature resistance is significantly reduced, with a viscosity retention rate of 45.9% after hot rolling at 240°C.

[0089] 2. Evaluation of salt resistance of flow pattern regulator

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

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

[0092] (3) The apparent viscosity (AV) of the prepared drilling fluid was tested with reference to the national standard GB / T 29170-2012 Laboratory Test of Drilling Fluids in the 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 of flow pattern regulator in Example 1 at different salt additions

[0099]

[0100] The high temperature resistant flow pattern regulator for drilling fluid prepared by Example 1 was added with different concentrations of sodium chloride in 4wt.% bentonite-based slurry. After aging at 240°C for 16h, the viscosity retention rate gradually decreased. When 15% NaCl was added, the viscosity retention rate reached 72.22%, which had good salt resistance. Due to the presence of strong hydration groups, sulfonic acid groups and zwitterionic groups between polymer molecules, and the superposition of cross-linking, steric hindrance and hydrophobic association, a large polymer hydrodynamic diameter was maintained in a high salt solution, and the viscosity retention rate was high. As the salt concentration increases, the polymer hydration double layer is further compressed, the molecular chain curls, and the viscosity gradually decreases until the equilibrium value is reached.

[0101] Based on the above embodiments, the present invention has developed a hydrophobic cross-linked high temperature resistant flow pattern regulator, which can resist temperatures up to 240°C and 15% NaCl. By simultaneously introducing strong hydration groups, zwitterionic cross-linkers and long-chain hydrophobic groups into the molecular structure, the polymer's ability to resist high temperature and salt is enhanced, which can meet the technical requirements for rheological control of drilling fluids in complex formations of ultra-deep wells.

[0102] The applicant declares that the present invention uses the above-mentioned embodiments to illustrate the zwitterionic crosslinking agent, copolymer flow pattern regulator, preparation method and application of the present invention, but the present invention is not limited to the above-mentioned embodiments, that is, it does not mean that the present invention must rely on the above-mentioned embodiments to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of various raw materials of the product 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. The method for preparing a zwitterionic crosslinking agent according to claim 1, characterized in that: The preparation method comprises the following steps: The disodium ethylenediaminetetraacetate reacts with 4-vinylbenzyl chloride to obtain the zwitterionic crosslinking agent; Preferably, the molar ratio of disodium ethylenediaminetetraacetate to 4-vinylbenzyl chloride is 1:(2-2.2); Preferably, the reaction temperature is 60-80°C and the reaction time is 8-12h; Preferably, the reaction is carried out in a solvent; Preferably, the solvent is selected from N,N-dimethylformamide.

3. A copolymer flow pattern regulator, characterized in that: The copolymer flow pattern regulator is a copolymer obtained by polymerization reaction of acrylamide monomers, sulfonic acid monomers, alkyl methacrylate and a zwitterionic crosslinking agent.

4. The copolymer flow pattern regulator according to claim 3, characterized in that The acrylamide monomers include N,N-dimethylacrylamide and / or N,N-diethylacrylamide; Preferably, the sulfonic acid monomer is 2-acrylamide-2-methylpropanesulfonic acid; Preferably, the mass ratio of the acrylamide monomer, the sulfonic acid monomer, the alkyl methacrylate and the zwitterionic crosslinking agent is (30-50): (40-60): (10-15): (5-10).

5. The copolymer flow pattern regulator according to claim 3 or 4, characterized in that: The alkyl methacrylate is selected from one or a combination of at least two of dodecyl methacrylate, hexadecyl acrylate, or octadecyl acrylate.

6. The copolymer flow pattern regulator according to any one of claims 3 to 5, characterized in that: The polymerization reaction is carried out under the initiation of an initiator; Preferably, the initiator is selected from any one or a combination of at least two of the azo initiators; Preferably, the initiator is selected from any one or a combination of at least two of azobisisobutyronitrile, 2,2'-azobisisobutylamidine dihydrochloride or azobisisobutylimidazoline hydrochloride; 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.

7. The method for preparing the copolymer flow pattern regulator according to any one of claims 3 to 5, characterized in that: The preparation method comprises the following steps: (1) mixing a solution of a sulfonic acid monomer with an acrylamide monomer, (2) adding alkyl methacrylate, zwitterionic crosslinking agent and initiator to the mixed solution of step (1), reacting to obtain the copolymer flow pattern regulator.

8. The preparation method according to claim 7, characterized in that: The solution of the sulfonic acid monomer is an aqueous solution of the sulfonic acid monomer; Preferably, before the mixing in step (1), the pH value of the solution of the sulfonic acid monomer is adjusted to neutral; Preferably, the pH value adjustment is performed using a sodium hydroxide solution; Preferably, the mixing in step (1) further comprises adding a surfactant; Preferably, the surfactant is sodium dodecylbenzene sulfonate; Preferably, the added amount of the surfactant is 3% to 5% of the total amount of the solvent in the solution of the sulfonic acid monomer.

9. The preparation method according to claim 7 or 8, characterized in that: After adding the alkyl methacrylate, zwitterionic crosslinking agent and initiator in step (2), the temperature is raised to 30-40° C. and stirred continuously to make them dissolve and disperse evenly, and then nitrogen is introduced to deoxygenate, and then the temperature is raised to 50-70° C. and reacted under nitrogen protection for 4-8 hours.

10. A drilling fluid, characterized in that: The drilling fluid comprises a copolymer flow pattern regulator as claimed in any one of claims 3 to 5; Preferably, the mass percentage of the copolymer flow pattern regulator in the drilling fluid is ≤4%.

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