A branched structure polyacrylamide coating agent and a preparation method thereof

Abstract

The present application relates to a kind of branched structure polyacrylamide coating agent and its preparation method.The method includes: 2-acetylamino acrylate and 1,1,1-tris (4-hydroxyphenyl) ethane are esterified, branched agent is obtained;With water, acrylamide, branched agent, anionic monomer, temperature-resistant monomer are mixed uniformly, and mixed liquor is obtained, then mixed liquor is deoxygenated by nitrogen, and then azo initiator, complexing agent, molecular weight regulator, oxidizing agent and reducing agent are added to initiate polymerization, and polymer is obtained;Polymer is sequentially washed, dried and crushed, and branched structure polyacrylamide coating agent is prepared.The branched structure polyacrylamide coating agent prepared in the present application has the characteristics of small shear effect, high-temperature aging resistance, and the cuttings recovery rate is more than 85%.

Description

Technical Field

[0001] This invention relates to the field of drilling technology, specifically to a branched polyacrylamide coating agent and its preparation method. Background Technology

[0002] Polymer coating agents are an important additive used in drilling fluid systems and are an indispensable component of water-based drilling fluids. They effectively coat drill cuttings, preventing hydration of drill cuttings and shale, preventing wellbore collapse, promoting wellbore stability, and increasing drilling speed. They also have functions such as reducing fluid loss, improving flow patterns, and increasing lubricity. However, with the development of oil exploration and development towards deep wells, complex wells, and unconventional energy sources such as shale oil and gas, polymer coating agents have shown one or more problems in field applications, including limited solubility, insufficient temperature resistance, and inadequate shear resistance. While laboratory evaluations show good results, field application performance is often poor.

[0003] In summary, it is essential to provide a branched polyacrylamide coating agent and its preparation method. Summary of the Invention

[0004] To address one or more technical problems existing in the prior art, this invention provides a branched polyacrylamide coating agent and its preparation method. The branched polyacrylamide coating agent prepared by this invention has advantages such as temperature resistance, low shear stress, and a rock cuttings recovery rate exceeding 85%.

[0005] The present invention provides a method for preparing a branched polyacrylamide coating agent in a first aspect, the method comprising the following steps:

[0006] (1) Esterification reaction of 2-acetamidoacrylic acid and 1,1,1-tris(4-hydroxyphenyl)ethane yields a branching agent;

[0007] (2) Mix acrylamide, branching agent, anionic monomer and heat-resistant monomer with water to obtain a mixture. Then, purify the mixture with nitrogen to remove oxygen. Add azo initiator, complexing agent, molecular weight regulator, oxidant and reducing agent to initiate the polymerization reaction and obtain polymer.

[0008] (3) The polymer is washed, dried and pulverized in sequence to obtain a branched polyacrylamide coating agent.

[0009] Preferably, in step (1): the esterification reaction is carried out in the presence of dimethylformamide, a dehydrating agent, a catalyst, and a polymerization inhibitor; preferably, the molar ratio of 1,1,1-tris(4-hydroxyphenyl)ethane, 2-acetamidoacrylic acid, and dimethylformamide is 1:(1.5-2):(18-22); preferably, the dehydrating agent is 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide, and the catalyst is... 4-Dimethylaminopyridine, wherein the polymerization inhibitor is phenothiazine; preferably, the molar ratio of the dehydrating agent to the 1,1,1-tris(4-hydroxyphenyl)ethane is 1:(0.8-1.2), the molar ratio of the catalyst to the 1,1,1-tris(4-hydroxyphenyl)ethane is (0.02-0.03):1, and the molar ratio of the polymerization inhibitor to the 1,1,1-tris(4-hydroxyphenyl)ethane is (0.01-0.02):1.

[0010] Preferably, in step (1): the temperature of the esterification reaction is 85℃~95℃, and the time of the esterification reaction is 4~5h.

[0011] Preferably, the raw materials for preparing the branched polyacrylamide coating agent comprise the following components by weight: 200-250 parts acrylamide, 8-12 parts branching agent, 5-10 parts anionic monomer, 4-8 parts heat-resistant monomer, 752-806 parts water, 0.02-0.04 parts azo initiator, 0.005-0.015 parts complexing agent, 0.005-0.015 parts molecular weight regulator, 0.01-0.02 parts oxidant, and 0.005-0.015 parts reducing agent.

[0012] Preferably, the anionic monomer is one or more of acrylic acid, sodium acrylate, itaconic acid, and 2-acrylamide-2-methylpropanesulfonic acid. More preferably, the anionic monomer is a mixture of acrylic acid and itaconic acid in a mass ratio of 1:(0.5-0.7), more preferably 1:0.6. And / or the heat-resistant monomer is one or more of 2-acrylamide-2-methylpropanesulfonic acid, tert-butylacrylamide sulfonic acid, potassium propyl methacrylate, vinylbenzene sulfonic acid, N-vinylpyrrolidone, sodium p-styrene sulfonate, and L-isoleucine allyl p-methylbenzene sulfonate. More preferably, the heat-resistant monomer is a mixture of 2-acrylamide-2-methylpropanesulfonic acid and L-isoleucine allyl p-methylbenzene sulfonate in a mass ratio of 1:(0.2-0.8), more preferably 1:0.5.

[0013] Preferably, the azo initiator is one or more of azobisisobutyronitrile, azobisisobutyramidine hydrochloride, and azobisisobutyramidazolin hydrochloride; the complexing agent is one or more of disodium ethylenediaminetetraacetate, trisodium diethyltriaminepentaacetate, sodium ethylenediaminetetramethylene phosphate, and sodium citrate; the molecular weight regulator is one or more of sodium formate, 2,4-diphenyl-4-methyl-1-pentene, and dodecyl mercaptan; the oxidizing agent is one or more of hydrogen peroxide, di-tert-butyl peroxide, tert-butyl hydroperoxide, potassium persulfate, and ammonium persulfate; and / or the reducing agent is one or more of sodium sulfite, sodium bisulfite, and sodium thiosulfate.

[0014] Preferably, in step (2): the pH value of the mixture is first adjusted to 7.0 to 7.2 using a pH adjuster, and then nitrogen is introduced for deoxygenation.

[0015] Preferably, the pH adjuster is an aqueous solution of acrylic acid and / or sodium hydroxide.

[0016] Preferably, in step (2): the nitrogen deoxygenation time is 30-50 min; the polymerization initiation temperature is 14-16℃; and / or after the polymerization reaction is initiated by adding the initiator, the polymerization reaction system is naturally heated, and after the temperature of the polymerization reaction system no longer rises, it is kept warm for 2-3 h, the peak temperature of the natural heating is 60-75℃, and the temperature of the heat preservation is the peak temperature of the natural heating.

[0017] In a second aspect, the present invention provides a branched polyacrylamide coating agent prepared by the preparation method described in the first aspect of the present invention.

[0018] Compared with the prior art, the present invention has at least the following beneficial effects:

[0019] (1) The branched polyacrylamide coating agent of the present invention has a non-linear molecular chain structure formed by polymerization, but a branched network structure. The branched polymer molecules are more extended than the linear polymer molecules, with more adsorption sites, and thus stronger adsorption capacity for drill cuttings. Moreover, the branched polyacrylamide coating agent prepared by the present invention is more conducive to coating drill cuttings than other branched polyacrylamides. The coating capacity is strong and durable. The branching agent used contains a rigid benzene ring structure, which is not easy to rotate within the molecule and reduces the possibility of macromolecular curling. This can effectively improve the rigidity of the molecular chain and improve its shear resistance. The steric hindrance effect generated by the benzene ring makes the main chain of the polymer more extended, which can effectively weaken the influence of salt effect on the polymer chain, thereby improving the salt resistance of the polymer. In addition, the benzene ring, as a large rigid spacer group, inhibits intramolecular association. The branched structure can further improve its structural stability, shear resistance, and mechanical strength, so that it is not affected by formation shear and damage in deep wells and can better adapt to high shear environment, which is conducive to improving the field application effect.

[0020] (2) The branched polyacrylamide coating agent prepared by the present invention introduces a heat-resistant monomer, which has a sulfonic acid group and a rigid group that are not sensitive to temperature, so that the resulting polymer has good viscosity even under high temperature conditions; the branched polyacrylamide coating agent prepared by the present invention has the characteristics of being less affected by shear and resistant to high temperature aging, and the rock cuttings recovery rate exceeds 85%. Attached Figure Description

[0021] Figure 1 This is a schematic diagram illustrating the reaction principle for preparing the branching agent according to the present invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0023] The present invention provides a method for preparing a branched polyacrylamide coating agent in a first aspect, the method comprising the following steps:

[0024] (1) An esterification reaction is carried out between 2-acetamidoacrylic acid and 1,1,1-tris(4-hydroxyphenyl)ethane to obtain a branching agent; the reaction principle diagram for preparing the branching agent in this invention is as follows: Figure 1 As shown;

[0025] (2) Acrylamide, branching agent, anionic monomer, and heat-resistant monomer are mixed evenly with water to obtain a mixture. Then, the mixture is purged with nitrogen to remove oxygen. Then, an azo initiator, complexing agent, molecular weight regulator, oxidant, and reducing agent are added to initiate a polymerization reaction to obtain a polymer. Specifically, for example, acrylamide, branching agent, anionic monomer, and heat-resistant monomer are dissolved in deionized water to obtain a mixture. The mixture is purged with nitrogen to remove oxygen. Then, an azo initiator, complexing agent, molecular weight regulator, and oxidant are added sequentially. Under oxygen-free, nitrogen-protected, and stirring conditions, a reducing agent is added dropwise to initiate a polymerization reaction to obtain a transparent and viscous polymer. The present invention does not specify the stirring speed, for example, it can be 100-800 r / min. In the present invention, the reducing agent can be prepared as an aqueous solution and then added to the mixture by injection using a micro-injection pump.

[0026] (3) The polymer is washed, dried and pulverized in sequence to obtain a branched polyacrylamide coating agent; the present invention does not specifically limit the conditions for washing, drying and pulverizing, and those skilled in the art can choose them conventionally.

[0027] This invention involves adding acrylamide, a branching agent, a molecular weight regulator, an anionic monomer, and a heat-resistant monomer to a reactor and obtaining a branched polyacrylamide coating agent through free radical polymerization. The branched polyacrylamide coating agent of this invention has a non-linear molecular chain structure, but rather a branched network structure. The branched polymer molecules are more extended than linear polymer molecules, resulting in more adsorption sites and a stronger adsorption capacity for drill cuttings particles. Furthermore, the branched polyacrylamide coating agent prepared by this invention is more effective at coating drill cuttings than other branched polyacrylamides, exhibiting strong and long-lasting coating capabilities. The branching agent used contains a rigid benzene ring structure, which makes intramolecular rotation difficult and reduces the possibility of macromolecular coiling, effectively improving the rigidity of the molecular chain and its shear resistance. The steric hindrance effect generated by the benzene ring makes the polymer backbone more extended, effectively weakening the influence of salt on the polymer chain, thereby improving the polymer's salt resistance. In addition, the benzene ring, as a large rigid spacer group, inhibits intramolecular association and branching, further improving its structural stability, shear resistance, and mechanical strength. This allows it to be unaffected by formation shear and damage in deep wells, better adapting to high-shear environments and improving field application results. The branched polyacrylamide coating agent prepared in this invention introduces a temperature-resistant monomer with temperature-insensitive sulfonic acid groups and rigid groups, enabling the resulting polymer to maintain good viscosity even under high-temperature conditions. The branched polyacrylamide coating agent prepared in this invention has the characteristics of low shear resistance and high-temperature aging resistance, with a cuttings recovery rate exceeding 85%.

[0028] According to some preferred embodiments, in step (1): the esterification reaction is carried out in the presence of dimethylformamide (also known as N,N-dimethylformamide), a dehydrating agent, a catalyst, and a polymerization inhibitor; preferably, the molar ratio of 1,1,1-tris(4-hydroxyphenyl)ethane, 2-acetaminopropyl acetate, and dimethylformamide is 1:(1.5-2):(18-22) (e.g., 1:1.5:18, 1:1.6:19, 1:1.7:20, 1:1.8:21, 1:1.9:22, or 1:2.0:22); in the esterification reaction of the present invention, it is preferable that one of the raw materials, 1,1,1-tris(4-hydroxyphenyl)ethane and 2-acetaminopropyl acetate, is used in excess, which is beneficial to promoting the forward reaction; preferably, the dehydrating agent is 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide (

[0029] CAS No.: 1892-57-5), the catalyst is 4-dimethylaminopyridine, and the polymerization inhibitor is phenothiazine; in this invention, preferably, the molar ratio of the dehydrating agent to the 1,1,1-tris(4-hydroxyphenyl)ethane is 1:(0.8-1.2), preferably 1:1; the molar ratio of the catalyst to the 1,1,1-tris(4-hydroxyphenyl)ethane is (0.02-0.03):1 (e.g., 0.021:1, 0.022:1, 0.023:1, 0.024:1). 1. 0.025:1, 0.026:1, 0.027:1, 0.028:1, 0.029:1 or 0.03:1); the molar ratio of the polymerization inhibitor to the 1,1,1-tris(4-hydroxyphenyl)ethane is (0.01-0.02):1 (e.g. 0.011:1, 0.012:1, 0.013:1, 0.014:1, 0.015:1, 0.016:1, 0.017:1, 0.018:1, 0.019:1 or 0.020:1).

[0030] According to some preferred embodiments, in step (1): the temperature of the esterification reaction is 85°C to 95°C (e.g., 85°C, 86°C, 87°C, 88°C, 89°C, 90°C, 91°C, 92°C, 93°C, 94°C or 95°C), and the time of the esterification reaction is 4 to 5 hours (e.g., 4, 4.5 or 5 hours).

[0031] According to some specific embodiments, the branching agent is prepared by: esterifying 1,1,1-tris(4-hydroxyphenyl)ethane and 2-acetaminopropylacrylic acid in dimethylformamide solvent, adding a dehydrating agent (1-(3-dimethylaminopropyl)-3-ethylcarbodiimide), a catalyst (4-dimethylaminopyridine), and a polymerization inhibitor (phenothiazine) during the esterification reaction, and refluxing at 85℃~95℃ for 4~5h, followed by cooling, filtration, washing, and drying.

[0032] According to some preferred embodiments, the raw materials for preparing the branched polyacrylamide coating agent contain the following components in parts by weight: 200-250 parts of acrylamide, 8-12 parts of branching agent, 5-10 parts of anionic monomer, 4-8 parts of heat-resistant monomer, 752-806 parts of water, and 0.02-0.2 parts of initiator, wherein the initiator includes an azo initiator, an oxidant, and a reducing agent.

[0033] According to some preferred embodiments, the raw materials for preparing the branched polyacrylamide coating agent comprise the following components by weight: 200-250 parts of acrylamide (e.g., 200, 210, 220, 230, 240, or 250 parts), 8-12 parts of branching agent (e.g., 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, or 12 parts), 5-10 parts of anionic monomer (e.g., 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, or 10 parts), 4-8 parts of heat-resistant monomer (e.g., 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, or 8 parts), and 752-806 parts of water (e.g., ...). 752, 760, 765, 770, 775, 780, 785, 790, 795, 800 or 806 parts), azo initiator 0.02 to 0.04 parts (e.g., 0.02, 0.03 or 0.04 parts), complexing agent 0.005 to 0.015 parts (e.g., 0.005, 0.01 or 0.015 parts), molecular weight regulator 0.005 to 0.015 parts (e.g., 0.005, 0.01 or 0.015 parts), oxidant 0.01 to 0.02 parts (e.g., 0.01, 0.015 or 0.02 parts), reducing agent 0.005 to 0.015 parts (e.g., 0.005, 0.01 or 0.015 parts).

[0034] In this invention, it is preferred that the mass ratio of the acrylamide, the branching agent, the anionic monomer, and the heat-resistant monomer is (200-250):(8-12):(5-10):(4-8). This is more conducive to obtaining a branched polyacrylamide coating agent that is less affected by shear, has better resistance to high-temperature aging, and has a higher rock cuttings recovery rate. In this invention, "parts" refers to "parts by weight." In specific embodiments and comparative examples, the unit of parts by weight can be uniformly expressed as "g" or "kg," etc.

[0035] According to some preferred embodiments, the anionic monomer is one or more of acrylic acid, sodium acrylate, itaconic acid, and 2-acrylamide-2-methylpropanesulfonic acid. Preferably, the anionic monomer is a mixture of acrylic acid and itaconic acid in a mass ratio of 1:(0.5-0.7) (e.g., 1:0.5, 1:0.6, or 1:0.7), preferably 1:0.6; and / or the heat-resistant monomer is 2-acrylamide-2-methylpropanesulfonic acid, tert-butylacrylamide sulfonic acid, potassium propyl methacrylate 3-sulfonate, vinylbenzene sulfonic acid, or N-vinylpyrrolidine. The monomer is selected from one or more of ketones, sodium p-styrene sulfonate, and L-isoleucine allyl ester p-toluenesulfonate (CAS No. 88224-05-9, alias: L-isoleucine allyl ester p-toluenesulfonate). Preferably, the heat-resistant monomer is prepared by mixing 2-acrylamido-2-methylpropanesulfonic acid and L-isoleucine allyl ester p-toluenesulfonate in a mass ratio of 1:(0.2 to 0.8) (e.g., 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7 or 1:0.8), more preferably 1:0.5.

[0036] According to some preferred embodiments, the anionic monomer is a mixture of acrylic acid and itaconic acid in a mass ratio of 1:(0.5-0.7), and the heat-resistant monomer is a mixture of 2-acrylamido-2-methylpropanesulfonic acid and L-isoleucine allyl ester p-toluenesulfonate in a mass ratio of 1:(0.2-0.8). This is more conducive to obtaining a branched polyacrylamide coating agent with less shear stress, better high-temperature aging resistance, and higher cuttings recovery rate. The possible reason is that introducing an appropriate amount of itaconic acid into the acrylic acid anionic monomer can increase the number of adsorption sites, which is beneficial to improving the adsorption capacity for drill cuttings particles. Introducing an appropriate amount of L-isoleucine allyl ester p-toluenesulfonate into the 2-acrylamido-2-methylpropanesulfonic acid heat-resistant monomer can make the branched polyacrylamide coating agent more stable in terms of high shear temperature resistance and salt resistance.

[0037] According to some preferred embodiments, the azo initiator is one or more of azobisisobutyronitrile, azobisisobutyramidine hydrochloride, and azobisisobutyramidazolin hydrochloride; the complexing agent is one or more of disodium ethylenediaminetetraacetate, trisodium diethyltriaminepentaacetate, sodium ethylenediaminetetramethylenephosphonate, and sodium citrate; the molecular weight regulator is one or more of sodium formate, 2,4-diphenyl-4-methyl-1-pentene, and dodecyl mercaptan; the oxidizing agent is one or more of hydrogen peroxide, di-tert-butyl peroxide, tert-butyl hydroperoxide, potassium persulfate, and ammonium persulfate; and / or the reducing agent is one or more of sodium sulfite (anhydrous sodium sulfite), sodium bisulfite, and sodium thiosulfate.

[0038] According to some preferred embodiments, in step (2): the pH value of the mixture is first adjusted to 7.0 to 7.2 (e.g., 7.0, 7.1 or 7.2) using a pH adjuster, and then nitrogen is passed through to remove oxygen; the present invention does not have any particular limitation on the type, concentration and amount of pH adjuster, as long as the pH value of the mixture can be adjusted to the target range.

[0039] According to some preferred embodiments, the pH adjuster is an aqueous solution of acrylic acid and / or sodium hydroxide.

[0040] According to some preferred embodiments, in step (2): the nitrogen deoxygenation time is 30-50 min (e.g., 30, 40 or 50 min); the initiation temperature of the polymerization reaction is 14-16℃ (e.g., 14℃, 15℃ or 16℃); and / or after adding the initiator to initiate the polymerization reaction, the polymerization reaction is allowed to heat up naturally, and after the temperature of the polymerization reaction system no longer rises, it is then kept warm for 2-3 h (e.g., 2, 2.5 or 3 h), the peak temperature of the natural heating is 60-75℃ (e.g., 60℃, 61℃, 62℃, 63℃, 64℃, 65℃, 66℃, 67℃, 68℃, 69℃, 70℃, 71℃, 72℃, 73℃, 74℃ or 75℃), and the holding temperature is the peak temperature of the natural heating.

[0041] Unless otherwise specified, the raw materials used in this invention are commercially available products or synthesized using existing methods. In this invention, the use of "and / or" between multiple technical features indicates that these technical features are connected by an "and / or" relationship, meaning that it can be any one of these technical features, or any combination of two or more of these technical features.

[0042] In a second aspect, the present invention provides a branched polyacrylamide coating agent prepared by the preparation method described in the first aspect of the present invention.

[0043] The present invention will be further described below by way of examples, but the scope of protection of the present invention is not limited to these embodiments.

[0044] Example 1

[0045] ① Preparation of branching agent: 30.6 g of 1,1,1-tris(4-hydroxyphenyl)ethane (molecular weight 306.36), 25.8 g of 2-acetamidoacrylic acid (molecular weight 129.11), and 146 g of dimethylformamide (molecular weight 73.09) were added to a three-necked flask equipped with an electric stirrer, a reflux condenser, and a thermometer and mixed thoroughly. Then, 15.5 g of dehydrating agent 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide (molecular weight 155.24), 0.3 g of catalyst (4-dimethylaminopyridine), and 0.3 g of polymerization inhibitor (phenothiazine) were added and refluxed at 90 °C for 4.5 h for esterification. After cooling, filtration, washing, and drying, the branching agent was obtained.

[0046] ② Preparation of branched polyacrylamide coating agent: The raw materials are: 220g acrylamide, 10g branching agent obtained in step ①, 7g anionic monomer, 6g heat-resistant monomer, 757g water, 0.03g azobisisobutyronitrile, 0.01g disodium ethylenediaminetetraacetate as a complexing agent, 0.01g sodium formate as a molecular weight regulator, 0.015g potassium persulfate (oxidizing agent), and 0.01g sodium bisulfite (reducing agent); the anionic monomer is composed of acrylic acid and itaconic acid mixed in a mass ratio of 1:0.6; the heat-resistant monomer is composed of 2-acrylamido-2-methylpropanesulfonic acid and L-isoleucine allyl ester p-methylbenzenesulfonate mixed in a mass ratio of 1:0.5; the preparation method is: in a reaction vessel, acrylamide, ... A branching agent, anionic monomer, and heat-resistant monomer were dissolved in deionized water to obtain a mixture. After adjusting the pH to 7.0, the mixture was purged with nitrogen for 30 minutes to remove oxygen. Then, an azo initiator, complexing agent, molecular weight regulator, and oxidant were added sequentially. Under anaerobic, nitrogen-protected, and stirring conditions, a reducing agent aqueous solution (sodium bisulfite was prepared into a 1% (w / w) reducing agent aqueous solution with water) was added dropwise using a micro-injection pump to initiate the polymerization reaction at 15°C. After initiation, the polymerization system was allowed to heat up naturally until the temperature reached a peak of 70°C. The system was then kept at 70°C for 2 hours to obtain a transparent, viscous polymer. After washing, drying, and pulverizing, a branched polyacrylamide coating agent was obtained.

[0047] Example 2

[0048] ① The preparation of the branching agent is the same as in Example 1.

[0049] ② Preparation of branched polyacrylamide coating agent: The raw materials are: 230g acrylamide, 8g branching agent, 5g anionic monomer, 5g heat-resistant monomer, 752g water, 0.03g azobisisobutyronitrile, 0.01g disodium ethylenediaminetetraacetate as a complexing agent, 0.01g sodium formate as a molecular weight regulator, 0.015g potassium persulfate (oxidizing agent), and 0.01g sodium bisulfite (reducing agent); the anionic monomer is composed of acrylic acid and itaconic acid mixed in a mass ratio of 1:0.6; the heat-resistant monomer is composed of 2-acrylamido-2-methylpropanesulfonic acid and L-isoleucine allyl ester p-methylbenzenesulfonate mixed in a mass ratio of 1:0.5; the preparation method is: acrylamide, branching agent... Anionic monomers and heat-resistant monomers were dissolved in deionized water to obtain a mixture. After adjusting the pH to 7.1, the mixture was purged with nitrogen for 30 minutes to remove oxygen. Then, an azo initiator, complexing agent, molecular weight regulator, and oxidant were added sequentially. Under anaerobic, nitrogen-protected, and stirring conditions, a reducing agent aqueous solution (sodium bisulfite was prepared into a 1% (w / w) reducing agent aqueous solution with water) was added dropwise using a micro-injection pump to initiate the polymerization reaction at 14°C. After initiation, the polymerization system was allowed to heat up naturally until the temperature reached a peak of 70°C. The system was then kept at 70°C for 2 hours to obtain a transparent, viscous polymer. After washing, drying, and pulverizing, a branched polyacrylamide coating agent was obtained.

[0050] Example 3

[0051] ① The preparation of the branching agent is the same as in Example 1.

[0052] ② Preparation of branched polyacrylamide coating agent: The raw materials are: 210g acrylamide, 9g branching agent obtained in step ①, 8g anionic monomer, 7g heat-resistant monomer, 766g water, 0.03g azobisisobutyronitrile, 0.01g disodium ethylenediaminetetraacetate as a complexing agent, 0.01g sodium formate as a molecular weight regulator, 0.015g potassium persulfate (oxidizing agent), and 0.01g sodium bisulfite (reducing agent); the anionic monomer is composed of acrylic acid and itaconic acid mixed in a mass ratio of 1:0.6; the heat-resistant monomer is composed of 2-acrylamido-2-methylpropanesulfonic acid and L-isoleucine allyl ester p-methylbenzenesulfonate mixed in a mass ratio of 1:0.5; the preparation method is: in a reaction vessel, acrylamide, ... A branching agent, anionic monomer, and heat-resistant monomer were dissolved in deionized water to obtain a mixture. After adjusting the pH to 7.2, the mixture was purged with nitrogen for 30 minutes to remove oxygen. Then, an azo initiator, complexing agent, molecular weight regulator, and oxidant were added sequentially. Under anaerobic, nitrogen-protected, and stirring conditions, a reducing agent aqueous solution (sodium bisulfite was prepared into a 1% (w / w) reducing agent aqueous solution with water) was added dropwise using a micro-injection pump to initiate the polymerization reaction at 16°C. After initiation, the polymerization system naturally heated up until the temperature reached a peak of 70°C. The system was then kept at 70°C for 2 hours to obtain a transparent, viscous polymer. After washing, drying, and pulverizing, a branched polyacrylamide coating agent was obtained.

[0053] Example 4

[0054] ① The preparation of the branching agent is the same as in Example 1.

[0055] ② Preparation of branched polyacrylamide coating agent: The raw materials are: 215g acrylamide, 11g branching agent obtained in step ①, 6g anionic monomer, 4g heat-resistant monomer, 754g water, 0.03g azobisisobutyronitrile, 0.01g disodium ethylenediaminetetraacetate as a complexing agent, 0.01g sodium formate as a molecular weight regulator, 0.015g potassium persulfate (oxidizing agent), and 0.01g sodium bisulfite (reducing agent); the anionic monomer is composed of acrylic acid and itaconic acid mixed in a mass ratio of 1:0.6; the heat-resistant monomer is composed of 2-acrylamido-2-methylpropanesulfonic acid and L-isoleucine allyl ester p-methylbenzenesulfonate mixed in a mass ratio of 1:0.5; the preparation method is: in a reaction vessel, acrylamide, ... A branching agent, anionic monomer, and heat-resistant monomer were dissolved in deionized water to obtain a mixture. After adjusting the pH to 7.1, the mixture was purged with nitrogen for 30 minutes to remove oxygen. Then, an azo initiator, complexing agent, molecular weight regulator, and oxidant were added sequentially. Under oxygen-free, nitrogen-protected, and stirring conditions, a reducing agent aqueous solution (sodium bisulfite was prepared into a 1% (w / w) reducing agent aqueous solution with water) was added dropwise using a micro-injection pump to initiate the polymerization reaction at 15°C. After initiation, the polymerization system was allowed to heat up naturally until the temperature reached a peak of 70°C. The system was then kept at 70°C for 2 hours to obtain a transparent, viscous polymer. After washing, drying, and pulverizing, a branched polyacrylamide coating agent was obtained.

[0056] Example 5

[0057] ① The preparation of the branching agent is the same as in Example 1.

[0058] ② Preparation of branched polyacrylamide coating agent: The raw materials are: 220g acrylamide, 10g branching agent obtained in step ①, 7g anionic monomer, 6g heat-resistant monomer, 757g water, 0.03g azobisisobutyronitrile, 0.01g disodium ethylenediaminetetraacetate as a complexing agent, 0.01g sodium formate as a molecular weight regulator, 0.015g potassium persulfate (oxidizing agent), and 0.01g sodium bisulfite (reducing agent); the anionic monomer is acrylic acid; the heat-resistant monomer is 2-acrylamido-2-methylpropanesulfonic acid; the preparation method is: dissolving acrylamide, branching agent, anionic monomer, and heat-resistant monomer in deionized water in a reaction vessel. The mixture was adjusted to pH 7.0 and then purged with nitrogen for 30 minutes to remove oxygen. Then, an azo initiator, complexing agent, molecular weight regulator, and oxidant were added sequentially. Under anaerobic, nitrogen-protected, and stirring conditions, a reducing agent aqueous solution (sodium bisulfite was prepared as a 1% (w / w) reducing agent aqueous solution with water) was added dropwise using a micro-injection pump to initiate the polymerization reaction at 15°C. After initiation, the polymerization system was allowed to heat up naturally until the temperature reached its peak. The system was then held at the peak temperature for 2 hours to obtain the polymer. After washing, drying, and pulverizing, a branched polyacrylamide coating agent was obtained.

[0059] Example 6

[0060] ① The preparation of the branching agent is the same as in Example 1.

[0061] ② Preparation of branched polyacrylamide coating agent: The raw materials are: 220g acrylamide, 10g branching agent obtained in step ①, 7g anionic monomer, 6g heat-resistant monomer, 757g water, 0.03g azobisisobutyronitrile, 0.01g disodium ethylenediaminetetraacetate as a complexing agent, 0.01g sodium formate as a molecular weight regulator, 0.015g potassium persulfate (oxidizing agent), and 0.01g sodium bisulfite (reducing agent); the anionic monomer is itaconic acid; the heat-resistant monomer is L-isoleucine allyl ester p-methylbenzenesulfonate; the preparation method is: dissolving acrylamide, branching agent, anionic monomer, and heat-resistant monomer in deionized water in a reaction vessel. In the process, a mixture was obtained, and after adjusting the pH to 7.0, the mixture was purged with nitrogen for 30 minutes to remove oxygen. Then, an azo initiator, a complexing agent, a molecular weight regulator, and an oxidant were added sequentially. Under oxygen-free, nitrogen-protected, and stirring conditions, a reducing agent aqueous solution (sodium bisulfite was prepared into a 1% (w / w) reducing agent aqueous solution with water) was added dropwise using a micro-injection pump to initiate the polymerization reaction at 15°C. After initiation, the polymerization system was allowed to heat up naturally until the temperature reached its peak temperature. The system was then kept at the peak temperature for 2 hours to obtain the polymer. After washing, drying, and pulverizing, a branched polyacrylamide coating agent was obtained.

[0062] Example 7

[0063] Example 7 is basically the same as Example 3, except that:

[0064] The preparation of branched polyacrylamide coating agent involves the following raw materials: 224g acrylamide, 5g branching agent obtained in step ①, 3g anionic monomer, 2g heat-resistant monomer, 766g water, 0.03g azobisisobutyronitrile, 0.01g disodium ethylenediaminetetraacetate as a complexing agent, 0.01g sodium formate as a molecular weight regulator, 0.015g potassium persulfate (oxidizing agent), and 0.01g sodium bisulfite (reducing agent). The anionic monomer is composed of acrylic acid and itaconic acid in a mass ratio of 1:0.6. The heat-resistant monomer is composed of 2-acrylamido-2-methylpropanesulfonic acid and L-isoleucine allyl ester p-methylbenzenesulfonate in a mass ratio of 1:0.5. The preparation method involves: in a reaction vessel, propylene... Amide, branching agent, anionic monomer, and heat-resistant monomer were dissolved in deionized water to obtain a mixture. After adjusting the pH to 7.2, the mixture was purged with nitrogen for 30 minutes to remove oxygen. Then, an azo initiator, complexing agent, molecular weight regulator, and oxidant were added sequentially. Under anaerobic, nitrogen-protected, and stirring conditions, a reducing agent aqueous solution (sodium bisulfite was prepared into a 1% (w / w) reducing agent aqueous solution with water) was added dropwise using a micro-injection pump to initiate the polymerization reaction at 16°C. After initiation, the polymerization system was allowed to heat up naturally until the temperature reached its peak temperature. The system was then kept at the peak temperature for 2 hours to obtain the polymer. After washing, drying, and pulverizing, a branched polyacrylamide coating agent was obtained.

[0065] Example 8

[0066] Example 8 is basically the same as Example 1, except that:

[0067] The preparation of a branched polyacrylamide coating agent involves the following raw materials: 197g acrylamide, 15g branching agent obtained in step ①, 12g anionic monomer, 10g heat-resistant monomer, 766g water, 0.03g azobisisobutyronitrile, 0.01g disodium ethylenediaminetetraacetate as a complexing agent, 0.01g sodium formate as a molecular weight regulator, 0.015g potassium persulfate (oxidizing agent), and 0.01g sodium bisulfite (reducing agent). The anionic monomer is composed of acrylic acid and itaconic acid in a mass ratio of 1:0.6. The heat-resistant monomer is composed of 2-acrylamido-2-methylpropanesulfonic acid and L-isoleucine allyl ester p-methylbenzenesulfonate in a mass ratio of 1:0.5. The preparation method involves: in a reaction vessel... Acrylamide, a branching agent, anionic monomer, and heat-resistant monomer were dissolved in deionized water to obtain a mixture. After adjusting the pH to 7.2, the mixture was purged with nitrogen for 30 minutes to remove oxygen. Then, an azo initiator, complexing agent, molecular weight regulator, and oxidant were added sequentially. Under anaerobic, nitrogen-protected, and stirring conditions, a reducing agent aqueous solution (sodium bisulfite was prepared into a 1% (w / w) reducing agent aqueous solution with water) was added dropwise using a micro-injection pump to initiate the polymerization reaction at 16°C. After initiation, the polymerization system was allowed to heat up naturally until the temperature reached its peak temperature. The system was then kept at the peak temperature for 2 hours to obtain the polymer. After washing, drying, and pulverizing, a branched polyacrylamide coating agent was obtained.

[0068] Comparative Example 1

[0069] Comparative Example 1 is basically the same as Example 1, except that:

[0070] ② Preparation of polyacrylamide coating agent: The raw materials are: 220g acrylamide, 7g anionic monomer, 6g heat-resistant monomer, 767g water, 0.03g azobisisobutyronitrile, 0.01g disodium ethylenediaminetetraacetate as a complexing agent, 0.01g sodium formate as a molecular weight regulator, 0.015g potassium persulfate (oxidizing agent), and 0.01g sodium bisulfite (reducing agent); the anionic monomer is composed of acrylic acid and itaconic acid mixed in a mass ratio of 1:0.6; the heat-resistant monomer is composed of 2-acrylamido-2-methylpropanesulfonic acid and L-isoleucine allyl ester p-methylbenzenesulfonate mixed in a mass ratio of 1:0.5; the preparation method is: in a reaction vessel, acrylamide, ... Anionic monomers and heat-resistant monomers were dissolved in deionized water to obtain a mixture. After adjusting the pH to 7.0, the mixture was purged with nitrogen for 30 minutes to remove oxygen. Then, an azo initiator, complexing agent, molecular weight regulator, and oxidant were added sequentially. Under anaerobic, nitrogen-protected, and stirring conditions, a reducing agent aqueous solution (a 1% (w / w) reducing agent aqueous solution prepared with water from sodium bisulfite) was added dropwise using a micro-injection pump to initiate the polymerization reaction at 15°C. After initiation, the polymerization system was allowed to heat up naturally until the temperature reached its peak temperature. The system was then kept at the peak temperature for 2 hours to obtain the polymer. After washing, drying, and pulverizing, the polyacrylamide coating agent was obtained.

[0071] Comparative Example 2

[0072] Comparative Example 2 is basically the same as Example 1, except that:

[0073] ② Preparation of polyacrylamide coating agent: The raw materials are: 220g acrylamide, 10g branching agent obtained in step ①, 7g anionic monomer, 763g water, 0.03g azobisisobutyronitrile, 0.01g disodium ethylenediaminetetraacetate as a complexing agent, 0.01g sodium formate as a molecular weight regulator, 0.015g potassium persulfate (oxidizing agent), and 0.01g sodium bisulfite (reducing agent); the anionic monomer is composed of acrylic acid and itaconic acid mixed in a mass ratio of 1:0.6; the preparation method is as follows: acrylamide, branching agent, and anionic monomer are dissolved in deionized water in a reaction vessel to obtain a mixed solution, and then adjusted... After adjusting the pH to 7.0, the mixture was purged with nitrogen for 30 minutes to remove oxygen. Then, an azo initiator, complexing agent, molecular weight regulator, and oxidant were added sequentially. Under anaerobic, nitrogen-protected, and stirring conditions, a reducing agent aqueous solution (sodium bisulfite was prepared into a 1% (w / w) reducing agent aqueous solution with water) was added dropwise using a micro-injection pump to initiate the polymerization reaction at 15°C. After initiation, the polymerization system was allowed to heat up naturally until the temperature reached its peak temperature. The system was then kept at the peak temperature for 2 hours to obtain the polymer. After washing, drying, and pulverizing, the polyacrylamide coating agent was obtained.

[0074] Comparative Example 3

[0075] ① Preparation of branched functional monomers: A single-necked round-bottom flask was placed in an oil bath, and diethylenetriamine and methyl acrylate were added, along with dimethyl sulfoxide as a solvent. The mixture was stirred uniformly in an ice bath for 6 hours. Then, ethylenediamine was added and transesterification was carried out at 80°C. After 6 hours, the mixture was distilled under reduced pressure for 4 hours using a diaphragm vacuum pump to remove all dimethyl sulfoxide and excess unreacted ethylenediamine. The molar ratio of diethylenetriamine, methyl acrylate, and ethylenediamine was 1:5:10. Then, a dimethyl sulfoxide solution of maleic anhydride was added to the flask, and the mixture was heated to 80°C and reacted for 6 hours. The dimethyl sulfoxide was then removed by reduced pressure distillation to obtain the branched functional monomers. The molar ratio of maleic anhydride to methyl acrylate in the dimethyl sulfoxide solution of maleic anhydride was 1:1.

[0076] ② Preparation of polyacrylamide coating agent: The raw materials are: 220g acrylamide, 10g branched functional monomer obtained in step ①, 7g anionic monomer, 6g heat-resistant monomer, 757g water, 0.03g azobisisobutyronitrile, 0.01g disodium ethylenediaminetetraacetate as a complexing agent, 0.01g sodium formate as a molecular weight regulator, 0.015g potassium persulfate (oxidizing agent), and 0.01g sodium bisulfite (reducing agent); the anionic monomer is composed of acrylic acid and itaconic acid mixed in a mass ratio of 1:0.6; the heat-resistant monomer is composed of 2-acrylamido-2-methylpropanesulfonic acid and L-isoleucine allyl ester p-methylbenzenesulfonate mixed in a mass ratio of 1:0.5; the preparation method is: in a reaction vessel, acrylamide is added to the reaction vessel... Enamide, branched functional monomers, anionic monomers, and heat-resistant monomers were dissolved in deionized water to obtain a mixture. After adjusting the pH to 7.0, the mixture was purged with nitrogen for 30 minutes to remove oxygen. Then, an azo initiator, complexing agent, molecular weight regulator, and oxidant were added sequentially. Under anaerobic, nitrogen-protected, and stirring conditions, a reducing agent aqueous solution (sodium bisulfite was prepared into a 1% (w / w) reducing agent aqueous solution with water) was added dropwise using a micro-injection pump to initiate the polymerization reaction at 15°C. After initiation, the polymerization system was allowed to heat up naturally until the temperature reached its peak temperature. The system was then kept at the peak temperature for 2 hours to obtain the polymer. After washing, drying, and pulverizing, the polyacrylamide coating agent was obtained.

[0077] Comparative Example 4

[0078] A polymerization reactor equipped with a stirrer, thermometer, constant pressure funnel, and vent pipe was placed in a constant temperature water bath. 82g of acrylamide, 18g of methacryloyloxyethyltrimethylammonium chloride, and 290g of deionized water were added and stirred until completely dissolved. Nitrogen gas was purged for 30 min to lower the solution temperature to below 5℃. Then, 10g of an aqueous solution containing 0.05g of ammonium persulfate and sodium bisulfite (mass ratio of ammonium persulfate to sodium bisulfite 1:1) was slowly added dropwise. After the addition was complete, the temperature was slowly raised to 45℃ and reacted for 3 h. Then, 50g of an aqueous solution containing 12g of sodium hydroxide was added, and the reaction was carried out at 90℃ for 2.5 h. The degree of hydrolysis of the cationic polyacrylamide was 25%. The product was discharged, dried, and pulverized. 300g of triethanolamine and 0.2g of phosphoric acid were added to the pulverized solid powder, and the reaction was carried out at 150℃ for 4 h. Filtration yielded a dendritic cationic polyacrylamide coating agent.

[0079] The coating agents finally prepared in Examples 1-8 and Comparative Examples 1-4 were subjected to performance tests. The test methods and results are as follows:

[0080] 1. The prepared coating agents were compared and evaluated according to the method in SY / T 5696-95 "Amphoteric Polymer Strong Coating Agents for Drilling Fluids FA367".

[0081] Method for detecting cuttings recovery rate: A polymer solution with a concentration of 2 wt‰ was prepared using brine (containing 25% NaCl and 5% KCl). 20g of shale cuttings (6-10 mesh) was placed in an aging tank, and 350mL of the polymer solution was added. The aging tank was then placed in a roller furnace at 200℃ for 16 hours. After cooling, the solution and cuttings (i.e., shale cuttings) were poured out and passed through a 40-mesh sieve. The cuttings remaining on the sieve were placed in an oven at 105℃ and dried to constant weight. The rolling recovery rate (recovery rate) was calculated by the ratio of the obtained cuttings mass to the initial cuttings mass. The test results are shown in Table 1.

[0082] Table 1

[0083] Example 1 90 Example 2 87 Example 3 88 Example 4 86 Example 5 69 Example 6 75 Example 7 65 Example 8 70 Comparative Example 1 45 Comparative Example 2 42 Comparative Example 3 78 Comparative Example 4 82

[0084] As shown in Table 1, the rolling recovery rate of the branched polyacrylamide coating agent prepared by this invention can be maintained above 85% at a high temperature of 200℃. A comparison between Example 1 and Comparative Example 1 shows that without the addition of a branching agent, a branched polyacrylamide coating agent cannot be formed, and the rolling recovery rate is significantly reduced at 200℃. A comparison between Example 1 and Comparative Example 2 shows that without the addition of a heat-resistant monomer, the recovery rate is significantly reduced at 200℃. A comparison between Example 1 and Comparative Examples 3-4 shows that the branched polyacrylamide coating agent prepared by this invention has a significantly higher rock cuttings recovery rate.

[0085] 2. Temperature resistance and shear strength test

[0086] Prepare a 1 wt% polymer solution using tap water for the coating agent products in each example and comparative example, and then... (The sentence is incomplete and requires more context to translate accurately.) -1 The prepared sample was continuously sheared at a certain shear rate, and the temperature was increased. After the temperature reached 150℃, the apparent viscosity was tested at 150℃ for 5 minutes. The effect of continuous temperature increase of 10℃ every 5 minutes on the temperature resistance and shear resistance in the range of 150℃ to 200℃ was investigated. The results are shown in Table 2.

[0087] Table 2

[0088]

[0089] As can be seen from the data in Table 2, the branched polyacrylamide coating agent prepared by this invention exhibits excellent temperature and shear resistance. A comparison between Example 1 and Comparative Example 1 shows that without the addition of a branching agent, a branched polyacrylamide coating agent cannot be formed, and its temperature and shear viscosity retention rate is significantly reduced. A comparison between Example 1 and Comparative Example 2 shows that without the addition of a temperature-resistant monomer, its temperature and shear viscosity retention rate is significantly lower than that with the addition of a temperature-resistant monomer. A comparison between Example 1 and Comparative Examples 3-4 shows that the branched polyacrylamide coating agent prepared by this invention has significantly superior temperature and shear resistance properties.

[0090] The parts of this invention not described in detail are techniques known to those skilled in the art.

[0091] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a branched polyacrylamide coating agent, characterized in that, The preparation method includes the following steps: (1) An esterification reaction is carried out between 2-acetamidopropylene and 1,1,1-tris(4-hydroxyphenyl)ethane to obtain a branching agent; the esterification reaction is carried out in the presence of dimethylformamide, a dehydrating agent, a catalyst and a polymerization inhibitor; the dehydrating agent is 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide, the catalyst is 4-dimethylaminopyridine, and the polymerization inhibitor is phenothiazine; the 1,1,1-tris(4-hydroxyphenyl)ethane and the 2-acetamidopropylene The molar ratio of acid to dimethylformamide is 1:(1.5~2):(18~22); the molar ratio of dehydrating agent to 1,1,1-tris(4-hydroxyphenyl)ethane is 1:(0.8~1.2); the molar ratio of catalyst to 1,1,1-tris(4-hydroxyphenyl)ethane is (0.02~0.03):1; and the molar ratio of polymerization inhibitor to 1,1,1-tris(4-hydroxyphenyl)ethane is (0.01~0.02):

1. (2) Acrylamide, branching agent, anionic monomer, and heat-resistant monomer are mixed evenly with water to obtain a mixture. Then, nitrogen is passed through the mixture to remove oxygen. Then, an azo initiator, complexing agent, molecular weight regulator, oxidant, and reducing agent are added to initiate the polymerization reaction to obtain a polymer. The anionic monomer is composed of acrylic acid and itaconic acid in a mass ratio of 1:(0.5~0.7). The heat-resistant monomer is composed of 2-acrylamido-2-methylpropanesulfonic acid and L-isoleucine allyl ester p-methylbenzenesulfonate in a mass ratio of 1:(0.2~0.8). (3) The polymer is washed, dried and pulverized in sequence to obtain a branched polyacrylamide coating agent; The raw materials for preparing the branched polyacrylamide coating agent comprise the following components in parts by weight: Acrylamide 200-250 parts, branching agent 8-12 parts, anionic monomer 5-10 parts, heat-resistant monomer 4-8 parts, water 752-806 parts, azo initiator 0.02-0.04 parts, complexing agent 0.005-0.015 parts, molecular weight regulator 0.005-0.015 parts, oxidant 0.01-0.02 parts, reducing agent 0.005-0.015 parts.

2. The preparation method according to claim 1, characterized in that, In step (1): The esterification reaction is carried out at a temperature of 85℃~95℃ for 4~5 hours.

3. The preparation method according to claim 1, characterized in that: The anionic monomer is composed of acrylic acid and itaconic acid mixed in a mass ratio of 1:0.6; and / or The heat-resistant monomer is composed of 2-acrylamide-2-methylpropanesulfonic acid and L-isoleucine allyl ester p-methylbenzenesulfonate in a mass ratio of 1:0.

5.

4. The preparation method according to claim 1, characterized in that: The azo initiator is one or more of azobisisobutyronitrile, azobisisobutyramidine hydrochloride, and azobisisobutyramidazolin hydrochloride; The complexing agent is one or more of the following: disodium ethylenediaminetetraacetate, trisodium diethyltriaminepentaacetate, sodium ethylenediaminetetramethylene phosphate, and sodium citrate. The molecular weight regulator is one or more of sodium formate, 2,4-diphenyl-4-methyl-1-pentene, and dodecyl mercaptan. The oxidant is one or more selected from hydrogen peroxide, di-tert-butyl peroxide, tert-butyl hydroperoxide, potassium persulfate, and ammonium persulfate; and / or The reducing agent is one or more of sodium sulfite, sodium bisulfite, and sodium thiosulfate.

5. The preparation method according to claim 1, characterized in that, In step (2): First, the pH of the mixture is adjusted to 7.0~7.2 using a pH adjuster, and then nitrogen is introduced for deoxygenation.

6. The preparation method according to claim 5, characterized in that: The pH adjuster is an aqueous solution of acrylic acid and / or sodium hydroxide.

7. The preparation method according to claim 1, characterized in that, In step (2): The nitrogen deoxygenation time is 30-50 minutes. The polymerization reaction is initiated at a temperature of 14-16°C; and / or After the polymerization reaction is initiated by adding an initiator, the polymerization reaction system is naturally heated. After the temperature of the polymerization reaction system stops rising, it is then kept at a certain temperature for 2 to 3 hours. The peak temperature of the natural heating is 60 to 75°C, and the temperature of the heat preservation is the peak temperature of the natural heating.

8. A branched polyacrylamide coating agent prepared by any one of claims 1 to 7.

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