Viscosity reducer for carbon dioxide pollution-resistant water-based drilling fluid as well as preparation method and application of viscosity reducer

Abstract

The invention provides a viscosity reducer for a water-based drilling fluid capable of resisting carbon dioxide pollution as well as a preparation method and application of the viscosity reducer, and belongs to the technical field of drilling fluid treating agents. The viscosity reducer for the water-based drilling fluid capable of resisting carbon dioxide pollution is prepared from the following raw materials in parts by mass: 0.5 to 1 part of acrylic acid, 7 to 10 parts of 2-acrylamido-2-methylpropanesulfonic acid, 5 to 8 parts of acryloyloxyethyl trimethyl ammonium chloride, 50 to 80 parts of ethylene glycol monovinyl polyethylene glycol ether, 0.04 to 0.08 part of an oxidizing agent, 0.05 to 0.07 part of a reducing agent, 0.03 to 0.06 part of a chain transfer agent and 130 to 180 parts of water. The prepared viscosity reducer shows excellent viscosity reduction performance in drilling fluid, especially has remarkable resistance to CO2 pollution, effectively reduces the apparent viscosity, plastic viscosity and dynamic shearing force of a drilling fluid system, remarkably improves the drilling efficiency and is suitable for a high-temperature and high-pressure complex stratum environment.

Description

Technical Field

[0001] The invention relates to a viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution and a preparation method and application thereof, belonging to the technical field of drilling fluid treatment agents. Background Art

[0002] With the continuous growth of global energy demand and the gradual depletion of oil resources, exploration and mining activities are gradually moving towards deeper and more complex formations. In these complex formations, drilling operations face many challenges, especially the harmful gases in the formation (such as H 2 S, CO 2 These pollutants not only destroy the rheology and filtration properties of the drilling fluid, but also accelerate the corrosion and wear of the drilling tools, seriously affecting the drilling efficiency and safety.

[0003] As a key component in drilling engineering, drilling fluid has multiple functions such as stabilizing the well wall, carrying cuttings, cooling the drill tool and lubricating the drill bit. 2 When invading the drilling fluid, it will ionize to produce carbonate ions and bicarbonate ions, which will reduce the pH value of the drilling fluid, increase the viscosity and shear force of the drilling fluid, and thus affect its fluidity. 2 There are limited means of treating contaminated drilling fluid, and the method of replacing the contaminated slurry is usually adopted, which not only increases operating costs, but also brings serious environmental problems because the discarded contaminated drilling fluid is difficult to treat and harmful to the environment.

[0004] In the field of drilling fluid treatment, a variety of viscosity reducers have been developed and applied. For example, Chinese patent document CN118530704A introduces a viscosity reducer for drilling fluid suitable for deep wells, which has a certain salt resistance. Chinese patent document CN118620111A discloses a viscosity reducer with a polyhydroxy monomer as the main component, which can withstand a high temperature of 220°C. However, most of these viscosity reducers are designed for conventional geological conditions and are specifically used for CO 2 Research on viscosity reducers that pollute the environment is still relatively scarce.

[0005] Therefore, we focus on the design and synthesis of new viscosity reducers to develop a new type of viscosity reducer that can effectively deal with CO 2 Contaminated drilling fluid viscosity reducers are of great significance for improving the rheological properties of drilling fluid under contaminated conditions, improving drilling efficiency and reducing environmental pollution. Summary of the invention

[0006] In view of the shortcomings of the prior art, the present invention provides a viscosity reducer for water-based drilling fluids resistant to carbon dioxide pollution, and a preparation method and application thereof. The viscosity reducer of the present invention can effectively solve the problem of carbon dioxide pollution. 2The problem of increased viscosity and increased filtration caused by the invasion of drilling fluid.

[0007] To achieve the above object, the technical solution of the present invention is as follows: A viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution is prepared from the following raw materials in parts by weight: 0.5-1 part of acrylic acid (AA), 7-10 parts of 2-acrylamido-2-methylpropanesulfonic acid (AMPS), 5-8 parts of acryloyloxyethyl trimethylammonium chloride (DAC), 50-80 parts of ethylene glycol monovinyl polyethylene glycol ether (EPEG), 0.04-0.08 parts of oxidant, 0.05-0.07 parts of reducing agent, 0.03-0.06 parts of chain transfer agent and 130-180 parts of water.

[0008] Preferably, the viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution is prepared by including the following raw materials in parts by weight: 0.72 parts of acrylic acid (AA), 8.28 parts of 2-acrylamido-2-methylpropanesulfonic acid (AMPS), 7.75 parts of acryloyloxyethyltrimethylammonium chloride (DAC), 60 parts of ethylene glycol monovinyl polyethylene glycol ether (EPEG), 0.06 parts of oxidant, 0.06 parts of reducing agent, 0.05 parts of chain transfer agent, and 150 parts of water.

[0009] Preferably according to the present invention, the number average molecular weight of the ethylene glycol monovinyl polyglycol ether is 2000-4000 g / mol.

[0010] Preferably according to the present invention, the oxidant is a hydrogen peroxide solution with a mass concentration of 5%.

[0011] According to the preferred embodiment of the present invention, the reducing agent is ascorbic acid (V C ).

[0012] Preferably according to the present invention, the chain transfer agent is thioglycolic acid (TGA) and / or n-dodecyl mercaptan (DDT).

[0013] According to the present invention, the method for preparing the above-mentioned viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution comprises the following steps: Ethylene glycol monovinyl polyethylene glycol ether (EPEG) and an oxidant are added to a portion of water A and stirred evenly to obtain a mixed solution I; acrylic acid (AA), 2-acrylamido-2-methylpropanesulfonic acid (AMPS), acryloyloxyethyl trimethylammonium chloride (DAC) and a portion of water B are mixed to obtain a mixed solution II; a reducing agent, a chain transfer agent and a portion of water C are mixed to obtain a mixed solution III; the mixed solution II and the mixed solution III are added to the mixed solution I to react; after the reaction is completed, the pH of the system is adjusted to obtain a viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution.

[0014] Preferably according to the present invention, the mass ratio of the partial water A, the partial water B and the partial water C is 3-5:1:1; the total mass of the partial water A, the partial water B and the partial water C is the mass of water.

[0015] Preferably, according to the present invention, the mixed solution II and the mixed solution III are simultaneously added dropwise to the system, and the adding time is 15-25 min; the adding is carried out under the protection of protective gas and stirring conditions; preferably, the protective gas is nitrogen.

[0016] Preferably, according to the present invention, the reaction temperature is 55-65° C., and the reaction time is 3-5 h; the reaction is carried out under protective gas protection and stirring conditions; preferably, the protective gas is nitrogen.

[0017] Preferably according to the present invention, a sodium hydroxide aqueous solution with a mass fraction of 20-40% is used to adjust the pH of the system to 7.

[0018] According to the present invention, the viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution is used as a viscosity reducer in drilling fluid polluted by carbon dioxide to reduce the viscosity and filtration loss of the drilling fluid.

[0019] The technical features and beneficial effects of the present invention are as follows: 1. The monomers used in the present invention (acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, acryloyloxyethyl trimethylammonium chloride, ethylene glycol monovinyl polyethylene glycol ether) are all common industrial raw materials, the synthesis process is simple, the reaction conditions are mild and easy to control, the prepared viscosity reducer has low production cost, and is suitable for large-scale industrial application.

[0020] 2. The viscosity reducer prepared by the present invention exhibits excellent viscosity reducing performance in drilling fluid, especially for CO 2 It has remarkable resistance to pollution. The active groups (sulfonic acid group, ether bond, amide group) in its molecular structure can react with CO 2 Competitive adsorption effectively reduces the apparent viscosity, plastic viscosity and dynamic shear force of the drilling fluid system, significantly improves drilling efficiency, and is suitable for high temperature, high pressure and complex formation environments.

[0021] 3. The 2-acrylamide-2-methylpropanesulfonic acid (AMPS) monomer introduced in the present invention contains a strongly adsorbable sulfonic acid group (-SO 3 H), which can dissociate into -SO in water 3 - , has a high charge density and strong hydration ability, and can react with CO 2 Competitive adsorption on the surface of clay particles effectively prevents CO 2It reacts with alkaline substances in the drilling fluid to form carbonates, thereby maintaining the stability of the drilling fluid system. In addition, the sulfonic acid group can also form a diffuse double layer on the surface of clay particles through electrostatic action, increase the repulsive force between particles, and significantly reduce the viscosity and shear force of the drilling fluid.

[0022] 4. The acrylic acid (AA) introduced in the present invention provides a carboxyl group (-COOH), which not only has a strong adsorption capacity and can be firmly adsorbed on the surface of clay particles through electrostatic action, but also has good thermal stability. Under high temperature conditions, the carboxyl group can maintain the stability of the molecular structure of the viscosity reducer through hydrogen bonding and ion exchange, thereby significantly improving the temperature resistance of the viscosity reducer, so that it can still maintain an excellent viscosity reduction effect under high temperature conditions.

[0023] 5. The addition of ethylene glycol monovinyl polyethylene glycol ether (EPEG) monomer in the present invention further optimizes the performance of the viscosity reducer. The ether bond (-O-) and polyoxyethylene segment in its molecular structure have excellent hydration ability, which can significantly improve the hydration dispersibility of clay particles and prevent particle aggregation and flocculation. At the same time, the flexible structure of the polyoxyethylene segment gives the viscosity reducer good rheological adjustment performance, which can effectively improve the rheological properties of the drilling fluid, reduce dynamic shear force and plastic viscosity. In addition, EPEG can also enhance the filtration loss reduction performance of the viscosity reducer, can form a dense filter cake on the well wall, reduce the filtrate intrusion into the formation, and improve the well wall stability. DETAILED DESCRIPTION

[0024] The present invention will be further described below by means of specific examples, but is not limited thereto.

[0025] The experimental methods described in the examples are conventional methods unless otherwise specified; the reagents and materials used are commercially available unless otherwise specified.

[0026] The number average molecular weight of ethylene glycol monovinyl polyethylene glycol ether (EPEG) used in the examples is 3000 g / mol and is available from Qingdao Zhongbangda Chemical Reagent Co., Ltd.

[0027] Example 1 A method for preparing a viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution comprises the following steps: (1) 60 g of ethylene glycol monovinyl polyethylene glycol ether (EPEG), 60 mg of 5% hydrogen peroxide solution and 100 g of deionized water were added into a three-necked round-bottom flask respectively, and stirred at room temperature under nitrogen protection for 4 h to obtain a mixed solution I; (2) 0.72 g of acrylic acid, 8.28 g of 2-acrylamido-2-methylpropanesulfonic acid and 7.75 g of acryloyloxyethyl trimethylammonium chloride were added to 25 g of deionized water to obtain a mixed solution II; 60 mg of ascorbic acid, 50 mg of thioglycolic acid and 25 g of deionized water were mixed to obtain a mixed solution III; (3) Mixed solution II and mixed solution III were added dropwise to mixed solution I using a constant pressure dropping funnel, and the dropping time was 20 min. After the dropping was completed, the mixture was stirred and reacted at 60 °C under nitrogen protection for 4 h. After the reaction was completed, it was naturally cooled to room temperature, and the pH value of the system was adjusted to 7 using a 30% by mass sodium hydroxide aqueous solution. The obtained product was a viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution.

[0028] Example 2 A method for preparing a viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution is as described in Example 1, except that: in step (1), the amount of ethylene glycol monovinyl polyglycol ether added is 80 g; and the other steps or conditions are the same as in Example 1.

[0029] Example 3 A method for preparing a viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution is as described in Example 1, except that: in step (1), the amount of hydrogen peroxide solution added is 80 mg; and the other steps or conditions are the same as in Example 1.

[0030] Example 4 A method for preparing a viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution is as described in Example 1, except that the amount of ascorbic acid added in step (2) is 80 mg; the other steps or conditions are the same as in Example 1.

[0031] Example 5 A method for preparing a viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution is as described in Example 1, except that: in step (2), the amount of 2-acrylamido-2-methylpropanesulfonic acid added is 9.38 g; the other steps or conditions are the same as in Example 1.

[0032] Example 6 A method for preparing a viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution is as described in Example 1, except that: in step (2), the amount of acryloyloxyethyl trimethyl ammonium chloride added is 8.5 g; the other steps or conditions are the same as in Example 1.

[0033] Example 7 A method for preparing a viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution is as described in Example 1, except that the amount of hydrogen peroxide solution added is 40 mg; and the other steps or conditions are the same as those in Example 1.

[0034] Example 8 A method for preparing a viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution is as described in Example 1, except that the amount of ascorbic acid added is 40 mg; and the other steps or conditions are the same as in Example 1.

[0035] Example 9 A method for preparing a viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution comprises the following steps: (1) 50 g of ethylene glycol monovinyl polyethylene glycol ether (EPEG), 40 mg of 5% hydrogen peroxide solution and 80 g of deionized water were added into a three-necked round-bottom flask respectively, and stirred at room temperature under nitrogen protection for 4 h to obtain a mixed solution I; (2) 0.5 g of acrylic acid, 7 g of 2-acrylamido-2-methylpropanesulfonic acid and 5 g of acryloyloxyethyl trimethylammonium chloride were added to 25 g of deionized water to obtain a mixed solution II; 50 mg of ascorbic acid, 30 mg of thioglycolic acid and 25 g of deionized water were mixed to obtain a mixed solution III; (3) Mixed solution II and mixed solution III were added dropwise to mixed solution I using a constant pressure dropping funnel, and the dropping time was 20 min. After the dropping was completed, the mixture was stirred and reacted at 60 °C under nitrogen protection for 4 h. After the reaction was completed, it was naturally cooled to room temperature, and the pH value of the system was adjusted to 7 using a 30% by mass sodium hydroxide aqueous solution. The obtained product was a viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution.

[0036] Example 10 A method for preparing a viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution comprises the following steps: (1) 80 g of ethylene glycol monovinyl polyethylene glycol ether (EPEG), 80 mg of 5% hydrogen peroxide solution and 120 g of deionized water were added into a three-necked round-bottom flask respectively, and stirred at room temperature under nitrogen protection for 4 h to obtain a mixed solution I; (2) 1 g of acrylic acid, 10 g of 2-acrylamido-2-methylpropanesulfonic acid and 8 g of acryloyloxyethyltrimethylammonium chloride were added to 30 g of deionized water to obtain a mixed solution II; 70 mg of ascorbic acid, 60 mg of thioglycolic acid and 30 g of deionized water were mixed to obtain a mixed solution III; (3) Mixed solution II and mixed solution III were added dropwise to mixed solution I using a constant pressure dropping funnel, and the dropping time was 20 min. After the dropping was completed, the mixture was stirred and reacted at 60 °C under nitrogen protection for 4 h. After the reaction was completed, it was naturally cooled to room temperature, and the pH value of the system was adjusted to 7 using a 30% by mass sodium hydroxide aqueous solution. The obtained product was a viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution.

[0037] Comparative Example 1 A method for preparing a viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution comprises the following steps: (1) 60 g of ethylene glycol monovinyl polyethylene glycol ether (EPEG), 60 mg of 5% hydrogen peroxide solution and 100 g of deionized water were added into a three-bottom round-mouth flask respectively, and stirred at room temperature under nitrogen protection for 4 h to obtain a mixed solution I; (2) 0.72 g of acrylic acid, 8.28 g of 2-acrylamido-2-methylpropanesulfonic acid and 7.75 g of acryloyloxyethyltrimethylammonium chloride were dissolved in 25 g of deionized water to obtain a mixed solution II; 60 mg of ascorbic acid was mixed with 25 g of deionized water to obtain a mixed solution III; (3) Mixed solution II and mixed solution III were added to mixed solution I simultaneously using a constant pressure dropping funnel, and the dropping time was 20 min. After the dropping was completed, the mixture was stirred and reacted at 60 ° C under nitrogen protection for 4 h. After the reaction was completed, a 30% by mass sodium hydroxide aqueous solution was used to adjust the pH value of the system to 7. The obtained product was a viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution.

[0038] In this comparative example, no chain transfer agent, thioglycolic acid, was added.

[0039] Comparative Example 2 A method for preparing a viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution is as described in Example 1, except that ascorbic acid in step (2) is replaced by azobisisobutyramidine hydrochloride (AIBA); other steps or conditions are the same as in Example 1.

[0040] Comparative Example 3 A method for preparing a viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution is as described in Example 1, except that in step (2), 2-acrylamido-2-methylpropanesulfonic acid is replaced by sodium allyl sulfonate; other steps or conditions are the same as those in Comparative Example 1.

[0041] Comparative Example 4 A method for preparing a viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution is as described in Example 1, except that in step (2), acryloyloxyethyl trimethyl ammonium chloride is replaced by acrylamidopropyl trimethyl ammonium chloride; and other steps or conditions are the same as those in Comparative Example 1.

[0042] Comparative Example 5 A method for preparing a viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution is as described in Example 1, except that acrylic acid is replaced by methacrylic acid in step (2); other steps or conditions are the same as those in Comparative Example 1.

[0043] Comparative Example 6 A method for preparing a viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution is as described in Example 1, except that in step (2), ethylene glycol monovinyl polyethylene glycol ether is replaced by isobutylene polyethylene glycol ether; other steps or conditions are the same as those in Comparative Example 1.

[0044] Comparative Example 7 A method for preparing a viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution is as described in Example 1, except that 2-acrylamido-2-methylpropanesulfonic acid (AMPS) is not added in step (2); other steps or conditions are the same as those in Comparative Example 1.

[0045] Comparative Example 8 A method for preparing a viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution is as described in Example 1, except that no acryloyloxyethyl trimethylammonium chloride is added in step (2); the other steps or conditions are the same as those in Comparative Example 1.

[0046] Test Example 1 The viscosity reducers prepared in the examples and comparative examples were tested for rheology and filtration.

[0047] (1) Sample preparation: Preparation of base slurry: First, add 240g bentonite into 6000mL water. Then, add 8.4g Na 2 CO 3 , and after stirring for 24 hours, the drilling fluid base slurry is obtained.

[0048] Preparation of drilling fluid sample: add 13.5 g of the viscosity reducer prepared in the embodiment or comparative example to 400 mL of drilling fluid base slurry and stir for 20 min to obtain a drilling fluid sample; CO 2 Preparation of contaminated drilling fluid or base slurry: Place the prepared drilling fluid sample or base slurry in an aging tank and introduce CO into the aging tank. 2 gas (5MPa, 1h), and then obtain CO 2 Contamination of drilling fluid or base slurry.

[0049] (2) Test method: The samples (base slurry, CO 2 Polluted slurry, CO 2 The rheological parameters of the contaminated base slurry + the viscosity reducer of the embodiment / comparative example) include apparent viscosity (AV), plastic viscosity (PV) and yield point (YP); the API filtration loss of the sample was measured at 0.69 MPa using a ZNSJ-5A medium-pressure filter loss meter.

[0050] The test results are shown in Tables 1 and 2.

[0051] Table 1 Performance test results of viscosity reducers prepared in Example

[0052] Table 2 Performance test results of viscosity reducers prepared in comparative examples

[0053] It can be seen from the data in Table 1 and Table 2 that the drilling fluid viscosity reducer prepared by the present invention has a high viscosity in CO 2 After pollution and high temperature aging, it shows good viscosity reduction and filtration loss reduction performance, and has good temperature resistance.

[0054] In summary, the viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution of the present invention can meet the requirements of drilling fluid CO2 pollution under high temperature well conditions. 2 Pollution situation.

[0055] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0056] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0057] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution, characterized in that: The method comprises the following raw materials in parts by weight: 0.5-1 part of acrylic acid, 7-10 parts of 2-acrylamido-2-methylpropanesulfonic acid, 5-8 parts of acryloyloxyethyl trimethylammonium chloride, 50-80 parts of ethylene glycol monovinyl polyethylene glycol ether, 0.04-0.08 parts of oxidant, 0.05-0.07 parts of reducing agent, 0.03-0.06 parts of chain transfer agent and 130-180 parts of water; The oxidant is a hydrogen peroxide solution with a mass concentration of 5%; the reducing agent is ascorbic acid; and the chain transfer agent is thioglycolic acid and / or n-dodecyl mercaptan.

2. The viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution according to claim 1, characterized in that: The viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution is prepared by including the following raw materials in parts by weight: 0.72 parts of acrylic acid, 8.28 parts of 2-acrylamido-2-methylpropanesulfonic acid, 7.75 parts of acryloyloxyethyl trimethylammonium chloride, 60 parts of ethylene glycol monovinyl polyethylene glycol ether, 0.06 parts of oxidant, 0.06 parts of reducing agent, 0.05 parts of chain transfer agent, and 150 parts of water.

3. The viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution according to claim 1, characterized in that: The number average molecular weight of the ethylene glycol monovinyl polyethylene glycol ether is 2000-4000 g / mol.

4. The method for preparing the viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution according to any one of claims 1 to 3, characterized in that: The steps include: Ethylene glycol monovinyl polyethylene glycol ether and an oxidant are added to a portion of water A and stirred evenly to obtain a mixed solution I; acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, acryloyloxyethyl trimethylammonium chloride and a portion of water B are mixed to obtain a mixed solution II; a reducing agent, a chain transfer agent and a portion of water C are mixed to obtain a mixed solution III; the mixed solution II and the mixed solution III are added to the mixed solution I to react; after the reaction is completed, the pH of the system is adjusted to obtain a viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution.

5. The method for preparing the viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution according to claim 4, characterized in that: The mass ratio of the part of water A, the part of water B and the part of water C is 3-5:1:

1.

6. The method for preparing the viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution according to claim 4, characterized in that: The mixed solution II and the mixed solution III are simultaneously added dropwise into the system for 15-25 min; The dropping is carried out under the protection of protective gas and stirring, and the protective gas is nitrogen.

7. The method for preparing the viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution according to claim 4, characterized in that: The reaction temperature is 55-65° C., and the reaction time is 3-5 h. The reaction is carried out under the protection of protective gas and stirring, and the protective gas is nitrogen.

8. The method for preparing the viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution according to claim 4, characterized in that: The pH of the system was adjusted to 7 using a 20-40% by mass sodium hydroxide aqueous solution.

9. The use of the viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution according to any one of claims 1 to 3, characterized in that: It is used as a viscosity reducer in drilling fluids contaminated by carbon dioxide to reduce drilling fluid viscosity and filtration loss.

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