A viscosity reducer for carbon dioxide contaminated water-based drilling fluid and a preparation method and application thereof

Abstract

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

Description

TECHNICAL FIELD

[0001] The present application relates to an anti-carbon dioxide contaminated water-based drilling fluid viscosity reducer and its preparation method and application, belonging to the technical field of drilling fluid treatment agent. BACKGROUND

[0002] With the continuous growth of global energy demand and the gradual depletion of oil resources, exploration and exploitation activities gradually move to deeper and more complex formations. In these complex formations, drilling operations face many challenges, especially the invasion of harmful gases (such as H2S, CO2, etc.) in the formation into the drilling fluid, which causes significant changes in its performance. These contaminants not only destroy the rheological properties and filtration properties of the drilling fluid, but also accelerate the corrosion and wear of the drilling tools, seriously affecting drilling efficiency and safety.

[0003] Drilling fluid, as a key component in drilling engineering, bears multiple functions such as stabilizing the wellbore, carrying cuttings, cooling the drilling tools, and lubricating the drill bit. However, when CO2 invades the drilling fluid, it ionizes to produce carbonate ions and bicarbonate ions, which reduces the pH value of the drilling fluid, leading to an increase in its viscosity and shear force, and thus affecting its flowability. Currently, there are limited means to treat CO2-contaminated drilling fluids, and the method of replacing contaminated mud is usually used, which not only increases the operation cost, but also causes serious environmental problems, as the discarded contaminated drilling fluid is difficult to dispose of 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 deep well drilling fluid, which has certain salt resistance. Chinese patent document CN118620111A discloses a viscosity reducer with a multi-hydroxy monomer as the main component, which can resist high temperatures of 220℃. However, most of these viscosity reducers are designed for conventional geological conditions, and the research on viscosity reducers specifically for CO2-contaminated environments is still relatively scarce.

[0005] Therefore, focusing on the design and synthesis of new viscosity reducers, developing a drilling fluid viscosity reducer that can effectively cope with CO2 contamination is of great significance for improving the rheological properties of drilling fluid under contaminated conditions, improving drilling efficiency, and reducing environmental pollution. SUMMARY

[0006] In view of the deficiencies in the prior art, the present application provides an anti-carbon dioxide contaminated water-based drilling fluid viscosity reducer and its preparation method and application. The viscosity reducer of the present application can effectively solve the problems of increased viscosity and increased filtration loss caused by the invasion of CO2 into the drilling fluid.

[0007] To achieve the above-mentioned purposes, the technical solutions of the present application are as follows:

[0008] The application discloses a viscosity reducer for carbon dioxide pollution resistant water-based drilling fluid, which is prepared from the following raw materials in mass fraction: 0.5-1 parts of acrylic acid (AA), 7-10 parts of 2-acrylamido-2-methylpropane sulfonic acid (AMPS), 5-8 parts of acryloyloxyethyl trimethyl ammonium chloride (DAC), 50-80 parts of ethylene glycol monovinyl polyethylene glycol ether (EPEG), 0.04-0.08 parts of an oxidizing agent, 0.05-0.07 parts of a reducing agent, 0.03-0.06 parts of a chain transfer agent and 130-180 parts of water.

[0009] Preferably, the viscosity reducer for carbon dioxide pollution resistant water-based drilling fluid is prepared from the following raw materials in mass fraction: 0.72 parts of acrylic acid (AA), 8.28 parts of 2-acrylamido-2-methylpropane sulfonic acid (AMPS), 7.75 parts of acryloyloxyethyl trimethyl ammonium chloride (DAC), 60 parts of ethylene glycol monovinyl polyethylene glycol ether (EPEG), 0.06 parts of an oxidizing agent, 0.06 parts of a reducing agent, 0.05 parts of a chain transfer agent and 150 parts of water.

[0010] According to the application, the number average molecular weight of the ethylene glycol monovinyl polyethylene glycol ether is 2000-4000 g / mol.

[0011] According to the application, the oxidizing agent is a hydrogen peroxide solution with a mass concentration of 5%.

[0012] According to the application, the reducing agent is ascorbic acid (V C ).

[0013] According to the application, the chain transfer agent is mercaptoacetic acid (TGA) and / or n-dodecanethiol (DDT).

[0014] According to the application, the preparation method of the viscosity reducer for carbon dioxide pollution resistant water-based drilling fluid comprises the following steps:

[0015] The ethylene glycol monovinyl polyethylene glycol ether (EPEG) and the oxidizing agent are added into part of water A, stirred uniformly to obtain a mixed solution I; the acrylic acid (AA), the 2-acrylamido-2-methylpropane sulfonic acid (AMPS), the acryloyloxyethyl trimethyl ammonium chloride (DAC) and part of water B are mixed to obtain a mixed solution II; the reducing agent, the chain transfer agent and part of water C are mixed to obtain a mixed solution III; the mixed solution II and the mixed solution III are added into the mixed solution I to perform a reaction; after the reaction is completed, the pH of the system is adjusted to obtain the viscosity reducer for carbon dioxide pollution resistant water-based drilling fluid.

[0016] According to the application, 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; the total mass of the part of water A, the part of water B and the part of water C is the mass of water.

[0017] According to the application, preferably, the mixed solution II and the mixed solution III are added dropwise into the system simultaneously, the dropwise adding time is 15-25 min, the dropwise adding is carried out under the protection of a protective gas and stirring, and preferably, the protective gas is nitrogen.

[0018] According to the application, preferably, the reaction temperature is 55-65 DEG C, the reaction time is 3-5 h, the reaction is carried out under the protection of a protective gas and stirring, and preferably, the protective gas is nitrogen.

[0019] According to the application, preferably, the pH of the system is adjusted to 7 by using a sodium hydroxide aqueous solution with a mass fraction of 20-40%.

[0020] According to the application, the above-mentioned anti-carbon dioxide pollution water-based drilling fluid viscosity reducer is applied to carbon dioxide pollution drilling fluid as a viscosity reducer, thereby reducing the viscosity and filtration loss of the drilling fluid.

[0021] The technical features and beneficial effects of the application are as follows:

[0022] 1. The monomers (acrylic acid, 2-acrylamido-2-methylpropane sulfonic acid, acryloyloxyethyl trimethyl ammonium chloride, ethylene glycol monovinyl polyethylene glycol ether) used in the application are common industrial raw materials, the synthesis process is simple, the reaction conditions are mild and easy to control, the production cost of the prepared viscosity reducer is low, and the viscosity reducer is suitable for large-scale industrial application.

[0023] 2. The viscosity reducer prepared in the application exhibits excellent viscosity reduction performance in the drilling fluid, and has remarkable resistance to CO2 pollution. The active groups (sulfonic acid group, ether bond and amide group) in the molecular structure of the viscosity reducer can compete with CO2 for adsorption, effectively reduce the apparent viscosity, plastic viscosity and dynamic shear force of the drilling fluid system, significantly improve the drilling efficiency, and are suitable for high temperature and high pressure complex formation environment.

[0024] 3. The 2-acrylamido-2-methylpropane sulfonic acid (AMPS) monomer introduced in the application has a strong adsorptive sulfonic acid group (-SO3H) in the molecular structure, which can be dissociated into -SO3 - in water, has a high charge density and strong hydration capacity, can compete with CO2 for adsorption on the surface of clay particles, effectively prevents CO2 from reacting with alkaline substances in the drilling fluid to generate carbonate, thereby maintaining the stability of the drilling fluid system. In addition, the sulfonic acid group can form a diffuse double electric layer on the surface of clay particles through electrostatic interaction, increase the repulsive force between particles, and significantly reduce the viscosity and shear force of the drilling fluid.

[0025] 4. The acrylic acid (AA) introduced in this invention provides carboxyl groups (-COOH), which not only have strong adsorption capacity, allowing them to adhere firmly to the surface of clay particles through electrostatic interaction, but also have good thermal stability. Under high temperature conditions, the carboxyl groups can maintain the stability of the viscosity reducer's molecular structure through hydrogen bonding and ion exchange, thereby significantly improving the viscosity reducer's temperature resistance and maintaining its excellent viscosity reduction effect even in high temperature environments.

[0026] 5. The addition of ethylene glycol monovinyl polyethylene glycol ether (EPEG) monomers in this invention further optimizes the performance of the viscosity reducer. The ether bonds (-O-) and polyoxyethylene segments in its molecular structure possess excellent hydration capacity, significantly improving the hydration and dispersibility of clay particles and preventing particle aggregation and flocculation. Furthermore, the flexible structure of the polyoxyethylene segments imparts excellent rheological properties to the viscosity reducer, effectively improving the rheological properties of drilling fluids and reducing dynamic shear stress and plastic viscosity. Furthermore, EPEG enhances the viscosity reducer's fluid loss performance, forming a dense filter cake on the wellbore wall, reducing filtrate intrusion into the formation and improving wellbore stability. DETAILED DESCRIPTION

[0027] The present invention will be further described below with reference to specific examples, but is not limited thereto.

[0028] The experimental methods described in the examples are conventional methods unless otherwise specified; the reagents and materials used are commercially available unless otherwise specified.

[0029] 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.

[0030] Example 1

[0031] A method for preparing a viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution comprises the following steps:

[0032] (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 to a three-necked round-bottom flask, and stirred at room temperature under nitrogen for 4 h to obtain a mixed solution I;

[0033] (2) 0.72 g of acrylic acid, 8.28 g of 2-acrylamido-2-methylpropanesulfonic acid, and 7.75 g of acryloyloxyethyltrimethylammonium 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;

[0034] (3) the mixed solution II and the mixed solution III are added into the mixed solution I by using constant pressure dropping funnels at the same time, and the dropping time is 20 min; after the dropping is completed, the reaction is stirred at 60°C under nitrogen protection for 4 h; after the reaction is completed, the system is naturally cooled to room temperature, the pH value of the system is adjusted to 7 by using a 30% sodium hydroxide aqueous solution, and the obtained product is a viscosity reducer for a carbon dioxide pollution resistant water-based drilling fluid.

[0035] Example 2

[0036] A preparation method of a viscosity reducer for a carbon dioxide pollution resistant water-based drilling fluid is as described in Example 1, except that the amount of ethylene glycol monovinyl polyethylene glycol ether in step (1) is 80 g; and other steps or conditions are the same as those in Example 1.

[0037] Example 3

[0038] A preparation method of a viscosity reducer for a carbon dioxide pollution resistant water-based drilling fluid is as described in Example 1, except that the amount of hydrogen peroxide solution in step (1) is 80 mg; and other steps or conditions are the same as those in Example 1.

[0039] Example 4

[0040] A preparation method of a viscosity reducer for a carbon dioxide pollution resistant water-based drilling fluid is as described in Example 1, except that the amount of ascorbic acid in step (2) is 80 mg; and other steps or conditions are the same as those in Example 1.

[0041] Example 5

[0042] A preparation method of a viscosity reducer for a carbon dioxide pollution resistant water-based drilling fluid is as described in Example 1, except that the amount of 2-acrylamido-2-methylpropanesulfonic acid in step (2) is 9.38 g; and other steps or conditions are the same as those in Example 1.

[0043] Example 6

[0044] A preparation method of a viscosity reducer for a carbon dioxide pollution resistant water-based drilling fluid is as described in Example 1, except that the amount of acryloyloxyethyl trimethyl ammonium chloride in step (2) is 8.5 g; and other steps or conditions are the same as those in Example 1.

[0045] Example 7

[0046] A preparation method of a viscosity reducer for a carbon dioxide pollution resistant water-based drilling fluid is as described in Example 1, except that the amount of hydrogen peroxide solution is 40 mg; and other steps or conditions are the same as those in Example 1.

[0047] Example 8

[0048] A preparation method of the viscosity reducer for the carbon dioxide pollution resistant water-based drilling fluid is as described in Embodiment 1, except that the ascorbic acid is added in an amount of 40 mg, and other steps or conditions are the same as in Embodiment 1.

[0049] Embodiment 9

[0050] A preparation method of the viscosity reducer for the carbon dioxide pollution resistant water-based drilling fluid comprises the following steps:

[0051] (1) 50 g of ethylene glycol monovinyl polyethylene glycol ether (EPEG), 40 mg of a hydrogen peroxide solution with a mass concentration of 5%, and 80 g of deionized water are respectively added into three round-bottom flasks, stirred for 4 h at room temperature under nitrogen protection, and a mixed solution I is obtained;

[0052] (2) 0.5 g of acrylic acid, 7 g of 2-acrylamido-2-methylpropane sulfonic acid, and 5 g of acryloyloxyethyl trimethyl ammonium chloride are added into 25 g of deionized water to obtain a mixed solution II; 50 mg of ascorbic acid, 30 mg of mercaptoacetic acid, and 25 g of deionized water are mixed to obtain a mixed solution III;

[0053] (3) The mixed solution II and the mixed solution III are simultaneously added into the mixed solution I using constant-pressure dropping funnels, and the dropping time is 20 min; after the dropping is completed, the reaction is stirred for 4 h at 60°C under nitrogen protection; after the reaction is completed, the system is naturally cooled to room temperature, the pH value of the system is adjusted to 7 using a 30% sodium hydroxide aqueous solution, and the obtained product is the viscosity reducer for the carbon dioxide pollution resistant water-based drilling fluid.

[0054] Embodiment 10

[0055] A preparation method of the viscosity reducer for the carbon dioxide pollution resistant water-based drilling fluid comprises the following steps:

[0056] (1) 80 g of ethylene glycol monovinyl polyethylene glycol ether (EPEG), 80 mg of a hydrogen peroxide solution with a mass concentration of 5%, and 120 g of deionized water are respectively added into three round-bottom flasks, stirred for 4 h at room temperature under nitrogen protection, and a mixed solution I is obtained;

[0057] (2) 1 g of acrylic acid, 10 g of 2-acrylamido-2-methylpropane sulfonic acid, and 8 g of acryloyloxyethyl trimethyl ammonium chloride are added into 30 g of deionized water to obtain a mixed solution II; 70 mg of ascorbic acid, 60 mg of mercaptoacetic acid, and 30 g of deionized water are mixed to obtain a mixed solution III;

[0058] (3) The mixed solution II and the mixed solution III are added into the mixed solution I by using constant pressure dropping funnels at the same time, and the dropping time is 20 min; after the dropping is completed, the reaction is stirred at 60°C under nitrogen protection for 4 h; after the reaction is completed, the system pH value is adjusted to 7 by using a 30% sodium hydroxide aqueous solution, and the obtained product is an anti-carbon dioxide pollution water-based drilling fluid viscosity reducer.

[0059] Comparative Example 1

[0060] A preparation method of an anti-carbon dioxide pollution water-based drilling fluid viscosity reducer comprises the following steps:

[0061] (1) 60 g of ethylene glycol monovinyl polyethylene glycol ether (EPEG), 60 mg of a 5% hydrogen peroxide solution and 100 g of deionized water are respectively added into three round-bottomed flasks, and stirred at room temperature under nitrogen protection for 4 h to obtain a mixed solution I;

[0062] (2) 0.72 g of acrylic acid, 8.28 g of 2-acrylamido-2-methylpropane sulfonic acid and 7.75 g of acryloyloxyethyl trimethyl ammonium chloride are dissolved in 25 g of deionized water to obtain a mixed solution II; 60 mg of ascorbic acid and 25 g of deionized water are mixed to obtain a mixed solution III;

[0063] (3) The mixed solution II and the mixed solution III are added into the mixed solution I by using constant pressure dropping funnels at the same time, and the dropping time is 20 min; after the dropping is completed, the reaction is stirred at 60°C under nitrogen protection for 4 h; after the reaction is completed, the system pH value is adjusted to 7 by using a 30% sodium hydroxide aqueous solution, and the obtained product is an anti-carbon dioxide pollution water-based drilling fluid viscosity reducer.

[0064] In the present comparative example, the chain transfer agent mercaptoacetic acid is not added.

[0065] Comparative Example 2

[0066] A preparation method of an anti-carbon dioxide pollution water-based drilling fluid viscosity reducer is as described in Example 1, except that the ascorbic acid in step (2) is replaced by azobisdimethylamino hydrochloride (AIBA); and other steps or conditions are the same as those in Example 1.

[0067] Comparative Example 3

[0068] A preparation method of an anti-carbon dioxide pollution water-based drilling fluid viscosity reducer is as described in Example 1, except that the 2-acrylamido-2-methylpropane sulfonic acid in step (2) is replaced by sodium allylsulfonate; and other steps or conditions are the same as those in Comparative Example 1.

[0069] Comparative Example 4

[0070] A method for preparing a viscosity reducer for a carbon dioxide pollution resistant water-based drilling fluid 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 in Comparative Example 1.

[0071] Comparative Example 5

[0072] A method for preparing a viscosity reducer for a carbon dioxide pollution resistant water-based drilling fluid is as described in Example 1, except that in step (2), acrylic acid is replaced by methacrylic acid; and other steps or conditions are the same as in Comparative Example 1.

[0073] Comparative Example 6

[0074] A method for preparing a viscosity reducer for a carbon dioxide pollution resistant water-based drilling fluid is as described in Example 1, except that in step (2), ethylene glycol monovinyl polyethylene glycol ether is replaced by isobutenyl polyethylene glycol ether; and other steps or conditions are the same as in Comparative Example 1.

[0075] Comparative Example 7

[0076] A method for preparing a viscosity reducer for a carbon dioxide pollution resistant water-based drilling fluid is as described in Example 1, except that in step (2), 2-acrylamido-2-methylpropane sulfonic acid (AMPS) is not added; and other steps or conditions are the same as in Comparative Example 1.

[0077] Comparative Example 8

[0078] A method for preparing a viscosity reducer for a carbon dioxide pollution resistant water-based drilling fluid is as described in Example 1, except that in step (2), acryloyloxyethyl trimethyl ammonium chloride is not added; and other steps or conditions are the same as in Comparative Example 1.

[0079] Test Example 1

[0080] The viscosity reducers prepared in the examples and comparative examples are subjected to rheological and filtration tests.

[0081] (1) Sample preparation:

[0082] Base slurry preparation: first, 240 g of bentonite is added to 6000 mL of water, and then 8.4 g of Na2CO3 is added to the above system, and after stirring for 24 hours, a drilling fluid base slurry is obtained.

[0083] Drilling fluid sample preparation: 13.5 g of the viscosity reducer prepared in the examples or comparative examples is added to 400 mL of the drilling fluid base slurry, and after stirring for 20 min, a drilling fluid sample is obtained.

[0084] CO2 pollution drilling fluid or base slurry preparation: the prepared drilling fluid sample or base slurry is placed in an aging tank, and CO2 gas (5 MPa, 1 h) is introduced into the aging tank to obtain the CO2 pollution drilling fluid or base slurry.

[0085] (2) Test method:

[0086] The rheological parameters of the samples (base slurry, CO2 pollution base slurry, CO2 pollution base slurry + viscosity reducer of the examples / counterexamples) are measured using a ZNN-D6B electronic six-speed rotary viscometer, including apparent viscosity (AV), plastic viscosity (PV) and yield point (YP); the API filtration amount of the sample is determined using a ZNSJ-5A medium pressure filtration instrument at 0.69 MPa.

[0087] The test results are shown in Tables 1 and 2.

[0088] Table 1 Performance test results of the viscosity reducer prepared in the examples

[0089]

[0090] Table 2 Performance test results of the viscosity reducer prepared in the counterexamples

[0091]

[0092] As can be seen from the data in Tables 1 and 2, the drilling fluid viscosity reducer prepared by the present application exhibits good viscosity reduction and filtration reduction performance after CO2 pollution and high temperature aging, and has good temperature resistance.

[0093] In summary, the viscosity reducer for carbon dioxide pollution water-based drilling fluid of the present application can meet the CO2 pollution condition of the drilling fluid under high temperature well conditions.

[0094] The above describes the preferred embodiments of the present application, but the present application is not limited to the specific details in the above embodiments, and various simple modifications can be made to the technical solutions of the present application within the technical concept of the present application, and these simple modifications all belong to the protection scope of the present application.

[0095] In addition, it should be noted that each specific technical feature described in the above specific embodiments can be combined in any appropriate manner without contradiction, and in order to avoid unnecessary repetition, the present application will not further describe various possible combinations.

[0096] In addition, various different embodiments of the present application can also be combined in any manner, as long as they do not deviate from the technical concept of the present application, and they should also be considered as disclosed by the present application.

Claims

1. A viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution, characterized in that: The method is prepared from 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 acryloyloxyethyltrimethylammonium chloride, 50-80 parts of ethylene glycol monovinyl polyethylene glycol ether, 0.04-0.08 parts of an oxidizing agent, 0.05-0.07 parts of a reducing agent, 0.03-0.06 parts of a chain transfer agent, and 130-180 parts of water; The oxidant is a 5% mass concentration of hydrogen peroxide solution; the reducing agent is ascorbic acid; the chain transfer agent is thioglycolic acid and / or n-dodecyl mercaptan; The method for preparing the viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution comprises the following steps: adding ethylene glycol monovinyl polyethylene glycol ether and an oxidant to a portion of water A and stirring uniformly to obtain a mixed solution I; mixing acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, acryloyloxyethyltrimethylammonium chloride, and a portion of water B to obtain a mixed solution II; mixing a reducing agent, a chain transfer agent, and a portion of water C to obtain a mixed solution III; adding the mixed solutions II and III to the mixed solution I to react; and after the reaction, adjusting the pH of the system to 7 to obtain the viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution.

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 from 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 acryloyloxyethyltrimethylammonium chloride, 60 parts of ethylene glycol monovinyl polyethylene glycol ether, 0.06 parts of an oxidant, 0.06 parts of a reducing agent, 0.05 parts of a 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 viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution according to claim 1, characterized in that: The mass ratio of the water A, the water B and the water C is 3-5:1:

1.

5. The viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution according to claim 1, characterized in that: The mixed solution II and mixed solution III are simultaneously added dropwise to the system for 15-25 minutes; The dropwise addition is carried out under the protection of protective gas and stirring, and the protective gas is nitrogen.

6. The viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution according to claim 1, 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 a protective gas and with stirring, and the protective gas is nitrogen.

7. The viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution according to claim 1, characterized in that: The pH of the system was adjusted to 7 using a 20-40% sodium hydroxide aqueous solution.

8. Use of the viscosity reducer for water-based drilling fluid resistant to carbon dioxide pollution according to any one of claims 1 to 7, characterized in that: It is used as a viscosity reducer in drilling fluids contaminated by carbon dioxide to reduce the viscosity and filtration loss of drilling fluids.

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