High-temperature-resistant zwitterionic polymer viscosity reducer as well as preparation method and application thereof

Abstract

The invention relates to the technical field of drilling fluid treating agents, in particular to a high-temperature-resistant zwitterionic polymer viscosity reducer as well as a preparation method and application thereof. The high-temperature-resistant zwitterionic polymer viscosity reducer comprises a polymerization product of a vinyl-containing monomer A, a vinyl-containing monomer B and a cationic monomer, the vinyl-containing monomer A contains a structural unit as shown in a formula I, and the vinyl-containing monomer B contains a structural unit as shown in a formula II; the high-temperature-resistant zwitterionic polymer viscosity reducer has the advantages of wide adaptability, good stability, remarkable viscosity reduction effect, temperature resistance and viscosity reduction capability; the viscosity reducer has excellent viscosity reduction performance at high temperature, can resist the temperature of 180 DEG C, has the viscosity reduction rate of 95%, and has the capability of inhibiting hydration expansion of shale.

Description

Technical Field

[0001] The present invention relates to the technical field of drilling fluid treatment agents, and particularly relates to a high-temperature resistant zwitterionic polymer viscosity reducer, its preparation method and application. Background Art

[0002] A water-based drilling fluid viscosity reducer is a treatment agent material used to control the viscosity of drilling fluid. Its main function is to reduce the viscosity of the drilling fluid, so that the liquid can flow more easily during the drilling process and improve the drilling efficiency. With the continuous increase in the demand for oil and gas, it is necessary to exploit deeper and more complex oil and gas reservoirs, and the exploitation of these oil and gas reservoirs requires more efficient and safer drilling technologies and drilling fluid formulations. Therefore, the research and development of new water-based drilling fluid viscosity reducers have become an important topic.

[0003] Since the end of the 1930s, inorganic phosphates have been used as viscosity reducers to control the viscosity of drilling fluid. In the 1940s, tannins were widely used as drilling fluid viscosity reducers. Tannin is a natural organic compound with good viscosity reduction effect, low price and easy availability. By adding tannin to the drilling fluid, the viscosity of the drilling fluid can be effectively controlled, and the drilling speed and efficiency can be improved. However, with the continuous development of drilling technology, the disadvantages of tannins have gradually emerged. First, the viscosity reduction effect of tannins is unstable and will be affected by factors such as temperature and pH value. Second, the molecular structure of tannins is complex, and it is difficult to control its properties and preparation process. Therefore, researchers began to seek more stable and controllable viscosity reducers. In the 1950s, the drilling fluid viscosity reducers mainly used natural polymer substances such as starch and xanthan gum, but these substances were easily affected by factors such as temperature and pH value, resulting in unstable viscosity reduction effect. In the 1960s, researchers began to study synthetic polymer viscosity reducers such as polyacrylamide and polyether amide. The viscosity reduction effects of these synthetic polymer materials are more stable and controllable, and thus are widely used in water-based drilling fluids.

[0004] With the increasing demand for oil and gas, it is necessary to exploit deeper and more complex oil and gas reservoirs, and water-based drilling fluid viscosity reducers have also been continuously developed and improved. For example, in extreme environments such as high temperature and high pressure, the stability and effectiveness of viscosity reducers face huge challenges. As the main research object of synthetic polymer viscosity reducers, Zhang Longjun used acrylic acid (AA) and 2-acrylamido-2-methylpropanesulfonic acid (AMPS) as monomers, and under the ammonium persulfate initiation system, sodium hypophosphite with antioxidant ability was used as a chain transfer agent to prepare a viscosity reducer with a temperature resistance of up to 200 °C. Ming Xiansen used sodium styrenesulfonate (SSS), acrylamide (AM), and AA as raw materials, and synthesized the SSS / AM / AA copolymer viscosity reducer with the optimal monomer molar ratio of n(SSS)∶n(AM)∶n(AA) = 2∶1∶4. It has good temperature resistance, and the viscosity reduction rate can still reach more than 60% in saltwater mud. Li Qiling used SSS, maleic anhydride (MA), and calcium lignosulfonate (SL) as the main raw materials, and synthesized a graft-modified calcium lignosulfonate viscosity reducer (SMLS) using the ammonium persulfate initiation system. This viscosity reducer exhibits excellent viscosity reduction performance and can achieve a viscosity reduction rate of more than 70% in fresh water, salt water, and calcium-treated drilling fluids.

[0005] To sum up, most of the polymer viscosity reducers are anionic. Some drilling practices have shown that anionic drilling fluid systems have many limitations, such as strong static structural forces and insufficient ability to inhibit the hydration and dispersion of drill cuttings and clay. To overcome these limitations, cationic monomers with different structures can be introduced for synthesis to obtain a series of zwitterionic copolymers. The molecular structures of these polymer viscosity reducers contain both cations and anions. Compared with traditional anionic polymers, zwitterionic polymer viscosity reducers have stronger properties.

[0006] During deep well drilling, high temperature easily causes the clay particles in the drilling fluid base slurry to expand and disperse, which in turn leads to an increase in the viscosity of the base slurry. The temperature resistance of the polymer and its ability to inhibit clay dispersion are particularly important in this case. Therefore, introducing cationic polymers makes the viscosity reducer contain a small amount of cationic groups to undergo ionic adsorption with clay particles, effectively inhibiting the hydration and dispersion of clay. This method can improve the temperature resistance of the polymer and its ability to inhibit the hydration and swelling of shale, thereby better controlling the viscosity of the drilling fluid and ensuring the efficiency and safety of drilling. Summary of the Invention

[0007] Aiming at the defects of insufficient temperature resistance and viscosity reduction performance of high-temperature-resistant drilling fluid viscosity reducers in the prior art, the present invention provides a high-temperature-resistant zwitterionic polymer viscosity reducer with both viscosity reduction and inhibition capabilities, which can play an excellent viscosity reduction role in the high-temperature environment at the bottom of the well and effectively inhibit the hydration and dispersion of clay.

[0008] Through extensive research, the inventors of the present invention found that by polymerizing three vinyl monomers with different ionic properties and hydrophilicities, the zwitterionic polymer has a wider range of adaptabilities. The introduction of two vinyl monomers containing sulfonic acid groups and amide groups can improve the temperature resistance of the polymer; the introduction of cationic monomers enhances the adsorption strength and adsorption rate on the clay surface and neutralizes the surface charge of the clay at the same time. Finally, the synthesized product has temperature resistance, adsorption, and inhibition properties at the same time, and is particularly suitable as a high-temperature resistant zwitterionic polymer viscosity reducer for water-based drilling fluids, thus completing the present invention.

[0009] To solve the above technical problems, the first aspect of the present invention provides a high-temperature resistant zwitterionic polymer viscosity reducer, which comprises a polymerization product of a vinyl-containing monomer A, a vinyl-containing monomer B, and a cationic monomer; the vinyl-containing monomer A contains a structural unit shown in Formula I, and the vinyl-containing monomer B contains a structural unit shown in Formula II;

[0010]

[0011] In Formula I, R1, R2, R3, and R4 are the same or different, and each independently selected from hydrogen and C1-C5 straight-chain alkyl groups or C3-C5 branched-chain alkyl groups. Preferably, R1, R2, R3, and R4 are the same or different, and each independently selected from hydrogen, methyl, ethyl, propyl, isopropyl, butyl, pentyl, and isopentyl;

[0012] In Formula II, R5, R6, R7, and R8 are the same or different, and each independently selected from hydrogen and C1-C5 straight-chain alkyl groups or C3-C5 branched-chain alkyl groups. Preferably, R5, R6, R7, and R8 are the same or different, and each independently selected from hydrogen, methyl, ethyl, propyl, isopropyl, butyl, pentyl, and isopentyl.

[0013] According to some embodiments of the present invention, the mass ratio of the vinyl-containing monomer A to the vinyl-containing monomer B is 1:0.25-3, preferably 1:0.75-2; the mass ratio of the cationic monomer to the sum of the masses of the vinyl-containing monomer A and the vinyl-containing monomer B is 1:0.25-3, preferably 1:0.75-2, and more preferably 1:1-1.75.

[0014] According to some embodiments of the present invention, the vinyl-containing monomer A is selected from at least one of N,N-dimethylacrylamide, acrylamide, and N-isopropylacrylamide.

[0015] According to some embodiments of the present invention, the vinyl-containing monomer B is selected from 2-acrylamido-2-methylpropanesulfonic acid.

[0016] In the present invention, the vinyl-containing monomer B may be selected from one of 3-[[2-(acryloyloxy)ethyl]dimethylammonio]propane-1-sulfonate, 3-[(3-acrylamidopropyl)dimethylammonio]propane-1-sulfonate, and 4-[[2-(methacryloyloxy)ethyl]dimethylammonio]butane-1-sulfonate.

[0017] According to some embodiments of the present invention, the cationic monomer is selected from at least one of methacryloyloxyethyltrimethylammonium chloride, dimethyldiallylammonium chloride, methacryloyloxyethyldimethylammonium chloride, and methacryloyloxybutyldimethylammonium chloride.

[0018] A second aspect of the present invention provides a method for preparing the above-mentioned high-temperature resistant zwitterionic polymer viscosity reducer, comprising the following steps:

[0019] 1) Mix the vinyl-containing monomer A and the vinyl-containing monomer B in water to obtain a mixed monomer solution;

[0020] 2) Perform a first reaction on the mixed monomer solution obtained in step 1) with the cationic monomer, and then add an initiator and a chain transfer agent to perform a second reaction to obtain the high-temperature resistant zwitterionic polymer viscosity reducer.

[0021] According to some embodiments of the present invention, in step 1), the water is selected from at least one of tap water, deionized water, and distilled water; preferably, the mass ratio of the water to the sum of the masses of the vinyl-containing monomer A and the vinyl-containing monomer B is (10-20):1.

[0022] According to some embodiments of the present invention, in step 2), the initiator is selected from at least one of ammonium persulfate, potassium persulfate, and cerium nitrate; preferably, the mass ratio of the initiator to the total weight of the vinyl-containing monomer A and the vinyl-containing monomer B is 1:50-400, preferably 1:100-350, and more preferably 1:150-300.

[0023] According to some embodiments of the present invention, the chain transfer agent is selected from at least one of isopropanol, mercaptoethanol, and trichloroethylene; preferably, the mass ratio of the chain transfer agent to the total mass of the vinyl-containing monomer A, the vinyl-containing monomer B, and the cationic monomer is 1:100-500, preferably 1:150-400, and more preferably 1:200-350.

[0024] According to some embodiments of the present invention, the conditions of the first reaction include: the reaction temperature is 40°C to 90°C, preferably 50°C to 85°C, more preferably 55°C to 75°C, and the time is 0.1 h to 0.9 h, for example, 0.5 h.

[0025] According to some embodiments of the present invention, the conditions of the second reaction include: reaction temperature of 40°C to 90°C, preferably 50°C to 85°C, more preferably 55°C to 75°C, and time of 1h to 5h, preferably 2h to 3h.

[0026] According to some embodiments of the present invention, the first reaction further comprises adjusting the pH using an alkali metal hydroxide; preferably, the alkali metal hydroxide is selected from at least one of sodium hydroxide and potassium hydroxide; further preferably, the pH is adjusted to 2-11, preferably 3-10, and more preferably 7-9.

[0027] According to some embodiments of the present invention, the second reaction further comprises drying and crushing; preferably, the drying conditions include: the reaction temperature is 50°C to 120°C, preferably 60°C.

[0028] According to some embodiments of the present invention, the viscosity reduction rate of the high temperature resistant zwitterionic polymer viscosity reducer is ≧89%.

[0029] A third aspect of the present invention provides a use of the above-mentioned high temperature resistant zwitterionic polymer viscosity reducer in drilling fluid.

[0030] Beneficial effects:

[0031] The high temperature resistant zwitterionic polymer viscosity reducer of the present invention has the following characteristics:

[0032] 1) Wide adaptability: They can be used in different drilling fluids, including fresh water and high-salinity water, which makes them more adaptable to different drilling environments and requirements;

[0033] 2) Good stability: It remains stable under harsh conditions such as high temperature, is not easy to decompose and fail, and can more stably control the viscosity of the drilling fluid;

[0034] 3) Significant viscosity reduction effect: Only a small amount of viscosity reducer is needed to achieve a significant viscosity reduction effect. A viscosity reduction rate of more than 90% can be achieved with an addition of 0.5wt%, and it is not easily affected by environmental factors;

[0035] 4) Multifunctional: By grafting and copolymerizing the cationic monomer with two vinyl monomers, the heat resistance and viscosity reduction capabilities can be further improved.

[0036] Through the above mechanism, the high temperature resistant zwitterionic polymer viscosity reducer of the present invention has excellent viscosity reducing performance at high temperature, with a temperature resistance of up to 180°C and a viscosity reducing rate of 95%, and has the ability to inhibit shale hydration expansion. DETAILED DESCRIPTION

[0037] The present invention will be further described below in conjunction with the embodiments, but the present invention is not limited by these embodiments.

[0038] In the embodiment of the present invention, N, N-dimethylacrylamide was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., with a purity > 99.0% (GC).

[0039] In the embodiment of the present invention, acrylamide was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., with a purity of 99.0% (AR).

[0040] In the present invention, 2-acrylamido-2-methylpropanesulfonic acid was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., with a purity of 98%.

[0041] In the present invention, methacryloyloxyethyltrimethylammonium chloride was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., content: 75 wt.% in H2O, containing 600 ppm MEHQ inhibitor.

[0042] In the present invention, isopropanol, ammonium persulfate, and sodium hydroxide are all commercially available without special instructions.

[0043] In the present invention, the six-speed rotational viscometer was purchased from Qingdao Haitongda Special Instrument Co., Ltd., model number HTD13145.

[0044] In the present invention, the roller heating furnace was purchased from Qingdao Haitongda Special Instrument Co., Ltd., model number XGRL-4A.

[0045] Example 1

[0046] This example provides a high-temperature resistant zwitterionic polymer viscosity reducer, and the preparation method is as follows:

[0047] 1) Add 2.4 kg of N, N-dimethylacrylamide, 3.4 kg of 2-acrylamido-2-methylpropanesulfonic acid, and 90 kg of deionized water to a container equipped with a stirrer, and stir until completely dissolved to obtain a mixed monomer solution;

[0048] 2) Use a constant temperature water bath to heat the mixed monomer solution obtained in step 1) to 65 °C, then add 4.2 kg of methacryloyloxyethyltrimethylammonium chloride, stir and react at 65 °C for 0.5 h, and then adjust the pH to 7 with NaOH;

[0049] 3) After step 2), add 0.03 kg of isopropanol and 0.03 kg of ammonium persulfate to the reaction solution, continue to react at 65 °C for 2 h, dry to constant weight at 60 °C, and pulverize to obtain the high-temperature resistant zwitterionic polymer viscosity reducer A1.

[0050] Example 2

[0051] This example provides a high-temperature resistant zwitterionic polymer viscosity reducer, and the preparation method is as follows:

[0052] 1) Add 2.4 kg of acrylamide, 3.4 kg of 2-acrylamido-2-methylpropanesulfonic acid and 90 kg of deionized water to a container equipped with a stirrer, and stir until completely dissolved to obtain a mixed monomer solution;

[0053] 2) Heat the mixed monomer solution obtained in step 1) to 65 °C using a constant temperature water bath, then add 4.2 kg of methacryloyloxyethyltrimethylammonium chloride, stir and react at 65 °C for 0.5 h, and then adjust the pH to 7 with NaOH;

[0054] 3) After step 2), add 0.03 kg of isopropanol and 0.03 kg of ammonium persulfate to the reaction solution, react at 65 °C for 2 h, dry to constant weight at 60 °C, and pulverize to obtain a high-temperature resistant zwitterionic polymer viscosity reducer A2.

[0055] Example 3

[0056] This example provides a high-temperature resistant zwitterionic polymer viscosity reducer, and the preparation method is as follows:

[0057] 1) Add 2.4 kg of N,N-dimethylacrylamide, 3.4 kg of 2-acrylamido-2-methylpropanesulfonic acid and 90 kg of deionized water to a container equipped with a stirrer, and stir until completely dissolved to obtain a mixed monomer solution;

[0058] 2) Heat the mixed monomer solution obtained in step 1) to 65 °C using a constant temperature water bath, then add 4.2 kg of methacryloyloxyethyltrimethylammonium chloride, stir and react at 65 °C for 0.5 h, and then adjust the pH to 9 with NaOH;

[0059] 3) After step 2), add 0.03 kg of isopropanol and 0.03 kg of ammonium persulfate to the reaction solution, react at 65 °C for 2 h, dry to constant weight at 60 °C, and pulverize to obtain a high-temperature resistant zwitterionic polymer viscosity reducer A3.

[0060] Example 4

[0061] This example provides a high-temperature resistant zwitterionic polymer viscosity reducer, and the preparation method is as follows:

[0062] 1) Add 2.4 kg of N,N-dimethylacrylamide, 3.4 kg of 2-acrylamido-2-methylpropanesulfonic acid and 90 kg of deionized water to a container equipped with a stirrer, and stir until completely dissolved to obtain a mixed monomer solution;

[0063] 2) Use a constant temperature water bath to heat the mixed monomer solution obtained in step 1) to 75 °C, then add 4.2 kg of methylacryloyloxyethyl trimethyl ammonium chloride, stir and react for 0.5 h at 75 °C, and then adjust the pH to 7 with NaOH;

[0064] 3) After step 2) is completed, add 0.03 kg of isopropanol and 0.03 kg of ammonium persulfate to the reaction solution, react for 2 h at 75 °C, dry to constant weight at 60 °C, and pulverize to obtain the high temperature resistant zwitterionic polymer viscosity reducer A4.

[0065] Example 5

[0066] This example provides a high temperature resistant zwitterionic polymer viscosity reducer, and the preparation method is as follows:

[0067] 1) Add 2.4 kg of N,N-dimethylacrylamide, 3.4 kg of 2-acrylamido-2-methylpropanesulfonic acid and 90 kg of deionized water to a container equipped with a stirrer, and stir until completely dissolved to obtain a mixed monomer solution;

[0068] 2) Use a constant temperature water bath to heat the mixed monomer solution obtained in step 1) to 75 °C, then add 4.2 kg of methylacryloyloxyethyl trimethyl ammonium chloride, stir and react for 0.5 h at 75 °C, and then adjust the pH to 9 with NaOH;

[0069] 3) After step 2) is completed, add 0.03 kg of isopropanol and 0.03 kg of ammonium persulfate to the reaction solution, react for 3 h at 75 °C, dry to constant weight at 60 °C, and pulverize to obtain the high temperature resistant zwitterionic polymer viscosity reducer A5.

[0070] Example 6

[0071] This example provides a high temperature resistant zwitterionic polymer viscosity reducer, and the preparation method is as follows:

[0072] 1) Add 2.4 kg of acrylamide, 3.4 kg of 2-acrylamido-2-methylpropanesulfonic acid and 90 kg of deionized water to a container equipped with a stirrer, and stir until completely dissolved to obtain a mixed monomer solution;

[0073] 2) Use a constant temperature water bath to heat the mixed monomer solution obtained in step 1) to 75 °C, then add 4.2 kg of methylacryloyloxyethyl trimethyl ammonium chloride, stir and react for 0.5 h at 75 °C, and then adjust the pH to 9 with NaOH;

[0074] 3) After step 2), 0.03 kg of isopropanol and 0.03 kg of ammonium persulfate are added to the reaction solution, and the reaction is carried out at 75 °C for 2 h, dried at 60 °C to constant weight, and pulverized to obtain the high-temperature resistant zwitterionic polymer viscosity reducer A6.

[0075] Example 7

[0076] This example provides a high-temperature resistant zwitterionic polymer viscosity reducer, and the preparation method is as follows:

[0077] 1) Add 3.3 kg of acrylamide, 2.6 kg of 2-acrylamido-2-methylpropanesulfonic acid and 90 kg of deionized water to a container equipped with a stirrer, and stir until completely dissolved to obtain a mixed monomer solution;

[0078] 2) Use a constant temperature water bath to heat the mixed monomer solution obtained in step 1) to 75 °C, then add 4.1 kg of methacryloyloxyethyl trimethyl ammonium chloride, stir and react at 75 °C for 0.5 h, and then adjust the pH to 9 with NaOH;

[0079] 3) After step 2), 0.03 kg of isopropanol and 0.03 kg of ammonium persulfate are added to the reaction solution, and the reaction is carried out at 75 °C for 2 h, dried at 60 °C to constant weight, and pulverized to obtain the high-temperature resistant zwitterionic polymer viscosity reducer A7.

[0080] Example 8

[0081] This example provides a high-temperature resistant zwitterionic polymer viscosity reducer, and the preparation method is as follows:

[0082] 1) Add 2.4 kg of N,N-dimethylacrylamide, 3.4 kg of 2-acrylamido-2-methylpropanesulfonic acid and 90 kg of deionized water to a container equipped with a stirrer, and stir until completely dissolved to obtain a mixed monomer solution;

[0083] 2) Use a constant temperature water bath to heat the mixed monomer solution obtained in step 1) to 65 °C, then add 4.2 kg of methacryloyloxyethyl trimethyl ammonium chloride, stir and react at 65 °C for 0.5 h, and then adjust the pH to 7 with NaOH;

[0084] 3) After step 2), 0.04 kg of isopropanol and 0.02 kg of ammonium persulfate are added to the reaction solution, and the reaction is carried out at 65 °C for 3 h, dried at 60 °C to constant weight, and pulverized to obtain the high-temperature resistant zwitterionic polymer viscosity reducer A8.

[0085] Example 9

[0086] This example provides a high-temperature resistant zwitterionic polymer viscosity reducer, and the preparation method is as follows:

[0087] 1) Add 3.3 kg of N,N-dimethylacrylamide, 2.6 kg of 2-acrylamido-2-methylpropanesulfonic acid and 90 kg of deionized water into a container equipped with a stirrer, and stir until completely dissolved to obtain a mixed monomer solution;

[0088] 2) Heat the mixed monomer solution obtained in step 1) to 65 °C using a constant temperature water bath, then add 4.1 kg of methacryloyloxyethyl trimethyl ammonium chloride, stir and react at 65 °C for 0.5 h, and then adjust the pH to 7 with NaOH;

[0089] 3) After step 2), add 0.03 kg of isopropanol and 0.03 kg of ammonium persulfate to the reaction solution, react at 65 °C for 3 h, dry to constant weight at 60 °C and pulverize to obtain the high-temperature resistant zwitterionic polymer viscosity reducer A9.

[0090] Example 10

[0091] This example provides a high-temperature resistant zwitterionic polymer viscosity reducer, and the preparation method is as follows:

[0092] 1) Add 1.75 kg of N,N-dimethylacrylamide, 6.5 kg of 2-acrylamido-2-methylpropanesulfonic acid and 90 kg of deionized water into a container equipped with a stirrer, and stir until completely dissolved to obtain a mixed monomer solution;

[0093] 2) Heat the mixed monomer solution obtained in step 1) to 65 °C using a constant temperature water bath, then add 1.75 kg of methacryloyloxyethyl trimethyl ammonium chloride, stir and react at 65 °C for 0.5 h, and then adjust the pH to 7 with NaOH;

[0094] 3) After step 2), add 0.03 kg of isopropanol and 0.03 kg of ammonium persulfate to the reaction solution, react at 65 °C for 3 h, dry to constant weight at 60 °C and pulverize to obtain the high-temperature resistant zwitterionic polymer viscosity reducer A10.

[0095] Example 11

[0096] This example provides a high-temperature resistant zwitterionic polymer viscosity reducer, and the preparation method is as follows:

[0097] 1) Add 2 kg of N,N-dimethylacrylamide, 6 kg of 2-acrylamido-2-methylpropanesulfonic acid and 90 kg of deionized water into a container equipped with a stirrer, and stir until completely dissolved to obtain a mixed monomer solution;

[0098] 2) Use a constant temperature water bath to heat the mixed monomer solution obtained in step 1) to 65°C, then add 2 kg of methacryloyloxyethyl trimethyl ammonium chloride, stir and react for 0.5 h at 65°C, and then adjust the pH to 7 with NaOH;

[0099] 3) After step 2) is completed, add 0.03 kg of isopropanol and 0.03 kg of ammonium persulfate to the reaction solution, react for 3 h at 65°C, dry to constant weight at 60°C, and pulverize to obtain the high-temperature resistant zwitterionic polymer viscosity reducer A11.

[0100] Example 12

[0101] This example provides a high-temperature resistant zwitterionic polymer viscosity reducer, and the preparation method is as follows:

[0102] 1) Add 2.5 kg of N,N-dimethylacrylamide, 6 kg of 2-acrylamido-2-methylpropanesulfonic acid and 90 kg of deionized water to a container equipped with a stirrer, and stir until completely dissolved to obtain a mixed monomer solution;

[0103] 2) Use a constant temperature water bath to heat the mixed monomer solution obtained in step 1) to 65°C, then add 1.5 kg of methacryloyloxyethyl trimethyl ammonium chloride, stir and react for 0.5 h at 65°C, and then adjust the pH to 7 with NaOH;

[0104] 3) After step 2) is completed, add 0.03 kg of isopropanol and 0.03 kg of ammonium persulfate to the reaction solution, react for 3 h at 65°C, dry to constant weight at 60°C, and pulverize to obtain the high-temperature resistant zwitterionic polymer viscosity reducer A12.

[0105] Comparative Example 1

[0106] Carry out according to the method described in Example 1, except that in step 1), N,N-dimethylacrylamide is not added to obtain polymer D1.

[0107] Comparative Example 2

[0108] Carry out according to the method described in Example 1, except that in step 1), 2-acrylamido-2-methylpropanesulfonic acid is not added to obtain polymer D2.

[0109] Comparative Example 3

[0110] Carry out according to the method described in Example 1, except that in step 2), methacryloyloxyethyl trimethyl ammonium chloride is not added to obtain polymer D3.

[0111] Comparative Example 4

[0112] The viscosity reducer polymer D4 used is the modified tannic acid (with a content of 96%) produced by Zhengzhou Shenglian Trading Co., Ltd.

[0113] Test Example

[0114] 1), Preparation of a bentonite-based slurry: Add 400 mL of distilled water to a high-speed stirring cup, then add 16.0 g of bentonite and 1.4 g of anhydrous sodium carbonate that have been weighed, and stir at high speed for 20 min. Stop at least twice during this period to scrape off the adherents on the container wall. Seal and cure at room temperature for 24 h. Prepare two portions of bentonite-based slurry using the same procedure.

[0115] b) Preparation of a brine-based slurry: Take 400 ml of the bentonite-based slurry (freshwater-based slurry) prepared in step a) and add it to a high-speed stirring cup. Add 100 g of sodium chloride to it and stir at high speed for 20 min, then hydrate for 24 h. Prepare two portions of brine-based slurry using the same procedure.

[0116] 2), a) Add 2.0 g of viscosity reducer A1 to one of the 400 ml bentonite-based slurries. Place the sample slurry and the other bentonite-based slurry in a high-temperature roller furnace and roll at a temperature of 180 °C for 16 h. After cooling, stir at high speed for 5 min at 10000 r / min. Use a six-speed rotational viscometer to measure the viscosity readings of the sample slurry and the other bentonite-based slurry at 100 r / min respectively.

[0117] b) Add 2.0 g of viscosity reducer A1 to one of the 400 ml brine-based slurries. Place the sample slurry and the other brine-based slurry in a high-temperature roller furnace and roll at a temperature of 180 °C for 16 h. After cooling, stir at high speed for 5 min at 10000 r / min. Use a six-speed rotational viscometer to measure the viscosity readings of the sample slurry and the other brine-based slurry at 100 r / min respectively.

[0118] The viscosity reduction rate of viscosity reducer A1 is calculated according to the following formula;

[0119]

[0120] In the above formula:

[0121] Φ1000 is the viscosity reading of the bentonite / brine-based slurry at 100 r / min;

[0122] Φ100 is the viscosity reading of the sample slurry at 100 r / min.

[0123] 3), Measure the viscosity reduction rates of viscosity reducers A2 - A12 and polymers D1 - D4 according to steps 1) and 2). The results are statistically shown in Table 1 and Table 2.

[0124] Table 1: Results of Viscosity Reduction Rate Measurement

[0125] Polymer Viscosity reduction rate / % A1 95 A2 90 A3 91 A4 89 A5 91 A6 90 A7 89 A8 91 A9 90 A10 85 A11 79 A12 81 D1 79 D2 75 D3 76 D4 84

[0126] Table 2: Viscosity reduction test results

[0127]

[0128]

[0129] It can be seen from the results of Table 1 and Table 2 that the zwitterionic polymer viscosity reducer prepared in the present invention is added to the bentonite-based slurry, and the viscosity reduction rate after high-temperature aging at a temperature of 180° C. for 16 hours can be as high as 89% or more, which is better than the modified tannic acid commonly used in China under the same high-temperature aging conditions. This shows that the polymer of the present invention has a good viscosity reducing effect as a viscosity reducer, has more excellent temperature resistance, and can effectively improve the rheology of water-based drilling fluids under high temperature environments.

[0130] It should be noted that the embodiments described above are only used to explain the present invention and do not constitute any limitation to the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words, rather than restrictive words. The present invention may be modified as specified within the scope of the claims of the present invention, and the present invention may be revised without departing from the scope and spirit of the present invention. Although the present invention described therein relates to specific methods, materials and embodiments, it does not mean that the present invention is limited to the specific examples disclosed therein, on the contrary, the present invention can be extended to all other methods and applications with the same functions.

Claims

1. An anti-high-temperature zwitterionic polymer viscosity reducer, characterized in that, The high-temperature resistant zwitterionic polymer viscosity reducer comprises a polymerization product of a vinyl-containing monomer A, a vinyl-containing monomer B and a cationic monomer; the vinyl-containing monomer A contains a structural unit shown in Formula I, and the vinyl-containing monomer B contains a structural unit shown in Formula II; In Formula I, R1, R2, R3 and R4 are the same or different, and are each independently selected from hydrogen and C1-C5 straight-chain alkyl groups or C3-C5 branched-chain alkyl groups; In Formula II, R5, R6, R7 and R8 are the same or different, and are each independently selected from hydrogen and C1-C5 straight-chain alkyl groups or C3-C5 branched-chain alkyl groups.

2. The high-temperature resistant zwitterionic polymer viscosifier according to claim 1, wherein The mass ratio of the vinyl-containing monomer A to the vinyl-containing monomer B is 1:0.25-3, preferably 1:0.75-2; the mass ratio of the cationic monomer to the sum of the masses of the vinyl-containing monomer A and the vinyl-containing monomer B is 1:0.25-3, preferably 1:0.75-2, more preferably 1:1-1.

75.

3. The high-temperature resistant zwitterionic polymer viscosifier according to claim 1 or 2, characterized in that, The vinyl-containing monomer A is selected from at least one of N,N-dimethylacrylamide, acrylamide, and N-isopropylacrylamide; and / or, the vinyl-containing monomer B is selected from 2-acrylamido-2-methylpropanesulfonic acid; and / or, the cationic monomer is selected from at least one of methacryloyloxyethyl trimethyl ammonium chloride, dimethyl diallyl ammonium chloride, methacryloyloxyethyl dimethyl ammonium chloride, and methacryloyloxybutyl dimethyl ammonium chloride.

4. A preparation method of a high-temperature resistant zwitterionic polymer viscosity reducer as described in any one of claims 1-3, characterized in that, It includes the following steps: 1) Mix the vinyl-containing monomer A and the vinyl-containing monomer B in water to obtain a mixed monomer solution; 2) Carry out a first reaction on the mixed monomer solution obtained in step 1) with the cationic monomer, and then add an initiator and a chain transfer agent to carry out a second reaction to obtain the high-temperature resistant zwitterionic polymer viscosity reducer.

5. The preparation method according to claim 4, wherein In step 1), the water is selected from at least one of tap water, deionized water, and distilled water; preferably, the mass ratio of the water to the sum of the masses of the vinyl-containing monomer A and the vinyl-containing monomer B is (10-20):

1.

6. The preparation method according to claim 4 or 5, characterized in that, In step 2), the initiator is selected from at least one of ammonium persulfate, potassium persulfate, and cerium nitrate; preferably, the mass ratio of the initiator to the total weight of the vinyl-containing monomer A and the vinyl-containing monomer B is 1:50-400, selected as 1:100-350, more preferably 1:150-300; and / or, the chain transfer agent is selected from at least one of isopropanol, mercaptoethanol, and trichloroethylene; preferably, the mass ratio of the chain transfer agent to the total mass of the vinyl-containing monomer A, the vinyl-containing monomer B, and the cationic monomer is 1:100-500, preferably 1:150-400, more preferably 1:200-350; and / or, the conditions of the first reaction include: the reaction temperature is 40°C to 90°C, preferably 50°C to 85°C, more preferably 55°C to 75°C, and the time is 0.1h to 0.9h; and / or, the conditions of the second reaction include: the reaction temperature is 40°C to 90°C, preferably 50°C to 85°C, more preferably 55°C to 75°C, and the time is 1h to 5h.

7. The preparation method according to any one of claims 4-6, characterized in that, After the first reaction, it further includes adjusting the pH with an alkali metal hydroxide; preferably, the alkali metal hydroxide is selected from at least one of sodium hydroxide and potassium hydroxide; further preferably, the pH is adjusted to 2-11, preferably 3-10, more preferably 7-9.

8. The preparation method according to any one of claims 4-7, characterized in that, After the second reaction, it further includes drying and pulverizing; preferably, the conditions for drying include: the temperature is 50°C to 120°C.

9. The preparation method according to any one of claims 4-8, characterized in that The viscosity reduction rate of the high-temperature resistant zwitterionic polymer viscosity reducer is ≥ 89%.

10. Application of the high-temperature resistant zwitterionic polymer viscosity reducer according to any one of claims 1-3 or the high-temperature resistant zwitterionic polymer viscosity reducer prepared by the preparation method according to any one of claims 4-9 in a drilling fluid.

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