Drag reducer for PVA cement slurry system and preparation method thereof

Abstract

The present application belongs to the technical field of drag reducing agent for cement slurry system, and particularly relates to a PVA-based cement slurry system drag reducing agent and a preparation method thereof, aiming to solve the problems of poor compatibility, weak temperature resistance and insufficient dispersion retention of the existing polycarboxylic acid drag reducing agent with the PVA-based cement slurry system. The drag reducing agent is configured into a mixed aqueous solution with a mass concentration of 40%-60% by 2-acrylamido-2-methylpropanesulfonic acid, acrylic acid, sodium p-styrenesulfonate and acrylamide in a molar ratio of 0.08-0.6:1:0.05-0.3:0.1-1.0, and a polyacrylic acid macromonomer is obtained through polymerization; a graft copolymerization type PVA-based cement slurry system drag reducing agent with a concentration of 20%-40% is obtained through polymerization reaction of the polyacrylic acid macromonomer and fatty acid vinyl ester, and the molar ratio of the fatty acid vinyl ester to the acrylic acid is 8-36:1. The compatibility of the drag reducing agent with the PVA-based cement slurry system is improved, and the drag reducing agent has good temperature resistance and dispersion capacity.

Description

Technical Field

[0001] This invention belongs to the technical field of drag-reducing agents for cement slurry systems, and specifically relates to a drag-reducing agent for PVA-based cement slurry systems and its preparation method. Background Technology

[0002] Polyvinyl alcohol (PVA) fluid loss reducing agents are a widely used type of non-ionic fluid loss reducing agent in China. The operating temperature of PVA fluid loss reducing agents generally does not exceed 95℃. Above this temperature, the cross-linking bonds are broken, and the fluid loss reduction performance deteriorates. For safety reasons, in oil and gas wells with well temperatures not exceeding 80℃, cement slurry systems formulated with PVA are mainly used for cementing operations. To improve the fluidity of the cement slurry during cementing operations, reduce cementing pressure, achieve turbulent flow at lower pumping speeds, improve the displacement efficiency of drilling fluid, and ensure cementing quality, oil well cement drag reducers need to be added to the cement slurry.

[0003] Currently, sulfonated aldehyde-ketone condensate polymers are commonly used drag-reducing agents for PVA-based cement slurry systems. These agents offer advantages such as low dosage, good dispersion, and significant improvement in the rheological properties of the cement slurry. However, the biggest drawback of sulfonated aldehyde-ketone condensate polymer drag-reducing agents is that the raw materials used in their production are mostly toxic and hazardous chemicals, resulting in a dark brown or dark red product. This leads to difficulties in the treatment of slurry preparation water used in cementing operations, creating significant environmental pressure. Due to environmental protection and other factors, in recent years, sulfonated aldehyde-ketone condensate polymer drag-reducing agents have been gradually replaced by polycarboxylate drag-reducing agents.

[0004] Polycarboxylate drag reducers are commonly referred to as high-performance water-reducing agents in the construction industry and are widely used in concrete. However, due to the harsh operating conditions such as high temperature, high pressure, and high salinity faced by drag reducers used in oil well cement, high-performance water-reducing agents used in the construction industry are difficult to meet the requirements of well cementing construction. For PVA-based cement slurry systems, the monomers of currently available polycarboxylate drag reducers contain a large number of hydroxyl groups. For example, Chinese patent CN108997536B discloses an amphoteric polycarboxylate dispersant for oil well cement and its preparation method. The polymer obtained by polymerization of unsaturated polyether macromonomers and carboxylate monomers contains ether bonds. These ether bonds react with the hydroxyl groups on the PVA molecular chain. Therefore, existing polycarboxylate drag reducers have poor compatibility with PVA-based water loss reducing agents, resulting in poor rheological properties of the cement slurry after curing. Summary of the Invention

[0005] This invention provides a drag-reducing agent for PVA-based cement slurry systems and its preparation method, in order to alleviate the problems of poor compatibility, weak temperature resistance, and insufficient dispersion retention of existing polycarboxylate drag-reducing agents with PVA-based cement slurry systems.

[0006] To alleviate the above-mentioned technical problems, the technical solution provided by the present invention is as follows:

[0007] A drag-reducing agent for PVA-based cement slurry systems is prepared by mixing 2-acrylamido-2-methylpropanesulfonic acid, acrylic acid, sodium p-styrenesulfonate, and acrylamide in a molar ratio of 0.08-0.6:1:0.05-0.3:0.1-1.0 to form a mixed aqueous solution with a mass concentration of 40%-60%. After polymerization, a polyacrylic acid macromonomer is obtained. The polyacrylic acid macromonomer and ethylene fatty acid ester are then polymerized to obtain a graft copolymer drag-reducing agent for PVA-based cement slurry systems with a concentration of 20%-40%, wherein the molar ratio of ethylene fatty acid ester to acrylic acid is 8-36:1.

[0008] Furthermore, fatty acid vinyl esters include vinyl acetate, vinyl propionate, or vinyl butyrate.

[0009] A method for preparing a drag-reducing agent for the above-mentioned PVA-based cement slurry system includes the following steps:

[0010] (1) Quaternary polymerization: 2-Acrylamido-2-methylpropanesulfonic acid, acrylic acid, sodium p-styrenesulfonate and acrylamide are placed in a reaction vessel and water is added to prepare a mixed aqueous solution with a mass concentration of 40% to 60%. The pH value of the mixed aqueous solution is adjusted to 2.5 to 6.5 by adding pH adjuster, and the mixture is stirred and heated to 40 to 80°C. Class A initiator and chain transfer agent are weighed and added to the mixed aqueous solution. The mixture is reacted at a constant temperature for 3 to 6 hours to obtain polyacrylic acid macromonomers.

[0011] (2) Graft copolymerization: Add ethylene fatty acid ester, molecular weight regulator and water to polyacrylic acid macromonomer in sequence, with a stirring time of 10 to 15 minutes between each addition. After adding the above raw materials, heat to 50-90℃ and add a 20% to 40% B type initiator solution dropwise. After the dropwise addition is completed, continue to stir at a constant temperature for 1 to 3 hours. Adjust the pH to 5 to 7 with a pH regulator and cool to obtain a 20% to 40% graft copolymer type PVA cement slurry system drag-reducing agent.

[0012] Furthermore, the pH adjuster in steps (1) and (2) is sodium hydroxide or potassium hydroxide.

[0013] Furthermore, in step (1), the type A initiator is ammonium persulfate, potassium persulfate, or sodium persulfate, and the amount of type A initiator is 0.8%-5.0% of the total mass of 2-acrylamido-2-methylpropanesulfonic acid, acrylic acid, sodium p-styrenesulfonate, and acrylamide in step (1).

[0014] Furthermore, the chain transfer agent is mercaptopropionic acid, mercaptoacetic acid, or sodium methacrylate sulfonate, and the molar ratio of the chain transfer agent to acrylic acid in step (1) is 0.01-0.05:1.

[0015] Furthermore, in step (2), the molecular weight regulator is n-dodecyl mercaptan or isopropanol, and the molar ratio of the amount of molecular weight regulator to the fatty acid vinyl ester is 0.0005-0.001:1.

[0016] Furthermore, in step (2), the type B initiator is benzoyl peroxide, lauroyl peroxide, diisopropyl peroxide, or dicyclohexyl peroxide, and the amount of type B initiator is 0.8%-1.5% of the total mass of 2-acrylamido-2-methylpropanesulfonic acid, acrylic acid, sodium p-styrenesulfonate, acrylamide, and ethylene fatty acid ester.

[0017] Furthermore, the amount of water used in step (2) is determined based on the required concentration of drag-reducing agent for the final PVA-type cement slurry system.

[0018] Furthermore, in step (2), the dropping time of the type B initiator solution is controlled to be 2-5 hours.

[0019] The beneficial effects of the drag-reducing agent for the PVA-based cement slurry system and its preparation method in this invention are analyzed as follows:

[0020] 1. This invention optimizes and improves the types and ratios of monomers. First, four monomers are copolymerized to obtain polyacrylic acid macromonomers. Then, unsaturated esters are grafted onto the tertiary carbon atoms of acrylic acid and polymerized to form a long-chain structure. The monomers on the main chain and side chains of the polymer do not contain ether bonds, thus avoiding the formation of hydrogen bonds between the hydroxyl groups on the PVA molecular chain and the ether bonds. Therefore, the adsorption model of polycarboxylic acid drag reducers on cement particles is not changed, and the compatibility of polycarboxylic acid drag reducers with PVA cement slurry systems is improved.

[0021] 2. The synthesized polymer drag reducer incorporates heat-resistant monomers into its main chain, such as 2-acrylamido-2-methylpropanesulfonic acid, sodium p-styrenesulfonate, and acrylamide, as well as fatty acid esters introduced on the side chain, all of which exhibit good heat resistance and do not decompose at high temperatures.

[0022] 3. The synthesized polymer drag reducer has active groups such as carboxylic acid group (-COOH) and sulfonic acid group (-SO3H) on its main chain, which can be effectively anchored to the surface of cement particles. The comb-shaped polymer drag reducer with a quaternary polymer as the main chain and polyvinyl fatty acid ester derivative as the side chain structure obtained by the two-step method is flexibly adsorbed on the surface of cement particles, with obvious steric hindrance effect, which improves the dispersion ability and rheological properties of polycarboxylic acid drag reducer.

[0023] 4. Compared with the traditional polycarboxylate drag reducer used in the building materials industry, the preparation method of the drag reducer for PVA cement slurry system in this invention requires more readily available raw materials, the entire reaction process is simple and controllable, there are no special requirements for equipment and experimental environment, the process flow is simple and easy to implement, and it has the application prospect of industrial production.

[0024] 5. The drag-reducing agent for PVA-type cement slurry system in this invention is applicable to different brands of G-grade oil well cement. It has the advantages of low dosage and good drag-reducing effect, while having no adverse effect on the thickening and compressive strength of PVA-type cement slurry system. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the specific embodiments of the present invention or related technologies, the accompanying drawings used in the description of the specific embodiments or related technologies will be briefly introduced below.

[0026] Figure 1 Thickening curve of PVA-based cement slurry system containing drag-reducing agent prepared in Example 2 at 52°C, provided as an embodiment of the present invention;

[0027] Figure 2 Thickening curve of PVA-based cement slurry system with drag-reducing agent prepared in Example 2 at 80°C, provided as an embodiment of the present invention. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention; that is, the described embodiments are merely a part of the embodiments of this invention, and not all of them.

[0029] Therefore, the following detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0030] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0031] Example 1:

[0032] (1) Weigh 16.56g of 2-acrylamido-2-methylpropanesulfonic acid, 72g of acrylic acid, 10.3g of sodium p-styrenesulfonate and 7.1g of acrylamide into a three-necked flask, add 70.6g of water to the three-necked flask to prepare a mixed aqueous solution with a mass concentration of 60%, stir evenly, add NaOH to adjust the pH of the mixed aqueous solution to 2.5, stir and heat to 40℃, weigh 0.8477g of ammonium persulfate and 0.53g of mercaptopropionic acid and add them to the mixed aqueous solution, react at a constant temperature of 40℃ for 5h to obtain a polyacrylic acid macromonomer for drag reduction.

[0033] (2) Add 688g of vinyl acetate, 0.808g of n-dodecyl mercaptan and 1191g of water to the polyacrylic acid macromonomer obtained in step (1) in sequence. Stir for 10 minutes between additions. After the water is added, raise the temperature to 50°C. After the temperature reaches 50°C, add 32g of benzoyl peroxide aqueous solution with a mass fraction of 20% dropwise to a three-necked flask. The dropwise addition time is 2 hours. After the dropwise addition is completed, continue to stir the reaction at a constant temperature for 2 hours. Adjust the pH to 5 with NaOH and cool to obtain a drag-reducing agent for PVA cement slurry system with a concentration of 40%, labeled as A1.

[0034] Example 2:

[0035] (1) Weigh 4.14g of 2-acrylamido-2-methylpropanesulfonic acid, 7.2g of acrylic acid, 4.12g of sodium p-styrenesulfonate and 2.13g of acrylamide and place them in a three-necked flask. Add 17.6g of water to the three-necked flask to prepare a mixed aqueous solution with a mass concentration of 50%. After stirring evenly, add NaOH to adjust the pH of the mixed aqueous solution to 5.0. Stir and heat to 55℃. Weigh 0.70g of ammonium persulfate and 0.37g of mercaptoacetic acid and add them to the mixed aqueous solution. React at a constant temperature of 55℃ for 4h to obtain a polyacrylic acid macromonomer for drag reduction.

[0036] (2) Add 215g of vinyl acetate, 0.3g of isopropanol and 758g of water to the polyacrylic acid macromonomer obtained in step (1) in sequence. Stir for 15min between additions. After the water is added, raise the temperature to 75℃. After the temperature reaches 75℃, add 13.95g of 20% dicyclohexyl peroxide dicarbonate aqueous solution to a three-necked flask dropwise over 2 hours. After the addition is completed, continue to stir the reaction at a constant temperature for 2 hours. Adjust the pH to 6 with NaOH and cool to obtain a drag-reducing agent for PVA cement slurry system with a concentration of 30%, labeled as A2.

[0037] Example 3:

[0038] (1) Weigh 12.4g of 2-acrylamido-2-methylpropanesulfonic acid, 7.2g of acrylic acid, 6.18g of sodium p-styrenesulfonate and 7.1g of acrylamide and place them in a three-necked flask. Add 49.4g of water to the three-necked flask to prepare a mixed aqueous solution with a mass concentration of 40%. After stirring evenly, add NaOH to adjust the pH of the mixed aqueous solution to 6.5. Stir and heat to 70℃. Weigh 1.65g of ammonium persulfate and 0.21g of mercaptopropionic acid and add them to the mixed aqueous solution. React at a constant temperature of 70℃ for 4h to obtain a polyacrylic acid macromonomer for drag reduction.

[0039] (2) Add 360g of vinyl propionate, 0.73g of n-dodecyl mercaptan and 867g of water to the polyacrylic acid macromonomer obtained in step (1) in sequence. Stir for 10min between additions. After the water is added, heat to 90℃. After the temperature reaches 90℃, add 19.6g of 30% diisopropyl peroxide dicarbonate aqueous solution to a three-necked flask dropwise over 3 hours. After the addition is completed, continue to stir at a constant temperature for 3 hours. Adjust the pH to 7 with NaOH and cool to obtain a 30% drag-reducing agent for PVA cement slurry system, labeled as A3.

[0040] Example 4:

[0041] (1) Weigh 10.8g of 2-acrylamido-2-methylpropanesulfonic acid, 36g of acrylic acid, 20.6g of sodium p-styrenesulfonate and 14.2g of acrylamide and place them in a three-necked flask. Add 100g of water to the three-necked flask to prepare a mixed aqueous solution with a mass concentration of 45%. After stirring evenly, add NaOH to adjust the pH of the mixed aqueous solution to 4.0. Stir and heat to 60℃. Weigh 2.45g of potassium persulfate and 3.95g of sodium methpropylenesulfonate and add them to the mixed aqueous solution. React at a constant temperature of 60℃ for 3h to obtain a polyacrylic acid macromonomer for drag reduction.

[0042] (2) Add 855g of vinyl butyrate, 0.45g of isopropanol and 4583g of water to the polyacrylic acid macromonomer obtained in step (1) in sequence. Stir for 15 minutes between additions. After adding water, adjust the temperature to 70°C. After adjusting the temperature to 70°C, add 46.8g of 20% lauroyl peroxide aqueous solution to a three-necked flask dropwise over 3 hours. After the addition is completed, continue to stir the reaction at a constant temperature for 2 hours. Adjust the pH to 6 with NaOH and cool to obtain a 20% drag-reducing agent for PVA cement slurry system, labeled A4.

[0043] Performance testing:

[0044] 1. Rheological properties of PVA-based cement slurry systems

[0045] To investigate the effects of the drag-reducing agent synthesized in this invention on the rheological properties, compressive strength, and thickening properties of PVA-based cement paste systems, a sulfonated aldehyde-ketone drag-reducing agent (denoted as D1) and a commercially available polycarboxylate drag-reducing agent (denoted as D2) were used as comparative examples for performance testing. Sulfonated aldehyde-ketone drag-reducing agent D1 was a solid drag-reducing agent, while commercially available polycarboxylate drag-reducing agent D2 was a liquid drag-reducing agent with an effective concentration of 30%. To compare the effects of the graft copolymer drag-reducing agent synthesized in this invention with those of sulfonated aldehyde-ketone drag-reducing agent D1 and commercially available polycarboxylate drag-reducing agent D2, the dosage of the three different drag-reducing agents was determined based on their effective concentration in the testing experiments, ensuring that the experiments were conducted under the same dosage conditions.

[0046] The preparation and performance testing methods of cement slurry were carried out in accordance with GB / T 19139-2012 "Test Methods for Oil Well Cement". The cement slurry formulation for the performance testing of the PVA-based cement slurry system using drag-reducing agents was: Grade G Shengwei oil well cement + drag-reducing agent (0-0.6%) + polyvinyl alcohol (PVA) type water loss reducing agent + defoamer + water. The prepared PVA-based cement slurry system had a liquid-to-solid ratio of 0.44 and a density of 1.90 g / cm³. 3 The amount of drag-reducing agent added is determined based on its physical state and effective concentration. The cement slurry system without drag-reducing agent is recorded as blank example D0. The addition amount of D1 is 0.12%, the addition amount of D2 is 0.4%, the addition amount of Example 2 (A2) and Example 3 (A3) is 0.4%, the addition amount of Example 1 (A1) is 0.3%, and the addition amount of Example 4 (A4) is 0.6% (the above / % refers to the mass percentage content of drag-reducing agent in G-grade Shengwei oil well cement).

[0047] 1. Rheological properties of PVA-based cement slurry systems

[0048] To investigate the effect of the drag-reducing agent of the present invention on the PVA-based cement slurry system after medium-temperature curing, the rheological parameters of the neat cement paste and PVA-based cement slurry systems with different drag-reducing agents of each embodiment and comparative example were measured at the same temperature (52℃ and 80℃). The test results are shown in Table 1 and Table 2.

[0049] Table 1. Rheological parameters of the paste containing drag-reducing agents prepared in Examples 1-4 and Comparative Example D2 drag-reducing agent:

[0050]

[0051]

[0052] Note: The cement slurry formula is: 100% Shengwei G-grade oil well cement + (0-0.6)% drag reducer + 44% tap water. (The percentages refer to the mass percentage of drag reducer in the Shengwei G-grade oil well cement.)

[0053] Table 2. Rheological parameters of PVA-based cement slurry systems with different drag-reducing agents.

[0054]

[0055] Note: The cement slurry formula is: 100% Grade G Shengwei oil well cement + (0-0.6)% drag reducer + 1.5% BZJS-2 + 44% tap water. (The percentages refer to the mass percentage of drag reducer and fluid loss reducer in Grade G Shengwei oil well cement.)

[0056] As shown in Table 1, after curing at certain temperatures (52℃ and 80℃), compared with blank pure cement paste, the pure cement paste with commercially available polycarboxylate drag reducer D2 and the drag reducer of the present invention both exhibited excellent rheological properties, with a flow index n≥0.72 and a consistency coefficient K<0.4. This indicates that both commercially available polycarboxylate drag reducer D2 and the drag reducer of the present invention have good dispersing effects on pure cement paste and significantly improve rheological properties.

[0057] Table 2 shows that after curing at certain temperatures (52℃ and 80℃), the rheological properties of PVA-based cement slurry systems with different drag-reducing agents varied greatly. Under the same effective solid content, sulfonated aldehyde-ketone drag-reducing agent D1 and commercially available polycarboxylate drag-reducing agent D2 had poor effects on improving the rheological properties of PVA-based cement slurry systems. At 52℃, both sulfonated aldehyde-ketone drag-reducing agent D1 and commercially available polycarboxylate drag-reducing agent D2 had a certain effect on reducing the dynamic shear force of PVA-based cement slurry systems. At 80℃, the commercially available polycarboxylate drag-reducing agent D2 had poor temperature resistance in PVA-based cement slurry systems, resulting in the cured cement slurry system being unable to flow and failing to play a dispersing role for PVA-based cement slurry systems. Compared with the comparative example, the drag-reducing agent of the present invention has a better dispersion effect on PVA-type cement slurry system and can significantly improve the rheological properties of PVA-type cement slurry system. Its rheological parameters can be adjusted as needed, with a flow index n≥0.72 and a consistency coefficient K<0.5.

[0058] As shown in Tables 1 and 2, both the commercially available polycarboxylate drag reducer D2 and the drag reducer of this invention significantly improve the rheological properties of pure cement paste at different temperatures. However, the commercially available polycarboxylate drag reducer D2 has poor compatibility with PVA-based cement paste systems, poor temperature resistance, and does not provide good dispersion for PVA-based cement paste systems, making it difficult to improve the rheological properties of the system. In contrast, the drag reducer of this invention has excellent dispersion effects on both pure cement paste systems and PVA-based cement paste systems, demonstrating a significant advantage in improving rheological properties.

[0059] 2. Compressive strength of PVA-based cement grout system

[0060] To investigate the effect of the drag-reducing agent of the present invention on the compressive strength of PVA-based cement slurry system after curing at a certain temperature, the compressive strength of cement stone of PVA-based cement slurry system with each embodiment and different drag-reducing agent added at different curing temperatures after 24 hours of curing was measured, and the ratio of its strength to that of blank cement slurry system was calculated. The test results are shown in Table 3.

[0061] Table 3 Compressive strength of PVA-based cement grout systems with drag-reducing agents

[0062]

[0063] Note: The cement slurry formula is: 100% Grade G Shengwei oil well cement + (0-0.6)% drag reducer + 1.5% BZJS-2 + 44% tap water. The curing conditions are: 52℃ and 80℃ water bath under normal pressure. (The percentages refer to the mass percentage of drag reducer and fluid loss reducer in Grade G Shengwei oil well cement.)

[0064] As shown in Table 3, the compressive strength of the cement stone of both PVA-based cement slurry systems without and with drag-reducing agents after curing in a normal pressure water bath at a certain temperature for 24 hours is greater than 23 MPa, and the ratio of compressive strength is not less than 0.95. This indicates that the drag-reducing agents in the embodiments of the present invention, commercially available polycarboxylate drag-reducing agents, and sulfonated aldehyde-ketone drag-reducing agents have almost no impact on the strength development of PVA-based cement slurry systems, thus meeting the requirements for cementing construction.

[0065] 3. Thickening properties of PVA-based cement slurry systems

[0066] To investigate the effect of the drag-reducing agent of the present invention on the thickening performance of PVA-based cement slurry system, the thickening performance of PVA-based cement slurry system with each embodiment and different drag-reducing agents added at different temperatures was experimentally determined, and the ratio of its thickening time to that of blank cement slurry system was calculated. The experimental results are shown in Table 4.

[0067] Table 4 Thickening properties of PVA-based cement slurry systems with drag-reducing agents

[0068]

[0069] Note: The cement slurry formula is: 100% Grade G Shengwei oil well cement + (0-0.6)% drag reducer + 1.5% BZJS-2 + 44% tap water. The experimental conditions are: 52℃ / 35.6MPa / 28min and 80℃ / 46.5MPa / 45min. (The percentages refer to the mass percentage of drag reducer and fluid loss reducer in Grade G Shengwei oil well cement).

[0070] As shown in Table 4, the thickening time of PVA-based cement slurry systems containing sulfonated aldehyde-ketone drag-reducing agents, commercially available polycarboxylate drag-reducing agents, and the drag-reducing agent of this invention was prolonged to varying degrees. Although the initial consistency of all systems decreased, the initial consistency of the PVA-based cement slurry system containing the drag-reducing agent of this invention decreased more significantly, with the initial consistency all less than 15 Bc and the thickening time ratio all less than 1.30. This indicates that the drag-reducing agent in the PVA-based cement slurry system of this invention has a weak retarding effect and does not adversely affect the thickening time of the cement slurry.

[0071] Figure 1 and Figure 2 The figures show the thickening curves of PVA-based cement slurry with the drag-reducing agent from Example 2 at 52℃ × 35.6 MPa and 80℃ × 46.5 MPa, respectively. Figure 1 and Figure 2 As can be seen from the results, the thickening curve of the PVA-based cement slurry system with the addition of Example 2 is stable. During the thickening experiment, the temperature and pressure in the thickening curve are smooth, and there are no abnormal thickening phenomena such as core encapsulation or step formation. This indicates that the drag-reducing agent has good dispersibility for the PVA-based cement slurry system and does not affect the normal thickening of the cement slurry system, thus meeting the requirements for cementing construction.

[0072] Those skilled in the art should recognize that the above embodiments are merely illustrative of the present invention and are not intended to limit the present invention. Any variations or modifications to the above embodiments that are within the spirit and essence of the present invention will fall within the scope of the claims of the present invention.

Claims

1. A drag-reducing agent for PVA-based cementitious grout systems, characterized in that, A mixed aqueous solution with a mass concentration of 40%-60% was prepared by mixing 2-acrylamido-2-methylpropanesulfonic acid, acrylic acid, sodium p-styrenesulfonate and acrylamide in a molar ratio of 0.08-0.6:1:0.05-0.3:0.1-1.0, and then polymerized to obtain polyacrylic acid macromonomers. The polymerization reaction of polyacrylic acid macromonomers and ethylene fatty acid esters yields a graft copolymerized PVA-based drag-reducing agent for cement slurry systems with a concentration of 20% to 40%, wherein the molar ratio of ethylene fatty acid esters to acrylic acid is 8-36:

1.

2. The drag-reducing agent for PVA-based cementitious slurry systems according to claim 1, characterized in that, The fatty acid vinyl esters include vinyl acetate, vinyl propionate, or vinyl butyrate.

3. A method for preparing a drag-reducing agent for a PVA-based cementitious slurry system as described in claim 2, characterized in that, Includes the following steps: (1) Quaternary polymerization: 2-Acrylamido-2-methylpropanesulfonic acid, acrylic acid, sodium p-styrenesulfonate and acrylamide are placed in a reaction vessel and water is added to prepare a mixed aqueous solution with a mass concentration of 40%~60%. The pH value of the mixed aqueous solution is adjusted to 2.5~6.5 by adding a pH adjuster. The mixture is stirred and heated to 40~80℃. A type A initiator and chain transfer agent are weighed and added to the mixed aqueous solution. The mixture is reacted at a constant temperature for 3~6h to obtain the polyacrylic acid macromonomer. The type A initiator is ammonium persulfate, potassium persulfate or sodium persulfate. (2) Graft copolymerization: Add the ethylene ester of fatty acid, molecular weight regulator and water to the polyacrylic macromonomer in sequence, with a stirring time of 10-15 min between each addition. After adding the above raw materials, heat to 50-90℃ and add a 20%-40% B-type initiator solution dropwise. After the dropwise addition is completed, continue to stir at a constant temperature for 1-3 hours. Adjust the pH to 5-7 with a pH regulator and cool to obtain a 20%-40% graft copolymerized PVA-type cement slurry system drag-reducing agent. The B-type initiator is benzoyl peroxide, lauroyl peroxide, diisopropyl peroxide, or dicyclohexyl peroxide.

4. The method according to claim 3, characterized in that, The pH adjuster mentioned in steps (1) and (2) is sodium hydroxide or potassium hydroxide.

5. The method according to claim 4, characterized in that, The amount of the Class A initiator is 0.8%-5.0% of the total mass of 2-acrylamido-2-methylpropanesulfonic acid, acrylic acid, sodium p-styrenesulfonate and acrylamide in step (1).

6. The method according to claim 5, characterized in that, The chain transfer agent is mercaptopropionic acid, mercaptoacetic acid, or sodium methacrylate sulfonate, and the molar ratio of the chain transfer agent to the acrylic acid in step (1) is 0.01-0.05:

1.

7. The method according to claim 3, characterized in that, The molecular weight regulator in step (2) is n-dodecyl mercaptan or isopropanol, and the molar ratio of the amount of the molecular weight regulator to the amount of the fatty acid ethylene ester is 0.0005-0.001:

1.

8. The method according to claim 7, characterized in that, The amount of the Class B initiator is 0.8%-1.5% of the total mass of the 2-acrylamido-2-methylpropanesulfonic acid, acrylic acid, sodium p-styrenesulfonate, acrylamide, and ethylene fatty acid ester.

9. The method according to claim 8, characterized in that, The amount of water used in step (2) is determined based on the required concentration of drag-reducing agent for the final PVA-type cement slurry system.

10. The method according to claim 8, characterized in that, The dropwise addition time of the type B initiator solution in step (2) is controlled at 2-5 hours.

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