Oil well cement fluid loss agent and preparation method thereof

Abstract

The invention discloses an oil well cement fluid loss agent and a preparation method thereof, and relates to the technical field of chemical additives. The fluid loss agent is prepared from the following raw materials in parts by mass through free radical aqueous solution polymerization and post-treatment: 20-45 parts of 2-acrylamido-2-methylpropanesulfonic acid; 15 to 35 parts of acrylic acid; 20 to 40 parts of antioxidant modified acrylamide; 5 to 20 parts of dimethyl diallyl ammonium chloride; 0.2 to 1.0 part of an initiator; 0.05 to 0.5 part of a chain transfer agent; 5 to 15 parts of a neutralizer; 80 to 150 parts of deionized water; and 10 to 30 parts of carrier salt. A hindered phenol antioxidant group is introduced into a polymerizable monomer in a chemical binding state and is copolymerized to a molecular chain, so that fixed-point free radical removal / chain oxidation blocking at a molecular level is realized, and the attenuation of the tackifying and adhesive protecting capability caused by main chain fracture is reduced, so that the rheology and water loss control maintaining trend after high-temperature aging is better.

Description

Technical Field

[0001] This invention relates to the field of chemical additives technology, specifically to an oil well cement fluid loss reducing agent and its preparation method. Background Technology

[0002] Cementing engineering for oil wells is a crucial step in the oil and gas exploration and development process, and its quality directly affects the lifespan and production of oil and gas wells. In cementing operations, fluid loss control agents are essential admixtures, whose main function is to control the fluid loss of the cement slurry, preventing thickening, decreased fluidity, and insufficient strength after curing due to excessive fluid loss. Currently, commonly used fluid loss control agents are mainly water-soluble polymers, such as polyvinyl alcohol, cellulose, and acrylamide / 2-acrylamido-2-methylpropanesulfonic acid (AM / AMPS) copolymers.

[0003] However, as oil and gas exploration moves towards deeper, ultra-deep wells and complex formations, bottomhole temperature and pressure conditions are becoming increasingly demanding. Traditional polymer-based fluid loss control agents face severe challenges under high-temperature and high-pressure environments. The main problem is that high temperatures easily trigger "thermal oxidative degradation" of the polymer molecular chains. In high-temperature, oxygen-rich environments or environments containing trace amounts of initiating impurities, the polymer backbone is susceptible to free radical attack and breakage, leading to a sharp decrease in molecular weight. This results in the loss of the polymer's thickening and protective properties, ultimately causing uncontrolled fluid loss in the cement slurry, leading to serious accidents such as channeling and cementing failure.

[0004] To address this issue, existing technologies typically employ a "physical blending" method, adding small-molecule antioxidants (such as hindered phenols and aromatic amines) to polymer solutions or powders. While this method can delay oxidation to some extent, it has significant drawbacks: first, the compatibility of small-molecule antioxidants with the polymer matrix is ​​poor, making them prone to migration and precipitation during long-term storage or use; second, because the antioxidants are in a free state, they cannot provide "site-specific protection" to the polymer chain at the molecular level, resulting in short-term temperature resistance and low anti-aging efficiency. Therefore, developing a novel monomer capable of directly bonding antioxidant functional groups to the polymer molecular chain and a corresponding dehydration-reducing agent is particularly important. Summary of the Invention

[0005] The purpose of this invention is to address the problems existing in the prior art by providing an oil well cement fluid loss control agent and its preparation method. This fluid loss control agent, through the introduction of antioxidant-modified monomers for multi-component copolymerization, chemically bonds antioxidant groups to the polymer molecular chain, endowing the material with "endogenous" antioxidant repair capabilities. This significantly improves its high-temperature aging resistance and rheological stability, effectively solving the problem of fluid loss control in deep well high-temperature cementing.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] First aspect: An oil well cement fluid loss reducing agent, which is prepared by free radical aqueous solution polymerization and post-treatment of the following raw materials in parts by weight:

[0008] 2-Acrylamido-2-methylpropanesulfonic acid: 20-45 parts;

[0009] Acrylic acid: 15-35 parts;

[0010] Antioxidant-modified acrylamide: 20-40 parts;

[0011] Dimethyl diallyl ammonium chloride: 5-20 parts;

[0012] Initiator: 0.2-1.0 parts;

[0013] Chain transfer agent: 0.05-0.5 parts;

[0014] Neutralizing agent: 5-15 parts;

[0015] Deionized water: 80-150 parts;

[0016] Carrier salt: 10-30 parts.

[0017] By adopting the above technical solution, the neutralizing agent is further described as an aqueous solution of sodium hydroxide, potassium hydroxide, or sodium carbonate; the neutralizing agent has a mass concentration of 10%-50%.

[0018] By adopting the above technical solution, the chain transfer agent is further selected from sodium hypophosphite, mercaptoacetic acid, or isopropanol.

[0019] Furthermore, by adopting the above technical solution, the initiator is an ammonium persulfate-sodium bisulfite redox system or azobisisobutyramidine hydrochloride.

[0020] By adopting the above technical solution, the carrier salt is one or a combination of at least two of potassium chloride, sodium chloride, sodium sulfate or sodium formate, and the carrier salt is added to the polymer colloid or solution after the polymerization reaction is completed and before drying.

[0021] Secondly: The preparation method of the modified antioxidant acrylamide is as follows:

[0022] S1. Dissolve a carboxyl-containing hindered phenolic antioxidant in anhydrous dichloromethane or anhydrous N,N-dimethylformamide. Under conditions of 0-5℃, add a carbodiimide condensing agent at a molar ratio of 1:1.0-1.2 between the carboxyl group in the antioxidant and the condensing agent, and add a catalytic amount of 4-dimethylaminopyridine to activate the carboxyl group.

[0023] S2. Then N-hydroxyethyl acrylamide is added to make the molar ratio of antioxidant to N-hydroxyethyl acrylamide 1:1.0-1.5. At the same time, 0.05%-0.1% of the polymerization inhibitor p-hydroxyanisole is added. The reaction is stirred at room temperature to 40°C and in the dark for 2-6 hours. After the reaction is completed, the by-products are filtered off and the solvent is removed by vacuum evaporation. The obtained product is washed with cold diethyl ether, recrystallized and vacuum dried to obtain antioxidant modified acrylamide with good free radical polymerization activity.

[0024] The carbodiimide condensing agent is selected from one or more of N,N′-dicyclohexylcarbodiimide, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride or diisopropylcarbodiimide;

[0025] The amount of 4-dimethylaminopyridine added is 1-10 mol% of the molar amount of the antioxidant.

[0026] The S1 reaction is stirred for 10-60 minutes;

[0027] The hindered phenolic antioxidant is 3-(3,5-di-tert-butyl-4-hydroxyphenyl)-3-(3-((4-hydroxyphenyl)(methyl)amino)phenyl)propionic acid.

[0028] By adopting the above technical solution, the structure of the hindered phenolic antioxidant is further as follows: .

[0029] By adopting the above technical solution, the reaction in the preparation of the modified antioxidant acrylamide is as follows: the "hindered phenolic antioxidant" in the raw material contains a carboxyl group (-COOH). Under the action of DCC / EDC / DIC (carbodiimide condensing agent) and the catalyst DMAP (4-dimethylaminopyridine), the carboxyl group is activated, generating an active intermediate (O-acylisourea). The added N-hydroxyethyl acrylamide (HEAA) contains a primary hydroxyl group (-OH). This hydroxyl group attacks the activated carboxyl group, undergoing nucleophilic substitution to form an ester bond (-COO-), while releasing urea byproducts (such as dicyclohexylurea, DCU). The addition of a polymerization inhibitor (p-hydroxyanisole) is to protect the double bond (C=C) in N-hydroxyethyl acrylamide and prevent it from undergoing self-polymerization during esterification.

[0030] By adopting the above technical solution, the structure of the modified antioxidant acrylamide is further as follows: .

[0031] Third aspect: A method for preparing an oil well cement fluid loss reducing agent, comprising the following steps:

[0032] (1) Monomer modification: Preparation of antioxidant modified acrylamide;

[0033] (2) Solution preparation and adjustment: Dissolve the 2-acrylamido-2-methylpropanesulfonic acid, acrylic acid, antioxidant modified acrylamide and dimethyldiallylammonium chloride in deionized water, add the neutralizing agent to adjust the pH value to 6-8, add the chain transfer agent, and mix evenly to obtain the reaction base solution;

[0034] (3) Polymerization reaction: After purging with nitrogen to remove oxygen, the initiator is added to carry out a free radical polymerization reaction to obtain a polymer colloid;

[0035] (4) Carrier composite: After granulation or shearing of the polymer colloid, the carrier salt is added and mixed evenly;

[0036] (5) Drying and pulverizing: The product mixed with carrier salt is dried and pulverized to obtain powdered oil well cement dehydration reducer.

[0037] By adopting the above technical solution, in step (2), 2-acrylamido-2-methylpropanesulfonic acid and acrylic acid are preferentially pre-neutralized with the neutralizing agent before use, and the degree of neutralization is controlled between 70% and 90%, and then mixed with other monomers.

[0038] By adopting the above technical solution, the polymerization reaction in step (3) is carried out by water bath constant temperature polymerization, the polymerization temperature is controlled at 50-70℃, and the reaction time is 3-5 hours; the initiator is added in batches, the first batch adds 60%-80% of the total amount, and the remaining initiator is added after 1-2 hours of reaction.

[0039] By adopting the above technical solution, the molar ratio of 2-acrylamido-2-methylpropanesulfonic acid: acrylic acid: antioxidant modified acrylamide: dimethyl diallyl ammonium chloride: initiator: chain transfer agent is further: 1:(1.5-3.0):(0.02-0.2):(0.2-0.8):(0.005-0.05):(0.002-0.05).

[0040] Fourth aspect: A cementing slurry, comprising G-grade oil well cement, water, and an oil well cement fluid loss reducing agent according to any one of claims 1-5, wherein the amount of fluid loss reducing agent added is 0.6%-1.5% of the cement mass.

[0041] Furthermore, by adopting the above technical solution, the oil well cement dehydration reducer described in this invention can also be used as a blending agent in marine cement, new wall materials, lightweight building materials, building energy-saving thermal insulation materials, and building energy-saving sound insulation materials to prepare high-performance products.

[0042] This invention effectively solves the technical problems of traditional polymer water loss control agents failing due to thermal oxidation degradation in high-temperature deep well environments and the easy migration and precipitation of physically compounded antioxidants through the organic synergy of "monomer molecular structure design" and "free radical copolymerization process". Its core mechanism lies in the following: the preparation process first utilizes a carbodiimide condensing agent to activate a carboxyl-containing hindered phenolic antioxidant, causing it to undergo an esterification reaction with N-hydroxyethyl acrylamide, successfully chemically bonding the antioxidant functional group to a polymerizable double-bonded monomer to obtain "antioxidant-modified acrylamide"; subsequently, this modified monomer is copolymerized in a specific ratio with 2-acrylamido-2-methylpropanesulfonic acid (AMPS) for temperature and salt resistance, acrylic acid (AA) for adsorption and hydration, and dimethyl diallyl ammonium chloride (DMDAAC) in a free radical aqueous solution. The synergistic effect of this formulation and process transforms the antioxidant from a traditional "physically free state" to a "chemically bound state," endowing the polymer molecular chain with "endogenous" antioxidant and repair capabilities. When high temperature and high pressure environments trigger free radical attacks, the hindered phenolic groups bonded to the polymer backbone can achieve "site protection" at the molecular level, promptly clearing free radicals and blocking chain reactions, thereby effectively preventing polymer backbone breakage and significantly improving the rheological stability and water loss control efficiency of the fluid loss reducer under harsh well conditions.

[0043] Compared with the prior art, the beneficial effects of the present invention are:

[0044] 1. Under the conditions of high temperature and high pressure in deep wells, the water loss reducing agent of this invention has a more lasting effect on inhibiting the filtration loss of cement slurry and a smaller performance degradation trend before and after aging, thereby reducing the risk of "uncontrolled water loss".

[0045] 2. By introducing hindered phenolic antioxidant groups into polymerizable monomers in a "chemically bound state" and copolymerizing them onto the molecular chain, "site-specific free radical scavenging / chain oxidation blocking" at the molecular level is achieved, reducing the decay of tackifying and protective properties caused by main chain breakage. Therefore, the rheological properties and controlled water loss retention trends after high-temperature aging are better.

[0046] 3. Compared with the traditional method of "physically blending" small molecule antioxidants into the system, this invention embeds the antioxidant function into the polymer structure, reducing the migration and precipitation tendency caused by poor compatibility, thereby improving the reliability and timeliness of storage and use. Attached Figure Description

[0047] Figure 1 This is the infrared spectrum of the hindered phenolic antioxidant of the present invention.

[0048] Figure 2 The infrared spectrum is shown for the modified antioxidant acrylamide prepared in Example 2 of this invention. Detailed Implementation

[0049] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0050] Preparation Example 1

[0051] Preparation of hindered phenolic antioxidants:

[0052] Raw material A: 3-(3-bromophenyl)-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid;

[0053] Raw material B: 4-(methylamino)phenol;

[0054] RuPhos: 2-Dicyclohexylphosphine-2',6'-diisopropoxy-1,1'-biphenyl;

[0055] 1,4-Dioxane: 1,4-dioxane;

[0056] Using a three-necked flask equipped with a mechanical stirrer, reflux condenser, and vent, 5.00 g of raw material A, 1.71 g of raw material B, 11.28 g of cesium carbonate, 2.15 g of RuPhos, and 60 ml of 1,4-Dioxane were added sequentially. The system was subjected to a "vacuum-nitrogen purging" cycle three times. Under nitrogen protection, 0.13 g of bis(di-benzylacetone)palladium was quickly added, and the system was evacuated and purged again to ensure oxygen-free conditions. The oil bath temperature was raised to 100.0 °C, and the mixture was stirred and refluxed for 15 h. After the reaction was completed, the reaction solution was cooled to room temperature and filtered through a diatomaceous earth filter to remove insoluble inorganic salts. The filter cake was washed with a small amount of ethyl acetate, and most of the 1,4-Dioxane was removed by rotary evaporation under reduced pressure. The concentrated residue was dissolved in water (50 mL) and ethyl acetate (25 mL), separated, and the aqueous phase was retained. The pH of the aqueous phase was adjusted to 3-4 by adding 2M HCl dropwise. The aqueous phase was extracted with ethyl acetate (3 × 80 mL), and the organic phases were combined and washed once with saturated brine (50 mL). The organic phase was dried over anhydrous Na2SO4 for 30 minutes, filtered, and concentrated to dryness under reduced pressure to obtain the crude product. The crude product was purified by silica gel column chromatography with a dichloromethane:methanol mixture of 20:1 as the eluent. The eluent was evaporated to dryness to obtain 3.49 g of hindered phenolic antioxidant.

[0057] Structural identification data of hindered phenolic antioxidants:

[0058] Mass spectrometry (MS) of hindered phenolic antioxidants: 476 M+1;

[0059] NMR of hindered phenolic antioxidants: δ 7.70 (s, 1H), 7.23 (s, 1H), 7.17-7.09 (m, 3H), 7.09-6.99 (m, 2H), 6.99-6.86 (m, 2H), 6.78-6.68 (m, 2H), 4.41 (tp, 1H), 4.33 (s, 1H), 3.28 (s, 3H), 3.09 (dd, 1H), 2.83 (dd, 1H), 1.42 (s, 18H);

[0060] For the infrared spectra of hindered phenolic antioxidants, see [link to relevant documentation]. Figure 1 .

[0061] Preparation Example 2

[0062] Preparation of modified antioxidant acrylamide:

[0063] S1. In a dry three-necked flask equipped with a mechanical stirrer, thermometer, and dropping funnel, add 3.00 g of the hindered phenolic antioxidant (3-(3,5-di-tert-butyl-4-hydroxyphenyl)-3-(3-((4-hydroxyphenyl)(methyl)amino)phenyl)propionic acid) obtained in Preparation Example 1, and add 30 mL of anhydrous N,N-dimethylformamide (DMF) to dissolve it completely. Maintain the system temperature at 0°C under ice-water bath conditions. Under nitrogen protection, add 1.10 molar amounts of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC·HCl) to the above solution, and add 5 mol% of 4-dimethylaminopyridine (DMAP) as a catalyst. Stir continuously for 30 min to activate the carboxyl groups in the hindered phenolic antioxidant molecule.

[0064] S2. Subsequently, while maintaining the system temperature no higher than 5°C, 1.2 molar amounts of N-hydroxyethylacrylamide were slowly added through a dropping funnel, along with 0.08% p-hydroxyanisole as a polymerization inhibitor. After the addition was complete, the ice-water bath was removed, and the reaction system was allowed to naturally heat to 35°C. The reaction was then stirred continuously for 4 hours under light-protected conditions. After the reaction was complete, the reaction solution was filtered to remove the generated urea byproducts. The filtrate was then evaporated under reduced pressure to remove the solvent. The resulting residue was washed three times with cold diethyl ether to remove unreacted raw materials and low-molecular-weight impurities. Subsequently, it was purified by recrystallization using an ethanol / diethyl ether system (ethanol:diethyl ether = 1:1.5 v / v). The final product was dried under vacuum at 40°C for 12 hours to obtain a pale yellow solid, which was the antioxidant-modified acrylamide monomer.

[0065] The infrared spectra of the modified antioxidant acrylamide are shown in Figure 2. (3300-3500 cm⁻¹) -1 An absorption band is shown at 3080-3020 cm⁻¹, corresponding to the stretching vibrations of amide-NH⁺ and hydroxyl groups; [the band appears in the 3080-3020 cm⁻¹ range].-1 A weak peak appears nearby, caused by the stretching vibration of CH, while the 2960-2860 cm⁻¹... -1 The -CH3 and -CH2- stretching vibrations of the tert-butyl and aliphatic chains are present at 1650-1670 cm⁻¹. -1 The strong absorption peak is for the amide carbonyl group (-CONH-), compared to the original carboxylic acid C=O (~1710 cm⁻¹). -1 A clear redshift indicates a successful reaction; at 1600-1500 cm⁻¹ -1 Multiple moderate-intensity peaks are visible within the range, corresponding to the C=C skeletal vibration of the aromatic ring; 1540-1555 cm⁻¹ -1 The appearance of amide II bands at 1450-1370 cm⁻¹ further confirms the formation of the amide structure; -1 The characteristic peak of deformation vibration of tert-butyl-C(CH3)3 was observed at 1260-1180 cm⁻¹. -1 The stretching vibrations are CN and CO of phenolic ethers and amides; while 990-910 cm -1 The region showed an out-of-plane bending vibration peak of the acrylamide end group =CH2. The infrared spectrum has confirmed successful conversion.

[0066] Comparative Preparation Example 1

[0067] The preparation of a modified antioxidant acrylamide is carried out by referring to the preparation method of Preparation Example 2, except that the hindered phenolic antioxidant is replaced with 3,5-di-tert-butyl-4-hydroxybenzoic acid, and the rest is the same as in Preparation Example 2.

[0068] Comparative Preparation Example 2

[0069] The preparation of a modified antioxidant acrylamide is carried out by referring to the preparation method of Preparation Example 2, except that the hindered phenolic antioxidant is replaced with β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid, and the rest is the same as in Preparation Example 2.

[0070] Examples 1-3, Comparative Examples 1-4

[0071] Preparation of an oil well cement fluid loss reducing agent:

[0072] 1. Raw material composition by weight, see Table 1:

[0073] Table 1

[0074] Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 2-Acrylamido-2-methylpropanesulfonic acid 45 45 45 45 45 45 45 acrylic acid 23.5 29.2 35 29.2 29.2 29.2 29.2 Antioxidant modified acrylamide 20 22.4 24.8 13.59 14.69 22.4 22.4 Dimethyldiallylammonium chloride 7 13.5 20 13.5 13.5 13.5 13.5 Initiator 0.3 0.65 1 0.65 0.65 0.65 0.65 Chain transfer agent 0.05 0.28 0.5 0.28 0.28 0.28 0.28 Neutralizing agent 5 10 15 10 10 10 10 Deionized water 80 115 150 115 115 115 115 carrier salt 10 20 30 20 20 20 20

[0075] The molar ratio of 2-acrylamido-2-methylpropanesulfonic acid, acrylic acid, antioxidant-modified acrylamide, dimethyldiallylammonium chloride, initiator, and chain transfer agent in Example 1 is approximately 1:1.50:0.16:0.20:0.005:0.002.

[0076] In Example 2, the molar ratio of 2-acrylamido-2-methylpropanesulfonic acid: acrylic acid: antioxidant-modified acrylamide: dimethyldiallyl ammonium chloride: initiator: chain transfer agent was approximately 1:1.86:0.18:0.38:0.011:0.014.

[0077] The molar ratio of 2-acrylamido-2-methylpropanesulfonic acid, acrylic acid, antioxidant-modified acrylamide, dimethyldiallylammonium chloride, initiator, and chain transfer agent in Example 3 is approximately 1:2.23:0.20:0.56:0.016:0.026.

[0078] The molar ratio of 2-acrylamido-2-methylpropanesulfonic acid, acrylic acid, antioxidant-modified acrylamide, dimethyldiallylammonium chloride, initiator, and chain transfer agent in Comparative Example 1 was approximately 1:1.86:0.18:0.38:0.011:0.014.

[0079] The molar ratio of 2-acrylamido-2-methylpropanesulfonic acid, acrylic acid, antioxidant-modified acrylamide, dimethyldiallylammonium chloride, initiator, and chain transfer agent in Comparative Example 2 was approximately 1:1.86:0.18:0.38:0.011:0.014.

[0080] The molar ratio of 2-acrylamido-2-methylpropanesulfonic acid, acrylic acid, antioxidant-modified acrylamide, dimethyldiallylammonium chloride, initiator, and chain transfer agent in Comparative Example 3 was approximately 1:1.86:0.89:0.38:0.011:0.014.

[0081] In Examples 1-3, the antioxidant-modified acrylamide was the antioxidant-modified acrylamide prepared in Example 2; in Comparative Examples 1-2, the antioxidant-modified acrylamide was the antioxidant-modified acrylamide prepared in Comparative Examples 1-2; in Comparative Example 3, N-hydroxyethyl acrylamide was used; and in Comparative Example 4, a mixture of N-hydroxyethyl acrylamide and antioxidant 1010 was used, with a mass ratio of 1:0.5.

[0082] The initiator is azobisisobutyramidine hydrochloride;

[0083] The chain transfer agent is sodium hypophosphite;

[0084] The neutralizing agent is a 30% sodium hydroxide aqueous solution;

[0085] The carrier salt is potassium chloride.

[0086] 2. Preparation method:

[0087] Add 80 parts of deionized water to a 500 mL three-necked flask and start mechanical stirring (500 rpm). Add 2-acrylamido-2-methylpropanesulfonic acid and acrylic acid sequentially, stirring until completely dissolved; then add 30% sodium hydroxide aqueous solution dropwise for pre-neutralization, controlling the neutralization degree of 2-acrylamido-2-methylpropanesulfonic acid and acrylic acid to 80%, and adjust the pH of the system to 7.0. Next, add antioxidant-modified acrylamide and dimethyldiallyl ammonium chloride, and continue stirring for 15 min to homogenize the system; then add sodium hypophosphite as a chain transfer agent to obtain the reaction base solution. The above formulation and dosage are shown in Table 1; place the reaction base solution in a 60℃ constant temperature water bath and purge with nitrogen to remove oxygen for 40 min (maintaining a slight positive pressure nitrogen protection). Azobisisobutyramidine hydrochloride (AIBA·2HCl) was dissolved in a small amount of deionized water and added as an initiator. 70% of the total amount was added initially, and polymerization was maintained at this temperature for 1.5 hours. The remaining 30% was then added, and the reaction continued at 60°C until the total polymerization time was 4 hours, yielding a polymer colloid. After polymerization, the mixture was cooled to room temperature, and the polymer colloid was sheared (high-speed shearing for 3 minutes). Ten parts of the carrier salt, potassium chloride, were then added and mixed thoroughly. The mixture was then dried in hot air circulation at 70°C until constant weight, pulverized, and sieved (60 mesh) to obtain the powdered oil well cement fluid loss reducer. The carrier salt was added "after polymerization and before drying."

[0088] Performance testing:

[0089] 1. Experimental materials: Grade G oil well cement, water, and fluid loss control agent. The fluid loss control agent dosage was 1.0% of the cement mass, and the water-cement ratio was 0.44. 10.0g of fluid loss control agent was first added to 440g of deionized water and magnetically stirred for 3 minutes (800rpm) to form a homogeneous solution / dispersion. The mixed water was poured into an API standard mixing cup, and the mixer was started at 4000rpm for 15 seconds of pre-mixing. 1000g of cement was added uniformly within 15 seconds; immediately after addition, the speed was increased to 12000rpm and high-speed mixing was performed for 35 seconds. After obtaining the cement slurry, it was allowed to stand for 2 minutes to defoam before use.

[0090] 2. High-Temperature and High-Pressure Water Loss: Heat the water loss meter to 90℃ and maintain the temperature for 10 minutes; fill the freshly mixed cement slurry into the HTHP water loss cup to the specified mark, add filter paper, and seal; after installing the water loss cup into the equipment, maintain a constant temperature of 90℃; apply a pressure difference of 6.9 MPa and start timing 30 minutes from the beginning of liquid discharge; collect the filtrate volume over 30 minutes and record it as V30 (mL); water loss FL (mL) = 2 × V30, and the data are shown in Table 2.

[0091] 3. Evaluation of heat and oxygen aging resistance:

[0092] Solution concentration: 1.00wt% (i.e., 1.00g water loss reducing agent + 99.0g deionized water);

[0093] Aging atmosphere: Air (sufficient air in the sealed reactor, no additional nitrogen is required);

[0094] Aging conditions: 150℃, 20h.

[0095] Prepare a 1.00wt% solution and stir for 10 min (600 rpm) until homogeneous; fill the solution into an aging vessel (the liquid filling rate is fixed at 70% of the vessel volume) and seal it; place it in an oven / oil bath and keep it at 150℃ for 16 h; remove it and let it cool naturally to 25℃ to obtain the "aging dehydration agent solution".

[0096] 3.1 Viscosity retention rate before / after aging: Rookfield viscometer, 25℃, rotor No. 2, speed 60 rpm, reading taken after 30s of stabilization. Measure the viscosity of the unaged 1.00wt% solution: η0 (mPa·s); Measure the viscosity of the aged solution: η1 (mPa·s); Calculate: Viscosity retention rate (%) = η1 / η0 × 100%, data are shown in Table 2.

[0097] 3.2 Changes in water loss under high temperature and pressure after aging: The water loss under high temperature and pressure was re-measured using "water loss reducing agent solution after aging" instead of the ordinary mixing water, and the change values ​​were calculated. The data are shown in Table 2.

[0098] Table 2

[0099] sample HTHP water loss FL η0 η1 Viscosity retention rate (%) Water loss (mL) of HTHP after aging Change in water loss ΔFL (mL) Example 1 48 220 180 81.8 54 6 Example 2 42 190 165 86.8 48 6 Example 3 40 160 132 82.5 50 10 Comparative Example 1 50 185 110 59.5 81 31 Comparative Example 2 52 180 95 52.8 91 39 Comparative Example 3 55 175 60 34.3 126 71 Comparative Example 4 53 178 85 47.8 101 48

[0100] The system in the example significantly outperformed the comparative examples in terms of initial controlled water loss, viscosity retention after thermo-oxidative aging, and stability of controlled water loss after aging. The core reason is that after the antioxidant groups are introduced into the polymer backbone / side chain through covalent bonding, they can more effectively and locally scavenge free radicals and inhibit chain oxidation reactions in a high-temperature oxygen-containing environment, reducing chain breakage and molecular weight decrease. Therefore, the solution viscosity decay is smaller, the polymer's adsorption-film formation / bridging ability on the cement particle surface is more stable, the resulting filter cake is denser and has lower permeability, resulting in smaller changes in water loss before and after aging. In contrast, the comparative examples without antioxidant structures are more prone to thermo-oxidative degradation, leading to a rapid decrease in viscosity, weakened blocking and water retention capacity, and significantly worsened water loss with aging. Although the physical compounding of hindered phenolic antioxidants can delay oxidation to some extent, it is limited by compatibility and migration / precipitation and cannot achieve "site protection". Therefore, its overall stability is between the two.

[0101] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An oil well cement fluid loss reducing agent, characterized in that, This water loss reducing agent is prepared from the following raw materials in parts by weight via free radical aqueous solution polymerization and post-treatment: 2-Acrylamido-2-methylpropanesulfonic acid: 20-45 parts; Acrylic acid: 15-35 parts; Antioxidant-modified acrylamide: 20-40 parts; Dimethyl diallyl ammonium chloride: 5-20 parts; Initiator: 0.2-1.0 parts; Chain transfer agent: 0.05-0.5 parts; Neutralizing agent: 5-15 parts; Deionized water: 80-150 parts; Carrier salt: 10-30 parts; The preparation method of the modified antioxidant acrylamide is as follows: S1. Dissolve a carboxyl-containing hindered phenolic antioxidant in anhydrous dichloromethane or anhydrous N,N-dimethylformamide. Under conditions of 0-5℃, add a carbodiimide condensing agent at a molar ratio of 1:1.0-1.2 between the carboxyl group in the antioxidant and the condensing agent, and add a catalytic amount of 4-dimethylaminopyridine to activate the carboxyl group. S2. Then N-hydroxyethyl acrylamide is added to make the molar ratio of antioxidant to N-hydroxyethyl acrylamide 1:1.0-1.

5. At the same time, 0.05%-0.1% of the polymerization inhibitor p-hydroxyanisole is added. The reaction is stirred at room temperature to 40°C and in the dark for 2-6 hours. After the reaction is completed, the by-products are filtered off and the solvent is removed by vacuum evaporation. The obtained product is washed with cold diethyl ether, recrystallized and vacuum dried to obtain antioxidant modified acrylamide with good free radical polymerization activity. The carbodiimide condensing agent is selected from one or more of N,N′-dicyclohexylcarbodiimide, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride or diisopropylcarbodiimide; The amount of 4-dimethylaminopyridine added is 1-10 mol% of the molar amount of the antioxidant. The S1 reaction is stirred for 10-60 minutes; The hindered phenolic antioxidant is 3-(3,5-di-tert-butyl-4-hydroxyphenyl)-3-(3-((4-hydroxyphenyl)(methyl)amino)phenyl)propionic acid.

2. The oil well cement fluid loss reducing agent according to claim 1, characterized in that, The neutralizing agent is an aqueous solution of sodium hydroxide, potassium hydroxide, or sodium carbonate; The neutralizing agent has a mass concentration of 10%-50%.

3. The oil well cement fluid loss reducing agent according to claim 1, characterized in that, The chain transfer agent is selected from sodium hypophosphite, mercaptoacetic acid, or isopropanol.

4. The oil well cement fluid loss reducing agent according to claim 1, characterized in that, The initiator is an ammonium persulfate-sodium bisulfite redox system or azobisisobutyramidine hydrochloride.

5. The oil well cement fluid loss reducing agent according to claim 1, characterized in that, The carrier salt is one or a combination of at least two of potassium chloride, sodium chloride, sodium sulfate, or sodium formate, and the carrier salt is added to the polymer colloid or solution after the polymerization reaction is completed and before drying.

6. A method for preparing an oil well cement fluid loss reducing agent as described in any one of claims 1-5, characterized in that, Includes the following steps: (1) Monomer modification: Preparation of antioxidant modified acrylamide; (2) Solution preparation and adjustment: Dissolve the 2-acrylamido-2-methylpropanesulfonic acid, acrylic acid, antioxidant modified acrylamide and dimethyldiallylammonium chloride in deionized water, add the neutralizing agent to adjust the pH value to 6-8, add the chain transfer agent, and mix evenly to obtain the reaction base solution; (3) Polymerization reaction: After purging with nitrogen to remove oxygen, the initiator is added to carry out a free radical polymerization reaction to obtain a polymer colloid; (4) Carrier composite: After granulation or shearing of the polymer colloid, the carrier salt is added and mixed evenly; (5) Drying and pulverizing: The product mixed with carrier salt is dried and pulverized to obtain powdered oil well cement dehydration reducer.

7. The method for preparing an oil well cement fluid loss reducing agent according to claim 6, characterized in that, In step (2), 2-acrylamido-2-methylpropanesulfonic acid and acrylic acid are preferentially pre-neutralized with a neutralizing agent before use, and the degree of neutralization is controlled between 70% and 90%, before being mixed with other monomers.

8. The method for preparing an oil well cement fluid loss reducing agent according to claim 6, characterized in that, The polymerization reaction in step (3) is carried out by water bath constant temperature polymerization, the polymerization temperature is controlled at 50-70℃, and the reaction time is 3-5 hours; the initiator is added in batches, the first batch is 60%-80% of the total amount, and the remaining initiator is added after 1-2 hours of reaction.

9. The method for preparing an oil well cement fluid loss reducing agent according to claim 6, characterized in that, The molar ratio of 2-acrylamido-2-methylpropanesulfonic acid: acrylic acid: antioxidant modified acrylamide: dimethyl diallyl ammonium chloride: initiator: chain transfer agent is 1:(1.5-3.0):(0.02-0.2):(0.2-0.8):(0.005-0.05):(0.002-0.05).

10. A cementing slurry, characterized in that, The composition comprises G-grade oil well cement mud, water, and an oil well cement fluid loss reducing agent according to any one of claims 1-5, wherein the amount of fluid loss reducing agent added is 0.6%-1.5% of the cement mass.

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