Preparation method of a fluid loss additive, and water-based drilling fluid resistant to 230 DEG C high temperature and preparation method thereof

Abstract

This invention discloses a method for preparing a filtration loss reducer, a water-based drilling fluid resistant to 230℃, and their preparation methods, belonging to the field of petroleum drilling technology. The filtration loss reducer is prepared by RAFT polymerization of 2-vinylnaphthalene, acrylic acid, and maleic anhydride to form a copolymer intermediate with a molecular weight of 1000-2500. After modification with hydrophilic monomers, it is copolymerized with maleic anhydride and grafted with vinylphosphonic acid, with precise control over the proportions of each raw material. The drilling fluid is prepared using water, compounded with slurry clay, the filtration loss reducer, and sulfonated lignite resin and other heat-resistant components. The components are added in stages, and the mixture is stirred at high speed until fully mixed. The filtration loss reducer prepared by this invention possesses 230℃ heat resistance, water solubility, and resistance to salt and calcium contamination. The drilling fluid forms a synergistic heat-resistant system, exhibiting low filtration loss and stable rheological properties at 230℃. The preparation process is simple and easy to operate on-site, suitable for the high-temperature and high-pressure drilling requirements of deep wells.

Description

Technical Field

[0001] This invention relates to the field of oil drilling technology, and in particular to a method for preparing a filtration loss reducer, a water-based drilling fluid resistant to 230°C, and a method for preparing the same. Background Technology

[0002] With the continued growth of global energy demand and the expansion of oil and gas exploration and development into deeper and ultra-deep formations, the formation temperatures encountered during drilling are increasing, and ultra-deep wells with bottom-hole temperatures exceeding 200°C are becoming more common. Drilling fluid, as the "blood" of drilling operations, directly affects the safety and efficiency of drilling operations due to its high-temperature stability.

[0003] Water-based drilling fluids are low-cost and environmentally friendly, but conventional systems generally suffer from problems such as treatment agent degradation, system thickening, uncontrolled filtration loss, and rheological deterioration at temperatures exceeding 200°C, making them unsuitable for ultra-deep well drilling. Oil-based drilling fluids, while exhibiting good temperature resistance, are expensive and require complex environmental treatment.

[0004] While there are reports on water-based drilling fluid formulations with a temperature resistance of 180-200℃ in the existing technology, after long-term (e.g., more than 72 hours) hot rolling aging at temperatures of 230℃ and above, they generally suffer from prominent problems such as degradation and failure of the core treatment agent, uncontrolled rheological properties of the system (excessive thickening or thinning), and a sharp increase in filtration loss under high temperature and high pressure. These issues make it difficult to ensure safe and efficient drilling of the entire section of ultra-deep wells.

[0005] Therefore, developing a water-based drilling fluid system that can withstand high temperatures of 230℃ for a long time and has excellent comprehensive performance is of great significance for the safe and efficient development of deep oil and gas resources and is of great importance to realizing the national strategy of "marching into the depths of the earth". Summary of the Invention

[0006] The present invention aims to provide a method for preparing a filtration loss reducer, a water-based drilling fluid resistant to 230℃ high temperature, and a method for preparing the same.

[0007] The technical solution adopted in this invention is: A method for preparing a filtration loss reducing agent includes the following steps: Step S1: Using 2-vinylnaphthalene, acrylic acid, and maleic anhydride as main raw materials, a polymer intermediate with a molecular weight of 1000-2500 is synthesized via RAFT polymerization. Then, a free radical grafting reaction is carried out with the intermediate to obtain a hydrophilic modified macromolecular copolymer. The mass ratio of 2-vinylnaphthalene, acrylic acid, and maleic anhydride is (0.2-0.4):1.5:(0.5-0.8); the mass of the hydrophilic modified monomer is 3-5 wt% of the polymer intermediate. Step S2 involves first performing a free radical copolymerization reaction between the hydrophilic modified macromolecular copolymer obtained in step S1 and maleic anhydride, 2-acrylamido-2-methylpropanesulfonic acid (AMPS), N-vinylpyrrolidone (NVP), and N,N-dimethylacrylamide (DMAA); then performing a grafting reaction with vinylphosphonic acid to obtain a filtration loss reducer. The weight ratio of the hydrophilic modified macromolecular copolymer to maleic anhydride, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone, and N,N-dimethylacrylamide is 1:(0.3~0.5):(1.0~1.5):(0.4~0.6):(0.2~0.4). The amount of vinylphosphonic acid used is 5~10 wt% of the total weight of the hydrophilic modified macromolecular copolymer, maleic anhydride, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone, and N,N-dimethylacrylamide.

[0008] Further, the preparation process of the polymer intermediate in step S1 includes: mixing 2-vinylnaphthalene, acrylic acid, maleic anhydride with RAFT reagent, first initiator and solvent according to the ratio, maintaining a nitrogen atmosphere, reacting at 60~80℃ and stirring speed of 600~1000r / min for 4~6h, adding anhydrous ethanol to precipitate, washing with water 2~3 times, and then vacuum drying at 50~60℃ to obtain the polymer intermediate. This invention clarifies the specific preparation process details of polymer intermediates. Anhydrous ethanol precipitation can efficiently precipitate RAFT polymerization products, achieving the separation of copolymers from unreacted monomers, RAFT reagents, and initiator residues. Washing with water 2-3 times further removes adsorbed impurities, and vacuum drying at 50-60℃ to a moisture content of ≤1% avoids copolymer structure damage caused by high-temperature drying and ensures the purity and dryness of the copolymer. This effectively prevents problems such as low grafting rate and uneven reaction in subsequent hydrophilic modification reactions due to the presence of impurities or moisture. Precise polymerization reaction conditions ensure that the molecular weight of polymer intermediates is strictly controlled within the range of 1000-2500, with a narrow molecular weight distribution and high product performance consistency, providing a structurally uniform basic raw material for subsequent hydrophilic modification and copolymer chain extension.

[0009] Furthermore, the RAFT reagent is one or both of benzyl dithiobenzoate and cyanoisopropyl dithiobenzoate, and its addition amount is 0.2~0.4% of the total mass of 2-vinylnaphthalene, acrylic acid, and maleic anhydride; And / or, the first initiator is azobisisobutyronitrile or benzoyl peroxide, and its addition amount is 0.3~0.8% of the total mass of 2-vinylnaphthalene, acrylic acid, and maleic anhydride; And / or, the solvent is one or more of 1,4-dioxane, butyl acetate, tetrahydrofuran, N,N-dimethylformamide, and dipropylene glycol dimethyl ether, and the amount used is 5 to 10 times the total mass of 2-vinylnaphthalene, acrylic acid, and maleic anhydride. This invention specifies the exact selection and dosage of the RAFT reagent, the first initiator, and the solvent. The RAFT reagent is selected from benzyl dithiobenzoate and cyanoisopropyl dithiobenzoate, with an addition of 0.2-0.4% to precisely control the RAFT polymerization process, ensuring that the molecular weight of the polymer intermediate is accurately controlled within the range of 1000-2500, and that the molecular weight distribution is narrow. The first initiator is selected from oil-soluble azobisisobutyronitrile or benzoyl peroxide, which are perfectly compatible with the organic solvent system. An optimized addition of 0.3-0.8% satisfies the initiation requirements of the polymerization reaction while avoiding the problems of increased side reactions and a wider molecular weight distribution caused by excessive initiator. Organic solvents such as 1,4-dioxane and butyl acetate are selected, which have good compatibility with oil-soluble 2-vinylnaphthalene and other monomers. A dosage of 5-10 times ensures that the monomers are fully dissolved and the reaction is uniform, avoiding uneven product structure caused by localized polymerization, and further improving the product quality of the polymer intermediate.

[0010] Further, the preparation process of the hydrophilic modified macromolecular copolymer in step S1 is as follows: the polymer intermediate, the hydrophilic modified monomer, the second initiator, and the water-acetone mixed solvent are mixed according to the formula, and the free radical grafting reaction is carried out at 60~80℃ and 600~1000r / min for 0.5~1h under nitrogen atmosphere. Then, the water-acetone mixed solvent is removed by rotary evaporation under reduced pressure at 40~50℃ to obtain the hydrophilic modified macromolecular copolymer. This invention clarifies the specific preparation process of hydrophilic modified macromolecular copolymers. Covalent bonding between the hydrophilic modified monomer and the polymer intermediate is achieved through a free radical grafting reaction. The grafting reaction conditions are mild and seamlessly integrated with the preceding RAFT polymerization process. The water-acetone mixed solvent is removed by vacuum rotary evaporation at 40-50°C, which efficiently removes the solvent at low temperatures, avoiding thermal degradation of the copolymer or loss of hydrophilic side chains caused by high-temperature solvent removal. Simultaneously, vacuum rotary evaporation leaves no solvent residue, ensuring the purity of the hydrophilic modified macromolecular copolymer and preventing solvent residue from affecting subsequent copolymerization and chain extension reactions. The resulting hydrophilic modified macromolecular copolymer exhibits significantly improved water solubility and retains complete copolymerization active sites, allowing it to directly participate in subsequent aqueous phase polymerization reactions.

[0011] Furthermore, the hydrophilic modifying monomer is polyethylene glycol methacrylate or hydroxyethyl methacrylate; And / or, the second initiator is an ammonium persulfate-sodium bisulfite compound initiator with a mass ratio of 1:1, and its dosage is 0.2~0.5% of the total mass of the polymer intermediate and the hydrophilic modified monomer; And / or, the water-acetone mixed solvent is composed of water and acetone in a volume ratio of 2:1, and its amount is 3 to 5 times the total mass of the polymer intermediate and the hydrophilic modified monomer. This invention specifies the exact selection, ratio, and dosage of the hydrophilic modified monomer, the second initiator, and the water-acetone mixed solvent. The hydrophilic modified monomer is selected from polyethylene glycol methacrylate or hydroxyethyl methacrylate. These short-chain hydrophilic compounds have good compatibility with drilling fluid systems and excellent thermal stability, and will not degrade at 230°C. The second initiator is a 1:1 mixture of ammonium persulfate and sodium bisulfite initiator. An addition of 0.2-0.5% can efficiently initiate the aqueous free radical grafting reaction. The mixture system has high initiation efficiency and a mild reaction. The water-acetone volume ratio is optimized to 2:1 to increase the proportion of the aqueous phase, ensuring the dissociation efficiency of the water-soluble initiator and improving the hydrophilic modification grafting rate. Simultaneously, a solvent dosage of 3-5 times ensures thorough mixing of the polymer intermediate and the hydrophilic modified monomer, achieving uniform grafting. The resulting hydrophilic modified macromolecular copolymer exhibits both good water solubility and thermal stability, making it fully compatible with subsequent aqueous copolymerization and chain extension processes.

[0012] Further, the preparation process of the filtration loss reducer in step S2 includes: mixing the hydrophilic modified macromolecular copolymer, maleic anhydride, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone, N,N-dimethylacrylamide with the third initiator and water-glycerol mixed solvent according to the formula, maintaining a nitrogen atmosphere, and performing a free radical copolymerization reaction at 50~70℃ and a stirring speed of 800~1200r / min for 2~3h; then adding vinylphosphonic acid and the fourth initiator, and performing a grafting reaction at 70~90℃ and a stirring speed of 800~1200r / min for 1~2h, cooling to room temperature, and then granulating by shearing, drying at 100~120℃, and pulverizing to 200~400 mesh to obtain the filtration loss reducer. This invention clarifies the complete copolymerization, chain extension, and grafting process details of the filtration loss reducer. The staged free radical copolymerization and grafting reaction conditions are mild and perfectly matched with the reactive sites of the hydrophilic modified macromolecular copolymer, ensuring the efficient polymerization of each monomer. The vinylphosphonic acid grafting temperature of 70~90℃ ensures the grafting efficiency of the phosphonic acid group while avoiding damage to the main chain structure caused by high temperature. After cooling, the filtration loss reducer is sheared, granulated, dried to a moisture content of less than 7%, and pulverized to 200~400 mesh. The standardized post-processing process makes the filtration loss reducer a fine powder solid, which dissolves quickly and disperses evenly in water-based drilling fluids without additional grinding and can be directly applied on-site. The 200~400 mesh particle size design ensures the solubility of the product while avoiding dust problems caused by excessively fine particle size, balancing performance and ease of operation.

[0013] Furthermore, the third initiator is a compound initiator of ammonium persulfate and sodium bisulfite, with a mass ratio of 1:1, and its dosage is 0.2~0.5% of the total mass of the hydrophilic modified macromolecular copolymer, maleic anhydride, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone, and N,N-dimethylacrylamide. And / or, the water-glycerol mixed solvent is composed of water and glycerol in a volume ratio of 4:1, and its amount is 4 to 5 times the total mass of the hydrophilic modified macromolecular copolymer, maleic anhydride, 2-acrylamide-2-methylpropanesulfonic acid, N-vinylpyrrolidone, and N,N-dimethylacrylamide. And / or, the fourth initiator is an ammonium persulfate-sodium bisulfite composite initiator with a mass ratio of 1:1, and its dosage is 0.2-0.4% of the total mass of the hydrophilic modified macromolecular copolymer, maleic anhydride, 2-acrylamide-2-methylpropanesulfonic acid, N-vinylpyrrolidone, N,N-dimethylacrylamide, and vinylphosphonic acid. This invention specifies the specific selection, ratio, and dosage of the third initiator, the water-glycerol mixed solvent, and the fourth initiator. The third initiator is an ammonium persulfate-sodium bisulfite composite initiator at a 1:1 ratio, and an addition of 0.2-0.5% can efficiently initiate the aqueous copolymerization chain extension reaction, ensuring the smooth synthesis of the branched copolymer. The water-glycerol volume ratio is optimized to 4:1, reducing the proportion of glycerol, which retains the dispersing and stabilizing effect of glycerol on the system while avoiding uneven monomer mixing and reduced reaction efficiency caused by high viscosity. To address the issue of low concentrations, a dosage of 4-5 times ensured the full dissolution and reaction of each monomer. The fourth initiator dosage was optimized to 0.2-0.4%, compensating for the thermal decomposition of the initiator at grafting temperatures of 70-90℃. This ensured efficient grafting of vinylphosphonic acid, enabling the successful introduction of phosphonic acid groups into the filtration loss reducer. These groups form dual salt- and calcium-resistant functional groups with the sulfonic acid groups of AMPS, significantly improving the performance of the filtration loss reducer in high-salt- and calcium-rich environments. Simultaneously, all reagents are compatible with the drilling fluid system, with no introduction of impurity ions, ensuring the stability of the subsequent drilling fluid system.

[0014] A water-based drilling fluid resistant to high temperatures of 230°C, comprising, by weight: Water, 100 portions; Mix 2.0 to 3.5 parts of mortar. Soda ash, 0.06~0.18 parts; The filtration loss reducing agent prepared by the aforementioned method, 2.5~4.0 parts; Sulfonated lignite resin, 2.0~4.0 parts; Natural bitumen powder, 10.0~18.0 parts; Lubricant, 3.0~6.0 parts; Sealing agent, 0.5~4.0 parts; Dilute the stabilizer to 1.0~2.0 parts; Emulsifier, 0.1~1.0 parts; Shale inhibitor, 5.0~10.0 parts; Barite powder, 47 parts.

[0015] Furthermore, the mortar mix is ​​selected from one of sepiolite, attapulgite, or drilling-grade bentonite; And / or, the particle size of natural bitumen powder is 300~400 mesh, and the softening point is higher than 200℃; And / or, the lubricant is #0 diesel fuel; And / or, the plugging agent is one or both of rigid calcium carbonate or chemical film-forming plugging agent (CN106479456B) with particle size distribution, wherein the rigid calcium carbonate is distributed in a ratio of 400 mesh calcium carbonate: 600 mesh calcium carbonate: 1000 mesh calcium carbonate = 1:1:1, and the chemical film-forming plugging agent emulsion particle size covers the nano-micron level; And / or, the high-temperature dilution stabilizer is a polycarboxylate-type dilution stabilizer with a temperature resistance of over 230°C; And / or, the high-temperature emulsifier is a fatty acid polyamide type emulsifier with a temperature resistance of over 230°C; And / or, the shale inhibitor is potassium chloride; And / or, the barite powder is high-density barite powder with a density ≥ 4.30 g / cm³. This invention specifies the specific selection and parameters of each functional component of the drilling fluid. The slurry mix uses sepiolite, attapulgite, or drilling-grade bentonite; the natural asphalt powder is limited to a particle size of 300-400 mesh and a softening point higher than 200℃. The fine particle size enables micropore sealing, and the high softening point ensures it does not melt at 230℃, providing long-term stable sealing performance; the lubricant is 0# diesel oil, suitable for high-temperature and high-salt drilling environments, offering excellent lubrication; the plugging agent uses rigid calcium carbonate with a wide particle size range or chemical film-forming plugging agents with nano- or micron-sized particles. The particle size matches the formation porosity, resulting in high sealing efficiency and compatibility with the drilling fluid system. It exhibits good compatibility; the polycarboxylate-based diluent stabilizer effectively regulates drilling fluid rheology at 230℃, preventing high-temperature viscosity increase; the fatty acid polyamide emulsifier is non-ionic, exhibiting strong resistance to salt and calcium, and its addition of 0.5~1.0% can achieve system stability without the risk of demulsification; the shale inhibitor uses potassium chloride, which is inexpensive, has a significant inhibitory effect, and does not conflict with other treatment agents; the barite powder has a density ≥4.30g / cm³; the precise selection of each component further enhances the drilling fluid system's long-term stability, plugging properties, inhibitory properties, and lubrication at 230℃, resulting in high construction safety.

[0016] A method for preparing a water-based drilling fluid resistant to 230℃ high temperature, used to prepare the aforementioned water-based drilling fluid resistant to 230℃ high temperature, includes the following steps: Step S1, base slurry preparation: Add the slurry mix and soda ash to the water in sequence, stir at 11000~12000r / min for 20~30min to form a uniform base slurry, and cure at room temperature for more than 24 hours to allow it to be fully prehydrated; Step S2, Addition of Filtration Loss Reduction System: Add the filtration loss reduction agent to the base slurry obtained in Step S1, and stir at high speed of 11000~12000 r / min for 10~15 min; then continue to add sulfonated lignite resin and natural asphalt powder, and stir at high speed of 11000~12000 r / min for 5~10 min; finally, add a caustic soda solution with a mass concentration of 30~40% to adjust the pH value of the system to 9~10; Step S3, adding lubricating components: add lubricant to the slurry obtained in step S2, and stir at high speed of 11000~12000r / min for 5-10min; Step S4, Adding the sealing component: Add the sealing agent to the slurry obtained in step S3, and stir at a high speed of 11000~12000r / min for 5-10min; Step S5, addition of high temperature synergistic additives: add high temperature diluent and stabilizer and high temperature emulsifier to the slurry obtained in step S4 in sequence. After each treatment agent is added, stir at high speed of 11000~12000r / min for 5-10min. Step S6, Addition of inhibitory components: Add shale inhibitor to the slurry obtained in step S5, and stir at high speed of 11000~12000r / min for 15-20min; Step S7, Weighting and Adjustment: Add barite powder to the slurry obtained in step S6, and stir at a high speed of 11000~12000r / min for more than 30min until the density is uniform and there are no particle agglomerations, to obtain a water-based drilling fluid resistant to 230℃ high temperature.

[0017] The beneficial effects of this invention are: 1. This invention precisely prepares a low molecular weight polymer intermediate (i.e., a 2-vinylnaphthalene-acrylic acid-maleic anhydride macromolecular copolymer) of 1000-2500 through RAFT polymerization. The low molecular weight design avoids molecular chain deentanglement and thermal degradation at high temperatures. The rigid naphthalene ring of the high proportion of 2-vinylnaphthalene provides a structural basis for the filtration loss reducer to be stable at 230℃ for a long time. The grafting of 3-5 wt% low proportion of hydrophilic modified monomers significantly improves the water solubility of the polymer intermediate and ensures subsequent polymerization in the aqueous phase, while retaining the rigid structure of the naphthalene ring to the greatest extent and avoiding excessive hydrophilic chains that reduce thermal stability. Subsequently, through precise ratio of free radical copolymerization chain extension and vinylphosphonic acid grafting, a dual salt-calcium-resistant functional group structure containing sulfonic acid group and phosphonic acid group is constructed. The ratio of each monomer is adapted to the high temperature drilling requirements of 230℃. The final filtration loss reducer can still effectively adsorb onto clay particles at the extreme high temperature of 230℃, playing the role of protecting the colloid and reducing filtration loss. At the same time, it provides a core adaptable treatment agent for subsequent water-based drilling fluid systems resistant to 230℃.

[0018] 2. The water-based drilling fluid system of this invention is constructed using a modular approach, achieving synergistic effects among key components. A self-made filtration loss reducer (main filtration loss reduction module), sulfonated lignite resin (auxiliary filtration loss reduction module), and natural bitumen powder (auxiliary filtration loss reduction module) form a "rigid-flexible" filtration loss control network. Rigid plugging agents (calcium carbonate) and elastic plugging agents (chemical film-forming plugging agents), used individually or in combination (plugging modules), effectively seal micro-fractures. Synergistic effects with lubricants and shale inhibitors at high temperatures ensure the overall performance of the system at high temperatures. Pre-added high-temperature diluents and stabilizers effectively suppress drill cuttings dispersion, clay flocculation, and system thickening caused by high temperatures. After hot rolling aging at 230℃ for 72 hours, the system exhibits stable rheology (apparent viscosity increase less than 6%), with no significant thickening or gelation, demonstrating excellent long-term thermal stability. Furthermore, the water-based drilling fluid of this invention maintains excellent comprehensive performance even after long-term high-temperature aging at 230℃: ① Excellent rheological properties, with good shear dilution and rock-carrying capacity; ② Low filtration loss, with high-temperature high-pressure (HTHP) filtration loss stably controlled below 21.0 mL, which is beneficial to wellbore stability; ③ Strong inhibition, effectively inhibiting shale hydration and dispersion; ④ Good lubricity, with extreme pressure lubrication coefficient reduced to below 0.11, fully meeting the requirements for safe drilling in ultra-deep wells. Moreover, the main treatment agents in the water-based drilling fluid system of this invention are non-toxic or low-toxic, with better biodegradability than oil-based systems, offering significant environmental advantages. Furthermore, its system cost is far lower than that of oil-based drilling fluids, and the preparation process is simple and clear. All steps can be completed using conventional drilling fluid mixing equipment without special processes, facilitating rapid on-site preparation and large-scale application.

[0019] 3. This invention clarifies the specific preparation process of a water-based drilling fluid resistant to 230℃ high temperature. Each functional component is added in stages, and after each component is added, high-speed stirring at 11000~12000 r / min is used to ensure that each component is fully dispersed and uniformly mixed in the drilling fluid, avoiding system inhomogeneity and performance fluctuations caused by excessively high local concentrations. The base slurry is cured for more than 24 hours to ensure full pre-hydration of the slurry mix, guaranteeing the basic colloidal stability of the drilling fluid. A 30% mass concentration caustic soda solution is used to adjust the pH to 9~10, precisely controlling the pH value of the system and avoiding solidification. The direct addition of caustic soda can prevent excessively high local pH values. This ensures that all treatment agents remain stable within a suitable pH environment. After adding barite powder, the mixture is stirred at high speed for at least 30 minutes until the density is uniform and there is no particle agglomeration, ensuring uniform drilling fluid density and preventing wellbore instability caused by downhole density fluctuations. The entire preparation process is clear, the conditions are mild, no complex equipment is required, and the operation is convenient. It can be quickly prepared on-site, and the prepared drilling fluid system exhibits stable performance with no significant performance degradation at 230℃, fully meeting the process and performance requirements of on-site construction. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the synthesis route of the filtration loss reducer in Example 1. Detailed Implementation

[0022] The embodiments of the invention will now be described in detail with reference to the accompanying drawings.

[0023] Example 1

[0024] (1) Preparation of hydrophilic modified macromolecular copolymers like Figure 1 As shown, the polymer intermediate was synthesized as follows: 2-vinylnaphthalene: acrylic acid: maleic anhydride = 0.2:1.5:0.5 (mass ratio); 0.2% benzyl dithiobenzoate (RAFT reagent, percentage of total monomer mass), 0.3% azobisisobutyronitrile (first initiator, percentage of total monomer mass), and 5 times the amount of dipropylene glycol dimethyl ether were added; the reaction was carried out at 60°C and 600 r / min for 4 h under a nitrogen atmosphere; anhydrous ethanol was used for precipitation, the mixture was washed twice with water, and vacuum dried at 50°C until the water content was ≤1%, yielding a polymer intermediate with a molecular weight of 1500.

[0025] Hydrophilic modification: Take the above polymer intermediate, add 3wt% polyethylene glycol methacrylate, 0.2% ammonium persulfate-sodium bisulfite (second initiator, 1:1, total mass), and 3 times the amount of water-acetone mixed solvent (2:1, volume ratio); under nitrogen atmosphere, perform free radical grafting reaction at 60℃ and 600r / min for 0.5h; remove the solvent by rotary evaporation under reduced pressure at 40℃ to obtain hydrophilic modified macromolecular copolymer.

[0026] (2) Preparation of filtration loss reducing agent Copolymerization and chain extension: Hydrophilic modified macromolecular copolymer: maleic anhydride: AMPS:NVP:DMAA=1:0.3:1.0:0.4:0.2 (mass ratio); add 0.2% ammonium persulfate-sodium bisulfite (third initiator, 1:1, total mass) and 4 times the amount of water-glycerol mixed solvent (4:1, volume ratio); copolymerize at 50℃ and 800r / min for 2h under nitrogen atmosphere.

[0027] Phosphonic acid grafting: After copolymerization and chain extension, without any further treatment, add 5wt% vinylphosphonic acid (total mass percentage of the copolymerization system) and 0.2% ammonium persulfate-sodium bisulfite (fourth initiator, 1:1, total mass percentage of the copolymerization system); under a nitrogen atmosphere, perform the grafting reaction at 70℃ and 800r / min for 1h; cool to room temperature, shear and granulate, dry at 100℃ until the moisture content is less than 7%, and pulverize to 200 mesh to obtain the filtration loss reducer.

[0028] (3) Water-based drilling fluid preparation Step S1: Preparation of base slurry: Add 100g of deionized water to the mixing tank, then add 3.5g of sepiolite and 0.175g of soda ash in sequence. Stir at 11000r / min for 30min and let it stand at room temperature for 24h until the slurry soil is fully pre-hydrated and a uniform base slurry is formed.

[0029] Step S2: Adding the filtration loss reducing agent from Example 1 to the base slurry and stirring at 11000 r / min for 15 min; then add 3.0 g of sulfonated lignite resin and 14.0 g of natural asphalt powder (350 mesh, softening point 210℃) and stir at 11000 r / min for 10 min; add 30% caustic soda solution dropwise to adjust the pH of the system to 10 and stir until the pH is stable.

[0030] Step S3: Add lubricating components: Add 6.0g of 0# diesel oil and stir at 11000r / min for 10min.

[0031] Step S4: Adding the sealing component: Add 4.0g of rigid calcium carbonate and stir at 11000r / min for 10min.

[0032] Step S5: Add high-temperature synergistic agent: Add 2.0g of polycarboxylate-type diluent stabilizer (HW Thin, the applicant's own product) and 0.5g of fatty acid polyamide-type emulsifier (HW Pmul-3, the applicant's own product) in sequence. After each reagent is added, stir at 11000r / min for 10min until the system is completely homogeneous.

[0033] Step S6: Add the inhibitory component: Add 10.0g of potassium chloride and stir at 11000r / min for 20min until the potassium chloride is completely dissolved.

[0034] Step S7: Weighting and Adjustment: Add 47g of high-density barite powder (density ≥ 4.30g / cm³), stir at 11000r / min for 60min until the drilling fluid has uniform density and no particle agglomeration, and a water-based drilling fluid resistant to 230℃ high temperature is obtained.

[0035] Example 2

[0036] (1) Preparation of hydrophilic modified macromolecular copolymers Synthesis of polymer intermediate: 2-vinylnaphthalene: acrylic acid: maleic anhydride = 0.3:1.5:0.7 (mass ratio); add 0.3% cyanoisopropyl dithiobenzoate (RAFT reagent, total monomer mass percentage), 0.5% benzoyl peroxide (first initiator, total monomer mass), and 7.5 times the amount of tetrahydrofuran; react at 70℃ and 800 r / min for 5 h under nitrogen atmosphere; precipitate with anhydrous ethanol, wash 3 times with water, and vacuum dry at 55℃ until the water content is ≤1% to obtain a polymer intermediate with a molecular weight of 2000.

[0037] Hydrophilic modification: Take the above polymer intermediate, add 4 wt% hydroxyethyl methacrylate, 0.35% ammonium persulfate-sodium bisulfite (second initiator, 1:1, total mass percentage), and 4 times the amount of water-acetone mixed solvent (2:1, volume ratio); under nitrogen atmosphere, perform free radical grafting reaction at 70℃ and 800 r / min for 0.8 h; remove the solvent by rotary evaporation under reduced pressure at 45℃ to obtain hydrophilic modified macromolecular copolymer.

[0038] (2) Preparation of filtration loss reducing agent Copolymerization chain extension: hydrophilic modified macromolecular copolymer: maleic anhydride: AMPS:NVP:DMAA=1:0.4:1.25:0.5:0.3 (mass ratio); add 0.35% ammonium persulfate-sodium bisulfite (third initiator, 1:1, total mass percentage of copolymerization system) and 4.5 times the amount of water-glycerol mixed solvent (4:1, volume ratio); copolymerize at 60℃ and 1000r / min for 2.5h under nitrogen atmosphere.

[0039] Phosphonic acid grafting: After copolymerization and chain extension, without any further treatment, add 7.5 wt% vinylphosphonic acid (total mass percentage of the copolymer system) and 0.3% ammonium persulfate-sodium bisulfite (fourth initiator, 1:1, total mass percentage of the copolymer system); under a nitrogen atmosphere, perform the grafting reaction at 80℃ and 1000 r / min for 1.5 h; cool to room temperature, shear and granulate, dry at 110℃ until the moisture content is less than 7%, and pulverize to 300 mesh to obtain the filtration loss reducer.

[0040] (3) Water-based drilling fluid preparation Step S1: Preparation of base slurry: Add 100g of deionized water to the mixing tank, then add 2.8g of drilling grade bentonite and 0.14g of soda ash in sequence. Stir at 11000r / min for 25min and cure at room temperature for 24h to obtain a uniform base slurry.

[0041] In step S2, the filtration loss reduction system is added as follows: 3g of the filtration loss reduction agent from Example 2 is added and stirred at 11000r / min for 12min; 2.0g of sulfonated lignite resin and 16.0g of natural asphalt powder (380 mesh, softening point 220℃) are added and stirred at 11000r / min for 8min; 30% caustic soda solution is added dropwise to adjust the pH to 9.5 and stirred until the pH is stable.

[0042] Step S3: Add lubricating components: Add 4.0g of 0# diesel oil and stir at 11000r / min for 7min.

[0043] Step S4: Add the blocking component: Add 0.5g of chemical film-forming blocking agent (FDM-1, the applicant's own product), and stir at 11000r / min for 7min.

[0044] Step S5: Add high-temperature synergistic additives: Add 1.5g of polycarboxylate-type diluent stabilizer (HW Thin, the applicant's own product) and 1.0g of fatty acid polyamide-type emulsifier (HW Pmul-3, the applicant's own product) in sequence. After each addition, stir at 11000r / min for 7min until the system is homogeneous.

[0045] Step S6: Add the inhibitory component: Add 7g of potassium chloride, stir at 11000r / min for 18min until completely dissolved.

[0046] Step S7: Weighting and Adjustment: Add 47g of high-density barite powder (density ≥ 4.30g / cm³), stir at 11000r / min for 40min until the density is uniform and there is no agglomeration, and the water-based drilling fluid resistant to 230℃ high temperature is obtained.

[0047] Example 3

[0048] (1) Preparation of hydrophilic modified macromolecular copolymers Synthesis of polymer intermediate: 2-vinylnaphthalene: acrylic acid: maleic anhydride = 0.4:1.5:0.8 (mass ratio); add 0.4% benzyl dithiobenzoate + cyanoisopropyl dithiobenzoate (1:1) (RAFT reagent, total monomer mass), 0.8% azobisisobutyronitrile (first initiator, total monomer mass), and 10 times the amount of N,N-dimethylformamide; react at 80℃ and 1000 r / min for 6 h under nitrogen atmosphere; precipitate with anhydrous ethanol, wash 3 times with water, and vacuum dry at 60℃ until the water content is ≤1%, to obtain a polymer intermediate with a molecular weight of 2500.

[0049] Hydrophilic modification: Take the above polymer intermediate, add 5wt% polyethylene glycol methacrylate, 0.5% ammonium persulfate-sodium bisulfite (second initiator, 1:1, total mass), and 5 times the amount of water-acetone mixed solvent (2:1, volume ratio); under nitrogen atmosphere, perform free radical grafting reaction at 80℃ and 1000r / min for 1h; remove the solvent by rotary evaporation under reduced pressure at 50℃ to obtain hydrophilic modified macromolecular copolymer.

[0050] (2) Preparation of filtration loss reducing agent Copolymerization chain extension: hydrophilic modified macromolecular copolymer: maleic anhydride: AMPS:NVP:DMAA=1:0.5:1.5:0.6:0.4 (mass ratio); add 0.5% ammonium persulfate-sodium bisulfite (third initiator, 1:1, total mass) and 5 times the amount of water-glycerol mixed solvent (4:1, volume ratio); copolymerize at 70℃ and 1200r / min for 3h under nitrogen atmosphere.

[0051] Phosphonic acid grafting: After copolymerization and chain extension, without any further treatment, add 10wt% vinylphosphonic acid (total mass percentage of the copolymerization system) and 0.4% ammonium persulfate-sodium bisulfite (fourth initiator, 1:1, total mass percentage of the copolymerization system); under a nitrogen atmosphere, perform the grafting reaction at 90℃ and 1200r / min for 2h; cool to room temperature, shear and granulate, dry at 120℃ until the moisture content is less than 7%, and pulverize to 400 mesh to obtain the filtration loss reducer.

[0052] (3) Water-based drilling fluid preparation Step S1: Preparation of base slurry: Add 100g of deionized water to the mixing tank, then add 2.0g of attapulgite and 0.06g of soda ash in sequence. Stir at 11000r / min for 20min and let it stand at room temperature for 24h until the slurry is fully pre-hydrated and a uniform base slurry is formed.

[0053] Step S2: Add the filtration loss reducing agent from Example 3 to the base slurry and stir at 11000 r / min for 10 min. Then add 3.0 g of sulfonated lignite resin and 14.0 g of natural asphalt powder (400 mesh, softening point 230℃) and stir at 11000 r / min for 5 min. Add 30% caustic soda solution dropwise to adjust the pH of the system to 9 and stir until the pH is stable.

[0054] Step S3: Add lubricating components: Add 3.0g of 0# diesel oil and stir at 11000r / min for 5min.

[0055] Step S4: Adding the plugging components: Add 2.0g of rigid calcium carbonate and 0.5g of chemical film-forming plugging agent (FDM-1, the applicant's own product). After each reagent is added, stir at 11000r / min for 5min.

[0056] Step S5: Add high-temperature synergistic agent: Add 1.0g of polycarboxylate-type diluent stabilizer (HW Thin, the applicant's own product) and 0.1g of fatty acid polyamide-type emulsifier (HW Pmul-3, the applicant's own product) in sequence. After each reagent is added, stir at 11000r / min for 5min until the system is completely homogeneous.

[0057] Step S6: Add the inhibitory component: Add 5.0 g of potassium chloride and stir at 11000 r / min for 15 min until the potassium chloride is completely dissolved.

[0058] Step S7: Weighting and Adjustment: Add 47g of high-density barite powder (density ≥ 4.30g / cm³), stir at 11000r / min for 30min until the drilling fluid has uniform density and no particle agglomeration, and a water-based drilling fluid resistant to 230℃ high temperature is obtained.

[0059] High-Temperature Aging and Performance Testing: The drilling fluids prepared in Examples 1-3 were respectively placed into high-temperature aging tanks. They were hot-rolled and aged in a roller furnace at 230℃ for 16 hours. After aging, they were removed and cooled to room temperature. The aged drilling fluids were then stirred at 11,000 rpm for 5 minutes to restore homogeneity. Subsequently, at 50℃, their rheological properties, API filtration loss, HTHP filtration loss (190℃, 3.5MPa), and lubrication coefficient were tested according to the provisions of GB / T 16783.1-2025 standard. The test results are shown in Tables 1 and 2.

[0060] Long-term stability test: The drilling fluid that had been aged for 16 hours was further aged by hot rolling at 230℃ for 48 hours (cumulative 72 hours). After cooling and stirring, its performance was tested using the same method. The test results are shown in Tables 1 and 2.

[0061] Comparative Example 1 used the exact same formulation and steps as Example 2 to prepare the drilling fluid, the only difference being that the filtration loss reducer was replaced with an equal amount of the filtration loss reducer prepared in Experiment 1 of the specific embodiment section of the specification (title: "A Filtration Loss Reducer for High-Temperature Drilling Fluid and Its Preparation Method", announcement number: CN103710008B). Aging was also performed at 230℃ for 16 hours and 230℃ for 72 hours, and the performance was tested. The test results are shown in Table 2.

[0062] Table 1 Drilling fluid performance test results

[0063] Table 2 Drilling fluid performance test results

[0064] The data in the table above shows that: (1) High temperature stability: After aging at 230℃ for a long time (72 hours), the rheological parameters of the systems in Examples 1-3 changed slowly, and the apparent viscosity and dynamic shear force changed little, without any abnormal thickening. In contrast, after aging for 72 hours, the low speed reading (3 / 6 rpm) of Comparative Example 1 increased sharply, and the dynamic shear force increased, showing a clear trend of high temperature thickening and gelation.

[0065] (2) Filtration loss control capability: After long-term high-temperature aging, the HTHP filtration loss of the systems in Examples 1-3 was basically controlled within 21.0 mL, and the increase was controllable, indicating that the self-made filtration loss reducing agent can still effectively maintain filtration loss control capability at high temperatures. However, the HTHP filtration loss of Comparative Example 1 deteriorated sharply from 10.0 mL to 28.0 mL, and the filtration loss control capability was severely degraded.

[0066] (3) Lubrication performance: The systems in Examples 1-3 maintained a lower lubrication coefficient throughout the aging process, indicating that they had better lubrication.

[0067] In summary, the drilling fluid system and its core filtration reduction agent provided by this invention can significantly improve the long-term thermal stability and overall performance of water-based drilling fluids under ultra-high temperature conditions of 230℃, fully meeting the technical requirements of ultra-deep well drilling. In contrast, the filtration reduction agent used in Comparative Example 1 exhibits severe performance degradation under long-term high temperatures, highlighting the indispensability of the core material innovation of this invention.

Claims

1. A method for preparing a fluid loss additive, characterized by, Includes the following steps: Step S1: Using 2-vinylnaphthalene, acrylic acid, and maleic anhydride as main raw materials, a polymer intermediate with a molecular weight of 1000-2500 is synthesized via RAFT polymerization. Then, a free radical grafting reaction is carried out with the intermediate to obtain a hydrophilic modified macromolecular copolymer. The mass ratio of 2-vinylnaphthalene, acrylic acid, and maleic anhydride is (0.2-0.4):1.5:(0.5-0.8); the mass of the hydrophilic modified monomer is 3-5 wt% of the polymer intermediate. Step S2 involves first performing a free radical copolymerization reaction between the hydrophilic modified macromolecular copolymer obtained in step S1 and maleic anhydride, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone, and N,N-dimethylacrylamide; then performing a grafting reaction with vinylphosphonic acid to obtain a filtration loss reducer. The weight ratio of the hydrophilic modified macromolecular copolymer to maleic anhydride, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone, and N,N-dimethylacrylamide is 1:(0.3~0.5):(1.0~1.5):(0.4~0.6):(0.2~0.4). The amount of vinylphosphonic acid used is 5~10 wt% of the total weight of the hydrophilic modified macromolecular copolymer, maleic anhydride, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone, and N,N-dimethylacrylamide.

2. The method of claim 1, wherein the fluid loss additive is prepared by the process of: The preparation process of the polymer intermediate in step S1 includes: mixing 2-vinylnaphthalene, acrylic acid, maleic anhydride, RAFT reagent, first initiator and solvent according to the ratio, maintaining a nitrogen atmosphere, reacting at 60~80℃ and stirring speed of 600~1000r / min for 4~6h, adding anhydrous ethanol to precipitate, washing with water 2~3 times, and then vacuum drying at 50~60℃ to obtain the polymer intermediate.

3. The method for preparing the filtration loss reducing agent according to claim 2, characterized in that, The RAFT reagent is one or both of benzyl dithiobenzoate and cyanoisopropyl dithiobenzoate, and its addition amount is 0.2-0.4% of the total mass of 2-vinylnaphthalene, acrylic acid, and maleic anhydride; And / or, the first initiator is azobisisobutyronitrile or benzoyl peroxide, and its addition amount is 0.3~0.8% of the total mass of 2-vinylnaphthalene, acrylic acid, and maleic anhydride; And / or, the solvent is one or more of 1,4-dioxane, butyl acetate, tetrahydrofuran, N,N-dimethylformamide, and dipropylene glycol dimethyl ether, and the amount used is 5 to 10 times the total mass of 2-vinylnaphthalene, acrylic acid, and maleic anhydride.

4. The method of claim 1, wherein the fluid loss additive is prepared by the process of: The preparation process of the hydrophilic modified macromolecular copolymer in step S1 is as follows: the polymer intermediate, the hydrophilic modified monomer, the second initiator, and the water-acetone mixed solvent are mixed according to the formula. Under a nitrogen atmosphere, the free radical grafting reaction is carried out at 60~80℃ and a stirring speed of 600~1000r / min for 0.5~1h. Then, the water-acetone mixed solvent is removed by rotary evaporation under reduced pressure at 40~50℃ to obtain the hydrophilic modified macromolecular copolymer.

5. The method of claim 4, wherein the fluid loss additive is prepared by the process of: The hydrophilic modifying monomer is polyethylene glycol methacrylate or hydroxyethyl methacrylate; And / or, the second initiator is an ammonium persulfate-sodium bisulfite compound initiator with a mass ratio of 1:1, and its dosage is 0.2~0.5% of the total mass of the polymer intermediate and the hydrophilic modified monomer; And / or, the water-acetone mixed solvent is composed of water and acetone in a volume ratio of 2:1, and its amount is 3 to 5 times the total mass of the polymer intermediate and the hydrophilic modified monomer.

6. The method of preparing a fluid loss additive according to any one of claims 1 to 5, wherein The preparation process of the filtration loss reducer in step S2 includes: mixing hydrophilic modified macromolecular copolymer, maleic anhydride, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone, N,N-dimethylacrylamide with a third initiator and a water-glycerol mixed solvent according to the formula, maintaining a nitrogen atmosphere, and performing a free radical copolymerization reaction at 50~70℃ and a stirring speed of 800~1200r / min for 2~3h; then adding vinylphosphonic acid and a fourth initiator, and performing a grafting reaction at 70~90℃ and a stirring speed of 800~1200r / min for 1~2h, cooling to room temperature, and then shearing and granulating, drying at 100~120℃, and pulverizing to 200~400 mesh to obtain the filtration loss reducer.

7. The method of claim 6, wherein the fluid loss additive is prepared by the process of: The third initiator is a compound initiator of ammonium persulfate and sodium bisulfite, with a mass ratio of 1:

1. Its dosage is 0.2~0.5% of the total mass of the hydrophilic modified macromolecular copolymer, maleic anhydride, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone, and N,N-dimethylacrylamide. And / or, the water-glycerol mixed solvent is composed of water and glycerol in a volume ratio of 4:1, and its amount is 4 to 5 times the total mass of the hydrophilic modified macromolecular copolymer, maleic anhydride, 2-acrylamide-2-methylpropanesulfonic acid, N-vinylpyrrolidone, and N,N-dimethylacrylamide. And / or, the fourth initiator is a compound initiator of ammonium persulfate and sodium bisulfite, with a mass ratio of 1:1, and its dosage is 0.2 to 0.4% of the total mass of the hydrophilic modified macromolecular copolymer, maleic anhydride, 2-acrylamide-2-methylpropanesulfonic acid, N-vinylpyrrolidone, N,N-dimethylacrylamide, and vinylphosphonic acid.

8. A 230°C high temperature tolerant water-based drilling fluid, characterized in that, By weight, it includes: Water, 100 portions; Mix 2.0 to 3.5 parts of mortar. Soda ash, 0.06~0.18 parts; The filtration loss reducing agent prepared by the method of any one of claims 1 to 7, in parts of 2.5 to 4.0; Sulfonated lignite resin, 2.0~4.0 parts; Natural bitumen powder, 10.0~18.0 parts; Lubricant, 3.0~6.0 parts; Sealing agent, 0.5~4.0 parts; Dilute the stabilizer to 1.0~2.0 parts; Emulsifier, 0.1~1.0 parts; Shale inhibitor, 5.0~10.0 parts; Barite powder, 47 parts.

9. The 230°C high temperature tolerant water-based drilling fluid of claim 8, wherein, The mortar mix is ​​selected from one of sepiolite, attapulgite, or drilling-grade bentonite. And / or, the particle size of natural bitumen powder is 300~400 mesh, and the softening point is higher than 200℃; And / or, the lubricant is #0 diesel fuel; And / or, the plugging agent is one or both of rigid calcium carbonate with particle size distribution or chemical film-forming plugging agent, wherein the rigid calcium carbonate has a particle size range of 200 nm to 40 μm; And / or, the diluent stabilizer is a polycarboxylate-based diluent stabilizer; And / or, the emulsifier is a fatty acid polyamide type emulsifier; And / or, the shale inhibitor is potassium chloride; And / or, the barite powder is high-density barite powder with a density ≥ 4.30 g / cm³.

10. A method for preparing a 230°C high temperature resistant water-based drilling fluid, for preparing a 230°C high temperature resistant water-based drilling fluid as claimed in claim 8 or 9, characterized in that, Includes the following steps: Step S1, base slurry preparation: Add the slurry mix and soda ash to the water in sequence, stir at 11000~12000r / min for 20~30min to form a uniform base slurry, and cure at room temperature for more than 24 hours to allow it to be fully prehydrated; Step S2, Addition of Filtration Loss Reduction System: Add the filtration loss reduction agent to the base slurry obtained in Step S1, and stir at high speed of 11000~12000 r / min for 10~15 min; then continue to add sulfonated lignite resin and natural asphalt powder, and stir at high speed of 11000~12000 r / min for 5~10 min; finally, add a caustic soda solution with a mass concentration of 30~40% to adjust the pH value of the system to 9~10; Step S3, adding lubricating components: add lubricant to the slurry obtained in step S2, and stir at high speed of 11000~12000r / min for 5-10min; Step S4, Adding the sealing component: Add the sealing agent to the slurry obtained in step S3, and stir at a high speed of 11000~12000r / min for 5-10min; Step S5, addition of high temperature synergistic additives: add diluent stabilizer and emulsifier to the slurry obtained in step S4 in sequence. After each treatment agent is added, stir at high speed of 11000~12000r / min for 5-10min. Step S6, Addition of inhibitory components: Add shale inhibitor to the slurry obtained in step S5, and stir at high speed of 11000~12000r / min for 15-20min; Step S7, Weighting and Adjustment: Add barite powder to the slurry obtained in step S6, and stir at a high speed of 11000~12000r / min for more than 30min until the density is uniform and there are no particle agglomerations, to obtain a water-based drilling fluid resistant to 230℃ high temperature.

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