Degradable polyanionic cellulose filtrate reducer for drilling fluid and preparation method thereof

Abstract

The invention relates to the technical field of filtrate loss reducers, in particular to a degradable polyanionic cellulose filtrate loss reducer for drilling fluid and a preparation method of the degradable polyanionic cellulose filtrate loss reducer, and the degradable polyanionic cellulose filtrate loss reducer is prepared from the following raw materials in parts by weight: 0.6-0.7 part of polyanionic cellulose, 0.08-0.09 part of modified nanocellulose and 0.01-0.015 part of modified cyclodextrin microspheres; by compounding the polyanionic cellulose, the modified nanocellulose and the modified cyclodextrin microspheres, the problem that the filtration performance of the existing polyanionic cellulose is reduced under high-temperature and high-salt conditions is solved; meanwhile, the problem of phase separation caused by electrostatic repulsion among polyanionic cellulose, nano cellulose and cyclodextrin microspheres is avoided through modification, and good biodegradability is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of filtration loss reducers, and specifically relates to a biodegradable polyanionic cellulose filtration loss reducer for drilling fluids and a preparation method thereof. Background Art

[0002] In oil and gas drilling engineering, the filtration loss control performance of drilling fluids is directly related to wellbore stability, reservoir protection, and operation safety. As an anionic natural polymer modified product, polyanionic cellulose is widely used in water-based drilling fluid systems due to its viscosity increasing, filtration loss reducing, and environmental protection characteristics. However, with the increasing demand for drilling in deep wells, ultra-deep wells, and complex formations, traditional polyanionic cellulose fails to control filtration loss under high temperature and high salt conditions, resulting in a significant increase in filtration loss. For example, in the patent CN202010654382.5 "An anti-salt filtration loss reducer for drilling fluids and its production method", by compounding polyacrylamide, starch ether, and polyanionic cellulose, the anti-filtration loss performance of the filtration loss reducer under high temperature and high salt conditions is improved. However, the introduction of polyacrylamide will reduce the biodegradability of the filtration loss reducer and is likely to stay in the formation for a long time, inducing reservoir damage. Therefore, there is a need for a polyanionic cellulose filtration loss reducer with good filtration loss reduction performance and biodegradability under high temperature and high salt conditions. Summary of the Invention

[0003] The purpose of the present invention is to provide a biodegradable polyanionic cellulose filtration loss reducer for drilling fluids and a preparation method thereof. By compounding polyanionic cellulose, modified nano-cellulose, and modified cyclodextrin microspheres, the problem of reduced filtration loss reduction performance of existing polyanionic cellulose under high temperature and high salt conditions is solved. At the same time, through modification, the phase separation problem caused by electrostatic repulsion between polyanionic cellulose, nano-cellulose, and cyclodextrin microspheres is avoided, and it has good biodegradability.

[0004] The purpose of the present invention can be achieved through the following technical solutions: A preparation method of a biodegradable polyanionic cellulose filtration loss reducer for drilling fluids, which includes the following steps: Weigh the following raw materials in parts by weight: 0.6 - 0.7 parts of polyanionic cellulose, 0.08 - 0.09 parts of modified nano-cellulose, and 0.01 - 0.015 parts of modified cyclodextrin microspheres; Mix polyanionic cellulose, modified nano-cellulose, and modified cyclodextrin microspheres to obtain a biodegradable polyanionic cellulose filtration loss reducer for drilling fluids.

[0005] The polyanionic cellulose is Kemic low-viscosity polyanionic cellulose; The modified nano-cellulose is prepared through the following steps: Step A1: Mix 2-(dodecyltrithiocarbonate)-2-methylpropanoic acid, oxalyl chloride and dichloromethane, stir and add ethyl acetate under the conditions of a stirring rate of 140 - 180 rpm and a temperature of room temperature, react for 6 - 8 h, and perform rotary evaporation to obtain Intermediate 1. Mix nanocellulose and N,N-dimethylacetamide, stir for 2 - 2.5 h under the conditions of a stirring rate of 140 - 180 rpm and a temperature of 150 °C, then add lithium chloride, stir for 10 - 12 h under the condition of a temperature of 80 °C, then add triethylamine and Intermediate 1, stir for 24 h under the condition of a temperature of room temperature, then add methanol, filter, wash, and dry to obtain modified cellulose; The dosage ratio of 2-(dodecyltrithiocarbonate)-2-methylpropanoic acid, oxalyl chloride, dichloromethane and ethyl acetate is 4.2 - 4.5 g : 2.5 - 2.8 g : 25 - 30 mL : 1.2 - 1.5 mL; the dosage ratio of nanocellulose, N,N-dimethylacetamide, lithium chloride, triethylamine and Intermediate 1 is 0.95 - 1.03 g : 40 - 45 mL : 2.5 - 2.65 g : 1.35 - 1.4 g : 0.28 - 0.32 g; During the reaction process, under the action of oxalyl chloride, the carboxyl group in 2-(dodecyltrithiocarbonate)-2-methylpropanoic acid is acylated to obtain Intermediate 1. Then, in the N,N-dimethylacetamide / lithium chloride system, the hydroxyl group in nanocellulose reacts with the acyl chloride group in Intermediate 1, and triethylamine is used as an acid-binding agent to obtain modified cellulose.

[0006] The nanocellulose is Kemic nanocellulose with a specification of 15 µm;

[0007] Step A2: Mix modified cellulose, azobisisobutyronitrile and tetrahydrofuran, stir and add 2-methylene-1,3-dioxepane, acrylamide and N,N-dimethylacetamide under the protection of nitrogen and under the conditions of a stirring rate of 80 - 120 rpm and a temperature of 80 °C, react for 10 - 12 h, perform rotary evaporation, add ether, filter, wash, and dry to obtain grafted cellulose; The dosage ratio of modified cellulose, azobisisobutyronitrile, tetrahydrofuran, 2-methylene-1,3-dioxepane, acrylamide and N,N-dimethylacetamide is 0.8 - 0.84 g : 0.002 - 0.0025 g : 12 - 15 mL : 0.6 - 0.8 g : 0.9 - 1 g : 12 - 15 mL; During the reaction process, under the condition of using azobisisobutyronitrile as an initiator, through the reversible addition-fragmentation chain transfer polymerization method, the dithioester bond in modified cellulose reacts with 2-methylene-1,3-dioxepane and acrylamide to obtain grafted cellulose.

[0008]

[0009] Step A3: Mix 4-hydroxyazobenzene and N,N-dimethylformamide, and under the conditions of a stirring rate of 120 - 140 rpm and a temperature of 60 °C, stir and add potassium carbonate and epibromohydrin, react for 8 - 10 h, add ethyl acetate for extraction, washing, drying, and solvent removal to obtain Intermediate 2. Mix grafted cellulose, Intermediate 2, N,N-dimethylacetamide, and tetrahydrofuran, under nitrogen protection and a stirring rate of 60 - 80 rpm at room temperature, stir and add dimethylphenylphosphine, stir for 30 min, then add sodium borohydride, raise the temperature to 30 - 32 °C, continue stirring for 24 h, perform rotary evaporation, chromatography, washing, and drying to obtain modified nanocellulose; The dosage ratio of 4-hydroxyazobenzene, N,N-dimethylformamide, potassium carbonate, and epibromohydrin is 4.8 - 5 g : 23 - 25 mL : 5.2 - 5.3 g : 6.3 - 6.5 g; the dosage ratio of grafted cellulose, Intermediate 2, N,N-dimethylacetamide, tetrahydrofuran, dimethylphenylphosphine, and sodium borohydride is 1.2 - 1.3 g : 0.012 - 0.015 g : 6 - 8 mL : 8 - 10 mL : 0.015 - 0.016 g : 0.008 - 0.009 g; During the reaction process, under the action of potassium carbonate, the hydroxyl group in 4-hydroxyazobenzene reacts with epibromohydrin to obtain Intermediate 2. While using sodium borohydride as a reducing agent, the terminal disulfide bond in the branched chain of grafted cellulose is reduced to a mercapto group, and then under the catalysis of dimethylphenylphosphine, the terminal mercapto group reacts with the epoxy group in Intermediate 2 to obtain modified nanocellulose.

[0010]

[0011] The modified cyclodextrin microspheres are prepared through the following steps: Step B1: Mix dimethylamine, 3-chloro-2-hydroxypropyl sulfate sodium salt, and deionized water, and under the conditions of a stirring rate of 180 - 240 rpm and a temperature of 50 °C, react for 6 - 8 h, perform rotary evaporation, washing, and drying to obtain Intermediate a. Mix Intermediate a, epichlorohydrin, and isopropanol, and under the conditions of a stirring rate of 180 - 240 rpm and a temperature of 60 °C, stir and add sodium carbonate, react for 4 - 6 h, perform vacuum distillation, washing, and drying to obtain Intermediate b; The dosage ratio of dimethylamine, 3-chloro-2-hydroxypropyl sulfate sodium salt, and deionized water is 2.55 - 2.6 g : 10 - 11 g : 35 - 40 mL; the dosage ratio of Intermediate a, epichlorohydrin, isopropanol, and sodium carbonate is 6.6 - 6.8 g : 4.1 - 4.2 mL : 8 - 10 mL : 1.2 - 1.5 g; During the reaction process, the amino group in dimethylamine undergoes a nucleophilic substitution reaction with 3-chloro-2-hydroxypropyl sodium sulfate to obtain intermediate a, and intermediate a then undergoes a quaternization reaction with epichlorohydrin to obtain intermediate b.

[0012]

[0013] Step B2: Mix kerosene, Tween-20, and Span-80, and stir at a stirring rate of 200 - 240 rpm at room temperature for 15 - 20 min to obtain the continuous phase. Mix β-cyclodextrin and sodium hydroxide solution, stir at a stirring rate of 120 - 140 rpm at room temperature for 15 - 20 min, then add epichlorohydrin and intermediate b, and continue stirring for 1 - 1.5 h to obtain the dispersed phase. Add the dispersed phase to the continuous phase, and react at a temperature of 80 - 85 °C and a stirring rate of 700 - 800 rpm for 4 - 6 h, then centrifuge, wash, and dry to obtain the modified cyclodextrin microspheres. The mass fraction of the sodium hydroxide solution is 35%, and the dosage ratio of kerosene, Tween-20, Span-80, β-cyclodextrin, sodium hydroxide solution, epichlorohydrin, and intermediate b is 80 - 90 mL : 0.3 - 0.32 g : 0.85 - 0.9 g : 2.3 - 2.5 g : 25 - 30 mL : 3.4 - 3.6 mL : 0.42 - 0.5 g. During the reaction process, using β-cyclodextrin as the raw material and epichlorohydrin as the cross-linking agent, through the inverse emulsion method, and adding intermediate b containing epoxy groups, under alkaline conditions, the epoxy groups undergo ring-opening and react with the hydroxyl groups in β-cyclodextrin for cross-linking, thereby obtaining the modified cyclodextrin microspheres.

[0014] Advantages of the present invention: The present invention discloses a biodegradable polyanionic cellulose filtrate reducer for drilling fluid and its preparation method. By compounding polyanionic cellulose, modified nano-cellulose, and modified cyclodextrin microspheres, since the modified nano-cellulose is based on nano-cellulose and introduces branched segments of ester groups and acrylamide through reversible addition-fragmentation chain transfer polymerization to form a brush-like structure, and the terminal disulfide bond reacts with intermediate 2 containing epoxy groups after being reduced to mercapto groups, thereby introducing an azobenzene structure at the end of the branched chain. The modified cyclodextrin microspheres have certain water absorption and swelling properties, and after water absorption and swelling, the cyclodextrin structure combines with the modified nano-cellulose containing azobenzene structure, and then is compounded with polyanionic cellulose, solving the problem that the filtrate reduction performance of existing polyanionic cellulose decreases under high temperature and high salt conditions. At the same time, due to the introduction of intermediate b with zwitterionic structure into the modified cyclodextrin microspheres, the existence of the zwitterionic structure avoids the phase separation problem caused by electrostatic repulsion between polyanionic cellulose, modified nano-cellulose, and modified cyclodextrin microspheres under high salt conditions. And because ester groups are introduced into the branched chains of the modified nano-cellulose, the compound of polyanionic cellulose, modified nano-cellulose, and modified cyclodextrin microspheres still has good biodegradability. Description of the Drawings

[0015] Figure 1 Infrared spectrum of intermediate 1 in Example 3; Figure 2 Infrared spectrum of intermediate 2 in Example 3; Figure 3 1H NMR spectrum of modified cellulose in Example 3; Figure 4 1H NMR spectrum of grafted cellulose in Example 3; Figure 5 1H NMR spectrum of modified nano-cellulose in Example 3. Detailed Embodiments

[0016] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0017] Example 1 A preparation method of a biodegradable polyanionic cellulose filtrate reducer for drilling fluid, which includes the following steps: Weigh the following raw materials in parts by weight: 0.6 part of polyanionic cellulose, 0.08 part of modified nano-cellulose, and 0.015 part of modified cyclodextrin microspheres; Mix polyanionic cellulose, modified nano-cellulose, and modified cyclodextrin microspheres to obtain a biodegradable polyanionic cellulose filtrate reducer for drilling fluid; The polyanionic cellulose is Kemic low-viscosity polyanionic cellulose; The modified nanocellulose is prepared through the following steps: Step A1: Mix 2-(dodecyltrithiocarbonate)-2-methylpropanoic acid, oxalyl chloride and dichloromethane, stir and add ethyl acetate under the conditions of a stirring rate of 140 rpm and a temperature of room temperature, react for 6 h, perform rotary evaporation to obtain Intermediate 1. Mix nanocellulose and N,N-dimethylacetamide, stir for 2 h under the conditions of a stirring rate of 140 rpm and a temperature of 150 °C, then add lithium chloride, stir for 10 h under the condition of a temperature of 80 °C, then add triethylamine and Intermediate 1, stir for 24 h under the condition of a temperature of room temperature, then add methanol, filter, wash and dry to obtain modified cellulose; The dosage ratio of 2-(dodecyltrithiocarbonate)-2-methylpropanoic acid, oxalyl chloride, dichloromethane and ethyl acetate is 4.2 g: 2.5 g: 25 mL: 1.2 mL; the dosage ratio of nanocellulose, N,N-dimethylacetamide, lithium chloride, triethylamine and Intermediate 1 is 0.95 g: 40 mL: 2.5 g: 1.35 g: 0.28 g; The nanocellulose is Kemic nanocellulose with a specification of 15 µm; Step A2: Mix modified cellulose, azobisisobutyronitrile and tetrahydrofuran, stir and add 2-methylene-1,3-dioxepane, acrylamide and N,N-dimethylacetamide under the protection of nitrogen and under the conditions of a stirring rate of 80 rpm and a temperature of 80 °C, react for 10 h, perform rotary evaporation, add diethyl ether, filter, wash and dry to obtain grafted cellulose; The dosage ratio of modified cellulose, azobisisobutyronitrile, tetrahydrofuran, 2-methylene-1,3-dioxepane, acrylamide and N,N-dimethylacetamide is 0.8 g: 0.002 g: 12 mL: 0.6 g: 0.9 g: 12 mL; Step A3: Mix 4-hydroxyazobenzene and N,N-dimethylformamide, stir and add potassium carbonate and epibromohydrin under the conditions of a stirring rate of 120 rpm and a temperature of 60 °C, react for 8 h, perform extraction with ethyl acetate, wash and dry, and remove the solvent to obtain Intermediate 2. Mix grafted cellulose, Intermediate 2, N,N-dimethylacetamide and tetrahydrofuran, stir under the protection of nitrogen and under the conditions of a stirring rate of 60 rpm and room temperature, stir and add dimethylphenylphosphine, stir for 30 min, then add sodium borohydride, raise the temperature to 30 °C, continue to stir for 24 h, perform rotary evaporation, chromatography, wash and dry to obtain modified nanocellulose; The dosage ratio of 4-hydroxyazobenzene, N,N-dimethylformamide, potassium carbonate and epibromohydrin is 4.8 g: 23 mL: 5.2 g: 6.3 g; the dosage ratio of grafted cellulose, intermediate 2, N,N-dimethylacetamide, tetrahydrofuran, dimethylphenylphosphine and sodium borohydride is 1.2 g: 0.012 g: 6 mL: 8 mL: 0.015 g: 0.008 g; The modified cyclodextrin microspheres are prepared by the following steps: Step B1: Mix dimethylamine, 3-chloro-2-hydroxypropyl sodium sulfate and deionized water, react at a stirring rate of 240 rpm and a temperature of 50 °C for 6 h, perform rotary evaporation, washing and drying to obtain intermediate a. Mix intermediate a, epichlorohydrin and isopropanol, stir at a stirring rate of 180 rpm and a temperature of 60 °C, add sodium carbonate while stirring, react for 6 h, perform vacuum distillation, washing and drying to obtain intermediate b; The dosage ratio of dimethylamine, 3-chloro-2-hydroxypropyl sodium sulfate and deionized water is 2.6 g: 10 g: 35 mL; the dosage ratio of intermediate a, epichlorohydrin, isopropanol and sodium carbonate is 6.8 g: 4.1 mL: 10 mL: 1.2 g; Step B2: Mix kerosene, Tween-20 and Span-80, stir at a stirring rate of 200 rpm at room temperature for 20 min to obtain the continuous phase. Mix β-cyclodextrin and sodium hydroxide solution, stir at a stirring rate of 120 rpm at room temperature for 20 min, then add epichlorohydrin and intermediate b, and continue to stir for 1 h to obtain the dispersed phase. Add the dispersed phase to the continuous phase, react at a temperature of 80 °C and a stirring rate of 800 rpm for 4 h, perform centrifugation, washing and drying to obtain the modified cyclodextrin microspheres; The mass fraction of the sodium hydroxide solution is 35%, and the dosage ratio of kerosene, Tween-20, Span-80, β-cyclodextrin, sodium hydroxide solution, epichlorohydrin and intermediate b is 90 mL: 0.3 g: 0.85 g: 2.3 g: 25 mL: 3.6 mL: 0.5 g.

[0018] Example 2 A preparation method of a degradable polyanionic cellulose filtrate reducer for drilling fluid, which includes the following steps: Weigh the following raw materials in parts by weight: 0.6 part of polyanionic cellulose, 0.09 part of modified nanocellulose and 0.01 part of modified cyclodextrin microspheres; Mix the polyanionic cellulose, modified nanocellulose and modified cyclodextrin microspheres to obtain a degradable polyanionic cellulose filtrate reducer for drilling fluid; The polyanionic cellulose is Kemic low-viscosity polyanionic cellulose; The modified nanocellulose is prepared by the following steps: Step A1: Mix 2-(dodecyltrithiocarbonato)-2-methylpropanoic acid, oxalyl chloride and dichloromethane. Under the conditions of a stirring rate of 180 rpm and at room temperature, stir and add ethyl acetate, react for 8 h, and perform rotary evaporation to obtain Intermediate 1. Mix nanocellulose and N,N-dimethylacetamide. Under the conditions of a stirring rate of 180 rpm and at 150 °C, stir for 2 h, then add lithium chloride. Under the condition of a temperature of 80 °C, stir for 10 h, then add triethylamine and Intermediate 1. Under the condition of a temperature of room temperature, stir for 24 h, then add methanol, filter, wash, and dry to obtain modified cellulose; The dosage ratio of 2-(dodecyltrithiocarbonato)-2-methylpropanoic acid, oxalyl chloride, dichloromethane and ethyl acetate is 4.5 g: 2.5 g: 30 mL: 1.2 mL; the dosage ratio of nanocellulose, N,N-dimethylacetamide, lithium chloride, triethylamine and Intermediate 1 is 1.03 g: 40 mL: 2.65 g: 1.4 g: 0.32 g; The nanocellulose is Kemic nanocellulose with a specification of 15 µm; Step A2: Mix modified cellulose, azobisisobutyronitrile and tetrahydrofuran. Under nitrogen protection, with a stirring rate of 80 rpm and at 80 °C, stir and add 2-methylene-1,3-dioxepane, acrylamide and N,N-dimethylacetamide, react for 12 h, perform rotary evaporation, add diethyl ether, filter, wash, and dry to obtain grafted cellulose; The dosage ratio of modified cellulose, azobisisobutyronitrile, tetrahydrofuran, 2-methylene-1,3-dioxepane, acrylamide and N,N-dimethylacetamide is 0.8 g: 0.0025 g: 12 mL: 0.8 g: 1 g: 12 mL; Step A3: Mix 4-hydroxyazobenzene and N,N-dimethylformamide. Under the conditions of a stirring rate of 120 rpm and at 60 °C, stir and add potassium carbonate and epibromohydrin, react for 10 h, add ethyl acetate for extraction, wash, dry, and remove the solvent to obtain Intermediate 2. Mix grafted cellulose, Intermediate 2, N,N-dimethylacetamide and tetrahydrofuran. Under nitrogen protection, with a stirring rate of 60 rpm and at room temperature, stir and add dimethylphenylphosphine, stir for 30 min, then add sodium borohydride, raise the temperature to 32 °C, continue to stir for 24 h, perform rotary evaporation, chromatography, wash, and dry to obtain modified nanocellulose; The dosage ratio of 4-hydroxyazobenzene, N,N-dimethylformamide, potassium carbonate and epibromohydrin is 4.8 g: 25 mL: 5.2 g: 6.3 g; the dosage ratio of grafted cellulose, Intermediate 2, N,N-dimethylacetamide, tetrahydrofuran, dimethylphenylphosphine and sodium borohydride is 1.3 g: 0.012 g: 8 mL: 8 mL: 0.016 g: 0.009 g; The modified cyclodextrin microspheres are prepared by the following steps: Step B1: Mix dimethylamine, 3-chloro-2-hydroxypropyl sodium sulfate and deionized water, react at a stirring rate of 180 rpm and a temperature of 50 °C for 6 h, perform rotary evaporation, washing and drying to obtain intermediate a. Mix intermediate a, epichlorohydrin and isopropanol, stir at a stirring rate of 180 rpm and a temperature of 60 °C, add sodium carbonate and react for 4 h, perform vacuum distillation, washing and drying to obtain intermediate b; The dosage ratio of dimethylamine, 3-chloro-2-hydroxypropyl sodium sulfate and deionized water is 2.55 g: 10 g: 35 mL; the dosage ratio of intermediate a, epichlorohydrin, isopropanol and sodium carbonate is 6.6 g: 4.1 mL: 8 mL: 1.2 g; Step B2: Mix kerosene, Tween-20 and Span-80, stir at a stirring rate of 200 rpm at room temperature for 15 min to obtain a continuous phase. Mix β-cyclodextrin and sodium hydroxide solution, stir at a stirring rate of 120 rpm at room temperature for 15 min, then add epichlorohydrin and intermediate b, and continue to stir for 1 h to obtain a dispersed phase. Add the dispersed phase to the continuous phase, react at a temperature of 80 °C and a stirring rate of 700 rpm for 4 h, perform centrifugation, washing and drying to obtain the modified cyclodextrin microspheres; The mass fraction of the sodium hydroxide solution is 35%, and the dosage ratio of kerosene, Tween-20, Span-80, β-cyclodextrin, sodium hydroxide solution, epichlorohydrin and intermediate b is 80 mL: 0.3 g: 0.85 g: 2.3 g: 25 mL: 3.4 mL: 0.42 g.

[0019] Example 3 A preparation method of a degradable polyanionic cellulose filtrate reducer for drilling fluid, which includes the following steps: Weigh the following raw materials in parts by weight: 0.7 part of polyanionic cellulose, 0.09 part of modified nanocellulose and 0.015 part of modified cyclodextrin microspheres; Mix the polyanionic cellulose, modified nanocellulose and modified cyclodextrin microspheres to obtain a degradable polyanionic cellulose filtrate reducer for drilling fluid; The polyanionic cellulose is Kemic low-viscosity polyanionic cellulose; The modified nanocellulose is prepared by the following steps: Step A1: Mix 2-(dodecyltrithiocarbonate)-2-methylpropanoic acid, oxalyl chloride and dichloromethane, stir and add ethyl acetate under the conditions of a stirring rate of 180 rpm and a temperature of room temperature, react for 8 h, and perform rotary evaporation to obtain Intermediate 1. Mix nanocellulose and N,N-dimethylacetamide, stir for 2.5 h under the conditions of a stirring rate of 180 rpm and a temperature of 150 °C, then add lithium chloride, stir for 12 h under the condition of a temperature of 80 °C, then add triethylamine and Intermediate 1, stir for 24 h under the condition of a temperature of room temperature, then add methanol, filter, wash, and dry to obtain modified cellulose; The dosage ratio of 2-(dodecyltrithiocarbonate)-2-methylpropanoic acid, oxalyl chloride, dichloromethane and ethyl acetate is 4.5 g: 2.8 g: 30 mL: 1.5 mL; the dosage ratio of nanocellulose, N,N-dimethylacetamide, lithium chloride, triethylamine and Intermediate 1 is 1.03 g: 45 mL: 2.65 g: 1.4 g: 0.32 g; Figure 3 is the 1H NMR spectrum of the modified cellulose in Example 3. From Figure 3 it can be seen that the long-chain alkane [-CH2-] in 2-(dodecyltrithiocarbonate)-2-methylpropanoic acid appears at δ = 1.2 - 1.3, indicating that 2-(dodecyltrithiocarbonate)-2-methylpropanoic acid is successfully grafted onto nanocellulose; The nanocellulose is Kemic nanocellulose with a specification of 15 µm; Step A2: Mix the modified cellulose, azobisisobutyronitrile and tetrahydrofuran, stir and add 2-methylene-1,3-dioxepane, acrylamide and N,N-dimethylacetamide under the protection of nitrogen and under the conditions of a stirring rate of 120 rpm and a temperature of 80 °C, react for 12 h, perform rotary evaporation, add diethyl ether, filter, wash, and dry to obtain grafted cellulose; The dosage ratio of the modified cellulose, azobisisobutyronitrile, tetrahydrofuran, 2-methylene-1,3-dioxepane, acrylamide and N,N-dimethylacetamide is 0.84 g: 0.0025 g: 15 mL: 0.8 g: 1 g: 15 mL; Figure 4 is the 1H NMR spectrum of the grafted cellulose in Example 3. From Figure 4 it can be seen that the characteristic peak after the ring-opening of 2-methylene-1,3-dioxepane appears at δ = 4.1 - 4.2, indicating that 2-methylene-1,3-dioxepane successfully participates in the polymerization. From Figure 4 it can be seen that the characteristic peak of acrylamide appears at δ = 7.1 - 7.2, indicating that acrylamide successfully participates in the polymerization; Step A3: Mix 4-hydroxyazobenzene and N,N-dimethylformamide, and under the conditions of a stirring rate of 140 rpm and a temperature of 60 °C, stir and add potassium carbonate and epibromohydrin, react for 10 h, add ethyl acetate for extraction, washing, drying, and solvent removal to obtain Intermediate 2. Mix grafted cellulose, Intermediate 2, N,N-dimethylacetamide, and tetrahydrofuran, under nitrogen protection and a stirring rate of 80 rpm at room temperature, stir and add dimethylphenylphosphine, stir for 30 min, then add sodium borohydride, raise the temperature to 32 °C, continue stirring for 24 h, rotary evaporate, chromatograph, wash, and dry to obtain modified nanocellulose; The dosage ratio of 4-hydroxyazobenzene, N,N-dimethylformamide, potassium carbonate, and epibromohydrin is 5 g: 25 mL: 5.3 g: 6.5 g; the dosage ratio of grafted cellulose, Intermediate 2, N,N-dimethylacetamide, tetrahydrofuran, dimethylphenylphosphine, and sodium borohydride is 1.3 g: 0.015 g: 8 mL: 10 mL: 0.016 g: 0.009 g; Figure 5 is the 1H NMR spectrum of the modified nanocellulose in Example 3. From Figure 5 it can be seen that a characteristic peak of the hydroxyl group appears at δ = 5.3 - 5.4 after the reaction of Intermediate 2, indicating that Intermediate 2 has successfully participated in the reaction; The modified cyclodextrin microspheres are prepared through the following steps: Step B1: Mix dimethylamine, 3-chloro-2-hydroxypropyl sulfate sodium salt, and deionized water, and under the conditions of a stirring rate of 240 rpm and a temperature of 50 °C, react for 8 h, rotary evaporate, wash, and dry to obtain Intermediate a. Mix Intermediate a, epichlorohydrin, and isopropanol, under the conditions of a stirring rate of 240 rpm and a temperature of 60 °C, stir and add sodium carbonate, react for 6 h, carry out vacuum distillation, wash, and dry to obtain Intermediate b; The dosage ratio of dimethylamine, 3-chloro-2-hydroxypropyl sulfate sodium salt, and deionized water is 2.6 g: 11 g: 40 mL; the dosage ratio of Intermediate a, epichlorohydrin, isopropanol, and sodium carbonate is 6.8 g: 4.2 mL: 10 mL: 1.5 g; Step B2: Mix kerosene, Tween-20, and Span-80, and under the conditions of a stirring rate of 240 rpm at room temperature, stir for 20 min to obtain the continuous phase. Mix β-cyclodextrin and sodium hydroxide solution, under the conditions of a stirring rate of 140 rpm at room temperature, stir for 20 min, then add epichlorohydrin and Intermediate b, and continue stirring for 1.5 h to obtain the dispersed phase. Add the dispersed phase to the continuous phase, and under the conditions of a temperature of 85 °C and a stirring rate of 800 rpm, react for 6 h, centrifuge, wash, and dry to obtain the modified cyclodextrin microspheres; The mass fraction of the sodium hydroxide solution is 35%, and the dosage ratio of kerosene, Tween-20, Span-80, β-cyclodextrin, sodium hydroxide solution, epichlorohydrin and intermediate b is 90 mL: 0.32 g: 0.9 g: 2.5 g: 30 mL: 3.6 mL: 0.5 g.

[0020] Comparative Example 1 Compared with Example 3, intermediate b in the preparation process of the modified cyclodextrin microspheres in Example 3 was removed, and the other steps were the same.

[0021] Comparative Example 2 Compared with Example 3, 2-methyl-1,3-dioxepane in the preparation process of the modified nanocellulose in Example 3 was removed, and the other steps were the same.

[0022] Comparative Example 3 Compared with Example 3, intermediate 2 in the preparation process of the modified nanocellulose in Example 3 was replaced with benzyl glycidyl ether, and the other steps were the same.

[0023] Take the biodegradable polyanionic cellulose filtrate reducer for drilling fluid prepared in Example 1, Example 2, Example 3, Comparative Example 1, Comparative Example 2 and Comparative Example 3. Mix 8 g of sodium carbonate, 120 g of sodium bentonite and 4000 mL of water, stir to obtain a fresh water slurry. Mix 1.5 g of the biodegradable polyanionic cellulose filtrate reducer for drilling fluid and 100 mL of the fresh water slurry. Refer to GB / T 16783.1-2014, and test its filtrate reduction performance under the conditions of a temperature of 110 °C and 160 °C and aging for 16 h. During the preparation process of the fresh water slurry, add 25 w% of sodium chloride and 1.5 w% of calcium chloride to obtain a salt water slurry, and then test its filtrate reduction performance under the conditions of a temperature of 160 °C and aging for 16 h. Refer to SY / T 6788-2020 to determine its biodegradation rate BOD5 / COD. The test results are shown in Table 1 below: Test Results Table Test Results Table Test Items Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Filtration Loss of Freshwater Slurry after Aging at 110°C (mL) 7.19 6.89 7.25 7.90 7.42 8.51 Filtration Loss of Freshwater Slurry after Aging at 160°C (mL) 9.49 9.36 9.74 10.52 9.98 11.37 Filtration Loss of Saltwater Slurry after Aging at 160°C (mL) 11.88 11.60 11.95 11.84 12.20 14.02 <![CDATA[Biodegradation rate BOD5 / COD (%)]]> 43.11 42.40 43.57 42.43 31.71 41.85 As can be seen from the detection results of the shown table, by comparing Example 1, Example 2 and Example 3 with Comparative Example 1, Comparative Example 2 and Comparative Example 3, in Comparative Example 1, the intermediate b in the preparation process of the modified cyclodextrin microspheres of Example 3 was removed, resulting in the lack of zwitterionic structure on its cyclodextrin microspheres. As a result, under high-salt conditions, the cyclodextrin microspheres without zwitterionic modification (i.e., Comparative Example 1) would have electrostatic repulsion with polyanionic cellulose containing anions, thus causing phase separation and affecting the filtration reduction performance; in Comparative Example 2, 2-methylen-1,3-dioxepane in the preparation process of the modified nanocellulose of Example 3 was removed, resulting in a decrease in its degradation performance due to the lack of ester group structure; in Comparative Example 3, the intermediate 2 in the preparation process of the modified nanocellulose of Example 3 was replaced with benzyl glycidyl ether, resulting in the lack of binding between it and the modified cyclodextrin microspheres, thereby affecting its filtration reduction performance.

[0024] In the description of the specification, the description referring to terms such as "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0025] The above content is only an example and illustration of the concept of the present invention. Those skilled in the art of the present technology can make various modifications or supplements to the described specific embodiments or use similar ways to replace them. As long as they do not deviate from the concept of the invention, they should all fall within the protection scope of the present invention.

Claims

1. A preparation method of a degradable polyanionic cellulose filtrate reducer for drilling fluid, characterized in that: It includes the following steps: Weigh the raw materials in the following parts by weight: 0.6 - 0.7 parts of polyanionic cellulose, 0.08 - 0.09 parts of modified nanocellulose, and 0.01 - 0.015 parts of modified cyclodextrin microspheres; mix the polyanionic cellulose, modified nanocellulose, and modified cyclodextrin microspheres to obtain a degradable polyanionic cellulose filtrate reducer for drilling fluid; The modified nanocellulose is prepared through the following steps: Step A1: Mix 2-(dodecyltrithiocarbonate)-2-methylpropanoic acid, oxalyl chloride, and dichloromethane, stir and add ethyl acetate at a stirring rate of 140 - 180 rpm and at room temperature for 6 - 8 h, then perform rotary evaporation to obtain Intermediate 1. Mix nanocellulose and N,N-dimethylacetamide, stir at a stirring rate of 140 - 180 rpm and at 150 °C for 2 - 2.5 h, then add lithium chloride, stir at 80 °C for 10 - 12 h, then add triethylamine and Intermediate 1, stir at room temperature for 24 h, then add methanol, filter, wash, and dry to obtain modified cellulose; Step A2: Mix the modified cellulose, azobisisobutyronitrile, and tetrahydrofuran, stir and add 2-methylene-1,3-dioxepane, acrylamide, and N,N-dimethylacetamide under nitrogen protection at a stirring rate of 80 - 120 rpm and at 80 °C for 10 - 12 h, then perform rotary evaporation, add diethyl ether, filter, wash, and dry to obtain grafted cellulose; Step A3: Mix 4-hydroxyazobenzene and N,N-dimethylformamide, stir and add potassium carbonate and epibromohydrin at a stirring rate of 120 - 140 rpm and at 60 °C for 8 - 10 h, then perform extraction with ethyl acetate, wash, dry, and remove the solvent to obtain Intermediate 2. Mix the grafted cellulose, Intermediate 2, N,N-dimethylacetamide, and tetrahydrofuran, stir under nitrogen protection at a stirring rate of 60 - 80 rpm at room temperature, stir and add dimethylphenylphosphine, stir for 30 min, then add sodium borohydride, raise the temperature to 30 - 32 °C, continue to stir for 24 h, then perform rotary evaporation, chromatography, wash, and dry to obtain modified nanocellulose; The modified cyclodextrin microspheres are prepared through the following steps: Step B1: Mix dimethylamine, 3-chloro-2-hydroxypropyl sodium sulfate, and deionized water, react at a stirring rate of 180 - 240 rpm and at 50 °C for 6 - 8 h, then perform rotary evaporation, wash, and dry to obtain Intermediate a. Mix Intermediate a, epichlorohydrin, and isopropyl alcohol, stir and add sodium carbonate at a stirring rate of 180 - 240 rpm and at 60 °C for 4 - 6 h, then perform vacuum distillation, wash, and dry to obtain Intermediate b; Step B2: Mix kerosene, Tween-20 and Span-80, and stir at a stirring rate of 200 - 240 rpm under room temperature conditions for 15 - 20 min to obtain a continuous phase. Mix β-cyclodextrin and sodium hydroxide solution, stir at a stirring rate of 120 - 140 rpm under room temperature conditions for 15 - 20 min, then add epichlorohydrin and intermediate b, and continue to stir for 1 - 1.5 h to obtain a dispersed phase. Add the dispersed phase to the continuous phase, react at a temperature of 80 - 85 °C and a stirring rate of 700 - 800 rpm for 4 - 6 h, centrifuge, wash, and dry to obtain modified cyclodextrin microspheres.

2. The preparation method of a degradable polyanionic cellulose filtrate reducer for drilling fluid according to claim 1, characterized in that: In Step A1: The dosage ratio of 2-(dodecyltrithiocarbonate)-2-methylpropanoic acid, oxalyl chloride, dichloromethane, and ethyl acetate is 4.2 - 4.5 g : 2.5 - 2.8 g : 25 - 30 mL : 1.2 - 1.5 mL; the dosage ratio of nanocellulose, N,N-dimethylacetamide, lithium chloride, triethylamine, and intermediate 1 is 0.95 - 1.03 g : 40 - 45 mL : 2.5 - 2.65 g : 1.35 - 1.4 g : 0.28 - 0.32 g.

3. The preparation method of a degradable polyanionic cellulose filtrate reducer for drilling fluid according to claim 1, characterized in that: In Step A2: The dosage ratio of modified cellulose, azobisisobutyronitrile, tetrahydrofuran, 2-methylene-1,3-dioxepane, acrylamide, and N,N-dimethylacetamide is 0.8 - 0.84 g : 0.002 - 0.0025 g : 12 - 15 mL : 0.6 - 0.8 g : 0.9 - 1 g : 12 - 15 mL.

4. The preparation method of a degradable polyanionic cellulose filtrate reducer for drilling fluid according to claim 1, characterized in that: In Step A3: The dosage ratio of 4-hydroxyazobenzene, N,N-dimethylformamide, potassium carbonate, and epibromohydrin is 4.8 - 5 g : 23 - 25 mL : 5.2 - 5.3 g : 6.3 - 6.5 g; the dosage ratio of grafted cellulose, intermediate 2, N,N-dimethylacetamide, tetrahydrofuran, dimethylphenylphosphine, and sodium borohydride is 1.2 - 1.3 g : 0.012 - 0.015 g : 6 - 8 mL : 8 - 10 mL : 0.015 - 0.016 g : 0.008 - 0.009 g.

5. The preparation method of a degradable polyanionic cellulose filtrate reducer for drilling fluid according to claim 1, characterized in that: In Step B1: The dosage ratio of dimethylamine, 3-chloro-2-hydroxypropylsulfate sodium salt, and deionized water is 2.55 - 2.6 g : 10 - 11 g : 35 - 40 mL; the dosage ratio of intermediate a, epichlorohydrin, isopropanol, and sodium carbonate is 6.6 - 6.8 g : 4.1 - 4.2 mL : 8 - 10 mL : 1.2 - 1.5 g.

6. The preparation method of a degradable polyanionic cellulose filtrate reducer for drilling fluid according to claim 1, characterized in that: In Step B2: The mass fraction of the sodium hydroxide solution is 35%, and the dosage ratio of kerosene, Tween-20, Span-80, β-cyclodextrin, sodium hydroxide solution, epichlorohydrin, and intermediate b is 80 - 90 mL : 0.3 - 0.32 g : 0.85 - 0.9 g : 2.3 - 2.5 g : 25 - 30 mL : 3.4 - 3.6 mL : 0.42 - 0.5 g.

7. A degradable polyanionic cellulose filtrate reducer for drilling fluid, characterized in that: Prepared by the preparation method according to any one of Claims 1 - 6.

Images