Temperature-resistant and salt-resistant polymeric cellulose filtrate reducer and preparation method thereof

Abstract

The invention relates to the technical field of preparation of chemical treatment agents for oil and gas drilling, and discloses a temperature-resistant and salt-resistant polymeric cellulose filtrate reducer and a preparation method thereof. The method comprises three stages of base catalytic activation, gradient etherification modification and controllable free radical graft polymerization which are performed in sequence. The preparation method comprises the following steps: activating and swelling microcrystalline cellulose in a ternary alkali metal hydroxide mixed alcohol-water solution in an inert atmosphere; sequentially etherifying to obtain a zwitterionic cellulose ether intermediate; and finally, in a lithium chloride / dimethyl sulfoxide complex solvent system, carrying out ultrasonic treatment assisted atom transfer radical graft copolymerization, and combining precipitation, washing, supercritical carbon dioxide drying and low-temperature crushing to obtain the product. The whole preparation process can be continuously completed, and the product has excellent temperature resistance and salt resistance and is suitable for filtrate loss reduction treatment of drilling fluid under complex oil and gas drilling working conditions.

Description

Technical Field

[0001] This invention relates to the field of chemical treatment agent preparation technology for oil and gas drilling, specifically to a temperature-resistant and salt-resistant polymeric cellulose filtration loss reducer and its preparation method. Background Technology

[0002] In oil and gas drilling, fluid loss control is a crucial aspect of ensuring drilling safety and improving drilling efficiency. Fluid loss reducers, as key treatment agents in the drilling fluid system, play a vital role in forming a dense and resilient filter cake on the wellbore, reducing fluid loss to the formation and preventing complex downhole situations such as wellbore collapse, stuck pipe, and formation damage. As oil and gas exploration and development continue to advance into deeper formations, drilling conditions are becoming increasingly demanding. High-temperature and high-salinity environments place higher requirements on the performance of fluid loss reducers. Deep formation temperatures typically exceed 150°C, and formation water is often rich in divalent cations such as calcium and magnesium. Traditional fluid loss reducers are prone to degradation, cross-linking failure, or salt-sensitive flocculation in such environments, leading to deterioration of filter cake quality, a surge in fluid loss, and an inability to meet the demands of on-site drilling.

[0003] Cellulose materials are widely used in the preparation of drilling fluid filtration reducers due to their wide availability, renewability, and environmental friendliness. However, the low reactivity of hydroxyl groups on the molecular chains of natural cellulose and the presence of strong intramolecular and intermolecular hydrogen bonds result in poor water solubility and insufficient temperature and salt resistance, limiting their application in complex working conditions. To improve the performance of cellulose, the industry commonly employs chemical modification methods such as etherification and graft copolymerization. Etherification modification introduces hydrophilic groups into the cellulose molecular chains, improving water solubility and salt resistance; common etherification methods include carboxymethylation, hydroxyethylation, and quaternization. Graft copolymerization, on the other hand, imparts excellent temperature and salt resistance properties to cellulose by introducing monomer segments with specific functions.

[0004] Current technologies for preparing cellulose-modified fluid loss reducers still have many shortcomings. Document CN101602938A discloses a cellulose-based drilling fluid fluid loss reducer and its preparation method, which prepares temperature- and salt-resistant products by modifying cellulose. However, this technology is prone to degradation under high-temperature and high-salt environments, resulting in insufficient performance stability. Some technologies employ single etherification modification, introducing a limited variety of functional groups, making it difficult to simultaneously achieve both temperature resistance and salt resistance, leading to a significant decrease in fluid loss control under high-temperature and high-salt environments. While some technologies combine etherification and graft copolymerization, improper control of reaction conditions during etherification results in incomplete etherification and uneven substitution distribution, affecting the efficiency of subsequent grafting reactions and the stability of product performance. In the graft polymerization stage, traditional free radical polymerization methods suffer from poor reaction controllability and a wide molecular weight distribution of the product, leading to significant fluctuations in product performance. Furthermore, existing preparation processes are mostly batch operations, requiring each reaction stage to be completed in different devices, resulting in cumbersome material transfer processes, low production efficiency, and difficulty in precisely controlling reaction parameters, which is detrimental to large-scale production. Meanwhile, some of the solvent systems used in the modification processes are highly toxic and difficult to recycle, posing environmental risks; the post-processing drying methods for the products are mostly conventional hot air drying, which can easily lead to product agglomeration and structural damage, further affecting the performance of the products. Summary of the Invention

[0005] The purpose of this invention is to provide a heat-resistant and salt-resistant polymeric cellulose filtration loss reducer and its preparation method, so as to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, this invention provides a heat-resistant and salt-resistant polymeric cellulose filtration loss reducer and its preparation method, the method comprising three sequential stages: alkali-catalyzed activation, gradient etherification modification, and controlled free radical grafting polymerization. (1) Under an inert atmosphere, 100g of microcrystalline cellulose was added and placed in a mixed alcoholic-aqueous solution of ternary alkali metal hydroxide containing a phase transfer catalyst for activation and swelling to obtain activated cellulose slurry; (2) Transfer all the activated cellulose slurry obtained in step (1) to a high-pressure reactor, and add 35g of sodium chloroacetate and 42g of glycidyltrimethylammonium chloride sequentially for etherification. The first stage of the sequential etherification is controlled at a temperature of 50-60℃ and a pressure of 0.2-0.5MPa for 1.5-2.5 hours. In the second stage, the temperature is raised to 75-85℃ and the pressure is released to atmospheric pressure. Simultaneously, a sodium 2-acrylamido-2-methylpropanesulfonate solution is added dropwise. The sodium 2-acrylamido-2-methylpropanesulfonate solution is prepared by dissolving 28g of sodium 2-acrylamido-2-methylpropanesulfonate in 80mL of deionized water. Continue the reaction for 2-3 hours to obtain the zwitterionic cellulose ether intermediate. (3) Disperse all the zwitterionic cellulose ethers obtained in step (2) in a lithium chloride / dimethyl sulfoxide complex solvent system. Under ultrasonic treatment, add acrylamide, N-vinylcaprolactam and atom transfer radical polymerization initiation system in sequence. Carry out atom transfer radical graft copolymerization reaction at 65-75℃ for 4-6 hours. After the reaction is completed, the filtrate loss reducer is obtained by precipitation, washing, supercritical carbon dioxide drying and low temperature pulverization.

[0007] Preferably, the ternary alkali metal hydroxide in step (1) is a mixture of lithium hydroxide, sodium hydroxide and potassium hydroxide in a molar ratio of 1:(2.5-3.5):(0.5-1), the volume ratio of ethanol to water in the mixed alcohol-water solution is (3:1)-(1:1), and it contains 1%-3% of hexadecyltrimethylammonium bromide as a phase transfer catalyst, with an activation temperature of 35-45℃ and an activation time of 90-150 minutes.

[0008] Preferably, the specific process parameters for the sequential etherification in step (2) are as follows: the first stage is a reaction at 0.3 MPa and 55°C for 2 hours, during which nitrogen gas is slowly introduced for protection; the second stage is a reaction at atmospheric pressure and 80°C, wherein the sodium 2-acrylamido-2-methylpropanesulfonate solution is added dropwise at a rate of 1 / 3 of its total amount per hour, and the reaction is kept at the temperature for 2.5 hours after the addition is completed.

[0009] Preferably, the amount of glycidyltrimethylammonium chloride added in step (2) is 0.8-1.2 times the molar amount of cellulose glucose unit, and it is added 30 minutes before the end of the first stage reaction and 10 minutes before the start of the second stage reaction.

[0010] Preferably, in the lithium chloride / dimethyl sulfoxide complex solvent system in step (3), the mass concentration of lithium chloride is 8%-12%; the frequency of the ultrasonic treatment is 40kHz and the power is 150-300W.

[0011] Preferably, the initiation system for the atom transfer radical graft copolymerization reaction in step (3) is a complex of pentamethyldiethylenetriamine and cuprous bromide, and the total molar ratio of acrylamide, N-vinylcaprolactam and the 2-acrylamido-2-methylpropanesulfonate sodium structural unit introduced in step (2) is (5-7):(2-3):1, the amount of acrylamide added is 120g, and the amount of N-vinylcaprolactam added is 45g.

[0012] Preferably, the conditions for supercritical carbon dioxide drying in step (3) are: pressure 10-15MPa, temperature 35-45℃, and time 4-8 hours; the low-temperature pulverization is carried out under liquid nitrogen protection using a fluidized bed impact jet mill, and the product particle size D90≤45μm is controlled.

[0013] Preferably, the degree of substitution of the zwitterionic cellulose ether intermediate obtained in step (2) satisfies the following: the degree of carboxymethyl substitution (DS_CM) is 0.15-0.25, the degree of quaternary ammonium salt substitution (DS_QA) is 0.05-0.12, the degree of sulfonic acid group substitution (DS_S) is ≥0.08, and the total degree of ionic substitution (DS_CM + DS_QA + DS_S) is controlled between 0.35-0.50.

[0014] Preferably, in the entire preparation process, the activation in step (1), the gradient etherification in step (2) and the graft polymerization in step (3) are all completed in the same continuous reaction device with multi-zone temperature control, online viscosity monitoring and micro-reaction feeding module, and the material is transported between different reaction zones by screw pump; After the reaction in step (3) is completed and before the precipitation step begins, 0.5%-1.5% by mass of epichlorohydrin is added to the reaction system for crosslinking treatment. The crosslinking reaction is carried out at 60°C for 0.5-1 hour. The amount of epichlorohydrin added accounts for 0.5%-2% of the dry weight of cellulose.

[0015] Preferably, the present invention also includes a heat-resistant and salt-resistant polymeric cellulose filtration loss reducer, which is prepared by the above-described method for preparing a heat-resistant and salt-resistant polymeric cellulose filtration loss reducer.

[0016] Compared with the prior art, the beneficial effects of the present invention are: This preparation method employs a three-stage progressive modification process. Through the synergistic effect of alkali-catalyzed activation, gradient etherification modification, and controlled free radical graft polymerization, the product's temperature and salt resistance, as well as filtration loss control, are significantly improved. In the alkali-catalyzed activation stage, a ternary alkali metal hydroxide mixed alcohol-water solution is selected as the activation system. Combined with a phase transfer catalyst, this effectively disrupts intramolecular and intermolecular hydrogen bonds in cellulose, enhances the reactivity of cellulose hydroxyl groups, and promotes uniform swelling of cellulose, creating favorable conditions for the efficient subsequent etherification reaction. Compared to a single alkali metal hydroxide activation system, the ternary mixed system allows for precise control of the activation degree by adjusting the proportions of each component, avoiding over-activation that could lead to cellulose chain degradation and ensuring the stability of the product structure during subsequent modification processes.

[0017] The gradient etherification modification stage employs a sequential etherification approach, introducing carboxymethyl, quaternary ammonium salt, and sulfonic acid groups in turn to form a structurally controllable zwitterionic cellulose ether intermediate. This design allows for precise stepwise grafting of different functional groups, avoiding competitive reactions between different etherifying agents and improving the uniformity and controllability of the substitution degree of each group. The introduced zwitterionic groups can form a synergistic effect on the molecular chain, enhancing the solubility and dispersibility of the product in the brine system and reducing the influence of salt ions on the conformation of the molecular chain. Among them, the sulfonic acid group has strong hydrophilicity and salt resistance, the quaternary ammonium salt group can increase the positive charge density of the molecular chain and form an adsorption effect with the surface of the formation rock, and the carboxymethyl group can enhance the binding ability of the product with water molecules. The three synergistically endow the intermediate with good initial salt resistance and filter cake forming ability. At the same time, by strictly controlling the substitution degree of each group and the range of total ionic substitution, it is ensured that the intermediate has suitable reactivity, providing sufficient active sites for subsequent graft polymerization reactions.

[0018] The controlled radical grafting polymerization stage employs atom transfer radical polymerization (ATRP) technology, using pentamethyldiethylenetriamine / cuprous bromide as the initiation system. Combined with ultrasonic treatment to assist dispersion, the molecular weight and distribution of the grafted chains can be precisely controlled, achieving directional grafting of functional monomers. The introduced acrylamide monomer segment enhances the product's water solubility and filter cake adhesion, while the N-vinylcaprolactam segment imparts excellent temperature resistance. Its unique heterocyclic structure forms a stable conformation at high temperatures, preventing molecular chain degradation. Synergistically with the previously introduced 2-acrylamido-2-methylpropanesulfonate sodium segment, it further strengthens the product's temperature and salt resistance synergistic effect. The application of ultrasonic treatment promotes uniform dispersion of intermediates in the solvent system, improves the contact efficiency between monomers and active sites, accelerates the reaction process, and reduces product structural defects caused by excessively vigorous local reactions.

[0019] The entire preparation process utilizes a continuous reaction apparatus with multi-zone temperature control, online viscosity monitoring, and a micro-reaction feeding module. This enables continuous operation from activation and etherification to graft polymerization, eliminating the need for multiple material transfers. This not only simplifies the production process and improves efficiency but also ensures the stability and repeatability of the reaction process by precisely controlling parameters such as temperature, pressure, and feed rate in each reaction zone, thus reducing product performance fluctuations. Introducing a cross-linking treatment step after the graft polymerization reaction further enhances the structural stability of the product and the density of the filter cake, thereby improving filtration loss control.

[0020] The post-processing of the product employs supercritical carbon dioxide drying technology. Compared to traditional hot air drying, this technology enables rapid solvent removal under low-temperature and high-pressure conditions, preventing product agglomeration, structural shrinkage, or thermal degradation during drying and ensuring the product's dispersibility and original structural integrity. Subsequent low-temperature pulverization is carried out under liquid nitrogen protection, effectively controlling the product particle size and ensuring a suitable specific surface area, thereby improving its dissolution and dispersion rate and efficiency in drilling fluids. Furthermore, the solvent system and modifiers used in the preparation process exhibit good environmental compatibility, and some solvents are recyclable, reducing the environmental impact of the production process and aligning with the trend of green chemical development. Attached Figure Description

[0021] Figure 1 This diagram illustrates the working steps of the preparation method of the temperature-resistant and salt-resistant polymeric cellulose filtration loss reducer described in this invention. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to specific embodiments and comparative examples, in order to make the technical solutions and advantages of the present invention clearer, and not to limit the present invention. All raw materials used in the following examples are commercially available industrial-grade raw materials. Among them, the degree of polymerization of microcrystalline cellulose is 200-300 and the purity is ≥98%; sodium chloroacetate purity is ≥99%; glycidyltrimethylammonium chloride purity is ≥98%; sodium 2-acrylamido-2-methylpropanesulfonate (AMPS) purity is ≥99%; acrylamide (AM) purity is ≥99.5%; N-vinylcaprolactam (NVC) purity is ≥98%; pentamethyldiethylenetriamine (PMDETA) purity is ≥99%; cuprous bromide (CuBr) purity is ≥99%; lithium chloride (LiCl) purity is ≥98%; dimethyl sulfoxide (DMSO) purity is ≥99.5%; epichlorohydrin purity is ≥99%; hexadecyltrimethylammonium bromide (CTAB) purity is ≥99%; lithium hydroxide, sodium hydroxide, and potassium hydroxide are all analytical grade; and ethanol is industrial-grade 95% ethanol.

[0023] The continuous reaction apparatus used in the following examples and comparative examples includes a multi-zone temperature control module (temperature control accuracy ±1℃), an online viscosity monitoring module (detection range 1-1000mPa·s) and a micro-reaction feeding module. Material is conveyed in each reaction zone by a screw pump with a material conveying accuracy of ±0.5mL / min.

[0024] Performance testing method description: 1. Filtration loss test: The test shall be conducted in accordance with GB / T 16783.1-2021 "Field testing of drilling fluids for oil and gas industry - Part 1: Water-based drilling fluids". The test conditions for API filtration loss at normal temperature and pressure are 25℃ and 0.69MPa, and the test time is 30min. The test conditions for HTHP filtration loss are 150℃ and 3.5MPa, and the test time is 30min.

[0025] 2. Salt resistance test: Prepare base slurry containing different concentrations of NaCl (5000mg / L, 10000mg / L, 20000mg / L, 30000mg / L), add 1.5% (mass fraction) of filtration loss reducer, stir evenly, and then test the API filtration loss and HTHP filtration loss respectively.

[0026] 3. Thermal stability test: The drilling fluid containing 1.5% filtration loss reducer was aged at 180℃ for 16 hours. After cooling to room temperature, the API filtration loss and HTHP filtration loss were tested.

[0027] 4. Degree of substitution test: The degree of carboxymethyl substitution (DS_CM) was determined by ashing method; the degree of quaternary ammonium salt substitution (DS_QA) was determined by potentiometric titration method; and the degree of sulfonic acid group substitution (DS_S) was determined by turbidimetric method.

[0028] 5. Product particle size test: The particle size was measured using a laser particle size analyzer. The test medium was deionized water, and the dispersion method was ultrasonic dispersion for 5 minutes. The D90 value (the particle size corresponding to 90% of the cumulative volume fraction) was recorded.

[0029] Example 1

[0030] The preparation method of the temperature-resistant and salt-resistant polymeric cellulose filtration loss reducer in this embodiment includes three stages: alkali-catalyzed activation, gradient etherification modification, and controlled free radical grafting polymerization. The specific steps are as follows: (1) Alkali-catalyzed activation: Under nitrogen protection (inert atmosphere), 100g of microcrystalline cellulose was added to the activation zone of the continuous reaction device, followed by 500mL of a pre-prepared ternary alkali metal hydroxide mixed alcohol-water solution; wherein the ternary alkali metal hydroxide was a mixture of lithium hydroxide, sodium hydroxide and potassium hydroxide in a molar ratio of 1:3:0.8, with a total mass of 25g; the volume ratio of ethanol to water in the mixed alcohol-water solution was 2:1, and it contained 2% hexadecyltrimethylammonium bromide as a phase transfer catalyst; the temperature of the activation zone was controlled at 40℃, and the activation time was 120 minutes. During this period, the viscosity of the system was monitored in real time by an online viscosity monitoring module, and finally activated cellulose slurry was obtained.

[0031] (2) Gradient etherification modification: The activated cellulose slurry obtained in step (1) is transported to the etherification zone (high-pressure reactor) of the continuous reaction device by a screw pump. First, 35g of sodium chloroacetate is added, and stirring is started (stirring rate 300r / min). The temperature of the first stage of the etherification zone is controlled at 55℃ and the pressure is 0.3MPa. The reaction is carried out for 2 hours. 30 minutes before the end of the first stage reaction, glycidyltrimethylammonium chloride (the amount added is 1.0 times the molar amount of cellulose glucose unit, i.e., 42g) is slowly added through the micro-reaction feed module. The addition is completed 10 minutes before the start of the second stage reaction. After the first stage reaction is completed, the temperature of the etherification zone is raised to 80℃ and the pressure is released to atmospheric pressure. At the same time, 2-acrylamido-2-methylpropanesulfonate sodium solution (28g) is added dropwise at a uniform rate through the micro-reaction feed module. Sodium 2-acrylamido-2-methylpropanesulfonate was dissolved in 80 mL of deionized water. The dropping rate was 1 / 3 of the total amount added per hour. After the dropping was completed, the reaction was kept at the temperature for 2.5 hours. Nitrogen gas was continuously introduced for protection during the reaction. The viscosity of the system was controlled between 200-300 mPa·s by an online viscosity monitoring module. Finally, the zwitterionic cellulose ether intermediate was obtained.

[0032] (3) Controlled free radical grafting polymerization: The zwitterionic cellulose ether intermediate obtained in step (2) was transported to the grafting polymerization zone of the continuous reaction device by a screw pump. 800 mL of the pre-prepared lithium chloride / dimethyl sulfoxide complex solvent system (in which the mass concentration of lithium chloride was 10%) was added, and the ultrasonic treatment device (frequency 40 kHz, power 200 W) was turned on and dispersed for 30 minutes. Then, 120 g of acrylamide, 45 g of N-vinylcaprolactam and the atom transfer radical polymerization initiation system (a complex composed of 0.5 g of pentamethyldiethylenetriamine and 0.3 g of cuprous bromide) were added in sequence. The temperature of the grafting polymerization zone was controlled at 70 °C and the atom transfer radical grafting copolymerization reaction was carried out for 5 hours. After the reaction was completed, 1.2 g of epichlorohydrin (accounting for 1.2% of the dry weight of cellulose) was added to the reaction system, and the temperature was controlled at 60 °C for crosslinking treatment for 0.8 hours. After the crosslinking reaction was completed, the reaction product was slowly added to 3000 mL of acetone for precipitation and allowed to stand for 2 hours. After 4 hours, the filter cake was obtained by filtration. The filter cake was washed three times with acetone (1000 mL each time) and then washed twice with deionized water (1000 mL each time) until the pH of the washing solution was neutral. The washed filter cake was placed in a supercritical carbon dioxide drying device and dried for 6 hours at a pressure of 12 MPa and a temperature of 40 °C. After drying, the product was pulverized at low temperature using a fluidized bed impingement jet mill under liquid nitrogen protection, and the particle size D90 was controlled to be ≤45 μm. Finally, the heat-resistant and salt-resistant polymeric cellulose filtration loss reducer was obtained.

[0033] Example 2

[0034] The preparation method of the temperature-resistant and salt-resistant polymeric cellulose filtration loss reducer in this embodiment includes three stages: alkali-catalyzed activation, gradient etherification modification, and controlled free radical grafting polymerization. The specific steps are as follows: (1) Alkali-catalyzed activation: Under nitrogen protection, 100g of microcrystalline cellulose was added to the activation zone of the continuous reaction device, followed by 500mL of a pre-prepared ternary alkali metal hydroxide mixed alcohol aqueous solution; wherein the ternary alkali metal hydroxide was a mixture of lithium hydroxide, sodium hydroxide and potassium hydroxide in a molar ratio of 1:2.5:0.5, with a total mass of 22g; the volume ratio of ethanol to water in the mixed alcohol aqueous solution was 3:1, and it contained 1% hexadecyltrimethylammonium bromide as a phase transfer catalyst; the temperature of the activation zone was controlled at 35℃, and the activation time was 150 minutes. During this period, the viscosity of the system was monitored in real time by an online viscosity monitoring module, and finally activated cellulose slurry was obtained.

[0035] (2) Gradient etherification modification: The activated cellulose slurry obtained in step (1) is transported to the etherification zone of the continuous reaction device by a screw pump. First, 30g of sodium chloroacetate is added, and stirring is started (stirring rate 280r / min). The temperature of the first stage of the etherification zone is controlled at 50℃ and the pressure is 0.2MPa. The reaction lasts for 2.5 hours. 30 minutes before the end of the first stage reaction, glycidyltrimethylammonium chloride (0.8 times the molar amount of cellulose glucose unit, i.e., 34g) is slowly added through the micro-reaction feed module. The addition is completed 10 minutes before the start of the second stage reaction. After the first stage reaction is completed, the temperature of the etherification zone is raised to 75℃ and the pressure is released to atmospheric pressure. At the same time, 2-acrylamido-2-methylpropanesulfonate sodium solution (22g) is added dropwise at a uniform rate through the micro-reaction feed module. Sodium 2-acrylamido-2-methylpropanesulfonate was dissolved in 60 mL of deionized water. The dropping rate was 1 / 3 of the total amount added per hour. After the dropping was completed, the reaction was kept at the temperature for 3 hours. Nitrogen gas was continuously introduced for protection during the reaction. The viscosity of the system was controlled between 180-250 mPa·s by an online viscosity monitoring module. Finally, the zwitterionic cellulose ether intermediate was obtained.

[0036] (3) Controlled free radical grafting polymerization: The zwitterionic cellulose ether intermediate obtained in step (2) was transported to the grafting polymerization zone of the continuous reaction device by a screw pump. 800 mL of the pre-prepared lithium chloride / dimethyl sulfoxide complex solvent system (in which the mass concentration of lithium chloride was 8%) was added, and the ultrasonic treatment device (frequency 40 kHz, power 150 W) was turned on and dispersed for 40 minutes. Then, 100 g of acrylamide, 36 g of N-vinylcaprolactam, and an atom transfer radical polymerization initiation system (a complex composed of 0.4 g of pentamethyldiethylenetriamine and 0.25 g of cuprous bromide) were added in sequence. The temperature of the grafting polymerization zone was controlled at 65 °C and the atom transfer radical grafting copolymerization reaction was carried out for 6 hours. After the reaction was completed, 0.8 g of epichlorohydrin (accounting for 0.8% of the dry weight of cellulose) was added to the reaction system, and the temperature was controlled at 60 °C for crosslinking treatment for 1 hour. After the crosslinking reaction was completed, the reaction product was slowly added to 3000 mL of acetone for precipitation and allowed to stand for 2 hours. After 4 hours, the filter cake was obtained by filtration. The filter cake was washed three times with acetone (1000 mL each time) and then washed twice with deionized water (1000 mL each time) until the pH of the washing solution was neutral. The washed filter cake was placed in a supercritical carbon dioxide drying device and dried for 8 hours at a pressure of 10 MPa and a temperature of 35°C. After drying, the product was pulverized at low temperature using a fluidized bed impingement jet mill under liquid nitrogen protection to control the particle size D90≤45μm, and finally the heat-resistant and salt-resistant polymeric cellulose filtration loss reducer was obtained.

[0037] Example 3

[0038] The preparation method of the temperature-resistant and salt-resistant polymeric cellulose filtration loss reducer in this embodiment includes three stages: alkali-catalyzed activation, gradient etherification modification, and controlled free radical grafting polymerization. The specific steps are as follows: (1) Alkali-catalyzed activation: Under nitrogen protection, 100g of microcrystalline cellulose was added to the activation zone of the continuous reaction device, followed by 500mL of a pre-prepared mixed alcohol-water solution of ternary alkali metal hydroxide; wherein the ternary alkali metal hydroxide was a mixture of lithium hydroxide, sodium hydroxide and potassium hydroxide in a molar ratio of 1:3.5:1, with a total mass of 28g; the volume ratio of ethanol to water in the mixed alcohol-water solution was 1:1, and it contained 3% hexadecyltrimethylammonium bromide as a phase transfer catalyst; the temperature of the activation zone was controlled at 45℃, and the activation time was 90 minutes. During this period, the viscosity of the system was monitored in real time by an online viscosity monitoring module, and finally activated cellulose slurry was obtained.

[0039] (2) Gradient etherification modification: The activated cellulose slurry obtained in step (1) is transported to the etherification zone of the continuous reaction device by a screw pump. First, 40g of sodium chloroacetate is added, and stirring is started (stirring rate 320r / min). The temperature of the first stage of the etherification zone is controlled at 60℃ and the pressure is 0.5MPa. The reaction lasts for 1.5 hours. 30 minutes before the end of the first stage reaction, glycidyltrimethylammonium chloride (the amount added is 1.2 times the molar amount of cellulose glucose unit, i.e., 50g) is slowly added through the micro-reaction feed module. The addition is completed 10 minutes before the start of the second stage reaction. After the first stage reaction is completed, the temperature of the etherification zone is raised to 85℃ and the pressure is released to atmospheric pressure. At the same time, 2-acrylamido-2-methylpropanesulfonate sodium solution (35g) is added dropwise at a uniform rate through the micro-reaction feed module. Sodium 2-acrylamido-2-methylpropanesulfonate was dissolved in 100 mL of deionized water. The dropping rate was 1 / 3 of the total amount added per hour. After the dropping was completed, the reaction was kept at the temperature for 2 hours. Nitrogen gas was continuously introduced for protection during the reaction. The viscosity of the system was controlled between 250-350 mPa·s by an online viscosity monitoring module. Finally, the zwitterionic cellulose ether intermediate was obtained.

[0040] (3) Controlled free radical grafting polymerization: The zwitterionic cellulose ether intermediate obtained in step (2) was transported to the grafting polymerization zone of the continuous reaction device by a screw pump. 800 mL of the pre-prepared lithium chloride / dimethyl sulfoxide complex solvent system (in which the mass concentration of lithium chloride was 12%) was added, and the ultrasonic treatment device (frequency 40 kHz, power 300 W) was turned on and dispersed for 20 minutes. Then, 140 g of acrylamide, 54 g of N-vinylcaprolactam, and an atom transfer radical polymerization initiation system (a complex composed of 0.6 g of pentamethyldiethylenetriamine and 0.35 g of cuprous bromide) were added in sequence. The temperature of the grafting polymerization zone was controlled at 75 °C and the atom transfer radical grafting copolymerization reaction was carried out for 4 hours. After the reaction was completed, 2.0 g of epichlorohydrin (accounting for 2.0% of the dry weight of cellulose) was added to the reaction system and the temperature was controlled at 60 °C for crosslinking treatment for 0.5 hours. After the crosslinking reaction was completed, the reaction product was slowly added to 3000 mL of acetone for precipitation and allowed to stand. After 24 hours, the filter cake was obtained by filtration. The filter cake was washed three times with acetone (1000 mL each time) and then washed twice with deionized water (1000 mL each time) until the pH of the washing solution was neutral. The washed filter cake was placed in a supercritical carbon dioxide drying device and dried for 4 hours at a pressure of 15 MPa and a temperature of 45 °C. After drying, the product was pulverized at low temperature using a fluidized bed impingement jet mill under liquid nitrogen protection to control the particle size D90≤45μm, and finally the heat-resistant and salt-resistant polymeric cellulose filtration loss reducer was obtained.

[0041] Comparative Example 1 (lacking the step of adding glycidyltrimethylammonium chloride in gradient etherification) The preparation method of this comparative example is exactly the same as that of Example 1, except that glycidyltrimethylammonium chloride is not added in step (2). The specific steps are as follows: (1) Alkali-catalyzed activation: Same as step (1) in Example 1.

[0042] (2) Gradient etherification modification: The activated cellulose slurry obtained in step (1) is transported to the etherification zone of the continuous reaction device by a screw pump. First, 35g of sodium chloroacetate is added and stirring is started (stirring rate 300r / min). The temperature of the first stage of the etherification zone is controlled at 55℃ and the pressure is 0.3MPa. The reaction is carried out for 2 hours. After the first stage of the reaction is completed, the temperature of the etherification zone is raised to 80℃ and the pressure is released to atmospheric pressure. At the same time, 2-acrylamido-2-methylpropanesulfonate sodium solution (prepared by dissolving 28g of 2-acrylamido-2-methylpropanesulfonate in 80mL of deionized water) is added dropwise at a uniform rate through the micro-reaction feeding module. The dropping rate is 1 / 3 of the total amount added per hour. After the dropping is completed, the reaction is kept at the temperature for 2.5 hours. Nitrogen gas is continuously introduced for protection during the reaction. The viscosity of the system is controlled between 200-300mPa·s by the online viscosity monitoring module. Finally, the modified cellulose ether intermediate is obtained.

[0043] (3) Controlled free radical grafting polymerization: Same as step (3) in Example 1, and finally the modified cellulose filtration loss reducer product is obtained.

[0044] Comparative Example 2 (using conventional free radical polymerization instead of controlled free radical graft polymerization) The preparation method of this comparative example is exactly the same as that of Example 1, except that in step (3) ordinary free radical polymerization initiated by ammonium persulfate / sodium sulfite is used instead of atom transfer radical graft copolymerization. The specific steps are as follows: (1) Alkali-catalyzed activation: Same as step (1) in Example 1.

[0045] (2) Gradient etherification modification: Same as step (2) in Example 1.

[0046] (3) Ordinary free radical polymerization: The zwitterionic cellulose ether intermediate obtained in step (2) is transported to the polymerization zone of the continuous reaction device by a screw pump, and 800 mL of the pre-prepared lithium chloride / dimethyl sulfoxide complex solvent system (in which the mass concentration of lithium chloride is 10%) is added. The ultrasonic treatment device (frequency 40 kHz, power 200 W) is turned on and dispersed for 30 minutes. Then, 120 g of acrylamide and 45 g of N-vinylcaprolactam are added in sequence. The temperature of the polymerization zone is controlled at 70 °C, and the initiation system (composed of 0.8 g of ammonium persulfate and 0.4 g of sodium sulfite) is added to carry out ordinary free radical polymerization for 5 hours. After the reaction is completed, 1.2 g of epichlorohydrin (accounting for 1.2% of the dry weight of cellulose) is added to the reaction system, and the temperature is controlled at 60 °C to carry out crosslinking treatment for 0.8 hours. The subsequent precipitation, washing, drying and pulverizing steps are the same as step (3) of Example 1, and finally the modified cellulose filtrate loss reducer product is obtained.

[0047] Comparative Example 3 (without cross-linking treatment) The preparation method of this comparative example is exactly the same as that of Example 1, except that epichlorohydrin is not added for crosslinking treatment after the reaction in step (3). The specific steps are as follows: (1) Alkali-catalyzed activation: Same as step (1) in Example 1.

[0048] (2) Gradient etherification modification: Same as step (2) in Example 1.

[0049] (3) Controlled free radical grafting polymerization: The zwitterionic cellulose ether intermediate obtained in step (2) is transported to the grafting polymerization zone of the continuous reaction device by a screw pump. 800 mL of the pre-prepared lithium chloride / dimethyl sulfoxide complex solvent system (in which the mass concentration of lithium chloride is 10%) is added. The ultrasonic treatment device (frequency 40 kHz, power 200 W) is turned on and dispersed for 30 minutes. Then, 120 g of acrylamide, 45 g of N-vinylcaprolactam, and an atom transfer radical polymerization initiation system (a complex composed of 0.5 g of pentamethyldiethylenetriamine and 0.3 g of cuprous bromide) are added in sequence. The temperature of the grafting polymerization zone is controlled at 70 °C and the atom transfer radical grafting copolymerization reaction is carried out for 5 hours. After the reaction is completed, the reaction product is slowly added to 3000 mL of acetone for precipitation. The subsequent standing, filtration, washing, drying and pulverizing steps are the same as step (3) of Example 1. Finally, the modified cellulose filtrate loss reducer product is obtained.

[0050] The degree of substitution was tested on the intermediates obtained during the preparation process of Examples 1-3 and Comparative Example 1. The test results are shown in Table 1.

[0051]

[0052] The zwitterionic cellulose ether intermediates prepared in Examples 1-3 all exhibit reasonable degree of substitution distributions: carboxymethyl substitution degree (DS_CM) between 0.18 and 0.23, quaternary ammonium salt substitution degree (DS_QA) between 0.06 and 0.10, sulfonic acid group substitution degree (DS_S) between 0.09 and 0.12, and total ionic substitution degree between 0.33 and 0.45, all conforming to the defined substitution degree ranges (DS_CM 0.15-0.25, DS_QA 0.05-0.12, DS_S ≥ 0.08, total ionic substitution degree 0.35-0.50). This indicates that the gradient etherification process employed in this invention can effectively introduce three ionic groups—carboxymethyl, quaternary ammonium salt, and sulfonic acid groups—on the cellulose molecular chain, and the degree of substitution is controllable.

[0053] Comparing the test results of Example 1 and Comparative Example 1, it can be found that Comparative Example 1, due to the absence of glycidyltrimethylammonium chloride, has a quaternary ammonium salt substitution degree of 0 and a total ionic substitution degree of only 0.32, lower than 0.38 in Example 1, and does not reach the lower limit of total ionic substitution degree (0.35). This indicates that the addition of glycidyltrimethylammonium chloride is key to introducing quaternary ammonium salt groups, and can also increase the total ionic substitution degree of the intermediate. The increase in the total ionic substitution degree helps to enhance the salt resistance of the subsequently prepared filtration loss reducing agent, because the ionic groups can increase the extent of molecular chain extension in salt solution through charge repulsion, thereby better exerting the filtration loss reducing effect.

[0054] Example 3 exhibited the highest total ionic substitution degree (0.45), which was related to its higher reaction temperature during gradient etherification (60°C in the first stage and 85°C in the second stage) and the larger amount of etherifying agent added (40g sodium chloroacetate, 50g glycidyltrimethylammonium chloride, and 35g AMPS). The higher reaction temperature and sufficient etherifying agent promoted the etherification reaction and increased the substitution degree. In contrast, Example 2 had the lowest total ionic substitution degree (0.33), which was close to the lower limit of total ionic substitution degree. This was related to its lower reaction temperature (50°C in the first stage and 75°C in the second stage) and the smaller amount of etherifying agent added. This indicates that the reaction conditions and reagent dosage have a significant impact on the substitution degree. The present invention can achieve precise control of the substitution degree by reasonably adjusting these parameters.

[0055] The particle size and filtration loss at room temperature and pressure (API filtration loss) and high temperature and high pressure (HTHP filtration loss) of the finished filtration loss reducers prepared in Examples 1-3 and Comparative Examples 1-3 were tested. The test results are shown in Table 2.

[0056]

[0057] Table 2 shows that the particle size D90 of the filtration loss reducer products prepared in Examples 1-3 are all between 35.7-42.5 μm, which meets the requirement of D90≤45 μm. This indicates that the fluidized bed collision air jet milling process under liquid nitrogen protection used in this invention can effectively control the product particle size. The appropriate particle size distribution helps the filtration loss reducer to be uniformly dispersed in the drilling fluid, forming a dense filter cake, thereby reducing filtration loss.

[0058] Regarding filtration loss performance, the API filtration loss of Examples 1-3 was between 5.9-7.8 mL, and the HTHP filtration loss was between 16.8-21.5 mL, demonstrating excellent filtration loss reduction performance. Example 3 exhibited the lowest API filtration loss (5.9 mL) and the lowest HTHP filtration loss (16.8 mL), which is related to the high total ionic substitution degree of its intermediate, the high reaction temperature during graft polymerization, and the sufficient monomer dosage. The high total ionic substitution degree gives the filtration loss reducer molecules good solubility and spreadability in drilling fluid, effectively sealing formation pores; the sufficient monomer dosage results in longer graft chains, further enhancing the molecular chain entanglement and sealing ability. Example 2 showed relatively high API and HTHP filtration losses, which is related to the lower total ionic substitution degree of its intermediate. The lower ionic substitution degree resulted in insufficient molecular chain spreadability in solution, leading to a slightly poorer sealing effect.

[0059] Comparing the filtration loss data of Example 1 with those of the comparative examples, it can be found that the filtration loss of each comparative example is significantly higher than that of Example 1: the API filtration loss of Comparative Example 1 is 12.3 mL and the HTHP filtration loss is 35.6 mL, which are 1.9 times and 1.95 times that of Example 1, respectively; the API filtration loss of Comparative Example 2 is 9.7 mL and the HTHP filtration loss is 28.9 mL, which are 1.49 times and 1.58 times that of Example 1, respectively; and the API filtration loss of Comparative Example 3 is 8.5 mL and the HTHP filtration loss is 25.7 mL, which are 1.31 times and 1.40 times that of Example 1, respectively. This fully demonstrates that the key process steps of the present invention (gradient etherification to introduce quaternary ammonium salt groups, controlled free radical graft polymerization, and crosslinking treatment) play an important role in improving the filtration loss reduction performance of the filtration loss reducing agent.

[0060] Comparative Example 1, lacking quaternary ammonium salt groups, had insufficient charge density in its molecular chains, making it prone to aggregation in solution and difficult to form a dense filter cake, resulting in a significant increase in filtration loss. Comparative Example 2 used ordinary free radical polymerization instead of controlled free radical grafting polymerization. The reaction process of ordinary free radical polymerization was difficult to control, and the grafted chain length distribution was uneven. Some grafted chains were too short or too long, affecting the entanglement and blocking effect of the molecular chains. Therefore, the filtration loss was higher than that of Example 1. Comparative Example 3 did not undergo crosslinking treatment, and the rigidity and structural stability of the filtration loss reducer molecular chains were insufficient. Under high temperature and high pressure conditions, it was prone to degradation and curling, resulting in a decrease in the density and stability of the filter cake and a significant increase in HTHP filtration loss.

[0061] To further verify the temperature and salt resistance of the filtration loss reducing agent of the present invention, filtration loss tests were conducted on the products of Examples 1-3 and Comparative Examples 1-3 at different salt concentrations and after high-temperature aging. The test results are shown in Table 3. The salt concentration tests used four gradients: 5000 mg / L, 10000 mg / L, 20000 mg / L, and 30000 mg / L. The high-temperature aging conditions were 180℃ for 16 hours.

[0062] Table 3: Filtration loss test at different salt concentrations and after high-temperature aging

[0063] The filtration loss reducers in Examples 1-3 all exhibited good salt resistance under different salt concentrations. As the salt concentration increased from 5000 mg / L to 30000 mg / L, the API filtration loss only increased slightly, with increases ranging from 2.7 to 3.3 mL. Example 3 showed the best salt resistance with an API filtration loss of only 8.9 mL at a high salt concentration of 30000 mg / L; Example 1 was second with 9.5 mL; and Example 2 was 11.8 mL, still significantly lower than the comparative examples. This is because the present invention introduces three zwitterionic groups—carboxymethyl, quaternary ammonium salt, and sulfonic acid groups—through gradient etherification. These ionic groups can form a stable charge layer in the salt solution, preventing molecular chain aggregation through charge repulsion and maintaining the molecular chains in a well-stretched state, thereby continuously sealing formation porosity and reducing filtration loss. In contrast, Comparative Example 1, lacking quaternary ammonium salt groups and having insufficient charge density, is prone to salting out and aggregation of molecular chains under high salt concentrations, resulting in a sharp increase in filtration loss. The API filtration loss reached 21.3 mL at a salt concentration of 30,000 mg / L, which cannot meet the requirements for use in high-salt drilling environments.

[0064] Regarding high-temperature stability, after aging at 180℃ for 16 hours, the API and HTHP filtration losses of the filtration loss agents in Examples 1-3 did not increase significantly. The API filtration loss after aging was between 7.5-9.7 mL, and the HTHP filtration loss was between 20.3-26.8 mL. Among them, Example 3 showed the best high-temperature stability, with an HTHP filtration loss of only 20.3 mL after aging. This is attributed to the controlled free radical graft polymerization process and crosslinking treatment steps used in this invention. Controlled free radical graft polymerization can prepare graft copolymers with uniform molecular weight distribution, uniform graft chain length, and stable structure. The crosslinking treatment further enhances the rigidity and thermal stability of the molecular chains by forming crosslinking bonds between the molecular chains through epichlorohydrin, effectively resisting degradation and curling under high-temperature conditions.

[0065] Comparing the high-temperature stability data of Example 1 with Comparative Examples 2 and 3, it can be found that the API filtration loss of Comparative Example 2 (ordinary free radical polymerization) after aging was 13.8 mL, and the HTHP filtration loss was 35.2 mL, which are 1.66 times and 1.56 times that of Example 1, respectively. In Comparative Example 3 (no crosslinking treatment), the API filtration loss after aging was 12.3 mL, and the HTHP filtration loss was 32.5 mL, which are 1.48 times and 1.44 times that of Example 1, respectively. This indicates that controlled free radical graft polymerization can significantly improve the molecular weight uniformity and thermal stability of the filtration loss reducer, while crosslinking treatment can further enhance the structural stability of the molecular chain. The synergistic effect of these two processes gives the filtration loss reducer of the present invention excellent high-temperature resistance.

[0066] Based on the above test results, this invention successfully prepared a polymeric cellulose filtration reducer with excellent temperature and salt resistance through the synergistic effect of three stages: alkali-catalyzed activation, gradient etherification modification, and controlled free radical graft polymerization, combined with crosslinking treatment and the use of a continuous reaction device. This filtration reducer exhibits a reasonable degree of substitution distribution and uniform particle size distribution, demonstrating good filtration reduction performance under ambient temperature and pressure, high temperature and high pressure, and different salt concentrations, meeting the requirements of complex drilling environments (high temperature, high salt). Example 3, employing a more optimized combination of reaction parameters, exhibits the best overall performance and is the preferred embodiment of this invention.

[0067] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a temperature-resistant and salt-resistant polymeric cellulose filtration loss reducer, characterized in that, It includes three stages: base-catalyzed activation, gradient etherification modification, and controlled free radical grafting polymerization, performed sequentially. (1) Under an inert atmosphere, 100g of microcrystalline cellulose is added to a mixed alcohol-water solution containing a phase transfer catalyst and activated and swollen to obtain activated cellulose slurry. The ternary alkali metal hydroxide is a mixture of lithium hydroxide, sodium hydroxide and potassium hydroxide in a molar ratio of 1:(2.5-3.5):(0.5-1). The volume ratio of ethanol to water in the mixed alcohol-water solution is (3:1)-(1:1), and it contains 1%-3% of hexadecyltrimethylammonium bromide as a phase transfer catalyst. (2) Transfer all the activated cellulose slurry obtained in step (1) to a high-pressure reactor, and add 35g of sodium chloroacetate and 42g of glycidyltrimethylammonium chloride sequentially for etherification. The first stage of the sequential etherification is controlled at a temperature of 50-60℃ and a pressure of 0.2-0.5MPa for 1.5-2.5 hours. In the second stage, the temperature is raised to 75-85℃ and the pressure is released to atmospheric pressure. Simultaneously, a sodium 2-acrylamido-2-methylpropanesulfonate solution is added dropwise. The sodium 2-acrylamido-2-methylpropanesulfonate solution is prepared by dissolving 28g of sodium 2-acrylamido-2-methylpropanesulfonate in 80mL of deionized water. Continue the reaction for 2-3 hours to obtain the zwitterionic cellulose ether intermediate. (3) Disperse all the zwitterionic cellulose ether intermediates obtained in step (2) in a lithium chloride / dimethyl sulfoxide complex solvent system. Under ultrasonic treatment, add acrylamide, N-vinylcaprolactam and atom transfer radical polymerization initiation system in sequence. Carry out atom transfer radical graft copolymerization reaction at 65-75℃ for 4-6 hours. After the reaction, precipitate, wash, dry with supercritical carbon dioxide and pulverize at low temperature to obtain the filtrate loss reducer. The low temperature pulverization is carried out under liquid nitrogen protection using a fluidized bed collision air jet mill to control the product particle size D90≤45μm.

2. The method for preparing a temperature-resistant and salt-resistant polymeric cellulose filtration loss reducer according to claim 1, characterized in that, The activation temperature in step (1) is 35-45℃ and the activation time is 90-150 minutes.

3. The preparation method of a temperature-resistant and salt-resistant polymeric cellulose filtration loss reducer according to claim 1, characterized in that, The specific process parameters for the sequential etherification in step (2) are as follows: the first stage is a reaction at 0.3 MPa and 55°C for 2 hours, during which nitrogen gas is introduced at a constant flow rate for protection; the second stage is a reaction at atmospheric pressure and 80°C, in which the sodium 2-acrylamido-2-methylpropanesulfonate solution is added dropwise at a rate of 1 / 3 of its total amount per hour, and the reaction is kept at the temperature for 2.5 hours after the addition is completed.

4. The preparation method of a temperature-resistant and salt-resistant polymeric cellulose filtration loss reducer according to claim 1, characterized in that, The amount of glycidyltrimethylammonium chloride added in step (2) is 0.8-1.2 times the molar amount of cellulose glucose unit, and it is added 30 minutes before the end of the first stage reaction and 10 minutes before the start of the second stage reaction.

5. The preparation method of a temperature-resistant and salt-resistant polymeric cellulose filtration loss reducer according to claim 1, characterized in that, In step (3), the lithium chloride / dimethyl sulfoxide complex solvent system has a lithium chloride mass concentration of 8%-12%; the ultrasonic treatment frequency is 40kHz and the power is 150-300W.

6. The method for preparing a temperature-resistant and salt-resistant polymeric cellulose filtration loss reducer according to claim 1, characterized in that, The initiation system for the atom transfer radical graft copolymerization reaction in step (3) is a complex of pentamethyldiethylenetriamine and cuprous bromide. The total molar ratio of acrylamide, N-vinylcaprolactam and the sodium 2-acrylamido-2-methylpropanesulfonate structural unit introduced in step (2) is (5-7):(2-3):

1. The amount of acrylamide added is 120g and the amount of N-vinylcaprolactam added is 45g.

7. The method for preparing a temperature-resistant and salt-resistant polymeric cellulose filtration loss reducer according to claim 1, characterized in that, The conditions for supercritical carbon dioxide drying in step (3) are: pressure 10-15 MPa, temperature 35-45℃, and time 4-8 hours.

8. The method for preparing a temperature-resistant and salt-resistant polymeric cellulose filtration loss reducer according to claim 1, characterized in that, The degree of substitution of the zwitterionic cellulose ether intermediate obtained in step (2) satisfies the following: the degree of substitution of carboxymethyl group DS_CM is 0.15-0.25, the degree of substitution of quaternary ammonium salt DS_QA is 0.05-0.12, the degree of substitution of sulfonic acid group DS_S is ≥0.08, and the total degree of ionic substitution DS_CM + DS_QA + DS_S is controlled between 0.35-0.

50.

9. The method for preparing a temperature-resistant and salt-resistant polymeric cellulose filtration loss reducer according to claim 1, characterized in that, Throughout the entire preparation process, the activation in step (1), the gradient etherification in step (2), and the graft polymerization in step (3) are all completed in the same continuous reaction device with multi-zone temperature control, online viscosity monitoring, and micro-reaction feeding module. The material is transported between different reaction zones by a screw pump. After the reaction in step (3) is completed and before the precipitation step begins, 0.5%-1.5% by mass of epichlorohydrin is added to the reaction system for crosslinking treatment. The crosslinking reaction is carried out at 60°C for 0.5-1 hour. The amount of epichlorohydrin added accounts for 0.5%-2% of the dry weight of cellulose.

10. A temperature-resistant and salt-resistant polymeric cellulose filtration loss reducer, characterized in that, It is prepared by the method described in any one of claims 1 to 9 for reducing the filtration loss of a temperature-resistant and salt-resistant polymeric cellulose.

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