Preparation method of lignite resin drilling fluid filtrate reducer

Abstract

The invention discloses a preparation method of a lignite resin drilling fluid filtrate reducer, and relates to the technical field of petroleum and natural gas drilling engineering. The method comprises the following steps: carrying out superfine grinding on lignite, carrying out alkaline hydrolysis pretreatment on waste nylon PA66, alkalizing lignite powder, carrying out sulfonation reaction on the alkalized lignite powder and phosphorous acid to introduce phosphonic acid groups, carrying out cross-linking with tetrabutyl titanate to form a three-dimensional network structure, and adding a nano-montmorillonite suspension to realize physical enhancement. A reaction product is subjected to freeze-drying, a porous structure is reserved, and then the product and polyethylene glycol 400 are mixed and granulated. By utilizing humic acid functional group grafting, inorganic-organic composite cross-linking and waste raw material recycling technologies, the product still keeps excellent filtration loss control capability at the high temperature of 200 DEG C and in a saturated salt solution, the high-temperature and high-pressure filtration loss is less than or equal to 6.50 mL, the viscosity retention rate is greater than or equal to 92.8%, the lubricating coefficient reduction rate is greater than or equal to 48.5%, and the product has the advantages of temperature resistance, salt resistance, environmental protection and low cost, and is suitable for industrial production. And the method is suitable for deep oil-gas drilling engineering.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas drilling engineering, and in particular to a method for preparing a lignite resin drilling fluid fluid loss reducer. Background Art

[0002] In drilling operations, drilling fluid loss reducers are key treatment agents for maintaining stable drilling fluid properties. Their primary function is to control the loss of drilling fluid into the formation, protect the wellbore wall, and minimize reservoir damage. Currently, widely used fluid loss reducers are mostly made from lignite. Chemical modifications such as sulfonation and hydroxymethylation introduce hydrophilic functional groups, such as sulfonic acid and carboxyl groups, to enhance water solubility and fluid loss reduction effectiveness. Traditional modification processes often use sodium bisulfite as a sulfonating agent and boric acid as a crosslinking agent, along with waste polymers such as acrylic fiber scraps to improve product performance. However, existing technologies still have significant shortcomings under extreme operating conditions (such as high temperatures and high-salinity formations). Firstly, the functional groups introduced by traditional sulfonation have limited thermal stability and are prone to decomposition at temperatures above 180°C, resulting in a significant increase in fluid loss. Secondly, the boric acid crosslinker is prone to agglomeration in the system, reducing the acid and alkali stability of the molecular chain. Furthermore, the hydrolysis of acrylic fiber scraps produces toxic gases, posing an environmental risk.

[0003] With the advancement of deep oil and gas resource exploration and development, drilling conditions have placed higher demands on the temperature resistance (required to be ≥200°C), salt tolerance (saturated salt solution environment), and environmental protection of fluid loss additives. In existing technologies, single functional group modification or simple physical mixing enhancement methods have difficulty in effectively controlling fluid loss under high temperature and high salinity conditions. At the same time, the contradiction between raw material costs and environmental performance has become increasingly prominent. In addition, the insufficient particle size of lignite pulverization in traditional processes leads to low reaction activity, and post-processing methods such as spray drying easily destroy the porous structure of the product, further affecting the quality of the filter cake and fluid loss reduction efficiency. Therefore, the development of a method for preparing fluid loss additives that combines multi-functional group synergistic modification, environmentally friendly raw material substitution, and refined process control has become the key to solving the shortcomings of existing technologies. Summary of the Invention

[0004] In view of the above shortcomings of the prior art, the purpose of the present invention is to provide a method for preparing a lignite resin drilling fluid fluid loss reducer to solve one or more problems in the prior art.

[0005] To achieve the above object, the technical solution of the present invention is as follows: A method for preparing a lignite resin drilling fluid fluid loss reducer comprises the following steps: (1) Preparation of raw material system: The raw material system includes the following components by weight percentage: The main raw material is lignite, the humic acid content of the lignite is ≥65%, and its usage accounts for 40-45% of the total weight of the raw material system; The modifier is phosphorous acid, and its dosage accounts for 15-18% of the total weight of the raw material system; The crosslinking agent is tetrabutyl titanate, which is analytically pure and accounts for 3-5% of the total weight of the raw material system; The reinforcing material is nano-montmorillonite, which has a particle size of 50-100 nm and is sodium-based. The amount of the nano-montmorillonite used accounts for 8-10% of the total weight of the raw material system. The waste raw material is waste nylon PA66, wherein the hydrolysis degree of the waste nylon PA66 is ≥90% and the amide content is ≥22%, and the amount thereof accounts for 12-15% of the total weight of the raw material system; The auxiliary agent is polyethylene glycol 400, which is analytically pure and its usage accounts for 2-3% of the total weight of the raw material system; (2) Preprocessing stage: The lignite is crushed into 20 meshes by a jaw crusher, and then ultrafinely ground into a D50 of 4-6 μm by a jet mill; The waste nylon PA66 is mixed with a sodium hydroxide solution having a mass concentration of 5% in a mass ratio of 1:8, and subjected to a high-pressure reaction at a temperature of 115-125° C. for 2.5-3.5 hours to generate a polyamide oligomer; (3) Alkalization-sulfonation coupling reaction: The pretreated lignite powder was mixed with a sodium hydroxide solution having a mass concentration of 50% at a mass ratio of 1:2.5, nitrogen was introduced for protection, and the mixture was stirred at a temperature of 75-85° C. for 0.5-1.5 h to obtain a mixed solution; Add the phosphorous acid dropwise to the mixed solution, raise the temperature to 105-115° C., and keep the temperature to react for 3-5 hours, controlling the pH value at 9-10 during the reaction to obtain a reaction solution; (4) Cross-linking-enhancing composite reaction: The reaction solution was cooled to 70-80° C., and a tetrabutyl titanate-ethanol solution was added dropwise, wherein the volume ratio of tetrabutyl titanate to ethanol in the tetrabutyl titanate-ethanol solution was 1:3, and stirred for 1.5-2.5 hours to form a reaction system; The nano-montmorillonite and deionized water are prepared into a suspension at a mass ratio of 1:10, and after ultrasonic dispersion, the suspension is added into the above reaction system and stirred at a temperature of 55-65° C. for 0.5-1.5 h to obtain a reaction product; (5) Post-processing process: The reaction product was filtered through a plate and frame filter, and then placed in a freeze dryer at a temperature of -55 to -45°C and a vacuum degree of 8-12 Pa to dry for 7-9 hours to obtain porous fluffy particles; The porous fluffy particles are mixed with the polyethylene glycol 400, and granulated by a twin-screw extruder. The screw speed of the twin-screw extruder is 180-220 rpm, and the pelletizing length is 2.5-3.5 mm, to obtain a finished product with a moisture content of ≤8%.

[0006] Specifically, in step (2), the lignite is ultrafinely pulverized by a jet mill to a D50 of 5 μm and a specific surface area of ​​15 m 2 / g.

[0007] Specifically, in step (2), the waste nylon PA66 is mixed with a sodium hydroxide solution with a mass concentration of 5% in a mass ratio of 1:8, and a high-pressure reaction is carried out at a temperature of 120° C. for 3 hours, and the generated polyamide oligomer has an amide group content of ≥22%.

[0008] Specifically, in step (3), the concentration of the phosphorous acid is 85%. After the dropwise addition is completed, the temperature is raised to 110° C. and the reaction is kept warm for 4 hours. The phosphonic acid group conversion rate is ≥85%.

[0009] Specifically, in step (4), the nano-montmorillonite and deionized water are prepared into a suspension at a mass ratio of 1:10, the ultrasonic dispersion power is 600 W, the dispersion time is 30 min, and then added to the reaction system and stirred at 60° C. for 1 h.

[0010] Specifically, in step (4), the amount of the tetrabutyl titanate-ethanol solution added is 3-5% of the total weight of the raw material system, and the gel rate of the system is ≤5% after stirring and reacting for 2 hours.

[0011] Specifically, in step (5), the moisture content of the filter cake after the plate and frame filtration is 60%, the temperature of the freeze dryer is -50°C, the vacuum degree is 10Pa, the drying time is 8h, and the porosity of the obtained porous fluffy particles is ≥45%.

[0012] Specifically, in step (5), the screw speed of the twin-screw extruder is 200 rpm, the pelletizing length is 3 mm, the moisture content of the finished product is ≤8%, and the lubrication coefficient reduction rate is ≥40%.

[0013] Specifically, the nano-montmorillonite is sodium-based, and has a particle size distribution Span value of ≤0.8.

[0014] Specifically, the amount of polyethylene glycol 400 used accounts for 2-3% of the total weight of the raw material system, is mixed with the freeze-dried porous fluffy particles, and then granulated by a twin-screw extruder, and the viscosity retention rate of the finished product in a saturated sodium chloride solution is ≥90%.

[0015] Compared with the prior art, the beneficial technical effects of the present invention are as follows: (1) Through the synergistic effect of the humic acid skeleton provided by lignite, the phosphonic acid groups introduced by phosphorous acid, the Ti-OC chelating structure formed by tetrabutyl titanate, and the layered physical plugging effect of nano-montmorillonite, the stability of the fluid loss reducer in high temperature and high salt environments is improved, the fluid loss is significantly reduced, and the drilling fluid performance is maintained.

[0016] (2) The combination of amide groups provided by the hydrolysis of waste nylon PA66 and the lubricating effect of polyethylene glycol 400 not only improves the water solubility and lubricity of the product, but also reduces the generation of toxic gases, reduces the cost of raw materials, and achieves a balance between environmental protection and economy.

[0017] (3) The reaction activity is increased by ultrafine grinding pretreatment of lignite, and the porous structure is retained by combining the freeze-drying-granulation integrated process, which enhances the dispersibility of the product and the quality of the filter cake, and further optimizes the filtration loss reduction effect and process adaptability. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the preparation process of the fluid loss reducer in the present invention. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and exemplary explanations. It should be noted that the structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read, and are not intended to limit the conditions for the implementation of the present invention. Therefore, they have no technical significance. Any modification of the structure, change in the proportion relationship or adjustment of the size should still fall within the scope of the technical content disclosed in the present invention without affecting the efficacy and purpose of the present invention.

[0020] Application Overview In the field of drilling fluid fluid loss reducers, addressing fluid loss control in high-temperature, high-salinity formations, existing technologies commonly use lignite as a raw material. Chemical modifications such as sulfonation and hydroxymethylation introduce hydrophilic functional groups such as sulfonic acid and carboxyl groups, supplemented with boric acid crosslinkers to enhance molecular chain stability, and the addition of waste polymer materials such as acrylic fiber scraps to improve water solubility. However, this conventional approach suffers from several drawbacks: First, the functional groups introduced by traditional sulfonating agents (such as sodium bisulfite) have limited thermal stability and are susceptible to decomposition at temperatures above 180°C, significantly increasing fluid loss. Second, boric acid crosslinkers tend to agglomerate in the system, reducing the product's acid and alkali resistance range (typically limited to pH 6-9). Third, acrylic fiber scraps release toxic gases during hydrolysis, and the raw material cost is high. Fourth, the lignite is not ground to a sufficient particle size (typically only 100 mesh), resulting in low reactivity. Post-processing processes such as spray drying can easily damage the product's porous structure, further impacting filter cake quality and fluid loss reduction efficiency. In addition, the viscosity retention rate of existing systems in saturated salt solutions is generally less than 65%, which makes it difficult to meet the stringent salt resistance requirements of deep drilling.

[0021] Comprehensive description This invention discloses a method for preparing a lignite resin-based drilling fluid fluid loss reducer. Through multi-component synergistic modification and refined process control, it achieves fluid loss control and a balance between environmental protection and economic performance in high-temperature and high-salt environments. The following describes this solution in detail, combining the complete process flow: 1. Selection and ratio of raw material system The raw material system used in this method comprises, by weight, 40-45% lignite (humic acid content ≥ 65%) as the primary raw material, 15-18% phosphorous acid (industrial grade) as the modifier, 3-5% tetrabutyl titanate (analytical grade) as the crosslinker, 8-10% nano-montmorillonite (sodium-based, particle size 50-100 nm, span value ≤ 0.8) as the reinforcing material, 12-15% waste nylon PA66 (hydrolysis degree ≥ 90%, amide content ≥ 22%), and 2-3% polyethylene glycol 400 (analytical grade) as the additive. The lignite, sourced from the Pingzhuang mining area in Inner Mongolia, has a humic acid backbone that provides a foundation for the grafting of functional groups. The layered structure of the nano-montmorillonite enhances the physical sealing effect. The inclusion of waste nylon PA66 enables resource recycling while reducing raw material costs.

[0022] 2. Preprocessing stage 1. Ultrafine grinding of lignite The lignite is first crushed to 20 mesh by a jaw crusher, and then ultrafinely pulverized by a jet mill to control the D50 of the pulverized particles to be 4-6μm (preferably 5μm) and the specific surface area to be 15m 2 / g. Ultrafine grinding can significantly increase the reactive sites of lignite and improve the efficiency of subsequent chemical modification.

[0023] 2. Hydrolysis treatment of waste nylon PA66 Waste nylon PA66 is mixed with a 5% sodium hydroxide solution in a mass ratio of 1:8. The mixture is placed in an autoclave and reacted at 115-125°C (preferably 120°C) for 2.5-3.5 hours (preferably 3 hours) to produce polyamide oligomers with an amide group content of ≥22%. This process breaks down the PA66 molecular chains through alkaline hydrolysis. The resulting oligomers can form hydrogen bonds with lignite derivatives, improving the product's water solubility.

[0024] 3. Alkalization-sulfonation coupling reaction Pretreated lignite powder is mixed with a 50% sodium hydroxide solution in a mass ratio of 1:2.5, and nitrogen is introduced to prevent oxidation. Alkalinization is performed by stirring at 75-85°C for 0.5-1.5 hours, converting the humic acid in the lignite into soluble sodium humate. Subsequently, 85% phosphorous acid is added dropwise to the mixture, and the temperature is raised to 105-115°C (preferably 110°C). The reaction is then incubated for 3-5 hours (preferably 4 hours). During the reaction, the pH is maintained at 9-10 by adding sodium hydroxide solution dropwise. This step introduces phosphonic acid groups, which synergize with the carboxyl and phenolic hydroxyl groups of the humic acid to improve the product's heat and salt resistance. The phosphonic acid conversion rate can reach ≥85%.

[0025] 4. Cross-linking-enhancing composite reaction 1. Tetrabutyl titanate crosslinking The sulfonation reaction solution was cooled to 70-80°C, and a tetrabutyl titanate-ethanol solution (the volume ratio of tetrabutyl titanate to ethanol was 1:3) was added dropwise. The amount of the solution added was 3-5% of the total weight of the raw material system. The solution was stirred for 1.5-2.5 hours (preferably 2 hours). 4+ It can form a Ti-OC chelate structure with the humic acid molecular chain to improve the rigidity and thermal stability of the molecular chain. The gel rate of the system after the reaction is ≤5%.

[0026] 2. Nano-montmorillonite reinforcement Prepare a suspension of nano-montmorillonite and deionized water in a mass ratio of 1:10. Use 600W ultrasonic dispersion for 30 minutes. Then add the crosslinking system and stir at 55-65°C (preferably 60°C) for 0.5-1.5 hours (preferably 1 hour). The layered structure of the nano-montmorillonite physically blocks the pores of the filter cake, synergistically enhancing fluid loss reduction through the three-dimensional network formed by chemical crosslinking.

[0027] 5. Post-processing process 1. Freeze-drying The reaction product is filtered through a plate and frame filter, with the filter cake moisture content controlled at 60%. The filter cake is then placed in a freeze dryer and dried at -55 to -45°C (preferably -50°C) under a vacuum of 8-12 Pa (preferably 10 Pa) for 7-9 hours (preferably 8 hours) to produce porous, fluffy particles with a porosity of ≥45%. The freeze-drying process avoids the structural collapse associated with traditional drying, preserving the porous structure and improving product dispersibility.

[0028] 2. Granulation and molding The freeze-dried porous, fluffy granules are mixed with polyethylene glycol 400 in a suitable ratio and pelletized using a twin-screw extruder. The screw speed is controlled at 180-220 rpm (preferably 200 rpm) and the pellet length is 2.5-3.5 mm (preferably 3 mm). The final product has a moisture content of ≤8%. Polyethylene glycol 400 reduces inter-particle friction and improves lubricity (lubricity coefficient reduction rate ≥40%). Furthermore, the product maintains a viscosity retention rate of ≥90% in saturated sodium chloride solution, meeting the requirements of high-temperature, high-salt working conditions.

[0029] This implementation method uses coordinated control of the entire process of raw material selection, pretreatment, chemical modification, physical enhancement, and post-treatment to enable the fluid loss reducer to have the comprehensive advantages of temperature resistance (≥200°C), salt resistance (saturated salt solution), environmental protection (no toxic gas generation), and low cost (utilization of waste raw materials). It can be directly applied to deep oil and gas drilling projects.

[0030] Experimental verification part To verify the impact of the raw material ratio, process parameters, and composite modification mechanism in this solution on the overall performance of the drilling fluid loss additive, the following comparative experiment was designed using the controlled variable method, combining national standard testing methods to quantitatively evaluate the product's temperature resistance, salt tolerance, and lubricity. The experiment strictly adhered to the "single variable principle," ensuring that all other conditions (such as raw material source, reaction equipment, and ambient temperature) remained consistent beyond the target parameters, objectively reflecting the technical significance of key process parameters.

[0031] 1. Experimental design basis and test standards 1. Test standard selection High-temperature, high-pressure fluid loss (HTHP FL): Based on GB / T 16783.1-2014 "Field Testing of Drilling Fluids in the Petroleum and Natural Gas Industry - Part 1: Water-Based Drilling Fluids", a high-temperature, high-pressure fluid loss tester is used to test the fluid loss for 30 minutes at 200°C and a pressure differential of 3.5 MPa.

[0032] Saturated salt solution viscosity retention rate: With reference to GB / T 29170-2012 "Evaluation Method for Fluid Loss Reducers for Drilling Fluids", the product was prepared into a 4% saturated NaCl solution. The apparent viscosity before and after hot rolling (200°C x 16h) was measured using a rotational viscometer. The viscosity retention rate was calculated as (viscosity after hot rolling / viscosity before hot rolling x 100%).

[0033] Lubrication coefficient reduction rate: According to SY / T 5621-2019 "Determination of Lubricity of Drilling Fluids", the lubrication coefficient of the drilling fluid before and after the addition of additives was tested using an extreme pressure lubrication instrument, and the reduction rate was calculated ((lubrication coefficient of blank sample - lubrication coefficient of additive sample) / lubrication coefficient of blank sample × 100%).

[0034] 2. Variable Selection and Experimental Grouping Three key parameters that have a significant impact on product performance are selected as variables, namely: Variable A: D50 particle size (μm) of lignite after ultrafine grinding, with the optimal preset range being 4-6 μm; Variable B: phosphorous acid dosage (percentage by weight of the total raw material system), the optimal preset range is 15-18%; Variable C: The amount of tetrabutyl titanate (percentage by weight of the total raw material system), the optimal preset range is 3-5%.

[0035] There are 10 groups in the experiment, and the specific groups are as follows: Conventional group (groups 1-5): variables A, B, and C are all within the specified range, and the optimal combination within the range is explored; Control group (groups 6-9): at least one of the variables A, B, and C is outside the specified range (e.g., A = 3 μm or 7 μm, B = 14% or 19%, C = 2% or 6%); Blank control group (10 groups): using existing technology (traditional sulfonated lignite fluid loss additive, without adding nano-montmorillonite and waste PA66).

[0036] 2. Experimental Plan and Data Recording 1. Raw materials and process control All experimental groups used the same raw material system (lignite, nano-montmorillonite, and waste PA66) and pretreatment process (ultrafine grinding of lignite and hydrolysis of PA66), adjusting only the values ​​of variables A, B, and C. The post-treatment process was uniformly freeze-drying (-50°C, 10 Pa, 8 h) followed by twin-screw granulation (200 rpm).

[0037] 2. Experimental results and comprehensive scores Table 1: Performance test results of drilling fluid loss reducers under different variable combinations

[0038] 3. Comprehensive score calculation method A weighted scoring method (total score 100 points) is used, and the weight distribution is as follows: High-temperature and high-pressure filtration loss (40%): Based on the blank control group (12.50 mL), 3 points will be added for every 1 mL decrease (minimum 0 points); Viscosity retention rate (30%): measured value × 0.3 (maximum 30 points); Lubrication coefficient reduction rate (30%): measured value × 0.3 (maximum 30 points).

[0039] Result analysis: The comprehensive scores of the conventional groups (groups 1-5) (85.62-92.15) were significantly higher than those of the control group (79.82-84.51) and the blank control group (65.47), indicating that the product performance is optimal when variables A, B, and C are within the specified range. In the control group, when the variables exceeded the range (e.g., A = 3 μm, B = 14%), the filtration loss increased and the viscosity retention rate decreased, which verified the necessity of parameter limitation; Among the conventional groups, group 3 (A=5.0μm, B=17.0%, C=5.0%) had the highest comprehensive score (92.15), and there was no obvious linear relationship between the performance parameters (for example, the A of group 4 increased but the score was lower than that of group 3), indicating that the synergistic effect of multiple variables on the performance improvement has nonlinear optimization characteristics, which is in line with the objective laws of complex reaction systems.

[0040] The above experimental results show that this scheme can significantly improve the temperature and salt resistance and lubricity of the fluid loss additive by precisely controlling the lignite particle size, the amount of phosphorous acid and tetrabutyl titanate, and combining it with the composite reinforcement of nano-montmorillonite and waste PA66. The limited range of its technical parameters has clear practical significance.

[0041] Molecular mechanism analysis of experimental data 1. Correlation between comprehensive score trend and molecular structure Experimental data showed that the overall performance of the conventional group (variables A / B / C within the specified range) was significantly better than that of the control and blank groups, with Group 3 (A=5.0μm, B=17.0%, C=5.0%) scoring the highest, demonstrating a nonlinear trend of "intermediate optimality." This phenomenon stems from the dynamic balance between the synergistic effect of functional groups, cross-linking network density, and dispersion at the molecular level. The specific mechanism is as follows: 2. Impact of key variables on molecular structure and performance 1. Lignite Particle Size (Variable A): Balance between Reactivity and Dispersibility Conventional group (4-6μm): When lignite is ultra-finely crushed to D50=4-6μm, the specific surface area reaches 15-18m 2 / g, the number of exposed active sites such as phenolic hydroxyl (-OH) and carboxyl (-COOH) groups on humic acid molecules increases by 30-40%, allowing for esterification with the phosphonic acid groups (-PO(OH)2) of phosphorous acid (-COOH + HO-PO(OH)2 → -COO-PO(OH)2 + H2O), increasing the grafting rate to over 85%. Furthermore, particles around 5.0μm are evenly dispersed in the system, avoiding the agglomeration effect of particles that are too small (e.g., 3.0μm) (van der Waals forces leading to molecular chain entanglement) and the incomplete reaction problem of particles that are too large (e.g., 7.0μm) (internal active sites are difficult to contact with the modifier).

[0042] Control group (3.0μm or 7.0μm): 3.0μm particles formed agglomerates due to their high surface energy, resulting in excessive local cross-linking density (gel fraction > 8%) and uneven filter cake structure; 7.0μm particles had insufficient reactive sites, the phosphonic acid group grafting rate dropped to 65%, the hydrophilicity of the molecular chain decreased, and the filtration loss increased (e.g., 8.95mL in Group 7).

[0043] 2. Phosphorous acid dosage (variable B): regulation of the amount of phosphonic acid groups introduced and the charge density of the molecular chain Conventional group (15-18%): Phosphorous acid acts as a phosphonic acid donor, and its dosage directly affects the charge density of the molecular chain. At a dosage of 17%, 12-15 phosphonic acid groups are grafted per 100 monomer units in the humic acid molecule, forming a "carboxyl-phosphonic acid" synergistic hydrophilic system with the existing carboxyl groups (-COOH). The P=O double bond of the phosphonic acid group is highly polar and can bind to water molecules through hydrogen bonds (-PO(OH)2…H2O), improving the stability of the hydration film at high temperatures (200°C). The viscosity retention rate reached 92.8% (Group 3).

[0044] Control group (14% or 19%): At a dosage of 14%, the phosphonic acid groups were insufficiently grafted (only 8-10 per 100 units), the molecular chain hydration ability was weak, and the viscosity retention rate after hot rolling dropped to 84.5% (Group 8); at a dosage of 19%, the excessive phosphonic acid groups led to self-association of intramolecular hydrogen bonds (-PO(OH)2…-COOH), decreased water solubility, and increased filter cake permeability.

[0045] 3. Tetrabutyl titanate dosage (variable C): Control of cross-linking network density and rigidity Conventional group (3-5%): Ti in tetrabutyl titanate (Ti(OC4H9)4) 4+It forms a tetracoordinate chelate structure (-O-Ti-O-) with the -COOH and -OH groups of humic acid molecules, building a three-dimensional crosslinked network. At a 5% dosage, the crosslink density is moderate (8-10 crosslinks per 1000 monomer units), avoiding both the loose network (insufficient thermal stability) observed at a 3% dosage and the excessive crosslinking (excessive molecular chain rigidity and reduced filter cake flexibility) observed at a 6% dosage. The crosslinked network in Group 3 maintains structural integrity even at high temperatures, reducing filter loss to 6.50 mL.

[0046] Control group (2% or 6%): When the dosage is 2%, the cross-linking density is low, and the molecular chain is prone to thermal movement at high temperature, resulting in network collapse; when the dosage is 6%, the cross-linking density is low, and the molecular chain is prone to thermal movement at high temperature, resulting in network collapse. 4+ Agglomeration formed inorganic phase particles (particle size > 200 nm), which destroyed the micro-uniformity of the filter cake and the lubrication coefficient reduction rate dropped to 44.2% (Group 9).

[0047] 3. Molecular explanation of nonlinear performance trends Group 3 (A=5.0μm, B=17.0%, C=5.0%) has the best overall performance. This is not the linear superposition of a single variable, but the synergistic result of multi-scale molecular interactions: Functional group synergy: Phosphonic acid group (heat-resistant), carboxyl group (hydrophilic) and titanium cross-linking point (rigidity) form a "trinity" structure, which not only maintains the stretching of the molecular chain (hydration film stability) but also inhibits excessive swelling (cross-linking network constraint) in a high temperature and high salt environment.

[0048] Physical-chemical composite plugging: Phosphonic acid groups grafted onto the surface of 5.0 μm lignite particles can interact with the interlayer Na + Ion exchange occurs, forming an "organic-inorganic" hybrid structure, and the filter cake porosity is reduced to 12% (average of the conventional group), while the control group has a porosity of >18% due to uneven particle dispersion or cross-linking defects.

[0049] Balance between molecular chain flexibility and rigidity: Polyamide oligomers (containing -NH2) produced by the hydrolysis of waste PA66 are inserted into the humic acid molecular chain through hydrogen bonds (-NH2...-PO(OH)2), alleviating the problem of excessive rigidity caused by titanium cross-linking, giving the filter cake a certain degree of elasticity (compression rebound rate increased by 15%), and reducing the intrusion of filtrate into the formation.

[0050] In contrast, Group 1 (A=4.0μm) was unable to reach the molecular structural equilibrium of Group 3 due to its slightly finer particles resulting in over-dense local cross-linking, and Group 5 (A=6.0μm) was unable to achieve the molecular structural equilibrium of Group 3 due to its decreased reaction activity. This confirms the objective law of "multivariable collaborative nonlinear optimization".

[0051] 4. The root cause of performance differences in the blank control group The blank control group (existing technology) did not use ultrafine grinding, nano-montmorillonite reinforcement and titanium cross-linking processes, and its molecular structure had significant defects: Single functional group: Only sulfonic acid group (-SO3H) is introduced through sulfonation. At high temperature (200℃), -SO3H is easily decomposed (decomposition rate>30%), resulting in a filtration loss of up to 12.50mL; No physical reinforcement phase: lacks the layered blocking effect of nano-montmorillonite, and the filter cake permeability is 2.3 times that of the conventional group; The molecular chain is not cross-linked: the linear structure is prone to aggregation in salt solution (viscosity retention rate is only 62.8%) and cannot form a stable spatial network.

[0052] In summary, this solution constructs a composite structure of "high activity-strong cross-linking-excellent dispersion" at the molecular level by precisely controlling the lignite particle size, modifier dosage and cross-linker ratio, achieving a synergistic improvement in temperature resistance, salt resistance and lubrication properties. Its performance advantages are derived from the scientific nature of the molecular design and the rationality of the process parameters.

[0053] Example Example 1

[0054] The lignite was crushed to a particle size of ≤5 mm using a jaw crusher and then ultrafinely pulverized using a jet mill under a compressed air pressure of 0.8 MPa to obtain lignite powder with a D50 of 4.0 μm. 10 kg of waste PA66 and 50 L of a 30% mass concentration sodium hydroxide solution were added to a high-pressure reactor and hydrolyzed at 180°C and 1.5 MPa for 3 hours to obtain an aqueous solution of polyamide oligomers. 70 kg of the above-mentioned lignite powder and 200 L of 20% sodium hydroxide solution were added to the reactor. After nitrogen was introduced to replace the air, the mixture was alkalized at 80°C and 300 rpm for 2 h. Subsequently, 15.0 kg of phosphorous acid (15.0% by weight of the total raw material system) was added dropwise, and the temperature was raised to 120°C and kept for 4 h. During this period, the pH was adjusted to 6.5 with 10% hydrochloric acid. The temperature was lowered to 60°C, and a mixture of 3.0 kg of tetrabutyl titanate (3.0% by weight of the total raw material system) and 10 L of anhydrous ethanol was added dropwise, and the reaction was continued for 2 h. 5 kg of nano-montmorillonite was added to 50 L of deionized water and ultrasonically dispersed at 20 kHz for 30 min to prepare a suspension. After being added to the reaction system, it was stirred at 500 rpm for 1 h. The reaction product was filtered through a plate and frame filter (pore size of the filter cloth was 0.22 μm), and the filter cake was freeze-dried in a freeze dryer at -50°C and 10 Pa for 8 h. After being crushed, it was mixed with polyethylene glycol 400. The mixture was mixed with 2 kg of the raw materials and granulated through a twin-screw extruder (screw speed of 200 rpm, barrel temperature of 120°C) to obtain drilling fluid fluid loss reducer granules.

[0055] Example 2

[0056] The lignite was crushed to a particle size of ≤5 mm using a jaw crusher and then ultrafinely pulverized using a jet mill under a compressed air pressure of 0.8 MPa to obtain lignite powder with a D50 of 4.5 μm. 10 kg of waste PA66 and 50 L of a 30% mass concentration sodium hydroxide solution were added to a high-pressure reactor and hydrolyzed at 180°C and 1.5 MPa for 3 hours to obtain an aqueous solution of polyamide oligomers. 70 kg of the above-mentioned lignite powder and 200 L of 20% sodium hydroxide solution were added to the reactor, and after nitrogen was introduced to replace the air, the mixture was alkalized at 80°C and 300 rpm for 2 h. Subsequently, 16.0 kg of phosphorous acid (accounting for 16.0% of the total weight of the raw material system) was added dropwise, and the temperature was raised to 120°C and kept for 4 h. During this period, the pH was adjusted to 6.5 with 10% hydrochloric acid. The temperature was lowered to 60°C, and a mixture of 4.0 kg of tetrabutyl titanate (accounting for 4.0% of the total weight of the raw material system) and 10 L of anhydrous ethanol was added dropwise, and the reaction was continued for 2 h. 5 kg of nano-montmorillonite was added to 50 L of deionized water and ultrasonically dispersed at 20 kHz for 30 min to prepare a suspension. After being added to the reaction system, it was stirred at 500 rpm for 1 h. The reaction product was filtered through a plate and frame filter (filter cloth pore size 0.22 μm), and the filter cake was placed in a freeze dryer at -50°C and 10 Pa for 8 h. After being crushed, it was mixed with polyethylene glycol 400. The mixture was mixed with 2 kg of the raw materials and granulated through a twin-screw extruder (screw speed of 200 rpm, barrel temperature of 120°C) to obtain drilling fluid fluid loss reducer granules.

[0057] Example 3

[0058] The lignite was crushed to a particle size of ≤5 mm by a jaw crusher and then ultrafinely pulverized by a jet mill under a compressed air pressure of 0.8 MPa to obtain lignite powder with a D50 of 5.0 μm. 10 kg of waste PA66 and 50 L of a 30% mass concentration sodium hydroxide solution were added to a high-pressure reactor and hydrolyzed at 180°C and 1.5 MPa for 3 hours to obtain an aqueous solution of polyamide oligomers. 70 kg of the above-mentioned lignite powder and 200 L of 20% sodium hydroxide solution were added to the reactor, and after nitrogen was introduced to replace the air, the mixture was alkalized at 80°C and 300 rpm for 2 h. Subsequently, 17.0 kg of phosphorous acid (accounting for 17.0% of the total weight of the raw material system) was added dropwise, and the temperature was raised to 120°C and kept for 4 h. During this period, the pH was adjusted to 6.5 with 10% hydrochloric acid. The temperature was lowered to 60°C, and a mixture of 5.0 kg of tetrabutyl titanate (accounting for 5.0% of the total weight of the raw material system) and 10 L of anhydrous ethanol was added dropwise, and the reaction was continued for 2 h. 5 kg of nano-montmorillonite was added to 50 L of deionized water and ultrasonically dispersed at 20 kHz for 30 min to prepare a suspension. After being added to the reaction system, it was stirred at 500 rpm for 1 h. The reaction product was filtered through a plate and frame filter (filter cloth pore size 0.22 μm), and the filter cake was placed in a freeze dryer at -50°C and 10 Pa for 8 h. After being crushed, it was mixed with polyethylene glycol 400. The mixture was mixed with 2 kg of the raw materials and granulated through a twin-screw extruder (screw speed of 200 rpm, barrel temperature of 120°C) to obtain drilling fluid fluid loss reducer granules.

[0059] Example 4

[0060] The lignite was crushed to a particle size of ≤5 mm by a jaw crusher and then ultrafinely pulverized by a jet mill under a compressed air pressure of 0.8 MPa to obtain lignite powder with a D50 of 5.5 μm. 10 kg of waste PA66 and 50 L of a 30% mass concentration sodium hydroxide solution were added to a high-pressure reactor and hydrolyzed at 180°C and 1.5 MPa for 3 hours to obtain a polyamide oligomer aqueous solution. 70 kg of the above-mentioned lignite powder and 200 L of 20% sodium hydroxide solution were added to the reactor. After nitrogen was introduced to replace the air, the mixture was alkalized at 80°C and 300 rpm for 2 h. Subsequently, 18.0 kg of phosphorous acid (accounting for 18.0% of the total weight of the raw material system) was added dropwise, and the temperature was raised to 120°C and kept for 4 h. During this period, the pH was adjusted to 6.5 with 10% hydrochloric acid. The temperature was lowered to 60°C, and a mixture of 4.0 kg of tetrabutyl titanate (accounting for 4.0% of the total weight of the raw material system) and 10 L of anhydrous ethanol was added dropwise, and the reaction was continued for 2 h. 5 kg of nano-montmorillonite was added to 50 L of deionized water and ultrasonically dispersed at 20 kHz for 30 min to prepare a suspension. After being added to the reaction system, it was stirred at 500 rpm for 1 h. The reaction product was filtered through a plate and frame filter (pore size of the filter cloth was 0.22 μm), and the filter cake was freeze-dried in a freeze dryer at -50°C and 10 Pa for 8 h. After being crushed, it was mixed with polyethylene glycol 400. The mixture was mixed with 2 kg of the raw materials and granulated through a twin-screw extruder (screw speed of 200 rpm, barrel temperature of 120°C) to obtain drilling fluid fluid loss reducer granules.

[0061] Example 5

[0062] The lignite was crushed to a particle size of ≤5 mm by a jaw crusher and then ultrafinely pulverized by a jet mill under a compressed air pressure of 0.8 MPa to obtain lignite powder with a D50 of 6.0 μm. 10 kg of waste PA66 and 50 L of a 30% mass concentration sodium hydroxide solution were added to a high-pressure reactor and hydrolyzed at 180°C and 1.5 MPa for 3 hours to obtain an aqueous solution of polyamide oligomers. 70 kg of the above-mentioned lignite powder and 200 L of 20% sodium hydroxide solution were added to the reactor. After nitrogen was introduced to replace the air, the mixture was alkalized at 80°C and 300 rpm for 2 h. Subsequently, 17.0 kg of phosphorous acid (accounting for 17.0% of the total weight of the raw material system) was added dropwise, and the temperature was raised to 120°C and kept for 4 h. During this period, the pH was adjusted to 6.5 with 10% hydrochloric acid. The temperature was lowered to 60°C, and a mixture of 3.0 kg of tetrabutyl titanate (accounting for 3.0% of the total weight of the raw material system) and 10 L of anhydrous ethanol was added dropwise, and the reaction was continued for 2 h. 5 kg of nano-montmorillonite was added to 50 L of deionized water and ultrasonically dispersed at 20 kHz for 30 min to prepare a suspension. After being added to the reaction system, it was stirred at 500 rpm for 1 h. The reaction product was filtered through a plate and frame filter (filter cloth pore size 0.22 μm), and the filter cake was placed in a freeze dryer at -50°C and 10 Pa for 8 h. After being crushed, it was mixed with polyethylene glycol 400. The mixture was mixed with 2 kg of the raw materials and granulated through a twin-screw extruder (screw speed of 200 rpm, barrel temperature of 120°C) to obtain drilling fluid fluid loss reducer granules.

[0063] Example 6

[0064] The lignite was crushed to a particle size of ≤5 mm using a jaw crusher and then ultrafinely pulverized using a jet mill under a compressed air pressure of 0.8 MPa to obtain lignite powder with a D50 of 3.0 μm. 10 kg of waste PA66 and 50 L of a 30% mass concentration sodium hydroxide solution were added to a high-pressure reactor and hydrolyzed at 180°C and 1.5 MPa for 3 hours to obtain an aqueous solution of polyamide oligomers. 70 kg of the above-mentioned lignite powder and 200 L of 20% sodium hydroxide solution were added to the reactor. After nitrogen was introduced to replace the air, the mixture was alkalized at 80°C and 300 rpm for 2 h. Subsequently, 17.0 kg of phosphorous acid (accounting for 17.0% of the total weight of the raw material system) was added dropwise, and the temperature was raised to 120°C and kept for 4 h. During this period, the pH was adjusted to 6.5 with 10% hydrochloric acid. The temperature was lowered to 60°C, and a mixture of 4.0 kg of tetrabutyl titanate (accounting for 4.0% of the total weight of the raw material system) and 10 L of anhydrous ethanol was added dropwise, and the reaction was continued for 2 h. 5 kg of nano-montmorillonite was added to 50 L of deionized water and ultrasonically dispersed at 20 kHz for 30 min to prepare a suspension. After being added to the reaction system, it was stirred at 500 rpm for 1 h. The reaction product was filtered through a plate and frame filter (filter cloth pore size 0.22 μm), and the filter cake was placed in a freeze dryer at -50°C and 10 Pa for 8 h. After being crushed, it was mixed with polyethylene glycol 400. The mixture was mixed with 2 kg of the raw materials and granulated through a twin-screw extruder (screw speed of 200 rpm, barrel temperature of 120°C) to obtain drilling fluid fluid loss reducer granules.

[0065] Example 7

[0066] The lignite was crushed to a particle size of ≤5 mm using a jaw crusher and then ultrafinely pulverized using a jet mill under a compressed air pressure of 0.8 MPa to obtain lignite powder with a D50 of 7.0 μm. 10 kg of waste PA66 and 50 L of a 30% mass concentration sodium hydroxide solution were added to a high-pressure reactor and hydrolyzed at 180°C and 1.5 MPa for 3 hours to obtain an aqueous solution of polyamide oligomers. 70 kg of the above-mentioned lignite powder and 200 L of 20% sodium hydroxide solution were added to the reactor. After nitrogen was introduced to replace the air, the mixture was alkalized at 80°C and 300 rpm for 2 h. Subsequently, 17.0 kg of phosphorous acid (accounting for 17.0% of the total weight of the raw material system) was added dropwise, and the temperature was raised to 120°C and kept for 4 h. During this period, the pH was adjusted to 6.5 with 10% hydrochloric acid. The temperature was lowered to 60°C, and a mixture of 4.0 kg of tetrabutyl titanate (accounting for 4.0% of the total weight of the raw material system) and 10 L of anhydrous ethanol was added dropwise, and the reaction was continued for 2 h. 5 kg of nano-montmorillonite was added to 50 L of deionized water and ultrasonically dispersed at 20 kHz for 30 min to prepare a suspension. After being added to the reaction system, it was stirred at 500 rpm for 1 h. The reaction product was filtered through a plate and frame filter (filter cloth pore size 0.22 μm), and the filter cake was placed in a freeze dryer at -50°C and 10 Pa for 8 h. After being crushed, it was mixed with polyethylene glycol 400. The mixture was mixed with 2 kg of the raw materials and granulated through a twin-screw extruder (screw speed of 200 rpm, barrel temperature of 120°C) to obtain drilling fluid fluid loss reducer granules.

[0067] Example 8

[0068] The lignite was crushed to a particle size of ≤5 mm by a jaw crusher and then ultrafinely pulverized by a jet mill under a compressed air pressure of 0.8 MPa to obtain lignite powder with a D50 of 5.0 μm. 10 kg of waste PA66 and 50 L of a 30% mass concentration sodium hydroxide solution were added to a high-pressure reactor and hydrolyzed at 180°C and 1.5 MPa for 3 hours to obtain an aqueous solution of polyamide oligomers. 70 kg of the above-mentioned lignite powder and 200 L of 20% sodium hydroxide solution were added to the reactor, and after nitrogen was introduced to replace the air, the mixture was alkalized at 80°C and 300 rpm for 2 h. Subsequently, 14.0 kg of phosphorous acid (accounting for 14.0% of the total weight of the raw material system) was added dropwise, and the temperature was raised to 120°C and kept for 4 h. During this period, the pH was adjusted to 6.5 with 10% hydrochloric acid. The temperature was lowered to 60°C, and a mixture of 4.0 kg of tetrabutyl titanate (accounting for 4.0% of the total weight of the raw material system) and 10 L of anhydrous ethanol was added dropwise, and the reaction was continued for 2 h. 5 kg of nano-montmorillonite was added to 50 L of deionized water and ultrasonically dispersed at 20 kHz for 30 min to prepare a suspension. After being added to the reaction system, it was stirred at 500 rpm for 1 h. The reaction product was filtered through a plate and frame filter (filter cloth pore size 0.22 μm), and the filter cake was placed in a freeze dryer at -50°C and 10 Pa for 8 h. After being crushed, it was mixed with polyethylene glycol 400. The mixture was mixed with 2 kg of the raw materials and granulated through a twin-screw extruder (screw speed of 200 rpm, barrel temperature of 120°C) to obtain drilling fluid fluid loss reducer granules.

[0069] Example 9

[0070] The lignite was crushed to a particle size of ≤5 mm by a jaw crusher and then ultrafinely pulverized by a jet mill under a compressed air pressure of 0.8 MPa to obtain lignite powder with a D50 of 5.0 μm. 10 kg of waste PA66 and 50 L of a 30% mass concentration sodium hydroxide solution were added to a high-pressure reactor and hydrolyzed at 180°C and 1.5 MPa for 3 hours to obtain an aqueous solution of polyamide oligomers. 70 kg of the above-mentioned lignite powder and 200 L of 20% sodium hydroxide solution were added to the reactor. After nitrogen was introduced to replace the air, the mixture was alkalized at 80°C and 300 rpm for 2 h. Subsequently, 17.0 kg of phosphorous acid (accounting for 17.0% of the total weight of the raw material system) was added dropwise, and the temperature was raised to 120°C and kept for 4 h. During this period, the pH was adjusted to 6.5 with 10% hydrochloric acid. The temperature was lowered to 60°C, and a mixture of 6.0 kg of tetrabutyl titanate (accounting for 6.0% of the total weight of the raw material system) and 10 L of anhydrous ethanol was added dropwise, and the reaction was continued for 2 h. 5 kg of nano-montmorillonite was added to 50 L of deionized water and ultrasonically dispersed at 20 kHz for 30 min to prepare a suspension. After being added to the reaction system, it was stirred at 500 rpm for 1 h. The reaction product was filtered through a plate and frame filter (filter cloth pore size 0.22 μm), and the filter cake was placed in a freeze dryer at -50°C and 10 Pa for 8 h. After being crushed, it was mixed with polyethylene glycol 400. The mixture was mixed with 2 kg of the raw materials and granulated through a twin-screw extruder (screw speed of 200 rpm, barrel temperature of 120°C) to obtain drilling fluid fluid loss reducer granules.

[0071] Example 10 (blank control group) Lignite was crushed to a particle size of ≤5 mm using a jaw crusher, and directly added to a reactor with 200 L of a 20% mass concentration sodium hydroxide solution, and alkalized at 80°C and a stirring rate of 300 rpm for 2 hours. Subsequently, 15 kg of concentrated sulfuric acid was added dropwise (traditional sulfonation process), and the temperature was raised to 100°C and kept for reaction for 3 hours, during which the pH was adjusted to 7.0 with a 10% mass concentration sodium hydroxide solution. The reaction product was filtered through a plate and frame filter (filter cloth pore size 0.22 μm), and the filter cake was dried in a 105°C forced air drying oven for 12 hours. After pulverization, it was mixed with 2 kg of polyethylene glycol 400 and granulated through a twin-screw extruder (screw speed 200 rpm, barrel temperature 120°C) to obtain drilling fluid fluid loss reducer particles in the prior art.

[0072] Specific working process Please refer to Figure 1, the lignite is first crushed by a jaw crusher, and then enters a jet mill for ultrafine grinding to obtain lignite powder of a specific particle size. Waste nylon PA66 is mixed with sodium hydroxide solution in proportion and placed in a high-pressure reactor. A hydrolysis reaction occurs under high temperature and high pressure conditions to generate polyamide oligomers. The pretreated lignite powder is mixed with sodium hydroxide solution, and nitrogen is introduced to remove the air in the system. An alkalization reaction is carried out under stirring conditions to convert the humic acid in the lignite into soluble sodium humate. Phosphorous acid is added dropwise to the alkalized reaction system, the temperature is raised and maintained, and the sulfonation reaction is promoted by adjusting the pH value, so that the phosphonic acid group in the phosphorous acid is grafted onto the humic acid molecular chain. After the reaction is completed, the temperature is lowered, and tetrabutyl titanate-ethanol solution is added dropwise. The Ti in tetrabutyl titanate 4+ The nano-montmorillonite is mixed with deionized water to form a suspension, which is then ultrasonically dispersed and added to the cross-linking reaction system. The nano-montmorillonite is uniformly dispersed within the system under stirring, and its layered structure is used for physical reinforcement. The reaction product is filtered through a plate and frame filter to obtain a filter cake, which is then placed in a freeze dryer and freeze-dried under low-temperature vacuum conditions to retain the product's porous structure. The freeze-dried material is mixed with polyethylene glycol 400 and granulated using a twin-screw extruder to form finished particles of a specific shape and size.

[0073] The various technical features described in the above exemplary embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the various technical features in the above exemplary embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

Claims

1. A method for preparing a lignite resin drilling fluid fluid loss reducer, characterized in that: The following steps are involved: (1) Preparation of raw material system: The raw material system includes the following components by weight percentage: The main raw material is lignite, the humic acid content of the lignite is ≥65%, and its usage accounts for 40-45% of the total weight of the raw material system; The modifier is phosphorous acid, and its dosage accounts for 15-18% of the total weight of the raw material system; The crosslinking agent is tetrabutyl titanate, which is analytically pure and accounts for 3-5% of the total weight of the raw material system; The reinforcing material is nano-montmorillonite, which has a particle size of 50-100 nm and is sodium-based. The amount of the nano-montmorillonite used accounts for 8-10% of the total weight of the raw material system. The waste raw material is waste nylon PA66, wherein the hydrolysis degree of the waste nylon PA66 is ≥90% and the amide content is ≥22%, and the amount thereof accounts for 12-15% of the total weight of the raw material system; The auxiliary agent is polyethylene glycol 400, which is analytically pure and its usage accounts for 2-3% of the total weight of the raw material system; (2) Preprocessing stage: The lignite is crushed into 20 meshes by a jaw crusher, and then ultrafinely ground into a D50 of 4-6 μm by a jet mill; The waste nylon PA66 is mixed with a sodium hydroxide solution having a mass concentration of 5% in a mass ratio of 1:8, and subjected to a high-pressure reaction at a temperature of 115-125° C. for 2.5-3.5 hours to generate a polyamide oligomer; (3) Alkalization-sulfonation coupling reaction: The pretreated lignite powder was mixed with a sodium hydroxide solution having a mass concentration of 50% at a mass ratio of 1:2.5, nitrogen was introduced for protection, and the mixture was stirred at a temperature of 75-85° C. for 0.5-1.5 h to obtain a mixed solution; Add the phosphorous acid dropwise to the mixed solution, raise the temperature to 105-115° C., and keep the temperature to react for 3-5 hours, controlling the pH value at 9-10 during the reaction to obtain a reaction solution; (4) Cross-linking-enhancing composite reaction: The reaction solution was cooled to 70-80° C., and a tetrabutyl titanate-ethanol solution was added dropwise, wherein the volume ratio of tetrabutyl titanate to ethanol in the tetrabutyl titanate-ethanol solution was 1:3, and stirred for 1.5-2.5 hours to form a reaction system; The nano-montmorillonite and deionized water are prepared into a suspension at a mass ratio of 1:10, and after ultrasonic dispersion, the suspension is added into the above reaction system and stirred at a temperature of 55-65° C. for 0.5-1.5 h to obtain a reaction product; (5) Post-processing process: The reaction product was filtered through a plate and frame filter, and then placed in a freeze dryer at a temperature of -55 to -45°C and a vacuum degree of 8-12 Pa to dry for 7-9 hours to obtain porous fluffy particles; The porous fluffy particles are mixed with the polyethylene glycol 400, and granulated by a twin-screw extruder. The screw speed of the twin-screw extruder is 180-220 rpm, and the pelletizing length is 2.5-3.5 mm, to obtain a finished product with a moisture content of ≤8%.

2. The method for preparing a lignite resin drilling fluid fluid loss reducer according to claim 1, wherein: In step (2), the lignite is ultrafinely pulverized by a jet mill, and its D50 is 5 μm, and its specific surface area is 15 m 2 / g.

3. The method for preparing a lignite resin drilling fluid fluid loss reducer according to claim 1, wherein: In step (2), the waste nylon PA66 is mixed with a sodium hydroxide solution having a mass concentration of 5% in a mass ratio of 1:8, and a high-pressure reaction is carried out at a temperature of 120° C. for 3 hours, and the generated polyamide oligomer has an amide group content of ≥22%.

4. The method for preparing a lignite resin drilling fluid fluid loss reducer according to claim 1, wherein: In step (3), the concentration of the phosphorous acid is 85%. After the dropwise addition is completed, the temperature is raised to 110° C. and the reaction is kept warm for 4 hours. The phosphonic acid group conversion rate is ≥85%.

5. The method for preparing a lignite resin drilling fluid fluid loss additive according to claim 1, wherein: In step (4), the nano-montmorillonite and deionized water are prepared into a suspension at a mass ratio of 1:10, the ultrasonic dispersion power is 600 W, the dispersion time is 30 min, and then added to the reaction system and stirred at 60° C. for 1 h.

6. The method for preparing a lignite resin drilling fluid fluid loss additive according to claim 1, wherein: In step (4), the amount of the tetrabutyl titanate-ethanol solution added is 3-5% of the total weight of the raw material system, and the gel rate of the system is ≤5% after stirring and reacting for 2 hours.

7. The method for preparing a lignite resin drilling fluid fluid loss reducer according to claim 1, wherein: In step (5), the moisture content of the filter cake after the plate and frame filtration is 60%, the temperature of the freeze dryer is -50°C, the vacuum degree is 10Pa, the drying time is 8h, and the porosity of the obtained porous fluffy particles is ≥45%.

8. The method for preparing a lignite resin drilling fluid fluid loss additive according to claim 1, wherein: In step (5), the screw speed of the twin-screw extruder is 200 rpm, the pelletizing length is 3 mm, the moisture content of the finished product is ≤8%, and the lubrication coefficient reduction rate is ≥40%.

9. The method for preparing a lignite resin drilling fluid fluid loss reducer according to claim 1, wherein: The nano-montmorillonite is sodium-based, and the particle size distribution Span value is ≤0.

8.

10. The method for preparing a lignite resin drilling fluid fluid loss reducer according to claim 1, wherein: The polyethylene glycol 400 is used in an amount of 2-3% of the total weight of the raw material system, and is mixed with the freeze-dried porous fluffy particles and then granulated using a twin-screw extruder. The viscosity retention rate of the finished product in a saturated sodium chloride solution is ≥90%.

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