Lignin nano-particle blocking agent for temperature-resistant environment-friendly water-based drilling fluid as well as preparation method and application of lignin nano-particle blocking agent

Abstract

The invention provides a lignin nanoparticle blocking agent for temperature-resistant environment-friendly water-based drilling fluid as well as a preparation method and application thereof, and belongs to the technical field of oilfield chemistry. The method comprises the following steps: extracting lignin from a biomass raw material, and obtaining lignin nanoparticles by adopting a dissolution-regeneration method; the preparation method comprises the following steps: carrying out a silanization reaction on lignin nanoparticles, grafting 3-(methacryloyloxy) propyltrimethoxysilane to the surfaces of the lignin nanoparticles, and polymerizing a high-temperature-resistant monomer 2-acrylamide-2-methylpropanesulfonic acid on the surfaces of the lignin nanoparticles under the action of an initiator to obtain the lignin nanoparticle plugging agent. The lignin nanoparticle plugging agent has excellent high-temperature resistance, can still keep the nano size and uniform dispersity under a high-temperature condition, can permeate into nano-micron pore throats and micro-cracks, forms mechanical interception and bridging in core pores, realizes efficient plugging of the micro-nano pore throats, reduces the filter loss of drilling fluid, and improves the drilling efficiency. The well wall stability is kept.

Description

Technical Field

[0001] The invention relates to a temperature-resistant and environment-friendly water-based drilling fluid lignin nanoparticle plugging agent and a preparation method and application thereof, belonging to the technical field of oilfield chemistry. Background Art

[0002] In recent years, with the depletion of conventional oil and gas reservoirs, oil and gas exploration and development has gradually shifted to unconventional areas. However, unconventional reservoirs have complex geological structures, strong heterogeneity, and are prone to the development of nanoscale pore throats and microfractures. Conventional drilling fluid plugging agents struggle to effectively seal these pore throats, which can easily lead to lost circulation and wellbore instability, hindering the smooth progress of oil and gas exploration and development. The development of nanoscale drilling fluid plugging agents to enhance the sealing properties of drilling fluids against micro- and nano-pores and fractures is a key technology to address this wellbore instability issue.

[0003] Currently, a variety of inorganic, organic, and inorganic-organic composite plugging materials have been developed. Among them, inorganic-organic composite materials combine the high strength and thermal stability of inorganic materials with the flexibility and easy processing of organic materials. They have become a research hotspot for high-performance micro-nano plugging agents in recent years. By controlling the synthesis steps, core-shell structure, and components, inorganic-organic composite materials can further improve their overall performance to cope with complex downhole environments. However, currently, inorganic-organic composite materials mostly use synthetic resins as the coating structure. In the long run, these materials will bring about environmental problems that cannot be ignored. For example, Chinese patent document CN113403042A provides an organic-inorganic nanocomposite hydrogel plugging agent, the synthetic raw materials of which include silica, methacrylic acid, N,N-dimethylacrylamide, and N,N-methylenebisacrylamide. However, inorganic-organic composite materials still face major challenges in terms of high cost, water dispersion stability, and high temperature resistance.

[0004] In summary, the research on micro-nano plugging agents for drilling fluids is still in its infancy, and how to achieve the green and environmentally friendly nature, strong plugging properties and high dispersion stability of plugging agents still faces huge challenges.

[0005] Lignin is abundant and inexpensive. Using lignin as a raw material for plugging agents can turn waste into valuable resources and reduce production costs. Existing research has focused on using lignin to directly compound and replace polymers to prepare gel-based plugging agents or directly prepare resin-based plugging agents. However, lignin has a low hydroxyl content and significant steric hindrance on the benzene ring, resulting in significantly insufficient reaction activity. Currently, there is relatively little research on lignin modification and cross-linker optimization, resulting in problems with lignin-based plugging agents, such as high concentrations, large amounts of cross-linkers, and high costs.

[0006] Therefore, there is an urgent need to develop environmentally friendly, low-cost, highly water-dispersible, high-temperature-resistant, green and high-performance water-based drilling fluid plugging agents to provide technical support for wellbore stability in unconventional formations. Summary of the Invention

[0007] In view of the deficiencies of the prior art, the present application provides a kind of lignin nanoparticle plugging agent for temperature-resistant environment-friendly water-based drilling fluid and its preparation method and application.The present application first extracts lignin (L) from biomass raw materials using a green and efficient extraction method, then, using the dissolution-regeneration method, by adjusting the preparation parameters, obtain size-controllable lignin nanoparticles (LNP);The active site of the obtained lignin nanoparticle LNP is multiple and strong, then, using silanization reaction, 3-(methacryloyloxy) propyl trimethoxysilane (KH570) with-C=C- bond is grafted to the surface of LNP, finally, under the action of initiator, high-temperature-resistant monomer 2-acrylamide-2-methylpropanesulfonic acid (AMPS) is polymerized on the surface of LNP, and finally lignin nanoparticle plugging agent is obtained;Since the active site of lignin nanoparticle LNP is multiple and strong, more KH570 and AMPS can be grafted, so the obtained lignin nanoparticle plugging agent has excellent high-temperature resistance, and can still maintain its nanometer size and uniform dispersity under high-temperature conditions.In addition, it can penetrate into nanometer-sized pore throat and microcracks, form mechanical interception and bridging in core pores, realize efficient plugging of micro-nano pore throat, reduce the filtration loss of drilling fluid, and thus maintain the stability of well wall.

[0008] The technical scheme of the present application is as follows: A preparation method of a lignin nanoparticle plugging agent for temperature-resistant environment-friendly water-based drilling fluid, comprising the following steps: (1) Mix alanine and lactic acid, heat and stir until a uniform binary eutectic solvent (BDES) is formed, add ethylene glycol to the binary eutectic solvent, stir uniformly, and obtain a ternary eutectic solvent (TDES); (2) Add biomass raw material to the ternary eutectic solvent and heat to react; after the reaction is completed, add water to the obtained reaction solution, filter, wash and dry to obtain lignin powder (L); (3) Add lignin powder (L) to tetrahydrofuran (THF) and stir to obtain a mixed solution, then add deionized water and stir to obtain a lignin nanoparticle suspension; dialyze the lignin nanoparticle suspension, centrifuge the dialysis solution, wash and dry the obtained precipitate to obtain lignin nanoparticles; (4) Add lignin nanoparticles to deionized water, stir uniformly, adjust the pH to 4-6, then add 3-(methacryloyloxy) propyl trimethoxysilane (KH570) and stir uniformly, then add initiator A and react; after the reaction is completed, filter, wash and dry to obtain an intermediate product; (5) 2-Acrylamide-2-methylpropanesulfonic acid (AMPS) was dissolved in deionized water, and the pH of the system was adjusted to 7-10. The intermediate product was added and stirred evenly. After nitrogen was passed through to deoxygenate, initiator B was added and reacted to obtain a heat-resistant and environmentally friendly water-based drilling fluid lignin nanoparticle plugging agent.

[0009] According to the present invention, preferably, the molar ratio of alanine to lactic acid in step (1) is 1:4-8, more preferably 1:6.

[0010] According to the preferred embodiment of the present invention, in step (1), the temperature of heating and stirring after mixing alanine and lactic acid is 70-100°C, more preferably 80°C; the speed of heating and stirring is 300-800 rpm, more preferably 500 rpm; and the time of heating and stirring is 100-150 min, more preferably 120 min.

[0011] According to the present invention, preferably, the molar ratio of alanine to ethylene glycol in step (1) is 1:0.5-2, more preferably 1:1.

[0012] According to the present invention, preferably, the biomass raw material in step (2) is red pine bark, pine bark, eucalyptus bark or palm bark, more preferably red pine bark.

[0013] According to the preferred embodiment of the present invention, the mass ratio of the biomass raw material to the ternary deep eutectic solvent in step (2) is 3-8:30-70.

[0014] According to the preferred embodiment of the present invention, the temperature of the heating reaction in step (2) is 60-100° C., more preferably 80° C.; the heating reaction time is 2-5 h, more preferably 3 h.

[0015] According to the preferred embodiment of the present invention, in step (2), the ratio of the volume of water added to the mass of the biomass raw material is 30-50 mL:1 g; the washing is performed by washing with water 3-5 times, and the drying is performed by vacuum drying at 70-90° C. to constant weight.

[0016] According to the preferred embodiment of the present invention, the ratio of the mass of the lignin powder to the volume of tetrahydrofuran in step (3) is 1-5 g:200-800 mL, and more preferably 2 g:500 mL.

[0017] According to the preferred embodiment of the present invention, the volume ratio of the deionized water to the mixed liquid in step (3) is 1.72:0.5-3, more preferably 1.72:1; the deionized water is added dropwise to the mixed liquid at a dropping speed of 5-10 mL / min, more preferably 8 mL / min; and the stirring time after adding the deionized water is 3-5 h.

[0018] According to the present invention, in step (3), deionized water is added to the tetrahydrofuran solution in which the lignin powder (L) is dissolved at a specific rate. Since deionized water is a poor solvent for the lignin powder (L), the molecules of the lignin powder (L) dissolved in THF assemble upon contact with the water molecules to form lignin nanoparticles.

[0019] According to the preferred embodiment of the present invention, the dialysis step in step (3) is as follows: transferring the lignin nanoparticle suspension to a dialysis bag with a molecular weight cutoff of 8000Da, dialyzing in deionized water, changing the water every 12 hours for 24 hours; the centrifugation is performed at 5000-10000rpm for 5-10min; the washing is performed by centrifuging the obtained precipitate with deionized water for 2-3 times; and the drying is performed by drying the washed solid at 50-60°C for 40-60h.

[0020] According to the preferred embodiment of the present invention, the ratio of the mass of the lignin nanoparticles to the volume of deionized water in step (4) is 1 g:100-500 mL, and more preferably 1 g:200 mL.

[0021] Preferably, according to the present invention, in step (4), a hydrochloric acid solution with a concentration of 0.1 mol / L is used to adjust the pH to 4-6.

[0022] According to the preferred embodiment of the present invention, the mass ratio of the lignin nanoparticles to 3-(methacryloyloxy)propyltrimethoxysilane (KH570) in step (4) is 0.5-3:0.2-0.8, and more preferably 1:0.4.

[0023] According to the preferred embodiment of the present invention, the initiator A in step (4) is sodium bisulfite; the mass ratio of the lignin nanoparticles to the initiator A is 0.5-3:0.05-0.1, and more preferably 1:0.075.

[0024] According to the preferred embodiment of the present invention, the reaction temperature in step (4) is 50-80°C, more preferably 60°C; the reaction time is 5-7h; and the reaction is carried out under nitrogen protection.

[0025] According to the preferred embodiment of the present invention, the washing in step (4) is to wash the filtered product in acetone with stirring for 2-4 times to remove unreacted monomers, and the drying is to dry at 50-60° C. for 10-15 hours.

[0026] According to the preferred embodiment of the present invention, the ratio of the mass of 2-acrylamide-2-methylpropanesulfonic acid (AMPS) to the volume of deionized water in step (5) is 0.5-2 g:50-100 mL, and more preferably 1.6 g:80 mL.

[0027] According to the preferred embodiment of the present invention, in step (5), a sodium hydroxide solution with a mass fraction of 1% is used to adjust the pH of the system to 7-10, more preferably 8.

[0028] According to the preferred embodiment of the present invention, the mass ratio of 2-acrylamide-2-methylpropanesulfonic acid (AMPS) to the intermediate product in step (5) is 0.5-2:2-5, preferably 1.6:3.

[0029] According to the preferred embodiment of the present invention, the initiator B in step (5) is ammonium persulfate, and the mass ratio of the initiator B to 2-acrylamide-2-methylpropanesulfonic acid (AMPS) is 0.04-0.075:0.5-2, preferably 0.06:1.6.

[0030] According to the preferred embodiment of the present invention, the reaction temperature in step (5) is 50-70° C., and the reaction time is 0.5-2 h, more preferably 1 h.

[0031] The present invention also provides a temperature-resistant and environmentally friendly lignin nanoparticle plugging agent for water-based drilling fluid, which is prepared by the above-mentioned preparation method.

[0032] According to the present invention, the above-mentioned temperature-resistant and environmentally friendly water-based drilling fluid lignin nanoparticle plugging agent is used in water-based drilling fluid.

[0033] The technical features and beneficial effects of the present invention are as follows: 1. The present invention first adopts a green, environmentally friendly and efficient lignin extraction method. Lignin (L) is extracted from biomass raw materials based on a ternary deep eutectic solvent system, and the lignin (L) is dissolved in tetrahydrofuran to obtain size-adjustable lignin nanoparticles (LNP) through a regeneration method.

[0034] 2. The prepared lignin nanoparticles are reacted with a silane coupling agent (KH570) and a high-temperature resistant monomer 2-acrylamide-2-methylpropanesulfonic acid (AMPS) to obtain a lignin nanoparticle plugging agent, which has both strong blocking and high-temperature resistance properties.

[0035] 3. The lignin nanoparticle plugging agent prepared by the present invention can penetrate into nano-micron pore throats and micro cracks, forming mechanical interception and bridging in the pores of clay cores, achieving efficient plugging of micro-nano pore throats, reducing the filtration loss of drilling fluid, and thus maintaining the stability of the wellbore wall.

[0036] 4. The high-temperature resistant and environmentally friendly water-based drilling fluid lignin nanoparticle plugging agent of the present invention realizes the regulation of the particle size of lignin nanoparticles by adjusting the mass ratio of lignin nanoparticle solution to deionized water and the rotation speed during the stirring process. The size of the lignin nanoparticles can meet the plugging particle size grading and can plug micro-nano pore throats and microcracks of different sizes in the formation. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a physical picture of the lignin powder obtained in Example 1.

[0038] Figure 2 This is an SEM image of the heat-resistant and environmentally friendly water-based drilling fluid lignin nanoparticle plugging agent obtained in Example 1. DETAILED DESCRIPTION

[0039] The technical solutions of the present invention are clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments.

[0040] The raw materials used in the examples are all conventional raw materials and can be obtained commercially; the methods described are all prior art unless otherwise specified. Based on the embodiments of the present invention, all other examples improved or modified by ordinary technicians in this field are within the scope of protection of the present invention.

[0041] Example 1 A method for preparing a heat-resistant and environmentally friendly water-based drilling fluid lignin nanoparticle plugging agent comprises the following steps: (1) The reaction flask and stirring rod were dried in an oven to remove moisture, and the reaction flask was flushed with nitrogen for 45 seconds. Alanine and lactic acid were added to the dried reaction flask at a molar ratio of 1:6, and stirred at 500 rpm at 80°C for 120 minutes to obtain a binary deep eutectic solvent (BDES). Subsequently, ethylene glycol in an amount equal to that of alanine was added and stirred evenly to obtain a ternary deep eutectic solvent (TDES); (2) Add crushed Korean pine bark to ternary deep eutectic solvent (TDES) at a mass ratio of 5:50, and then react at 80°C for 3 h. Stir at 400 rpm during the reaction. After the reaction is completed, add 200 mL of ultrapure water and filter to obtain a solid. Wash the filtered solid with water 4 times, using 100 mL of water each time. Dry the washed solid at 80°C in a vacuum oven to a constant weight to obtain lignin powder (L). (3) At room temperature, lignin powder (L) was dissolved in tetrahydrofuran (THF), and the ratio of the mass of lignin powder to the volume of tetrahydrofuran was 2g:500mL. During the dissolution process, the mixture was stirred at 400rpm to obtain a THF solution containing lignin powder. Deionized water was then added dropwise to the THF solution containing lignin powder at a rate of 8mL / min, and the volume ratio of deionized water to the THF solution containing lignin powder was 1.72:1. After the addition was completed, the mixture was stirred for 4h to obtain a lignin nanoparticle suspension. The obtained lignin nanoparticle suspension was transferred to a dialysis bag with a molecular weight cutoff of 8000Da and dialyzed in deionized water, changing the water every 12h for 24h. The obtained solution was centrifuged at 8000rpm for 5min, and the supernatant was removed. The obtained precipitate was washed twice with deionized water by centrifugation. The washed solid was dried at 60℃ for 48h to obtain lignin nanoparticles. (4) 3 g of lignin nanoparticles were added to 600 mL of deionized water, and the pH of the system was adjusted to 4 using a 0.1 mol / L hydrochloric acid solution. 1.2 g of 3-(methacryloyloxy)propyltrimethoxysilane (KH570) and 225 mg of sodium bisulfite were added, and the mixture was reacted at 60 °C under nitrogen protection for 6 h. After the reaction was completed, the mixture was filtered, and the filtered product was stirred and washed in acetone three times (i.e., the filtered product was added to acetone, stirred, and filtered, and then the filtered product was added to acetone, stirred, and filtered, and then added to acetone again, stirred, and filtered) to remove unreacted monomers. The product was dried at 60 °C for 12 h to obtain an intermediate product. (5) 1.6 g of 2-acrylamide-2-methylpropanesulfonic acid (AMPS) was added to 80 mL of deionized water, and then a 1% sodium hydroxide solution was added to adjust the pH value to 8. Then, 3 g of the intermediate product was added, the temperature was raised to 60 °C, and nitrogen was passed through to deoxygenate for 10 min. Then, 60 mg of the initiator ammonium persulfate was added, and the mixture was stirred evenly and reacted at 60 °C for 1 h to obtain a heat-resistant and environmentally friendly water-based drilling fluid lignin nanoparticle plugging agent (A1).

[0042] The actual picture of the lignin powder obtained in step (2) of this embodiment is as follows Figure 1 shown.

[0043] The SEM image of the heat-resistant and environmentally friendly water-based drilling fluid lignin nanoparticle plugging agent obtained in this embodiment is as follows: Figure 2 As shown by Figure 2 It can be seen that the synthesized lignin nanoparticles have a relatively uniform particle size and a relatively smooth surface, with a particle size of about 200 nm, which is suitable for sealing formations with nano-micron-scale cracks.

[0044] Example 2 A method for preparing a heat-resistant and environmentally friendly water-based drilling fluid lignin nanoparticle plugging agent is as described in Example 1, except that in step (3), the volume ratio of deionized water to the THF solution containing lignin powder is 1:1, thereby obtaining a heat-resistant and environmentally friendly water-based drilling fluid lignin nanoparticle plugging agent (A2).

[0045] Example 3 A method for preparing a heat-resistant and environmentally friendly water-based drilling fluid lignin nanoparticle plugging agent is as described in Example 1, except that 2.1 g of 3-(methacryloyloxy)propyltrimethoxysilane (KH570) is added in step (4) to obtain a heat-resistant and environmentally friendly water-based drilling fluid lignin nanoparticle plugging agent (A3).

[0046] Example 4 A method for preparing a heat-resistant and environmentally friendly water-based drilling fluid lignin nanoparticle plugging agent is as described in Example 1, except that 2 g of 2-acrylamide-2-methylpropanesulfonic acid (AMPS) is added in step (5) to obtain a heat-resistant and environmentally friendly water-based drilling fluid lignin nanoparticle plugging agent (A4).

[0047] Comparative Example 1 A method for preparing a plugging agent for water-based drilling fluid is as described in Example 1, except that the nano-treatment of lignin in step (3) is not performed, and the lignin powder obtained in step (2) is directly used in step (4) to obtain a plugging agent for water-based drilling fluid (B1).

[0048] Comparative Example 2 A method for preparing a plugging agent for a water-based drilling fluid is as described in Example 1, except that 3-(methacryloyloxy)propyltrimethoxysilane (KH570) is not added in step (4), thereby obtaining a plugging agent for a water-based drilling fluid (B2).

[0049] Comparative Example 3 A method for preparing a plugging agent for a water-based drilling fluid is as described in Example 1, except that 2-acrylamide-2-methylpropanesulfonic acid (AMPS) is not added in step (5), thereby obtaining a plugging agent for a water-based drilling fluid (B3).

[0050] Comparative Example 4 A method for preparing a plugging agent for water-based drilling fluid comprises the following steps: (1) 3 g of commercially available lignin particles were added to 600 mL of deionized water, and the pH of the system was adjusted to 4 using a 0.1 mol / L hydrochloric acid solution. 1.2 g of 3-(methacryloyloxy)propyltrimethoxysilane (KH570) and 225 mg of sodium bisulfite were added, and the mixture was reacted at 60 °C under nitrogen protection for 6 h. After the reaction was completed, the mixture was filtered, and the filtered product was stirred and washed in acetone three times (i.e., the filtered product was added to acetone, stirred, and filtered, and then the filtered product was added to acetone, stirred, and filtered, and then added to acetone again, stirred, and filtered) to remove unreacted monomers. The mixture was dried at 60 °C for 12 h to obtain an intermediate product. (2) 1.6 g of 2-acrylamide-2-methylpropanesulfonic acid (AMPS) was added to 80 mL of deionized water, and then a 1% sodium hydroxide solution was added to adjust the pH value to 8. Then, 3 g of the intermediate product was added, and the temperature was raised to 60 °C. After nitrogen was passed through to deoxygenate for 10 min, 60 mg of initiator ammonium persulfate was added. After stirring evenly, the mixture was reacted at 60 °C for 1 h to obtain a water-based drilling fluid plugging agent (B4).

[0051] Test Example 1 The following performance evaluations were performed on the plugging agents prepared in the examples and comparative examples: 1. Particle size test The average particle size test method after centrifugation is as follows: first, the plugging agent is centrifuged at 6000 rpm for 20 minutes, the resulting precipitate is dried at 60°C for 12 hours, and then dispersed in water to obtain a dispersion with a mass concentration of 1wt%, and then the particle size test is performed.

[0052] The redispersed particle size test method is as follows: the dispersion obtained in the average particle size test after centrifugation is centrifuged at 6000 rpm for 20 minutes, the resulting precipitate is dried at 60°C for 12 hours, and then dispersed in water again to obtain a dispersion with a mass concentration of 1 wt% for particle size testing.

[0053] The particle size test results of the plugging agents prepared in the examples and comparative examples are shown in Table 1 below.

[0054] Table 1 Particle size test results

[0055] As can be seen from the experimental results in Table 1, the average particle size of the environmentally friendly water-based drilling fluid lignin nanoparticle plugging agent of each embodiment and comparative example is approximately between 192 and 275 nm, which can effectively match nano-micron-scale pores and form efficient plugging. After centrifugation at 6000 rpm / 20 min, the average particle size of the plugging agent of the present invention does not change much, indicating that it has excellent long-term dispersion stability. Among them, in Comparative Example 1, the lignin powder was not nano-processed, and the particle size of the resulting plugging agent was relatively large, failing to achieve adaptive plugging of cracks in the formation. In addition, after drying and redispersion, the average particle size of the plugging agent of the present invention only slightly increases, demonstrating excellent redispersion ability, which facilitates the use of the plugging agent of the present invention in both emulsion and solid forms.

[0056] 2. Testing of micropore blocking performance The plugging agents prepared in the examples and comparative examples were used as evaluation objects to evaluate the micropore plugging performance.

[0057] Preparation of 4% bentonite-based slurry: add 16 g bentonite and 0.56 g anhydrous sodium carbonate to 400 mL water, stir thoroughly at 8000 rpm at room temperature for 2 h, seal and let stand at room temperature for 24 h to obtain 4% bentonite-based slurry.

[0058] Preparation of the sample: 400 mL of 4% bentonite-based slurry was added with 8 g of the prepared plugging agent, and the mixture was stirred at a speed of 6000 r / min for 20 min to obtain a sample.

[0059] Microporous filter membranes with diameters of 300 nm, 500 nm, and 700 nm were used as filtration loss media to test the microporous filtration vectors of the base slurry and various embodiments and comparative examples at room temperature (25°C), medium pressure (0.7 MPa), and high temperature (180°C), high pressure (3.5 MPa). The test results are shown in Table 2.

[0060] Table 2 Test results of micropore blocking performance of blocking agents prepared by adding examples and comparative examples

[0061] As shown in Table 2, the lignin nanoparticle plugging agent prepared in the present invention significantly improves the micropore plugging ability of drilling fluids and reduces micropore filtration loss at both room temperature and high temperature and high pressure. At room temperature, the plugging agent has a nanometer-micrometer dispersion in the drilling fluid, bridging and filling the fine folds and gaps formed by clay particles to form a preliminary plug, quickly forming an inner plugging layer, which helps inhibit the generation, expansion, and connection of secondary microcracks. Simultaneously, through adsorption and polymerization on the surface of the inner plugging layer, the filtrate's intrusion into the rock formation is rapidly reduced, reducing the permeability of the plugging layer. By regulating the size of the plugging agent's nanoparticles, the material exhibits adaptive plugging properties. Its size can meet the plugging particle size gradation, allowing it to plug micron-sized pore throats and microcracks of varying sizes in the formation. Furthermore, the plugging agent possesses a certain viscosity, penetrating into nanometer-sized pore throats and microcracks, forming mechanical interception and bridging within the clay core pores, maintaining wellbore stability. Under high temperature conditions, the plugging agent is bridged with rigid rock particles, promoting a close connection between rock particles. Due to the adhesion between particles in the sedimentary plugging layer, the plugging agent can enter the micropores in the formation under the action of pressure difference, forming a strong physical adhesion on the surface of clay particles. Nano-sized particles form a dense structural layer on the mud cake, improving the rheological properties of the drilling fluid and enhancing the density of the mud cake, thereby reducing the filtration vector of the drilling fluid and achieving effective plugging of the formation. It effectively reduces the high-temperature and high-pressure micropore filtration loss. In addition, the lignin-based nanoparticle plugging agent prepared by the present invention can form an effective plug for filtration loss media of 300-700nm.

[0062] 3. Changes in permeability of artificial mud cake before and after plugging with plugging agent Preparation of artificial mud cake: Add 16g of bentonite and 0.56g of anhydrous sodium carbonate to 400mL of water, stir thoroughly at 8000rpm for 2h at room temperature, and then seal and hydrate at room temperature for 24h to obtain a 4% bentonite slurry. After high-speed stirring for 20min, pour the 4% bentonite slurry into a high-temperature, high-pressure filter loss instrument and filter at room temperature and 3.5MPa for 30min. After the filter loss, pour out the slurry from the upper tank, and the mud cake formed at the lower tank is the required material for the experiment.

[0063] The mud cake permeability is calculated according to Darcy's law, and the calculation formula is: (1) Where K i is the mud cake permeability, μm 2 ;q i is the seepage rate of clean water, cm 3 ·s -1 ; μ is the viscosity of clean water, which is 0.89 mPa·s at 25°C; L is the thickness of the filter cake, cm; ΔP is the pressure difference on both sides of the mud cake, Pa; A is the area of ​​the mud cake, cm2 .

[0064] Mud cake permeability determination: After the mud cake is prepared, clean water is added to the top of the tank and allowed to flow slowly along the tank wall to ensure that the mud cake is not damaged. The filter is lost for 30 minutes at room temperature and a pressure of 3.5 MPa. The filter loss is recorded and the permeability (K1) of the mud cake before plugging is calculated. After the experiment, the clean water is poured out and a 2 wt% aqueous dispersion of the plugging agent before and after aging is added. Under the same experimental conditions, the filter is lost for 30 minutes. The plugging agent dispersion is poured out and clean water is added again. The filter is lost for 30 minutes. The filter loss is recorded and the permeability (K2) of the mud cake after plugging is calculated.

[0065] According to formula (2), the permeability reduction rate K of the mud cake can be obtained: K=(K1-K2) / K1×100% (2) The changes in mud cake permeability of a 2 wt% plugging agent aqueous dispersion after aging at room temperature and 180 °C for 16 h were tested. The test results are shown in Table 3.

[0066] Table 3 Changes in permeability of artificial mud cake before and after plugging by plugging agent

[0067] Under the conditions of room temperature and aging at 180°C, after adding the above experimental examples and comparative examples, the permeability of the artificial mud cake decreased to varying degrees. Among them, A1 has the best sealing performance on the artificial mud cake. According to the experimental results, the lignin nanoparticles invented by the present invention have good sealing performance and good heat resistance, and still have certain sealing properties after aging at 180°C for 16 hours. Under the pressure difference, the lignin nanoparticles are carried out of the artificial mud cake by the fluid and filled in the artificial mud cake, thereby reducing the permeability of the artificial mud cake. High temperature will cause the molecular chain of the plugging agent to degrade to varying degrees, resulting in a smaller particle size of the plugging agent, a lower strength, and a worse sealing property of the artificial mud cake, which leads to a slight increase in the permeability of the artificial mud cake.

[0068] 4. Effect of plugging agent on rheological and filtration properties of base slurry before and after aging Preparation of 4% bentonite-based slurry: add 16 g bentonite and 0.56 g anhydrous sodium carbonate to 400 mL water, stir thoroughly at 8000 rpm at room temperature for 2 h, seal and let stand at room temperature for 24 h to obtain 4% bentonite-based slurry.

[0069] Sample preparation: 400 mL of 4% bentonite-based slurry was added with 8 g of the prepared plugging agent, and the mixture was stirred at a speed of 6000 r / min for 20 min to obtain a sample.

[0070] Drilling fluid aging: The drilling fluid samples were placed in a roller furnace at an aging temperature of 180°C for 16 h. The rheological and filtration properties of the drilling fluids were tested according to the American Petroleum Institute (API) standard (API RP 13B-1, 2023). The test results are shown in Table 4.

[0071] Table 4 Rheological and filtration performance data of drilling fluids obtained by adding plugging agents prepared in Examples and Comparative Examples

[0072] As can be seen from the results of Table 4, the lignin-based nanoparticle plugging agent of the present invention has good compatibility with bentonite-based slurry, has the functions of viscosity increase, shear enhancement and fluid loss reduction, and can significantly reduce high-temperature and high-pressure fluid loss. Among them, Example 1 shows excellent rheological properties and fluid loss reduction effect. Its size can meet the plugging particle size gradation, and can plug micron-sized pores and microcracks of different sizes in the formation. In addition, the plugging agent of the present invention has a certain viscosity, penetrates into nano-micron-sized pores and microcracks, forms mechanical interception and bridging in the clay core pores, and maintains wellbore stability. The adhesion between particles in the sedimentary plugging layer allows the plugging agent to enter the micropores in the formation under the action of pressure difference, forming a firm physical adhesion on the surface of the clay particles, and forming a dense structural layer with nano-sized particles on the mud cake, improving the rheological properties of the drilling fluid, enhancing the density of the mud cake, thereby reducing the filtration vector of the drilling fluid and achieving effective plugging of the formation.

[0073] The environmentally friendly water-based drilling fluid lignin nanoparticle plugging agent prepared by the invention still has excellent rheological properties and fluid loss reduction performance after high-temperature (180° C.) aging.

[0074] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the scope of protection of the present invention.

[0075] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0076] In addition, the various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for preparing a heat-resistant and environmentally friendly water-based drilling fluid lignin nanoparticle plugging agent, characterized in that: The steps are as follows: (1) Alanine and lactic acid are mixed, heated and stirred until a uniform binary deep eutectic solvent is formed, ethylene glycol is added to the binary deep eutectic solvent, and stirred uniformly to obtain a ternary deep eutectic solvent; the molar ratio of alanine to lactic acid is 1:4-8; the molar ratio of alanine to ethylene glycol is 1:0.5-2; (2) adding a biomass raw material to a ternary low eutectic solvent and heating the mixture for reaction; after the reaction is completed, adding water to the reaction solution, filtering, washing, and drying the mixture to obtain lignin powder; the biomass raw material is red pine bark, pine bark, eucalyptus bark, or palm bark; and the mass ratio of the biomass raw material to the ternary low eutectic solvent is 3-8:30-70; (3) adding lignin powder to tetrahydrofuran and stirring to obtain a mixed solution, then adding deionized water and stirring to obtain a lignin nanoparticle suspension; dialyzing the lignin nanoparticle suspension, centrifuging the dialyzed solution, washing and drying the obtained precipitate to obtain lignin nanoparticles; the mass ratio of the lignin powder to the volume of tetrahydrofuran is 1-5 g: 200-800 mL; the volume ratio of the deionized water to the mixed solution is 1.72: 0.5-3; (4) Adding lignin nanoparticles to deionized water, stirring evenly, adjusting the pH to 4-6, then adding 3-(methacryloyloxy)propyltrimethoxysilane, stirring evenly, and then adding initiator A to react; after the reaction is completed, filtering, washing, and drying to obtain an intermediate product; the mass ratio of the lignin nanoparticles to 3-(methacryloyloxy)propyltrimethoxysilane is 0.5-3:0.2-0.8; the initiator A is sodium bisulfite; the mass ratio of the lignin nanoparticles to initiator A is 0.5-3:0.05-0.1; (5) 2-acrylamide-2-methylpropanesulfonic acid is dissolved in deionized water, and after adjusting the pH of the system to 7-10, the intermediate product is added, stirred evenly, and after nitrogen is passed through to deoxygenate, initiator B is added and reacted to obtain a heat-resistant and environmentally friendly water-based drilling fluid lignin nanoparticle plugging agent; the mass ratio of the 2-acrylamide-2-methylpropanesulfonic acid to the intermediate product is 0.5-2:2-5; the initiator B is ammonium persulfate, and the mass ratio of the initiator B to the 2-acrylamide-2-methylpropanesulfonic acid is 0.04-0.075:0.5-2.

2. The method for preparing the heat-resistant and environmentally friendly water-based drilling fluid lignin nanoparticle plugging agent according to claim 1, characterized in that: In step (1), the molar ratio of alanine to lactic acid is 1:6; the molar ratio of alanine to ethylene glycol is 1:1; After alanine and lactic acid are mixed, the temperature for heating and stirring is 70-100° C.; the speed for heating and stirring is 300-800 rpm; and the time for heating and stirring is 100-150 minutes.

3. The method for preparing the heat-resistant and environmentally friendly water-based drilling fluid lignin nanoparticle plugging agent according to claim 1, characterized in that: The temperature of the heating reaction in step (2) is 60-100°C; the heating reaction time is 2-5h; the ratio of the volume of added water to the mass of the biomass raw material is 30-50mL:1g; the washing is performed by washing with water 3-5 times, and the drying is performed by vacuum drying at 70-90°C to constant weight.

4. The method for preparing the heat-resistant and environmentally friendly water-based drilling fluid lignin nanoparticle plugging agent according to claim 1, characterized in that: The ratio of the mass of the lignin powder to the volume of tetrahydrofuran in step (3) is 2 g:500 mL; the volume ratio of the deionized water to the mixed solution is 1.72:1; the deionized water is added dropwise to the mixed solution at a dropping rate of 5-10 mL / min; and the stirring time after adding the deionized water is 3-5 h; The dialysis step comprises: transferring the lignin nanoparticle suspension into a dialysis bag with a molecular weight cutoff of 8000Da, dialyzing in deionized water, changing the water every 12 hours for 24 hours; the centrifugation comprises centrifugation at 5000-10000 rpm for 5-10 minutes; the washing comprises centrifuging the obtained precipitate with deionized water for 2-3 times; and the drying comprises drying the washed solid at 50-60°C for 40-60 hours.

5. The method for preparing the heat-resistant and environmentally friendly water-based drilling fluid lignin nanoparticle plugging agent according to claim 1, characterized in that: In step (4), the ratio of the mass of the lignin nanoparticles to the volume of deionized water is 1 g:100-500 mL; a hydrochloric acid solution with a concentration of 0.1 mol / L is used to adjust the pH to 4-6; and the mass ratio of the lignin nanoparticles to 3-(methacryloyloxy)propyltrimethoxysilane is 1:0.

4.

6. The method for preparing the heat-resistant and environmentally friendly water-based drilling fluid lignin nanoparticle plugging agent according to claim 1, characterized in that: The mass ratio of the lignin nanoparticles to the initiator A in step (4) is 1:0.075; the reaction temperature is 50-80°C; the reaction time is 5-7 hours; the reaction is carried out under nitrogen protection; the washing is to stir and wash the obtained product in acetone for 2-4 times, and the drying is to dry it at 50-60°C for 10-15 hours.

7. The method for preparing the heat-resistant and environmentally friendly water-based drilling fluid lignin nanoparticle plugging agent according to claim 1, characterized in that: The ratio of the mass of 2-acrylamide-2-methylpropanesulfonic acid to the volume of deionized water in step (5) is 0.5-2 g:50-100 mL; and the pH of the solution is adjusted to 7-10 using a 1% sodium hydroxide solution.

8. The method for preparing the heat-resistant and environmentally friendly water-based drilling fluid lignin nanoparticle plugging agent according to claim 1, characterized in that: In step (5), the mass ratio of 2-acrylamide-2-methylpropanesulfonic acid to the intermediate product is 1.6:3; the mass ratio of initiator B to 2-acrylamide-2-methylpropanesulfonic acid is 0.06:1.6; the reaction temperature is 50-70° C., and the reaction time is 0.5-2 h.

9. A heat-resistant and environmentally friendly water-based drilling fluid lignin nanoparticle plugging agent, characterized in that: The preparation method is described in any one of claims 1 to 8.

10. Use of the heat-resistant and environmentally friendly lignin nanoparticle plugging agent for water-based drilling fluid according to claim 9 in water-based drilling fluid.

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