A lignin nanoparticle plugging agent for a temperature-resistant environment-friendly water-based drilling fluid, a preparation method and application thereof

Abstract

The application provides a lignin nanoparticle plugging agent for a temperature-resistant environment-friendly water-based drilling fluid and a preparation method and application thereof, and belongs to the technical field of oil field chemicals. Lignin is extracted from biomass raw materials, and a dissolution-regeneration method is used to obtain lignin nanoparticles. A silanization reaction is used on the lignin nanoparticles, 3-(methacryloyloxy)propyl trimethoxysilane is grafted to the surface of the lignin nanoparticles, under the action of an initiator, a high-temperature-resistant monomer 2-acrylamide-2-methylpropanesulfonic acid is polymerized on the surface of the lignin nanoparticles, and the lignin nanoparticle plugging agent is obtained. The lignin nanoparticle plugging agent has excellent high-temperature resistance, can maintain its nanometer size and uniform dispersity under high-temperature conditions, can permeate into nanometer and micrometer pore throats and microcracks, can form mechanical interception and bridging in core pores, can realize efficient plugging of micro-nanometer pore throats, can reduce the filtration loss of a drilling fluid, and can maintain the stability of a well wall.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of lignin nanoparticles for temperature-resistant environmentally friendly water-based drilling fluid and its preparation method and application, belong to oilfield chemical technical field. BACKGROUND

[0002] In recent years, with the depletion of conventional oil and gas reservoirs, oil and gas exploration and development gradually develop in unconventional areas. However, the geological structure of unconventional oil and gas layers is complex, with strong heterogeneity, and nanometer and micrometer pore throats and microfractures are generally developed. Conventional drilling fluid plugging agents cannot effectively plug them, which can easily cause well leakage and wellbore instability, restricting the smooth progress of oil and gas resource exploration and development. Developing nanometer and micrometer scale drilling fluid plugging agents to strengthen the plugging of micro and nanometer pores and cracks is one of the key technologies to solve the problem of wellbore instability.

[0003] At present, various inorganic, organic and inorganic-organic composite plugging materials have been developed, among which inorganic-organic composite materials have high strength, thermal stability of inorganic materials and flexibility and easy processing of organic materials, and are the research focus of high-performance micro and nanometer plugging agents in recent years. By controlling the synthesis steps, core-shell structure and components, the comprehensive performance of inorganic-organic composite materials can be further improved to cope with complex downhole environments. However, most inorganic-organic composite materials currently use synthetic resins as coating structures, which will bring environmental problems that cannot be ignored in the long run. For example, Chinese patent document CN113403042A provides an organic-inorganic nanocomposite hydrogel plugging agent, and the synthesis raw materials include silicon dioxide, methacrylic acid, N,N-dimethyl acrylamide and N,N-methylene bisacrylamide. However, inorganic-organic composite materials have high cost, and water dispersion stability and high temperature resistance still face major challenges.

[0004] In summary, the research on micro and nanometer plugging agents for drilling fluids is still in its infancy, and how to achieve the green environmental protection, strong plugging and high dispersion stability of the plugging agent still faces great challenges.

[0005] Lignin is abundant in resources and low in price. Using lignin as a raw material to prepare plugging agents can turn waste into treasure and reduce production costs. Existing researches mainly focus on preparing gel-type plugging agents by directly compounding lignin to replace polymers or directly preparing resin-type plugging agents. However, the content of hydroxyl groups in lignin structure is low, and the steric hindrance on benzene ring is large, so the reaction activity is obviously insufficient. At present, the research on lignin modification and optimization of crosslinking agent is also relatively less, which leads to the problems of high use concentration of lignin-based plugging agent, large amount of crosslinking agent and high cost.

[0006] Therefore, it is urgent to develop environmentally friendly, low-cost, high water dispersion stability and high-temperature-resistant green high-performance water-based drilling fluid plugging agent to provide technical support for wellbore stability in unconventional formations. SUMMARY

[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 material using green and efficient extraction method, then, using dissolution-regeneration method, by adjusting the preparation parameters, obtain size-controllable lignin nanoparticle (LNP);The active site of the obtained lignin nanoparticle LNP is more, and the activity is 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 more, and the activity is strong, more KH570 and AMPS can be grafted, so the obtained lignin nanoparticle plugging agent has excellent high-temperature-resistant property, and can still maintain its nanometer size and uniform dispersibility under high-temperature condition.In addition, it can permeate into nanometer-sized pore throat and microcrack, form mechanical interception and bridging in core pore, 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:

[0009] A preparation method of a lignin nanoparticle plugging agent for temperature-resistant environment-friendly water-based drilling fluid, comprising the following steps:

[0010] (1) mix alanine and lactic acid, heat and stir until a uniform binary deep eutectic solvent (BDES) is formed, add ethylene glycol to the binary deep eutectic solvent, stir uniformly to obtain a ternary deep eutectic solvent (TDES);

[0011] (2) add biomass raw material to the ternary deep 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);

[0012] (3) add the 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 solution obtained by dialysis, wash and dry the obtained precipitate to obtain lignin nanoparticles;

[0013] (4) add the 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;

[0014] (5) 2-acrylamide-2-methylpropanesulfonic acid (AMPS) is dissolved in deionized water, the pH of the system is adjusted to 7-10, then the intermediate product is added, stirred uniformly, deoxygenated by nitrogen, then the initiator B is added to react, to obtain a lignin nanoparticle plugging agent for a temperature-resistant and environmentally-friendly water-based drilling fluid.

[0015] According to the application, preferably, the molar ratio of alanine to lactic acid in step (1) is 1:4-8, and more preferably 1:6.

[0016] According to the application, preferably, in step (1), the temperature for heating and stirring after mixing alanine and lactic acid is 70-100℃, and more preferably 80℃; the stirring speed is 300-800 rpm, and more preferably 500 rpm; and the heating and stirring time is 100-150 min, and more preferably 120 min.

[0017] According to the application, preferably, the molar ratio of alanine to ethylene glycol in step (1) is 1:0.5-2, and more preferably 1:1.

[0018] According to the application, preferably, the biomass raw material in step (2) is red pine bark, pine bark, eucalyptus bark or palm wood bark, and more preferably red pine bark.

[0019] According to the application, preferably, the mass ratio of the biomass raw material to the ternary eutectic solvent in step (2) is 3-8:30-70.

[0020] According to the application, preferably, the temperature for heating reaction in step (2) is 60-100℃, and more preferably 80℃; and the heating reaction time is 2-5 h, and more preferably 3 h.

[0021] According to the application, preferably, in step (2), the volume ratio of water to the mass of the biomass raw material is 30-50 mL:1 g; the washing is performed by washing with water for 3-5 times; and the drying is performed by vacuum drying at 70-90℃ until constant weight.

[0022] According to the application, preferably, the mass ratio 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.

[0023] According to the application, preferably, the volume ratio of deionized water to the mixed solution in step (3) is 1.72:0.5-3, and more preferably 1.72:1; the deionized water is added dropwise into the mixed solution at a dropwise adding speed of 5-10 mL / min, and more preferably 8 mL / min; and the stirring time after adding the deionized water is 3-5 h.

[0024] According to the present application, in step (3), the deionized water is added to the THF solution in which the lignin powder (L) is dissolved at a specific speed. Since the deionized water is a poor solvent for the lignin powder (L), the lignin powder (L) molecules dissolved in THF assemble after contacting with water molecules to generate lignin nanoparticles.

[0025] According to the present application, preferably, in step (3), the dialysis step is that the lignin nanoparticle suspension is transferred to a dialysis bag with a molecular weight cut-off of 8000 Da, and dialysis is performed in deionized water, the water is changed every 12 h, and the dialysis is continued for 24 h; the centrifugation is centrifugation at 5000-10000 rpm for 5-10 min; the washing is that the obtained precipitate is washed by centrifugation with deionized water for 2-3 times; and the drying is that the obtained solid after washing is dried at 50-60℃ for 40-60 h.

[0026] According to the present application, preferably, in step (4), the mass ratio of the lignin nanoparticles to deionized water is 1 g:100-500 mL, and further preferably 1 g:200 mL.

[0027] According to the present application, preferably, in step (4), the pH is adjusted to 4-6 using a hydrochloric acid solution with a concentration of 0.1 mol / L.

[0028] According to the present application, preferably, in step (4), the mass ratio of the lignin nanoparticles to 3-(methacryloyloxy)propyltrimethoxysilane (KH570) is 0.5-3:0.2-0.8, and further preferably 1:0.4.

[0029] According to the present application, preferably, in step (4), the initiator A is sodium bisulfite; and the mass ratio of the lignin nanoparticles to the initiator A is 0.5-3:0.05-0.1, and further preferably 1:0.075.

[0030] According to the present application, preferably, in step (4), the temperature of the reaction is 50-80℃, and further preferably 60℃; the time of the reaction is 5-7 h; and the reaction is carried out under nitrogen protection.

[0031] According to the present application, preferably, in step (4), the washing is that the obtained product after filtration is stirred and washed in acetone for 2-4 times to remove unreacted monomers; and the drying is drying at 50-60℃ for 10-15 h.

[0032] According to the present application, preferably, in step (5), the mass ratio of 2-acrylamide-2-methylpropanesulfonic acid (AMPS) to deionized water is 0.5-2 g:50-100 mL, and further preferably 1.6 g:80 mL.

[0033] According to the application, preferably, in step (5), the pH of the system is adjusted to 7-10, further preferably 8, using a 1% sodium hydroxide solution.

[0034] According to the application, preferably, in step (5), the mass ratio of 2-acrylamide-2-methylpropanesulfonic acid (AMPS) to the intermediate product is 0.5-2:2-5, preferably 1.6:3.

[0035] According to the application, preferably, in step (5), the initiator B 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.

[0036] According to the application, preferably, in step (5), the reaction temperature is 50-70℃, and the reaction time is 0.5-2h, further preferably 1h.

[0037] The application also provides a lignin nanoparticle plugging agent for a temperature-resistant and environmentally-friendly water-based drilling fluid, which is prepared by the above preparation method.

[0038] According to the application, the lignin nanoparticle plugging agent for a temperature-resistant and environmentally-friendly water-based drilling fluid is applied in a water-based drilling fluid.

[0039] The technical features and advantages of the application are as follows:

[0040] 1. The application first uses a green, environmentally-friendly and efficient lignin extraction method, extracts lignin (L) from biomass raw materials based on a ternary eutectic solvent system, and dissolves the lignin (L) in tetrahydrofuran to obtain size-controllable lignin nanoparticles (LNP) by a regeneration method.

[0041] 2. The 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 strong plugging and high-temperature-resistant properties.

[0042] 3. The lignin nanoparticle plugging agent prepared by the application can penetrate into nanometer and micrometer pore throats and microcracks, form mechanical interception and bridging in clay core pores, realize efficient plugging of micro-nano pore throats, reduce the filtration loss of drilling fluid, and thus maintain the stability of the wellbore.

[0043] 4. The lignin nanoparticle plugging agent for high-temperature-resistant and environmentally-friendly water-based drilling fluid provided by the application can realize the regulation of the particle size of the lignin nanoparticles by adjusting the mass ratio of the lignin nanoparticle solution to deionized water and the rotating speed during stirring, and the size can meet the plugging particle size grading, and can plug the micro-nano-sized pore throats and micro-cracks in the formation. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 A physical map of the lignin powder obtained in Example 1.

[0045] Figure 2 An SEM image of the lignin nanoparticle plugging agent for high-temperature-resistant and environmentally-friendly water-based drilling fluid obtained in Example 1. DETAILED DESCRIPTION

[0046] The technical solutions in the application will be described in detail below in combination with specific embodiments. Obviously, the described embodiments are only some of the embodiments of the application, rather than all the embodiments.

[0047] The raw materials used in the embodiments are all conventional raw materials and can be commercially available; the methods are all prior art unless otherwise specified. Based on the embodiments in the application, all other examples improved or modified by those skilled in the art also belong to the protection scope of the application.

[0048] Example 1

[0049] A preparation method of a lignin nanoparticle plugging agent for high-temperature-resistant and environmentally-friendly water-based drilling fluid, comprising the following steps:

[0050] (1) Dry the reaction bottle and stirring rod in an oven to remove water, and flush the reaction bottle with nitrogen for 45 s, then add alanine and lactic acid in a molar ratio of 1:6 into the dried reaction bottle, stir at 500 rpm at 80 DEG C for 120 min to obtain a binary deep eutectic solvent (BDES), and then add ethylene glycol in an equal molar amount to the BDES and stir uniformly to obtain a ternary deep eutectic solvent (TDES);

[0051] (2) Add the crushed red pine bark into the ternary deep eutectic solvent (TDES), and the mass ratio of the crushed red pine bark to the ternary deep eutectic solvent (TDES) is 5:50, then react at 80 DEG C for 3 h, and stir at a speed of 400 rpm during the reaction; after the reaction is completed, add 200 mL of ultrapure water, filter to obtain a solid; wash the obtained solid with water for 4 times, each time using 100 mL of water, and dry the obtained solid at 80 DEG C under vacuum to a constant weight to obtain a lignin powder (L);

[0052] (3) At room temperature, lignin powder (L) was dissolved in tetrahydrofuran (THF) to obtain a THF solution containing lignin powder, wherein the mass of lignin powder to the volume of THF was 2 g:500 mL, and the dissolution process was stirred at 400 rpm; then deionized water was added dropwise into the THF solution containing lignin powder at a rate of 8 mL / min, and the volume ratio of deionized water to the THF solution containing lignin powder was 1.72:1; after the dropwise addition was completed, the stirring was continued for 4 h to obtain a lignin nanoparticle suspension; the obtained lignin nanoparticle suspension was transferred into a dialysis bag with a molecular weight cut-off of 8000 Da, dialyzed in deionized water, and the water was changed every 12 h for 24 h; the obtained solution was centrifuged at 8000 rpm for 5 min, the supernatant was removed, the obtained precipitate was washed with deionized water for 2 times, and the washed solid was dried at 60°C for 48 h to obtain lignin nanoparticles;

[0053] (4) 3 g of lignin nanoparticles were added into 600 mL of deionized water, the pH of the system was adjusted to 4 using a hydrochloric acid solution with a concentration of 0.1 mol / L, then 1.2 g of 3-(methacryloyloxy)propyltrimethoxysilane (KH570) and 225 mg of sodium bisulfite were added, and the reaction was carried out at 60°C for 6 h under nitrogen protection; after the reaction was completed, the product was filtered, and the filtered product was washed with acetone for 3 times (i.e., the filtered product was added into acetone, stirred, and then filtered, the filtered product was added into acetone again, stirred, and then filtered, and the filtered product was added into acetone again, stirred, and then filtered) to remove unreacted monomers, and the product was dried at 60°C for 12 h to obtain an intermediate product;

[0054] (5) 1.6 g of 2-acrylamido-2-methylpropanesulfonic acid (AMPS) was added into 80 mL of deionized water, then a sodium hydroxide solution with a mass fraction of 1% was added to adjust the pH value to 8, then 3 g of the intermediate product was added, the temperature was increased to 60°C, nitrogen was introduced to remove oxygen for 10 min, then 60 mg of an initiator ammonium persulfate was added, and the reaction was carried out at 60°C for 1 h to obtain a temperature-resistant and environmentally friendly water-based lignin nanoparticle plugging agent (A1) for drilling fluid.

[0055] The actual picture of the lignin powder obtained in step (2) of the example is shown in Figure 1 .

[0056] The SEM image of the temperature-resistant and environmentally friendly water-based lignin nanoparticle plugging agent for drilling fluid obtained in the example is shown in Figure 2 . As can be seen from Figure 2 , the synthesized lignin nanoparticles have a relatively uniform particle size and a smooth surface, and the particle size is about 200 nm, which is suitable for plugging microcrack developed formations.

[0057] Example 2

[0058] A preparation method of a lignin nanoparticle plugging agent for a temperature-resistant and environmentally friendly water-based drilling fluid is as described in Embodiment 1, except that in step (3), the volume ratio of deionized water to the THF solution containing lignin powder is 1:1, to obtain a lignin nanoparticle plugging agent for a temperature-resistant and environmentally friendly water-based drilling fluid (A2).

[0059] Embodiment 3

[0060] A preparation method of a lignin nanoparticle plugging agent for a temperature-resistant and environmentally friendly water-based drilling fluid is as described in Embodiment 1, except that in step (4), 2.1 g of 3-(methacryloyloxy)propyltrimethoxysilane (KH570) is added, to obtain a lignin nanoparticle plugging agent for a temperature-resistant and environmentally friendly water-based drilling fluid (A3).

[0061] Embodiment 4

[0062] A preparation method of a lignin nanoparticle plugging agent for a temperature-resistant and environmentally friendly water-based drilling fluid is as described in Embodiment 1, except that in step (5), 2 g of 2-acrylamido-2-methylpropanesulfonic acid (AMPS) is added, to obtain a lignin nanoparticle plugging agent for a temperature-resistant and environmentally friendly water-based drilling fluid (A4).

[0063] Comparative Example 1

[0064] A preparation method of a plugging agent for a water-based drilling fluid is as described in Embodiment 1, except that step (3) of nanocrystallization of lignin is not performed, and the lignin powder obtained in step (2) is directly used in step (4), to obtain a plugging agent for a water-based drilling fluid (B1).

[0065] Comparative Example 2

[0066] A preparation method of a plugging agent for a water-based drilling fluid is as described in Embodiment 1, except that 3-(methacryloyloxy)propyltrimethoxysilane (KH570) is not added in step (4), to obtain a plugging agent for a water-based drilling fluid (B2).

[0067] Comparative Example 3

[0068] A preparation method of a plugging agent for a water-based drilling fluid is as described in Embodiment 1, except that 2-acrylamido-2-methylpropanesulfonic acid (AMPS) is not added in step (5), to obtain a plugging agent for a water-based drilling fluid (B3).

[0069] Comparative Example 4

[0070] A preparation method of a plugging agent for a water-based drilling fluid includes the following steps:

[0071] (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 hydrochloric acid solution with a concentration of 0.1 mol / L. Then, 1.2 g of 3-(methacryloyloxy)propyltrimethoxysilane (KH570) and 225 mg of sodium bisulfite were added, and the reaction was carried out at 60°C for 6 h under nitrogen protection. After the reaction was completed, the product was filtered, and the filtered product was washed with acetone three times (i.e., the filtered product was added to acetone, stirred, and then filtered; the filtered product was added to acetone again, stirred, and then filtered; and the filtered product was added to acetone once more, stirred, and then filtered) to remove unreacted monomers. The product was dried at 60°C for 12 h to obtain an intermediate product;

[0072] (2) 1.6 g of 2-acrylamido-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 to 8. Then, 3 g of the intermediate product was added, and the temperature was raised to 60°C. After oxygen was removed by nitrogen for 10 min, 60 mg of an initiator, ammonium persulfate, was added, and the reaction was carried out at 60°C for 1 h to obtain a water-based drilling fluid plugging agent (B4).

[0073] Test Example 1

[0074] The plugging agents prepared in the examples and comparative examples were evaluated for the following properties:

[0075] 1. Particle size test

[0076] The average particle size test method after centrifugation was as follows: first, the plugging agent was centrifuged at a speed of 6000 rpm for 20 min, and the obtained precipitate was dried at 60°C for 12 h. Then, the precipitate was dispersed in water to obtain a dispersion liquid with a mass concentration of 1 wt%, and the particle size was tested.

[0077] The re-dispersion particle size test method was as follows: the dispersion liquid obtained in the above average particle size test after centrifugation was centrifuged at a speed of 6000 rpm for 20 min, and the obtained precipitate was dried at 60°C for 12 h. Then, the precipitate was dispersed in water again to obtain a dispersion liquid with a mass concentration of 1 wt%, and the particle size was tested.

[0078] The particle size test results of the plugging agents prepared in the examples and comparative examples are shown in Table 1 below.

[0079] Table 1 Particle size test results

[0080]

[0081] It can be seen from the experimental results in Table 1 that the average particle size of the lignin nanoparticle plugging agent for the environment-friendly water-based drilling fluid in each example and the comparative example is about 192-275 nm, which can effectively match the nanometer and micrometer level pores and form efficient plugging; after centrifugation at 6000 rpm / 20 min, the average particle size of the plugging agent of the application changes little, indicating that it has excellent long-acting dispersion stability; among them, in the comparative example 1, the lignin powder is not nano-treated, and the obtained plugging agent has a larger particle size and cannot realize self-adaptive plugging of the cracks in the formation. In addition, after drying and redispersion, the average particle size of the plugging agent of the application only increases slightly, showing excellent redispersion ability, which is helpful to the use of the plugging agent of the application in the form of emulsion and solid.

[0082] 2. Test of micro-pore plugging performance

[0083] The plugging agent prepared in the examples and the comparative examples was taken as the evaluation object to perform the evaluation of the micro-pore plugging performance.

[0084] 4% bentonite-based slurry preparation: 16 g of bentonite and 0.56 g of anhydrous sodium carbonate were added to 400 mL of water, and stirred at a room temperature and a rotation speed of 8000 rpm for 2 h, and then the water was sealed and placed at a room temperature for 24 h to obtain a 4% bentonite-based slurry.

[0085] Sample preparation: 400 mL of the 4% bentonite-based slurry was taken, 8 g of the prepared plugging agent was added, and stirred at a rotation speed of 6000 r / min for 20 min to obtain a sample.

[0086] The micro-pore filter vectors of the base slurry and each example and the comparative example at a normal temperature of 25℃, a medium pressure of 0.7 MPa and a high temperature of 180℃, a high pressure of 3.5 MPa were tested using 300 nm, 500 nm and 700 nm micro-pore filter membranes as the filtration medium, and the test results are shown in Table 2.

[0087] Table 2 Test results of the micro-pore plugging performance of the plugging agent prepared by adding the examples and the comparative examples

[0088]

[0089] As shown in Table 2, the lignin nanoparticle plugging agent prepared by the present application can obviously improve the micro-pore plugging capacity of the drilling fluid and reduce the micro-pore filtration loss at normal temperature and high temperature and high pressure. At normal temperature, the plugging agent has nanometer and micrometer scale dispersion in the drilling fluid, can bridge and fill the micro-fine wrinkles and gaps formed by clay particles to form initial plugging, rapidly form an inner plugging layer, and help to inhibit the generation, expansion and connection of secondary micro-cracks. At the same time, the plugging agent rapidly reduces the invasion of the filtrate into the rock formation and reduces the permeability of the plugging layer through adsorption, polymerization and other means on the surface of the inner plugging layer. By regulating the size of the nanoparticles of the plugging agent, the material shows self-adaptive plugging, and the size can meet the plugging particle size gradation, so that the material can plug the micron-level pore throat and micro-cracks in the formation. In addition, the plugging agent has certain viscosity, penetrates into the nanometer and micrometer level pore throat and micro-cracks, forms mechanical interception and bridging in the clay core pore, and maintains the stability of the wellbore. Under high temperature conditions, the plugging agent is bridged together with the rigid rock particles, promotes the close connection between the rock particles. The adhesion between the particles in the deposited plugging layer enables the plugging agent to enter the micro-pores in the formation under the action of pressure difference, form a firm physical adhesion on the surface of the clay particles, form a dense structure layer on the mud cake by the nanoparticles, improve the rheological property of the drilling fluid, enhance the density of the mud cake, thereby reducing the filtration vector of the drilling fluid and effectively plugging the formation. The high-temperature and high-pressure micro-pore filtration loss is effectively reduced. In addition, the lignin-based nanoparticle plugging agent prepared by the present application can effectively plug the filtration medium with a size of 300-700 nm.

[0090] 3. Change of permeability of artificial mud cake before and after plugging by the plugging agent

[0091] Preparation of artificial mud cake:

[0092] 16 g of bentonite and 0.56 g of anhydrous sodium carbonate were added to 400 mL of water, stirred at a speed of 8000 rpm for 2 h at room temperature, and then sealed and placed at room temperature for hydration for 24 h to obtain 4% bentonite-based slurry. The 4% bentonite-based slurry was stirred at high speed for 20 min, then poured into a high-temperature and high-pressure filtration instrument, and the filtration was carried out at normal temperature and a pressure of 3.5 MPa for 30 min. After filtration, the slurry at the upper part of the tank was poured out, and the mud cake formed at the lower part of the tank was the required mud cake.

[0093] The permeability of the mud cake was calculated according to Darcy's law, and the calculation formula was as follows:

[0094] (1)

[0095] In the formula, K i is the permeability of the mud cake, μm 2 ; q i is the seepage rate of the clean water, cm 3 ·s -1; μ is the viscosity of clean water, the viscosity of clean water at 25℃ is 0.89 mPa·s; 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, cm 2 .

[0096] Mud cake permeability determination: After the preparation of the mud cake, clean water is added to the upper part of the tank to ensure that the mud cake is not damaged, and the filtration loss is recorded under the condition of room temperature and pressure of 3.5 MPa for 30 min, and the permeability K1 of the mud cake before plugging is calculated. After the experiment, the clean water is poured out, and the water dispersion liquid of the plugging agent with a concentration of 2wt% before and after aging is added respectively, and the filtration loss is recorded under the same experimental conditions for 30 min. The water dispersion liquid of the plugging agent is poured out, and the clean water is added again, and the filtration loss is recorded for 30 min, and the permeability K2 of the mud cake after plugging is calculated.

[0097] According to formula (2), the permeability reduction rate K of the mud cake can be obtained:

[0098] K= (K1-K2) / K1 × 100% (2)

[0099] The change of the permeability of the mud cake after the water dispersion liquid of the plugging agent with a concentration of 2wt% is tested at room temperature and 180℃ for 16h respectively, and the test results are shown in Table 3.

[0100] Table 3 Change of permeability of artificial mud cake before and after plugging by plugging agent

[0101]

[0102] Under the conditions of room temperature and 180℃ aging, the permeability of the artificial mud cake is reduced to different degrees after adding the experimental examples and comparative examples. Among them, the plugging performance of A1 on the artificial mud cake is the best. According to the experimental results, the lignin nanoparticles invented by the application have good plugging performance, and have good temperature resistance, and still have certain plugging performance after aging at 180℃ for 16h. The lignin nanoparticles are filled in the artificial mud cake under the pressure difference of the fluid brought out of the artificial mud cake, thereby reducing the permeability of the artificial mud cake. High temperature can cause different degrees of degradation of the molecular chain of the plugging agent, resulting in smaller particle size and lower strength of the plugging agent, and the plugging performance of the artificial mud cake is poor, thereby causing the permeability of the artificial mud cake to increase slightly.

[0103] 4, Effect of plugging agent on rheological property and filtration property of base slurry before and after aging

[0104] 4% bentonite base slurry preparation: 16g of bentonite and 0.56g of anhydrous sodium carbonate are added to 400mL of water, and the mixture is stirred at a speed of 8000rpm for 2h at room temperature, and then the mixture is sealed and left to stand for 24h at room temperature to obtain a 4% bentonite base slurry.

[0105] Sample preparation: 400 mL of 4% bentonite base slurry was taken, 8 g of the prepared plugging agent was added, stirred at 6000 r / min for 20 min to obtain the sample.

[0106] Drilling fluid aging: the above drilling fluid sample was placed in a roller heating furnace, the aging temperature was 180 DEG C, and the aging time was 16 h; the rheological and filtration properties of the drilling fluid were tested according to the American Petroleum Institute (API) standard (API RP 13B-1, 2023), and the test results are shown in Table 4.

[0107] Table 4 rheological and filtration properties of the drilling fluid obtained by adding the plugging agent prepared in the examples and comparative examples

[0108]

[0109] As can be seen from the results in Table 4, the lignin-based nanoparticle plugging agent of the present application has good compatibility with the bentonite base slurry, has the functions of thickening, increasing viscosity and reducing filtration, and can significantly reduce the high temperature and high pressure filtration amount, wherein example 1 shows excellent rheological properties and filtration reduction effect, and the size can meet the particle size grading of plugging, and can plug the micron-sized pore throat and micro-cracks in the formation. In addition, the plugging agent of the present application has certain viscosity, penetrates into the nanometer and micrometer-sized pore throat and micro-cracks, forms mechanical interception and bridging in the clay core pore, and maintains the stability of the wellbore. The adhesion between the particles in the deposition plugging layer can make the plugging agent enter the micro-pores in the formation under the action of pressure difference, form a firm physical adhesion on the surface of the clay particles, and the particles with nanometer size form a dense structure layer on the mud cake, improve the rheological property of the drilling fluid, enhance the density of the mud cake, thereby reducing the filtration vector of the drilling fluid, and effectively plugging the formation.

[0110] The environmentally friendly water-based drilling fluid lignin nanoparticle plugging agent prepared in the present application still has excellent rheological property and filtration reduction performance after aging at high temperature (180 DEG C).

[0111] The above detailed the preferred embodiments of the present application, however, the present application is not limited to the specific details in the above embodiments, within the technical concept range of the present application, various simple modifications can be made to the technical solutions of the present application, and these simple modifications all belong to the protection scope of the present application.

[0112] In addition, it should be noted that each specific technical feature described in the above specific embodiments can be combined in any appropriate manner without contradiction, and in order to avoid unnecessary repetition, the present application will not further describe various possible combinations.

[0113] Furthermore, the various embodiments of the present application can be combined with each other, as long as it does not violate the spirit of the present application, and it should be considered as disclosed in the present application.

Claims

1. A method for preparing a lignin nanoparticle plugging agent for temperature-resistant and environmentally friendly water-based drilling fluid, characterized in that, The steps include the following: (1) Mix alanine and lactic acid, heat and stir until a uniform binary eutectic solvent is formed, add ethylene glycol to the binary eutectic solvent and stir evenly to obtain a ternary 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) Add biomass raw materials to a ternary eutectic solvent and heat to react; after the reaction is completed, add water to the resulting reaction solution, filter, wash and dry to obtain lignin powder; the biomass raw materials are red pine bark, pine bark, eucalyptus bark or palm bark; the mass ratio of the biomass raw materials to the ternary eutectic solvent is 3-8:30-70; (3) Add lignin powder to tetrahydrofuran and stir to obtain a mixture. Then, add deionized water and stir to obtain a lignin nanoparticle suspension. Dialyze the lignin nanoparticle suspension, centrifuge the dialysis solution, and wash and dry the 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 mixture is 1.72: 0.5-3. (4) Add lignin nanoparticles to deionized water, stir evenly, adjust pH to 4-6, add 3-(methacryloyloxy)propyltrimethoxysilane, stir evenly, then add initiator A to carry out the reaction; after the reaction is completed, filter, wash and dry to obtain intermediate product; the mass ratio of lignin nanoparticles to 3-(methacryloyloxy)propyltrimethoxysilane is 0.5-3:0.2-0.8; the initiator A is sodium bisulfite; the mass ratio of lignin nanoparticles to initiator A is 0.5-3:0.05-0.1; (5) Dissolve 2-acrylamide-2-methylpropanesulfonic acid in deionized water, adjust the pH of the system to 7-10, add the intermediate product, stir evenly, remove oxygen by purging with nitrogen, add initiator B, and react to obtain a temperature-resistant and environmentally friendly water-based drilling fluid lignin nanoparticle plugging agent; the mass ratio of 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 2-acrylamide-2-methylpropanesulfonic acid is 0.04-0.075:0.5-2.

2. The preparation method of the lignin nanoparticle plugging agent for temperature-resistant and environmentally friendly water-based drilling fluid according to claim 1, characterized in that, The molar ratio of alanine to lactic acid in step (1) is 1:6; the molar ratio of alanine to ethylene glycol is 1:

1. The temperature for heating and stirring after mixing alanine and lactic acid is 70-100℃; the stirring speed is 300-800 rpm; and the stirring time is 100-150 min.

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

4. The preparation method of the lignin nanoparticle plugging agent for temperature-resistant and environmentally friendly water-based drilling fluid according to claim 1, characterized in that, In step (3), the mass ratio of lignin powder to the volume of tetrahydrofuran is 2g:500mL; the volume ratio of deionized water to the mixture is 1.72:1; the deionized water is added to the mixture at a rate of 5-10mL / min; and the stirring time after adding the deionized water is 3-5h. The dialysis steps are as follows: the lignin nanoparticle suspension is transferred to a dialysis bag with a molecular weight cutoff of 8000 Da, and dialysis is performed in deionized water, with the water changed every 12 hours for 24 hours; the centrifugation is performed at 5000-10000 rpm for 5-10 minutes; the washing is performed by centrifuging and washing the obtained precipitate with deionized water 2-3 times; the drying is performed by drying the washed solid at 50-60℃ for 40-60 hours.

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

4.

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

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

8. The preparation method of the lignin nanoparticle plugging agent for temperature-resistant and environmentally friendly water-based drilling fluid 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℃; and the reaction time is 0.5-2h.

9. A lignin nanoparticle plugging agent for temperature-resistant and environmentally friendly water-based drilling fluid, characterized in that, It is prepared by the preparation method described in any one of claims 1-8.

10. The application of the lignin nanoparticle plugging agent for temperature-resistant and environmentally friendly water-based drilling fluid as described in claim 9 in water-based drilling fluid.

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