Modified nano-silica lubricant for drilling fluid and preparation method and application thereof

Abstract

The application provides a modified nano-silica lubricant for drilling fluid and a preparation method and application thereof, and belongs to the technical field of lubricants for drilling fluid. The preparation method of the lubricant comprises the following steps: (1) adding nano-silica into an ethanol aqueous solution, uniformly ultrasonically dispersing, adding a silane coupling agent, and performing reaction; after the reaction is completed, filtering, washing, and drying are performed to obtain silane coupling agent modified nano-silica; (2) adding the silane coupling agent modified nano-silica into an ethanol aqueous solution, uniformly stirring, then adding n-dodecanethiol and an initiator ethanol solution, uniformly stirring, then removing oxygen by blowing nitrogen, and then performing reaction; after the reaction is completed, cooling is performed, dilution is performed after adding ethanol, centrifugation, washing, and drying are performed, and the lubricant is obtained. The lubricant can reduce the flow resistance of the drilling fluid and the filter cake friction coefficient, has excellent wear resistance and corrosion resistance, can effectively improve the drilling efficiency, and meets the drilling demand of super-deep and ultra-deep wells.

Description

TECHNICAL FIELD

[0001] The present application relates to a modified nano-silica lubricant for drilling fluid and its preparation method and application, belonging to the technical field of lubricants for drilling fluid. BACKGROUND

[0002] In the process of ultra-deep and super-deep well drilling, high friction and high torque seriously affect the safety and efficiency of drilling. Lubricant is one of the core treatment agents of drilling fluid, which can effectively reduce the friction between drilling tools and casing and well wall, improve the lubricating performance of drilling fluid, and achieve the goal of lubrication speed-up.

[0003] Therefore, various lubricants for drilling fluid have been developed, which are mainly divided into two categories: liquid lubricants and solid lubricants. Liquid lubricants, such as fatty acid esters and mineral oil lubricants, are easily oxidized and degraded at high temperatures (greater than 180℃), leading to deterioration of the lubricating performance of drilling fluid. Moreover, they cannot adaptively adjust the lubrication strength according to the friction difference of different formations, and the lubrication effect is insufficient in high friction areas. Solid lubricants have excellent temperature resistance and wear resistance, which makes up for the use limitations of liquid lubricants in extreme working conditions, and have developed rapidly in recent years. However, conventional solid lubricants still have defects. For example, unmodified nano-silica has a high surface hydroxyl group density, is easy to agglomerate in drilling fluid, has poor dispersion stability, lacks long-acting lubricating groups, and has low lubricating film strength and limited wear resistance. Nano-silica modified by a single silane coupling agent (such as KH570) improves the dispersion, but does not introduce special lubricating groups, and the reduction rate of the lubrication coefficient is usually less than 80%. Moreover, in a high-salt environment, the surface charge balance is easily destroyed, and there is still a risk of agglomeration. Commercially available composite lubricants have a reduction rate of the extreme pressure lubrication coefficient of less than 12% after 16 hours of hot rolling at 220℃, and their temperature resistance and salt tolerance are far from the requirements of ultra-deep and super-deep well conditions. There are also patent documents on modified lubricants. For example, Chinese patent document CN111560238A provides an environmentally friendly drilling fluid lubricant, which includes cationic alkyl glycoside and quaternary ammonium nano-silica. The weight ratio of cationic alkyl glycoside to quaternary ammonium nano-silica is (40-90):(10-50). The quaternary ammonium nano-silica is polymerized from methylacryloyloxyethyl trimethylammonium chloride, styrene and nano-silica containing a polymerizable double bond. However, this lubricant has a large addition amount, has a large impact on the rheological properties of the drilling fluid system, and some materials have insufficient temperature resistance, making it difficult to meet the needs of deep and ultra-deep drilling. Chinese patent document CN116396491A provides a modified lubricant, which is nano-silica modified by a silane coupling agent, acrylate and polyether. However, the synthesis steps are complex, the cost is high, and it is difficult to achieve large-scale industrial application.

[0004] In summary, the prior art lacks a drilling fluid lubricant that can simultaneously meet the core requirements of "high-efficiency lubrication and drag reduction, high-temperature resistance (greater than 260℃), high-salt resistance (greater than 30% NaCl), and dispersion stability" for ultra-deep and super-deep wells, and there is an urgent need to break through the above bottlenecks through structural design and process optimization. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application provides a modified nano-silica lubricant for drilling fluid, as well as a preparation method and application thereof. The present application grafts a long-chain hydrophobic group of dodecanethiol onto the surface of nano-silica through the bridging action of a silane coupling agent, forming a "nano core-coupling agent-thiol" composite structure, and realizing the synergistic functions of "dispersion stability, high-efficiency lubrication, temperature resistance, and salt resistance". The lubricant of the present application can significantly reduce the flow resistance and filter cake friction coefficient of the drilling fluid, slow down the wear of the drilling tools, and has excellent wear and corrosion resistance, which can effectively improve the drilling efficiency and prolong the service life of the drill bit, meeting the drilling requirements of ultra-deep and super-deep wells.

[0006] The technical scheme of the present application is as follows:

[0007] A preparation method of a modified nano-silica lubricant for drilling fluid, comprising the following steps:

[0008] (1) Add nano-silica to an ethanol aqueous solution, ultrasonically disperse uniformly, and add a silane coupling agent for reaction; after the reaction is completed, filter, wash, and dry to obtain silane coupling agent modified nano-silica;

[0009] (2) Add the silane coupling agent modified nano-silica to an ethanol aqueous solution, stir uniformly, then add n-dodecanethiol and an initiator ethanol solution, stir uniformly, remove oxygen by passing nitrogen gas, and then react; after the reaction is completed, cool, dilute with ethanol, centrifuge, wash, and dry to obtain the modified nano-silica lubricant for drilling fluid.

[0010] According to the present application, the particle size of the nano-silica in step (1) is preferably 10-40 nm.

[0011] According to the present application, the ethanol aqueous solution in step (1) is prepared by mixing anhydrous ethanol and deionized water in a volume ratio of 2-4:1, and then adjusting the pH of the system to 4 using a 2 mol / L HCl aqueous solution.

[0012] According to the present application, the ratio of the volume of the ethanol aqueous solution to the mass of the nano-silica in step (1) is 50-80 mL:1 g.

[0013] According to the present application, the ultrasonic treatment time in step (1) is 20-30 min.

[0014] According to the application, preferably, the silane coupling agent in step (1) is one or more of vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriisopropoxysilane, 3-methacryloyloxypropylmethyldimethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, vinyltris(2-methoxyethoxy)silane, and propyltrimethoxysilane; the mass ratio of the silane coupling agent to nano-silica is 0.1-0.3:1.

[0015] According to the application, preferably, the temperature of the reaction in step (1) is 65-75℃, and the reaction time is 2-3h.

[0016] According to the application, preferably, the washing in step (1) is centrifugal washing with anhydrous ethanol for 3-4 times, and the drying is vacuum drying at 60-70℃ for 20-30h.

[0017] According to the application, preferably, in step (2), the volume ratio of anhydrous ethanol to deionized water in the aqueous ethanol solution is 1:1-2; the volume of the aqueous ethanol solution to the mass of the silane coupling agent modified nano-silica is 40-60mL:1g.

[0018] According to the application, preferably, in step (2), the mass ratio of n-dodecanethiol to the silane coupling agent modified nano-silica is 1.5-2:1.

[0019] According to the application, preferably, in step (2), the initiator is azobisisobutyronitrile, benzoyl peroxide, or tert-butyl hydroperoxide; the mass of the initiator is 1-3% of the total mass of the silane coupling agent modified nano-silica and n-dodecanethiol; and the concentration of the initiator ethanol solution is 0.004-0.005g / mL.

[0020] According to the application, preferably, in step (2), the time for oxygen removal by nitrogen is 15-30min.

[0021] According to the application, preferably, in step (2), the temperature of the reaction is 65-75℃, and the reaction time is 6-10h; and the reaction is carried out under nitrogen protection.

[0022] According to the application, preferably, in step (2), after the reaction is completed, the volume of ethanol added to the mass of the silane coupling agent modified nano-silica is 6-8mL:1g.

[0023] According to the application, preferably, the speed of centrifugation in step (2) is 8000-12000 rpm, and the centrifugation time is 5-15 min; the washing is washing 2-4 times with ethanol aqueous solution, the volume ratio of ethanol to water in the ethanol aqueous solution is 1:1; and the drying is vacuum drying at 60-70 DEG C for 10-15 h.

[0024] The application further provides a modified nano-silica lubricant for drilling fluid, which is prepared by the above preparation method.

[0025] According to the application, the modified nano-silica lubricant for drilling fluid is applied in a water-based drilling fluid, and is used in the drilling process to achieve the drilling target of reducing resistance and increasing speed; the concentration of the modified nano-silica lubricant for drilling fluid in the water-based drilling fluid is 0.1-0.3 wt%.

[0026] The technical features and beneficial effects of the application are as follows:

[0027] 1. In the application, the long-chain hydrophobic group of dodecanethiol is grafted on the surface of nano-silica through the bridging action of silane coupling agent, forming a "nano core-coupling agent-thiol" composite structure, realizing the synergistic functions of "stable dispersion, high-efficiency lubrication, temperature resistance and salt resistance", the obtained lubricant can greatly reduce the flow resistance of drilling fluid and the filter cake friction coefficient, slow down the wear of drilling tools, and has excellent wear and corrosion resistance, realizing the synergistic lubrication of solid microsphere lubrication, particle filling lubrication and boundary adsorption layer lubrication, and meanwhile, the excellent temperature resistance and wear resistance of SiO2 are retained.

[0028] 2. The lubricant has excellent lubricating performance, and has excellent high-temperature and high-salt resistance, when the addition amount is 0.2 wt% in 4% bentonite-based slurry, the lubrication coefficient reduction rate is 90.87%, which is significantly better than traditional solid lubricants; after 260 DEG C high-temperature aging for 16 h, the lubrication coefficient reduction rate still remains 88.36%; in a 30% NaCl high-salt environment, the lubrication coefficient reduction rate can still reach 86.78%, which can adapt to the extreme working conditions faced by ultra-deep and super-deep wells.

[0029] 3. The lubricant has the functions of protecting reservoir and stabilizing well wall, the introduced hydrophobic long chain in the lubricant can form a dense adsorption layer on the surface of rocks such as shale, and inhibit water penetration; when acting on the surface of drilling tools, it can also reduce the adhesive friction between the drilling tools and the well wall, and assist in maintaining the stability of the well wall, which is of great significance for drilling shale reservoir directional wells, horizontal large displacement wells and the like.

[0030] 4、The lubricant preparation method is simple, the reaction condition is relatively mild, the optimal addition amount is only 0.2wt%, far lower than that of the existing lubricant (1-3wt%), and the raw material cost is low and the source is extensive. It is extremely suitable for extremely complex well conditions, has the prospect of large-scale industrial production, and shows great potential for the exploitation of oil and gas in deep, ultra-deep, deep water and complex structure wells. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 The infrared spectrum of the modified nanometer silicon dioxide lubricant for drilling fluid prepared in Example 1. DETAILED DESCRIPTION

[0032] The application will be further described below in conjunction with specific examples, but is not limited thereto.

[0033] Meanwhile, the experimental methods in the following examples are all conventional methods unless otherwise specified; and the reagents, materials and equipment can be obtained from commercial channels unless otherwise specified.

[0034] The particle size of the nanometer silicon dioxide used in the examples is 20-30nm.

[0035] Example 1

[0036] A preparation method of a modified nanometer silicon dioxide lubricant for drilling fluid, comprising the following steps:

[0037] (1) 300mL of anhydrous ethanol and 100mL of deionized water are added to a beaker, and the pH of the system is adjusted to 4 using a 2mol / L HCl aqueous solution to obtain a mixed solution; 6g of nanometer silicon dioxide is weighed and added to the mixed solution, and ultrasonic dispersion is performed for 20min to ensure uniform dispersion of the nanoparticles; then 1.2g of silane coupling agent γ-methacryloyloxypropyl trimethoxysilane (KH570) is added, and after stirring uniformly, it is transferred to a three-necked flask and stirred magnetically at 70℃ for 2h; after the reaction is completed, it is naturally cooled to room temperature, the obtained reaction liquid is filtered, and the obtained product is washed with anhydrous ethanol by centrifugation for 4 times (10000rpm for each time, 10min for each time), to remove unreacted KH570; the obtained precipitate after washing is placed in a 70℃ vacuum drying oven and dried for 24h to obtain silane coupling agent modified nanometer silicon dioxide.

[0038] (2) Mix 60 mL of anhydrous ethanol with 90 mL of deionized water, add 3.0 g of silane coupling agent modified nano silica prepared in step (1), stir evenly, add 5.07 g of n-dodecyl mercaptan, and then add an initiator ethanol solution (0.14 g of azobisisobutyronitrile dissolved in 30 mL of ethanol), stir at room temperature for 20 min; introduce nitrogen into the system to remove oxygen for 20 min, and then stir the reaction for 8 h under nitrogen protection, stirring rate of 600 rpm and temperature of 70 °C; after the reaction is completed, cool naturally to room temperature, add 20 mL of ethanol to dilute the obtained reaction solution, then centrifuge at 10000 rpm for 10 min, discard the supernatant, wash the precipitate three times with an ethanol aqueous solution (the volume ratio of ethanol to water in the ethanol aqueous solution is 1:1), and vacuum dry the washed precipitate at 70 °C for 12 h to obtain a modified nano silica lubricant for drilling fluid.

[0039] The infrared spectrum of the modified nano-silica lubricant for drilling fluid obtained in this embodiment is as follows: Figure 1 As shown, by Figure 1 It can be known that 3300-3500cm -1 The peak at 2800-3000 cm⁻¹ represents the stretching vibration peak of incompletely reacted silanol groups (Si-OH) on the silica surface. -1 The peak at 1600-1700 cm⁻¹ corresponds to the CH stretching vibration of the alkyl chain (-CH₂-, -CH₃-) in dodecyl mercaptan; -1 The peak at 1000-1200 cm⁻¹ represents the C=O stretching vibration, indicating that the double bond structure of KH570 (γ-methacryloyloxypropyltrimethoxysilane) has been successfully grafted; -1 The characteristic absorption peak at 500-800 cm⁻¹ indicates that the basic structure of silicon dioxide still exists. -1 The bending vibration peak of Si-O at this point further confirms the presence of silica; the above results indicate that dodecanethiol and KH570 have been grafted onto the surface of nano-silica.

[0040] Example 2

[0041] A method for preparing a modified nano-silica lubricant for drilling fluid is described in Example 1, except that the mass of silane coupling agent added in step (1) is 0.6g.

[0042] Example 3

[0043] A method for preparing a modified nano-silica lubricant for drilling fluid is described in Example 1, except that the mass of silane coupling agent added in step (1) is 1.8g.

[0044] Example 4

[0045] A method for preparing a modified nano-silica lubricant for drilling fluid is as described in Example 1, except that in step (1) the silane coupling agent used is vinyl tri(2-methoxyethoxy)silane.

[0046] Example 5

[0047] A method for preparing a modified nano-silica lubricant for drilling fluid is as described in Example 1, except that in step (2) the mass of n-dodecanethiol added is 4.5 g.

[0048] Example 6

[0049] A method for preparing a modified nano-silica lubricant for drilling fluid is as described in Example 1, except that in step (1) the mass of n-dodecanethiol added is 6 g.

[0050] Comparative Example 1

[0051] A method for preparing a modified nano-silica lubricant for drilling fluid is as described in Example 1, except that step (2) is not performed.

[0052] Comparative Example 2

[0053] A method for preparing a modified nano-silica lubricant for drilling fluid is as described in Example 1, except that step (1) is not performed and in step (2) nano-silica is used instead of silane coupling agent nano-silica.

[0054] Comparative Example 3

[0055] A method for preparing a modified nano-silica lubricant for drilling fluid is as described in Example 1, except that in step (2) n-dodecanethiol is replaced by n-octanethiol.

[0056] Comparative Example 4

[0057] A method for preparing a modified nano-silica lubricant for drilling fluid is as described in Example 1, except that in step (2) n-dodecanethiol is replaced by octadecyl acrylate.

[0058] Comparative Example 5

[0059] A method for preparing a modified nano-silica lubricant for drilling fluid is as described in Example 1, except that in step (1) nano-silica is replaced by nano-silicon carbide.

[0060] Test Example 1

[0061] The lubricants obtained in the examples and comparative examples are tested for lubricating performance, salt resistance and temperature resistance.

[0062] Lubrication performance is the primary factor to evaluate whether the drilling fluid lubricant meets the use conditions. According to SY / T6094-1994 "Drilling fluid lubricant evaluation procedure" and GB / T16783.1-2006 "Petroleum and natural gas industry drilling fluid field testing" standards, the extreme pressure lubricator is used to determine the lubrication performance of the base paste after adding different lubricants. When the smaller the lubrication coefficient or the greater the lubrication coefficient reduction rate, the better the lubricant's friction reduction and drag reduction performance. The lubrication coefficient calculation formula of the drilling fluid is as follows:

[0063] Correction factor = standard reading value of water / actual reading value of water;

[0064] Actual lubrication coefficient = table reading value / 100 x correction factor;

[0065] Lubrication coefficient reduction rate R = (η0-η1) / η0x100%;

[0066] In the formula: R: lubrication coefficient reduction rate, %; η0: lubrication coefficient of the base paste without adding lubricant; η1: lubrication coefficient of the base paste after adding lubricant.

[0067] 4% bentonite base paste preparation: 400g of drilling fluid bentonite and 14g of anhydrous sodium carbonate are slowly added to 10L of water while stirring, and the water is hydrated for 24h at room temperature to obtain a 4% bentonite base paste.

[0068] 1. Lubrication and temperature resistance performance test

[0069] 0.2wt% of the lubricant prepared in the examples or comparative examples is added to the 4% bentonite base paste, respectively, and stirred at 8000rpm for 10min to obtain the experimental paste, and then transferred into a high temperature roller heating furnace, and heated and rolled at 260℃ for 16h. The extreme pressure lubricator is used to test the lubrication coefficient of the above experimental paste before and after aging, and the base paste with 1wt% polytetrafluoroethylene and 1wt% molybdenum disulfide is added as a comparison. The test results are shown in Table 1.

[0070] Table 1 Lubrication performance and temperature resistance performance of the base paste after adding different lubricants

[0071]

[0072] As can be seen from Table 1, the lubricant prepared in the embodiment of the application has excellent lubricating performance, and after aging at 260℃, the lubricating coefficient of the lubricant prepared in the embodiment of the application changes little, and the lubricant still has excellent lubricating ability after aging at 260℃, which indicates that the lubricant prepared in the application has excellent temperature resistance and meets the requirements of ultra-deep and super-deep drilling. In Examples 2-6, the addition amount and type of silane coupling agent and the addition amount of n-dodecanethiol are changed, which affects the grafting effect and further affects the lubricating performance of the lubricant. In Comparative Example 1, n-dodecanethiol is not grafted and modified, and the core hydrophobic functional group is missing, so the lubricating performance is reduced; in Comparative Example 2, the silane coupling agent is not modified, and n-dodecanethiol cannot be effectively grafted, so the lubricating performance is greatly reduced; in Comparative Example 3, n-octanethiol is used instead of n-dodecanethiol, and the hydrophobic chain length is insufficient, so the lubricating film performance is attenuated; in Comparative Example 4, octadecyl acrylate is used, which cannot adsorb the surface of the drilling tool to form a lubricating film, so the lubricating performance is reduced; in Comparative Example 5, nano silicon carbide is used instead of nano silicon dioxide, and the inorganic carrier surface activity is insufficient, the surface bonding sites are few, the modification is difficult, the modification ratio is low, and the lubricating performance is greatly reduced.

[0073] 2. Salt resistance test

[0074] In 4% bentonite-based slurry, 30wt% NaCl was added, and then 0.2wt% of the lubricant prepared in the embodiment or comparative example was added, and the lubricating coefficient was tested, and the results are shown in Table 2.

[0075] Table 2 Salt resistance of the lubricant prepared in the embodiment and comparative example

[0076]

[0077] As can be seen from Table 2, when 30wt% NaCl is added to the base slurry with the lubricant prepared in the embodiment of the application, the lubricating coefficient increases to different degrees, and the lubricating coefficient reduction rate decreases, but the lubricating performance is still excellent. Among them, when the addition amount of the lubricant prepared in Example 1 is 0.2wt%, the lubricating coefficient reduction rate of the base slurry with 30wt% NaCl concentration is still 86.78%, and the friction and drag reduction performance of the lubricant only decreases slightly, which indicates that the lubricant prepared in the application still has excellent lubricating performance under high salt conditions. While the lubricating performance of the comparative examples is poor, and after adding high concentration of NaCl, the lubricating performance decreases to different degrees, and the salt resistance is generally insufficient, which makes it difficult to efficiently lubricate under high salt conditions, and some even fail under high salt conditions. The decrease in the lubricating coefficient after adding high concentration of sodium chloride in the drilling fluid base slurry is the result of the multiple regulation of salt on the dispersion state of clay particles, the rheological property of drilling fluid and the interfacial action. NaCl promotes the coalescence of bentonite particles by compressing the double electric layer, which converts sliding friction into rolling friction; at the same time, it reduces the viscosity of the base slurry to optimize the flowability, and also forms an ionic lubricating film on the surface of the drilling tool and inhibits the adverse effects of impurities, thereby improving the lubricating performance.

[0078] Test Example 2

[0079] Steel sheet and shale sheet surface contact angle test

[0080] The steel sheet and shale sheet were respectively immersed in the base slurry with 0.2wt% lubricant for 20h, and then dried at 70°C. The contact angle of pure water on the surface of the immersed steel sheet or shale sheet was measured by a contact angle measuring instrument, and the contact angle of pure water on the surface of the unimmersed steel sheet or shale sheet was also measured. The results are shown in Table 3.

[0081] Table 3 Contact angle of steel sheet and shale sheet immersed in lubricant of different examples

[0082]

[0083] As can be seen from Table 3, the contact angle of water droplets on the surface of the steel sheet immersed in the lubricant prepared by the examples of the present application is significantly improved, and is increased by up to 83.3°. Compared with the unprocessed shale sheet, the contact angle of water droplets on the surface of the shale sheet immersed in the lubricant prepared by the examples of the present application is significantly increased, and is increased by up to 109.1°. The surface contact angle is obviously different from that of the unprocessed steel sheet or shale sheet, indicating that the lubricant prepared by the present application can form a hydrophobic layer on the surface of the steel sheet or shale sheet, and effectively improve the hydrophobic performance of the steel sheet or shale sheet.

Claims

1. A method for preparing a modified nano-silica lubricant for drilling fluids, characterized in that, The steps include the following: (1) Add nano-silica to an ethanol aqueous solution, disperse it evenly by ultrasonication, add a silane coupling agent, and react; after the reaction is completed, filter, wash and dry to obtain silane coupling agent modified nano-silica; the silane coupling agent is one or more of vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriisopropoxysilane, 3-methacryloyloxypropylmethyldimethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, and vinyltri(2-methoxyethoxy)silane; the mass ratio of the silane coupling agent to nano-silica is 0.1-0.3:1; (2) Add the silane coupling agent modified nano-silica to an ethanol aqueous solution, stir evenly, add n-dodecyl mercaptan and initiator ethanol solution, stir evenly, then purge with nitrogen to remove oxygen, and then carry out the reaction; after the reaction is completed, cool, add ethanol to dilute, centrifuge, wash and dry to obtain a drilling fluid modified nano-silica lubricant; the mass ratio of n-dodecyl mercaptan to silane coupling agent modified nano-silica is 1.5-2:1; the initiator is azobisisobutyronitrile, benzoyl peroxide or tert-butyl hydroperoxide.

2. The method for preparing the modified nano-silica lubricant for drilling fluid according to claim 1, characterized in that, The particle size of the nano-silica in step (1) is 10-40 nm.

3. The method for preparing the modified nano-silica lubricant for drilling fluid according to claim 1, characterized in that, The ethanol aqueous solution in step (1) is prepared by the following method: anhydrous ethanol and deionized water are mixed in a volume ratio of 2-4:1, and then the pH of the system is adjusted to 4 using a 2mol / L HCl aqueous solution. The volume ratio of the ethanol aqueous solution to the mass of nano-silica is 50-80mL:1g.

4. The method for preparing the modified nano-silica lubricant for drilling fluid according to claim 1, characterized in that, The ultrasonic treatment in step (1) takes 20-30 minutes; the reaction temperature is 65-75°C and the reaction time is 2-3 hours; the washing is centrifugation with anhydrous ethanol 3-4 times; and the drying is vacuum drying at 60-70°C for 20-30 hours.

5. The method for preparing the modified nano-silica lubricant for drilling fluid according to claim 1, characterized in that, In step (2), the volume ratio of anhydrous ethanol to deionized water in the ethanol aqueous solution is 1:1-2; the volume ratio of the ethanol aqueous solution to the mass ratio of the silane coupling agent modified nano-silica is 40-60 mL:1 g.

6. The method for preparing the modified nano-silica lubricant for drilling fluid according to claim 1, characterized in that, The mass of the initiator in step (2) is 1-3% of the total mass of silane coupling agent modified nano-silica and n-dodecyl mercaptan; the concentration of the initiator ethanol solution is 0.004-0.005 g / mL.

7. The method for preparing the modified nano-silica lubricant for drilling fluid according to claim 1, characterized in that, In step (2), the time for nitrogen deoxygenation is 15-30 min; the reaction temperature is 65-75℃; the reaction time is 6-10 h; the reaction is carried out under nitrogen protection.

8. The method for preparing the modified nano-silica lubricant for drilling fluid according to claim 1, characterized in that, In step (2), after the reaction is complete, the volume ratio of ethanol added to the mass of silane coupling agent modified nano-silica is 6-8 mL: 1 g; the centrifugation speed is 8000-12000 rpm, and the centrifugation time is 5-15 min; the washing is performed by washing 2-4 times with an ethanol aqueous solution, and the volume ratio of ethanol to water in the ethanol aqueous solution is 1:1; the drying is performed by vacuum drying at 60-70℃ for 10-15 h.

9. A modified nano-silica lubricant for drilling fluids, characterized in that, It is prepared by the preparation method described in any one of claims 1-8.

10. The application of the modified nano-silica lubricant for drilling fluid according to claim 9 in water-based drilling fluids, used in the drilling process to achieve the drilling objective of drag reduction and speed increase, characterized in that... The concentration of the modified nano-silica lubricant in the water-based drilling fluid is 0.1-0.3 wt%.

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