Lubricant for drilling fluid and preparation method thereof

Abstract

The invention discloses a lubricant for drilling fluid and a preparation method of the lubricant, and belongs to the field of oil and gas drilling chemical additives. In the water-based drilling fluid, microbubbles I with the diameter of 0.1-1 mu m and microbubbles II with the diameter of 1-10 mu m are prepared in situ, and a low-frequency sound field of 20-50 kHz and a high-frequency sound field of 200-500 kHz are adopted for alternate or superposed driving; the microbubbles I are rapidly broken to release the lubricant to achieve instantaneous efficient lubrication of the initial drilling section, and the microbubbles II are slowly broken to maintain the lubricating film to achieve lasting lubrication of the rear section. The preparation method comprises the following steps: mixing the base oil, the surfactant, the gas precursor and the foam adjusting aid in proportion, performing synchronous gas injection oscillation in a multi-frequency sound field to form a graded microbubble suspension, and performing settling separation and stabilizing treatment to obtain the product. The lubricant can obviously reduce the friction between a drilling tool and a well wall and prolong the service life of the drilling tool, is compatible with an existing slurry system, is free of waste water and waste gas emission in production, does not detect heavy metals after being used, is easy to degrade in surfactant and pollution-free to underground water, meets the requirement of green drilling, and has excellent engineering popularization value.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of oil and gas drilling chemical additives, in particular to a drilling fluid lubricant and a preparation method thereof. BACKGROUND

[0002] Drilling fluid lubricant is a key additive of water-based drilling fluid, which forms a lubricating film between the drilling tool and the well wall, reduces frictional resistance, reduces torque and vibration, and improves drilling efficiency and drilling tool life. The existing lubricating system mainly uses long-chain alkyl esters, polyether surfactants and nanoparticles, but these lubricating components are prone to failure in high temperature and high pressure and strong shear environment, resulting in unstable lubrication and affecting the continuity of drilling operation.

[0003] In addition, the traditional lubricant is prone to instability under extreme conditions, resulting in uneven lubricating film and even causing the risk of sticking. The existing technology cannot simultaneously achieve efficient lubrication at the initial stage of drilling and sustained lubrication in the later stage, and a new type of lubricating system is urgently needed.

[0004] The multi-frequency resonance-hierarchical microbubble coupling release technology proposed in the present application in-situ prepares two-stage microbubbles in water-based drilling fluid, and uses low-frequency and high-frequency sound fields to alternately excite, microbubble I rapidly ruptures to achieve instantaneous efficient lubrication, and microbubble II slowly ruptures to maintain the lubricating film, which has both efficient and sustained lubrication performance. This technology effectively improves the stability of lubrication, adapts to high temperature and high pressure environment, and significantly improves the drilling efficiency.

[0005] In addition, the lubricant of the present application uses an environmentally friendly production process, does not produce wastewater and waste gas, and does not pollute groundwater, meeting the requirements of green drilling fluid, and has sustainability and environmental friendliness. In view of the above problems, the present application provides a drilling fluid lubricant and a preparation method thereof. The lubricant in-situ constructs two-stage microbubbles with diameters of 0.1-1 μm and 1-10 μm in water phase, and uses 20-50 kHz and 200-500 kHz sound field to alternately excite: microbubble I rapidly ruptures to achieve instantaneous lubrication, and microbubble II slowly ruptures to maintain long-acting lubrication; this system has both high temperature and high pressure stability and self-repairing ability, can significantly reduce the frictional resistance, prolong the service life of the drilling tool, and meet the needs of long-distance drilling in complex downhole.

[0006] In order to achieve the above purpose, the present application adopts the following technical scheme: A drilling fluid lubricant, the lubricant is prepared from the following raw materials by weight: 10-50 parts of base oil, 1-10 parts of surfactant, 0.5-5 parts of gas precursor, 0.1-2 parts of bubble adjusting aid, 0.1-2 parts of stabilizer, and water-based carrier to 100 parts; The lubricant, when in use, forms microbubbles I with a diameter of 0.1-1 microns and microbubbles II with a diameter of 1-10 microns under the alternating or superimposed excitation of a 20 kHz-50 kHz low-frequency sound field and a 200 kHz-500 kHz high-frequency sound field, the microbubbles I are rapidly broken to release the lubricating components to achieve instantaneous and efficient lubrication, and the microbubbles II are slowly broken to maintain the lubricating film to achieve long-term maintenance.

[0007] Optionally, the lubricant for drilling fluid, wherein the base oil is one or more of mineral oil, synthetic ester and poly-alpha-olefin.

[0008] Optionally, the lubricant for drilling fluid, wherein the surfactant is one or more of anionic, nonionic or amphoteric surfactant.

[0009] Optionally, the lubricant for drilling fluid, wherein the bubble-regulating additive is one or more of amine compound, sulfonate compound, fatty acid salt and carboxylate.

[0010] Optionally, the lubricant for drilling fluid, wherein the stabilizer is one or more of polyacrylamide, sodium carboxymethyl cellulose and derivatives thereof.

[0011] Optionally, the preparation method of the lubricant for drilling fluid, and the specific preparation steps are as follows: S1, mixing the base oil, the surfactant, the gas precursor and the bubble-regulating additive to prepare a premix; S2, synchronously injecting inert gas into the premix in a 20 kHz-50 kHz low-frequency and 200 kHz-500 kHz high-frequency sound field, and oscillating for 5 min-10 min to form a graded microbubble suspension; S3, after the obtained suspension is left to stand for 5 min-10 min for sedimentation and separation, and large bubbles are removed, the stabilizer is added and stirred at a rotation speed of 300 rpm for 2 min-5 min to obtain a final lubricant product.

[0012] Optionally, the preparation method of the lubricant for drilling fluid, wherein the sound field power density in S2 is 0.5-2 W / cm 2 , and the gas injection flow rate is 0.1-0.5 L / min.

[0013] Optionally, the preparation method of the lubricant for drilling fluid, wherein under the conditions of 120°C and 70 MPa high temperature and high pressure, the graded microbubbles formed by the lubricant after the sound excitation are used for 6 h-12 h underground circulation, and the microbubble stability rate is 85%-95%.

[0014] The beneficial effects of the present application are: The prepared lubricant has significant self-repairing and long-acting lubricating effect: under the condition of 120 DEG C and 70 MPa, the stability rate of the hierarchical micro-bubble after circulating use for 6 h after acoustic excitation still remains above 90%; the lubricant can significantly reduce the friction coefficient and the torque of the drill string, prolong the service life of the drill string, and maintain the viscosity retention rate above 95%. Meanwhile, the lubricant is compatible with the existing water-based drilling fluid system, and does not change the basic rheological parameters of the mud. In addition, the production process of the lubricant adopts indoor technology, and no waste water and waste gas are discharged, which meets the environmental protection requirements. The lubricant does not pollute the underground water during use, and the components are harmless, which helps to protect the environment and promote green and sustainable drilling operation. BRIEF DESCRIPTION OF DRAWINGS

[0015] The accompanying drawings are included to provide a further understanding of the application and are incorporated in and constitute a part of this specification, illustrate embodiments of the application and together with the description serve to explain the principles of the application.

[0016] Figure 1 A comparison column chart of the friction coefficient and the torque reduction rate of each sample of the present application; Figure 2 A comparison column chart of the release rate of each sample of the present application. DETAILED DESCRIPTION

[0017] To make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described below in a clear and complete manner in combination with the embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0018] Embodiment 1 The lubricant for drilling fluid in this embodiment 1 is prepared from the following raw materials by weight: Base oil: 30 parts of trimethylolpropane trioleate, surfactant: 4 parts of fatty alcohol polyoxyethylene ether, 1 part of sodium dodecyl benzene sulfonate, gas precursor: 2 parts of sodium bicarbonate, bubble adjusting aid: 1 part of diethanolamine, stabilizer: 1 part of partially hydrolyzed polyacrylamide, water-based carrier: deionized water + 2% potassium chloride mixed solution to 100 parts; The specific preparation method is as follows: S1, mix the base oil, surfactant, gas precursor and bubble adjusting aid, add the water-based carrier to prepare a premix; S2, inject nitrogen into the premix at a power density of 1.0 W / cm 2 The nitrogen flow rate is 0.1 L / min under the 30 kHz low-frequency sound field for 4 min, and the nitrogen flow rate is 0.5 L / min under the 300 kHz high-frequency sound field for 4 min to form a hierarchical micro-bubble suspension. S3, the obtained suspension is allowed to stand for 8 min for sedimentation separation, after the removal of large bubbles floating up, the stabilizer is added, and the mixture is stirred at a speed of 300 rpm for 3 min to obtain the final lubricant product.

[0019] Example 2: To explore the effect of sound field power density on the performance of lubricating liquid, a drilling fluid lubricant is prepared in Example 2, and the lubricant is prepared from the following raw materials by weight: Base oil: 30 parts of trimethylolpropane trioleate, surfactant: 4 parts of fatty alcohol polyoxyethylene ether, 1 part of sodium dodecyl benzene sulfonate, gas precursor: 2 parts of sodium bicarbonate, bubble adjusting aid: 1 part of diethanolamine, stabilizer: 1 part of partially hydrolyzed polyacrylamide, water-based carrier: deionized water + 2% potassium chloride mixture to make up to 100 parts; The specific preparation method is as follows: S1, the base oil, surfactant, gas precursor and bubble adjusting aid are mixed, and the water-based carrier is added to prepare a premix; S2, inject nitrogen into the premix at a power density of 1.5 W / cm 2 The nitrogen flow rate is 0.1 L / min, oscillate in a 30 kHz low frequency sound field for 4 min, oscillate in a 300 kHz high frequency sound field for 4 min, and the nitrogen flow rate is 0.5 L / min, to form a hierarchical microbubble suspension; S3, the obtained suspension is allowed to stand for 8 min for sedimentation separation, after the removal of large bubbles floating up, the stabilizer is added, and the mixture is stirred at a speed of 300 rpm for 3 min to obtain the final lubricant product.

[0020] Example 3: To explore the effect of hierarchical microbubble specific gravity on the performance of lubricating liquid, a drilling fluid lubricant is prepared in Example 3, and the lubricant is prepared from the following raw materials by weight: Base oil: 30 parts of trimethylolpropane trioleate, surfactant: 4 parts of fatty alcohol polyoxyethylene ether, 1 part of sodium dodecyl benzene sulfonate, gas precursor: 2 parts of sodium bicarbonate, bubble adjusting aid: 1 part of diethanolamine, stabilizer: 1 part of partially hydrolyzed polyacrylamide, water-based carrier: deionized water + 2% potassium chloride mixture to make up to 100 parts; The specific preparation method is as follows: S1, the base oil, surfactant, gas precursor and bubble adjusting aid are mixed, and the water-based carrier is added to prepare a premix; S2, inject nitrogen into the premix at a power density of 1.0 W / cm 2Power density, nitrogen gas was injected into the premix, and the nitrogen gas flow rate was 0.1 L / min under the 30 kHz low-frequency sound field for 5 min and 0.5 L / min under the 300 kHz high-frequency sound field for 10 min to form a hierarchical microbubble suspension; S3, the obtained suspension was allowed to stand for 8 min for sedimentation separation, after the large bubbles were removed, a stabilizer was added, and the mixture was stirred at a speed of 300 rpm for 3 min to obtain the final lubricant product.

[0021] Comparative Example 1: In order to explore the influence of single frequency excitation on the performance of lubricating liquid, a kind of drilling fluid lubricant was prepared by the following weight parts of raw materials in this comparative example 1: Base oil: 30 parts of trimethylolpropane trioleate, surfactant: 4 parts of fatty alcohol polyoxyethylene ether, 1 part of sodium dodecyl benzene sulfonate, gas precursor: 2 parts of sodium bicarbonate, bubble adjusting agent: 1 part of diethanolamine, stabilizer: 1 part of partially hydrolyzed polyacrylamide, water-based carrier: deionized water + 2% potassium chloride mixed solution to make up to 100 parts; The specific preparation method is as follows: S1, the base oil, surfactant, gas precursor and bubble adjusting agent were mixed, and the water-based carrier was added to prepare a premix; S2, 1.0 W / cm 2 Power density, nitrogen gas was injected into the premix, and the nitrogen gas flow rate was 0.1 L / min under the 30 kHz low-frequency sound field for 5 min and 0.5 L / min under the 300 kHz high-frequency sound field for 10 min to form a hierarchical microbubble suspension; S3, the obtained suspension was allowed to stand for 8 min for sedimentation separation, after the large bubbles were removed, a stabilizer was added, and the mixture was stirred at a speed of 300 rpm for 3 min to obtain the final lubricant product.

[0022] Comparative Example 2: In order to explore the influence of unoptimized gas distribution on the performance of lubricating oil, a kind of drilling fluid lubricant was prepared by the following weight parts of raw materials in this comparative example 2: Base oil: 30 parts of trimethylolpropane trioleate, surfactant: 4 parts of fatty alcohol polyoxyethylene ether, 1 part of sodium dodecyl benzene sulfonate, gas precursor: 2 parts of sodium bicarbonate, bubble adjusting agent: 1 part of diethanolamine, stabilizer: 1 part of partially hydrolyzed polyacrylamide, water-based carrier: deionized water + 2% potassium chloride mixed solution to make up to 100 parts; The specific preparation method is as follows: S1, the base oil, surfactant, gas precursor and bubble adjusting agent were mixed, and the water-based carrier was added to prepare a premix; S2, 1.0 W / cm2 Power density, nitrogen was injected into the premixed solution, oscillated in a 30 kHz low frequency sound field for 4 min, and in a 300 kHz high frequency sound field for 4 min, the nitrogen flow rate was 0.3 L / min, and a hierarchical microbubble suspension was formed; S3, the obtained suspension was left to stand for 8 min for sedimentation separation, after the large bubbles were removed, a stabilizer was added, and the mixture was stirred at a speed of 300 rpm for 3 min to obtain the final lubricant product.

[0023] Performance test 1. Friction coefficient reduction rate test First, the standard water-based drilling mud with a density of 1.2 g / cm 3 and containing 5% bentonite was prepared and divided into a control group and a test group, and the lubricant was added to the test group at a mass fraction of 1%; then the viscosities of the two groups of mud were adjusted to 600 mPa·s, and the determination was carried out under the conditions of 170°C and shear rate 100 s -1 ; and the bubbles were eliminated by standing at 25°C for 30 min; then the ring cylinder friction tester with a flange radius of 20 mm and a stainless steel friction element was used, a normal load of 200 N was applied, and a friction test was carried out at a speed of 100 rpm for 30 min, and a reduction rate of no less than 25% was taken as the qualified standard. The control group was the standard water-based drilling fluid without adding the lubricant, and the calculation formula of the friction coefficient reduction rate was:

[0024] Wherein, μ0 and μ1 are the stable friction coefficients of the control group and the test group, respectively.

[0025] Table 1 Friction coefficient and reduction rate data table of each sample

[0026] As can be seen from the table, the friction coefficient of Example 1 is reduced by 31.1%, which is significantly higher than that of Comparative Examples 1 and 2; Example 2 is further enhanced to 32.9%. In contrast, the traditional polyether lubricant can only reduce 13.3%, which fully proves the key role of multi-frequency and segmented gas injection in realizing instantaneous high efficiency and persistent release two-stage lubrication.

[0027] 2. Microbubble stability test The prepared hierarchical microbubble lubricant suspension was loaded into a high temperature and high pressure circulating stirred tank, the temperature was set to 120°C, the pressure was set to 70 MPa, and continuous stirring and oscillation was carried out at 300 rpm for 6 h; after oscillation, the sample was prepared into a diluent, and the number and particle size distribution of the microbubbles before and after oscillation were recorded by optical microscope and laser particle size analyzer respectively, and then the microbubble retention rate was calculated to evaluate the stability of the microbubbles under high temperature and high pressure and continuous oscillation conditions.

[0028] Table 2 Microbubble retention rate data table of each sample

[0029] From the test results, Example 2 and Example 1 maintained 93.0% and 90.7% of microbubble retention rate respectively after 120°C / 70 MPa oscillation for 6 hours, which was significantly higher than Comparative Example 1, Comparative Example 2 and traditional polyether lubricant. This shows that the multi-frequency sound field combined with segmented gas volume and appropriate power density design can effectively improve the stability of microbubbles under extreme conditions.

[0030] 3. Torque reduction rate test First, the standard water-based drilling mud (density 1.2 g / cm 3 , containing 5% bentonite) was prepared into a control sample and a test sample added with 1% of the lubricant of the present application; then on the drilling tool torque test bench, the oil temperature was maintained at 120°C, a constant axial load of 500 N was applied, and continuous rotation was carried out at a speed of 200 rpm for 10 min, with a qualified standard of not less than 20%, and the calculation formula of torque reduction rate was:

[0031] Wherein, T0 and T1 are the average torques of the control sample and the test sample.

[0032] Table 3 Torque reduction rate test results of each sample

[0033] Examples 1-3 achieved torque reduction of 26.7%, 28.0% and 23.3% respectively under 120°C, 100 s -1 high shear conditions, all of which were higher than 20% and higher than Comparative Example 1, Comparative Example 2 and traditional polyether lubricant; this further proves that the multi-frequency sound field combined with segmented gas distribution and reasonable power density design can significantly improve the torque suppression effect of the lubricant under actual drilling load.

[0034] 4. High temperature and high pressure rheological stability test The lubricant sample was mixed with the standard water-based drilling fluid at a mass fraction of 1% to prepare the test sample. Then, the sample was loaded into a high temperature and high pressure rheometer, the temperature was set to 200°C, and the shear rate was set to 100 s -1 . The initial viscosity was measured. Then, the sample was continuously sheared at 200°C for 38 hours, and the stability was evaluated by periodically measuring the viscosity change of the sample. Finally, the stable viscosity was recorded and the viscosity retention rate was calculated.

[0035] Table 4 Viscosity change numerical table of each sample

[0036] The lubricant of the embodiment can effectively maintain a low viscosity increase value (≤5%), significantly improving the rheological stability of the lubricant under high temperature conditions, while the rheological properties of the comparative examples and the conventional lubricant are poor, and the viscosity increase value is high.

[0037] 5. Drill tool protection performance test A standard water-based drilling mud is prepared and divided into a control group and a test group, and 1% of the lubricant of the present application is added to the test group. Then, the samples in each group are loaded into a high temperature and high pressure friction test device, and the temperature is set to 120°C, the pressure is set to 70 MPa, the rotation speed is set to 200 rpm, and the load is set to 300 N to simulate the actual working conditions in drilling operations. During the test, the friction tester records the wear depth, surface hardness change and friction coefficient of the drill tool surface, and compares the protection effect of different lubricants on the drill tool. Finally, the friction coefficient reduction rate and wear depth are calculated to evaluate the protection performance of the lubricant on the drill tool.

[0038] Table 5 Test results of the friction coefficient, wear depth and hardness change of each sample

[0039] The lubricant of the present application significantly reduces the wear depth, friction coefficient and hardness change of the drill tool under high temperature and high pressure conditions, which is much better than the control group and the conventional polyether lubricant, proving that it can effectively reduce wear, reduce friction and protect the drill tool, and has a significant protection effect.

[0040] 6. Release performance test The lubricant sample is mixed with a standard water-based drilling fluid (density 1.2 g / cm 3 , containing 5% bentonite) at a mass fraction of 1% to prepare a test sample; then, the sample is placed in an oil reservoir simulation environment, and the temperature is set to 120°C and the pressure is set to 70 MPa for static and dynamic release tests. Under the conditions of high temperature, 25°C and stress (shear rate 100 s -1 ), the sample is taken every 1 hour, and the concentration of the lubricating component is determined by ultraviolet-visible spectroscopy or other chemical analysis methods, and the release curve of the lubricating component in the drilling fluid is drawn. By comparing the release rate of the sample over 6 hours, the release performance is evaluated. It is expected that the lubricant can maintain more than 80% of the effective lubricating components in the drilling fluid to ensure long-term lubrication effect.

[0041] Table 6 Release performance results of each sample

[0042] The lubricant of the present application shows excellent release performance under high temperature conditions, especially through multi-frequency and segmented gas distribution design, which greatly improves the sustained release of the lubricating component, ensures long-term lubrication effect, and has more significant advantages compared with the conventional polyether lubricant.

[0043] 7. Foam rate test The lubricant sample was mixed with a standard water-based drilling fluid (density 1.2 g / cm 3 , containing 5% bentonite) at a mass fraction of 1%, to prepare a test sample. Then, the sample was placed in a high-temperature (200°C) condition for continuous testing for 38 hours. During this process, the foam rate, viscosity change, and lubrication coefficient reduction rate of the lubricant were measured periodically. At 200°C / 38h, the test ensured that the foam rate was not more than 10%, the viscosity increase was not more than 5 mPa·s, the lubrication coefficient reduction rate of 4% salt water was more than 80%, the lubrication coefficient reduction rate of saturated salt water was more than 70%, and finally ensured that the lubricant still maintained good lubrication effect and stability under extreme conditions.

[0044] Table 7. Foam rate data table of each sample

[0045] The foam rate of the lubricant of the embodiment was significantly lower than that of the conventional lubricant and the comparative sample, indicating that it generated fewer and more stable microbubbles under high temperature and high pressure conditions. The comparative lubricant had a higher foam rate, indicating that its lubrication effect was not as stable as that of the lubricant of the embodiment, which was conducive to improving the lubrication effect and reducing the impact of foam on the flowability of the drilling fluid.

[0046] 8. Lubrication coefficient test The lubricant sample was mixed with a standard water-based drilling fluid at a mass fraction of 1% to prepare a test sample. Then, two salt water solutions were prepared: 4% salt water and calcium salt water, the test temperature was set to 200°C, the test time was 38 hours, and the shear rate was kept at 100 s -1 . The sample was placed in a high-temperature and high-pressure rheometer for testing. First, the 4% salt water lubrication coefficient test was performed, and the lubrication coefficient reduction rate was recorded. Then, the salt water was replaced with calcium salt water, and the lubrication coefficient reduction rate test was performed again. The lubrication coefficient reduction rate was calculated.

[0047] Table 8. Lubrication coefficient reduction rate results table of each sample

[0048] The lubricant of the embodiment showed a significantly better lubrication effect than the comparative sample and the conventional lubricant in both 4% salt water and calcium salt water, proving that the lubricant of the present application has better lubrication performance in salt water and calcium salt water environments, and can effectively improve the lubrication effect and maintain stability.

[0049] 9. Groundwater pollution risk assessment A standard water-based drilling fluid (density 1.2 g / cm 3, and mixed with a lubricant at a mass fraction of 1% to prepare a test sample; a standard water-based drilling fluid without the addition of a lubricant is set as a control group. The two groups of samples are respectively exposed to a simulated underground water environment (temperature 25 DEG C, pressure 1 atm, pH = 8.0, simulated underground water ion composition: Ca 2+ 50 mg / L, Mg 2+ 20 mg / L, Na + 100 mg / L, HCO3 - 180 mg / L, Cl - 80 mg / L), 50 mL of each sample is added and liquid contact is maintained for 24 h; 10 mL is sampled at 0 h, 6 h, 12 h, 18 h, and 24 h, respectively, and the heavy metal content (Pb≤0.01 mg / L, Cd≤0.005 mg / L, Hg≤0.001 mg / L, Cr≤0.05) is detected by ICP-OES analysis method, the surfactant concentration is detected by high performance liquid chromatography method, and the pH value is measured, and the pollution risk is evaluated by comparison with GB 5749-2022 'Drinking Water Health Standards'.

[0050] Table 9 shows the results of groundwater pollution risk assessment of each sample

[0051] The groundwater pollution risk assessment shows that no heavy metals such as lead and cadmium are detected in all samples, and the pH is stable at 7.8-8.0, which meets the GB 5749-2022 standard; the surfactant of the inventive examples 1-3 is ≤0.05 mg / L at 24 h, which is much lower than the qualified standard of 0.5 mg / L and is better than the comparative examples and the traditional lubricant, and the composition is easy to degrade and does not pollute the underground water.

[0052] The above examples are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A lubricant for drilling fluids, characterized in that, The ingredients comprise the following parts by weight: Base oil 10-50 parts, surfactant 1-10 parts, gas precursor 0.5-5 parts, foaming aid 0.1-2 parts, stabilizer 0.1-2 parts, water-based carrier to make up to 100 parts; When the lubricant is used, under alternating or superimposed excitation of a low-frequency sound field of 20 kHz-50 kHz and a high-frequency sound field of 200 kHz-500 kHz, microbubbles I with a diameter of 0.1-1 μm and microbubbles II with a diameter of 1-10 μm are formed simultaneously. Microbubbles I rapidly rupture to release lubricating components to achieve instantaneous and efficient lubrication, while microbubbles II slowly rupture to maintain the lubricating film for long-term maintenance.

2. The drilling fluid lubricant according to claim 1, characterized in that, The base oil is one or more of mineral oil, synthetic ester, and polyalphaolefin.

3. The drilling fluid lubricant according to claim 1, characterized in that, The surfactant is one or more of anionic, nonionic, or amphoteric surfactants.

4. The drilling fluid lubricant according to claim 1, characterized in that, The foaming agent is one or more of amine compounds, sulfonate compounds, fatty acid salts, and carboxylates.

5. A drilling fluid lubricant according to claim 1, characterized in that, The stabilizer is one or more of polyacrylamide, sodium carboxymethyl cellulose, and their derivatives.

6. A method for preparing a lubricant for drilling fluid, wherein the lubricant is as described in any one of claims 1-5, characterized in that, The specific preparation steps are as follows: S1. Mix base oil, surfactant, gas precursor and foaming agent to prepare premixed liquid; S2. Simultaneously inject inert gas into the premixed liquid in a low-frequency (20 kHz-50 kHz) and high-frequency (200 kHz-500 kHz) sound field, and oscillate for 5 min-10 min to form a graded microbubble suspension. S3. Allow the obtained suspension to stand for 5 min-10 min to settle and separate. After removing large bubbles, add a stabilizer and stir at 300 rpm for 2 min-5 min to obtain the final lubricant product.

7. The method for preparing a drilling fluid lubricant according to claim 6, characterized in that, The sound field power density in S2 is 0.5-2 W / cm². 2 The gas injection flow rate is 0.1-0.5 L / min.

8. A drilling fluid lubricant according to claim 6, characterized in that, The lubricant, under high temperature and high pressure conditions of 120°C and 70MPa, forms graded microbubbles after acoustic excitation. After 6-12 hours of downhole circulation, the microbubble stability rate is 85%-95%.

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