A drilling composite lubricating material

Abstract

This invention discloses a drilling composite lubricant material, comprising a core layer, a protective shell layer, a phase change layer, and a smooth outer shell layer, sequentially encapsulated from the inside out to form micron-sized spherical structures. The core layer is a liquid lubricant, the protective shell layer is an inorganic protective shell layer, the phase change layer is prepared using a solid-liquid conversion phase change material, and the smooth outer shell layer is prepared using an inert material. This invention utilizes the four-layer structure of the drilling composite lubricant material to enable it to adhere precisely to critical areas with severe frictional wear, providing lubrication. Furthermore, it maintains low foaming and high lubricity even after repeated exposure to the high-temperature downhole environment, providing technical support for drilling operations.

Description

Technical Field

[0001] This invention relates to the field of lubrication materials technology, and in particular to a drilling composite lubrication material. Background Art

[0002] With the advent of the "10,000-meter era" in my country's exploration wells, the requirements for drilling technology are constantly increasing. During drilling operations, friction constantly occurs between the drill string and the rock and casing. This friction increases the drill string's rotational resistance, making tripping and running difficult. Excessive rotational resistance can also cause drill string vibration, potentially leading to drill string breakage and wellbore instability, thus halting drilling operations and causing significant economic losses. The friction mechanism in drilling originates from boundary friction between two solid surfaces and fluid friction. Fluid friction is caused by the viscosity of the fluid between the friction surfaces and typically has a low coefficient of friction. Boundary friction is the primary source of friction in drilling. To address boundary friction, lubricating materials are mainly added to the drilling fluid to reduce the coefficient of friction and wear during drilling. Lubricating materials can form an adsorption film or reactive film on the friction surface, converting friction between rough surfaces into friction between adsorption films. This reduces the frictional torque between the drill string and the wellbore, as well as the friction coefficient of the drilling fluid filter cake, effectively improving the hydraulic power of the drill bit and preventing phenomena such as stuck drill bit and pressure buildup.

[0003] Currently, commonly used drilling lubricants include solid lubricants and liquid lubricants. Solid lubricants isolate friction surfaces and reduce friction and wear. They can transform sliding friction between surfaces into rolling friction in a spherical form, or they can adhere to the friction surface in the form of a sheet-like structure, transforming friction between surfaces into sliding friction between sheet-like structures. Because the atoms of individual sheets of layered materials are bonded by covalent bonds, but the sheets are connected by weak van der Waals forces, the shear resistance of sliding between layered lubricants is very low, thus reducing friction. Liquid lubricants are generally based on amphiphilic compounds, with a common structure being a linear alkyl chain with one or more polar functional groups attached to one end. Through the adsorption of polar groups on the friction surface and the dense arrangement of non-polar ends, they effectively prevent the friction surfaces from contacting each other. During sliding, this densely arranged linear alkyl chain layer exhibits extremely low frictional resistance, significantly outperforming solid lubricants (generally by 1-2 orders of magnitude) in reducing the coefficient of friction. In addition, due to environmental protection needs and to reduce the impact of fluorescence of lubricating materials on logging, liquid lubricating materials are currently mainly used as drilling lubricants in drilling operations.

[0004] However, currently widely used liquid lubricants are dispersed in drilling fluid and circulated into the system to provide lubrication. During circulation, a large amount of lubricant adheres to areas that do not require lubrication, resulting in significant material loss. Commonly used ester-based drilling fluid lubricants are prone to hydrolysis under formation temperatures and alkaline conditions, leading to a significant increase in their foaming ability. Due to the high concentration of the lubricant in the drilling fluid system, excessive foaming occurs, resulting in a large density difference between the drilling fluid inlet and outlet. This affects normal drilling, drilling fluid level monitoring, and mud pump efficiency, and may even lead to well control safety issues, increasing downhole safety risks. Furthermore, when circulating to deeper wells, the lubricant gradually loses its optimal lubrication performance or even completely loses its lubrication ability due to the high-temperature environment. Summary of the Invention

[0005] To address the aforementioned problems, this invention aims to provide a composite drilling lubricant.

[0006] The technical solution of the present invention is as follows:

[0007] A drilling composite lubricant material includes a core layer, a protective shell layer, a phase change layer, and a smooth outer shell layer that are sequentially wrapped from the inside out to form micron-sized spherical objects.

[0008] The core layer is a liquid lubricant, the protective shell layer is an inorganic protective shell layer, the phase change layer is made of a solid-liquid conversion phase change material, and the smooth outer shell layer is made of an inert material.

[0009] Preferably, the liquid lubricant is any one of modified vegetable oil lubricant, polyol ester lubricant, alcohol ether lubricant, phosphate ester lubricant, and mineral oil lubricant.

[0010] Preferably, the inorganic material of the inorganic protective shell is silicon dioxide or calcium carbonate.

[0011] Preferably, the solid-liquid conversion phase change material is any one of paraffin, fatty acid, polyol, molten salt, and hydrated salt.

[0012] Preferably, the inert material is any one of epoxy resin, vinyl ester resin, phenolic resin, urea-formaldehyde resin, melamine resin, polymethyl methacrylate, and natural polysaccharide derivatives.

[0013] Preferably, when the protective shell is a silica inorganic protective shell and the smooth outer shell is a urea-formaldehyde resin polymer outer shell, the drilling composite lubricating material is prepared by the following steps:

[0014] S1: Mix 10-30g of liquid lubricant with 5-15g of tetraethyl silicate solution to obtain an oil phase, and add the oil phase to 200-400g of ionic surfactant solution to react and obtain silica-coated liquid lubricant particles;

[0015] S2: The silica-coated liquid lubricant particles are subjected to hydrophobic treatment to obtain silica-encapsulated particles with hydrophobic surfaces.

[0016] S3: Add 20-30g of urea and 50-70g of formaldehyde to 500g of water, add triethanolamine dropwise to adjust the pH to 8-9, then heat in a water bath at 60-70℃ for 40-90min, and cool to obtain a polymer shell prepolymer solution;

[0017] S4: The solid-liquid phase change material is heated to convert it into a liquid state to obtain a liquid phase change material; and the silica encapsulated particles with hydrophobic surfaces are placed in the liquid phase change material and ultrasonically dispersed to obtain a dispersion.

[0018] S5: The dispersion is sprayed into the polymer shell prepolymer solution using a microdroplet spraying method. The temperature of the polymer shell prepolymer solution is used to solidify the liquid phase change material and attach it to the surface of the silica encapsulation particles with hydrophobic surfaces.

[0019] S6: Adjust the pH of the mixed solution obtained in step S5 to 3-4, then heat it at 50-70°C with stirring for 2-5 hours, and wash it to obtain the drilling composite lubricant material.

[0020] Preferably, in step S1, the solvent for the tetraethyl silicate solution is dichloromethane with a concentration of 10%.

[0021] Preferably, in step S1, the solute weight ratio of the ionic surfactant solution is 0.3% to 1%.

[0022] Preferably, in step S1, during the reaction, the mixture is first stirred at a speed of 1000-1500 r / min for 20-40 min, then heated to 40-50°C and stirred for 1.5-3 h, then the pH value is adjusted to 2-3, and finally heated to 75-85°C and stirred for 30 min to obtain the silica-coated liquid lubricant particles.

[0023] Preferably, in step S6, stirring is performed at a rotation speed of 800–1200 r / min; during washing, the mixture is washed sequentially with anhydrous ethanol and deionized water.

[0024] The beneficial effects of the present invention are:

[0025] The drilling composite lubricant of this invention consists of micron-sized spherical particles with a four-layered, progressively coated structure. This structure protects the core layer of liquid lubricant by absorbing heat and lowering its temperature during drilling fluid circulation. The outermost smooth outer shell has sufficient strength to provide mechanical protection for the internal materials. The second layer, a phase change material, absorbs heat in deep, high-temperature regions through a solid-to-liquid transition. Upon circulation back to the wellhead, this absorbed heat is released, thus providing cooling protection for the internal liquid lubricant upon recirculation downhole. This multi-layered structure effectively mitigates the problems of adhesion loss and high-temperature failure of liquid lubricant in non-critical lubrication areas downhole.

[0026] The inorganic protective shell isolates the core liquid lubricant from the phase change material of the phase change layer, reducing the risk that the phase change material cannot effectively solidify and release heat in the low-temperature region after it absorbs heat and transforms into a liquid state and then fuses with the liquid lubricant. This ensures that the phase change material maintains good performance after multiple heat absorption and release cycles.

[0027] The smooth outer shell of the composite lubricant material only ruptures under high shear stress at high-friction areas, releasing the core liquid lubricant. This allows it to lubricate critical parts, avoiding the low lubricant utilization problem caused by the general lubrication mode of traditional liquid lubricants. It achieves targeted lubricant delivery, improving lubricant efficiency while reducing lubricant consumption. Furthermore, the smooth outer shell not only provides mechanical protection, enhanced dispersion, and controlled lubricant release, but also provides some ball bearing lubrication even when it doesn't rupture.

[0028] This invention utilizes the isolation of multi-layer shell materials to prevent a large amount of liquid lubricant from directly mixing into the drilling fluid, thereby overcoming the problem of significantly increased foaming rate of drilling fluid caused by hydrolysis of liquid lubricant when used directly.

[0029] In summary, the drilling composite lubricating material of the present invention can adhere to key parts with severe friction loss during construction to play a lubricating role. It can also achieve physical isolation and heat absorption and cooling protection of the core liquid lubricant through a multi-layer functional protective structure, which can alleviate the problem of rapid increase in foaming of drilling fluid during circulation and maintain excellent lubrication ability. Attached Figure Description

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0031] Figure 1 This is a schematic diagram of the structure of the drilling composite lubricant material of the present invention. Detailed Implementation

[0032] The present invention will be further described below with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and technical features described in this application can be combined with each other. It should also be pointed out that, unless otherwise indicated, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. The terms "comprising" or "including" and similar words used in this invention refer to elements or objects preceding the word that encompass the elements or objects listed following the word and their equivalents, without excluding other elements or objects.

[0033] like Figure 1 As shown, the present invention provides a drilling composite lubricant, comprising a core layer, a protective shell layer, a phase change layer, and a smooth outer shell layer that are sequentially wrapped from the inside out to form micron-sized spheres; the core layer is a liquid lubricant, the protective shell layer is an inorganic protective shell layer, the phase change layer is made of a solid-liquid conversion phase change material, and the smooth outer shell layer is made of an inert material.

[0034] In the above embodiments, the present invention employs multiple materials to encapsulate the liquid lubricant in multiple layers, achieving dual protection of mechanical isolation and heat absorption / cooling for the core liquid lubricant. The smooth outer shell layer, made of inert materials, prevents a large amount of liquid lubricant from mixing into the drilling fluid, maintaining a low concentration of lubricating grease in the entire drilling fluid system and avoiding a significant increase in the foaming rate of the drilling fluid caused by the hydrolysis of a large amount of liquid lubricant in the drilling fluid. Encasing the phase change material within the inorganic protective shell layer and the smooth outer shell layer prevents it from absorbing heat and transforming into a liquid state, thus preventing leakage into the drilling fluid or the core lubricating fluid. The smooth outer shell layer of the composite material fractures under certain frictional shear forces, enabling targeted release of the lubricating material in high-friction critical areas.

[0035] In this invention, the smooth outer shell layer not only provides protection and releases heat at specific points during breakage, but also provides lubrication in low-friction areas through ball bearing action. The phase change material in the phase change layer gradually transforms into a liquid in the high-temperature environment downhole, absorbing a large amount of heat, thus preventing the core layer's liquid lubricant from overheating and reducing its lubrication performance. After circulating with the drilling fluid to the low-temperature environment at the surface, the phase change material releases the heat absorbed downhole and transforms back into a solid. Furthermore, after the smooth outer shell layer breaks, the phase change material also provides lubrication and cooling in high-heat friction areas. The protective shell layer of the inner phase change layer prevents the phase change material, which absorbs heat and transforms into a liquid state during circulation, from merging with the core layer's liquid lubricant, thereby affecting the phase change material's heat absorption and release performance. The core layer's liquid lubricant is protected by multiple layers, maintaining stable performance during drilling fluid circulation and achieving efficient lubrication in critical areas during pressure release.

[0036] When using this invention, the drilling composite lubricant is dispersed in the drilling fluid during drilling operations, circulating freely with the drilling fluid on the surface and downhole. Due to the protection of the smooth outer shell, the core layer's liquid lubricant does not experience adhesion loss in low-friction or frictionless areas. When the drilling composite lubricant enters a high-friction area and is subjected to strong extrusion and shearing, the smooth outer shell ruptures, and the high-performance liquid lubricant in the core layer is released at a high concentration to the high-friction area, providing targeted lubrication and drag reduction. The isolation effect of the smooth outer shell, made of inert materials, also helps maintain the dispersibility of the liquid lubricant in the drilling fluid, reducing the probability of hydrolysis and thus improving the utilization rate of the liquid lubricant. Furthermore, the smooth outer shell, made of inert materials, prevents the core liquid lubricant from directly mixing into the drilling fluid system. Therefore, the concentration of lubricant in the drilling fluid is extremely low. This not only helps reduce liquid lubricant loss but also prevents excessively high concentrations of hydrolyzed liquid lubricant in the drilling fluid, which could significantly increase the foaming rate. When the material reaches the high-temperature zone downhole, the phase change material in the drilling composite lubricant gradually transforms into a liquid state, absorbing a large amount of heat in the process. When it circulates to the low-temperature zone near the wellhead, the phase change material that has transformed into a liquid state releases heat and transforms back into a solid state. The entire heat absorption and release process of the phase change can effectively alleviate the adverse effects of the high temperature at deep wells on the performance of the liquid lubricant in the core layer of the drilling composite lubricant, enabling it to maintain excellent performance over a long period of time.

[0037] In one specific embodiment, the liquid lubricant is any one of modified vegetable oil lubricant, polyol ester lubricant, alcohol ether lubricant, phosphate ester lubricant, and mineral oil lubricant; the inorganic material of the inorganic protective shell is silicon dioxide or calcium carbonate; the solid-liquid conversion phase change material is any one of paraffin wax, fatty acid, polyol, molten salt, and hydrated salt; and the inert material is any one of epoxy resin, vinyl ester resin, phenolic resin, urea-formaldehyde resin, melamine resin, polymethyl methacrylate, and natural polysaccharide derivatives.

[0038] It should be noted that the materials used in the above embodiments are only preferred materials of the present invention. In addition to these materials, other similar materials in the prior art that can achieve the same function can also be applied to the present invention.

[0039] In a specific embodiment, when the protective shell is a silica inorganic protective shell and the smooth outer shell is a urea-formaldehyde resin polymer outer shell, the drilling composite lubricating material is prepared by the following steps:

[0040] S1: Mix 10-30g of liquid lubricant with 5-15g of tetraethyl silicate solution to obtain an oil phase, and add the oil phase to 200-400g of ionic surfactant solution to react and obtain silica-coated liquid lubricant particles.

[0041] In one specific embodiment, the solvent of the tetraethyl silicate solution is dichloromethane with a concentration of 10%; the solute weight ratio of the ionic surfactant solution is 0.3-1%.

[0042] In one specific embodiment, during the reaction, the mixture is first stirred at a speed of 1000-1500 r / min for 20-40 min, then heated to 40-50°C and stirred for 1.5-3 h, then the pH value is adjusted to 2-3, and finally heated to 75-85°C and stirred for 30 min to obtain the silica-coated liquid lubricant particles.

[0043] S2: The silica-coated liquid lubricant particles are subjected to hydrophobic treatment to obtain silica-encapsulated particles with hydrophobic surfaces.

[0044] In one specific embodiment, during the hydrophobic treatment, the particles are first soaked in a dichloromethane solution containing 10-25% silane coupling agent for 2-4 hours, then cleaned with an organic solvent, and dried to obtain the silicon dioxide encapsulated particles with a hydrophobic surface.

[0045] It should be noted that the hydrophobic treatment is mainly to make the particles oleophilic, thus making them easier to be adsorbed by the phase change material. Besides the hydrophobic treatment methods described in the above embodiments, other methods in the prior art that can make particles hydrophobic and oleophilic can also be applied to this invention.

[0046] S3: Add 20-30g of urea and 50-70g of formaldehyde to 500g of water, add triethanolamine dropwise to adjust the pH to 8-9, then heat in a water bath at 60-70℃ for 40-90min, and cool to obtain a polymer shell prepolymer solution.

[0047] S4: The solid-liquid phase change material is heated to convert it into a liquid state to obtain a liquid phase change material; and the silica encapsulated particles with hydrophobic surfaces are placed in the liquid phase change material and ultrasonically dispersed to obtain a dispersion.

[0048] S5: The dispersion is sprayed into the polymer shell prepolymer solution using a microdroplet jetting method. The temperature of the polymer shell prepolymer solution is used to solidify the liquid phase change material and attach it to the surface of the silica encapsulation particles with a hydrophobic surface.

[0049] In this invention, the microdroplet jetting method utilizes a high-speed airflow to agitate the dispersion into tiny droplets, which are then sprayed into the polymer shell prepolymer solution. It should be noted that, to accelerate the curing rate of the liquid phase change material, it can also be cured by cooling.

[0050] S6: Adjust the pH of the mixed solution obtained in step S5 to 3-4, then heat it at 50-70°C with stirring for 2-5 hours, and wash it to obtain the drilling composite lubricant material.

[0051] In one specific embodiment, stirring is performed at a rotation speed of 800–1200 r / min; during washing, the mixture is washed sequentially with anhydrous ethanol and deionized water.

[0052] It should be noted that the above embodiments are only a preferred embodiment of the preparation method of a drilling composite lubricating material with a protective shell layer of silica inorganic protective shell layer and a smooth outer shell layer of urea-formaldehyde resin polymer outer shell layer. Those skilled in the art can prepare the drilling composite lubricating material of the present invention using existing technology based on the materials selected for each layer and the four-layer structure of the drilling composite lubricating material of the present invention.

[0053] Example 1

[0054] A drilling composite lubricant is prepared by the following steps:

[0055] (1) Preparation of micron-sized particles of polyol ester lubricant encapsulated with silica.

[0056] 20g of polyol ester lubricant was mixed with 10g of tetraethyl silicate (TEOS) dissolved in dichloromethane (DCM) at a concentration of 10% to form the oil phase. The oil phase was added to 300g of water containing 1% by weight of hexadecyltrimethylammonium bromide (CTAB), and stirred at 1200 rpm for 30 min. The mixture was then heated to 40°C and stirred for 2 h to form a phase-separated emulsion template. The pH of the aqueous phase was adjusted to 3, and the reaction temperature was increased to 80°C to promote the hydrolysis and condensation reaction of TEOS at the oil-water interface. Stirring continued for 30 min to form micron-sized particles of the polyol ester lubricant encapsulated in a SiO2 shell. The reaction principle involved in this step is as follows:

[0057]

[0058] (2) Preparation of urea-formaldehyde resin prepolymer.

[0059] Add 25g of urea and 65g of formaldehyde to 500g of deionized water, add triethanolamine dropwise to adjust the pH to 8.5, then heat the mixture in a water bath at 65°C for 60 minutes, and cool to obtain a urea-formaldehyde resin prepolymer solution.

[0060] (3) Hydrophobic treatment of SiO2 encapsulated particle surface and paraffin coating treatment.

[0061] The micron-sized particles of the SiO2-encapsulated polyol ester lubricant prepared in step (1) were immersed in a 20% tert-butyldimethylchlorosilane (TBSCl) DCM solution for 2 hours, then removed, washed with toluene and acetone, and dried. The reaction principle involved in this step is as follows:

[0062]

[0063] The paraffin phase change material is heated to convert it into a liquid state. The SiO2 encapsulated particles, which have been hydrophobically treated with TBSCl silane coupling agent, are placed in the molten liquid paraffin and dispersed using ultrasound. Then, the dispersion is sprayed into tiny droplets by a high-speed airflow using a micro-droplet spraying method. This allows the liquid paraffin to solidify at a lower temperature and adhere to the particle surface.

[0064] (4) Urea-formaldehyde resin encapsulation.

[0065] The pH of the urea-formaldehyde resin prepolymer solution sprayed with paraffin-coated particles was adjusted to 4.0, and then heated in a 60°C water bath for 3 hours with mechanical stirring at 900 rpm to complete the curing reaction of the urea-formaldehyde resin. Finally, it was washed sequentially with anhydrous ethanol and deionized water to obtain the drilling composite lubricant material SS-1 with a four-layer structure. The reaction principle involved in this step is as follows:

[0066]

[0067] Example 2

[0068] A drilling composite lubricant is prepared by the following steps:

[0069] (1) Preparation of micron-sized particles of polyol ester lubricant encapsulated with silica.

[0070] 15g of polyol ester lubricant was mixed with 10g of tetraethyl silicate (TEOS) dissolved in dichloromethane (DCM) at a concentration of 10% to form the oil phase. The oil phase was added to 300g of water containing 1% by weight of hexadecyltrimethylammonium bromide (CTAB), and stirred at 1000 rpm for 30 min. The mixture was then heated to 45°C and stirred for 2 h to form a phase-separated emulsion template. The pH of the aqueous phase was adjusted to 3, and the reaction temperature was increased to 80°C to promote the hydrolysis and condensation reaction of TEOS at the oil-water interface. Stirring continued for 30 min to form micron-sized particles of the polyol ester lubricant encapsulated in a SiO2 shell.

[0071] (2) Preparation of urea-formaldehyde resin prepolymer.

[0072] Add 20g of urea and 50g of formaldehyde to 500g of deionized water, add triethanolamine dropwise to adjust the pH to 8.5, then heat the mixture in a 60°C water bath for 60 minutes, and cool to obtain a urea-formaldehyde resin prepolymer solution.

[0073] (3) Hydrophobic treatment of SiO2 encapsulated particle surface and paraffin coating treatment.

[0074] The micron-sized particles of the SiO2-encapsulated polyol ester lubricant prepared in step (1) were immersed in a 20% tert-butyldimethylchlorosilane (TBSCl) DCM solution for 2 hours, then removed, washed with toluene and acetone, and dried.

[0075] The paraffin phase change material is heated to convert it into a liquid state. The SiO2 encapsulated particles, which have been hydrophobically treated with TBSCl silane coupling agent, are placed in the molten liquid paraffin and dispersed using ultrasound. Then, the dispersion is sprayed into tiny droplets by a high-speed airflow using a micro-droplet spraying method. This allows the liquid paraffin to solidify at a lower temperature and adhere to the particle surface.

[0076] (4) Urea-formaldehyde resin encapsulation.

[0077] The pH of the urea-formaldehyde resin prepolymer solution sprayed with paraffin-coated particles was adjusted to 4.0, and then heated in a water bath at 70°C for 3 hours with mechanical stirring at 900 rpm to complete the curing reaction of the urea-formaldehyde resin. Finally, it was washed sequentially with anhydrous ethanol and deionized water to obtain SS-2, a drilling composite lubricant material with a four-layer structure.

[0078] Example 3

[0079] Unlike Example 1, in this example, the phase change material used in step (3) is pentaerythritol, resulting in a drilling composite lubricant material SS-3 with a four-layer structure.

[0080] Example 4

[0081] Unlike Example 1, in this example, the liquid lubricant used in step (1) is a phosphate ester lubricant, resulting in a drilling composite lubricant material SS-4 with a four-layer structure.

[0082] Comparative Example 1

[0083] This comparative example uses only the core liquid lubricant, that is, a polyol ester lubricant without any shell (material) encapsulation, denoted as lubricant material DB-1.

[0084] Comparative Example 2

[0085] This comparative example lacks the SiO2 inorganic protective shell layer in the four-layer structure. 20g of liquid polyol ester lubricant and 5g of paraffin were mixed and directly dispersed in a urea-formaldehyde resin prepolymer solution. The mixture was then encapsulated using the urea-formaldehyde resin encapsulation method described in Example 1 to obtain lubricating material DB-2.

[0086] Comparative Example 3

[0087] This comparative example lacks the phase change layer in the four-layer structure. After preparing silica-encapsulated polyol ester lubricant micron-sized particles according to the method in Example 1, the steps of surface hydrophobization and paraffin coating of SiO2-encapsulated particles were skipped, and urea-formaldehyde resin encapsulation was performed directly to obtain lubricant material DB-3.

[0088] Comparative Example 4

[0089] This comparative example lacks the smooth outer shell layer in the four-layer structure. Micron-sized particles of silica-encapsulated polyol ester lubricant were prepared according to the method in Example 1, and after being coated with paraffin, the urea-formaldehyde resin encapsulation step was skipped, directly completing the preparation to obtain lubricant DB-4.

[0090] Test case

[0091] 3% bentonite, 0.1% Na2CO3, 2% anti-collapse and filtration loss reducer, 3% sulfomethylphenol resin, 2% lignite resin, and barite were added to tap water and stirred at 1000 rpm for 20 minutes. The mixture was then cured in a sealed container at 25℃±1℃ for 24 hours to obtain a density of 1.94 g / cm³. 3 The water-based drilling fluid slurry was prepared by adding 3% of the lubricating materials from the above-mentioned embodiments and comparative examples. After stirring at 1500 r / min for 10 min, the foaming behavior of the above-mentioned embodiments and comparative examples was observed. The apparent viscosity increase, density change, and lubrication coefficient reduction rate of the above-mentioned embodiments and comparative examples were tested according to Chinese standard Q / SY 17088-2016 "Technical Specification for Liquid Lubricants for Drilling Fluids". The experimental results are shown in Table 1.

[0092] Table 1 Performance indicators of lubricating materials at room temperature

[0093] name Foaming situation Apparent viscosity increase (mPa·s) <![CDATA[Density change value (g / cm 3 )]]> Lubrication coefficient reduction rate (%) Example 1 No bubbles -1 -0.02 55 Example 2 No bubbles 0 0.02 53 Example 3 No bubbles 0 0.01 54 Example 4 No bubbles -1 -0.01 58 Comparative Example 1 A small number of bubbles 2 -0.02 31 Comparative Example 2 No bubbles -1 -0.01 49 Comparative Example 3 No bubbles 0 0.01 57 Comparative Example 4 No bubbles 4 -0.02 43

[0094] Each drilling fluid containing the lubricating material was placed in an aging tank and subjected to hot rolling aging at 160°C for 1 hour. Afterward, it was removed and cooled to room temperature for 1 hour. This heating-aging-cooling cycle was repeated 8 times before the fluid was removed from the aging tank. Once the drilling fluid temperature had cooled to room temperature, it was stirred at 1500 r / min for 10 minutes. The foaming behavior of the above examples and comparative examples was observed. The apparent viscosity increase, density change, and lubrication coefficient reduction rate of the above examples and comparative examples were tested according to Chinese standard Q / SY17088-2016 "Technical Specification for Liquid Lubricants for Drilling Fluids". The experimental results are shown in Table 2.

[0095] Table 2 Performance indicators of lubricating materials after 160℃ hot rolling aging cycle

[0096] name Foaming situation Apparent viscosity increase (mPa·s) <![CDATA[Density change value (g / cm 3 )]]> Lubrication coefficient reduction rate (%) Example 1 No bubbles -1 -0.01 56 Example 2 No bubbles 1 0.02 55 Example 3 No bubbles -1 -0.01 58 Example 4 No bubbles -1 -0.01 51 Comparative Example 1 More bubbles 1 -0.02 26 Comparative Example 2 No bubbles 0 0 43 Comparative Example 3 No bubbles 1 0.02 42 Comparative Example 4 No bubbles 2 0.01 39

[0097] As shown in Tables 1 and 2, the presence of the shell material can improve the lubrication performance of the drilling fluid and suppress foaming. Furthermore, the drilling composite lubricant must maintain a complete four-layer structure to effectively preserve its lubrication performance after thermal rolling aging.

[0098] It should be noted that the above embodiments are only some embodiments of the present invention. The drilling composite lubricating material of the present invention, which is formed by using other materials and includes a core layer, a protective shell layer, a phase change layer and a smooth outer shell layer that sequentially wrap around micron-sized spheres from the inside out, has similar performance to the above embodiments and can outperform single liquid lubricants and composite lubricating materials without a four-layer structure.

[0099] In summary, this invention utilizes the four-layer structure of the drilling composite lubricant, enabling it to adhere precisely to critical areas experiencing severe frictional wear and maintain low foaming and high lubricity even after repeated exposure to the high-temperature downhole environment. Compared to existing technologies, this invention represents a significant advancement.

[0100] The above description is merely a representative embodiment of the present invention and is not intended to limit the present invention in any way. Any embodiment made by those skilled in the art without departing from the scope of the present invention and utilizing the disclosed technical content is an equivalent embodiment of the present invention. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A drilling composite lubricant, characterized in that, It includes a core layer, a protective shell layer, a phase change layer, and a smooth outer shell layer that sequentially enclose and form a micron-sized sphere from the inside out; The core layer is a liquid lubricant, the protective shell layer is an inorganic protective shell layer, the phase change layer is made of a solid-liquid conversion phase change material, and the smooth outer shell layer is made of an inert material. When the protective shell is an inorganic silica protective shell and the smooth outer shell is a urea-formaldehyde resin polymer outer shell, the drilling composite lubricant is prepared through the following steps: S1: Mix 10~30g of liquid lubricant with 5~15g of tetraethyl silicate solution to obtain an oil phase, and add the oil phase to 200~400g of ionic surfactant solution to react and obtain silica-coated liquid lubricant particles; S2: The silica-coated liquid lubricant particles are subjected to hydrophobic treatment to obtain silica-encapsulated particles with hydrophobic surfaces. S3: Add 20-30g of urea and 50-70g of formaldehyde to 500g of water, add triethanolamine dropwise to adjust the pH to 8-9, then heat in a water bath at 60-70℃ for 40-90min, and cool to obtain a polymer shell prepolymer solution; S4: The solid-liquid phase change material is heated to convert it into a liquid state to obtain a liquid phase change material; and the silica encapsulated particles with hydrophobic surfaces are placed in the liquid phase change material and ultrasonically dispersed to obtain a dispersion. S5: The dispersion is sprayed into the polymer shell prepolymer solution using a microdroplet spraying method. The temperature of the polymer shell prepolymer solution is used to solidify the liquid phase change material and attach it to the surface of the silica encapsulation particles with hydrophobic surfaces. S6: Adjust the pH of the mixed solution obtained in step S5 to 3-4, then heat it at 50-70°C with stirring for 2-5 hours, and wash it to obtain the drilling composite lubricant material.

2. The drilling composite lubricant material according to claim 1, characterized in that, The liquid lubricant is any one of modified vegetable oil lubricant, polyol ester lubricant, alcohol ether lubricant, phosphate ester lubricant, and mineral oil lubricant.

3. The drilling composite lubricant material according to claim 1, characterized in that, The inorganic material of the inorganic protective shell can also be calcium carbonate.

4. The drilling composite lubricant material according to claim 1, characterized in that, The solid-liquid conversion phase change material is any one of paraffin, fatty acid, polyol, molten salt, and hydrated salt.

5. The drilling composite lubricant material according to claim 1, characterized in that, The inert material can also be any one of epoxy resin, vinyl ester resin, phenolic resin, melamine resin, polymethyl methacrylate, or natural polysaccharide derivatives.

6. The drilling composite lubricant according to claim 1, characterized in that, In step S1, the solvent for the tetraethyl silicate solution is dichloromethane with a concentration of 10%.

7. The drilling composite lubricant material according to claim 1, characterized in that, In step S1, the solute weight ratio of the ionic surfactant solution is 0.3~1%.

8. The drilling composite lubricant material according to claim 1, characterized in that, In step S1, during the reaction, the mixture is first stirred at a speed of 1000~1500 r / min for 20~40 min, then heated to 40~50℃ and stirred for 1.5~3 h, then the pH value is adjusted to 2~3, and finally heated to 75~85℃ and stirred for 30 min to obtain the silica-coated liquid lubricant particles.

9. The drilling composite lubricant material according to claim 1, characterized in that, In step S6, stirring is performed at a speed of 800~1200 r / min; during washing, the mixture is washed sequentially with anhydrous ethanol and deionized water.

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