Anti-impact and anti-corrosion composite coating, preparation method and downhole instrument of anti-impact and anti-corrosion composite coating

Abstract

According to the anti-impact and anti-corrosion composite coating, the preparation method and the downhole instrument thereof, the preparation method is simple, the binding force is high, and the anti-impact and anti-corrosion composite coating which is excellent in corrosion resistance, impact resistance and abrasion resistance can be coordinated at the same time, so that the anti-impact and anti-corrosion composite coating can be applied to the unique use environment of the downhole instrument; according to the present invention, the technical contradiction that the high hardness and the high toughness are difficult to concurrently exist is solved, such that the service life of the downhole instrument under the severe working condition is significantly prolonged, and the coating is the polydimethylsiloxane-based composite coating, and is formed by curing polydimethylsiloxane, the silicon carbide nanoparticles with the average particle size of 100 nm, and the N75 curing agent; wherein the mass percent of the silicon carbide nanoparticles in the coating is 3%-8%, and the thickness of the coating is 50-60 microns.

Description

Technical Field

[0001] This invention relates to the field of drilling for oil and gas exploration and development. Specifically, it relates to an impact-resistant and corrosion-resistant composite coating, its preparation method, and its application to downhole instruments, particularly for protecting the metal surfaces of downhole instruments that are susceptible to corrosion and impact during drilling. Background Technology

[0002] In the field of oil and gas exploration and development drilling, downhole instruments face extremely harsh environmental challenges during operation, mainly in two aspects: First, there is the severe impact and vibration generated by the interaction between the drill string and the hard formation. For example, when drilling into hard formations, greater drilling pressure and torque are required, which will put a greater load on the drilling tool system and easily cause impacts. These impacts can damage downhole instruments. Depending on the formation structure and rock properties, the drill string will generate vibrations such as axial vibration, lateral vibration and torsional vibration during the drilling process. Secondly, corrosion problems arise from the chemical reactions between the inorganic salts, acids, alkalis, dissolved oxygen, and other chemical media abundant in drilling fluids and the metal components of downhole instruments. For example, different metals can form galvanic cells under the action of electrolytes (such as drilling fluids), leading to electrochemical corrosion. Furthermore, as drilling depth increases, downhole temperature and pressure gradually rise, and high-temperature, high-pressure conditions accelerate the rate of chemical reactions, making metallic materials more susceptible to corrosion.

[0003] These two destructive effects often exacerbate each other, significantly shortening the service life of downhole instruments, leading to equipment failure, tripping out of the well, and replacement, resulting in huge economic losses.

[0004] To protect the metal surfaces of downhole instruments from corrosion and impact during drilling, various protective measures can be taken, such as: 1. Optimize the materials of downhole instruments, select metal materials with strong corrosion resistance, such as stainless steel containing alloying elements such as chromium, nickel, and molybdenum; select materials with high strength, high toughness and good wear resistance, such as cemented carbide. 2. Optimize the drilling fluid by reducing the content of corrosive components or adding an appropriate amount of corrosion inhibitor to the drilling fluid. This can form a protective film on the metal surface and inhibit the occurrence of corrosion reactions. 3. Add a coating to downhole instruments.

[0005] A typical approach to enhancing coating performance involves constructing superhydrophobic coatings with micro / nano hierarchical structures. For example, prior art document 1 (patent application number: CN202510697846.3) discloses a wear-resistant, corrosion-resistant, superhydrophobic, and anti-icing coating. This coating employs a two-layer structure combining a micro-framework layer and a nano-functional layer. The micro-framework layer contains epoxy resin, a curing agent, and micron-sized silicon carbide particles, while the nano-functional layer introduces nanoparticles. This type of design blocks corrosive media by trapping an air film and enhances wear resistance using micron-sized particles. However, its complex multilayer structure has significant inherent drawbacks: 1. It requires step-by-step preparation and coating, resulting in low production efficiency, difficulty in quality control, and complex processes; 2. Under continuous impact and vibration conditions downhole, layers with different physical properties are prone to peeling or cracking, leading to rapid failure of protective functions; 3. Many superhydrophobic coatings that rely on fragile micro-nano structures often struggle to achieve both wear resistance and impact resistance, and are prone to losing their superhydrophobicity under sand erosion and mechanical friction.

[0006] Another approach involves using functionally graded coatings or metal-based coatings. Some studies have proposed NiCrAlY / AT20 gradient coatings or high-entropy alloy gradient composite coatings for the outer casing of measurement-while-drilling (MWD) instruments to combat the erosion and wear caused by drilling fluids. Additionally, some research has employed supersonic flame spraying technology to prepare amorphous alloy coatings, utilizing their high hardness for protection. While these coatings offer high hardness and erosion resistance, their toughness is typically poor, making them prone to macroscopic cracking or spalling under the intense dynamic impacts of downhole drilling. Furthermore, the complex gradient design significantly increases manufacturing costs. Summary of the Invention

[0007] The purpose of this invention is to provide an impact-resistant and corrosion-resistant composite coating and its preparation method. The preparation method is simple, has strong adhesion, and can simultaneously coordinate excellent corrosion resistance and impact resistance. This coating and its preparation method can be applied to the operating environment of downhole instruments, solving the technical contradiction of the difficulty in achieving both high hardness and high toughness, thereby extending the service life of downhole instruments under harsh operating conditions.

[0008] The embodiments of the present invention are implemented as follows: An impact-resistant and corrosion-resistant composite coating for downhole instruments is a polydimethylsiloxane composite coating, which is formed by curing polydimethylsiloxane, silicon carbide nanoparticles with an average particle size of 100 nanometers and N75 curing agent; wherein the mass percentage of silicon carbide nanoparticles in the coating is 3% to 8%.

[0009] In a preferred embodiment of the present invention, the mass percentage of the silicon carbide nanoparticles in the coating is 5%.

[0010] In a preferred embodiment of the present invention, the N75 curing agent is a biuret derivative of hexamethylene diisocyanate.

[0011] In a preferred embodiment of the present invention, the thickness of the coating is 50 micrometers to 60 micrometers.

[0012] This invention also provides a method for preparing an impact-resistant and corrosion-resistant composite coating for downhole instruments, comprising the following steps: Raw material preparation steps: Prepare polydimethylsiloxane, silicon carbide nanopowder with an average particle size of 100 nanometers, solvent and N75 curing agent; Dispersion step: Silicon carbide nanoparticles and polydimethylsiloxane are dispersed in a solvent at high speed to form a homogeneous mixture; Curing agent addition step: Add N75 curing agent to the homogeneous mixture and mix well; Coating step: Apply the mixture with added curing agent to the surface of the downhole instrument's metal substrate; Curing step: Allow the coated layer to cure under natural conditions.

[0013] In a preferred embodiment of the present invention, in the above dispersion step, a high-speed disperser is used to disperse the material at a speed of 1000 rpm for 2 hours.

[0014] In a preferred embodiment of the present invention, the solvent is xylene.

[0015] In a preferred embodiment of the present invention, the above coating step is specifically performed using an air spraying process.

[0016] In a preferred embodiment of the present invention, the mass ratio of the silicon carbide nanopowder, polydimethylsiloxane and solvent is 0.8g : 15g : 100mL, and the amount of N75 curing agent added is 1.5g.

[0017] A downhole instrument, wherein at least one surface of the metal component is provided with an impact-resistant and corrosion-resistant composite coating as described in any of the preceding claims.

[0018] In a preferred embodiment of the present invention, the metal component is an aluminum alloy substrate.

[0019] In a preferred embodiment of the present invention, the aluminum alloy substrate is 2024-T3 aluminum alloy.

[0020] The beneficial effects of the embodiments of the present invention are: 1. A highly dense and stable composite coating is formed by uniformly dispersing SiC particles with an average particle size of 100 nanometers in a PDMS matrix at an optimal mass percentage of 5%, and cross-linking with N75 curing agent. The nano-SiC particles effectively fill the free volume of the PDMS matrix, forming a tortuous path that efficiently blocks Cl from drilling fluid. - It prevents corrosive media such as O2 and H2O from penetrating into the metal substrate; PDMS itself has excellent chemical inertness, and SiC nanoparticles also have extremely high hardness and stability. The combination of the two forms a dense and stable physical barrier, which enables the coating to resist the erosion of various acid, alkali and salt substances in drilling fluid; after 20 days of rigorous salt spray test, the surface morphology remained basically unchanged, proving its long-term effective anti-corrosion ability. 2. The PDMS matrix provides flexibility, while the high-hardness SiC nanoparticles provide support points and wear-resistant points. The high cross-linking density network formed by the N75 curing agent endows the coating with excellent adhesion and overall strength. In the cyclic sandpaper friction test, the coating exhibits good wear resistance, and the microstructure of the main areas is preserved, proving that it can effectively resist the scouring and abrasion of cuttings and well walls during drilling. At the same time, the rigid SiC particles and the flexible PDMS matrix constitute a rigid-flexible energy-absorbing structure. When subjected to severe downhole vibration or instantaneous impact, the flexible matrix can absorb energy through deformation, while the rigid particles resist impact stress, preventing the coating from cracking or falling off the matrix, and providing buffer protection for precision downhole instruments. 3. The PDMS molecular chain structure in the new composite coating is stable, and the properties of SiC nanoparticles do not change with time and environment, giving the coating excellent anti-aging properties. The ultraviolet aging test shows that the macroscopic morphology and micro-rough structure of the coating have not changed significantly, and the hydrophobic properties are maintained, ensuring that the performance does not degrade during long-term storage or use. The PDMS-SiC composite system can withstand the high temperature and high pressure in the downhole environment, with small performance degradation and long service life. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a surface view of the coating of sample B in Embodiment 3 of the present invention after a 20-day salt spray test; Figure 2 This is a SEM image of sample B in Embodiment 3 of the present invention without salt spray testing; Figure 3This is a SEM image of sample B from Example 3 of the present invention after a 20-day salt spray test; Figure 4 This is a surface view of the coating of sample C in Embodiment 3 of the present invention after a 10-day salt spray test; Figure 5 This is a surface view of the coating of sample A in Embodiment 3 of the present invention after 15 days of salt spray testing; Figure 6 This is a surface image of the coating of sample B in Embodiment 4 of the present invention after 20 days of continuous ultraviolet aging; Figure 7 This is a SEM image of sample B in Embodiment 4 of the present invention before UV aging; Figure 8 This is a SEM image of sample B in Example 4 of the present invention after 20 days of UV aging; Figure 9 The image shows the coating surface and SEM image of sample B in Embodiment 5 of the present invention before reciprocating cyclic friction. Figure 10 The image shows the coating surface and SEM image of sample B after reciprocating cyclic friction in Embodiment 5 of the present invention. Detailed Implementation

[0023] The present invention will be further illustrated below with reference to specific embodiments. These embodiments are only for illustrating the present invention and are not intended to limit the scope of the present invention. The best implementation methods and materials described herein are for illustrative purposes only. The present invention will be described in detail below with reference to specific embodiments.

[0024] In this document, the terms “comprising,” “having,” or “including” are open-ended expressions, meaning they include the contents specified in this invention but do not exclude other aspects.

[0025] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0026] To facilitate understanding of the invention, certain technical and scientific terms are specifically defined below. Unless otherwise expressly defined elsewhere in this document, all other technical and scientific terms used herein have the meanings commonly understood by one of ordinary skill in the art to which this invention pertains.

[0027] For the purposes of the following detailed description, it should be understood that various alternative variations and sequences of steps may be assumed in the invention, unless otherwise expressly stated to the contrary. Furthermore, except in any operational instance or where otherwise indicated, all numerical expressions used in the specification, such as amounts of ingredients, should be understood to be modified by the term "about" in all instances. It should be noted that, unless otherwise stated, all percentages given in this specification and the appended claims refer to weight percentages in the total composition.

[0028] Therefore, before describing the invention in detail, it should be understood that the invention is not limited to the specifically illustrated system or process parameters, which can of course vary. It should also be understood that the terminology used herein is for the purpose of describing specific embodiments of the invention and is not intended to limit the scope of the invention in any way.

[0029] This invention addresses the problems of complex layered structures, easy peeling between layers, and loss of superhydrophobicity under sand erosion and mechanical friction in current downhole instrument coatings. It provides a simple yet cleverly designed single composite coating that successfully solves the comprehensive problems of corrosion, impact, and wear faced by downhole instruments. In particular, the 5 wt.% SiC-PDMS composite coating provided by this invention achieves synergistic effects through the chemical inertness and high cross-linking density of the PDMS matrix, combined with the dense filling effect, rigidity enhancement effect, and UV shielding effect produced by SiC nanoparticles of specific content and size. This results in optimal corrosion resistance, aging resistance, and wear resistance, providing a simple, cost-effective, comprehensive, and specialized technical solution for harsh downhole environments. Compared to existing technologies, it represents a significant advancement and has outstanding substantive features.

[0030] First Embodiment Raw material preparation Prepare 15g of polydimethylsiloxane, three portions of silicon carbide nanopowder with an average particle size of 100 nm of different masses, 100ml of xylene solvent with masses of 0.5g, 0.8g and 1.3g respectively, and 1.5g of N75 curing agent.

[0031] Polydimethylsiloxane is a type of PDMS silicone rubber.

[0032] SiC nanoparticles with an average particle size of 100 nm were selected. Compared with conventional SiC particles, the particle size is reduced from micrometers to nanometers, resulting in a denser protective layer and stronger protective performance. At the same time, since smaller particle sizes are more expensive, selecting particles with a particle size of 100 nm is sufficient to meet the requirements, while also controlling the cost.

[0033] The main component of curing agent N75 is a biuret derivative of hexamethylene diisocyanate (HDI). The isocyanate groups in N75 curing agent have high reactivity and can react with active groups such as hydroxyl and amino groups in polymer materials such as epoxy resin, polyurethane, and unsaturated polyester to achieve material curing. The cured product has a high crosslinking density and a dense network structure, resulting in high hardness and good wear resistance.

[0034] 0.5g of silicon carbide nanopowder corresponds to a 3% mass ratio; 0.8g of silicon carbide nanopowder corresponds to a 5% mass ratio; and 1.3g of silicon carbide nanopowder corresponds to an 8% mass ratio.

[0035] Coating preparation 0.5 g of silicon carbide nanoparticles and 15 g of PDMS were added to 100 mL of xylene. The mixture was dispersed continuously at 1000 rpm for 2 hours using a high-speed disperser until the mixture was homogeneous and free of visible agglomerates. Add 1.5 g of N75 curing agent to the above homogeneous mixture, and then stir at 500 rpm for 10 minutes to ensure that the curing agent is fully and uniformly mixed. The isocyanate groups in the N75 curing agent react with the hydroxyl groups at the ends of the PDMS chains to form a three-dimensional network structure with high cross-linking density, thus obtaining the mixed coating slurry A.

[0036] Using the same method, 0.8 g / 1.3 g silicon carbide nanopowder and 15 g PDMS were added to 100 mL xylene respectively, and subsequent operations were performed to obtain mixed coating slurries B and C.

[0037] Second Embodiment Substrate pretreatment A 2024-T3 aluminum alloy plate measuring 100mm × 50mm × 2mm was selected as the test substrate, serving as a key metal component of the downhole instrument. The aluminum plate was ultrasonically cleaned with acetone for 10 minutes to thoroughly remove surface oil. Subsequently, it was sanded using sandpaper, starting at 120 grit and gradually increasing to 1000 grit, to obtain a smooth surface. The sanded substrate was then rinsed with distilled water and anhydrous ethanol to remove residual abrasive debris and contaminants. Finally, the substrate was dried with clean compressed air and placed in a desiccator for later use, yielding the experimental substrate.

[0038] An air spraying device was used to uniformly spray mixed coating slurries A, B, and C onto the pretreated aluminum alloy substrate surface. The spraying parameters were controlled as follows: nozzle diameter 1.2 mm, spraying pressure 0.4 MPa, and spray gun distance from the substrate approximately 20 cm.

[0039] After spraying, samples A, B, and C of the mixed coating slurry were allowed to stand naturally at room temperature (25°C) for 48 hours to allow the coating to fully crosslink and cure. During this process, the uniformly dispersed 100 nm SiC nanoparticles were firmly anchored in the crosslinked network of PDMS, forming a strong and flexible composite structure. Ten random measurements were taken on the sample surface, and the coating thickness was 55 ± 3 µm, exhibiting good uniformity. In this embodiment, the coating refers to a deposited layer applied to part or all exposed surfaces of the substrate.

[0040] An aluminum alloy plate without the mixed coating slurry was used as blank sample D.

[0041] Surface observation: During the preparation process, it can be observed that the viscosity of the mixed coating slurry C increases significantly, and the surface of the coating sample C formed after spraying is slightly rough.

[0042] Samples A and C were tested and rated using the cross-cut adhesion test. The test results showed that sample B's coating had a higher cross-cut adhesion rating than samples A and C, indicating that the coating bonded extremely strongly to the substrate.

[0043] The hardness of sample AC was tested using pencil hardness. The hardness of the AC coating reached 3H-5H. Among them, the coating hardness of sample B was greater than that of samples A and C, indicating that the coating of sample B has sufficient rigidity to resist indentation and scratching.

[0044] Third Embodiment The sample AD prepared in the second embodiment was subjected to a neutral salt spray test to evaluate the corrosion resistance of the coating under accelerated corrosion conditions. The salt spray test was conducted in an F-750C salt spray chamber according to ASTM B117 standard. The chamber temperature was set to 35±2℃, the saturated air chamber temperature was set to 47±2℃, and a 5 wt.% NaCl solution was used as the corrosive medium for continuous spraying.

[0045] Within 24 hours, sample D showed large-area uniform corrosion and white corrosion products on the substrate surface.

[0046] Sample C showed obvious chalking after 5 days, with microcracks appearing on the coating surface. Please refer to [link / reference needed]. Figure 4 The surface of the coating showed fine particles falling off, cracks expanding and accompanied by pulverization, and later localized damage due to insufficient coating cohesion. According to microstructural observation, when the SiC nanoparticle content was too high (8%), the particles agglomerated, which destroyed the continuity of the PDMS matrix, resulting in a decrease in coating cohesive strength and a loose structure, thus causing premature failure, but it still had a certain degree of corrosion resistance.

[0047] Analysis revealed that this was caused by the following: when the SiC nanoparticle content was too high (8%), the nanoparticles were prone to agglomeration in the matrix due to excessively high interfacial energy. These agglomerates disrupted the continuity of the PDMS crosslinking network, becoming stress concentration points and structural defects, leading to a significant decrease in the coating's cohesive strength. Under the combined action of corrosive media and stress, the coating began to fail from these weak points, manifesting as powdering and premature damage.

[0048] Sample A began to show slight localized dark corrosion spots after approximately 14 days, and the coating surface exhibited slight localized blistering and bubbling. Please refer to [link / reference needed]. Figure 5 Subsequently, the corrosion area gradually expanded, cracks propagated, and pulverization occurred. This result demonstrates that when the SiC nanoparticle content is below 3%, a sufficiently dense physical barrier network cannot be formed in the PDMS matrix, making it easier for corrosive media to penetrate to the substrate interface, resulting in insufficient protective performance. However, its corrosion resistance is still stronger than that of 8% SiC nanoparticles.

[0049] Analysis revealed that the reason for this was that when the SiC nanoparticle content was too low (3%), the nanoparticles were insufficient to form a continuous and dense physical barrier network in the PDMS matrix. The spacing between the particles was too large, providing too many "fast channels" for the diffusion of corrosive media, resulting in insufficient physical shielding effect and reduced protective performance.

[0050] Please refer to the results after 20 days of testing for Sample B. Figure 1 No blistering, peeling, or obvious rust spots were observed on the coating surface. Figure 2 and Figure 3 SEM comparisons showed that the micro-roughness of the coating surface remained essentially unchanged before and after the test, demonstrating its excellent long-term corrosion resistance. A 5% SiC nanoparticle content reached near the critical percolation threshold of the filler in the polymer matrix. At this level, the SiC nanoparticles could form the most effective three-dimensional network structure, maximizing their reinforcement and shielding effects without causing severe agglomeration, thus perfectly balancing performance and integrity.

[0051] The samples coated with the PDMS-SiC composite coating showed stronger corrosion resistance compared to those without the coating. The PDMS-SiC composite coating prepared with 5% silicon carbide nanoparticles by mass exhibited particularly outstanding corrosion resistance. Analysis revealed that its superior corrosion resistance stemmed from three main effects: 1. 100 nm SiC particles perfectly fill the free volume between PDMS polymer chains, forming an extremely dense composite film with PDMS, which is highly resistant to corrosive media (Cl). - The penetration of substances such as H2O and O2 has a significant labyrinth effect and a delaying effect, forming a dense physical barrier effect. 2. PDMS itself has extremely low surface energy and excellent chemical stability, while SiC is an ultra-hard and highly inert material. The combination of the two makes the coating exhibit inherent resistance to electrolyte erosion and a chemical inert barrier. 3. The highly cross-linked network formed by N75 curing, and the good combination of nanoparticles and the substrate, ensure excellent adhesion between the coating and the metal substrate, effectively preventing the lateral penetration of corrosive media at the interface and under-coating corrosion, and exhibiting strong interfacial bonding.

[0052] Fourth embodiment The ultraviolet aging test was continued. Sample B was placed in an ultraviolet aging chamber and ultraviolet lamp UVA-340 was used to irradiate the sample every 8 hours with 4 hours of condensation to simulate the aging conditions under the high temperature environment downhole.

[0053] After a specified period of ultraviolet irradiation, such as Figure 6 As shown, after 20 days of UV irradiation, the coating surface did not exhibit chalking, discoloration, or cracking; the surface morphology remained essentially unchanged. For further observation of the surface microstructure before and after 20 days of UV irradiation, please refer to [link to relevant documentation]. Figure 7 and 8 As can be seen, the rough surface structure was not greatly damaged, its micro-nano structure was well preserved, and the hydrophobic properties did not decrease significantly, indicating that the coating has excellent aging resistance.

[0054] In summary, the excellent UV aging resistance of the PDMS-SiC composite coating prepared by adding 5% silicon carbide nanoparticles by mass is attributed to: 1. The main chain of PDMS molecules is composed of high-bond-energy Si-O bonds, which are much more stable than C-C bonds that are easily degraded by ultraviolet light. Therefore, they are difficult to undergo photo-oxidative cleavage and exhibit intrinsic stability. 2. SiC nanoparticles themselves have good absorption and scattering capabilities for ultraviolet light. They are dispersed in the coating like "miniature sunshades", effectively weakening the attack of ultraviolet light on the deep PDMS molecular chains, thereby protecting the overall structure of the polymer.

[0055] Fifth embodiment The abrasion resistance test was continued, using 400-grit sandpaper as the friction pair. A pressure of 5 kPa was applied to sample B, and 200 reciprocating cycles of friction were performed.

[0056] After 200 cycles of friction, please see Figure 9 and 10As shown, the main area of ​​the coating remained intact after friction, with only slight wear at the outermost edge, likely due to the thinner coating at the edges. Further SEM observation confirmed that the main rough structure of the coating surface was still preserved, demonstrating its excellent wear resistance and toughness, effectively resisting erosion from downhole cuttings.

[0057] In summary, the excellent wear resistance and damage resistance of the PDMS-SiC composite coating prepared by adding 5% silicon carbide nanoparticles by mass stem from its unique rigid-flexible structure: the PDMS matrix provides excellent elasticity and toughness, and can absorb energy through deformation and buffer external forces when subjected to frictional stress; the high-hardness SiC nanoparticles, as the main load-bearing phase, directly withstand the cutting and plowing action from sandpaper, protecting the soft PDMS matrix. It is this microstructure of "rigid islands (SiC nanoparticles) distributed in a flexible ocean (PDMS)" that allows the coating to dissipate energy through plastic deformation while maintaining the integrity of the macrostructure when subjected to mechanical stress, thus exhibiting wear resistance and damage resistance far exceeding that of a single component.

[0058] Sixth Embodiment The impact resistance of the coating sample B was characterized by the drop hammer impact test.

[0059] The coated sample B was horizontally fixed in a fixture with the coated side facing upwards. A 1kg hammer was dropped freely from a height of 500mm, impacting the center of the sample surface. The hammer head was hemispherical with a diameter of 12.7mm to simulate localized impact. The impact resistance limit of the coating was quantified by varying the impact energy.

[0060] Test results show that under an impact energy of 5J, no cracks or spalling were observed in the impact area of ​​coating sample B; only slight, recoverable indentations were observed, indicating its excellent dynamic impact resistance. Analysis reveals that its superior impact resistance stems from the coating's unique microstructure and the synergistic effect of its components. 1. As an energy-absorbing flexible matrix, PDMS matrix has extremely high elasticity and elongation at break. When subjected to instantaneous impact, it can effectively absorb and dissipate most of the impact energy through large-scale viscoelastic deformation, converting the concentrated impact force into internal frictional heat of the molecular chains, thereby buffering the impact stress. 2. Uniformly dispersed SiC nanoparticles, acting as a reinforcing phase and rigid particles for stress transfer and dispersion, play a crucial role in stress transfer and dispersion. They effectively transfer locally concentrated impact stress to a larger PDMS matrix region, preventing excessive stress concentration in a single direction. Simultaneously, these hard particles can inhibit the initiation and propagation of crazes and microcracks. 3. SiC nanoparticles are firmly "anchored" in the highly cross-linked network of PDMS through physical and chemical interactions. This strong interfacial bonding ensures that stress can be efficiently transferred from the matrix to the particles during impact, rather than debonding and forming defects at the interface. The highly cross-linked three-dimensional network formed by the N75 curing agent further strengthens this interfacial bonding and endows the coating with higher overall cohesive strength.

[0061] 4. Ultimately, the "flexible PDMS ocean" and the "rigid SiC islands" together construct a robust composite system. This system combines the energy absorption capacity of the flexible phase with the load-bearing and stress-dispersing capacity of the rigid phase, thus achieving high hardness and high toughness that are difficult to achieve with a single material, enabling it to withstand severe dynamic impact loads downhole without being damaged.

[0062] Seventh Embodiment A 5:1 SiC-PDMS composite coating was applied to austenitic stainless steel substrates and AISI 1045 carbon steel substrates. The coated samples underwent the same full set of performance tests as the aluminum alloy plates, including salt spray test, aging test, abrasion resistance test, and drop hammer impact test.

[0063] Neutral salt spray test: After 20 days of testing, the surface of the composite coating remained intact, without blistering or peeling, and no pitting or rust appeared on the stainless steel and carbon steel substrates. This proves that the coating system has excellent compatibility with stainless steel and carbon steel substrates, and its dense barrier effect can provide long-term protection for the core metal.

[0064] Aging test: After 20 days of ultraviolet radiation, no powdering, discoloration or cracking occurred on the coating surface, and the surface morphology of the coating remained basically unchanged.

[0065] Abrasion resistance test: After 200 cycles of sandpaper rubbing, the main coating area remained intact, exhibiting abrasion resistance comparable to that on aluminum alloy. The SiC-PDMS composite coating of this invention provides extremely effective protection for highly corroded stainless steel and carbon steel materials, significantly extending their service life in harsh downhole environments, and possesses significant economic value and promotional potential.

[0066] Drop hammer impact test: After impact, the coating showed no cracks or peeling, only slight indentations. The results indicate that the coating forms a strong interfacial bond with the stainless steel and carbon steel substrates, and its "rigid-flexible" composite structure can effectively absorb and disperse impact energy on the metal substrates of different downhole equipment.

[0067] The SiC-PDMS composite coating of this invention also exhibits excellent comprehensive protective performance on the surface of austenitic stainless steel and can be widely used in key stainless steel components such as downhole drill collars and instrument housings.

[0068] In summary, this SiC-PDMS composite coating process is simple, requiring only one spraying step to complete the coating, eliminating the need for multiple molding processes and complex interlayer control, making it more suitable for large-scale industrial production with high efficiency. Its single structure avoids risks such as wrinkling and peeling caused by mismatched interlayer thermal expansion coefficients, resulting in a more uniform stress distribution within the coating and higher long-term reliability. The simplified process directly reduces production time, equipment investment, and labor costs. Furthermore, it performs excellently in various stringent tests, including salt spray corrosion, UV aging, and mechanical wear, demonstrating comprehensive, balanced, and long-lasting protective performance, making it suitable for complex and variable downhole environments.

[0069] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "embodiment," or "specific embodiment," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment is included in at least one embodiment of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment. Furthermore, the specific features, structures, materials, or characteristics described may be combined in a suitable manner in any one or more embodiments. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments and features described in this specification.

[0070] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A shock- and corrosion- resistant composite coating for downhole instruments, characterized in that, The coating is a polydimethylsiloxane-based composite coating formed by polydimethylsiloxane, silicon carbide nanoparticles with an average particle size of 100 nanometers, and N75 curing agent; wherein the mass percentage of the silicon carbide nanoparticles in the coating is 3% to 8% [a1].

2. The impact and corrosion protection composite coating for downhole instruments of claim 1, wherein, The mass percentage of the silicon carbide nanoparticles in the coating is 5%.

3. The impact and corrosion protection composite coating for downhole instruments of claim 1, wherein, The N75 curing agent is a biuret derivative of hexamethylene diisocyanate.

4. The shock and corrosion resistant composite coating for downhole instruments of claim 1, wherein, The thickness of the coating is 50 microns to 60 microns.

5. A method for the preparation of an impact and corrosion resistant composite coating for downhole instruments, characterized by, The method comprises the following steps: A raw material preparation step: polydimethylsiloxane, silicon carbide nanopowder with an average particle size of 100 nanometers, a solvent, and N75 curing agent are prepared; A dispersion step: the silicon carbide nanopowder and polydimethylsiloxane are dispersed in the solvent, high-speed dispersion is performed, and a uniform mixture is formed; A curing agent addition step: the N75 curing agent is added to the uniform mixture and mixed uniformly; A coating step: the mixture with the added curing agent is coated onto the surface of the metal substrate of the downhole instrument; A curing step: the coated coating is left to stand and cure under natural conditions for at least 48 hours.

6. The method of claim 5, wherein the method further comprises, In the dispersion step, a high-speed dispersion machine is used at a rotation speed of 1000 rpm for 2 hours.

7. The method of claim 5, wherein the method further comprises, The solvent is xylene.

8. The method of claim 5, wherein the shock and erosion resistant composite coating for downhole tools is prepared by, The coating step is specifically performed using an air spraying process.

9. The method of claim 5, wherein the shock and corrosion resistant composite coating for downhole instruments is prepared by, The mass ratio of the silicon carbide nanopowder, polydimethylsiloxane, and solvent is 0.8g: 15g: 100mL, and the addition amount of the N75 curing agent is 1.5g.

10. A downhole instrument, characterized by The metal part of the downhole instrument is provided with at least one surface of the anti-impact and anti-corrosion composite coating as claimed in any one of claims 1 to 4.

11. The downhole instrument of claim 10, wherein, The metal part is an aluminum alloy substrate.

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