High-strength nano-hybrid soluble bridge plug, preparation method and application thereof

Abstract

The application belongs to the technical field of gas adsorbents, and specifically discloses a high-strength nanometer hybrid dissolvable bridge plug as well as a preparation method and application thereof. The high-strength nanometer hybrid dissolvable bridge plug comprises a bridge plug body, a carbon nitride film intermediate layer and a polybenzimidazole and nanometer silicon oxide composite film outermost layer. The bridge plug body comprises a hollow metal tube, and a plurality of annular grooves are formed on the outer surface of the hollow metal tube and surround the axis of the hollow metal tube. The carbon nitride film intermediate layer is located on the outer surface of the bridge plug body. The polybenzimidazole and nanometer silicon oxide composite film outermost layer is located on the outer surface of the carbon nitride film intermediate layer. The material of the hollow metal tube is a zinc-based alloy, which is composed of the following components in percentage by mass: titanium 5-7%, magnesium 2-4%, bismuth 0.5-2%, and the balance being zinc. The bridge plug has high plugging strength, controllable dissolving time, and is suitable for high-temperature high-salt or acidic environments. After dissolving, the particle size of the residue is small, which can meet the harsh requirements of ultra-deep well fracturing. Moreover, the bridge plug is prepared by using a one-step forming process, which significantly reduces the production cost.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of multistage fracturing of oil and gas wells, and specifically discloses a high-strength nanometer hybrid soluble bridge plug as well as a preparation method and application thereof, which is suitable for temporary plugging and controllable dissolution of downhole tools in oil and gas exploitation. BACKGROUND

[0002] The soluble bridge plug is a key tool for segmented fracturing operation in the oil and gas industry, and is widely used in shale gas, tight oil and gas, and deep oil and gas reservoir development, especially in ultra-deep wells (well depth greater than 6000 m, pressure greater than 100 MPa, temperature 140-160 ℃). The fracturing operation forms temporary plugging in the wellbore by the bridge plug, realizes separate layer exploitation, and after the operation is completed, the bridge plug needs to be dissolved in the downhole environment (typical conditions: 140-160 ℃, 10-20% sodium chloride solution, pH 3.5-6.5) through corrosion or chemical degradation, without mechanical drilling or recovery, thereby improving operation efficiency and reducing operating costs. In recent years, with the in-depth development of unconventional oil and gas, the fracturing of ultra-deep wells has put forward higher requirements for the bridge plug. The existing bridge plug technology includes traditional non-soluble bridge plug, aluminum-magnesium alloy soluble bridge plug, improved aluminum-magnesium alloy, composite material bridge plug and polymer-based bridge plug. However, these existing bridge plug technologies have significant deficiencies in strength, dissolution performance, residue control, sealing performance and process efficiency, and are difficult to meet the requirements of complex working conditions.

[0003] Traditional non-dissolvable bridge plugs are based on high-strength steel, using 4140 alloy steel containing 0.8-1.1wt% chromium and 0.15-0.25wt% molybdenum, with compressive strength up to 800MPa. The bridge plug is cylindrical, with diameter 50-150mm and length 200-400mm, with a fluororubber or nitrile rubber seal ring embedded on the outside, with thickness 5-15mm. The bridge plug relies on mechanical expansion to adhere to the casing (inner diameter 70-200mm) with a sealing pressure of about 90MPa. The preparation process includes hot rolling or forging the base (temperature 1100-1200℃, pressure 50-80MPa), machining the shape on a CNC lathe, and hot pressing the seal ring (temperature 180-220℃, pressure 5-10MPa). The equipment includes a hot rolling machine and a CNC lathe (e.g. Haas, model TL-2, USA). This technology has been widely used in conventional oil and gas wells since the late 20th century. However, the shortcomings of traditional non-dissolvable bridge plugs have significantly limited their application in modern fracturing operations. First, the steel base and rubber seal ring cannot be dissolved downhole and need to be removed by drilling and grinding, which takes 2-5 days and is inefficient. Second, drilling and grinding generates 1-5mm of metal and rubber fragments, increasing the risk of downhole plugging and requiring additional cleaning, which is costly. Third, the rubber seal ring ages at high temperatures (greater than 150℃) or in acidic environments (pH less than 4), reducing the sealing pressure to less than 70MPa, making it difficult to meet the high pressure requirements of ultra-deep wells. Fourth, the forging and multi-step mechanical processing process is complex, with a long production cycle (2-3h per piece) and high cost. In addition, the drilling and grinding fragments need to be treated on the ground, increasing the environmental burden. These shortcomings indicate that traditional non-dissolvable bridge plugs cannot adapt to efficient and low-cost fracturing operations in ultra-deep wells.

[0004] Aluminum-magnesium alloy dissolvable bridge plug is the current mainstream technology, which is composed of aluminum (80-85wt%), magnesium (10-15wt%) and a small amount of zinc, with a grain size of 10-20 pm. The bridge plug is cylindrical, with a diameter of 50-120 mm and a length of 100-250 mm. It has a fluid channel (8-15 mm in diameter) inside and a dissolvable rubber seal (5-10 mm thick) outside. The dissolution time is 7-30 days, the rate is 0.1-2.0 mm / d, the compressive strength is 400-500 MPa, and the sealing pressure is about 70 MPa. The preparation process includes vacuum melting of the alloy, extrusion of the base body, mechanical processing of the shape, and hot pressing of the sealing ring. The equipment includes a vacuum melting furnace and an extruder. Although the aluminum-magnesium alloy bridge plug realizes the dissolvable function, it has significant shortcomings. First, the compressive strength is only 400-500 MPa, which is difficult to withstand the high pressure in ultra-deep wells and is prone to plastic deformation or fracture. Second, the dissolution time is as long as 7-30 days, and the rate fluctuates greatly (0.1-2.0 mm / day), which prolongs the operation cycle and increases the cost due to uneven distribution of alloy components and unstable degradation of polyglycolic acid. Third, the residue particle size is 0.8-1.2 mm, and the residue larger than 1 mm easily blocks the wellbore, which requires additional cleaning. Fourth, the sealing ring degrades too quickly at high temperatures (greater than 150°C) or in acidic environments (pH less than 4), with a sealing pressure of less than 70 MPa, affecting reliability. These shortcomings limit its application in ultra-deep wells.

[0005] The improved alloy bridge plug attempts to improve performance, the base body uses aluminum magnesium alloy, containing 75-80wt% aluminum, 12-18wt% magnesium, 2-5wt% nickel, and the grain size is 8-15μm. The surface is sprayed with polyether ether ketone coating, the thickness is 20-50 microns, and part of the rubber sealing ring is replaced. The bridge plug diameter is 60-150mm, the length is 120-300mm, the internal passage diameter is 10-20mm, and the surface roughness Ra is 0.4-0.8μm. In the downhole environment, the alloy dissolves by corrosion, the polyether ether ketone coating slowly hydrolyzes, the dissolution time is 7-20 days, the rate is 0.2-1.5mm / d, the compressive strength is 550MPa, and the sealing pressure is about 85MPa. The preparation process includes gas atomization preparation of alloy powder (cooling rate 1000-10000℃ / s, particle size 50-100μm), hot isostatic pressing (temperature 450-500℃, pressure 100-120MPa), and flame spraying of polyether ether ketone (temperature 300-350℃). However, the improved alloy bridge plug still has some shortcomings. First, the compressive strength of 550MPa still cannot cope with the high pressure (greater than 100MPa) of ultra-deep wells, and the base body is prone to micro-cracks under high pressure. Second, the polyether ether ketone time. Third, the residual particle size is 0.6-0.9mm, and the polyether ether ketone residue is 0.5-0.7mm, which needs to be cleaned and processed, increasing the cost. Fourth, the hot isostatic pressing process requires high-pressure equipment (100MPa), the production cycle is long (2-3h / piece), the cost is high, and the scale production is limited. These shortcomings show that the improved bridge plug is still not ideal in the application of ultra-deep wells.

[0006] The composite bridge plug is a research direction in recent years, the base body contains 85-90wt% magnesium and 5-10wt% aluminum, and the surface is embedded with zirconia ceramic particles (particle size 50-100nm, content 5-10wt%), with a hardness of about 200 Vickers hardness. The outside is coated with a polyglycolic acid coating, with a thickness of 10-20μm, and there is no middle groove group design. The bridge plug diameter is 70-130mm, and the length is 150-280mm. In the downhole environment, the magnesium-based alloy corrodes rapidly, the polyglycolic acid coating hydrolyzes, the dissolution time is 5-15d, the rate is 0.3-2.5mm / d, the compressive strength is 450-520MPa, and the sealing pressure is about 75MPa. The preparation process includes vacuum melting, mechanical mixing of zirconia particles, extrusion molding, and arc spraying coating. This technology is widely used in shale gas working conditions, and the shortcomings of the composite bridge plug are more obvious. First, the compressive strength of 450-520MPa makes it difficult to meet the high pressure demand of ultra-deep wells. Second, the zirconia particles enhance the hardness but hinder the uniform corrosion of the magnesium-based alloy, making it difficult to control the dissolution time. Third, the magnesium-based alloy residue particle size is 0.7-1.0mm, and the zirconia particle residue is larger, which needs to be cleaned and processed. Fourth, there is no middle groove group design, relying on the coating for sealing, with a sealing pressure of less than 80MPa, which is prone to leakage. These shortcomings limit its application in complex working conditions.

[0007] Polymer-based bridge plug is developed for shallow well, the base body adopts polylactic acid or polyglycolic acid composite material, fiber reinforced (fiber content 20-30wt%), and the outside is coated with polyether ether ketone coating with thickness of 15-30μm. The bridge plug has a diameter of 60-140mm, a length of 100-200mm, and an internal passage diameter of 8-12mm. In the downhole environment, the polymer base body is decomposed by hydrolysis, the dissolution time is 3-10d, the rate is 0.5-3.0mm / d, the compressive strength is 300-400MPa, and the sealing pressure is about 60MPa. The preparation process comprises injection molding of the base body (temperature 200-250℃, pressure 10-20MPa) and thermal spraying of polyether ether ketone (temperature 280-320℃). The technology is also applied to shale gas wells. The disadvantages of the polymer-based bridge plug are particularly prominent. First, the compressive strength is only 300-400MPa, which is only suitable for shallow wells (pressure less than 60MPa) and cannot withstand high pressure in ultra-deep wells. Second, polylactic acid or polyglycolic acid hydrolyzes too fast at high temperature (greater than 140℃), and the dissolution time is difficult to accurately control, which affects the operation plan. Third, the residual particle size is 0.3-0.8mm, and the fiber reinforced material residue is 0.1-0.5mm, which increases the risk of downhole plugging. Fourth, the adhesion of the polyether ether ketone coating is weak (interfacial strength less than 50MPa), the sealing pressure is less than 60MPa, and it is easy to fail. These deficiencies make it impossible to meet the needs of ultra-deep wells.

[0008] Therefore, the common deficiencies of the existing bridge plug technology in ultra-deep well fracturing include that the compressive strength is generally less than 550MPa, it is difficult to withstand pressure greater than 100MPa; the dissolution time is 7-30d, the rate fluctuates greatly (0.1-3.0mm / d), and it is difficult to accurately control; the residual particle size is greater than 0.8mm, which increases the risk of plugging; the sealing pressure is 60-85MPa, and it is easy to fail in high-temperature acidic environment (140-160℃, pH 3.5-4.5); the traditional casting, extrusion or injection molding process is complex, the production efficiency is low, and the cost is high. SUMMARY

[0009] In view of the above problems in the prior art, the present application provides a high-strength nano-hybrid dissolvable bridge plug, a preparation method and application thereof. The bridge plug has high sealing strength, controllable dissolution time, and can adapt to high-temperature high-salt or acidic environment, and the residual particle size after dissolution is small, which can meet the harsh requirements of ultra-deep well fracturing. Moreover, the bridge plug is prepared by one-step forming process, which significantly reduces the production cost.

[0010] In a first aspect, the present invention provides a high-strength nano-hybrid soluble bridge plug, comprising: a bridge plug body including a hollow metal tube, wherein a plurality of annular grooves are formed on the outer surface of the hollow metal tube around the axis of the hollow metal tube; a carbon nitride thin film intermediate layer located on the outer surface of the bridge plug body; and an outermost layer of a polybenzimidazole and nano-silica composite film located on the outer surface of the carbon nitride thin film intermediate layer; wherein the hollow metal tube is made of a zinc-based alloy and is composed of the following components by mass percentage: 5-7% titanium, 2-4% magnesium, 0.5-2% bismuth, with the balance being zinc.

[0011] According to the high-strength nano-hybrid soluble bridge plug of the present invention, the hollow metal tube of the bridge plug body is made of a zinc-based alloy, comprising a zinc-based solid solution and titanium-magnesium-bismuth precipitates, with a grain size of 5~10μm. Titanium strengthens the grains and improves strength through solid solution and precipitates. Magnesium improves toughness and dissolution uniformity, reducing crack propagation. Bismuth promotes galvanic corrosion and accelerates dissolution, resulting in a residue particle size of less than 0.15mm. Specifically, zinc (electrode potential -0.76V) and bismuth (+0.31V) form a micro-cell effect (electrode potential difference 1.07V), accelerating corrosion. This zinc-based alloy material provides the bridge plug with a tensile strength of 450~500MPa and a compressive strength of 700~750MPa, meeting the requirements of ultra-deep well high-pressure fracturing (greater than 100MPa). Compared to traditional aluminum-magnesium alloy bridge plugs with a strength of 400-550 MPa and a residue larger than 0.8 mm after dissolution, zinc-based alloy bridge plugs offer a 30-40% increase in strength and significantly reduce the particle size of the residue after dissolution, resulting in more uniform dissolution. The internal cavity of the metal tube balances internal and external pressures, guides downhole fluid flow, assists in positioning the setting tool, and optimizes stress distribution. The annular grooves on the surface of the hollow metal tube replace traditional rubber seals (such as polyglycolic acid and fluororubber), ensuring a tight fit with the downhole casing (70-150 mm inner diameter) to achieve a mechanical seal. This sealing method achieves a sealing pressure greater than 100 MPa, a 25% improvement over traditional rubber seals, meeting the requirements of high-pressure fracturing in ultra-deep wells, extending operational life, and reducing the risk of failure.

[0012] According to the present invention, the high-strength nano-hybrid soluble bridge plug has a carbon nitride thin film interlayer that forms a metallurgical bond with the bridge plug body through plasma sintering, with an interfacial bonding strength greater than 100 MPa, thus playing a dispersion strengthening role. Compared with traditional ceramic material reinforcement (such as zirconium oxide, with a porosity greater than 10%), nano-carbon nitride has a low density (approximately 2.3 g / cm³). 3It has high hardness and compressive strength (hardness greater than 30 GPa, compressive strength greater than 700 MPa), better resistance to deformation, stronger chemical stability, and its network microporous structure helps to increase the fluid contact area, regulate the dissolution rate to 0.2~1.8 mm / d (140~160℃, 10~20% sodium chloride solution, pH 3.5~6.5), promote corrosion reaction, and its decomposition products are gaseous (such as ammonia and carbon dioxide). The residue particle size is less than 0.15 mm, which helps to reduce solid residue.

[0013] The high-strength nano-hybrid soluble bridge plug of the present invention comprises a polybenzimidazole and nano-silica composite membrane, which is a hybrid membrane material formed by doping nano-silica filler into a polybenzimidazole polymer substrate. It can be adhered to the surface of a carbon nitride film using a conventional thermal spraying process at a spraying temperature of 300-340℃ and a pressure of 0.3-0.5 MPa, achieving a bonding strength greater than 50 MPa. It can withstand downhole ambient temperatures of 140-160℃ and acidic conditions of pH 3.5-6.5, maintaining sealing performance and structural integrity. Specifically, it provides a flexible seal during the initial stage of fracturing operations (6-8 hours), functioning similarly to a traditional rubber sealing ring, ensuring a sealing pressure greater than 100 MPa to meet the high-pressure requirements of ultra-deep wells. Nano-silica enhances the composite membrane's hardness (150-200 Vickers hardness) and corrosion resistance, regulates the contact between the composite membrane and downhole acidic media (such as 10-20% sodium chloride solution, pH 3.5-6.5), and extends the seal's durability. The composite membrane achieves controlled dissolution through acidic hydrolysis, with a dissolution time of 4–12 days, a rate of 0.2–1.8 mm / day, and a residue particle size of less than 0.15 mm, far superior to traditional polyglycolic acid coatings (residue greater than 1 mm) or polyetheretherketone coatings (residue 0.5–0.7 mm). In comparison, the polybenzimidazole and nano-silica composite membrane exhibits higher thermal stability (greater than 400℃) and more uniform degradation. Degradation principle: The benzimidazole units of polybenzimidazole are degraded through acidic hydrolysis in a downhole environment of 140–160℃ and pH 3.5–6.5, generating small molecule products. The degradation rate is regulated by the molecular weight of polybenzimidazole and the content of nano-silica. Nano-silica catalyzes the hydrolysis reaction through surface hydroxyl groups, reducing the activation energy and enhancing acid resistance and mechanical strength.

[0014] In some implementations, the hollow metal tube has a conical cavity inside. In other implementations, the cone angle of the conical cavity is 4–8°, the inlet diameter is 10–14 mm, and the outlet diameter is 6–10 mm. In still other implementations, the hollow metal tube has a diameter of 50–100 mm and a length of 100–200 mm.

[0015] In some embodiments, the annular grooves are located on the outer surface of the middle section of the hollow metal tube, and the number of them is 5 to 12, for example, 5, 6, 8, 10, or 12. In other embodiments, the groove depth is 2 to 4 mm, the groove width is 4 to 8 mm, and the groove spacing is 8 to 12 mm. In still other embodiments, the annular grooves are located 25 to 70 mm from the top and bottom of the hollow metal tube, and the total axial width is 30 to 150 mm. In still other embodiments, the surface roughness Ra of the middle section of the hollow metal tube is less than 0.25 μm, while the top and bottom are smooth surfaces.

[0016] In some implementation examples, the carbon nitride film has a network-reinforced structure with a porosity of 3-6%, for example, 3%, 4%, 5%, or 6%; a pore size of 30-80 nm, for example, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, or 80 nm; and a surface hardness of 250-300 kgf / mm. 2 For example, it could be 250 kgf / mm 2 260kgf / mm 2 270kgf / mm 2 280kgf / mm 2 290kgf / mm 2 300kgf / mm 2 In other implementations, the carbon nitride film consists of nano-carbon nitride particles with a diameter of 10-30 nm dispersed in a single layer or multiple layers on the outer surface of the bridge plug body, with a thickness of 0.2-0.5 mm, for example, 0.2 mm, 0.3 mm, 0.4 mm, or 0.5 mm. The mass of the carbon nitride film accounts for 1.5-2.5% of the total mass of the bridge plug body surface layer.

[0017] In some implementations, the thickness of the polybenzimidazole and nano-silica composite film is 8–15 μm, for example, 8 μm, 10 μm, 12 μm, or 15 μm, with a thickness deviation of less than 1 μm, ensuring uniformity and stability. In other implementations, the surface roughness Ra of the polybenzimidazole and nano-silica composite film is less than 0.2 μm, providing a smooth contact surface and reducing fluid resistance. The polybenzimidazole and nano-silica composite film is bonded to the nano-carbon nitride reinforcement layer on the surface of the bridge plug body through van der Waals forces, forming a stable interface structure that enhances adhesion and durability.

[0018] In some implementation examples, the mass ratio of polybenzimidazole to nano-silica in the polybenzimidazole and nano-silica composite film is 80-90:10-20, for example, 80:10, 85:15, 80:20, 90:10, 90:15, or 90:20. Within this range, decreasing the nano-silica content weakens the catalysis and slows down the degradation; increasing the nano-silica content enhances the catalysis and accelerates the degradation. In other implementation examples, the number-average molecular weight of polybenzimidazole is 3 × 10⁻⁶. 4 ~4.5×10 4 For example, it could be 3×10 4 4×10 4 4.5×10 4 In other implementations, the particle size of nano-silica ranges from 15 to 40 nm. At a particle size of 15 nm, the composite membrane is dense, resulting in slow media permeation; at 40 nm, the micropores increase, leading to faster permeation. Furthermore, the degradation of the composite membrane is primarily affected by pH (faster at 3.5, slower at 6.5) and ion conduction in the sodium chloride solution, with less influence from temperature.

[0019] Secondly, the present invention provides a method for preparing a high-strength nano-hybrid soluble bridge plug, comprising: Step 1: preparing zinc-based alloy powder, wherein the zinc-based alloy is composed of the following components by mass percentage: titanium 5-7%, magnesium 2-4%, bismuth 0.5-2%, with the balance being zinc; Step 2: mixing the zinc-based alloy powder with nano-carbon nitride powder, sintering it in a mold to form a solid cylinder, machining it to form a hollow tubular semi-finished product, and forming multiple annular grooves around the axis of the hollow tubular semi-finished product on the outer surface of the hollow tubular semi-finished product; Step 3: preparing a slurry containing polybenzimidazole powder and nano-silica powder, spraying the slurry onto the surface of the hollow tubular semi-finished product, and drying it to obtain a high-strength nano-hybrid soluble bridge plug.

[0020] In some implementation examples, step 1 includes: weighing zinc ingots, titanium particles, magnesium ingots, and bismuth particles according to a specified ratio, heating them in a vacuum induction furnace to 650~720℃, holding at that temperature for 20~30min, introducing argon gas with a purity greater than 99.99% to a furnace pressure of 0.05~0.1MPa, and electromagnetically stirring at 100~200r / min to form a melt; pouring the melt into an inert gas atomization tower, and spraying high-pressure argon gas through a stainless steel nozzle (orifice diameter 0.5~1.0mm) to prevent oxidation, with a nozzle pressure of 0.7~0.9MPa, an argon flow rate of 20~50L / min, a melt superheating temperature of 680~740℃, and a cooling rate of 100~1000℃ / s to atomize the melt into droplets, which are then rapidly cooled and solidified into powder. The powder is placed on a vibrating screen with a mesh size of 30~100μm to separate powder with a particle size of 30~90μm. The sieved powder was placed in a vacuum drying oven at a temperature of 80-100℃ for 2-4 hours, with a vacuum level below 0.1 Pa. After drying, it was sealed and stored. Vacuum melting ensured uniform alloy composition and prevented oxidation. High-pressure argon gas atomized the melt into droplets and rapidly cooled it to form micron-sized powder (5-10 μm grains), facilitating subsequent plasma sintering. Sieving controlled particle size consistency, and drying prevented the powder from becoming damp.

[0021] In some implementation examples, step 2 includes: mixing zinc-based alloy powder and nano-carbon nitride powder and ball milling them at a ball-to-powder mass ratio of 8:1 to 12:1, a ball milling speed of 250 to 450 r / min, and a time of 15 to 35 min to obtain a mixed powder. The mixed powder is dried at 80 to 100℃ under a vacuum of less than 0.1 Pa for 2 to 4 hours, then placed in a mold and sintered in a plasma sintering furnace to form a solid cylinder. The sintering conditions include: evacuating to a pressure below 0.01 Pa, applying an axial pressure of 35 to 45 MPa, heating to 460 to 480℃ at a heating rate of 80 to 120℃ / min, and holding at that temperature for 8 to 12 min. The solid cylinder is then clamped onto a CNC lathe, fitted with a tapered drill bit (taper angle 4 to 8°), set at a speed of 700 to 1300 r / min and a feed rate of 0.08 to 0.35 mm / revolution, cooled using a water-based emulsion, and a tapered channel is machined. Replace the carbide turning tool (tip radius 0.2~0.4mm), set the rotation speed to 500~1100r / min, feed rate to 0.04~0.25mm / rpm, use water-based emulsion for cooling, and machine 5~12 annular grooves in the center. Then place it in a polishing machine, using a grinding wheel (1800~2200 mesh) or a phosphate-based chemical polishing slurry (10~20%wt concentration), and polish for 5~10 minutes to achieve a surface roughness Ra less than 0.25μm. Ball milling ensures uniform dispersion of nano-carbon nitride, plasma sintering forms the nano-carbon nitride in one step and embeds it into the surface layer, CNC machining ensures geometric accuracy, and polishing enhances coating adhesion. The sintering temperature is 460~480℃, lower than the melting point of zinc-based alloys (approximately 600℃), to avoid decomposition of the nano-carbon nitride; an axial pressure of 35~45MPa is applied via a hydraulic pressure plate to ensure metallurgical bonding.

[0022] In some implementation cases, step 3 includes: mixing polybenzimidazole (PBI) powder, nano-silica powder, and... N,NA stable and uniform slurry is prepared by mixing dimethylacetamide and ultrasonically treating it (frequency 35-45 kHz, power 150-250 W) for 20-30 min. The slurry is then uniformly coated onto the outer surface of the hollow tubular semi-finished product using flameless air spraying, scraping, or spin coating to form a wet film. Pre-baking at 60-120 °C (10-60 min) is preferred to remove low-boiling components; followed by drying in a vacuum drying environment (absolute pressure ≤1000 Pa, preferably 200-800 Pa) at 80-120 °C for 2-12 h to further remove solvents and reduce internal stress; then heat treatment / densification is performed at 200-260 °C for 2–6 h (preferably 220-240 °C for 3–4 h) to promote the formation of a dense and continuous PBI film. The final coating thickness is 8-15 μm, with a surface roughness Ra of approximately 0.2 μm, exhibiting good density and solvent resistance. Ultrasonic mixing helps to uniformly disperse nano-silica in high-viscosity systems; graded drying and heat treatment effectively avoid solvent residue and coating cracking. The cured coating has initial flexible sealing ability (68 h), and its dissolution time can be controlled between 4 and 12 days through formulation.

[0023] In some implementation cases, the mass ratio of polybenzimidazole powder to nano-silica powder in the slurry is 80~90:10~20, for example, it can be 80:10, 85:15, 80:20, 90:10, 90:15, or 90:20. The total mass of polybenzimidazole powder and nano-silica powder accounts for 88~92% of the slurry mass, for example, it can be 88%, 89%, 90%, 91%, or 92%.

[0024] In some implementation cases, the particle size of nano carbon nitride is 10~30nm, for example, it can be 10nm, 12nm, 16nm, 18nm, 20nm, 22nm, 24nm, 26nm, 28nm, or 30nm.

[0025] In some implementations, the particle size of nano-silica is 15~40nm, for example, it can be 15nm, 20nm, 25nm, 30nm, 35nm, or 40nm.

[0026] Thirdly, the present invention provides a high-strength nano-hybrid soluble bridge plug prepared by the aforementioned method.

[0027] Fourthly, the present invention provides the application of the aforementioned high-strength nano-hybrid soluble bridge plug in staged fracturing operations in the oil and gas industry.

[0028] The beneficial effects of this invention are as follows:

[0029] The bridge plug provided by this invention has the following characteristics: (1) Ultra-high sealing strength: tensile strength 450~500MPa, compressive strength 700~750MPa, which is 30~40% higher than that of traditional aluminum-magnesium alloy bridge plugs. The annular groove structure and the polybenzimidazole and nano-silica composite film coating on its surface provide a sealing pressure close to 100MPa, which is 25% higher than that of traditional rubber seals. It ensures the sealing reliability of ultra-deep well high-pressure fracturing operations, extends the service life, and reduces the risk of failure. (2) Controllable dissolution time: the dissolution time can be precisely controlled within 4~12 days, with a dissolution rate of 0.2~1.8mm / d, which is suitable for high temperature, high salt or acidic environments (140~160℃, 10~20% sodium chloride, pH 3.5~6.5), which shortens the dissolution time by 40~60% compared with the existing technology. It is beneficial to improve the efficiency of fracturing operations, reduce downhole waiting time, and reduce operating costs. (3) Extremely small residue particle size: Ensures that the residue particle size after dissolution is less than 0.15 mm, which is more than 80% smaller than the existing technology (greater than 0.8 mm). This significantly reduces the risk of downhole blockage, eliminates the need for additional cleaning, and lowers operating costs.

[0030] The preparation method provided by this invention forms the substrate and reinforcing layer in one step through plasma sintering, reducing the number of process steps by 20-30% compared to traditional casting. Precision and consistency are ensured by CNC machining of the annular groove and thermal spraying of the coating. This preparation method greatly improves production efficiency and product quality stability, making it suitable for industrial production. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] Example 1: High-strength, rapid-dissolving bridge plug

[0033] 1. Purpose

[0034] A bridge plug with high compressive strength and a dissolution time of about 6 days was prepared, which is suitable for rapid fracturing operations.

[0035] 2. Shape and Structure

[0036] Matrix: Cylindrical, 80mm in diameter, 150mm in length, grain size 5~7μm. Internal conical channel (cone angle 6°, inlet diameter 12mm, outlet diameter 8mm). Eight annular grooves on the outer surface of the middle section (groove depth 3mm, groove width 6mm, groove spacing 10mm, total axial width 80mm, distance from top and bottom 35mm each), surface roughness Ra 0.2μm.

[0037] Reinforcing layer: 2.0 wt% nano-carbon nitride (particle size 10~20 nm) (relative to the total mass of the surface layer), embedded 0.3 mm into the substrate surface, with a porosity of 4% and a pore size of 40~60 nm. It has a network structure, a surface hardness of 280 Vickers, and is metallurgically bonded to the substrate with an interfacial strength of 120 MPa.

[0038] Coating: Polybenzimidazole (molecular weight 3×10) 4 The coating consists of 85 wt% nano-silica (20 nm particle size) and 15 wt% nano-silica, with a thickness of 10 μm. It uniformly covers the substrate surface and grooves, with a roughness Ra of 0.15 μm and a thickness deviation of less than 0.8 μm.

[0039] 3. Preparation process

[0040] Step 1: Alloy Powder Preparation

[0041] Weigh 90 kg of high-purity zinc ingots (99.9% purity), 6 kg of titanium granules (99.8% purity), 3.5 kg of magnesium ingots (99.8% purity), and 0.5 kg of bismuth granules (99.9% purity). Place them in a vacuum induction furnace (graphite crucible, capacity 100 kg), evacuate to 0.008 Pa, purge with argon gas (99.99% purity) to 0.08 MPa, heat to 680 ℃, stir electromagnetically at 150 r / min, and hold for 25 min.

[0042] The melt was poured into an inert gas atomization tower, and argon gas (pressure 0.8MPa, flow rate 30L / min) was injected through a stainless steel nozzle (orifice diameter 0.8mm). The melt was superheated to 720℃ and cooled at a rate of 500,000℃ / second to prepare powder with a particle size of 30~70μm. The powder was then dried (90℃, vacuum degree 0.08Pa, 3h) to obtain alloy powder.

[0043] Step 2: Matrix molding and reinforcement layer embedding

[0044] Weigh 2 kg of alloy powder and 40 g of nano carbon nitride powder (particle size 10~20 nm, purity 99.5%), place them in a high-speed planetary ball mill (stainless steel jar, 1 L), add cemented carbide grinding balls (ball-to-material mass ratio 10:1), dry mix at 350 r / min for 20 min, and dry (90 ℃, vacuum degree 0.08 Pa, 3 h) to obtain mixed powder.

[0045] Graphite lubricant was applied to the inner wall of a high-purity, dense graphite mold (80mm inner diameter, formed by high temperature and high pressure molding of graphite powder), mixed powder was filled in, and compacted to 85% of the mold volume. The mold was placed in a plasma sintering furnace, evacuated to 0.008Pa, and subjected to 40MPa hydraulic pressure. The mold was heated to 470℃ (heating rate 100℃ / min), held for 10min, allowed to cool naturally, and the substrate (80mm diameter, 150mm length) was removed.

[0046] The conical channel (cone angle 6°, speed 1000r / min, feed rate 0.2mm / revolution, water-based emulsion cooling) and eight annular grooves (groove depth 3mm, groove width 6mm, speed 800r / min, feed rate 0.1mm / revolution) on the middle outer surface are machined on a CNC lathe and polished to a roughness Ra of 0.2μm (grind wheel 2000 mesh, polishing for 8min).

[0047] Step 3: Coating application

[0048] Weigh out 0.85 kg of polybenzimidazole powder (99% purity) and 0.15 kg of nano-silica (99.5% purity), and add... N, N Dimethylacetamide (10 wt%) was ultrasonically dispersed (40 kHz, 200 W, 25 min) to obtain a slurry. The substrate was preheated to 110 °C, and the slurry was uniformly coated onto the outer surface of the substrate obtained in step 2 using a flameless air spraying method to form a wet film. The film was first pre-baked at 85 °C for 30 min to remove low-boiling components; then placed in a vacuum drying environment (750 Pa) and dried at 90 °C for 10 h to further remove solvents and reduce internal stress; subsequently, heat treatment / densification was performed at 220 °C for 3 h to promote the formation of a dense and continuous PBI film. The final coating thickness was 10 μm, with a surface roughness Ra of approximately 0.2 μm, exhibiting good density and solvent resistance.

[0049] 4. Performance Testing

[0050] High-temperature and high-pressure reactor (150 ℃, 110 MPa, 15% sodium chloride, pH 4.5), tested for 6 days, dissolution rate 1.2 mm / d. Residue particle size 0.04 mm (laser scattering method). Compressive strength 740 MPa (loading rate 0.8 mm / min, 20 ℃).

[0051] Example 2: Moderate strength dissolved bridge plug

[0052] 1. Purpose

[0053] A bridge plug with a high compressive strength of approximately 720 MPa and a dissolution time of approximately 10 days was prepared, which is suitable for conventional ultra-deep wells.

[0054] 2. Shape and Structure

[0055] Matrix: 60mm in diameter, 180mm in length, grain size 6~8μm. Conical channel (cone angle 5°, inlet diameter 10mm, outlet diameter 7mm). Ten annular grooves on the outer surface of the middle section (groove depth 2.5mm, groove width 5mm, groove spacing 9mm, total axial width 90mm, distance from top and bottom 45mm each), roughness Ra 0.22μm.

[0056] Reinforcing layer: 1.8wt% nano-carbon nitride (particle size 15~25nm) (relative to the total mass of the surface layer), embedded 0.4mm into the surface layer, with a porosity of 5% and a pore size of 50~70nm. Hardness 270 Vickers hardness, bonding strength 115MPa.

[0057] Coating: Polybenzimidazole (molecular weight 4.5×10⁻⁶) 4 The coating consists of 88 wt% nano-silica (30 nm particle size) and 12 wt% nano-silica, with a coating thickness of 12 μm. The roughness Ra is 0.18 μm, and the thickness deviation is less than 0.9 μm.

[0058] 3. Preparation process

[0059] Step 1: Alloy Powder Preparation

[0060] Weigh out 88 kg of zinc ingots, 7 kg of titanium particles, 3 kg of magnesium ingots, and 2 kg of bismuth particles, and melt them (700 ℃, 0.07 MPa argon gas, stirring 180 r / min, holding for 22 min). Then, atomize the mixture (0.7 mm nozzle, 0.85 MPa pressure, 35 L / min flow rate, 730 ℃ superheating temperature, 300000 ℃ / s cooling rate) to prepare powder with a particle size of 40~80 μm. Dry the powder (85 ℃, 0.09 Pa, 3.5 h) to obtain alloy powder.

[0061] Step 2: Matrix molding and reinforcement layer embedding

[0062] Weigh 1.5 kg of alloy powder and 27 g of nano carbon nitride, wet mix (ethanol, 300 r / min, 25 min), and dry (85 ℃, 0.09 Pa, 3 h). Fill the mold (60 mm inner diameter) with powder, sinter (465 ℃, 42 MPa, heating rate 90 ℃ / min, holding for 11 min), machine a conical channel (900 r / min, feed 0.15 mm / revolution) and 10 annular grooves on the outer surface of the middle (700 r / min, feed 0.08 mm / revolution), and polish (15 wt% chemical polishing solution, 7 min, Ra 0.22 μm).

[0063] Step 3: Coating application

[0064] Weigh out 0.88 kg of polybenzimidazole and 0.12 kg of nano-silica, and add... N,N Dimethylacetamide (10 wt%) was ultrasonically dispersed (38 kHz, 180 W, 22 min) to obtain a slurry. The slurry was then uniformly coated onto the outer surface of the substrate obtained in step 2 using a blade coating method to form a wet film. The film was first pre-baked at 70 °C for 15 min to remove low-boiling components; then placed in a vacuum drying environment (600 Pa) and dried at 90 °C for 11 h to further remove solvents and reduce internal stress; subsequently, heat treatment / densification was performed at 260 °C for 6 h to promote the formation of a dense and continuous PBI film. The film exhibits good densification and solvent resistance.

[0065] 4. Performance Testing

[0066] Test (155 ℃, 105 MPa, 12% sodium chloride, pH 5.0), dissolution 10 days, rate 0.8 mm / d, residue 0.045 mm, compressive strength 720 MPa.

[0067] Example 3 High-strength long dissolution bridge plug

[0068] 1. Purpose

[0069] A bridge plug with high compressive strength and a dissolution time of about 12 days was prepared, which is suitable for high-intensity and long-cycle operations.

[0070] 2. Shape and Structure

[0071] Matrix: 100mm in diameter, 200mm in length. Conical channel (7° cone angle, 14mm inlet diameter, 10mm outlet diameter), grain size 7~9μm. 12 annular grooves on the outer surface of the middle section (groove depth 4mm, groove width 8mm, groove spacing 12mm, total axial width 120mm, 40mm from the top and bottom each), roughness Ra 0.18μm.

[0072] Reinforcing layer: 2.5wt% nano-carbon nitride (particle size 20~30nm) (relative to the total mass of the surface layer), embedded 0.5mm into the surface layer, with a porosity of 3.5% and a pore size of 60~80nm. Hardness 290 Vickers hardness, bonding strength 130MPa.

[0073] Coating: Polybenzimidazole (molecular weight 4.5×10⁻⁶) 4 90wt% of nano-silica (40nm particle size) and 10wt% of coating thickness. Roughness Ra 0.12μm, thickness deviation less than 0.7μm.

[0074] 3. Preparation process

[0075] Step 1: Powder Preparation

[0076] Weigh 92 kg of zinc ingots, 5 kg of titanium particles, 2.5 kg of magnesium ingots, and 0.5 kg of bismuth particles, and melt them (710 ℃, 0.06 MPa argon gas, stirring 200 r / min, holding for 20 min). Atomize the mixture (1.0 mm nozzle, 0.9 MPa pressure, 40 L / min flow rate, 740 ℃ superheating temperature, 800000 ℃ / s cooling rate) to prepare powder with a particle size of 50~90 μm. Dry the powder (95 ℃, 0.07 Pa, 4 h) to obtain alloy powder.

[0077] Step 2: Matrix molding and reinforcement layer embedding

[0078] Weigh 3 kg of alloy powder and 75 g of nano carbon nitride, dry mix (400 r / min, 30 min), and dry (95 ℃, 0.07 Pa, 4 h). Fill the mold (100 mm inner diameter) with powder, sinter (480 ℃, 45 MPa, heating rate 110 ℃ / min, holding for 12 min), machine a conical channel (1100 r / min, feed 0.25 mm / revolution) and 12 annular grooves on the outer surface of the middle (900 r / min, feed 0.12 mm / revolution), and polish (2200 mesh grinding wheel, 9 min, Ra 0.18 μm).

[0079] Step 3: Coating application

[0080] Weigh out 1.8 kg of polybenzimidazole and 0.2 kg of nano-silica, and add... N,N Dimethylacetamide (10 wt%) was ultrasonically dispersed (45 kHz, 220 W, 28 min) to obtain a slurry. The slurry was then spin-coated uniformly onto the outer surface of the substrate obtained in step 2 to form a wet film. The film was first pre-baked at 65 °C for 10 min to remove low-boiling components; then placed in a vacuum drying environment (300 Pa) and dried at 85 °C for 8 h to further remove solvents and reduce internal stress; subsequently, heat treatment / densification was performed at 210 °C for 2 h to promote the formation of a dense and continuous PBI film. The final coating exhibited good density and solvent resistance.

[0081] 4. Performance Testing

[0082] Tests (160 ℃, 120 MPa, 18% sodium chloride, pH 4.0), dissolution time 12 days, dissolution rate 0.5 mm / d, residue 0.03 mm, compressive strength 750 MPa.

[0083] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

Claims

1. A high-strength nano-hybrid soluble bridge plug, characterized in that, The bridge plug includes: Bridge plug body: includes a hollow metal tube, and multiple annular grooves are formed on the outer surface of the hollow metal tube around the axis of the hollow metal tube; Carbon nitride thin film intermediate layer: located on the outer surface of the bridge plug body; and, The outermost layer of the polybenzimidazole and nano-silica composite film: located on the outer surface of the intermediate layer of the carbon nitride film; The hollow metal tube is made of zinc-based alloy and consists of the following components by mass percentage: 5-7% titanium, 2-4% magnesium, 0.5-2% bismuth, with the balance being zinc.

2. The high-strength nano-hybrid soluble bridge plug according to claim 1, characterized in that, The hollow metal tube has a conical cavity inside; And / or; the annular groove is located on the outer surface of the middle part of the hollow metal tube; And / or; the number of the annular grooves is 5 to 12.

3. The high-strength nano-hybrid soluble bridge plug according to claim 2, characterized in that, The cone angle of the conical cavity is 4~8°, the inlet diameter is 10~14mm, and the outlet diameter is 6~10mm; And / or; the groove depth of the annular groove is 2~4mm, the groove width is 4~8mm, and the groove spacing is 8~12mm.

4. The high-strength nano-hybrid soluble bridge plug according to claim 1, characterized in that, The thickness of the carbon nitride film is 0.2~0.5 mm; And / or; the porosity of the carbon nitride film is 3~6%, and the pore size is 30~80nm.

5. The high-strength nano-hybrid soluble bridge plug according to claim 1, characterized in that, The thickness of the polybenzimidazole and nano-silica composite film is 8~15μm; And / or; in the polybenzimidazole and nano-silica composite film, the mass ratio of polybenzimidazole to nano-silica is 80~90:10~20; And / or; the number-average molecular weight of the polybenzimidazole is 3 × 10⁻⁶. 4 ~4.5×10 4 ; And / or; the particle size of the nano-silica is 15~40nm.

6. A method for preparing a high-strength nano-hybrid soluble bridge plug, characterized in that, The preparation method includes: Prepare zinc-based alloy powder, wherein the zinc-based alloy is composed of the following components by mass percentage: 5-7% titanium, 2-4% magnesium, 0.5-2% bismuth, and the balance being zinc; Zinc-based alloy powder is mixed with nano carbon nitride powder and sintered in a mold to form a solid cylinder. The cylinder is then machined to form a hollow tubular semi-finished product. Multiple annular grooves are formed on the outer surface of the hollow tubular semi-finished product around its axis. A slurry containing polybenzimidazole powder and nano-silica powder is prepared, and the slurry is sprayed onto the surface of a hollow tubular semi-finished product and dried to obtain the high-strength nano-hybrid soluble bridge plug.

7. The preparation method according to claim 6, characterized in that, The plasma sintering conditions include: being carried out under vacuum conditions, with a pressure of 35~45MPa, a temperature of 460~480℃, and a holding time of 8~12min.

8. The preparation method according to claim 6, characterized in that, In the slurry, the mass ratio of polybenzimidazole powder to nano-silica powder is 80~90:10~20, and the total mass of polybenzimidazole powder and nano-silica powder accounts for 88~92% of the mass of the slurry. And / or, the particle size of the nano-carbon nitride is 10~30nm; And / or, the particle size of the nano-silica is 15~40nm.

9. The high-strength nano-hybrid soluble bridge plug prepared by the method according to any one of claims 6 to 8.

10. The application of the high-strength nano-hybrid soluble bridge plug according to any one of claims 1 to 5, and claim 9 in staged fracturing operations in the oil and gas industry.