A downhole high-temperature composite fiber Bragg grating sensor and its manufacturing method

Abstract

The present invention discloses an underground high-temperature composite fiber Bragg grating sensor and a manufacturing method thereof. The manufacturing method comprises the following steps: placing a pressure-measuring fiber Bragg grating with a surface coated with polyimide in a hot pressing mold, and then laying a glass fiber composite material substrate layer by layer on the pressure-measuring fiber Bragg grating; placing the hot pressing mold in a hot pressing furnace for pre-curing and secondary curing; placing glass powder in the concave groove at the liquid inlet of the base, welding the glass fiber composite material substrate to the base, and the temperature-measuring fiber Bragg grating to the L-shaped cantilever beam; connecting the base and the L-shaped cantilever beam to the sealing seat. The present invention adopts an optical fiber with a high-temperature resistant polyimide coating layer, and adopts a femtosecond laser through-coating writing process to obtain a fiber Bragg grating, thereby ensuring that the optical fiber coating layer will not be burned when welding with low-melting-point glass solder. The composite diaphragm obtained by encapsulating using the pre-curing and secondary curing processes meets the measurement requirements under special underground environments.

Description

Technical Field

[0001] The invention relates to an underground high-temperature composite material optical fiber Bragg grating sensor and a manufacturing method thereof, and belongs to the field of optical fiber sensing. Background Art

[0002] A fiber Bragg grating (FBG) is a diffraction grating formed by periodic axial modulation of its refractive index. It is a passive filter device. While it offers excellent properties such as light weight, compact size, corrosion resistance, and immunity to electromagnetic interference, its small core diameter makes it fragile and susceptible to breakage and inactivation in practical engineering applications. Therefore, the bare FBG requires packaging or performance enhancement. However, the results obtained from different packaging treatments or performance enhancements can vary significantly. Choosing packaging materials with high-performance parameters and appropriate packaging processes can produce high-performance fiber Bragg grating sensors.

[0003] Currently, the two most common FBG packaging methods are narrow-necked tube protection and substrate-based packaging. The former places the FBG on the central axis of a narrow-necked stainless steel tube, secured and protected by a colloid such as epoxy resin. This packaging method is complex and difficult to maintain, and the adhesive performance requirements vary under different usage conditions, further complicating the packaging process. The latter typically uses an adhesive-based substrate or a grooved steel plate as the base, onto which the FBG is bonded, creating a substrate-based sensor. In comparison, the FBG substrate-based packaging process is simpler, with a simple structure, easy installation, and convenient disassembly, and is widely used.

[0004] There are also various packaging options for substrate protection. While metal-substrate FBG sensors offer a simple structure and easy installation, the inherent corrosion susceptibility of metal presents limitations and cost issues in engineering applications. Furthermore, when the structure to be measured is very small, the surface-mounted metal-substrate FBG sensor acts as a reinforcing rib, affecting measurement results. While resin-substrate FBG sensors offer good corrosion resistance, their strength, modulus, and shear resistance are relatively low, and they cannot be used in high-temperature environments. Summary of the Invention

[0005] The purpose of the present invention is to provide a downhole high-temperature composite fiber Bragg grating sensor and a manufacturing method thereof, which aims to solve the existing packaging problem of sensors in special environments such as downhole high temperature and high pressure.

[0006] The present invention provides a method for manufacturing a downhole high-temperature composite fiber Bragg grating sensor, comprising the following steps:

[0007] S1, placing a pressure-measuring fiber Bragg grating coated with polyimide in a hot pressing mold, and then laying a glass fiber composite material substrate layer by layer on the pressure-measuring fiber Bragg grating;

[0008] S2, placing the hot pressing mold in a hot pressing furnace for pre-curing;

[0009] S3, performing secondary curing on the pressure-measuring fiber Bragg grating processed in step S2;

[0010] S4, placing glass powder in the concave groove at the liquid inlet of the base, welding the glass fiber composite material substrate to the base, and welding the temperature measuring fiber Bragg grating to the L-shaped cantilever beam;

[0011] S5. Connect the base, the L-shaped cantilever beam and the sealing seat.

[0012] In the above-mentioned manufacturing method, in step S1, before coating the polyimide, the pressure-measuring fiber Bragg grating is subjected to high-temperature annealing.

[0013] In the above-mentioned manufacturing method, in step S1, the material of the hot pressing mold is nickel alloy, and its size can be designed according to actual needs.

[0014] In the above-mentioned manufacturing method, in step S1, the glass fiber composite material substrate is obtained by compression molding glass fiber / polyimide prepreg.

[0015] In the above-mentioned manufacturing method, in step S2, the pre-curing process is as follows:

[0016] The hot pressing furnace is evacuated, the temperature is raised to 130-800° C., the glass fiber composite material substrate is sintered after the hot pressing furnace is heated for 60-120 minutes, and then the polyimide cured at room temperature is vacuum-assisted infused. After the vacuum-assisted infusion process is completed, the polyimide is naturally cooled at room temperature for 6-8 hours and then taken out;

[0017] During the pre-curing, the pressure of the hot pressing furnace is 0.5-15 MPa, and the vacuum degree is 20-100 Pa.

[0018] In the above-mentioned manufacturing method, in step S3, the secondary curing is carried out in the hot pressing furnace, and the curing is carried out at a constant temperature of 130-135° C. for 90-100 minutes.

[0019] In the above-mentioned manufacturing method, in step S4, the glass powder is low-temperature and low-melting-point glass powder; and the material of the base and the L-shaped cantilever beam is nickel alloy.

[0020] In the above-mentioned manufacturing method, in step S4, the welding is performed by glass welding, and the steps are as follows:

[0021] The surfaces of the base and the L-shaped cantilever beam are cleaned by mechanical purification, degreasing, chemical or electrochemical cleaning and drying; then hydrogen burning treatment is performed and the sealing parts are oxidized; during the oxidation treatment, the degree of oxidation must be strictly controlled and the thickness of the oxide film must be moderate; after adding the glass powder, the temperature is placed in a heating box and raised to 270-380°C, maintained for 60-70 minutes, and then naturally cooled to room temperature.

[0022] In the above-mentioned manufacturing method, in step S5, laser welding is used for connection.

[0023] This invention utilizes optical fibers with high-temperature-resistant polyimide coatings and a femtosecond laser through-coating inscription process to produce fiber Bragg gratings (FBGs), ensuring that the fiber coating is not burned during welding with low-melting-point glass solder. Furthermore, a glass fiber composite laminate serves as the substrate, with dry fiberglass cloth applied over the substrate and liquid polyesterimide vacuum-infused into the substrate. The resulting composite membrane, encapsulated using these pre-curing and post-curing processes, meets the measurement requirements of underground mines. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a cross-sectional view of the completed packaging of the downhole high-temperature composite fiber Bragg grating sensor of the present invention.

[0025] Figure 2 It is a schematic diagram of the layout and structure of a fiber Bragg grating and a glass material composite material substrate coated with polyimide inside a hot pressing mold provided by an embodiment of the present invention.

[0026] Figure 3 It is a schematic diagram of an integrated packaged fiber Bragg grating composite material diaphragm provided by an embodiment of the present invention.

[0027] Among them: 1 is a glass fiber composite material substrate, 2 is a base, 3 is an outer cover, 4 is a sealing seat, 5 is an L-shaped cantilever beam, 6 is a sealing seat, 7 is a liquid inlet, 8 is a connector, 9 is a connector, 10 is a pressure measuring fiber Bragg grating, and 11 is a temperature measuring fiber Bragg grating. DETAILED DESCRIPTION

[0028] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0029] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0030] The method for manufacturing a downhole high-temperature composite fiber Bragg grating sensor provided by the present invention mainly includes the following steps:

[0031] S1, coating polyimide on the surface of the pressure measuring fiber Bragg grating 10;

[0032] S2, placing a polyimide-coated pressure-measuring fiber Bragg grating in a designed hot-pressing mold;

[0033] S3, laying the glass fiber composite material substrate 1 layer by layer on the grating in the hot pressing mold;

[0034] S4, placing it in a vacuum hot pressing furnace for compression molding using a pre-curing molding process (partial curing of polyimide);

[0035] S5, performing secondary curing after the pressure measuring fiber Bragg grating packaging is completed to release the residual stress;

[0036] S6, placing glass powder in the concave groove at the liquid inlet 7 of the base 2, and welding the glass fiber composite material substrate 1 and the base 2, as well as the temperature measuring fiber Bragg grating 11 and the L-shaped cantilever beam 5 using a high temperature curing process;

[0037] S7, connect the base 2 and the sealing seat 4, the base 2 and the sealing seat 6, and the sealing seat and the L-shaped cantilever beam 5 by laser welding.

[0038] In step S1, the pressure measuring optical fiber is a PI-coated carbon optical fiber.

[0039] In step S1, the pressure-measuring fiber Bragg grating adopts a pressure-measuring fiber Bragg grating that has been subjected to high-temperature annealing treatment.

[0040] In step S2, the mold is made of high-temperature resistant nickel alloy, and its size can be designed according to actual needs.

[0041] In step S3 , the glass fiber composite material substrate 1 is obtained by compression molding of glass fiber / polyimide prepreg.

[0042] In step S4, the pre-curing process steps are: evacuating the hot press furnace, heating it to 130-800°C, sintering the glass fiber layered composite material after the hot press furnace is 60-120 minutes, and then vacuum-assisted infusion is performed to cure the polyimide at room temperature. After the vacuum-assisted infusion process is completed, the glass fiber layered composite material is naturally cooled at room temperature for 6-8 hours and taken out; the pressure of the hot press furnace in the pre-curing process step is 0.5-15MPa, and the vacuum degree is 20-100Pa.

[0043] In step S5, the secondary curing step is: placing the preformed fiber Bragg grating composite material membrane in a hot press furnace for secondary curing without adding any external additives during the curing process, keeping the membrane at a constant temperature of 130° C. for 90 minutes, then taking it out and cutting it.

[0044] In step S6, the base 2 and the L-shaped cantilever beam 5 are made of a high-temperature resistant nickel alloy, whose thermal expansion coefficient is similar to that of the optical fiber, glass solder and composite material.

[0045] In step S6 , the glass solder is low-temperature and low-melting-point glass powder.

[0046] In step S6, the glass welding process steps are as follows: the surfaces of the base and the L-shaped cantilever beam are cleaned by mechanical purification, degreasing, chemical or electrochemical cleaning and drying; then hydrogen burning treatment is performed and the sealing parts are oxidized. During the oxidation treatment, the degree of oxidation must be strictly controlled and the thickness of the oxide film must be moderate; finally, different sealing processes are selected according to the structural characteristics of the sealing parts. Here, the glass powder is placed in a designed groove, and then placed in a heating box and heated to 270-380°C. After maintaining for a period of time, it is naturally cooled to room temperature.

[0047] In step S7 , laser welding uses a continuous laser beam to complete the connection of the materials.

[0048] Example 1: Fabrication of Downhole High-Temperature Composite Fiber Bragg Grating Sensor

[0049] S1. Annealing the polyimide coated grating to further improve the high temperature resistance of the fiber Bragg grating. The annealing temperature is 950-1200°C and the annealing time is 1-3 hours. After annealing, the fiber Bragg grating can withstand a maximum temperature of 1200°C.

[0050] S2. Preparation of glass fiber composite substrate: Cut glass fiber prepreg and release cloth with a size of 100×100 mm, with the glass fibers in the prepreg being woven orthogonally; then neatly lay the release cloth on the lower template, lay multiple layers of glass fiber prepreg on it, and then lay another layer of release cloth on it, and finally cover the template; place the above device in a vulcanizer for hot pressing and naturally cool to obtain a glass fiber composite substrate ( Figure 3 shown).

[0051] S3, laying the composite material substrate obtained in the above steps on the upper and lower sides of the pressure measuring fiber Bragg grating, as shown in FIG. Figure 2 The glass fiber layered composite material is then placed in a hot press mold, the hot press furnace is evacuated, the temperature is raised to 130-800°C, and the hot press furnace is heated for 60-120 minutes to sinter the glass fiber layered composite material. Subsequently, vacuum-assisted infusion is performed to cure polyimide at room temperature. After the vacuum-assisted infusion process is completed, the glass fiber layered composite material is naturally cooled at room temperature for 6-8 hours and then removed. Subsequently, the preformed fiber Bragg grating composite film is placed in a hot press furnace for secondary curing. No external additives are added during the curing process. The film is kept at a constant temperature of 130°C for 90 minutes, then removed and cut.

[0052] S4. Clean the surface of the base and L-shaped cantilever beam by mechanical purification, degreasing, chemical or electrochemical cleaning and drying; then perform hydrogen burning treatment and oxidation treatment on the sealing parts. When performing oxidation treatment, the degree of oxidation must be strictly controlled and the thickness of the oxide film must be moderate; finally, different sealing processes are selected according to the structural characteristics of the sealing parts. Here, the glass powder is placed in the designed groove, and then placed in a heating box to heat it to 270-380℃, keep it for a period of time, and then cool it naturally to room temperature.

[0053] S5. Connect and seal the remaining components by laser welding.

[0054] like Figure 1 The figure shows a cross-sectional view of the completed underground high-temperature composite fiber Bragg grating sensor package. It can be used in harsh underground environments such as high temperature, high pressure, acid and alkali corrosion, and has excellent sealing and accuracy.

Claims

1. A method for manufacturing a downhole high-temperature composite fiber Bragg grating sensor, comprising the following steps: S1, placing a pressure-measuring fiber Bragg grating coated with polyimide in a hot pressing mold, and then laying a glass fiber composite material substrate layer by layer on the pressure-measuring fiber Bragg grating; The hot pressing mold is made of nickel alloy; The glass fiber composite material substrate is obtained by compression molding of glass fiber / polyimide prepreg; Before coating the polyimide, the pressure-measuring fiber Bragg grating is subjected to high-temperature annealing treatment; S2, placing the hot pressing mold in a hot pressing furnace for pre-curing; The pre-curing process is as follows: The hot pressing furnace is evacuated, the temperature is raised to 130-800° C., the glass fiber composite material substrate is sintered after the hot pressing furnace is heated for 60-120 minutes, and the polyimide cured at room temperature is then vacuum-assisted infused. After the vacuum-assisted infusion process is completed, the polyimide is naturally cooled at room temperature for 6-8 hours before being taken out; During the pre-curing, the pressure of the hot pressing furnace is 0.5-15 MPa, and the vacuum degree is 20-100 Pa; S3, performing secondary curing on the glass fiber composite material substrate encapsulated with the pressure grating after the treatment in step S2; The secondary curing is carried out in the hot press furnace without applying external pressure during the curing process, and the curing is carried out at a constant temperature of 130-135° C. for 90-100 minutes; S4, placing glass powder in the concave groove at the liquid inlet of the base, welding the glass fiber composite material substrate to the base, and welding the temperature measuring fiber Bragg grating to the L-shaped cantilever beam; The glass powder is low-temperature and low-melting-point glass powder; The base and the L-shaped cantilever beam are both made of nickel alloy; The welding is performed by glass welding, and the steps are as follows: The surfaces of the base and the L-shaped cantilever beam are cleaned by mechanical cleaning, degreasing, chemical or electrochemical cleaning, and drying; hydrogen burning treatment is then performed and the sealing portion is oxidized; after adding the glass powder, the temperature is raised to 270-380° C. in a heating box, maintained for 60-70 minutes, and then naturally cooled to room temperature; S5, connecting the base and the L-shaped cantilever beam to the sealing seat; The connection is made by laser welding.

2. A downhole high-temperature composite fiber Bragg grating sensor manufactured by the method of claim 1.

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