A fiber Bragg grating temperature and pressure sensor based on a combination of diaphragm and lever

Abstract

A fiber Bragg grating temperature and pressure sensor based on a diaphragm and a lever combination, comprising a housing, a packaging shell, an oil inlet, a diaphragm, a lever structure, a fixed column, an optical fiber transmission hole, a temperature sensing fiber Bragg grating, and a pressure sensing fiber Bragg grating. The two ends of the pressure sensing fiber Bragg grating are respectively attached to the fixed column and the top of the lever resistance arm, and the temperature sensing grating is attached to the fixed column. Pressure enters from the oil inlet on the housing and is applied to the diaphragm, causing the diaphragm to deform. The deformation of the diaphragm pushes the support rod to move the support rod upward. The upward displacement is amplified by a lever structure, causing the pressure sensing fiber Bragg grating to deform, resulting in a wavelength drift. Two gratings are used to distinguish between measured temperature and pressure. The present invention is used to solve the problem that temperature and pressure measurement in oil and gas wells is difficult, and it is difficult to achieve real-time measurement and multi-point quasi-distributed measurement.

Description

Technical Field

[0001] The present invention belongs to the field of pressure sensors and relates to a fiber Bragg grating temperature and pressure sensor based on a diaphragm and a lever combination, and in particular to a fiber Bragg grating sensor based on a diaphragm and a lever combination for measuring temperature and pressure in oil and gas wells. Background Art

[0002] As oil production continues to increase, the demand for downhole operations continues to escalate. Pressure and temperature detection has become extremely important during deep oil production and downhole operations. Traditional downhole pressure measurement systems primarily use mechanical and electronic sensors. While mechanical pressure sensors can operate for extended periods underground, they can only measure a single point and struggle to transmit signals in real time. While electronic pressure sensors can measure downhole pressure in real time, they are not heat-resistant and therefore cannot operate in high-temperature, high-pressure downhole environments. Furthermore, because traditional downhole pressure and temperature detection systems are active monitoring systems, they are susceptible to interference in environments sensitive to electromagnetic interference, such as oil and gas wells and pipelines. Distortion is also common during long-distance transmission, making long-term measurement difficult in oil and gas wells.

[0003] Fiber Bragg grating (FBG) sensors offer significant advantages over electrical sensors due to their compact size, high sensitivity, immunity to electromagnetic interference, corrosion resistance, and high-temperature resistance. However, current fiber Bragg grating (FBG) downhole temperature and pressure sensors suffer from a balance between size and sensitivity, and cannot achieve distributed measurement. Therefore, a new, smaller and more sensitive FBG sensor is needed. Summary of the Invention

[0004] In order to overcome the above-mentioned deficiencies of the prior art, the purpose of the present invention is to provide a fiber Bragg grating temperature and pressure sensor based on a combination of a diaphragm and a lever, which is used to solve the problem that temperature and pressure measurement in oil and gas wells is difficult and it is difficult to achieve real-time measurement and distributed measurement.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A fiber Bragg grating temperature and pressure sensor based on a combination of a diaphragm and a lever comprises a housing (6), characterized in that a through fiber transmission hole (10) is provided on one side of the housing (6), a cylindrical hollow is provided downwardly on the upper surface, and an oil inlet hole (5) is provided in the cylindrical hollow; the housing (6) is closed by a diaphragm (4); a power arm support column (2) is provided on the diaphragm, a support rod (3) is provided on the housing, and a lever (1) is provided above the power arm support column (2) and the support rod (3) to form a lever structure; the lever structure is combined with the diaphragm (4) and is located on the axis of the diaphragm; one end of the lever (1) is connected to one end of a fiber Bragg grating A (7); the other end of the fiber Bragg grating A (7) is adhered to a fixing column (8), and the fixing column (8) is located on the through hole of the fiber transmission hole (10) of the diaphragm (4); a fiber Bragg grating B (9) is adhered to the middle of the fixing column (8); and the packaging housing (11) is fixed to the housing (6) by screw threads.

[0007] The fiber grating A (7) is pasted on the fixed column (8) and the lever (1). The shorter the pasting distance, the higher the sensitivity.

[0008] The power arm in the lever structure is arranged near the support rod.

[0009] Reducing the thickness of the support rod in the lever structure can significantly increase the sensitivity of the sensor.

[0010] The heights of the power arm and the fulcrum in the lever structure are increased, and the sensitivity of the sensor is improved.

[0011] The beneficial effects of the present invention are:

[0012] The device can accurately measure temperature and pressure in high-temperature environments and can operate for long periods of time in high-temperature, high-pressure, electromagnetic interference, and corrosive environments. It can achieve real-time monitoring of temperature and pressure with a simple structure. It addresses the problems of single-diaphragm pressure sensors, such as low sensitivity, the need for large prestress during packaging, and the difficulty in achieving distributed measurement. The present invention allows sensors to be connected in series vertically, exhibits high sensitivity, and enables quasi-distributed measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a schematic diagram of the structural cross-section of the present invention.

[0014] Figure 2 Schematic diagram of the core components of the present invention.

[0015] Figure 3 To simplify the model diagram,

[0016] Figure 4 This is a simplified diagram of the model deformation.

[0017] Figure 5Schematic diagram of the force on the lever structure.

[0018] Figure 6 This is the sensor experimental data diagram.

[0019] Figure 7 This is the relationship curve between the position of the support rod and the sensitivity.

[0020] Figure 1 and Figure 2 In the figure, 1 is a lever; 2 is a power arm support column; 3 is a support rod; 4 is a diaphragm; 5 is an oil inlet hole; 6 is a shell; 7 is a fiber Bragg grating A; 8 is a fixing column; 9 is a fiber Bragg grating B; 10 is a fiber transmission hole; and 11 is a packaging shell. DETAILED DESCRIPTION

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0022] like Figure 1 、 2 As shown, a fiber Bragg grating temperature and pressure sensor based on a combination of a diaphragm and a lever comprises a housing (6), characterized in that a through fiber transmission hole (10) is provided on one side of the housing (6), a cylindrical hollow is provided on the upper surface downwardly, and an oil inlet hole (5) is provided in the cylindrical hollow; the housing (6) is closed by a diaphragm (4); a power arm support column (2) is provided on the diaphragm, a support rod (3) is provided on the housing, and a lever (1) is provided above the power arm support column (2) and the support rod (3) to form a lever structure; the lever structure is combined with the diaphragm (4) and is located on the axis of the diaphragm; one end of the lever (1) is connected to one end of the fiber Bragg grating A (7); the other end of the fiber Bragg grating A (7) is adhered to a fixing column (8), and the fixing column (8) is located on the through hole of the fiber transmission hole (10) of the diaphragm (4); the fiber Bragg grating B (9) is adhered to the middle of the fixing column (8); and the packaging housing (11) is fixed to the housing (6) by screws.

[0023] The fiber grating A (7) is pasted on the fixed column (8) and the lever (1). The shorter the pasting distance, the higher the sensitivity.

[0024] The power arm in the lever structure is arranged at an edge area of ​​the diaphragm close to the support rod.

[0025] Reducing the thickness of the support rod in the lever structure can significantly increase the sensitivity of the sensor.

[0026] The heights of the power arm and the fulcrum in the lever structure are increased, and the sensitivity of the sensor is improved.

[0027] like Figure 3 、 4 As shown:

[0028] For a circular flat thick diaphragm with peripheral clamping, under the action of uniform pressure P, is the effective radius of the diaphragm, E is the Young's modulus of the diaphragm, H is the thickness of the diaphragm, is Poisson's ratio. A is the cross-sectional area of ​​the rod, and I is the axial moment of inertia of the rod.

[0029] Longitudinal displacement of point d:

[0030]

[0031] in is the axial displacement of the diaphragm surface, It is the diaphragm displacement caused by the lever reaction force F1. is the displacement of point "c", which is also the vertical displacement of the lever structure caused by force F1. is the axial compression of the "cd" rod.

[0032] For a circular thick diaphragm with peripheral clamping, under the action of uniform pressure P, R is the effective radius of the diaphragm, E1 is the Young's modulus of the diaphragm, and H is the thickness of the diaphragm. is Poisson's ratio. The axial displacement of the circular flat diaphragm can be expressed as:

[0033]

[0034] The vertical displacement of the support rod is

[0035]

[0036] To rigidify the ab segment, The vertical displacement of the segment, For the general Duan Ganghua, The vertical displacement of the segment and the involved displacement of the ac segment.

[0037] For the asymmetry of thick diaphragms, the influence of circumferential stress needs to be considered, which makes the calculation more complicated. However, this influence is ignored in the theoretical calculation.

[0038]

[0039] Support rod compression

[0040]

[0041] Substituting equations (2)-(5) into equation (1) can calculate F1.

[0042] The radial displacement of point "d" can be expressed as:

[0043]

[0044] The radial displacement of the circular flat thick diaphragm is

[0045] The radial displacement of the diaphragm causes the horizontal displacement of the lever support rod

[0046]

[0047] Ignore the horizontal displacement of the lever support rod squeezing the diaphragm

[0048]

[0049] Substituting equations (7)-(9) into equation (6) can calculate F2;

[0050] like Figure 5 As shown, F1 causes the vertical displacement of the lever

[0051]

[0052] F1 causes horizontal displacement of the lever

[0053]

[0054] F2 causes the vertical displacement of the lever

[0055]

[0056] F2 is the horizontal displacement of the lever

[0057]

[0058] Total displacement

[0059]

[0060] Sensitivity is

[0061]

[0062] In the formula is the initial center wavelength of the fiber Bragg grating, is the effective elastic-optical coefficient of the optical fiber, which is generally 0.22. Figure 7 The figure shows the relationship between the position r of the support rod (3) and the sensitivity in the present invention. It can be seen that the design of the eccentric lever structure in the pressure sensor combining the diaphragm type and the lever can increase the sensitivity of the structure. In the present invention, l is the bonding length of the fiber Bragg grating. The shorter the bonding distance, the higher the sensitivity.

[0063] Working principle of the present invention:

[0064] Pressure enters through the oil inlet (5) and is applied to the diaphragm, causing it to deform. This deformation pushes the support rod, causing it to move upward. The fiber Bragg grating (FBG) is attached to the fixed column and the top of the lever resistance arm. The upward displacement is amplified by a lever structure, causing the fiber Bragg grating (FBG) A (7) to deform. The fiber Bragg grating (FBG) B (9) only measures the temperature change, while the fiber Bragg grating (FBG) A (7) measures both the temperature change and the pressure change. The optical fiber transmits light vertically through the hole (10). The temperature and pressure can be measured by calculation.

[0065] Example 1: How to use the temperature and pressure sensor: Take the downhole casing as an example, connect the joints above and below the sensor and connect it to the pipeline. Multiple sensors can be arranged. The main dimensions of the sensor are as follows: Figure 1 As shown, the radius of the main component shell (6) is R1 = 10mm, the radius of the diaphragm (4) is R2 = 4mm, the thickness of the diaphragm is h1 = 1.5mm, the distance between the power arm support column (2) and the center of the diaphragm is r = 1mm, the width of the vertical rod of the support rod (3) is h2 = 3mm, the height of the lever structure is H = 10mm, and the fiber grating pasting distance is h3 = 8mm. The fiber grating uses ordinary coated optical fiber, the grating area length is 3mm, and the fiber grating center wavelength is 1550nm. After the pipeline pressure enters the sensor, the diaphragm is deformed. The upward displacement of the diaphragm is amplified by the lever structure, causing the fiber grating pasted on the top of the lever to stretch, thereby measuring the pressure. In addition, the optical fiber can be connected in series in the vertical direction through the optical fiber transmission hole (10) to achieve quasi-distributed measurement of oil and gas pipeline temperature and pressure.

[0066] Example 2: How to use the temperature and pressure sensor: Take the casing in a deep well as an example, connect the joints above and below the sensor and connect it to the pipeline. Multiple sensors can be arranged. The main dimensions of the sensor are as follows: Figure 1 As shown, the radius of the main component housing (6) is R1=10mm, the radius of the diaphragm (4) is R2=4mm, the thickness of the diaphragm is h1=2mm, the distance between the power arm support column (2) and the center of the diaphragm is r=2mm, the vertical rod width of the support rod (3) is h2=1.5mm, the height of the lever structure is H=15mm, the fiber Bragg grating pasting distance is h3=6mm, the fiber Bragg grating uses a polyimide coated fiber, the grating area length is 3mm, and the fiber Bragg grating center wavelength is 1550nm. The sensitivity curve of the sensor described in Example 2 is as follows Figure 6 As shown. When the pipeline pressure enters the sensor, the diaphragm is deformed. The upward displacement of the diaphragm is amplified by the lever structure, causing the fiber Bragg grating attached to the top of the lever to stretch, thereby measuring the pressure. In addition, the various sensors can be connected in series in the vertical direction through the optical fiber transmission hole (10), thereby realizing quasi-distributed measurement of oil and gas pipeline temperature and pressure.

[0067] Example 3: How to use the temperature and pressure sensor: Take the ultra-deep well casing as an example, connect the joints above and below the sensor and connect it to the pipeline. Multiple sensors can be arranged. The main dimensions of the sensor are as follows: Figure 1 As shown, the main component shell (6) has a radius of R1 = 10mm, the diaphragm (4) has a radius of R2 = 4mm, the diaphragm thickness h1 = 3mm, the power arm support column (2) is r = 2mm away from the center of the diaphragm, the vertical rod width of the support rod (3) is h2 = 1.5mm, the lever structure height H = 15mm, the fiber Bragg grating pasting distance h3 = 5mm, the fiber Bragg grating uses a polyimide coated fiber, the grating area length is 3mm, and the fiber Bragg grating center wavelength is 1550nm. It is three times the sensitivity of a single diaphragm structure. After the pipeline pressure enters the sensor, the diaphragm is deformed. The upward displacement of the diaphragm is amplified by the lever structure, causing the fiber Bragg grating pasted on the top of the lever to stretch, thereby measuring the pressure. In addition, the various sensors can be connected in series in the vertical direction through the optical fiber transmission hole (10), thereby realizing quasi-distributed measurement of oil and gas pipeline temperature and pressure.

[0068] In summary, changing the thickness of the diaphragm (4) can change the applicable field of the present invention. The thicker the diaphragm, the larger the measuring range. The position r of the support rod in this structure is an important factor affecting the sensitivity, such as Figure 7 As shown, the sensitivity and linearity of the structure can be affected by reducing the thickness of the support rod (3) in the lever structure. Optical fibers with different coatings can be used at different temperatures to adapt to different environments. By arranging the sensors in the vertical direction through downhole optical cables, quasi-distributed measurement of temperature and pressure in oil and gas wells can be achieved.

Claims

1. A fiber Bragg grating temperature and pressure sensor based on a combination of a diaphragm and a lever, comprising a housing (6), characterized in that: A through fiber transmission hole (10) is provided on one side of the shell (6), and a cylindrical hollow is provided on the upper surface downward, and an oil inlet hole (5) is provided in the cylindrical hollow; the shell (6) is closed by a diaphragm (4); a power arm support column (2) is provided on the diaphragm, a support rod (3) is provided on the shell, and a lever (1) is provided above the power arm support column (2) and the support rod (3) to form a lever structure; the lever structure is combined with the diaphragm (4) and is located on the axis of the diaphragm; one end of the lever (1) is connected to one end of the fiber grating A (7); the other end of the fiber grating A (7) is adhered to the fixing column (8), and the fixing column (8) is located on the through hole of the fiber transmission hole (10) of the diaphragm (4); the fiber grating B (9) is adhered to the middle of the fixing column (8); the packaging shell (11) is fixed to the shell (6) by screw threads; The distance between the power arm support column (2) and the center position of the diaphragm is r=1mm, the width of the vertical rod of the support rod (3) is h2=3mm, the height of the lever structure is H=10mm, the fiber Bragg grating pasting distance is h3=8mm, and the length of the grating area is 3mm; or the distance between the power arm support column (2) and the center position of the diaphragm is r=2mm, the width of the vertical rod of the support rod (3) is h2=1.5mm, the height of the lever structure is H=15mm, the fiber Bragg grating pasting distance is h3=6mm, and the length of the grating area is 3mm; or the distance between the power arm support column (2) and the center position of the diaphragm is r=2mm, the width of the vertical rod of the support rod (3) is h2=1.5mm, the height of the lever structure is H=15mm, the fiber Bragg grating pasting distance is h3=5mm, and the length of the grating area is 3mm: the vertical through-hole design supports multiple sensors in series.

2. The fiber Bragg grating temperature and pressure sensor based on the combination of a diaphragm and a lever according to claim 1, characterized in that: The fiber grating A (7) is pasted on the fixed column (8) and the lever (1). The shorter the pasting distance, the higher the pressure sensitivity.

3. The fiber Bragg grating temperature and pressure sensor based on the combination of a diaphragm and a lever according to claim 1, characterized in that: The reduction in thickness of the support rod (3) in the lever structure can significantly increase the pressure sensitivity of the sensor.

4. The fiber Bragg grating temperature and pressure sensor based on the combination of a diaphragm and a lever according to claim 1, characterized in that: In the lever structure, the power arm support column (2) and the support rod (3) have the same height; and as the height is increased, the pressure sensitivity of the sensor is improved.

5. The fiber Bragg grating temperature and pressure sensor based on the combination of a diaphragm and a lever according to claim 1, characterized in that: An encapsulation shell (11) is provided outside the shell (6).

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