Optical Fiber Grating Temperature and Pressure Sensor for Oil and Gas Well Downhole and Its Manufacturing Method

Abstract

An optical fiber grating temperature and pressure sensor for oil and gas wells downhole. Connectors for series connection are provided at both ends of the sensor protective sleeve, and a sensing operation hole is radially drilled through the middle part. A sensing unit and a sealing cover are installed in the sensing operation hole. An optical fiber installation hole is machined at the axial center position of the sensor protective sleeve, and an optical fiber is provided in the optical fiber installation hole. The sensing unit is a cylindrical pressure-sensitive component, with a hydraulic hole with a pressure-bearing diaphragm at the bottom axially machined at one end center. A diamond hinge and a bracket are provided on the other end face of the pressure-sensitive component. An adjusting bolt is provided on the bracket. One top end of the diamond hinge is fixed on the pressure-bearing diaphragm, and the other top end of the same diagonal line abuts against the end of the adjusting bolt. A long beam and a short beam are horizontally arranged on the other two top ends of the diamond hinge respectively; the optical fiber is pasted on the long beam and the short beam with glue so that the optical fiber is suspended in the optical fiber installation hole. A first grating is provided on the optical fiber between the long beam and the short beam, and a second grating is provided on the optical fiber on the long beam.

Description

Technical Field

[0001] The present invention belongs to the technical field of fiber optic sensing, and particularly relates to a fiber Bragg grating temperature and pressure sensor for oil and gas wells. Background Art

[0002] In the process of oilfield exploration and production, the monitoring of downhole parameters such as temperature, pressure, and flow rate is an important means to improve the ultimate recovery rate of oil and gas fields and develop oil and gas fields scientifically, economically, and reasonably. With the continuous development of oil and gas exploration and development, the depth of oil and gas wells is getting deeper, the temperature and pressure are getting higher, and the downhole operating environment is getting more complex. Especially when the downhole temperature exceeds 175 °C, traditional downhole electronic instruments cannot achieve long-term monitoring. Fiber Bragg grating (FBG) has the advantages of anti-electromagnetic interference, large data transmission capacity, high speed, good long-term stability, and high temperature resistance, and is one of the alternative solutions to solve the problem that traditional electrical sensors cannot work in high-temperature environments.

[0003] The currently reported fiber Bragg grating pressure sensors mainly utilize the strain sensing principle of fiber Bragg gratings. The fiber Bragg gratings are pasted on elastic pressure-bearing components such as thin-walled cylinders, bellows, cantilever beams, and elastic diaphragms. The pressure is converted into component strain by the pressure-bearing components and acts on the fiber Bragg gratings, thereby realizing the measurement of pressure. Most of the fiber Bragg grating pressure sensors based on elastic diaphragms work on the principle that a pre-stretched fiber Bragg grating is connected to an elastic diaphragm. When the ambient pressure changes, it causes a change in the central deflection of the elastic diaphragm, which is then transmitted to the fiber Bragg grating, causing the fiber Bragg grating to contract, release the pre-tension, and cause a drift in the central wavelength of the fiber Bragg grating to monitor the ambient pressure. For example, Chinese Patent No. ZL202010740090.3, titled "Diaphragm-Type Fiber Bragg Grating Pressure Sensor with Sensitivity Enhancement Based on Lateral Load", and Chinese Patent No. ZL202011384965.7, titled "A Diaphragm-Type Cascade Structure Fiber Bragg Grating Pressure Sensor and Its Manufacturing Method" are both based on the above diaphragm-type pressure sensing working principle. The pressure sensors with the above structures have the problem that the magnitude of the pre-tension applied to the pressure fiber Bragg grating during packaging determines the range and sensitivity of the pressure sensor. The control of the magnitude of the pre-tension and the packaging process requirements during packaging are very high, which is not conducive to the mass production of sensors. In addition, the sensor fiber Bragg grating designed in Chinese Patent No. ZL202010740090.3, titled "Diaphragm-Type Fiber Bragg Grating Pressure Sensor with Sensitivity Enhancement Based on Lateral Load", has only one pigtail for reflecting and transmitting the detection signals of pressure and temperature, and it is impossible to connect multiple fiber Bragg grating sensors in series to achieve quasi-distributed arrangement, which cannot meet the needs of multi-point monitoring of different layers in oil and gas wells. In Patent ZL202011384965.7, titled "A Diaphragm-Type Cascade Structure Fiber Bragg Grating Pressure Sensor and Its Manufacturing Method", the pigtails of the pressure-measuring fiber Bragg grating and the temperature-measuring fiber Bragg grating penetrate the center of the diaphragm and are connected in series with other sensors, but this series packaging process requires even higher requirements. In addition, since the temperature-measuring grating is immersed in the liquid to be measured, the grating is easily broken by impact and cannot be used for the long-term operation of sensors in corrosive environments such as oil and gas wells. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a fiber Bragg grating temperature and pressure sensor for oil and gas wells with simple packaging, high sensitivity, realization of dual-parameter monitoring of temperature and pressure, and multi-point series monitoring.

[0005] The technical solution adopted to solve the above technical problems is as follows: A fiber Bragg grating temperature and pressure sensor for oil and gas wells downhole. Connectors for series connection are provided at both ends of the sensor protective sleeve, and a sensing operation hole is radially drilled through the middle part. A sensing unit and a sealing cover are installed in the sensing operation hole. An optical fiber installation hole is drilled at the axial center position of the sensor protective sleeve, and an optical fiber is arranged in the optical fiber installation hole. The sensing unit is a cylindrical pressure-sensitive component. An axial hydraulic hole b is drilled at the center position of one end, and the bottom of the hydraulic hole b is a pressure-bearing diaphragm. A diamond hinge and a bracket are arranged on the other end face of the pressure-sensitive component. An adjusting bolt is arranged on the bracket. One top end of the diamond hinge is fixed on the pressure-bearing diaphragm, and the other top end of the same diagonal line abuts against the end of the adjusting bolt. A long beam and a short beam are horizontally arranged on the other two top ends of the diamond hinge respectively; The optical fiber is pasted on the long beam and the short beam with glue so that the optical fiber is suspended in the optical fiber installation hole. A first grating is arranged on the optical fiber between the long beam and the short beam, and a second grating is arranged on the optical fiber in the glue-covered area on the long beam. The central wavelengths of the second grating and the first grating are not equal.

[0006] As a preferred technical solution, a pressure buffer cover is installed on the hydraulic hole b of the pressure-sensitive component, and a pressure-taking hole a is drilled on the end face of the pressure buffer cover.

[0007] As a preferred technical solution, the diamond hinge is formed by connecting four identical link bars end to end. The length of the link bar is 5-20 mm, the width is 1-3 mm, and the thickness is 0.5-1.5 mm. Grooves with opposite openings are drilled in the width direction of the link bar.

[0008] As a preferred technical solution, the thickness of the pressure-bearing diaphragm is 0.5-3.5 mm, the diameter is 8-20 mm, and the material is 316 stainless steel or 304 stainless steel.

[0009] As a preferred technical solution, the distance between the long beam and the short beam is 2-10 mm, and the distance between the second grating and the first grating is 2-6 mm.

[0010] The present invention also provides a manufacturing method for a fiber Bragg grating temperature and pressure sensor for oil and gas wells downhole, including the following steps:

[0011] S1. Place the sensing unit into the sensing operation hole of the sensor protective sleeve, and fix the pressure-sensitive component of the sensing unit on the sensor protective sleeve through threads, so that the upper surfaces of the long beam and the short beam are coplanar with the axis of the sensor protective sleeve;

[0012] S2. Thread the optical fiber engraved with the first grating and the second grating into one end of the sensor protective sleeve and out of the other end of the sensor protective sleeve. Place the optical fiber on the long beam and the short beam, and adjust the position of the optical fiber so that the first grating is suspended between the long beam and the short beam, and the grating area of the second grating is located on the long beam;

[0013] S3. Coat the surfaces of the long beam and the short beam with a high-temperature curing agent and cover the optical fiber. The second grating grating area is completely covered by the high-temperature curing agent. Use a high-temperature heating device to cure according to the curing process of the high-temperature curing agent, so that the optical fiber is fixed on the long beam and the short beam;

[0014] S4. After high-temperature curing and returning to room temperature, rotate the adjusting bolt to deform the rhombic hinge, so that the central wavelength of the first grating is greater than the initial wavelength before being fixed with the high-temperature curing agent, that is, ensure that the first grating after encapsulation is in a taut state;

[0015] S5. First, place the sensor in a temperature chamber for calibration of the temperature response of the sensor, and then connect the hydraulic hole b of the pressure-sensitive component to a general pressure gauge calibration device to perform calibration of the pressure response of the sensor;

[0016] S6. After completing the calibration of the temperature and pressure responses of the sensor, apply sealant to the threads of the sealing cover and install it on the sensing operation hole of the sensor protective sleeve for sealing installation through threads. Install the pressure buffer cover on the hydraulic hole b of the pressure-sensitive component to complete the production.

[0017] The beneficial effects of the present invention are as follows:

[0018] 1. In the present invention, the rhombic hinge converts the axial displacement of the center of the diaphragm due to pressure into the lateral displacement of the long beam and the short beam provided on the rhombic hinge, so that the wavelength drift of the first grating is used for pressure detection. In the prior art, the fiber grating is fixed along the axial direction of the diaphragm center. The sensor range is determined by the magnitude of the prestress applied to the fiber grating, and the fiber grating pasting process is difficult and the yield is low. The fiber grating in the present invention is fixed in a manner parallel to the diaphragm plane, with a simple encapsulation process, high yield, and the sensor pressure range and sensitivity can be determined by adjusting the thickness and pressure-bearing area of the pressure-bearing diaphragm. By replacing the pressure-sensitive component with a pressure-bearing diaphragm of different sizes, different oil and gas well downhole pressure monitoring ranges and sensitivity requirements can be achieved.

[0019] 2. The pressure sensitivity of the present invention can also be further improved by adjusting the link structure size of the rhombic hinge and the distance between the long beam and the short beam, solving the problem of mutual restriction of the sensor measurement range and sensitivity by the thickness dimension of the pressure-bearing diaphragm.

[0020] 3. Both ends of the optical fiber in the present invention are led out from both ends of the sensor protective sleeve, and multiple sensors can be connected in series, solving the problem that it is difficult to connect multiple points in series for diaphragm-type fiber grating pressure sensors.

[0021] 4. The adjusting bolt of the present invention is used to adjust the wavelength of the first grating 4, which can reduce the technical problem of accurately controlling the prestress applied to both ends of the optical fiber 2 during the high-temperature curing and pasting of the fiber grating and the metal bonding beam, improve the finished product rate of the sensor packaging and the wavelength consistency, and avoid the phenomenon that when the pressure-sensing fiber grating and the metal bonding beam in the prior art are cured and pasted at high temperature, if the prestress applied to both ends of the fiber grating is not properly controlled, due to the thermal expansion coefficient of the metal being greater than that of the fiber grating, when returning to room temperature, the pressure-sensing fiber grating pasted at two points will bend and cannot correctly respond to the pressure change, resulting in the failure of the sensor packaging.

[0022] 5. The present invention is a sensor that works completely immersed in the environment of the liquid to be measured. Compared with the similar fiber grating pressure sensors, the present invention can realize the calibration of the pressure sensor by connecting the internal thread provided at the open end of the hydraulic hole b of the pressure-sensitive part with the general pressure calibration device, without the need to put the sensor into a customized special test equipment for calibration, reducing the test conditions and difficulty of the sensor.

[0023] 6. The present invention has the advantages of simple sensor packaging process, dual-parameter monitoring of temperature and pressure, and easy series connection of multiple sensors, and is easy to meet the requirement of multi-point monitoring of different layers in the oil and gas well. Brief Description of the Drawings

[0024] Figure 1 is the structural schematic diagram of the present invention.

[0025] Figure 2 is the cross-sectional structural schematic diagram of the sensing unit 6 of the present invention.

[0026] Figure 3 is the three-dimensional structural schematic diagram of the sensing unit 6 of the present invention.

[0027] Figure 4 is the temperature response calibration curve graph of the present invention.

[0028] Figure 5 is the pressure response calibration curve graph of the present invention.

[0029] Wherein: sensor protective sleeve 1; optical fiber 2; sealing cover 3; first grating 4; second grating 5; sensing unit 6; pressure buffer cover 7; pressure-sensitive part 6-1; diamond hinge 6-2; bracket 6-3; adjusting bolt 6-4; long beam 6-6; short beam 6-5; pressure-bearing diaphragm 6-7. Detailed Embodiment

[0030] The present invention will be further described in detail below with reference to the drawings and embodiments, but the present invention is not limited to the following embodiments.

[0031] Embodiment 1

[0032] In Figures 1 to 3In this case, an optical fiber grating temperature and pressure sensor for downhole oil and gas is composed of a sensor protective sleeve 1, a sensing unit 6, a sealing cover 3, a pressure buffer cover 7, and an optical fiber 2. Sealing ring installation grooves and external threads are machined on the outer side walls at both ends of the sensor protective sleeve 1 as series connection joints. A sensing operation hole is radially drilled through the middle part. The sensing unit 6 is installed in the sensing operation hole. The sealing cover 3 is fixedly installed on the port of the sensing operation hole by threads. An optical fiber 2 installation hole is machined at the axial center position of the sensor protective sleeve 1. The optical fiber 2 is arranged in the optical fiber 2 installation hole. The two ends of the optical fiber 2 extend out of the sensor protective sleeve 1. One end of the tail fiber is used to connect to the ground demodulation device, and the other end of the tail fiber is suspended or connected in series with other optical fiber sensors, such as flow sensors and vibration sensors, to realize multi-parameter measurement of temperature, pressure, flow, vibration, etc. on the same level. The sensor can also be installed in different oil and gas layers, and the two ends of the tail fiber of this sensor are used for series connection to meet the requirements of multi-point and multi-layer temperature and pressure monitoring. The sensing unit 6 is a cylindrical pressure-sensitive component 6-1. An axial hydraulic hole b is machined at the center position of one end. The bottom of the hydraulic hole b is a pressure-bearing diaphragm 6-7. The thickness of the pressure-bearing diaphragm 6-7 is 2.5 mm and the diameter is 10 mm. The material of the pressure-sensitive component 6-1 is 316 stainless steel. A diamond hinge 6-2 and a bracket 6-3 are fixedly installed on the other end face of the pressure-sensitive component 6-1. An adjusting bolt 6-4 is installed on the bracket 6-3 by threads. One top end of the diamond hinge 6-2 is fixedly installed on the pressure-bearing diaphragm 6-7, and the other top end on the same diagonal abuts against the end of the adjusting bolt 6-4. Two other top ends of the diamond hinge 6-2 are respectively horizontally fixed with a long beam 6-6 and a short beam 6-5. The distance between the long beam 6-6 and the short beam 6-5 is 4 mm. The optical fiber 2 is pasted on the long beam 6-6 and the short beam 6-5 with glue so that the optical fiber 2 is suspended in the optical fiber 2 installation hole. A first grating 4, which is a pressure-sensing grating, is inscribed on the optical fiber 2 between the long beam 6-6 and the short beam 6-5. The first grating 4 is in a suspended state. A second grating 5, which is a temperature-sensing grating, is inscribed on the optical fiber 2 in the glue-covered area on the long beam 6-6. The distance between the second grating 5 and the first grating 4 is 4 mm. The grating region lengths of both the second grating 5 and the first grating 4 are 3 mm. The central wavelengths of the second grating 5 and the first grating 4 are not equal. The central wavelength of the first grating 4 is 1550.427 nm, and the central wavelength of the second grating 5 is 1540.851 nm. The diamond hinge 6-2 converts the axial displacement of the center of the diaphragm caused by pressure on the pressure-bearing diaphragm 6-7 into the lateral displacement of the long beam 6-6 and the short beam 6-5 arranged on the diamond hinge, causing the wavelength drift of the first grating 4 for pressure detection. A pressure buffer cover 7 is fixedly installed on the hydraulic hole b of the pressure-sensitive component 6-1 by threads. A pressure-taking hole a is machined on the end face of the pressure buffer cover 7. The pressure buffer cover 7 is used to prevent the impact on the diaphragm when the downhole pressure suddenly changes and to prevent foreign objects in the downhole from filling the hydraulic hole b and causing uneven pressure on the diaphragm, thereby realizing the protection of the first grating 4 for pressure sensing.

[0033] The diamond hinge 6-2 in this embodiment is formed by connecting four identical link rods end to end. The link rod has a length of 5.5 mm, a width of 2 mm, and a thickness of 1 mm. Grooves with opposite openings are machined in the width direction of the link rod to improve sensitivity.

[0034] The working principle of the present invention is as follows:

[0035] When the present invention is used for downhole temperature and pressure detection of oil and gas, the threads at both ends of the sensor protective sleeve 1 are used to connect with other downhole logging equipment. Through the sealing rings and the fiber optic 2 pigtail sealing threads provided at both ends of the sensor protective sleeve 1, the inside of the sensing operation hole is isolated from the downhole oil and gas. The downhole oil and gas with a certain pressure enter the hydraulic hole b of the pressure sensitive element 6-1 through the pressure taking hole a on the pressure buffer cover 7 and act on the pressure bearing diaphragm 6-7. The center of the pressure bearing diaphragm 6-7 generates an axial deformation under the action of the pressure. The diamond hinge 6-2 converts the axial deformation of the pressure bearing diaphragm 6-7 into its lateral deformation, so that the distance between the long beam 6-6 and the short beam 6-5 with the second grating 5 pasted thereon increases. In this way, the first grating 4 pasted between the long beam 6-6 and the short beam 6-5 at both ends is stretched along the axial direction of the fiber optic 2, causing the center wavelength thereof to drift towards the long wavelength direction. By detecting the drift amount of the wavelength, the change of the downhole oil and gas pressure can be obtained; while the center wavelength of the second grating 5 fully coated and pasted on the long beam 6-6 is not affected by the pressure change.

[0036] The change of the downhole temperature will simultaneously cause the change of the center wavelengths of the first grating 4 and the second grating 5. By detecting the information of the center wavelength of the second grating 5, the downhole temperature can be obtained, and at the same time, the wavelength drift caused by temperature during the pressure detection of the first grating 4 can be corrected.

[0037] A manufacturing method of an optical fiber grating temperature and pressure sensor for downhole oil and gas includes the following steps:

[0038] S1. Place the sensing unit 6 into the sensing operation hole of the sensor protective sleeve 1, and fix the pressure sensitive element 6-1 of the sensing unit 6 on the sensor protective sleeve 1 through threads, so that the upper surfaces of the long beam 6-6 and the short beam 6-5 are coplanar with the axis of the sensor protective sleeve 1;

[0039] S2. Thread the optical fiber 2 engraved with the first grating 4 and the second grating 5 into one end of the sensor protective sleeve 1 and out of the other end of the sensor protective sleeve 1. Place the optical fiber 2 on the long beam 6-6 and the short beam 6-5, and adjust the position of the optical fiber 2 so that the grating area of the first grating 4 is suspended between the long beam 6-6 and the short beam 6-5, and the grating area of the second grating 5 is located on the long beam 6-6;

[0040] S3. Coat the surfaces of the long beam 6-6 and the short beam 6-5 with a high-temperature curing agent and cover the optical fiber 2. The grating area of the second grating 5 is completely covered by the high-temperature curing agent. Cure it using a high-temperature heating device according to the curing process of the high-temperature curing agent, so that the optical fiber 2 is fixed on the long beam 6-6 and the short beam 6-5;

[0041] S4. After high-temperature curing and returning to room temperature, rotate the adjusting bolt 6-4 to deform the diamond hinge 6-2, so that the central wavelength of the first grating 4 is greater than the initial wavelength of 1550.427 nm, that is, ensure that the packaged first grating 4 is in a taut state;

[0042] S5. First, place the sensor in a temperature chamber for sensor temperature response calibration. Then, connect the hydraulic hole b of the pressure-sensitive part 6-1 to a general pressure gauge calibration device through the threaded opening for sensor pressure response calibration;

[0043] S6. After completing the temperature and pressure response calibrations of the sensor, apply sealant to the threads of the sealing cover 3 and install it on the sensing operation hole of the sensor protective sleeve 1 for sealed installation through the threads. Install the pressure buffer cover 7 on the hydraulic hole b of the pressure-sensitive part 6-1 to complete the production.

[0044] Example 2

[0045] In this embodiment, the sensing unit 6 is a cylindrical pressure-sensitive component 6-1. An axial hydraulic hole b is machined at the center position of one end of the pressure-sensitive component 6-1. The bottom of the hydraulic hole b is a pressure-bearing diaphragm 6-7. The thickness of the pressure-bearing diaphragm 6-7 is 0.5 mm and the diameter is 8 mm. The material of the pressure-sensitive component 6-1 is 304 stainless steel. A diamond hinge 6-2 and a bracket 6-3 are fixedly installed on the other end surface of the pressure-sensitive component 6-1. An adjusting bolt 6-4 is installed on the bracket 6-3 by means of a thread. One top end of the diamond hinge 6-2 is fixedly installed on the pressure-bearing diaphragm 6-7, and the other top end of the same diagonal line abuts against the end of the adjusting bolt 6-4. A long beam 6-6 and a short beam 6-5 are horizontally and fixedly installed on the other two top ends of the diamond hinge 6-2 respectively. The distance between the long beam 6-6 and the short beam 6-5 is 2 mm. The optical fiber 2 is glued to the long beam 6-6 and the short beam 6-5 so that the optical fiber 2 is suspended in the optical fiber 2 installation hole. A first grating 4 is inscribed on the optical fiber 2 between the long beam 6-6 and the short beam 6-5, which is a pressure-sensing grating. The first grating 4 is in a suspended state. A second grating 5 is inscribed on the optical fiber 2 in the glue-covered area on the long beam 6-6, which is a temperature-sensing grating. The distance between the second grating 5 and the first grating 4 is 6 mm. The grating region lengths of both the second grating 5 and the first grating 4 are 1 mm. The central wavelengths of the second grating 5 and the first grating 4 are not equal. The central wavelength of the first grating 4 is 1540.356 nm, and the central wavelength of the second grating 5 is 1530.843 nm. The diamond hinge 6-2 is formed by connecting four identical link rods end to end. The length of the link rod is 5 mm, the width is 1 mm, and the thickness is 0.5 mm. Grooves with opposite openings are machined in the width direction of the link rod to improve the sensitivity. The connection relationships of other components and components are the same as those in Embodiment 1, and the manufacturing method of the sensor is the same as that in Embodiment 1.

[0046] Embodiment 3

[0047] In this embodiment, the sensing unit 6 is a cylindrical pressure-sensitive component 6-1. An axial hydraulic hole b is machined at the center of one end of the pressure-sensitive component 6-1. The bottom of the hydraulic hole b is a pressure-bearing diaphragm 6-7. The thickness of the pressure-bearing diaphragm 6-7 is 3.5 mm and the diameter is 20 mm. The material of the pressure-sensitive component 6-1 is 304 stainless steel. A diamond hinge 6-2 and a bracket 6-3 are fixedly installed on the other end face of the pressure-sensitive component 6-1. An adjusting bolt 6-4 is installed on the bracket 6-3 by means of a thread. One top end of the diamond hinge 6-2 is fixedly installed on the pressure-bearing diaphragm 6-7, and the other top end of the same diagonal line abuts against the end of the adjusting bolt 6-4. A long beam 6-6 and a short beam 6-5 are horizontally fixed on the other two top ends of the diamond hinge 6-2 respectively. The distance between the long beam 6-6 and the short beam 6-5 is 10 mm. The optical fiber 2 is pasted on the long beam 6-6 and the short beam 6-5 with glue so that the optical fiber 2 is suspended in the optical fiber 2 installation hole. A first grating 4, which is a pressure-sensing grating, is inscribed on the optical fiber 2 between the long beam 6-6 and the short beam 6-5. The first grating 4 is in a suspended state. A second grating 5, which is a temperature-sensing grating, is inscribed on the optical fiber 2 in the glue-covered area on the long beam 6-6. The distance between the second grating 5 and the first grating 4 is 2 mm. The grating region lengths of both the second grating 5 and the first grating 4 are 8 mm. The central wavelengths of the second grating 5 and the first grating 4 are not equal. The central wavelength of the first grating 4 is 1570.267 nm, and the central wavelength of the second grating 5 is 1560.691 nm. The diamond hinge 6-2 is formed by connecting four identical link rods end to end. The length of the link rod is 20 mm, the width is 3 mm, and the thickness is 1.5 mm. Grooves with opposite openings are machined in the width direction of the link rod to improve the sensitivity. The connection relationships of other components and the components are the same as those in Embodiment 1, and the manufacturing method of the sensor is the same as that in Embodiment 1.

[0048] In order to verify the beneficial effects of the present invention, temperature and pressure calibration tests were carried out on the fiber Bragg grating temperature and pressure sensor for oil and gas wells in Embodiment 1. The temperature response calibration curve of the sensor is as Figure 4 shown. The test results show that the temperature-sensing grating (the second grating 5) and the pressure-sensing grating (the first grating 4) have the same temperature sensitivity and good linearity. The real-time detection of the downhole temperature can be realized through the temperature-sensing grating, and the correction of the wavelength drift of the pressure-sensing grating caused by temperature when detecting the downhole pressure can be achieved. The pressure response calibration curve of the sensor is as Figure 5 shown. The test results show that the wavelength of the temperature-sensing grating (the second grating 5) has no response to the change of the downhole pressure. The wavelength of the pressure-sensing grating (the first grating 4) drifts towards the long-wave direction as the pressure increases, and has a good linear response relationship with the pressure.

Claims

1. An optical fiber grating temperature and pressure sensor for oil and gas wellbores, characterized in that: The sensor protective sleeve (1) is provided with connectors for series connection at both ends, and a sensing operation hole is radially penetrated in the middle, in which a sensing unit (6) and a sealing cover (3) are installed, and an optical fiber installation hole is processed at the axial center position of the sensor protective sleeve (1), in which an optical fiber (2) is installed, the sensing unit (6) is a cylindrical pressure sensitive part (6-1) with an axial hydraulic hole b processed at the center position of one end, the bottom of the hydraulic hole b is a pressure-bearing diaphragm (6-7), and a diamond hinge (6-2) and a bracket (6-3) are arranged on the other end surface of the pressure sensitive part (6-1), and an adjusting bolt (6-4) is arranged on the bracket (6-3), and the diamond hinge ( One top end of the rhombus hinge (6-2) is fixed on the pressure-bearing diaphragm (6-7), and the other top end on the same diagonal line abuts against the end of the adjusting bolt (6-4); a long beam (6-6) and a short beam (6-5) are respectively arranged horizontally on the other two top ends of the rhombus hinge (6-2); the optical fiber (2) is glued to the long beam (6-6) and the short beam (6-5) so that the optical fiber (2) is suspended in the optical fiber installation hole; a first grating (4) is arranged on the optical fiber (2) between the long beam (6-6) and the short beam (6-5); a second grating (5) is arranged on the optical fiber (2) in the glue-covered area on the long beam (6-6); and the central wavelength of the second grating (5) is not equal to that of the first grating (4); A pressure buffer cover (7) is installed on the hydraulic hole b of the pressure sensitive component (6-1), and a pressure taking hole a is processed on the end surface of the pressure buffer cover (7); The pressure-bearing diaphragm (6-7) has a thickness of 0.5 to 3.5 mm and a diameter of 8 to 20 mm, and is made of 316 stainless steel or 304 stainless steel.

2. The fiber Bragg grating temperature and pressure sensor for downhole oil and gas according to claim 1, characterized in that: The diamond hinge (6-2) is composed of four identical chain rods connected end to end into one body, the chain rods are 5 to 20 mm long, 1 to 3 mm wide, and 0.5 to 1.5 mm thick, and the chain rods are processed with grooves with openings facing each other in the width direction.

3. The fiber Bragg grating temperature and pressure sensor for downhole oil and gas according to claim 1, wherein: The distance between the long beam (6-6) and the short beam (6-5) is 2 to 10 mm, and the distance between the second grating (5) and the first grating (4) is 2 to 6 mm.

4. The manufacturing method of the fiber Bragg grating temperature and pressure sensor for downhole oil and gas according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1. Place the sensing unit (6) into the sensing operation hole of the sensor protective cover (1), and fix the pressure sensitive part (6-1) of the sensing unit (6) to the sensor protective cover (1) by means of a thread, so that the upper surfaces of the long beam (6-6) and the short beam (6-5) are coplanar with the axis of the sensor protective cover (1); S2. Insert the optical fiber (2) engraved with the first grating (4) and the second grating (5) from one end of the sensor protective cover (1) and exit from the other end of the sensor protective cover (1), place the optical fiber (2) on the long beam (6-6) and the short beam (6-5), and adjust the position of the optical fiber (2) so that the first grating (4) is suspended between the long beam (6-6) and the short beam (6-5), and the grating area of ​​the second grating (5) is located on the long beam (6-6); S3. Coat the surfaces of the long beam (6-6) and the short beam (6-5) with a high-temperature curing agent and cover the optical fiber (2). The grating area of the second grating (5) is completely covered by the high-temperature curing agent. Cure it using a high-temperature heating device according to the curing process of the high-temperature curing agent, so that the optical fiber (2) is fixed on the long beam (6-6) and the short beam (6-5). S4. After high-temperature curing and returning to room temperature, rotate the adjusting bolt (6-4) to deform the diamond hinge (6-2), so that the central wavelength of the first grating (4) is greater than the initial wavelength before being fixed with the high-temperature curing agent, that is, ensure that the packaged first grating (4) is in a taut state. S5. First, place the sensor in a temperature chamber for sensor temperature response calibration, and then connect the hydraulic hole b of the pressure-sensitive component (6-1) to a general pressure gauge calibration device for sensor pressure response calibration. S6. After completing the temperature and pressure response calibrations of the sensor, apply sealant to the threads of the sealing cover (3), install it on the sensing operation hole of the sensor protective sleeve (1) for sealed installation by threading, and install the pressure buffer cover (7) on the hydraulic hole b of the pressure-sensitive component (6-1) to complete the production.

Images