CN117490874A - High-sensitivity tubular fiber bragg grating temperature sensor for oil and gas well - Google Patents
High-sensitivity tubular fiber bragg grating temperature sensor for oil and gas well Download PDFInfo
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- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
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- G01K11/32—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres
- G01K11/3206—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres at discrete locations in the fibre, e.g. using Bragg scattering
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Abstract
The high-sensitivity tubular fiber bragg grating temperature sensor for the oil and gas well is characterized in that a first temperature sensing tube is sleeved with a second temperature sensing tube, a rectangular notch I is formed in the side wall of one end of the first temperature sensing tube, one end of the second temperature sensing tube in the first temperature sensing tube is located in the middle of the rectangular notch I, a rectangular notch II is formed in the side wall of the other end of the second temperature sensing tube, the other end of the first temperature sensing tube is located in the middle of the rectangular notch II, optical fibers are fixed in the first temperature sensing tube and the second temperature sensing tube through four fixed points in an axial direction, a first grating is inscribed on the optical fiber at the first position of the rectangular notch and is in a suspended state, and a second grating is inscribed on the optical fiber at the second position of the rectangular notch and is in a suspended state; the first temperature sensing pipe and the second temperature sensing pipe have different thermal expansion coefficients. The sensor with the tubular structure has the advantages of simple structure and easy processing, the size in the radial direction can be small, the axial direction can be adjusted according to the specific measurement sensitivity and the measuring range, and the sensor is particularly suitable for being used in a tubular narrow environment in an oil gas well.
Description
Technical Field
The invention belongs to the technical field of optical fiber sensing, and particularly relates to a high-sensitivity tubular optical fiber grating temperature sensor for an oil gas well.
Background
Temperature is one of seven basic physical quantities, and temperature logging is one of important parameters in oil and gas field development, and is commonly used for production well production layer dynamic evaluation, casing channeling, leakage condition judgment, sand fracturing post-pressure evaluation and the like.
At present, the most commonly used temperature sensors in oil and gas well temperature measurement are still electrical temperature sensors, such as thermocouples, platinum resistors, semiconductor temperature sensors and the like, which are easily subjected to electromagnetic interference, have low sensitivity and cannot withstand high temperature for a long time. The fiber bragg grating temperature sensor has the advantages of electromagnetic interference resistance, corrosion resistance, high temperature resistance, high sensitivity, strong multiplexing capability, small volume, light weight, easiness in embedding into materials and the like, so that the fiber bragg grating temperature sensor has obvious advantages in oil and gas well measurement. The fiber grating has temperature sensitivity, but the temperature sensitivity is only about 10 pm/DEG C under the condition of not carrying out any package sensitization, and the requirement of high-precision temperature measurement cannot be met. Therefore, the method for improving the temperature measurement sensitivity of the fiber bragg grating is continuously researched, and various sensitization methods such as single metal substrate encapsulation, polymer encapsulation, bimetal substrate encapsulation and the like are reported.
The Chinese patent with application number 2021112016636 discloses a double-F-shaped fiber bragg grating temperature sensor. The fiber bragg grating is characterized by comprising two F-shaped structural members and fiber bragg gratings, wherein the F-shaped structural members and the fiber bragg gratings are made of materials with different thermal expansion coefficients, the middle parts of the two F-shaped structural members are fixed together to form central symmetry, and the two fiber bragg gratings are respectively fixed at the head end and the tail end of the two F-shaped structural members. When the temperature changes, the two F-shaped structural members generate relative displacement changes due to different thermal expansion coefficients, and the fiber bragg grating fixed between the F-shaped structural members is driven to generate strain changes, so that the sensitivity of the temperature sensor is improved. Although the sensitivity of the fiber bragg grating temperature sensing is improved, the fiber bragg grating is large due to the inherent characteristics of the F-shaped structure, the fiber bragg grating is difficult to fix at the front end and the tail end of the two F-shaped structural members, and the middle of the fiber bragg grating is required to be bent and fixed. In addition, the optical fiber in the sensor is positioned on the outer side of the structure, and is easy to touch in actual use, so that the optical fiber is broken, and the sensor is invalid.
Chinese patent application No. CN202010954557.4 discloses a "FBG temperature sensor based on bi-metal cantilever beam and application thereof. The thermal bimetal cantilever beam is built, the optical fiber Bragg grating extends in the direction between the fixed end and the free end of the thermal bimetal cantilever beam, and the thermal bimetal strip is utilized to deform by heating, so that additional deformation is introduced to the optical fiber Bragg grating, and the sensing sensitivity of the optical fiber Bragg grating is improved. The sensor has limited sensitivity improvement because the additional deformation of the fiber bragg grating depends on the thermal deformation of the bimetal cantilever. The patent only describes that the optical fiber Bragg grating is laid at the position of the thermal bimetallic strip or the optical fiber Bragg grating is welded with the thermal bimetallic strip, but the type of the cantilever beam and the pasting position of the grating are not described, and the possibility that the normal use of the sensor is influenced due to the chirp of the optical fiber grating exists.
The Chinese patent with the application number of CN200810105788.7 discloses a manufacturing method of a high-sensitivity fiber grating temperature sensor working at high and low temperatures. The sensor adopts a special bimetal structure, and the temperature for starting the sensor can be adjusted by adjusting the pre-loosening length of the fiber bragg grating, so that the sensitivity is very high. However, the method is limited by the tensile strength of the common fiber bragg grating, so that the manufactured sensor has a small measuring range, and the displacement adjustment of the sensor in the setting of the working temperature range takes 1/100mm as a unit, so that the requirement on the packaging operation is high.
Chinese patent application No. CN202111201664.0 discloses a "cold-hot elongated fiber bragg grating temperature sensor". According to the sensor, two fiber gratings are respectively fixed in a gap between two mounting pieces, when temperature rise and reduction are realized by utilizing the difference of thermal expansion coefficients between the mounting pieces, one fiber grating is always in a tensile state, so that chirp and initial large prestress are avoided, and the sensitivity is higher. However, in the sensor, the fiber bragg gratings are respectively fixed on the outer surfaces of the first mounting piece platform and the second mounting piece boss, and the fiber bragg gratings are easy to damage in the mounting and using processes. Simultaneously, the first mounting piece platform is larger than the second mounting piece, so that the whole size of the sensor is larger, and the sensor is not easy to use in a narrow space under an oil gas well.
In the whole, the existing fiber bragg grating temperature sensor has the problems of large volume, insufficient sensitivity or measuring range, insufficient protection for the fiber, and the like, and cannot meet the requirement of large-range high-sensitivity temperature monitoring under an oil gas well.
Disclosure of Invention
The invention aims to overcome the defects of the traditional fiber bragg grating temperature sensor and provide the tubular fiber bragg grating temperature sensor for the oil gas well, which has the advantages of simple structure, small volume, protection effect on the fiber and flexible adjustment of measurement range and sensitivity.
The technical scheme adopted for solving the technical problems is as follows: the high-sensitivity tubular fiber bragg grating temperature sensor for the oil and gas well is characterized in that a first temperature sensing tube is sleeved with a second temperature sensing tube, a rectangular notch I is formed in the side wall of one end of the first temperature sensing tube, one end of the second temperature sensing tube in the first temperature sensing tube is positioned in the middle of the rectangular notch I, a rectangular notch II is formed in the side wall of the other end of the second temperature sensing tube, the rectangular notch II and the rectangular notch I are positioned on the same side, the other end of the first temperature sensing tube is positioned in the middle of the rectangular notch II, optical fibers are fixed in the first temperature sensing tube and the second temperature sensing tube in the axial direction through four fixed points, a first fixed point A is arranged on the first temperature sensing tube at the rectangular notch I, a second fixed point B is arranged on the end of the second end of the temperature sensing tube, a third fixed point C is arranged on the end of the first temperature sensing tube at the rectangular notch II, a fourth fixed point D is arranged on the end of the second temperature sensing tube, a first grating is inscribed on the optical fiber between the first fixed point A and the second fixed point B, and the optical fiber is in a suspended state, and the second grating is inscribed on the optical fiber between the third fixed point C and the fourth fixed point D; the first temperature sensing pipe and the second temperature sensing pipe are different in thermal expansion coefficient.
As a preferable technical scheme, the first grating and the second grating are directly inscribed on the optical fiber without the stripping coating layer by a femtosecond laser.
As a preferable technical scheme, the lengths of the grating areas of the first grating and the second grating are equal to 1 mm-10 mm, and the difference of the center wavelengths is more than or equal to 3nm.
As a preferable technical scheme, the difference between the first inner diameter of the temperature sensing tube and the second outer diameter of the temperature sensing tube is 0.1mm.
As a preferable technical scheme, two packaging openings I are processed on the opposite side of a rectangular notch I on one side wall of the temperature sensing tube, the two packaging openings I are aligned with a first fixed point A and a second fixed point B respectively, and a U-shaped groove I which is coincident with the packaging opening I corresponding to the second fixed point B is arranged at one end part of the two ends of the temperature sensing tube; the other side of the second side wall of the temperature sensing tube, which is opposite to the second rectangular notch, is provided with a second packaging opening, the two packaging openings are respectively aligned with a third fixed point C and a fourth fixed point D, and the end part of the other end of the temperature sensing tube is provided with a second U-shaped groove which is coincident with the second packaging opening corresponding to the third fixed point C.
As a preferable technical scheme, the first temperature sensing pipe and the second temperature sensing pipe are fixedly connected through a threaded fastening connecting piece.
As an optimized technical scheme, the screw fastening connector is positioned at the axial middle part of the whole body of the first temperature sensing pipe and the second temperature sensing pipe.
As a preferable technical scheme, the first temperature sensing tube is made of one of aluminum alloy and stainless steel, the second temperature sensing tube is made of one of invar alloy and carbon fiber, or the first temperature sensing tube is made of one of invar alloy and carbon fiber, and the second temperature sensing tube is made of one of aluminum alloy and stainless steel.
As a preferable technical scheme, the thickness of the first temperature sensing pipe and the second temperature sensing pipe is equal to 0.1 mm-0.5 mm.
As a preferable technical scheme, the sensitivity S ∈r of the sensor in the temperature rising environment is:
wherein L is 2 Is the effective length of the first temperature sensing pipe L 3 Is the effective length of the second temperature sensing pipe, P eff Is the effective elasto-optical coefficient of the optical fiber, ζ is the thermo-optical coefficient of the optical fiber material, α is the thermal expansion coefficient of the optical fiber material, α 2 And alpha 3 The thermal expansion coefficients of the first temperature sensing pipe and the second temperature sensing pipe are L 12 Is the effective length of the second grating lambda B-12 The Bragg center wavelength of the second grating at the calibration temperature and without external stress;
the sensitivity S ∈ of the sensor in the cooling environment is as follows:
wherein lambda is B-11 Is the center wavelength of the Bragg at the calibration temperature and without the applied stress.
The beneficial effects of the invention are as follows:
the two temperature sensing pipes have thermal expansion coefficient difference, and can convert the relative displacement change of the two temperature sensing pipes caused by temperature into the strain change of the grating packaged on the temperature sensing pipes, thereby effectively improving the sensitivity of the grating temperature sensor. When the temperature rises and falls, the central wavelength of one grating is changed to detect, so that the measuring range of the sensor is doubled compared with that of the normal sensor under the condition of higher sensitivity. According to the invention, two gratings are inscribed on one optical fiber and are respectively packaged in a two-point fixed manner, and the gratings in a working state are in a tensile state no matter the temperature is increased or reduced, so that the chirp problem of the full-viscosity optical fiber grating temperature sensor can be effectively avoided.
The sensor with the tubular structure has the advantages of simple structure and easy processing, the size in the radial direction can be small, the axial direction can be adjusted according to the specific measurement sensitivity and the measuring range, and the sensor is particularly suitable for being used in a tubular narrow environment in an oil gas well. In the fiber bragg grating packaging process, one side, with a rectangular notch, of the first temperature sensing tube and the second temperature sensing tube is arranged below, the fiber bragg grating is arranged inside the tube and is parallel to the axis of the tube easily by utilizing the characteristics of the round tube, and the bonding glue naturally and uniformly covers the optical fiber and the inner wall of the tube under the action of gravity, so that the consistency and reliability of bonding are ensured. Meanwhile, the optical fiber passes through the first temperature sensing pipe and the second temperature sensing pipe, both the optical fiber and the two gratings on the optical fiber are effectively protected, and the reliability of the sensor in the well descending and working process is greatly improved.
The invention can realize the parallel of the axes of the first temperature sensing pipe and the second temperature sensing pipe under the action of the fastening connector due to the inherent characteristic of the circular pipe, ensures the radial strength of the pipes to be consistent, ensures the relative position stability of the first temperature sensing pipe and the second temperature sensing pipe, overcomes the defect that the output of the sensor is influenced due to the easy change of the positions between the end points of the fixed fiber gratings in the Chinese patent with application numbers 2021112016636 and 202111201664.0, and has the characteristics of simple structure and good stability.
Drawings
FIG. 1 is a schematic diagram of the structure of a high-sensitivity tubular fiber bragg grating temperature sensor for an oil and gas well.
Fig. 2 is a schematic structural diagram of a temperature sensing tube 2 according to the present invention.
Fig. 3 is a schematic structural diagram of a second temperature sensing tube 3 of the present invention.
Wherein: the optical fiber comprises an optical fiber 1, a first grating 11, a second grating 12, a first temperature sensing tube 2, a first rectangular notch 21, a first U-shaped groove 32, a second temperature sensing tube 3, a second rectangular notch 31, a second U-shaped groove 22, a second packaging opening 4, a threaded fastening connector 5 and a first packaging opening 6.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, but the present invention is not limited to the following embodiments.
Example 1
In fig. 1, 2 and 3, the high-sensitivity tubular fiber bragg grating temperature sensor for the oil and gas well of the embodiment comprises a first temperature sensing tube 2, a second temperature sensing tube 3, a threaded fastening connector 5 and an optical fiber 1. The temperature sensing tube I2 is sleeved with the temperature sensing tube II 3, the difference between the inner diameter of the temperature sensing tube I2 and the outer diameter of the temperature sensing tube II 3 is 0.1mm, the integral stability of the two temperature sensing tubes is ensured, the lower side walls of the temperature sensing tube I2 and the temperature sensing tube II 3 are fixedly connected through a screw fastening connector 5, the screw fastening connector 5 is positioned at the axial middle part of the integral body of the temperature sensing tube I2 and the temperature sensing tube II 3, a rectangular notch I21 is processed on the upper side wall of the left end of the temperature sensing tube II 3 positioned in the temperature sensing tube I2, a rectangular notch II 31 is processed on the upper side wall of the right end of the temperature sensing tube II 3, the right end of the temperature sensing tube I2 is positioned at the middle part of the rectangular notch II 31, optical fibers 1 are installed on the inner axes of the temperature sensing tube I2 and the temperature sensing tube II 3 through four fixed points, the optical fiber 1 is positioned in the first temperature sensing tube 2 and the second temperature sensing tube 3, a first fixed point A is arranged at the left side edge of the first rectangular notch 21, a second fixed point B is arranged at the left end part of the second temperature sensing tube 3, a third fixed point C is arranged at the right end part of the second temperature sensing tube 3, a fourth fixed point D is arranged at the right side edge of the second rectangular notch 31, a first grating 11 is inscribed on the optical fiber 1 between the first fixed point A and the second fixed point B and is in a suspended state, a second grating 12 is inscribed on the optical fiber 1 between the third fixed point C and the fourth fixed point D and is in a suspended state, the grating area lengths of the second grating 12 and the first grating 11 are equal, and the difference of center wavelengths is more than or equal to 3nm. The lower side wall of the first temperature sensing tube 2 is provided with two first packaging openings 6, the first packaging openings 6 are respectively aligned with a first fixed point A and a second fixed point B, the left end part of the second temperature sensing tube 3 is provided with a first U-shaped groove 32 which is coincident with the first packaging opening 6 corresponding to the second fixed point B, and the first U-shaped groove 32 is a abdication groove. The lower side wall of the temperature sensing tube II 3 is provided with two packaging openings II 4, the two packaging openings II 4 are respectively aligned with a third fixed point C and a fourth fixed point D, the end part of the right end of the temperature sensing tube I2 is provided with a U-shaped groove II 22 which is coincident with the packaging opening II 4 corresponding to the third fixed point C, the U-shaped groove II 22 is a abdicating groove, and the four packaging openings are specially used for adjusting the positions of the two gratings and smearing adhesive to the fixed points.
The first temperature sensing tube 2 and the second temperature sensing tube 3 are metal tubes with equal thickness and different thermal expansion coefficients, the material of the first temperature sensing tube 2 of the embodiment is invar alloy, and the thermal expansion coefficient is 1.2 multiplied by 10 -6 The temperature-sensing tube II 3 is made of aluminum alloy with the thickness of 0.3mm at the temperature of/DEG C, and the thermal expansion coefficient is 2.2 multiplied by 10 -5 /℃。
In this embodiment, the first grating 11 and the second grating 12 are directly inscribed on the optical fiber 1 without the stripping layer by a femtosecond laser, the grating area length of the first grating 11 is 4mm, the center wavelength is 1525nm, the grating area length of the second grating 12 is 4mm, and the center wavelength is 1545nm.
In the fiber bragg grating packaging process, one side, with a rectangular notch, of the first temperature sensing tube 2 and the second temperature sensing tube 3 is integrally processed, is placed below, two groups of packaging openings are located above, the characteristics of a round tube are well utilized, the fiber bragg grating is arranged inside the tube and is parallel to the axis of the tube easily, glue is dispensed through the packaging openings, the glue naturally and uniformly covers the optical fiber and the inner wall of the tube under the action of gravity, and the consistency and reliability of bonding are guaranteed. Meanwhile, the optical fiber 1 passes through the first temperature sensing pipe 2 and the second temperature sensing pipe 3, and both the optical fiber 1 and the two gratings on the optical fiber are effectively protected, so that the reliability of the sensor in the well descending and working process is greatly improved.
The working principle of the invention is as follows:
when the sensor is put down in an oil-gas well, the thermal expansion effect and the thermo-optic effect of the material of the optical fiber 1 can shift the central wavelengths of the two gratings under the influence of the temperature in the well, and the relative shift amount is that
Wherein lambda is B-n The Bragg center wavelength of the optical fiber 1 grating is the Bragg center wavelength of the optical fiber 1 grating at the calibration temperature without external stress, and n is the serial number of the optical fiber 1 grating; Δλ (delta lambda) B-n For the drift amount of the grating Bragg central wavelength of the optical fiber 1 with a certain serial number caused by the temperature change delta T, zeta is the thermo-optical coefficient of the optical fiber 1 material, alpha is the thermal expansion coefficient of the optical fiber 1 material, and delta T is the change amount of the temperature in the well where the sensor is positioned relative to the calibration temperature.
Meanwhile, since the difference of the thermal expansion coefficients of the two temperature sensing pipes is larger, as in the case of the thermal expansion coefficient of the first temperature sensing pipe 2 < the thermal expansion coefficient of the second temperature sensing pipe 3 in embodiment 1, the thermal expansion of the first temperature sensing pipe 2 is smaller after the temperature is raised, and the thermal expansion of the second temperature sensing pipe 3 is larger, since the first temperature sensing pipe 2 and the second temperature sensing pipe 3 are fixed by the screw fastening connector 5, when the temperature is raised, the distance between the right end of the first temperature sensing pipe 2 and the right side edge of the rectangular notch second 31 of the second temperature sensing pipe 3 becomes larger, and the increment value ΔL thereof is increased 12 Is that
ΔL 12 ＝(L 3 ×α 3 -L 2 ×α 2 )×ΔT
Wherein L is 2 Is the effective length of the first temperature sensing pipe 2, namely the length of the right end of the first temperature sensing pipe 2 away from the screw fastening connector 5, L 3 Is the effective length of the second temperature sensing pipe 3, namely the length alpha of the right side edge of the second rectangular notch 31 from the screw fastening connector 5 2 And alpha 3 The thermal expansion coefficients of the materials of the first temperature sensing pipe 2 and the second temperature sensing pipe 3 are respectively.
ΔL 12 The increase in (2) stretches the second grating 12 such that the second grating 12 is subjected to an additional axial strain epsilon in addition to the effect of the temperature change, the strain having a value of
ε＝ΔL 12 /L 12
Wherein L is 12 Is the distance between the right end of the first temperature sensing tube 2 and the right side edge of the second rectangular notch 31 at the calibration temperature.
According to the strain sensing principle of the optical fiber 1 grating, the relative wavelength drift of the second grating 12 caused by the axial strain is as follows
Wherein Deltalambda B-12ε To the shift amount of the center wavelength of the second grating 12 caused by the relative displacement of the two temperature sensing tubes, P eff Is the effective elasto-optical coefficient of the optical fiber 1.
In summary, when the tubular fiber 1 grating temperature sensor is placed in an oil-gas well, the second grating 12 is in a working state due to the increase of the ambient temperature, and the relative wavelength drift amount of the second grating 12 is the sum of formulas (1) and (2)
The sensitivity S ∈r of the sensor at this time is
Thus, by optimizing the dimensions and materials of the first and second temperature sensing pipes 2 and 33, the initial distance L between the end surfaces of the same side is adjusted 12 The response sensitivity of the second grating 12 to temperature can be varied.
For the first grating 11, when the temperature increases, the center wavelength of the grating caused by the temperature increases, but at this time, the distance between the left end of the rectangular notch 21 of the first temperature sensing tube 2 and the left end of the second temperature sensing tube 3 is shortened, so that the prestress of the first grating 11 fixed thereto is released. When the temperature continues to rise to a certain value, the prestressing force of the first grating 11 is completely released. In the whole process, the first grating 11 is in a non-working state, the tubular structure has no temperature sensitization effect on the first grating, and the sensitivity of the first grating is only simple temperature response and can be obtained according to the formula (1).
When the ambient temperature decreases, the first grating 11 will be subjected to additional tensile strain due to the tubular structure, in addition to its normal temperature response, as soon as it is in operation. The center wavelength of the first grating 11 will be smaller due to the temperature decrease, but the strain applied by the tubular structure is a tensile strain, which will increase the center wavelength of the first grating 11. Considering the above, the decrease in ambient temperature results in a relative wavelength shift of the first grating 11 of the difference between the formulas (1) and (2), i.e
The sensitivity S ∈of the sensor at this time is
In the above formula, the strain response of the first optical fiber 1 grating is about an order of magnitude higher than the simple temperature influence due to the temperature reduction of the tubular structure, so that the overall response sensitivity of the first optical fiber 1 grating to the temperature is greatly improved, and the first optical fiber 1 grating is always in a tensile state and cannot be influenced by the initial prestress. The second optical fiber 1 is in a non-working state and is only subjected to simple temperature response, and the tubular structure has no sensitization effect on the second optical fiber.
The temperature reduction and the temperature increase are respectively measured through the two optical fiber 1 gratings, and under the condition that the tensile strength of the optical fiber 1 gratings is the same, the measuring range of the tubular structure optical fiber 1 grating temperature sensor is doubled compared with that of the tubular structure optical fiber 1 grating temperature sensor under the normal condition.
Example 2
In this embodiment, the thicknesses of the first temperature sensing tube 2 and the second temperature sensing tube 3 are the same as each other by 0.1mm, the first temperature sensing tube 2 is made of aluminum alloy, and the second temperature sensing tube 3 is made of invar alloy. In this embodiment, the first grating 11 and the second grating 12 are directly inscribed on the optical fiber 1 without the stripping coating layer by a femtosecond laser, the grating area length of the first grating 11 is 1mm, the central wavelength is 1530nm, the grating area length of the second grating 12 is 1mm, and the central wavelength is 1555nm. The other components and the coupling relation of the components are the same as those of embodiment 1.
Example 3
In this embodiment, the thicknesses of the first temperature sensing tube 2 and the second temperature sensing tube 3 are the same as each other by 0.5mm, the first temperature sensing tube 2 is made of stainless steel, and the second temperature sensing tube 3 is made of carbon fiber. In this embodiment, the first grating 11 and the second grating 12 are directly inscribed on the optical fiber 1 without the stripping coating layer by a femtosecond laser, the grating area length of the first grating 11 is 10mm, the central wavelength is 1530nm, the grating area length of the second grating 12 is 10mm, and the central wavelength is 1555nm. The other components and the coupling relation of the components are the same as those of embodiment 1.
Example 4
In the embodiments 1 to 3, the first temperature sensing tube 2 is made of stainless steel, and the second temperature sensing tube 3 is made of invar alloy. The other components and the coupling relation of the components are the same as those of the corresponding embodiments.
Claims (10)
1. A high-sensitivity tubular fiber bragg grating temperature sensor for an oil gas well is characterized in that: a first temperature sensing tube (2) is sleeved with a second temperature sensing tube (3), a rectangular notch (21) is processed on the side wall of the end of the first temperature sensing tube (2), one end of the second temperature sensing tube (3) is positioned in the middle of the rectangular notch (21), a rectangular notch (31) is processed on the side wall of the other end of the first temperature sensing tube (3), the rectangular notch (31) and the rectangular notch (21) are positioned on the same side, the other end of the first temperature sensing tube (2) is positioned in the middle of the rectangular notch (31), an optical fiber (1) is axially fixed on the first temperature sensing tube (2) and the second temperature sensing tube (3) through four fixing points, a first fixing point A is arranged on the first temperature sensing tube (2) at the rectangular notch (21), a second fixing point B is arranged on one end of the second temperature sensing tube (3), a third fixing point C is arranged on the other end of the first temperature sensing tube (2), a fourth fixing point D is arranged on the second temperature sensing tube (3), a first optical fiber (11) is written on the optical fiber (1) between the first fixing point A and the second fixing point B in a suspended state and a second optical fiber (12) is written on the third fixing point C and the third fixing point is in a suspended state; the first temperature sensing pipe (2) and the second temperature sensing pipe (3) are different in thermal expansion coefficient.
2. The high-sensitivity tubular fiber bragg grating temperature sensor for an oil and gas well according to claim 1, wherein: the first grating (11) and the second grating (12) are directly inscribed on the optical fiber (1) without the stripping coating layer through a femtosecond laser.
3. The high-sensitivity tubular fiber bragg grating temperature sensor for an oil and gas well according to claim 1, wherein: the lengths of the grating areas of the first grating (11) and the second grating (12) are equal to each other and are 1-10 mm, and the difference between the center wavelengths is more than or equal to 3nm.
4. The high-sensitivity tubular fiber bragg grating temperature sensor for an oil and gas well according to claim 1, wherein: the difference between the inner diameter of the first temperature sensing pipe (2) and the outer diameter of the second temperature sensing pipe (3) is 0.1mm.
5. The high-sensitivity tubular fiber bragg grating temperature sensor for an oil and gas well according to claim 1, wherein: two packaging openings I (6) are formed in the other side, opposite to the rectangular notch I (21), of the side wall of the temperature sensing tube I (2), the two packaging openings I (6) are aligned to a first fixed point A and a second fixed point B respectively, and a U-shaped groove I (32) which is coincident with the packaging opening I (6) corresponding to the second fixed point B is formed in one end part of one end of the temperature sensing tube II (3); two packaging openings (4) are formed in the other side, opposite to the rectangular notch (31), of the side wall of the temperature sensing tube (3), the two packaging openings (4) are aligned to a third fixed point C and a fourth fixed point D respectively, and a U-shaped groove (22) which is coincident with the packaging opening (4) corresponding to the third fixed point C is formed in the end part of the other end of the temperature sensing tube (2).
6. The high-sensitivity tubular fiber bragg grating temperature sensor for an oil and gas well according to claim 1, wherein: the first temperature sensing pipe (2) and the second temperature sensing pipe (3) are fixedly connected through a screw fastening connector (5).
7. The high-sensitivity tubular fiber bragg grating temperature sensor for an oil and gas well according to claim 1, wherein: the screw fastening connector (5) is positioned in the axial middle of the whole body formed by the first temperature sensing pipe (2) and the second temperature sensing pipe (3).
8. The high-sensitivity tubular fiber bragg grating temperature sensor for an oil and gas well according to any one of claims 1 to 7, wherein the material of the first temperature sensing tube (2) is one of an aluminum alloy and a stainless steel, the material of the second temperature sensing tube (3) is one of an invar alloy and a carbon fiber, or the material of the first temperature sensing tube (2) is one of an invar alloy and a carbon fiber, and the material of the second temperature sensing tube (3) is one of an aluminum alloy and a stainless steel.
9. The high-sensitivity tubular fiber bragg grating temperature sensor for the oil and gas well according to claim 8, wherein the thickness of the first temperature sensing tube (2) and the second temperature sensing tube (3) is equal to 0.1 mm-0.5 mm.
10. The high-sensitivity tubular fiber bragg grating temperature sensor for the oil and gas well according to claim 8, wherein the sensitivity S ∈ of the sensor in a temperature rising environment is:
wherein L is 2 Is the effective length of the first temperature sensing tube (2), L 3 Is the effective length of the second temperature sensing pipe (3), P eff Is the effective elastance of the optical fiber (1), ζ is the thermo-optic coefficient of the optical fiber (1) material, α is the thermal expansion coefficient of the optical fiber (1) material, α 2 And alpha 3 The thermal expansion coefficients of the first temperature sensing pipe (2) and the second temperature sensing pipe (3) are L 12 Is the effective length lambda of the second grating (12) B-12 Is the Bragg center wavelength of the second grating (12) at the calibration temperature and without the applied stress;
the sensitivity S ∈ of the sensor in the cooling environment is as follows:
wherein lambda is B-11 Is the Bragg center wavelength of the first grating (11) at the calibration temperature and without the applied stress.
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