Distributed optical fiber temperature measurement system for online calibration

Abstract

The utility model relates to the technical field of optical fiber sensing, in particular to a distributed optical fiber temperature measurement system for online calibration. Comprising an optical fiber body, a host connected with the optical fiber body and used for correcting temperature and length, and a plurality of mark points preset on the optical fiber body at intervals, and the plurality of mark points comprise a plurality of temperature mark points used for temperature calibration and a plurality of length mark points used for length calibration. The host comprises a light source which is connected to one end of the optical fiber body and transmits a pulse optical signal, a calibration device which is connected with the optical fiber body and is used for calibrating the temperature of each position of the optical fiber body and the total length of the optical fiber body, and a demodulation device which is connected with the optical fiber body and is used for measuring the temperature of the temperature marking point. According to the utility model, the length marking points and the temperature marking points are used for marking the length and the temperature of the sensing optical fiber of the distributed optical fiber temperature measurement system, so that the on-line accurate calibration of the sensing optical fiber is realized, and the temperature detection accuracy of the distributed optical fiber temperature measurement system is improved.

Description

Technical Field

[0001] The utility model relates to the technical field of optical fiber sensing, in particular to an online calibrated distributed optical fiber temperature measurement system. Background Art

[0002] Oil well profile temperature is an important parameter for evaluating oil well status. By measuring the oil well temperature profile, we can not only determine the location of the oil well's water and gas production points, judge and evaluate the quality of cementing, and determine the location of casing leakage, but also use the oil well temperature profile data to invert the liquid production profile and achieve quantitative evaluation of the oil well's liquid production profile.

[0003] Distributed fiber-optic temperature sensing technology offers a new approach for measuring oil well temperature profiles. It exploits the temperature-dependent nature of the Raman scattered light signals generated by light traveling through an optical fiber. By detecting the Raman scattered light signals generated at different locations along the fiber, the temperature can be measured at these locations. Due to its flexible sensing structure, continuous distribution, long monitoring distance, and high operating temperature, this technology simplifies the process of measuring oil well temperature profiles, shortens measurement time, and enables rapid, high-spatial-resolution measurements of oil well temperature profiles. This technology is a key area of ​​research in dynamic oil well monitoring.

[0004] Distributed fiber optic temperature measurement systems (DTS) use optical time-domain reflectometry to locate temperature measurement points. This method calculates the location of the measurement point based on the propagation speed of light in the fiber and the echo time of backscattered light, resulting in high accuracy. In actual well logging applications, the logging fiber is often integrated with downhole fiber optic logging equipment such as coiled tubing to facilitate measurement operations. However, temperature calibration presents numerous challenges. Existing technologies typically use thermostats for calibration, but these cannot meet the requirements for thermostat setup and use in the high-temperature, high-pressure working environment downhole.

[0005] Furthermore, repeated use of oil well temperature measurement cables, such as fiber end processing, can cause changes in the actual length of the fiber. Furthermore, the effects of fiber dispersion make fiber positioning demandingly accurate parameters such as the fiber's refractive index. The complex environment within oil wells exposes optical cables to excessive tension, twisting, compression, and high temperatures, leading to localized stress concentrations and even damage to the sensing fibers within the cable. These factors can cause changes in optical loss at locations of stress concentration or damage, triggering optical loss dispersion effects and causing localized changes in the fiber's refractive index. This not only affects the positioning accuracy of the temperature measurement cable but also adversely impacts system performance, such as spatial resolution.

[0006] Currently, the positioning and calibration of logging fiber optic cables primarily relies on auxiliary references such as cable deployment winches and electrical sensors. However, many factors influence the calibration effect. For distributed fiber optic temperature measurement applications that require high fiber positioning and accurate temperature measurement, it is necessary to develop a distributed fiber optic temperature measurement system with online calibration. Utility Model Content

[0007] In order to solve the above-mentioned problems of calibrating optical fiber length and temperature, the utility model provides an online calibrated distributed optical fiber temperature measurement system, which solves the error problem of the distributed optical fiber temperature measurement system in calculating the length of the sensing optical fiber, and improves the tolerance of the distributed temperature measurement optical cable for the length measurement of the DTS temperature measurement host and the accuracy of temperature measurement.

[0008] The utility model provides an online calibrated distributed optical fiber temperature measurement system, which includes an optical fiber body, a host connected to the optical fiber body for calibrating temperature and length, a plurality of marking points preset on the optical fiber body at intervals, the plurality of marking points including a plurality of temperature marking points for temperature calibration and a plurality of length marking points for length calibration, the host including a light source connected to one end of the optical fiber body for emitting a pulsed light signal, a calibration device connected to the optical fiber body for calibrating the temperature of each position of the optical fiber body and the total length of the optical fiber body, and a demodulation device connected to the optical fiber body for measuring the temperature of the temperature marking points.

[0009] Furthermore, the length marking point includes a first optical fiber, a first optical fiber end face formed at the end of the first optical fiber, a second optical fiber, a second optical fiber end face formed at the end of the second optical fiber, and a principal reflection surface for coupling the first optical fiber end face and the second optical fiber end face to reflect the pulsed light signal.

[0010] Furthermore, the temperature marking point includes a third optical fiber, a third optical fiber end face formed at the end of the third optical fiber, a hollow optical fiber, a fourth optical fiber, and a fourth optical fiber end face formed at the end of the fourth optical fiber. The third optical fiber end face and the fourth optical fiber end face are respectively coupled at both ends of the hollow optical fiber to form two temperature correction reflection surfaces.

[0011] Furthermore, the diameter of the hollow optical fibers in the plurality of temperature marking points is the same as that of the optical fiber body.

[0012] Furthermore, the hollow-core optical fibers at the multiple temperature marking points have different lengths.

[0013] Furthermore, the first temperature-corrected reflecting surface at one end of the optical fiber body principle light source is plated with a reflecting film for increasing the reflection intensity.

[0014] Furthermore, a protective cover is provided outside the plurality of marking points, and a glue injection hole for filling protective glue is provided on the protective cover, and the space between the protective cover and the optical fiber body is filled with filling glue.

[0015] Furthermore, the filling glue is any one of epoxy glue and epoxy resin.

[0016] Furthermore, the demodulation device includes:

[0017] The first acquisition module is used to obtain interference signals of two temperature calibration reflective surfaces;

[0018] The demodulation module is used to calculate the actual temperature value of the temperature mark point using the interference signal.

[0019] Furthermore, the calibration device includes:

[0020] The second acquisition module is used to obtain the time difference by acquiring the time when the light source first emits a pulse light signal and the time when the calibration device receives the Rayleigh scattered light returned at different times;

[0021] A third acquisition module is used to acquire Raman scattered light signals at various positions of the optical fiber body;

[0022] The length calculation module is used to calculate the positions of different marking points based on the time difference, compare the calculated positions with the actual positions preset in the computer, and obtain the length correction coefficient;

[0023] a length calibration module, configured to perform correction calculation on the length of the optical fiber body according to the length correction coefficient, obtain the sensing fiber refractive index of the optical fiber body, and calculate the actual length of the optical fiber body using the sensing fiber refractive index;

[0024] a temperature calculation module, configured to calculate the temperature value to be calibrated using the Raman scattered light signal at each position of the optical fiber body acquired by the third acquisition module;

[0025] The temperature calibration module is used to obtain a temperature correction coefficient based on the comparison of the actual temperature value of the temperature mark point with the temperature value to be calibrated of the temperature mark point, and calculate the actual temperature of each position of the optical fiber body using the temperature correction coefficient.

[0026] In summary, the present invention has the following beneficial technical effects:

[0027] This utility model proposes an online calibrated distributed fiber optic temperature measurement system. By setting multiple length calibration markers on the optical fiber, combined with the time difference of the optical signal acquired by the second acquisition module in the calibration device, and the precise calculations of the length calculation module and the length calibration module, it can accurately correct the length of the optical fiber. This effectively solves the problem of length measurement errors caused by the complex environment of the oil well, such as actual fiber length changes, fiber dispersion, and local stress concentration, and provides more accurate position information for oil well temperature profile measurement.

[0028] 2. This utility model proposes an online calibrated distributed fiber-optic temperature measurement system. The system features a uniquely designed temperature marker, composed of a third optical fiber, a hollow optical fiber, and a fourth optical fiber, forming two temperature calibration reflective surfaces. The first acquisition module of the demodulation device captures the interference signal, and the demodulation module accurately calculates the actual temperature value of the temperature marker. Combined with the temperature calculation module and temperature calibration module in the calibration device, this effectively overcomes the limitations of traditional thermostat calibration in the high-temperature and high-pressure underground environment, significantly improving temperature measurement accuracy.

[0029] 3. The utility model proposes an online calibrated distributed optical fiber temperature measurement system. The temperature measurement optical fiber system has a simple structure and can be integrated with other optical fiber cables after packaging to accurately achieve the corresponding measurement of position and temperature. It is highly adaptable to various types of temperature measurement optical fiber cables, whether single-mode optical fiber cables, multi-mode optical fiber cables, or special optical fiber cables. It can be well compatible with them, give full play to its temperature measurement function, and has practical engineering value. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a structural diagram of an online calibrated distributed optical fiber temperature measurement system according to an embodiment of the present utility model;

[0031] Figure 2 This is a schematic diagram of the length marking point structure of an embodiment of the utility model;

[0032] Figure 3 This is a schematic diagram of the temperature marking point structure of an embodiment of the present utility model;

[0033] Figure 4 is a schematic diagram of a processor according to an embodiment of the present utility model;

[0034] Figure 5 It is a schematic diagram of a thermostat according to an embodiment of the present invention.

[0035] Among them, 1. Optical fiber body; 2. Host; 3. Temperature marking point; 4. Length marking point; 5. First optical fiber; 6. Second optical fiber; 7. Principal reflective surface; 8. Protective cover; 9. Glue injection hole; 10. Filling glue; 11. Third optical fiber; 12. Hollow optical fiber; 13. Fourth optical fiber; 14. Temperature correction reflective surface. DETAILED DESCRIPTION

[0036] The present invention will be described in further detail below with reference to the accompanying drawings.

[0037] Reference Figure 1, Example 1 The utility model provides an online calibrated distributed optical fiber temperature measurement system (DTS), including an optical fiber body 1, a host 2 connected to the optical fiber body 1 for calibrating temperature and length, a plurality of marking points preset on the optical fiber body 1 at intervals, the plurality of marking points including a plurality of temperature marking points 3 for temperature calibration and a plurality of length marking points 4 for length calibration, the host 2 including a light source connected to one end of the optical fiber body for emitting a pulsed light signal, a calibration device connected to the optical fiber body 1 for calibrating the temperature of each position of the optical fiber body 1 and the total length of the optical fiber body 1, and a demodulation device connected to the optical fiber body 1 for measuring the temperature of the temperature marking point 3.

[0038] The wavelength of the DTS host 2 light source is commonly used at 980nm, 1064nm, 1550nm, etc. The DTS temperature measurement system in this embodiment uses a light source with a wavelength of 980nm as the excitation light source wavelength, and adopts a single-ended method to perform optical fiber temperature measurement.

[0039] The type of the optical fiber body 1 should be an optical fiber compatible with the light source of the DTS temperature measurement system. In this embodiment, the optical fiber body 1 is a multimode optical fiber, and the operating wavelength of the optical fiber body 1 should be in the same band as the wavelength of the pulsed light signal excited by the light source of the DTS temperature measurement system.

[0040] The number of the marking points should be determined according to the length positioning requirements of the optical fiber body 1.

[0041] The optical fiber body 1 with the positioning mark function can be integrated into different types of optical cables for optical fiber temperature measurement after being packaged.

[0042] Reference Figure 2 The length marking point 4 includes a first optical fiber 5, a first optical fiber 5 end face formed at the end of the first optical fiber 5, a second optical fiber 6, a second optical fiber 6 end face formed at the end of the second optical fiber 6, and a principal reflection surface 7 that couples the first optical fiber 5 end face and the second optical fiber 6 end face to reflect the pulse light signal.

[0043] In this embodiment, the reflective surface can be produced by cutting the optical fiber at the location where the optical fiber length needs to be marked and then re-fusing it, or by laser etching the location where the marking is required to form the first optical fiber 5 and the second optical fiber 6, and forming a reflective surface at the coupling point between the first optical fiber 5 and the second optical fiber 6. The reflective surface can also be produced by laser etching.

[0044] Reference Figure 3 The temperature marking point 3 includes a third optical fiber 11, an end face of the third optical fiber 11 formed at the end of the third optical fiber 11, a hollow optical fiber 12, a fourth optical fiber 13, and an end face of the fourth optical fiber 13 formed at the end of the fourth optical fiber 13. The end face of the third optical fiber 11 and the end face of the fourth optical fiber 13 are respectively coupled to the two ends of the hollow optical fiber 12 to form two temperature correction reflection surfaces 14.

[0045] The diameter of the hollow optical fibers 12 in the plurality of temperature marking points 3 is the same as that of the optical fiber body 1 .

[0046] The hollow-core optical fibers 12 in the plurality of temperature marking points 3 have different lengths.

[0047] The first temperature-correcting reflective surface 14 at one end of the optical fiber body 1 serving as the light source is coated with a reflective film for increasing the reflection intensity.

[0048] A protective cover 8 is provided outside the plurality of marking points. The protective cover 8 is provided with a glue injection hole 9 for filling protective glue. A filling glue 10 is filled between the protective cover 8 and the optical fiber body 1 .

[0049] The filling glue 10 is any one of epoxy glue and epoxy resin.

[0050] The protective tube is made of metal or non-metal material according to the actual application environment.

[0051] The temperature marking points 3 constitute an optical fiber FP temperature sensor. Different temperature marking points 3 have different lengths of hollow-core optical fibers 12, that is, different cavity lengths of the optical fiber FP temperature sensors, which facilitates multiplexing and demodulation of multiple FP sensors. For example, the cavity length of the first marking point is 100 nm, the cavity length of the second point is 200 nm, and the cavity length of the third point is 300 nm.

[0052] The optical fiber body 1 is provided with a total of several length marking points 4 and two to three temperature marking points 3, wherein one temperature marking point 3 is located at the tail end of the sensing optical fiber, one to two in the middle, and the temperature marking point 3 at the tail end. The second reflective surface needs to be coated with a reflective film to increase the reflection intensity, thereby forming a high-precision FP temperature sensor.

[0053] The demodulator's wavelength should be separated from the DTS host's 2 wavelength and should not operate simultaneously to avoid mutual interference. For example, the DTS light source operates at 980nm and the fiber optic FP demodulator operates at 1550nm.

[0054] Reference Figure 4 , the demodulation device includes,

[0055] The first acquisition module is used to obtain the interference signal of the two temperature calibration reflective surfaces 14;

[0056] The demodulation module is used to calculate the actual temperature value of the temperature mark point 3 using the interference signal.

[0057] Reference Figure 5 , the calibration device includes,

[0058] The second acquisition module is used to obtain the time difference by acquiring the time when the light source first emits a pulse light signal and the time when the calibration device receives the Rayleigh scattered light returned at different times;

[0059] A third acquisition module is used to acquire Raman scattered light signals at various positions of the optical fiber body 1;

[0060] The length calculation module is used to calculate the positions of different marking points based on the time difference, compare the calculated positions with the actual positions preset in the computer, and obtain the length correction coefficient;

[0061] a length calibration module, configured to perform correction calculation on the length of the optical fiber body 1 according to the length correction coefficient, obtain the sensing fiber refractive index of the optical fiber body 1, and calculate the actual length of the optical fiber body 1 using the sensing fiber refractive index;

[0062] a temperature calculation module, configured to calculate the temperature value to be calibrated using the Raman scattered light signal at each position of the optical fiber body 1 acquired by the third acquisition module;

[0063] The temperature calibration module is used to obtain a temperature correction coefficient based on the comparison of the actual temperature value of the temperature mark point 3 with the temperature value to be calibrated of the temperature mark point 3, and calculate the actual temperature of each position of the optical fiber body 1 using the temperature correction coefficient.

[0064] During operation, after the light source emits a pulsed light signal, a second acquisition module detects the time of the first pulsed light signal. When the pulsed light signal propagates along the optical fiber and encounters the reflective component at the marker point, it generates Rayleigh scattered light. The detector in the calibration device then uses the second acquisition module to detect the time of each return of the Rayleigh scattered light at different times. The length calculation module then calculates the positions of the various marker points based on the time difference between each return of the Rayleigh scattered light and the known propagation speed of light in the optical fiber. Taking into account local stress concentration or damage caused by stretching, twisting, squeezing, and high temperatures in the oil well environment, the calculated marker point positions are then compared with the actual positions preset in the computer. Since the actual length of the deployed optical fiber may vary, this comparison can detect discrepancies. Based on the comparison results, the optical fiber's refractive index and other parameters are then recalculated. Finally, based on the corrected refractive index and the time difference between the transmission and reception of the optical signal, the optical fiber length is recalculated, achieving calibration to meet the requirements for temperature measurement cable positioning and the system's spatial resolution.

[0065] In practical applications, accurate detection of the temperature at each position of the optical fiber is achieved through the following steps:

[0066] First, the light source emits a pulsed light signal, which propagates along the optical fiber body 1. During the propagation process, due to the different temperatures at different positions of the optical fiber, Stokes scattered light and anti-Stokes scattered light of different intensities will be generated. At the same time, the marking points set at intervals on the optical fiber will reflect the pulsed light signal and generate Rayleigh scattered light, thereby determining the position of the marking point and realizing the calibration of the optical fiber length. The demodulation module in the demodulation device obtains the actual temperature value of the temperature marking point 3 as a reference temperature. The third acquisition module obtains the photoelectric conversion value of the Stokes scattered light and anti-Stokes scattered light generated by the pulsed light signal and calculates their intensity ratio. Then, the temperature calculation module calculates the temperature value to be calibrated at the temperature marking point 3 based on their intensity ratio. The temperature correction coefficient is obtained by the actual temperature value and the temperature value to be calibrated. The temperature correction coefficient is used to correct the temperature to be calibrated at each position of the optical fiber body 1 to obtain the actual temperature value of each position of the optical fiber body 1, thereby improving the accuracy of temperature measurement.

[0067] The above are all preferred embodiments of the present invention, and are not intended to limit the scope of protection of the present invention. Therefore, any equivalent changes made based on the structure, shape, and principle of the present invention should be included in the scope of protection of the present invention.

Claims

1. An online calibrated distributed optical fiber temperature measurement system, characterized in that: The invention comprises an optical fiber body (1), a host (2) connected to the optical fiber body (1) and used for calibrating temperature and length, a plurality of marking points preset at intervals on the optical fiber body (1), the plurality of marking points comprising a plurality of temperature marking points (3) for temperature calibration and a plurality of length marking points (4) for length calibration, the host (2) comprising a light source connected to one end of the optical fiber body for emitting a pulsed light signal, a calibration device connected to the optical fiber body (1) and used for calibrating the temperature of each position of the optical fiber body (1) and the total length of the optical fiber body (1), and a demodulation device connected to the optical fiber body (1) and used for measuring the temperature of the temperature marking points (3).

2. The distributed optical fiber temperature measurement system with online calibration according to claim 1, characterized in that: The length marking point (4) includes a first optical fiber (5), a first optical fiber (5) end face formed at the end of the first optical fiber (5), a second optical fiber (6), a second optical fiber (6) end face formed at the end of the second optical fiber (6), and a principal reflection surface (7) for coupling the first optical fiber (5) end face and the second optical fiber (6) end face to reflect the pulse light signal.

3. The distributed optical fiber temperature measurement system with online calibration according to claim 1, characterized in that: The temperature marking point (3) comprises a third optical fiber (11), an end face of the third optical fiber (11) formed at the end of the third optical fiber (11), a hollow optical fiber (12), a fourth optical fiber (13), and an end face of the fourth optical fiber (13) formed at the end of the fourth optical fiber (13); the end face of the third optical fiber (11) and the end face of the fourth optical fiber (13) are respectively coupled to the two ends of the hollow optical fiber (12) to form two temperature correction reflection surfaces (14).

4. The distributed optical fiber temperature measurement system with online calibration according to claim 1, characterized in that: The hollow optical fibers (12) in the plurality of temperature marking points (3) have the same diameter as the optical fiber body (1).

5. The distributed optical fiber temperature measurement system with online calibration according to claim 3, characterized in that: The hollow optical fibers (12) in the plurality of temperature marking points (3) have different lengths.

6. The distributed optical fiber temperature measurement system with online calibration according to claim 3, characterized in that: The first temperature-correcting reflecting surface (14) at one end of the optical fiber body (1) is plated with a reflecting film for increasing the reflection intensity.

7. The distributed optical fiber temperature measurement system with online calibration according to claim 1, characterized in that: A protective cover (8) is provided outside the plurality of marking points, a glue injection hole (9) for filling protective glue is provided on the protective cover (8), and a filling glue (10) is filled between the protective cover (8) and the optical fiber body (1).

8. The distributed optical fiber temperature measurement system with online calibration according to claim 5, characterized in that: The filling glue (10) is any one of epoxy glue and epoxy resin.

9. The distributed optical fiber temperature measurement system with online calibration according to claim 1, characterized in that: The demodulation device includes: A first acquisition module is used to acquire interference signals of two temperature calibration reflection surfaces (14); The demodulation module is used to calculate the actual temperature value of the temperature mark point (3) using the interference signal.

10. The distributed optical fiber temperature measurement system with online calibration according to claim 9, characterized in that: The calibration device comprises, The second acquisition module is used to obtain the time difference by acquiring the time when the light source first emits a pulse light signal and the time when the calibration device receives the Rayleigh scattered light returned at different times; A third acquisition module is used to acquire Raman scattered light signals at various positions of the optical fiber body (1); The length calculation module is used to calculate the positions of different marking points based on the time difference, compare the calculated positions with the actual positions preset in the computer, and obtain the length correction coefficient; A length calibration module is used to perform correction calculation on the length of the optical fiber body (1) according to the length correction coefficient, obtain the sensing optical fiber refractive index of the optical fiber body (1), and calculate the actual length of the optical fiber body (1) using the sensing optical fiber refractive index; A temperature calculation module, used for calculating the Raman scattered light signal at each position of the optical fiber body (1) obtained by the third acquisition module as a temperature value to be calibrated; The temperature calibration module is used to obtain a temperature correction coefficient based on the comparison of the actual temperature value of the temperature mark point (3) with the temperature value to be calibrated of the temperature mark point (3), and calculate the actual temperature of each position of the optical fiber body (1) using the temperature correction coefficient.

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