Distributed optical fiber temperature detection double-end correction device and method

Abstract

The invention provides a distributed optical fiber temperature detection double-end correction device and method, and belongs to the technical field of optical fiber logging, the upper end of a logging optical cable is connected with a ground reference optical fiber ring, and the lower end of the logging optical cable is connected with an optical fiber grating sensor; the electronic temperature sensor is placed in the ground reference optical fiber ring, the measurement and control module is connected with the electronic temperature sensor, and the temperature of the ground reference optical fiber ring is measured through the electronic temperature sensor; the pump light source and the DTS measurement module are connected with the COM optical splitter; the optical switch is used for switching DTS distributed optical fiber measurement and optical fiber grating sensor measurement; temperature values measured by the DTS distributed optical fiber and the optical fiber grating sensor serve as reference data to adjust measurement parameters of the DTS measurement module, and double-end correction of DTS temperature measurement data is completed. The ground reference optical fiber is combined with the electronic thermometer, and the optical fiber grating sensor is adopted underground, so that distributed optical fiber temperature measurement double-end correction is realized.

Description

Technical Field

[0001] The invention belongs to the technical field of optical fiber well logging, and in particular to a distributed optical fiber temperature detection double-end correction device and method. Background Art

[0002] Distributed fiber optic logging technology, where the optical fiber is both a transmission channel and a sensor, can achieve real-time monitoring of temperature and acoustic vibration at different locations in the well through a single optical fiber. The optical fiber does not need to be moved during the logging process, and does not interfere with the dynamic environment downhole, making logging more efficient and accurate. Combined with the promotion and application of long-term optical fiber monitoring technology, it can provide Party A with more intelligent technical services such as well site monitoring, wellbore integrity detection, fracturing effect monitoring, injection volume monitoring, etc., and provide better solutions for the development of digital oil fields.

[0003] Distributed fiber temperature sensing system (DTS) is an optical instrument that uses optical fiber as a sensor for temperature perception. The system uses a single optical fiber to simultaneously monitor temperature and transmit signals. It can detect tiny temperature changes, provide accurate and continuous temperature data in real time, and can achieve real-time, fast, multi-point measurement of spatial temperature distribution over a large range and long distance. The existing distributed fiber temperature measurement DTS system uses the principle of optical time domain reflectometry (OTDR) and Raman scattering effect to achieve temperature monitoring. Raman scattering is due to the thermal vibration of optical fiber molecules, which will produce a light longer than the wavelength of the light source - Stokes light and a light shorter than the wavelength of the light source - Anti-Stokes light. The modulation of the external temperature of the optical fiber causes the intensity of the Anti-Stokes light in the optical fiber to change. The ratio of Anti-Stokes to Stokes provides an absolute indication of the temperature. This principle is used to achieve distributed measurement of the temperature field along the optical fiber. Combined with high-quality pulse light sources and high-speed signal acquisition and processing technology, accurate temperature values ​​at all points along the optical fiber can be obtained.

[0004] In the actual measurement process, the Stokes and anti-Stokes scattering in the reflected light are usually collected separately, and then the temperature signal is demodulated using the ratio of the light intensity of the two. The relationship between temperature and reflected light is:

[0005]

[0006] Where: T is temperature; k is proportionality coefficient; a is constant; Ia is anti-Stokes intensity; Is is Stokes intensity.

[0007] During the process of lowering the optical cable into the well, the scattered light intensity will change due to the bending and stress of the optical cable, as well as the operating temperature of the laser in the measuring device. In order to obtain an accurate temperature measurement structure, it is necessary to correct the temperature coefficient through the bottom-hole temperature and the ground environment after the optical cable is lowered into the well. Currently, the traditional method is to measure the optical cable on the ground first, determine the coefficients k and a through the ground data, use a stored electronic temperature measuring instrument to measure the bottom-hole temperature after the optical cable is lowered into the well, and then use the stored temperature to correct the data after the instrument reaches the ground. If the storage instrument fails, the measurement data cannot be corrected, resulting in a large error in the measurement result.

[0008] The traditional DTS measurement results can well reflect the temperature changes along the fiber optic cable layout, but the measurement results are affected by factors such as the output power of the laser light source, the type of optical fiber, the cable winding method, and the stress on the optical cable. Although the influence of the optical fiber type can be eliminated through ground testing calibration of the optical cable, after the optical cable is lowered into the well, the stress and bending state of the optical cable change, and the measurement results using the parameters of the ground calibration of the optical cable have a large difference from the actual temperature. Due to the fact that different DTS measurement data have slightly different laser light sources, there are also certain differences in the measurement results of the same optical fiber.

[0009] In summary, in the prior art, due to different types of optical fibers and different laying processes, there are significant differences in the distributed optical fiber temperature measurement results. Summary of the Invention

[0010] In order to solve the problems existing in the prior art, the present invention provides a distributed optical fiber temperature detection dual-end calibration device and method, which are used to solve the problem that there are significant differences in the distributed optical fiber temperature measurement results due to different types of optical fibers and different laying processes.

[0011] To achieve the above object, the present invention provides the following technical solutions:

[0012] A distributed optical fiber temperature detection dual-end calibration device includes a pump light source, a COM optical splitter, an optical switch, a ground reference fiber optic loop, an electronic temperature sensor, a logging optical cable, a fiber grating sensor, a DTS measurement module, a fiber grating FBG measurement module, a measurement and control module, and a computer;

[0013] The upper end of the logging optical cable is connected to the ground reference fiber optic loop, and the lower end of the logging optical cable is connected to the fiber grating sensor;

[0014] The electronic temperature sensor is placed inside the ground reference fiber optic loop, and the measurement and control module is connected to the electronic temperature sensor to measure the temperature of the ground reference fiber optic loop through the electronic temperature sensor;

[0015] The pump light source and the DTS measurement module are connected to a COM optical splitter; the FBG measurement module is connected to an optical switch; the measurement and control module is connected to the optical switch;

[0016] The DTS measurement module, the FBG measurement module, and the measurement and control module are connected to a computer;

[0017] The switching between DTS distributed optical fiber measurement and fiber Bragg grating sensor measurement is performed through an optical switch; the temperature values of DTS distributed optical fiber measurement and fiber Bragg grating sensor measurement are used as reference data to adjust the measurement parameters of the DTS measurement module, and the double-end calibration of DTS temperature measurement data is completed.

[0018] Preferably, the ground reference optical fiber loop is an optical fiber loop wound with 100 optical fibers with a diameter of 100 mm.

[0019] Preferably, the electronic temperature sensor is placed at the central position inside the ground reference optical fiber loop.

[0020] Preferably, the logging optical cable and the fiber Bragg grating sensor are connected by fusion splicing.

[0021] A double-end calibration method for distributed optical fiber temperature detection, based on the distributed optical fiber temperature detection double-end calibration device described in any one of the above, includes the following processes,

[0022] The switching between DTS distributed optical fiber measurement and fiber Bragg grating sensor measurement is performed through an optical switch;

[0023] The temperature at the bottom of the lower end of the logging optical cable is measured by using the fiber Bragg grating sensor and the FBG measurement module;

[0024] The temperatures at both ends of the logging optical cable are accurately measured by the electronic temperature sensor and the fiber Bragg grating sensor. The measurement parameters of the DTS measurement module are adjusted by using these two measured temperature values as reference data, and the double-end calibration of DTS temperature measurement data is completed.

[0025] Preferably, during the DTS temperature measurement process, the temperature value is calculated through the measured Stokes Is and anti-Stokes Ia signals.

[0026] Furthermore, the calculation formulas for the Stokes Is and anti-Stokes Ia are as follows:

[0027]

[0028] In the formula: T is the temperature; k is the proportionality coefficient; a is a constant; Ia is the anti-Stokes light intensity; Is is the Stokes light intensity.

[0029] Further, by using the temperature T1 measured by the electronic temperature sensor and the temperature T2 measured by the fiber Bragg grating sensor, the values of the parameters k and a to be determined are solved according to the equations.

[0030] Further, the parameter solving equations are as follows:

[0031]

[0032]

[0033] Compared with the prior art, the present invention has the following beneficial technical effects:

[0034] The present invention provides a distributed optical fiber temperature detection double-end correction device. By combining a ground reference optical fiber with an electronic thermometer and using fiber Bragg grating sensors downhole, a method for double-end correction of distributed optical fiber temperature measurement is realized. This device can observe and record the temperature changes on the ground and at the bottom of the well in real time during a single downhole operation, ensuring the accuracy and consistency of the distributed optical fiber temperature measurement results.

[0035] The present invention realizes the double-end correction of distributed optical fiber temperature measurement through the combination of a reference optical fiber, a thermometer, and fiber Bragg gratings, improving the measurement accuracy of the device and ensuring the consistency of measurement results of different devices. This technology provides a reliable measurement means for measuring the production and injection profiles of oil and gas wells. With the popularization of optical fiber logging technology, the logging demand will be increasing, and the market prospect is broad.

[0036] The present invention accurately measures the temperatures at both ends of the optical cable by adding a reference optical fiber, an electronic thermometer, and fiber Bragg gratings. The temperature measurement results at both ends are not affected by the optical cable and DTS equipment. The temperature measurement accuracy of the electronic thermometer and fiber Bragg gratings can reach 0.1 °C. This method provides a double-end precise correction method for DTS measurement. Using different devices or different optical cables, the DTS measurement results can ensure good measurement accuracy and consistency. In addition, the present invention uses an optical switch to realize the switching between DTS distributed optical fiber measurement and fiber Bragg grating sensor measurement. Using one optical fiber, DTS measurement can be carried out, and fiber Bragg grating temperature measurement can also be realized, improving the utilization rate of the optical fiber. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a schematic diagram of a distributed optical fiber temperature detection double-end correction device;

[0038] Figure 2 It is a schematic diagram of DTS double-end correction construction;

[0039] Figure 3 It is a schematic diagram of the principle of fiber Bragg grating temperature measurement;

[0040] In the attached drawings: 1 is a pump light source; 2 is a COM optical splitter; 3 is an optical switch; 4 is a ground reference optical fiber loop; 5 is an electronic temperature sensor; 6 is a logging optical cable; 7 is an optical fiber grating sensor; 8 is a DTS measurement module; 9 is an optical fiber grating FBG measurement module; 10 is a measurement and control module; 11 is a computer; 12 is a DTS double-end calibration measurement system; 13 is a wellbore. Detailed implementation manners

[0041] The present invention will be further described in detail below in conjunction with specific embodiments, which are explanations of the present invention rather than limitations.

[0042] In view of the phenomenon that in current distributed optical fiber temperature measurement, due to different types of optical fibers and different laying processes, there are significant differences in the distributed optical fiber temperature measurement results. Through the distributed optical fiber temperature logging curve, quantitative interpretation of the production and injection profiles can be achieved. Therefore, accurate measurement of the downhole absolute temperature is required. Currently, distributed optical fiber temperature measurement devices generally adopt the method of single-end calibration on the ground. Since the optical cable is generally more than 5000m, there is a large error in the measured bottom hole temperature. The present invention proposes a method that combines a ground reference optical fiber and an electronic thermometer, and uses an optical fiber grating sensor downhole to achieve the double-end calibration method of distributed optical fiber temperature measurement. This method can observe and record the temperature changes on the ground and at the bottom hole in real time during one trip downhole, ensuring the accuracy and consistency of the distributed optical fiber temperature measurement results.

[0043] The present invention realizes the double-end calibration of distributed optical fiber temperature measurement through the combination of a reference optical fiber, a thermometer and an optical fiber grating, improves the measurement accuracy of the device, and also ensures the consistency of the measurement results of different devices. This technology provides a reliable measurement means for the measurement of the production and injection profiles of oil and gas wells. With the popularization of optical fiber logging technology, the logging demand will be increasing, and the market prospect is broad.

[0044] The present invention combines the distributed optical fiber DTS technology with the optical fiber grating measurement technology to realize the double-end calibration measurement method of distributed optical fiber measurement, which makes up for the measurement error caused by environmental temperature or optical fiber material parameter changes in DTS measurement.

[0045] Point temperature measurement uses the optical fiber Bragg grating (FBG) measurement technology. The Bragg grating is an optical fiber passive device formed by a permanent periodic perturbation of the refractive index of the optical fiber core. It can reflect the light that satisfies the Bragg condition in the incident light back to the ground, and the wavelength of the reflected light has a linear relationship with the physical quantity of temperature. Therefore, the temperature parameter at the position where the grating is located can be measured according to the change of the wavelength. The essence of the optical fiber grating is to form a narrowband filter or mirror in the core, selectively reflect the incident broadband light, reflect a narrowband light modulated by the grating area, and the transmitted light continues to propagate along the optical fiber. The temperature measurement principle is asFigure 3 as shown

[0046] Fiber Bragg grating sensors have good temperature stability, small size, and high measurement accuracy, with an accuracy of up to 0.1 °C. Precise temperature measurement can be achieved through optical fibers.

[0047] By combining distributed optical fiber temperature measurement with fiber Bragg grating point temperature sensors and correcting the distributed optical fiber temperature measurement data with the point fiber Bragg grating temperature measurement data, the temperature measurement accuracy of DTS can be improved, and the consistency of measurement results of different DTS devices can also be improved.

[0048] Embodiment

[0049] As Figure 1 shown, a distributed optical fiber temperature detection dual-end correction device of the present invention includes a pump light source 1, a COM optical splitter 2, an optical switch 3, a ground reference optical fiber loop 4, an electronic temperature sensor 5, a logging optical cable 6, a fiber Bragg grating sensor 7, a DTS measurement module 8, a fiber Bragg grating FBG measurement module 9, a measurement and control module 10, and a computer 11.

[0050] The pump light source 1, the COM optical splitter 2, the optical switch 3, the ground reference optical fiber loop 4, the electronic temperature sensor 5, the logging optical cable 6, the fiber Bragg grating sensor 7, the DTS measurement module 8, the fiber Bragg grating FBG measurement module 9, the measurement and control module 10, and the computer 11 form a DTS dual-end correction measurement system.

[0051] Among them, the ground reference optical fiber loop 4 is an optical fiber loop wound with 100 optical fibers with a diameter of 100 mm. The upper end of the logging optical cable 6 is connected to the ground reference optical fiber loop 4, and the lower end is connected to the fiber Bragg grating sensor 7. The electronic temperature sensor 5 is placed at the center of the optical fiber loop. The measurement and control module 10 is connected to the electronic temperature sensor 5. By measuring the electronic temperature sensor 5, the temperature of the optical fiber loop can be known. The temperature of the distributed optical fiber measured by the DTS measurement module 8 at the position of the ground reference optical fiber loop 4 is a temperature segment with a consistent temperature. The fiber Bragg grating sensor 7 and the fiber Bragg grating FBG measurement module 9 are used to measure the temperature at the bottom of the well at the lower end of the logging optical cable 6. The accurate measurement of the temperatures at both ends of the logging optical cable 6 is realized through the electronic temperature sensor 5 and the fiber Bragg grating sensor 7. By using these two measured temperature values as reference data to adjust the measurement parameters of the DTS measurement module 6, the dual-end correction of the DTS temperature measurement data is realized.

[0052] During the DTS temperature measurement process, the temperature value is calculated using the measured Stokes (Is) and anti-Stokes (Ia) signals with formula (1). The k and a values in formula (1) are two parameters to be determined. The temperature T1 measured by the electronic temperature sensor 5 and the temperature T2 measured by the fiber Bragg grating sensor 7 are used. From formula (1), a system of equations can be formed:

[0053]

[0054]

[0055] The parameters k and a can be solved through Formulas (2) and (3).

[0056] The present invention adopts the method of DTS measurement and double-end temperature correction, making the result of DTS distributed optical fiber temperature measurement more accurate.

[0057] The traditional DTS measurement result can well reflect the temperature change along the optical fiber layout. However, the measurement result is affected by factors such as the output power of the laser light source, the type of optical fiber, the cable coiling method, and the stress on the optical cable. Although the influence of the optical fiber type can be eliminated through the ground test calibration of the optical cable, after the optical cable is lowered into the well, both the stress and the bending state of the optical cable change, and the measurement result using the parameters of the ground calibration of the optical cable has a large difference from the actual temperature. Due to the fact that different DTS measurement data have laser light sources that are not completely the same, there are also certain differences in the measurement results of the same optical fiber. The present invention realizes the accurate measurement of the temperatures at both ends of the optical cable by adding a reference optical fiber, an electronic thermometer, and an optical fiber grating. The temperature measurement results at both ends are not affected by the optical cable and the DTS device, and the temperature measurement accuracy of the electronic thermometer and the optical fiber grating can reach 0.1 °C. This method provides a double-end precise correction method for DTS measurement. Using different devices or different optical cables, the measurement results of DTS can ensure good measurement accuracy and consistency. In addition, the present invention uses an optical switch 3 to realize the switching between DTS distributed optical fiber measurement and optical fiber grating sensor measurement. Using one optical fiber, both DTS measurement and optical fiber grating temperature measurement can be realized, improving the utilization rate of the optical fiber.

[0058] A double-end correction method for distributed optical fiber temperature detection according to the present invention includes the following process.

[0059] During the well logging construction process, one optical fiber grating sensor 7 is fusion-spliced to the lower end of the optical fiber inside the optical cable. After the well logging optical cable 6 is lowered to the bottom of the wellbore 14, the bottom hole temperature of the well logging optical cable 6 is measured using the optical fiber grating sensor 7.

[0060] There is a reference optical fiber and an electronic thermometer inside the ground DTS device. Since the optical fiber of the ground part of the well logging optical cable is connected to the reference optical fiber inside the DTS device, the temperature of the upper end of the optical cable can be measured using the electronic thermometer. The temperature values at both ends of the optical fiber can be accurately measured using the optical fiber grating sensor 7 and the electronic temperature sensor of the DTS ground device.

[0061] During the logging process, while measuring the Stokes (Is) and anti-Stokes (Ia) signals each time, the temperature at the upper end of the optical fiber is measured with an electronic thermometer and the temperature at the lower end of the optical fiber is measured using a fiber Bragg grating temperature sensor. By combining the accurate temperature measurement values at both ends with the distributed optical fiber temperature calculation formula (1), the parameters k and a in the formula can be accurately calculated. Since the temperature measurement results of the electronic thermometer and the fiber Bragg grating sensor can truly reflect the external environmental temperature, this method ensures that the temperatures at both ends of the optical cable during the DTS measurement process are exactly the same as the actual environmental temperature. Using this measurement method makes the measurement results of DTS basically consistent with the actual temperature, and the measurement results are more accurate. At the same time, due to the good consistency of the electronic temperature sensor and the fiber temperature sensor, the DTS data is corrected using the temperatures measured by them, so that the measurement results of different DTS devices can maintain good consistency.

[0062] The foregoing has shown and described the basic principles, main features and advantages of the present invention. For those skilled in the art, it is obvious that the present invention is not limited to the details of the above-described exemplary embodiments, and without departing from the spirit or basic characteristics of the present invention, the present invention can be implemented in other specific forms. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be embraced within the present invention. Any reference signs in the claims should not be construed as limiting the claims involved.

[0063] In addition, it should be understood that although this specification is described according to embodiments, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art. The above content is only to illustrate the technical idea of the present invention and cannot be used to limit the protection scope of the present invention. Any modification made on the basis of the technical solution according to the technical idea proposed by the present invention falls within the protection scope of the claims of the present invention.

Claims

1. A dual - end calibration device for distributed optical fiber temperature detection, characterized in that, it includes a pump light source (1), a COM optical splitter (2), an optical switch (3), a ground reference optical fiber loop (4), an electronic temperature sensor (5), a logging optical cable (6), an optical fiber grating sensor (7), a DTS measurement module (8), an optical fiber grating FBG measurement module (9), a measurement and control module (10) and a computer (11); The upper end of the logging optical cable (6) is connected to the ground reference optical fiber loop (4), and the lower end of the logging optical cable (6) is connected to the optical fiber grating sensor (7); The electronic temperature sensor (5) is placed inside the ground reference optical fiber loop (4), and the measurement and control module (10) is connected to the electronic temperature sensor (5) to measure the temperature of the ground reference optical fiber loop (4) through the electronic temperature sensor (5); The pump light source (1) and the DTS measurement module (8) are connected to the COM optical splitter (2); the FBG measurement module (9) is connected to the optical switch (3); the measurement and control module (10) is connected to the optical switch (3); The DTS measurement module (8), the FBG measurement module (9), and the measurement and control module (10) are connected to the computer (11); The optical switch (3) is used to switch between DTS distributed optical fiber measurement and optical fiber grating sensor measurement; the temperature values of DTS distributed optical fiber measurement and optical fiber grating sensor measurement are used as reference data to adjust the measurement parameters of the DTS measurement module, and the dual - end calibration of DTS temperature measurement data is completed.

2. The dual - end calibration device for distributed optical fiber temperature detection according to claim 1, characterized in that, The ground reference optical fiber loop (4) is an optical fiber loop wound with 100 optical fibers with a diameter of 100 mm.

3. The dual - end calibration device for distributed optical fiber temperature detection according to claim 1, characterized in that, The electronic temperature sensor (5) is placed at the central position inside the ground reference optical fiber loop (4).

4. The dual - end calibration device for distributed optical fiber temperature detection according to claim 1, characterized in that, The logging optical cable (6) and the optical fiber grating sensor (7) are connected by fusion splicing.

5. A dual - end calibration method for distributed optical fiber temperature detection, characterized in that, Based on the dual - end calibration device for distributed optical fiber temperature detection according to any one of claims 1 to 4, it includes the following processes, The optical switch (3) is used to switch between DTS distributed optical fiber measurement and optical fiber grating sensor measurement; The optical fiber grating sensor (7) and the FBG measurement module (9) are used to measure the bottom - hole temperature at the lower end of the logging optical cable (6); The electronic temperature sensor (5) and the optical fiber grating sensor (7) are used to accurately measure the temperatures at both ends of the logging optical cable (6), and the two measured temperature values are used as reference data to adjust the measurement parameters of the DTS measurement module (6), and the dual - end calibration of DTS temperature measurement data is completed.

6. The dual - end calibration method for distributed optical fiber temperature detection according to claim 5, characterized in that, During the DTS temperature measurement, the temperature value is calculated through the measured Stokes Is and anti-Stokes Ia signals.

7. A dual-end calibration method for distributed optical fiber temperature detection according to claim 6, characterized in that the calculation formulas for the Stokes Is and anti-Stokes Ia are: In the formula: T is the temperature; k is the proportionality coefficient; a is a constant; Ia is the anti-Stokes light intensity; Is is the Stokes light intensity.

8. A dual-end calibration method for distributed optical fiber temperature detection according to claim 7, characterized in that by using the temperature T1 measured by the electronic temperature sensor (5) and the temperature T2 measured by the fiber Bragg grating sensor (7), the values of the parameters k and a to be determined are solved according to the system of equations.

9. A dual-end calibration method for distributed optical fiber temperature detection according to claim 8, characterized in that the parameter solving system of equations is:

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