Optical cable quality detection method for underground temperature measurement

Abstract

The invention belongs to the technical field of optical fiber temperature sensing, and particularly relates to an optical cable quality detection method for underground temperature measurement, which comprises the following steps of: spirally bending an optical cable to form an optical cable ring, stripping the middle part of the optical cable ring, and attaching a temperature probe of a heating cable and a high-precision temperature probe to a steel pipe; meanwhile, the heating cable is spirally wound on the optical cable, the outer layer of the heating cable and the outer layer of the whole optical cable are sleeved with heat preservation cotton, the output temperature of the heating cable is adjusted so that stable staying can be conducted at the preset temperature, and the difference between the numerical values of the DTS equipment and the high-precision probe at the preset temperature is calculated; if the value is within the temperature measurement precision range of the DTS equipment, the value can be used on site, and otherwise, the value cannot be used on site. According to the invention, the temperature measurement precision of subsequent DTS equipment is improved, the quality detection and calibration can be carried out before the optical cable which is used in the well is used in the well again, and the reliability and safety of the optical cable in a high-temperature environment are ensured.

Description

Technical Field

[0001] The invention relates to the technical field of optical fiber temperature sensing, and in particular to an optical cable quality detection method for underground temperature measurement. Background Art

[0002] Fiber-optic distributed temperature sensing system (DTS) is a temperature detection system that uses optical fiber as a sensing and transmission carrier. It has many advantages, including anti-electromagnetic interference, high stability, cost-effectiveness, low energy consumption, and supports continuous temperature monitoring. Traditional fiber-optic distributed temperature sensing system (DTS) is widely used in oil and gas pipeline leakage monitoring, oil field development, power system thermal state monitoring and other fields.

[0003] In related technologies, DTS needs to be connected to a sensing optical fiber for temperature calibration, and the optical fiber used for temperature calibration is often a bare optical fiber. In engineering applications, the optical fiber is made into an optical cable and then connected to the DTS for temperature measurement. The temperature characteristics of the optical fiber may change after the optical fiber is made into an optical cable. This results in DTS being able to ensure temperature measurement accuracy when testing bare optical fibers, but deviations may occur when testing the temperature of optical cables. In addition, hydrogen loss may occur when the optical cable works in a high-temperature environment for a long time, causing changes in the temperature characteristics of the optical cable itself. Therefore, for used optical cables, if they are used directly without secondary temperature calibration, the temperature measurement accuracy of the DTS may also decrease.

[0004] Therefore, the prior art needs to be improved. Summary of the invention

[0005] In order to remedy the deficiencies of the prior art, the present application proposes a method for detecting the quality of an optical cable for downhole temperature measurement.

[0006] The present invention solves the technical problem by adopting the following technical solutions:

[0007] A method for detecting the quality of an optical cable for measuring downhole temperature comprises the following steps:

[0008] S1: Optical cable preparation: remove a portion of the optical cable to be tested, and spirally bend the portion of the optical cable to form an optical cable ring;

[0009] S2: Temperature probe installation: The middle part of the optical cable is stripped to expose the steel pipe of the optical cable, and the temperature probe of the heating cable and the high-precision temperature probe are installed on the exposed steel pipe of the optical cable. At the same time, the spiral of the heating cable is wound on the optical cable, and finally the outer layer of the heating cable and the entire optical cable is covered with thermal insulation cotton;

[0010] S3: Optical fiber connection: connect one end of the optical cable ring to form a loop, and connect the other end to the DTS;

[0011] S4: Temperature detection: adjusting the output temperature of the heating cable so that the temperature of the heating cable stays stable at a plurality of preset temperature points, and measuring the values ​​at the corresponding temperature points by the DTS and the high-precision temperature probe respectively;

[0012] S5: Temperature error calculation: Calculate the difference between the values ​​measured by the DTS and the high-precision temperature probe at the corresponding temperature point;

[0013] S6: Determine whether the optical cable can be used: If the value of the temperature error is within the temperature measurement accuracy range of the DTS, the optical cable can be used; if the value of the temperature error is greater than the temperature measurement accuracy range of the DTS, the optical cable cannot be used.

[0014] Preferably, in S2, the temperature probe of the heating cable and the high-precision temperature probe are coated with a heat-conducting medium when installed on the steel pipe.

[0015] Preferably, in S4, a heat insulating material is provided at the stripping position of the optical cable ring, and the heat insulating material wraps the temperature probe of the heating cable, the high-precision temperature probe and the leaked steel pipe.

[0016] Preferably, S6 also includes the following steps: if the value of the temperature error is greater than the temperature measurement accuracy range requirement of the DTS, the optical cable needs to be recalibrated; if the temperature error detected by the recalibrated optical cable is within the temperature measurement accuracy of the DTS device, the optical cable can be used; if the temperature error is still greater than the temperature measurement accuracy of the DTS device, the optical cable cannot be used on-site.

[0017] To sum up, the beneficial technical effect of the present application is as follows: when DTS is used to measure the temperature of the optical cable at the downhole site, the temperature of the optical cable is detected at the same temperature by DTS and a high-precision temperature probe respectively, and the temperature difference measured by the two is determined whether it is within the temperature measurement accuracy range of DTS. If so, the optical cable can be used at the downhole site; if it exceeds the range, the optical cable needs to be calibrated, and then the calibrated optical cable is temperature-measured again. If the temperature difference this time is within the temperature measurement range of DTS, it can be used; if it still is not, the optical cable is stopped from being used downhole, and the temperature detection and judgment of the optical cable can be performed at the downhole site, thereby improving the temperature measurement accuracy of subsequent DTS equipment, ensuring that the optical cable used downhole can be quality inspected and calibrated before being used downhole again, and ensuring the reliability and safety of the optical cable in high temperature environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0019] Figure 1 This is a schematic diagram of the steps of the temperature detection method in the embodiment of the present application;

[0020] Figure 2 This is an overall schematic diagram of optical cable temperature detection in an embodiment of the present application;

[0021] Figure 3 It is a schematic diagram of the stripped portion of the optical cable in an embodiment of the present application.

[0022] Explanation of the accompanying drawings: 1. Optical cable; 11. Steel pipe; 2. Heating cable; 21. Temperature probe of heating cable; 3. High-precision temperature probe; 4. Thermal insulation cotton; 5. Thermal insulation material. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] The present application embodiment discloses a method for detecting the quality of an optical cable used for downhole temperature measurement. Figure 1 A method for detecting the temperature of a downhole optical cable 1 comprises the following steps:

[0025] S1: Optical cable preparation: first remove about 10m of the end of the optical cable 1 after lifting, and wind the section of the optical cable 1 into an optical cable 1 ring with a diameter of 1m, and extend the optical cable 1 from the ends of the optical cable 1 ring by not less than 1m;

[0026] S2: Temperature probe installation: first, strip the outer protective layer of the optical cable 1 at the middle part of the optical cable 1, with a range of 11mm×11mm, so that the steel pipe 11 of the optical cable 1 is leaked, and the stripping length of the optical cable 1 is not less than 60mm, then stick the high-precision temperature probe 3 on the steel pipe 11 to measure the temperature of the steel pipe 11, then evenly wind the heating cable 2 on the optical cable 1 along the distribution spiral of the optical cable 1, so that the heating cable 2 evenly heats the optical cable 1, and stick the temperature probe 21 of the heating cable on the steel pipe 11, and after the heating cable 2 is evenly wound on the optical cable 1, the outer side of the optical cable 1 and the heating cable 2 are wrapped with thermal insulation cotton 4, which can also be other thermal insulation media, so that the heat of the heating cable 2 can cover the entire optical cable 1, so that the heating cable 2 heats the optical cable 1 more evenly, so that the temperature is as stable as possible, which helps to improve the accuracy of the measurement;

[0027] S3: Fiber connection: connect one end of the optical cable 1 loop to form a loop, and connect the other end to the DTS device;

[0028] S4: Temperature measurement: Start the DTS device first, and set "ZONE" on the optical cable 1, then start the heating cable 2, and make the heating cable 2 stay stably at multiple preset temperature points, such as 120℃, 100℃, 80℃, and 50℃. In order to make the temperature measured by the high-precision temperature probe 3 accurate, set the heating cable 2 to keep each temperature point for 4-6 hours, and record the reading of the high-precision temperature probe 3 and the temperature of the detection zone on the optical cable 1 of the DTS device respectively;

[0029] S5: Temperature error calculation: According to the data measured by the DTS device and the high-precision temperature probe 3, the difference between the reading of the high-precision temperature probe 3 and the reading of the DTS device at each preset temperature is calculated, which is the error value of the optical cable 1 at the preset temperature;

[0030] S6: Determination of whether the optical cable can be used: If the temperature error value is within the temperature measurement accuracy range of the DTS device, then the optical cable 1 can be used on site. If the temperature error value exceeds the temperature measurement accuracy range of the DTS device, then the optical cable 1 cannot be used on site.

[0031] In this embodiment, the measurement accuracy range of the optical cable 1 is: + / -0.5℃@0-140℃, + / -2.0℃@50-250℃. The measurement accuracy range of the optical cable 1 is generally determined according to the ambient temperature of the optical cable 1. The higher the operating temperature of the optical cable 1, the greater the allowable error. In other embodiments, there may also be other ranges of measurement accuracy for the optical cable 1.

[0032] In some embodiments, in step S4, after the heating cable 2 is spirally and evenly wound on the optical cable 1, the outer side of the entire ring of the optical cable 1 is wrapped with thermal insulation cotton 4, which can also be other thermal insulation media. Therefore, when the heating cable 2 heats the optical cable 1, the thermal insulation cotton 4 will wrap the entire optical cable 1 and the heating cable 2. Therefore, when the heating cable 2 heats the optical cable 1, the heat of the heating cable 2 can cover the entire optical cable 1, so that the heating cable 2 heats the optical cable 1 more evenly, and the temperature can be as stable as possible, which helps to improve the accuracy of the measurement.

[0033] In some embodiments, in step S4, a thermal insulation material 5 is provided at the position where the optical cable 1 is stripped, and the thermal insulation material 5 wraps the steel pipe 11 and the high-precision temperature probe 3 and the temperature probe 21 of the heating cable. This can prevent the heating cable 2 from directly heating the high-precision temperature probe 3 when the heating cable 2 heats the optical cable 1, thereby avoiding affecting the reading of the high-precision temperature probe.

[0034] In addition, step S6 also includes that if it is detected for the first time that the difference between the reading of the high-precision temperature probe 3 and the temperature measured by the DTS device exceeds the temperature measurement accuracy of the DTS device, the optical cable 1 can be calibrated. The calibration method can adopt the calibration method in patent number "202410659718.5", or other calibration methods can be adopted. If the temperature error of the optical cable 1 after calibration is within the temperature measurement accuracy of the DTS device, the optical cable 1 can be used downhole. If the temperature error exceeds the temperature measurement accuracy of the DTS device, the optical cable 1 cannot be used. Through this step, the optical cable 1 can be recalibrated, and the part of the optical cable 1 that slightly exceeds the temperature measurement accuracy can be recalibrated and reused, thereby reducing the use cost of the downhole optical cable 1.

[0035] The implementation principle of an optical cable quality detection method for downhole temperature measurement in an embodiment of the present application is as follows: before using the optical cable 1 on site, the optical cable 1 is detected at the same temperature by a DTS device and a high-precision temperature probe respectively. If the temperature difference measured by the two is within the temperature measurement accuracy range of the DTS device, the optical cable 1 can be used. If it is not within the temperature measurement accuracy range of the DTS device, the optical cable 1 needs to be recalibrated. If the difference measured by the recalibrated optical cable 1 is within the temperature measurement accuracy range of the DTS device, it can be used. If not, the optical cable 1 should be stopped from being used downhole. This design method can improve the temperature detection accuracy of subsequent DTS equipment, ensure that the optical cable 1 used downhole can be quality tested and calibrated before being used downhole again, and ensure the reliability and safety of the optical cable 1 in a high temperature environment.

[0036] The above are all preferred embodiments of the present application, and the protection scope of the present application is not limited thereto. Therefore, any equivalent changes made according to the structure, shape, and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for detecting the quality of an optical cable for downhole temperature measurement, characterized in that: The following steps are involved: S1: Optical cable preparation: remove a portion of the optical cable to be tested, and spirally bend the portion of the optical cable to form an optical cable ring; S2: Temperature probe installation: The middle part of the optical cable is stripped to expose the steel pipe of the optical cable, and the temperature probe of the heating cable and the high-precision temperature probe are installed on the exposed steel pipe of the optical cable. At the same time, the spiral of the heating cable is wound on the optical cable, and finally the outer layer of the heating cable and the entire optical cable is covered with thermal insulation cotton; S3: Optical fiber connection: connect one end of the optical cable ring to form a loop, and connect the other end to the DTS; S4: Temperature detection: adjusting the output temperature of the heating cable so that the temperature of the heating cable stays stable at a plurality of preset temperature points, and measuring the values ​​at the corresponding temperature points respectively by the DTS device and the high-precision temperature probe; S5: Temperature error calculation: Calculate the difference between the DTS and the value measured by the high-precision temperature probe of the device at the corresponding temperature point; S6: Determination of whether the optical cable can be used: If the value of the temperature error is within the temperature measurement accuracy range required by the DTS device, the optical cable can be used; if the value of the temperature error is greater than the temperature measurement accuracy range required by the DTS device, the optical cable cannot be used.

2. The optical cable quality detection method for downhole temperature measurement according to claim 1, characterized in that: In S2, the temperature probe of the heating cable and the high-precision temperature probe are coated with a heat-conducting medium when installed on the steel pipe.

3. The optical cable quality detection method for downhole temperature measurement according to claim 1 is characterized in that: In S4, a heat insulating material is provided at the stripping position of the optical cable ring, and the heat insulating material wraps the temperature probe of the heating cable, the high-precision temperature probe and the leaked steel pipe.

4. The optical cable quality detection method for downhole temperature measurement according to claim 1, characterized in that: The S6 also includes the following steps: if the value of the temperature error is greater than the temperature measurement accuracy range requirement of the DTS, the optical cable needs to be recalibrated. If the temperature error detected by the recalibrated optical cable is within the temperature measurement accuracy of the DTS device, the optical cable can be used. If the temperature error is still greater than the temperature measurement accuracy of the DTS device, the optical cable cannot be used on-site.

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