Oil and gas pipeline stress-strain monitoring system

Abstract

The oil and gas pipeline stress-strain monitoring system comprises a composite cable, the composite cable is an optical fiber connected with an optical fiber composite coaxial cable in series, and a plurality of coaxial cable strain sensors are connected to the optical fiber composite coaxial cable in series; the optical fiber section is used for being laid in an oil-gas pipeline area where large strain does not need to be measured, and the optical fiber composite coaxial cable section is used for being laid in an oil-gas pipeline area where large strain needs to be measured. The BOTDR host is accessed from the end part of the optical fiber section and is used for providing and receiving a laser signal; and the vector network analyzer is accessed from the end part of the optical fiber composite coaxial cable section and is used for providing and receiving a microwave signal. Two technologies for monitoring stress and strain of the oil and gas pipeline are fused, the optical fiber composite coaxial cable is laid in an oil and gas pipeline area with large strain monitoring requirements, the BOTDR technology is used for measurement when the strain is small, the advantage of long-distance strain measurement of the BOTDR technology is brought into play, and the advantage of large strain measurement of the coaxial cable is also brought into play.

Description

Technical Field

[0001] The present invention relates to a stress and strain monitoring system for oil and gas pipelines, specifically to a monitoring system using coaxial cables and optical fibers, and belongs to the technical field of structural health monitoring. Background Art

[0002] The integrity monitoring of medium and long-distance oil and gas pipelines is related to the safety of the pipelines themselves, as well as the stability of energy supply and the requirements of environmental protection. Especially in areas where geological disasters occur frequently, the safe operation of oil and gas pipelines faces severe challenges. These disasters, such as earthquakes, landslides, debris flows, water flow scouring, etc., may not only directly damage the pipelines, but also indirectly affect the stress distribution and stability of the pipelines by changing the topography and soil structure. At this time, it is particularly important to monitor the stress and strain of oil and gas pipelines.

[0003] Installing vibrating wire strain gauges on oil and gas pipelines and performing distributed optical fiber monitoring on pipelines are common means of pipeline stress and strain monitoring. These two monitoring means have relatively high accuracy in measuring the strain of oil and gas pipelines, and can achieve a measurement accuracy of 10 microstrains or even better in most cases. However, both of these monitoring means have a disadvantage, that is, the strain measurement range is small, not exceeding the range of ±20,000 microstrains. However, in areas where geological disasters occur frequently, oil and gas pipelines may be subjected to large strains, exceeding the measurement ranges of vibrating wire strain gauges and distributed optical fibers. The monitoring scheme using coaxial cables can effectively solve the problem of large strain measurement. The strain measurement range of coaxial cables can reach ±150,000 microstrains, but the measurement accuracy is low, about 500 microstrains. The short measurement distance restricts the application of coaxial cable strain measurement technology. Since the attenuation of laser in glass optical fibers is very small, distributed optical fibers can measure the strain of pipelines dozens of kilometers long. Since the attenuation of microwave in coaxial cables is relatively fast, using coaxial cables to measure strain can only measure pipelines dozens of meters long.

[0004] The measurement of the maximum strain and stress of any cross-section of an oil and gas pipeline can be calculated by measuring the strain at three different points on one cross-section of the oil and gas pipeline body.

[0005] How to meet the measurement requirements of large strains of oil and gas pipelines while ensuring the measurement accuracy is a problem existing in the field of oil and gas pipeline stress and strain monitoring. Summary of the Invention

[0006] In order to solve the deficiencies of the prior art, the purpose of the present invention is to provide a stress and strain monitoring system for oil and gas pipelines.

[0007] In order to achieve the above objectives, the present invention adopts the following technical solutions:

[0008] An oil and gas pipeline stress and strain monitoring system, comprising a composite cable, a BOTDR host, and a vector network analyzer;

[0009] The composite cable is an optical fiber in series with an optical fiber composite coaxial cable, and a number of coaxial cable strain sensors are connected in series on the optical fiber composite coaxial cable;

[0010] The optical fiber section of the composite cable is used for laying in the area of the oil and gas pipeline where large strain measurement is not required;

[0011] The optical fiber composite coaxial cable section of the composite cable is used for laying in the area of the oil and gas pipeline where large strain measurement is required;

[0012] The BOTDR host is connected from the end of the optical fiber section and is used to provide and receive laser signals;

[0013] The vector network analyzer is connected from the end of the optical fiber composite coaxial cable section and is used to provide and receive microwave signals.

[0014] There are 3 such composite cables, which are laid on the oil and gas pipeline in a "pin" shape along the length direction.

[0015] The above-mentioned BOTDR host is used to measure the strain value when the absolute value of the strain is relatively small.

[0016] The above-mentioned vector network analyzer is used to measure the strain value when the absolute value of the strain is relatively large.

[0017] The end of the above-mentioned optical fiber composite coaxial cable is connected to a matching resistor.

[0018] The above-mentioned BOTDR host and vector network analyzer are respectively connected to a data reading device, and the data reading device is connected to a cloud host through a wireless module.

[0019] The length of the above-mentioned optical fiber is 1 - 99 km.

[0020] The length of the above-mentioned optical fiber composite coaxial cable is 1 - 99 m.

[0021] The beneficial effects of the present invention are as follows:

[0022] An oil and gas pipeline stress and strain monitoring system of the present invention integrates two technologies for monitoring the stress and strain of oil and gas pipelines by connecting an optical fiber composite coaxial cable and coaxial cable strain sensors in series in the optical fiber. The optical fiber composite coaxial cable is laid in the area of the oil and gas pipeline where large strain monitoring is required. When the strain is small, the BOTDR technology is used for measurement, which not only gives play to the advantages of long-distance strain measurement of the BOTDR technology but also gives play to the advantages of large strain measurement of the coaxial cable.

[0023] An oil and gas pipeline stress and strain monitoring system of the present invention has a simple structure, is convenient to use, measures in a zoned and time-sharing manner, effectively improves the measurement accuracy, reduces the engineering quantity of measurement, and has strong practicability and wide applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic structural diagram of the monitoring system.

[0025] Figure 2 It is a sectional view taken along line A-A in FIG. 1.

[0026] Figure 3 It is a sectional view taken along line B-B in FIG. 1.

[0027] Figure 4 It is a sectional view of the fiber optic composite coaxial cable.

[0028] Figure 5 It is a schematic connection diagram of the fiber optic composite coaxial cable with the optical fiber and the coaxial cable.

[0029] Figure 6 It is a schematic connection diagram of the fiber optic composite coaxial cable with the matching resistor.

[0030] The meanings of the marks in the drawings are as follows:

[0031] 1. Oil and gas pipeline, 2. Optical fiber, 3. Fiber optic composite coaxial cable, 4. Coaxial cable strain sensor, 5. Matching resistor, 6. BOTDR host, 7. Vector network analyzer, 8. Cloud host, 9. Optical fiber connector, 10. Coaxial cable, 11. Protective layer, 12. Optical fiber core, 13. Outer conductor, 14. Insulator, 15. Inner conductor, 16. Conducting wire. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] The present invention will be specifically introduced below in conjunction with the drawings and specific embodiments.

[0033] An oil and gas pipeline stress and strain monitoring system is composed of a composite cable, a BOTDR host, a vector network analyzer, a data reading device, and a cloud host.

[0034] The composite cable is composed of an optical fiber and a fiber optic composite coaxial cable.

[0035] As Figure 4 shown is the sectional structure of the fiber optic composite coaxial cable 3. From the outermost to the innermost, they are in sequence: protective layer 11, optical fiber core 12, protective layer 11, outer conductor 13, insulator 14, inner conductor 15.

[0036] As Figure 5The figure shows a schematic connection diagram of the fiber-optic composite coaxial cable 3 with the optical fiber 2 and the coaxial cable 10. The optical fiber cores 12 in the optical fiber 2 and the fiber-optic composite coaxial cable 3 are connected through an optical fiber connector 9. The vector network analyzer is connected in series with the fiber-optic composite coaxial cable through the coaxial cable 10. The inner conductor 15 and the outer conductor 13 in the coaxial cable 10 are respectively welded to the inner conductor 15 and the outer conductor 13 in the fiber-optic composite coaxial cable 3. A number of coaxial cable strain sensors are connected in series on the fiber-optic composite coaxial cable.

[0037] Preferably, a matching resistor 5 is connected to the end of the fiber-optic composite coaxial cable 3. The connection structure is as Figure 6 shown. The inner conductor 15 of the fiber-optic composite coaxial cable 3 is connected to the connection wire 16 and the matching resistor 5 through welding, and then connected to the outer conductor 13 to form a loop. The matching resistor can enable the coaxial cable strain sensor to obtain more accurate measurement data.

[0038] As Figure 1 shown, three composite cable lines are laid on the oil and gas pipeline in a "pin" shape along the length direction. Among them, the optical fiber section is laid in the area of the oil and gas pipeline where large strains do not need to be measured, and the fiber-optic composite coaxial cable section is laid in the area of the oil and gas pipeline where large strains need to be measured.

[0039] The BOTDR host is connected from the end of the optical fiber section and is used to provide and receive laser signals;

[0040] The vector network analyzer is connected from the end of the fiber-optic composite coaxial cable section and is used to provide and receive microwave signals.

[0041] The BOTDR host and the vector network analyzer are respectively connected to a data reading device, and the data reading device is connected to the cloud host through a wireless module.

[0042] During use,

[0043] Laser beams are emitted from the three ports of the BOTDR host 6 and enter the three optical fibers 2. The length of the optical fiber 2 is 1 - 99 km, and a set of strain data is measured every 0.5 m to 4 m, and then transmitted to the cloud host 8 by the BOTDR host 6 through the data reading device.

[0044] The length of the fiber-optic composite coaxial cable 3 connected in series in the optical fiber 2 is 1 - 99 m.

[0045] Microwaves are emitted from the three ports of the vector network analyzer 7 and enter the fiber-optic composite coaxial cable 3, and the strain data is measured, and then transmitted to the cloud host 8 by the vector network analyzer 7 through the data reading device.

[0046] The fiber-optic composite coaxial cable 3 is laid in the area where large strains are likely to occur in the oil and gas pipeline 1:

[0047] When the absolute value of the strain generated in this area is small, such as less than 20,000 microstrains, the strain value measured by the BOTDR host 6 shall be taken as the standard because the measurement accuracy of the BOTDR method is relatively high;

[0048] When the absolute value of the strain generated in this area is large, such as greater than 20,000 microstrains, the strain value measured by the vector network analyzer 7 shall be taken as the standard because the strain has exceeded the measurement range of the BOTDR host 6 at this time.

[0049] The cloud host calculates the maximum stress and strain of the cross-section according to the national standard "GB / T 40702-2021 Technical Specification for the Protection of Geological Disasters of Oil and Gas Pipelines".

[0050] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the above embodiments do not limit the present invention in any form. Any technical solutions obtained by using equivalent replacements or equivalent transformations fall within the protection scope of the present invention.

Claims

1. An oil and gas pipeline stress and strain monitoring system, characterized in that: It includes a composite cable, a BOTDR host, and a vector network analyzer; The composite cable is an optical fiber in series with a fiber optic composite coaxial cable, and several coaxial cable strain sensors are connected in series on the fiber optic composite coaxial cable; The optical fiber section of the composite cable is used for laying in the oil and gas pipeline area where large strains do not need to be measured; The fiber optic composite coaxial cable section of the composite cable is used for laying in the oil and gas pipeline area where large strains need to be measured; The BOTDR host is connected from the end of the optical fiber section and is used to provide and receive laser signals; The vector network analyzer is connected from the end of the fiber optic composite coaxial cable section and is used to provide and receive microwave signals.

2. The monitoring system according to claim 1, characterized in that: There are 3 composite cables, which are laid on the oil and gas pipeline in a "pin" shape along the length direction.

3. The monitoring system according to claim 1, characterized in that: The BOTDR host is used to measure the strain value when the absolute value of the strain is small.

4. The monitoring system according to claim 1, characterized in that: The vector network analyzer is used to measure the strain value when the absolute value of the strain is large.

5. The monitoring system according to claim 1, characterized in that: The end of the fiber optic composite coaxial cable is connected to a matching resistor.

6. The monitoring system according to claim 1, characterized in that: The BOTDR host and the vector network analyzer are respectively connected to a data reading device, and the data reading device is connected to a cloud host through a wireless module.

7. The monitoring system according to claim 1, characterized in that: The length of the optical fiber is 1 - 99 km.

8. The monitoring system according to claim 1, characterized in that: The length of the fiber optic composite coaxial cable is 1 - 99 m.

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