A method and system for distributed monitoring of oil pipelines based on forward stimulated Brillouin scattering

Abstract

The application discloses a kind of distributed oil pipeline monitoring method and system based on forward stimulated Brillouin scattering, it is related to oil pipeline monitoring technical field, to solve the problem that the existing pipeline leakage monitoring based on distributed temperature sensing cannot effectively monitor the large temperature difference change or normal temperature oil.The technical points of the present application include: collecting the optical power data of the sensing optical fiber to be measured, and processing the optical power data to obtain the spectral width of the forward stimulated Brillouin scattering spectrum of the optical fiber;The spectral width of the forward stimulated Brillouin scattering spectrum is compared with the preset threshold value to determine whether the oil pipeline is leaking;Wherein, the preset threshold value is the spectral width of the forward stimulated Brillouin scattering spectrum corresponding to the air outside the optical fiber.The present application can realize stable measurement, high robustness distributed optical fiber oil pipeline monitoring without special treatment on the structure of the sensing optical fiber;At the same time, it can realize the identification of different kinds of oil transported by pipeline.

Description

Technical Field

[0001] This invention relates to the field of oil pipeline monitoring technology, specifically to a distributed oil pipeline monitoring method and system based on forward stimulated Brillouin scattering. Background Technology

[0002] Pipeline transportation is one of the main methods of transporting oil and gas. However, during transmission, pipeline structures are susceptible to deformation or damage due to factors such as surrounding construction, natural corrosion, geological disasters, and internal pressure fluctuations. This poses serious safety hazards and pollution problems, and leaks can cause huge economic losses and unnecessary resource waste. Therefore, timely detection and accurate location of pipeline leaks are of great safety significance. Conventional methods for structural health monitoring of such large-scale facilities include manual monitoring, segmented pressure testing, and flow or pressure surge methods. These methods are time-consuming and labor-intensive, cannot achieve real-time monitoring, and are far from meeting the needs of modern automated monitoring.

[0003] Compared with traditional oil and gas pipeline detection technologies, distributed fiber optic sensing technology has advantages such as high sensitivity, long-distance sensing, accurate positioning, short response time, and continuous spatial measurement, thus showing significant application prospects. Currently, the physical quantities used for pipeline leak detection based on distributed fiber optic sensing technology mainly include: measuring temperature, strain distribution along the pipeline, and sound waves / vibration, corrosion / pressure within the pipeline. Because oil exhibits high viscosity and easy solidification characteristics, heating is typically used to reduce viscosity and ensure normal flow within pipelines. Once a leak occurs in the pipeline, the temperature outside the pipeline changes. By continuously measuring the temperature distribution along the pipeline in real time, the leak point can be detected. Therefore, fiber optic-based distributed temperature sensing has become one of the most commonly used methods for oil pipeline monitoring. However, my country's long-distance oil and gas pipelines are widely distributed across complex terrains. When pipelines face harsh geographical environments, large temperature variations, or transport oil at ambient temperatures, leak detection methods based on distributed temperature sensing become ineffective. Summary of the Invention

[0004] To address this issue, the present invention proposes a distributed oil pipeline monitoring method and system based on forward stimulated Brillouin scattering, in order to solve the problem that existing pipeline leak monitoring based on distributed temperature sensing cannot effectively monitor oil with large temperature differences or at normal temperature.

[0005] According to one aspect of the present invention, a distributed oil pipeline monitoring method based on forward stimulated Brillouin scattering is proposed, the method comprising the following steps:

[0006] Step 1: Collect optical power data of the optical fiber under test and process the optical power data to obtain the spectral width of the forward stimulated Brillouin scattering spectrum of the optical fiber; wherein, the optical fiber under test is laid along the oil pipeline or surrounds the pipeline.

[0007] Step 2: Compare the spectral width of the forward stimulated Brillouin scattering spectrum with a preset threshold to determine whether the oil pipeline is leaking; wherein, the preset threshold is the spectral width of the forward stimulated Brillouin scattering spectrum when the external medium of the optical fiber is air.

[0008] Further, in step one, the optical power data of the sensing fiber under test is acquired using the following device, which includes: a narrow-linewidth tunable fiber laser, a single-mode fiber coupler, a first single-mode fiber polarization controller, a second single-mode fiber polarization controller, an arbitrary waveform generator, a first double-sided charged optical modulator, a first erbium-doped fiber amplifier, a third single-mode fiber polarization controller, an orthogonal polarization scrambler, a single-mode fiber circulator, a microwave source, a second double-sided charged optical modulator, an optically tunable filter, a second erbium-doped fiber amplifier, a single-mode fiber isolator, a single-mode fiber grating filter, a photodetector, and a data acquisition card; wherein,

[0009] The narrow linewidth tunable fiber laser is connected to the single-mode fiber coupler, and the single-mode fiber coupler is connected to the first single-mode fiber polarization controller and the second single-mode fiber polarization controller.

[0010] The first single-mode fiber polarization controller and the arbitrary waveform generator are respectively connected to the first double-sideband electro-optic modulator. The arbitrary waveform generator is used to generate a cascaded excitation long pulse and a probe short pulse in the time domain and load them onto the first double-sideband electro-optic modulator in a carrier-suppressed state to coherently excite and probe the transverse acoustic field. The first double-sideband electro-optic modulator is connected to the first erbium-doped fiber amplifier, which is used to amplify the peak power of the two pulses. The first erbium-doped fiber amplifier is connected to the third single-mode fiber polarization controller, which is connected to an orthogonal polarization scrambler. The orthogonal polarization scrambler is connected to port 1 of the single-mode fiber circulator, so that the modulated pulse is injected into the sensing fiber under test through port 2 of the single-mode fiber circulator.

[0011] The second single-mode fiber polarization controller and the microwave source are respectively connected to the second double-sideband electro-optic modulator. The microwave source is used to load a microwave signal with a frequency equal to the backward Brillouin frequency shift of the sensing fiber onto the second double-sideband electro-optic modulator in a carrier-suppressed state. The second double-sideband electro-optic modulator is connected to the optically tunable filter, which is used to filter out low-frequency sidebands and output single-sideband continuous probe light. The optically tunable filter is connected to the second erbium-doped fiber amplifier, which is used to amplify the continuous optical power and inject it into the sensing fiber under test through a single-mode fiber isolator.

[0012] The information-carrying scattered light is output from port 3 of a single-mode fiber circulator and filtered by a single-mode fiber grating filter. The single-mode fiber grating filter is connected to a photodetector to convert the information-carrying scattered light into an electrical signal, which is then acquired by the data acquisition card.

[0013] Furthermore, the second double-sideband electro-optic modulator and the optically tunable filter in the device are replaced with a single-sideband electro-optic modulator.

[0014] Furthermore, the third single-mode fiber polarization controller and the orthogonal polarization scrambler are replaced with a random polarization scrambler in the device.

[0015] Furthermore, the process of acquiring the optical power data of the optical fiber under test in step one is as follows:

[0016] An arbitrary waveform generator is used to inject a time-domain cascaded long excitation pulse and a short probe pulse into one end of the optical fiber under test. These pulses are used to excite a stable transverse acoustic field and to probe the acoustic field, respectively, with a frequency interval of f. m ;

[0017] Using a microwave source, frequencies of ν0+(ν) are successively injected into the other end of the optical fiber of the sensor under test. B +f m / 2) and ν0+(ν B -f m / 2), or frequency ν0-(ν B +f m / 2) and ν0-(ν B -f m / 2) of the continuous light for detection, where ν B ν0 represents the backward Brillouin frequency shift of the sensing fiber under test, and ν0 is the frequency of the output laser of the narrow linewidth tunable fiber laser.

[0018] By adjusting the arbitrary waveform generator, the FSBS frequency f of the excitation pulse and probe pulse is... m A scan is performed to measure and obtain the optical power P1(z) and P2(z) of the high-frequency and low-frequency components of the probe pulse.

[0019] Furthermore, the process of processing the optical power data in step one includes:

[0020] By comparing and differentiating the two optical powers P1(z) and P2(z), the corresponding distributed FSBS scattering spectrum g(f) can be obtained by demodulation using the following formula. m ,z):

[0021]

[0022]

[0023] In the formula, z represents any position along the length of the sensing fiber to be measured;

[0024] Select the FSBS scattering spectrum at a specified location in the fiber under test, perform Lorentz fitting on it, and the abscissa of the highest point of the intensity spectrum corresponds to the FSBS resonance frequency at that location in the fiber. The full width at half maximum (FWHM) of the spectrum corresponds to the FSBS spectral width.

[0025] Furthermore, the preset threshold mentioned in step two is calculated using the following formula:

[0026]

[0027] Among them, Γ m The preset threshold is the FSBS spectral width; Γ s For the intrinsic spectral width of the optical fiber; V d denoted as ρ, where d is the longitudinal wave velocity of the optical fiber; d is the diameter of the optical fiber; and r is the total reflectivity of the transverse sound wave at the boundary. Z s Z is the acoustic impedance of the fiber cladding. i The acoustic impedance is the medium outside the fiber cladding – air.

[0028] Furthermore, the optical fiber under test includes single-mode optical fiber, aluminized optical fiber, alumina-coated optical fiber, aluminum alloy-coated optical fiber, or polyimide-coated optical fiber.

[0029] According to another aspect of the present invention, a distributed oil pipeline monitoring system based on forward stimulated Brillouin scattering is proposed, the system comprising:

[0030] The FSBS spectral width acquisition module is configured to acquire optical power data from the optical fiber under test and process the optical power data to obtain the spectral width of the forward stimulated Brillouin scattering spectrum of the optical fiber; wherein the optical fiber under test is laid along or around an oil pipeline; the process of acquiring the optical power data of the optical fiber under test is as follows:

[0031] A cascaded excitation long pulse and a probe short pulse, both in the time domain, are injected into one end of the sensing fiber under test. These pulses are used to excite a stable transverse acoustic field and to probe the acoustic field, respectively, with a frequency interval of f. m ; Injecting at a frequency of ν0+(ν) into the other end of the optical fiber of the sensor under test B +f m / 2) and ν0+(ν B -f m / 2), or frequency ν0-(ν B +f m / 2) and ν0-(ν B -f m / 2) of the continuous light for detection, where ν B The backward Brillouin frequency shift of the sensing fiber under test is given by ν0, where ν0 is the frequency of the output laser; the FSBS frequencies f of the excitation and probe pulses are given by ν0. m A scan is performed to measure and obtain the optical power P1(z) and P2(z) of the high-frequency and low-frequency components of the probe pulse;

[0032] The process of processing optical power data includes:

[0033] By comparing and differentiating the two optical powers P1(z) and P2(z), the corresponding distributed FSBS scattering spectrum g(f) can be obtained by demodulation using the following formula. m ,z):

[0034]

[0035]

[0036] In the formula, z represents any position along the length of the sensing fiber to be measured;

[0037] Select the FSBS scattering spectrum at a specified location in the fiber under test, perform Lorentz fitting on it, and the abscissa of the highest point of the intensity spectrum corresponds to the FSBS resonance frequency at that location in the fiber. The full width at half maximum (FWHM) of the spectrum corresponds to the FSBS spectral width.

[0038] A pipeline leak monitoring module is configured to compare the spectral width of the forward stimulated Brillouin scattering spectrum with a preset threshold to determine whether an oil pipeline is leaking; wherein, the preset threshold is the spectral width of the forward stimulated Brillouin scattering spectrum when the external medium of the optical fiber is air; the preset threshold is calculated using the following formula:

[0039]

[0040] Among them, Γ m The preset threshold is the FSBS spectral width; Γ s For the intrinsic spectral width of the optical fiber; V ddenoted as ρ, where d is the longitudinal wave velocity of the optical fiber; d is the diameter of the optical fiber; and r is the total reflectivity of the transverse sound wave at the boundary. Z s Z is the acoustic impedance of the fiber cladding. i The acoustic impedance is the medium outside the fiber cladding – air.

[0041] The beneficial technical effects of this invention are:

[0042] This invention enables stable and robust distributed fiber optic oil pipeline monitoring without requiring special structural modifications to the sensing fiber. It also allows for rapid detection and location of oil pipeline leaks and identification of different types of oil transported through the pipeline. Attached Figure Description

[0043] The above and other objects, features, and advantages of exemplary embodiments of the present invention will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings. Several embodiments of the invention are illustrated in the drawings by way of example and not limitation, wherein:

[0044] Figure 1 This is a flowchart of a distributed oil pipeline monitoring method based on forward stimulated Brillouin scattering, according to an embodiment of the present invention.

[0045] Figure 2 This is a schematic diagram of the optical power data acquisition device in an embodiment of the present invention;

[0046] Figure 3 This is a schematic diagram comparing the modal intensity of the sensing fiber and the sound field displacement distribution in an embodiment of the present invention. Detailed Implementation

[0047] The principles and spirit of the invention will now be described with reference to several exemplary embodiments. It should be understood that these embodiments are given merely to enable those skilled in the art to better understand and implement the invention, and are not intended to limit the scope of the invention in any way. Rather, these embodiments are provided to make this disclosure more thorough and complete, and to fully convey the scope of this disclosure to those skilled in the art.

[0048] Brillouin scattering in optical fibers, as a typical acousto-optic interaction, has been widely studied and applied by scholars both domestically and internationally due to its ability to realize distributed optical fiber sensing. Stimulated Brillouin scattering is a nonlinear effect between two optical wave components and an acoustic wave, which are guided and propagated in a common medium. The optical field components can excite the oscillation of the acoustic wave, while the acoustic wave can couple power between two driving optical fields, and can also scatter and modulate the applied optical probe wave. Distributed optical fiber sensors based on backward stimulated Brillouin scattering (BSBS) are limited to temperature or strain measurements because the longitudinal acoustic and optical waves involved are confined within the fiber core. Forward stimulated Brillouin scattering (FSBS), on the other hand, takes a different approach, using sound instead of light as the probe, and using lossless optical fiber to identify and detect external substances. It has significant application potential in fossil energy exploration, pollutant leakage monitoring, energy pipeline safety inspection, and ionizing radiation safety monitoring.

[0049] Therefore, this invention proposes a distributed oil pipeline monitoring method and system based on forward stimulated Brillouin scattering (FSBS). Utilizing the acoustic impedance differences of the external medium of the optical fiber, distributed oil leak detection is achieved through changes in the FSBS scattering spectrum width, avoiding temperature crosstalk. Based on the FSBS principle, this invention uses single-mode optical fiber and measures the FSBS spectrum width of its transverse sound waves after passing through air and oil media to characterize the mechanical properties of the external substances, enabling real-time monitoring of the oil pipeline. Simultaneously, due to the differences in acoustic impedance between different types of oil, the type of oil can be identified while monitoring pipeline leaks.

[0050] This invention provides a distributed oil pipeline monitoring method based on forward stimulated Brillouin scattering, such as... Figure 1 As shown, the method includes the following steps: Step 1: Collect the optical power data of the optical fiber under test and process the optical power data to obtain the spectral width of the forward stimulated Brillouin scattering spectrum of the optical fiber; wherein, the optical fiber under test is laid along the oil pipeline or surrounds the pipeline.

[0051] Step 2: Compare the spectral width of the forward stimulated Brillouin scattering spectrum with a preset threshold to determine whether the oil pipeline is leaking; wherein, the preset threshold is the spectral width of the forward stimulated Brillouin scattering spectrum when the external medium of the optical fiber is air.

[0052] In step one, using, as Figure 2 The device shown collects optical power data from the optical fiber under test.

[0053] The device consists of a narrow-linewidth tunable fiber laser 1 as the light source (operating wavelength 1544nm-1556nm, adjustable output power, maximum 125mW), which is divided into upper and lower branches by a single-mode fiber coupler 2 with a coupling ratio of 90:10. The single-mode fiber coupler 2 is connected to a first single-mode fiber polarization controller 3 and a second single-mode fiber polarization controller 4, respectively. The two single-mode fiber polarization controllers are used to control the polarization state of the light when it enters the electro-optic modulator.

[0054] In the upper branch, the first single-mode fiber polarization controller 3 is connected to the first double-sideband electro-optic modulator 6, and uses an arbitrary waveform generator 5 to generate cascaded excitation long pulses and probe short pulses in the time domain for coherent excitation and detection of the transverse acoustic field. Through the first double-sideband electro-optic modulator 6 operating in carrier-suppressed mode, continuous radio frequency pulse signals are applied to the optical wave. To eliminate the BSBS effect between the excitation pulse and the continuous probe light, an additional frequency f1 is added to the excitation pulse. The initially injected excitation long pulse contains two radio frequency components f1 and f1+f. m After modulation, four optical frequency components are generated; subsequently, an injection radio frequency of f is performed. m / 2 detects short pulses, which are modulated to generate frequency intervals of f. m Dual-frequency optical pulses.

[0055] The first double-sided charged optical modulator 6 is connected to the first erbium-doped fiber amplifier 7, which is used to amplify the peak power of two pulses. The first erbium-doped fiber amplifier 7 is connected to the third single-mode fiber polarization controller 8, so that the measurement signal is protected from polarization fading and fluctuations by using the third single-mode fiber polarization controller 8 and the high-speed orthogonal polarization scrambler 9. The high-speed orthogonal polarization scrambler 9 is connected to port 1 of the single-mode fiber circulator 10, so that the modulated pulse is injected into the sensing fiber 11 through port 2 of the single-mode fiber circulator 10.

[0056] In the lower branch, the second single-mode fiber polarization controller 4 is connected to the second double-sided bandgap electro-optic modulator 13, and uses a microwave source 12 to shift the frequency of the sensing fiber backward Brillouin frequency ν. B The microwave signal is loaded onto the second double-sideband electro-optic modulator 13 in a carrier-suppressed state, which also generates a first-order high-frequency sideband and a low-frequency sideband. The second double-sideband electro-optic modulator 13 is connected to an optically tunable filter 14. The optically tunable filter 14 is used to filter out the low-frequency sideband and output a single-sideband continuous probe light, the frequency of which falls within the Brillouin gain region of the probe pulse. The optically tunable filter 14 is connected to a second erbium-doped fiber amplifier 15. The second erbium-doped fiber amplifier 15 amplifies the continuous optical power and then injects it into the sensing fiber 11 through a single-mode fiber isolator 16.

[0057] Change the frequency of microwave source 12 to ν B +fm / 2 and ν B -f m / 2. The optical power of the two frequency components of the probe pulse at each position was indirectly measured using Brillouin Optical Time Domain Analysis (BOTDA). The distribution of optical power variation of the high-frequency and low-frequency components of the probe pulse was recorded by the backscattering signal of the continuous light wave, denoted as P. l (z) and P2(z). Here, the frequency ν of the continuous light wave is fixed. B The aim is to shorten the measurement time, avoid interference caused by changes in ambient temperature and system stability, and obtain a good signal-to-noise ratio.

[0058] Finally, by adjusting the arbitrary waveform generator 5, the FSBS frequency f of the excitation pulse and probe pulse is... m The scanning process involves outputting the information-carrying scattered light from port 3 of the single-mode fiber circulator 10, which is then filtered by the single-mode fiber grating filter 17 to remove excitation long pulses, Rayleigh scattering, and spontaneous noise. The scanning is performed using a forward Brillouin frequency shift f. m The scattered light carrying information is converted into an electrical signal by the photodetector 18 and collected by the acquisition card 19.

[0059] Furthermore, the third single-mode fiber polarization controller 8 and the high-speed orthogonal polarization scrambler 9 can be replaced by a random polarization scrambler, but the averaging number needs to be increased to reduce noise, and the time consumed in acquiring the signal increases; the combination of the second double-sideband electro-optic modulator 13 and the tunable filter 14 can be replaced by a single-sideband electro-optic modulator.

[0060] In this embodiment of the invention, the process of acquiring optical power data of the optical fiber under test using the above-described device is as follows:

[0061] A cascaded excitation long pulse and a probe short pulse, both in the time domain, are injected into one end of the sensing fiber under test. These pulses are used to excite a stable transverse acoustic field and to probe the acoustic field, respectively, with a frequency interval of f. m This is obtained by frequency shifting of a laser with frequency ν0;

[0062] Injecting frequencies of ν0+(ν) into the other end of the optical fiber of the sensor under test successively B +f m / 2) and ν0+(ν B -f m / 2)(or the injection frequency is ν0-(ν B +f m / 2) and ν0-(ν B -f m / 2)) detection continuous light, where, ν Bν0 represents the backward Brillouin frequency shift of the sensing fiber under test; ν0 represents the frequency of the output laser of the narrow linewidth tunable fiber laser 1.

[0063] Setting a preset frequency range for the forward Brillouin shift of the fiber under test relative to f m A scan is performed to measure the optical power of the high-frequency and low-frequency components of the probe pulse, denoted as P. l (z) and P2(z).

[0064] After acquiring the optical power data, the optical power data is processed. The processing includes:

[0065] For two optical powers P l By comparing and differentiating P(z) and P2(z), and using the formula... Demodulate the distributed FSBS scattering spectrum. As an example, the BOTDA time-domain signals of the high-frequency and low-frequency components of the probe pulse are plotted together, divided into two groups: high-frequency components and low-frequency components, and then smoothed and filtered. The BOTDA signals of the high-frequency and low-frequency components of the probe pulse are converted into FSBS power changes, and the energy transfer is obtained by comparing the high-frequency and low-frequency components. By segmenting the ratio of the high-frequency and low-frequency components, the distributed FSBS spectrum can be obtained.

[0066] Select the FSBS spectrum at a specified location in the fiber under test and perform Lorentz fitting. The abscissa of the highest point of the intensity spectrum corresponds to the FSBS resonance frequency at that location in the fiber, and the full width at half maximum (FWHM) of the spectrum corresponds to the FSBS spectral width.

[0067] In step two, the spectral width of the forward stimulated Brillouin scattering spectrum of the optical fiber is compared with a preset threshold to determine whether the oil pipeline is leaking. The preset threshold is the spectral width of the forward stimulated Brillouin scattering spectrum when the external medium of the optical fiber is air. When the external medium of the optical fiber is oil, i.e., when the pipeline is leaking oil, the acoustic impedance of the medium increases, the reflectivity of the transverse sound wave reaching the fiber boundary decreases, and the spectral width of its forward spectrum will broaden. Therefore, the change in the spectral width of the forward Brillouin spectrum can be used to detect whether the oil pipeline is leaking.

[0068] The relationship between acoustic impedance and the spectral width of the forward stimulated Brillouin scattering spectrum is as follows:

[0069] By reading the external information carried by the acoustic waves through the FSBS process, the acoustic impedance of the external medium of the sensing fiber can be calculated using the following quantitative formula:

[0070]

[0071]

[0072] Among them, Γ mΓ represents the total FSBS spectral width, i.e., the spectral width of the forward stimulated Brillouin scattering spectrum; s For the intrinsic spectral width of the optical fiber; V d Z is the longitudinal wave velocity of the optical fiber; d is the diameter of the optical fiber; r is the total reflectivity of the transverse sound wave at the boundary; s Z is the acoustic impedance of the fiber cladding. i The acoustic impedance is the medium surrounding the fiber cladding.

[0073] It should be noted that the sensing fiber can be a single-mode fiber without the coating or an aluminum-coated fiber. The aluminum coating and the fiber cladding meet the quasi-acoustic impedance matching condition. The acoustic wave reflectivity at the boundary between the cladding and the coating is small, which has the advantages of high transverse acoustic wave transmission efficiency and high mechanical strength. Moreover, it is not affected by the ambient humidity and can realize acoustic impedance sensing measurement with high spatial resolution and high signal-to-noise ratio.

[0074] Sensing optical fibers use alumina, aluminum alloys, and other metals as fiber coatings instead of aluminum-plated fibers. These materials only need to meet the acoustic impedance matching or quasi-acoustic impedance matching conditions with the fiber cladding to ensure that transverse acoustic waves can be transmitted with low loss in the coating. Alternatively, polyimide-coated fibers can be used. The thin polyimide coating allows transverse acoustic waves to propagate at the boundary between the cladding and the coating, ensuring that the acoustic waves have enough energy to complete the round trip in the transverse cavity, and also has excellent mechanical strength.

[0075] Furthermore, since different types of oil have different acoustic impedances, the above process can also be used to identify the type of oil being transported in pipelines. This method can also be applied to leak detection in other liquid transport applications.

[0076] The technical effects of the present invention were further verified through experiments.

[0077] First, combined Figure 3 The modal intensity and acoustic wave displacement distribution of aluminized fiber sensing optical fiber were analyzed. The aluminum coating and silica cladding of the aluminized fiber satisfy quasi-acoustic impedance matching, allowing transverse acoustic waves to pass through the cladding-coating boundary with low loss and enter the coating oscillation. The acoustic wave displacement field is distributed throughout the entire fiber cross-section. Therefore, the transverse acoustic waves of the aluminized fiber can be transmitted to the coating interface (i.e., the fiber surface) and directly interact with the external medium, realizing acoustic impedance sensing of oil. When an oil pipeline leaks, the sensing fiber detects changes in external acoustic impedance, and the forward spectrum broadens, enabling the detection and location of the leak point.

[0078] Then, using, for example Figure 2 The device shown acquires optical power data of the optical fiber under test, wherein:

[0079] Laser 1 is a narrow linewidth tunable fiber laser with an operating wavelength of 1544nm-1556nm and adjustable output power, with a maximum of 125mW. In order to eliminate the BSBS effect between the excitation pulse and the continuous probe light, an additional frequency f1 = 1.5GHz is added to the excitation pulse.

[0080] The first erbium-doped fiber amplifier 7 amplifies the peak power of pulses to the watt level;

[0081] Backscattering frequency ν B =~10.825GHz; The second erbium-doped fiber amplifier 15 amplifies the optical power to the milliwatt level and performs real-time BSBS with the probe pulse;

[0082] The center wavelength of the single-mode fiber grating filter 17 is 1549.6 nm.

[0083] After acquiring the optical power data of the fiber under test, the data is processed to obtain the spectral width of the forward stimulated Brillouin scattering spectrum of the fiber. Due to the different acoustic impedances of air and oil, taking aluminized fiber as an example, the forward Brillouin frequency shift is preset to f. m =209MHz, when the aluminized optical fiber is surrounded by air, its acoustic impedance is approximately 439.6kg / m 2 s, according to the formula The forward spectrum width can be calculated to be approximately 1.7 MHz. When the fiber under test is surrounded by oil, the acoustic impedance of different oil types is shown in Table 1. As the acoustic impedance increases, the forward spectrum can be calculated to broaden to 3.5 MHz according to the above formula. Therefore, oil pipeline leak detection can be performed by observing the change in the forward spectrum width.

[0084] Based on the specific parameters of different petroleum types in Table 1, this invention investigated the basic physical properties of different types of petroleum, such as density, sound velocity, and acoustic impedance. Heavy oil has the highest density and the highest acoustic impedance, approaching that of water, while gasoline has the lowest density and the lowest acoustic impedance, approaching that of alcohol. Therefore, the distributed oil pipeline monitoring method based on FSBS can detect and locate pipeline leaks, and the use of FSBS to measure the acoustic impedance of petroleum can enable its type identification.

[0085] Table 1 Specific parameters for different types of petroleum

[0086]

[0087] Another embodiment of the present invention proposes a distributed oil pipeline monitoring system based on forward stimulated Brillouin scattering, the system comprising:

[0088] The FSBS spectral width acquisition module is configured to acquire optical power data from the optical fiber under test and process the optical power data to obtain the spectral width of the forward stimulated Brillouin scattering spectrum of the fiber; wherein the optical fiber under test is laid along or around an oil pipeline; the process of acquiring the optical power data of the optical fiber under test is as follows:

[0089] A cascaded excitation long pulse and a probe short pulse, both in the time domain, are injected into one end of the sensing fiber under test. These pulses are used to excite a stable transverse acoustic field and to probe the acoustic field, respectively, with a frequency interval of f. m ; Injecting at a frequency of ν0+(ν) into the other end of the optical fiber of the sensor under test B +f m / 2) and ν0+(ν B -f m / 2), or frequency ν0-(ν B +f m / 2) and ν0-(ν B -f m / 2) of the continuous light for detection, where ν B The backward Brillouin frequency shift of the sensing fiber under test is given by ν0, where ν0 is the frequency of the output laser; the FSBS frequencies f of the excitation and probe pulses are given by ν0. m A scan is performed to measure and obtain the optical power P1(z) and P2(z) of the high-frequency and low-frequency components of the probe pulse;

[0090] The process of processing optical power data includes:

[0091] By comparing and differentiating the two optical powers P1(z) and P2(z), the corresponding distributed FSBS scattering spectrum g(f) can be obtained by demodulation using the following formula. m ,z):

[0092]

[0093]

[0094] In the formula, z represents any position along the length of the sensing fiber to be measured;

[0095] Select the FSBS scattering spectrum at a specified location in the fiber under test, perform Lorentz fitting on it, and the abscissa of the highest point of the intensity spectrum corresponds to the FSBS resonance frequency at that location in the fiber. The full width at half maximum (FWHM) of the spectrum corresponds to the FSBS spectral width.

[0096] A pipeline leak monitoring module is configured to compare the spectral width of the forward stimulated Brillouin scattering spectrum with a preset threshold to determine whether an oil pipeline is leaking; wherein, the preset threshold is the spectral width of the forward stimulated Brillouin scattering spectrum when the external medium of the optical fiber is air; the preset threshold is calculated using the following formula:

[0097]

[0098] Among them, Γ m The preset threshold is the FSBS spectral width; Γ s For the intrinsic spectral width of the optical fiber; V d denoted as ρ, where d is the longitudinal wave velocity of the optical fiber; d is the diameter of the optical fiber; and r is the total reflectivity of the transverse sound wave at the boundary. Z s Z is the acoustic impedance of the fiber cladding. i The acoustic impedance is the medium outside the fiber cladding – air.

[0099] The function of the distributed oil pipeline monitoring system based on forward stimulated Brillouin scattering described in this embodiment can be explained by the aforementioned distributed oil pipeline monitoring method based on forward stimulated Brillouin scattering. Therefore, for the parts not described in detail in this embodiment, please refer to the above method embodiments, and they will not be repeated here.

[0100] It should be noted that although several units, modules, or sub-modules are mentioned in the detailed description above, this division is merely exemplary and not mandatory. In fact, according to embodiments of the present invention, the features and functions of two or more modules described above can be embodied in one module. Conversely, the features and functions of one module described above can be further divided and embodied by multiple modules.

[0101] Furthermore, although the operations of the method of the present invention are described in a specific order in the accompanying drawings, this does not require or imply that these operations must be performed in that specific order, or that all the operations shown must be performed to achieve the desired result. Additionally or alternatively, certain steps may be omitted, multiple steps may be combined into one step, and / or one step may be broken down into multiple steps.

[0102] While the spirit and principles of the invention have been described with reference to several specific embodiments, it should be understood that the invention is not limited to the disclosed specific embodiments, and the division of aspects does not imply that features in these aspects cannot be combined for benefit; such division is merely for ease of description. The invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. A distributed oil pipeline monitoring method based on forward stimulated Brillouin scattering, characterized in that, Includes the following steps: Step 1: Collect the optical power data of the fiber under test and process the optical power data to obtain the spectral width of the forward stimulated Brillouin scattering spectrum of the fiber; wherein, the fiber under test is laid along or around the oil pipeline; the optical power data of the fiber under test is collected using the following device, the device including: narrow linewidth tunable fiber laser (1), single-mode fiber coupler (2), first single-mode fiber polarization controller (3), second single-mode fiber polarization controller (4), arbitrary waveform generator (5), first double-sided charged optical modulator (6), first erbium-doped fiber amplifier (7), third single-mode fiber polarization controller (8), orthogonal polarization scrambler (9), single-mode fiber circulator (10), microwave source (12), and the first... The system comprises a double-sided bandgap optical modulator (13), an optical tunable filter (14), a second erbium-doped fiber amplifier (15), a single-mode fiber isolator (16), a single-mode fiber grating filter (17), a photodetector (18), and a data acquisition card (19). The narrow-linewidth tunable fiber laser (1) is connected to the single-mode fiber coupler (2), which is connected to a first single-mode fiber polarization controller (3) and a second single-mode fiber polarization controller (4). The first single-mode fiber polarization controller (3) and the arbitrary waveform generator (5) are connected to the first double-sided bandgap optical modulator (6). The arbitrary waveform generator (5) is used to generate cascaded excitation long pulses and probe short pulses in the time domain. The pulse is loaded onto the first double-sided band-electro-optic modulator (6) in a carrier-suppressed state to coherently excite and probe the transverse acoustic field; the first double-sided band-electro-optic modulator (6) is connected to the first erbium-doped fiber amplifier (7), which is used to amplify the peak power of the two pulses; the first erbium-doped fiber amplifier (7) is connected to the third single-mode fiber polarization controller (8), which is connected to the orthogonal polarization scrambler (9), which is connected to port 1 of the single-mode fiber circulator (10), so that the modulated pulse is injected into the sensing fiber (11) under test through port 2 of the single-mode fiber circulator (10); the second single-mode fiber polarization... The controller (4) and the microwave source (12) are respectively connected to the second double-sideband electro-optic modulator (13). The microwave source (12) is used to load a microwave signal with a frequency of backward Brillouin frequency shift of the sensing fiber onto the second double-sideband electro-optic modulator (13) in carrier suppression state. The second double-sideband electro-optic modulator (13) is connected to the optical tunable filter (14). The optical tunable filter (14) is used to filter out low-frequency sidebands and output single-sideband continuous probe light. The optical tunable filter (14) is connected to the second erbium-doped fiber amplifier (15). The second erbium-doped fiber amplifier (15) is used to amplify continuous optical power and inject it into the sensing fiber (11) under test through a single-mode fiber isolator (16).The information-carrying scattered light is output from port 3 of the single-mode fiber circulator (10) and filtered by a single-mode fiber grating filter (17), which is connected to a photodetector (18) to convert the information-carrying scattered light into an electrical signal, which is then collected by the acquisition card (19). Step 2: Compare the spectral width of the forward stimulated Brillouin scattering spectrum with a preset threshold to determine whether the oil pipeline is leaking; wherein, the preset threshold is the spectral width of the forward stimulated Brillouin scattering spectrum when the external medium of the optical fiber is air.

2. The distributed oil pipeline monitoring method based on forward stimulated Brillouin scattering according to claim 1, characterized in that, The second double-sideband electro-optic modulator (13) and the optically tunable filter (14) in the device are replaced with a single-sideband electro-optic modulator.

3. The distributed oil pipeline monitoring method based on forward stimulated Brillouin scattering according to claim 1, characterized in that, The third single-mode fiber polarization controller (8) and the orthogonal polarization scrambler (9) in the device are replaced with a random polarization scrambler.

4. A distributed oil pipeline monitoring method based on forward stimulated Brillouin scattering according to any one of claims 1-3, characterized in that, The process of acquiring optical power data of the optical fiber under test in step one is as follows: An arbitrary waveform generator (5) injects a cascaded excitation long pulse and a probe short pulse in the time domain into one end of the sensing fiber under test. These pulses are used to excite a stable transverse acoustic field and to probe the acoustic field, respectively. The frequency interval between the two pulses is f. m ; Using a microwave source (12), frequencies of 1000 and 10000 are successively injected into the other end of the optical fiber of the sensor under test. and +( / 2), or frequency is -( + / 2) and -( / 2) Detection continuous light, of which, The backward Brillouin frequency shift of the optical fiber under test. The frequency of the output laser of a narrow linewidth tunable fiber laser (1); By adjusting the arbitrary waveform generator (5), the FSBS frequencies of the excitation pulse and the probe pulse are controlled. A scan is performed to measure and obtain the optical power P1(z) and P2(z) of the high-frequency and low-frequency components of the probe pulse.

5. A distributed oil pipeline monitoring method based on forward stimulated Brillouin scattering according to claim 4, characterized in that, The process of processing optical power data in step one includes: By comparing and differentiating the two optical powers P1(z) and P2(z), the corresponding distributed FSBS scattering spectrum can be obtained by demodulation using the following formula. : ； ； In the formula, This refers to any position along the length of the sensing fiber to be measured. Select the FSBS scattering spectrum at a specified location in the fiber under test, perform Lorentz fitting on it, and the abscissa of the highest point of the intensity spectrum corresponds to the FSBS resonance frequency at that location in the fiber. The full width at half maximum (FWHM) of the spectrum corresponds to the FSBS spectral width.

6. The distributed oil pipeline monitoring method based on forward stimulated Brillouin scattering according to claim 1, characterized in that, The preset threshold mentioned in step two is calculated using the following formula: ； in, The preset threshold is the FSBS spectral width. For the intrinsic spectral width of optical fiber; d is the longitudinal wave velocity of the optical fiber; d is the diameter of the optical fiber. The total reflectivity of transverse sound waves at the boundary. , The acoustic impedance of the fiber optic cladding. The acoustic impedance is the medium outside the fiber cladding – air.

7. The distributed oil pipeline monitoring method based on forward stimulated Brillouin scattering according to claim 1, characterized in that, The optical fiber under test includes single-mode optical fiber, aluminized optical fiber, alumina-coated optical fiber, aluminum alloy-coated optical fiber, or polyimide-coated optical fiber.

8. A distributed oil pipeline monitoring system based on forward stimulated Brillouin scattering, characterized in that, The system is used to implement the distributed oil pipeline monitoring method based on forward stimulated Brillouin scattering as described in any one of claims 1 to 7; the system includes: The FSBS spectral width acquisition module is configured to acquire optical power data from the optical fiber under test and process the optical power data to obtain the spectral width of the forward stimulated Brillouin scattering spectrum of the optical fiber; wherein the optical fiber under test is laid along or around an oil pipeline; the process of acquiring the optical power data of the optical fiber under test is as follows: A cascaded excitation long pulse and a probe short pulse, both in the time domain, are injected into one end of the sensing fiber under test. These pulses are used to excite a stable transverse acoustic field and to probe the acoustic field, respectively, with a frequency interval of [missing information]. ; Injecting frequencies of into the other end of the optical fiber under test successively +( + / 2) and +( / 2), or frequency is -( + / 2) and -( / 2) Detection continuous light, of which, The backward Brillouin frequency shift of the optical fiber under test. The frequency of the output laser; the FSBS frequency of the excitation pulse and probe pulse. A scan is performed to measure and obtain the optical power P1(z) and P2(z) of the high-frequency and low-frequency components of the probe pulse; The process of processing optical power data includes: comparing and differentiating the two optical powers P1(z) and P2(z), and then using the following formula to demodulate and obtain the corresponding distributed FSBS scattering spectrum. : ； ； In the formula, This refers to any position along the length of the sensing fiber to be measured. Select the FSBS scattering spectrum at a specified location in the fiber under test, perform Lorentz fitting on it, and the abscissa of the highest point of the intensity spectrum corresponds to the FSBS resonance frequency at that location in the fiber. The full width at half maximum (FWHM) of the spectrum corresponds to the FSBS spectral width. A pipeline leakage monitoring module is configured to compare the spectral width of the forward stimulated Brillouin scattering spectrum with a preset threshold to determine whether an oil pipeline is leaking; the preset threshold is the spectral width of the forward stimulated Brillouin scattering spectrum when the external medium of the optical fiber is air.

9. A distributed oil pipeline monitoring system based on forward stimulated Brillouin scattering according to claim 8, characterized in that, The preset threshold in the pipeline leakage monitoring module is calculated using the following formula: ； in, The preset threshold is the FSBS spectral width. For the intrinsic spectral width of optical fiber; d is the longitudinal wave velocity of the optical fiber; d is the diameter of the optical fiber. The total reflectivity of transverse sound waves at the boundary. , The acoustic impedance of the fiber optic cladding. The acoustic impedance is the medium outside the fiber cladding – air.

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