Oil and gas pipeline leakage monitoring method based on optical fiber oil and gas pipeline leakage monitoring system

Abstract

An oil and gas pipeline leakage monitoring method based on an optical fiber oil and gas pipeline leakage monitoring system comprises: a DAS system based on a time-gated optical frequency domain reflectometer, a signal processor and an optical fiber to be tested, wherein: the optical fiber to be tested is arranged at the input end of the DAS system, and the signal processor is arranged at the output end of the DAS system. The present invention applies high-performance distributed optical fiber acoustic wave sensing technology and wavelet noise reduction algorithm to the detection of gas pipeline leakage, and the spatial resolution is determined by the sweep frequency range of the detection optical signal and has nothing to do with the duration of the optical pulse, thereby solving the contradiction between the spatial resolution and the detection distance in the traditional φ-OTDR technology, and can achieve meter-level high spatial resolution, high sensitivity and long sensing distance, while removing the influence of environmental noise, significantly improving the detection sensitivity of weak leakage signals.

Description

Technical Field

[0001] The present invention relates to a technology in the field of optical fiber sensor applications, and in particular to an oil and gas pipeline leakage monitoring system based on distributed optical fiber sensing technology, which can realize real-time monitoring and positioning of oil and gas pipeline leakage. Background Art

[0002] Nowadays, real-time and accurate detection of pipeline leakage is achieved through fiber-optic distributed acoustic sensors (DAS), among which the most commonly used ones are based on phase-sensitive optical time-domain reflectometry. Pipeline monitoring technology has the following disadvantages: 1) There is a contradictory relationship between the spatial resolution and the sensing distance: the shorter the duration of the detection light pulse, the higher the spatial resolution, but this will lead to a decrease in pulse energy, a decrease in the signal-to-noise ratio of the Rayleigh scattered light, and a deterioration in the sensing distance and measurement sensitivity; 2) The coherent fading noise caused by the interference between the Rayleigh scattered light will affect the detection capability of the sensor. In DAS systems, various solutions for removing coherent fading noise are accompanied by degradation of other performances (e.g., frequency response, spatial resolution). Summary of the invention

[0003] The present invention is aimed at the existing The existing DAS scheme cannot meet the needs of long-distance monitoring under the conditions of high spatial resolution and high sensitivity. This paper proposes an oil and gas pipeline leakage monitoring method based on an optical fiber oil and gas pipeline leakage monitoring system. The high-performance distributed optical fiber acoustic wave sensing technology and wavelet noise reduction algorithm are applied to the detection of gas pipeline leakage. The spatial resolution is determined by the sweep frequency range of the detection optical signal and is independent of the optical pulse duration, thus solving the problem of the traditional The contradiction between spatial resolution and detection distance in the technology can achieve meter-level high spatial resolution, high sensitivity and long sensing distance, while removing the influence of environmental noise, significantly improving the detection sensitivity of weak leakage signals.

[0004] The present invention is achieved through the following technical solutions:

[0005] The present invention relates to an oil and gas pipeline leakage monitoring system based on optical fiber, comprising: a DAS system based on time-gated optical frequency domain reflectometry (TGD-OFDR), a signal processor and an optical fiber to be tested, wherein: the optical fiber to be tested is arranged at the input end of the DAS system, and the signal processor is arranged at the output end of the DAS system.

[0006] The optical fiber to be tested is arranged in parallel with the pipeline through soil to obtain pipeline status information.

[0007] The DAS system comprises: a narrow linewidth laser and a detection optical path and a local optical path connected in parallel to the output end thereof, wherein: the two ends of the local optical path are respectively connected to the narrow linewidth laser and the signal processor, the detection optical path is composed of an acousto-optic modulator, an erbium-doped fiber amplifier for enhancing optical power and the first port of a circulator connected in sequence, and the second port and the third port of the circulator are respectively connected to the optical fiber to be tested and the signal processor.

[0008] The acousto-optic modulator is further provided with a signal transmitter, and the detection light is modulated by the acousto-optic modulator to form a linear frequency-sweeping light pulse and injected into the optical fiber to be tested.

[0009] The signal processor comprises: a balanced photoelectric detector, a data acquisition card and a signal processor which are connected in sequence, wherein: the input end of the balanced photoelectric detector is connected to the output ends of the detection optical path and the local optical path.

[0010] The present invention relates to an oil and gas pipeline leakage monitoring method based on the above system, which forms a linear frequency-sweeping optical pulse by modulating a narrow-linewidth laser, further enhances the optical power through an erbium-doped fiber amplifier, and then injects the optical pulse into the optical fiber to be tested. The backward Rayleigh scattering signal generated by the transmission beats with the local narrow-linewidth laser, and the pipeline leakage is located by converting the optical signal after the beat into an electrical signal and demodulating it.

[0011] The demodulation refers to: using the rotating vector averaging algorithm to eliminate the influence of coherent fading noise, and then performing phase space differential operation to eliminate the influence of laser light source phase noise, to obtain differential phase information, the position where the differential phase changes significantly is the position of oil and gas pipeline leakage or external intrusion and damage, thereby locating the pipeline leakage.

[0012] In order to obtain the Rayleigh scattering signal at various positions along the optical fiber in real time, a field programmable gate array (FPGA) is preferably used to perform real-time matched filtering, rotating vector averaging algorithm and phase differential operation on the data stream output by the data acquisition card to monitor the differential phase information at various positions of the optical fiber in real time.

[0013] In order to further improve the detection accuracy, the differential phase information at each position of the optical fiber to be tested obtained by the above demodulation is filtered out with a high-pass filter to remove low-frequency drift, and the cut-off frequency of the high-pass filter is preferably 100 Hz.

[0014] In order to reduce the impact of environmental noise, wavelet denoising is performed on the differential phase information after high-pass filtering, and wavelet decomposition is performed on the noisy signal. The high-frequency coefficients obtained contain both useful signals and noise. Since the noise coefficient is relatively small and the wavelet coefficient of the useful signal is large, the high-frequency components of each decomposition layer are threshold processed by selecting a suitable threshold, and the wavelet coefficients with a high noise ratio are removed, while the wavelet coefficients controlled by the signal are retained. Finally, these wavelet coefficients are used to reconstruct the denoised signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 A schematic diagram of an oil and gas pipeline leakage monitoring system based on a high-performance distributed optical fiber acoustic wave sensor provided in an embodiment;

[0016] Figure 2 This is a schematic diagram of the construction site for the simulation experiment;

[0017] Figure 3 It is a schematic diagram of 2560 phase trajectories when the pressure is increased by 0.2MPa;

[0018] Figure 4 It is a schematic diagram of 2560 phase trajectories when the pressure is increased by 0.05MPa;

[0019] In the figure: 1 is a narrow linewidth laser, 2 is a fiber coupler, 3 is an acousto-optic modulator, 4 is a signal generator, 5 is an erbium-doped fiber amplifier, 6 is a circulator, 7 is a fiber coupler, 8 is a balanced photodetector, 9 is a data acquisition card, 10 is a signal processor, and 11 is the optical fiber to be tested. DETAILED DESCRIPTION

[0020] In this embodiment, Figure 1 and Figure 2 As shown in the figure, the pipeline leakage simulation experiment is as follows: a small hole with a diameter of 4.2 mm is drilled on a metal pipe with a length of 12 m and a diameter of 32 mm as a leakage hole. One end of the pipe is sealed, and the other end is connected to the air pressure tank through a transmission pipe. Soil is filled around the pipe until the pipe is covered to simulate the buried pipe. After filling with a certain thickness of soil, a 50m armored optical fiber to be tested is laid on the soil, as shown in the figure. Figure 2 As shown, the soil is then filled on the optical cable to cover the entire cable. The armored optical cable is connected to the DAS demodulator after passing through a transmission optical cable of about 950m. In each experiment, the pressure parameters on the air pressure tank are changed first, and gases of different pressures are delivered to the pipeline to simulate the strength of the pipeline leakage.

[0021] like Figure 1 As shown, the signal generator 4 generates a sweeping pulse sequence with a pulse duration of 2 μs and a pulse interval of 250 μs to drive the acousto-optic modulator 3, and the sweeping frequency range is 100-200 MHz.

[0022] The light waves emitted by the narrow linewidth laser 1 are respectively entered into the detection optical path and the local optical path by the optical fiber coupler, wherein the detection optical path is modulated by the acousto-optic modulator 3 to form a linear frequency-sweeping optical pulse, which is injected into the optical fiber to be tested 11 after further enhancing the optical power by the erbium-doped fiber amplifier 5, and the backward Rayleigh scattering signal generated by the linear frequency-sweeping optical pulse in the optical fiber to be tested beats with the light wave in the local optical path, which is converted into a photocurrent signal by the balanced photodetector 8, and a data stream is obtained after analog-to-digital conversion by the digital acquisition card 9, and then pulse compression is performed by the matching filter in the signal processor to obtain the Rayleigh scattering signal at each position on the optical fiber, which is processed by the rotating vector averaging algorithm to eliminate the influence of coherent fading noise, and then a phase space differential operation is performed to eliminate the influence of the laser light source phase noise, and phase differential information is obtained. The position where the differential phase changes significantly is the position where the oil and gas pipeline leaks or is damaged by external intrusion, thereby locating the pipeline leak.

[0023] To further improve the detection accuracy, the differential phase information of each position of the optical fiber to be tested obtained by demodulation is filtered out with a high-pass filter to remove low-frequency drift, and the cut-off frequency of the high-pass filter is preferably 100 Hz.

[0024] In order to reduce the impact of environmental noise, the differential phase information after high-pass filtering is subjected to wavelet denoising. The noisy signal is decomposed by wavelet and decomposed into 6 layers using Haar wavelet. The soft threshold processing method is used to perform threshold processing on the high-frequency components of each decomposition layer, and then the denoised signal is reconstructed by these wavelet coefficients.

[0025] In this embodiment, 2560 sets of continuous data are collected in each experiment. In this embodiment, the parameters on the air pressure tank are first adjusted to 0.2MPa, and the following data are obtained after demodulation and noise reduction processing by the above method: Figure 3 The 2560 phase trajectory diagrams shown in the figure show that there is a leakage at the spatial position 975m.

[0026] When the gas pressure is further reduced to 0.05 MPa, the following is obtained after demodulation and noise reduction by the above method: Figure 4 The 2560 phase trajectory diagrams shown in the figure show that a leak was detected at 975m.

[0027] The above-mentioned specific implementation can be partially adjusted in different ways by those skilled in the art without departing from the principle and purpose of the present invention. The protection scope of the present invention shall be based on the claims and shall not be limited by the above-mentioned specific implementation. Each implementation scheme within its scope shall be subject to the constraints of the present invention.

Claims

1. An oil and gas pipeline leakage monitoring method based on an optical fiber oil and gas pipeline leakage monitoring system, characterized in that: The monitoring system comprises: an optical fiber distributed acoustic wave sensor system based on a time-gated optical frequency domain reflectometer, a signal processing unit and an optical fiber to be tested, wherein: the optical fiber to be tested is arranged at the input end of the optical fiber distributed acoustic wave sensor system, and the signal processing unit is arranged at the output end of the optical fiber distributed acoustic wave sensor system; The fiber-optic distributed acoustic wave sensor system comprises: a narrow-linewidth laser and a detection optical path and a local optical path connected in parallel to the output end thereof, wherein: the two ends of the local optical path are respectively connected to the narrow-linewidth laser and the signal processing unit, the detection optical path is composed of an acousto-optic modulator, an erbium-doped fiber amplifier for enhancing optical power and the first port of a circulator connected in sequence, and the second port and the third port of the circulator are respectively connected to the optical fiber to be tested and the signal processing unit; The acousto-optic modulator is further provided with a signal transmitter, and the detection light is modulated by the acousto-optic modulator to form a linear frequency-sweep light pulse and injected into the optical fiber to be tested; The signal processing unit comprises: a balanced photoelectric detector, a data acquisition card and a signal processor connected in sequence, wherein: the input end of the balanced photoelectric detector is connected to the output ends of the detection optical path and the local optical path; The narrow linewidth laser is modulated to form a linear frequency-sweep optical pulse, and the optical power is further enhanced by an erbium-doped fiber amplifier before being injected into the optical fiber to be tested. The backward Rayleigh scattering signal generated by the transmission beats with the local narrow linewidth laser. The optical signal after the beat is converted into an electrical signal and demodulated to locate the pipeline leak. The demodulation refers to: using the rotating vector average algorithm to eliminate the influence of coherent fading noise, and then performing phase space differential operation to eliminate the influence of laser light source phase noise, to obtain differential phase information, the position where the differential phase changes significantly is the position where the oil and gas pipeline leaks or is damaged by external intrusion, so as to locate the pipeline leak; The field programmable logic gate array is used to perform real-time matching filtering, rotating vector averaging algorithm and differential phase operation on the data stream output by the data acquisition card to monitor the differential phase information at each position of the optical fiber in real time; The differential phase information of each position of the optical fiber to be tested obtained by demodulation is filtered out with a high-pass filter to remove low-frequency drift; The differential phase information after high-pass filtering is subjected to wavelet denoising, specifically: Haar wavelet is used for 6-layer decomposition, soft threshold processing is selected to perform threshold processing on the high-frequency components of each decomposition layer, and then the denoised signal is reconstructed by these wavelet coefficients.

2. The oil and gas pipeline leakage monitoring method according to claim 1 is characterized in that: The cut-off frequency of the high-pass filter is 100 Hz.

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