CN107727226A - The oil-gas pipeline safety detection method perceived based on optical fiber - Google Patents

Abstract

The invention discloses a kind of oil-gas pipeline safety detection method perceived based on optical fiber, U-shaped distributed sensing fiber is arranged along oil-gas pipeline first, its structure is：Sensor fibre that vibration source is invaded caused by pipe leakage will be detected and be arranged as the U-shaped optical fiber structure that both sides are parallel to each other, a series of continuous and isometric subchannel is in turn divided into from initiating terminal, the length of each subchannel is the half of sensor fibre incident pulse laser linewidth, subchannel position on the both sides that U-shaped optical fiber structure is parallel to each other is interlaced, and two subchannels form one group of virtual sensing passage corresponding to both sides；A series of pulse laser is continuously transmitted in one end of U-shaped distributed sensing fiber, and receives the backscattering laser as caused by every group of plan sensing passage in transmitting terminal simultaneously；Positioning to invading vibration source caused by pipe leakage is realized based on backscattering laser, obtains pipe leakage position.Detection mode of the present invention is simple, reliability is high and electromagnetism interference.

Description

Oil and gas pipeline safety detection method based on optical fiber sensing

technical field

The invention relates to the fields of optical fiber sensing, optical fiber communication and signal processing, in particular to optical fiber sensing and signal processing technologies.

Background technique

As the most efficient way to transport oil and gas resources, pipeline transmission has been widely used. However, in recent years, pipeline leakage incidents caused by drilling oil theft, natural disasters and pipeline aging

Repeatedly, the economy and the environment have paid a huge price. Therefore, the safety monitoring of oil and gas pipelines

Work is particularly important. In recent years, optical fiber sensing technology has developed rapidly. It has the advantages of anti-electromagnetic interference, high sensitivity, and large dynamic range, and has been applied in the field of oil and gas pipeline safety monitoring. When events such as vibration or stress caused by oil and gas pipeline leakage events act on the optical fiber, the parameters such as the phase and polarization state of the light transmitted in the optical fiber will change. Therefore, the oil and gas pipeline can be monitored by monitoring the change of the optical signal. security monitoring. To realize the safety monitoring of oil and gas pipelines, the distributed optical fiber sensors based on Optical Time Domain Reflectometry (OTDR) are mainly used.

The principle of Optical Time Domain Reflectometry (OTDR) technology is due to the limitation of optical fiber preparation process, resulting in uneven density of each point on the optical fiber, and then uneven refractive index. This unevenness causes Rayleigh to occur when light is transmitted in the optical fiber. scattering. At the same time, when the optical fiber is subjected to various external forces (strong mechanical vibration or weak acoustic vibration), the local refractive index will also change, and the scattered light in the optical fiber will also change. In this way, when a pulsed laser is injected at one end of the fiber for transmission, a part of the backscattered light is transmitted back to the light incident end, which is usually a reflection loss for optical fiber communication, but it is precisely because of this characteristic , the stress change on the optical fiber link can be monitored by detecting the received backscattered light signal that changes with time.

When a pulse laser with a certain repetition rate is injected into the fiber for detection, its spatial resolution is limited by the laser pulse width (T), and the minimum spatial resolution is less than half of the pulse width (T/2). Therefore, if the method of shortening the pulse width is used to improve the spatial resolution, the laser energy injected into the fiber will be correspondingly reduced, resulting in a significant decrease in the detection distance, and the signal-to-noise ratio of the detection system will drop sharply. On the other hand, due to the limitations of existing laser technology, reducing the pulse width of laser is very costly and difficult to achieve integration. The spatial resolution is difficult to improve.

At the same time, another factor that determines the spatial resolution of the optical fiber distributed sensor is the minimum integration time of the photodetector used to detect the backscattered light signal. Since the photodetector cannot distinguish the "high repetition frequency" signal, each point of the electrical signal output by the photodetector is the accumulation of the number of photons in a short period of time. The signal is the accumulation of photon counts in a small section of fiber. Therefore, after the received optical time domain reflection signal is photoelectrically converted, the value of each point on the time domain waveform is the intensity of backscattered light in a small section of optical fiber. It can be seen that the minimum integration time of the photodetector also limits the spatial resolution of the optical fiber distributed sensor.

The optical fiber distributed sensor based on the optical time domain reflectometry (OTDR) has high sensitivity and strong anti-electromagnetic interference characteristics, and can use ordinary communication optical cables to realize long-distance distributed transmission on the existing infrastructure. sense, so it plays an important role in the monitoring field of oil and gas pipelines. However, the pulse width of the incident laser and the minimum integration time of the photodetector greatly limit the spatial resolution of this type of system. If high-precision safety monitoring of oil and gas pipelines is to be realized, the spatial resolution of the optical fiber distributed sensing system must be further improved.

Contents of the invention

The purpose of the present invention is to provide a safety detection method for oil and gas pipelines based on optical fiber sensing in order to improve the positioning accuracy of pipeline leaks in view of the above existing problems.

The optical fiber sensing-based oil and gas pipeline safety detection method of the present invention comprises the following steps:

U-shaped distributed sensing optical fibers are arranged along the oil and gas pipeline, and the structure of the U-shaped distributed sensing optical fibers is as follows: the sensing optical fibers for detecting the intrusion vibration source caused by pipeline leakage are arranged as a U-shaped optical fiber structure with two sides parallel to each other, Divide the sensing fiber from the starting end into a series of continuous and equal-length sub-channels, and the length of each sub-channel is half of the linewidth of the incident pulse laser of the sensing fiber, and the sub-channels are evenly distributed in the U-shaped fiber structure On both sides parallel to each other, and the positions of the sub-channels on both sides are staggered, and the corresponding two sub-channels on both sides form a set of virtual sensing channels;

Continuously sending a series of pulsed lasers at one end of the U-shaped distributed sensing fiber, and simultaneously receiving backscattered lasers generated by each group of quasi-sensing channels at the sending end;

Based on the backscattered laser light, the location of the vibration source caused by the pipeline leakage is realized, and the position of the pipeline leakage is acquired.

The present invention shortens the sampling length of the backscattered light on the optical fiber link in terms of positioning processing by superimposing the data of the interlaced virtual sensing channel groups. Compared with the spatial resolution of the existing optical fiber distributed sensor, if Deployed in a structure in which the corresponding channels on both sides overlap by 50% of the channel length, the spatial resolution can be increased by 2 times, so the system can monitor the force and vibration of the entire optical fiber link with a higher spatial resolution.

In order to further improve the detection and positioning accuracy and improve the spatial resolution, N parallel sensing optical fiber lines can also be arranged along the perimeter fence to form N-1 U-shaped distributed sensing optical fibers, and each sub-unit on each line The positions of the channels and the corresponding sub-channels on other lines are interleaved, where N is greater than 2. When the corresponding channels on N parallel lines overlap by 1/N channel length, the positioning spatial resolution of the vibration caused by human intrusion can be increased by N times.

In summary, owing to adopting above-mentioned technical scheme, the beneficial effect of the present invention is:

The invention has the characteristics of low cost, high signal-to-noise ratio, simple structure, and easy deployment, and is suitable for practical engineering applications; at the same time, the invention does not require reducing the pulse width of the light source, does not sacrifice the incident power of the light source, and does not require reducing the photodetector On the basis of the minimum integration time, the resolution of the traditional optical fiber distributed sensor based on a single sensing optical fiber can be increased by N(N≥2) times; furthermore, the invention has strong practicability and can completely realize the detection of potential safety hazards in oil and gas pipelines. High resolution positioning.

Description of drawings

Fig. 1 is a schematic diagram of a distributed optical fiber sensing system with a single U-shaped structure;

Fig. 2 is a schematic diagram of a distributed optical fiber sensing system with a single optical fiber structure;

3 is a schematic diagram of a distributed optical fiber sensing system with an overlapping single U-shaped structure;

Figure 4 is a schematic diagram of interlaced single U-shaped structure to improve spatial resolution by superposition of interleaved channel signals;

Figure 5 is a schematic diagram of a distributed optical fiber sensing system with a staggered 3U structure;

Fig. 6 is a schematic diagram of a distributed optical fiber sensing system with a staggered multi-U structure;

Reference signs: F1 is an optical fiber for sensing; W is an oil and gas pipeline; D is a pipeline leakage point; C1, C2, C3...C69 are each channel; T represents channel C5; S1, S2, S3, S4, S5 ...S(N-2), S(N-1) are the midpoints of each U-shaped structure; H1 is a circulator; L is a narrow-band pulse laser light source; M is a photoelectric detection module; N is an electrical signal processing module; A0, A1, A2, A3, A4...A(N-1), A(N) are incident light pulses; R0, R1, R2, R3, R4...R(N-1), R(N) are Backscattered light; Z is the vibration signal generated by man-made damage or pipeline leakage, which is represented as the vibration source here; 4-A is the vibration signal (Z1) waveform, 4-B is the channel C21 when the optical pulse is transmitted in the optical fiber , C22, C23, C24, C25, and C26 sampled backscattered light signal waveforms, 4-C is the backscattered light signal sampled by channels C10, C11, C12, C13, and C14 when the optical pulse is transmitted in the optical fiber Waveform, 4-D is to superimpose the sampling values of the above-mentioned corresponding channels to form virtual channels D1, D2, D3, D4...D10; 5-A is the vibration signal (Z1) waveform, 5-B is the light pulse at When transmitting in the optical fiber, the backscattered light signal waveforms sampled by channels C56, C57, C58, C59, C60, and C61, 5-C are the channels C50, C49, C48, C47, C46, The backscattered light signal waveform sampled by C45, 5-D is the backscattered light signal waveform sampled by channels C22, C23, C24, C25, and C26 when the optical pulse is transmitted in the optical fiber, and 5-E is the optical pulse at When transmitting in the optical fiber, the backscattered light signal waveforms sampled by the channels C13, C12, C11, C10, and C9, 5-F, superimpose the sampling values of the above-mentioned corresponding channels to form virtual channels D1, D2, D3, D4...D20.

detailed description

In order to make the purpose, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the implementation methods and accompanying drawings.

Embodiment 1: A distributed optical fiber sensing system based on a single U-shaped structure:

Figure 1 shows a distributed optical fiber sensing system based on a single U-shaped structure. A single U-shaped optical fiber F1 is buried in the soil below the surface close to the oil and gas pipeline to ensure that the sensing optical fiber maintains high sensitivity to vibration. The vibration signal (Z1) caused by man-made damage or pipeline aging leakage will act indirectly on the sensing fiber to change the transmission and scattering characteristics of the sensing fiber. According to the pulse width (T) of the pulsed laser used in the system, the sensing fiber is sequentially divided into continuous channels (C1, C2, C3...C34) with a length of (T/2) from the laser incident end, and the incident pulsed laser A0, A1 passes through the circulator to extend the forward transmission of the optical fiber, and the backscattered light R1 and R2 generated by each channel during the forward transmission process are transmitted back to the incident end in reverse, and after passing through the circulator H1, they are detected by the photodetector (M) Receive and detect, and finally, send the photoelectrically converted signal to the signal processing module (N), use the interleaved corresponding characteristics of each corresponding channel, and use the corresponding channel superposition algorithm to demodulate and represent the sensing signal, which can improve the space of the system The resolution is doubled, thereby improving the positioning accuracy of pipeline safety hazards.

Figure 2 shows the single-line structure adopted by the traditional distributed optical fiber sensing system. Its main feature is that its spatial resolution is lower than that of the optical fiber distributed sensing system based on the single U-shaped sensing optical fiber distribution structure shown in Figure 1. in half.

Further, Fig. 3 shows a distributed optical fiber sensing system with an overlapping single U-shaped structure. Overlapping to form an overlapping U-shaped distribution structure, and this structure does not interleave the backscattered light signals of the corresponding channels (C12&C23, C11&C24...) on both sides of the U-shape in space, and cannot improve the system resolution. In contrast, as shown in Figure 4, the midpoint (S1) of the U-shaped structure is located at 1/4 of the channel length from the port where the point is located, so the corresponding channels on both sides of the U-shaped structure will have 50% of the channel length. Dislocation, forming a staggered optical fiber distribution structure (C13&C23, C12&C23, C12&C24, C11&C24, C11&C25...), this structure makes the received backscattered optical signals interlaced in space, and the corresponding channel superposition algorithm can be greatly improved increase the spatial resolution of the system.

According to the characteristics of the above two structures in Figure 3 and Figure 4, the overlapping U-shaped distribution structure cannot improve the spatial resolution of the system, and the general sensing fiber length is 10 to 200 kilometers, and the length of a fiber channel is 10 meters to 50 meters, in the actual deployment of the U-shaped structure, in order to control the overlapping ratio of the channels on both sides of the U-shaped optical fiber, the distribution position of each channel on the optical fiber link can be adjusted by adjusting the position of the light source at the incident end of the optical fiber to avoid overlapping U-shaped distribution structure, at the same time, the misalignment ratio of the corresponding channels on both sides of the U-shape can be adjusted. The whole adjustment is very simple, accurate and controllable.

Figure 4 shows the principle of improving the spatial resolution of the system by using the staggered single U-shaped distribution structure. 4-A indicates the vibration signal (Z1) caused by man-made damage or pipeline leakage, which is a continuous analog signal; 4-B indicates that when the optical pulse is transmitted in the optical fiber, the channel C21, C22, C23, C24, C25, C26 samples Similarly, 4-C represents the backscattered light signals sampled by channels C10, C11, C12, C13, and C14 when the optical pulse is transmitted in the optical fiber. The above two groups of channels correspond to each other in spatial position and are interlaced with each other. Therefore, as shown in 4-D, the sampling values of the above-mentioned mutually corresponding channels are superimposed to form virtual channels D1, D2, D3, D4...D10,

The calculation method of each virtual channel is:

D1=C14+C21;

D2=C14+C22;

D3=C13+C22;

...

D10=C10+C26;

It can be seen from the figure that since the corresponding channels to be added are staggered by 50% of the channel length, it is not required to reduce the pulse width of the light source, the incident power of the light source is not sacrificed, and the minimum integration time of the photodetector is not required to be reduced. Above, the result of the superposition doubles the spatial resolution, so the sampling accuracy is higher, and the digital-to-analog conversion will be more in line with the original signal waveform.

Embodiment 2: Distributed optical fiber sensing system based on 3U structure:

As shown in FIG. 5 , on the basis of the above-mentioned single U interleaved distribution structure, a 3U optical fiber distribution structure can be further adopted, in which the corresponding channels have a 1/4 channel length dislocation. 5-A represents the vibration signal (Z1) caused by man-made damage or pipeline leakage, and 5-B represents the backscattered light signal waveform sampled by channels C56, C57, C58, C59, C60, and C61 when the optical pulse is transmitted in the optical fiber , 5-C is the backscattered light signal waveform sampled by channels C50, C49, C48, C47, C46, and C45 when the optical pulse is transmitted in the optical fiber, 5-D is the channel C22, The backscattered light signal waveforms sampled by C23, C24, C25, and C26, 5-E is the backscattered light signal waveform sampled by channels C13, C12, C11, C10, and C9 when the optical pulse is transmitted in the optical fiber, 5 -F is to superimpose the sampling values of the above-mentioned channels corresponding to each other to form virtual channels D1, D2, D3, D4...D20.

Also, the virtual channel formed by using the same superposition algorithm as above can increase the spatial resolution of the system to four times that of the original system (shown in Figure 2), which is the fiber distribution of the single U-shaped fiber distribution structure shown in Figure 1 2 times the spatial resolution of conventional sensing systems. As shown in 5-F, it can be clearly seen that compared with the sampling results shown in 4-D, the resolution is significantly improved, and the details of the original signal are more refined.

According to the description of the specific implementation of the above two cases, as further shown in Figure 6, one optical fiber can be further deployed as N (N>2) parallel lines to form N-1 U-shaped structures, while using the above The processing method of data superposition of corresponding channel sampling values can further improve the spatial resolution of the system. When the corresponding channels on N parallel lines overlap by 1/N channel length, the spatial resolution of the multi-U-shaped optical fiber distributed sensing system can be increased by N times compared with the traditional single-line distributed optical fiber sensing system. Greatly improve the positioning accuracy of oil and gas pipeline safety hazards.

The above is only a specific embodiment of the present invention. Any feature disclosed in this specification, unless specifically stated, can be replaced by other equivalent or alternative features with similar purposes; all the disclosed features, or All method or process steps may be combined in any way, except for mutually exclusive features and/or steps.

Claims (2)

1. the oil-gas pipeline safety detection method perceived based on optical fiber, it is characterised in that comprise the following steps：

U-shaped distributed sensing fiber is arranged along oil-gas pipeline, the structure of the U-shaped distributed sensing fiber is：Will detection The sensor fibre that vibration source is invaded caused by pipe leakage is arranged as the U-shaped optical fiber structure that both sides are parallel to each other, by sensor fibre from Initiating terminal is in turn divided into a series of continuous and isometric subchannel, and the length of each subchannel is sensor fibre incident pulse The half of laser linewidth, and the subchannel is evenly distributed on the both sides that U-shaped optical fiber structure is parallel to each other, and the son on both sides Channel position is interlaced, and two subchannels form one group of virtual sensing passage corresponding to both sides；

A series of pulse laser is continuously transmitted in one end of the U-shaped distributed sensing fiber, and is received simultaneously in transmitting terminal The backscattering laser as caused by every group of plan sensing passage；

Positioning to invading vibration source caused by pipe leakage is realized based on the backscattering laser, obtains pipe leakage position.

2. the method as described in claim 1, it is characterised in that the sense light that N bars are parallel to each other is arranged along oil-gas pipeline Fine circuit, N-1 U-shaped distributed sensing fibers are formed, and each subchannel on every circuit is corresponding with All other routes The position of subchannel is interlaced, and wherein N is more than 2.