CN110031945B - Underwater exploration towing optical cable with self-attitude tracking capability - Google Patents
Underwater exploration towing optical cable with self-attitude tracking capability Download PDFInfo
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- G—PHYSICS
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- G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
- G01H9/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means
- G01H9/004—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means using fibre optic sensors
- G01H9/006—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means using fibre optic sensors the vibrations causing a variation in the relative position of the end of a fibre and another element
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- G01L1/242—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet the material being an optical fibre
- G01L1/243—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet the material being an optical fibre using means for applying force perpendicular to the fibre axis
- G01L1/245—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet the material being an optical fibre using means for applying force perpendicular to the fibre axis using microbending
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- G02B6/44—Mechanical structures for providing tensile strength and external protection for fibres, e.g. optical transmission cables
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Abstract
The invention discloses an underwater exploration towing optical cable with self attitude tracking capability, which comprises: the sensor comprises an outer protective layer (1), 2n metal reinforcing pieces (4) inserted in the outer protective layer, 2n surrounding optical fiber sensing units (2) and a central sensing unit (3); the central sensing unit (3) is arranged in the center of the outer protective layer (1), and 2n peripheral optical fiber sensing units (2) and 2n metal reinforcing pieces (4) are centrally symmetrically and alternately inserted in the periphery of the central sensing unit in a staggered manner by adopting a layer-twisted structure; and the peripheral optical fiber sensing units (2) and the central sensing unit (3) are respectively packaged with an optical fiber, all the optical fibers are connected in series end to end through a jumper to form a long optical fiber, and only one end of the optical fiber packaged by the central sensing unit is reserved as a port of the optical cable access detection system. The invention can reconstruct the space attitude of the optical cable, realizes the correction of the signals measured by the phi-OTDR, improves the positioning precision of the restored seismic wave signals, and has the advantages of insulation, high temperature corrosion resistance and long service life.
Description
Technical Field
The invention relates to an underwater exploration towing optical cable with self attitude tracking capability, and belongs to the technical field of optical cables.
Background
Energy is an important basic stone for the current national economy and social development, however, the petroleum capacity of China can not meet the actual demand all the time in the last two decades, and the supply of crude oil still mostly depends on import. For example, the specific gravity of crude oil import in China is higher than 60% in 2017, and the transition dependence on the imported crude oil poses a great hidden danger for energy safety and even national safety burying in China. In order to solve the contradiction between supply and demand of the energy, the search for new oil and gas resources is urgent. However, with the deep development of crude oil resources in the world in recent decades, shallow oil and gas reservoirs which are simple in geological structure type and convenient to explore are almost completely exploited, the exploration and development difficulty of the oil and gas resources is continuously increased, and meanwhile, higher requirements are provided for exploration technologies. Currently, underwater seismic wave exploration is the most important technical means for finding offshore oil and gas, but no underwater seismic exploration navigation positioning technology with completely independent intellectual property rights exists in China at present. Although the foreign comprehensive system has superior performance and complete functions, the price is high and the technical blockade to China exists. Therefore, the research on the submarine seismic wave detection technology has important influence on the oil and gas resource exploration on one hand, so that China can get rid of the technical dependence and save a large amount of oil and gas exploration cost on the other hand, the technical blank of China in the field can be made up, and the development and progress of national science and technology are facilitated.
The seismic wave exploration is carried out by adopting the towing optical cable, namely the seismic sound field signal receiving and sensing device is positioned in a water body and is not submerged under the water body, so that the seismic sound field signal receiving and sensing device can receive the sound field vibration signals in motion. When the optical cable is dragged by the exploration ship to pass through a target detection area, the exploration ship transmits a seismic wave sound field to the underwater through manual excitation, and reflects at a geological structure interface, and the optical cable can receive sound field vibration signals reflected to the water surface. By processing and analyzing the received data, the sound field signal can be reconstructed, and the geological structure and the position information of the detection area can be reproduced. In addition to being used primarily for submarine relief and oil and gas exploration, the trailing cable may also be applied to submarine relief exploration of various bodies of water, including rivers and lakes.
The sensing optical cable based on the phase-sensitive optical time domain reflection (phi-OTDR) distributed optical fiber sensing technology can use the whole optical fiber as an optical transmission and sensing unit, when a certain position is disturbed by a vibration signal, the length of the optical fiber at the position is changed, so that the phase of Rayleigh scattering light is changed, the detected interference optical power intensity is changed and is recorded by data acquisition equipment, and the disturbance signal can be restored by analyzing the interference optical power change. The optical cable based on the phi-OTDR distributed optical fiber sensing technology has the advantages of insulation, high temperature corrosion resistance, long-distance transmission, electromagnetic interference resistance and the like, and can be fully suitable for the severe environment of seismic exploration.
The overall shape and the relative spatial relationship of the sensing optical fiber need to be known for the reconstruction of the sound field signal, but the sensing optical fiber is influenced by towing ship wake flow, water wave motion and the like, the sensing optical cable can be bent and deformed in the towing process, and the straight line state parallel to the horizontal plane cannot be maintained, so that the reconstructed sound field signal generates deviation in spatial distribution, and the positioning accuracy of the submarine seismic sound field vibration signal is influenced by the fact that the signal reflection position obtained through analysis generates errors compared with the actual position.
Disclosure of Invention
The invention aims to solve the technical problem that the reconstructed sound field signal generates deviation in spatial distribution due to integral bending deformation of a sensing optical cable when the sensing optical cable is towed on water is solved, the stress state of the optical cable, the vibration signal sound field restoration and the detection error correction are better understood, and the underwater exploration towing optical cable with the self posture tracking capability is provided.
The invention specifically adopts the following technical scheme to solve the technical problems:
an underwater exploration towed optical cable with self attitude tracking capability based on two optical time domain reflection technologies comprises: the optical fiber sensor comprises an outer protective layer, 2n metal reinforcing pieces inserted in the outer protective layer, 2n surrounding optical fiber sensing units and a central sensing unit, wherein n is a natural number more than 1; the central sensing unit is arranged in the center of the outer protective layer, and the 2n peripheral optical fiber sensing units and the 2n metal reinforcing pieces are centrally symmetrically staggered and inserted on the periphery of the central sensing unit in a layer-twisted structure; each of the 2n peripheral optical fiber sensing units and the central sensing unit is packaged with an optical fiber, all the optical fibers are connected in series into a long optical fiber through end-to-end connection, and only one end of the optical fiber packaged by the central sensing unit is left as a port of an optical cable access detection system;
the optical fiber packaged in the central sensing unit is used as the sensing end of the phase sensitive optical time domain reflection detection system, and the optical fiber packaged in each peripheral optical fiber sensing unit is used as the sensing end of the Brillouin optical time domain reflection detection system.
Further, as a preferred technical solution of the present invention: the outer protective layer sequentially wraps the armored sheath, the PE outer sheath, the PE inner sheath, the polyester tape and the water-blocking non-woven fabric binding tape from outside to inside.
Further, as a preferred technical solution of the present invention: the armored sheath is an aluminum-plastic or embossed steel strip armored sheath.
Further, as a preferred technical solution of the present invention: the central sensing unit is sequentially coated with a single sensing optical fiber, a tight sleeve, a water-blocking yarn and a PBT sheath layer from inside to outside.
Further, as a preferred technical solution of the present invention: the surrounding optical fiber sensing units are sequentially coated with a single optical fiber, optical fiber ointment and a PBT (polybutylene terephthalate) sheath layer from inside to outside.
Further, as a preferred technical solution of the present invention: the outer protective layer also comprises optical cable ointment filled in gaps among the metal reinforcing piece, the optical fiber sensing unit and the central sensing unit.
Further, as a preferred technical solution of the present invention: the metal reinforcing part adopts a steel wire reinforcing part.
By adopting the technical scheme, the invention can produce the following technical effects:
the novel optical cable is used as a receiving and sensing device for seismic wave sound field signals in water body geological exploration and comprises 2n +1 optical fiber sensing units, each sensing unit is packaged with an optical fiber, and 2n surrounding optical fiber sensing units and metal reinforcing parts are staggered into centrosymmetric arrangement around a central sensing unit. 2n +1 optical fibers of all sensing units in the optical cable are connected end to end through jumper wires to form a long optical fiber, only one end of a central sensing unit packaging optical fiber is reserved to be used as an access end of a phi-OTDR and BOTDR mixing system, and the system realizes the function of simultaneously measuring dynamic vibration and static strain: since the rayleigh scattered light and the spontaneous brillouin scattered light are a kind of natural frequency multiplexed light, the system can realize synchronous demodulation of two scattered signals by heterodyne asynchronous demodulation of frequency shift keying. The hybrid system can realize the comprehensive analysis of the vibration and the strain of the optical cable and provide more useful information for the positioning accuracy of seismic wave exploration.
Therefore, compared with the prior art, the invention has the following advantages:
(1) the invention adopts a well-developed and commercially available phi-OTDR and BOTDR distributed optical fiber sensing fusion system by increasing the fiber core, ensures the detection sensitivity of seismic wave sound field vibration signals, realizes the space form reduction of the towing optical cable, further improves the positioning precision of the reduced seismic wave signals, has high detection sensitivity of the seismic wave vibration signals on one hand, and can better recover the underwater space posture of the towing optical cable on the other hand.
(2) The invention provides an all-fiber solution for geological survey of various water bodies, which effectively reduces the energy consumption of the whole survey system and improves the survey time.
(3) The invention provides a novel armored optical cable suitable for underwater severe dragging environments such as wind and rain, insolation, corrosion or underwater biological attack, which is insulated, resistant to high temperature and corrosion, long in service life and suitable for long-time work in offshore severe environments.
(4) The phi-OTDR and BOTDR hybrid system accessed by the invention can fully resist electromagnetic interference and is not easy to be disturbed by electromagnetic signals sent by ships sailing around in practical application.
(5) The invention provides an optical cable for long-distance transmission, which is easy to obtain manufacturing materials, low in manufacturing cost, long in manufactured length and suitable for industrial production and use.
Drawings
FIG. 1 is a schematic diagram of the seismic wave detection technique of the present invention based on a towed underwater survey cable.
Fig. 2 is a cross-sectional view of the overall construction of a trailing cable of the present invention.
Fig. 3 is a cross-sectional view of the outer jacket of a trailing cable of the present invention.
Fig. 4 is a cross-sectional view of a central fiber sensing unit of a trailing cable of the present invention.
Fig. 5 is a cross-sectional view of a surrounding fiber sensing unit of a trailing cable of the present invention.
Fig. 6(a) and 6(b) are a connection view and a cross-sectional view, respectively, of an optical fiber in a trailing cable according to the present invention.
Wherein the reference numerals explain: 201-towing ship, 202-towing optical cable, 203-seismic wave sound field signal emitted by the towing ship, 204-reflected seismic wave sound field vibration signal, 205-optical cable receiving signal position; 1-an outer protective layer, 2-a peripheral optical fiber sensing unit, 3-a central sensing unit and 4-a metal reinforcing part; 11-optical cable ointment, 12-polyester tape and water-blocking non-woven fabric bundling tape, 13-PE inner sheath, 14-PE outer sheath and 15-armored sheath; 21-optical fiber of the optical fiber sensing unit, 22-optical fiber ointment and 23-PBT sheath layer; 31-optical fiber of a central sensing unit, 32-a tight sleeve, 33-water-blocking yarn and 34-PBT sheath layer; 1. 2, 3, 4-optical fiber; 31' -system access terminal.
Detailed Description
The following describes embodiments of the present invention with reference to the drawings.
The invention designs an underwater exploration towing optical cable with self attitude tracking capability based on two optical time domain reflection technologies, and the underwater exploration towing optical cable using two optical time domain reflection technologies of phi-OTDR and BOTDR is used as a sensing receiving device based on a seismic wave detection technology used for underwater geology or oil gas exploration. As shown in FIG. 1, on the water surface, a towing vessel 201 pulls a towing optical cable 202 through a target detection area at the tail part, and the towing optical cable 202 serves as a sound field vibration signal receiving and sensing device. The towing ship artificially excites a seismic wave sound field 203 underwater, the sound field meets the underwater mine deposit geological interface, and a seismic wave sound field vibration signal 204 is reflected to a place 205 on the optical cable. By processing and analyzing the sound field vibration signals detected by the sensing optical cable and the sensed integral strain, the integral space attitude of the optical cable can be restored, the seismic wave sound field vibration signals can be reconstructed, the geological structure of the detection area can be reproduced, and fixed point positioning can be realized.
As shown in fig. 2, a cross-sectional view of the overall structure of a trailing cable 202 according to the present invention includes: the optical fiber sensing module comprises an outer protective layer 1, 2n metal reinforcing members 4 and 2n surrounding optical fiber sensing units 2 which are inserted in the outer protective layer, and a central sensing unit 3, wherein n is a natural number more than 1, and in the embodiment, n is 2, that is, the optical fiber sensing module comprises 4 metal reinforcing members 4 and 4 surrounding optical fiber sensing units 2, but not limited to the number; the central sensing unit 3 is arranged in the center of the outer protective layer 1, 4 peripheral optical fiber sensing units 2 and 4 metal reinforcing pieces 4 are centrally symmetrically staggered and inserted on the periphery of the central sensing unit in a layer-twisted structure, and the spatial postures and stress conditions of the optical cable in all directions can be more completely and accurately restored by adopting central symmetrical structural arrangement; and the 4 peripheral optical fiber sensing units 2 and the central sensing unit 3 are respectively packaged with an optical fiber, all the optical fibers are connected in series into a long optical fiber in an end-to-end manner, only one end of the optical fiber packaged by the central sensing unit is reserved as a port for accessing an optical cable into an external detection system, and the accessed system is a hybrid synchronous demodulation system of phi-OTDR and BOTDR.
As shown in fig. 3, which is a schematic cross-sectional view of the outer protective layer 1 of the present invention, an armor sheath 15, a PE outer sheath 14, a PE inner sheath 13, a polyester tape, and a water-blocking non-woven fabric wrapping tape 12, which are sequentially wrapped with aluminum-plastic or embossed steel tape, are sequentially disposed from outside to inside. The 15 structures of armor sheath protect the inside of optical cable to and prevent external corruption or sun insolate etc. to reply abominable dragging environment on the surface of water, the waterproof material of increase volume prevents to ooze water and influences optical cable performance. The outer sheath can also be wrapped with a cable ointment 11 to fill the gap between the metal reinforcing members 4.
As shown in fig. 4, which is a schematic cross-sectional view of the central sensing unit 3 of the present invention, the central sensing unit 3 is sequentially covered with an optical fiber 31, a tight sleeve 32, a water-blocking yarn 33, and a PBT jacket layer 34 from inside to outside, where the optical fiber 31 is a sensing end of a Φ -OTDR detection system and is used for detecting a sound field vibration signal.
As shown in fig. 5, which is a schematic cross-sectional view of the peripheral optical fiber sensing unit 2 of the present invention, an optical fiber 21, an optical fiber ointment 22, and a PBT jacket layer 23 are sequentially coated from inside to outside, where the optical fiber 21 serves as a sensing end of a BOTDR detection system, and senses the overall strain experienced by the optical cable during dragging, so that the present invention may be based on two optical time domain reflection technologies, namely, a phase-sensitive optical time domain reflection technology Φ -OTDR and a brillouin optical time domain reflection technology BOTDR.
The optical cable adopts a structure that a central beam tube type optical cable and a layer-stranded optical cable are combined, the central element is an optical fiber sensing unit, and a plurality of optical fiber sensing units and metal reinforcing pieces alternately surround the central element. The central optical fiber sensing unit 3 is based on a phi-OTDR system for sensing, and the periphery is surrounded by the peripheral optical fiber sensing unit 2 based on a BOTDR system for sensing. All the metal reinforcing members 4 and the surrounding optical fiber sensing units 2 are placed in parallel. Preferably, the metal strength member 4 may employ a high strength steel wire strength member for improving the tensile strength of the optical cable. The optical fiber used by the invention can be a common single-mode optical fiber or a special optical fiber, and is selected according to actual requirements.
As shown in fig. 6(a), which is a connection diagram of 5 optical fiber sensing units in the optical cable of the present invention, taking an optical cable 202 structure including 5 optical fibers 31, 1, 2, 3, 4 as an example, all the optical fibers are connected end to end through a jumper to form 1 long optical fiber, that is, the optical fibers 31 and 1, the optical fibers 1 and 2, the optical fibers 2 and 3, and the optical fibers 3 and 4 are connected end to end in sequence. The outlet 31' is connected to an optical fiber 31 as an access port of a hybrid Φ -OTDR and BOTDR system, the cross-sectional connection of which is shown in fig. 6 (b).
Based on the structure, the working principle of the underwater exploration towed optical cable is as follows:
this novel optical cable includes 2n +1 optical fiber sensing units as seismic wave sound field signal's among the geological exploration of water, respectively encapsulates an optic fibre in every sensing unit, and 2n optical fiber sensing units and metal reinforcement are crisscross to become central symmetry around central sensing unit around and arrange. The optical fiber packaged by the central sensing unit is used as a sensing end of the phi-OTDR system, the phi-OTDR system adopts an ultra-narrow linewidth laser as a light source, and the response sensitivity of the system to external disturbance is improved by utilizing the interference effect between backward Rayleigh scattering light and intrinsic light generated in the light pulse coverage width in the sensing optical fiber. After the exploration ship excites the seismic waves underwater, the seismic waves are reflected when encountering geological boundary surfaces in the propagation process, and when the reflected seismic wave signals reach a certain position on the towing cable, disturbance is generated on the optical fibers. When the optical fiber is disturbed by the outside, the length of the optical fiber at the position of the disturbance event changes, so that the optical path difference changes, and further the phase of light changes after passing through the area. The interference result of Rayleigh scattering light in the area also changes, and the phi-OTDR detection system can acquire the position information of the disturbed optical fiber by demodulating the phase change condition along the optical fiber and can further demodulate seismic wave vibration signals.
However, under the influence of the towing ship wake and the motion of the water body, the posture of the sensing optical cable has great deviation relative to the ideal horizontal linear state, so that the optical cable reconstructs seismic wave sound field vibration signals to carry out positioning detection to generate errors, and the positioning precision is reduced. In order to correct and restore the vibration sound field monitored by the optical cable, the optical cable uses the optical fibers packaged in 2n surrounding optical fiber sensing units which are symmetrically distributed around the optical cable as the sensing end of the BOTDR detection system. The BOTDR detection system realizes distributed sensing of strain by using the characteristic that the frequency difference between spontaneous Brillouin scattering light and incident light is sensitive to the change of strain. Brillouin scattering is inelastic light scattering produced by interaction of an incident optical field with acoustic phonons of a medium, and brillouin scattering propagates in an optical fiber with a frequency shift related to the sound velocity due to the doppler effect, the frequency shift being proportional to the effective refractive index in the optical fiber and the acoustic velocity in the optical fiber and inversely proportional to the wavelength of the incident light. When the optical cable is bent in the process of dragging on water, the strain of the optical fiber is changed, so that the refractive index of the optical cable is changed, the change of Brillouin frequency shift quantity is influenced, the strain of the optical cable is measured by using a BOTDR detection system, the three-dimensional stress actually suffered by the optical cable is restored, the dynamic evolution process of the optical cable is continuously tracked, the spatial attitude of the dragging optical cable can be reconstructed, the correction of the seismic wave vibration signal measured by the phi-OTDR detection system is realized, and the real seismic wave sound field vibration signal is restored and obtained.
In the optical cable, 2n +1 optical fibers are connected end to end through jumper wires to form a long optical fiber, only one end of a single-mode optical fiber packaged by a central sensing unit is reserved to be used as an access port of a phi-OTDR and BOTDR hybrid system, and the realization of time division multiplexing, transformation and space division multiplexing is completed by utilizing single-end measurement. The system realizes the function of simultaneously measuring dynamic vibration and static strain: since the rayleigh scattered light and the spontaneous brillouin scattered light are a kind of natural frequency multiplexed light, the system can realize synchronous demodulation of two scattered signals by heterodyne asynchronous demodulation of frequency shift keying. The hybrid system can realize the comprehensive analysis of the vibration and the strain of the optical cable and provide more useful information for the positioning accuracy of seismic wave exploration. By collecting strain information of the optical cable, the stress condition of the optical cable can be recovered, and further the spatial attitude of the optical cable can be reconstructed, so that the correction of the signals measured by the phi-OTDR is realized, and a real seismic wave mapping map is obtained.
Therefore, the underwater exploration towing optical cable ensures the detection sensitivity of seismic wave sound field vibration signals, realizes the space form restoration of the towing optical cable, further improves the positioning precision of the restored seismic wave signals, has high detection sensitivity on the seismic wave vibration signals, and can better restore the underwater space posture of the towing optical cable. The optical cable is insulated, resistant to high temperature corrosion, long in service life, capable of sufficiently resisting electromagnetic interference, suitable for long-time work in severe marine environments, and suitable for submarine geomorphology and submarine oil gas exploration, and can be applied to river bottom exploration.
The embodiments of the present invention have been described in detail with reference to the drawings, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the gist of the present invention.
Claims (7)
1. An underwater exploration towed optical cable with self attitude tracking capability, comprising: the sensor comprises an outer protective layer (1), 2n metal reinforcing pieces (4) inserted in the outer protective layer, 2n surrounding optical fiber sensing units (2) and a central sensing unit (3), wherein n is a natural number more than 1; the central sensing unit (3) is arranged in the center of the outer protective layer (1), and 2n peripheral optical fiber sensing units (2) and 2n metal reinforcing pieces (4) are centrally symmetrically and alternately inserted in the periphery of the central sensing unit in a staggered manner by adopting a layer-twisted structure; each of the 2n peripheral optical fiber sensing units (2) and the central sensing unit (3) is packaged with an optical fiber, all the optical fibers are connected in series end to end through jumper wires to form a long optical fiber, and only one end of the optical fiber packaged by the central sensing unit is reserved as a port accessed to the detection system;
the optical fiber packaged in the central sensing unit (3) is used as a sensing end of the phase sensitive optical time domain reflection detection system, and the optical fiber packaged in each peripheral optical fiber sensing unit (2) is used as a sensing end of the Brillouin optical time domain reflection detection system.
2. The underwater exploration towed optical cable with the self attitude tracking capability of claim 1, wherein: the outer protective layer (1) sequentially wraps the armored sheath (15), the PE outer sheath (14), the PE inner sheath (13), the polyester tape and the water-blocking non-woven fabric binding tape (12) from outside to inside.
3. The underwater exploration towed optical cable with self attitude tracking capability of claim 2, wherein: the armor sheath (15) is made of aluminum plastic or embossed steel belt.
4. The underwater exploration towed optical cable with the self attitude tracking capability of claim 1, wherein: the central sensing unit (3) is sequentially coated with an optical fiber (31), a tight sleeve (32), a water-blocking yarn (33) and a PBT sheath layer (34) from inside to outside.
5. The underwater exploration towed optical cable with the self attitude tracking capability of claim 1, wherein: the surrounding optical fiber sensing unit (2) is sequentially coated with an optical fiber (21), optical fiber ointment (22) and a PBT (polybutylene terephthalate) sheath layer (23) from inside to outside.
6. The underwater exploration towed optical cable with the self attitude tracking capability of claim 1, wherein: the outer protective layer (1) further comprises optical cable ointment filled in gaps among the metal reinforcing piece, the optical fiber sensing unit and the central sensing unit.
7. The underwater exploration towed optical cable with the self attitude tracking capability of claim 1, wherein: the metal reinforcing piece (4) is a steel wire reinforcing piece.
Priority Applications (1)
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