CN115524742A - Three-component seismic wave sensing optical cable, seismic wave sensing system and method - Google Patents

Three-component seismic wave sensing optical cable, seismic wave sensing system and method Download PDF

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CN115524742A
CN115524742A CN202211293655.3A CN202211293655A CN115524742A CN 115524742 A CN115524742 A CN 115524742A CN 202211293655 A CN202211293655 A CN 202211293655A CN 115524742 A CN115524742 A CN 115524742A
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wave sensing
elastic body
optical fiber
seismic wave
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饶云江
敬强
张丽霞
杨天元
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University of Electronic Science and Technology of China
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
    • G01V1/22—Transmitting seismic signals to recording or processing apparatus
    • G01V1/226—Optoseismic systems
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/16—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge
    • G01B11/165—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge by means of a grating deformed by the object
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • 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
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
    • G01V1/16—Receiving elements for seismic signals; Arrangements or adaptations of receiving elements
    • G01V1/18—Receiving elements, e.g. seismometer, geophone or torque detectors, for localised single point measurements
    • G01V1/181—Geophones
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V2210/00—Details of seismic processing or analysis
    • G01V2210/10—Aspects of acoustic signal generation or detection
    • G01V2210/14—Signal detection
    • G01V2210/144—Signal detection with functionally associated receivers, e.g. hydrophone and geophone pairs

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Abstract

The invention relates to the technical field of distributed optical fiber sensing, and the fields of seismic wave detection and geophysical prospecting, and discloses a three-component seismic wave sensing optical cable, a seismic wave sensing system and a method, wherein the quasi-distributed optical fiber three-component seismic wave sensing system comprises the following components: s1, injecting detection pulse light into a three-component seismic wave sensing optical cable by a three-channel distributed optical fiber acoustic wave sensing system demodulation host; s2, collecting Rayleigh scattering signals returned from the three-component seismic wave sensing optical cable by a receiving end of the three-channel distributed optical fiber acoustic wave sensing system demodulation host; and S3, calculating three-component strain generated by the seismic waves according to the Rayleigh scattering signals. According to the invention, two spirally wound optical fibers are fixed on the surface of the cylindrical elastic body, and the straight optical fibers are fixed on the surface of the square elastic body, and as the Young modulus of the elastic body is far lower than that of the optical fibers, the elastic body generates larger deformation under the action of seismic waves and transmits the larger deformation to the optical fibers, so that the strain sensitivity of the optical cable is obviously improved.

Description

Three-component seismic wave sensing optical cable, seismic wave sensing system and method
Technical Field
The invention relates to the technical field of distributed optical fiber sensing and the fields of earthquake wave detection and geophysical prospecting, in particular to a three-component earthquake wave sensing optical cable, an earthquake wave sensing system and an earthquake wave sensing method.
Background
With the increasing awareness of the human society on the earth and the increasing demand for energy, seismic exploration techniques are rapidly developing. Among them, the multi-wave multi-component exploration technology is beginning in the 80 s of the world, and has been developed into one of the mainstream technologies in the field of seismic exploration for many years. The multi-wave multi-component exploration technology utilizes a three-component detector to pick up multi-wave multi-component seismic data, and has obvious superiority in the aspects of describing formation parameters, predicting oil and gas distribution and the like. The quality of earthquake acquisition data depends on the quality of a seismic detection instrument, and a three-component detector applied in the field of geophysical prospecting at present is mainly a point type three-component electronic detector, has the advantages of high sensitivity, mature process and the like, but is also limited by the principle defects of poor instantaneity, difficult maintenance, electromagnetic interference and the like of the electronic detector. In recent years, optical fiber group detectors are mainly concerned with the advantages of good real-time performance, high sensitivity, light weight, strong environmental adaptability and the like, and researchers research point-type three-component optical fiber group detectors with various sensing structures, including interferometer type, optical fiber group grating type and optical fiber group laser type optical fiber group detectors, for detecting various physical quantities such as seismic acceleration, displacement, strain and the like. However, the point type three-component fiber detector can only perform point type sensing to pick up seismic wave signals, has limited multiplexing capability and cannot realize large-scale networking, so that the requirements of large-scale, high-precision and high-density seismic acquisition application are difficult to meet, and the networking cost is high. Therefore, a Distributed Acoustic Sensing (DAS) technique has been developed.
The core of the DAS technology is the Phase-sensitive Optical Time Domain Reflectometry (Φ -OTDR). And the phi-OTDR realizes external disturbance positioning by detecting the light intensity or phase information of the backward Rayleigh scattering signal. When the optical fiber is vibrated by the outside, the length of the optical fiber is changed, and the refractive index of the optical fiber is correspondingly changed due to the photoelastic effect, so that the phase of a Rayleigh scattering interference light signal in the optical fiber is changed, and the interference light intensity is also changed. And the backward Rayleigh scattering signals are collected for demodulation, so that distributed monitoring along the optical fiber can be realized. The DAS technology based on the phi-OTDR utilizes the linear relation between the phase change of backward Rayleigh scattering light and the axial strain generated by the optical fiber to reconstruct an external acoustic wave signal and realize the continuous distributed detection of the acoustic wave along the optical fiber. The DAS has the advantages of high temperature and high pressure resistance, electromagnetic interference resistance, light weight, small volume, no source and adaptability to extreme environments such as oil wells, deep sea and the like of a common optical fiber sensor, can realize high-sensitivity long-distance distributed sound wave monitoring, can meet the sensing application requirements of large range, high precision and high density, becomes a research hotspot at home and abroad, and has wide application prospect in the fields of perimeter security, earthquake monitoring, oil gas exploration, traffic monitoring and the like.
In recent years, the DAS technology has been rapidly developed, and performance improvement studies in the aspects of signal-to-noise ratio enhancement, sensing distance extension, and the like of the DAS system have been focused. However, the DAS is configured to acquire external acoustic information by detecting axial strain of the optical fiber, and only detects a component of the acoustic wave projected in the axial direction of the optical fiber, and seismic waves incident at other angles are coupled in the axial direction of the optical fiber at a square amplitude of a cosine function of an incident angle. Thus, DAS technology suffers from the significant disadvantages of single component detection and wide-area insensitivity compared to existing three-component detectors. Aiming at the problem that the DAS technology is insensitive in width, scientific researchers provide two solutions. One is cable deployment in real three-dimensional space. In 2018, feigl et al, madison division school, wisconsin university, deployed optical cables vertically in wells and horizontally on the ground, with a vertical optical cable length of 400m and a horizontal optical cable length of 8700m, combined with DAS technology to monitor Reservoir rock property changes [ Feigl K.L.et al,42nd Workshop on Geothermal Reservoir engineering, 2017. However, the method is difficult and cumbersome to deploy in practical application, and signals acquired by three components are difficult to combine accurately. And the other is a spiral winding optical fiber structure. In 2013, shell company proposed a spiral wound fiber technology to solve the problem of width insensitivity of DAS technology [ Hornman K.et al,75th EAGE conference and inhibition in coordination SPE EUROPEC, 2013. Further, a method for qualitatively realizing three-component DAS is provided [ Detecting hybrid electrical signals with a fibrous distributed electrical sensing (DAS) estimation, WO2013090544A1,2013 ]. In 2014, schlumberger also proposed a method for qualitatively achieving three-component DAS [ Fiber optical distributed sensing with direct sensing, wo2014201313a1,2014 ], but has not been successful in achieving three-component DAS due to the lack of a specific theoretical model. In 2016, shell Kuvshinov's theory of signal acquisition for helically wound cables was analyzed and combined with DAS to improve the broadside sensitivity of fiber optic cables [ Kuvshinov B., geographic sensing, 2016,64 (3): 671-688 ]. In 2018, eaid et al, university of Cargary, canada, proposed a quadric helix cable to better characterize the sound field [ Eaid M., CSEG geoconvement Expanded Abstracts,2018 ]. However, as the complexity of the optical fiber geometry increases significantly, the separation of the collected signals is very complex and difficult to achieve. In 2018, lim et al, the Colorado institute of technology, USA, proposed a method for reconstructing all components of strain tensor by respectively obtaining strain projection in six different directions by using a single optical fiber and a plurality of optical fibers based on the design of a spiral wound optical fiber [ Ning I.L.C.et al, geophysics,2018,83 (2): P1-P8 ]; ning I.L.C.et al, geographic profiling, 2018,66 (6): 1111-1122 ]. In 2020, the university of electronic technology, yunjiang, based on the design of Optical fiber spiral wound on elastic layer, developed an Optical fiber hydrophone with sensitivity as high as-131 dB re rad/μ Pa, [ Guan H.et al,2020Asia Communications and Photonics Conference (ACP) and International Conference on Information Photonics (IPOC), 2020. Although the spiral wound optical fiber structure is sensitive to seismic waves incident in different directions and can realize three-component signal acquisition, three-component information of the seismic waves cannot be separated, the main reason is that no breakthrough is realized in the sensing principle, and the bottleneck problem of single-component detection of the DAS technology still exists. Therefore, the research on the method for separating and extracting the seismic wave three-component information based on the quasi-distributed three-component seismic wave sensing unit is a key problem for realizing the quasi-distributed optical fiber three-component seismic wave sensing technology.
Disclosure of Invention
The invention provides a three-component seismic wave sensing optical cable, a seismic wave sensing system and a method, aiming at the limitation of single-component seismic detection of the existing distributed optical fiber sensing unit.
The invention is realized by the following technical scheme:
the utility model provides a three-component seismic wave sensing optical cable, includes the optical cable body the axial direction interval of optical cable body is provided with accurate distribution three-component seismic wave sensing unit, through the size of three-component strain that accurate distribution three-component seismic wave sensing unit produced can obtain with the seismic wave coupling the three-component that just meets an emergency that the seismic wave produced, accurate distribution three-component seismic wave sensing unit includes:
the elastic body group comprises a first elastic body, a second elastic body and a third elastic body which are axially arranged in the x direction, the y direction and the z direction respectively, wherein the first elastic body and the second elastic body are cylindrical elastic bodies, and the z direction is the axial direction of the optical cable body;
optical fibers respectively set on the first elastic body, the second elastic body and the third elastic body in a predetermined mode;
the outer sheath wraps the optical cable body, the elastomer group and the optical fiber and is made of a corrosion-resistant and sealing material;
the grease layer is arranged among the optical cable body, the elastomer group, the optical fiber and the outer sheath.
Preferably, the third elastic body is a cylindrical elastic body, the optical fiber comprises three spirally wound optical fibers, and the three spirally wound optical fibers are spirally wound and fixed on the circumferential side surfaces of the first elastic body, the second elastic body and the third elastic body respectively with the same prestress.
Preferably, the third elastic body is a square elastic body, the optical fiber includes two spirally wound optical fibers and a straight optical fiber, the two spirally wound optical fibers are respectively fixed on the circumferential side surfaces of the first elastic body and the second elastic body by winding with the same prestress thread, and the straight optical fiber is fixed on the surface of the third elastic body by the same prestress with that of the spirally wound optical fiber.
Specifically, the optical fiber includes a bend-resistant optical fiber as the spirally-wound optical fiber, but is not limited to a single-mode optical fiber, a bend-resistant optical fiber and an ultra-low loss optical fiber as the straight optical fiber, and the cladding diameter of the optical fiber is greater than 40 μm and not greater than 125 μm.
And optimally, continuously writing a fiber grating array in the optical fiber, wherein the reflectivity of the fiber grating array is less than a first threshold value, so that the intensity of backward Rayleigh scattering light can be improved.
As optimization, the spiral winding angle value range of the spiral winding optical fiber is [0, pi/2 ].
Preferably, the elastomer group is of a solid structure, the young's modulus of the elastomer group is not more than 1Gpa, the material of the elastomer group includes but is not limited to elastomer plastics such as rubber and polyurethane, and the elastomer is tightly bonded with the optical fiber, so that the deformation of the elastomer can be transmitted to the inside of the optical fiber.
The invention also discloses a quasi-distributed optical fiber three-component seismic wave sensing system, which comprises:
the three-component seismic wave sensing optical cable;
the three-channel distributed optical fiber acoustic wave sensing system demodulation host is connected with the three-component seismic wave sensing optical cable and comprises a light source, a driving source, a pulse modulator, a random laser amplifier, a wavelength division/air division multiplexer, a detection module, a demodulation module and a data analysis module, wherein the light source and the driving source are respectively connected with the pulse modulator, the random laser amplifier and the output end of the pulse modulator are connected with the input end of the three-component seismic wave sensing optical cable through the wavelength division/air division multiplexer, the output end of the three-component seismic wave sensing optical cable is connected with the input end of the detection module through the wavelength division/air division multiplexer, and the output end of the detection module is connected with the data analysis module through the demodulation module.
The invention also discloses a quasi-distributed optical fiber three-component seismic wave sensing method, which uses the quasi-distributed optical fiber three-component seismic wave sensing system and comprises the following steps:
s1, injecting detection pulse light into a three-component seismic wave sensing optical cable by a three-channel distributed optical fiber acoustic wave sensing system demodulation host;
s2, collecting Rayleigh scattering signals returned from the three-component seismic wave sensing optical cable by a receiving end of the three-channel distributed optical fiber acoustic wave sensing system demodulation host;
and S3, calculating three-component strain generated by the seismic waves according to the Rayleigh scattering signals.
As an optimization, when the third elastic body is a square elastic body, the specific steps of S3 are:
s3.1, when the quasi-distributed three-component seismic wave sensing unit is in a near-balance state under the action of far-field plane seismic waves, obtaining the magnitude of three-component strain generated by the quasi-distributed three-component seismic wave sensing unit through the following formula based on the interaction between an elastic body and an optical fiber in the quasi-distributed three-component seismic wave sensing unit:
Figure BDA0003902351500000041
wherein e is (c) Representing the strain produced by a three-component seismic wave sensing cable, e l (f) Representing the strain induced in the optical fiber; α represents a helix angle of the spirally wound optical fiber; f. of 1，2，3 And c denotes an optical fiber and an optical cable, respectively; l, x, y and z represent axial, x, y and z directions, respectively;
s3.2, when the rotation angle of the spiral wound optical fiber on the first elastic body and the second elastic body is 0, the coupling of the quasi-distributed three-component seismic wave sensing unit and the seismic wave can obtain the magnitude of three-component strain generated by the seismic wave through the following formula:
Figure BDA0003902351500000042
Figure BDA0003902351500000043
wherein λ and N represent Lame constants of the formation, λ c And N c Expressing the Lame constant of the optical fiber cable, E c And mu c Expressing Young's modulus and Poisson's ratio, e, of the optical fiber cable (ω) Representing the strain produced by the seismic waves; omega represents seismic waves, and l, x, y and z respectively represent axial directions and x, y and z directions;
s3.3, when the quasi-distributed three-component seismic wave sensing unit is acted by an acceleration signal, obtaining the relation between strain and the acceleration signal generated by three optical fibers in the quasi-distributed three-component seismic wave sensing unit through the following formula:
Figure BDA0003902351500000051
wherein a represents an acceleration applied to the elastic body; a represents the area perpendicular to the direction of the equivalent force applied to the elastic body; r represents the radius of the cross section of the cylindrical elastomer; m represents the equivalent mass of the cylindrical elastomer, and m' represents the equivalent mass of the square strip elastomer; x, y and z represent x, y and z directions, respectively.
As an optimization, when the third elastic body is a cylindrical elastic body, the specific step of S3 is:
s3.1, when the sensing unit is in a near-balance state under the action of far-field plane seismic waves, based on the interaction between an elastic body and an optical fiber in the quasi-distribution three-component seismic wave sensing unit, obtaining the three-component strain magnitude generated by the quasi-distribution three-component seismic wave sensing unit through the following formula:
Figure BDA0003902351500000052
wherein e is (c) Representing the strain, e, produced by a three-component seismic wave sensing cable l (f) Representing the strain induced in the fiber; α represents a helix angle of the spirally wound optical fiber; f. of 1，2，3 And c denotes an optical fiber and an optical cable, respectively; l, x, y and z represent axial directions, x, y,The z direction;
s3.2, when the rotation angle of the spiral wound optical fiber on the first elastic body, the second elastic body and the third elastic body is 0, the coupling of the quasi-distributed three-component seismic wave sensing unit and seismic waves can obtain the magnitude of three-component strain generated by the seismic waves through the following formula:
Figure BDA0003902351500000053
Figure BDA0003902351500000054
where λ and N represent Lame constants of the formation, λ c And N c Expressing Lame constant of the optical fiber cable, e (ω) The strain generated by seismic waves is represented, omega represents the seismic waves, and l, x, y and z respectively represent the axial direction and the x, y and z directions;
s3.3, when the quasi-distributed three-component seismic wave sensing unit is acted by an acceleration signal, obtaining the relation between the strain and the acceleration signal of the three optical fibers in the quasi-distributed three-component seismic wave sensing unit through the following formula:
Figure BDA0003902351500000061
wherein a represents an acceleration applied to the elastic body; a represents an area perpendicular to the direction of the equivalent force applied to the elastic body; r represents the radius of the cross section of the cylindrical elastomer; m represents the equivalent mass of the cylindrical elastomer, and m' represents the equivalent mass of the square strip elastomer; x, y and z represent x, y and z directions, respectively.
Compared with the prior art, the invention has the following advantages and beneficial effects:
1. the invention establishes a theoretical analysis model of high-sensitivity quantitative sensing of the quasi-distributed optical fiber three-component seismic wave based on the interaction of optical fibers and an elastic body and the coupling of an optical cable and the seismic wave, establishes a quasi-distributed optical fiber three-component acoustic wave sensing system, utilizes the combination of three optical fibers to sense the seismic wave, collects three optical fiber backward Rayleigh scattering light to demodulate the phase, inverts three-component information generated by the seismic wave based on axial strain generated by the three optical fibers, and solves the problem of single-component seismic wave detection of the optical fiber distributed optical fiber acoustic wave sensing optical cable.
2. Compared with a point type three-component optical fiber detector, the quasi-distributed optical fiber three-component seismic wave sensing method provided by the invention can demodulate all seismic signals along the optical fiber in a distributed manner, and can realize large-scale networking based on a DAS instrument and a single optical cable, so that the bottleneck of large-scale networking of the point type three-component optical fiber detector is fundamentally broken through, and a new important technical means is provided for multi-wave multi-component seismic exploration.
3. According to the invention, two spirally wound optical fibers are fixed on the surface of the cylindrical elastic body, and the straight optical fibers are fixed on the surface of the square elastic body, and as the Young modulus of the elastic body is far lower than that of the optical fibers, the elastic body generates larger deformation under the action of seismic waves and transmits the larger deformation to the optical fibers, so that the strain sensitivity of the optical cable is obviously improved.
4. According to the invention, the weak reflecting fiber grating array is continuously inscribed in the optical fiber, so that Rayleigh scattering is enhanced, the signal-to-noise ratio of signal light is improved, the strain sensitivity of the optical cable is improved, and the sensing distance of the system is prolonged.
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In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the drawings that are required to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and that for those skilled in the art, other related drawings can be obtained from these drawings without inventive effort. In the drawings:
FIG. 1 is a schematic structural diagram of a quasi-distributed three-component seismic wave sensing unit (a third elastic body is a square strip elastic body) according to the present invention;
FIG. 2 is a schematic cross-sectional view of the quasi-distributed three-component seismic wave sensing unit of FIG. 1;
FIG. 3 is a graph showing the variation of sound pressure sensitivity with elastomer parameters for a helically close-wound fiber in accordance with the present invention;
FIG. 4 is a schematic diagram of a quasi-distributed optical fiber three-component acoustic wave sensing system according to the present invention;
FIG. 5 is a schematic structural diagram of a quasi-distributed three-component seismic wave sensing unit (a third elastic body is a cylindrical elastic body) according to the present invention;
FIG. 6 is a schematic diagram of a quasi-distributed optical fiber three-component acoustic wave sensing system according to the present invention;
FIG. 7 is a graph showing the effect of comparing the waveforms of a quasi-distributed optical fiber three-component seismic wave sensing structure unit (the third elastic body is a square strip elastic body) and a three-component electronic acceleration detector; (a) 6Hz; (b) 10Hz;
reference numerals: 1-three-component seismic wave sensing optical cable, 101-elastic body group, 1021-first spiral wound optical fiber, 1022-second spiral wound optical fiber, 1023-straight optical fiber, 1024-third spiral wound optical fiber, 103-grease layer, 104-outer sheath, 105-first quasi-distribution three-component seismic wave sensing unit, 106-second quasi-distribution three-component seismic wave sensing unit, 2-three-channel distributed optical fiber acoustic wave sensing system demodulation host, 201-light source, 202-driving source, 203-pulse modulator, 204-random laser amplifier, 205-wavelength division/air division multiplexer, 206-detection module, 207-demodulation module and 208-data analysis module.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to examples and the accompanying drawings, and the exemplary embodiments and descriptions thereof are only used for explaining the present invention and are not used as limiting the present invention.
Example 1
The utility model provides a three components seismic wave sensing optical cable 1, includes the optical cable body the axial direction interval of optical cable body is provided with accurate distribution three components seismic wave sensing unit, through the size of three components of meeting an emergency that accurate distribution three components seismic wave sensing unit produced can obtain with the seismic wave coupling the three components of orthostrain that the seismic wave produced, accurate distribution three components seismic wave sensing unit includes:
the elastic body group 101 comprises a first elastic body, a second elastic body and a third elastic body which are arranged in the x, y and z directions along the three axial directions, wherein the first elastic body and the second elastic body are cylindrical elastic bodies, the third elastic body is a square elastic body, and the z direction is the axial direction of the optical cable body; the first elastic body and the second elastic body are fixed on the surface of the third elastic body; the elastomer group 101 is of a solid structure, the young's modulus of the elastomer group 101 is not more than 1Gpa, the material of the elastomer group 101 includes but is not limited to elastomer plastics such as rubber and polyurethane, and the elastomer is tightly bonded with the optical fiber, so that the deformation of the elastomer can be transmitted to the inside of the optical fiber.
Optical fibers respectively set on the first elastic body, the second elastic body and the third elastic body in a predetermined mode; and the optic fibre contains two spiral winding optic fibres and a straight optic fibre 1023, and the spiral winding angle value range of spiral winding optic fibre is [0, pi/2 ], uses the bending resistance optic fibre, and straight optic fibre 1023 uses but not limited to single mode fiber, bending resistance optic fibre and ultra-low loss optic fibre, and the cladding diameter of optic fibre is greater than 40 μm, less than or equal to 125 μm, inscribe the fiber grating array in the optic fibre in succession, the reflectivity of fiber grating array is less than first threshold value (-50 dB), can improve backward rayleigh scattered light intensity like this.
Two spiral-wound optical fibers are respectively fixed on the circumferential side surfaces of the first elastic body and the second elastic body in a threaded winding way with the same prestress, and the straight optical fiber 1023 is fixed on the surface of the third elastic body in a prestress which is the same as the prestress of the spiral-wound optical fiber.
Specifically, the first helically-wound optical fiber 1021 and the second helically-wound optical fiber 1022 are respectively fixed to circumferential side surfaces of the first elastic body and the second elastic body by being spirally wound, and the straight optical fiber 1023 is fixed to a surface of the third elastic body with a certain pre-stress.
The outer sheath 104 wraps the optical cable body, the elastomer group 101 and the optical fibers and is made of a corrosion-resistant and sealing material;
an oil-paste layer 103 disposed between the cable body and the outer jacket 104.
Example 2
The only difference from the embodiment 1 is that the third elastic body is a cylindrical elastic body which is the same as the first elastic body and the second elastic body, the optical fiber comprises three spirally wound optical fibers, and the three spirally wound optical fibers are respectively wound and fixed on the circumferential side surfaces of the first elastic body, the second elastic body and the third elastic body by the same prestress threads. Specifically, the first helically wound optical fiber 1021, the second helically wound optical fiber 1022, and the third helically wound optical fiber 1024 are respectively fixed to the circumferential sides of the first elastic body, the second elastic body, and the third elastic body by being helically wound with the same pre-stress.
Example 3
The invention also discloses a quasi-distributed optical fiber three-component seismic wave sensing system, which comprises:
the three-component seismic wave sensing optical cable 1 of embodiment 1;
the three-channel distributed optical fiber acoustic wave sensing system demodulation host is connected with the three-component seismic wave sensing optical cable 1 and comprises a light source 201, a driving source 202, a pulse modulator 203, a random laser amplifier 204, a wavelength division/space division multiplexer 205, a detection module 206, a demodulation module 207 and a data analysis module 208, wherein the light source 201 and the driving source 202 are respectively connected with the pulse modulator 203, the random laser amplifier 204 and the output end of the pulse modulator 203 are connected with the input end of the three-component seismic wave sensing optical cable 1 through the wavelength division/space division multiplexer 205, the output end of the three-component seismic wave sensing optical cable 1 is connected with the input end of the detection module 206 through the wavelength division/space division multiplexer 205, and the output end of the detection module 206 is connected with the data analysis module 208 through the demodulation module 207.
Example 4
The invention also discloses a quasi-distributed optical fiber three-component seismic wave sensing system, which comprises:
the three-component seismic wave sensing optical cable 1 of embodiment 2;
the three-channel distributed optical fiber acoustic wave sensing system demodulation host is connected with the three-component seismic wave sensing optical cable 1 and comprises a light source 201, a driving source 202, a pulse modulator 203, a random laser amplifier 204, a wavelength division/space division multiplexer 205, a detection module 206, a demodulation module 207 and a data analysis module 208, wherein the light source 201 and the driving source 202 are respectively connected with the pulse modulator 203, the random laser amplifier 204 and the output end of the pulse modulator 203 are connected with the input end of the three-component seismic wave sensing optical cable 1 through the wavelength division/space division multiplexer 205, the output end of the three-component seismic wave sensing optical cable 1 is connected with the input end of the detection module 206 through the wavelength division/space division multiplexer 205, and the output end of the detection module 206 is connected with the data analysis module 208 through the demodulation module 207.
Example 5
Sensing calculation is performed on the quasi-distributed optical fiber three-component seismic wave sensing system of embodiment 3, as shown in fig. 1 to 2, the first quasi-distributed three-component seismic wave sensing unit 105 (the elastic body group 101 is composed of the first elastic body, the second elastic body are cylindrical elastic bodies, and the third elastic body is a square elastic body group 101) includes two cylindrical elastic bodies (the first elastic body and the second elastic body) which are respectively axially along the x and y directions, and a square elastic body (the third elastic body) which is axially along the z direction, wherein the two cylindrical elastic bodies are fixed on the surface of the square elastic body, the two spiral-wound optical fibers (the first spiral-wound optical fiber 1021 and the second spiral-wound optical fiber 1022) are respectively fixed on the surfaces of the two cylindrical elastic bodies, and a straight optical fiber 1023 (1023) is fixed on the surface of the square elastic body with a certain pre-stress.
First, the mechanical analysis is performed on the elastomer package 101 and the optical fibers (by the first helically wound optical fiber 1021, the second helically wound optical fiber 1022, and the straight optical fiber 1023), and the fiber-detected strain is expressed as:
Figure BDA0003902351500000091
wherein α represents the helix of the helically wound optical fiberAn angle; e.g. of the type l (f) Representing the strain induced in the fibre, e (c) Representing the strain induced in the cable; f. of 1，2，3 Optical fibers (first helically wound fiber 1021, second helically wound fiber 1022, straight fiber 1023) are shown, with l, x, y, and z representing the axial and x, y, and z directions, respectively.
When the spiral angle α of the first spirally-wound optical fiber 1021 and the second spirally-wound optical fiber 1022 is equal to 0, the first spirally-wound optical fiber 1021 detects the strain generated by the first elastic body in the YZ plane, the second spirally-wound optical fiber 1022 detects the strain generated by the second elastic body of the elastic body in the XZ plane, the straight optical fiber 1023 detects the strain generated by the third elastic body of the elastic body in the Z direction, and the optical fibers (the first spirally-wound optical fiber 1021, the second spirally-wound optical fiber 1022, and the straight optical fiber 1023) are sensitive to the strains generated by the elastic body group 101 in different directions. Assuming that the three-component seismic wave sensing optical cable is well coupled with the stratum, when planar seismic waves with wavelengths larger than the radius of the cross section of the optical cable body act on the three-component seismic wave sensing optical cable, the torsional deformation of the three-component seismic wave sensing optical cable can be ignored. Establishing a motion differential equation of the elastic medium:
Figure BDA0003902351500000101
in the formula, ρ represents a density of the medium, u represents a displacement of the solid particles, σ represents a stress, and x, y, and z represent directions in x, y, and z, respectively. Stress and strain e x ，e y ，e z And the Lame constants λ, N are expressed as:
Figure BDA0003902351500000102
when seismic waves act on the three-component seismic wave sensing optical cable 1, the three-component seismic wave sensing optical cable 1 is in a near-balanced state, and according to a strain edge value condition and a normal displacement boundary condition, a relational expression of strain generated by the three-component seismic wave sensing optical cable 1 at the position of the first spirally-wound optical fiber 1021 and strain generated by the seismic waves is calculated as follows:
Figure BDA0003902351500000103
in the formula, θ represents a projection angle between seismic waves and the three-component seismic wave sensing optical cable 1, λ c And N c Respectively represents the Lame constant of the three-component seismic wave sensing optical cable 1, the Lame constant of the optical cable body and the Young modulus E of the three-component seismic wave sensing optical cable 1 c And poisson ratio mu c The relational expression of (a) is:
Figure BDA0003902351500000104
according to the interaction of the three-component seismic wave sensing optical cable 1 and the seismic waves and the strain direction sensitivity generated by the optical fibers, the three-component strain magnitude of the seismic waves can be separated and extracted:
Figure BDA0003902351500000105
Figure BDA0003902351500000111
in the formula, e (ω) Representing the strain produced by the seismic waves; x, y and z represent x, y, z directions, respectively.
When the first quasi-distributed three-component seismic wave sensing unit 105 (the elastic body group 101 is the first elastic body, the second elastic body is the cylindrical elastic body, and the third elastic body is the square strip elastic body group 101) is subjected to the action of an acceleration signal with the frequency far lower than the natural frequency, the first quasi-distributed three-component seismic wave sensing unit 105 generates accelerated motion relative to an inertial system, and an inertial force proportional to the acceleration acts on the first quasi-distributed three-component seismic wave sensing unit 105, so that the elastic body group 101 deforms to drive the optical fiber to deform. Based on Hooke's law, the strain generated by the optical fiber under the action of the acceleration signal can be calculated as follows:
Figure BDA0003902351500000112
wherein a represents the acceleration applied to the elastic body, a represents the area perpendicular to the direction of the equivalent force applied to the elastic body, R represents the radius of the cross section of the cylindrical elastic body, m represents the equivalent mass of the cylindrical elastic body, m' represents the equivalent mass of the square bar elastic body, and x, y and z represent the directions x, y and z, respectively.
The quasi-distributed optical fiber three-component acoustic wave sensing system is shown in fig. 4, wherein a three-channel distributed optical fiber acoustic wave sensing system demodulation host 2) adopts a wavelength division multiplexing or space division multiplexing technology, can simultaneously acquire signals of three optical fibers on a three-component seismic wave sensing optical cable 1, performs phase demodulation on backward rayleigh scattered light through a demodulation module 207, calculates axial strain generated by the three optical fibers, and accordingly inverts three-component strain information of seismic waves.
Measuring a vibration signal by using a quasi-distributed optical fiber three-component seismic wave sensing method:
two spiral tightly-wound optical fibers (a first spiral tightly-wound optical fiber and a second spiral tightly-wound optical fiber) fixed on the surface of the elastic body group 101, a straight optical fiber 1023 and a spaced optical cable body (single-mode optical fibers are used) are sequentially connected to form a first quasi-distributed three-component seismic wave sensing unit, and the first quasi-distributed three-component seismic wave sensing unit is connected with a demodulation host of a single-channel distributed optical fiber acoustic wave sensing system to form the quasi-distributed optical fiber three-component acoustic wave sensing system (in an actual experiment, because no three-channel host exists, the two spiral tightly-wound optical fibers and the straight optical fiber are connected to a channel at a certain interval in series and then measured by the single-channel host). And placing the first quasi-distributed three-component seismic wave sensing unit and the three-component electronic acceleration detector on a vibration table, and testing the response to the same vibration signal. And demodulating signals of three optical fibers acquired by the host 2 by using a single-channel distributed optical fiber sound wave sensing system, and processing data. The experimental result is shown in fig. 7, and the normalized acceleration waveform signals picked up by the quasi-distributed three-component seismic wave sensing unit and the three-component electronic acceleration detector have good consistency.
Example 6
Sensing calculation is performed on the quasi-distributed optical fiber three-component seismic wave sensing system in example 4, as shown in fig. 5, the second quasi-distributed three-component seismic wave sensing unit 106 (the elastic body group 101 is a cylindrical elastic body including the first elastic body, the second elastic body, and the third elastic body) includes three cylindrical elastic bodies whose axial directions are respectively along the x, y, and z directions, and three spirally-wound optical fibers (a first spirally-wound optical fiber 1021, a second spirally-wound optical fiber 1022, and a third spirally-wound optical fiber 1024) are respectively fixed on surfaces of the three cylindrical elastic bodies. The elastic body group 101 in the three-component seismic wave sensing optical cable 1 is made of materials with small Young modulus such as soft rubber or elastic body plastic, the strain resolution of the optical cable can be effectively improved, the three spirally wound optical fibers use the bending-resistant optical fibers to reduce the bending loss, the signal-to-noise ratio of optical signals can be improved, and the three-component distributed seismic wave long-distance sensing can be realized.
Mechanical analysis is carried out on the elastomer group 101 and the optical fiber, and three-component strain information of far-field seismic plane waves is separated and extracted:
Figure BDA0003902351500000121
Figure BDA0003902351500000122
the quasi-distributed optical fiber three-component acoustic wave sensing system is shown in fig. 6, and adopts a wavelength division multiplexing or space division multiplexing scheme to collect and demodulate backward rayleigh scattered light generated by three optical fibers on a three-component seismic wave sensing optical cable 1, and calculate axial strain generated by the three optical fibers, so as to invert three-component strain information of seismic waves.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are merely exemplary embodiments of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (10)

1. The three-component seismic wave sensing optical cable is characterized by comprising an optical cable body, wherein a quasi-distribution three-component seismic wave sensing unit is arranged at intervals in the axial direction of the optical cable body, three-component strain generated by the quasi-distribution three-component seismic wave sensing unit and seismic wave coupling can obtain a positive strain three-component generated by seismic waves, and the quasi-distribution three-component seismic wave sensing unit comprises:
the elastic body group comprises a first elastic body, a second elastic body and a third elastic body which are axially arranged in the x direction, the y direction and the z direction respectively, wherein the first elastic body and the second elastic body are cylindrical elastic bodies, and the z direction is the axial direction of the optical cable body;
optical fiber groups respectively set on the first elastic body, the second elastic body and the third elastic body in a predetermined mode;
the outer sheath wraps the optical cable body, the elastomer group and the optical fiber group;
the grease layer is arranged among the optical cable body, the elastomer group, the optical fiber group and the outer sheath.
2. A three-component seismic wave sensing optical cable as claimed in claim 1, wherein said third elastomer is a cylindrical elastomer, and said optical fiber set comprises three helically wound optical fibers, each of said three helically wound optical fibers being fixed to circumferential sides of said first, second and third elastomers by helical winding with the same pre-stress.
3. A three-component seismic wave sensing optical cable according to claim 1, wherein said third elastic body is a square bar elastic body, and said optical fiber set comprises two helically wound optical fibers and a straight optical fiber, said two helically wound optical fibers being respectively fixed to circumferential side surfaces of said first elastic body and said second elastic body by being spirally wound with the same prestress, and said straight optical fiber being fixed to a surface of said third elastic body by being fixed with the same prestress as that of said helically wound optical fiber.
4. A three-component seismic wave sensing cable according to claim 1, wherein a fiber grating array is continuously written within said optical fiber assembly, said fiber grating array having a reflectivity less than a first threshold value.
5. A three-component seismic wave sensing cable as claimed in claim 2 or 3, wherein the helically wound optical fibre has a helical winding angle in the range of [0, pi/2 ].
6. A three-component seismic wave sensing cable according to claim 2 or 3, wherein said elastomer member is of solid construction and has a young's modulus not exceeding 1Gpa.
7. A quasi-distributed optical fiber three-component seismic wave sensing system is characterized by comprising:
the three-component seismic wave sensing optical cable of any one of claims 1-6;
the three-channel distributed optical fiber acoustic wave sensing system demodulation host is connected with the three-component seismic wave sensing optical cable and comprises a light source, a driving source, a pulse modulator, a random laser amplifier, a wavelength division/air division multiplexer, a detection module, a demodulation module and a data analysis module, wherein the light source and the driving source are respectively connected with the pulse modulator, the random laser amplifier and the output end of the pulse modulator are connected with the input end of the three-component seismic wave sensing optical cable through the wavelength division/air division multiplexer, the output end of the three-component seismic wave sensing optical cable is connected with the input end of the detection module through the wavelength division/air division multiplexer, and the output end of the detection module is connected with the data analysis module through the demodulation module.
8. A quasi-distributed optical fiber three-component seismic wave sensing method using the quasi-distributed optical fiber three-component seismic wave sensing system according to claim 7, comprising:
s1, injecting detection pulse light into a three-component seismic wave sensing optical cable by a three-channel distributed optical fiber acoustic wave sensing system demodulation host;
s2, collecting Rayleigh scattering signals returned from the three-component seismic wave sensing optical cable by a receiving end of the three-channel distributed optical fiber acoustic wave sensing system demodulation host;
and S3, calculating three-component strain generated by the seismic waves according to the Rayleigh scattering signals.
9. The method for sensing the seismic waves of the quasi-distributed optical fiber and the three components according to claim 8, wherein when the third elastic body is a square bar elastic body, the specific steps of S3 are as follows:
s3.1, when the quasi-distribution three-component seismic wave sensing unit is in a near-balance state under the action of far-field plane seismic waves, the three-component strain generated by the quasi-distribution three-component seismic wave sensing unit is as follows:
Figure FDA0003902351490000021
wherein e is (c) Representing the strain, e, produced by a three-component seismic wave sensing cable l (f) Representing the strain induced in the fiber set; α represents a helix angle of the spirally wound optical fiber; f. of 1，2，3 And c represent the optical fiber group and the optical cable, respectively; l, x, y and z represent axial, x, y, z directions, respectively;
s3.2, when the rotation angle of the spiral wound optical fiber on the first elastic body and the second elastic body is 0, the coupling of the quasi-distributed three-component seismic wave sensing unit and the seismic wave can obtain the magnitude of three-component strain generated by the seismic wave through the following formula:
Figure FDA0003902351490000022
Figure FDA0003902351490000023
wherein λ and N represent Lame constants of the formation, λ c And N c Denotes the Lame constant, E, of the optical cable c And mu c Expressing Young's modulus and Poisson's ratio, e, of the optical fiber cable (ω) Representing the strain produced by the seismic waves; omega represents seismic waves, and l, x, y and z respectively represent axial directions and x, y and z directions;
s3.3, when the quasi-distributed three-component seismic wave sensing unit is acted by an acceleration signal, obtaining the relation between strain and the acceleration signal generated by three optical fiber groups in the quasi-distributed three-component seismic wave sensing unit through the following formula:
Figure FDA0003902351490000031
wherein a represents an acceleration applied to the elastic body; a represents the area perpendicular to the direction of the equivalent force applied to the elastic body; r represents the radius of the cross section of the cylindrical elastomer; m represents the equivalent mass of the cylindrical elastomer, and m represents the equivalent mass of the square strip elastomer; x, y and z represent x, y and z directions, respectively.
10. The method for sensing the seismic waves of the quasi-distributed optical fiber and the three components according to claim 8, wherein when the third elastic body is a cylindrical elastic body, the specific steps of S3 are as follows:
s3.1, when the sensing unit is in a near-equilibrium state under the action of the far-field plane seismic waves, the three-component strain generated by the quasi-distribution three-component seismic wave sensing unit is as follows:
Figure FDA0003902351490000032
wherein e is (c) Representing the strain, e, produced by a three-component seismic wave sensing cable l (f) Representing strain induced in the fiber set; α represents a helix angle of the spirally wound optical fiber; f. of 1，2，3 And c represents the optical fiber group and the optical cable, respectively; l, x, y and z represent axial, x, y, z directions, respectively;
s3.2, when the rotation angle of the spiral wound optical fiber on the first elastic body, the second elastic body and the third elastic body is 0, the coupling of the quasi-distributed three-component seismic wave sensing unit and seismic waves can obtain the magnitude of three-component strain generated by the seismic waves through the following formula:
Figure FDA0003902351490000033
Figure FDA0003902351490000034
wherein λ and N represent Lame constants of the formation, λ c And N c Expressing Lame constant of the optical fiber cable, e (ω) The strain generated by seismic waves is represented, omega represents the seismic waves, and l, x, y and z respectively represent the axial direction and the x, y and z directions;
s3.3, when the quasi-distributed three-component seismic wave sensing unit is acted by an acceleration signal, obtaining the relation between the strain and the acceleration signal generated by the three optical fiber groups in the quasi-distributed three-component seismic wave sensing unit through the following formula:
Figure FDA0003902351490000041
wherein a represents an acceleration applied to the elastic body; a represents the area perpendicular to the direction of the equivalent force applied to the elastic body; r represents the radius of the cross section of the cylindrical elastomer; m represents the equivalent mass of the cylindrical elastomer, and m' represents the equivalent mass of the square strip elastomer; x, y and z represent x, y and z directions, respectively.
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