CN112946729B - Cross winding push-pull type underground three-component optical fiber seismometer - Google Patents

Abstract

The invention provides a cross winding push-pull type underground three-component optical fiber seismometer, which belongs to the field of optical fiber interferometry and mainly comprises a signal processing system, a signal acquisition system, a vector accelerometer, a communication cable and an optical cable, wherein three sensing units with the same structure are orthogonally stacked in the vector accelerometer to form a three-dimensional vector sensing probe, the outside of the vector accelerometer is protected by an outer cylinder and a sealing end cover, a sensitive optical fiber adopts an external winding form, a main structural component is surrounded in the sensitive optical fiber, the sensitive optical fiber is crossly wound between two leaf spring fixing blocks and two fiber winding columns and forms a push-pull structure together with a mass block, and the mass block directly stretches the sensitive optical fiber through the fiber winding columns at two ends. The device has the advantages that the vibration directivity of the mass block is good, the transverse crosstalk is low, high strain transmission efficiency and sensitivity can be realized, the structure is compact, the measurement requirement of a narrow space can be met, and the device is particularly suitable for deep well earthquake observation.

Description

A cross-wound push-pull downhole three-component fiber optic seismometer

technical field

The invention relates to a cross-winding push-pull type downhole three-component optical fiber seismometer, and the field of optical fiber interference measurement.

Background technique

The earth is a very active sphere. The continental plates move every moment. Earthquakes occur almost every day. Among them, there are more than 100 destructive earthquakes every year, causing countless disasters to the world. Since the 20th century, more than 30% of the world's destructive earthquakes have occurred in my country, and 70% of them are shallow earthquakes, which are highly destructive. More than 80% of my country's provinces have been affected by earthquake disasters. A total of 660,000 people have lost their lives due to the earthquake, and the number of injured has reached one million. Hundreds of millions of people have been affected. The earthquake has caused huge losses to my country's economy and people's livelihood. Therefore, it is imminent to improve the level and ability of earthquake prediction. In order to achieve this goal, we must first develop accurate and reliable earthquake detection methods, obtain a large amount of earthquake-related data, and improve the understanding of earthquakes, thereby improving the ability to predict earthquakes. Compared with ground observations, deep well seismic observations can better remove the influence of ground human activities on observations, and can clearly identify and identify a large number of small earthquakes mixed in a high-noise background and weak geophysical information from the ground. Observation has become the best means of seismic observation, so it is very important to develop a seismometer that can meet the needs of deep well seismic observation, and the accelerometer type seismometer can achieve a small volume (the size of a strong earthquake meter) and is often used to observe earthquakes. , more suitable for the needs of downhole seismometers.

Accelerometer is a common tool for measuring earthquakes. Traditional accelerometers mainly include piezoresistive, capacitive, piezoelectric, etc. The basic principle is to convert the response of the mass block to acceleration into the output voltage, capacitance, etc. of the circuit system. The relationship between acceleration and output physical quantity can measure the magnitude of acceleration. The research of traditional accelerometers started early, and the technology is quite mature. However, its electronic system still has obvious shortcomings, such as being susceptible to electromagnetic interference, not resistant to high temperature, and not resistant to corrosion. In recent years, due to the rapid development of optical fiber sensing technology, especially the development of optical signal demodulation technology, many researchers have devoted a lot of energy to the research of optical fiber sensing technology, and more and more optical fiber-based sensors have come out one after another. And thanks to the advancement of optical signal demodulation technology, the amount of information that can be carried by optical fiber systems is becoming more and more abundant. Due to the very small size of the optical fiber itself, it is difficult to directly use the optical fiber as a sensor to exert the full performance of the optical fiber. Therefore, it is necessary to combine the optical fiber with other structures to further tap the potential of the optical fiber sensor. The optical fiber and the mechanical structure are combined to form a transduction The device structure can realize the measurement of displacement, velocity, acceleration, etc. Optical fiber accelerometer is a new type of accelerometer based on optical fiber sensing technology. Because of its anti-electromagnetic interference, high temperature resistance, corrosion resistance, high sensitivity, large dynamic range, long-term reliability and good stability, it can be used in aviation Aerospace, seismic exploration, oil exploration and other fields.

Zhang Wentao et al. reported a push-pull fiber optic detector (Zhang Wentao, Li Fang. Push-pull fiber optic detector [P]. Beijing: CN102353982A, 2012-02-15.), by winding the support beam and the mass block The volume of the push-pull fiber optic detector can be reduced by using the diaphragm as an elastic element, and the transverse crosstalk can be suppressed by using the elastic directivity of the diaphragm. The length of the optical fiber used in this structure is overall short, and high sensitivity cannot be obtained. At the same time, the mass block will be disturbed by the torsional signal, which will affect the measurement accuracy. Zhang Wentao et al. proposed a fiber grating accelerometer based on cantilever deflection (Zhang Wentao, Li Fang, Liu Yuliang. Fiber Bragg Grating Accelerometer Based on Cantilever Deflection [P]. Beijing: CN101285846, 2008-10-15.), mainly The front end of the cantilever beam is used to fix the mass block and is connected with the fiber grating, and the deformation of the cantilever beam drives the fiber grating to extend or shorten to realize the measurement of vibration signals such as acceleration. This structure uses fiber grating as the sensing element, which is limited by the working characteristics of fiber grating. Compared with the interferometric measurement principle, its strain resolution is much smaller, resulting in lower sensitivity of its accelerometer. Using the principle of interference, the effects caused by strain can be accumulated by means of optical path folding, and a much higher strain resolution capability than that of fiber gratings can often be obtained.

In 2016, Oleg T.Kamenev et al. proposed a highly sensitive, low-noise fiber-optic seismometer based on the Mach-Zehnder interferometer (Kamenev OT, Kulchin YN, Petrov YS, et al. Fiber-opticseismometer on the basis of Mach -Zehnder interferometer[J].Sensors and Actuators A-physical,2016:133-137.), in the seismometer sensing structure, multiple turns of sensitive optical fibers are wound between two cylinders, one of which is fixed horizontally as the base The other cylinder is suspended as a mass block, and the suspended mass block is used to sense the seismic signal and transmit it to the sensitive fiber to stretch or shrink the sensitive fiber, although it can obtain up to 6.1×10 ³ V/g in the range of 1-20 Hz However, the resonant frequency of the structure is low, only about 60 Hz, and it can only measure the seismic signal in one dimension in the vertical direction, and cannot be extended in three dimensions, which limits the application of the structure.

The invention provides a cross-wound push-pull downhole three-component fiber optic seismometer, the design idea of which is: in view of the sensing principle and structural characteristics of the traditional mandrel type or disc type fiber optic accelerometer, the strain transfer model is generally a mass Indirect strain transfer from the bulk to the elastomer and then to the sensitive fiber, resulting in low transfer efficiency. The improved scheme adopts the form of the mass block to directly stretch the sensitive optical fiber, which improves the transmission efficiency and thus the sensitivity; the double reed support at both ends of the mass block can further improve the vibration guidance of the mass block and reduce the lateral crosstalk; In the way of external optical fiber, the main structure is integrated inside the sensing optical fiber, which makes the structure more compact and can greatly reduce the volume. Thanks to the small size of the probe, it can meet many measurement scenarios with large size restrictions, especially suitable for seismic observations in deep well environments.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a cross-wound push-pull downhole three-component fiber optic seismometer.

The purpose of the present invention is achieved as follows: including a signal processing system 1, a signal acquisition system 2, a vector accelerometer 3, a communication cable 27 and an optical cable 28, wherein the three-dimensional sensing units 31, 32, and 33 of the vector accelerometer 3 use a cross Winding push-pull structure, the vector accelerometer 3 mainly includes a horizontal sensing unit A31, a horizontal sensing unit B32, and a vertical sensing unit 33. The three sensing units have the same sensing structure and are connected end-to-end and orthogonally stacked. A vector sensing probe is formed; the mass block 313 of the vertical sensing unit 33 is placed in the middle of the vertical unit frame 331 and penetrates through the interior of 3312. The mass block 313 is connected to the mass block mounting hole 3142 through the plate spring mounting holes 3131 on both sides. The spring 314 is installed on the plate spring fixing hole 3314 of the vertical plate spring installation position 3313 through the frame mounting hole 3141. The outer side of the plate spring is fixed by the plate spring fixing block A315 and the plate spring fixing block B316 respectively, and the plate spring fixing block is a middle through structure. The two ends of the mass block 313 extend the cylinder 3132 to the outside of the leaf spring fixing block through the middle part through A3-151 and the middle part through B3-161, and are connected with the fiber winding column A317 and the fiber winding column B318, wherein the leaf spring fixing block A315 It is located on one side with the fiber winding column B318, and the leaf spring fixing block B316 and the fiber winding column A317 are located on the other side; the sensitive fibers C1-425 and C2-426 are wound on the leaf spring fixing blocks A315, B316 and the fiber winding in the form of cross winding. Between the columns A317 and B318, and together with the mass block 313, a push-pull structure is formed, in which the sensitive fiber C1425 is wound on the fiber winding slot A3153 and the fiber winding column A317, and the sensitive fiber C2426 is wound on the fiber winding slot B3163 and the fiber winding column B318. ; The core structure of the horizontal sensing unit A31 and the horizontal sensing unit B32 is similar to the vertical sensing unit 33, and the frame support column 312 is installed between the flat plates on both sides of the frame through the column mounting hole 3121;

The optical fiber device box 34 is installed on the vertical supporting circular plate 332 outside the vertical sensing unit 33, and is used to place the optical fiber device and optical path of the vector sensing probe; the vector sensing probe and the sealing end cap 352 pass through the unit frame fixing hole 3522 Fixed as a whole, the waterproof sealed optical cable joint 36 is installed in the optical cable installation hole 3523, and is connected with the internal optical fiber device box 34 through the thread hole 3113; the outer cylinder 351 is installed from one side of the optical fiber device box 34 to the sealing end cover 352, and the other Side mount seal tail cap 353.

The present invention also includes such structural features:

1. The vector accelerometer 3, its sensing optical path part includes a one-point three-coupler 417, couplers A1-411, A2-412, B1-413, B2-414, C1-415, C2-416, sensitive Optical fibers A1-421, A2-422, B1-423, B2-424, C1-425, C2-426, the light output from the signal acquisition system 2 is connected to the input port of the one-to-three coupler 417 through the optical cable 28, one to three The three output ports of the coupler 417 are respectively connected to the three sensing optical paths; in the first path, one output port of the one-to-three coupler 417 is connected to the input port of the coupler A1-411; The output ports are respectively connected with the input ports of the sensitive fibers A1-421 and A2-422; the output ports of the sensitive fibers A1-421 and A2-422 are respectively connected with the two input ports of the coupler A2-412; the coupler A2-412 The two output ports of the sensor are respectively connected to the first detector 241 and the second detector 242 of the signal acquisition system 2 through the optical cable 28; The two output ports of the coupler B2-414 are respectively connected to the third detector 243 and the fourth detector 244 of the number acquisition system 2 through the optical cable 28; the two output ports of the coupler C2-416 in the third channel are respectively connected through the optical cable 28 is connected to the fifth detector 245 and the sixth detector 246 of the number acquisition system 2; wherein the couplers A1-411, A2-412, B1-413, B2-414, C1-415, C2-416 and one point three Coupler 417 is installed in fiber optic device cassette 34 .

2. The vector accelerometer 3, wherein the horizontal sensing unit A31 includes a horizontal unit frame 311, a frame support column 312, a mass block 313, a flat spring 314, a leaf spring fixing block A315, a leaf spring fixing block B316, a fiber winding The core structure of the horizontal sensing unit B32 and the vertical sensing unit 33 is basically the same as that of the horizontal sensing unit A31.

1) The horizontal unit frame 311 includes a fixed mounting hole 3111, a unit frame connection hole 3112, a threading hole 3113, a column fixing hole 3114, a central penetration 3115, a leaf spring installation position 3116, and a leaf spring fixing hole 3117; the horizontal unit frame 311 is a cylinder as a whole The diameter is 90mm, the height is 50mm, and there are two connecting vertical plates between the two end faces. The hollow structure between the connecting vertical plates is the middle through 3115. The inner dimension is slightly larger than the outer dimension of the mass block 313. The plate spring installation position 3116 has plate spring fixing holes 3117 on the plate spring installation position 3116. The distance between the plate spring installation positions 3116 at both ends is equal to the distance between the planes where the plate spring installation holes 3131 at both ends of the mass block 313 are located; the two ends of the horizontal unit frame 311 There are fixed installation holes 3111, unit frame connection holes 3112, threading holes 3113 and column fixing holes 3114;

2) The vertical unit frame 331 includes a vertical frame connecting hole 3311, a vertical central penetration 3312, a vertical leaf spring mounting position 3313, a vertical leaf spring fixing hole 3314, and a supporting circular plate fixing hole 3315; the vertical unit frame 331 is a rectangle as a whole , the height is 85mm, there are two connecting vertical plates between the two sides, the hollow structure between the connecting vertical plates is a vertical middle through 3312, the inner dimension is slightly larger than the outer dimension of the mass block 313, and the two ends of the connecting vertical plates are vertical plates The spring mounting position 3313, the vertical leaf spring mounting position 3313 has vertical leaf spring fixing holes 3314, and the distance between the vertical leaf spring mounting positions 3313 at both ends is equal to the distance between the planes where the leaf spring mounting holes 3131 at both ends of the mass block 313 are located; vertical The outer bottoms of the two sides of the unit frame 331 are vertical frame connection holes 3311, and the top is a supporting circular plate fixing hole 3315;

3) The mass block 313 includes a plate spring mounting hole 3131, two end extension cylinders 3132, and fiber winding column fixing holes 3133; the mass block 313 is rounded and rectangular as a whole, and the middle position of the two sides is the two end extension cylinders 3132, and its top is a winding cylinder. Fiber column fixing holes 3133, both sides of the column are plate spring mounting holes 3131; The distances to the plate spring installation positions 3313 are equal, and the outer dimensions of the extending cylinders 3132 at both ends are slightly smaller than the inner dimensions of the installation slots on the fiber winding column A317 and the fiber winding column B318;

4) The flat spring 314 includes a frame mounting hole 3141, a mass mounting hole 3142, and a hollow 3143 in the middle; the flat spring 314 is a flat plate as a whole, with a width of 8 mm on one side and a thickness of 0.5 mm. The side is the mass block mounting hole 3142, and the two ends are the frame mounting hole 3141;

5) The leaf spring fixing block A315 includes a central penetration A3-151, a mounting hole 3152 for the fixing block A, and a fiber winding groove A3-153; the leaf spring fixing block B316 includes a central penetration B3-161, the fixing block B mounting hole 3162, and the fiber winding groove. B3-163; the fiber winding column A317 includes the fiber winding column A mounting hole 3171; the fiber winding column B318 includes the fiber winding column B mounting hole 3181.

Compared with the prior art, the beneficial effects of the present invention are: 1) the use of the mass block to directly stretch the sensitive optical fiber, compared with the indirect strain transmission from the mass block to the elastic body and then to the sensitive optical fiber, the transmission efficiency can be improved, and the coordination The push-pull structure can further improve the sensitivity; 2) The inertial mass block is supported by double flat reeds at both ends. With the help of the vibration characteristics of the flat reeds, the vibration directionality of the mass block can be improved and the lateral crosstalk can be reduced; 3) Sensing fiber The main sensing structure is integrated inside the sensing fiber by means of external cross-winding, which makes the structure more compact, can greatly reduce the volume, and satisfies many measurement scenarios with relatively large size restrictions, especially suitable for earthquakes in deep well environments. observation.

Description of drawings

Fig. 1 is a system structure diagram of a cross-wound push-pull downhole three-component fiber optic seismometer;

Fig. 2 is the structural schematic diagram of downhole three-component fiber optic seismometer;

Figure 3 is a schematic diagram of a downhole three-component fiber optic seismometer;

4 is a schematic structural diagram of a horizontal sensing unit;

Fig. 5 is the structural representation of horizontal unit frame;

Fig. 6 is the structural representation of vertical unit frame;

Fig. 7 is the structural representation of mass block;

8 is a schematic structural diagram of a flat spring sheet;

Figure 9 is a schematic structural diagram of a leaf spring fixing block and a fiber winding column;

Figure 10 is a schematic diagram of the application of the downhole three-component fiber optic seismometer in deep well seismic observation;

Figure 11 is a simplified block diagram of the apparatus used for the theoretical derivation of transfer efficiency.

Detailed ways

The present invention will be described in further detail below with reference to the accompanying drawings and specific embodiments.

1 to 11, the present invention is a cross-wound push-pull downhole three-component fiber optic seismometer. The light emitted by the light source 21 passes through the isolator 22, the optical cable 28 and the one-to-three coupler 417 in turn, and then enters three channels respectively. Sensing optical path with the same optical path structure: the first path enters the sensitive fibers A1-421 and A2-422 through the two arms of the coupler A1-411, and then passes through the two arms of the coupler A2-412 to join the coupler A2-412 , the unbalanced Mach-Zeder interferometer structure is composed of the couplers A1-411, A2-412 and the sensitive fibers A1-421, A2-422; when an acceleration acts on the mass block 313, the mass block 313 is displaced and driven The flat spring 314 and the sensitive fibers A1-421 and A2-422 are deformed, one of the fibers of the two interference arms of the unbalanced Mach-Zeder interferometer is elongated and the other is shortened, thereby generating an interference signal at the coupler A2-412; the last three The interference signal of the sensing optical path enters the first to sixth detectors 241, 242, 243, 244, 245, 246 through the optical cable 28, and is converted into electrical signals, which are then received by the acquisition card 23, and finally processed by the signal processing system 1. The interference signal is processed; the signal processing method adopts the PGC modulation technology, and the internal modulation method is used to apply the modulation signal to the light source 21 through the acquisition card 23, and then the signal processing system 1 demodulates the interference signal, and finally obtains the acceleration signal. In order to improve the sensitivity of the vector accelerometer 3, the mass block is used to directly stretch the sensitive fiber, which has higher strain transfer efficiency than the indirect strain transfer from the mass block to the elastic body and then to the sensitive fiber, thereby improving the sensitivity; The optical fiber adopts the form of cross-winding, and the two sensitive optical fibers are cross-wound on the leaf spring fixing block and the fiber-winding column, and the mass block is placed inside the sensitive optical fiber. The sensitive optical fiber has the effect of pushing and pulling, thus forming a push-pull structure, which doubles the detection sensitivity. At the same time, the structure of the mass block and other structures placed inside the sensitive optical fiber can greatly improve the space utilization rate and make the structure more compact. The overall size is smaller.

The relevant theories are deduced as follows:

1) Principle of acceleration measurement

The Michelson interferometer is used to measure the change of axial acceleration. When the inertial mass drives the winding column wrapped with the sensitive optical fiber under the action of acceleration, the working state of the optical fiber will change, causing the phase of the interferometer to change, and the interferometer will change due to external factors. The induced phase change can be simply expressed as:

β=2π·n/λ is the propagation constant of the light wave in the fiber, the first term represents the phase delay (strain effect) caused by the change of the fiber length, and the second term represents the phase delay caused by the change of the refractive index (elastic light effect),

The bouncing light effect can be expressed as:

μ is the Poisson's ratio of the fiber material, p ₁₁ and p ₁₂ are the elastic-optic coefficients of the fiber material respectively, and ε ₃ =ΔL/L is the longitudinal strain of the fiber. Bringing in the parameters of single-mode fiber, we get:

Δφ=0.79·2β·ΔL (3)

Using the modulator to modulate the Michelson interferometer, the output signal form of the interference light can be obtained as:

Among them, I ₁ and I ₂ are the light intensities of the two interference beams respectively, A is the DC component of the interference light intensity, B is the AC component of the interference light intensity, and φ(t) is the change value of the interference phase. The optical signal is converted and collected by the photodetector and AD converter, and the phase of the interference signal can be solved through PGC modulation and demodulation, and the solution of the acceleration can be obtained according to the phase change of the interference signal.

2) The principle of improving transfer efficiency:

The cross-push-pull structure of the acceleration measuring device is simplified as: the two ends of the rectangular leaf spring are fixed on the frame, the mass block is installed in the middle of the leaf spring, the fiber winding column is fixed on the mass block, and the corresponding frame also has a winding column. Fiber pillar, the sensitive optical fiber is wound between two fiber winding pillars. It is assumed that the part of the optical fiber in contact with the spool is completely fixed with glue, and no deformation occurs during the moving and stretching of the mass block.

The acceleration signal acts on the mass block to make it move. According to the conservation of energy, the kinetic energy of the mass block is all converted into the elastic potential energy of the sensitive fiber and the leaf spring. Let x be the displacement of the mass block, l is the spacing between the fiber posts, and N is the fiber winding circle. E _f is the Young's modulus of the fiber, A _f is the cross-sectional area of the fiber, k is the light wave number, p _e is the elastic-optical coefficient of the fiber, n is the refractive index of the fiber, L is the length of the elastic disc, b is the width of the elastic spring , h is the thickness of the elastic reed, E is the Young's modulus of the elastic reed, μ is the Poisson's ratio of the elastic reed, and the calculation process is as follows:

The stiffness coefficient of a single fiber on one side:

Elastic potential energy of a single fiber on one side:

Elastic potential energy of N-loop fiber: (2N refers to double-sided fiber)

When the rectangular leaf spring fixed at both ends is acted by the middle concentrated force F, the deflection is equal to the displacement x of the mass block. According to the Roche Stress-Strain Manual, the deflection calculation formula is as follows:

Its equivalent stiffness is:

Then the elastic potential energy of the rectangular leaf spring under the action of the intermediate concentrated force F is:

According to the elastic potential energy of the sensitive fiber and the leaf spring, the energy distribution ratio of the sensitive fiber in this structure can be obtained:

In a common mandrel accelerometer, the elastic potential energy of the compliance cylinder is E _r , and the proportion of the elastic potential energy E _f in the fiber is:

It can be seen from the above calculation results that in the conformable cylinder structure, nearly half of the energy is lost on the silica gel cylinder, while most of the energy of the mass in the device of the present invention is transferred to the sensitive fiber, and the transfer efficiency is improved by 1.4%. times, achieving higher strain transfer efficiency.

An implementation case of the present invention is given in conjunction with specific parameters—the application of a cross-wound push-pull downhole three-component fiber optic seismometer in deep well seismic observation:

A cross-wound push-pull downhole three-component fiber optic seismometer is shown in Figures 2 and 3. The observation system when the seismometer is applied to a deep well is shown in Figure 1. The observation system includes a signal processing system 1, a signal acquisition system 2, a vector Accelerometer 3, optical cable 28, communication cable 27, optical cable winch 5, pulley support 6, well wall fixing device 7 and deep well borehole 8 and peripheral equipment. The device parameters and structural dimensions of each part are as follows:

1) The light source 21 is a laser light source, the center wavelength is 1550nm, the half-spectrum width is less than 20nm, the power is 10mW, and the modulation frequency is not less than 20K;

2) The working wavelength of the isolator 22 is 1550nm, the insertion loss is <0.8dB, and the isolation is >35dB;

3) The one-to-three coupler 417 is a 1×3 coupler, the working wavelength is 1550nm, and the splitting ratio is 33:33:33; the couplers A1-411, B1-413, C1-415 are 1×2 couplers, working The wavelength is 1550nm, the splitting ratio is 50:50; the couplers A2-412, B2-414, C2-416 are 2×2 couplers, the working wavelength is 1550nm, and the splitting ratio is 50:50;

4) The sensitive fibers A1-421, A2-422, B1-423, B2-424, C1-425, and C2-426 are ordinary single-mode fibers with a diameter of 125 μm. Each sensitive fiber is divided into two parts and wound with a certain prestress In the fiber winding grooves of the three sensing units, a circle of optical fiber is 150 mm, and the number of winding circles is 50, and each sensitive optical fiber has an input port and an output port respectively;

5) The photosensitive materials of the first detector 241, the second detector 242, the third detector 243, the fourth detector 244, the fifth detector 245, and the sixth detector 246 are all InGaAs, and the light detection range is 1100~ 1700nm, the responsivity is greater than 0.85;

6) The length of one side of the flat spring 314 is 26mm, the width is 8mm, and the thickness is 0.5mm;

7) The size of the sealing groove 3521 of the sealing end cover 352 and the sealing groove 3531 of the sealing tail cover 353 is 5mm in width and 4mm in depth, and a circular sealing ring with a diameter of 5mm is applicable;

8) The outer diameter of the outer cylinder 351 is 100mm, the inner diameter is 90mm, and the length is 246mm;

9) The number of 28 cores of the optical cable is not less than 8, the pressure resistance and waterproof depth is greater than 1000m, and there are tensile reinforcements inside;

10) The length of the 5 coils of the optical cable winch is greater than 1000m;

11) The pulley height of pulley bracket 6 is not less than 3m;

12) The outer diameter of the well wall fixing device 7 is smaller than the inner diameter of the deep well borehole 8 when it is contracted, and the outer diameter is larger than the inner diameter of the deep well borehole 8 when it is opened.

The working principle of the measuring device is as follows:

The light emitted by the light source 21 passes through the isolator 22, the optical cable 28 and the one-to-three coupler 417 in sequence, and then enters three sensing optical paths with the same optical path structure: the first path enters the sensing optical path through the two arms of the coupler A1-411. Fibers A1-421 and A2-422, then pass through the two arms of coupler A2-412 and merge into coupler A2-412, which is composed of couplers A1-411, A2-412 and sensitive fibers A1-421 and A2-422. The structure of the unbalanced Mach-Zehnder interferometer; when an acceleration acts on the mass block 313, the mass block 313 is displaced and drives the flat spring 314 and the sensitive fibers A1-421 and A2-422 to deform. One of the optical fibers of the two interference arms is elongated and the other is shortened, thereby generating an interference signal at the coupler A2-412; the interference signals of the last three sensing optical paths enter the first to sixth detectors 241, 242, 243 through the optical cable 28 , 244, 245, 246, and converted into electrical signals, which are then received by the acquisition card 23, and finally processed by the signal processing system 1; A modulated signal is applied to the light source 21 , and then the interference signal is demodulated by the signal processing system 1 to finally obtain an acceleration signal.

The working process when the measuring device is applied to deep well seismic observation is as follows:

When conducting deep well observation, the signal processing system 1 and the signal acquisition system 2 are connected through the communication cable 27, and the vector accelerometer 3 and the signal acquisition system 2 are connected through the optical cable 28; The bracket 6 puts the vector accelerometer 3 into the deep well borehole 8; starts the optical cable winch 5, gradually releases the optical cable, lowers the vector accelerometer 3 to the specified depth, and then starts the well wall fixing device 7 to fix the vector accelerometer 3 to the deep well On the inner wall of the borehole 8, the optical cable is fixed to prevent interference with the vector accelerometer 3; the working state of the accelerometer observation system is detected, and after everything is normal, the deep well seismic observation work can be carried out.

In summary, the present invention belongs to the field of optical fiber interferometry, and specifically relates to a cross-winding push-pull downhole three-component optical fiber seismometer. It mainly includes a signal processing system, a signal acquisition system, a vector accelerometer, a communication cable and an optical fiber cable. The vector accelerometer is internally composed of three orthogonally stacked sensing units with the same structure to form a three-dimensional vector sensing probe. It is protected with a sealed end cap, in which the sensitive optical fiber adopts the form of external winding, and the main structural components are enclosed inside the sensitive optical fiber. The mass blocks together form a push-pull structure, in which the mass blocks directly stretch the sensitive fiber through the fiber-wrapped columns at both ends. The advantages of the device are that the vibration direction of the mass block is good, the lateral crosstalk is low, high strain transfer efficiency and sensitivity can be achieved, and the structure is compact, which can meet the measurement requirements in narrow spaces, and is especially suitable for deep well seismic observation.

Claims (6)

1. A cross-wound push-pull downhole three-component fiber optic seismometer, comprising a signal processing system (1), a signal acquisition system (2), a vector accelerometer (3), a communication cable (27) and an optical fiber cable (28), It is characterized in that: the three-dimensional sensing units (31, 32, 33) of the vector accelerometer (3) adopt a cross-wound push-pull structure, and the vector accelerometer (3) includes a horizontal sensing unit A (31), a horizontal transmission A sensing unit B (32), a vertical sensing unit (33), the three sensing units have the same sensing structure, and are connected end-to-end and orthogonally stacked to form a vector sensing probe; wherein the quality of the vertical sensing unit (33) The block (313) is placed in the vertical middle of the vertical unit frame (331) through the interior of (3312). (314) Install it on the plate spring fixing hole (3314) of the vertical plate spring installation position (3313) through the frame mounting hole (3141), and use the plate spring fixing block A (315) and the plate spring fixing block B ( 316) fixed; the two ends of the mass block (313) extend the cylinder (3132) through the middle part of the plate spring fixing block A (315) through A (3151) and the middle part of the plate spring fixing block B (316) through B ( 3161) extends to the outside of the leaf spring fixing block, and is connected to the fiber winding column A (317) and the fiber winding column B (318), the leaf spring fixing block A (315) and the fiber winding column B (318) The spring fixing block B (316) and the fiber winding column A (317) are located on the other side; the sensitive optical fibers C1 (425) and C2 (426) are wound on the leaf spring fixing blocks A (315) and B (316) in a cross-wound form. ) and the fiber winding columns A (317) and B (318), and together with the mass block (313) to form a push-pull structure, the sensitive fiber C1 (425) is wound in the fiber winding slot A (3153) and the fiber winding column A (317), the sensitive optical fiber C2 (426) is wound around the fiber winding groove B (3163) and the fiber winding column B (318); The core structure is similar to the vertical sensing unit (33), the frame support column (312) is installed between the flat plates on both sides of the frame through the column mounting holes (3121); the optical fiber device box (34) is installed on the vertical sensing unit (33) ) on the outer vertical support circular plate (332) for placing the optical fiber components and optical paths of the vector sensing probe; the vector sensing probe and the sealing end cover (352) are fixed into one through the unit frame fixing hole (3522), waterproof The sealed optical cable joint (36) is installed in the optical cable installation hole (3523), and is connected with the inner optical fiber device box (34) through the threaded hole (3113); the outer cylinder (351) is installed from the optical fiber device box (34) side to the sealing On the end cover (352), a sealing tail cover (353) is installed on the other side. 2. A cross-wound push-pull downhole three-component fiber optic seismometer according to claim 1, characterized in that: the sensing optical path part of the vector accelerometer (3) comprises a one-point three-coupler (417) , couplers A1, A2, B1, B2, C1, C2 (411, 412, 413, 414, 415, 416), sensitive fibers A1, A2, B1, B2, C1, C2 (421, 422, 423, 424, 425, 426), the light output from the signal acquisition system (2) is connected to the input port of the one-to-three coupler (417) through the optical cable (28), and the three output ports of the one-to-three coupler (417) are respectively connected to the three output ports. In the first way, one output port of the one-to-three coupler (417) is connected to the input port of the coupler A1 (411); the two output ports of the coupler A1 (411) are respectively connected with the sensitive fiber A1 , the input ports of A2 (421, 422) are connected; the output ports of the sensitive fibers A1, A2 (421, 422) are respectively connected with the two input ports of the coupler A2 (412); the two outputs of the coupler A2 (412) The ports are respectively connected to the first detector (241) and the second detector (242) of the signal acquisition system (2) through the optical cable (28); the connection modes of the second and third sensing optical paths are consistent with the first path, The two output ports of the coupler B2 (414) in the second channel are respectively connected to the third detector (243) and the fourth detector (244) of the signal acquisition system (2) through the optical cable (28); The two output ports of the coupler C2 (416) are respectively connected to the fifth detector (245) and the sixth detector (246) of the signal acquisition system (2) through the optical cable (28); wherein the couplers A1, A2, B1 , B2, C1, C2 (411, 412, 413, 414, 415, 416) and one-to-three couplers (417) are installed in the optical fiber device box (34). 3. A cross-wound push-pull downhole three-component fiber optic seismometer according to claim 1 or 2, characterized in that: the horizontal direction sensing unit A (31) of the vector accelerometer (3) comprises a horizontal Unit frame (311), frame support column (312), mass block (313), flat spring (314), leaf spring fixing block A (315), leaf spring fixing block B (316), fiber winding column A (317) , the fiber winding column B (318); the core structures of the horizontal sensing unit B (32) and the vertical sensing unit (33) are consistent with the horizontal sensing unit A (31), and the horizontal unit frame (311) includes a fixed Mounting hole (3111), unit frame connection hole (3112), threading hole (3113), column fixing hole (3114), central penetration (3115), leaf spring installation position (3116), leaf spring fixing hole (3117); horizontal The unit frame (311) is cylindrical as a whole, and there are two connecting vertical plates between the two end faces. The hollow structure between the connecting vertical plates is a central penetration (3115), and the two ends of the connecting vertical plates are leaf spring installation positions (3116). There are plate spring fixing holes (3117) on the spring installation position (3116), and the distance between the plate spring installation positions (3116) at both ends is equal to the distance between the planes where the plate spring installation holes (3131) at both ends of the mass block (313) are located; the horizontal unit frame (311) There are fixed installation holes (3111), unit frame connection holes (3112), threading holes (3113) and column fixing holes (3114) distributed on both ends; the vertical unit frame (331) includes vertical frame connection holes (3311) , vertical central penetration (3312), vertical leaf spring installation position (3313), vertical leaf spring fixing hole (3314), supporting circular plate fixing hole (3315); the vertical unit frame (331) is a rectangle as a whole, with two sides There are two connecting vertical plates in between, the hollow structure between the connecting vertical plates is a vertical central penetration (3312), the two ends of the connecting vertical plates are the vertical leaf spring installation positions (3313), and the vertical leaf spring installation positions (3313) There are vertical leaf spring fixing holes (3314) on it, and the distance between the vertical leaf spring mounting positions (3313) at both ends is equal to the distance between the planes where the leaf spring mounting holes (3131) at both ends of the mass block (313) are located; the vertical unit frame (331) ) on both sides of the outer bottom is a vertical frame connecting hole (3311), and the top is a supporting circular plate fixing hole (3315). 4. A cross-wound push-pull downhole three-component fiber optic seismometer according to claim 3, characterized in that: the mass block (313) comprises a leaf spring mounting hole (3131), a cylinder extending at both ends (3132), The fiber winding column fixing hole (3133); the mass block (313) is rounded and rectangular as a whole; Plate spring mounting holes (3131); the distance between the planes where the plate spring mounting holes (3131) at both ends are located and the distance between the plate spring mounting positions (3116) at both ends of the horizontal unit frame (311) and the vertical direction of the two ends of the vertical unit frame (331) The distance between the leaf spring installation positions (3313) is equal, and the outer dimensions of the extending cylinders (3132) at both ends are slightly smaller than the inner dimensions of the installation slots on the fiber winding column A (317) and the fiber winding column B (318). 5. A cross-wound push-pull downhole three-component fiber optic seismometer according to claim 4, characterized in that: the plate spring (314) comprises a frame mounting hole (3141), a mass mounting hole (3142), a middle hollow (3143); the plate spring (314) is in the shape of a flat plate as a whole, the middle position is a hollow (3143) in the middle, the two sides of the hollow position are mass block mounting holes (3142), and the two ends are frame mounting holes (3141). 6. A cross-wound push-pull downhole three-component fiber optic seismometer according to claim 5, wherein the plate spring fixing block A (315) comprises a central penetration A (3151), a fixing block A mounting hole (3152) ), fiber winding slot A (3153); leaf spring fixing block B (316) includes central penetration B (3161), fixing block B mounting hole (3162), fiber winding slot B (3163); fiber winding column A (317) It includes the installation hole (3171) of the fiber winding column A; the fiber winding column B (318) includes the installation hole (3181) of the fiber winding column B.

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