CN218068302U - Deep stratum low-frequency weak seismic wave signal detection system - Google Patents

Abstract

A deep stratum low-frequency weak seismic wave signal detection system comprises a control center, a memory, a transmitting end modulation unit, a receiving end demodulation unit, a transmitting optical fiber, a receiving optical fiber and an optical fiber detector array, wherein the control center is connected with corresponding control signal ends of the transmitting end modulation unit and the receiving end demodulation unit; meanwhile, the optical fiber detector array detection optical signals are transmitted to a receiving end demodulation unit through receiving optical fibers, and are transmitted to a storage for storage after demodulation. The utility model discloses an optical fiber detector is seismic detection promptly, gathers the extremely weak low frequency seismic signal who comes from deep stratum, transmits receiving terminal demodulation unit via the optic fibre cable to convert seismic exploration special format and take notes.

Description

Deep stratum low-frequency weak seismic wave signal detection system

Technical Field

The utility model belongs to the technical field of seismic wave signal detection and specifically relates to adopt the optical fiber detector array to acquire the device that comes from the extremely weak low frequency signal in deep stratum for look for deep oil gas and hide and mineral resources, specifically speaking is deep stratum low frequency weak seismic wave signal detection system.

Background

Seismic exploration is based on the echo sounding principle. The artificial seismic source is used for generating vibration, receiving reflection information from each underground stratum interface, and acquiring the propagation speed in a stratum medium and the travel time thereof to determine the geometric form of each underground stratum interface. Seismic waves contain information about the physical properties of the formation medium in addition to the geometric morphology of subsurface formation interfaces. The current situation is as follows: the detectors used in the method are electromagnetic induction moving coil detectors, a few are MEMS detectors, and equipment matched with the detectors, such as (428, 508 of Sercel company, typically), jointly form a seismic data acquisition system to complete the acquisition task of seismic original data.

The existing various instruments and matched detectors can accurately survey the depth: the east region of China is about 6000-8000 m in the west region of 5000 m. As exploration progresses, two major problems must be encountered: firstly, the signal of deep stratum is more and more weak along with the increase of the degree of depth, secondly the frequency is lower and more, and this is that the physics nature of vibration wave decides, and high frequency decay is fast, and low frequency decay is slow, and high frequency decay is far more than low frequency decay promptly, and this is exactly that low frequency signal can reach the physics basis of deep distance. The deep detection is restricted by geophysical instruments, and the dominant factor for the restriction is the most critical equipment in the acquisition system, namely the geophone.

At present, seismic prospecting detectors mainly comprise: electromagnetic induction moving coil type detectors and MEMS;

1. electromagnetic induction moving coil detector: that is, the coil cuts magnetic lines of force in the magnetic field to generate induced current, thereby converting the mechanical vibration into electric signals. The main defect is that the dynamic range is small by 50-60 dB, and seismic signals with a large dynamic range of 120-130 dB cannot be acquired; secondly, due to the limitation of magnetic materials and the number of turns of the coil, the sensitivity cannot be made very high, extremely weak seismic signals from deep strata cannot be acquired, and the sensitivity is improved by generally adopting a weighted combination method, so that the resolution ratio is reduced; thirdly, because of the limitation of the spring pieces, the frequency cannot be very low, generally more than 10Hz, and low-frequency seismic wave signals from deep stratum under 10Hz cannot be obtained; fourthly, because of the limit of the inherent false frequency of the detector, the upper limit frequency cannot be made very high, generally about 240 Hz; therefore, the passband of the moving-coil detector is relatively narrow, 10Hz to 240Hz, and seismic wave signals in a wide frequency range cannot be acquired; fifthly, as the spring plate is gradually fatigued, the overall performance index is reduced, especially the fidelity index is reduced, and the fidelity of the acquired signals is also influenced; sixthly, because the electric signals are transmitted by the electromagnetic interference sensor, the electromagnetic interference sensor can be subjected to various electromagnetic interferences in the transmission process; and seventhly, because seismic wave signals from deep stratum are extremely weak, the seismic wave signals must be processed by an electronic amplification circuit, and thus, because the noise floor number of an electronic device, various electromagnetic interferences and the effective seismic wave signals are mixed together, the signal-to-noise ratio is reduced, and it is required to know that: the improvement of the signal-to-noise ratio is a permanent subject for obtaining all effective signals.

2. The MEMS (Micro-Electrical-Mechanical-System) is also a geophone for collecting seismic wave signals, the MEMS chip is an electronic device, noise exists in the MEMS chip, the MEMS chip is processed by an electronic circuit, transmitted Electrical signals exist in the MEMS chip, various electromagnetic interferences can be caused in the transmission process, the signal to noise ratio is reduced, and the special MEMS chip is expensive.

The detector bandwidth and low signal-to-noise ratio can be used for seismic exploration within 6000 meters, and the geological task can be completed. However, four problems that must be solved for low-frequency weak seismic wave information from deep formations below 6000 meters: the first is the problem of receiving extremely weak signals from deep strata: as described above, both the electromagnetic induction moving-coil detector and the MEMS detector need to be processed by a subsequent electronic device circuit (including a node type instrument), and as is well known, all electronic device circuits have noise floor numbers, in principle, when an effective signal amplitude is lower than a floor noise, or when the floor noise is higher than the effective signal amplitude, an effective signal cannot be received, that is, the reception of a weak signal is limited by the floor noise problem. Secondly, the dynamic range problem: the dynamic range of seismic signals is usually 120 db-130 db, the main machine part of a seismic instrument can easily meet the requirement, but the dynamic range of a conventional detector matched with the instrument is usually 50-60 db, so that the problem is how can a conventional detector with a dynamic range of 50-60 db actually, accurately and with high fidelity record seismic signals with a dynamic range of 120 db-130 db? Although the dynamic range of the instrument can be 130db or even larger, the fact that the seismic information of 50-60 db collected by the detector is amplified to 120 db-130 db is undoubtedly distorted and distorted, and the dynamic range of the detector is an insurmountable bottleneck. It can be said that: geophones limit seismic exploration high quality data acquisition. Thirdly, the low frequency problem: the characteristics of deep stratum signals are attenuated by stratum absorption of each exploratory area according to the law that the frequency of shallow layer hundreds of hertz is slowly reduced to a few hertz along with the change of depth until the frequency reaches a few tenths of hertz of a limit value, and the lower frequency is required by deep detection. The frequency response of the current electromagnetic induction moving-coil detector is more difficult to realize due to lower frequency as the limit of the electromagnetic induction theory and the prior art is limited, and most of the low cut-off is 10Hz, so that the conventional detector cannot receive deep signals lower than 10 Hz. As the depth of investigation increases, the effective signal of seismic waves from deep formations is precisely at a frequency of only a few hertz. Fourthly, the electromagnetic interference problem: after the detector converts mechanical vibration into an electrical signal, a weak electrical signal can be subjected to various electromagnetic interferences when being transmitted in a long lead (the existing seismic array is generally long), and the long-distance transmission of the weak signal with a high signal-to-noise ratio is also not facilitated.

In summary, the conventional seismic prospecting geophone is difficult to detect low-frequency weak seismic wave signals from deep strata below 6000 meters.

SUMMERY OF THE UTILITY MODEL

The utility model aims at providing a weak seismic wave signal detection system of deep stratum low frequency to the problem that current seismic exploration geophone can't carry out the detection to the weak seismic wave signal of low frequency that comes from deep stratum below 6000 meters. The utility model discloses an optical fiber wave detector is seismic detection, gathers the extremely weak low frequency seismic signal who comes from deep stratum, transmits receiving terminal demodulation unit via the optic fibre cable to convert data formats such as the special SEG-D of seismic exploration or SEG-Y to record, the storage is on storage medium such as magnetic tape, magnetic disc or electronic disk.

The technical scheme of the utility model is that:

the utility model provides a deep stratum low frequency weak seismic wave signal detection system, this system include control center, memory, transmitting terminal modulation unit, receiving terminal demodulation unit, transmission optic fibre, receipt optic fibre and optic fibre wave detector array, control center and transmitting terminal modulation unit, receiving terminal demodulation unit's corresponding control signal end link to each other, transmitting terminal modulation unit be used for transmitting the laser signal after the modulation, through the transmission optic fibre transmission to the optic fibre wave detector array output of detection terminal; meanwhile, the optical fiber detector array detection optical signals are transmitted to a receiving end demodulation unit through receiving optical fibers, and are transmitted to a memory for storage after being demodulated.

Further, the transmitting end modulation unit includes: laser source, transmission light modulation module, light amplification distributor, transmitting terminal processing module, clock source and clock synchronization module, the light signal output part of laser source links to each other with the light signal input part of transmission light modulation module, and the light signal output part of transmission light modulation module passes through the input that light amplification distributor exported to transmission optic fibre, the control signal end and the two-way electric connection of transmitting terminal processing module of transmission light modulation module and light amplification distributor, the control signal input part of laser source and the corresponding control signal output part electric connection of transmitting terminal processing module, the clock signal output part of clock source links to each other with the corresponding clock signal input part of transmitting terminal processing module, transmitting terminal processing module passes through clock synchronization module and receiving terminal processing module electric connection of receiving terminal demodulation unit, carries out clock signal synchronization, the control signal end and the control center electric connection of transmitting terminal processing module.

Further, the receiving end demodulation unit includes: the optical amplifier comprises an optical amplifier, an optical/electrical conversion module, a receiving end processing module and an A/D conversion module, wherein the optical signal input end of the optical amplifier is connected with the optical signal output end of a receiving optical fiber, the optical signal output end of the optical amplifier is connected with the optical signal input end of the optical/electrical conversion module, the electrical signal output end of the optical/electrical conversion module is connected with the input end of the A/D conversion module, the output end of the A/D conversion module is connected with the corresponding input end of a memory, the control signal input end of the A/D conversion module is connected with the corresponding control signal output end of the receiving end processing module, the clock synchronization signal input end of the receiving end processing module is connected with the clock synchronization module output end of the transmitting end processing module to carry out clock signal synchronization, and the control signal end of the receiving end processing module is electrically connected with a control center.

Further, the fiber detector array includes a plurality of fiber detectors arranged in sequence, and the fiber detector includes: the device comprises a shell, a bracket, a transmitting optical fiber leading-out hole, a receiving optical fiber leading-out hole, a rubber cylinder, a spring block, a mass block and a cover plate;

the inner part of the shell is sequentially provided with a cover plate, a mass block, a spring block and a rubber cylinder from top to bottom, and the support is arranged in the rubber cylinder;

a tubular cavity for accommodating coiled transmitting optical fibers and receiving optical fibers is formed below the spring block, between the outer wall of the rubber cylinder and the inner wall of the shell, and the transmitting optical fibers and the receiving optical fibers are coiled in the tubular cavity;

and a transmitting optical fiber leading-out hole and a receiving optical fiber leading-out hole which are communicated with the tubular cavity are arranged on the side wall of the shell and are respectively connected with the end parts of the transmitting optical fiber and the receiving optical fiber.

Furthermore, the transmitting optical fiber leading-out hole and the receiving optical fiber leading-out hole are arranged on the cover plate.

Further, the rubber cylinder is in a hollow cylindrical shape.

Further, the height of the support is slightly lower than that of the rubber barrel.

The utility model has the advantages that:

the frequency bandwidth, especially the low frequency, detected by the optical fiber detector array detection system of the utility model is currently 0.2Hz; the sensitivity is high, and 30pm particle vibration displacement can be measured at present; the dynamic range is large and is as high as 140dB; the signal-to-noise ratio is high, and the sensor body is not provided with electronic components, so that the noise is very low; the linearity is good, the distortion degree is low, and the fidelity is high; the electromagnetic interference resistance is strong, the lightning stroke resistance is strong, the performance is stable, the weight is light, the water resistance is good, the seismic exploration arrangement is easy to form, the field construction laying is easy, and the method is particularly suitable for the detection of extremely weak signals from deep strata in seismic exploration.

The utility model is in charge of controlling, data collecting, data transmitting and data processing of the overall system of the optical fiber detector array through a control center, a transmitting terminal modulation unit and a receiving terminal demodulation unit; the modulation unit is an emission part, and sends a laser source generated by a laser to an optical fiber detector array through transmission optical fibers after the laser source is subjected to acoustic modulation and amplified and distributed by an optical amplification distributor; the optical fiber wave detector array returns the collected seismic signals to the receiving end demodulation unit through the transmission optical fiber, the receiving end demodulation unit is a receiving part, the optical signals are converted into electric signals after being amplified by the optical amplifier and converted by the optical/electric converter, the electric signals are digitized into 32-bit data, the 32-bit data are recorded according to the data formats of SEG-D or SEG-Y and the like special for seismic exploration and are stored on storage media such as a magnetic tape, a magnetic disk or an electronic disk.

The optical fiber detector of the utility model has simple structure and good stability; the top cover plate is made of brass alloy materials, and has good rigidity, corrosion resistance, oxidation resistance and stable performance; the mass block is made of aluminum bronze alloy material, and has the advantages of high density, high specific gravity, corrosion resistance, oxidation resistance and stable performance. The rubber cylinder is a hollow cylinder made of soft elastic material, has good elasticity, corrosion resistance and aging resistance, and is little influenced by temperature; the optical fiber detector can detect extremely weak seismic signals from deep stratum, and can acquire, transmit, convert, store and display the extremely weak seismic signals in real time.

The optical fiber detector and the transmission optical cable adopted by the utility model work by light without power supply, thereby avoiding the trouble of field power supply and facilitating field construction operation. The optical cable has small transmission loss and flexible and convenient use, can work in an arrangement mode of any number of optical cables, any channel spacing and any line spacing, and can be arranged in two dimensions or three dimensions.

Other features and advantages of the present invention will be described in detail in the detailed description which follows.

Drawings

The above and other objects, features and advantages of the present invention will become more apparent by describing in more detail exemplary embodiments thereof with reference to the attached drawings, in which like reference numerals generally represent like parts throughout the exemplary embodiments of the present invention.

Fig. 1 shows the overall structure diagram of the present invention.

Fig. 2 shows a schematic block diagram of the present invention.

Fig. 3 shows a structure diagram of the fiber detector of the present invention.

Fig. 4 shows a schematic diagram of amplitude-frequency characteristics of the fiber detector of the present invention.

Fig. 5 shows a schematic diagram of the self-consistency of the fiber detector of the present invention.

Fig. 6 shows a comparison diagram of the fiber-optic geophone system, MEMS, and conventional moving-coil geophone with the same source and receiving position.

FIG. 7 is a graph showing the waveform comparison results of the vibration signals of 6 traces detected by the same seismic source and the same receiving position of the fiber-optic geophone system and the MEMS in FIG. 6.

FIG. 8 is a graph showing the same source and the same receiving location of the fiber-optic geophone system and MEMS of FIG. 6 comparing the detected waveforms of the same vibration signal.

Fig. 9 is a schematic diagram showing the comparison result of the vibration signal waveforms of 6 channels detected by the fiber seismic wave detection system and the conventional moving-coil wave detector in fig. 6 at the same seismic source and the same receiving position.

FIG. 10 is a schematic diagram showing the comparison of the waveforms of the same vibration signal detected by the fiber seismic system and the conventional moving-coil detector of FIG. 6 at the same seismic source and the same receiving position.

FIG. 11 is a schematic diagram showing a spectral comparison of the same vibration signal detected by the fiber-optic geophone system and MEMS at the same source and at the same receiver location in FIG. 6.

In the figure: 1. a housing; 2. a support; 3. a launch fiber exit aperture; 4. receiving an optical fiber lead-out hole; 5. a rubber cylinder; 6. a spring block; 7. a mass block; 8. a cover plate; 9. a tubular cavity.

Detailed Description

Preferred embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. While the preferred embodiments of the present invention have been illustrated in the accompanying drawings, it is to be understood that the invention may be embodied in various forms and should not be limited to the embodiments set forth herein.

As shown in fig. 1, a deep formation low-frequency weak seismic wave signal detection system includes a control center, a memory, a transmitting end modulation unit, a receiving end demodulation unit, a transmitting optical fiber, a receiving optical fiber, and an optical fiber detector array, where the control center is connected to corresponding control signal ends of the transmitting end modulation unit and the receiving end demodulation unit, the transmitting end modulation unit is used to transmit a modulated laser signal, and transmit the modulated laser signal to the optical fiber detector array of a detecting end through the transmitting optical fiber for output; meanwhile, the optical fiber detector array detection optical signals are transmitted to a receiving end demodulation unit through receiving optical fibers, and are transmitted to a memory for storage after being demodulated;

as shown in fig. 2, the transmitting end modulation unit includes: the optical signal output end of the laser source is connected with the optical signal input end of the transmitting optical modulation module, the optical signal output end of the transmitting optical modulation module is output to the input end of the transmitting optical fiber through the optical amplification distributor, the control signal ends of the transmitting optical modulation module and the optical amplification distributor are electrically connected with the transmitting end processing module in a bidirectional mode, the control signal input end of the laser source is electrically connected with the corresponding control signal output end of the transmitting end processing module, the clock signal output end of the clock source is connected with the corresponding clock signal input end of the transmitting end processing module, the transmitting end processing module is electrically connected with the receiving end processing module of the receiving end demodulation unit through the clock synchronization module to perform clock signal synchronization, and the control signal end of the transmitting end processing module is electrically connected with the control center;

the receiving end demodulation unit comprises: the optical amplifier comprises an optical amplifier, an optical/electrical conversion module, a receiving end processing module and an A/D conversion module, wherein the optical signal input end of the optical amplifier is connected with the optical signal output end of a receiving optical fiber, the optical signal output end of the optical amplifier is connected with the optical signal input end of the optical/electrical conversion module, the electrical signal output end of the optical/electrical conversion module is connected with the input end of the A/D conversion module, the output end of the A/D conversion module is connected with the corresponding input end of a memory, the control signal input end of the A/D conversion module is connected with the corresponding control signal output end of the receiving end processing module, the clock synchronization signal input end of the receiving end processing module is connected with the clock synchronization module output end of the transmitting end processing module to carry out clock signal synchronization, and the control signal end of the receiving end processing module is electrically connected with a control center.

As shown in fig. 3, the fiber detector array includes a plurality of fiber detectors arranged in sequence, and the fiber detector includes: the device comprises a shell 1, a bracket 2, a transmitting optical fiber leading-out hole 3, a receiving optical fiber leading-out hole 4, a rubber cylinder 5, a spring block 6, a mass block 7 and a cover plate 8;

a cover plate 8, a mass block 7, a spring block 6 and a rubber tube 5 are sequentially arranged in the shell 1 from top to bottom, and the support 2 is arranged in the rubber tube 5;

a tubular cavity 9 for accommodating coiled transmitting optical fibers and receiving optical fibers is formed below the spring block 6, between the outer wall of the rubber barrel 5 and the inner wall of the shell 1, and the transmitting optical fibers and the receiving optical fibers are coiled in the tubular cavity 9;

a transmitting optical fiber leading-out hole 3 and a receiving optical fiber leading-out hole 4 which are communicated with the tubular cavity 9 are arranged on the side wall of the shell 1 and are respectively connected with the end parts of the transmitting optical fiber and the receiving optical fiber;

the transmitting optical fiber leading-out hole 3 and the receiving optical fiber leading-out hole 4 are arranged on the cover plate 8.

The rubber cylinder 5 is in a hollow cylindrical shape; the height of the bracket 2 is slightly lower than that of the rubber tube 5.

The utility model discloses a when detection system uses, adopt following step:

s1, a transmitting end modulation unit receives a control signal of a control center, transmits the modulated laser signal to an optical fiber detector array located at an external detection position through a transmitting optical fiber, and outputs the optical signal;

s2, respectively detecting external vibration by each optical fiber detector in the optical fiber detector array; when the receiving end processing module receives external vibration, the mass block 7 moves along with the external vibration, so that the spring piece 6 vibrates, the vibration is acted on the receiving optical fiber through the rubber cylinder 5 to generate optical phase shift, and the optical signal is transmitted to the receiving end processing module through the receiving optical fiber;

and S3, the receiving end processing module synchronizes with the transmitting end modulation unit through the clock synchronization module, processes phase change generated between the received optical signal and the transmitting optical signal which is synchronized with the received optical signal and serves as reference light, acquires a vibration signal and sends the vibration signal to the memory.

In the specific implementation:

1. the utility model discloses a system includes the way part: the optical path component is composed of a laser source, a modulation module, an optical amplification distributor, a transmission optical cable, an optical fiber detector array in the modulation emission component, an optical amplifier in the receiving end demodulation unit, an optical/electrical converter and the like.

A modulation transmitting section: the laser generates a laser light source, the output end of the laser light source is connected with the input end of the light emitting modulation module, the light emitting modulation module modulates light signals, the output end of the light emitting modulation module is connected with the input end of the light amplification distributor, the light signals which are amplified and distributed by the light amplification distributor are output to the input end of the transmission optical cable, the output end of the transmission optical cable is connected with the optical fiber detector array, and the modulated, amplified and distributed light signals are output to the optical fiber detector array through the transmission optical cable.

Demodulation reception means: the return signal of the optical fiber detector array is output to the transmission optical cable, the output of the transmission optical cable is connected with the input end of the optical amplifier, the signal detected by the optical fiber detector array transmitted by the transmission optical cable is input to the optical amplifier, the optical amplifier amplifies the signal detected by the optical fiber detector array and transmitted by the optical cable, the output end of the optical amplifier is connected with the input end of the optical/electrical converter, and the optical signal is converted into an electrical signal by the optical/electrical converter.

The output end of the optical/electric converter is connected with the input end of the A/D conversion module, the acquired signal data is demodulated and arranged and then output to the data memory, and finally the data which is processed by the data demodulator is stored and output according to the required format, such as SEG-D format, SEG-Y format and the like.

2. The utility model discloses a system includes circuit component: the circuit component is composed of a clock source, a main controller, a clock synchronizer and a power supply component.

The clock source generates the standard clock of the system, the output end of the clock source is connected to the input end of the transmitting end processing module, the output end of the transmitting end processing module is connected to the input end of the clock synchronizer, and the clock synchronization pulse is sent to the receiving end processing module under the relevant clock synchronization instruction of the clock synchronizer. The output end of the transmitting end processing module is also respectively connected with the laser source, the transmitting light modulation module and the light amplification distributor, the work of the optical component is controlled under the action of the synchronous pulse, and meanwhile, the working state of the optical component is timely fed back to the transmitting end processing module.

The output end of the clock synchronizer is also connected to the receiving end processing module to provide clock pulse synchronization signals for data acquisition work of the receiving end. In summary, the entire fiber detector array system operates systematically under the unified coordination of the clock synchronizers.

3. The utility model discloses in, the structure of optical fiber detector is as shown in fig. 3, and the superiors are the apron, adopt rigidity good, corrosion-resistant, anti-oxidant, the brass alloy material of stable performance, and the lateral wall is porose for leading-in and the derivation of optic fibre, and the import of apron top trompil also can be followed to optic fibre of course and derived, and the apron plays the effect of sensor core upper cover encapsulation. The mass block is arranged below the cover plate and is made of metal aluminum bronze alloy materials with high density, high specific gravity, corrosion resistance, oxidation resistance and stable performance. A spring piece is arranged below the mass block and made of beryllium bronze alloy material with good elasticity. The hollow cylinder made of soft elastic material is arranged under the spring leaf, and has good elasticity, corrosion resistance, aging resistance, small change caused by temperature and stable performance. The periphery of the soft elastic material cylinder is wound with optical fibers. The inner side of the elastic material hollow cylinder is provided with a metal cylinder support for fixing the soft elastic material hollow cylinder, in order to have enough rigidity and reduce weight, a magnesium-aluminum alloy material can be selected, and the height of the metal cylinder support is slightly lower than that of the soft elastic material hollow cylinder.

The working principle of the optical fiber detector is as follows: the mass block moves along with the vibration of the outside, the vibration is applied to the spring piece, and then the spring piece moves along with the vibration, the movement of the spring piece is applied to the optical fiber winding through the hollow cylinder made of soft elastic material, at the moment, the measured light moves, and the reference light does not move. A moving and a non-moving state are formed, so that the change of the optical phase is generated, the optical phase shift is caused, the grating stripe is moved, the direction and the size of the measured vibration can be measured by measuring the moving direction and the moving amount of the stripe, and a vibration signal is obtained.

The core components of the fiber-optic seismic detection system are as follows: the optical fiber modulation and demodulation component comprises an optical device, wherein the optical device selects a high-quality optical device, particularly a laser source according to the actual application requirement, and selects continuous laser emitted by an ultra-narrow line width low-phase noise laser. The number of bits of the optical/electrical converter in the demodulation component is contingent on the specific application requirements, for example: 32 bits.

When the optical fiber wave detection system is used for seismic exploration, the connection among all the single bodies is realized by the transmission optical cable, the transmission optical cable is required to bear enough tension, and the optical fiber wave detector and the transmission optical cable are used in a field environment, so that the optical cable is required to be additionally protected to prevent animals from biting and rock from colliding. Tensile, compressive resistant protective materials such as Kevlar; of course, even if the optical cable is slightly damaged for some reason, such as skin breaking, the optical fiber is still used as it is without influence as long as the optical fiber is continuous, which is an advantage of the optical cable.

The optical fiber detector and the transmission optical cable work optically without power supply, so that the trouble of field power supply is avoided, and the field construction operation is facilitated. And the transmission loss of the optical cable is very small, and the use is flexible and convenient. The device can work in an arrangement mode of any number of tracks, any track pitch and any line pitch, in other words, the device can be arranged in two dimensions or three dimensions.

The effect of the comparative test is shown as follows:

arranging an optical fiber seismic detection system for detection, wherein the amplitude-frequency characteristic of an optical fiber detector is shown in figure 4, and the consistency of the optical fiber detector is shown in figure 5;

under the conditions that the embedding conditions are the same, the distance from the vibration source is the same, and the set acquisition parameters of the instrument are completely the same, comparing the optical fiber seismic detection system, the MEMS and the traditional moving coil detector with the same seismic source and the same receiving position, as shown in FIG. 6:

1. the comparison between the fiber detector of the 6 traces and the MEMS of the 6 traces for the same seismic source and the same receiving position is shown in fig. 7 and 8, and in fig. 7: the left 6 paths are MEMS, and the right 6 paths are fiber geophones; FIG. 8 is a diagram of: and the same vibration signal waveforms detected by the same seismic source and the same receiving position are compared, wherein the solid line is an optical fiber geophone, and the dotted line is an MEMS sensor.

2. The comparison between the optical fiber geophone with 6 traces and the traditional moving coil geophone with 6 traces at the same seismic source and the same receiving position is shown in fig. 9 and 10, in fig. 9, the left 6 traces are the optical fiber geophone and the right 6 traces are the traditional moving coil geophone; FIG. 10 is a diagram: the same vibration signal waveform detected by the same seismic source and the same receiving position is compared, the solid line is an optical fiber detector, and the dotted line is a moving coil type detector.

3. FIG. 11 is a diagram: the same vibration source, the same receiving position, the same vibration signal detected, the spectrum comparison condition of the optical fiber detector and the MEMS, and the solid line optical fiber detector; dashed line MEMS sensors.

The following conclusions were drawn from the actual comparison:

1. the sensitivity of the fiber detector is superior to MEMS.

2. MEMS sensitivity is superior to moving coils.

3. The optical fiber detector has better inhibition capability on noise and electromagnetic interference than MEMS and traditional moving coil type; that is, the signal-to-noise ratio of the fiber detector is superior to that of MEMS and traditional moving coil type

4. The frequency characteristic of the fiber detector is equivalent to that of an MEMS (micro-electromechanical system), and is superior to that of a moving coil type.

5. The dynamic range of the fiber detector is equivalent to that of an MEMS (micro-electromechanical system), and is superior to that of a moving coil type.

6. The optical fiber detector has low distortion degree and high fidelity of the acquired signal.

7. The optical fiber detector has high reliability and long service life.

8. The optical fiber detector has no power supply and electronic components, so that the lightning stroke problem of other seismic instruments is avoided fundamentally

In conclusion: the optical fiber detector avoids the bottom noise of electronic components and various electromagnetic interferences, greatly improves the signal-to-noise ratio, can acquire low-frequency weak seismic wave signals from deep stratums and is necessary for exploring deep oil-gas reservoirs and mineral resources.

The optical fiber detector detects and transmits optical information without any electronic component, the optical fiber transmission loss is negligibly small, and a detection optical signal returns to a host and realizes optical/electrical conversion, so that the optical fiber detector is formed: 1. wide frequency band (especially low frequency, which is currently 0.2 Hz), high sensitivity (which is currently capable of measuring particle vibration displacement of 30 pm), large dynamic range (140 dB), high signal-to-noise ratio (no electronic component bottom noise in the sensor body), good linearity, low distortion (high fidelity), and strong anti-electromagnetic interference; the lightning stroke resistance is strong; the performance is stable; the weight is light; the high water resistance is easy to form seismic exploration arrangement and is also easy to construct and lay in the field, so the method is particularly suitable for detecting extremely weak signals from deep strata in seismic exploration.

While various embodiments of the present invention have been described above, the above description is intended to be illustrative, not exhaustive, and not limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments.

Claims (7)

1. A deep stratum low-frequency weak seismic wave signal detection system is characterized by comprising a control center, a storage, a transmitting end modulation unit, a receiving end demodulation unit, a transmitting optical fiber, a receiving optical fiber and an optical fiber detector array, wherein the control center is connected with corresponding control signal ends of the transmitting end modulation unit and the receiving end demodulation unit; meanwhile, the optical fiber detector array detection optical signals are transmitted to a receiving end demodulation unit through receiving optical fibers, and are transmitted to a memory for storage after being demodulated.

2. The deep formation low-frequency weak seismic signal detection system as claimed in claim 1, wherein said emitter modulation unit comprises: laser source, transmission light modulation module, light amplification distributor, transmitting terminal processing module, clock source and clock synchronization module, the light signal output part of laser source links to each other with the light signal input part of transmission light modulation module, and the light signal output part of transmission light modulation module passes through the input that light amplification distributor exported to transmission optic fibre, the control signal end and the two-way electric connection of transmitting terminal processing module of transmission light modulation module and light amplification distributor, the control signal input part of laser source and the corresponding control signal output part electric connection of transmitting terminal processing module, the clock signal output part of clock source links to each other with the corresponding clock signal input part of transmitting terminal processing module, transmitting terminal processing module passes through clock synchronization module and receiving terminal processing module electric connection of receiving terminal demodulation unit, carries out clock signal synchronization, the control signal end and the control center electric connection of transmitting terminal processing module.

3. The deep formation low-frequency weak seismic signal detection system according to claim 1, wherein the receiving end demodulation unit comprises: the optical amplifier comprises an optical amplifier, an optical/electrical conversion module, a receiving end processing module and an A/D conversion module, wherein the optical signal input end of the optical amplifier is connected with the optical signal output end of a receiving optical fiber, the optical signal output end of the optical amplifier is connected with the optical signal input end of the optical/electrical conversion module, the electrical signal output end of the optical/electrical conversion module is connected with the input end of the A/D conversion module, the output end of the A/D conversion module is connected with the corresponding input end of a memory, the control signal input end of the A/D conversion module is connected with the corresponding control signal output end of the receiving end processing module, the clock synchronization signal input end of the receiving end processing module is connected with the clock synchronization module output end of the transmitting end processing module to carry out clock signal synchronization, and the control signal end of the receiving end processing module is electrically connected with a control center.

4. The deep formation low frequency weak seismic signal detection system of claim 1, wherein the fiber detector array comprises a plurality of sequentially arranged fiber detectors, the fiber detectors comprising: the device comprises a shell (1), a bracket (2), a transmitting optical fiber leading-out hole (3), a receiving optical fiber leading-out hole (4), a rubber cylinder (5), a spring block (6), a mass block (7) and a cover plate (8);

a cover plate (8), a mass block (7), a spring block (6) and a rubber cylinder (5) are sequentially arranged in the shell (1) from top to bottom, and the support (2) is arranged in the rubber cylinder (5);

a tubular cavity (9) for accommodating the coiled transmitting optical fiber and the coiled receiving optical fiber is formed below the spring block (6), between the outer wall of the rubber cylinder (5) and the inner wall of the shell (1), and the transmitting optical fiber and the receiving optical fiber are coiled in the tubular cavity (9);

and a transmitting optical fiber leading-out hole (3) and a receiving optical fiber leading-out hole (4) which are communicated with the tubular cavity (9) are arranged on the side wall of the shell (1) and are respectively connected with the end parts of the transmitting optical fiber and the receiving optical fiber.

5. The deep stratum low-frequency weak seismic signal detection system as claimed in claim 4, wherein the transmitting optical fiber leading-out hole (3) and the receiving optical fiber leading-out hole (4) are formed in the cover plate (8) or are formed in the cover plate.

6. The deep stratum low-frequency weak seismic signal detection system as claimed in claim 4, wherein the rubber cylinder (5) is hollow cylindrical.

7. The deep stratum low-frequency weak seismic signal detection system as claimed in claim 4, characterized in that the height of the support (2) is slightly lower than that of the rubber cylinder (5).

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