Seismic single-component or three-component fiber grating geophone

Abstract

The single-component or three-component fiber grating detector for earthquake is characterized in that a single-component detector one is arranged on the bottom of the shell, a single-component detector two is arranged on the inner side wall of the middle of the shell, and a single-component detector three is arranged on the inner side wall of the top of the shell; the installation directions of the single-component detector one, the single-component detector two and the single-component detector three are perpendicular to each other; the single-component detector one is used as an X-component detector, the single-component detector two is used as a Z-component detector, and the single-component detector three is used as a Y-component detector; and the single-component detector one, the single-component detector two and the single-component detector three are all single-component fiber grating detectors for earthquake. The single-component fiber grating detector for earthquake adopts an elliptical ring elastic sheet as a transducer component, can load the vibration acceleration perceived by a mass block on the fiber grating, has the effect of high sensitivity, and can realize three-dimensional vibration detection.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of seismic wave detection, and particularly relates to a seismic wave fiber grating detector. BACKGROUND

[0002] The per capita energy possession of China is small, the dependence on foreign countries is high, the emergency capability is weak, and the energy security situation is severe. Therefore, as a crucial link in the oil and chemical industry, the survey and development of oil and gas resources are related to the national security strategy and affect the overall economic and social development. As the most effective and cost-effective method for solving the problem of oil and gas exploration, the artificial seismic wave exploration method, the seismic detector is the most critical core device. The requirements for the frequency bandwidth, dynamic range, sensitivity, fidelity and anti-interference ability of the seismic detector are increasingly improved with the complexity of the exploration target. On the one hand, the advanced detection instrument for seismic wave exploration in China is basically monopolized by foreign oil and gas exploration companies represented by Schlumberger and Geospace of the United States, Sercel of France and Avalon of the United Kingdom, and the core technology is facing the problem of "neck block"; on the other hand, the currently used seismic detector in China has high cost and huge cost for each laying and maintenance; most importantly, the technical difficulty of seismic wave exploration is getting higher and higher, which can be summarized as four characteristics of low, deep, difficult and hidden. Around the major needs of the research and exploration and development of oil and gas resources in China, the traditional detection technology has many limitations and cannot solve the above problems. Therefore, it is of great significance to develop a new type of detector with independent intellectual property rights.

[0003] The seismic detector receives the return wave of the elastic wave generated by artificial earthquake through reflection or refraction after the interface of the rock layer, and after processing, the geological structure, stratum lithology, rock physical properties and fluid containing properties and other parameters are inferred, and then the fine description of the underground resources such as oil and gas reservoirs is obtained. At present, the traditional electromagnetic type detector represented by the moving coil detector is mostly of the velocity type, and its linear working frequency band is relatively narrow (17Hz-200Hz), the dynamic range is relatively small (60dB-80dB), the sensitivity of a single detector is low, the transient signal receiving ability is weak, and the integrity and accuracy of the signal cannot be guaranteed. As a new type of detector, the fiber grating (FBG) vibration acceleration detector has the advantages of low cost, flexible structure, strong space adaptability, high sensitivity, wide frequency band, anti-electromagnetic interference, high temperature and pressure resistance, downhole "passive", quasi-distributed sensing, easy networking and multiplexing, etc. It overcomes the inherent defects of the traditional electromagnetic type detector, and has attracted wide attention and research, and has broad market application potential. However, there are still some problems to be solved for the existing fiber detector, such as component crosstalk, consistency, and the contradiction between high sensitivity and wide frequency band in the performance index of the fiber detector. The contradiction between high sensitivity and wide frequency band in the performance index of the fiber detector refers to the fact that the sensitivity of the fiber detector is proportional to the total mass of the inertial body and its fixing device, and the square of the resonance frequency is inversely proportional to the total mass of the inertial body and its fixing device, that is, the resonance frequency will be reduced when the sensitivity is improved, and the sensitivity will be reduced when the resonance frequency is increased.

[0004] Therefore, the development of a wide-band high-sensitivity fiber grating detector for seismic wave exploration has important theoretical significance and practical value for widening the exploration dimension, exploring the propagation law of seismic waves, realizing efficient seismic data acquisition, and ultimately improving oil and gas production. SUMMARY

[0005] The technical problem to be solved by the present application is to overcome the shortcomings of the existing fiber detector, and to provide a seismic single-component or three-component fiber grating detector with reasonable design, simple structure, high sensitivity in wide frequency band.

[0006] The technical scheme adopted to solve the above technical problems is: a seismic single-component fiber grating detector, an elliptical ring spring plate is provided with an optical fiber with a certain pre-tightening force in the long axis direction of the middle part, the optical fiber is engraved with a grating, the elliptical ring spring plate is provided with a base on one side of the short axis direction and a top plate on the other side, and a mass block is arranged on the top plate.

[0007] As a preferred technical scheme, the long axis of the elliptical ring spring plate is 35-45mm, the short axis is 20-30mm, the wall thickness is 0.15-0.25mm, and the width is 15-25mm.

[0008] As a preferred technical scheme, the pre-tightening force makes the center wavelength of the grating drift in a range of 0.01nm-0.08nm.

[0009] As a preferred technical scheme, the mass weight is 30-40g.

[0010] As a preferred technical scheme, the material of the elliptical ring spring is stainless steel.

[0011] As a preferred technical scheme, the sensitivity S of the detector is

[0012]

[0013] In the formula, λ is the center wavelength of the grating, m is the total weight of the load, L is the long axis length of the elliptical ring spring, t is the spring thickness, π is the circular constant, E is the Young's modulus of the elliptical ring spring, and b is the width of the elliptical ring spring.

[0014] The application further provides a seismic wave three-component fiber grating detector, wherein a single-component detector one is mounted on the inner bottom of a shell, a single-component detector two is mounted on the inner side wall of the middle of the shell, and a single-component detector three is mounted on the inner side wall of the top of the shell; the mounting directions of the single-component detector one, the single-component detector two and the single-component detector three are perpendicular to each other; the single-component detector one is used as an X-component detector, the single-component detector two is used as a Z-component detector, and the single-component detector three is used as a Y-component detector; and the single-component detector one, the single-component detector two and the single-component detector three are the seismic single-component fiber grating detectors according to claim 6.

[0015] As a preferred technical scheme, the shell is a cylindrical shell, the height of the shell is 150-160mm, the inner diameter of the shell is 50-55mm, the wall thickness of the shell is 2mm, the material of the shell is stainless steel, a handle and three fiber holes are arranged on the top cover of the shell.

[0016] As a preferred technical scheme, the single-component detector one arranged on the inner bottom of the shell is provided with a fiber guide wheel on one side, and one end of the fiber of the single-component detector one is wound around the fiber guide wheel and then passes out from one fiber hole on the top cover of the shell.

[0017] As a preferred technical scheme, the single-component detector two and the single-component detector three are both provided with coupling modules between the single-component detectors and the inner wall of the shell.

[0018] The application has the following beneficial effects:

[0019] The application adopts the elliptical ring elastic sheet as the transducing component, reduces the stiffness of the total detector, ensures the width of the measuring frequency band, and improves the sensitivity of the detector, and the application can fully sense the vibration signal in the range of 10-110Hz, and solves the contradiction between high sensitivity and wide frequency band in the prior art; the accurate modulation of the optical fiber pre-tightening force of the three single-component detectors in the three-component fiber grating detector makes the resonance frequency and the sensitivity of the three components have good consistency, and the better transverse anti-interference characteristic makes the three-component fiber grating detector have a standard 8-shaped directional response. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a structural schematic diagram of the single-component fiber grating detector of the application.

[0021] Figure 2 is a structural schematic diagram of the three-component fiber grating detector of the application.

[0022] Figure 3 is a test diagram of the anti-transverse interference capability of the single-component fiber grating detector of the application in the X and Y directions.

[0023] Figure 4 is a diagram of the amplitude-frequency characteristic curve of the three-component fiber grating detector of the application in the range of 10-110Hz and the sensitivity linear diagram of the three components when vibrating in the X, Y and Z directions.

[0024] Wherein: the base 1, the elliptical ring elastic sheet 2, the optical fiber 3, the grating 4, the top plate 5, the mass block 6, the shell 103, the single-component detector one 101, the single-component detector two 106, the single-component detector three 104, the handle 105, the optical fiber guide wheel 102, and the coupling module 107. DETAILED DESCRIPTION

[0025] The application will be further described in detail in combination with the drawings and examples, but the application is not limited to the following embodiments.

[0026] Example 1

[0027] In Figure 1In the embodiment, the seismic single-component fiber grating detector is composed of a base 1, an elliptical ring spring 2, an optical fiber 3, a top plate 5 and a mass 6. The elliptical ring spring 2 is made of stainless steel. The long axis of the elliptical ring spring 2 is 40 mm, the short axis is 20 mm, the wall thickness is 0.2 mm and the width is 20 mm. The optical fiber 3 with a certain pre-tightening force is fixed on the long axis of the middle part of the elliptical ring spring 2 by glue. The grating 4 is written on the optical fiber 3. The pre-tightening force makes the center wavelength drift range of the grating 4 be between 3 nm and 8 nm. The grating length of the grating 4 is 2 mm and the center wavelength is 1550 nm. The base 1 is fixed on the middle part of one side of the elliptical ring spring 2 in the short axis direction by a threaded fastener. The top plate 5 is fixed on the other side of the elliptical ring spring 2 in the short axis direction by a threaded fastener. The mass 6 is fixed on the top plate 5 by a threaded fastener. The weight of the mass 6 is 35 g.

[0028] The sensitivity S of the seismic single-component fiber grating detector of the embodiment is

[0029]

[0030] In the formula, λ is the center wavelength of the grating 4, λ = 1550 nm, m is the total weight of the load, m = 50.2 g, L is the long axis length of the elliptical ring spring 2, L = 40 mm, t is the spring thickness, t = 0.2 mm, π is the circular constant, E is the Young's modulus of the elliptical ring spring 2, E = 200 GPa, b is the width of the elliptical ring spring 2, b = 20 mm. The calculation result of the sensitivity S is 1037.5 pm / g.

[0031] When the vibration signal acts on the detector, the vibration signal is transmitted to the elliptical ring spring 2 through the mass 6 amplification. The elliptical ring spring 2 vibrates up and down in the short axis direction under the vibration signal, and the optical fiber 3 generates axial stretching. The vibration signal is detected by monitoring the center wavelength drift of the grating 4 on the optical fiber 3.

[0032] Embodiment 2

[0033] In the embodiment, the long axis of the elliptical ring spring 2 is 35 mm, the short axis is 20 mm, the wall thickness is 0.15 mm and the width is 15 mm. The optical fiber 3 with a certain pre-tightening force is fixed on the long axis of the middle part of the elliptical ring spring 2 by glue. The grating 4 is written on the optical fiber 3. The pre-tightening force makes the center wavelength drift range of the grating 4 be between 3 nm and 8 nm. The grating length of the grating 4 is 2 mm and the center wavelength is 1550 nm. The base 1 is fixed on the middle part of one side of the elliptical ring spring 2 in the short axis direction by a threaded fastener. The top plate 5 is fixed on the other side of the elliptical ring spring 2 in the short axis direction by a threaded fastener. The mass 6 is fixed on the top plate 5 by a threaded fastener. The weight of the mass 6 is 40 g. The calculation method of the sensitivity is the same as that of embodiment 1.

[0034] Embodiment 3

[0035] In this embodiment, the elliptical ring spring 2 has a major axis of 45mm, a minor axis of 35mm, a wall thickness of 0.25mm, and a width of 25mm. An optical fiber 3 with a certain preload is fixed to the major axis of the elliptical ring spring 2 with adhesive. A grating 4 is engraved on the optical fiber 3. The preload causes the center wavelength of the grating 4 to drift within the range of 3nm to 8nm. The grating area of ​​the grating 4 has a length of 2mm and a center wavelength of 1550nm. A base 1 is fixed to the middle of one side of the elliptical ring spring 2 with threaded fasteners, and a top plate 5 is fixed to the other side with threaded fasteners. A mass block 6 with a weight of 30g is fixed to the top plate 5 with threaded fasteners. The sensitivity calculation method is the same as in Embodiment 1.

[0036] Example 4

[0037] exist Figure 2 In this embodiment, the seismic wave three-component fiber optic grating detector is composed of a housing 103, a single-component detector 101, a single-component detector 2 106, a single-component detector 3 104, a handle 105, an optical fiber guide wheel 102, and a coupling module 107.

[0038] The housing 103 is a cylindrical housing with a height of 154 mm, an inner diameter of 52 mm, a wall thickness of 2 mm, and is made of stainless steel. The top cover of the housing 103 has a handle 105 and three fiber optic holes. A single-component detector 101 is installed at the bottom of the housing 103, a single-component detector 106 is installed on the inner wall of the middle section, and a single-component detector 104 is installed on the inner wall of the top section. The installation directions of the single-component detectors 101, 106, and 104 are perpendicular to each other. The single-component detector 101 serves as the X-component detector, used to detect vibration signals in the X direction. Device 2 106 serves as a Z-component detector, used to detect vibration signals in the Z direction. Single-component detector 3 104 serves as a Y-component detector, used to detect vibration signals in the Y direction. Coupling modules 107 are provided between single-component detector 2 106, single-component detector 3 104 and the inner wall of housing 103. The coupling modules 107 are used to ensure that the single-component detectors are fully fitted to the curved inner wall of housing 103, so that the single-component detectors can fully sense vibration signals. One end of the optical fiber 3 of single-component detector 2 106 passes through an optical fiber hole on the top cover of housing 103, and one end of the optical fiber of single-component detector 3 104 passes through another optical fiber hole on the top cover of housing 103.

[0039] A fiber guide wheel 102 is installed on one side of the single-component detector 101 at the bottom of the housing 103. One end of the fiber of the single-component detector 101 passes around the fiber guide wheel 102 and passes through the remaining fiber hole on the top cover of the housing 103. The fiber guide wheel 102 prevents the fiber from experiencing macro-bending loss or breakage due to bending.

[0040] The single-component detector one 101, the single-component detector two 106 and the single-component detector three 104 of the embodiment adopt the seismic wave single-component fiber grating detector as described in the embodiment 1, the pre-tightening force applied on the fiber in the three single-component detectors makes the grating center wavelength drift equal, so that the resonance frequency and the sensitivity of the three components have better consistency.

[0041] The X direction sensing, the Y direction sensing and the Z direction sensing of the seismic wave three-component fiber grating detector of the embodiment are independent of each other, three-dimensional vibration detection can be realized, and the demand of low-frequency three-component detection in the well is met.

[0042] Experiment 1

[0043] In order to verify the beneficial effects of the application, the inventor uses the seismic wave single-component fiber grating detector of the embodiment 1 to perform the anti-lateral interference capability test on the vibration table.

[0044] First, the anti-lateral interference capability test in the X direction is performed by fixing the detector, the fixed vibration frequency is set to 30Hz, the acceleration size is increased by 1m / s 2 as an interval, from 5m / s 2 to 20m / s 2 , and the sensitivity of the seismic wave single-component fiber grating detector in the X direction is measured to be 1050.5pm / g; secondly, the anti-lateral interference capability test in the Y direction is performed by fixing the detector, the fixed vibration frequency is set to 30Hz, the acceleration size is increased by 1m / s 2 as an interval, from 5m / s 2 to 20m / s 2 , and the sensitivity of the seismic wave single-component fiber grating detector in the Y direction is measured to be 82.5pm / g, as Figure 3 .

[0045] Experiment 2

[0046] In order to verify the beneficial effects of the application, the inventor uses the seismic wave three-component fiber grating detector of the embodiment 4 to perform the test by installing on the vibration table, and simultaneously measures the amplitude-frequency characteristic and the sensitivity characteristic. The frequency range of the amplitude-frequency characteristic test is 10-110Hz, when the vibration direction is along the X direction, the sensitivity S XX =1040.0pm / g, S YX =66.21pm / g, S ZX =64.24pm / g; when the vibration direction is along the Y direction, S XY =76.81pm / g, S YY =1004.0pm / g, S ZY =65.1pm / g, and when the vibration direction is along the Z direction, S XZ =81.01pm / g, S YZ= 87.57 pm / g, S ZZ = 1093.7 pm / g, the results are as Figure 4 .

[0047] In conclusion, the seismic wave three-component fiber grating detector can realize high sensitivity detection under wide frequency band of three-axis vibration signals, and the three components have good consistency, directional response and cross sensitivity.

Claims

1. A single-component fiber optic grating detector for seismic waves, characterized in that: An optical fiber with a certain preload is provided along the long axis of the elliptical ring spring. A grating is engraved on the optical fiber. A base is provided on one side of the short axis of the elliptical ring spring and a top plate is provided on the other side. A mass block is provided on the top plate. The sensitivity S of the detector is In the formula, λ is the center wavelength of the grating, m is the total weight of the load, L is the length of the major axis of the elliptical ring spring, t is the thickness of the spring, π is pi, E is the Young's modulus of the elliptical ring spring, and b is the width of the elliptical ring spring.

2. The seismic wave single-component fiber optic grating detector according to claim 1, characterized in that: The elliptical ring spring has a major axis of 35-45mm, a minor axis of 20-30mm, a wall thickness of 0.15-0.25mm, and a width of 15-25mm.

3. The seismic wave single-component fiber optic grating detector according to claim 1, characterized in that: The preload force causes the center wavelength of the grating to drift within the range of 3nm to 8nm.

4. The seismic wave single-component fiber optic grating detector according to claim 1, characterized in that: The mass block weighs 30-40g.

5. The seismic wave single-component fiber optic grating detector according to claim 1, characterized in that: The elliptical ring spring is made of stainless steel.

6. A three-component fiber optic grating detector for seismic waves, characterized in that: A single-component detector 1 is installed at the bottom of the housing, a single-component detector 2 is installed on the inner wall of the middle section, and a single-component detector 3 is installed on the inner wall of the top section. The installation directions of the single-component detectors 1, 2, and 3 are perpendicular to each other. The single-component detector 1 serves as an X-component detector, the single-component detector 2 serves as a Z-component detector, and the single-component detector 3 serves as a Y-component detector. The single-component detectors 1, 2, and 3 are seismic wave single-component fiber optic grating detectors as described in claim 1.

7. The three-component fiber optic grating detector for seismic waves according to claim 6, characterized in that: The housing is a cylindrical housing with a height of 150-160mm, an inner diameter of 50-55mm, a wall thickness of 2mm, and is made of stainless steel. The top cover of the housing is equipped with a handle and three fiber optic holes.

8. The seismic wave three-component fiber optic grating detector according to claim 6 or 7, characterized in that: A fiber optic guide wheel is provided on one side of the single-component detector at the bottom of the housing. One end of the fiber optic cable of the single-component detector passes around the fiber optic guide wheel and emerges from a fiber optic hole on the top cover of the housing.

9. The seismic wave three-component fiber optic grating detector according to claim 7, characterized in that: Both the single-component detector 2 and the single-component detector 3 are equipped with coupling modules between themselves and the inner wall of the housing.

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