Underground six-component seismograph based on double-fiber ring structure

Abstract

The invention discloses an underground six-component seismograph based on a double-fiber ring structure. The underground six-component seismograph comprises a shell, a three-component accelerometer and three angular velocimeters, each angular velocity meter comprises a double-four-stage symmetrically wound double-fiber ring, and the three double-fiber rings are respectively fixed on three mutually orthogonal surfaces of the shell and are used for respectively detecting rotation signals in three directions by the three angular velocity meters; the three-component accelerometer is fixed on the shell and is used for measuring translation signals in three directions; the angular velocity meter and the three-component accelerometer are connected with clock signals input by the same external clock source, so that time alignment of measurement signals of the angular velocity meter and the three-component accelerometer is guaranteed. The device can simultaneously measure a translation signal and a rotation signal of object motion, can effectively inhibit relative intensity noise, greatly improves the sensitivity of an angular velocity meter, improves the environmental adaptability of a six-component seismograph during underground work, and reduces the influence of an underground environment.

Description

Technical Field

[0001] This invention relates to a downhole six-component seismograph based on a dual-fiber ring structure, which can directly measure motion in six dimensions. This device is of great value for seismic signal detection, geological structure research, downhole environmental seismic exploration, and environmental monitoring. Background Technology

[0002] For a finite volume element located at any two points X and X+δX, the displacements after deformation can be expressed as U(X) and U(X+δX), where δX represents the infinitesimal distance between the two points. They can be represented as:

[0003] U(x+δX)=UX)+εδX+ω×δX#(1)

[0004] Where U(X) is the translation component, εδX is the strain component, and ω×δX is the rotation component.

[0005] As can be seen from the above formula, the seismic signal includes not only translational components but also rotational components. After obtaining the signal with all six components, the phase velocity of the seismic wave propagating along the Earth's surface can be expressed as:

[0006]

[0007] Among them, c h For phase velocity, ü y The tangential acceleration along the horizontal line of the y-axis. This represents the vertical component of the angular velocity.

[0008] The observation and study of rotational signals can provide more information. Combining rotational and translational components can yield more information on stratigraphic structure, which is of great significance for geological structure research and environmental monitoring.

[0009] Current seismographs are mainly divided into three-component translational seismographs and three-component rotational seismographs. Three-component translational seismographs can only measure the translational acceleration of an object in three components, while three-component rotational seismographs can only measure the rotational angular velocity of an object in three components. Meanwhile, the downhole environment is complex, with large temperature variations, which significantly impacts seismographs. Existing seismographs cannot meet the environmental adaptability requirements for downhole exploration. Therefore, manufacturing a high-precision, wide-bandwidth, and highly adaptable six-component seismograph is of great significance for downhole seismic exploration. Summary of the Invention

[0010] To address the problems existing in the prior art, the present invention aims to provide a high-precision, wide-bandwidth downhole six-component seismograph based on a dual-fiber loop structure. The instrument of this invention integrates a three-component accelerometer and a three-component angular velocity meter, simultaneously acquiring data to obtain six motion signals at once. The instrument's three-component angular velocity meter utilizes the Sagnac effect to measure the rotational angular velocity of an object, and the dual-fiber loop structure suppresses Shupe errors caused by relative intensity noise and environmental temperature variations, effectively improving the measurement accuracy and observation bandwidth of the seismograph while reducing the impact of the downhole environment on the seismograph.

[0011] This invention fixes a three-component accelerometer to the lower left corner of the instrument and three angular velocity meters to the three surfaces of the instrument, for measuring angular velocities in three different directions. The instrument's structural principle diagram is shown below. Figure 1 As shown in the diagram, the yellow portion represents three double-quadrupole symmetrically wound dual-fiber loops, each fixed to one of the instrument's three mutually orthogonal planes. Each angular velocity meter includes one double-quadrupole symmetrically wound dual-fiber loop, and the three angular velocity meters detect rotational signals in three directions respectively. Figure 1 The black portion in the image represents a three-component accelerometer, used to measure translational signals in three directions. Both the angular velocity meter and the three-component accelerometer can be connected to an external clock signal. When both use the same external clock source, the angular velocity meter and the three-component accelerometer can measure signals simultaneously, ensuring time alignment.

[0012] The angular velocity meter used in this invention is a Sagnac interferometer. Because a high-precision, wide-bandwidth seismograph is required, the angular velocity meter in this invention utilizes the co-source Sagnac interferometer structure based on a dual-fiber ring structure proposed by our research group. A schematic diagram of the device is shown below. Figure 2 As shown. Each angular velocity meter includes two Sagnac interferometers, each using one of two double-quadrupole symmetrically wound fiber loops. Since both Sagnac interferometers use the same light source, the relative intensity noise in both interferometers is consistent. The Sagnac phase error φ caused by the relative intensity noise on the two fiber loops is... RIN The consistency is also maintained, and can be effectively suppressed during demodulation. The two fiber rings in this structure employ a dual quadruple-level symmetrical winding scheme; that is, fiber ring A and fiber ring B each use a quadruple-level symmetrical winding scheme, and the fibers at the same position on both fiber rings are tightly wound together. This winding method effectively ensures the consistency of the two fiber rings. The Shupe error caused by temperature changes remains consistent on both fiber rings and can be used as common-mode noise φ. com It is suppressed.

[0013] Fiber optic rings A and B are wound in opposite directions, therefore the phase difference caused by the Sagnac effect on the two rings is opposite. The phase difference on the two rings caused by rotation, relative intensity noise, and ambient noise can be written as:

[0014] φ A =φ s +φ RIN +φ com

[0015] φ B =-φ s +φ RIN +φ com

[0016] The phase φ of the two paths is calculated separately by the demodulation system. A φ B Then, the phases on the two fiber rings are subtracted and averaged:

[0017]

[0018] This allows us to obtain only the Sagnac phase difference φ caused by rotation. s According to Sagnac's principle, the phase difference φ s It is directly proportional to the angular velocity of the object's rotational motion, and thus the angular velocity of the object's rotational motion can be obtained.

[0019] The technical solution of this invention is as follows:

[0020] A downhole six-component seismograph based on a dual-fiber loop structure is characterized by comprising a shell, a three-component accelerometer, and three angular velocity meters;

[0021] Each of the aforementioned angular velocity meters includes a double quadrupole symmetrically wound double fiber optic loop, and the three double fiber optic loops are respectively fixed on three mutually orthogonal surfaces of the housing, for the three angular velocity meters to detect rotational signals in three directions respectively.

[0022] The three-component accelerometer is fixed to the housing and is used to measure translational signals in three directions;

[0023] The angular velocity meter and the three-component accelerometer are both connected to the same external clock source to ensure that the measurement signals of the angular velocity meter and the three-component accelerometer are time-aligned.

[0024] Furthermore, each of the aforementioned angular velocity meters includes two Sagnac interferometers, each Sagnac interferometer using one of the fiber loops in the dual quadruple symmetrical winding double fiber loop; wherein the dual quadruple symmetrical winding double fiber loop includes fiber loop A and fiber loop B, fiber loop A and fiber loop B are respectively quadruple symmetrically wound and share the same light source, and the winding direction of fiber loop A is opposite to the winding direction of fiber loop B.

[0025] Furthermore, the fiber lengths of fiber rings A and B are equal.

[0026] Furthermore, based on the Sagnac phase difference measured by each of the aforementioned angular velocity meters... The angular velocity of the object's rotation is proportional to its rotational velocity, and is used as a rotation signal in one direction; where φ A The phase on fiber ring A caused by rotational, relative intensity noise, and ambient noise, φ B The phase on fiber ring B is caused by rotational, relative intensity noise, and ambient noise.

[0027] Furthermore, φ A =φ s +φ RIN +φ com , φ E =-φ s +φ RIN +φ com ;φ RIN φ is the Sagnac phase error caused by relative intensity noise on the two fiber loops. com The Shupe error caused by temperature changes on the two fiber optic loops is taken as common-mode noise.

[0028] Compared with the prior art, the positive effects of the present invention are as follows:

[0029] This device integrates a three-component accelerometer and a three-component angular velocity meter into a single six-component seismograph, enabling simultaneous measurement of translational and rotational motion signals. The dual fiber optic loops in this device employ a dual four-stage symmetrical winding technique, requiring consistent lengths of the two loops and ensuring that common-mode noise is out of phase with the Sagnac signal, thus suppressing it. Furthermore, the angular velocity meter and the three-component accelerometer share the same clock source, necessitating an external clock for the calculation circuitry to overcome clock synchronization issues caused by the external clock. After obtaining the rotational angular velocity and horizontal acceleration, the phase velocity can be obtained by comparing the two, making it possible to invert the seismic phase velocity using single-point six-component seismograph data, eliminating the need for multi-site data and travel time parameters. Additionally, this device utilizes a common-source Sagnac interferometer structure based on dual fiber optic loops, which effectively suppresses relative intensity noise and significantly improves the sensitivity of the angular velocity meter. The dual fiber optic loop structure also effectively compensates for common-mode noise caused by ambient temperature variations, improving the environmental adaptability of the six-component seismograph during downhole operation and reducing the impact of the downhole environment on the seismograph. This invention makes it possible to manufacture a high-precision, wide-bandwidth, and highly environmentally adaptable six-component seismograph. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the structure of a six-component seismograph.

[0031] Figure 2 This is a schematic diagram of the principle of a Sagnac interferometer based on a dual-fiber ring structure with a common light source. Detailed Implementation

[0032] The present invention will now be described in further detail with reference to the accompanying drawings.

[0033] The structural schematic diagram of the present invention is shown below. Figure 1 As shown, the six-component seismograph has an aluminum alloy casing, with three double quadrupole symmetrically wound fiber optic loops fixed to three mutually perpendicular surfaces, enabling the detection of angular velocities in three different directions. A three-component accelerometer is fixed to the lower left corner of the six-component seismograph, tightly integrated with other components, and can detect acceleration in three different directions.

[0034] The schematic diagram of the present invention is as follows: Figure 2As shown. In this invention, the angular velocity meter employs a common-source Sagnac interferometer based on a dual-fiber ring structure. The relative intensity noise in the light source originates from the optical power fluctuations caused by random phase beats between different frequency components in the broadband light source, and is the most prevalent noise in the Sagnac interferometer. The light sources of the two Sagnac interferometers are split from the same light source, thus ensuring the consistency of the relative intensity noise in the two interferometers. The Shupe error originates from the thermally induced non-reciprocal phase shift caused by the different temperatures of the two beams of light propagating in opposite directions when passing through the same point due to changes in ambient temperature. The downhole environment is complex with large temperature variations, and the seismograph is affected by these temperature changes, resulting in poor environmental adaptability.

[0035] The fiber optic rings used in this invention employ a dual quadruple-level symmetrical winding scheme, meaning that two fiber optic rings each use a quadruple-level symmetrical winding scheme and are tightly wound together. This ensures that the noise generated by the fiber at the same location in the external environment is identical, effectively suppressing common-mode noise. Simultaneously, the two fiber optic rings are oriented in opposite directions, resulting in opposite Sagnac phase differences caused by rotation.

[0036] Two Sagnac interferometers employ in-phase modulation, demodulating their respective signals. Subtracting the two signals eliminates relative intensity noise and common-mode noise caused by environmental variations. This method effectively improves the accuracy of the angular velocity meter, expands its bandwidth, and enhances the stability of the seismograph in downhole environments. It contributes to the development of a high-precision, wide-bandwidth, and highly environmentally adaptable six-component downhole seismograph.

[0037] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A downhole six-component seismograph based on a dual-fiber ring structure, characterized in that, It includes a housing, a three-component accelerometer, and three angular velocity meters; Each of the aforementioned angular velocity meters includes a double quadrupole symmetrically wound double fiber optic loop, and the three double fiber optic loops are respectively fixed on three mutually orthogonal surfaces of the housing, for the three angular velocity meters to detect rotational signals in three directions respectively. The three-component accelerometer is fixed to the housing and is used to measure translational signals in three directions; The angular velocity meter and the three-component accelerometer are both connected to the same external clock source to ensure that the measurement signals of the angular velocity meter and the three-component accelerometer are time-aligned.

2. The downhole six-component seismograph according to claim 1, characterized in that, Each of the aforementioned angular velocity meters includes two Sagnac interferometers, each Sagnac interferometer using one of the fiber loops of the dual quadruple symmetrical winding double fiber loops; wherein the dual quadruple symmetrical winding double fiber loops include fiber loop A and fiber loop B, fiber loop A and fiber loop B are respectively quadruple symmetrically wound and share the same light source, and the winding direction of fiber loop A is opposite to the winding direction of fiber loop B.

3. The downhole six-component seismograph according to claim 2, characterized in that, The fiber lengths of fiber ring A and fiber ring B are equal.

4. The downhole six-component seismograph according to claim 2 or 3, characterized in that, Based on the Sagnac phase difference measured by each of the aforementioned angular velocity meters The angular velocity of the object's rotation is proportional to its rotational velocity, and is used as a rotation signal in one direction; where φ A The phase on fiber ring A caused by rotational, relative intensity noise, and ambient noise, φ B The phase on fiber ring B is caused by rotational, relative intensity noise, and ambient noise.

5. The downhole six-component seismograph according to claim 4, characterized in that, φ A =φ s +φ RIN +φ com , φ B =-φ s +φ RIN +φ com ;φ RIN φ is the Sagnac phase error caused by relative intensity noise on the two fiber loops. com The Shupe error caused by temperature changes on the two fiber optic loops is taken as common-mode noise.

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