CN105652312A - Optical fiber geophone system based on distributed optical fiber acoustic sensing technology - Google Patents

Abstract

The invention discloses an optical fiber detector system based on distributed optical fiber acoustic sensing technology, comprising: a distributed optical fiber acoustic sensing demodulator (1), which is used to emit light pulses , and perform phase demodulation on the reflected Rayleigh scattered light; the transmission optical cable (2) is used to transmit light pulses and generate Rayleigh scattered light. The optical fiber detector array (3) includes a plurality of optical fiber detector units (30), each fiber detector unit is fixed on the transmission optical cable at a certain interval, and is used for detecting weak seismic wave signals. The invention realizes large-scale sensing unit networking through distributed optical fiber acoustic sensing technology, realizes detection of weak seismic wave signals through sound pressure sensitization, and the optical fiber detector system has the characteristics of simple structure, strong networking ability, and low cost.

Description

Optical Fiber Detector System Based on Distributed Optical Fiber Acoustic Sensing Technology

technical field

The invention relates to the technical field of exploration of oil and gas mineral resources, in particular to the field of optical fiber sensing for detecting seismic waves.

Background technique

The geophone is a special sensor used in geological exploration and engineering survey. The performance of the geophone directly determines the quality of the seismic exploration data. With the shortage of oil and gas resources, seismic exploration is developing in the direction of high-resolution, high-precision, and deep exploration, which also puts forward higher requirements for the performance of geophones. Traditional moving coil detectors have small dynamic range, low sensitivity, and poor ability to resist electromagnetic interference. In the downhole vertical seismic profiling method that can obtain higher resolution, the traditional geophone has the disadvantages of bulky volume, complicated operation and low system reliability. Therefore, the performance of the geophone itself has increasingly become the primary technical requirement in various exploration fields such as geophysical exploration. Compared with the traditional moving coil geophone, the fiber optic geophone has the characteristics of small size, light weight, corrosion resistance, anti-electromagnetic interference, long transmission distance and convenient use. As a new type of seismic detection technology, it is widely used in oil and gas mineral resource exploration field has important application value.

In recent years, various types of fiber detector systems have emerged: one is based on fiber gratings or lasers (application number: CN101915940A), which uses fiber gratings or fiber lasers as sensitive units, and is encapsulated by sensitivity enhancement. (such as coating) to form a fiber optic detector, and increase the number of detector units through wavelength division multiplexing and space division multiplexing, so many beam splitting and combining units and connection protection units are required between fiber optic detectors, resulting in the The optical path of the system is complicated, there are too many optical components, the fabrication is difficult, and the cost is high. One is an interferometer-based optical fiber detector system (application number: CN104199086A), which uses a pair of fiber gratings with the same wavelength to form an FP interferometer, and realizes an optical fiber detector array through cascading. This type of fiber optic detector system requires fiber gratings as reflectors. Fiber gratings will degrade in reflectivity under high temperature conditions, which will affect system performance indicators. In addition, with the increase in the number of fiber optic detectors, the number of fiber gratings will inevitably increase, which will lead to signal light Therefore, the number of detectors in this type of optical fiber detector system is limited, and large-scale networking cannot be realized.

Distributed optical fiber sensing technology utilizes the phase signal of detecting Rayleigh backscattered light in the transmission fiber to realize distributed vibration or acoustic sensing. When external vibration or sound acts on a certain position of the transmission fiber, the fiber at this position will feel the effect of external stress or strain, which will cause the fiber to stretch and change the refractive index, which in turn will cause backscattered light during transmission. The phase changes, so the measurement of external vibration or sound is realized by detecting the phase change. The distributed optical fiber acoustic sensing system based on phase generation carrier technology (application number CN201410032610) can detect vibration or acoustic signals at any position of the transmission fiber, but it is difficult to detect weak seismic wave signals due to the poor sensitivity of the transmission fiber.

Contents of the invention

The main purpose of the present invention is to provide an optical fiber detector system based on distributed optical fiber acoustic sensing technology, which has the advantage of a large number of array elements, and has the ability to detect weak seismic wave signals, and has a simple structure and low cost.

In order to achieve the above object, the present invention proposes a fiber optic detector system based on distributed fiber optic acoustic sensing technology, including:

Distributed fiber optic acoustic sensor demodulator, the distributed fiber optic acoustic sensor demodulator is used to emit light pulses and perform phase demodulation on the reflected Rayleigh scattered light;

Transmission cables for transmitting light pulses and generating Rayleigh scattered light.

The optical fiber detector array includes a plurality of optical fiber detector units, each fiber detector unit is fixed on the transmission optical cable at a certain interval, and is used for detecting weak seismic wave signals.

The advantages of the present invention are that large-scale sensing unit networking is realized through distributed optical fiber acoustic sensing technology, weak seismic wave signal detection is realized through sound pressure sensitization, and the optical fiber detector system has simple structure, strong networking capability, low cost low-level features.

Description of drawings

For further illustrating concrete technical content of the present invention, below in conjunction with example and accompanying drawing, the present invention is described in detail, wherein:

Fig. 1 is a schematic diagram of an optical fiber detector system based on distributed optical fiber acoustic sensing technology provided by the present invention.

Fig. 2 is a structural schematic diagram of a cantilever beam optical fiber detector unit in the present invention.

Fig. 3 is a schematic structural view of a mandrel-type optical fiber detector unit in the present invention.

In Fig. 1, 1 is a distributed optical fiber acoustic sensor demodulator, 2 is a transmission optical cable, 3 is a fiber optic detector array, and 30 is a fiber optic detector unit.

In FIG. 2 , 301 is a transmission optical fiber in a transmission optical cable, 302 is a cantilever beam structure, and 303 is a mass block. In FIG. 3 , 301 is a transmission fiber in the transmission cable, 304 is an elastic cylinder, 305 is a mass block, and 306 is a rigid support.

detailed description

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be described in further detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

Please refer to Fig. 1, the present invention provides a kind of optical fiber detector system based on distributed optical fiber acoustic sensing technology, including:

A distributed optical fiber acoustic sensor demodulator 1, the distributed optical fiber acoustic sensor demodulator is used to emit light pulses and perform phase demodulation on reflected Rayleigh scattered light.

A transmission optical cable 2 is used to transmit light pulses and generate reverse Rayleigh scattered light.

A fiber optic detector array 3, the fiber optic detector array is composed of several fiber optic detector units 30 to realize the detection of weak seismic wave signals.

The optical fiber detector unit is used to sensitize the vibration of the transmission optical fiber, and can adopt a cantilever beam type or a mandrel type structure.

In this embodiment, the distributed optical fiber acoustic sensor demodulator is used to emit light pulses and perform phase demodulation on the Rayleigh scattered light of the optical fiber. The distributed optical fiber acoustic sensor demodulator can restore the vibration or acoustic signal at any position of the transmission optical cable and optical fiber detector array, and its spatial resolution is generally between 1m and 10m. 10000 sensing units. The transmission optical cable generally adopts armored optical cable. The transmission optical fiber inside the optical cable can detect external vibration or acoustic signal, but the detection ability is limited, which cannot meet the detection of weak signals. For weak seismic wave signals, it is necessary to sensitize the transmission fiber inside the transmission cable to form a fiber detector unit. The fiber detector units are connected in space to form a fiber detector array. There is no optical device between the detector units and no fusion is required. In order to ensure that there is no crosstalk between the fiber optic detector units, the distance between the fiber optic detector units should be greater than or equal to the spatial resolution of the fiber optic acoustic sensor demodulator.

The optical fiber detector unit based on distributed acoustic sensing technology is an independent sensing unit formed by directly sensitizing a section of transmission optical fiber in the sensing optical cable, without any optical fiber grating, fiber laser, fiber coupler, etc. components, so the structure is simple, easy to manufacture and low cost. According to different types of optical fiber detector units corresponding to different sensitization methods, Fig. 2 is a schematic structural diagram of a cantilever beam optical fiber detector unit, and Fig. 3 is a structural schematic diagram of a mandrel type optical fiber detector unit.

As shown in Figure 2, the cantilever beam type optical fiber detector unit includes a cantilever beam structure 302 and a quality block, the bottom edge of the cantilever beam structure 302 is fixed on the object to be measured, and the mass block 303 is fixed on the suspended top of the cantilever beam structure 302 The cantilever beam type optical fiber detector unit is used to paste a section of transmission optical fiber 301 on the upper surface of the cantilever beam structure 302 (defined as the XY plane), and the mass block 303 of the cantilever beam is used to feel the surface perpendicular to the cantilever beam structure. The external vibration signal in the Z direction (Z direction), when there is vibration in the Z direction, the mass block will cause the deformation of the cantilever beam structure, and then drive the deformation of the optical fiber pasted on the surface of the cantilever beam structure, so as to realize the detection of weak vibration signals (such as detection of seismic waves). The transmission optical fiber can be pasted on the surface of the cantilever beam structure in various shapes, such as straight, S-shaped, etc. The sensitivity of the cantilever beam optical fiber detector unit is adjusted by adjusting the length of the sensing optical fiber pasted on the surface of the cantilever beam structure. The cantilever beam structure is a structure with a certain shape, one end of which is fixed and the other end is suspended. For example, the commonly used shapes are triangles, rectangles, etc. The main structure of the transmission optical cable is composed of sensing optical fiber and protective sleeve. The protective sleeve of the sensing optical cable is stripped to expose the sensing optical fiber, and then the sensing optical fiber is pasted on the cantilever beam structure.

As shown in Figure 3, the mandrel-type optical fiber detector unit includes an elastic cylinder 304, a mass block 305 and a support frame 306; the support frame 306 is fixed on the measured object, and the upper and lower end surfaces of the elastic cylinder 304 are fixed On the support frame 306, the mass block 305 is fixed on the side of the elastic cylinder. The mandrel-type optical fiber detector unit winds and fixes a section of transmission optical fiber on the side of an elastic cylinder formed by casting and curing elastic rubber. When the axial vibration of the elastic cylinder acts on the detector unit, the mass block has a relatively Large mechanical inertia will squeeze or stretch the elastic cylinder to produce deformation, and then drive the optical fiber fixed on the side of the elastic cylinder to deform, realizing the detection of weak vibration signals (such as seismic waves). The sensitivity of the mandrel fiber optic detector unit is adjusted by adjusting the length of the fiber wound on the surface of the elastic cylinder.

The specific embodiments described above have further described the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above descriptions are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (10)

1., based on an optical fiber detector system for distribution type fiber-optic sound sensing technology, comprising:

Distribution type fiber-optic sound sensing demodulator (1), this distribution type fiber-optic sound sensing demodulator is for launching light pulse, and the Rayleigh scattering light of reflection is carried out phase place demodulation;

Transmission optical cable (2), for transmitting light pulse, and produces Rayleigh scattering light.

Optical fiber detector array (3), it comprises multiple optical fiber detector unit (30), and each optical fiber detector unit is fixed on described transmission optical cable according to certain interval, for the detection to slight earthquake ripple signal.

2. a kind of optical fiber detector system based on distribution type fiber-optic sound sensing technology according to claim 1, wherein, the interval of described optical fiber detector unit should be more than or equal to the spatial resolution of described distribution type fiber-optic sound sensing demodulator.

3. a kind of optical fiber detector system based on distribution type fiber-optic sound sensing technology according to claim 1, for the Transmission Fibers in described transmission optical cable being carried out, seismic wave increases quick wherein said optical fiber detector unit (30).

4. a kind of optical fiber detector system based on distribution type fiber-optic sound sensing technology according to claim 1, wherein said optical fiber detector unit (30) adopts beam type or core axis structure.

5. a kind of optical fiber detector system based on distribution type fiber-optic sound sensing technology according to claim 4, wherein said optical fiber detector unit (30) comprises cantilever beam structure part (302) and quality block (303); The base of described cantilever beam structure part (302) is fixed; Wherein, the Transmission Fibers in described transmission optical cable is pasted onto described cantilever beam structure part upper surface, and described quality block 303 is fixed on the upper surface of described cantilevered beam members.

6. a kind of optical fiber detector system based on distribution type fiber-optic sound sensing technology according to claim 5, wherein said quality block is perpendicular to the extraneous vibration signal in cantilever beam structure part upper surface direction for experiencing, and cause cantilever beam structure part deformation, and then drive the Transmission Fibers generation deformation being pasted onto on cantilever beam structure part, it is achieved to the detection of Vibration Signal in Frequency Domain.

7. a kind of optical fiber detector system based on distribution type fiber-optic sound sensing technology according to claim 4, wherein said optical fiber detector unit (30) comprises bracing frame (306), quality block (305) and Elastic Circular cylinder (304), described Elastic Circular cylinder (304) two ends are fixed on bracing frame (306), described quality block (305) is fixed on described Elastic Circular cylinder (304), and the Transmission Fibers in described transmission optical cable is wrapped in described Elastic Circular cylinder (304) side.

8. a kind of optical fiber detector system based on distribution type fiber-optic sound sensing technology according to claim 7, wherein, when acting on described pick-up unit along Elastic Circular cylinder axial vibration, quality block causes the elastic cylinder bodily form to become, and then drive the Transmission Fibers generation deformation being fixed on elastic cylinder body side surface, it is achieved to the detection of Vibration Signal in Frequency Domain.

9. a kind of optical fiber detector system based on distribution type fiber-optic sound sensing technology as claimed in claim 5, wherein, the sensitivity of described beam type optical fiber detector unit regulates by being pasted onto the fiber lengths on cantilever beam structure part surface.

10. a kind of optical fiber detector system based on distribution type fiber-optic sound sensing technology as claimed in claim 7, wherein, the sensitivity of described mandrel formula optical fiber detector unit regulates by being wrapped in the fiber lengths of elastic cylinder body side surface.