CN110749927A - Optical fiber acoustic sensing orthogonal dipole acoustic logging system and measuring method thereof - Google Patents
Optical fiber acoustic sensing orthogonal dipole acoustic logging system and measuring method thereof Download PDFInfo
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- CN110749927A CN110749927A CN201911131975.7A CN201911131975A CN110749927A CN 110749927 A CN110749927 A CN 110749927A CN 201911131975 A CN201911131975 A CN 201911131975A CN 110749927 A CN110749927 A CN 110749927A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
- G01V1/40—Seismology; Seismic or acoustic prospecting or detecting specially adapted for well-logging
- G01V1/42—Seismology; Seismic or acoustic prospecting or detecting specially adapted for well-logging using generators in one well and receivers elsewhere or vice versa
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- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B47/00—Survey of boreholes or wells
- E21B47/12—Means for transmitting measuring-signals or control signals from the well to the surface, or from the surface to the well, e.g. for logging while drilling
- E21B47/14—Means for transmitting measuring-signals or control signals from the well to the surface, or from the surface to the well, e.g. for logging while drilling using acoustic waves
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V2210/00—Details of seismic processing or analysis
- G01V2210/10—Aspects of acoustic signal generation or detection
- G01V2210/14—Signal detection
- G01V2210/142—Receiver location
- G01V2210/1429—Subsurface, e.g. in borehole or below weathering layer or mud line
Abstract
The invention provides an optical fiber acoustic sensing orthogonal dipole acoustic logging system and a measuring method thereof, wherein the optical fiber acoustic sensing orthogonal dipole acoustic logging system comprises an underground optical fiber acoustic sensing orthogonal dipole acoustic logging device, and the underground optical fiber acoustic sensing orthogonal dipole acoustic logging device comprises a cylindrical instrument shell and an optical fiber acoustic dipole sensor; and the lower part of the optical fiber acoustic wave dipole sensor is vertically and sequentially provided with an optical fiber gyroscope, a sound insulator short joint and a dipole sound source generator. The fiber-optic acoustic sensing orthogonal dipole acoustic logging device in the ground wellhead logging truck well is used for descending and ascending the well, and provides a power supply for the fiber-optic acoustic sensing orthogonal dipole acoustic logging device, so that a dipole acoustic source generator is driven to continuously and repeatedly emit dipole transmitting acoustic signals during operation; the ground DAS transmits laser pulses to the optical fiber acoustic wave dipole sensor, and backscattering Rayleigh waves in the optical fiber acoustic wave dipole sensor are collected. The invention can work for a long time at high temperature and realize the function of transmitting data upwards at high speed.
Description
Technical Field
The invention relates to the technical field of geophysical exploration, in particular to an optical fiber acoustic sensing orthogonal dipole acoustic logging system and a measuring method thereof.
Background
The acoustic logging is a logging method for researching a geological profile of a drilled well and judging the well cementation quality by utilizing different acoustic characteristics such as speed, amplitude, frequency change and the like when acoustic waves propagate in different rocks. Sonic logging is a method of logging the properties of a formation in a borehole by studying the speed of sound propagation in the formation. A commonly used acoustic velocity logging tool comprises an acoustic generator (T) and two receivers (R, R)1) The recorded parameter is the time difference (△ t) between the arrival of the sound wave at the two receivers, i.e., the time required for the sound wave to travel in the formation between the two receivers.
A controlled acoustic vibration source is placed in the well, and acoustic waves emitted by the acoustic source cause vibration of surrounding particles, bulk waves, i.e., longitudinal waves and transverse waves, are generated in the formation, and induced interfacial waves, i.e., pseudo-Rayleigh waves and Stoneley waves, are generated at the well wall-drilling fluid interface. These waves are used as carriers of formation information, received by downhole receivers, sent to the surface for recording, and are used for acoustic logging. The receivers and the sound sources are collectively called as a sound system, and the acoustic logging instruments can be divided into a compensated logging instrument (BHC), a long-source-distance acoustic logging instrument (LSS) and an array acoustic logging instrument according to the difference of arrangement and size of the sound system. The speed, amplitude and even frequency of the wave that propagates in the formation in the well changes due to changes in the rock composition, structure, and fluid composition in the pores of the formation. Sonic logging is divided into sonic logging and acoustic amplitude logging. Recording only changes in acoustic velocity is called sonic logging (AC), while recording changes in acoustic amplitude is called acoustic amplitude logging. In the acoustic velocity logging, a short-source acoustic system only records the propagation time difference of longitudinal waves (namely, head waves), a long-source distance acoustic system can record the propagation time difference of various wavetrains such as longitudinal waves, transverse waves, pseudo-Rayleigh waves, Stoneley waves and the like, so the acoustic velocity logging is also called full-wave acoustic logging, and an array acoustic instrument can record the sound velocity of the longitudinal waves, the sound velocity of the full wavetrain and the sound amplitude due to the complex acoustic system.
Sonic logging measures the formation acoustic velocity. The formation acoustic velocity is related to factors such as the lithology, porosity, and pore fluid properties of the formation. According to the propagation speed of the sound wave in the stratum, the porosity and lithology of the stratum, namely the property of pore fluid, can be determined. Sonic velocity logging can be used to classify lithology, determine porosity of oil and gas reservoirs, and to classify gas reservoirs, and can also provide velocity data necessary for seismic exploration.
The acoustic velocity logging is called acoustic velocity logging for short, and records the time required for acoustic wave to pass through 1 m rock stratum, and measures the time difference △ t (reciprocal of longitudinal wave, transverse wave and Stoneley wave velocity) of formation gliding wave (refracted wave).
The dipole array acoustic logging combines monopole technology and dipole technology of common acoustic logging instrument organically, its most advantage is that when the transverse wave speed of stratum is lower than the acoustic speed of fluid in the well, the accurate time difference of longitudinal wave, transverse wave and Stoneley wave and the amplitude and attenuation coefficient of various waveforms on different receivers can be obtained, and the orthogonal (cross) dipole array acoustic logging can provide the size and direction of the anisotropy of transverse wave of stratum, and the above-mentioned result can be comprehensively analyzed, and can assist conventional logging information to effectively evaluate the reservoir. In addition, the method has unique effects in the aspects of calculating rock mechanical parameters, engineering stress parameters and evaluating the stability of the borehole.
The dipole or multipole piezoelectric acoustic transducer is used in the existing underground orthogonal dipole array acoustic logging instrument to receive acoustic (longitudinal wave, transverse wave and Stoneley wave) signals in different directions in a borehole, and the dipole or multipole piezoelectric acoustic transducer and an amplifier, an analog-to-digital conversion and data storage device, an underground data transmission module and the like which are matched with the dipole or multipole piezoelectric acoustic transducer cannot work for a long time in a high-temperature environment (deep well). In addition, because the underground orthogonal dipole array acoustic logging instrument is an electronic instrument at present, the underground data transmission module of the underground orthogonal dipole array acoustic logging instrument cannot solve the bottleneck problem that underground big data are transmitted to a control computer in a logging truck at a wellhead at a high speed in real time at present.
Disclosure of Invention
The invention aims to provide an optical fiber acoustic sensing orthogonal dipole acoustic logging system, which mainly uses an array optical fiber acoustic dipole sensor which is arranged above an underground array dipole acoustic source generator and is wound to a small cylindrical structure by using high-temperature-resistant optical fibers according to a spiral tube shape, replaces a dipole or multipole piezoelectric acoustic transducer which is widely used at present, and receives acoustic signals which are propagated to different directions in a borehole, thereby realizing the aim of measuring the underground orthogonal dipole array acoustic.
The technical scheme of the invention is as follows:
the optical fiber acoustic wave sensing orthogonal dipole acoustic wave logging system comprises an optical fiber acoustic wave sensing orthogonal dipole acoustic wave logging device in a well, a ground wellhead logging truck and a ground DAS modulation and demodulation instrument;
the optical fiber acoustic sensing orthogonal dipole acoustic logging device in the well comprises a cylindrical structure instrument shell and an array type optical fiber acoustic dipole sensor which is wound on a small cylindrical structure by high-temperature resistant optical fibers according to a spiral tube shape and serves as an orthogonal dipole acoustic signal receiving unit in the well; the lower part of the optical fiber acoustic wave dipole sensor is vertically and sequentially provided with an optical fiber gyroscope, a sound insulator short joint and a dipole sound source generator;
the armored photoelectric composite cable extends into the cylindrical structure instrument shell and is connected with the optical fiber sound wave dipole sensor and the dipole sound source generator;
the ground wellhead logging truck is connected with the optical fiber acoustic wave dipole sensor, the optical fiber gyroscope and the dipole acoustic source generator through an armored photoelectric composite cable;
the ground wellhead logging truck controls the well descending and well ascending of the optical fiber acoustic sensing orthogonal dipole acoustic logging device in the well, supplies power to the optical fiber acoustic sensing orthogonal dipole acoustic logging device in the well, and drives a dipole acoustic source generator located in the well to continuously and repeatedly emit dipole acoustic signals during operation;
the ground DAS modulation and demodulation instrument arranged at a wellhead is connected with the optical fiber acoustic wave dipole sensor through an armored photoelectric composite cable, emits laser pulses into the underground optical fiber acoustic wave dipole sensor, and collects phase data of backward scattering Rayleigh waves in the optical fiber acoustic wave dipole sensor.
The fiber acoustic wave dipole sensor is characterized in that a single-mode or multi-mode fiber is wound on a small cylindrical structure according to a certain angle, the winding angle is 20-70 degrees, a protective sleeve is sleeved outside the fiber acoustic wave dipole sensor according to the winding of a coil, the outermost layer of the protective sleeve is a cylindrical structure instrument shell, and the cylindrical structure instrument shell is made of high-strength corrosion-resistant titanium alloy or metal.
Each stage of the optical fiber acoustic wave dipole sensor comprises 4 or 8 optical fiber acoustic wave sensing dipole receivers, the 4 or 8 optical fiber acoustic wave sensing dipole receivers of each stage are symmetrically distributed on a plane, and the optical fiber acoustic wave sensing dipole receivers of each stage record underground acoustic wave data of 4 directions or 8 directions; the fiber-optic acoustic wave dipole sensor has at least an array of fiber-optic acoustic wave sensing dipole receivers of 8 levels or more than 8 levels.
The dipole acoustic source generator comprises transmitting electronic circuits, one or a plurality of monopole acoustic source transmitters, and 2 or 4 or 6 or 8 dipole acoustic source transmitters.
The dipole sound source generator is formed by orthogonally combining a monopole array and a dipole array, wherein the two arrays are completely independent and respectively provided with different sensors; the monopole array comprises one or a plurality of monopole sound sources, 8 or more than 8 optical fiber sound wave receiving sensors, and sound waves emitted by the monopole sound source emitters are all-directional; the dipole array is composed of 2 or 4 or 8 dipole sound sources which are orthogonally arranged pairwise and 8 or more than 8 crossed dipole optical fiber sound wave receiving sensors.
The dipole sound source generator can be an array monopole, dipole or multipole piezoelectric ceramic (crystal), an electric spark seismic source, an electromechanical seismic source, a downhole controllable seismic source and other dipole sound source generators, and an optical fiber sound wave dipole sensor above the dipole sound source generator replaces a dipole or multipole piezoelectric sound wave transducer which is widely used at present. The dipole sound source generator continuously and repeatedly transmits high-power dipole sound wave signals to underground media around the borehole under the action of ground control signals and driving signals, and after the dipole sound wave signals transmitted by the dipole emission source are propagated to wave impedance interfaces around the borehole, according to the total reflection principle: when the incident angle of the acoustic wave satisfies the critical angle condition, the incident acoustic wave will propagate along the borehole wall, generating a slip wave, which can be detected by the receiver. The high-temperature-resistant optical fiber acoustic wave dipole sensor arranged above the underground dipole acoustic source generator can receive gliding wave (refracted wave) acoustic wave signals which are transmitted to different directions in a borehole, so that the aim of underground orthogonal dipole array acoustic wave measurement is fulfilled.
According to Snell's Law (Snell Law), the refracted wave is sin α/sin β ═ V1/V2When β is 90 deg., the refracted wave slides along the interface in the second medium, the critical angle is the incident angle when the sliding wave is generated, and the total reflection wave is the one when the incident angle is greater than the critical angle, the ray will be totally reflected back to the first medium.
When a gliding wave acoustic signal reaches the high-temperature-resistant fiber acoustic wave dipole sensor and acts on the high-temperature-resistant fiber, the fluctuation signal of the gliding wave can cause the high-temperature-resistant fiber in the array type high-temperature-resistant fiber acoustic wave dipole sensor wound according to the shape of the spiral tube to generate strain (stretching or compression), so that the phase of the backward Rayleigh scattering wave in the high-temperature-resistant fiber is changed with the same frequency as the fluctuation signal. The collected phase data of the backward Rayleigh scattered waves are modulated and demodulated through hardware and software in a DAS modulation and demodulation instrument connected with a high-temperature-resistant optical fiber acoustic wave dipole sensor near a ground wellhead, and then the phase change of the backward Rayleigh scattered waves can be converted into a fluctuation signal of the gliding waves. Through further processing and interpretation of the gliding wave signals (data), the acoustic velocity of the medium, the elastic or viscoelastic properties of the medium, and lithology, porosity, permeability, type and saturation of fluids in the pores of the subsurface medium outside the borehole, and the distribution of different fluids in the downhole medium can be understood.
Because the high-temperature-resistant optical fiber acoustic wave dipole sensor arranged in the optical fiber acoustic wave sensing orthogonal dipole acoustic logging device in the well can completely collect the glide wave signals in a high-temperature deep well for a long time, the difficult problem that an underground dipole or multipole piezoelectric acoustic wave transducer, an amplifier, an analog-to-digital conversion and data storage device, an underground data transmission module and the like cannot work at a high temperature for a long time is solved. The high-temperature-resistant fiber acoustic wave dipole sensor positioned in the armored photoelectric composite cable can transmit backward Rayleigh scattering optical signals of optical fibers in the array high-temperature-resistant fiber acoustic wave dipole sensor wound according to the shape of a spiral tube to a ground DAS modulation and demodulation instrument at a high speed, and the bottleneck problem that a large amount of electric signal data acquired by an underground logging instrument are difficult to realize long-distance high-speed upward transmission of a logging cable is solved.
The high-temperature resistant optical fiber is wound according to a spiral shape, the inside of the high-temperature resistant optical fiber is of a cylindrical structure with the diameter of about 1 cm, the cylindrical structure is made of a solid or hollow composite material capable of being curled or is made of a hollow metal pipe capable of being curled, the high-temperature resistant single-mode or multi-mode optical fiber is wound on the cylindrical structure according to a certain angle, the winding angle is 20-70 degrees, and one or more layers of protective sleeves are sleeved on the outer surface of the cylindrical structure on which the high-temperature resistant optical fiber wound according to the spiral shape is wound for protecting the high-temperature resistant optical fiber wound according to the spiral shape on the cylindrical structure from being damaged in a high-pressure environment.
The optical fiber gyroscope, namely an optical fiber inertial navigation directional positioning system is arranged between the high-temperature-resistant optical fiber acoustic wave dipole sensor and the underground array type dipole acoustic source generator. When the optical fiber acoustic sensing orthogonal dipole acoustic logging device in the well works, the optical fiber gyroscope synchronously records the real-time position, speed and attitude information of the underground array dipole acoustic source generator and the high-temperature-resistant optical fiber acoustic sensing dipole sensor. When the optical fiber acoustic sensing orthogonal dipole acoustic logging device in the well is in communication connection with the multi-channel control and data acquisition subsystem in the ground logging truck, the optical fiber acoustic sensing orthogonal dipole acoustic logging device in the well uploads the measured well orthogonal dipole acoustic logging data to the ground control and data acquisition processing subsystem, and the optical fiber gyroscope uploads the measured real-time position, speed and attitude information of the underground array dipole acoustic source generator and the high-temperature-resistant optical fiber acoustic sensor to the ground control and data acquisition processing subsystem. The real-time position, speed and attitude information of the underground array dipole sound source generator and the high-temperature-resistant optical fiber sound wave dipole sensor recorded by the optical fiber gyroscope in real time is used for positioning and orienting the underground orthogonal dipole sound wave data acquired by the system so as to identify the position and specific orientation of a wave impedance interface far away from a borehole, and realize accurate and reliable detection of an underground target far away from the borehole.
The ground DAS modulation and demodulation instrument is a high-performance phase demodulation-based time domain optical reflectometer phi-OTDR technology. And the method adopts the technology of injecting subcarriers, high energy, high extinction ratio, high optical signal-to-noise ratio and high coherent light pulse into the optical fiber to realize high-performance phi-OTDR technology so as to accurately extract phase change information from extremely weak Rayleigh scattering interference signals. In addition, a novel long-period fiber grating filter is introduced into the erbium-doped fiber amplifier to realize a low-noise optical amplification technology, so that the noise of optical signal amplification in a DAS modulation and demodulation instrument system is effectively reduced to improve the optical signal-to-noise ratio. Meanwhile, a multi-frequency, high-coherence and low-noise detection light pulse is adopted to realize a multi-frequency light pulse anti-attenuation technology so as to effectively inhibit the degradation influence of Rayleigh scattering signal random fading on the system performance. And finally, a feedback control circuit is introduced to carry out feedback control, so that the interferometer always works in a stable optical path difference state, and the influence of an external interference signal on the system stability and the signal fidelity is effectively inhibited by utilizing an interferometer active stabilization technology.
The trigger signal for triggering the ground DAS to start synchronous acquisition of the dipole acoustic data in the well while being excited by the underground dipole acoustic source is a signal consistent with the trigger signal of the underground dipole acoustic emission source sent by the optical fiber acoustic sensing orthogonal dipole acoustic logging device on the logging truck, and can be directly sent to the trigger port of the ground DAS in a wired or wireless mode to be used as the trigger signal for starting the DAS to acquire the dipole acoustic data in the well.
The phase data of Rayleigh scattering light reflected from the high-temperature-resistant optical fiber acoustic wave dipole sensor and collected by a ground DAS modulation and demodulation instrument is subjected to modulation and demodulation processing, so that dipole acoustic wave data distributed according to each position of the high-temperature-resistant optical fiber acoustic wave dipole sensor can be obtained. According to the distance from any one wave detection point to each dipole sound source point on the high-temperature-resistant optical fiber sound wave dipole sensor, and data such as the travelling time of a gliding wave which is detected from the wave detection point and is refracted to the wave detection point along a borehole external wave impedance interface, the travelling time of a reflected wave which is reflected to the wave detection point from a ground wave impedance interface and the like, the longitudinal wave speed, the transverse wave speed and the Stoneley wave speed of the underground medium can be obtained through inversion calculation, the speed anisotropies of the longitudinal wave speed and the transverse wave speed in different directions, the attenuation coefficients (characteristics) of the longitudinal wave, the transverse wave and the Stoneley wave which are propagated in the underground medium, the distance, the position and the direction of the wave impedance interface far away from the borehole are obtained, and then a two-dimensional or three-dimensional sound wave speed model of the underground medium and a two-dimensional or three-dimensional elastic or viscoelastic.
The invention also provides a measuring method of the orthogonal dipole acoustic logging device in the well, which comprises the following steps:
s1: placing an optical fiber acoustic sensing orthogonal dipole acoustic logging device in a well, wherein the upper end and the lower end of the optical fiber acoustic sensing orthogonal dipole acoustic logging device are respectively fixed with a centralizer, into the bottom of the well to be logged;
s2: when the optical fiber acoustic sensing orthogonal dipole acoustic logging device in the well is lifted up slowly from the bottom of the well, a dipole acoustic source generator is started to continuously emit acoustic signals, a ground DAS modulation and demodulation instrument near the well head is started, and DAS data of an optical fiber acoustic sensor are continuously acquired;
s3: carrying out modulation and demodulation processing on DAS data acquired by each underground fiber acoustic wave dipole sensor, and converting the DAS data into dipole acoustic wave data with corresponding depth;
s4: calculating the average speed of sound waves between the known dipole sound source generator and each known fiber sound wave dipole sensor according to the travel time of the sound waves reaching each fiber sound wave dipole sensor from the position of the underground dipole sound source generator and the shortest distance between the position of the dipole sound source generator and the known fiber sound wave dipole sensor;
s5: if the sound wave speed of the underground medium is uniform, the sound wave speed of longitudinal waves or transverse waves which are vertically propagated and propagated along the peripheral horizontal direction is the same, and the velocity anisotropy does not exist, if the sound wave speed of the underground medium is non-uniform, the vertical sound wave speed measured at the position of a downhole receiving point is different from the velocity of sound waves which are incident to a borehole from the peripheral horizontal direction or a large angle, and the velocity anisotropy and the distribution characteristics of the sound wave velocity in a three-dimensional space around the borehole are calculated according to the phenomenon that the velocity of the sound waves propagated along different directions in the same medium is not uniform;
s6: for the acoustic wave data collected along each optical fiber acoustic wave dipole sensor position in the underground, the acoustic wave attenuation coefficient or the Q value of the underground medium can be calculated or extracted by a frequency spectrum ratio method, a centroid frequency shift method or a frequency spectrum fitting method according to the characteristics of the amplitude and the frequency spectrum change of the acoustic wave recorded at different optical fiber acoustic wave dipole sensor positions.
The invention has the beneficial effects that:
the invention provides an underground optical fiber acoustic sensing orthogonal dipole acoustic logging device, which uses a plurality of array high-temperature resistant optical fiber dipole acoustic sensors wound according to a spiral tube shape, can completely collect dipole acoustic signals in a high-temperature deep well for a long time, does not need any electronic device and circuit underground, and solves the problem that an underground dipole or multipole piezoelectric acoustic transducer, a high-cost high-temperature resistant amplifier, an analog-to-digital conversion and data storage device, an underground data transmission module and the like which are matched with the underground dipole or multipole piezoelectric acoustic transducer cannot work for a long time at a high temperature.
The array high-temperature-resistant optical fiber acoustic wave dipole sensor wound according to the spiral shape and the high-temperature-resistant optical fiber in the underground armored photoelectric composite cable are the same optical fiber, backward Rayleigh scattering optical signals in the high-temperature-resistant optical fiber wound according to the spiral shape can be transmitted to a distributed optical fiber acoustic wave signal modulation and demodulation instrument (DAS) at the well head at a high speed, and the bottleneck problem that a large amount of electric signal data acquired by an underground optical fiber acoustic wave sensing orthogonal dipole acoustic wave logging device cannot be transmitted upwards at a high speed through a logging cable is solved.
The invention can greatly reduce the manufacturing cost of the equipment for collecting the dipole acoustic data underground, realize the high-efficiency collection of the underground dipole acoustic data with ultrahigh density or ultrahigh spatial resolution, know the distance and the direction of a wave impedance interface far away from a well hole, the medium acoustic velocity at two sides of the wave impedance interface, the elastic parameter characteristic or the viscoelastic parameter characteristic of media at two sides, the lithology, the porosity, the permeability, the type and the saturation of fluid in the pore and the distribution rule of different fluids in the underground medium through processing and analysis, and also can obtain the information of cracks and holes in the stratum far away from the well hole and the stratum structure information of a plurality of meters around the well, further know the direction, the inclination angle and the distribution of the cracks and the holes in the stratum and realize the wide popularization and application of the dipole acoustic logging technology.
Drawings
FIG. 1 is a schematic diagram of the working principle of the fiber acoustic sensing cross-dipole acoustic logging system of the present invention.
FIG. 2 is a schematic diagram of a fiber optic acoustic sensing cross dipole acoustic logging apparatus in a well according to the present invention.
Fig. 3 is a 4-azimuth dipole acoustic wave sensing unit formed by symmetrically arranging 4 high-temperature-resistant optical fiber acoustic wave dipole sensors.
Fig. 4 is an 8-azimuth dipole acoustic wave sensing unit formed by symmetrically arranging 8 high-temperature-resistant optical fiber acoustic wave dipole sensors.
Fig. 5 is a structural diagram of two groups of dipole acoustic wave transmitters arranged orthogonally to each other.
Fig. 6 shows the optical fiber wound spirally on the small cylindrical structure AB and the acoustic wave propagated to the cable perpendicular to the direction of extension of the cable (AB direction) according to the invention arranged in the vertical direction.
Fig. 7 shows the invention with a high temperature resistant fiber wound in a spiral shape on a cylindrical structure AB and with sound waves propagating perpendicular to the direction of extension of the cable (AB direction).
Fig. 8 shows a high temperature resistant optical fiber wound in a spiral shape on a cylindrical structure AB and a sound wave propagated to the cable perpendicular to the direction of extension of the cable (AB direction) according to the present invention, which is spread out in a plane.
Detailed Description
The invention is further described with reference to the following figures and specific examples.
The following description of the embodiments of the present invention is provided to facilitate the understanding of the present invention by those skilled in the art, but it should be understood that the present invention is not limited to the scope of the embodiments, and it will be apparent to those skilled in the art that various changes may be made without departing from the spirit and scope of the invention as defined and defined in the appended claims, and all matters produced by the invention using the inventive concept are protected.
As shown in fig. 1, the optical fiber acoustic sensing quadrature dipole acoustic logging system includes an optical fiber acoustic sensing quadrature dipole acoustic logging device in a well, a ground wellhead logging truck 11, and a ground DAS modulation and demodulation instrument 12;
the optical fiber acoustic sensing orthogonal dipole acoustic logging device in the well comprises a cylindrical structure instrument shell 1 and an array type optical fiber acoustic dipole sensor 2 wound on a small cylindrical structure by high-temperature resistant optical fibers according to a spiral tube shape, wherein the array type optical fiber acoustic dipole sensor is used as an orthogonal dipole acoustic signal receiving unit in the well; the lower part of the optical fiber acoustic wave dipole sensor 2 is vertically and sequentially provided with an optical fiber gyroscope 4, a sound insulator short joint 5 and an underground array type monopole and dipole sound source generator 3; the device also comprises an armored photoelectric composite cable 6, wherein the armored photoelectric composite cable 6 extends into the cylindrical instrument shell 1 and is connected with the optical fiber acoustic wave dipole sensor 2 and the dipole acoustic source generator 3 in the optical fiber acoustic wave sensing orthogonal dipole acoustic logging device in the well. The ground wellhead logging truck 11 is connected with the optical fiber acoustic wave dipole sensor 2, the optical fiber gyroscope 4 and the dipole sound source generator 3 through an armored photoelectric composite cable 6, as shown in figure 2.
The ground wellhead logging truck 11 controls the down-hole and up-hole of the optical fiber acoustic sensing orthogonal dipole acoustic logging device in the well, provides power for the optical fiber acoustic sensing orthogonal dipole acoustic logging device in the well, and drives the dipole acoustic source generator 3 in the well to continuously and repeatedly emit dipole acoustic signals during operation.
A ground DAS modulation and demodulation instrument 12 arranged at a wellhead is connected with an underground optical fiber acoustic wave dipole sensor 2 through an armored photoelectric composite cable 6, emits laser pulses into the optical fiber acoustic wave dipole sensor 2, and collects phase data of backward scattering Rayleigh waves in the optical fiber acoustic wave dipole sensor 2.
The optical fiber acoustic wave dipole sensor 2 is formed by winding a single-mode or multi-mode optical fiber on a small cylindrical structure according to a certain angle, the winding angle is 20-70 degrees, a protective sleeve is sleeved outside the optical fiber acoustic wave dipole sensor 2, and the outermost layer of the protective sleeve is a cylindrical structure instrument shell 1 made of high-strength corrosion-resistant titanium alloy or metal.
Each stage of the underground optical fiber acoustic wave dipole sensor 2 comprises 4 or 8 optical fiber acoustic wave sensing dipole receivers, the 4 or 8 optical fiber acoustic wave sensing dipole receivers of each stage are symmetrically distributed on a plane, and each stage of the optical fiber acoustic wave sensing dipole receivers records underground acoustic wave data of 4 directions or 8 directions. The fiber acoustic wave dipole sensor 2 has at least 8 or more levels of fiber acoustic wave sensing dipole receiver arrays, as shown in fig. 3 and 4.
The dipole sound source generator 3 comprises a transmitting electronic circuit, one or a plurality of monopole sound source transmitters, 2 or 4 or 6 or 8 dipole sound wave transmitters;
the dipole sound source generator 3 is a combination of a monopole array and a dipole array orthogonally arranged in a completely independent configuration, each with a different transducer. The monopole array comprises one or a plurality of monopole sound sources, and 8 or more than 8 fiber-optic sound wave receiving sensors. The acoustic waves emitted by a monopole acoustic source emitter are omnidirectional. As shown in fig. 5, the dipole array is composed of 2 or 4 or 8 dipole sound sources arranged orthogonally (with a 90-degree difference) in pairs and 8 or more than 8 crossed dipole optical fiber sound wave receiving sensors.
During the specific construction, as shown in fig. 1, a special technical process is firstly performed on the tail end of each fiber acoustic wave dipole sensor 2, such as installing an extinction device or tying a knot on the optical fiber, so as to eliminate the strong reflected signal of the optical fiber at the tail end, and then the head end of the fiber acoustic wave dipole sensor 2 connected in series in the fiber acoustic wave sensing orthogonal dipole acoustic logging device in the well is connected to the DAS modem 12 installed on the ground. The fiber-optic acoustic sensing orthogonal dipole acoustic logging device in the well, the upper end and the lower end of which are respectively fixed with a centralizer, is lowered from the wellhead to the bottom of the well to be logged through an armored photoelectric composite cable 6; when the optical fiber acoustic sensing orthogonal dipole acoustic logging device in the well is lifted up slowly from the bottom of the well, the dipole acoustic source generator 3 is started to continuously emit dipole acoustic signals, the ground DAS modulation and demodulation instrument 12 synchronously starts to record direct acoustic waves, refracted acoustic waves, reflected acoustic waves and surface wave and multiple-order wave signals which are transmitted from the medium around the well hole to the inside of the well hole and received by the optical fiber acoustic sensing dipole acoustic dipole sensor 2 according to a trigger signal from the optical fiber acoustic sensing orthogonal dipole acoustic logging device in the well, and the optical fiber gyroscope 4 records the real-time position, speed and attitude information of the dipole acoustic source generator 3 and the optical fiber acoustic sensing orthogonal dipole acoustic logging device in the well in real time; and simultaneously starting a winch on a wellhead ground logging truck 11, slowly lifting the fiber acoustic wave sensing orthogonal dipole acoustic wave logging device in the well upwards through the armored photoelectric composite cable 6, continuously acquiring dipole acoustic wave signals in the well by the fiber acoustic wave sensing orthogonal dipole acoustic wave logging device in the well, modulating and demodulating DAS data acquired by each fiber acoustic wave dipole sensor 2, and converting the DAS data into dipole acoustic wave data with corresponding depth. After the pre-designed well section needing to be measured of the optical fiber acoustic sensing orthogonal dipole acoustic logging device in the well is finished, the dipole acoustic source generator 3 and the ground DAS modulation and demodulation instrument 12 are stopped to work, and the optical fiber acoustic sensing orthogonal dipole acoustic logging device in the well is lifted out of the well head.
Calculating the average speed of the sound waves (longitudinal waves, transverse waves and Stoneley waves) from the known dipole sound source generator 3 to each known fiber sound wave dipole sensor 2 according to the travel time of the sound waves (longitudinal waves, transverse waves and Stoneley waves) from the position of the dipole sound source generator 3 to each fiber sound wave dipole sensor 2 and the shortest distance from the position of the dipole sound source generator 3 to the known fiber sound wave dipole sensor 2;
if the sound wave speed of the underground medium is uniform, the sound wave speed of longitudinal waves or transverse waves which are vertically propagated and propagated along the peripheral horizontal direction is the same, and the velocity anisotropy does not exist, if the sound wave speed of the underground medium is non-uniform, the vertical sound wave speed measured at the position of a downhole receiving point is different from the velocity of sound waves which are incident to a borehole from the peripheral horizontal direction or a large angle, and the velocity anisotropy and the distribution characteristics of the sound wave velocity in a three-dimensional space around the borehole are calculated according to the phenomenon that the velocity of the sound waves propagated along different directions in the same medium is not uniform;
for the acoustic data collected along each fiber acoustic wave dipole sensor 2 position in the well, the acoustic attenuation coefficient or the Q value of the underground medium can be calculated or extracted by using a frequency spectrum ratio method, a centroid frequency shift method or a frequency spectrum fitting method according to the characteristics of the amplitude and the frequency spectrum change of the dipole acoustic wave recorded at different fiber acoustic wave dipole sensors 2 positions.
The well dipole acoustic signal receiving unit of the embodiment is 4 or 8 symmetrically-arranged optical fiber acoustic wave dipole sensors 2 arranged above the underground array dipole acoustic source generator.
More specifically, the main control device may be a computer-controlled ground DAS modem 12, which controls the acquisition and storage of all (DAS) downhole dipole acoustic data in real time, i.e., the data acquisition device is connected to the main control device, and the acquisition and storage of (DAS) downhole dipole acoustic data are completed by controlling the data acquisition device by the main control device. The sensing of the down-hole dipole acoustic wave signals is realized by 4 or 8 symmetrically arranged optical fiber acoustic wave dipole sensors 2 which are arranged above a down-hole array dipole acoustic source generator, and the system can directly measure the two-dimensional or three-dimensional acoustic wave speed of the down-hole medium and calculate the two-dimensional or three-dimensional elasticity or viscoelasticity parameters of the down-hole medium (stratum or rock stratum).
The dipole sound source generator 3 can be an array monopole, dipole or multipole piezoelectric ceramic (crystal), an electric spark seismic source, an electromechanical seismic source, a downhole controllable seismic source and other dipole sound source generators;
4 or 8 symmetrically distributed optical fiber sound wave dipole sensors 2 are arranged above the underground dipole sound source generator 3 and are used for sensing direct sound waves, refracted sound waves, reflected sound waves, surface waves and multiple signals excited by the underground array dipole sound source generator;
the optical fiber gyroscope 4 arranged in the middle of the optical fiber acoustic sensing orthogonal dipole acoustic logging device in the well records the real-time position, speed and attitude information of the underground dipole acoustic source generator 3 and each optical fiber acoustic dipole sensor 2 when acquiring dipole acoustic data in the well;
a ground DAS (data acquisition System) modulation and demodulation instrument 12 connected to the head end of an underground fiber acoustic wave dipole sensor 2 on the ground of a work area receives phase change information of backward Rayleigh scattered waves of each point on an optical fiber caused by wave propagation of acoustic waves in the fiber acoustic wave dipole sensor 2, converts the received phase change information of the backward Rayleigh scattered waves of the optical fiber into actual fluctuation signals of dipole acoustic waves through a modulation and demodulation circuit and data processing software in the instrument, converts the analog fluctuation signals into digital fluctuation signals through an analog-to-digital conversion circuit, and stores the digital fluctuation signals into a computer for subsequent data processing work.
As shown in FIG. 1, in the surface well head logging truck 11 for controlling and driving the fiber acoustic sensing cross dipole acoustic logging device, acoustic waves emitted by the downhole dipole acoustic source generator 3 into the medium around the borehole are sensed by the downhole fiber acoustic dipole sensor 2. Due to the presence of the wave impedance interface 10 remote from the borehole, the direct acoustic waves 7 propagating from the borehole, after encountering the wave impedance interface 10, will reflect from the wave impedance interface 10 back into the borehole at the same angle of reflection as the angle of incidence according to fresnel's law. The reflected acoustic waves 8 reflected back into the borehole are sensed by the fiber optic acoustic wave dipole sensor 2. When the fiber acoustic wave dipole sensor 2 senses a direct acoustic wave 7, a reflected acoustic wave 8 and a refracted (gliding) acoustic wave 9 propagating in a medium around a well, each point (each position) on the fiber acoustic wave dipole sensor 2 generates strain (stretching or compressing) with the same frequency along with the propagation of acoustic wave, the strain causes the phase of a backward rayleigh scattered wave of each point (each position) in the fiber acoustic wave dipole sensor 2 to change correspondingly, the ground DAS modulation and demodulation instrument 12 can detect the change of the phase, the received phase change information of the backward scattered rayleigh wave of each detection point (each position) in the fiber acoustic wave dipole sensor 2 is converted into an actual fluctuation signal of the acoustic wave through a modulation and demodulation circuit and data processing software in the instrument, and the analog fluctuation signal is converted into a digital fluctuation signal in the DAS instrument through an analog-to-digital conversion circuit, the digital wobble signal is then stored in a computer for subsequent acoustic data processing.
Fig. 6 is a schematic view of the fiber-optic acoustic dipole sensor 2 placed in a vertical direction, the high temperature resistant fiber 20 is wound on the cylindrical structural member according to a certain angle α, the composite material or steel sheath for protecting the fiber optic cable is added, and the outermost layer is a wear-resistant and pressure-resistant armor woven by non-metal or metal materials, and fig. 7 is a perspective view of the fiber-optic acoustic dipole sensor 2 placed in a vertical direction.
FIG. 8 is a schematic diagram of the fiber optic acoustic wave dipole sensor 2 extending in the transverse direction AB along the cylindrical structure 21. the high temperature resistant optical fiber 20 wound in a spiral shape at a certain angle α on the cylindrical structure 21 is expanded in the transverse direction AB to become a straight optical fiber forming an angle α with the end expansion line AA or BB of the cylindrical structure 21. if a vertical optical fiber is arranged in a well, when the reflected acoustic wave 8 propagating back into the well hole in the horizontal direction reaches the straight optical fiber arranged in the well hole, the fluctuation propagated in the horizontal direction cannot cause the strain of the straight optical fiber in the vertical extending direction, and the phase of the backward Rayleigh scattered wave at each point (each position) in the optical fiber is changed correspondingly, so that the horizontal acoustic wave signal vertically incident to the straight optical fiber cannot be detected by the ground modem 122The relationship (2) of (c). I.e. when the direction of wave propagation of the acoustic wave is parallel to the direction in which the optical fiber extends (theta 0 deg.), cos theta2When the sensitivity of the straight fiber to the wave signal (the straight wave propagating vertically upward) reaches a maximum value 1; i.e. when the direction of wave propagation of the acoustic wave is perpendicular to the direction in which the optical fiber extends (theta 90 deg.), cos theta2When the sensitivity of the straight optical fiber to the wave signal (horizontal reflection wave) perpendicular to the extending direction of the optical fiber reaches a minimum value of 0, the straight optical fiber cannot detect the wave signal perpendicular to the optical fiberThe direction of propagation of the wave signal is extended.
After the wave signal propagated perpendicular to the fiber acoustic wave dipole sensor 2 in fig. 6, 7 and 8 reaches the fiber acoustic wave dipole sensor 2, because the incident angle between the high temperature resistant optical fiber 20 on the fiber acoustic wave dipole sensor 2 and the wave signal is not 90 degrees but α degrees, the fiber acoustic wave dipole sensor 2 can detect the direct acoustic wave propagated vertically upwards and the reflected acoustic wave 8 propagated horizontally or at a large incident angle, so that the fiber acoustic wave dipole sensor 2 arranged underground can detect the full wave field signals of the acoustic wave propagated to the fiber acoustic wave dipole sensor 2, including the direct acoustic wave 7, the refracted acoustic wave 9, the reflected acoustic wave 8, the surface wave and the multiple waves, and thus the invention can acquire the dipole acoustic wave data in the well.
After dipole acoustic data acquisition of the optical fiber acoustic sensing orthogonal dipole acoustic logging device in the well is finished, firstly, dipole acoustic data acquired at different depth positions in the well are processed, and according to the travel time of direct waves from each acoustic source point, namely a dipole acoustic source generator 3 to each fluctuation signal detection point on the optical fiber acoustic dipole sensor 2 and the distance from the acoustic source point to each known detection point, the average speed of acoustic waves from the acoustic source point to each known detection point can be calculated very accurately and easily. If the data processing personnel picks up the travel time of the direct longitudinal wave, the average velocity of the longitudinal wave is calculated. If the travel time of the direct shear wave is picked up, the average velocity of the shear wave is calculated. If the travel time of the direct Stoneley wave is picked up, the average speed of the Stoneley wave is calculated.
If the acoustic velocity of the surrounding medium downhole is uniform, then the velocity of the longitudinal or transverse wave propagating vertically upward and horizontally across the well profile will be the same, with no velocity anisotropy; if the acoustic velocity of the subsurface medium is non-uniform, then the vertical acoustic velocity measured at the downhole pickup will be different from the velocity of the acoustic waves incident horizontally or near horizontally or at large angles; according to the phenomenon that the speeds of the sound waves propagating in the same medium along different directions are inconsistent, the anisotropy of the vertical speed and the horizontal speed of the sound wave speed along the two-dimensional medium passing through the well section is calculated;
if the sound wave velocity of the underground medium is uniform, the sound wave velocity of longitudinal waves or transverse waves which are vertically propagated and propagated along the peripheral horizontal direction is the same, and the velocity anisotropy does not exist, if the sound wave velocity of the underground medium is non-uniform, the vertical sound wave velocity measured at the position of a downhole receiving point is different from the velocity of sound waves which are incident along the horizontal direction or a large angle, and the velocity anisotropy and the distribution characteristics of the sound wave velocity in the three-dimensional space around the borehole are calculated according to the phenomenon that the velocities of the sound waves which are propagated along different directions in the same medium are not uniform;
for two-dimensional dipole acoustic data acquired at different demodulator probes along a two-dimensional cross-well profile or three-dimensional dipole acoustic data acquired in a well, the acoustic attenuation coefficient or Q value of the underground medium can be calculated or extracted by using a frequency spectrum ratio method, a centroid frequency shift method or a frequency spectrum fitting method according to the characteristics of the amplitude and the frequency spectrum change of the dipole acoustic recorded at different demodulator probes.
In the implementation of the embodiment, the fiber acoustic wave dipole sensor 2 arranged at the upper part of the fiber acoustic wave sensing orthogonal dipole acoustic logging device in the well is used for directly measuring the two-dimensional or three-dimensional acoustic wave velocity of the medium around the well and calculating the elasticity or viscoelastic parameters of the underground medium (stratum or rock stratum), so that a two-dimensional or three-dimensional acoustic wave velocity model of the underground medium and a two-dimensional or three-dimensional elasticity or viscoelastic parameter model of the underground medium can be accurately established, and the two-dimensional or three-dimensional acoustic wave velocity model and the two-dimensional or three-dimensional elasticity or viscoelastic parameter model are used for carrying out data processing and imaging on dipole acoustic wave data in the well, such as an isotropic wave equation or reverse time depth migration, an anisotropic wave equation. Utilize real-time position, speed and the attitude information of the dipole sound source generator 3 of the real-time recording of fiber optic gyroscope 4 and fiber optic sound wave dipole sensor 2, just can accurate definite specific position and the distance from the well bore of the wave impedance interface of keeping away from the well bore when the skew formation of image, thereby really realize keeping away from the accurate detection of the geological target of well bore in the pit, and can analyze and obtain the crack in keeping away from the well bore stratum, hole information, can also obtain the stratum structure information of several meters to tens of meters in well week, and then know the crack in the stratum, hole position, inclination and distribution.
Claims (6)
1. The optical fiber acoustic sensing orthogonal dipole acoustic logging system is characterized by comprising an optical fiber acoustic sensing orthogonal dipole acoustic logging device in a well, a ground wellhead logging truck (11) and a ground DAS modulation and demodulation instrument (12);
the optical fiber acoustic sensing orthogonal dipole acoustic logging device in the well comprises a cylindrical structure instrument shell (1) and an array type optical fiber acoustic dipole sensor (2) which is wound on a small cylindrical structure by high-temperature resistant optical fibers according to a spiral tube shape and serves as an orthogonal dipole acoustic signal receiving unit in the well; the lower part of the optical fiber acoustic wave dipole sensor (2) is vertically and sequentially provided with an optical fiber gyroscope (4), a sound insulator short joint (5) and a dipole sound source generator (3);
the device also comprises an armored photoelectric composite cable (6), wherein the armored photoelectric composite cable (6) extends into the cylindrical structure instrument shell (1) and is connected with the optical fiber sound wave dipole sensor (2) and the dipole sound source generator (3);
the ground wellhead logging truck (11) is connected with the optical fiber acoustic wave dipole sensor (2), the optical fiber gyroscope (4) and the dipole sound source generator (3) through an armored photoelectric composite cable (6);
the ground wellhead logging truck (11) controls the downhole and the well-raising of the optical fiber acoustic sensing orthogonal dipole acoustic logging device in the well, provides power for the optical fiber acoustic sensing orthogonal dipole acoustic logging device in the well, and drives a dipole acoustic source generator (3) located in the well to continuously and repeatedly emit dipole acoustic signals during operation;
a ground DAS modulation and demodulation instrument (12) arranged at a wellhead is connected with the optical fiber acoustic wave dipole sensor (2) through an armored photoelectric composite cable (6), laser pulses are emitted into the underground optical fiber acoustic wave dipole sensor (2), and phase data of backscattered Rayleigh waves in the optical fiber acoustic wave dipole sensor (2) are collected.
2. The fiber acoustic sensing quadrature dipole acoustic logging system according to claim 1, wherein the fiber acoustic sensing quadrature dipole sensor (2) is formed by winding a single-mode or multi-mode fiber on a small cylindrical structure at an angle of 20 to 70 degrees, winding the fiber in a coil shape, and sleeving a protective sleeve on the fiber acoustic sensing quadrature dipole acoustic logging system, wherein the outermost layer of the protective sleeve is a cylindrical structure instrument housing (1), and the cylindrical structure instrument housing (1) is made of a high-strength corrosion-resistant titanium alloy or metal material.
3. The fiber acoustic sensing quadrature dipole acoustic logging system according to claim 1, wherein the fiber acoustic sensing dipole sensor (2) comprises 4 or 8 fiber acoustic sensing dipole receivers per stage, the 4 or 8 fiber acoustic sensing dipole receivers per stage are symmetrically arranged on a plane, and each stage of the fiber acoustic sensing dipole receivers records downhole acoustic data of 4 or 8 directions; the fiber acoustic wave dipole sensor (2) is provided with at least 8 or more than 8 fiber acoustic wave sensing dipole receiver arrays.
4. The fiber optic acoustic sensing quadrature dipole acoustic logging system of claim 1, wherein the dipole acoustic source generator (3) comprises transmitting electronics, one or several monopole acoustic source transmitters, 2 or 4 or 6 or 8 dipole acoustic transmitters.
5. The fiber optic acoustic sensing quadrature dipole acoustic logging system of claim 1, wherein the dipole acoustic source generator (3) is an orthogonal combination of a monopole array and a dipole array, both arrays being completely independent in configuration, each with a different sensor; the monopole array comprises one or a plurality of monopole sound sources, 8 or more than 8 fiber-optic sound wave dipole receiving sensors, and sound waves emitted by monopole sound source emitters are all-directional; the dipole array is composed of 2 or 4 or 8 dipole sound sources which are orthogonally arranged pairwise and 8 or more than 8 crossed dipole optical fiber sound wave receiving sensors.
6. A measurement method for a fiber optic acoustic sensing quadrature dipole acoustic logging system as claimed in any of claims 1 to 5, comprising the steps of:
s1: placing an optical fiber acoustic sensing orthogonal dipole acoustic logging device in a well, wherein the upper end and the lower end of the optical fiber acoustic sensing orthogonal dipole acoustic logging device are respectively fixed with a centralizer, into the bottom of the well to be logged;
s2: when the optical fiber acoustic sensing orthogonal dipole acoustic logging device in the well is lifted up slowly from the bottom of the well, a dipole acoustic source generator (3) is started to continuously emit acoustic signals, a ground DAS modulation and demodulation instrument (12) near the well head is started, and DAS data of an optical fiber acoustic sensing dipole sensor (2) are continuously collected;
s3: the DAS data collected by each underground fiber acoustic wave dipole sensor (2) are subjected to modulation and demodulation processing, and are converted into dipole acoustic wave data with corresponding depths;
s4: calculating the average speed of sound waves between the known dipole sound source generator (3) and each known fiber sound wave dipole sensor (2) according to the travel time of the sound waves reaching each fiber sound wave dipole sensor (2) from the position of the underground dipole sound source generator (3) and the shortest distance between the position of the dipole sound source generator (3) and the known fiber sound wave dipole sensor (2);
s5: if the sound wave speed of the underground medium is uniform, the sound wave speed of longitudinal waves or transverse waves which are vertically propagated and propagated along the peripheral horizontal direction is the same, and the velocity anisotropy does not exist, if the sound wave speed of the underground medium is non-uniform, the vertical sound wave speed measured at the position of a downhole receiving point is different from the velocity of sound waves which are incident to a borehole from the peripheral horizontal direction or a large angle, and the velocity anisotropy and the distribution characteristics of the sound wave velocity in a three-dimensional space around the borehole are calculated according to the phenomenon that the velocity of the sound waves propagated along different directions in the same medium is not uniform;
s6: for sound wave data collected along each optical fiber sound wave dipole sensor (2) position in the underground, the sound wave attenuation coefficient or the Q value of the underground medium can be calculated or extracted by a frequency spectrum ratio method, a centroid frequency shift method or a frequency spectrum fitting method according to the characteristics of the amplitude and the frequency spectrum change of the sound wave recorded at different optical fiber sound wave dipole sensors (2).
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