阅读说明：本技术 分布式光纤地震数据采集系统及其数据收集转换方法 (Distributed optical fiber seismic data acquisition system and data collection and conversion method thereof ) 是由 余刚 苟量 梁兼栋 吴俊军 王熙明 夏淑君 安树杰 冉曾令 肖梦雄 于 2021-09-13 设计创作，主要内容包括：本发明提出分布式光纤地震数据采集系统及其数据收集转换方法,包括对井下或地面光纤采集的光纤质点位移数据进行对时间的微分处理,将其转换成与速度检波器记录的地震数据量纲相同的DAS地震数据,然后对检波器记录的地震数据和微分处理后的DAS地震数据做离散傅里叶变换(DFT),把离散傅里叶变换后的两种数据的振幅谱进行对比,并在全频段的振幅谱上求取每个离散角频率ω对应的检波器记录的地震数据振幅谱和转换后的DAS地震数据振幅谱之间的比值ΔA-(G/F)(ω),在DAS地震数据各频点对应的系数乘上ΔA-(G/F)(ω),最后对进行过振幅谱补偿处理的DAS地震数据的校正振幅谱做离散傅里叶逆变换,即可得到在同一个接收位置与检波器记录的地震数据完全一样的DAS地震数据。(The invention provides a distributed optical fiber seismic data acquisition system and a data collection and conversion method thereof, which comprises the steps of carrying out time differential processing on optical fiber particle displacement data acquired by underground or ground optical fibers, converting the optical fiber particle displacement data into DAS seismic data with the same dimension as the seismic data recorded by a velocity detector, then carrying out Discrete Fourier Transform (DFT) on the seismic data recorded by the detector and the DAS seismic data after the differential processing, comparing amplitude spectrums of two kinds of data after the discrete Fourier transform, and solving the ratio delta A between the seismic data amplitude spectrum recorded by the detector corresponding to each discrete angular frequency omega and the DAS seismic data amplitude spectrum after the conversion on the amplitude spectrum of a full frequency band G/F (ω) multiplying the coefficient corresponding to each frequency point of the DAS seismic data by Δ A G/F (omega) where the amplitude spectrum compensation is finally performedAnd performing inverse discrete Fourier transform on the corrected amplitude spectrum of the DAS seismic data to obtain DAS seismic data which are identical to the seismic data recorded by the detector at the same receiving position.)

1. The distributed optical fiber seismic data acquisition system is characterized by comprising an armored optical cable (2) arranged on the ground or in a well, a plurality of detectors (5) arranged on the ground or in the well, a ground seismic source (6) and a modulation and demodulation instrument (7);

the detectors (5) are embedded at equal intervals along the measuring line of the armored optical cable (2);

a high-sensitivity hydrogen loss-resistant single-mode optical fiber is arranged in the armored optical cable (2); the modulation and demodulation instrument (7) is connected with the single-mode optical fiber in the armored optical cable (2); the tail end of the single-mode fiber is provided with a deluster (4);

the ground seismic sources (6) are distributed point by point at equal intervals according to a two-dimensional seismic source excitation line or a three-dimensional seismic source excitation net, and the intervals of the ground seismic sources (6) are 6.25 meters, or 12.5 meters, or 25 meters, or 50 meters;

when the underground distributed optical fiber seismic data acquisition system is used, the underground distributed optical fiber seismic data acquisition system further comprises metal sleeves (1), a metal clip (3) is installed at a coupling of each metal sleeve (1), and an underground armored optical cable (2) is fixed on the outer side of each metal sleeve (1); a downhole geophone (5) is arranged in the metal casing (1);

when the system is used as a ground distributed optical fiber seismic data acquisition system, the system comprises a shallow trench excavated along a survey line, and an armored optical cable (2) is buried in the shallow trench; the detectors (5) are distributed on the ground; the spacing of the detectors (5) is 3.125 meters, or 6.25 meters, or 12.5 meters, or 25 meters.

2. A distributed fibre optic seismic data acquisition system according to claim 1, wherein the surface seismic source (6) is one of an explosive source or a vibroseis source or an air gun source or a hammer source or an electric spark source.

3. The data collection and conversion method for the distributed optical fiber seismic data acquisition system according to claim 1 or 2, wherein when the system is used as a downhole distributed optical fiber seismic data acquisition system: the method comprises the following steps:

(a) installing an underground distributed optical fiber seismic data acquisition system;

synchronously and slowly putting the metal sleeve (1) and the armored optical cable (2) into a drilled well hole;

the metal clip (3) is arranged at the joint of two metal casing pipes (1) at a wellhead, and the armored optical cable (2) is fixed and protected from rotating and moving and/or being damaged in the casing pipe descending process;

pumping cement slurry from the well bottom by using a high-pressure pump truck, returning the cement slurry to the well head from the well bottom along an annular area between the outer wall of the metal casing (1) and the drilled hole, and permanently fixing the metal casing (1), the armored optical cable (2) and formation rock together after the cement slurry is solidified;

connecting the single-mode optical fiber in the armored optical cable (2) to the DAS signal input end of a modulation and demodulation instrument (7) at a wellhead;

(b) exciting seismic source signals of a ground seismic source (6) point by point, measuring a particle displacement signal along an optical fiber in an underground armored optical cable (2) caused by seismic waves excited by the ground seismic source (6) underground by a modulation and demodulation instrument (7), and synchronously acquiring the seismic signals excited by the ground seismic source (6) by an underground detector (5);

(c) carrying out time differential processing on the particle displacement signals along the optical fiber measured by the modulation and demodulation instrument (7), and converting the displacement signals along the optical fiber into seismic data with the same dimension as the seismic data acquired by the detector (5);

when the underground distributed optical fiber seismic data acquisition system is used, the underground distributed optical fiber seismic data processed in the step (c) and the data measured by the underground detector (5) are well seismic data;

(d) discretely sampled seismic data f recorded by downhole geophones (5)_G(t), t ═ 0, 1.., N-1, do the discrete fourier transform:

wherein, f in the formula_G(t) time domain gather seismic data recorded by downhole geophones (5), F_G(ω) is a discrete fourier transform of the seismic data recorded by the downhole detector (5), ω ═ 0, 1.., N-1;

(e) DAS seismic data f after time differential processing_F(t) performing discrete Fourier transform:

wherein, f in the formula_F(t) DAS time domain gather seismic data recorded by an underground armored optical cable (2) and subjected to differential processing, F_F(omega) is the discrete Fourier transform of DAS time domain gather seismic data recorded by the underground armored optical cable (2) and subjected to differential processing, wherein omega is 0,1, the.

(f) Amplitude spectrum | F of two kinds of data after discrete Fourier transform_G(ω) | and | F_F(omega) | is compared, and the seismic data amplitude spectrum | F recorded by the underground detector (5) corresponding to each discrete angular frequency omega is obtained on the amplitude spectrum of the full frequency band_G(ω) I and the converted DAS seismic data amplitude spectrum | F_FThe ratio between (ω) | Δ A_G/F(ω):

ΔA_G/F(ω)＝|F_G(ω)|/|F_F(ω)|

(g) The coefficient corresponding to each discrete angular frequency point (omega) of DAS seismic data recorded by an underground armored optical cable (2) and subjected to differential processing is multiplied by delta A_G/F(ω)：

|F_FG(ω)|＝ΔA_G/F(ω)|F_F(ω)|

Wherein, | F_FG(omega) is a DAS frequency domain coefficient of which the amplitude is corrected to the full frequency band corresponding to the seismic data amplitude spectrum of the underground detector, wherein omega is 0,1, a.

(h) And (3) performing inverse discrete Fourier transform on the amplitude spectrum of the DAS time domain gather seismic data after amplitude correction:

wherein f is_FG(t) DAS time domain gather seismic data after amplitude correction to the full frequency band corresponding to the borehole seismic data amplitude spectrum of the downhole detector (5), where t is 0, 1.

(i) And (c) converting the data and processing flow from the step (c) to the step (h) to convert the downhole direct downward wave (81) and the upward reflected wave (91) collected by the downhole armored optical cable (2) into the seismic wave data which are the same as the downhole direct downward wave (81) and the upward reflected wave (91) collected by the downhole detector (5).

4. The data collection and conversion method of the distributed optical fiber seismic data acquisition system according to claim 1 or 2, when used as a ground distributed optical fiber seismic data acquisition system, comprising the steps of:

(a) installing a ground distributed optical fiber seismic data acquisition system;

excavating a shallow trench on the ground along a designed two-dimensional measuring line or three-dimensional measuring net, burying the armored optical cable (2) into the shallow trench, and backfilling the shallow trench for compaction; burying detectors (5) at equal intervals on the ground along the measuring line in which the armored optical cable (2) is buried;

(b) the method comprises the steps that a ground seismic source (6) signal is excited point by point, a modulation and demodulation instrument (7) measures displacement signals along an optical fiber in an armored optical cable (2) caused by seismic waves excited by the ground seismic source (6) below the ground, and a geophone (5) distributed on the ground synchronously acquires seismic signals excited by the ground seismic source (6);

(c) carrying out differential processing on time on displacement signals along the optical fiber measured by a modulation and demodulation instrument (7), and converting the displacement signals along the optical fiber into seismic data with the same dimension as that of seismic data acquired by a ground detector (5);

when the system is used as a ground distributed optical fiber seismic data acquisition system, the ground distributed optical fiber seismic data processed in the step (c) and data measured by the ground geophone (5) are ground seismic data;

(d) discretely sampled seismic data f recorded by geophones (5) at the ground_G(t), t ═ 0, 1.., N-1, do the discrete fourier transform:

wherein, f in the formula_G(t) time domain gather seismic data recorded by geophones (5) at the ground, F_G(ω) is a discrete fourier transform of the seismic data recorded by the geophone (5) at the ground, ω -0, 1.., N-1;

(e) DAS seismic data f after time differential processing_F(t) performing discrete Fourier transform:

wherein, f in the formula_F(t) DAS time domain gather seismic data recorded by the armored optical cable (2) on the ground and subjected to differential processing, F_F(omega) is the dispersion of DAS time domain channel set seismic data recorded by the armored optical cable (2) on the ground and subjected to differential processingA fourier transform, ω ═ 0, 1.., N-1;

(f) amplitude spectrum | F of two kinds of data after discrete Fourier transform_G(ω) | and | F_F(omega) | is compared, and the seismic data amplitude spectrum | F recorded by the ground detector (5) corresponding to each discrete angular frequency omega is obtained on the amplitude spectrum of the full frequency band_G(ω) | and the converted DAS seismic data amplitude spectrum | F_FThe ratio between (ω) | Δ A_G/F(ω):

ΔA_G/F(ω)＝|F_G(ω)|/|F_F(ω)|

(g) The coefficient corresponding to each discrete angular frequency point (omega) of DAS seismic data recorded by an underground armored optical cable (2) and subjected to differential processing is multiplied by delta A_G/F(ω)：

|F_FG(ω)|＝ΔA_G/F(ω)|F_F(ω)|

Wherein, | F_FG(omega) | is a DAS frequency domain coefficient after amplitude correction is carried out on the amplitude spectrum of the seismic data of the detector corresponding to the ground on the full frequency band, and omega is 0, 1., N-1;

(h) and (3) performing inverse discrete Fourier transform on the amplitude spectrum of the DAS time domain gather seismic data after amplitude correction:

wherein f is_FG(t) DAS time domain gather seismic data after amplitude correction to the full-band in-well seismic data amplitude spectrum of the detector (5) corresponding to the ground, where t is 0, 1.

(i) The data conversion and processing flow from the step (c) to the step (h) can be used for converting the uplink reflected wave (92) collected by the armored optical cable (2) on the ground into the same data as the uplink reflected wave (92) collected by the detector (5) on the ground.

Technical Field

The invention belongs to the technical field of seismic data processing, and particularly relates to a distributed optical fiber seismic data acquisition system and a data collection and conversion method thereof.

Background

Distributed optical fiber Acoustic Sensing (DAS) technology is a novel Sensing technology capable of realizing continuous Distributed detection of vibration and Acoustic fields. The method utilizes the characteristic that coherent Rayleigh scattering excited by narrow-linewidth single-frequency laser in optical fiber is highly sensitive to strain change, and combines the principle of a reflectometer to sense the environmental vibration and sound field information interacted with the optical fiber at long distance and high space-time precision. This unique information perception capability has led DAS technology to receive a great deal of attention from both academic and industrial areas. DAS technology performance is continuously improved, application is rapidly developed, and unique technical advantages and potentials of DAS technology are shown in the aspects of perimeter intrusion detection, railway safety online monitoring, geophysical exploration and the like.

Distributed optical fiber acoustic sensing systems (DAS) are a high-density, low-cost seismic survey technology that has been developed in recent years and is rapidly evolving. The DAS detects signals such as sound or vibration in an audio frequency range by using the phase of coherent rayleigh scattering light rather than the light intensity, and not only provides sound or vibration event intensity information by using the magnitude of the phase amplitude, but also obtains the sound or vibration event phase and frequency information by using a linear quantitative measurement value. The DAS may be a moving interferometric acoustic wave sensor that detects an external signal on a sensing optical fiber, and when a linear change in phase of interference light at a position is caused by sound or vibration, quantitative measurement of an external physical quantity may be performed by extracting and demodulating interference signals at different times at the position.

The DAS measuring process comprises the steps that a laser emits light pulses along an optical fiber, some light and incident light are interfered in the pulses in a backscattering mode, after the interference light is reflected back, the backscattering interference light returns to a signal processing device, and meanwhile, the optical fiber vibrates along the optical fiber to bring an acoustic wave signal to the signal processing device. Since the speed of light remains constant, a measurement of the acoustic vibration per meter of fiber can be obtained.

A detector is a device for detecting some useful information in a wave signal. Means for identifying the presence or change of a wave, oscillation or signal. The detector is typically used to extract the information carried. The detectors are classified into envelope detectors and synchronous detectors. The output signal of the former corresponds to the envelope of the input signal, and is mainly used for demodulating the standard amplitude modulation signal. The latter is in fact an analog multiplier, and in order to obtain the demodulation action, it is necessary to add in addition an oscillating signal (coherent signal) perfectly aligned with the carrier of the input signal. The synchronous detector is mainly used for demodulating a single-sideband amplitude-modulated signal or demodulating a vestigial sideband amplitude-modulated signal.

When underground armored optical cables or armored optical cables buried in the ground are used for acquiring seismic data in a well or on the ground, the armored optical cables acquire displacement of mass points in optical fibers at the action positions of the seismic waves, namely stretching and compressing the optical fibers, caused by the propagation of the seismic waves along the armored optical cables; the velocity of up-and-down movement of a coil surrounding a magnetic core inside the geophone along with the fluctuation of the seismic wave when the seismic wave propagates to each geophone is recorded by using a downhole three-component velocity geophone or a geophone arranged on the ground. In addition, the distributed optical fiber acoustic wave sensing system has different acquisition and wave detector responses to seismic wave fluctuation. If the displacement data of the distributed optical fiber inner mass point acquired by the armored optical cable along with the seismic wave fluctuation and the speed data of the coil recorded by the geophone along with the up-and-down movement of the seismic wave fluctuation are compared, analyzed or combined, dimension conversion and amplitude spectrum compensation processing are required to be carried out on the displacement data of the optical fiber mass point underground or on the ground acquired by the armored optical cable.

Disclosure of Invention

In order to perform comparative analysis or combined processing on displacement data of distributed optical fiber internal mass points acquired by an armored optical cable when the internal mass points fluctuate with seismic waves and speed data of up-and-down movement of a coil recorded by a geophone when the internal mass points fluctuate with the seismic waves, dimension conversion and amplitude spectrum compensation processing need to be performed on the displacement data of underground or ground distributed optical fiber mass points acquired by the armored optical cable. The invention provides a distributed optical fiber seismic data acquisition system and a method for converting seismic data acquired by a geophone, which convert well seismic data and ground seismic data acquired by underground or ground distributed optical fiber acoustic sensing optical fibers into seismic data acquired by a geophone in a well or on the ground at a corresponding position, and comprises the steps of firstly carrying out time differential processing on distributed optical fiber particle displacement data at each measuring point position acquired by underground or ground optical fibers, converting the data into DAS data with the same dimension as the seismic data recorded by the geophone, then discrete Fourier transform is carried out on the seismic data recorded by the detector and the DAS seismic data after differential processing, the amplitude spectra of the two data after the discrete Fourier transform are compared, and solving the difference value delta A between the seismic data recorded by the detector corresponding to each micro frequency band delta omega and the converted DAS seismic data amplitude spectrum on the full-frequency-band amplitude spectrum._G-FAdding delta A to the amplitude spectrum corresponding to each frequency point of DAS seismic data_G-FAnd finally, performing inverse discrete Fourier transform on the corrected amplitude spectrum of the DAS seismic data subjected to amplitude spectrum compensation processing to obtain DAS seismic data which are completely the same as the seismic data recorded by the detectors at the same receiving position, so that the DAS seismic data acquired by distributed optical fibers underground or on the ground and the seismic data acquired by the detectors are subjected to comparative analysis and combined processing.

In order to achieve the purpose, the specific technical scheme of the invention is as follows:

the distributed optical fiber seismic data acquisition system comprises an armored optical cable arranged on the ground or in a well, a plurality of detectors arranged on the ground or in the well, a ground seismic source and a modulation and demodulation instrument;

a plurality of detectors are embedded at equal intervals along the measuring line of the armored optical cable;

a high-sensitivity hydrogen loss-resistant single-mode optical fiber is arranged in the armored optical cable; the modulation and demodulation instrument is connected with the single-mode optical fiber in the armored optical cable; the tail end of the single-mode fiber is provided with an extinction device;

the ground seismic sources are distributed point by point at equal intervals according to a two-dimensional seismic source excitation line or a three-dimensional seismic source excitation net, and the distance between the ground seismic sources is 6.25 meters, or 12.5 meters, or 25 meters, or 50 meters;

when the underground distributed optical fiber seismic data acquisition system is used, the underground distributed optical fiber seismic data acquisition system further comprises metal sleeves, wherein a coupling of each metal sleeve is provided with a metal clip, and an underground armored optical cable is fixed on the outer side of each metal sleeve; a downhole geophone is arranged in the metal sleeve;

when the system is used as a ground distributed optical fiber seismic data acquisition system, the system comprises a shallow trench excavated along a survey line, and an armored optical cable is buried in the shallow trench; the detector is arranged on the ground; the spacing between the detectors is 3.125 meters, or 6.25 meters, or 12.5 meters, or 25 meters.

The ground seismic source is one of an explosive source, a controllable seismic source, an air gun seismic source, a heavy hammer seismic source or an electric spark seismic source.

The data collection and conversion method of the distributed optical fiber seismic data acquisition system comprises the following steps:

when the fiber optic seismic data acquisition system is used as a downhole distributed fiber optic seismic data acquisition system: the method comprises the following steps:

(1) installing an underground distributed optical fiber seismic data acquisition system;

synchronously and slowly putting the metal sleeve and the underground armored optical cable into a drilled well hole;

the metal clip is arranged at the joint of two metal casing pipes at a wellhead, so as to fix and protect the underground armored optical cable from rotating and moving and/or being damaged in the casing pipe setting process;

pumping cement slurry from the well bottom by using a high-pressure pump truck, returning the cement slurry to the well head from the well bottom along an annular area between the outer wall of the metal casing and the drill hole, and permanently fixing the metal casing, the underground armored optical cable and the stratum rock together after the cement slurry is solidified;

connecting the single-mode optical fiber in the underground armored optical cable to the DAS signal input end of a modulation and demodulation instrument at a wellhead;

(2) exciting a ground seismic source signal point by point, measuring a particle displacement signal along an optical fiber in an underground armored optical cable caused by seismic waves excited by the ground seismic source by a modulation and demodulation instrument, and synchronously acquiring the seismic signals excited by the ground seismic source by an underground detector;

(3) carrying out time differential processing on the particle displacement signals along the optical fiber measured by the modulation and demodulation instrument, and converting the displacement signals along the optical fiber into seismic data with the same dimension as the seismic data acquired by the detector;

when the underground distributed optical fiber seismic data acquisition system is used, the underground distributed optical fiber seismic data processed in the step (3) and the data measured by the underground detector are well seismic data;

(4) discretely sampled seismic data f recorded for downhole geophones_G(t), t ═ 0, 1.., N-1, do the discrete fourier transform:

wherein, f in the formula_G(t) time domain gather seismic data recorded for downhole receivers, F_G(ω) is a discrete fourier transform of seismic data recorded by a downhole geophone, ω -0, 1.., N-1;

(5) DAS seismic data f after time differential processing_F(t) performing discrete Fourier transform:

wherein, f in the formula_F(t) recording and over-differentiating for an armored cable downholeProcessed DAS time domain gather seismic data, F_F(omega) is the discrete Fourier transform of DAS time domain gather seismic data recorded by an underground armored optical cable and subjected to differential processing, wherein omega is 0,1, the.

(6) Amplitude spectrum | F of two kinds of data after discrete Fourier transform_G(ω) | and | F_F(omega) | is compared, and the seismic data amplitude spectrum | F recorded by the underground detector (5) corresponding to each discrete angular frequency omega is obtained on the amplitude spectrum of the full frequency band_G(ω) | and the converted DAS seismic data amplitude spectrum | F_FThe ratio between (ω) | Δ A_G/F(ω):

ΔA_G/F(ω)＝|F_G(ω)|/|F_F(ω)|

(7) Multiplying the coefficient corresponding to each discrete angular frequency point (omega) of DAS seismic data recorded by an underground armored optical cable and subjected to differential processing by delta A_G/F(ω)：

|F_FG(ω)|＝ΔA_G/F(ω)|F_F(ω)|

Wherein, | F_FG(omega) is a DAS frequency domain coefficient of which the amplitude is corrected to the full frequency band corresponding to the seismic data amplitude spectrum of the underground detector, wherein omega is 0,1, a.

(8) And (3) performing inverse discrete Fourier transform on the amplitude spectrum of the DAS time domain gather seismic data after amplitude correction:

wherein f is_FGAnd (t) the DAS time domain gather seismic data after the amplitude is corrected to the full-band corresponding borehole seismic data amplitude spectrum of the borehole detector, wherein t is 0, 1.

(9) And (4) converting the underground downward direct waves and the upward reflected waves acquired by the underground armored optical cable into seismic wave data which are the same as the underground downward direct waves and the upward reflected waves acquired by the underground detector by utilizing the data conversion and processing procedures from the step (3) to the step (8).

When the optical fiber seismic data acquisition system is used as a ground distributed optical fiber seismic data acquisition system, the method comprises the following steps:

(1) installing a ground distributed optical fiber seismic data acquisition system;

excavating a shallow trench on the ground along the designed two-dimensional measuring line or three-dimensional measuring net, burying the armored optical cable into the shallow trench, and backfilling and compacting the shallow trench; embedding detectors at equal intervals on the ground along the measuring line in which the armored optical cable is embedded;

(2) exciting a ground seismic source signal point by point, measuring a displacement signal along an optical fiber in an armored optical cable on the ground caused by seismic waves excited by the ground seismic source below the ground by a modulation and demodulation instrument, and synchronously acquiring the seismic signals excited by the ground seismic source by a detector arranged on the ground;

(3) carrying out time differential processing on displacement signals along the optical fiber measured by a modulation and demodulation instrument, and converting the displacement signals along the optical fiber into seismic data with the same dimension as that of seismic data collected by a ground detector;

when the system is used as a ground distributed optical fiber seismic data acquisition system, the ground distributed optical fiber seismic data processed in the step (3) and data measured by a ground geophone are ground seismic data;

(4) discretely sampled seismic data f recorded by geophones at the ground_G(t), t ═ 0, 1.., N-1, do the discrete fourier transform:

wherein, f in the formula_G(t) time domain gather seismic data recorded for geophones at the ground, F_G(ω) is a discrete fourier transform of the seismic data recorded by the geophone at the surface, ω -0, 1.., N-1;

(5) DAS seismic data f after time differential processing_F(t) performing discrete Fourier transform:

wherein, f in the formula_F(t) DAS time domain gather seismic data recorded by armored optical cables on the ground and subjected to differential processing, F_F(omega) is the discrete Fourier transform of DAS time domain gather seismic data recorded by the armored optical cable on the ground and subjected to differential processing, wherein omega is 0,1, the.

(6) Amplitude spectrum | F of two kinds of data after discrete Fourier transform_G(ω) | and | F_F(omega) | is compared, and the seismic data amplitude spectrum | F recorded by the ground geophone corresponding to each discrete angular frequency omega is obtained on the amplitude spectrum of the full frequency band_G(ω) | and the converted DAS seismic data amplitude spectrum | F_FThe ratio between (ω) | Δ A_G/F(ω):

ΔA_G/F(ω)＝|F_G(ω)|/|F_F(ω)|

(7) Multiplying the coefficient corresponding to each discrete angular frequency point (omega) of DAS seismic data recorded by an underground armored optical cable and subjected to differential processing by delta A_G/F(ω)：

|F_FG(ω)|＝ΔA_G/F(ω)|F_F(ω)|

Wherein, | F_FG(omega) | is a DAS frequency domain coefficient after amplitude correction is carried out on the amplitude spectrum of the seismic data of the detector corresponding to the ground on the full frequency band, and omega is 0, 1., N-1;

(8) and (3) performing inverse discrete Fourier transform on the amplitude spectrum of the DAS time domain gather seismic data after amplitude correction:

wherein f is_FG(t) DAS time domain gather seismic data after amplitude correction to the full-band corresponding to the borehole seismic data amplitude spectrum of the earth detector, where t is 0, 1.

(9) And (4) converting the uplink reflected wave acquired by the armored optical cable on the ground into the same data as the uplink reflected wave data acquired by the detector on the ground by using the data conversion and processing flows from the step (3) to the step (8).

The invention provides a distributed optical fiber seismic data acquisition system and a data acquisition and conversion method thereof, which convert well seismic wave data and ground seismic wave data acquired by underground or underground distributed optical fiber acoustic sensing optical fibers into seismic wave data acquired by geophones in a well or on the ground at corresponding positions so as to compare, analyze and combine the seismic wave data acquired by underground or ground optical fibers and the seismic wave data acquired by the geophones.

Drawings

FIG. 1 is a schematic representation of a downhole wireline and downhole geophone and a down-going direct wave in accordance with example 1 of the present invention.

FIG. 2 is a schematic representation of a downhole armored fiber optic cable and downhole geophones and an upstream reflection wave in accordance with example 1 of the present invention.

Fig. 3 is a schematic diagram of a geophone and an upstream reflection wave from the ground and an armored optical cable under the ground according to embodiment 2 of the present invention.

FIG. 4 is a comparison of borehole seismic data acquired by downhole geophones in accordance with the present invention and borehole DAS seismic data acquired by downhole optical fibers.

FIG. 5 is a graph of amplitude spectra corresponding to borehole seismic data acquired by the downhole geophone of FIG. 4 and borehole DAS seismic data acquired by the downhole fiber optic.

FIG. 6 is a comparison of borehole direct wave seismic data acquired by downhole geophones of the present invention and borehole DAS seismic data acquired by downhole optical fibers.

FIG. 7 is a comparison graph of amplitude spectra corresponding to borehole direct wave seismic data acquired by the downhole geophone of FIG. 6 and borehole DAS direct wave seismic data acquired by the downhole optical fiber.

Detailed Description

In order to facilitate an understanding of the invention, the invention is described in more detail below with reference to the accompanying drawings and specific examples. The accompanying drawings illustrate preferred embodiments of the present invention. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete. They are not to be construed as limiting the invention but merely as exemplifications, while the advantages thereof will be more clearly understood and appreciated by way of illustration.

Example 1

The schematic diagram of the arrangement of the underground armored cable 2 and the underground geophone 5 and the schematic diagram of the downward direct wave 81 are shown in figure 1.

FIG. 2 is a schematic diagram of the deployment of the downhole armored fiber optic cable 2 and downhole geophones 5 and the upgoing reflected wave 91 of the present invention.

Fig. 3 is a schematic diagram of a geophone and an upstream reflection wave from the ground and an armored optical cable under the ground according to embodiment 2 of the present invention.

The distributed optical fiber seismic data acquisition system and the conversion method of the data acquired by the detectors comprise an armored optical cable 2 arranged on the ground or in a well, a plurality of detectors 5 arranged on the ground or in the well, a ground seismic source 6 and a modulation and demodulation instrument 7.

The detectors 5 are embedded at equal intervals along the measuring line of the armored optical cable 2; a high-sensitivity hydrogen loss-resistant single-mode optical fiber is arranged in the armored optical cable 2; the modulation and demodulation instrument 7 is connected with the single-mode optical fiber in the armored optical cable 2; the tail end of the single-mode optical fiber of the armored optical cable 2 is provided with a deluster 4;

the ground seismic sources 6 are distributed point by point at equal intervals according to a two-dimensional seismic source excitation line or a three-dimensional seismic source excitation net, and the interval of the ground seismic sources 6 can be 6.25 meters, or 12.5 meters, or 25 meters, or 50 meters;

the ground seismic source 6 is one of an explosive source, a controllable seismic source, an air gun seismic source, a heavy hammer seismic source or an electric spark seismic source.

When the underground distributed optical fiber seismic data acquisition system is used, the underground distributed optical fiber seismic data acquisition system further comprises metal sleeves 1, wherein a metal clip 3 is installed at a coupling of each metal sleeve 1, and an underground armored optical cable 2 is fixed on the outer side of each metal sleeve 1; a downhole geophone 5 is arranged inside the metal casing 1;

when the optical fiber seismic data acquisition system is used as a ground distributed optical fiber seismic data acquisition system, the optical fiber seismic data acquisition system comprises a shallow trench which is excavated along the measuring line of a detector 5 on the ground, and an armored optical cable 2 on the ground is buried in the shallow trench; on the ground, the ground detectors 5 are buried at equal intervals along the measuring line of the armored optical cable 2 on the ground, and the intervals of the ground detectors 5 can be 3.125 meters, 6.25 meters, 12.5 meters or 25 meters.

In the invention, when underground armored optical cables or armored optical cables buried under the ground are used for acquiring well or seismic data, the armored optical cables acquire seismic waves which cause displacement of mass points in distributed optical fibers at various seismic wave action positions when the seismic waves are transmitted along the armored optical cables, namely stretching and compressing of the optical fibers; the velocity of up-and-down movement of a coil surrounding a magnetic core inside the geophone along with the fluctuation of the seismic wave when the seismic wave propagates to each geophone is recorded by using a downhole three-component velocity geophone or a geophone arranged on the ground.

Because the coupling conditions of the underground geophone 5 and the armored optical cable 2 arranged outside the metal sleeve 1 are different, the response of the electronic geophone 5 and the response of the optical fiber in the armored optical cable 2 to the vibration signal are not completely consistent, and the borehole seismic data 10 acquired by the underground geophone 5 and the borehole DAS seismic data 11 acquired by the underground optical fiber shown in FIG. 4 are different. Fig. 5 shows the amplitude spectra 100 and 111 corresponding to the borehole seismic data 10 acquired by the downhole geophone 5 and the borehole DAS seismic data 11 acquired by the downhole optical fiber in fig. 4, and although the time differential processing is performed on the particle displacement signal along the optical fiber in the armored optical cable 2 measured by the modem apparatus 7, and the displacement signal along the optical fiber is converted into seismic data with the same dimension as the seismic data acquired by the geophone 5, the amplitude spectrum 100 of the borehole seismic data 10 acquired by the downhole geophone 5 is different from the amplitude spectrum 111 of the borehole DAS seismic data 11.

FIG. 6 is a comparison of borehole direct wave seismic data 12 acquired by downhole geophones 5 of the present invention and borehole DAS seismic data 13 acquired by downhole optical fibers.

FIG. 7 is a comparison of the amplitude spectrum 122 of borehole direct wave seismic data 12 acquired by the downhole geophone 5 of FIG. 6 and the amplitude spectrum 133 of borehole direct wave DAS seismic data 13 acquired by the downhole optical fiber.

It can also be seen from fig. 6 and 7 that there is also a difference between the borehole direct wave seismic data 12 collected by the downhole geophone 5 and the borehole direct wave DAS seismic data 13 collected by the downhole optical fiber, and their corresponding amplitude spectra 122 and 133.

If DAS seismic data 11 and 13 acquired by the armored fiber optic cable 2 and seismic data 10 and 12 recorded by the geophones are to be analyzed by comparison or processed in combination, conversion of DAS seismic data 11 and 13 acquired downhole or at the surface by the armored fiber optic cable is required.

When the distributed optical fiber seismic data acquisition system and the method for converting the data acquired by the distributed optical fiber seismic data acquisition system and the geophone are used as the underground distributed optical fiber seismic data acquisition system: the method comprises the following steps:

(a) installing an underground distributed optical fiber seismic data acquisition system;

synchronously and slowly putting the metal sleeve 1 and the armored optical cable 2 into a drilled well hole;

installing a metal clip 3 at the joint of two metal casing pipes 1 at a wellhead, fixing and protecting an underground armored optical cable 2 from rotating and moving and/or being damaged in the casing pipe setting process;

pumping cement slurry from the well bottom by using a high-pressure pump truck, returning the cement slurry to the well head from the well bottom along an annular area between the outer wall of the metal casing 1 and the drill hole, and permanently fixing the metal casing 1, the armored optical cable 2 and the stratum rock together after the cement slurry is solidified;

connecting the single mode optical fiber in the armored optical cable 2 to the DAS signal input end of the modulation and demodulation instrument 7 at the wellhead;

(b) exciting a ground seismic source 6 seismic source signal point by point, measuring a particle displacement signal along an optical fiber in an underground armored optical cable 2 caused by seismic waves excited by the ground seismic source 6 underground by a modulation and demodulation instrument 7, and synchronously acquiring the seismic signals excited by the ground seismic source 6 by an underground detector 5;

(c) carrying out time differential processing on the particle displacement signals along the optical fiber measured by the modulation and demodulation instrument 7, and converting the displacement signals along the optical fiber into seismic data with the same dimension as the seismic data acquired by the detector 5;

when the underground distributed optical fiber seismic data acquisition system is used, the underground distributed optical fiber seismic data processed in the step (c) and the data measured by the underground detector 5 are well seismic data;

(d) discretely sampled seismic data f recorded by geophones 5 at the ground_G(t), t ═ 0, 1.., N-1, do the discrete fourier transform:

wherein, f in the formula_G(t) time domain gather seismic data recorded by geophones 5 at the surface, F_G(ω) is a discrete fourier transform of the seismic data recorded by the geophone 5 at the surface, ω -0, 1.., N-1;

(e) DAS seismic data f after time differential processing_F(t) performing discrete Fourier transform:

wherein, f in the formula_F(t) DAS time domain gather seismic data recorded by the armored optical cable 2 on the ground and subjected to differential processing, F_F(omega) is the discrete fourier transform of DAS time domain gather seismic data recorded by the armored optical cable 2 on the ground and subjected to differential processing, where omega is 0, 1.

(f) Amplitude spectrum | F of two kinds of data after discrete Fourier transform_G(ω) | and | F_F(omega) | is compared, and the seismic data amplitude spectrum | F recorded by the detector 5 on the ground corresponding to each discrete angular frequency omega is obtained on the amplitude spectrum of the full frequency band_G(ω) | and the converted DAS seismic data amplitude spectrum | F_FThe ratio between (ω) | Δ A_G/F(ω):

ΔA_G/F(ω)＝|F_G(ω)|/|F_F(ω)|

(g) The coefficient corresponding to each discrete angular frequency point (omega t) of DAS seismic data recorded by an underground armored optical cable (2) and subjected to differential processing is multiplied by delta A_G/F(ω)：

|F_FG(ω)|＝ΔA_G/F(ω)|F_F(ω)|

Wherein, | F_FG(ω) I is a DAS frequency domain after amplitude is corrected to a full-band corresponding to the seismic data amplitude spectrum of the detector on the ground, and omega is 0, 1.

(h) And (3) performing inverse discrete Fourier transform on the amplitude spectrum of the DAS time domain gather seismic data after amplitude correction:

wherein f is_FG(t) DAS time domain gather seismic data after amplitude correction to the full-band corresponding to the borehole seismic data amplitude spectrum of the detector 5 on the ground, where t is 0, 1.

(i) The data conversion and processing flow from the step (c) to the step (h) can be used for converting the downhole direct downward wave 81 and the uplink reflected wave 91 collected by the downhole armored optical cable 2 into the same seismic data as the downhole direct downward wave 81 and the uplink reflected wave 91 collected by the downhole geophone 5.

When the ground optical fiber seismic data acquisition system and the method for converting the data acquired by the ground optical fiber seismic data acquisition system and the geophone are used as the ground distributed optical fiber seismic data acquisition system, the method comprises the following steps:

(a) installing a ground distributed optical fiber seismic data acquisition system;

excavating a shallow trench on the ground along the designed two-dimensional measuring line or three-dimensional measuring net, burying the armored optical cable 2 into the shallow trench, and backfilling and compacting the shallow trench; burying detectors 5 at equal intervals on the ground along the measuring line in which the armored optical cable 2 is buried;

(b) exciting a ground seismic source 6 signal point by point, measuring a displacement signal along an optical fiber in the armored optical cable 2 on the ground caused by seismic waves excited by the ground seismic source 6 below the ground by a modulation and demodulation instrument 7, and synchronously acquiring a seismic signal excited by the ground seismic source 6 by a detector 5 arranged on the ground;

(c) carrying out differential processing on time on displacement signals along the optical fiber measured by a modulation and demodulation instrument 7, and converting the displacement signals along the optical fiber into seismic data with the same dimension as that of seismic data collected by a ground geophone 5;

when the system is used as a ground distributed optical fiber seismic data acquisition system, the ground distributed optical fiber seismic data processed in the step (c) and data measured by the ground geophone 5 are ground seismic data;

(d) discretely sampled seismic data f recorded by geophones 5 at the ground_G(t), t ═ 0, 1.., N-1, do the discrete fourier transform:

wherein, f in the formula_G(t) time domain gather seismic data recorded by geophones 5 at the surface, F_G(ω) is a discrete fourier transform of the seismic data recorded by the geophone 5 at the surface, ω -0, 1.., N-1;

(e) DAS seismic data f after time differential processing_F(t) performing discrete Fourier transform:

wherein, f in the formula_F(t) DAS time domain gather seismic data recorded by the armored optical cable 2 on the ground and subjected to differential processing, F_F(omega) is the discrete fourier transform of DAS time domain gather seismic data recorded by the armored optical cable 2 on the ground and subjected to differential processing, where omega is 0, 1.

(f) Amplitude spectrum | F of two kinds of data after discrete Fourier transform_G(ω) | and | F_F(omega) | is compared, and the seismic data amplitude spectrum | F recorded by the detector 5 on the ground corresponding to each discrete angular frequency omega is obtained on the amplitude spectrum of the full frequency band_G(ω) | and the converted DAS seismic data amplitude spectrum | F_FThe ratio between (ω) | Δ A_G/F(ω):

ΔA_G/F(ω)＝|F_G(ω)|/|F_F(ω)|

(g) Multiplying the coefficient corresponding to each discrete angular frequency point (omega t) of the DAS seismic data recorded by the underground armored optical cable 2 and subjected to differential processing by delta A_G/F(ω)：

|F_FG(ω)|＝ΔA_G/F(ω)|F_F(ω)|

Wherein, | F_FG(ω) | is the DAS frequency domain after the amplitude is corrected to the detector seismic data amplitude spectrum corresponding to the ground over the full frequency band, ω ═ 0, 1.., N-1;

(h) and (3) performing inverse discrete Fourier transform on the amplitude spectrum of the DAS time domain gather seismic data after amplitude correction:

wherein f is_FG(t) DAS time domain gather seismic data after amplitude correction to the full-band corresponding to the borehole seismic data amplitude spectrum of the detector 5 on the ground, where t is 0, 1.

(i) The data conversion and processing flow from the step (c) to the step (h) can convert the upgoing reflected wave 92 collected by the armored optical cable 2 on the ground into the same data as the upgoing reflected wave 92 collected by the detector 5 on the ground.