Goaf grouting effect monitoring method based on optical fiber sensing

Abstract

The invention discloses a goaf grouting effect monitoring method based on optical fiber sensing, and the method comprises the steps: placing a sensing optical cable assembly into a vertical grouting hole, slowly placing the sensing optical cable assembly to the bottom of a goaf through an orifice optical cable winch, and enabling an orifice optical cable to pass through a grouting sealing flange and to be connected with distributed optical fiber DAS equipment; in the grouting process, the distributed optical fiber DAS equipment collects sound wave data in real time, a liquid level significant peak channel is recognized through mathematical modeling and optimization constraint according to an energy accumulation integral value of the sound wave data, and the position of the slurry liquid level is positioned; and finally determining the position of the liquid level in the goaf by combining the laying depth information of the optical cable in the hole. Optical fiber scattering signals are continuously collected and processed through distributed optical fiber DAS equipment, and real-time dynamic monitoring of the height of the liquid level in the hole is achieved. According to the invention, the change condition of the slurry level in the grouting process can be automatically monitored, the grouting effect is evaluated in real time, and data support is provided for real-time regulation and control of the grouting process.

Description

Technical Field

[0001] The invention belongs to the technical field of coal mines and relates to a method for monitoring grouting effects in goaf areas based on optical fiber sensing. Background Art

[0002] Goafs are hollow areas formed during the coal mining process. Their existence may lead to geological disasters such as surface subsidence, collapse, and spontaneous combustion, seriously threatening the safety of life and property and the ecological environment. Ground drilling and grouting filling is a common method for goaf management. By injecting slurry materials (such as cement slurry, fly ash slurry, etc.) into the goaf, the cavities are filled and the rock layer is reinforced, thereby preventing the goaf from spontaneous combustion, surface subsidence and collapse. However, traditional monitoring methods of the grouting process, such as coring and surface settlement monitoring, cannot monitor the dynamic changes of the slurry during the grouting process in real time, and it is difficult to meet the real-time control requirements of the grouting process. Summary of the Invention

[0003] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a method for monitoring the grouting effect of goaf areas based on optical fiber sensing. By laying sensor optical cables in vertical grouting holes, using distributed optical fiber DAS equipment to transmit pulsed light signals and receive Rayleigh backscattered signals, the changes in the slurry liquid level during the grouting process are automatically monitored, the grouting effect is evaluated in real time, and data support is provided for real-time regulation of the grouting process.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0005] A method for monitoring grouting effect in a goaf area based on optical fiber sensing comprises the following steps:

[0006] Step 1: Lower the sensor cable assembly into the vertical grouting hole, and then slowly lower the sensor cable assembly to the bottom of the goaf using the hole-mouth cable winch. The hole-mouth cable passes through the grouting sealing flange and connects to the distributed optical fiber DAS equipment.

[0007] Step 2: During the grouting process, the distributed optical fiber DAS equipment collects acoustic wave data in real time. Based on the energy accumulation integral value of the acoustic wave data, the significant peak channel of the liquid level is identified through mathematical modeling and optimization constraints to determine the slurry level position;

[0008] Step 3: Based on the spatial position of the slurry surface corresponding to the axial direction of the optical cable and the depth information of the optical cable in the hole, the actual height of the slurry surface in the hole is calculated; the distributed optical fiber DAS equipment continuously collects and processes the optical fiber scattering signal to realize real-time dynamic monitoring of the liquid level in the hole.

[0009] The present invention also includes the following technical features:

[0010] Specifically, the sensing optical cable assembly includes a sensing optical cable, a reflector fused to the front end of the sensing optical cable, and an inner hollow guide device arranged around the reflector.

[0011] Specifically, the end of the reflector is plated with a high-reflection film, and the high-reflection characteristics of the reflector can be used to enhance the reflection intensity of the optical signal and improve the signal sensitivity of the sensor optical cable.

[0012] Specifically, the inner hollow guide device includes a rear guide, a reflector protective shell, a two-component epoxy resin glue, a rear guide centralizing piece, a roller, a front guide centralizing piece, a counterweight and a front guide;

[0013] The reflector protection shell is wrapped around the reflector to provide physical protection for it;

[0014] The two-component epoxy resin glue is filled in the space between the reflector and the reflector protective shell to ensure the stability and safety of the reflector in complex environments;

[0015] The rear guide centralizing piece and the front guide centralizing piece are both spring pieces, which surround the reflector protection shell respectively; the front end of the front guide centralizing piece is connected to the reflector protection shell, and the rear end is connected to the front end of the rear guide centralizing piece, and the rear end of the rear guide centralizing piece is connected to the reflector protection shell;

[0016] The counterweight is set at the bottom of the reflector protective shell, and the counterweight is flexibly adjusted according to the drilling depth and the length of the optical cable to ensure that the optical cable is smoothly lowered to the bottom of the hole under the action of gravity;

[0017] The upper portion of the reflector protection shell is a conical rear guide, and the lower end of the counterweight is a conical front guide.

[0018] Specifically, the rear end of the rear guide straightening piece can slide back and forth on the reflector protective shell, and a roller is provided at the junction of the front guide straightening piece and the rear guide straightening piece to reduce friction. When passing through different apertures, the rear end of the rear guide straightening piece moves backward, and the front guide straightening piece and the rear guide straightening piece deform and contract radially to ensure that the optical cable passes coaxially smoothly under different apertures.

[0019] Specifically, the distributed optical fiber DAS device includes a main control board, a laser, a driver, an acousto-optic modulator, an optical fiber amplifier, a circulator, a photodetector and a demodulation host;

[0020] The main control board controls the laser to emit high-coherence continuous light, and the driver drives the acousto-optic modulator to modulate the continuous light into high-precision nanosecond pulse light, which is then amplified by a fiber optic amplifier and injected into the sensing optical cable through a circulator. When the light pulse propagates in the sensing optical cable, Rayleigh backscattering is generated, and the acoustic wave signal acts on the sensing optical cable, causing the refractive index and length of the optical fiber to change, thereby changing the phase and intensity of the scattered light. After returning through the circulator, the backscattered light is received by a high-sensitivity photodetector through the fiber optic amplifier. The demodulation host determines the vibration position by analyzing the round-trip time of the light pulse and extracts the phase change characteristics to collect acoustic wave data.

[0021] Specifically, the step 2 includes:

[0022] Step 2.1, identify the start time of the grouting pump:

[0023] Energy distribution of acoustic wave data collected by distributed fiber optic DAS equipment at different frequencies:

[0024]

[0025] In formula (1), PSD is the power spectral density, X(f) is the amplitude of the frequency domain data, and N is the number of data points;

[0026] For the effective frequency domain fragment, perform the cumulative integral E of PSD in the frequency domain:

[0027]

[0028] In formula (2), f1 and f2 are the starting and ending frequencies of the effective frequency domain segment;

[0029] The operating status of the grouting pump is determined based on the cumulative integral value E of the power spectrum density in the effective frequency domain segment. The PSD cumulative integral value E during the pump-off period is significantly lower than that during the pump-on period, and the energy of the entire channel is significantly increased during the pump-on period. The start-up time of the grouting pump can be automatically identified by setting a threshold value.

[0030] Step 2.2, determine the mutation position range of the energy accumulation integral value of the acoustic wave data:

[0031] When the grouting pump is turned on, the sound wave propagating downward along the wellbore is the incident wave. When it encounters the interface where the acoustic impedance of the liquid surface changes sharply, it is reflected. Most of the incident wave propagates in the opposite direction along the original path to form a reflected wave. The incident wave and the reflected wave are superimposed to form a standing wave field. This standing wave field causes a disturbance in the local stress σ, which in turn produces an energy mutation Δn.

[0032] Δn=p·σ (4)

[0033] Where: p is the photoelastic coefficient;

[0034] The energy mutation Δn changes the Rayleigh scattering characteristics of the light emitted by the laser of the distributed fiber optic DAS device deployed in the sensing optical cable in the area. This is then recognized by the distributed fiber optic DAS device's photoelectric detector, which manifests as a significant jump in the energy accumulation integral value E of the acoustic wave data in the corresponding channel. By capturing this energy mutation feature, the channel range corresponding to the mutation in the energy accumulation integral value E can be obtained, and the well depth range where the liquid level is located can be determined.

[0035] Step 2.3: Accurately identify the location of the energy accumulation integral value mutation to determine the slurry level position:

[0036] A multi-level signal processing process is constructed based on the Findpeaks function, which realizes robust detection of peaks through mathematical modeling and optimization constraints: first, based on the energy cumulative integral value mutation position range obtained in 2.2, the original DAS signal of the channel with a significant jump in the energy cumulative integral value E is scanned locally to extract candidate peaks, combined with multi-dimensional threshold screening, and Savitzky-Golay / wavelet soft threshold denoising preprocessing to improve the signal-to-noise ratio, based on dynamic parameter optimization and non-maximum suppression algorithm, and combined with peak base width and energy spectrum entropy analysis, the significant peak of the liquid surface is identified, and finally the liquid surface position is accurately located.

[0037] Compared with the prior art, the present invention has the following technical effects:

[0038] The present invention integrates a reflector and an inner hollow guide device into the sensing optical cable, thereby significantly improving the efficiency of lowering the sensing optical cable and the sensitivity of collecting signals; by emitting pulsed light signals through the distributed optical fiber DAS equipment and receiving Rayleigh backscattered signals, the start and stop times of the grouting pump can be automatically identified, thereby realizing intelligent judgment of the operating status of the grouting pump; the position range of the liquid level can be judged through the mutation point of the energy integration result of the distributed optical fiber monitoring data at the time of starting the grouting pump; further, according to the energy surge principle, a liquid level recognition method based on the energy surge peak is established, which can automatically identify the precise position of the grouting liquid level in the goaf, thereby providing data support for real-time regulation of the grouting process. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 Schematic diagram of the optical cable reflector and inner hollow guide device.

[0040] Figure 2 This is a three-dimensional structural diagram of the optical cable reflector and inner hollow guide device.

[0041] Figure 3 This is a structural diagram of distributed optical fiber DAS equipment.

[0042] Figure 4 PSD cumulative integral value (a) full-channel integral value when the pump is off; (b) full-channel integral value when the pump is on.

[0043] Figure 5 It is the PSD integral value of all channels in the pump-on state.

[0044] The meaning of each number in the figure is:

[0045] 1. Sensor cable, 2. Reflector, 3. Rear guide, 4. Reflector protective housing, 5. Two-component epoxy resin adhesive, 6. Rear guide centralizer, 7. Roller, 8. Front guide centralizer, 9. Counterweight, 10. Front guide. DETAILED DESCRIPTION

[0046] Specific embodiments of the present invention are given below. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent modifications made on the basis of the technical solution of this application fall within the protection scope of the present invention.

[0047] Example 1:

[0048] This embodiment provides a method for monitoring grouting effect in a goaf area based on optical fiber sensing, the method comprising the following steps:

[0049] Step 1: Lower the sensor cable assembly into the vertical grouting hole. Use the hole-mouth optical cable winch to slowly lower the sensor cable assembly to the bottom of the goaf. Pass the hole-mouth optical cable through the grouting sealing flange and connect it to the distributed optical fiber DAS equipment.

[0050] Among them, such as Figure 1 The sensing optical cable assembly includes a sensing optical cable, a reflector fused to the front end of the sensing optical cable, and an inner hollow guide device arranged around the reflector;

[0051] Specifically, the top of the reflector is plated with a high-reflection film (such as gold film, silver film or multi-layer dielectric film), and the reflectivity can reach more than 90%. The high reflective characteristics of the reflector can enhance the reflection intensity of the optical signal and improve the signal sensitivity of the sensor cable.

[0052] The hollow guide device includes a rear guide, a reflector protective shell, two-component epoxy resin glue, a rear guide straightening piece, rollers, a front guide straightening piece, a counterweight, and a front guide; the reflector protective shell is wrapped around the outside of the reflector to provide physical protection. The two-component epoxy resin glue fills the space between the reflector and the reflector protective shell to ensure the stability and safety of the reflector in complex environments. The rear guide straightening piece and the front guide straightening piece are both composed of four spring leaves, evenly distributed around the reflector protective shell. The front end of the front guide straightening piece is connected to the reflector protective shell, and the rear end is connected to the front end of the rear guide straightening piece. The rear end of the rear guide straightening piece is connected to the reflector protective shell and can slide back and forth on the reflector protective shell. Rollers are installed at the junction of the front and rear guide straightening pieces to reduce friction. When passing through a variable diameter, the deformation of the front and rear guide straightening pieces is reduced, and the rear end of the rear guide straightening piece moves backward to ensure the smooth coaxial passage of optical cables with different apertures. An adjustable counterweight module is integrated into the bottom of the reflector housing. The counterweight can be flexibly adjusted based on the drilling depth and cable length, ensuring that the cable is lowered smoothly to the bottom of the hole under the action of gravity. The upper portion of the reflector housing features a tapered rear guide, while the lower end of the counterweight features a tapered front guide.

[0053] Among them, such as Figure 3 ,Distributed fiber optic DAS equipment includes main control board, laser, driver, acousto-optic modulator, fiber amplifier, circulator, photodetector and demodulation host.

[0054] Specifically, the main control board controls the laser to emit highly coherent continuous light. The driver drives the acousto-optic modulator to modulate the continuous light into high-precision nanosecond pulses. This light is then amplified by a fiber amplifier and injected into the sensing cable through a circulator. As the light pulse propagates through the sensing cable, it generates Rayleigh backscattering. The acoustic signal acts on the sensing cable, causing changes in the fiber's refractive index and length, thereby altering the phase and intensity of the scattered light. After returning through the circulator, the backscattered light is received by a highly sensitive photodetector via the fiber amplifier. The demodulation host analyzes the round-trip time of the light pulse to determine the vibration position and extracts phase change characteristics to collect acoustic data.

[0055] Step 2: During the grouting process, the distributed fiber optic DAS device stores the real-time collected acoustic wave data every 10 seconds as a SEG-Y file to monitor the slurry level in the goaf. The specific monitoring method is as follows:

[0056] Step 2.1: The time-domain acoustic wave data collected by the distributed fiber DAS device is grouped every ten minutes. A fixed number of SEG-Y files are randomly selected from each group. The time-domain data is converted into frequency-domain data by Fourier transform. The amplitude and phase information of each frequency component are obtained through Fourier transform. The amplitude result is converted into power spectral density (PSD) as shown in formula (1), which is used to describe the energy distribution of the acoustic wave data at different frequencies:

[0057]

[0058] In formula (1), X(f) is the amplitude of the frequency domain data, and N is the number of data points.

[0059] In the frequency domain data results in the frequency range of 0-2000Hz, 0-0.01Hz is the ultra-low frequency background noise of the formation, which is not generated by the grouting process and is invalid background noise. The power spectral density PSD value of 200-2000Hz is close to 0. Therefore, the data is band-pass filtered from 0.01 to 200Hz, and the cumulative integral E of PSD in the frequency domain is performed for the effective frequency domain segments:

[0060]

[0061] In formula (2), f1 and f2 are the starting and ending frequencies of the effective frequency domain segment.

[0062] According to the accumulated integral value E of the power spectrum density on the effective frequency domain segment, the operating status of the grouting pump can be judged. Figure 4 The PSD cumulative integral value E of a) is significantly lower than that of the pump-on period ( Figure 4 b) The energy of all channels increases significantly during the pump start-up period. By setting a threshold, the start-up time of the grouting pump can be automatically identified.

[0063] Step 2.2: When the grouting pump is turned on, at the slurry surface, due to the order of magnitude difference in the density ρ and the speed of sound c of the liquid and air media, the acoustic impedance Z can be expressed as:

[0064] Z=ρc

[0065] At the interface between liquid and air, the reflection coefficient R is expressed as:

[0066]

[0067] When Z 液体 With Z 空气 The larger the acoustic impedance difference, the closer the reflection coefficient R is to ±1, so most of the sound waves are reflected.

[0068] The acoustic wave propagating downward in the wellbore direction in the slurry is the incident wave. When it encounters an interface with a sharp change in the acoustic impedance of the liquid surface, it will be reflected. Most of the incident wave will propagate in the opposite direction along the original path to form a reflected wave. The incident wave and the reflected wave are superimposed to form a standing wave field. This standing wave field causes a disturbance in the local stress σ, which in turn produces a significant energy mutation Δn.

[0069] Δn=p·σ (4)

[0070] Where: p is the photoelastic coefficient; the energy mutation Δn causes the Rayleigh scattering characteristics of the light emitted by the laser of the distributed fiber optic DAS device deployed in the sensing optical cable in the area to change, which is then recognized by the photoelectric detector of the distributed fiber optic DAS device, which is reflected in the energy accumulation integral value E of the acoustic wave data of the corresponding channel. Compared with other channels, the slope of the energy curve of this part of the channel changes significantly, and the energy increase far exceeds the growth rate of the adjacent channels, showing a sharp upward trend. By capturing this energy mutation feature, the channel range corresponding to the mutation of the energy accumulation integral value E can be obtained, and the channel range where the liquid level is located can be obtained. Figure 5 As shown, according to the PSD energy accumulated integral value E when the pump is started, the distributed optical fiber DAS device detects the mutation position range of the energy accumulated integral value E in the range of channels 131-133.

[0071] In step 2.3, a multi-level signal processing process is constructed based on the Findpeaks function to accurately identify the position range of the energy cumulative integral value E mutation near the liquid surface. This function realizes robust detection of peaks through mathematical modeling and optimization constraints: first, based on the energy cumulative integral value mutation position range obtained in 2.2, the original DAS signal of the channel where the energy cumulative integral value E jumps significantly is scanned for local extreme values to extract candidate peaks, combined with multi-dimensional threshold screening, and Savitzky-Golay / wavelet soft threshold denoising preprocessing to improve the signal-to-noise ratio. Based on dynamic parameter optimization (amplitude threshold, minimum peak spacing, peak protrusion threshold) and non-maximum suppression algorithm, and combined with peak base width and energy spectrum entropy analysis, significant peaks of the liquid surface are identified, and finally the liquid surface position is accurately located.

[0072] More specifically, the original signal is first scanned for local extremes to define candidate peaks in the discrete signal sequence that meet strict local maximum conditions (x[n]>x[n±k], where k is the neighborhood radius). Multidimensional threshold screening is then applied, combining the physical characteristics of the fluid and the statistical properties of the noise. To account for the inherent non-stationarity and high-frequency noise interference of DAS signals, preprocessing using Savitzky-Golay filtering or wavelet soft threshold denoising is required to improve the signal-to-noise ratio and suppress spurious peaks caused by turbulent vortex breakup or bubble collapse.

[0073] At the parameter optimization level, amplitude thresholds, minimum peak spacing, and peak prominence thresholds are dynamically set based on signal statistical characteristics, and a non-maximum suppression algorithm is used to eliminate multiple detections caused by dense oscillations. To address the broadband energy accumulation caused by sudden changes in acoustic impedance at the liquid surface interface, the algorithm jointly verifies peak significance by calculating the peak base width (half-maximum width w ≥ 5Δt, where Δt is the time resolution) and the energy spectrum entropy (H = -∑PSD(f)logPSD(f)), thereby distinguishing true liquid surface signals from vibration noise.

[0074] In step 3, based on the calculated spatial position of the liquid surface along the optical cable axis, combined with the depth of the optical cable in the hole, the actual height of the slurry level in the hole can be accurately calculated. Distributed DAS equipment continuously collects and processes the fiber scattering signal, enabling real-time dynamic monitoring of the liquid level in the hole and generating a graph of the liquid level over time. This monitoring result provides quantitative data support for parameter control during the grouting process, thereby improving grouting efficiency and safety.

[0075] The preferred embodiments of the present invention are described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the scope of protection of the present invention.

[0076] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. To avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0077] In addition, the various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for monitoring grouting effect in goaf area based on optical fiber sensing, characterized in that: The following steps are involved: Step 1: Lower the sensor cable assembly into the vertical grouting hole, and then slowly lower the sensor cable assembly to the bottom of the goaf using the hole-mouth cable winch. The hole-mouth cable passes through the grouting sealing flange and connects to the distributed optical fiber DAS equipment. Step 2: During the grouting process, the distributed optical fiber DAS equipment collects acoustic wave data in real time. Based on the energy accumulation integral value of the acoustic wave data, the significant peak channel of the liquid level is identified through mathematical modeling and optimization constraints to determine the slurry level position; Step 3: Based on the spatial position of the slurry surface corresponding to the axial direction of the optical cable and the depth information of the optical cable in the hole, the actual height of the slurry surface in the hole is calculated; The distributed optical fiber DAS equipment continuously collects and processes the optical fiber scattered signals to achieve real-time dynamic monitoring of the liquid level in the hole.

2. The method for monitoring grouting effect of goaf area based on optical fiber sensing according to claim 1, characterized in that: The sensing optical cable assembly comprises a sensing optical cable, a reflector fused to the front end of the sensing optical cable, and an inner hollow guide device arranged around the reflector.

3. The method for monitoring grouting effect of goaf area based on optical fiber sensing according to claim 2, characterized in that: The end of the reflector is plated with a high-reflection film, and the high-reflection characteristics of the reflector can be used to enhance the reflection intensity of the light signal and improve the signal sensitivity of the sensor optical cable.

4. The method for monitoring grouting effect of goaf area based on optical fiber sensing according to claim 2, characterized in that: The inner hollow guide device includes a rear guide, a reflector protective shell, a two-component epoxy resin glue, a rear guide centralizing piece, a roller, a front guide centralizing piece, a counterweight and a front guide; The reflector protection shell is wrapped around the reflector to provide physical protection for it; The two-component epoxy resin glue is filled in the space between the reflector and the reflector protective shell to ensure the stability and safety of the reflector in complex environments; The rear guide centralizing piece and the front guide centralizing piece are both spring pieces, which surround the reflector protection shell respectively; the front end of the front guide centralizing piece is connected to the reflector protection shell, and the rear end is connected to the front end of the rear guide centralizing piece, and the rear end of the rear guide centralizing piece is connected to the reflector protection shell; The counterweight is set at the bottom of the reflector protective shell, and the counterweight is flexibly adjusted according to the drilling depth and the length of the optical cable to ensure that the optical cable is smoothly lowered to the bottom of the hole under the action of gravity; The upper portion of the reflector protection shell is a conical rear guide, and the lower end of the counterweight is a conical front guide.

5. The method for monitoring grouting effect of goaf area based on optical fiber sensing according to claim 4, characterized in that: The rear end of the rear guide centralizing piece can slide back and forth on the reflector protective shell. A roller is provided at the junction of the front guide centralizing piece and the rear guide centralizing piece to reduce friction. When passing through different apertures, the rear end of the rear guide centralizing piece moves backward, and the front guide centralizing piece and the rear guide centralizing piece deform and contract radially to ensure that the optical cable passes coaxially and smoothly under different apertures.

6. The method for monitoring grouting effect of goaf area based on optical fiber sensing according to claim 1, characterized in that: The distributed optical fiber DAS device includes a main control board, a laser, a driver, an acousto-optic modulator, an optical fiber amplifier, a circulator, a photodetector and a demodulation host; The main control board controls the laser to emit high-coherence continuous light, and the driver drives the acousto-optic modulator to modulate the continuous light into high-precision nanosecond pulse light, which is then amplified by the optical fiber amplifier and injected into the sensor cable through the circulator; When a light pulse propagates in a sensing optical cable, it generates Rayleigh backscattering. The acoustic wave signal acts on the sensing optical cable, causing the refractive index and length of the optical fiber to change, thereby changing the phase and intensity of the scattered light. The backscattered light returns through the circulator and is received by a high-sensitivity photodetector through a fiber amplifier. The demodulation host determines the vibration position by analyzing the round-trip time of the light pulse and extracts the phase change characteristics to collect acoustic wave data.

7. The method for monitoring grouting effect of goaf area based on optical fiber sensing according to claim 1, characterized in that: The step 2 includes: Step 2.1, identify the start time of the grouting pump: Energy distribution of acoustic wave data collected by distributed fiber optic DAS equipment at different frequencies: In formula (1), PSD is the power spectral density, X(f) is the amplitude of the frequency domain data, and N is the number of data points; For the effective frequency domain fragment, perform the cumulative integral E of PSD in the frequency domain: In formula (2), f1 and f2 are the starting and ending frequencies of the effective frequency domain segment; The operating status of the grouting pump is determined based on the cumulative integral value E of the power spectrum density in the effective frequency domain segment. The PSD cumulative integral value E during the pump-off period is significantly lower than that during the pump-on period, and the energy of the entire channel is significantly increased during the pump-on period. The start-up time of the grouting pump can be automatically identified by setting a threshold value. Step 2.2, determine the mutation position range of the energy accumulation integral value of the acoustic wave data: When the grouting pump is turned on, the sound wave propagating downward along the wellbore is the incident wave. When it encounters the interface where the acoustic impedance of the liquid surface changes sharply, it is reflected. Most of the incident wave propagates in the opposite direction along the original path to form a reflected wave. The incident wave and the reflected wave are superimposed to form a standing wave field. This standing wave field causes a disturbance in the local stress σ, which in turn produces an energy mutation Δn. Δn=p·σ (4) Where: p is the photoelastic coefficient; The energy mutation Δn changes the Rayleigh scattering characteristics of the light emitted by the laser of the distributed fiber optic DAS device deployed in the sensing optical cable in the area. This is then recognized by the distributed fiber optic DAS device's photoelectric detector, which manifests as a significant jump in the energy accumulation integral value E of the acoustic wave data in the corresponding channel. By capturing this energy mutation feature, the channel range corresponding to the mutation in the energy accumulation integral value E can be obtained, and the well depth range where the liquid level is located can be determined. Step 2.3: Accurately identify the location of the energy accumulation integral value mutation to determine the slurry level position: A multi-level signal processing process is constructed based on the Findpeaks function, which realizes robust detection of peaks through mathematical modeling and optimization constraints: first, based on the energy cumulative integral value mutation position range obtained in 2.2, the original DAS signal of the channel with a significant jump in the energy cumulative integral value E is scanned locally to extract candidate peaks, combined with multi-dimensional threshold screening, and Savitzky-Golay / wavelet soft threshold denoising preprocessing to improve the signal-to-noise ratio, based on dynamic parameter optimization and non-maximum suppression algorithm, and combined with peak base width and energy spectrum entropy analysis, the significant peak of the liquid surface is identified, and finally the liquid surface position is accurately located.

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