An airgun shooting zero time correction method and device based on underwater vibration record

Abstract

This application relates to the field of geophysical exploration technology, and in particular to a method and device for zero-time correction of air gun excitation based on underwater vibration recording. The method includes: real-time measurement of the geodetic coordinates of the floating platform and the underwater seismometer at the moment of air gun excitation, and calculation of the distance between the air gun and the reservoir bottom; determining the propagation path of the air gun excitation sound wave based on the sound wave velocity in the reservoir bottom medium and water, the distance between the air gun and the reservoir bottom, the geodetic coordinates of the floating platform and the underwater seismometer at the moment of air gun excitation; obtaining the initial vibration time of the reservoir bottom at the geodetic coordinates of the underwater seismometer location based on the recorded near-field vibration waveform; and calculating the initial vibration time of the reservoir bottom vertically below the air gun based on the distance between the air gun and the reservoir bottom, the propagation path of the air gun excitation sound wave, the sound wave velocity, and the initial vibration time of the reservoir bottom. This application helps to achieve high-precision zero-time correction of air gun excitation.

Description

Technical Field

[0001] This application relates to the field of geophysical exploration technology, and in particular to a method and device for zero-time correction of air gun excitation based on underwater vibration recording. Background Technology

[0002] Large-capacity airgun active seismic source detection on land is an emerging geophysical exploration method. This method uses an airgun as the excitation source and a large-capacity water body (such as a reservoir) as the excitation carrier. The water oscillations caused by the airgun excitation trigger vibrations at the reservoir bottom, thereby generating effective seismic wave signals. Airgun active seismic sources are characterized by repeatability, high consistency, and environmental friendliness. Repeated detection using airgun active seismic sources can effectively obtain information on wave velocity changes in the subsurface medium.

[0003] The changes in wave velocity in the underground medium are extremely subtle and require precise measurement. Therefore, in active seismic source detection using airguns, it is crucial to obtain accurate propagation distance and time of the seismic excitation signal. The arrival location and time of the excitation signal are obtained from waveform records at distant seismic stations, making the accurate determination of the initial location and time of reservoir bottom vibration key to detecting wave velocity changes. The airgun excitation system includes a surface working platform and an underwater high-pressure airgun, which is fixed and suspended in the water by the working platform. When the airgun is activated, the initial location of the reservoir bottom vibration is directly below the airgun, and this location can be accurately obtained by GNSS equipment mounted on the airgun's fixed platform. Compared to the initial location, the initial time of reservoir bottom vibration caused by airgun excitation is difficult to measure accurately. This is because a series of mechanical actions during airgun excitation, such as air chamber compression and triggering, introduce time lag, making it impossible to obtain the precise airgun excitation time through the excitation control system and calculate the initial time of reservoir bottom vibration.

[0004] In active seismic source detection using airguns, a seismic instrument close to the airgun's firing location is typically selected as a reference instrument. A specific firing waveform recorded by this instrument is used as a template, and a high-precision firing time is obtained from the continuous waveforms recorded by this instrument using cross-correlation methods. However, this time is actually the arrival time of the seismic wave after the airgun firing, not the initial time of the reservoir bottom vibration. If the reference instrument is far from the airgun, or if the airgun undergoes significant positional changes within the water body, the initial vibration time obtained from the reference instrument will have a large error compared to the actual initial time. Therefore, how to directly and accurately determine the initial vibration time of the reservoir bottom corresponding to airgun firing has become a pressing technical problem to be solved in this field. Summary of the Invention

[0005] Therefore, it is necessary to provide a method and apparatus for zero-time air gun excitation correction based on underwater vibration recording, which can achieve high-precision correction of zero-time air gun excitation and address the above-mentioned technical problems.

[0006] In a first aspect, this application provides a method for zero-time correction of air gun excitation based on underwater vibration recording, the method comprising: The geodetic coordinates of the floating platform on the water surface and the geodetic coordinates of the underwater seismometer at the moment of air gun firing are measured in real time using a real-time dynamic differential positioning device, and the distance between the air gun and the bottom of the reservoir is calculated. The velocity of sound waves in the medium at the bottom of the reservoir and in the water is measured, and the propagation path of the sound waves excited by the air gun is determined based on the velocity of sound waves, the geodetic coordinates of the working floating platform on the water surface at the moment of the air gun excitation, and the geodetic coordinates of the underwater seismometer. The underwater seismometer records the near-field vibration waveform excited by the air gun, and based on the recorded near-field vibration waveform, the initial time of the reservoir bottom vibration at the geodetic coordinates of the underwater seismometer is obtained. The initial vibration time of the reservoir bottom is calculated based on the distance between the air gun and the reservoir bottom, the propagation path of the sound wave excited by the air gun, the speed of the sound wave, and the initial vibration time of the reservoir bottom.

[0007] In one embodiment, calculating the initial vibration time of the reservoir bottom vertically below the air gun, based on the distance between the air gun and the reservoir bottom, the propagation path of the sound wave excited by the air gun, the sound wave velocity, and the initial vibration time of the reservoir bottom, includes: Based on the propagation path of the sound wave excited by the air gun and the speed of the sound wave, calculate the propagation time of the sound wave excited by the air gun from the air gun to the bottom of the reservoir where the underwater seismometer is located. The air gun excitation time is calculated based on the difference between the initial time of the reservoir bottom vibration recorded by the underwater seismometer and the propagation time. The initial vibration time of the reservoir bottom perpendicularly below the air gun is calculated based on the air gun's firing time, the distance between the air gun and the reservoir bottom, and the sound wave velocity.

[0008] In one embodiment, calculating the propagation time of the air gun-excited sound wave from the air gun to the bottom of the reservoir where the underwater seismometer is located, based on the propagation path of the sound wave excited by the air gun and the sound wave velocity, includes: The propagation path of the sound waves generated by the air gun is divided into a water propagation segment and a reservoir bottom medium propagation segment. The propagation time of the water segment is calculated based on the path length of the water propagation segment and the speed of sound in water. The propagation time of the bottom section is calculated based on the path length of the propagation segment in the reservoir bottom medium and the sound wave velocity in the reservoir bottom medium. Based on the propagation time in the water section and the propagation time at the bottom of the reservoir, the propagation time of the sound wave excited by the air gun from the air gun to the location at the bottom of the reservoir where the underwater seismometer is located is obtained.

[0009] In one embodiment, the underwater seismometer is fixedly installed in the reservoir and located in the area directly below and adjacent to the air gun's firing point; the real-time dynamic differential positioning device is fixedly installed on the surface working platform and is used to obtain the geodetic coordinates of the air gun in real time through successive firings.

[0010] In one embodiment, the step of using a real-time dynamic differential positioning device to measure the geodetic coordinates of the floating platform on the water surface and the geodetic coordinates of the underwater seismometer at the moment of air gun firing, and calculating the distance between the air gun and the reservoir bottom, includes: The geodetic coordinates of the floating platform and the underwater seismometer at the moment of air gun excitation are measured in real time using a real-time dynamic differential positioning device. The depth at which the air gun was submerged in the reservoir was measured, and the water depth in the area corresponding to the submerged position of the air gun was measured using a depth sounder. Calculate the distance between the air gun and the bottom of the reservoir based on the immersion depth and the water depth of the reservoir.

[0011] In one embodiment, measuring the velocity of sound waves in the reservoir bottom medium and water, and determining the propagation path of the sound waves excited by the air gun based on the velocity of sound waves, the geodetic coordinates of the floating platform at the moment of air gun excitation, and the geodetic coordinates of the underwater seismometer includes: The sound velocity of the water in the reservoir was collected in layers from the water surface to the bottom of the reservoir using a sound velocity profiler, and a vertical sound velocity distribution model of the water in the reservoir was constructed. By combining in-situ testing with medium inversion, the acoustic velocity of the medium at the bottom of the reservoir is obtained. Combined with the vertical acoustic velocity distribution model of the reservoir water, a dual-medium acoustic parameter model is established. Based on the geodetic coordinates of the floating platform at the moment of air gun firing and the geodetic coordinates of the underwater seismometer, combined with the air gun's immersion depth and the reservoir's water depth, the three-dimensional spatial propagation geometric path from the air gun to the underwater seismometer is calculated. Based on the three-dimensional spatial propagation geometry path and the dual-medium acoustic parameter model, the propagation path of the air gun-excited sound wave is determined.

[0012] In one embodiment, the step of calculating the three-dimensional spatial propagation geometric path from the air gun to the underwater seismometer based on the geodetic coordinates of the floating platform at the moment of air gun excitation, the geodetic coordinates of the underwater seismometer, and the air gun's immersion depth and the reservoir's water depth includes: Based on the geodetic coordinates of the working platform on the water surface at the moment of air gun firing and the immersion depth of the air gun, the three-dimensional spatial coordinates of the air gun firing point underwater are determined. Based on the geodetic coordinates of the underwater seismometer and the water depth of the reservoir, the three-dimensional spatial coordinates of the receiving point of the underwater seismometer at the bottom of the reservoir are determined. Based on the coordinates of the three-dimensional excitation point and the coordinates of the three-dimensional receiving point, spatial geometric calculations are performed to obtain the three-dimensional spatial propagation geometric path from the air gun to the underwater seismometer.

[0013] In one embodiment, determining the propagation path of the air gun-excited sound wave based on the three-dimensional spatial propagation geometry path and the dual-medium acoustic parameter model includes: Based on the three-dimensional spatial propagation geometric path, the incident point and incident angle of the sound wave from the air gun to the bottom interface of the reservoir are determined, wherein the bottom interface of the reservoir refers to the refraction interface that the sound wave passes through when it enters the reservoir bottom medium from the water. Based on the vertical sound velocity distribution of the water body and the sound wave velocity of the reservoir bottom medium in the dual-medium acoustic parameter model, and combined with the incident angle, the refraction angle of the sound wave in the reservoir bottom medium is calculated based on Snell's law. Based on the refraction angle, the location of the refraction point of the sound wave on the interface of the reservoir bottom is determined, and the water propagation segment and the reservoir bottom medium propagation segment are divided. The propagation time of the water body segment is calculated based on the path length of the water body propagation segment and the sound wave velocity of the water body. The propagation time of the reservoir bottom segment is calculated based on the path length of the reservoir bottom medium propagation segment and the sound wave velocity of the reservoir bottom medium. Based on the propagation time of the water section and the propagation time of the reservoir bottom section, and in combination with the three-dimensional spatial propagation geometry path, the propagation path of the air gun-excited sound wave is determined.

[0014] Secondly, this application also provides a zero-time correction device for air gun excitation based on underwater vibration recording. The device includes: The distance calculation module is used to measure the geodetic coordinates of the floating platform on the water surface and the geodetic coordinates of the underwater seismometer at the moment of air gun firing using a real-time dynamic differential positioning device, and to calculate the distance between the air gun and the bottom of the reservoir. The propagation path determination module is used to measure the velocity of sound waves in the medium at the bottom of the reservoir and in the water, and to determine the propagation path of the sound waves excited by the air gun based on the velocity of the sound waves, the geodetic coordinates of the working platform on the water surface at the moment of the air gun excitation, and the geodetic coordinates of the underwater seismometer. The first-time acquisition module is used to record the near-field vibration waveform excited by the air gun through the underwater seismometer, and obtain the initial time of the reservoir bottom vibration at the geodetic coordinate position of the underwater seismometer based on the recorded near-field vibration waveform. The second time acquisition module is used to calculate the initial vibration time of the reservoir bottom vertically below the air gun based on the distance between the air gun and the reservoir bottom, the propagation path of the sound wave excited by the air gun, the sound wave velocity, and the initial vibration time of the reservoir bottom.

[0015] In summary, this application includes the following beneficial technical effects: By using a real-time dynamic differential positioning device to measure the geodetic coordinates of the floating platform and the underwater seismometer at the instant of air gun excitation, and calculating the distance between the air gun and the reservoir bottom, high-precision three-dimensional positioning of the excitation and receiving points can be achieved. This accurately obtains the vertical distance from the air gun to the reservoir bottom, avoiding zero-time calculation errors caused by positional deviations. Based on the sound wave velocity, the geodetic coordinates of the floating platform and the underwater seismometer at the instant of air gun excitation, the true propagation path of the sound wave can be accurately calculated, eliminating the timing distortion caused by uneven sound velocity and path deviation, providing a physical basis for accurately tracing back to the zero-time of excitation. The initial vibration time of the reservoir bottom at the geodetic coordinates of the underwater seismometer location can be calculated. Based on the distance between the air gun and the reservoir bottom, the propagation path of the sound wave from the air gun excitation, the sound wave velocity, and the initial vibration time of the reservoir bottom, the initial vibration time of the reservoir bottom vertically below the air gun can be calculated. This eliminates the propagation delay error of traditional methods at its source, effectively improving the detection accuracy of changes in the wave velocity of the underground medium, thereby achieving high-precision correction of the zero-time of air gun excitation. Attached Figure Description

[0016] Figure 1 This is a flowchart illustrating a zero-time correction method for air gun excitation based on underwater vibration recording in one embodiment. Figure 2 This is a flowchart illustrating a zero-time correction method for air gun excitation based on underwater vibration recording in another embodiment. Figure 3 This is a schematic diagram of the active vibration source excitation system and environment for an air gun; Figure 4 This is a structural block diagram of an air gun excitation zero-time correction device based on underwater vibration recording in one embodiment. Detailed Implementation

[0017] This invention provides a method and apparatus for zero-time correction of air gun excitation based on underwater vibration recording.

[0018] The embodiments of the present invention will now be described in more detail with reference to the accompanying drawings. While some embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the present disclosure. It should be understood that the accompanying drawings and embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.

[0019] In the description of the embodiments disclosed in this invention, the term "comprising" and similar terms should be understood as open-ended inclusion, i.e., "including but not limited to". The term "based on" should be understood as "at least partially based on". The term "one embodiment" or "the embodiment" should be understood as "at least one embodiment". The terms "first", "second", etc., may refer to different or the same objects. Other explicit and implicit definitions may also be included below.

[0020] For ease of understanding, the specific process of the embodiments of the present invention is described below. Please refer to [link / reference]. Figure 1 One embodiment of the air gun excitation zero-time correction method based on underwater vibration recording in this invention includes: The S100 uses a real-time dynamic differential positioning device to measure the geodetic coordinates of the floating platform on the water surface and the geodetic coordinates of the underwater seismometer at the moment the air gun is fired, and calculates the distance between the air gun and the bottom of the reservoir.

[0021] Specifically, by incorporating a Real-Time Kinematic (RTK) device and an underwater seismometer into the air gun firing system, theoretically, if the firing time of the air gun's electronic control can be obtained and the propagation delay of the electrical signal can be ignored, the firing time of the air gun can be directly determined, and the initial vibration time of the reservoir bottom can be further calculated by combining the air gun's immersion depth. However, in actual operation, after electronic firing, the air gun undergoes a series of mechanical behaviors such as air chamber compression and triggering, making it difficult to obtain the true firing time of the air gun using this method. Therefore, this application uses an underwater seismometer to directly record the near-field vibration waveform of the reservoir bottom, and uses this as a basis to accurately obtain the initial moment of the reservoir bottom vibration, thereby avoiding errors caused by mechanical delays. To solve the problem of calculation error of the initial vibration time of the reservoir bottom caused by the uncertainty of the location in the air gun active source detection, the RTK device is first used to perform high-precision geodetic coordinate synchronous measurement of the working platform on the water surface at the moment of air gun firing and the underwater seismometer pre-deployed at the bottom of the reservoir. Specifically, an RTK mobile station is fixedly installed on the surface working platform. Simultaneously with the triggering of the air gun's excitation control signal, the RTK device captures the platform's three-dimensional geodetic coordinates at the instant of excitation. At the same time, during the deployment of the underwater seismometer, the same RTK mobile station is used to perform a one-time, high-precision calibration of the underwater seismometer's geodetic coordinates at its fixed installation point on the reservoir bottom. Since the underwater seismometer's position remains unchanged after deployment, its geodetic coordinates can be used as known parameters for subsequent calculations. After obtaining the geodetic coordinates of the surface working platform and the underwater seismometer at the instant of air gun excitation, the spatial distance between the air gun and the reservoir bottom is calculated by combining the actual underwater depth of the air gun with the corresponding reservoir water depth data. Unlike traditional methods that rely solely on empirical values ​​or rough measurements, this scheme uses real-time acquired platform coordinates and pre-calibrated seismometer coordinates, combined with on-site measured water depth parameters, effectively eliminating positional deviations caused by the surface platform's drift with wind and waves and the undulating terrain of the reservoir bottom.

[0022] S200 measures the velocity of sound waves in the medium at the bottom of the reservoir and in the water. Based on the velocity of sound waves, the geodetic coordinates of the working platform on the water surface at the moment of air gun excitation, and the geodetic coordinates of the underwater seismometer, the propagation path of the sound waves excited by the air gun is determined.

[0023] Specifically, based on the determination of the geodetic coordinates of the floating platform and the underwater seismometer at the moment of air gun activation, and the calculation of the distance between the air gun and the reservoir bottom, the acoustic velocity of the water body and the reservoir bottom medium through which the sound wave propagates is further measured. Based on the obtained acoustic velocity parameters, spatial geometric parameters, and coordinate information, the actual propagation path of the acoustic wave generated by the air gun from the air gun to the underwater seismometer is determined. Specifically, the acoustic velocity in the reservoir water is measured first. Considering that differences in temperature, pressure, and other factors at different depths in the reservoir water may cause changes in acoustic velocity, this scheme obtains velocity parameters along the water depth direction that reflect the actual distribution of acoustic velocity in the water. Simultaneously, the acoustic velocity of the reservoir bottom medium is measured independently. This is because the acoustic velocity in the sedimentary layer or bedrock at the reservoir bottom is usually significantly different from the acoustic velocity in the water body. The acoustic wave undergoes refraction when passing through the water-bottom medium interface, and its propagation path is not a simple straight line. After obtaining the aforementioned sound velocity parameters, a three-dimensional spatial geometric relationship, including the excitation point and the receiving point, is constructed by comprehensively utilizing the measured geodetic coordinates of the floating platform at the moment of air gun excitation, the geodetic coordinates of the underwater seismometer, and the distance between the air gun and the reservoir bottom. The sound wave originates from the air gun excitation point at a certain depth underwater, propagates through the water to a point on the water-bottom medium interface, then enters the reservoir bottom medium, changes its propagation direction, and continues to propagate to the receiving position of the underwater seismometer. By jointly calculating the measured sound wave velocity in the water, the sound wave velocity in the reservoir bottom medium, the distance between the air gun and the reservoir bottom, and the geodetic coordinates of the excitation point and the receiving point, the actual propagation path followed by the sound wave during cross-medium propagation can be determined. This method provides a physical path reflecting the propagation behavior of sound waves in the real reservoir environment, offering a reliable geometric and physical basis for subsequent calculations of the sound wave propagation time from the air gun to the underwater seismometer.

[0024] The S300 records the near-field vibration waveform excited by the air gun using an underwater seismometer, and obtains the initial time of the reservoir bottom vibration at the geodetic coordinates of the location of the underwater seismometer based on the recorded near-field vibration waveform.

[0025] Specifically, after determining the propagation path of the sound waves generated by the air gun, the near-field vibrations generated by the air gun are directly recorded using underwater seismometers pre-deployed at the bottom of the reservoir. Based on the recorded vibration waveforms, the initial time of the reservoir bottom vibration at the geodetic coordinates of the underwater seismometer's location is extracted. Specifically, when the air gun is activated underwater, the generated sound / seismic waves propagate through the water and the reservoir bottom medium to the reservoir bottom. The underwater seismometer, fixedly installed at the bottom, collects the vibration signals in this area in real time, forming a near-field vibration waveform record. Because the underwater seismometer is installed close to the reservoir bottom medium, its recorded waveforms accurately reflect the vibration initiation time when the sound waves reach a specific location at the bottom of the reservoir. Compared to traditional methods that deploy reference instruments far from the excitation point (such as on the shore or a floating platform), this scheme uses near-field recording at the reservoir bottom, which significantly shortens the sound wave propagation distance and reduces time errors introduced by factors such as medium inhomogeneity and path curvature during propagation. After obtaining the near-field vibration waveform, the exact moment when the sound wave first arrives at the underwater seismometer's installation location can be determined by detecting and identifying the waveform's starting point. This moment is the initial vibration time of the reservoir bottom at the geodetic coordinates of the underwater seismometer's location. This time parameter directly reflects the actual arrival time of the sound wave generated by the air gun to the specific receiving point on the reservoir bottom, and is a key input parameter for subsequent calculations of the air gun's excitation time and the initial vibration time of the reservoir bottom vertically below the air gun. Through the above method, this scheme achieves near-field, direct, and high-precision acquisition of the initial vibration time of the reservoir bottom, providing a reliable waveform basis for zero-time calibration of the air gun excitation.

[0026] S400: Based on the distance between the air gun and the bottom of the reservoir, the propagation path of the sound wave excited by the air gun, the sound wave velocity, and the initial vibration time of the reservoir bottom, the initial vibration time of the reservoir bottom vertically below the air gun is calculated.

[0027] Specifically, after obtaining the initial vibration time of the reservoir bottom at the location of the underwater seismometer, the propagation path of the sound waves excited by the air gun, the sound wave velocity in the water and reservoir bottom medium, and the distance between the air gun and the reservoir bottom, the initial vibration time of the reservoir bottom vertically below the air gun is further calculated. Specifically, the sound waves generated by the air gun require a certain amount of time to propagate from the air gun to the location of the underwater seismometer at the reservoir bottom. This propagation time depends on the determined sound wave propagation path length and the sound wave propagation velocity in the water and reservoir bottom medium. Since the initial vibration time of the reservoir bottom recorded by the underwater seismometer is actually the absolute moment when the sound waves arrive at the receiving point, subtracting the propagation time required for the sound waves to travel from the air gun to the underwater seismometer from this moment allows for the reverse calculation of the actual zero-time of the air gun's excitation. After obtaining the zero-time of the air gun's excitation, the process of the sound waves propagating vertically downwards from the air gun to the reservoir bottom directly below it is further considered. The sound wave travels vertically from the air gun, passes through the water, and reaches the reservoir bottom. Its propagation distance is the measured distance between the air gun and the reservoir bottom. The propagation speed is the speed of sound waves in the water. Therefore, by adding the time required for the sound wave to travel vertically from the air gun to the reservoir bottom at the moment of air gun excitation, the initial vibration time of the reservoir bottom directly below the air gun can be calculated. This time parameter represents the initial start time of the seismic signal triggered by the air gun excitation at the reservoir bottom directly below the air gun, and is a crucial benchmark for subsequent detection of underground medium wave velocity changes. Compared to the traditional method of directly using the arrival time recorded by the reference instrument as the initial vibration time of the reservoir bottom, this scheme, through propagation path calculation, propagation time subtraction and compensation, restores the true initial moment of the reservoir bottom vibration from a physical mechanism perspective. This effectively eliminates the time error caused by the offset of the receiving point and the curvature of the propagation path, thus providing a reliable time benchmark for high-precision detection of underground medium wave velocity changes.

[0028] In one embodiment, such as Figure 2 As shown, S400 includes: S410, Based on the propagation path and velocity of the sound waves excited by the air gun, calculate the propagation time of the sound waves excited by the air gun from the air gun to the bottom of the reservoir where the underwater seismometer is located. S420, the air gun excitation time is calculated based on the difference between the initial time and the propagation time of the reservoir bottom vibration recorded by the underwater seismometer; S430, based on the air gun excitation time, the distance between the air gun and the bottom of the reservoir, and the sound wave velocity, calculates the initial vibration time of the reservoir bottom vertically below the air gun.

[0029] Specifically, firstly, based on the determined propagation path of the air gun-excited sound waves and the measured sound wave velocities in the water and the reservoir bottom medium, the propagation time required for the sound waves generated by the air gun to travel from the air gun to the reservoir bottom where the underwater seismometer is located is calculated. Since this propagation path crosses two different acoustic media—water and the reservoir bottom medium—and the sound waves travel at different speeds in these two media, it is necessary to calculate the propagation time in the water and the propagation time in the reservoir bottom medium segmentally, based on the actual geometry of the propagation path. Secondly, the air gun excitation time is calculated based on the difference between the initial time of the reservoir bottom vibration recorded by the underwater seismometer and the aforementioned propagation time. Specifically, the initial time of the reservoir bottom vibration recorded by the underwater seismometer is the absolute moment when the sound waves arrive at the receiving point. Since the sound waves require a certain propagation time to travel from the air gun to the underwater seismometer, subtracting the sound wave propagation time from the initial time of the reservoir bottom vibration allows for the reverse calculation of the actual excitation time of the air gun. Finally, based on the calculated air gun excitation time, the measured vertical distance between the air gun and the reservoir bottom, and the water sound wave velocity, the initial vibration time of the reservoir bottom directly below the air gun is calculated. In this step, the sound wave propagates vertically downwards from the air gun to the reservoir bottom surface directly below it, and the propagation path is entirely within the water body; therefore, the water sound wave velocity is used for calculation. Adding the air gun excitation time to the time required for the sound wave to propagate vertically from the air gun to the reservoir bottom yields the initial vibration time of the reservoir bottom directly below the air gun.

[0030] In this embodiment, starting from the initial time of the reservoir bottom vibration recorded by the underwater seismometer, the propagation time of the oblique propagation path is successively subtracted to obtain the zero time of air gun excitation. Then, the propagation time of the vertical propagation path is compensated, and finally the true initial vibration time of the reservoir bottom surface directly below the air gun is restored. This calculation process fully considers the cross-medium propagation characteristics of sound waves in the actual environment and the path differences in different directions. It can effectively eliminate the time error caused by the offset of the receiving point position and the approximation of the propagation path in traditional methods, and provide an accurate time reference for the detection of changes in the wave velocity of underground media.

[0031] In one embodiment, the calculation of the propagation time of the air gun-generated sound wave from the air gun to the bottom of the reservoir where the underwater seismometer is located, based on the propagation path and velocity of the sound wave, includes: The propagation path of the air gun-excited sound wave is divided into a water propagation segment and a reservoir bottom medium propagation segment. The propagation time in the water segment is calculated based on the path length and the velocity of the sound wave in the water. The propagation time in the reservoir bottom medium segment is calculated based on the path length and the velocity of the sound wave in the reservoir bottom medium. Based on the propagation time in the water segment and the propagation time in the reservoir bottom segment, the propagation time of the air gun-excited sound wave from the air gun to the location of the underwater seismometer at the bottom of the reservoir is obtained.

[0032] Specifically, the established propagation path of the air gun-excited sound waves is first divided into two segments according to the medium type: one is the propagation path in the water body, called the water propagation segment; the other is the propagation path in the reservoir bottom medium, called the reservoir bottom medium propagation segment. These two propagation segments are spatially continuous, with the refraction point at the water-bottom medium interface as the dividing point. The water propagation segment begins at the air gun excitation point and ends at the refraction point at the water-bottom medium interface; the reservoir bottom medium propagation segment begins at the refraction point and ends at the receiving point of the underwater seismometer. After completing the segmentation of the propagation path, the propagation time of each segment is calculated. For the water propagation segment, the propagation time is calculated by dividing the path length by the propagation speed, based on the actual geometric length of the path and the pre-measured sound wave velocity in the water. Since the sound wave velocity in the water may vary with depth, the average sound velocity along the path or integral calculation along the path can be used to improve time accuracy. For the propagation segment in the reservoir bottom medium, the propagation time is calculated by dividing the path length by the propagation speed, based on the actual geometric length of the path and the pre-measured acoustic wave velocity in the reservoir bottom medium. Finally, the propagation time in the water body segment and the propagation time in the reservoir bottom segment are added together to obtain the total propagation time of the air gun-excited sound wave from the air gun to the location of the underwater seismometer at the bottom of the reservoir.

[0033] In this embodiment, the segmented calculation and accumulation process described above can accurately reflect the impact of the difference in the propagation speed of sound waves in different media on the total propagation time. This avoids the time calculation error introduced by approximating the cross-medium propagation path as a single homogeneous path, and provides reliable time parameters for the accurate inversion of the zero time of subsequent air gun excitation.

[0034] In one embodiment, an underwater seismometer is fixedly installed in a reservoir and located in the area directly below and adjacent to the excitation point of the air gun; a real-time dynamic differential positioning device is fixedly installed on a floating platform on the water surface to obtain the geodetic coordinates of the air gun in real time with each excitation.

[0035] Specifically, the underwater seismometer is installed on the bottom of the reservoir using a fixed deployment method, such as... Figure 3As shown, the underwater seismometer is positioned in the area directly below and adjacent to the excitation point of the air gun. This "directly below and adjacent" area refers to a certain range near the surface of the reservoir bottom directly below the air gun, not an arbitrarily distant location on the reservoir bottom. The core purpose of placing the underwater seismometer in this area is to minimize the distance the sound wave travels from the air gun to the underwater seismometer, thereby reducing time errors introduced by factors such as medium inhomogeneity and path curvature during sound wave propagation. Simultaneously, it ensures a high signal-to-noise ratio for the received near-field vibration waveform, facilitating accurate identification of the initial vibration moment. It should be noted that this scheme does not impose stringent requirements on the deployment accuracy of the underwater seismometer. Even if there is a certain deviation from the position directly below the air gun, it can still be corrected through subsequent propagation path calculations, reducing the difficulty of deployment in the field. Meanwhile, the real-time dynamic differential positioning device is fixedly installed on the surface working platform, such as... Figure 3 As shown, the working platform may drift due to factors such as wind, waves, and currents on the water surface. A static positioning method cannot reflect the platform's true position at the moment of air gun firing, and the resulting coordinate error will directly affect subsequent distance calculations and time corrections. To address this issue, this solution links a real-time dynamic differential positioning device with the air gun firing control system. Each air gun firing triggers the positioning device to acquire real-time coordinates, thereby successively obtaining the real-time geodetic coordinates of the working platform on the water surface at the moment of firing. This sequential firing and real-time acquisition dynamic positioning method effectively eliminates the positional uncertainty caused by platform drift, ensuring that the geodetic coordinates of the air gun corresponding to each firing accurately reflect the actual position at the moment of firing.

[0036] In one embodiment, the geodetic coordinates of the floating platform on the water surface and the geodetic coordinates of the underwater seismometer at the moment of air gun firing are measured in real time using a real-time dynamic differential positioning device, and the distance between the air gun and the bottom of the reservoir is calculated, including: The geodetic coordinates of the floating platform and the underwater seismometer at the moment of air gun firing are determined in real time using a real-time dynamic differential positioning device; the immersion depth of the air gun in the reservoir is measured, and the water depth of the reservoir corresponding to the immersion position of the air gun is measured using a depth sounder; based on the immersion depth and the water depth of the reservoir, the distance between the air gun and the bottom of the reservoir is calculated.

[0037] Specifically, firstly, the geodetic coordinates of the working platform on the water surface at the moment of air gun firing are determined in real time using a real-time dynamic differential positioning device. These coordinates represent the precise position of the vertical projection point of the air gun on the water surface. Simultaneously, the geodetic coordinates of underwater seismometers pre-fixed at the bottom of the reservoir are obtained using the same real-time dynamic differential positioning device or a joint measurement method. Secondly, the immersion depth of the air gun in the reservoir is measured. The air gun is suspended below the working platform on the water surface by a cable, and its immersion depth can be measured based on the length of the cable or a depth sensor installed at the air gun. This depth parameter reflects the vertical distance of the air gun below the water surface. At the same time, the water depth of the reservoir corresponding to the immersion location of the air gun is measured using a depth sounder. The depth sounder is usually installed near the working platform on the water surface or near the air gun, and uses the principle of acoustic ranging to measure the vertical distance from the water surface to the bottom of the reservoir, i.e., the water depth at that location. Because the reservoir bottom topography may be undulating, the depth sounder measures the depth of the reservoir bottom directly below the location where the air gun is placed, rather than the average water depth of the entire reservoir. This ensures the spatial correspondence between the water depth data and the air gun's location. Finally, based on the measured air gun placement depth and reservoir water depth, the distance between the air gun and the reservoir bottom is calculated. Specifically, the air gun is located at its placement depth below the water surface, and the reservoir bottom is located at its deepest point below the water surface. Therefore, the vertical distance between the air gun and the reservoir bottom is equal to the reservoir water depth minus the air gun placement depth. Through this calculation, the vertical distance parameter from the air gun to the surface of the reservoir bottom directly below it can be obtained.

[0038] In one embodiment, the sound wave velocity in the reservoir bottom medium and water is measured, and the propagation path of the sound wave excited by the air gun is determined based on the sound wave velocity, the geodetic coordinates of the working floating platform at the moment of air gun excitation, and the geodetic coordinates of the underwater seismometer, including: The sound velocity of the water in the reservoir from the surface to the bottom was collected in layers using a sound velocity profiler, and a vertical sound velocity distribution model of the reservoir water was constructed. The sound velocity of the medium at the bottom of the reservoir was obtained by combining in-situ testing with medium inversion. Combined with the vertical sound velocity distribution model of the reservoir water, a dual-medium acoustic parameter model was established. Based on the geodetic coordinates of the working platform on the water surface and the geodetic coordinates of the underwater seismometer at the moment of air gun excitation, combined with the air gun's immersion depth and the reservoir water depth, the three-dimensional spatial propagation geometric path from the air gun to the underwater seismometer was calculated. Based on the three-dimensional spatial propagation geometric path and the dual-medium acoustic parameter model, the propagation path of the sound wave excited by the air gun was determined.

[0039] Specifically, the first step is to conduct precise measurements of the sound velocity in the reservoir water. Due to differences in temperature, pressure, and impurity content at different depths within the reservoir water, the sound velocity exhibits a vertically stratified variation. To address this characteristic, this scheme uses a sound velocity profiler to collect data stratified along the water depth from the surface to the reservoir bottom, obtaining sound velocity data at different depths. Based on these discrete measurement points, a continuous vertical sound velocity distribution model of the reservoir water is constructed. This model accurately reflects the variation of sound wave velocity with depth during propagation in the water, providing precise velocity parameters for subsequent propagation time calculations. Secondly, the sound velocity in the reservoir bottom medium is measured. The reservoir bottom medium is typically composed of sedimentary layers or bedrock, and its sound velocity differs significantly from that in the water, making it difficult to obtain through direct measurement. To address this challenge, this solution employs a combination of in-situ testing and medium inversion: In-situ acoustic testing is conducted using a seismic source and receiving device deployed on-site to acquire the response signal of the reservoir bottom medium. This signal is then combined with the medium's density, elastic modulus, and other physical properties for inversion calculations, yielding the acoustic velocity of the reservoir bottom medium. This obtained acoustic velocity is then combined with a previously constructed vertical sound velocity distribution model of the water body to establish a dual-medium acoustic parameter model incorporating different acoustic parameters from both the water body and the reservoir bottom medium. This model comprehensively describes the velocity characteristics of sound waves propagating in both media and their variation at the interface. Next, the three-dimensional spatial propagation geometric path from the air gun to the underwater seismometer is calculated. Based on the geodetic coordinates of the floating platform at the moment of air gun excitation, determined by a real-time dynamic differential positioning device, and the geodetic coordinates of the underwater seismometer, along with the air gun's immersion depth and the reservoir depth, the three-dimensional spatial excitation point coordinates of the air gun underwater and the three-dimensional spatial receiving point coordinates of the underwater seismometer at the reservoir bottom are determined. Based on this, a three-dimensional spatial propagation geometric path connecting the excitation point and the receiving point is obtained through spatial geometric calculation. This path reflects the straight or broken geometric shape of the sound wave propagating from the air gun to the underwater seismometer without considering the influence of the medium. Finally, the three-dimensional spatial propagation geometric path obtained above is matched with the established dual-medium acoustic parameter model to determine the actual propagation path of the sound wave excited by the air gun. Due to the different propagation speeds of the sound wave in the water and the reservoir bottom medium, it will be refracted when passing through the water-bottom medium interface. The actual propagation path is not a simple straight line, but a broken path following Snell's law. By jointly solving the geometric path with the dual-medium acoustic parameter model, and fully considering the influence of the sound speed difference on the propagation direction, the actual curved propagation path of the sound wave starting from the air gun, propagating through the water to a point on the water-bottom medium interface, then refracting into the reservoir bottom medium, and finally propagating to the receiving point of the underwater seismometer can be determined.

[0040] In one embodiment, based on the geodetic coordinates of the floating platform at the moment of air gun firing and the geodetic coordinates of the underwater seismometer, combined with the air gun's immersion depth and the reservoir's water depth, the three-dimensional spatial propagation geometric path from the air gun to the underwater seismometer is calculated, including: Based on the geodetic coordinates of the floating platform at the moment of air gun firing and the depth of the air gun's immersion, the three-dimensional spatial firing point coordinates of the air gun are determined underwater. Based on the geodetic coordinates of the underwater seismometer and the water depth of the reservoir, the three-dimensional spatial receiving point coordinates of the underwater seismometer at the bottom of the reservoir are determined. Based on the three-dimensional spatial firing point coordinates and the three-dimensional spatial receiving point coordinates, spatial geometric calculations are performed to obtain the three-dimensional spatial propagation geometric path from the air gun to the underwater seismometer.

[0041] Specifically, firstly, based on the geodetic coordinates of the working platform on the water surface at the moment of air gun firing and the air gun's submersion depth, the three-dimensional spatial firing point coordinates of the air gun underwater are determined. The real-time dynamic differential positioning device measures the geodetic coordinates of the working platform on the water surface at the moment of firing, which represents the vertical projection point of the air gun on the water surface. Since the air gun is suspended below the platform by cables, its actual underwater position is directly below the platform, with the horizontal direction consistent with the platform's coordinates, and the vertical direction located at the air gun's submersion depth below the water surface. Therefore, by using the platform's geodetic coordinates as the horizontal coordinates and combining them with the air gun's submersion depth as the vertical coordinates, the three-dimensional spatial firing point coordinates of the air gun underwater can be completely determined. Secondly, based on the geodetic coordinates of the underwater seismometer and the reservoir depth, the three-dimensional spatial receiving point coordinates of the underwater seismometer on the reservoir bottom are determined. The underwater seismometer is fixedly deployed on the reservoir bottom, and its geodetic coordinates have been accurately measured in advance by the real-time dynamic differential positioning device, reflecting the seismometer's horizontal position. Since the underwater seismometer is located on the reservoir bottom surface, its vertical coordinates depend on the reservoir depth at that location, i.e., the distance vertically downwards from the water surface to the reservoir bottom. Therefore, by using the geodetic coordinates of the underwater seismometer as the horizontal coordinates and combining them with the reservoir depth at that location as the vertical coordinates, the three-dimensional spatial coordinates of the underwater seismometer's receiving point on the reservoir bottom can be completely determined. Finally, based on the obtained three-dimensional spatial excitation point coordinates and three-dimensional spatial receiving point coordinates, spatial geometric calculations are performed to obtain the three-dimensional spatial propagation geometric path from the air gun to the underwater seismometer. This calculation process is based on the geometric principle that two points determine a spatial straight line. By calculating parameters such as the horizontal distance, vertical height difference, and spatial straight-line distance between the excitation and receiving points, a three-dimensional spatial geometric connection is constructed from the air gun excitation point to the underwater seismometer receiving point. This connection represents the shortest spatial path for sound waves to propagate from the excitation point to the receiving point without considering the effects of medium refraction, providing an initial geometric reference for subsequently determining the actual curved propagation path using a dual-medium acoustic parameter model.

[0042] In one embodiment, determining the propagation path of the air gun-excited sound wave based on the three-dimensional spatial propagation geometry path and the dual-medium acoustic parameter model includes: Based on the three-dimensional propagation geometry, the incident point and angle of the sound wave from the air gun to the reservoir bottom interface are determined. The reservoir bottom interface refers to the refraction interface that the sound wave passes through when entering the reservoir bottom medium from the water. Based on the vertical sound velocity distribution of the water body and the sound wave velocity in the reservoir bottom medium in the dual-medium acoustic parameter model, combined with the incident angle, the refraction angle of the sound wave in the reservoir bottom medium is calculated based on Snell's law. Based on the refraction angle, the location of the refraction point of the sound wave on the reservoir bottom interface is determined, and the water body propagation segment and the reservoir bottom medium propagation segment are divided. Based on the path length of the water body propagation segment and the sound wave velocity in the water body, the propagation time of the water body segment is calculated, and based on the path length of the reservoir bottom medium propagation segment and the sound wave velocity in the reservoir bottom medium, the propagation time of the reservoir bottom segment is calculated. Based on the propagation time of the water body segment and the propagation time of the reservoir bottom segment, combined with the three-dimensional propagation geometry, the propagation path of the sound wave excited by the air gun is determined.

[0043] Specifically, firstly, based on the three-dimensional propagation geometry, the incident point and incident angle of the sound wave propagating from the air gun to the reservoir bottom interface are determined. The reservoir bottom interface refers to the interface between the water body and the reservoir bottom medium, i.e., the refraction interface that the sound wave passes through when entering the reservoir bottom medium from the water. The three-dimensional propagation geometry provides a straight line connecting the excitation point and the receiving point; the intersection of this line and the reservoir bottom interface is the initial incident point, and the angle between this line at the incident point and the interface normal is the incident angle. Secondly, based on the vertical sound velocity distribution in the water body and the sound wave velocity in the reservoir bottom medium in the dual-medium acoustic parameter model, combined with the aforementioned incident angle, the refraction angle of the sound wave in the reservoir bottom medium is calculated based on Snell's law. Snell's law describes the relationship that when a sound wave passes through the interface of two different media, the ratio of the refractive index to the refraction angle satisfies the ratio of the sound velocities in the two media. Since the dual-medium acoustic parameter model includes the vertical sound velocity distribution in the water, the refractive index can be calculated based on the sound velocity in the water and the sound velocity in the reservoir bottom medium at the incident point, and then the refraction angle can be solved. This refraction angle reflects the change in the propagation direction of the sound wave after entering the reservoir bottom medium. Then, based on the calculated refraction angle, the location of the refraction point on the interface between the sound wave and the reservoir bottom is determined, and the water propagation segment and the reservoir bottom medium propagation segment are divided. The refraction point is the actual spatial location of the sound wave passing through the water-bottom medium interface, which may differ from the initial incident point and needs to be corrected based on the refraction angle. After determining the refraction point, the sound wave propagation path is divided into a water propagation segment from the air gun to the refraction point and a reservoir bottom medium propagation segment from the refraction point to the underwater seismometer. The two segments are connected at the refraction point and satisfy the refraction relationship. Then, the propagation time of each segment is calculated. For the water propagation segment, the propagation time is calculated based on the actual geometric length of the path and the water sound wave velocity at the corresponding location in the dual-medium acoustic parameter model. Since the velocity of sound waves in water may exhibit vertical stratification, path integration can be used to improve accuracy during calculation. For the propagation segment in the reservoir bottom medium, the propagation time of the reservoir bottom segment is calculated based on the actual geometric length of the path and the sound wave velocity in the reservoir bottom medium. Finally, based on the propagation times in the water segment and the reservoir bottom segment, and combined with the three-dimensional spatial propagation geometry, the propagation path of the air gun-excited sound waves is determined. Specifically, the propagation times in the water segment and the reservoir bottom segment are added together to obtain the total propagation time of the sound waves from the air gun to the underwater seismometer. Simultaneously, the water segment and the reservoir bottom medium propagation segment are connected at the refraction point to form a complete broken-line path from the excitation point through the refraction point to the receiving point. This path is the actual propagation path of the air gun-excited sound waves.

[0044] In one embodiment, such as Figure 4As shown, a zero-time correction device for air gun excitation based on underwater vibration recording is provided, comprising: a distance calculation module 10, a propagation path determination module 20, a first time acquisition module 30, and a second time acquisition module 40, wherein: The distance calculation module 10 is used to measure the geodetic coordinates of the working platform on the water surface and the geodetic coordinates of the underwater seismometer at the moment of air gun firing through a real-time dynamic differential positioning device, and to calculate the distance between the air gun and the bottom of the reservoir. The propagation path determination module 20 is used to measure the velocity of sound waves in the medium at the bottom of the reservoir and in the water, and to determine the propagation path of the sound waves excited by the air gun based on the velocity of sound waves, the geodetic coordinates of the working floating platform on the water surface at the moment of air gun excitation, and the geodetic coordinates of the underwater seismometer. The first-time acquisition module 30 is used to record the near-field vibration waveform excited by the air gun through the underwater seismometer, and to obtain the initial time of the reservoir bottom vibration at the geodetic coordinate position of the underwater seismometer based on the recorded near-field vibration waveform. The second time acquisition module 40 is used to calculate the initial vibration time of the reservoir bottom vertically below the air gun based on the distance between the air gun and the bottom of the reservoir, the propagation path of the sound wave excited by the air gun, the sound wave velocity, and the initial vibration time of the reservoir bottom.

[0045] In one embodiment, the second time acquisition module 40 is further configured to calculate the propagation time of the air gun-excited sound wave from the air gun to the bottom of the reservoir where the underwater seismometer is located, based on the propagation path and velocity of the sound wave excited by the air gun; calculate the air gun excitation time based on the difference between the initial vibration time of the reservoir bottom recorded by the underwater seismometer and the propagation time; and calculate the initial vibration time of the reservoir bottom vertically below the air gun based on the air gun excitation time, the distance between the air gun and the reservoir bottom, and the velocity of the sound wave.

[0046] In one embodiment, the second time acquisition module 40 is further configured to divide the propagation path of the air gun-excited sound wave into a water propagation segment and a reservoir bottom medium propagation segment; calculate the water propagation time based on the path length of the water propagation segment and the sound wave velocity in the water; calculate the reservoir bottom propagation time based on the path length of the reservoir bottom medium propagation segment and the sound wave velocity in the reservoir bottom medium; and obtain the propagation time of the air gun-excited sound wave from the air gun to the location of the underwater seismometer at the bottom of the reservoir based on the water propagation time and the reservoir bottom propagation time.

[0047] In one embodiment, the distance calculation module 10 is also used to determine the geodetic coordinates of the working platform on the water surface and the geodetic coordinates of the underwater seismometer at the moment of air gun firing using a real-time dynamic differential positioning device; measure the immersion depth of the air gun in the reservoir, and measure the water depth of the reservoir in the area corresponding to the immersion position of the air gun using a depth sounder; and calculate the distance between the air gun and the bottom of the reservoir based on the immersion depth and the water depth of the reservoir.

[0048] In one embodiment, the propagation path determination module 20 is further configured to: collect the sound wave velocity from the water surface to the bottom of the reservoir using a sound velocity profiler to construct a vertical sound velocity distribution model of the reservoir water; obtain the sound wave velocity of the medium at the bottom of the reservoir by combining in-situ testing with medium inversion; establish a dual-medium acoustic parameter model based on the vertical sound velocity distribution model of the reservoir water; calculate the three-dimensional spatial propagation geometric path from the air gun to the underwater seismometer based on the geodetic coordinates of the working platform on the water surface and the geodetic coordinates of the underwater seismometer at the moment of air gun excitation, combined with the air gun immersion depth and the reservoir water depth; and determine the propagation path of the sound wave excited by the air gun based on the three-dimensional spatial propagation geometric path and the dual-medium acoustic parameter model.

[0049] In one embodiment, the propagation path determination module 20 is further used to determine the three-dimensional spatial excitation point coordinates of the air gun underwater based on the geodetic coordinates of the working platform on the water surface at the moment of air gun excitation and the immersion depth of the air gun; to determine the three-dimensional spatial receiving point coordinates of the underwater seismometer at the bottom of the reservoir based on the geodetic coordinates of the underwater seismometer and the water depth of the reservoir; and to perform spatial geometric calculations based on the three-dimensional spatial excitation point coordinates and the three-dimensional spatial receiving point coordinates to obtain the three-dimensional spatial propagation geometric path from the air gun to the underwater seismometer.

[0050] In one embodiment, the propagation path determination module 20 determines the incident point and incident angle of the sound wave propagating from the air gun to the reservoir bottom interface based on the three-dimensional spatial propagation geometry path. The reservoir bottom interface refers to the refraction interface through which the sound wave passes when entering the reservoir bottom medium from the water. Based on the vertical sound velocity distribution in the water body and the sound wave velocity in the reservoir bottom medium in the dual-medium acoustic parameter model, and combined with the incident angle, the refraction angle of the sound wave in the reservoir bottom medium is calculated based on Snell's law. Based on the refraction angle, the refraction point position of the sound wave on the reservoir bottom interface is determined, and the water body propagation segment and the reservoir bottom medium propagation segment are divided. Based on the path length of the water body propagation segment and the sound wave velocity in the water body, the propagation time of the water body segment is calculated, and based on the path length of the reservoir bottom medium propagation segment and the sound wave velocity in the reservoir bottom medium, the propagation time of the reservoir bottom segment is calculated. Based on the propagation time of the water body segment and the propagation time of the reservoir bottom segment, and combined with the three-dimensional spatial propagation geometry path, the propagation path of the sound wave excited by the air gun is determined.

[0051] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A method for zero-time correction of air gun excitation based on underwater vibration recording, characterized in that, include: The geodetic coordinates of the floating platform on the water surface and the geodetic coordinates of the underwater seismometer at the moment of air gun firing are measured in real time using a real-time dynamic differential positioning device, and the distance between the air gun and the bottom of the reservoir is calculated. The velocity of sound waves in the medium at the bottom of the reservoir and in the water is measured, and the propagation path of the sound waves excited by the air gun is determined based on the velocity of sound waves, the geodetic coordinates of the working floating platform on the water surface at the moment of the air gun excitation, and the geodetic coordinates of the underwater seismometer. The underwater seismometer records the near-field vibration waveform excited by the air gun, and based on the recorded near-field vibration waveform, the initial time of the reservoir bottom vibration at the geodetic coordinates of the underwater seismometer is obtained. The initial vibration time of the reservoir bottom is calculated based on the distance between the air gun and the reservoir bottom, the propagation path of the sound wave excited by the air gun, the speed of the sound wave, and the initial vibration time of the reservoir bottom.

2. The method for zero-time correction of air gun excitation based on underwater vibration recording according to claim 1, characterized in that, The calculation of the initial vibration time of the reservoir bottom vertically below the air gun, based on the distance between the air gun and the reservoir bottom, the propagation path of the sound wave excited by the air gun, the sound wave velocity, and the initial vibration time of the reservoir bottom, includes: Based on the propagation path of the sound wave excited by the air gun and the speed of the sound wave, calculate the propagation time of the sound wave excited by the air gun from the air gun to the bottom of the reservoir where the underwater seismometer is located. The air gun excitation time is calculated based on the difference between the initial time of the reservoir bottom vibration recorded by the underwater seismometer and the propagation time. The initial vibration time of the reservoir bottom perpendicularly below the air gun is calculated based on the air gun's firing time, the distance between the air gun and the reservoir bottom, and the sound wave velocity.

3. The method for zero-time correction of air gun excitation based on underwater vibration recording according to claim 2, characterized in that, The calculation of the propagation time of the air gun-generated sound wave from the air gun to the bottom of the reservoir where the underwater seismometer is located, based on the propagation path of the sound wave and the sound wave velocity, includes: The propagation path of the sound waves generated by the air gun is divided into a water propagation segment and a reservoir bottom medium propagation segment. The propagation time of the water segment is calculated based on the path length of the water propagation segment and the speed of sound in water. The propagation time of the bottom section is calculated based on the path length of the propagation segment in the reservoir bottom medium and the sound wave velocity in the reservoir bottom medium. Based on the propagation time in the water section and the propagation time at the bottom of the reservoir, the propagation time of the sound wave excited by the air gun from the air gun to the location at the bottom of the reservoir where the underwater seismometer is located is obtained.

4. The method for zero-time correction of air gun excitation based on underwater vibration recording according to claim 1, characterized in that, The underwater seismometer is fixedly deployed in the reservoir and located in the area directly below and adjacent to the air gun's firing point; the real-time dynamic differential positioning device is fixedly installed on the surface working platform and is used to obtain the geodetic coordinates of the air gun in real time with each firing.

5. The method for zero-time correction of air gun excitation based on underwater vibration recording according to claim 1, characterized in that, The process of using a real-time dynamic differential positioning device to measure the geodetic coordinates of the floating platform on the water surface and the geodetic coordinates of the underwater seismometer at the moment of air gun firing, and calculating the distance between the air gun and the reservoir bottom, includes: The geodetic coordinates of the floating platform and the underwater seismometer at the moment of air gun excitation are measured in real time using a real-time dynamic differential positioning device. The depth at which the air gun was submerged in the reservoir was measured, and the water depth in the area corresponding to the submerged position of the air gun was measured using a depth sounder. Calculate the distance between the air gun and the bottom of the reservoir based on the immersion depth and the water depth of the reservoir.

6. The method for zero-time correction of air gun excitation based on underwater vibration recording according to claim 1, characterized in that, The measurement of the sound wave velocity in the reservoir bottom medium and water, and the determination of the propagation path of the sound wave excited by the air gun based on the sound wave velocity, the geodetic coordinates of the floating platform at the moment of air gun excitation, and the geodetic coordinates of the underwater seismometer, include: The sound velocity of the water in the reservoir was collected in layers from the water surface to the bottom of the reservoir using a sound velocity profiler, and a vertical sound velocity distribution model of the water in the reservoir was constructed. By combining in-situ testing with medium inversion, the acoustic velocity of the medium at the bottom of the reservoir is obtained. Combined with the vertical acoustic velocity distribution model of the reservoir water, a dual-medium acoustic parameter model is established. Based on the geodetic coordinates of the floating platform at the moment of air gun firing and the geodetic coordinates of the underwater seismometer, combined with the air gun's immersion depth and the reservoir's water depth, the three-dimensional spatial propagation geometric path from the air gun to the underwater seismometer is calculated. Based on the three-dimensional spatial propagation geometry path and the dual-medium acoustic parameter model, the propagation path of the air gun-excited sound wave is determined.

7. The method for zero-time correction of air gun excitation based on underwater vibration recording according to claim 6, characterized in that, The calculation of the three-dimensional spatial propagation geometric path from the air gun to the underwater seismometer, based on the geodetic coordinates of the floating platform at the moment of air gun excitation, the geodetic coordinates of the underwater seismometer, and the submersion depth of the air gun and the water depth of the reservoir, includes: Based on the geodetic coordinates of the working platform on the water surface at the moment of air gun firing and the immersion depth of the air gun, the three-dimensional spatial coordinates of the air gun firing point underwater are determined. Based on the geodetic coordinates of the underwater seismometer and the water depth of the reservoir, the three-dimensional spatial coordinates of the receiving point of the underwater seismometer at the bottom of the reservoir are determined. Based on the coordinates of the three-dimensional excitation point and the coordinates of the three-dimensional receiving point, spatial geometric calculations are performed to obtain the three-dimensional spatial propagation geometric path from the air gun to the underwater seismometer.

8. The method for zero-time correction of air gun excitation based on underwater vibration recording according to claim 6, characterized in that, The step of determining the propagation path of the air gun-excited sound wave based on the three-dimensional spatial propagation geometry path and the dual-medium acoustic parameter model includes: Based on the three-dimensional spatial propagation geometric path, the incident point and incident angle of the sound wave from the air gun to the bottom interface of the reservoir are determined, wherein the bottom interface of the reservoir refers to the refraction interface that the sound wave passes through when it enters the reservoir bottom medium from the water. Based on the vertical sound velocity distribution of the water body and the sound wave velocity of the reservoir bottom medium in the dual-medium acoustic parameter model, and combined with the incident angle, the refraction angle of the sound wave in the reservoir bottom medium is calculated based on Snell's law. Based on the refraction angle, the location of the refraction point of the sound wave on the interface of the reservoir bottom is determined, and the water propagation segment and the reservoir bottom medium propagation segment are divided. The propagation time of the water body segment is calculated based on the path length of the water body propagation segment and the sound wave velocity of the water body. The propagation time of the reservoir bottom segment is calculated based on the path length of the reservoir bottom medium propagation segment and the sound wave velocity of the reservoir bottom medium. Based on the propagation time of the water section and the propagation time of the reservoir bottom section, and in combination with the three-dimensional spatial propagation geometry path, the propagation path of the air gun-excited sound wave is determined.

9. A zero-time correction device for air gun excitation based on underwater vibration recording, characterized in that, include: The distance calculation module is used to measure the geodetic coordinates of the floating platform on the water surface and the geodetic coordinates of the underwater seismometer at the moment of air gun firing using a real-time dynamic differential positioning device, and to calculate the distance between the air gun and the bottom of the reservoir. The propagation path determination module is used to measure the velocity of sound waves in the medium at the bottom of the reservoir and in the water, and to determine the propagation path of the sound waves excited by the air gun based on the velocity of the sound waves, the geodetic coordinates of the working platform on the water surface at the moment of the air gun excitation, and the geodetic coordinates of the underwater seismometer. The first-time acquisition module is used to record the near-field vibration waveform excited by the air gun through the underwater seismometer, and obtain the initial time of the reservoir bottom vibration at the geodetic coordinate position of the underwater seismometer based on the recorded near-field vibration waveform. The second time acquisition module is used to calculate the initial vibration time of the reservoir bottom vertically below the air gun based on the distance between the air gun and the reservoir bottom, the propagation path of the sound wave excited by the air gun, the sound wave velocity, and the initial vibration time of the reservoir bottom.

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