Reflected wave travel time difference measurement method and system based on transverse constraint

Abstract

The invention discloses a reflected wave travel time difference measurement method and system based on transverse constraint, and the method comprises the steps: carrying out the migration imaging of observed seismic data under a given speed model, obtaining an imaging result through the cross-correlation of a seismic source end wave field and a receiving end wave field, and obtaining the information of an underground reflection structure based on a multi-attribute Markov decision process. And then solving a background wave field and a primary reflection wave field in a given speed model and an underground reflection structure, and extracting a simulated seismic record at a detection point position. And calculating zero-offset travel time by using the depth of the reflection horizon, and executing transverse tracking in the reflection event direction by taking the travel time as a seed to obtain simulated travel time of each offset position. A local transverse constraint time window is constructed based on simulation travel time, cross-correlation operation is performed on observation data and simulation data in the time window, and a local extreme point is extracted. And finally, performing transverse tracking by taking the zero-offset travel time position as a starting point to obtain continuous and consistent reflected wave travel time difference, thereby realizing stable and accurate measurement of the reflected travel time.

Description

Technical Field

[0001] This invention relates to the field of geophysical exploration technology, specifically to a method and system for measuring the travel time difference of reflected waves based on lateral constraints. Background Technology

[0002] In seismic exploration, constructing an accurate subsurface velocity model is a crucial step for high-resolution imaging and inversion. Especially in the deep sea and deep / ultra-deep subsurface regions, conventional velocity models are insufficient to meet imaging accuracy requirements. To update deep-subsurface velocity models, inversion using reflected wave information becomes essential. The general process of reflected wave inversion includes: performing migration imaging under a given velocity model to obtain reflection interface information; generating simulated seismic records through inverse migration; comparing the observed seismic records with the simulated records to construct a target functional; and calculating the gradient based on the adjoint state method to update the velocity model. With iterative processing, the error gradually decreases, resulting in a velocity model that accurately reflects the actual subsurface structure.

[0003] In comparing observed and simulated data, waveform matching is used to form a conventional full waveform inversion (FWI). However, when the initial velocity model error is large, the observed and simulated waveforms often cannot be correctly matched, leading to distorted results. This is because seismic wave amplitude is affected by multiple factors such as surface conditions, propagation path, and absorption attenuation. To reduce amplitude dependence and improve inversion stability, travel-time-based inversion methods are commonly used, the core of which lies in accurately measuring the travel-time differences of reflected waves. Currently, commonly used travel-time measurement methods mainly include the following categories:

[0004] (1) Cross-correlation methods: These include single-channel local cross-correlation and time-space local cross-correlation methods. These methods calculate the cross-correlation coefficient between observed and simulated data and take the time shift corresponding to the maximum correlation coefficient as the travel time difference. However, this method is only applicable to a single dominant wave event, is easily affected by amplitude, and is sensitive to window selection. While the improved time-space local cross-correlation method introduces lateral information, it is prone to getting trapped in local extrema, leading to larger travel time estimation errors.

[0005] (2) Dynamic Time Warping (DTW) method: This method performs global matching on a single channel scale and obtains the optimal time shift path through dynamic programming. Although it can avoid the problem of mismatch in a single event, it requires that the two sets of data signals have the same order and the same number of events, and does not consider the lateral continuity between multiple channels, which can easily lead to unreasonable time jumps.

[0006] (3) Optimal Transport (OT) method: This method describes seismic data as two probability distributions and seeks the minimum cost path that maps mode A to mode B. Although it has global matching properties and strong robustness, it is sensitive to noise and high-frequency components, has high computational cost, and faces difficulties in multichannel expansion.

[0007] In summary, most existing methods are based on single-channel waveform matching and do not fully utilize the lateral continuity of reflection events, resulting in insufficient accuracy and stability of travel time measurement. Therefore, this invention proposes a travel time measurement method for reflected waves that considers lateral constraints. By introducing lateral structural constraints from the same underground reflection layer, the method tracks and constrains reflection information from the same layer during travel time measurement, thereby improving the accuracy and stability of travel time measurement. Summary of the Invention

[0008] The purpose of this invention is to provide a method and system for measuring the travel time difference of reflected waves based on lateral constraints, which aims to solve the problems of traditional reflected wave travel time measurement methods lacking lateral structural constraints and being inaccurate and unstable in extracting travel time differences in complex underground media.

[0009] In a first aspect, the present invention provides a method for measuring the travel time difference of reflected waves based on transverse constraints, comprising the following steps:

[0010] S1, under a given velocity model, perform migration imaging on the observed seismic data to obtain subsurface imaging results, and extract subsurface reflection structure information from the imaging results;

[0011] S2, based on the velocity model and the underground reflection structure information, perform inverse migration calculation, extract simulated reflected wave seismic records at the receiver point location, and form simulated reflected wave data;

[0012] S3, Calculate the two-way travel time of the simulated reflected wave at the zero-offset position based on the reflective layer structure information. The zero offset travel time is used as the initial seed point for the corresponding reflection layer.

[0013] S4. Using the initial seed point as the starting constraint, search for waveform extreme points channel by channel in the simulated reflected wave data along the transverse arrangement direction of the detector. Lateral tracking is performed based on the continuity of adjacent channel extrema to obtain the travel time position of the simulated reflected wave at a non-zero offset. ;

[0014] S5. Based on the travel time of the simulated reflected wave at each spatial location, a local lateral constraint time window is constructed, and the cross-correlation function between the observed seismic data and the simulated reflected wave data is calculated within the local lateral constraint time window. ;

[0015] S6, Extract the corresponding extreme points from the cross-correlation function. Using the time offset corresponding to the extreme point as the travel time constraint, lateral tracking is performed in the direction of the reflection layer to obtain the travel time difference between the observed reflected wave and the simulated reflected wave. .

[0016] As a preferred technical solution of the present invention, the velocity model is used to describe the velocity model of the underground medium at different spatial locations. And participates in the offset imaging and inverse offset calculation process in the form of a spatially continuous velocity field;

[0017] The velocity model can be an initially constructed background velocity model or an intermediate velocity model obtained by successive updates based on reflected wave inversion.

[0018] As a preferred technical solution of the present invention, the underground reflective structure information Based on imaging results of underground space locations Obtained through structured extraction;

[0019] The structured extraction is used to identify reflection in-phase axes with lateral continuity in the imaging results and to characterize the reflection in-phase axes with spatial position parameters.

[0020] The information on the underground reflection structure is only used to define the distribution location of reflection events in the underground space, and does not participate in the amplitude adjustment or spectrum transformation of the original seismic waveform, thereby ensuring that the simulated reflection wave data in the subsequent back-migration calculation retains only the main reflection events corresponding to the underground reflection layer.

[0021] As a preferred technical solution of the present invention, the zero-offset travel time is, under the condition that the source location and the receiver location coincide, along the corresponding underground reflection layer. The two-way travel time of the reflected wave is calculated under given velocity model constraints;

[0022] The zero-offset travel time serves as a time reference for the reflection layer along the survey line direction. It is used to establish initial travel time constraints for different reflection layers, so that the subsequent lateral tracking process has a clear starting reference point in the time dimension, thereby avoiding mismatches between different reflection events.

[0023] As a preferred technical solution of the present invention, the lateral tracking includes:

[0024] With the current detector point The travel time of the reflected wave at the location is used as the seed point, and the seed point is located at the adjacent receiver point. Within the corresponding simulated reflected wave data, a time search range is defined, and the extreme point with the smallest time distance from the seed point is determined within the time search range. ; the time position corresponding to the extreme point The travel times of reflected waves at adjacent receiver points are used as the new seed points to continue tracing along the survey line, thereby obtaining a complete simulated travel time distribution of reflected waves while maintaining the lateral continuity of the reflection events. .

[0025] As a preferred technical solution of the present invention, the extreme point is a sampling point within a preset time search range where the absolute value of the waveform amplitude of the simulated reflected wave and the observed reflected wave reaches a local maximum value; the extreme point is used to characterize the significant arrival position of the reflection event in the time axis direction, and its selection process depends only on the relative change characteristics of the waveform, rather than on the absolute amplitude of the waveform, thereby reducing the impact of amplitude difference, energy attenuation and noise interference on the time travel identification process.

[0026] As a preferred technical solution of the present invention, the local lateral constraint time window travels with the simulated reflected wave at the corresponding spatial location. Centered on the time axis, a predetermined number of time sampling points are extended along both the positive and negative directions of the time axis. The upper and lower boundaries of the local lateral constraint window are respectively represented as:

[0027] ;

[0028] ;

[0029] in, and These are the upper and lower time window positions, The time window size is a preset time window half-width parameter used to limit the time range of cross-correlation calculations, so as to suppress non-target events and noise interference while ensuring the integrity of target reflection events; This represents the simulated travel time of the reflected wave at spatial location x of the i-th reflective layer;

[0030] The local lateral constraint time window is used to limit the time range of cross-correlation calculation, so that the cross-correlation operation is only performed within the time interval corresponding to the target reflection layer, thereby suppressing the interference of non-target reflection events and random noise on the travel time difference calculation results without introducing additional waveforms.

[0031] As a preferred technical solution of the present invention, the cross-correlation function calculated within the local lateral constraint time window is... In the middle, the extreme point corresponding to the maximum correlation. The time offset represented is defined as the local travel time difference of the observed reflected wave relative to the simulated reflected wave;

[0032] The local travel time difference is used to quantify the time offset relationship between observed data and simulated data at the same reflectance layer and the same spatial location, and serves as a time constraint for subsequent lateral tracking along the reflectance layer direction.

[0033] As a preferred technical solution of the present invention, by performing lateral tracking of the travel time difference along the direction of the reflection layer, the travel time difference at adjacent receiver locations exhibits a continuous variation characteristic along the survey line direction, thereby forming a reflected wave travel time difference result distributed along the survey line direction. The travel time difference results can reflect the overall time offset trend between observed data and simulated data at the reflection layer level, and serve as the input basis for subsequent velocity model analysis or update processes.

[0034] In a second aspect, the present invention provides a reflected wave time difference measurement system considering lateral constraints, for implementing the first aspect, comprising:

[0035] The observation data input module is used to acquire observed seismic records and velocity models;

[0036] The reflection structure constraint module, connected to the observation data input module, is used to perform migration imaging on the observed seismic records under the constraints of the velocity model, obtain subsurface imaging results, and extract subsurface reflection stratigraphic information from the subsurface imaging results. The reflection structure constraint module is also used to perform inverse migration calculation based on the subsurface reflection stratigraphic information and the velocity model, generate simulated reflected wave data at the receiver location, and obtain the travel time position of the simulated reflected wave at different offset positions through zero offset travel time calculation and lateral tracking.

[0037] The local time window module, connected to the reflection structure constraint module, is used to construct a local lateral constraint time window corresponding to the reflection layer based on the travel time position of the simulated reflected wave at each spatial location.

[0038] The estimated reflection time difference module, connected to the local time window module, is used to calculate the cross-correlation function between the observed seismic record and the simulated reflection wave data within the local lateral constraint time window, and to extract the extreme points from the cross-correlation function; the estimated reflection time difference module is also used to perform lateral tracking in the direction of the reflection layer with the time offset corresponding to the extreme points as the travel time constraint, and to obtain the travel time difference distribution results of the observed reflection wave relative to the simulated reflection wave.

[0039] The technical effects and advantages provided by the present invention in the above technical solution are as follows:

[0040] This invention employs a multi-attribute Markov decision process for reflection phase axis extraction during the migration imaging stage, ensuring that the obtained reflection stratigraphic structure possesses clear spatial continuity and geological significance. During the travel time calculation stage, zero-offset travel time is used as a lateral tracking seed to guarantee lateral consistency across different offset travel times. In the cross-correlation calculation stage, a local lateral constraint time window limits the comparison range, effectively suppressing noise interference and mismatched peak values. Finally, in the peak extraction stage, confidence discrimination and lateral tracking extension are introduced to maintain a smooth spatial variation in local time shifts. Attached Figure Description

[0041] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0042] Figure 1 A flowchart of a method for measuring the time difference of reflected waves considering lateral constraints, provided in the first embodiment of the present invention;

[0043] Figure 2 An observation data diagram of a method for measuring the time difference of reflected waves considering lateral constraints, provided in the second embodiment of the present invention;

[0044] Figure 3 Simulation data diagram of a method for measuring the time difference of reflected waves considering lateral constraints, provided in the second embodiment of the present invention;

[0045] Figure 4 The simulation data travel time position and time window diagram of a reflected wave time difference measurement method considering lateral constraints provided in the second embodiment of the present invention;

[0046] Figure 5 A time window diagram of observation data for a method for measuring the time difference of reflected waves considering lateral constraints, provided in the second embodiment of the present invention;

[0047] Figure 6 A cross-correlation result diagram of a reflected wave time difference measurement method considering lateral constraints provided in the second embodiment of the present invention;

[0048] Figure 7 An extreme point diagram of a reflected wave time difference measurement method considering lateral constraints provided in the second embodiment of the present invention;

[0049] Figure 8 A reflection time difference map of a reflection wave time difference measurement method considering lateral constraints provided in the second embodiment of the present invention;

[0050] Figure 9The observation data travel time position diagram of a method for measuring the time difference of reflected waves considering lateral constraints provided in the second embodiment of the present invention;

[0051] Figure 10 The following is an overall flowchart of a method system for measuring the time difference of reflected waves considering lateral constraints, provided for the third embodiment of the present invention. Detailed Implementation

[0052] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be described in more detail below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0053] Throughout the accompanying drawings, the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions. The described embodiments are only a part of the embodiments of this application, not all of them. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application. The embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0054] Example 1

[0055] Reference Figure 1 As an embodiment of the present invention, a method for measuring the time difference of reflected waves considering lateral constraints is provided, comprising the following steps:

[0056] S1: Perform migration imaging on the observed seismic data under a given velocity model to obtain imaging results, and extract subsurface reflection structure information from the imaging results;

[0057] Specifically, the velocity model is used to describe the distribution of seismic wave propagation velocity in the subsurface medium at different spatial locations, and is a necessary input parameter for migration imaging and inverse migration calculations. The velocity model can be an initial velocity model or an arbitrary velocity model updated during the reflection wave inversion iteration process, and its function is to provide subsurface medium velocity information for wavefield propagation.

[0058] The observed seismic data refers to common-channel seismic records acquired by a seismic exploration acquisition system. These records include the source location, geophone location, sampling interval, recording duration, and corresponding seismic waveform data for each channel. A common-channel seismic record is a collection of seismic records from multiple geophones corresponding to the same source point. This collection comprehensively records the propagation information of reflected waves as the offset changes, consistent with the observed seismic data described in this invention.

[0059] Additionally, it's worth mentioning that migration imaging is used to correct reflection events in observational data back to their subsurface reflection locations. Under a given velocity model, it utilizes wave equations to convert seismic records into spatial imaging results of subsurface reflection interfaces. Migration imaging can convert time-domain reflected waves in common-channel records into spatial-domain subsurface reflection interfaces, providing a foundation for further extraction of reflection stratigraphic structure information.

[0060] To further explain, the imaging results are obtained in the following way:

[0061] Given a velocity model and the location of the epicenter First, forward modeling is performed using the acoustic wave equation to obtain the wave field at the source end. ;

[0062]

[0063] in: This indicates the coordinates of the seismic wave's location in underground space. Represents a time variable. This represents a velocity model used to describe the distribution of seismic wave propagation velocity at different spatial locations in the subsurface medium. This represents the second-order time derivative, used to characterize the changes in the wave field over time. This represents the Laplace operator, used to characterize the diffusion and propagation characteristics of wave fields in underground space; This represents the background wave field response at the source end, formed by the source excitation and propagation in the subsurface medium under the constraints of the background velocity model. Indicates the coordinates of the earthquake source location. This represents the source wavelet, used to describe the excitation pattern of the earthquake source in the time dimension. This represents the Dirichlet function, used to characterize the concentrated action of the seismic source on the location of the seismic source in space.

[0064] The observed seismic data were backpropagated using the same velocity model to obtain the receiver wavefield. , representing the wave field obtained by the back propagation of the received signal;

[0065] Perform cross-correlation calculations between the source wavefield and the receiver wavefield in the time domain to obtain the corresponding imaging results.

[0066]

[0067] in, The imaging results representing the location of underground space are used to characterize the response intensity of underground reflective structures at the corresponding spatial location; they carry information about the underground reflective structures. It represents the receiver wavefield obtained by backpropagation of the observed seismic record; the integral operation represents the accumulation of the product of the source background wavefield and the receiver wavefield in the time dimension within a preset time range, which is used to characterize the temporal correspondence between the two at the same spatial location. In the calculation of imaging conditions, it forms an imaging result that reflects the distribution characteristics of the reflection interface in the underground space.

[0068] Furthermore, information on subsurface reflection structures is extracted from the imaging results to obtain the subsurface reflection structures, including:

[0069]

[0070] in, Indicates information about underground reflective structures. The reflection structure extraction operator is represented by a multi-attribute Markov decision process. Other image processing methods can also be applied to this process to obtain the corresponding reflection structure.

[0071] In this embodiment, the reflection structure extraction operator is constructed using a Markov decision process based on multi-attribute constraints. It maps the amplitude attribute, continuity attribute, and local coherence attribute in the imaging results to represent state features and selects the state sequence in the lateral extension direction of the reflection event to obtain a stable reflection layer structure.

[0072] It should be noted that the function of the reflection structure extraction operator is to obtain the spatial distribution of underground reflection layers, without changing the waveform characteristics of the original seismic data. Without violating the above-mentioned mechanism, those skilled in the art can also use other structured processing methods with reflection event extraction functions to achieve the same purpose.

[0073] S2: Perform reverse migration on the velocity model and reflection structure, extract simulated seismic records at the receiver locations, and form simulated reflected wave data;

[0074] Specifically, firstly, on the given velocity model Calculate the background wave field at the source end.

[0075] ;

[0076] in, This indicates the coordinates of the seismic wave's location in underground space. Represents a time variable. Represents the velocity model; This represents the background wave field at the source end, formed by the earthquake source excitation and propagation in the underground medium under the constraints of the background velocity model. This represents the source wavelet, used to describe the excitation form of the source in the time dimension; The Dirichlet function represents the concentration of the seismic source in space at the location of the seismic source. Place.

[0077] Then, based on the information of the underground reflective structure... and the background wave field at the source end Perform inverse offset calculations to obtain the first reflection wave field from the simulation data. It satisfies the following relationship, and the reflected wave field in the simulation data can be obtained by performing inverse offset:

[0078] ;

[0079] in, It is to obtain a reflected wave field. This represents information about underground reflective structures, used to characterize the distribution location of reflective interfaces in underground space. It interacts with the background wave field to generate a simulated reflected wave response.

[0080] At the receiver location, the primary reflected wave field is spatially sampled to obtain a simulated reflected wave seismic record, the expression of which is:

[0081] ;

[0082] in, This indicates the coordinates of the geophone's location in the underground space. denoted by the Dirichlet function, used to achieve spatial extraction of the primary reflected wave field at the receiver location; This represents the simulated reflected wave seismic record obtained at the corresponding receiver location; through inverse migration calculation and spatial sampling, simulated reflected wave data corresponding to the underground reflecting structure can be generated at each receiver location.

[0083] S3, Calculate the two-way travel time of the simulated reflected wave at the zero-offset position based on the reflective layer structure information. The zero offset travel time is used as the initial seed point for the corresponding reflection layer.

[0084] Using subsurface reflection horizon information and velocity models, at a zero offset location (where the source and detector positions coincide), based on the reflection horizon structure and background velocity model, the travel time of reflected waves at each reflection horizon under zero offset conditions is calculated, serving as the initial travel time seed point for subsequent lateral tracking. The zero offset travel time can be expressed as:

[0085]

[0086] in, This represents the i-th reflective layer. This indicates that the i-th reflected wave is at the zero offset position. The time of travel. Among them, This represents the spatial coordinates at the zero offset position, i.e., the underground spatial position corresponding to the coincidence of the source position and the receiver position; i represents the reflection layer number. The function representing the position of the reflection interface of the i-th underground reflective layer at the spatial location; Represents the background velocity model value at the stated spatial location; integral symbol This represents the integral calculation of the propagation path from the reflector interface to the Earth's surface along the vertical direction; coefficient 2 represents the two-way propagation process of the reflected wave from the source downwards to the reflector interface and back to the Earth's surface, which allows us to obtain the position of the i-th reflected wave at zero offset. Two-way travel time at the location And use it as the initial travel time constraint for the reflected wave corresponding to the reflective layer.

[0087] S4. Using the initial seed point as the starting constraint, search for waveform extreme points channel by channel in the simulated reflected wave data along the transverse arrangement direction of the detector. Lateral tracking is performed based on the continuity of adjacent channel extrema to obtain the travel time position of the simulated reflected wave at a non-zero offset. ;

[0088] The lateral tracking involves using the travel time of the reflected wave at the zero offset position as the initial seed point, and calculating the extreme points of the wavefield channel by channel along the lateral arrangement direction of the detector. These extreme points are significant feature points of the waveform along the time axis, representing the arrival position of the reflection event. In this invention, the extreme point refers to the sampling point where the absolute value of the waveform amplitude reaches a local maximum within a given time search range. The process is updated based on the extreme positions of adjacent channels to obtain the simulated travel time of the reflected wave at non-zero offset positions. Since this process is implemented on simulated reflected wave data, which only contains filtered reflected waves, the travel time position of the reflected wave can be obtained relatively easily using extreme point constraints.

[0089] Specifically, the travel time of the zero offset of the i-th reflective layer As a seed point, calculate adjacent paths extreme values In adjacent channels, search for the extreme point that is closest to the current seed point, and record the time position corresponding to the extreme point. The travel time of the reflected wave at adjacent receiver points is used as the new seed point, and the tracking is continued track by track along the survey line. Then, the current track is... Get time As a new seed point, continue calculating adjacent paths. extreme values Continue searching for the nearest extreme point to obtain the new time position. Repeat the above process until all offsets have been searched, and obtain the travel times of reflected waves at all non-zero offsets of the current reflector layer i. Finally, by iterating through all the seed points of the reflection layers, the travel time positions of all reflected waves in the simulation data are obtained, so as to obtain a complete simulated travel time distribution of reflected waves while maintaining the lateral continuity of the reflection events.

[0090] S5. Based on the travel time of the simulated reflected wave at each spatial location, a local lateral constraint time window is constructed, and the cross-correlation function between the observed seismic data and the simulated reflected wave data is calculated within the local lateral constraint time window. ;

[0091] The local lateral constraint time window is used to limit the time range of cross-correlation calculation. Its center position is determined by the simulated time travel at the corresponding spatial position. The size of the time window is controlled by the parameter nwin, which represents the number of time sampling points extending above and below the center position of the time travel. It is used to suppress non-target events and noise interference while ensuring the integrity of the reflection event.

[0092] Specifically, a local time window is obtained along the travel time position of each reflected wave data point.

[0093] ;

[0094] ;

[0095] in, and These are the upper and lower time window positions, The time window size is a preset half-width parameter used to limit the time range of cross-correlation calculations, so as to suppress non-target events and noise interference while ensuring the integrity of target reflection events. This represents the simulated travel time of the reflected wave at spatial location x of the i-th reflective layer.

[0096] S6, Extract the corresponding extreme points from the cross-correlation function. Using the time offset corresponding to the extreme point as the travel time constraint, lateral tracking is performed in the direction of the reflection layer to obtain the travel time difference between the observed reflected wave and the simulated reflected wave. ;

[0097] Specifically, within the local lateral constraint time window, the cross-correlation function between the observed data and the simulated data is calculated, and the extreme point corresponding to the maximum correlation is extracted from the cross-correlation function; the time offset corresponding to the extreme point represents the local travel time difference of the observed reflected wave relative to the simulated reflected wave.

[0098] Using the time offset as a new travel time constraint, lateral tracking is performed in the direction of the reflection layer, so that the travel time difference at adjacent spatial locations remains continuously changing in the lateral direction, thereby obtaining the distribution result of the travel time difference of the reflected wave throughout the entire survey line.

[0099] In other words, along the newly constructed local time window, the cross-correlation and extreme points within the local window are calculated:

[0100] ;

[0101] in, This represents the spatial location x, the reflector layer number i, and the time offset. The cross-correlation value calculated under the given conditions; This represents the observed seismic record obtained at spatial location x; Let w represent the simulated reflected seismic record obtained at the same spatial location, and w represent the time integral variable within the local time window; based on the cross-correlation function, the corresponding extreme points are extracted from the time migration dimension, and its expression is:

[0102] ;

[0103] in, This indicates the location of the extreme point of the cross-correlation function in the time offset dimension, which is used to characterize the optimal time alignment relationship between the observed reflected wave and the simulated reflected wave under the corresponding spatial location and reflection horizon conditions.

[0104] Furthermore, the travel time of the reflected wave calculated under the condition of zero offset is... As an initial seed point, the extreme point is laterally tracked along the reflection layer direction, and the corresponding travel time difference of the reflected wave is determined based on the position of the extreme point in the time offset dimension. The mapping relationship can be expressed as follows:

[0105] ;

[0106] in, This represents the travel time difference between the observed reflected wave and the simulated reflected wave, calculated from the reflective layer numbered i at spatial location x. This represents the extreme point filtering and tracking rule executed with the zero offset travel time of the i-th reflective layer as a reference constraint.

[0107] Example 2

[0108] Reference Figure 2-9 To verify the effectiveness of the reflected wave time difference measurement method considering lateral constraints proposed in this invention, a theoretical model experiment was conducted to test the effectiveness of the method.

[0109] Figure 2 The figure shows observational data synthesized using an accurate velocity model, where the horizontal axis represents the detector location and the vertical axis represents the recording time. It can be seen that the observational data contains numerous in-phase axes of reflected waves; this information carries subsurface medium information and represents the subsurface reflecting interface. Therefore, this reflected wave information can be used to update the velocity model. Simulation data obtained by using the background velocity model for inverse migration is shown below. Figure 3 As shown in the figure, the horizontal axis represents the detector position, and the vertical axis represents the recording time. (Comparison) Figure 2 and Figure 3 As can be seen, constrained by the underground reflective interface, Figure 3 The simulated reflected waves only contain the filtered main in-phase reflection axes; other wave phenomena are effectively removed. However, Figure 3 The time position of the phase axis of the reflected wave and Figure 2 The inconsistencies in the observed locations indicate a difference between our background velocity model and the actual velocity model, necessitating the extraction of [data / materials]. Figure 2 and Figure 3 The time difference of the phase axis of the reflected wave can be used to perform velocity inversion and update the velocity model.

[0110] Then, using subsurface reflection horizon information and velocity models, we can calculate the travel time of the reflected wave at the zero offset position (where the source and detector positions coincide). Taking the reflection axis of the lowest layer as an example, the zero offset travel time of the obtained simulation data is as follows: Figure 4 As shown by the black pentagram in the image. Using the position of the black pentagram as the seed point, lateral tracing is performed to obtain the non-zero time travel of the simulated data, as shown below. Figure 4 As shown by the black dashed line, the travel time of the obtained simulation data is consistent with the phase axis position of the reflected wave in the simulation data, indicating that the calculated travel time is correct. Based on this, a local time window is constructed, with its upper and lower boundaries as shown in the figure. Figure 4 As shown by the black line. Correspondingly, the same local time window is also set in the observation data, as shown in the example below. Figure 5As shown. The cross-correlation and extrema are calculated within a local time window, and the results are as follows. Figure 6 and Figure 7 As shown, the vertical axis represents the size of the local time window. Under the constraint of zero-offset travel time of the simulated data, the travel time difference of the reflected wave is obtained by lateral tracking, as shown... Figure 8 As shown in the figure. By adding the travel time difference of the reflected wave to the travel time of the simulated data, the travel time position of the observed data can be obtained, as shown in the figure. Figure 9 As shown by the black line. (Comparison) Figure 2 and Figure 9 It can be observed that the obtained reflected wave position is basically consistent with the actual reflected wave position, indicating that the method can accurately estimate the difference in reflected wave travel time. Furthermore, in comparison... Figure 4 and Figure 5 As can be seen, at large offsets, the position difference between the observed data and the simulated reflected wave is large, far exceeding one wavelet period. However, using this method, the correct travel time difference can still be accurately obtained, thus proving the effectiveness of this method.

[0111] Example 3

[0112] Reference Figure 10 This embodiment provides a reflected wave travel time difference measurement system considering lateral constraints, used to implement the reflected wave travel time difference measurement method described in Embodiment 1 above; it includes an observation data input module, a reflection structure constraint module, a local time window module, and a reflection travel time difference estimation module; wherein,

[0113] The observation data input module is used to acquire input data related to the travel time difference measurement of reflected waves. The input data includes at least the observed seismic records and velocity models. The observation data input module provides the acquired observed seismic records and velocity models to the reflection structure constraint module as the basic input conditions for subsequent migration imaging, inverse migration calculation and travel time calculation. Its function corresponds to executing step S1 in Embodiment 1.

[0114] The reflection structure constraint module is used to perform migration imaging on the observed seismic records under the constraint of the velocity model to obtain subsurface imaging results, and extract subsurface reflection layer structure information based on the subsurface imaging results; on this basis, the reflection structure constraint module further performs inverse migration calculation based on the subsurface reflection layer structure information and the velocity model to generate simulated reflected wave data at the receiver point location, and obtains the travel time position of the simulated reflected wave at different offset positions through zero offset travel time calculation and lateral tracking, and its function corresponds to executing steps S1 to S4 in Embodiment 1.

[0115] The local time window module is used to construct a local lateral constraint time window corresponding to the reflection layer based on the travel time position of the simulated reflected wave at each spatial location. The local lateral constraint time window is used to limit the time range of cross-correlation calculation between the observed seismic record and the simulated reflected wave data, so as to ensure that the cross-correlation calculation is performed within the time interval corresponding to the target reflection event. Its function corresponds to step S5 in embodiment 1.

[0116] The estimated reflection time difference module is used to calculate the cross-correlation function between the observed seismic record and the simulated reflection wave data within the local lateral constraint time window, and extract the extreme point from the cross-correlation function; the estimated reflection time difference module uses the time offset corresponding to the extreme point as the travel time constraint, performs lateral tracking in the reflection layer direction, thereby obtaining the travel time difference result of the observed reflection wave relative to the simulated reflection wave, and its function corresponds to the execution of step S6 in embodiment 1.

[0117] Through the coordinated operation of the above modules, the reflected wave travel time measurement system can achieve stable measurement of the travel time difference of reflected waves between observed seismic data and simulated data under the constraints of the reflected layer structure and the lateral continuity.

[0118] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method of measuring the difference in travel times of reflected waves based on lateral constraints, characterized in that, The method comprises the following steps: S1, performing migration imaging on observed seismic data under a given velocity model to obtain underground imaging results, and extracting underground reflection structure information from the imaging results; S2, performing reverse migration calculation based on the velocity model and the underground reflection structure information to extract simulated reflection wave seismic records at receiver point positions and form simulated reflection wave data; S3, calculating the two-way travel time of the simulated reflection wave at the zero-offset position based on the reflection layer position structure information at the zero-offset position and taking the zero-offset travel time as the initial seed point of the corresponding reflection layer position; S4, starting from the initial seed point, searching for waveform extreme points along the crossline direction of the receiver in the simulated reflection wave data and performing crossline tracking based on the continuity of the extreme points of adjacent traces to obtain the travel-time position of the simulated reflection wave at the non-zero offset ; S5, constructing a local lateral constraint time window according to the travel-time positions of the simulated reflection waves at each spatial position, and calculating a cross-correlation function between the observed seismic data and the simulated reflection wave data within the local lateral constraint time window ; S6, extracting a corresponding extreme point from the cross-correlation function , and taking the time offset corresponding to the extreme point as a travel time constraint, performing lateral tracking in the direction of the reflection layer position to obtain a reflection travel time difference result of the observed reflection wave relative to the simulated reflection wave .

2. The method of claim 1, wherein, The velocity model is used to describe the velocity model of the underground medium at different spatial positions and participates in the migration imaging and de-migration calculation process in the form of a spatially continuous velocity field. The velocity model can be an initially constructed background velocity model or an intermediate velocity model obtained by gradually updating based on reflection wave inversion.

3. A method of measuring the difference in travel times of reflected waves based on lateral constraints according to claim 2, characterized in that, said sub-surface reflector information by imaging results of sub-surface space locations obtained by structured extraction; The structured extraction is used to identify reflection events with lateral continuity in the imaging results and to characterize the reflection events with spatial position parameters; The underground reflection structure information is only used to define the distribution positions of reflection events in the underground space, and does not participate in amplitude adjustment or spectrum transformation of original seismic waveforms, so that the simulated reflection wave data in the subsequent reverse migration calculation only retains main reflection events corresponding to underground reflection horizons.

4. The method of claim 3, wherein, The zero-offset travel time is the travel time along the corresponding underground reflection layer position under the condition that the source position and the receiver position are overlapped The reflection wave two-way travel time calculated under the constraint of a given velocity model; The zero-offset travel time serves as a time reference of reflection horizons in the line direction, is used to establish initial travel time constraints for different reflection horizons respectively, and enables the subsequent lateral tracking process to have a clear starting reference point in the time dimension, thereby avoiding mis-matching between different reflection events.

5. A method of measuring the difference in travel times of reflected waves based on lateral constraints according to claim 4, characterized in that, The lateral tracking comprises: with the current receiver point as a seed point, the travel time of the reflected wave at the adjacent receiver point defines a time search range in the corresponding simulated reflected wave data, and determines an extreme point with the minimum time distance from the seed point in the time search range ; the time position corresponding to the extreme point as the travel time of the reflected wave at the adjacent receiver point, and updates it as a new seed point to continue the trace in the direction of the survey line to obtain the complete simulated reflected wave travel time distribution under the premise of maintaining the lateral continuity of the reflected event .

6. A method of measuring the difference in travel times of reflected waves based on lateral constraints according to claim 5, characterized in that, The extreme point is a sampling point that makes the absolute value of waveform amplitudes of the simulated reflection wave and the observed reflection wave reach a local maximum in a preset time search range; the extreme point is used to characterize a significant arrival position of a reflection event in the time axis direction, and its selection process only depends on the relative variation characteristics of the waveforms, and does not depend on the absolute amplitude size of the waveforms, thereby reducing the influence of amplitude difference, energy attenuation and noise interference on the travel time identification process.

7. A method of measuring the difference in travel times of reflected waves based on lateral constraints according to claim 6, characterized in that, the local lateral constraint time window is determined according to the simulated reflection wave travel time at the corresponding spatial position is the central position, and extends along the positive and negative directions of the time axis respectively by a preset number of time sampling points the upper and lower boundaries of the local lateral constraint time window are respectively represented as ； ； wherein, and are the upper and lower time window positions, respectively, is the time window size, and is a preset time window half-width parameter, used to limit the time range of the cross-correlation calculation, so as to suppress non-target events and noise interference while ensuring the integrity of the target reflection event; represents the simulated reflection wave travel time of the i-th reflection layer at the spatial position x. The local lateral constraint time window is used to limit the time range of the cross-correlation calculation, so that the cross-correlation operation is only performed in a time interval corresponding to a target reflection horizon, thereby suppressing the interference of non-target reflection events and random noise on the travel time difference calculation result without introducing additional waveforms.

8. A method of measuring the difference in travel times of reflected waves based on lateral constraint according to claim 7, characterized in that, the cross-correlation function computed within said local lateral constraint time window corresponding to the maximum correlation the characterized time shift is defined as the local traveltime difference of the observed reflection wave with respect to the simulated reflection wave; The local travel time difference is used to quantify the time offset relationship between the observed data and the simulated data at the same reflection horizon and the same spatial position, and serves as a time constraint condition for the subsequent lateral tracking along the reflection horizon direction.

9. A method of measuring the difference in travel times of reflected waves based on lateral constraints according to claim 8, characterized in that, By performing lateral tracking on the travel time difference in the reflection layer direction, the travel time difference at adjacent geophone positions presents a continuous change feature in the profile direction, thereby forming a travel time difference result of the reflected wave distributed along the profile direction The travel time difference result can reflect the overall time migration trend between the observation data and the simulation data at the reflection layer level, and serve as an input basis for subsequent velocity model analysis or updating process.

10. A system for cross-coupling constrained reflected traveltime difference measurement for implementing the method of any one of claims 1-9, wherein, The method comprises the following steps: The observed data input module is used to acquire observed seismic records and a velocity model; The reflection structure constraint module, connected with the observed data input module, is used to perform migration imaging on the observed seismic records under the constraint of the velocity model to obtain underground imaging results, and extract underground reflection horizon structure information from the underground imaging results; the reflection structure constraint module is further used to perform reverse migration calculation based on the underground reflection horizon structure information and the velocity model to generate simulated reflection wave data at receiver point positions, and obtain travel time positions of simulated reflection waves at different offset positions through zero-offset travel time calculation and lateral tracking; The local time window module, connected with the reflection structure constraint module, is used to construct a local lateral constraint time window corresponding to a reflection horizon according to the travel time positions of the simulated reflection waves at various spatial positions; ​ The estimated reflection time difference module is connected with the local time window module, and is configured to calculate a cross-correlation function between the observed seismic record and the simulated reflection wave data in the local lateral constraint time window, and extract an extreme point from the cross-correlation function; the estimated reflection time difference module is also configured to take a time offset corresponding to the extreme point as a travel time constraint, perform lateral tracking in the reflection horizon direction, and obtain a travel time difference distribution result of the observed reflection wave relative to the simulated reflection wave.

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