A method and system for modeling approximate true surface velocity

Abstract

The present invention provides a method and system for approximating true surface velocity modeling. The method uses a near-surface velocity model obtained by first-arrival wave inversion as an initial velocity model, determines a high-speed top interface based on the model, and then calculates a corresponding surface elevation smoothing surface as the migration starting surface for velocity modeling and migration imaging. The near-surface velocity model is interpolated within the range determined by the high-speed top interface and the surface elevation smoothing surface to ensure that there are no velocity blank areas within the calculation range. Based on this, the relevant velocities within the range determined after interpolation optimization are smoothed to obtain an approximate true surface velocity model for depth-domain velocity modeling. Modeling using this method eliminates imaging errors caused by elevation changes and local velocity anomalies while retaining background velocity. The method can be effectively applied to various surface conditions, including undulating surface conditions and conditions with thick low-velocity reduction zones, and can effectively improve the imaging accuracy of subsequent pre-stack depth migration in various surface conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of geophysical exploration modeling optimization, and in particular to a method and system for approximate true surface velocity modeling. Background Art

[0002] With the development of computer technology, computing power has been continuously improved, and its application in various fields has gradually deepened. Accordingly, pre-stack depth domain seismic imaging processing has been increasingly widely used because it can directly obtain the location of the underground structural reflection interface. Among them, when performing depth domain modeling, in order to eliminate the influence of surface elevation or near-surface structure on the seismic reflection signal, it is usually necessary to use static correction technology to correct the seismic data, and use a fixed surface or a large smooth surface on the surface as the starting surface for migration imaging for velocity modeling and imaging. However, in the presence of terrain undulations or certain lateral changes in the near-surface low velocity reduction zone, the near-surface model obtained by conventional modeling methods has a large difference between the near-surface model and the actual near-surface velocity structure because the replacement velocity is used to replace the near-surface low velocity reduction zone structure. Based on this, the seismic wave field in the imaging process is distorted, affecting the accuracy of seismic data imaging in complex surface conditions.

[0003] As oil exploration targets move into mountainous areas and regions with complex near-surface structures, static correction techniques based on the vertical propagation assumption are unable to correct severely distorted seismic wavefields in areas with severe surface relief or complex near-surface structures. Consequently, seismic data processing techniques based on floating surfaces and undulating surfaces have begun to gain widespread application. Floating surface processing techniques are primarily used for conventional time-domain processing, while processing techniques based on undulating surfaces primarily focus on prestack time and prestack depth-domain imaging. True surface prestack depth-domain migration imaging, a type of undulating surface migration imaging technique, has been widely researched and promoted in recent years because it preserves the near-surface velocity structure as much as possible.

[0004] Establishing an accurate underground velocity model is the first prerequisite for obtaining accurate pre-stack depth domain imaging results, especially for reverse time migration imaging based on the two-way wave equation. An accurate velocity model determines the success or failure of the imaging results. Among them, since the wave equation-based method simulates the propagation process of seismic waves in the structural model, and the accuracy of the near-surface velocity model often affects the propagation of the seismic wave field in the middle and deep layers, near-surface modeling has received widespread attention in recent years. Existing research schemes usually use the following two methods to achieve near-surface velocity modeling for undulating surfaces: one is the undulating surface modeling method based on replacement velocity, and the other is the method of obtaining the near-surface velocity model based on first-arrival tomographic inversion.

[0005] For the first type of modeling of an undulating surface, after applying static corrections, the seismic data are corrected to the undulating surface, and the replacement velocity is filled between the undulating surface and the interface at the top of the high-velocity layer (Lin Boxiang, 2005). This method is simple to implement, but because the near-surface low-velocity zone is replaced with a higher replacement velocity, the change in the normal reflection time (t0) of the seismic wave from the source to the interface leads to a large error between the picked velocity data and the actual velocity data. Although certain methods can be used to adjust the elevation of the undulating surface to reduce the error, this is difficult to effectively implement with actual seismic data. The second type of method directly models the velocity model obtained by first-arrival tomographic inversion. This method first obtains a near-surface velocity model and uses it as the basis for the near-surface velocity model. Then, based on the position of the undulating surface in the velocity model, a correction is calculated to correct the seismic data to the position of the undulating surface. The near-surface model obtained using this method largely ensures the consistency between the near-surface velocity model and the real surface. However, under complex near-surface conditions (such as the loess plateau area overlying a thick loess layer), the near-surface velocity is low, the elevation changes dramatically, and the high-frequency static correction problem is serious. The velocity model obtained by first-arrival tomographic inversion is not accurate enough. On the one hand, it is difficult to directly use this velocity model for near-surface velocity modeling and migration imaging; on the other hand, when the near-surface velocity is low, the imaging method itself faces the dual obstacles of stability and computational efficiency.

[0006] Additionally, based on the second category of methods mentioned above, some researchers directly use the velocity model derived from the inversion method during static correction calculations, combined with the results of shot and checkpoint static corrections, to create a model. Their near-surface model is composed of the inverted velocity model and the migration datum. The time required to correct the seismic data to the migration datum is calculated from the surface elevation, the migration datum, and the high-velocity top interface. However, these methods still present the following challenges: First, due to the limitations of the static correction algorithm itself, there is a certain degree of error between the inverted velocity model and the actual velocity model, and directly applying this model to migration can affect imaging accuracy. Second, in complex near-surface conditions, the inverted velocity model can contain localized velocity anomalies. When applied to currently available high-precision imaging methods, such as the ray-based Kirchhoff integral method or two-way wave equation reverse time migration, the former is sensitive to dramatic lateral velocity variations, while the latter often exceeds current computing capabilities when near-surface velocities are low. In summary, a new approach to approximate true surface velocity modeling is needed to rationally support high-precision imaging. Summary of the Invention

[0007] To address the above-mentioned issues, the present invention provides a method and system for modeling near-true surface velocity. The method of the present invention can establish a near-surface velocity model that is close to the true surface and suitable for pre-stack depth migration imaging of undulating surfaces. The target near-true surface velocity model is obtained by smoothing the velocity model obtained by first-arrival inversion, eliminating high-wavenumber velocity components that affect imaging and retaining background velocities close to the true near-surface velocity distribution, thereby improving the imaging accuracy of pre-stack depth migration. In one embodiment, the method includes:

[0008] Initial model acquisition step: obtaining a near-surface velocity model obtained by inversion of seismic first arrival waves as an initial velocity model;

[0009] High-speed top interface determination step: obtaining the replacement velocity provided by the work area during static correction calculation, and determining the high-speed top interface in the near-surface velocity model based on the replacement velocity;

[0010] Starting surface decision step: Calculate the surface elevation smoothing surface as the migration starting surface for velocity modeling and migration imaging;

[0011] Interpolation optimization steps: interpolate the near-surface velocity model within the range determined by the high-speed top interface and the surface elevation smoothing surface to ensure that there is no velocity blank area within the range;

[0012] Target model generation steps: Select the optimal smoothing parameters, smooth the relevant velocities within the range determined after interpolation optimization, and obtain an approximate true surface velocity model in depth domain velocity modeling.

[0013] Furthermore, the method further includes: correcting the seismic data based on the obtained fixed reference surface, offset starting surface, elevation smoothing surface and approximate true surface velocity model to obtain seismic data that is consistent with the near-surface velocity model to the greatest extent.

[0014] In one embodiment, the method further comprises:

[0015] Before executing the starting surface decision step, the shot check point static correction value in the seismic first arrival wave inversion process is used as the initial correction value, and the seismic data is corrected to the fixed reference surface by applying the initial static correction value.

[0016] Furthermore, in one embodiment, the method further comprises:

[0017] Based on the replacement speed when calculating the initial static correction, a first intermediate static correction is determined by integrating the fixed reference surface elevation and the migration start surface elevation, and the seismic data is corrected to the migration start surface using the first intermediate static correction.

[0018] In one embodiment, the method further comprises:

[0019] After obtaining the approximate true surface velocity model, a target static correction amount of the seismic data relative to the approximate true surface velocity model is determined, and the target static correction amount is applied to correct the seismic data.

[0020] Specifically, in one embodiment, the target static correction amount is determined by the following steps:

[0021] Calculating a second intermediate static correction amount of the seismic data relative to the approximate true surface velocity model based on thickness data and velocity data corresponding to the seismic data in the approximate true surface velocity model;

[0022] Calculating a third intermediate static correction amount of the seismic data obtained by using the replacement velocity in the approximate true surface velocity model based on thickness data and replacement velocity data corresponding to the seismic data in the approximate true surface velocity model;

[0023] A difference between the second intermediate static correction value and the third intermediate static correction value is calculated as the target static correction value.

[0024] Furthermore, in the process of determining the target static correction, the second intermediate static correction t2 of the seismic data relative to the approximate true surface velocity model is calculated according to the following formula:

[0025]

[0026] Where t2 is the vertical travel time of the seismic data relative to the approximate true surface velocity model, h i is the thickness of the i-th layer in the approximate true surface velocity model, V i is the speed corresponding to this layer.

[0027] In one embodiment, in the process of determining the target static correction value, the third intermediate static correction value t3 obtained by replacing the velocity of the seismic data in the approximate true surface velocity model is calculated according to the following formula:

[0028]

[0029] Where t3 is the vertical travel time of seismic data obtained by replacing the velocity in the approximate true surface velocity model, h i is the thickness of the i-th layer in the velocity model, V rep is the replacement speed corresponding to the calculation of t3.

[0030] Based on the method described in any one or more of the above embodiments, the present invention further provides a storage medium storing program codes that can implement the method described in any one or more of the above embodiments.

[0031] Based on other aspects of the method described in any one or more of the above embodiments, the present invention further provides an approximate true surface velocity modeling system, the system comprising:

[0032] An initial model acquisition module is configured to acquire a near-surface velocity model obtained by inversion of seismic first arrival waves as an initial velocity model;

[0033] a high-speed top interface determination module configured to determine a high-speed top interface in the near-surface velocity model;

[0034] a starting surface decision module configured to calculate a surface elevation smoothing surface as a migration starting surface for velocity modeling and migration imaging;

[0035] an interpolation optimization module configured to interpolate a near-surface velocity model within a range determined by a high-speed top interface and a surface elevation smoothing surface, ensuring that there is no velocity blank area within the range;

[0036] The target model generation module is configured to select corresponding smoothing parameters, smooth the relevant velocities within the range determined after interpolation optimization, and obtain an approximate true surface velocity model in depth domain velocity modeling.

[0037] Compared with the closest prior art, the present invention also has the following beneficial effects:

[0038] The present invention provides a method and system for approximating true surface velocity modeling. Based on the near-surface velocity model obtained through inversion, the top interface of the high-velocity layer is determined, and the corresponding surface elevation smoothing surface is calculated as the migration starting surface. The near-surface velocity model is interpolated within the range determined by the high-velocity top interface and the surface elevation smoothing surface, and further smoothed based on the aforementioned operations to obtain an approximate true surface velocity model for depth-domain velocity modeling. This modeling method, while preserving background velocity, eliminates imaging errors caused by sudden elevation changes and local velocity anomalies. The method can be effectively applied to various surface conditions, including undulating surfaces and those with thick, low-velocity reduction zones, effectively improving the imaging accuracy of subsequent prestack depth migration in various surface conditions.

[0039] In addition, the present invention provides a matching seismic data correction method suitable for the modeling process, which can effectively teach and achieve the effect of maintaining consistency between the seismic data and the velocity model on the starting surface and the near-surface velocity model.

[0040] Other features and advantages of the present invention will be described in the following description, and in part will become apparent from the description, or will be understood by practicing the present invention. The purposes and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0042] Figure 1 This is a schematic diagram of the near-surface modeling process in the prior art provided by an embodiment of the present invention;

[0043] Figure 2 This is a schematic diagram of the seismic data correction process in the prior art provided by an embodiment of the present invention;

[0044] Figure 3 1 is a flow chart of a method for approximating true surface velocity modeling provided by an embodiment of the present invention;

[0045] Figure 4 1 is a flow chart of implementing seismic data correction in the approximate true surface velocity modeling method provided by an embodiment of the present invention;

[0046] Figure 5 It is a structural diagram of an approximate true surface velocity modeling system provided by another embodiment of the present invention. DETAILED DESCRIPTION

[0047] The following will describe in detail the implementation methods of the present invention in conjunction with the accompanying drawings and embodiments, so that practitioners of the present invention can fully understand how the present invention applies technical means to solve technical problems and achieve the implementation process of technical effects, and can implement the present invention in accordance with the above implementation process. It should be noted that as long as no conflict exists, the various embodiments and various features of each embodiment in the present invention can be combined with each other, and the resulting technical solutions are all within the scope of protection of the present invention.

[0048] Although the flowcharts depict the operations as sequential processes, many of the operations can be performed in parallel, concurrently, or simultaneously. The order of the operations can be rearranged. A process can be terminated when its operations are completed, but can also have additional steps not included in the figures. A process can correspond to a method, function, procedure, subroutine, subprogram, etc.

[0049] Computer devices include user devices and network devices. User devices or clients include, but are not limited to, computers, smartphones, PDAs, and the like; network devices include, but are not limited to, a single network server, a server group consisting of multiple network servers, or a cloud computing-based cloud consisting of a large number of computers or network servers. Computer devices can operate independently to implement the present invention, or they can connect to a network and interact with other computer devices in the network to implement the present invention. Networks in which computer devices reside include, but are not limited to, the Internet, wide area networks, metropolitan area networks, local area networks, VPN networks, and the like.

[0050] The terms "first," "second," and the like may be used herein to describe various elements, but these elements should not be limited by these terms, and these terms are used merely to distinguish one element from another. The term "and / or" as used herein includes any and all combinations of one or more of the listed associated items. When an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element, or intervening elements may be present.

[0051] The terms used herein are intended only to describe specific embodiments and are not intended to limit exemplary embodiments. Unless the context clearly indicates otherwise, the singular forms "a", "an", "an item" used herein are also intended to include the plural. It should also be understood that the terms "comprise" and / or "include" used herein specify the presence of stated features, integers, steps, operations, units and / or components, and do not preclude the presence or addition of one or more other features, integers, steps, operations, units, components and / or combinations thereof.

[0052] In geophysical exploration, prestack deep-domain seismic imaging processing is gaining increasing popularity due to its ability to directly determine the locations of subsurface structural reflection interfaces (Wang Yanguang, 2017). Typically, when performing deep-domain modeling, static correction techniques are used to correct seismic data to eliminate the effects of surface elevation or near-surface structures on seismic reflection signals. Velocity modeling and imaging are performed using a fixed surface or a large smooth surface as the starting surface for migration imaging. However, in situations with undulating terrain or lateral variations in the near-surface low-velocity zone, conventional modeling methods can generate near-surface models that differ significantly from the actual near-surface velocity structure due to the replacement velocity used to replace the near-surface low-velocity zone structure. This can lead to distortions in the seismic wavefield during imaging, compromising the accuracy of seismic data imaging in complex surface conditions. As oil exploration targets move toward mountainous areas and those with complex near-surface structures, static correction techniques based on the vertical propagation assumption are unable to correct for severely distorted seismic wavefields in areas with severe surface undulation or complex near-surface structures. Consequently, seismic data processing techniques based on floating surfaces and undulating surfaces have gained widespread application. Floating surface processing is primarily used for conventional processing in the time domain, while processing techniques based on topographical relief primarily focus on prestack time and depth domain imaging. True surface prestack depth domain migration imaging, a type of topographical relief migration imaging technique, has been widely researched and promoted in recent years due to its ability to preserve near-surface velocity structure.

[0053] To obtain accurate prestack depth-domain imaging results, it is necessary to first establish an accurate subsurface velocity model. This is particularly true for reverse time migration (RTM) imaging based on the two-way wave equation, where an accurate velocity model determines the success or failure of the imaging results. Since wave equation-based methods simulate the propagation of seismic waves in tectonic models, and the accuracy of near-surface velocity models often affects the propagation of seismic wavefields in intermediate and deep layers, near-surface modeling has received widespread attention in recent years. Numerous methods and techniques for constructing near-surface models for prestack depth-domain imaging have emerged, all of which are based on the undulating surface (Li Zhenchun, 2017).

[0054] Current methods for modeling near-surface velocities on uneven surfaces fall into two main categories: one based on replacement velocities and the other based on a near-surface velocity model derived from first-arrival tomographic inversion. For the first type of modeling, after applying static corrections, seismic data are recalibrated to the uneven surface, filling the interface between the surface and the top of the high-velocity layer with replacement velocities (Lin Boxiang, 2005). This method is simple to implement, but because the near-surface low-velocity zone is replaced with a higher replacement velocity, the change in time t0 leads to a large error between the picked velocity and the actual velocity. Although methods exist to reduce this error by adjusting the elevation of the uneven surface, this approach presents challenges with actual seismic data. The second type of method directly models the surface based on the velocity model derived from first-arrival tomographic inversion. This method first obtains a near-surface velocity model, uses it as the basis for the near-surface velocity model, and then calculates corrections based on the position of the uneven surface in the velocity model to calibrate the seismic data to the position of the uneven surface (Cheng Yukun, 2017). The near-surface model obtained using this method maximizes the consistency between the near-surface velocity model and the real surface. However, under complex near-surface conditions, such as the loess plateau area overlying a thick loess layer, the near-surface velocity is low, the elevation changes dramatically, and the high-frequency static correction problem is serious. The velocity model obtained by first-arrival tomographic inversion is not accurate enough. On the one hand, it is difficult to directly use this velocity model for near-surface velocity modeling and migration imaging; on the other hand, when the near-surface velocity is low, the imaging method itself faces the dual challenges of stability and computational efficiency.

[0055] Furthermore, based on the second category of methods, patent CN107783186A provides a near-surface velocity modeling method and apparatus. This method directly uses the velocity model obtained by inversion during static correction calculation, as well as the shot and checkpoint static correction results. The near-surface model is composed of the inverted velocity model and the migration datum. The time for correcting the seismic data to the migration datum is calculated from the surface elevation, the migration datum, and the high-velocity top interface. Its characteristic is that the velocities in the near-surface model are consistent with the inverted velocities. However, there are some problems with this method. First, due to the limitations of the static correction algorithm itself, there is a certain error between the inverted velocity model and the actual velocity model, and directly using this model for migration can affect imaging accuracy. Second, in complex near-surface conditions, the inverted velocity model may contain local velocity anomalies. Current high-precision imaging methods, such as the ray-based Kirchhoff integral method and the two-way wave equation reverse time migration imaging method, are sensitive to large lateral velocity variations. The computational complexity of the latter often exceeds current computing capabilities when near-surface velocities are low. Therefore, directly using the velocity model obtained by first-break inversion in velocity modeling often leads to a decrease in imaging accuracy.

[0056] The near-surface modeling process in existing technologies is as follows: Figure 1 As shown, referring to the information in the figure, it can be seen that in the prior art, a near-surface velocity model is constructed based on the offset reference plane and the velocity model obtained by inversion, and the near-surface model is directly generated.

[0057] Accordingly, in the prior art, the travel time of the seismic wave in the offset reference plane and the interface of the high-speed layer is calculated, and then the travel time is subtracted from the static correction value of the shot check point to obtain the seismic data on the offset reference plane to complete the seismic data correction process, as shown in the attached figure. Figure 2 When constructing a near-surface velocity model using the aforementioned principles of the prior art, when the surface is highly undulating or there is a thick low-velocity zone (such as in the loess plateau), the near-surface velocity model deviates from the actual surface background velocity, causing distortion during seismic wave propagation. Correcting the seismic data to a fixed reference plane distorts the wavefield characteristics to a certain extent.

[0058] To solve the above problems, the present invention provides a method and system for approximating true surface velocity modeling. This solution is suitable for near-surface modeling under undulating surfaces and complex surfaces with strong lateral velocity variations. It can be used to construct a near-surface velocity model that is close to the true surface velocity structure, in order to reduce the distortion of the seismic wave field propagating in the velocity model and effectively improve the accuracy of pre-stack depth domain migration imaging.

[0059] Next, the detailed process of the method according to the embodiment of the present invention is described in detail based on the accompanying drawings. The steps shown in the flowcharts of the accompanying drawings can be executed in a computer system including, for example, a set of computer-executable instructions. Although the logical order of the steps is shown in the flowcharts, in some cases, the steps shown or described can be executed in a different order than here.

[0060] Example 1

[0061] Figure 1 The schematic diagram of the flow chart of the approximate true surface velocity modeling method provided by the first embodiment of the present invention is shown. Figure 1 As can be seen, the method for constructing an approximate true surface velocity model in the present invention uses the near-surface velocity model obtained from seismic first-arrival inversion, the migration starting surface, and the high-velocity top interface to construct an intermediate initial near-surface velocity model. This model is then interpolated and smoothed to obtain an approximate true surface velocity model. Specifically, the method includes the following steps.

[0062] Initial model acquisition step: obtaining a near-surface velocity model obtained by inversion of seismic first arrival waves as an initial velocity model;

[0063] High-speed top interface determination step: obtaining the replacement velocity provided by the work area during static correction calculation, and determining the high-speed top interface in the near-surface velocity model based on the replacement velocity;

[0064] Starting surface decision-making steps: Calculate a surface elevation smoothing surface as the migration starting surface for velocity modeling and migration imaging. The smoothing radius of the surface elevation smoothing surface can be selected based on the degree of surface undulation and generally does not need to exceed the maximum offset of the receiving array consisting of the source and receivers. Furthermore, imaging effects can be tested using different smoothing radii, with the smoothing radius that achieves the best imaging effect being selected as the optimal parameter.

[0065] In actual application, in one embodiment, several available smoothing radii can be selected based on the comprehensive constraints of the surface undulation and the maximum offset matrix in the receiving arrangement, and the imaging effect of each available smoothing radius can be further tested to select the best smoothing radius.

[0066] Interpolation optimization steps: interpolate the near-surface velocity model within the range determined by the high-speed top interface and the surface elevation smoothing surface to ensure that there is no velocity blank area within the range;

[0067] Target model generation steps: Select the optimal smoothing parameter and smooth the relevant velocities within the range determined after interpolation optimization to obtain an approximate true surface velocity model for depth-domain velocity modeling. The optimal smoothing parameter needs to be determined through testing. That is, different smoothing parameters are used to obtain multiple approximate true surface velocity models. Based on these models, the data is stacked or imaged, and the smoothing parameter is determined based on the optimal stacking or imaging results. Using this smoothing parameter determination technique, a certain degree of local velocity anomaly can be retained while ensuring ideal imaging results.

[0068] In actual application, in the initial model acquisition step, the near-surface velocity model V obtained by inversion of the seismic first arrival wave is read in. mod , in this near-surface velocity model, the high-speed top interface S is determined high_top , and then calculate the surface elevation smooth surface as the migration starting surface S for velocity modeling and migration imaging mig ; Further, the near-surface velocity model is interpolated within the range determined by the high-speed top interface and the surface elevation smoothing surface to ensure that there is no velocity blank area within the range; finally, a suitable smoothing parameter is selected (such as the Gaussian smoothing method with a smoothing radius of 500 meters) to smooth the velocity within the range determined by step 4 to obtain the approximate true surface velocity model V in the depth domain velocity modeling. real_mod .

[0069] During seismic data processing, the seismic data and the velocity model must be consistent. Specifically, the elevation surfaces of the shot and receiver points in the seismic data must be consistent with the effective velocity starting surface in the velocity model, and the corrections made to the seismic data during static correction must be consistent with the corrections made to the near-surface low-velocity zone in the velocity model. Therefore, for the target model (approximate true surface velocity model) obtained above, the seismic data must be corrected simultaneously.

[0070] Furthermore, researchers considered that through correction processing, the seismic data can be corrected to the migration starting surface of the approximate true surface velocity model, and the velocity changes within the near-surface model range can be corrected, so that the data and model can maintain matching in terms of both the migration starting surface and the near-surface velocity changes. Therefore, in one embodiment, the method further includes: correcting the seismic data based on the obtained fixed reference surface, the migration starting surface, the elevation smoothing surface, and the approximate true surface velocity model to obtain seismic data that is most consistent with the near-surface velocity model.

[0071] Specifically, before executing the starting plane decision step, the static correction value of the shot check point in the seismic first arrival wave inversion process is used as the initial correction value, and the initial static correction value is applied to correct the seismic data to the fixed reference plane. In actual application, the following steps are included:

[0072] Step a: read in the seismic data obtained by the seismic first arrival wave inversion process and the static correction values ​​t corresponding to each shot and check point. s , t g , as the initial correction amount;

[0073] Step b: Apply the static correction values ​​obtained in step a to calibrate the data to a corresponding fixed datum, wherein the fixed datum is a horizontal plane with a fixed elevation. When applied, the elevation plane corresponding to the maximum elevation in the work area can be selected as the fixed datum; that is, apply the initial static correction values ​​obtained in step a to the seismic data to calibrate the seismic data to the fixed datum;

[0074] The static correction value at the corresponding position of each seismic trace can be calculated using the fixed reference surface, the high-speed top interface, the near-surface velocity model, and the replacement velocity, wherein the high-speed top interface is an interface with a higher velocity determined based on the replacement velocity. Therefore, further, in one embodiment, the method further includes:

[0075] Based on the replacement velocity when calculating the initial static correction, a first intermediate static correction is determined by combining the fixed reference elevation and the offset starting surface elevation, and the seismic data is corrected to the offset starting surface using the first intermediate static correction. That is, the following steps are further performed:

[0076] Step c: Calculate the correction amount t1 from the fixed reference surface to the offset starting surface. Specifically, use the replacement speed when calculating the static correction amount and calculate the static correction amount from the fixed reference surface to the surface elevation smoothing surface according to the following formula:

[0077]

[0078] Among them, H final is the fixed datum elevation, H topo is the elevation on the offset datum plane, V rep is the replacement velocity used in calculating static correction;

[0079] Step d: applying the correction amount t1 obtained in step c to correct the seismic data to the migration starting plane;

[0080] In a preferred embodiment, the method further comprises:

[0081] After obtaining the approximate true surface velocity model, a target static correction of the seismic data relative to the approximate true surface velocity model is determined to characterize the correction caused by the approximate true surface velocity model, and the target static correction is applied to correct the seismic data.

[0082] That is, continue with the following steps:

[0083] Step e: Calculate the correction amount t4 caused by the approximate true surface velocity model;

[0084] Step f: Apply the static correction t4 to obtain seismic data consistent with the approximate true surface velocity model.

[0085] In actual application, the target static correction amount is determined by the following steps:

[0086] Calculating a second intermediate static correction amount of the seismic data relative to the approximate true surface velocity model based on thickness data and velocity data corresponding to the seismic data in the approximate true surface velocity model;

[0087] Calculating a third intermediate static correction amount of the seismic data obtained by using the replacement velocity in the approximate true surface velocity model based on thickness data and replacement velocity data corresponding to the seismic data in the approximate true surface velocity model;

[0088] A difference between the second intermediate static correction value and the third intermediate static correction value is calculated as the target static correction value.

[0089] Specifically, in the process of determining the target static correction amount, the second intermediate static correction amount t2 of the seismic data relative to the approximate true surface velocity model is calculated according to the following formula:

[0090]

[0091] Where t2 is the vertical travel time of the seismic data relative to the approximate true surface velocity model, h i is the thickness of the i-th layer in the approximate true surface velocity model, V i is the speed corresponding to this layer.

[0092] The third intermediate static correction t3 obtained by replacing the velocity of seismic data in the approximate true surface velocity model is calculated according to the following formula:

[0093]

[0094] Where t3 is the vertical travel time of seismic data obtained by replacing the velocity in the approximate true surface velocity model, h i is the thickness of the i-th layer in the velocity model, V rep is the replacement speed corresponding to the calculation of t3.

[0095] Based on the above steps, further, the difference between the second intermediate static correction amount and the third intermediate static correction amount is calculated according to the formula: t4 = t2-t3, which is used as the static correction amount t4 of the seismic data relative to the target approximate true surface velocity model, and t4 is applied to the seismic data to complete the synchronization and consistency processing of the data and the velocity model on the starting surface and the near-surface velocity model.

[0096] For simplicity of description, the aforementioned method embodiments are described as a series of actions. However, those skilled in the art should be aware that the present invention is not limited by the order of the actions described, as certain steps can be performed in other orders or simultaneously according to the present invention. Furthermore, those skilled in the art should also be aware that the embodiments described in this specification are preferred embodiments, and the actions and modules involved are not necessarily required for the present invention.

[0097] It should be noted that, in other embodiments of the present invention, the method can also obtain a new approximate true surface velocity modeling method by combining one or more of the above embodiments.

[0098] The approximate true surface velocity modeling method proposed in the present invention can effectively solve the near-surface modeling problem when there are large elevation differences and complex near-surface geological structures on the surface, and provide a more reliable near-surface velocity model for pre-stack depth migration imaging on undulating surfaces. At the same time, a seismic data correction method for use with the constructed approximate true surface velocity model is provided. While retaining the background velocity, the imaging error problem caused by sudden elevation changes and local velocity anomalies is eliminated, and the approximate true surface velocity is then used for subsequent imaging processing, which can effectively improve the accuracy of migration imaging.

[0099] It should be noted that, based on the method in any one or more of the above-mentioned embodiments of the present invention, the present invention also provides a storage medium, on which is stored a program code that can implement the method described in any one or more of the above-mentioned embodiments. When the code is executed by the operating system, the approximate true surface velocity modeling method described above can be implemented.

[0100] The methods disclosed in the embodiments of the present invention are described in detail. The methods of the present invention can be implemented using various devices or systems. Therefore, based on other aspects of the methods described in any one or more of the above embodiments, the present invention further provides an approximate true surface velocity modeling system for executing the methods described in any one or more of the above embodiments. A specific embodiment is provided below for detailed explanation.

[0101] Specifically, Figure 5 FIG. 4 shows a schematic structural diagram of the approximate true surface velocity modeling system provided in an embodiment of the present invention. Figure 5 As shown, the system includes:

[0102] An initial model acquisition module is configured to acquire a near-surface velocity model obtained by inversion of seismic first arrival waves as an initial velocity model;

[0103] a high-speed top interface determination module configured to determine a high-speed top interface in the near-surface velocity model;

[0104] a starting surface decision module configured to calculate a surface elevation smoothing surface as a migration starting surface for velocity modeling and migration imaging;

[0105] an interpolation optimization module configured to interpolate a near-surface velocity model within a range determined by a high-speed top interface and a surface elevation smoothing surface, ensuring that there is no velocity blank area within the range;

[0106] The target model generation module is configured to select corresponding smoothing parameters, smooth the relevant velocities within the range determined after interpolation optimization, and obtain an approximate true surface velocity model in depth domain velocity modeling.

[0107] Furthermore, in one embodiment, the system further includes: a data correction module configured to:

[0108] The seismic data is corrected based on the obtained fixed reference surface, the offset starting surface, the elevation smoothing surface and the approximate true surface velocity model to obtain seismic data that is consistent with the near-surface velocity model to the greatest extent possible.

[0109] Specifically, in one embodiment, the data correction module is configured as follows:

[0110] Before executing the starting surface decision step, the shot check point static correction value in the seismic first arrival wave inversion process is used as the initial correction value, and the seismic data is corrected to the fixed reference surface by applying the initial static correction value.

[0111] In one embodiment, the data correction module determines a first intermediate static correction based on the replacement velocity of the initial static correction, the fixed reference surface elevation and the offset starting surface elevation, and applies the first intermediate static correction to correct the seismic data to the offset starting surface.

[0112] The static correction from the fixed datum to the surface elevation smoothing surface is calculated according to the following formula:

[0113]

[0114] Among them, H final is the fixed datum elevation, H topo is the elevation on the offset datum plane, V rep is the replacement velocity used when calculating static correction.

[0115] Furthermore, after obtaining the approximate true surface velocity model, the data correction module determines a target static correction amount of the seismic data relative to the approximate true surface velocity model, and applies the target static correction amount to correct the seismic data.

[0116] Specifically, the data correction module determines the target static correction amount through the following steps:

[0117] Calculating a second intermediate static correction amount of the seismic data relative to the approximate true surface velocity model based on thickness data and velocity data corresponding to the seismic data in the approximate true surface velocity model;

[0118] Calculating a third intermediate static correction amount of the seismic data obtained by using the replacement velocity in the approximate true surface velocity model based on thickness data and replacement velocity data corresponding to the seismic data in the approximate true surface velocity model;

[0119] A difference between the second intermediate static correction value and the third intermediate static correction value is calculated as the target static correction value.

[0120] In one embodiment, the data correction module is configured to calculate the second intermediate static correction t2 of the seismic data relative to the approximate true surface velocity model according to the following formula:

[0121]

[0122] Where t2 is the vertical travel time of the seismic data relative to the approximate true surface velocity model, h i is the thickness of the i-th layer in the approximate true surface velocity model, V i is the speed corresponding to this layer.

[0123] In one embodiment, the data correction module is configured to calculate a third intermediate static correction t3 obtained by replacing the seismic data with the velocity in the approximate true surface velocity model according to the following formula during the process of determining the target static correction:

[0124]

[0125] Where t3 is the vertical travel time of seismic data obtained by replacing the velocity in the approximate true surface velocity model, h i is the thickness of the i-th layer in the velocity model, V rep To calculate the replacement speed corresponding to t3

[0126] In the approximate true surface velocity modeling system provided by the embodiment of the present invention, each module or unit structure can be operated independently or in combination according to actual analysis and modeling requirements to achieve corresponding technical effects.

[0127] It should be understood that the embodiments disclosed herein are not limited to the specific structures, processing steps, or materials disclosed herein, but should extend to equivalent substitutions of these features understood by those skilled in the relevant art. It should also be understood that the terminology used herein is for the purpose of describing specific embodiments only and is not intended to be limiting.

[0128] The phrase "one embodiment" mentioned in the specification means that a particular feature, structure, or characteristic described in conjunction with the embodiment is included in at least one embodiment of the present invention. Therefore, the phrase "one embodiment" appearing in various places throughout the specification does not necessarily refer to the same embodiment.

[0129] Although the embodiments disclosed herein are as described above, the contents described herein are merely embodiments for facilitating understanding of the present invention and are not intended to limit the present invention. Any person skilled in the art may make any modifications and variations in the form and details of the embodiments without departing from the spirit and scope of the present invention. However, the scope of patent protection of the present invention shall remain subject to the scope defined by the appended claims.

Claims

1. A method for approximating true surface velocity modeling, characterized in that: The method comprises: Initial model acquisition step: obtaining a near-surface velocity model obtained by inversion of seismic first arrival waves as an initial velocity model; High-speed top interface determination step: obtaining the replacement velocity provided by the work area during static correction calculation, and determining the high-speed top interface in the near-surface velocity model based on the replacement velocity; Starting surface decision step: Calculate the surface elevation smoothing surface as the migration starting surface for velocity modeling and migration imaging; Interpolation optimization steps: interpolate the near-surface velocity model within the range determined by the high-speed top interface and the surface elevation smoothing surface to ensure that there is no velocity blank area within the range; Target model generation steps: Select the optimal smoothing parameter and smooth the relevant velocities within the range determined after interpolation optimization to obtain an approximate true surface velocity model in depth domain velocity modeling; The method further includes: correcting the seismic data based on the obtained fixed reference surface, the offset starting surface, the elevation smoothing surface and the approximate true surface velocity model to obtain seismic data that is consistent with the near-surface velocity model to the greatest extent.

2. The method according to claim 1, characterized in that The method further comprises: Before executing the starting surface decision step, the shot checkpoint static correction value in the seismic first arrival wave inversion process is used as the initial static correction value, and the seismic data is corrected to the fixed reference surface by applying the initial static correction value.

3. The method according to claim 2, characterized in that The method further comprises: Based on the replacement speed when calculating the initial static correction, a first intermediate static correction is determined by integrating the fixed reference surface elevation and the migration start surface elevation, and the seismic data is corrected to the migration start surface using the first intermediate static correction.

4. The method according to claim 3, characterized in that The method further comprises: After obtaining the approximate true surface velocity model, a target static correction amount of the seismic data relative to the approximate true surface velocity model is determined, and the target static correction amount is applied to correct the seismic data.

5. The method according to claim 4, characterized in that The target static correction amount is determined by the following steps: Calculating a second intermediate static correction amount of the seismic data relative to the approximate true surface velocity model based on thickness data and velocity data corresponding to the seismic data in the approximate true surface velocity model; Calculating a third intermediate static correction amount of the seismic data obtained by using the replacement velocity in the approximate true surface velocity model based on thickness data and replacement velocity data corresponding to the seismic data in the approximate true surface velocity model; A difference between the second intermediate static correction value and the third intermediate static correction value is calculated as the target static correction value.

6. The method according to claim 5, characterized in that In the process of determining the target static correction, the second intermediate static correction t2 of the seismic data relative to the approximate true surface velocity model is calculated according to the following formula: Where t2 is the vertical travel time of the seismic data relative to the approximate true surface velocity model, h i is the thickness of the i-th layer in the approximate true surface velocity model, V i is the speed corresponding to this layer.

7. The method according to claim 5, characterized in that In the process of determining the target static correction, the third intermediate static correction t3 obtained by replacing the seismic data with the velocity in the approximate true surface velocity model is calculated according to the following formula: Where t3 is the vertical travel time of seismic data obtained by replacing the velocity in the approximate true surface velocity model, h i is the thickness of the i-th layer in the velocity model, V rep is the replacement speed corresponding to the calculation of t3.

8. A storage medium, characterized in that: The storage medium stores program code that can implement the method according to any one of claims 1 to 7.

9. A system for modeling approximate true surface velocity, characterized in that: The system comprises: An initial model acquisition module is configured to acquire a near-surface velocity model obtained by inversion of seismic first arrival waves as an initial velocity model; a high-speed top interface determination module configured to determine a high-speed top interface in the near-surface velocity model; a data correction module configured to correct the seismic data based on the obtained fixed reference surface, the offset starting surface, the elevation smoothing surface, and the approximate true surface velocity model to obtain seismic data that is consistent with the near-surface velocity model to the greatest extent possible; a starting surface decision module configured to calculate a surface elevation smoothing surface as a migration starting surface for velocity modeling and migration imaging; an interpolation optimization module configured to interpolate a near-surface velocity model within a range determined by a high-speed top interface and a surface elevation smoothing surface, ensuring that there is no velocity blank area within the range; The target model generation module is configured to select corresponding smoothing parameters, smooth the relevant velocities within the range determined after interpolation optimization, and obtain an approximate true surface velocity model in depth domain velocity modeling.

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