A velocity modeling method and system for all-directional gathers in OVT domain

Abstract

The present invention discloses a velocity modeling method of an omnidirectional gather in an OVT domain, wherein the method comprises: converting wide-azimuth seismic data to the OVT domain, and obtaining an OVG gather through preprocessing and initial depth migration; decomposing the reflection angle in the OVG gather into components along the main survey line direction and the connecting survey line direction; constructing a finite difference model according to the components; picking up the residual time difference for the OVG gather using the finite difference model; performing unified ray tracing, establishing an inversion equation, and performing omnidirectional tomographic inversion according to the picked-up residual time difference to obtain an optimal velocity model; and imaging a geological body using the optimal velocity model. The present invention obtains an OVG gather by converting wide-azimuth seismic data to the OVT domain for preprocessing and migration, then picking up the residual time difference for the OVG gather, and performing omnidirectional tomographic inversion according to the picked-up residual time difference to obtain the final velocity, which can better depict the details of velocity changes and improve subsequent imaging accuracy.

Description

Technical Field

[0001] The present invention belongs to the technical field of seismic imaging, and more specifically, relates to an OVT domain omnidirectional gather velocity modeling method and system. Background Art

[0002] With the development of oil and gas exploration and development, the precision requirements for seismic imaging are getting higher and higher. The results of seismic imaging are obtained by iterative inversion based on the velocity model. At present, the mainstream velocity modeling method used in the industry is still the velocity modeling method based on seismic wave travel time tomographic inversion, such as grid tomographic inversion, Gaussian beam tomographic inversion, and tomographic inversion under structural and well constraints.

[0003] In the past, due to data limitations, the influence of anisotropy was often ignored in the processing of narrow azimuth data, and the azimuth information was not considered in velocity modeling. With the large-scale acquisition of wide azimuth data, the anisotropic characteristics are more prominent in wide azimuth data, and the change of velocity with azimuth also needs to be considered in the processing. Therefore, the velocity modeling method for wide azimuth data came into being. One is the azimuth velocity modeling method proposed by Buia (2011). Its specific idea is to divide the data into multiple azimuths according to the azimuth, and use the azimuth processing method to perform tomographic velocity modeling. The obvious disadvantage of this technology is that it is highly prone to human intervention. The processor divides the data body into multiple azimuths based on experience and processes it in each azimuth. However, no matter how fine the division is, there are more seismic traces in some azimuths and fewer seismic traces in some azimuths, which ultimately leads to an uneven coverage of the azimuths, making the velocity accuracy of multi-azimuth tomographic inversion low.

[0004] With the development of OVT (Offset Vector Tile, OVT) domain processing technology, OVT domain tomographic inversion velocity modeling technology has gradually become an important link in OVT domain processing. Although OVT domain velocity modeling does not have the situation of artificially dividing azimuths as mentioned above, the gathers used for OVT domain modeling are still used for conventional common offset gathers in the past. The specific idea is: perform OVT domain conversion on wide azimuth data, perform denoising, regularization and other processing in the OVT domain, and then use conventional imaging methods to perform migration imaging to obtain CIG gathers, but the gathers at this time also do not contain azimuth information. Use CIG gathers for velocity modeling, and then use the obtained velocity model to perform OVT domain migration to obtain the full-scale gathers after migration, and then perform azimuthal anisotropy processing on the full-scale gathers. The disadvantage of this method is that the residual time difference on the azimuth gathers obtained after migration is not necessarily a true reflection of underground fractures, which may be caused by insufficient accuracy of the velocity model. Therefore, the use of this azimuth gather for fracture prediction or seismic imaging has the problem of low accuracy. Summary of the invention

[0005] The purpose of the present invention is to provide an OVT domain omnidirectional gather velocity modeling method and system to solve the problem of inaccurate seismic imaging results due to insufficient velocity model accuracy.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] A velocity modeling method for all-directional gathers in an OVT domain, comprising the following steps:

[0008] Step 1: Acquire wide-azimuth seismic data;

[0009] Step 2: converting the wide-azimuth seismic data into the OVT domain to obtain an OVT gather;

[0010] Step 3: Preprocessing and prestack depth migration of the OVT gathers to obtain OVG gathers;

[0011] Step 4: Convert the offset in the OVG gather into a reflection angle, and decompose the reflection angle into components along the Inline direction and along the Crossline direction;

[0012] Step 5: constructing a finite difference model according to the components along the Inline direction and along the Crossline direction;

[0013] Step 6: Pick the residual time difference of the OVG gather using the finite difference model;

[0014] Step 7: Perform ray tracing and full-scale tomographic inversion based on the picked residual time difference to obtain the optimal velocity model;

[0015] Step 8: Image the geological body using the optimal velocity model.

[0016] Preferably, the step 4: converting the offset in the OVG gather into a reflection angle, and decomposing the reflection angle into components along the Inline direction and along the Crossline direction, further comprises:

[0017] The components along the Inline direction and the Crossline direction are expressed in a Cartesian coordinate system to obtain a relationship between the reflection angle and the azimuth angle; wherein the relationship is:

[0018]

[0019]

[0020] Where θ is the reflection angle; is the azimuth.

[0021] Preferably, the finite difference model is:

[0022]

[0023] Among them, Δx represents the increment in the x direction, and Δy represents the increment in the y direction. Represents discrete points In the x-direction time increment, Represents discrete points In the y direction, the time increment is Represents discrete points Pressure increment in the x direction.

[0024] Preferably, the step 8: imaging the geological body using the optimal velocity model comprises:

[0025] Step 8.1: Use the best velocity model to perform grid tomography inversion on the picked residual time difference to obtain the group velocity and azimuth; wherein the best velocity model is:

[0026]

[0027] Among them, δt i represents the travel time error of the ith track on the OVG gather, D ij It represents the ray path length of the i-th track in the j-th grid in the OVG gather;

[0028] Step 8.2: Obtaining a fast wave velocity and a slow wave velocity according to the group velocity and the azimuth angle;

[0029] Step 8.3: Image the geological body using the fast wave velocity and the slow wave velocity.

[0030] Preferably, the step 8.2: obtaining the fast wave velocity and the slow wave velocity according to the group velocity and the azimuth angle comprises: using the formula:

[0031]

[0032]

[0033] The fast wave velocity and slow wave velocity are obtained; where V represents the group velocity, V f Indicates the fast wave velocity, V s represents the slow wave velocity, α represents the azimuth angle, Indicates the angle between the inspection direction and the Inline direction.

[0034] The present invention also provides an OVT domain omnidirectional gather velocity modeling system, comprising:

[0035] A seismic data acquisition module, used for acquiring wide-azimuth seismic data;

[0036] A seismic data conversion module, used for converting the wide azimuth seismic data into an OVT domain to obtain an OVT gather;

[0037] A gather preprocessing module, used for preprocessing the OVT gather and performing prestack depth migration to obtain an OVG gather;

[0038] A reflection angle decomposition module, used for converting the offset in the OVG gather into a reflection angle, and decomposing the reflection angle into components along the Inline direction and along the Crossline direction;

[0039] A finite difference model building module, used for building a finite difference model according to the components along the Inline direction and along the Crossline direction;

[0040] A residual time difference picking module, used for picking the residual time difference of the OVG gather using the finite difference model;

[0041] The velocity solution module is used to perform ray tracing and full-scale tomographic inversion according to the picked residual time difference to obtain the best velocity model;

[0042] An imaging module is used to image the geological body using the optimal velocity model.

[0043] Preferably, it also includes:

[0044] A coordinate system conversion module is used to express the components along the Inline direction and the Crossline direction using a Cartesian coordinate system to obtain a relationship between the reflection angle and the azimuth angle; wherein the relationship is:

[0045]

[0046]

[0047] Where θ is the reflection angle; is the azimuth.

[0048] Preferably, the finite difference model is:

[0049]

[0050] Among them, Δx represents the increment in the x direction, and Δy represents the increment in the y direction. Represents discrete points In the x-direction time increment, Represents discrete points In the y direction, the time increment is Represents discrete points Pressure increment in the x direction.

[0051] Preferably, the speed solving module comprises:

[0052] The grid tomography inversion unit is used to perform grid tomography inversion on the picked residual time difference using the optimal velocity model to obtain the group velocity and azimuth; wherein the optimal velocity model is:

[0053]

[0054] Among them, δt i represents the travel time error of the ith track on the OVG gather, D ij It represents the ray path length of the i-th track in the j-th grid in the OVG gather;

[0055] A velocity solving unit, used for obtaining a fast wave velocity and a slow wave velocity according to the group velocity and the azimuth angle;

[0056] An imaging unit is used to image the geological body using the fast wave velocity and the slow wave velocity.

[0057] Preferably, the speed solving unit comprises: a speed solving subunit, which is used to adopt the formula:

[0058]

[0059]

[0060] The fast wave velocity and slow wave velocity are obtained; where V represents the group velocity, V f Indicates the fast wave velocity, V s represents the slow wave velocity, α represents the azimuth angle, Indicates the angle between the inspection direction and the Inline direction.

[0061] The beneficial effect of the velocity modeling method of an OVT domain omnidirectional gather provided by the present invention is that: compared with the prior art, the velocity modeling method of an OVT domain omnidirectional gather provided by the present invention includes: converting wide azimuth seismic data to the OVT domain to obtain an OVT gather; preprocessing the OVT gather to obtain an OVG gather; converting the shot offset in the OVG gather into a reflection angle, and decomposing the reflection angle into components along the Inline direction and along the Crossline direction; constructing a finite difference model according to the components along the Inline direction and along the Crossline direction; using the finite difference model to pick up the residual time difference for the OVG gather; performing ray tracing and omnidirectional tomography inversion according to the picked up residual time difference to obtain the optimal velocity model; and imaging the geological body using fast wave velocity and slow wave velocity. The present invention obtains an OVT gather by converting wide azimuth seismic data to the OVT domain, then picking up the residual time difference for the OVT gather, and obtaining the final velocity according to the picked up residual time difference, which can better characterize the details of velocity changes and improve the subsequent imaging accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0063] Figure 1 A flow chart of a velocity modeling method of an OVT domain omnidirectional gather provided by the present invention;

[0064] Figure 2 The CIG gathers of conventional migration provided by the present invention;

[0065] Figure 3 The OVG gathers of the OVT domain migration provided by the present invention;

[0066] Figure 4 The initial velocity model provided by the present invention;

[0067] Figure 5 The final iterative velocity model provided by the present invention;

[0068] Figure 6 Azimuthally anisotropic gathers of initial migration provided by the present invention;

[0069] Figure 7 The azimuthal anisotropic gathers of the final iterative migration provided by the present invention;

[0070] Figure 8 The initial offset profile provided by the present invention;

[0071] Fig. 9 The final offset profile provided by the present invention. DETAILED DESCRIPTION

[0072] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0073] The purpose of the present invention is to provide an OVT domain omnidirectional gather velocity modeling method to solve the problem of inaccurate seismic imaging results due to insufficient velocity model accuracy.

[0074] See also Figure 1 To achieve the above purpose, the technical solution adopted by the present invention is: a velocity modeling method of omnidirectional gathers in OVT domain, comprising the following steps:

[0075] Step 1: Acquire wide-azimuth seismic data;

[0076] Step 2: Convert the wide-azimuth seismic data into the OVT domain to obtain the OVT gathers;

[0077] It should be noted that the OVT (Offset Vector Tile) gathers are mainly obtained by converting wide azimuth data into the OVT domain for offset. The formation of the OVT domain is mainly divided into three steps: First, the cross-arranged seismic traces in the observation system are extracted to form a cross-arranged gather. Among them, the extracted cross-arranged gathers are divided into several small rectangles according to the equal distance between the gun line and the detection line. Each rectangle is an OVT piece (also called a vector piece). Each OVT piece is divided by the same gun spacing and the same detection line spacing, and has approximately the same offset and azimuth. Second, a coordinate system is constructed according to the position of the OVT vector piece in the cross-arrangement. Specifically, the intersection of the gun line and the detection line is taken as the coordinate origin, the receiving line is the X-axis, the gun line is the Y-axis, the distance from the center of the vector piece to the coordinate origin is the offset, and the angle between the line connecting the coordinate origin and the vertical axis is the azimuth. Third, according to the above processing method, several cross-arranged gathers are extracted for the observation system of the entire work area, and the OVT vector pieces with the same coordinates are extracted and arranged according to the corresponding Inline number and crossline number to form an OVT gather for the entire area. The OVT gather is a single coverage data body, similar to a conventional offset data body. The data body contains information such as three-dimensional spatial coordinates, offset and azimuth, and is a five-dimensional data body.

[0078] According to the above process, the wide azimuth data is converted to the OVT domain, and the cross arrangement of the entire area is extracted to form the OVT gather of the entire work area. Since the offset and azimuth of each OVT gather are almost the same, that is, the OVT gather contains both azimuth and offset information, the energy consistency of the OVT gather is good, whether it is near offset, medium offset or far offset.

[0079] Step 3: Preprocess the OVT gather to obtain the OVG (Offset Vector Gather) gather. In practical applications, the OVT gather needs to be preprocessed by denoising, interpolation and offset, and the preprocessed gather is the OVG gather.

[0080] Step 4: Convert the offset in the OVG gather into reflection angle, and decompose the reflection angle into components along the Inline direction (the main survey line direction) and along the Crossline direction (the connection survey line direction);

[0081] The OVT domain tomographic inversion of the present invention is to perform residual time difference picking on the OVG data set after the OVT domain migration, and use the Poisson equation algorithm to solve it. Since the Poisson equation is expressed by a Cartesian coordinate system, and the residual time difference of the OVG data set in the OVT domain needs to consider the azimuth information, it is necessary to convert the shot distance of the OVG data set into a reflection angle, and then decompose the reflection angle into components along the Inline direction and the Crossline direction, and express it in a Cartesian coordinate system. Specifically, the components along the Inline direction and along the Crossline direction are expressed in a Cartesian coordinate system to obtain the relationship between the reflection angle and the azimuth; wherein, the relationship is:

[0082]

[0083]

[0084] Where θ is the reflection angle; is the azimuth.

[0085] Step 5: Construct a finite difference model based on the components along the Inline direction and along the Crossline direction;

[0086] It should be noted that in the Cartesian coordinate system, the residual time difference of depth τ(x,y) can be expressed as a surface on a three-dimensional data volume. τ(x,y) is the solution of the Poisson equation.

[0087]

[0088] In the formula, t represents the time difference. Represents the vector gradient, and the time difference components in the x and y directions can be obtained by applying the plane wave deconstruction algorithm to the migrated gathers. In practical applications, the depth residual time difference τ(x,y) needs to be discretized into τ i,j , the time difference vector p is shifted by half the sampling interval is given; its divergence is expressed in the form of a finite difference model:

[0089]

[0090] Among them, Δx represents the increment in the x direction, and Δy represents the increment in the y direction. Represents discrete points In the x-direction time increment, Represents discrete points In the y direction, the time increment is Represents discrete points Pressure increment in the x direction.

[0091] Step 6: Use the finite difference model to pick the residual time difference of the OVG gather;

[0092] Step 7: Perform ray tracing and full-scale tomographic inversion based on the picked residual time difference to obtain the optimal velocity model;

[0093] Furthermore, step 7 includes:

[0094] The optimal velocity model is used to perform grid tomography inversion on the picked residual time difference to obtain the group velocity and azimuth. Specifically, according to the picked residual time difference, grid tomography inversion is performed to divide the underground into cube grids containing velocity information. The relationship between the cube grid and the velocity can be expressed by the following matrix:

[0095]

[0096] Among them, δt i represents the travel time error of the ith track on the OVG gather, D ij represents the ray path length of the i-th track in the j-th grid in the OVG gather; δs i represents the slowness error in the j-th grid.

[0097] After inversion, the velocities at different azimuths are obtained, and the velocity parameters are used to perform ellipse fitting to obtain the group velocity v and the corresponding azimuth angle α at different azimuths.

[0098] Step 8: Imaging the geological body using the optimal velocity model, including:

[0099] Furthermore, step 8 includes:

[0100] Step 8.1: Use the best velocity model to perform grid tomographic inversion on the picked residual time difference to obtain the group velocity and azimuth;

[0101] Step 8.2: Obtaining a fast wave velocity and a slow wave velocity according to the group velocity and the azimuth angle;

[0102] Specifically, the present invention can adopt the formula:

[0103]

[0104]

[0105] The fast wave velocity and slow wave velocity are obtained; where V represents the group velocity, V f Indicates the fast wave velocity, V s represents the slow wave velocity, α represents the azimuth angle, Indicates the angle between the inspection direction and the Inline direction.

[0106] Step 8.3: Image the geological body using the fast wave velocity and the slow wave velocity.

[0107] The tomographic inversion velocity modeling principle of the present invention is applied to the velocity modeling of wide-azimuth seismic data in a certain work area to illustrate the technical effect and principle of the present invention.

[0108] The wide azimuth data collection in this work area is an orthogonal observation system with an aspect ratio of 0.9, a 5m×5m face, and 256 coverage times, which belongs to small face and high coverage collection. The pre-processed CMP gathers are extracted to the OVT domain to obtain OVT gathers. The number of OVT gathers is basically the same as the number of coverage times of the entire area, which is 256 OVT gathers. Each OVT gather is a single coverage data body with a uniform shot offset and azimuth. The wide azimuth data needs to be pre-processed before modeling, mainly including: OVT domain denoising, extraction of OVT azimuth gathers, pre-stack regularization and migration processing for OVT gathers, so that the azimuth anisotropic gathers obtained after migration retain the information of offset distance and azimuth. At this time, the azimuth gathers do not need to be anisotropically processed and are used to pick up the residual time difference in subsequent modeling. The migration velocity can be used as the initial velocity model for velocity modeling. Figure 2-3 The CIG gathers obtained by conventional depth migration and the azimuthal anisotropic gathers obtained by OVT domain depth migration use the same velocity model. Figure 2 The CIG gathers in the middle do not reflect the change in orientation. Figure 3 The azimuth of the azimuth anisotropic gathers varies periodically. By comparing the two, it can be seen that the CIG gathers of conventional depth migration seem to be completely leveled and the velocity is relatively accurate, but Figure 3There is an obvious time difference phenomenon on the azimuth anisotropic gathers that changes with the azimuth fluctuation. This time difference changes regularly with the azimuth angle, especially at a depth of 2500m-3000m in the figure (marked in the box). This shows that the existing velocity cannot level the azimuth gathers. Through research, it is believed that the residual time difference generated on the azimuth anisotropic gathers after migration in this area is caused by the insufficient accuracy of the migration velocity model. Since the conventional offset range domain velocity modeling method does not consider the azimuth information, the velocity inversion and smoothing use large-scale velocity parameters, which cannot reflect the small-scale velocity disturbance. Therefore, according to the original depth migration and velocity update method, even if the scale of velocity smoothing becomes smaller, the required accuracy cannot be achieved. If the azimuth angle information is added to the velocity inversion iteration in the OVT domain wide azimuth data tomography inversion velocity modeling, and the smoothing parameters are gradually iterated from a relatively large scale to a small scale in this process, the velocity detail problem can be solved and the influence of the residual time difference can be truly eliminated, because the details of the velocity change are the key factors in solving the residual time difference. According to the above analysis, tomographic inversion velocity modeling is carried out in the OVT domain, and the Poisson algorithm is used to pick the residual time difference on the azimuthal anisotropic gathers, which can reduce the lateral smoothing parameter from 2800m to 1800m and finally to 800m, and the longitudinal smoothing parameter from 600m to 400m and then to 200m, thereby gradually improving the imaging accuracy of the geological body.

[0109] Figure 4 and Figure 5 They are the initial velocity model and the velocity model obtained after the OVT domain tomographic velocity inversion iteration. It can be seen from the figure that the final velocity obtained after the OVT domain tomographic inversion iteration can better describe the details of the velocity change (below 2000m in the figure). Figure 6-7 The azimuth anisotropy gathers of the initial migration and the azimuth anisotropy gathers of the final migration after iteration. By comparing the two, it can be seen that there is a strong residual time difference that varies with azimuth on the gathers of the initial migration. After iteration, the velocity accuracy is improved, the azimuth anisotropy gathers are well leveled, and the residual time difference is well eliminated (marked in the box in the figure). It can be seen that the residual time difference on the azimuth gathers in this area is not a true reflection of the underground azimuth anisotropy characteristics, but is caused by the low accuracy of the velocity model. Although the velocity accuracy has been continuously improved through multiple iterations in the early processing, the traditional depth migration velocity modeling lacks azimuth information, and the changes in different azimuths are not considered during ray tracing, so the details of velocity changes cannot be well described, and therefore only large-scale information can be reflected. The OVT domain migration can effectively preserve the azimuth information. Through multiple inversion iterations, the final velocity model can invert the details of small-scale velocity changes.

[0110] Figure 8-9This is a comparison of the initial migration and final migration profiles in the OVT domain. It can be seen that the continuous updating and iteration of the velocity model can obtain more accurate velocities, which greatly improves the accuracy of the final migration imaging, especially the outline of the entire basement is very clear, which well depicts the detailed changes of the entire structure, and the imaging of the interior and steep-angle formations below the basement is improved. The contact relationship of the formation is clearer (the ellipse marked part in the figure), which provides reliable data guarantee for subsequent interpretation and reservoir prediction.

[0111] In summary, there are certain differences between the existing wide-azimuth data modeling methods and the OVT domain omnidirectional gather velocity modeling method proposed in the present invention, which are mainly reflected in the following aspects: (1) The input gathers for velocity modeling are different. The gathers input for conventional velocity modeling and azimuth velocity modeling are CIG gathers, which are two-dimensional and do not contain azimuth information; while the gathers input for the OVT domain velocity modeling of the present invention are azimuth gathers after OVT domain offset, which directly contain azimuth and offset information. (2) The equations used to construct and pick up the residual time difference are different. The residual time difference picking for conventional velocity modeling is directly picked up on the CIG gather, and ray tracing is performed to establish an inversion equation group, and finally an iterative solution is performed. The azimuth information is not reflected in the entire modeling process; while the OVT domain velocity modeling of the present invention is to pick up the residual time difference on the OVT domain omnidirectional gather, uniformly perform ray tracing, and uniformly establish an inversion equation group for iterative solution. (3) The workload of modeling and the final velocity accuracy are different. Although the workload of the conventional velocity modeling method is small, the accuracy of the velocity model finally obtained is much lower than that of the present invention.

[0112] The present invention also provides an OVT domain omnidirectional gather velocity modeling system, comprising:

[0113] A seismic data acquisition module, used for acquiring wide-azimuth seismic data;

[0114] A seismic data conversion module, used for converting the wide azimuth seismic data into an OVT domain to obtain an OVT gather;

[0115] A gather preprocessing module, used for preprocessing the OVT gather and performing prestack depth migration to obtain an OVG gather;

[0116] A reflection angle decomposition module, used for converting the offset in the OVG gather into a reflection angle, and decomposing the reflection angle into components along the Inline direction and along the Crossline direction;

[0117] A finite difference model building module, used for building a finite difference model according to the components along the Inline direction and along the Crossline direction;

[0118] A residual time difference picking module, used for picking the residual time difference of the OVG gather using the finite difference model;

[0119] The velocity solution module is used to perform ray tracing and full-scale tomographic inversion according to the picked residual time difference to obtain the best velocity model;

[0120] An imaging module is used to image the geological body using the optimal velocity model.

[0121] Preferably, it also includes:

[0122] A coordinate system conversion module is used to express the components along the Inline direction and the Crossline direction using a Cartesian coordinate system to obtain a relationship between the reflection angle and the azimuth angle; wherein the relationship is:

[0123]

[0124]

[0125] Where θ is the reflection angle; is the azimuth.

[0126] Preferably, the finite difference model is:

[0127]

[0128] Among them, Δx represents the increment in the x direction, and Δy represents the increment in the y direction. Represents discrete points In the x-direction time increment, Represents discrete points In the y direction, the time increment is Represents discrete points Pressure increment in the x direction.

[0129] Preferably, the speed solving module comprises:

[0130] The grid tomography inversion unit is used to perform grid tomography inversion on the picked residual time difference using the optimal velocity model to obtain the group velocity and azimuth; wherein the optimal velocity model is:

[0131]

[0132] Among them, δt i represents the travel time error of the ith track on the OVG gather, D ij It represents the ray path length of the i-th track in the j-th grid in the OVG gather;

[0133] A velocity solving unit, used for obtaining a fast wave velocity and a slow wave velocity according to the group velocity and the azimuth angle;

[0134] An imaging unit is used to image the geological body using the fast wave velocity and the slow wave velocity.

[0135] Preferably, the speed solving unit comprises: a speed solving subunit, which is used to adopt the formula:

[0136]

[0137]

[0138] The fast wave velocity and slow wave velocity are obtained; where V represents the group velocity, V f Indicates the fast wave velocity, V s represents the slow wave velocity, α represents the azimuth angle, Indicates the angle between the inspection direction and the Inline direction.

[0139] The beneficial effect of the OVT domain omnidirectional gather velocity modeling method provided by the present invention is that: compared with the prior art, the present invention obtains OVT gathers by converting wide-azimuth seismic data into the OVT domain, and then preprocesses and offsets the OVT gathers to obtain OVG gathers to pick up residual time differences, and obtains the final velocity based on the picked residual time differences, which can better characterize the details of velocity changes and improve subsequent imaging accuracy.

[0140] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A velocity modeling method for omnidirectional gathers in OVT domain, characterized in that: The following steps are involved: Step 1: Acquire wide-azimuth seismic data; Step 2: converting the wide-azimuth seismic data into the OVT domain to obtain an OVT gather; Step 3: Preprocessing and prestack depth migration of the OVT gathers to obtain OVG gathers; Step 4: Convert the offset in the OVG gather into a reflection angle, and decompose the reflection angle into components along the Inline direction and along the Crossline direction; The step 4: converting the offset in the OVG gather into a reflection angle, and decomposing the reflection angle into components along the Inline direction and along the Crossline direction, further includes: The components along the Inline direction and the Crossline direction are expressed in a Cartesian coordinate system to obtain a relationship between the reflection angle and the azimuth angle; wherein the relationship is: Where θ is the reflection angle; is the azimuth; Step 5: constructing a finite difference model according to the components along the Inline direction and along the Crossline direction; The finite difference model is: Among them, Δx represents the increment in the x direction, and Δy represents the increment in the y direction. Represents discrete points In the x-direction time increment, Represents discrete points In the y direction, the time increment is Represents discrete points Pressure increment in the x direction; Step 6: Pick the residual time difference of the OVG gather using the finite difference model; Step 7: Perform ray tracing, establish inversion equations and perform full-scale tomographic inversion according to the picked residual time difference to obtain the optimal velocity model; Step 8: imaging the geological body using the optimal velocity model; The step 8: using the optimal velocity model to image the geological body includes: Step 8.1: Use the best velocity model to perform grid tomography inversion on the picked residual time difference to obtain the group velocity and azimuth; wherein the best velocity model is: Among them, δt i represents the travel time error of the ith track on the OVG gather, D ij It represents the ray path length of the i-th track in the j-th grid in the OVG gather; Step 8.2: Obtaining a fast wave velocity and a slow wave velocity according to the group velocity and the azimuth angle; The step 8.2: obtaining the fast wave velocity and the slow wave velocity according to the group velocity and the azimuth angle, comprises: Using the formula: The fast wave velocity and slow wave velocity are obtained; where V represents the group velocity, V f Indicates the fast wave velocity, V s represents the slow wave velocity, α represents the azimuth angle, Indicates the angle between the inspection direction and the Inline direction; Step 8.3: Image the geological body using the fast wave velocity and the slow wave velocity.

2. An OVT domain omnidirectional gather velocity modeling system, characterized in that: include: A seismic data acquisition module, used for acquiring wide-azimuth seismic data; A seismic data conversion module, used for converting the wide azimuth seismic data into an OVT domain to obtain an OVT gather; A gather preprocessing module, used for preprocessing the OVT gather and performing prestack depth migration to obtain an OVG gather; A reflection angle decomposition module, used for converting the offset in the OVG gather into a reflection angle, and decomposing the reflection angle into components along the Inline direction and along the Crossline direction; A coordinate system conversion module is used to express the components along the Inline direction and the Crossline direction using a Cartesian coordinate system to obtain a relationship between the reflection angle and the azimuth angle; wherein the relationship is: Where θ is the reflection angle; is the azimuth; A finite difference model building module, used for building a finite difference model according to the components along the Inline direction and along the Crossline direction; The finite difference model is: Among them, Δx represents the increment in the x direction, and Δy represents the increment in the y direction. Represents discrete points In the x-direction time increment, Represents discrete points In the y direction, the time increment is Represents discrete points Pressure increment in the x direction; A residual time difference picking module, used for picking the residual time difference of the OVG gather using the finite difference model; The velocity solution module is used to perform ray tracing and full-scale tomographic inversion according to the picked residual time difference to obtain the best velocity model; The speed solving module comprises: The grid tomography inversion unit is used to perform grid tomography inversion on the picked residual time difference using the optimal velocity model to obtain the group velocity and azimuth; wherein the optimal velocity model is: Among them, δt i represents the travel time error of the ith track on the OVG gather, D ij It represents the ray path length of the i-th track in the j-th grid in the OVG gather; A velocity solving unit, used for obtaining a fast wave velocity and a slow wave velocity according to the group velocity and the azimuth angle; The speed solving unit includes: a speed solving subunit, which is used to adopt the formula: The fast wave velocity and slow wave velocity are obtained; where V represents the group velocity, V f Indicates the fast wave velocity, V s represents the slow wave velocity, α represents the azimuth angle, Indicates the angle between the inspection direction and the Inline direction; An imaging unit, used for imaging the geological body using the fast wave velocity and the slow wave velocity; An imaging module is used to image the geological body using the optimal velocity model.

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