A residual static correction method based on prestack depth migration imaging

Abstract

This application relates to the field of oil and gas geophysics and discloses a residual static correction method based on prestack depth migration imaging. This application addresses the imaging error problem caused by the mismatch between the time-domain dynamic correction method and the actual prestack depth migration when using time-domain stacking velocity for dynamic correction and then calculating the residual static correction value in existing undulating terrain. This application uses depth-domain velocity to perform dynamic correction based on ray travel times, ensuring that the final calculated residual static correction value matches the final prestack depth migration model. This significantly improves imaging quality and is more accurate and direct than existing technologies.

Description

Technical Field

[0001] The present application relates to the field of oil and gas geophysics, more specifically to the field of oil and gas field exploration and development, and in particular to a residual static correction method based on prestack depth migration imaging. Background Art

[0002] Surface consistency residual statics are corrections made to seismic data to compensate for the effects of elevation, weathering thickness, and weathering velocity, aligning the data to a specified datum. It is a primary data processing method used in seismic exploration to eliminate near-surface effects and improve the quality of seismic reflection imaging. This is primarily achieved by improving the focus and continuity of events in stacked seismic data sections.

[0003] Currently, there is no direct residual static correction method for depth migration. The current technical approach is to calculate the residual statics in the time domain. Dynamically moving (NMO) correction uses manually picked stacking velocities in the time domain. Long-wavelength statics are then removed through smoothing, while medium- and short-wavelength statics are retained. These are then applied to the depth migration input data. Consequently, existing techniques suffer from the following major problems and shortcomings: 1. The NMO correction of the common-center point gathers before residual static correction uses the root mean square (RMS) velocity in the time domain. In complex surfaces and when prestack depth migration is required, the NMO velocity does not match the migration data and method. 2. In complex surfaces and structures, this can lead to inaccurate ray tracing traveltimes calculated from the surface, affecting velocity model updates and, consequently, the effectiveness of prestack depth migration. Summary of the Invention

[0004] In response to the problems and defects existing in the above-mentioned prior art, the present application provides a residual static correction method based on pre-stack depth migration imaging. This method uses depth domain velocity to perform dynamic correction based on ray travel time, so that the final residual static correction amount matches the final pre-stack depth migration model, and at the same time can greatly improve the imaging quality.

[0005] In order to achieve the above-mentioned invention objectives, the technical solutions of this application are as follows:

[0006] A residual static correction method based on prestack depth migration imaging, the method specifically comprising the following steps:

[0007] S1. Obtain surface elevation information, common center point gathers, and pre-stack depth migration velocity models within the exploration area;

[0008] S2. Optimize the common center point gathers to improve the signal-to-noise ratio of the common center point gathers;

[0009] S3. Establishing a travel time table using the ray tracing method based on the pre-stack depth migration velocity model and surface elevation information;

[0010] S4. Performing depth domain dynamic correction on the optimized common center point gathers according to the travel time table obtained from the ray path;

[0011] S5. Convert the CMP gathers after NMO correction to the time domain using the depth domain layer velocity model.

[0012] S6. Use the residual static correction method to calculate the residual static correction amount of the gun and check point;

[0013] S7. Apply the residual static correction value obtained in step S6 to the common center point gather data to perform pre-stack depth migration processing.

[0014] Furthermore, step S2 is specifically as follows: through four-dimensional denoising, an optimized common center point gather is obtained, the pre-stack seismic data volume is regarded as a four-dimensional data volume, one dimension is the main survey line number, two dimensions are the connecting survey line number, three dimensions are the offset distance within the common center point gather, and four dimensions are the recording time. The matrix descending denoising method is used to attenuate random noise, and the angle of resection is performed for large incident angles or far offset distances, and data of 35° and below is retained. The common center point gather is frequency scanned, the best signal-to-noise ratio frequency band is selected, and bandpass filtering is performed.

[0015] Furthermore, step S3 specifically includes: when the elevations of the seismic data shot and receiver points change, the travel time table from the shot point to the receiver point at different positions in the entire work area is obtained according to the pre-stack depth migration velocity model using the ray tracing method.

[0016] Furthermore, the step S4 is specifically as follows: the travel time table of the source (i) and the receiver (j) is calculated according to the depth domain layer velocity model, and for each depth sample point z k , calculate the time t from the travel time table k The total travel time, at the same time, the time domain gathers at t k The amplitude is mapped to the corresponding depth sample z k .

[0017] Furthermore, the time and propagation path of the seismic wave rays from the shot point to the detection point are obtained according to the travel time table. The vertical depth corresponding to each common reflection point is calculated using the pre-stack depth migration velocity model, and the position of the common reflection point in the time domain is subjected to dynamic correction to correct the position in the depth domain.

[0018] Furthermore, step S5 is specifically as follows: obtaining the average layer velocity, absolute depth and sampling interval in each depth domain sampling interval according to the depth domain layer velocity model, calculating the time parameters, and obtaining the round-trip time parameters of the corresponding time domain, thereby completing the conversion from the depth domain to the time domain.

[0019] Furthermore, in step S6, a conventional method is used to calculate the residual static correction to obtain the residual static correction values ​​of the shot and check points.

[0020] Furthermore, step S7 specifically includes applying shot and check point residual statics to the pre-stack depth migration gather, comparing the common imaging point gathers before and after pre-stack depth migration and the migration profile events to see whether they are improved. If not, it is necessary to adjust the parameters and check the accuracy of the pre-stack depth migration velocity model.

[0021] Furthermore, in step S2, the matrix reduction denoising is specifically as follows: transforming the seismic trace from the XT domain to the FX domain, performing Kallio spectrum / singular spectrum analysis filtering in the FX domain, reducing the rank of the three-dimensional Hank matrix by singular value decomposition, and then taking the average of the obtained matrix along the anti-diagonal to obtain the denoised signal, and finally transforming the data to the XT domain by Fourier transform.

[0022] Furthermore, in step S3, a wavefront reconstruction method is used to perform ray path tracing.

[0023] Beneficial effects of this application:

[0024] (1) This application solves the problem of imaging errors caused by the mismatch between the time domain dynamic correction method and the actual pre-stack depth migration when using time domain stacking velocity for dynamic correction and then calculating the residual static correction in existing undulating terrain. This application uses depth domain velocity to perform dynamic correction based on ray travel time, so that the residual static correction finally calculated matches the model of the final pre-stack depth migration, and can greatly improve the imaging quality. Compared with the existing technology, it is more accurate and more direct.

[0025] (2) This application can be directly applied iteratively on existing technologies, which can further improve the accuracy of depth migration imaging, especially the focusing of the phase axis.

[0026] (3) This application solves the problem of calculating shot and checkpoint statics based on the actual imaging position of underground structures in complex underground structures, such as high-steep structures or gypsum-developed structures, thereby avoiding the inaccuracies calculated by previous technologies. Conventional surface consistency residual static correction technologies are mostly performed on time-domain CDP gathers. In the absence of offset homing, CDP reflects the diffraction information of underground strata, which is not the actual position in complex structures. Therefore, the calculated residual statics deviate from the actual position. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The foregoing and following detailed description of the present application will become more apparent when read in conjunction with the following drawings, in which:

[0028] Figure 1 This is a flow chart of the application method;

[0029] Figure 2 This is a schematic diagram of the dynamic correction based on the depth domain velocity model of this application;

[0030] Figure 3 A comparison chart showing the effect of depth-domain model-based residual static correction on prestack depth migration common imaging point gathers applied in this application.

[0031] Figure 4 This is the effect of residual static correction based on the depth domain model applied in this application on the prestack depth migration section. DETAILED DESCRIPTION

[0032] The following is a further explanation of the technical solution for achieving the purpose of the invention of this application through several specific embodiments. It should be noted that the technical solution claimed for protection in this application includes but is not limited to the following embodiments.

[0033] Example 1

[0034] This embodiment discloses a residual static correction method based on prestack depth migration imaging. Figure 1 As shown, the method specifically includes the following steps:

[0035] Step 1: First, obtain the surface elevation information, common center point gathers and pre-stack depth migration velocity model in the exploration area;

[0036] Step 2: Optimize the acquired common center point gathers to improve the signal-to-noise ratio of the common center point gathers;

[0037] Step 3: Based on the obtained pre-stack depth migration velocity model and surface elevation information, a travel time table is established using the ray tracing method;

[0038] Step 4: Perform depth domain dynamic correction on the optimized common center point gathers according to the travel time table obtained from the ray path;

[0039] Step 5: Convert the CMP gathers after NMO correction to the time domain using the acquired depth-domain layer velocity model.

[0040] Step 6: Use the traditional and existing residual static correction method to calculate the residual static correction value of the shot and check point;

[0041] Step 7: Apply the residual static correction obtained in step 6 to the common center point gather data to perform pre-stack depth migration processing.

[0042] This application addresses the imaging error problem caused by the mismatch between the time-domain NMO method and the actual pre-stack depth migration when using time-domain stacking velocities for dynamic correction and then calculating the residual statics in existing undulating terrain. This application uses depth-domain velocities for ray traveltime-based dynamic correction, ensuring that the resulting residual statics match the final pre-stack depth migration model. This significantly improves imaging quality and is more accurate and direct than existing technologies.

[0043] Example 2

[0044] This embodiment discloses a residual static correction method based on prestack depth migration imaging. Figure 1 As shown, the method specifically includes the following steps:

[0045] Step 1: Obtain surface elevation information, common center point gathers, and pre-stack depth migration velocity models within the exploration area;

[0046] Step 2: Optimize the acquired common center point gathers and improve the signal-to-noise ratio of the common center point gathers through four-dimensional denoising.

[0047] First, the pre-stack seismic data volume is regarded as a four-dimensional data volume, where the first dimension is the main survey line number, the second dimension is the connecting survey line number, the third dimension is the offset distance within the common center point gather, and the fourth dimension is the recording time. The matrix descending denoising method is used to attenuate random noise, and the seismic trace is transformed from the XT domain to the FX domain. The left spectrum / singular spectrum analysis filtering is performed in the FX domain. The rank of the three-dimensional Hank matrix is ​​reduced by singular value decomposition. The resulting matrix is ​​then averaged along the anti-diagonal to obtain the denoised signal. Finally, the data is transformed to the XT domain by Fourier transform. Finally, the common center point gather is frequency scanned, the best signal-to-noise ratio frequency band is selected, and bandpass filtering is performed to finally obtain the optimized common center point gather. During the optimization process, angle cutting is performed for large incident angles or far offsets, and data of 35° and below is retained;

[0048] Step 3: When the elevation of the seismic data shot and detection points changes, the travel time table from the shot point to the detection point at different locations in the entire work area is obtained according to the depth domain layer velocity model using the ray tracing method;

[0049] The depth domain layer velocity model can be an isotropic model or an anisotropic model; the ISO isotropic model only includes the velocity model, and the anisotropy can be VTI anisotropy or STI anisotropy. Therefore, the input velocity model is Vp, or Vp, Delta, Epsilon, Theta, and Phi. Among them, ISO is isotropy, VTI is transverse anisotropy with a vertical symmetry axis; Vp is the longitudinal wave velocity, Delta and Epsilon are anisotropy parameters; Theta is the angle in the vertical plane of the formation, and Phi is the angle in the horizontal plane of the formation. By discretizing the model into uniform square units, the travel time and ray path are related to the points on the unit boundary.

[0050] There are many methods for establishing traveltime tables using ray tracing, including the shortest path method, finite difference method, and wavefront reconstruction. This embodiment primarily uses the wavefront reconstruction method for ray path tracing. This method uses time as an independent variable and can simultaneously calculate ray paths and traveltimes. For real-world data, given the surface elevation and depth-domain layer velocity model, the wavefront reconstruction method can be used to determine the propagation path of seismic waves from the shot point to the detector point, generating a ray traveltime file.

[0051] Step 4: Perform depth domain dynamic correction on the optimized common center point gathers according to the travel time table obtained from the ray path;

[0052] First, the travel time tables of the source (i) and receiver (j) are calculated based on the depth layer velocity model. For each depth sample point z k , calculate the time t from the travel time table k The total travel time, at the same time, the time domain gathers at t k The amplitude is mapped to the corresponding depth sample z k ,like Figure 2 The travel time table can provide the time and propagation path of seismic wave rays from the shot point to the receiver point. Therefore, once the layer velocity model is known, the vertical depth corresponding to each common reflection point can be calculated. In other words, the common reflection point position in the time domain can be corrected by dynamic correction to the correct position in the depth domain.

[0053] Step 5: Convert the CMP gathers after NMO correction to the time domain using the depth domain layer velocity model.

[0054] Converting the depth-domain to the time-domain after DNO correction is the process of performing time-depth conversion when the depth-domain interval velocity and depth are known. Assuming that the stratum is composed of many thin layers, the thickness of the thin layer is the sampling interval in the depth domain. Each thin layer is considered a homogeneous medium, and the average of the true velocities is taken as the interval velocity for each thin layer. This assumption is the basis for using the depth-domain interval velocity model for time-depth conversion. The interval velocity formula is as follows:

[0055]

[0056] Where Vi is the average interval velocity within each depth domain sampling interval, ∆t is the time it takes for the seismic wave to pass through each sampling interval, and ∆H is each sampling interval. The known depth domain interval velocity model provides information about Vi, absolute depth H, and sampling interval ∆H, from which the time parameters can be calculated and the two-way time parameters of the corresponding time domain can be obtained, completing the conversion from depth domain to time domain.

[0057] Step 6: Use the traditional residual static correction method to calculate the residual static correction value of the shot and check point;

[0058] The traditional residual static correction method is an existing technology. The process is as follows: first, the data is extracted into CDP gathers, cross-correlation is performed within the CDP gathers to obtain the time difference between the traces, and finally, this time difference is uniformly decomposed into shot points and receiver points. At the same time, this is an iterative process that can be repeated multiple times to finally obtain the optimal residual static correction value.

[0059] Step 7: Apply the obtained residual static correction to the common center point gather data to perform pre-stack depth migration;

[0060] Apply the shot and checkpoint residual statics to the pre-stack depth migration gathers. Compare the common imaging point gathers and migration profile events before and after pre-stack depth migration to see if there is improvement. If not, adjust parameters such as the calculation window and maximum statics time shift, and check the accuracy of the depth domain layer velocity.

[0061] Refer to the instruction manual Figure 4 As shown in the figure, the effect of applying residual static correction based on the depth domain model on the pre-stack depth migration section. The left figure is the pre-stack depth migration section before application, the section imaging effect is poor and the phase axis is not focused. The right figure is the pre-stack depth migration section after application, the section imaging effect is greatly improved, and the horizon continuity becomes better.

[0062] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be understood as limiting the scope of protection of this application.

[0063] It should also be noted that, in the description of this application, unless otherwise expressly specified or limited, the terms "disposed," "installed," and "connected" should be understood broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal connections between two components. Those skilled in the art will understand the specific meanings of the above terms in this application based on the specific circumstances.

[0064] The above description is merely a preferred embodiment of the present application and does not constitute any form of limitation to the present application. Any simple modification or equivalent change made to the above embodiment based on the technical essence of the present application shall fall within the scope of protection of the present application.

Claims

1. A residual static correction method based on prestack depth migration imaging, characterized in that: The method specifically comprises the following steps: S1. Obtain surface elevation information, common center point gathers, and pre-stack depth migration velocity models within the exploration area; S2. Optimize the common center point gathers; S3. Establishing a travel time table using the ray tracing method based on the pre-stack depth migration velocity model and surface elevation information; S4. Performing depth domain dynamic correction on the optimized common center point gathers according to the travel time table obtained from the ray path; S5. Convert the CMP gathers after NMO correction to the time domain using the prestack depth migration velocity model. S6. Use the residual static correction method to calculate the residual static correction amount of the gun and check point; S7. Apply the obtained residual static correction value to the common center point gather data to perform pre-stack depth migration processing.

2. The residual static correction method based on prestack depth migration imaging according to claim 1, characterized in that: The step S2 specifically comprises: obtaining an optimized common midpoint gather through four-dimensional denoising, treating the pre-stack seismic data volume as a four-dimensional data volume, wherein one dimension is the main survey line number, two dimensions are the connecting survey line numbers, three dimensions are the offset distance within the common midpoint gather, and four dimensions are the recording time, using a matrix descending denoising method to attenuate random noise, removing data with large incident angles or far offsets, retaining data at 35° and below, performing frequency scanning on the common midpoint gather, selecting the frequency band with the best signal-to-noise ratio, and performing bandpass filtering; Matrix reduction denoising is specifically performed as follows: transforming the seismic trace from the XT domain to the FX domain, performing Kallio spectrum / singular spectrum analysis filtering in the FX domain, reducing the rank of the three-dimensional Hank matrix through singular value decomposition, and then taking the average of the resulting matrix along the anti-diagonal to obtain the denoised signal. Finally, the data is transformed to the XT domain through Fourier transform.

3. The residual static correction method based on prestack depth migration imaging according to claim 1, characterized in that: The step S3 specifically comprises: when the elevations of the seismic data shots and receivers change, the travel time table from the shot points to the receivers at different positions in the entire work area is obtained using the ray tracing method according to the pre-stack depth migration velocity model.

4. The residual static correction method based on prestack depth migration imaging according to claim 1, characterized in that: The step S4 is specifically as follows: the travel time table of the source (i) and the receiver (j) is calculated according to the depth domain layer velocity model. For each depth sample point z k , calculate the time t from the travel time table k The total travel time, at the same time, the time domain gathers at t k The amplitude is mapped to the corresponding depth sample z k .

5. The residual static correction method based on prestack depth migration imaging according to claim 4, characterized in that: The time and propagation path of seismic wave rays from the shot point to the detector point are obtained according to the travel time table. The vertical depth corresponding to each common reflection point is calculated using the pre-stack depth migration velocity model. The position of the common reflection point in the time domain is corrected to the correct position in the depth domain by dynamic correction.

6. The residual static correction method based on prestack depth migration imaging according to claim 1, characterized in that: The step S5 specifically comprises: obtaining the average interval velocity, absolute depth, and sampling interval within each depth domain sampling interval according to the depth domain interval velocity model, calculating the time parameters, and obtaining the round-trip time parameters of the corresponding time domain, thereby completing the conversion from the depth domain to the time domain.

7. The residual static correction method based on prestack depth migration imaging according to claim 1, characterized in that: In step S6, the residual static correction is calculated using a traditional method to obtain the residual static correction values ​​of the shot and check points.

8. The residual static correction method based on prestack depth migration imaging according to claim 1, characterized in that: The step S7 specifically includes applying shot and check point residual statics to the pre-stack depth migration gathers, comparing the common imaging point gathers before and after the pre-stack depth migration and the migration profile events to see whether they are improved. If not, parameters need to be adjusted, and the accuracy of the pre-stack depth migration velocity model is checked.

9. The residual static correction method based on prestack depth migration imaging according to claim 1 or 3, characterized in that: In step S3, the wavefront reconstruction method is used to perform ray path tracing.

10. The residual static correction method based on prestack depth migration imaging according to claim 1 or 3, characterized in that: The travel time table established according to the ray tracing method includes the shortest path method, the finite difference method and the wavefront reconstruction method.

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