Method and system for obtaining point spread function

Abstract

The invention provides a method and system for obtaining a point spread function, and belongs to the technical field of seismic wave imaging. The method comprises the following steps: firstly, carrying out finite difference calculation one by one to obtain a background wave field and a scattered wave field, recording the scattered wave field at each moment of a receiving point position as demigration data of a single shot, then obtaining a back propagation wave field by using the demigration data of the single shot, and finally, carrying out imaging by using the background wave field and the back propagation wave field to obtain a point spread function. According to the method, the problem that the precision of the point spread function based on the isotropic medium is not high is solved by adopting a demigration and migration mode, technical preparation is provided for subsequent anisotropic imaging domain least square reverse time migration, and further application of the technology in an actual work area is facilitated.

Description

Technical Field

[0001] The present invention belongs to the technical field of seismic wave imaging, and particularly relates to a method and system for obtaining a point spread function. Background Art

[0002] Anisotropy is widespread in seismic exploration. If the anisotropy effect is ignored in the actual seismic data imaging process, large errors will be introduced, reducing the imaging resolution. In recent years, with the development of computer technology, high-precision seismic imaging and parameter inversion techniques in anisotropic media have received increasing attention and have gradually been applied to actual production. Currently, isotropic imaging domain least squares reverse time migration has achieved certain results in practice. However, the anisotropic characteristics of the medium are still not considered. In some areas with developed anisotropy, problems such as inaccurate imaging position and poor imaging quality will occur, having a serious negative impact on subsequent production and development.

[0003] Therefore, it is extremely necessary to develop anisotropic imaging domain least squares reverse time migration technology. Anisotropic imaging domain least squares reverse time migration uses the anisotropic point spread function to approximate the Hessian matrix, and directly defuzzifies the conventional anisotropic migration result to obtain the least squares migration result of the anisotropic medium. Summary of the Invention

[0004] The purpose of the present invention is to solve the problems existing in the above-mentioned prior art, and provide a method for obtaining a point spread function. By performing reverse migration calculation of a TTI medium on a scattering point model, and then performing migration of the TTI medium on the output reverse migration result, the finally obtained migration profile is used as the point spread function of the TTI medium, providing support for the subsequent least squares migration technology of the TTI medium.

[0005] The present invention is realized through the following technical solutions:

[0006] In the first aspect of the present invention, a method for obtaining a point spread function is provided. The method first performs finite difference calculation shot by shot to obtain a background wave field and a scattered wave field, records the scattered wave field at each moment at the receiver position as the reverse migration data of a single shot, then obtains a reverse propagation wave field using the reverse migration data of the single shot, and finally performs imaging using the background wave field and the reverse propagation wave field to obtain the point spread function.

[0007] A further improvement of the present invention lies in:

[0008] The method includes:

[0009] (1) Input data;

[0010] (2) Decompose shot by shot to obtain the shot point position, receiver position, velocity field, scatterer region, and source wavelet for each shot;

[0011] (3) Solve the background wave field and the scattered wave field, and record the scattered wave field at each moment of the receiver position as the reverse migration data;

[0012] (4) Obtain the reverse propagated wave field using the reverse migration data;

[0013] (5) Use the reverse propagated wave field and the background wave field for imaging to obtain the point spread function of a single shot;

[0014] (6) Obtain the final point spread function using the point spread functions of all single shots.

[0015] A further improvement of the present invention lies in:

[0016] The input data in step (1) includes: acquisition system information, velocity field, anisotropic parameter field, and scatterer model.

[0017] A further improvement of the present invention lies in:

[0018] The operations in step (3) include:

[0019] Solve the background wave field using the following formula:

[0020]

[0021]

[0022] Solve the scattered wave field using the following formula:

[0023]

[0024]

[0025] d demig (x r ,t) = p s (x r ,t)

[0026] where v 0 is the qP-wave background velocity field model, p 0 (x,t) is the qP-wave background wave field, q 0 (x,t) is the auxiliary wave field of the background wave field, p s (x,t) is the qP-wave scattered wave field, q s (x,t) is the auxiliary wave field of the scattered wave field, δ and ε are the Thomsen parameter fields, θ is the anisotropic medium dip angle field, f(x s ,t) is the source wavelet, x sIndicates the specific seismic source location, x represents the spatial location, t represents the time, and m 0 (x) represents the scatterer model, and d demig (x r ,t) represents the reverse migration data, and x r represents the receiver location.

[0027] A further improvement of the present invention lies in:

[0028] The operation in step (4) includes:

[0029] Solving for the reverse propagated wavefield using the following formula:

[0030]

[0031]

[0032] where p r (x,t) is the reverse propagated wavefield, and q r (x,t) is the auxiliary wavefield of the reverse propagated wavefield.

[0033] A further improvement of the present invention lies in:

[0034] The operation in step (5) includes:

[0035] Obtaining the point spread function of a single shot using the following formula:

[0036]

[0037] where p r (x,t) is the reverse propagated wavefield, and p s (x,t) is the scattered wavefield, x represents the spatial location, t represents the time, tmax represents the maximum propagation time of the seismic wavefield, and I psf represents the point spread function of a single shot.

[0038] A further improvement of the present invention lies in:

[0039] The operation in step (6) includes:

[0040] Performing the operations in steps (3) to (5) on each single shot in sequence to obtain the point spread functions of all single shots, and then superimposing the point spread functions of all single shots to obtain the final point spread function.

[0041] The second aspect of the present invention provides a system for obtaining a point spread function, and the system includes:

[0042] An input data module for inputting data;

[0043] The decomposition module, connected to the input data module, is used for shot-by-shot decomposition to obtain the shot point position, receiving point position, velocity field, scattering point region, and source wavelet for each shot.

[0044] The reverse migration data acquisition module, connected to the decomposition module, is used for solving the background wave field and scattering wave field, and recording the scattering wave field at each moment of the receiving point position as the reverse migration data.

[0045] The reverse propagation wave field acquisition module, connected to the reverse migration data acquisition module, is used for obtaining the reverse propagation wave field by using the reverse migration data.

[0046] The imaging module, respectively connected to the reverse migration data acquisition module and the reverse propagation wave field acquisition module, is used for imaging by using the reverse propagation wave field and the background wave field to obtain the point spread function of a single shot.

[0047] The point spread function generation module, connected to the imaging module, is used for obtaining the final point spread function by using the point spread functions of all single shots.

[0048] In the third aspect of the present invention, there is provided a computer-readable storage medium storing at least one computer-executable program, and when the at least one program is executed by the computer, the computer is caused to execute the steps in the method for obtaining the point spread function as described above.

[0049] In the fourth aspect of the present invention, there is provided a computer device including a memory and a processor, where the memory stores a computer program, and when the computer program is executed by the processor, the processor is caused to execute the steps of the method for obtaining the point spread function as described above.

[0050] Compared with the prior art, the beneficial effects of the present invention are as follows: By adopting the method of reverse migration plus migration, the present invention improves the problem of low accuracy of the point spread function based on isotropic media, provides technical preparation for subsequent anisotropic imaging domain least-squares reverse time migration, and helps the further application of this technology in the actual work area. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 It is the velocity field model of the sag model in the embodiment;

[0052] Figure 2 It is the Thomsen parameter ε field model of the sag model in the embodiment;

[0053] Figure 3 It is the Thomsen parameter δ field model of the sag model in the embodiment;

[0054] Figure 4 It is the anisotropic dip angle θ field model of the sag model in the embodiment;

[0055] Figure 5 is the scattering point model;

[0056] Figure 6 is the input shot record;

[0057] Figure 7 is the point spread function of the generated TTI medium;

[0058] Figure 8 is the step block diagram of the method of the present invention. Detailed implementation manners

[0059] The present invention will be further described in detail below with reference to the accompanying drawings:

[0060] The imaging domain least squares migration of anisotropic media has great advantages in solving the problem of high-precision imaging of complex media. The key to this technology lies in how to obtain an accurate point spread function of anisotropic media. At present, the point spread functions are all based on isotropic media, which severely restricts the application of the imaging domain least squares migration technology in actual work areas.

[0061] Aiming at the problems existing in the above-mentioned imaging domain least squares migration technology of anisotropic media, the present invention selects the typical TTI medium in anisotropic media and develops a method for obtaining the point spread function, improving the calculation accuracy of the point spread function and providing guarantee for the subsequent calculation of the imaging domain least squares migration of anisotropy.

[0062] The method first performs finite difference calculations shot by shot to obtain the background wave field and the scattered wave field, and records the scattered wave field at each moment at the receiver position as the reverse migration data of a single shot (stored in memory, without the need for a re-writing and reading process, directly used as input data). Then, the reverse propagation wave field is obtained by using the reverse migration data of a single shot. Finally, the background wave field and the reverse propagation wave field are used for imaging to obtain the point spread function.

[0063] As Figure 8 shown, the method includes:

[0064] (1) Input data;

[0065] (2) Decompose shot by shot to obtain the shot point position, receiver position, velocity field, scattering point region, and source wavelet of each shot;

[0066] (3) Solve the background wave field and the scattered wave field, and record the scattered wave field at each moment at the receiver position as the reverse migration data;

[0067] (4) Obtain the reverse propagation wave field by using the reverse migration data;

[0068] (5) Image using the reverse propagated wavefield and the background wavefield to obtain the point spread function of a single shot.

[0069] (6) Obtain the final point spread function using the point spread functions of all single shots.

[0070] An embodiment of the method of the present invention is as follows:

[0071] Embodiment 1:

[0072] The input data in step (1) includes: acquisition system information, velocity field v 0 and anisotropic parameter field, as well as the corresponding scatterer model m 0 .

[0073] Among them, the anisotropic parameter field includes: Thomsen parameter fields δ and ε, anisotropic medium dip angle field θ. Among them, δ represents the longitudinal wave variation coefficient, indicating the speed of anisotropic change of the longitudinal wave in the vertical direction, and ε represents the longitudinal wave anisotropy, which is a parameter measuring the strength of quasi-longitudinal wave anisotropy.

[0074] Embodiment 2:

[0075] The operations in step (2) include: distributing the data of each shot to different nodes for calculation, and after the calculation is completed, combining the result data to obtain the final result. These are all prior arts and will not be elaborated here.

[0076] Embodiment 3:

[0077] The operations in step (3) include:

[0078] Solve for the background wavefield using the following formula:

[0079]

[0080]

[0081] Formula (1) is a system of equations composed of two formulas, and one calculation is performed at each moment.

[0082] Among them, v 0 is the qP-wave background velocity field model, p 0 (x,t) is the qP-wave background wavefield, q 0 (x,t) is the auxiliary wavefield of the background wavefield. δ and ε are Thomsen parameter fields, θ is the anisotropic medium dip angle field, f(x s ,t) is the source wavelet, x s represents the specific source position, x represents the spatial position, and t represents the time.

[0083] Solve for the scattered wavefield using the following formula:

[0084]

[0085]

[0086] d demig (x r ,t) = p s (x r ,t) (2)

[0087] where v 0 is the qP-wave background velocity field model, p s (x,t) is the qP-wave scattered wave field, q s (x,t) is the auxiliary wave field of the scattered wave field. δ and ε are Thomsen parameter fields, θ is the anisotropic medium dip angle field, p 0 (x,t) is the qP-wave background wave field. m 0 (x) represents the scatterer model, x s represents the specific source location, x represents the spatial location, and t represents the time. d demig (x r ,t) represents the de-migrated data, x r represents the receiver location. The source location and the receiver location are both included in the acquisition system information.

[0088] At each time step, the entire-space p s (x,t) is calculated from the first two equations in formula (2), and then the value at the receiver location at that time step is recorded by the last equation. After all time steps are recorded, the de-migrated data is obtained.

[0089] Example 4:

[0090] The operation in step (4) includes:

[0091] Solving for the back-propagated wave field using the following formula:

[0092]

[0093]

[0094] where v 0 is the qP-wave background velocity field model, p r (x,t) is the back-propagated wave field, q r (x,t) is the auxiliary wave field of the back-propagated wave field. δ and ε are Thomsen parameter fields, θ is the anisotropic medium dip angle field, d demig represents the de-migrated data, x s represents the specific source location, x represents the spatial location, and t represents the time.

[0095] Example 5:

[0096] The operation in step (5) includes:

[0097] Calculate the point spread function of a single shot using the following formula:

[0098]

[0099] where p r (x, t) is the backpropagated wavefield, p s (x, t) is the scattered wavefield, x represents the spatial position, t represents the time, tmax represents the maximum propagation time of the seismic wavefield, and I psf represents the point spread function of a single shot.

[0100] Example 6:

[0101] The operation in step (6) includes:

[0102] Perform the operations in steps (3) to (5) on each single shot in sequence to obtain the point spread functions of all single shots, and then directly superimpose the point spread functions of all single shots to obtain the final point spread function.

[0103] Example 7:

[0104] Taking the sag model as an example, the present invention will be further described in conjunction with the accompanying drawings and specific embodiments.

[0105] (1) Read the velocity model v as Figure 1 shown, the Thomsen parameter models ε, δ, and the anisotropic medium dip angle, respectively as Figure 2 , Figure 3 and Figure 4 shown, the scatterer model m, as Figure 5 shown, and the original shot record, as Figure 6 shown;

[0106] (2) Decompose shot by shot to obtain the shot point position, receiver position, corresponding velocity field, scatterer region, and source wavelet f for each shot;

[0107] (3) Perform the qP-wave wave equation calculation in TTI media to solve the background wavefield u 0 and the scattered wavefield u 1 , and record the scattered wavefield at each moment of the receiver position as the reverse migration data d demig ;

[0108] (4) Without outputting the reverse migration data, directly use it as the shot data during the migration process and input it. According to formula (3), solve the backpropagated wavefield;

[0109] (5) Image using the reverse propagation wavefield and the background wavefield, and obtain the point spread function of this shot.

[0110] (6) Regularize the point spread functions obtained from all shots to obtain the final point spread function of the TTI medium, as Figure 7 shown.

[0111] The finally obtained point spread function of the TTI medium can be combined with the conventional migration of the TTI medium to generate the least-squares migration result in the imaging domain of the TTI medium with high resolution, promoting the practical application of the technology.

[0112] The present invention adopts the calculation mode of TTI medium reverse migration plus TTI medium migration to obtain the point spread function of the TTI medium with high precision, creating conditions for the subsequent development of the least-squares migration technology in the imaging domain based on anisotropic media, and strongly promoting its practical application process.

[0113] The above technical solution is only one implementation manner of the present invention. For those skilled in the art, based on the disclosed principle of the present invention, it is very easy to make various types of improvements or deformations, not limited to the technical solution described in the above specific embodiments of the present invention. Therefore, the foregoing description is only preferred and does not have a restrictive meaning.

Claims

1. A method for obtaining a point spread function, characterized in that: The method first performs finite-difference calculations shot by shot to obtain the background wavefield and the scattered wavefield, records the scattered wavefield at each moment at the receiver positions as the reverse migration data for a single shot, then obtains the reverse-propagating wavefield using the reverse migration data for a single shot, and finally performs imaging using the background wavefield and the reverse-propagating wavefield to obtain the point spread function.

2. The method for obtaining a point spread function according to claim 1, characterized in that: The method includes: (1) Inputting data; (2) Decomposing shot by shot to obtain the shot point position, receiver position, velocity field, scattered point region, and source wavelet for each shot; (3) Solving for the background wavefield and the scattered wavefield, and recording the scattered wavefield at each moment at the receiver positions as the reverse migration data; (4) Obtaining the reverse-propagating wavefield using the reverse migration data; (5) Performing imaging using the reverse-propagating wavefield and the background wavefield to obtain the point spread function for a single shot; (6) Obtaining the final point spread function using the point spread functions for all single shots.

3. The method for obtaining a point spread function according to claim 2, characterized in that: The data input in step (1) includes: acquisition system information, velocity field, anisotropy parameter field, and scattered point model.

4. The method for obtaining a point spread function according to claim 3, characterized in that: The operations in step (3) include: Solving for the background wavefield using the following formula: Solving for the scattered wavefield using the following formula: d demig (x r ,t) = p s (x r ,t) Among them, v 0 is the qP-wave background velocity field model, p 0 (x, t) is the qP-wave background wave field, q 0 (x, t) is the auxiliary wave field of the background wave field, p s (x, t) is the qP-wave scattered wave field, q s (x, t) is the auxiliary wave field of the scattered wave field, δ and ε are the Thomsen parameter fields, θ is the anisotropic medium dip angle field, f(x s , t) is the source wavelet, x s represents the specific source position, x represents the spatial position, t represents the time, m 0 (x) represents the scatterer model, d demig (x r , t) represents the reverse migration data, x r represents the receiver position.

5. The method for obtaining a point spread function according to claim 4, characterized in that: The operations in step (4) include: Solving for the reverse-propagating wavefield using the following formula: where p r (x, t) is the reverse propagated wave field, and q r (x, t) is the auxiliary wave field of the reverse propagated wave field.

6. The method for obtaining a point spread function according to claim 5, characterized in that: The operations in step (5) include: Obtaining the point spread function for a single shot using the following formula: where p r (x, t) is the backpropagated wavefield, and p s (x, t) is the scattered wavefield, x represents the spatial position, t represents the time, tmax represents the maximum propagation time of the seismic wavefield, and I psf represents the point spread function of a single shot.

7. The method for obtaining a point spread function according to claim 1, characterized in that: The operations in step (6) include: Performing the operations in steps (3) to (5) on each single shot in sequence to obtain the point spread functions for all single shots, and then superimposing the point spread functions for all single shots to obtain the final point spread function.

8. A system for obtaining a point spread function, characterized in that, The system includes: An input data module for inputting data; A decomposition module connected to the input data module for decomposing shot by shot to obtain the shot point position, receiver position, velocity field, scattered point region, and source wavelet for each shot; A reverse migration data acquisition module connected to the decomposition module for solving for the background wavefield and the scattered wavefield, and recording the scattered wavefield at each moment at the receiver positions as the reverse migration data; A reverse-propagating wavefield acquisition module connected to the reverse migration data acquisition module for obtaining the reverse-propagating wavefield using the reverse migration data; An imaging module connected to the reverse migration data acquisition module and the reverse-propagating wavefield acquisition module respectively for performing imaging using the reverse-propagating wavefield and the background wavefield to obtain the point spread function for a single shot; A point spread function generation module connected to the imaging module for obtaining the final point spread function using the point spread functions for all single shots.

9. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores at least one computer-executable program, and when the at least one program is executed by the computer, the computer is caused to execute the steps in the method for obtaining a point spread function according to any one of claims 1-7.

10. A computer device, characterized in that it includes a memory and a processor, the memory stores a computer program, and when the computer program is executed by the processor, the processor is caused to execute the steps of the method for obtaining a point spread function according to any one of claims 1-7.

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