De-migration method and system based on TTI medium qP wave equation

Abstract

The invention provides a demigration method and system based on a TTI medium qP wave equation, and belongs to the technical field of seismic wave imaging. According to the method, a background wave field is obtained by using seismic wavelets through a finite difference algorithm, the background wave field is used as a seismic source to obtain a scattering point wave field, and finally, according to observation system information, demigration data of a TTI medium is obtained. Through the finite difference algorithm, fast mapping from the seismic section to the demigration data is achieved, the problem that an existing forward modeling algorithm cannot be applied to least square migration and FWI is solved, meanwhile, the problem that the precision of an isotropic demigration algorithm is insufficient is solved, simulation precision is improved, and the method has a good application prospect for subsequent TTI medium migration and inversion. And technical preparation is provided.

Description

Technical Field

[0001] The present invention belongs to the field of seismic wave imaging, and particularly relates to an inverse migration method and system based on the qP-wave equation in TTI media. Background Art

[0002] The inverse migration technology is a technology for numerical simulation of seismic data starting from the migration result, and is also an indispensable part of technologies such as least-squares migration and full-waveform inversion. Its accuracy will directly affect the accuracy of subsequent results.

[0003] Currently, anisotropic characteristics widely exist in actual seismic exploration targets. If this point is ignored during the processing of actual data and an isotropic method is directly used for calculation, the calculation accuracy of the seismic wave field will inevitably be reduced.

[0004] Therefore, in order to obtain a high-precision imaging profile or inversion result subsequently, a wave equation inverse migration method applicable to anisotropic media is required. Summary of the Invention

[0005] The purpose of the present invention is to solve the problems existing in the above-mentioned prior art, and provide an inverse migration method and system based on the qP-wave equation in TTI media, realizing a rapid mapping from a seismic profile to inverse migration data and improving the simulation accuracy.

[0006] The present invention is realized through the following technical solutions:

[0007] In the first aspect of the present invention, an inverse migration method based on the qP-wave equation in TTI media is provided. The method obtains a background wave field by using a finite difference algorithm with a seismic wavelet, takes the background wave field as a seismic source to obtain a scattered point wave field, and finally obtains inverse migration data of the TTI medium according to the information of the observation system.

[0008] A further improvement of the present invention lies in:

[0009] The method includes:

[0010] (1) Input an anisotropic parameter field model, a seismic profile or a reflection coefficient model, as well as observation system information and a seismic wavelet;

[0011] (2) Calculate the background wave field by using a finite difference algorithm;

[0012] (3) Take the background wave field as a seismic source and calculate the scattered wave field by using a finite difference algorithm;

[0013] (4) Obtain inverse migration data of a single shot by using the scattered wave field;

[0014] (5) Obtain inverse migration data of the entire observation system.

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

[0016] In step (1), the anisotropic parameter field model includes five models, namely the qP-wave background velocity field model, the Thomsen parameter field model, the anisotropic medium dip angle field model, and the azimuth angle model.

[0017] In step (2), the background wave field is calculated using the following formula:

[0018]

[0019]

[0020] where v p 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, δ and ε are the Thomsen parameter field models, θ is the anisotropic medium dip angle field model, f(x s , t) represents the source wavelet, x s represents the source position, x and z respectively represent the x-axis and z-axis directions of the spatial position, and t represents time.

[0021] A further improvement of the present invention lies in that:

[0022] In step (3), the scattered wave field is calculated using the following formula:

[0023]

[0024]

[0025] where v p 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 the Thomsen parameter field models, θ is the anisotropic medium dip angle field model, p 0 (x, t) is the qP-wave background wave field, m(x) represents the reflection coefficient model or the migration profile, x s represents the source position, x and z respectively represent the x-axis and z-axis directions of the spatial position, and t represents time.

[0026] A further improvement of the present invention lies in that:

[0027] The operations in step (4) include:

[0028] Record the values of the scattered wave field at each moment at the receiving point. The values of the scattered wave field at all moments at the receiving point constitute the reverse migration data of a single shot.

[0029] A further improvement of the present invention lies in:

[0030] The operation in step (5) includes:

[0031] Repeat steps (1) to (4) for each shot point in sequence to obtain the reverse migration data of all single shots. The reverse migration data of all single shots constitutes the reverse migration data of the entire observation system, that is, the reverse migration data of the TTI medium.

[0032] The second aspect of the present invention provides a reverse migration system based on the qP-wave equation of the TTI medium. The system includes:

[0033] An input unit for inputting the anisotropic parameter field model, seismic profile or reflection coefficient model, as well as the observation system information and seismic wavelet;

[0034] A background wave field calculation unit connected to the input unit for calculating the background wave field through the finite difference algorithm:

[0035] A scattered wave field calculation unit connected to the input unit and the background wave field calculation unit respectively for using the background wave field as the source and calculating the scattered wave field through the finite difference algorithm:

[0036] A single-shot data acquisition unit connected to the scattered wave field calculation unit for obtaining the reverse migration data of a single shot by using the scattered wave field;

[0037] A multi-shot data acquisition unit connected to the single-shot data acquisition unit for obtaining the reverse migration data of the entire observation system.

[0038] The third aspect of the present invention provides a computer-readable storage medium. The computer-readable storage medium stores at least one computer-executable program. When the at least one program is executed by the computer, the computer executes the steps in the above-mentioned reverse migration method based on the qP-wave equation of the TTI medium.

[0039] The fourth aspect of the present invention provides a computer device including a memory and a processor. The memory stores a computer program. When the computer program is executed by the processor, the processor executes the steps of the reverse migration method based on the qP-wave equation of the TTI medium as described above.

[0040] Compared with the prior art, the beneficial effects of the present invention are as follows: By means of a finite-difference algorithm, the present invention realizes a rapid mapping from a seismic profile to reverse migration data, solves the problem that the current forward modeling algorithm cannot be applied to least-squares migration and FWI, and at the same time solves the problem of insufficient accuracy of the isotropic reverse migration algorithm, improves the simulation accuracy, and provides technical preparation for subsequent migration and inversion problems of TTI media. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 is the background velocity field model of the flat layer model in the embodiment;

[0042] Figure 2 is the Thomsen parameter ε field model of the flat layer model in the embodiment;

[0043] Figure 3 is the Thomsen parameter δ field model of the flat layer model in the embodiment;

[0044] Figure 4 is the anisotropic dip angle θ field model of the flat layer model in the embodiment;

[0045] Figure 5 is the reflection coefficient field of the flat layer model in the embodiment;

[0046] Figure 6 is the wave field snapshot of TTI reverse migration;

[0047] Figure 7 is the wave field snapshot of TTI forward modeling;

[0048] Figure 8 is the comparison diagram of the cross-line amplitudes of the wave field snapshots of TTI reverse migration and TTI forward modeling;

[0049] Figure 9 is the single-shot simulation data of TTI reverse migration;

[0050] Figure 10 is the multi-shot simulation data of TTI reverse migration;

[0051] Figure 11 is the block diagram of the steps of the method of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0052] The present invention will be further described in detail below with reference to the accompanying drawings:

[0053] At present, the methods for simulating seismic data include forward modeling technology and reverse migration technology. However, the forward modeling technology will generate direct waves, seriously affecting subsequent use. Moreover, the method of simulating seismic data through reverse migration technology requires reverse migration technology as a support for both least-squares migration, full waveform inversion, and the calculation of diffusion functions.

[0054] The present invention proposes an anti-migration method based on the TTI medium qP-wave equation. Starting from the qP-wave wave equation and using the finite-difference algorithm, it realizes the mapping from the seismic profile to the simulated seismic data. Compared with the anti-migration method for isotropic media, the TTI medium anti-migration method can improve the simulation accuracy and provide an effective tool for subsequent seismic imaging and inversion.

[0055] The method of the present invention uses the seismic wavelet to obtain the background wave field through the finite-difference algorithm, takes the background wave field as the source to obtain the scattered wave field, and finally obtains the scattered wave field at the receiving point at each moment (the position information of the receiving point is read from the input observation system information) according to the observation system information. The scattered wave field at the receiving point position at each moment is the final anti-migration data of the TTI medium.

[0056] Specifically, as Figure 11 shown, the method of the present invention includes the following steps:

[0057] (1) Input the anisotropic parameter field model, seismic profile or reflection coefficient model, as well as the observation system information and seismic wavelet;

[0058] (2) Calculate the background wave field through the finite-difference algorithm:

[0059] (3) While calculating the background wave field, take the background wave field as the source and calculate the scattered wave field through the finite-difference algorithm:

[0060] (4) Use the scattered wave field to obtain the anti-migration data of a single shot;

[0061] (5) Obtain the anti-migration data of the entire observation system.

[0062] An embodiment of the method of the present invention is as follows:

[0063] Embodiment 1:

[0064] In step (1), the anisotropic parameter field model includes 5 models, namely the qP-wave background velocity field model, the Thomsen parameter field model (δ and ε), the anisotropic medium dip angle field model and the azimuth angle model.

[0065] Embodiment 2:

[0066] In step (2), the background wave field is calculated using the following formula:

[0067]

[0068]

[0069] Formula (1) is a system of equations composed of two equations.

[0070] Among them, vp 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 (obtained through formula (1) p 0 (x, t) and q 0 (x, t), p 0 (x, t) is the final required result, q 0 (x, t) is the intermediate result of the auxiliary calculation). δ and ε are the Thomsen parameter field models, where δ represents the longitudinal wave coefficient of variation, indicating the speed of change of the longitudinal wave anisotropy in the vertical direction, ε represents the longitudinal wave anisotropy, which is a parameter measuring the strength of the quasi-longitudinal wave anisotropy, θ is the anisotropic medium dip angle field model, f(x s , t) represents the source wavelet, x s represents the specific source position (the input acquisition system information includes the shot point position (i.e., the source position) of each shot and the corresponding geophone position), x and z respectively represent the x-axis and z-axis directions of the spatial position, and t represents time.

[0071] Example 3:

[0072] In step (3), the scattered wave field is calculated using the following formula:

[0073]

[0074]

[0075] Formula (2) is a system of equations composed of two equations.

[0076] Among them, v p 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 (obtained through formula (2) p s (x, t) and q s (x, t), p s (x, t) is the final required result, q s (x, t) is the intermediate result of the auxiliary calculation). δ and ε are the Thomsen parameter field models, where δ represents the longitudinal wave coefficient of variation, indicating the speed of change of the longitudinal wave anisotropy in the vertical direction, ε is the longitudinal wave anisotropy, which is a parameter measuring the strength of the quasi-longitudinal wave anisotropy, θ is the anisotropic medium dip angle field model, p 0(x, t) is the qP-wave background wavefield, and m(x) represents the reflection coefficient model or the migration profile (generally speaking, the result obtained using the reflection coefficient model has higher accuracy, but an accurate reflection coefficient model can only be obtained during model testing. The result obtained from the migration profile has lower accuracy, but the migration result is easily obtained. Select one model according to the actual situation), x s represents the specific source location (the input acquisition system information includes the shot point location (i.e., the source location) of each shot and the corresponding geophone location), x and z respectively represent the spatial position in the x-axis and z-axis directions, and t represents time.

[0077] Example 4:

[0078] The operation in step (4) includes:

[0079] Record the values of the scattered wavefield at each moment at the receiving point (the scattered wavefield obtained in step (3) is the value of the entire space, and here only record the values of the scattered wavefield at each moment at each receiving point). The values of the scattered wavefield at all moments at the receiving point constitute the reverse migration data of a single shot.

[0080] Example 5:

[0081] The operation in step (5) includes:

[0082] Repeat steps (1) to (4) for each shot point in sequence to obtain the reverse migration data of all single shots. The reverse migration data of all single shots constitutes the reverse migration data of the entire acquisition system, providing support for subsequent migration or inversion.

[0083] Example 6:

[0084] Next, taking a flat layer model as an example, the present invention will be further described in conjunction with the accompanying drawings and specific embodiments.

[0085] (1) Read the background velocity field v of the flat layer model p and the Thomsen parameters ε and δ, as well as the anisotropic medium dip angle field θ and the reflection coefficient model m, as Figures 1 to 5 shown;

[0086] (2) Input the wavelet f and perform finite difference calculation according to formula (1) to obtain the background wavefield;

[0087] (3) Use the background wavefield as the source and perform finite difference calculation according to formula (2) to obtain the scattered wavefield;

[0088] (4) At the receiving point position, record the scattered wavefield data at each moment to obtain the reverse migration data of each single shot, as Figure 9 shown;

[0089] (5) Change the shot point position, repeat steps (1) to (4), obtain the reverse migration data of the next single shot, and finally obtain the reverse migration data of the entire acquisition system, that is, the reverse migration data of the final TTI medium.

[0090] Figure 6 and Figure 7 are the results obtained from the reverse migration of the TTI medium and the forward modeling of the TTI medium respectively. Figure 8 is for Figure 6 and Figure 7 The results are sampled along the red line for amplitude comparison. It can be seen that the wavefield snapshots of the TTI reverse migration and the TTI forward modeling can be perfectly matched, indicating the correctness of the TTI reverse migration technology in the present invention. Figure 9 is the single-shot simulation data of the TTI reverse migration. Figure 10 is the multi-shot simulation data of the TTI reverse migration.

[0091] The reverse migration technology realizes the mapping from the seismic profile or reflection coefficient to the seismic simulation data through multiple finite difference algorithms, and is an important part of technologies such as least squares migration, full-waveform inversion, and point spread function calculation. The present invention proposes a reverse migration method based on the qP-wave equation in the TTI medium. Starting from the qP-wave wave equation, the reverse migration calculation formula in the TTI medium is derived, realizing the accurate simulation of seismic data, providing a high-precision wavefield simulation tool for subsequent inversion, imaging and other technologies, and contributing to the practical application process of the latter.

[0092] In the description of the present invention, it should be noted that unless otherwise clearly specified and limited, the terms "connected" and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0093] In the description of the present invention, unless otherwise specified, the orientation or positional relationship indicated by the terms "upper", "lower", "left", "right", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0094] 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. An inverse migration method based on the TTI medium qP-wave equation, characterized in that: The method obtains the background wave field by using the seismic wavelet through the finite difference algorithm, takes the background wave field as the source to obtain the scattered wave field, and finally obtains the inverse migration data of the TTI medium according to the observation system information.

2. The inverse migration method based on the TTI medium qP-wave equation according to claim 1, characterized in that: The method includes: (1) Input the anisotropic parameter field model, seismic profile or reflection coefficient model, as well as the observation system information and seismic wavelet; (2) Calculate the background wave field through the finite difference algorithm; (3) Take the background wave field as the source and calculate the scattered wave field through the finite difference algorithm; (4) Obtain the inverse migration data of a single shot by using the scattered wave field; (5) Obtain the inverse migration data of the entire observation system.

3. The inverse migration method based on the TTI medium qP-wave equation according to claim 2, characterized in that: In step (1), the anisotropic parameter field model includes 5 models, namely the qP-wave background velocity field model, the Thomsen parameter field model, the anisotropic medium dip angle field model and the azimuth angle model.

4. The inverse migration method based on the TTI medium qP-wave equation according to claim 2, characterized in that: In step (2), the background wave field is calculated by using the following formula: where v p 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, δ and ε are the Thomsen parameter field models, θ is the anisotropic medium dip angle field model, f(x s , t) represents the source wavelet, x s represents the source position, x and z represent the spatial position in the x-axis and z-axis directions respectively, and t represents time.

5. The inverse migration method based on the TTI medium qP-wave equation according to claim 2, characterized in that: In step (3), the scattered wave field is calculated by using the following formula: where, v p 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 the Thomsen parameter field models, θ is the anisotropic medium dip angle field model, p 0 (x, t) is the qP-wave background wave field, m(x) represents the reflection coefficient model or the migration profile, x s represents the source location, x and z respectively represent the spatial position in the x-axis and z-axis directions, and t represents time.

6. The inverse migration method based on the TTI medium qP-wave equation according to claim 2, characterized in that: The operation of step (4) includes: Recording the values of the scattered wave field at each moment at the receiving point, and the values of the scattered wave field at all moments at the receiving point constitute the inverse migration data of a single shot.

7. The inverse migration method based on the TTI medium qP-wave equation according to claim 2, characterized in that: The operation of step (5) includes: Repeating steps (1) to (4) for each shot point in turn to obtain the inverse migration data of all single shots, and the inverse migration data of all single shots constitute the inverse migration data of the entire observation system, that is, the final inverse migration data of the TTI medium.

8. An inverse migration system based on the TTI medium qP-wave equation, characterized in that, The system includes: An input unit for inputting the anisotropic parameter field model, seismic profile or reflection coefficient model, as well as the observation system information and seismic wavelet; A background wave field calculation unit connected to the input unit for calculating the background wave field through the finite difference algorithm: A scattered wave field calculation unit connected to the input unit and the background wave field calculation unit respectively for taking the background wave field as the source and calculating the scattered wave field through the finite difference algorithm: A single-shot data acquisition unit connected to the scattered wave field calculation unit for obtaining the inverse migration data of a single shot by using the scattered wave field; A multi-shot data acquisition unit connected to the single-shot data acquisition unit for obtaining the inverse migration data of the entire observation system.

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 reverse migration method based on the TTI medium qP-wave equation 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 reverse migration method based on the TTI medium qP-wave equation according to any one of claims 1-7.

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