A two-way wave deep migration method for VTI medium

Abstract

The present application relates to the technical field of seismic exploration, in particular to a two-way wave depth migration method for VTI medium; a geophone wave field and a source wave field are formed respectively; single-shot seismic data and the source wave field are read respectively, and anisotropy parameters are obtained; Fourier transform is performed on the source wave field and the geophone wave field data to obtain frequency-space domain wave field data; parameters required for migration are calculated; anisotropy vertical wave number is calculated; wave field of the second depth grid is obtained; wave field propagation operators are obtained layer by layer according to bilateral boundary conditions; evanescent waves and pseudo S waves are eliminated at each depth position; migration imaging is performed; extension calculation is repeated until the maximum depth is calculated, and migration results are output; the two-way wave migration is extended from isotropic medium to anisotropic medium, the application range of the two-way wave depth migration is expanded, and the underground structure can be better imaged.

Description

Technical Field

[0001] This invention relates to the field of seismic exploration technology, and in particular to a two-way wave depth migration method for VTI media. Background Technology

[0002] With the continuous development of seismic exploration, exploration targets have gradually shifted to complex and steep structural zones, where the subsurface media generally exhibit anisotropy. Actual subsurface structures can be approximated as VTI media. Currently, wave equation depth migration methods for anisotropic media are all one-way wave equation depth migration methods. Two-way wave equation depth migration, however, offers better angular imaging capabilities and amplitude preservation characteristics compared to one-way wave equation depth migration. Current two-way wave depth migration methods are only applicable to isotropic media. For example, patent application CN105911587B discloses a two-way wave pre-stack depth migration method using a one-way wave operator to extrapolate the two-way wavefield depth. Specifically, it extrapolates the two-way wavefield depth of the receiver and shot fields, and then images the extended receiver and shot fields using cross-correlation imaging principles or reflection coefficient imaging principles.

[0003] Furthermore, the single-pass wave operator used in the above-mentioned isotropic two-way wave depth migration method is a traditional single-pass wave operator based on reference velocity approximation, which has a large error in wave field propagation and cannot better image underground structures.

[0004] Therefore, a two-way wave depth migration method for anisotropic media is proposed. This method extends traditional two-way wave depth migration from isotropic to anisotropic media, expanding its application range, and improves the computational accuracy of the propagation operator, enabling better imaging of subsurface structures. Summary of the Invention

[0005] The purpose of this invention is to provide a two-way wave depth migration method for VTI media, aiming to fill the gap in the existing two-way wave depth migration methods for anisotropic media; at the same time, it solves the technical problem that the single-way wave operator used in the traditional two-way wave method is based on the reference velocity approximation, which has a large propagation error in the recursion of the wave field depth direction and cannot better image the underground structure.

[0006] To achieve the above objectives, the present invention employs a two-way wave depth migration method for VTI media, comprising the following steps:

[0007] Acquire seismic data from the geophone and generate the geophone wavefield;

[0008] Seismic wavelet information is extracted from the seismic data from the geophone detector to form the source wavefield;

[0009] Seismic data and source wavefield from a single shot were read separately to obtain the anisotropy parameter V. P ε and δ;

[0010] Fourier transform is performed on the source wavefield and detector wavefield data to obtain frequency-space domain wavefield data;

[0011] The parameters required for the offset are calculated based on the anisotropy parameters;

[0012] Calculate the anisotropic vertical wavenumber k z ;

[0013] Determine the wave field of the second depth grid. Provide boundary conditions for two-way depth extrapolation;

[0014] Based on the double boundary condition, the wave field propagation operator is calculated layer by layer. Perform two-way depth extension in the frequency-space domain;

[0015] Eliminate evanescent waves and pseudo-S-waves at each depth location;

[0016] Perform offset imaging;

[0017] Repeat the extension calculation until the maximum depth is calculated, and output the offset result.

[0018] In the step of calculating the parameters required for the offset based on the anisotropy parameters:

[0019] Key parameters in ground earthquakes can all be expressed as normal time difference velocity V. nmo and horizontal velocity V h The formula is:

[0020]

[0021] In the step of calculating the parameters required for the offset based on the anisotropy parameters:

[0022] The number of parameters is reduced to a single parameter η, defined as the ellipticity, and the formula is:

[0023]

[0024] Among them, in calculating the anisotropic vertical wavenumber k z In the steps:

[0025] Anisotropic vertical wavenumber k z The calculation formula is:

[0026]

[0027] Rewrite the anisotropic dispersion relation:

[0028]

[0029] Among them, in obtaining the wave field of the second depth grid In the steps of providing boundary conditions for two-way depth extrapolation:

[0030] Tron The formula for obtaining this is:

[0031]

[0032] Where F' represents the inverse Fourier transform.

[0033] Among them, the wave field propagation operator is obtained layer by layer based on the double boundary condition. In the steps of performing two-way depth extension in the frequency-space domain:

[0034] The continuation formula is:

[0035]

[0036] In the step of performing offset imaging:

[0037] Migration imaging can be performed using the principles of cross-correlation imaging and reflectance coefficient imaging.

[0038] This invention discloses a two-way wave depth migration method for VTI media, which involves acquiring detector seismic data to form a detector wavefield; extracting seismic wavelet information from the detector seismic data to form a source wavefield; and reading the seismic data and source wavefield of a single shot to obtain the anisotropy parameter V. P ε and δ; Fourier transform the source wavefield and detector wavefield data to obtain frequency-space domain wavefield data; calculate the parameters required for migration based on anisotropic parameters; calculate the anisotropic vertical wavenumber k. z Determine the wave field of the second depth grid. Boundary conditions are provided for two-way depth extrapolation; based on the two boundary conditions, wavefield propagation operators are calculated layer by layer. Two-way depth extrapolation is performed in the frequency-spatial domain; evanescent waves and pseudo-S-waves are eliminated at each depth location; migration imaging is performed; the extrapolation calculation is repeated until the maximum depth is calculated, and the migration results are output; by extending two-way wave migration from isotropic media to anisotropic media, the application range of two-way wave depth migration is expanded, which can better image underground structures. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0040] Figure 1 This invention relates to the P-wave velocity model for non-uniform variable speed media.

[0041] Figure 2 This is a schematic diagram of the impulse response results of the present invention.

[0042] Figure 3 This is a schematic diagram of the parameters of the simple anisotropic model of the present invention.

[0043] Figure 4 This is a schematic diagram comparing the two-way wave depth migration results of the present invention.

[0044] Figure 5 This is a schematic diagram comparing the imaging amplitude of the present invention.

[0045] Figure 6 This is a flowchart of the steps of the two-way wave depth migration method for VTI media according to the present invention. Detailed Implementation

[0046] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application.

[0047] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The singular forms “a,” “the,” and “the” used in this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0048] It should be understood that although the terms first, second, third, etc., may be used in this application to describe various information, such information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, without departing from the scope of this application, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Depending on the context, the word "if" as used herein may be interpreted as "when," "when," or "in response to determination."

[0049] Please see Figures 1-6 ,in Figure 1 It is a P-wave velocity model for non-uniform variable-speed media. Figure 2 This is a schematic diagram of the impulse response results. Figure 3 This is a schematic diagram of the parameters of a simple anisotropic model. Figure 4 This is a schematic diagram comparing the results of two-way wave depth migration. Figure 5 This is a schematic diagram comparing imaging amplitudes. Figure 6 This is a flowchart of the steps for the two-way wave depth migration method for VTI media.

[0050] This invention provides a two-way wave depth migration method for VTI media, comprising the following steps:

[0051] S101: Acquire geophone seismic data and form geophone wavefield;

[0052] S102: Extract seismic wavelet information from the seismic data from the geophone detector to form the source wave field;

[0053] S103: Read the seismic data and source wavefield of a single shot respectively, and obtain the anisotropy parameter V. P ε and δ;

[0054] S104: Perform Fourier transform on the source wavefield and detector wavefield data to obtain frequency-space domain wavefield data.

[0055] In this embodiment, seismic data from the geophone is first acquired through seismic acquisition to form the geophone wavefield; then, seismic wavelet information is extracted from the geophone seismic data to form the source wavefield; and the anisotropy parameter V is obtained by reading the seismic data of a single shot and the source wavefield respectively. P ε and δ; then perform Fourier transform on the source wavefield and detector wavefield data to obtain frequency-space domain wavefield data.

[0056] S105: Calculate the parameters required for the offset based on the anisotropic parameters.

[0057] In this embodiment, the parameters required for migration are calculated based on anisotropic parameters. In anisotropic seismic exploration, the Thomson parameters can be equated to different measurable velocities. Key parameters estimated in surface seismic surveys can all be expressed as normal time-of-motion (NMO) velocities V. nmo and horizontal velocity V h The formula is:

[0058]

[0059] Although the Thomsen parameter is introduced to address weak anisotropy, it is convenient to use regardless of the magnitude of anisotropy. Considering only P-wave kinematics, the Thomsen parameter is not sensitive to S-waves along the symmetry axes x and y in VTI media. Therefore, the number of parameters is further reduced to a new parameter η, defined as the ellipticity, as follows:

[0060]

[0061] S106: Calculate the anisotropic vertical wavenumber k z ;

[0062] In this embodiment, the anisotropic vertical wavenumber k is calculated. z Anisotropic vertical wavenumber k z The calculation formula is:

[0063]

[0064] This invention uses a generalized two-way phase shift operator based on locally accurate velocity calculation to extrapolate the wavefield, ensuring the accuracy of the propagation operator. Simultaneously, for ease of calculation, a modified anisotropic dispersion relation is used:

[0065]

[0066] S107: Obtain the wavefield of the second depth grid Provide boundary conditions for two-way depth extrapolation.

[0067] In this embodiment, the wave field of the second depth grid is obtained. Tron The formula for obtaining this is:

[0068]

[0069] Where F' represents the inverse Fourier transform.

[0070] S108: Based on the double boundary condition, calculate the wave field propagation operator layer by layer. Perform two-way depth extension in the frequency-space domain;

[0071] In this embodiment, the wave field propagation operator is calculated layer by layer based on the double boundary condition. The continuation formula is:

[0072]

[0073] S109: Eliminate evanescent waves and pseudo-S-waves at each depth location;

[0074] In this embodiment, evanescent waves and pseudo-S-waves are eliminated at each depth location; if A or B is negative, evanescent waves will be generated, which can be addressed by setting k in the formula. z The value of 0 is removed; if A<0 and B<0, a pseudo-S wave is obtained, which can be eliminated by filtering out the negative values ​​of A and B in the dispersion relation.

[0075] S110: Perform offset imaging.

[0076] In this embodiment, offset imaging is performed; wherein the offset imaging is performed by means of cross-correlation imaging principle and reflectance coefficient imaging principle.

[0077] S111: Repeat the extension calculation until the maximum depth is calculated, and output the offset result.

[0078] In this embodiment, the extension calculations in steps S108 to S110 are repeated until the maximum depth is calculated, and the offset result is output.

[0079] In this application, as Figure 6 As shown, geophone seismic data is acquired to form the geophone wavefield; seismic wavelet information is extracted from the geophone seismic data to form the source wavefield; seismic data from a single shot and the source wavefield are read respectively to obtain the anisotropy parameter V. P ε and δ; Fourier transform the source wavefield and detector wavefield data to obtain frequency-space domain wavefield data; calculate the parameters required for migration based on anisotropic parameters; calculate the anisotropic vertical wavenumber k. z Determine the wave field of the second depth grid. Boundary conditions are provided for two-way depth extrapolation; based on the two boundary conditions, wavefield propagation operators are calculated layer by layer. Two-way depth extrapolation is performed in the frequency-spatial domain; evanescent waves and pseudo-S-waves are eliminated at each depth; migration imaging is performed; the extrapolation calculation is repeated until the maximum depth is reached, and the migration results are output; by extending two-way wave migration from isotropic media to anisotropic media, the application range of two-way wave depth migration is expanded, enabling better imaging of subsurface structures. Figures 1-5 As shown, Figure 1 This invention relates to the P-wave velocity model for non-uniform variable speed media. Figure 2 This is a schematic diagram of the impulse response results of the present invention; wherein, Figure 2 (a) ε = 0 and δ = 0; Figure 2 (b) ε = 0.5 and δ = 0 (pseudo-S waves not filtered out); Figure 2 (c) ε = 0.5 and δ = 0.5; Figure 2 (d) ε = 0.5 and δ = 0 (filtering out pseudo-S waves). Figure 3 This is a schematic diagram of the parameters of a simple anisotropic model of the present invention, wherein... Figure 3(a)V P , Figure 3 (b)ε、 Figure 3 (c)δ. Figure 4 This is a comparative schematic diagram of the two-way wave depth migration results of the present invention, wherein... Figure 4 (a) shows the two-way wave depth migration results for VTI medium. Figure 4 (b) shows the depth migration results for isotropic two-way waves. Figure 4 (c) shows the results of one-way wave depth migration imaging in VTI medium. It can be seen that anisotropic time was not considered, and the imaging results show obvious errors and noise. Figure 5 This is a schematic diagram comparing the imaging amplitude of the present invention. Specifically, Figure 5 for Figure 4 A comparison of the imaging amplitudes extracted at x = 1700m shows that the two-way wave VTI medium depth migration method proposed in this invention has better amplitude preservation compared to the traditional single-way wave VTI medium depth migration method.

[0080] Other embodiments of this application will readily occur to those skilled in the art upon consideration of the specification and practice of the disclosure herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein.

[0081] It should be understood that this application is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope.

Claims

1. A two-way wave depth migration method for VTI media, characterized in that, Includes the following steps: Acquire seismic data from the geophone and generate the geophone wavefield; Seismic wavelet information is extracted from the seismic data from the geophone detector to form the source wavefield; Seismic data and source wavefield from a single shot were read separately to obtain the anisotropy parameter V. P ε and δ; Fourier transform is performed on the source wavefield and detector wavefield data to obtain frequency-space domain wavefield data; The parameters required for the offset are calculated based on the anisotropy parameters; Calculate the anisotropic vertical wavenumber k z Anisotropic vertical wavenumber k z The calculation formula is: ； Rewrite the anisotropic dispersion relation: ； Determine the wave field of the second depth grid. This provides boundary conditions for two-way depth extrapolation; wave field The formula for obtaining this is: ； in, Represents the inverse Fourier transform; Based on the double boundary condition, the wave field propagation operator is calculated layer by layer. Two-way depth extension is performed in the frequency-space domain; Eliminate evanescent waves and pseudo-S-waves at each depth location; Perform offset imaging; Repeat the extension calculation until the maximum depth is calculated, and output the offset result.

2. The two-way wave depth migration method for VTI media as described in claim 1, characterized in that, In the step of calculating the parameters required for the offset based on the anisotropy parameters: Key parameters in ground earthquakes can all be expressed as normal time difference velocities. and horizontal velocity V h The formula is: 。 3. The two-way wave depth migration method for VTI media as described in claim 2, characterized in that, In the step of calculating the parameters required for the offset based on the anisotropy parameters: The number of parameters is reduced to a single parameter η, defined as the ellipticity, and the formula is: 。 4. The two-way wave depth migration method for VTI media as described in claim 1, characterized in that, Based on the double boundary condition, the wave field propagation operator is calculated layer by layer. In the steps of two-way depth extension in the frequency-space domain: The continuation formula is: 。 5. The two-way wave depth migration method for VTI media as described in claim 1, characterized in that, In the process of performing migration imaging: Migration imaging can be performed using the principles of cross-correlation imaging and reflectance coefficient imaging.

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