Method and apparatus for medium modeling of simulating seismic wave propagation at any discontinuous interface

Abstract

The present invention discloses a method and device for medium modeling of simulating the propagation of seismic waves at any discontinuous interface, including: reading the source wavelet and the parameters of the model; selecting a spatial step size and a time step size according to the parameters of the model, and setting the spatial order of the finite difference numerical simulation; discretizing the continuous interface in the medium, and according to the threshold judgment criterion, multiple stepped discretization results can be obtained for the continuous interface; performing forward simulation by the finite difference method on the stepped discretization results of the obtained multiple continuous interfaces respectively, and setting the parameters of the forward simulation; and superimposing the results of all the forward simulations to obtain the final forward simulation result. In the present invention, high-order finite difference operators can be applied to achieve a computational accuracy equivalent to that of the exact implementation method based on the weak solution of partial differential equations, and the computational efficiency can be greatly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of high-performance numerical simulation of medium seismic waves, and specifically to a method and device for medium modeling that simulates the propagation of seismic waves at any discontinuous interface. Background Technique

[0002] The finite difference method is currently the mainstream method used in the oil and gas exploration and development industry to simulate and study the propagation law of seismic waves. It has the advantages of high calculation accuracy, fast operation speed, small memory consumption, and easy programming implementation. Essentially, the finite difference method is an algorithm based on the strong solution form of partial differential equations, and its main applicable range is for media with uniform or smoothly varying parameters. However, in the case of media with strong discontinuous interfaces of medium parameters, problems such as calculation instability, numerical artifacts, and reduced calculation accuracy often occur. For this situation, the usual treatment method is to perform grid encryption and parameter smoothing at the strong discontinuous interface of the medium to alleviate the parameter contrast on both sides of the interface, thereby ensuring the stability and accuracy of the numerical simulation algorithm as a whole (except near the interface). However, the grid encryption at the discontinuous interface in this operation will increase the amount of calculation, consuming more calculation time and memory space. In addition, the smoothing of the medium parameters on both sides of the strong discontinuous interface will reduce the accuracy of the numerical simulation of wave propagation at the interface, and these strong discontinuous interfaces often have important significance in seismology and oil and gas exploration and development. Summary of the Invention

[0003] The purpose of the present invention is to provide a method and device for medium modeling that simulates the propagation of seismic waves at any discontinuous interface, so as to solve the problems proposed in the above background technique.

[0004] To achieve the above purpose, the present invention provides the following technical solutions:

[0005] A method for medium modeling that simulates the propagation of seismic waves at any discontinuous interface, including the following steps:

[0006] S101. Read the source wavelet and the parameters of the model;

[0007] S102. Select the spatial step and the time step according to the parameters of the model, and set the spatial order of the finite difference numerical simulation;

[0008] S103. Discretize the continuous surfaces in the medium, and according to the threshold judgment criterion, multiple stepped discretization results can be obtained for the continuous surfaces;

[0009] S104. Perform forward modeling simulation of the finite difference method on the obtained stepped discretization results of multiple continuous surfaces respectively, and set the parameters of the forward modeling simulation;

[0010] S105. Superimpose all the results of the forward simulation to obtain the final forward simulation result.

[0011] Furthermore, the parameters of the model include the source wavelet frequency, shear wave velocity, compressional wave velocity, medium density, and anisotropy parameter.

[0012] Furthermore, the continuous interfaces in the medium are discretized using the principle of the superposition method.

[0013] Furthermore, the threshold judgment criterion is obtained using the following formula: The simulation result is obtained using the following formula: where κ n (x, z) represents the medium type of the grid node. κ n (x, z) = 1 represents that the grid node is the medium below the discontinuous interface. κ n (x, z) = 0 represents that the grid node is the medium above the discontinuous interface. α(x, z) represents the weight coefficient, x and z represent the grid coordinates, t represents time, v represents the particle velocity, n represents the result of the nth stepwise discretization, and N represents the number of stepwise discretizations.

[0014] Furthermore, for the discretization of each discontinuous interface, the constitutive relation and density at the free surface are corrected using the medium parameter correction method, and numerical simulation is performed for each case, and it is judged whether the maximum number of time steps is reached.

[0015] Furthermore, if the maximum number of time steps is reached, the results of all discretization cases are superimposed to obtain the final numerical simulation result. If the maximum number of time steps is not reached, the particle velocity and particle stress are updated, then the geophone data is extracted, the data is written into a file, and it is re-judged whether the maximum number of time steps is reached.

[0016] To achieve the above object, the present invention also provides the following technical solution:

[0017] A device for medium modeling of simulating the propagation of seismic waves at any discontinuous interface, comprising:

[0018] An acquisition module for reading the source wavelet and the parameters of the model;

[0019] A setting module for selecting the spatial step and the time step according to the parameters of the model and setting the spatial order of the finite difference numerical simulation;

[0020] A discretization module for discretizing the continuous interfaces in the medium, and according to the threshold judgment criterion, multiple stepwise discretization results can be obtained for the continuous interfaces;

[0021] A simulation module, configured to perform forward simulation using the finite difference method on the stepped discretization results of multiple obtained continuous surfaces respectively, and set the parameters of the forward simulation;

[0022] A superposition module, configured to superpose the results of all forward simulations to obtain the final forward simulation result.

[0023] To achieve the above object, the present invention provides the following technical solutions:

[0024] A computer device, including a memory and a processor, where the memory stores a computer program, and when the processor executes the computer program, the steps of the method described in any one of the above are implemented.

[0025] To achieve the above object, the present invention further provides the following technical solutions:

[0026] A computer-readable storage medium, on which a computer program is stored, and when the computer program is executed by a processor, the steps of the method described in any one of the above are implemented.

[0027] Compared with the prior art, the beneficial effects of the present invention are:

[0028] It can be used as a discretization model generation and preparation program, and can be directly integrated and applied to the existing mainstream velocity-stress staggered grid finite difference numerical programs in the industrial and academic fields;

[0029] It accurately fits the spatial position of the discontinuous surface, without the rounding approximation in the traditional stepped approximation method, and does not require grid encryption and parameter smoothing processing at the strong discontinuous interface of the medium;

[0030] In the whole numerical simulation, only one generation of the medium model is required, which has the advantages of high computing efficiency and simple operation;

[0031] The medium models generated by this method are independent of each other, and their respective numerical simulations can be calculated in a parallelized manner (MPI or GPU), and finally all wave fields are superposed, which can greatly improve the computing efficiency;

[0032] The stepped approximation of the strong discontinuous interface of the medium can realize the numerical simulation of arbitrarily undulating discontinuous surfaces, and there is no stability problem restricted by the maximum curvature;

[0033] Higher-order finite difference operators can be applied to achieve a computing accuracy equivalent to that of the exact implementation method based on the weak solution of partial differential equations. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a flowchart of the method for medium modeling of simulating seismic wave propagation at an arbitrary discontinuous interface provided by the present invention.

[0035] Figure 2 Schematic diagram of implementing an arbitrary discontinuous interface by the step approximation and medium average parameter method.

[0036] Figure 3 Schematic diagram of the superposition method principle Figure 1 。

[0037] Figure 4 Schematic diagram of the superposition method principle Figure 2 。

[0038] Figure 5 Schematic diagram of the superposition method principle Figure 3 。

[0039] Figure 6 Schematic diagram of the superposition method principle Figure 4 。

[0040] Figure 7 Flowchart of the algorithm.

[0041] Figure 8 Block diagram of the device for medium modeling of simulating seismic wave propagation at an arbitrary discontinuous interface provided by the present invention.

[0042] Figure 9 Internal structure diagram of the computer device provided by the present invention. Specific implementation manner

[0043] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0044] Please refer to Figures 1-9 , the present invention provides a technical solution:

[0045] In seismology, the place where the seismic wave propagation suddenly changes is called a discontinuous surface. According to the physical properties of the media on both sides of the discontinuous surface (solid, liquid, and gas), we can divide the discontinuous surface into the following four categories:

[0046] 1) Solid / solid discontinuous surface,

[0047] 2) Solid / liquid discontinuous surface,

[0048] 3) Solid free surface (land surface) - solid / vacuum discontinuous surface,

[0049] 4) Liquid free surface (sea level) - liquid / vacuum discontinuous surface.

[0050] Complex wave conversion phenomena and the generation of strong-energy interface waves occur near these physical discontinuities. For example, solid / liquid discontinuities are often used to describe the seabed interface or the boundary between the inner and outer cores of the Earth. Near these discontinuities, a Scholte wave that propagates along the interface is generated, as well as P-S wave conversion; the solid free surface is used to describe the land surface. As the discontinuity with the strongest impedance contrast on Earth, it generates strong-amplitude surface waves (Rayleigh wave or Love wave), whose dispersion characteristics are of great significance and use in near-surface seismic exploration; the liquid free surface is used to describe the ocean surface and is the cause of multiple waves in marine exploration. It can either be regarded as noise and removed (multiple wave denoising technology) or used for illumination angle and area compensation (multiple wave imaging technology).

[0051] In the numerical simulation of seismic waves in complex media, combinations of the above discontinuities are often encountered. The correct numerical modeling and expression of these discontinuities will directly affect the accuracy and precision of numerical simulation. Especially for near-surface observed seismic data and seafloor seismograph observed seismic data, the geophones and seismographs are directly located on or near the discontinuities, so they are more affected by the discontinuities. Whether the wave field near the discontinuities can be correctly numerically simulated will directly affect the extraction and analysis of information from such seismic data.

[0052] 1) Mesh encryption and parameter smoothing are performed at the strong discontinuity interface of the medium to alleviate the parameter contrast on both sides of the interface, thereby ensuring the overall stability and accuracy of the numerical simulation algorithm. Insufficiency: It increases the computational amount and memory occupancy, and reduces the numerical simulation accuracy of wave propagation at the interface. Specifically, there are many related studies on parameter smoothing methods such as parameter geometry, algebraic mean, and wavenumber domain low-pass filtering.

[0053] 2) Finite element methods, including spectral element method and discontinuous finite element method (Komatitsch and Tromp, 1999; Komatitsch et al., 1999; Tromp et al., 2008; Peter et al., 2011), this type of numerical simulation method based on the weak solution form of partial differential equations. The existing open-source program packages of spectral element method can be referred to: SPECFEM2D and SPECFEM3D

[0054] Insufficiency: The original finite difference method program framework is no longer applicable. All forward and inverse programs need to be redeveloped under the framework of the finite element method. Moreover, compared with the finite difference method, the finite element method has complex algorithm theory and implementation, large computational amount, and high memory consumption.

[0055] 3) Discrete methods based on the Mimetic operator, such as de la Puente et al. (2014), Shragge and Tapley (2017), Konuk and Shragge (2020), Shragge and Konuk (2020), Sethi et al. (2021)

[0056] This is a method between the finite difference method and the finite element - like methods. Special operators derived from the finite element - like methods are used at strong discontinuous interfaces, while traditional finite difference operators are adopted in regions without strong discontinuous interfaces. Similar to this is the Curvilinear finite difference method

[0057] Disadvantages: The algorithm implementation is complex, additional memory space needs to be allocated to store geometric topology variables, and the computational stability is also affected by the maximum curvature of the discontinuous interface. The greater the curvature, the more likely it is to be unstable.

[0058] Method Invention:

[0059] Based on the average theory in isotropic media and the linear superposition principle in multi - dimensional spaces, a method for parameter modeling of media that can be used to accurately and efficiently simulate seismic wave propagation at strong discontinuous interfaces is proposed in sequence:

[0060] 1) Solid / liquid discontinuity: It can be further extended to be applicable to anisotropic media in the solid part

[0061] 2) Solid free surface (land surface) - solid / vacuum discontinuity: It can be further extended to two other cases. When the shear modulus μ of the medium below the discontinuity is zero, it is applicable to the liquid free surface (sea level) - liquid / vacuum discontinuity; it is applicable to anisotropic media in the solid part.

[0062] The present invention

[0063] 1) It can be used as a discretization model generation and preparation program, and can be directly integrated and applied to the existing mainstream velocity - stress staggered - grid finite - difference numerical programs in the industrial and academic fields;

[0064] 2) It precisely fits the spatial position of the discontinuous surface, without the rounding approximation in the traditional step - approximation method, and does not require grid encryption and parameter smoothing at the strong discontinuous interfaces of the medium;

[0065] 3) During the whole numerical simulation, only one - time generation of the medium model (i.e., the method of the present invention) is required, which has the advantages of high computational efficiency and simple operation;

[0066] 4) The medium models generated by this method are independent of each other, and their respective numerical simulations can be calculated in a parallelized manner (MPI or GPU). Finally, the superposition of all wave fields is performed, which can greatly improve the calculation efficiency;

[0067] 5) The step approximation of the strong discontinuous interface of the medium can realize the numerical simulation of arbitrarily undulating discontinuous surfaces, and there is no stability problem restricted by the maximum curvature

[0068] 6) High-order finite difference operators can be applied to achieve a computational accuracy equivalent to that of the exact implementation method based on the weak solution of partial differential equations

[0069] Taking the discontinuous surface in anisotropic media as an example, as Figure 2 shown, the step approximation method is used to represent discontinuous interfaces of arbitrary shapes. At the same time, the medium parameter averaging method is used for numerical simulation at the discontinuous interface. For the superposition method, its schematic diagram is as Figure 3 shown. Figure 3 Each grid point in represents a grid cell, and the red line (the diagonal line between the vertical coordinates 5 and 6) represents the discontinuous interface. For the traditional step approximation, for the grid cells intersecting the red line, when the proportion of the grid area below the discontinuous surface in the entire grid area (this proportion is called the weight coefficient α(x,z)) is greater than 0.5, it is designated as the medium type below the discontinuous interface. For the superposition method, we perform multiple step discretizations of the discontinuous interface through the parameter N. The method of each step discretization is determined by a threshold. When the weight coefficient α(x,z) is greater than this threshold, the grid node is considered to be the medium below the discontinuous interface, and the threshold is determined by formula (1), κ n (x,z) represents the medium type of the grid node, κ n (x,z) = 1 represents that the grid node is the medium below the discontinuous interface, κ n (x,z) = 0 represents that the grid node is the medium above the discontinuous surface. Taking Figures 4 to 6 as an example, at this time N is equal to 3. Therefore, we perform three step discretizations on the discontinuous interface, perform numerical simulations on the results of each discretization respectively, and then superimpose the obtained results through formula (2) to obtain the final numerical simulation result. In formulas (1) and (2), x and z represent the grid coordinates, t represents time, and v represents the particle velocity.

[0070]

[0071]

[0072] Among them Figures 3 to 6 where: τ xx τ zz τ xzdenote stress components, Vx and Vz denote velocity components, ρ x , ρ z denotes density, μ xz denotes Lame constant, anisotropic medium denotes anisotropic medium, Air denotes air medium, Free surface denotes free surface.

[0073] Algorithm flow:

[0074] First step: Read the source wavelet and the medium model (the medium model refers to reading parameters such as the velocity and density of the medium, such as shear wave velocity, compressional wave velocity, medium density, anisotropic parameters, etc.).

[0075] Second step: Select appropriate spatial and temporal step sizes according to the parameters of the model (such as shear wave velocity, source wavelet frequency, etc.), and set the spatial order of the finite difference numerical simulation.

[0076] Third step: Use the medium modeling method to discretize the continuous interface in the medium by the principle of superposition method. According to the threshold judgment criterion in formula (1), multiple stepped discrete results can be obtained for the continuous interface.

[0077] Fourth step: Conduct forward modeling simulations for the multiple stepped discrete results of the continuous interfaces obtained in the previous step respectively, and set the parameters of the forward modeling simulation (such as simulation time, geophone position, source position, etc.).

[0078] Fifth step: Superpose all the results of the forward modeling simulations to obtain the final forward modeling result.

[0079] In the present invention, the computer device may include a memory, a storage controller, one or more (only one is shown in the figure) processors, etc. Each component is directly or indirectly electrically connected to achieve data transmission or interaction. For example, these components can be electrically connected through one or more communication buses or signal buses. The method for medium modeling of simulating seismic wave propagation at any discontinuous interface respectively includes at least one software function module that can be stored in the memory in the form of software or firmware, such as the software function modules or computer programs included in the device for medium modeling of simulating seismic wave propagation at any discontinuous interface. The memory can store various software programs and modules, such as the program instructions / modules corresponding to the method and device for medium modeling of simulating seismic wave propagation at any discontinuous interface provided in the embodiments of the present application. The processor executes various functional applications and data processing by running the software programs and modules stored in the memory, that is, implements the analysis method in the embodiments of the present application.

[0080] Although embodiments of the present invention have been shown and described, those of ordinary skill in the art will appreciate that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for medium modeling of simulating the propagation of seismic waves at any discontinuous interface, characterized in that, Including: Read the source wavelet and the parameters of the model; Select the spatial step and the temporal step according to the parameters of the model, and set the spatial order of the finite-difference numerical simulation; Discretize the continuous interfaces in the medium, and according to the threshold judgment criterion, multiple stepped discretization results can be obtained for the continuous interfaces; Perform forward modeling by the finite-difference method on the obtained stepped discretization results of multiple continuous interfaces respectively, and set the parameters of the forward modeling; Superpose all the results of the forward modeling to obtain the final forward modeling result, where The threshold judgment criterion is obtained by using the following formula: The simulation result is obtained by using the following formula: where κ n (x, z) represents the medium type of the grid node, and κ n (x, z) = 1 represents that the grid node is the medium below the discontinuous interface, and κ n (x, z) = 0 represents that the grid node is the medium above the discontinuous surface. α(x, z) represents the weight coefficient, x and z represent the grid coordinates, t represents the time, v represents the particle velocity, n represents the result of the nth step discretization, and N represents the number of step discretizations.

2. The method according to claim 1, wherein the parameters of the model include the source wavelet frequency, the shear wave velocity, the compressional wave velocity, the medium density, and the anisotropy parameter.

3. The method according to claim 1, wherein Discretize the continuous interfaces in the medium by using the principle of the superposition method.

4. The method according to claim 1, characterized in that, For the discretization of each discontinuous interface, apply the medium parameter correction method to correct the constitutive relationship and density at the free surface, perform numerical simulation for each case, and judge whether the maximum number of time steps is reached.

5. The method according to claim 4, wherein If the maximum number of time steps is reached, superpose the results of all discretization cases to obtain the final numerical simulation result. If the maximum number of time steps is not reached, update the particle velocity and particle stress, then extract the geophone data, write the data into a file, and re-judge whether the maximum number of time steps is reached.

6. An apparatus for modeling a medium for simulating the propagation of seismic waves at any discontinuous interface, characterized in that, Including: An acquisition module, configured to read the source wavelet and the parameters of the model; A setting module, configured to select the spatial step and the temporal step according to the parameters of the model, and set the spatial order of the finite-difference numerical simulation; A discretization module, configured to discretize the continuous interfaces in the medium, and according to the threshold judgment criterion, multiple stepped discretization results can be obtained for the continuous interfaces; A simulation module, configured to perform forward modeling by the finite-difference method on the obtained stepped discretization results of multiple continuous interfaces respectively, and set the parameters of the forward modeling; A superposition module, configured to superpose all the results of the forward modeling to obtain the final forward modeling result, where The threshold judgment criterion is obtained by using the following formula: The simulation result is obtained by using the following formula: where κ n (x, z) represents the medium type of the grid node, κ n (x, z) = 1 represents that the grid node is the medium below the discontinuous interface, κ n (x, z) = 0 represents that the grid node is the medium above the discontinuous surface, α(x, z) represents the weight coefficient, x and z represent the grid coordinates, t represents the time, v represents the particle velocity, n represents the result of the nth step discretization, and N represents the number of step discretizations.

7. A computer device, including a memory and a processor, the memory stores a computer program, and when the processor executes the computer program, the steps of the method according to any one of claims 1 to 5 are implemented.

8. A computer-readable storage medium, on which a computer program is stored, and when the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 5 are implemented.

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