A method and device for elastic wave variable grid finite difference forward modeling

Abstract

The embodiment of this specification discloses a machine device for elastic wave variable grid finite difference forward modeling. By inputting the initial underground medium longitudinal wave and transverse wave velocity model, and presetting the forward modeling parameters, the initial underground medium longitudinal wave and transverse wave velocity model is subjected to variable grid processing to obtain the underground medium longitudinal wave and transverse wave velocity model after the variable grid; c. According to the underground medium longitudinal wave and transverse wave velocity model after the variable grid, elastic wave forward modeling is performed to obtain the horizontal and vertical wave field information at a specific moment after the variable grid; according to the horizontal and vertical wave field information at a specific moment after the variable grid, the final regular grid horizontal and vertical wave field information is generated. Thereby, the amount of calculation and computer memory usage are greatly reduced, and the calculation speed is fast.

Description

Technical Field

[0001] The present specification relates to an elastic wave variable grid finite difference forward modeling method and equipment thereof, belonging to the field of oil and gas exploration geophysics. Background Art

[0002] Forward modeling is one of the key steps in seismic data processing and an indispensable part of seismic exploration and development. Forward modeling determines the quality of subsequent migration imaging, and the efficiency of forward modeling restricts the cost of seismic data processing. With the continuous in-depth development of my country's seismic exploration field, the data obtained from seismic data acquisition has gradually shifted from two-dimensional to three-dimensional, from single component to multi-component, and the amount of data has continued to increase. Therefore, improving simulation accuracy, reducing calculation efficiency, and alleviating computer memory pressure are key issues faced in my country's oil and gas exploration and development field.

[0003] Based on this, an elastic wave forward modeling method is needed that can ensure the accuracy of forward modeling and greatly improve the calculation efficiency. Summary of the invention

[0004] The purpose of the present invention is to provide an elastic wave variable grid finite difference forward modeling method and equipment, which can solve the problems of large calculation amount, low calculation efficiency and low simulation accuracy in the current conventional elastic wave forward modeling technology, and accurately and highly precisely simulate the seismic wave field.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] In a first aspect, a method for elastic wave variable grid finite difference forward modeling is provided, comprising:

[0007] Input the initial underground medium P-wave and S-wave velocity models and pre-set the forward modeling parameters

[0008] Performing grid-changing processing on the initial underground medium longitudinal wave and transverse wave velocity model to obtain a grid-changing underground medium longitudinal wave and transverse wave velocity model;

[0009] c. Based on the P-wave and S-wave velocity models of the underground medium after the grid is changed, elastic wave forward modeling is performed in the following manner to obtain horizontal and vertical wave field information at a specific time after the grid is changed:

[0010]

[0011] in is the mapping from the variable grid model to the initial model, ρ is the ordinate, z is the ordinate, ξ is the abscissa after the variable grid, and η is the ordinate after the variable grid; v ξ is the horizontal wave field information at a specific time after the grid is changed, v ηis the vertical wave field information at a specific time after the grid is changed, σ ξξ , σ ηη , τ ξη is the stress component, λ and μ are the Lame constants;

[0012] The final regular grid horizontal and vertical wavefield information is generated according to the horizontal wavefield information and the vertical wavefield information at a specific time after the grid is changed.

[0013] In a second aspect, an electronic device is provided, comprising:

[0014] at least one processor; and,

[0015] a memory communicatively connected to the at least one processor; wherein,

[0016] The memory stores instructions that can be executed by the at least one processor, and the instructions are executed by the at least one processor to enable the at least one processor to perform the method according to the first aspect.

[0017] Compared with the prior art, the method of the present invention inputs the initial underground medium longitudinal wave and transverse wave velocity model, and pre-sets the forward simulation parameters to perform variable grid processing on the initial underground medium longitudinal wave and transverse wave velocity model, so as to obtain the underground medium longitudinal wave and transverse wave velocity model after the variable grid; c. Perform elastic wave forward simulation according to the underground medium longitudinal wave and transverse wave velocity model after the variable grid, and obtain the horizontal and vertical wave field information at a specific moment after the variable grid; and generate the final regular grid horizontal and vertical wave field information according to the horizontal and vertical wave field information at a specific moment after the variable grid. Thereby, the amount of calculation and the amount of computer memory occupied are greatly reduced, and the calculation speed is fast. In addition, the method of the present invention hardly reduces the accuracy of the wave field obtained by the forward simulation. Therefore, the present invention has the advantages of high simulation accuracy and high calculation efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A schematic diagram of a flow chart of an elastic wave variable grid finite difference forward modeling method provided in an embodiment of this specification;

[0019] Figure 2 An initial Marmousi model longitudinal wave velocity model diagram of an embodiment of the present invention;

[0020] Figure 3 A longitudinal wave velocity model diagram of a variable grid Marmousi model according to an embodiment of the present invention;

[0021] Figure 4 A longitudinal grid spacing diagram of a variable grid Marmousi model in one embodiment of the present invention;

[0022] Figure 5 This is a variable grid horizontal direction wave field diagram at 1.0s in one embodiment of the present invention;

[0023] Figure 6 This is a wave field diagram in the vertical direction of a variable grid at 1.0s in an embodiment of the present invention;

[0024] Figure 7 A linear interpolation wave field of a variable grid horizontal direction wave field in one embodiment of the present invention;

[0025] Figure 8 A linear interpolation wave field of a variable grid vertical direction wave field in one embodiment of the present invention; DETAILED DESCRIPTION

[0026] In order to enable those skilled in the art to better understand the technical solutions in this specification, the technical solutions in the embodiments of this specification will be clearly and completely described below in conjunction with the drawings in the embodiments of this specification. Obviously, the described embodiments are only part of the embodiments of this application, not all of them. Based on the embodiments of this specification, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of this application.

[0027] In the first aspect, Figure 1 As shown, Figure 1 A schematic flow chart of an elastic wave variable grid finite difference forward modeling method provided in the embodiments of this specification specifically includes:

[0028] S1, input the initial underground medium longitudinal wave and transverse wave velocity model, and pre-set the forward simulation parameters. The forward simulation parameters here include but are not limited to the number of model transverse and longitudinal grid points, the initial transverse and longitudinal grid spacing dz, dz, the main frequency of the source wavelet f, and the time sampling interval dt.

[0029] S2, performing variable grid processing on the initial underground medium longitudinal wave and shear wave velocity model to obtain the underground medium longitudinal wave and shear wave velocity model after variable grid processing.

[0030] The method formula for obtaining the variable grid longitudinal wave and shear wave velocity model is:

[0031]

[0032] Among them, v min(z) is the minimum velocity value of each layer of the initial P-wave or S-wave model, dz(z) is the longitudinal grid spacing of the variable grid P-wave or S-wave velocity model, and f is the main frequency of the source used in the numerical simulation. In formula (1), in order to make the depth of the variable grid P-wave or S-wave velocity model equal to that of the initial P-wave or S-wave velocity model, the initial model needs to be resampled. First, a trial step size is given, and the trial step size is continuously increased until a point z is found. 1 , so that z 1 =dz(z 1 ); then, from z 1 Starting from point z, repeat the first step until you find the second point z 2 , so that z 2 -z 1 =dz(z 2 ); Finally, repeat the previous step until the maximum depth is reached and all new grid points are obtained. The new model composed of new grid points is the variable grid model.

[0033] S3, according to the underground medium longitudinal wave and transverse wave velocity model after the grid is changed, elastic wave forward simulation is performed in the following manner to obtain horizontal direction wave field information and vertical direction wave field information at a specific time after the grid is changed.

[0034] Assume that the coordinate system A(x,z) is the Cartesian coordinate system where the regular grid velocity model is located, and the coordinate system B(ξ,η) after the variable grid represents the rectangular coordinate system where the variable grid velocity model is located. Then the mapping relationship between the two coordinate systems can be recorded as:

[0035]

[0036] Definition F a is the first-order derivative of any variable F with respect to the coordinate variable a:

[0037]

[0038] Using the chain rule of coordinate transformation, we can obtain the transformation relationship between the first-order derivative of any variable F in the coordinate system A(x,z) and B(ξ,η):

[0039]

[0040] In the coordinate system A(x,z), the first-order stress-velocity elastic wave equation can be written as:

[0041]

[0042]

[0043]

[0044]

[0045]

[0046] Substituting formula (4) into formula (5), the expression form of formula (5) in the coordinate system B (ξ, η) can be obtained, that is, the elastic wave equation used in the forward simulation in the embodiment of the present invention:

[0047]

[0048] In the above formula, It is the mapping from the variable grid model to the initial model and can be solved using the high-order finite difference method. ξ and v η is the velocity component, σ ξξ , σ ηη , τ ξη are stress components, λ and μ are Lame constants.

[0049] S4, generating final regular grid horizontal and vertical wavefield information according to the horizontal wavefield information and vertical wavefield information at a specific time after the grid is changed.

[0050] It should be noted that the forward modeling wave field obtained in step S3 is a variable grid wave field, so it is necessary to apply interpolation processing or fitting processing to convert the variable grid wave field into the initial model wave field. The interpolation processing here can consider using interpolation methods such as linear interpolation or cubic spline interpolation. In order to reduce the amount of calculation, the present invention uses linear interpolation.

[0051] In order to more specifically illustrate the method of the present invention, the implementation process of the present invention is explained in combination with the Marmousi model, and the technical solution of the present invention is described completely and clearly. In addition, the implementation cases described in the present invention are only some of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention specification, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0052] The specific process is as follows Figure 1 The initial Marmousi longitudinal wave velocity model used is as follows: Figure 2 As shown in Figure 1, the shear wave velocity of the model is set to 0.577 times the longitudinal wave velocity. The forward simulation parameters are as follows: the initial model has 1360 and 700 transverse and longitudinal grid points, respectively, the transverse and longitudinal grid spacing is 5m, the time sampling interval is 0.3ms, and the source uses a Ricker wavelet with a main frequency of 30Hz. Figure 3It is the Marmousi longitudinal wave velocity model with variable grid, that is, the resampling result of the initial model. The number of longitudinal grid points of the variable grid model is reduced from 700 to 449, and the number of grid points is reduced by 35.9%. The percentage of grid point reduction shows that the present invention can reduce the dimension of the offset velocity field, thereby reducing the calculation memory, and the percentage of memory reduction is the same as the percentage of grid point reduction, both of which are 35.9%. Figure 4 is the longitudinal grid spacing of the variable grid model. The longitudinal grid spacing changes smoothly with the increase of depth. The transverse grid spacing of the variable grid model is still 5m. In addition, the velocity value of the variable grid Marmousi shear wave model is 0.577 times the velocity of the longitudinal wave model. The finite difference technique is used to perform forward simulation on the variable grid model. Figure 5 and Figure 6 They are the variable grid horizontal and vertical wave fields at 1.0s. Apply linear interpolation to convert the variable grid horizontal and vertical wave fields into regular grid horizontal and vertical wave fields, as shown in Figure 7 and Figure 8 As shown above, it can be seen that the variable grid method adopted by the present invention can greatly improve the calculation efficiency and save memory space without reducing the accuracy of forward simulation.

[0053] In a second aspect, an embodiment of the present specification further provides an electronic device, the device comprising:

[0054] at least one processor; and,

[0055] a memory communicatively connected to the at least one processor; wherein,

[0056] The memory stores instructions that can be executed by the at least one processor, and the instructions are executed by the at least one processor to enable the at least one processor to perform the method according to the first aspect.

[0057] The above is a description of a specific embodiment of the specification. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recorded in the claims can be performed in an order different from that in the embodiments and still achieve the desired results. In addition, the processes depicted in the drawings do not necessarily require the specific order or continuous order shown to achieve the desired results. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0058] The above description is only one or more embodiments of this specification and is not intended to limit this specification. For those skilled in the art, one or more embodiments of this specification may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of one or more embodiments of this specification shall be included in the scope of the claims of this specification.

Claims

1. A variable-grid finite-difference forward modeling method for elastic waves. include: Input the initial underground medium P-wave and S-wave velocity models and pre-set the forward modeling parameters; The initial underground medium longitudinal wave and shear wave velocity model is subjected to variable grid processing to obtain the underground medium longitudinal wave and shear wave velocity model after variable grid processing, specifically in the following manner: v min (z) is the minimum velocity value of each layer of the initial P-wave or S-wave model, dz(z) is the longitudinal grid spacing of the variable grid P-wave or S-wave velocity model, and f is the main frequency of the source used in the numerical simulation. In order to make the depth of the variable grid P-wave or S-wave velocity model equal to that of the initial P-wave or S-wave velocity model, the initial model needs to be resampled: first, a trial step size is given, and the trial step size is continuously increased until a point z is found. 1 , so that z 1 =dz(z 1 ); then, from z 1 Starting from point z, repeat the first step until you find the second point z 2 , so that z 2 -z 1 =dz(z 2 ); Finally, repeat the previous step until the maximum depth is reached and all new grid points are obtained; According to the underground medium longitudinal wave and transverse wave velocity model after the grid is changed, elastic wave forward simulation is performed in the following manner to obtain horizontal direction wave field information and vertical direction wave field information at a specific time after the grid is changed: in is the mapping from the variable grid model to the initial model, ρ is the medium density, z is the ordinate, ξ is the abscissa after the variable grid, and η is the ordinate after the variable grid; v ξ is the horizontal wave field information at a specific time after the grid is changed, v η is the vertical wave field information at a specific time after the grid is changed, σ ξξ , σ ηη , τ ξη is the stress component, λ and μ are the Lame constants; The final regular grid horizontal and vertical wavefield information is generated according to the horizontal wavefield information and the vertical wavefield information at a specific time after the grid is changed.

2. The method according to claim 1, in, Generating final regular grid horizontal and vertical wavefield information according to the horizontal wavefield information and the vertical wavefield information at a specific time after the grid is changed, including: Interpolation processing or fitting processing is performed on the horizontal direction wave field information and the vertical direction wave field information at the specific moment after the grid is changed to generate regular grid horizontal and vertical direction wave fields.

3. An electronic device, include: at least one processor; as well as, a memory communicatively connected to the at least one processor; wherein, The memory stores instructions that can be executed by the at least one processor, and the instructions are executed by the at least one processor to enable the at least one processor to perform the method according to any one of claims 1 to 2.

Images