A High-Precision Compact Difference Reverse Time Migration Imaging Method and Its Equipment

Abstract

An embodiment of this specification discloses a high-precision compact difference reverse time migration imaging method and its device. By inputting a migration velocity model and seismic records, and simultaneously setting imaging parameters, a seismic wave field is generated according to the migration velocity model, seismic records, and imaging parameters; the seismic wave field is extended along the forward propagation direction of time, and the wave field values at each moment are stored to generate a forward extended wave field; the geophone wave field is reversely extended along the reverse propagation direction of time to generate a reverse extended wave field; the forward extended wave field and the reverse extended wave field are subjected to cross-correlation imaging to generate a reverse time migration profile; the reverse time migration profiles of each shot point are stacked to obtain an imaging result. Thus, during acoustic wave equation reverse time migration imaging, high-precision imaging is achieved through finite difference format calculation.

Description

Technical Field

[0001] This specification relates to a high-precision compact difference reverse time migration imaging method and its device, belonging to the field of geophysics for oil and gas exploration. Background Art

[0002] In the field of seismic exploration and development, reverse time migration imaging is one of the indispensable key steps in seismic data processing. With the exploration focus gradually shifting to lithologic reservoirs, the demand for high-precision imaging is increasing day by day. The reverse time migration imaging technology can obtain high-precision and high-amplitude-preserving seismic profiles. However, the traditional reverse time migration imaging method based on the central finite difference scheme has limited ability to improve accuracy, and the improvement of accuracy often comes at the cost of computational efficiency. The accuracy and efficiency of reverse time migration imaging restrict the effect and cost of seismic data processing, and the amount of collected data is increasing day by day. Therefore, how to reduce the production cost while improving the imaging accuracy is one of the key problems faced by the oil and gas exploration field.

[0003] Based on this, there is an urgent need for a reverse time migration imaging method that can improve the computational accuracy while ensuring the computational efficiency. Summary of the Invention

[0004] The purpose of the present invention is to provide a high-precision compact difference reverse time migration imaging method and its device, which is a second-order central finite difference scheme in time and a fourth-order compact finite difference scheme in space, and it can solve the problem of relatively low computational accuracy of the current same-order central finite difference scheme.

[0005] To solve the above technical problems, the present invention adopts the following technical solutions:

[0006] In the first aspect, a high-precision compact difference reverse time migration imaging method is provided, including:

[0007] Input the migration velocity model and seismic records, and at the same time set the imaging parameters, and generate a seismic wave field according to the migration velocity model, seismic records and imaging parameters

[0008] Extend the seismic wave field along the forward time propagation direction, and store the wave field values at each moment to generate a forward extended wave field, where the specific way of extension is as follows:

[0009] Wherein, is the second derivative of the sound pressure with respect to the spatial coordinate x, and is is the second derivative of the sound pressure with respect to the spatial coordinate z, u(x, z) is the sound pressure, v(x, z) is the velocity, t represents time, x and z are spatial coordinates, and f(t) is the source time function;

[0010] is determined based on the following way:

[0011]

[0012] Determined in the following manner:

[0013]

[0014] Perform reverse time continuation on the detector point wave field along the reverse time propagation direction to generate a reverse continued wave field;

[0015] Perform cross-correlation imaging on the forward continued wave field and the reverse continued wave field to generate a reverse time migration profile;

[0016] Superimpose the reverse time migration profiles of each shot point to obtain an imaging result.

[0017] In a second aspect, there is provided an electronic device, including:

[0018] At least one processor; and,

[0019] A memory communicatively connected to the at least one processor; wherein,

[0020] The memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor so that the at least one processor can execute the method described in the first aspect.

[0021] Compared with the prior art, the method of the present invention generates a seismic wave field by inputting an offset velocity model and seismic records, and simultaneously setting imaging parameters, according to the offset velocity model, seismic records, and imaging parameters; continue the seismic wave field along the forward time propagation direction, and store the wave field values at each moment to generate a forward continued wave field; perform reverse time continuation on the detector point wave field along the reverse time propagation direction to generate a reverse continued wave field; perform cross-correlation imaging on the forward continued wave field and the reverse continued wave field to generate a reverse time migration profile; superimpose the reverse time migration profiles of each shot point to obtain an imaging result. Thus, when performing reverse time migration imaging of the acoustic wave equation, higher-precision imaging is achieved through finite-difference format calculation. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Is a schematic flow chart provided by an embodiment of this specification;

[0023] Figure 2 Is an offset velocity model diagram in an embodiment of this specification;

[0024] Figure 3 Is a seismic record diagram in an embodiment of this specification;

[0025] Figure 4This is the forward-propagated wavefield map of the 35th shot at 1 s in the embodiments of this specification;

[0026] Figure 5 This is the backward-propagated wavefield map of the 35th shot at 1 s in the embodiments of this specification;

[0027] Figure 6 This is the reverse-time migration profile obtained by cross-correlation imaging in the embodiments of this specification;

[0028] Figure 7 This is the stacked profile in the embodiments of this specification;

[0029] Figure 8 This is the final imaging result in the embodiments of this specification. Detailed implementation manners

[0030] 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 with reference to the accompanying drawings in the embodiments of this specification. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of this specification without making creative efforts shall fall within the protection scope of this application.

[0031] In the first aspect, as Figure 1 shown, Figure 1 This is the flowchart of the high-precision compact difference reverse-time migration imaging method provided by the embodiments of this specification, which specifically includes:

[0032] S1, input the migration velocity model and seismic records, and at the same time set the imaging parameters. Generate the seismic wavefield according to the migration velocity model, seismic records, and imaging parameters.

[0033] The imaging parameters here include the spatial sampling step sizes dx and dz of the model, the time sampling step size dt, the maximum calculation time t max , the source wavelet frequency f, the number of shots n s , the shot interval d s , the number of receiving points n r , and the receiving point interval d r .

[0034] S2, extend the seismic wavefield in the forward time propagation direction, and store the wavefield values at each moment to generate the forward-propagated wavefield

[0035] The extension of the seismic wavefield uses the two-dimensional acoustic wave equation, as shown below:

[0036]

[0037] Wherein, u(x, z) is the sound pressure, v(x, z) is the velocity, t represents time, x and z are spatial coordinates, and f(t) is the source time function.

[0038] Forward continuation uses a Ricker wavelet as the source, starting from time t = 0 until the set maximum calculation time t max , and stores the seismic wave field at each discrete time during the continuation process.

[0039] The solution to equation (1) uses a second-order central difference in time and a fourth-order compact difference in space. Among them, the fourth-order compact difference in space for solving the second derivative of the sound pressure u(x, z) with respect to the spatial coordinate x is as follows:

[0040]

[0041] Similarly, the fourth-order compact difference in space for solving the second derivative of the sound pressure u(x, z) with respect to the spatial coordinate z is as follows:

[0042]

[0043] In equations (2) and (3), M and N are the horizontal and vertical grid points of the migration velocity model, respectively.

[0044] Thus, the discrete format of equation (1) with second-order central difference in time and fourth-order compact difference in space can be written as:

[0045]

[0046] Wherein, and are the second derivatives of the sound pressure u(x, z) with respect to the spatial coordinates x and z, respectively, and are calculated by equations (2) and (3).

[0047] S3. Perform reverse time continuation on the geophone wave field along the reverse time propagation direction to generate a reverse continuation wave field.

[0048] The and used in reverse continuation are the same as those in forward continuation. Starting from the maximum time t max , perform reverse time continuation on the geophone wave field along the reverse time propagation direction until reaching the moment t = 0.

[0049] S4. Perform cross-correlation imaging on the forward continuation wave field and the reverse continuation wave field to generate a reverse time migration profile.

[0050] For example, the cross-correlation imaging condition here can adopt a source-normalized imaging condition:

[0051]

[0052] According to actual needs, other mutually related imaging methods can also be adopted. In the formula, R im (x, z) is the imaging result, F(x, z, t) is the forward-propagating wavefield, and B(x, z, t) is the backward-propagating wavefield.

[0053] S5. Stack the reverse-time migration profiles of each shot point to obtain the imaging result.

[0054] Stack the multi-shot reverse-time migration profiles to obtain the stacked profile, and perform Laplace filtering on the stacked profile to filter out low-frequency noise and obtain the final imaging result.

[0055] By inputting the migration velocity model and seismic records, and setting the imaging parameters at the same time, generate the seismic wavefield according to the migration velocity model, seismic records, and imaging parameters; extend the seismic wavefield along the forward propagation direction of time, and store the wavefield values at each moment to generate the forward-propagating wavefield; perform reverse-time extension on the geophone wavefield along the reverse propagation direction of time to generate the backward-propagating wavefield; perform cross-correlation imaging on the forward-propagating wavefield and the backward-propagating wavefield to generate the reverse-time migration profile; stack the reverse-time migration profiles of each shot point to obtain the imaging result. Thus, when performing reverse-time migration imaging of the acoustic wave equation, higher-precision imaging can be achieved through finite-difference calculation.

[0056] To illustrate the method of the present invention in more detail, the actual application effect of the present invention in the Marmousi model is given, and the specific process is as Figure 1 shown. Input the migration velocity model (as Figure 2 shown), seismic records (as Figure 3 shown), and set the imaging parameters at the same time: the number of grid points of the model is 1360x700, the spatial sampling step is 5m, the time sampling step is 0.3ms, the maximum calculation time is 2.1s, the source wavelet frequency is 30Hz, the number of shots is 68, the shot interval is 100m, the number of receiving points is 1360, and the receiving point interval is 5m. Note that Figure 3 shows the seismic record diagram of the 35th shot, not all the seismic records. Extend the seismic wavefield along the forward propagation direction of time, and store the wavefield values at each moment. Taking the 35th shot as an example, Figure 4 is the forward-propagating wavefield of the 35th shot at 1s. Perform reverse-time extension on the geophone wavefield along the reverse propagation direction of time, and perform cross-correlation imaging on the wavefields at the same moment during the forward and backward propagation processes to obtain the reverse-time migration profile; Figure 5 is the backward-propagating wavefield of the 35th shot at 1s, Figure 6 is the reverse-time migration profile diagram obtained by performing cross-correlation imaging. Stack the multi-shot reverse-time migration profiles, and perform Laplace filtering on the stacked profile to filter out low-frequency noise and obtain the final imaging result.Figure 7 It is the stacked profile before filtering, Figure 8 It is the final imaging result after filtering. It can be seen that the method described in the present invention can accurately image the Marmousi model with complex structures, especially for deep horizons.

[0057] In a second aspect, an embodiment of this specification further provides an electronic device, and the device includes:

[0058] At least one processor; and,

[0059] A memory communicatively connected to the at least one processor; wherein,

[0060] The memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor so that the at least one processor can execute the method as described in the first aspect.

[0061] The above describes specific embodiments of this specification. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recited in the claims may be performed in a different order than in the embodiments and still achieve the desired result. Additionally, the processes depicted in the figures do not necessarily require the particular order or sequential order shown to achieve the desired result. In certain implementations, multitasking and parallel processing are also possible or may be advantageous.

[0062] The above is only one or more embodiments of this specification and is not used to limit this specification. For those skilled in the art, one or more embodiments of this specification can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of one or more embodiments of this specification shall be included within the scope of the claims of this specification.

Claims

1. A high-precision compact finite-difference reverse-time migration imaging method, comprising: Inputting a migration velocity model and seismic records, and simultaneously setting imaging parameters, and generating a seismic wavefield according to the migration velocity model, seismic records and imaging parameters; Extending the seismic wavefield along the forward propagation direction of time, and storing the wavefield values at each moment to generate a forward-extended wavefield, wherein the specific way of extension is as follows: Among them, is the second derivative of the sound pressure with respect to the spatial coordinate x, is the second derivative of the sound pressure with respect to the spatial coordinate z, u(x, z) is the sound pressure, v(x, z) is the velocity, t represents time, x and z are spatial coordinates, and f(t) is the source time function; Determined in the following manner: Determined in the following manner: Performing reverse-time extension on the geophone wavefield along the reverse propagation direction of time to generate a reverse-extended wavefield; Performing cross-correlation imaging on the forward-extended wavefield and the reverse-extended wavefield to generate a reverse-time migration profile; Stacking the reverse-time migration profiles of each shot point to obtain an imaging result.

2. The method according to claim 1, wherein, Performing cross-correlation imaging on the forward-extended wavefield and the reverse-extended wavefield to generate a reverse-time migration profile, including: Cross-correlation imaging is performed in the following manner: wherein, R im (x, z) is the imaging result, F(x, z, t) is the forward-propagated wavefield, B(x, z, t) is the backward-propagated wavefield, and t max is the maximum time in the backward propagation.

3. The method according to claim 1, wherein, Stacking the reverse-time migration profiles of each shot point to obtain an imaging result, including: Stacking the reverse-time migration profiles of each shot point to generate a stacked profile; filtering the stacked profile to obtain an imaging result.

4. An electronic device, comprising: At least one processor; And, A memory communicatively connected to the at least one processor; wherein, The memory stores instructions executable 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 execute the method according to any one of claims 1 to 3.

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