Initial value determination method for reverse-time migration imaging and reverse-time migration imaging method

Abstract

This disclosure relates to an initial value determination method and a method for reverse time migration imaging. The initial value determination method includes: acquiring detector wavefield data; extracting the seismic wavefield at the ground surface based on the detector wavefield data; and determining the vertical velocity component based on the seismic wavefield at the ground surface according to the local plane wave assumption. The vertical velocity component is used to generate the initial value for reverse time migration imaging. Compared to assuming the initial value of the vertical velocity component is zero, reverse time migration imaging based on this initial value provides a more accurate structural imaging location, overcoming the limitations of traditional methods that assume v... z The limitation of 0 is particularly addressed by improving the imaging sharpness of steeply tilted structures; overall, it offers the advantages of reducing data acquisition costs and improving imaging accuracy. In terms of amplitude preservation, the method provided in this disclosure is superior to conventional reverse-time migration methods.

Description

Technical Field

[0001] This disclosure relates to the field of seismic exploration technology, and in particular to a method for determining initial values ​​and a method for reverse time migration imaging. Background Technology

[0002] The essence of migration imaging technology lies in solving the wave equation. An accurate solution to the wave equation is crucial for obtaining a precise description of the wave field and is a fundamental basis for achieving good imaging results. Reverse-time migration (RTM) is a key imaging technique in seismic exploration. Based on the full wave equation, RTM is not limited by tectonic dip angles or velocity variations, thus possessing excellent tectonic imaging capabilities and amplitude preservation. However, RTM also requires certain initial assumptions, which can affect the accuracy and amplitude preservation of the migration imaging to some extent.

[0003] In realizing the concept disclosed herein, the inventors discovered at least the following technical problems in the related technologies: Initial conditions can have a significant impact on the calculation results during the solution of partial differential equations; in some related technologies, when assuming initial values ​​for reverse time migration imaging, the initial value of the vertical velocity component is assumed to be zero, which introduces a large error into the wavefield calculation; in some solutions, the vertical velocity component is calculated from two layers of seismic wavefields acquired by a land-based dual-detector acquisition system. This system requires burying two layers of geophones at different depths, which, for actual seismic exploration, means a significant increase in hardware and manpower investment; moreover, the construction difficulty is greatly increased, and under certain surface conditions, it is even impossible to deploy two layers of geophones, resulting in high deployment difficulty and high hardware and manpower costs. Summary of the Invention

[0004] To solve the above-mentioned technical problems, or at least partially solve them, embodiments of this disclosure provide a method for determining initial values ​​and a method for reverse time-shift imaging.

[0005] In a first aspect, embodiments of this disclosure provide a method for determining initial values ​​for reverse time migration imaging. The method includes: acquiring detector wavefield data; extracting a seismic wavefield at the Earth's surface based on the detector wavefield data; and determining a vertical velocity component based on the seismic wavefield at the Earth's surface, according to the local plane wave assumption; wherein the vertical velocity component is used to generate initial values ​​for the reverse time migration imaging.

[0006] In some embodiments, the aforementioned local plane wave assumption includes: near the Earth's surface, the seismic wave field is considered to be composed of multiple superimposed local plane waves, each plane wave propagating perpendicularly to the wavefront. Specifically, determining the surface vertical component based on the local plane wave assumption and the seismic wave field at the surface includes: determining the surface vertical component in the spatial-frequency domain based on the seismic wave field at the surface; and determining the velocity vertical component in the spatial-frequency domain based on the surface vertical component. The velocity vertical component in the spatial-frequency domain is then subjected to an inverse Fourier transform to obtain the velocity vertical component in the spatial-time domain, and this spatial-time velocity vertical component is used as the initial value for reverse-time migration imaging.

[0007] In some embodiments, determining the surface vertical component in the space-frequency domain based on the seismic wave field at the surface includes: performing a Fourier transform on the seismic wave field at the surface to obtain the target surface seismic wave field in the space-frequency domain; and calculating the vertical partial derivative of the target surface seismic wave field to obtain the surface vertical component in the space-frequency domain.

[0008] The corresponding relationship is as follows:

[0009]

[0010] Where d(x,0,t) represents the seismic wave field at the Earth's surface; x represents the horizontal coordinate; z represents the vertical coordinate; t represents time; FT represents Fourier transform; ω represents the angular frequency, which is obtained by Fourier transforming the time dimension; Represents the target surface seismic wave field in the space-frequency domain; j 2 =-1, j is the imaginary part of the complex number; k represents the wave vector, k = ω / c, c is the longitudinal wave velocity of the propagation medium; Represents the vertical component of the Earth's surface in the space-frequency domain.

[0011] In some embodiments, the above-mentioned vertical velocity component satisfies the following expression:

[0012]

[0013] in, Represents the vertical component of the Earth's surface in the space-frequency domain; The vertical component of velocity in the space-frequency domain is represented by: x; z; ω; ω (the angular frequency), obtained by Fourier transform of the time dimension; and j. 2 =-1, where j is the imaginary part of the complex number; ρ represents the density of the propagation medium.

[0014] In some embodiments, the initial value determination method further includes: preprocessing the seismic wavefield at the surface. The preprocessing includes: performing local time window segmentation based on the wavefield d(x,0,t), spatial sampling interval Δx, and temporal sampling interval Δt recorded by the surface geophone, ensuring that the wavefield within each time window satisfies the local plane wave assumption; wherein, the vertical velocity component is determined based on the preprocessed seismic wavefield at the surface.

[0015] Secondly, embodiments of this disclosure provide a method for reverse time migration imaging. The method includes: determining initial values ​​for the reverse time migration imaging, the initial values ​​including a vertical velocity component; the vertical velocity component being obtained using the initial value determination method for reverse time migration imaging provided in the first aspect embodiment; based on the initial values, performing wavefield extrapolation along the time dimension to obtain an extrapolated target depth-corresponding wavefield; and performing imaging processing based on the target depth-corresponding wavefield to obtain a reverse time migration imaging result.

[0016] In some embodiments, the initial value further includes a velocity transverse component; the velocity transverse component takes a value of 0 when time t exceeds the maximum recording time. Based on the initial value, wavefield extrapolation is performed along the time dimension to obtain the extrapolated target depth-corresponding wavefield, including: based on the initial value, forward extrapolation of the shot point wavefield along the time-increasing direction until the maximum recording time is reached to obtain the source wavefield; based on the initial value, reverse extrapolation of the receiver point wavefield along the time-decreasing direction until the minimum time is reached to obtain the received wavefield. Imaging processing is performed based on the target depth-corresponding wavefield to obtain the reverse-time migration imaging result, including: based on the source wavefield obtained by forward extrapolation and the received wavefield obtained by reverse extrapolation, wavefield imaging is performed at each time point based on cross-correlation imaging conditions to obtain the reverse-time migration imaging result.

[0017] Thirdly, embodiments of this disclosure provide an initial value determination device for reverse time migration imaging. The initial value determination device includes: a geophone data acquisition module, a surface wavefield extraction module, and a velocity vertical component initial value determination module. The geophone data acquisition module is used to acquire geophone wavefield data. The surface wavefield extraction module is used to extract the seismic wavefield at the surface based on the geophone wavefield data. The velocity vertical component initial value determination module is used to determine the vertical velocity component based on the seismic wavefield at the surface, according to the local plane wave assumption; wherein the vertical velocity component is used to generate the initial values ​​for reverse time migration imaging.

[0018] Fourthly, embodiments of this disclosure provide an apparatus for reverse-time migration imaging. The apparatus includes: an initial value determination module, a wavefield extrapolation module, and an imaging processing module. The initial value determination module determines initial values ​​for the reverse-time migration imaging, the initial values ​​including a vertical velocity component; the vertical velocity component is obtained based on the initial value determination method for reverse-time migration imaging provided in the first aspect embodiment or using the initial value determination apparatus for reverse-time migration imaging provided in the third aspect embodiment; the wavefield extrapolation module performs wavefield extrapolation along the time dimension based on the initial values ​​to obtain the extrapolated target depth-corresponding wavefield. The imaging processing module performs imaging processing based on the target depth-corresponding wavefield to obtain the reverse-time migration imaging result.

[0019] Fifthly, embodiments of this disclosure provide an electronic device. The electronic device includes a processor, a communication interface, a memory, and a communication bus, wherein the processor, communication interface, and memory communicate with each other via the communication bus; the memory stores computer programs; and the processor, when executing the program stored in the memory, implements the initial value determination method or the reverse time-shift imaging method described above.

[0020] Sixthly, embodiments of this disclosure provide a computer-readable storage medium. The computer-readable storage medium stores a computer program, which, when executed by a processor, implements the initial value determination method or the method for reverse time-shift imaging as described above.

[0021] The technical solutions provided by some embodiments of this disclosure have at least some or all of the following advantages:

[0022] In the aforementioned method for determining the initial value of reverse-time migration imaging, the seismic wavefield at the Earth's surface is extracted based on the detector wavefield data. Based on the local plane wave assumption, the vertical velocity component is determined from the seismic wavefield at the surface. This vertical velocity component is used to generate the initial value for reverse-time migration imaging. The obtained vertical velocity component is relatively accurate and does not require additional data acquisition equipment or manpower. Compared to assuming the initial value of the vertical velocity component is zero, reverse-time migration imaging based on this initial value provides a more accurate structural imaging location, overcoming the limitations of traditional methods that assume v. z Despite the limitations of 0, it particularly improves the imaging clarity of steeply dipping structures (such as the flanks of salt domes and faults); overall, it has the advantages of reducing data acquisition costs and improving imaging accuracy.

[0023] The technical solutions provided by some embodiments of this disclosure have at least some or all of the following advantages:

[0024] The imaging results obtained based on the above-described reverse time migration imaging method show that the calculated reflectance coefficient curve and the theoretical reflectance coefficient curve match very well within the effective imaging area, with the relative error near zero. Even at the abrupt change point of the reflectance coefficient, the relative error does not exceed 20%, indicating that the method provided in this disclosure has good amplitude preservation. Moreover, through experimental comparison, the average relative error between the calculated reflectance coefficient and the theoretical reflectance coefficient curve in the imaging results obtained by the method provided in this disclosure is 0.0286, while the average relative error between the calculated reflectance coefficient and the theoretical reflectance coefficient curve of the conventional reverse time migration method is 0.0338. The relative error corresponding to the method provided in this disclosure is smaller, indicating that the method provided in this disclosure is superior to the conventional reverse time migration method in terms of amplitude preservation. Attached Figure Description

[0025] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure.

[0026] To more clearly illustrate the technical solutions in the embodiments of this disclosure or the prior art, the accompanying drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, those skilled in the art can obtain other drawings based on these drawings without creative effort.

[0027] Figure 1 A flowchart illustrating an initial value determination method for reverse time-shift imaging according to an embodiment of the present disclosure is shown schematically.

[0028] Figure 2 A detailed implementation flowchart of step S130 according to an embodiment of the present disclosure is shown schematically.

[0029] Figure 3 A flowchart illustrating a method for reverse time-shift imaging according to an embodiment of the present disclosure is shown schematically.

[0030] Figure 4 The diagram schematically illustrates the experimental results of the reverse time migration imaging method when the initial value of the vertical velocity component is assumed to be zero in the conventional approach. (a) is the velocity model of the horizontal unconformity interface, (b) is the migration profile of the conventional reverse time migration method, (c) is the comparison between the reflection coefficient extracted and calculated from the migration profile of the conventional reverse time migration method and the theoretical reflection coefficient, and (d) is the relative error between the reflection coefficient and the theoretical reflection.

[0031] Figure 5The diagram schematically illustrates experimental results of the reverse time migration imaging method provided by the embodiments of the present disclosure, wherein (a) is a horizontal unconformity interface velocity model, (b) is a migration profile obtained by applying the reverse time migration imaging method of the embodiments of the present disclosure, (c) is a comparison between the reflection coefficient extracted and calculated from the migration profile obtained by applying the reverse time migration imaging method of the embodiments of the present disclosure and the theoretical reflection coefficient, and (d) is the relative error between the reflection coefficient and the theoretical reflection.

[0032] Figure 6 A schematic block diagram of an initial value determination apparatus for reverse time-shift imaging according to an embodiment of the present disclosure is shown.

[0033] Figure 7 A structural block diagram of an apparatus for reverse time-shift imaging according to an embodiment of the present disclosure is shown schematically.

[0034] Figure 8 A schematic block diagram of an electronic device provided in an embodiment of the present disclosure is shown. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. Based on the embodiments of this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0036] During the research and development process, it was discovered that initial conditions have a significant impact on the calculation results when solving partial differential equations. In some related technologies, when making initial assumptions for the initial values ​​of reverse time migration imaging, the initial value of the vertical velocity component is assumed to be zero, which introduces a large error into the wavefield calculation. In other schemes, the vertical velocity component is calculated from two layers of seismic wavefields acquired by a land-based dual-detector acquisition system. This land-based dual-detector acquisition system requires burying two layers of detectors at different depths. For actual seismic exploration, simultaneously recording two layers of wavefields means a significant increase in hardware and manpower investment. Moreover, the construction difficulty is greatly increased, and under certain surface conditions, it is even impossible to deploy two layers of detectors. This has the disadvantages of being difficult to deploy and consuming a lot of hardware and manpower.

[0037] In view of this, embodiments of the present disclosure provide an initial value determination method and a method for reverse time migration imaging. The method involves extracting the seismic wavefield at the Earth's surface from detector wavefield data; determining the vertical velocity component based on the local plane wave assumption and the aforementioned seismic wavefield at the Earth's surface; wherein the aforementioned vertical velocity component is used to generate the initial value for reverse time migration imaging. The obtained vertical velocity component is more accurate and does not require additional data acquisition equipment or manpower costs. Compared to assuming the initial value of the vertical velocity component is zero, reverse time migration imaging based on this initial value provides a more accurate structural imaging location. Regarding amplitude preservation, the reverse time migration imaging method provided by the embodiments of the present disclosure is superior to conventional reverse time migration methods.

[0038] The first exemplary embodiment of this disclosure provides a method for determining initial values ​​for reverse time migration imaging. In some exemplary application scenarios, the above-described initial value determination method can be applied to surface exploration or marine exploration.

[0039] Figure 1 A flowchart illustrating an initial value determination method for reverse time-shift imaging according to an embodiment of the present disclosure is shown schematically.

[0040] Reference Figure 1 As shown, the method for determining the initial value of reverse time-shifted imaging provided in this embodiment includes the following steps: S110, S120 and S130.

[0041] In step S110, the detector wave field data is acquired.

[0042] In step S120, the seismic wave field at the ground surface is extracted based on the above-mentioned detector wave field data.

[0043] The seismic wavefield at the Earth's surface is obtained by extracting the seismic wavefield corresponding to the vertical coordinate z = 0 from the geophone wavefield data. For example, d(x,0,t) can be used to represent the seismic wavefield at the Earth's surface extracted from the geophone data record, where x represents the horizontal coordinate, z represents the vertical coordinate, and t represents time.

[0044] In step S130, based on the local plane wave assumption, the vertical velocity component is determined according to the seismic wave field at the surface; wherein the vertical velocity component is used to generate the initial value for the reverse time migration imaging.

[0045] In some embodiments, the above local plane wave assumption includes: near the Earth's surface, the seismic wave field is considered to be composed of multiple superimposed local plane waves, each plane wave propagating in a direction perpendicular to the wavefront.

[0046] Figure 2 A detailed implementation flowchart of step S130 according to an embodiment of the present disclosure is shown schematically.

[0047] Reference Figure 2 As shown, in step S130 above, based on the local plane wave assumption, the vertical component of the ground surface is determined according to the seismic wave field at the ground surface, including the following steps: S210 and S220.

[0048] In step S210, the vertical component of the Earth's surface in the spatial-frequency domain is determined based on the seismic wave field at the Earth's surface described above.

[0049] In some embodiments, in step S210 above, determining the surface vertical component in the spatial-frequency domain based on the seismic wavefield at the surface includes:

[0050] Fourier transform is performed on the seismic wave field at the above-mentioned surface to obtain the target surface seismic wave field in the space-frequency domain.

[0051] Vertical partial derivatives of the seismic wavefield at the target surface are calculated to obtain the vertical surface component in the space-frequency domain.

[0052] The correspondence between the vertical components of the Earth's surface in the spatial-frequency domain is determined as follows:

[0053]

[0054] Where d(x,0,t) represents the seismic wave field at the Earth's surface; x represents the horizontal coordinate; z represents the vertical coordinate; t represents time; FT represents Fourier transform; ω represents the angular frequency, which is obtained by Fourier transforming the time dimension; Represents the target surface seismic wave field in the space-frequency domain; j 2 =-1, j is the imaginary part of the complex number; k represents the wave vector, k = ω / c, c is the longitudinal wave velocity of the propagation medium; Represents the vertical component of the Earth's surface in the space-frequency domain.

[0055] In step S220, the velocity vertical component in the spatial-frequency domain is determined based on the above-mentioned surface vertical component; wherein, the velocity vertical component in the spatial-frequency domain is subjected to inverse Fourier transform to obtain the velocity vertical component in the spatial-time domain, and the velocity vertical component in the spatial-time domain is used as the initial value for reverse time migration imaging.

[0056] In some embodiments, the above-mentioned vertical velocity component satisfies the following expression:

[0057]

[0058] in, Represents the vertical component of the Earth's surface in the space-frequency domain; The vertical component of velocity in the space-frequency domain is represented by: x; z; ω; ω (the angular frequency), obtained by Fourier transform of the time dimension; and j. 2 =-1, where j is the imaginary part of the complex number; ρ represents the density of the propagation medium.

[0059] In some embodiments, the initial value determination method further includes: preprocessing the seismic wavefield at the surface. The preprocessing includes: performing local time window segmentation based on the wavefield d(x,0,t), spatial sampling interval Δx, and temporal sampling interval Δt recorded by the surface geophone, ensuring that the wavefield within each time window satisfies the local plane wave assumption; wherein, the vertical velocity component is determined based on the preprocessed seismic wavefield at the surface.

[0060] In the initial value determination method for reverse time migration imaging provided in this embodiment, the seismic wave field at the ground surface is extracted based on the detector wavefield data; based on the local plane wave assumption, the vertical velocity component is determined based on the aforementioned seismic wave field at the ground surface; wherein, the aforementioned vertical velocity component is used to generate the initial value for reverse time migration imaging. The obtained vertical velocity component is relatively accurate and does not require additional data acquisition equipment or manpower costs. Compared to assuming the initial value of the vertical velocity component is zero, reverse time migration imaging based on this initial value has a more accurate structural imaging location, breaking through the traditional method's assumption of v z Despite the limitations of 0, it particularly improves the imaging clarity of steeply dipping structures (such as the flanks of salt domes and faults); overall, it has the advantages of reducing data acquisition costs and improving imaging accuracy.

[0061] A second exemplary embodiment of this disclosure provides a method for reverse time-shift imaging.

[0062] Figure 3 A flowchart illustrating a method for reverse time-shift imaging according to an embodiment of the present disclosure is shown schematically.

[0063] Reference Figure 3 As shown, the method for reverse time-shift imaging provided in this embodiment includes the following steps: S310, S320 and S330.

[0064] In step S310, the initial values ​​of the reverse time migration imaging are determined. The initial values ​​include the vertical velocity component. The vertical velocity component is obtained using the above-described method for determining the initial values ​​of the reverse time migration imaging.

[0065] In step S320, based on the above initial values, the wave field is extended along the time dimension to obtain the extended wave field corresponding to the target depth.

[0066] In step S320, the wave field is extended along the time dimension to obtain the wave field corresponding to the target depth after extension.

[0067] In some embodiments, the initial value further includes a velocity lateral component; the velocity lateral component takes a value of 0 when time t exceeds the maximum recording time.

[0068] In step S320 above, based on the initial values, wavefield extrapolation is performed along the time dimension to obtain the extrapolated wavefield corresponding to the target depth, including:

[0069] Based on the above initial values, the wavefield at the shot point is forward extended along the time-increasing direction until the maximum recording time is reached to obtain the source wavefield; in some embodiments, the wavefield snapshots corresponding to each time moment are stored; the forward extension uses the high-order finite difference method to solve the acoustic wave equation and adopts the perfectly matched layer (PML) absorbing boundary condition.

[0070] Based on the above initial values, the wavefield at the detector point is extended in the reverse direction along the decreasing time until the minimum time value is reached, thus obtaining the received wavefield.

[0071] In step S330, imaging processing is performed based on the wavefield corresponding to the target depth to obtain the reverse time migration imaging result.

[0072] The above step S330 specifically includes: based on the source wave field obtained by forward continuation and the received wave field obtained by reverse continuation, wave field imaging is performed at each time point based on cross-correlation imaging conditions to obtain the reverse time migration imaging result.

[0073] The relationship between wavefield extension and reverse time migration is as follows:

[0074]

[0075] Where P(x,z=0,t) represents the seismic wave field at the Earth's surface in the space-time domain; v z (x, z = 0, t) represents the vertical velocity component in the space-time domain, which is derived from the vertical velocity component in the space-frequency domain. The result obtained after inverse Fourier transform (IFT) processing; v x Represents the lateral component of velocity; v x (x,z,t≥t max ) = 0 indicates that the lateral component of velocity exceeds the maximum recording time t at time t. max In this case, the corresponding value is 0; This represents the partial derivative of the seismic wave field P with respect to time t; Represents the lateral component of velocity v x The partial derivative with respect to the horizontal coordinate x; Represents the vertical component of velocity v z The partial derivative with respect to the vertical coordinate z; Represents the lateral component of velocity vx Partial derivative with respect to time t; This represents the partial derivative of the seismic wave field P with respect to the horizontal coordinate x; This represents the partial derivative of the vertical component of velocity with respect to time t; ρ represents the partial derivative of the seismic wave field P with respect to the vertical coordinate z; ρ represents the density of the propagation medium.

[0076] Figure 4 The diagram schematically illustrates the experimental results of the reverse time migration imaging method when the initial value of the vertical velocity component is assumed to be zero in the conventional approach. (a) is the velocity model of the horizontal unconformity interface, (b) is the migration profile of the conventional reverse time migration method, (c) is the comparison between the reflection coefficient extracted and calculated from the migration profile of the conventional reverse time migration method and the theoretical reflection coefficient, and (d) is the relative error between the reflection coefficient and the theoretical reflection.

[0077] Figure 5 The diagram illustrates experimental results of a method for reverse time migration imaging based on embodiments of the present disclosure, wherein (a) is a horizontal unconformity interface velocity model, (b) is a migration profile obtained by applying the reverse time migration imaging method of the present disclosure, (c) is a comparison between the reflection coefficient extracted and calculated from the migration profile obtained by applying the reverse time migration imaging method of the present disclosure and the theoretical reflection coefficient, and (d) is the relative error between the reflection coefficient and the theoretical reflection.

[0078] Reference Figure 4 (a) and Figure 5 As shown in Figure (a), for the same level of unconformity interface model, data experiments were conducted using the reverse time migration imaging method based on the conventional method assuming the initial value of the vertical velocity component is zero, and the reverse time migration imaging method based on the embodiment of this disclosure. In this model, the number of grid points nz (representing the number of grid points along the z-direction) = 200, nx (representing the number of grid points along the x-direction) = 480; the grid spacing dx = dz = 5m. In the forward modeling calculation, the dominant frequency of the Ricker wavelet is 30Hz.

[0079] contrast Figure 4 (b) and Figure 5 As shown in the imaging profile in (b), the reverse time migration imaging method provided in this embodiment constructs the imaging position more accurately. Compared to assuming the initial value of the vertical velocity component is zero, the reverse time migration imaging method based on determining the initial value of the vertical velocity component provided in this disclosure has a more accurate constructed imaging position, breaking through the traditional method's assumption of v z The limitation of 0 is particularly improved in terms of imaging clarity for steeply dipping structures (such as the flanks of salt domes and faults).

[0080] Reference Figure 5As can be seen from (c) and (d), the calculated reflectance coefficient curve of the reverse time migration imaging method provided in this embodiment of the present disclosure matches the theoretical reflectance coefficient curve very well in the effective imaging area, and the relative error is near zero. Even at the point of abrupt change in the reflectance coefficient, the relative error does not exceed 20%. This shows that the reverse time migration imaging method provided in this embodiment of the present disclosure has good amplitude preservation.

[0081] contrast Figure 4 (c), (d) and Figure 5 As can be seen from (c) and (d), the method of this embodiment of the present disclosure achieves a better match between the calculated reflectance coefficient curve and the theoretical reflectance coefficient curve compared to the conventional method. Within the range of x = 300m to 2100m, the average relative error between the calculated reflectance coefficient and the theoretical reflectance coefficient curve obtained by the method of this embodiment of the present disclosure is 0.0286, while the average relative error between the calculated reflectance coefficient and the theoretical reflectance coefficient curve obtained by the conventional method is 0.0338. The smaller relative error of the method of this embodiment of the present disclosure indicates that, in terms of amplitude preservation, the reverse time migration imaging method provided by this embodiment of the present disclosure is superior to the conventional reverse time migration imaging method.

[0082] In summary, the imaging results obtained based on the reverse time migration imaging method provided in this embodiment show that the calculated reflectance coefficient curve and the theoretical reflectance coefficient curve match very well within the effective imaging area, with the relative error near zero. Even at the abrupt change point of the reflectance coefficient, the relative error does not exceed 20%, indicating that the method provided in this embodiment has good amplitude preservation. Moreover, experimental comparison shows that the method provided in this embodiment is superior to the conventional reverse time migration method in terms of amplitude preservation.

[0083] A third exemplary embodiment of this disclosure provides an initial value determination apparatus for reverse time-shift imaging.

[0084] Figure 6 A schematic block diagram of an initial value determination apparatus for reverse time-shift imaging according to an embodiment of the present disclosure is shown.

[0085] Reference Figure 6 As shown, the initial value determination device 600 for reverse time migration imaging provided in this embodiment includes: a detector data acquisition module 610, a surface wavefield extraction module 620, and an initial value determination module 630 for the vertical velocity component.

[0086] The detector data acquisition module 610 described above is used to acquire detector wavefield data.

[0087] The aforementioned surface wavefield extraction module 620 is used to extract the seismic wavefield at the surface based on the aforementioned detector wavefield data.

[0088] The aforementioned velocity vertical component initial value determination module 630 is used to determine the velocity vertical component based on the local plane wave assumption and the seismic wave field at the surface; wherein, the aforementioned velocity vertical component is used to generate the initial value for reverse time migration imaging.

[0089] In some embodiments, the initial value determination device 600 further includes a preprocessing module.

[0090] The aforementioned preprocessing module is used to preprocess the seismic wavefield at the surface. The preprocessing includes: performing local time window segmentation based on the wavefield d(x,0,t), spatial sampling interval Δx, and temporal sampling interval Δt recorded by the surface geophone, ensuring that the wavefield within each time window satisfies the local plane wave assumption; wherein, the aforementioned vertical velocity component is determined based on the preprocessed seismic wavefield at the surface.

[0091] In some embodiments, the aforementioned local plane wave assumption includes: near the Earth's surface, the seismic wave field is considered to be composed of multiple superimposed local plane waves, each plane wave propagating perpendicularly to the wavefront. Specifically, determining the surface vertical component based on the local plane wave assumption and the seismic wave field at the surface includes: determining the surface vertical component in the spatial-frequency domain based on the seismic wave field at the surface; and determining the velocity vertical component in the spatial-frequency domain based on the surface vertical component. The velocity vertical component in the spatial-frequency domain is then subjected to an inverse Fourier transform to obtain the velocity vertical component in the spatial-time domain, and this spatial-time velocity vertical component is used as the initial value for reverse-time migration imaging.

[0092] In some embodiments, determining the surface vertical component in the space-frequency domain based on the seismic wave field at the surface includes: performing a Fourier transform on the seismic wave field at the surface to obtain the target surface seismic wave field in the space-frequency domain; and calculating the vertical partial derivative of the target surface seismic wave field to obtain the surface vertical component in the space-frequency domain.

[0093] More details and beneficial effects of this embodiment can be found in the relevant description of the first embodiment, which will not be repeated here.

[0094] A fourth exemplary embodiment of this disclosure provides an apparatus for reverse time-shift imaging.

[0095] Figure 7 A structural block diagram of an apparatus for reverse time-shift imaging according to an embodiment of the present disclosure is shown schematically.

[0096] Reference Figure 7 As shown, the reverse time-shift imaging apparatus 700 provided in this embodiment includes: an initial value determination module 710, a wavefield extension module 720, and an imaging processing module 730.

[0097] The initial value determination module 710 is used to determine the initial value of the reverse time migration imaging. The initial value includes a vertical velocity component. The vertical velocity component is obtained based on the initial value determination method of the reverse time migration imaging provided in the first embodiment or by using the initial value determination device of the reverse time migration imaging provided in the third embodiment.

[0098] The wave field extension module 720 is used to perform wave field extension along the time dimension based on the above initial values ​​to obtain the wave field corresponding to the target depth after extension.

[0099] The imaging processing module 730 is used to perform imaging processing based on the wavefield corresponding to the target depth to obtain the reverse time migration imaging result.

[0100] In some embodiments, the initial value further includes a velocity transverse component; the velocity transverse component takes a value of 0 when time t exceeds the maximum recording time. Based on the initial value, wavefield extrapolation is performed along the time dimension to obtain the extrapolated target depth-corresponding wavefield, including: based on the initial value, forward extrapolation of the shot point wavefield along the time-increasing direction until the maximum recording time is reached to obtain the source wavefield; based on the initial value, reverse extrapolation of the receiver point wavefield along the time-decreasing direction until the minimum time is reached to obtain the received wavefield. Imaging processing is performed based on the target depth-corresponding wavefield to obtain the reverse-time migration imaging result, including: based on the source wavefield obtained by forward extrapolation and the received wavefield obtained by reverse extrapolation, wavefield imaging is performed at each time point based on cross-correlation imaging conditions to obtain the reverse-time migration imaging result.

[0101] Any plurality of the functional modules included in the aforementioned device 600 or device 700 may be combined into one module, or any one of these modules may be split into multiple modules. Alternatively, at least a portion of the functionality of one or more of these modules may be combined with at least a portion of the functionality of other modules and implemented in one module. At least one of the functional modules included in the aforementioned device 600 or device 700 may be at least partially implemented as hardware circuitry, such as a Field Programmable Gate Array (FPGA), a Programmable Logic Array (PLA), a System-on-Chip, a System-on-Substrate, a System-on-Package, an Application-Specific Integrated Circuit (ASIC), or any other reasonable means of integrating or packaging circuitry, or implemented in hardware or firmware, or in any one of software, hardware, and firmware implementations, or in a suitable combination of any of these. Alternatively, at least one of the functional modules included in the aforementioned device 600 or device 700 may be at least partially implemented as a computer program module, which, when run, can perform corresponding functions.

[0102] The fifth exemplary embodiment of this disclosure provides an electronic device.

[0103] Figure 8 A schematic block diagram of an electronic device provided in an embodiment of the present disclosure is shown.

[0104] Reference Figure 8 As shown, the electronic device 800 provided in this embodiment includes a processor 801, a communication interface 802, a memory 803, and a communication bus 804. The processor 801, the communication interface 802, and the memory 803 communicate with each other through the communication bus 804. The memory 803 is used to store computer programs. When the processor 801 executes the program stored in the memory, it implements the initial value determination method or the reverse time-shift imaging method described above.

[0105] A sixth exemplary embodiment of this disclosure also provides a computer-readable storage medium. The computer-readable storage medium stores a computer program that, when executed by a processor, implements the initial value determination method or the method for reverse time-shift imaging as described above.

[0106] The computer-readable storage medium may be included in the device or apparatus described in the above embodiments; or it may exist independently and not assembled into the device or apparatus. The computer-readable storage medium carries one or more programs that, when executed, implement the method according to the embodiments of this disclosure.

[0107] According to embodiments of this disclosure, the computer-readable storage medium can be a non-volatile computer-readable storage medium, such as including, but not limited to: portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), portable compact disk read-only memory (CD-ROM), optical storage devices, magnetic storage devices, or any suitable combination thereof. In this disclosure, the computer-readable storage medium can be any tangible medium that contains or stores a program that can be used by or in conjunction with an instruction execution system, apparatus, or device.

[0108] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0109] The above description is merely a specific embodiment of this disclosure, enabling those skilled in the art to understand or implement it. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this disclosure. Therefore, this disclosure is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for determining initial values ​​in reverse time migration imaging, characterized in that, include: Acquire detector wavefield data; Seismic wavefield at the Earth's surface is extracted based on the detector wavefield data. Based on the local plane wave assumption, the vertical velocity component is determined according to the seismic wave field at the Earth's surface; wherein, the vertical velocity component is used to generate the initial values ​​for reverse time migration imaging.

2. The initial value determination method according to claim 1, characterized in that, The local plane wave assumption includes: near the Earth's surface, the seismic wave field is considered to be composed of multiple superimposed local plane waves, and the propagation direction of each plane wave is perpendicular to the wavefront; Among them, based on the local plane wave assumption, the vertical component of the Earth's surface is determined according to the seismic wave field at the surface, including: Based on the seismic wave field at the Earth's surface, determine the vertical component of the Earth's surface in the spatial-frequency domain; Based on the surface vertical component, determine the velocity vertical component in the spatial-frequency domain; Specifically, the vertical velocity component in the space-frequency domain is transformed by inverse Fourier transform to obtain the vertical velocity component in the space-time domain, and the vertical velocity component in the space-time domain is used as the initial value for reverse time migration imaging.

3. The initial value determination method according to claim 2, characterized in that, Based on the seismic wavefield at the Earth's surface, determine the vertical component of the Earth's surface in the spatial-frequency domain, including: A Fourier transform is performed on the seismic wave field at the surface to obtain the target surface seismic wave field in the space-frequency domain. The vertical partial derivatives of the target surface seismic wavefield are calculated to obtain the surface vertical component in the space-frequency domain. The corresponding relationship is as follows: Where d(x,0,t) represents the seismic wave field at the Earth's surface; x represents the horizontal coordinate; z represents the vertical coordinate; t represents time; FT represents Fourier transform; ω represents the angular frequency, which is obtained by Fourier transforming the time dimension; Represents the target surface seismic wave field in the space-frequency domain; j 2 =-1, j is the imaginary part of the complex number; k represents the wave vector, k = ω / c, c is the longitudinal wave velocity of the propagation medium; Represents the vertical component of the Earth's surface in the space-frequency domain.

4. The initial value determination method according to any one of claims 1-3, characterized in that, The vertical component of the velocity satisfies the following expression: in, Represents the vertical component of the Earth's surface in the space-frequency domain; The vertical component of velocity in the space-frequency domain is represented by: x; z; ω; ω (the angular frequency), obtained by Fourier transform of the time dimension; and j. 2 =-1, where j is the imaginary part of the complex number; ρ represents the density of the propagation medium.

5. The initial value determination method according to claim 1, characterized in that, Also includes: The seismic wavefield at the surface is preprocessed, which includes: performing local time window segmentation based on the wavefield d(x,0,t), spatial sampling interval Δx, and temporal sampling interval Δt recorded by the surface geophone, to ensure that the wavefield in each time window satisfies the local plane wave assumption; Specifically, the vertical velocity component is determined based on the preprocessed seismic wave field at the Earth's surface.

6. A method for reverse time-shift imaging, characterized in that, include: Determine the initial values ​​for the reverse time migration imaging, the initial values ​​including: a vertical velocity component; the vertical velocity component is obtained based on the method of any one of claims 1-5; Based on the initial value, the wave field is extended along the time dimension to obtain the extended wave field corresponding to the target depth. Imaging processing is performed based on the wavefield corresponding to the target depth to obtain the reverse time migration imaging result.

7. The method according to claim 6, characterized in that, The initial value also includes: a velocity lateral component; the velocity lateral component takes a value of 0 when time t exceeds the maximum recording time; Based on the initial values, wavefield extrapolation is performed along the time dimension to obtain the extrapolated wavefield corresponding to the target depth, including: Based on the initial value, the shot point wavefield is extended in the direction of increasing time until the maximum recording time is reached to obtain the source wavefield. Based on the initial value, the detector wavefield is extended backward along the time decreasing direction until the minimum time value is reached to obtain the received wavefield. The imaging process, based on the wavefield corresponding to the target depth, yields a reverse-time migration imaging result, including: Based on the source wavefield obtained by forward continuation and the received wavefield obtained by reverse continuation, wavefield imaging is performed at each time point based on cross-correlation imaging conditions to obtain the reverse time migration imaging results.

8. An initial value determination device for reverse time-shift imaging, characterized in that, include: The detector data acquisition module is used to acquire detector wavefield data; The surface wavefield extraction module is used to extract the seismic wavefield at the surface based on the detector wavefield data. The initial value determination module for the vertical velocity component is used to determine the vertical velocity component based on the local plane wave assumption and the seismic wave field at the Earth's surface; wherein the vertical velocity component is used to generate the initial value for the reverse time migration imaging.

9. A device for reverse time-shift imaging, characterized in that, include: An initial value determination module is used to determine the initial values ​​for reverse time migration imaging, the initial values ​​including: a vertical velocity component; the vertical velocity component is obtained based on the method of any one of claims 1-5 or using the apparatus of claim 8; The wave field extension module is used to perform wave field extension along the time dimension based on the initial value to obtain the extended wave field corresponding to the target depth. The imaging processing module is used to perform imaging processing based on the wavefield corresponding to the target depth to obtain the reverse time migration imaging result.

10. An electronic device, characterized in that, It includes a processor, a communication interface, a memory, and a communication bus, wherein the processor, the communication interface, and the memory communicate with each other through the communication bus; Memory, used to store computer programs; A processor, when executing a program stored in memory, implements the method of any one of claims 1-7.

11. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the method of any one of claims 1-7.

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