CN112904426B - Decoupling elastic wave reverse time migration method, system and application - Google Patents
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Abstract
The invention belongs to the technical field of exploration seismology data processing, and discloses a decoupling elastic wave reverse time migration method, a system and application, wherein an input seismic record, seismic wavelets, a density model and a velocity model are obtained; obtaining a seismic source and wave detection point continuation wave field by solving an elastic medium wave equation; elastic wave field separation is carried out by using vector Helmholtz decomposition, and separated amplitude-preserving pure longitudinal wave and transverse wave vector wave fields are obtained; calculating imaging conditions by using an elastic wave impedance sensitive kernel function to obtain high signal-to-noise ratio and high precision longitudinal wave-longitudinal wave (PP) and longitudinal wave-transverse wave (PS) imaging results; and superposing all shot integrated image results to obtain a final offset imaging section. The invention can obtain the separation result of pure longitudinal wave and pure transverse wave vector wave fields with true amplitude, improve the fidelity of imaging amplitude, automatically avoid low-frequency noise generated by cross-correlation of double-pass wave fields, improve the signal-to-noise ratio and resolution of imaging, and assist in high-precision longitudinal and transverse wave combined seismic interpretation.
Description
Technical Field
The invention belongs to the technical field of exploration seismology data processing, and particularly relates to a decoupling elastic wave reverse time migration method, a system and application.
Background
At present, in the processing of multi-wave multi-component exploration seismic data, elastic wave reverse time migration is a migration method with the highest imaging precision at present. However, because the double-pass wave information is used for wave field extension, strong low-frequency noise and migration false images are often generated in complex areas such as salt domes, fault blocks, retrograde faults and the like, the spatial resolution and the imaging signal-to-noise ratio of migration results are reduced, and the accuracy of subsequent seismic interpretation is seriously influenced. In addition, the traditional elastic wave imaging method does not usually adopt longitudinal and transverse wave field separation, and the extended transverse and vertical wave field components are directly used for cross-correlation imaging, so that the physical meaning of an imaging result is not clear, and serious longitudinal and transverse wave crosstalk noise is easily caused.
Through the above analysis, the problems and defects of the prior art are as follows:
(1) in the conventional multiwave multicomponent elastic wave reverse-time migration method, because the wave field continuation is carried out by solving a two-way wave equation, strong low-frequency noise and migration false images are often generated in complex areas such as salt domes, fault blocks, reverse-impact faults and the like, the imaging resolution and the signal-to-noise ratio are reduced, and the precision of subsequent seismic interpretation is seriously influenced.
(2) The traditional elastic wave imaging method does not usually carry out longitudinal and transverse wave field separation, and directly uses the extended transverse and vertical elastic wave field components to carry out cross-correlation imaging, so that the physical meaning of an imaging result is not clear, and serious longitudinal and transverse wave crosstalk noise is easily caused.
The difficulty in solving the above problems and defects is:
(1) for low-frequency noise occurring in elastic wave reverse time migration, a conventional processing mode is to firstly use elastic wave reverse time migration to obtain an imaging result with low-frequency noise, and then use a post-stack laplacian high-pass filter to filter the low-frequency noise, and the processing flow easily causes phase distortion of the filtered imaging result and inaccurate imaging amplitude. And imaging processing methods to remove these low frequency noise are less studied directly in wavefield continuation and application imaging conditions.
(2) In order to reduce the cross-wave noise in elastic wave imaging, the extended wave fields of the seismic source and the wave detection point need to be subjected to longitudinal and transverse wave separation before the imaging conditions are applied, and although pure longitudinal wave and pure transverse wave fields can be extracted by using simple Helmholtz decomposition, the phase and amplitude of the separated wave fields are inconsistent with those of the original wave fields, so that the final imaging amplitude is inaccurate.
The significance of solving the problems and the defects is as follows:
(1) the invention aims at the problem of elastic wave reverse time migration low-frequency noise, a brand-new impedance sensitive kernel function is constructed through linear combination of wave fields of a seismic source and a wave detection point, and the sensitive kernel function is used for calculating a zero-delay cross-correlation imaging condition so as to achieve the effect of directly removing the low-frequency noise in the imaging process.
(2) In addition, the invention provides a novel true amplitude vector wave Helmholtz wave field decomposition method, compared with the conventional simple scalar Helmholtz decomposition, the method firstly obtains an auxiliary wave field by solving a Poisson equation, and then obtains separated true amplitude vector pure longitudinal wave and pure transverse wave fields by applying divergence and rotation operations to the auxiliary wave field twice.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a decoupling elastic wave reverse time migration theoretical method, a processing algorithm and a technical process, in particular relates to a decoupling elastic wave reverse time migration theoretical method, an efficient algorithm and a processing process based on vector Helmholtz decomposition and impedance sensitive nuclear imaging conditions, and aims to solve the problems of low-frequency noise and cross wave crosstalk artifact in elastic wave reverse time migration.
The invention is realized in such a way, and provides a decoupling elastic wave reverse time migration method, which comprises the following steps: acquiring input seismic records, seismic wavelets, density and velocity models; obtaining a seismic source and a wave detection point continuation wave field by solving an elastic wave fluctuation equation; performing wave field separation by using vector Helmholtz decomposition to obtain separated pure longitudinal (P) wave and pure transverse (S) wave vector wave fields with true amplitude; calculating imaging conditions by using an elastic wave impedance sensitive kernel function to obtain high-precision PP and PS imaging results; and superposing all shot integrated image results to obtain a final offset imaging section.
Further, the decoupling elastic wave reverse time migration method comprises the following steps:
step one, acquiring input data; wherein the input data comprises: longitudinal wave offset velocity model v p (x) Transverse wave migration velocity model v s (x) Density model rho (x), source function wavelet f (t), and multi-wave multi-component observation data d (x) r T), providing a model and seismic data basis for subsequent wavefield continuation;
step two, according to the input seismic source wavelet f (t), the density model rho (x) and the longitudinal wave velocity model v p (x) And transverse wave velocity model v s (x) By solving for first order velocity-stress elasticityWave equation, calculating extended vector wave field u at one side of seismic source s (x, t) providing a required source wavefield for subsequent wavefield separation and application of imaging conditions;
thirdly, according to the input density model rho (x) and the longitudinal wave velocity model v p (x) Transverse wave velocity model v s (x) And observed data d (x) r T), calculating the extended wave field u of the wave detection point vector by solving the elastic wave equation r (x, t) providing a required demodulator point wavefield for subsequent wavefield separation and application of imaging conditions;
step four, adopting vector Helmholtz decomposition to carry out longitudinal and transverse wave separation on extended seismic source and wave detection point wave fields, and extracting vector pure longitudinal wave and pure transverse wave fields, wherein the innovative processing step can eliminate crosstalk noise of longitudinal waves and transverse waves in an imaging result, improve the imaging quality and enable the imaging result to have clear physical significance;
step five, after the separated seismic source and wave detection point wave fields are obtained, cross-correlation imaging is carried out by using elastic impedance sensitive nuclear imaging conditions to obtain PP and PS imaging results, and the innovative processing step can automatically remove low-frequency noise in the imaging results when the imaging conditions are applied, and improve the signal-to-noise ratio and the resolution of imaging;
and step six, adding the imaging results of all shot gathers to obtain a final offset imaging section, and improving the balance of deep imaging amplitude by using seismic source illumination.
Further, in the second step, the first-order velocity-stress elasticity fluctuation equation is in the form of:
where x is the imaging spatial position, x s For the seismic source location, t is the wavefield travel time, u s ＝[u s,x u s,y u s,z ] T For the seismic source polarization velocity wave field, σ s ＝[σ s,xx σ s,yy σ s,zz σ s,xy σ s,xz σ s,yz ] T As seismic source stress waveThe field, T, is the transposed sign, and δ is the Crohn's function. L is a partial derivative matrix, C (x) is a parameter matrix, having the following expression:
further, in step three, the expression of the elastic wave equation is as follows:
wherein x is r For the position of the detector point, L is a partial derivative matrix, C (x) is a parameter matrix, and the expression is:
further, in step four, the longitudinal and transverse wave separation is performed on the wave fields of the source and the demodulator probe by using vector helmholtz decomposition, and the following expression is provided:
wherein,
in order to perform the gradient operation, the method comprises the following steps,
in order to calculate the divergence, the method comprises the following steps,
in order to calculate the rotation degree,
for the separated longitudinal wave source wavefield,
is the shear wave source wavefield and,
is a longitudinal wave demodulator probe wave field,
is a shear wave demodulator probe wavefield. w is a s And w r To assist the vector wavefield, it can be obtained by solving the following poisson equation:
where Δ is the laplace operator.
Further, in the fifth step, after the separated seismic source and geophone point wave fields are obtained, cross-correlation imaging is performed by using the elastic impedance sensitive nuclear imaging condition to obtain PP and PS imaging results, which have the following expression:
wherein,
in order to be able to obtain a shear modulus,
in order to be the bulk modulus,
i is an identity matrix。
Another object of the present invention is to provide a decoupling elastic wave reverse time migration system using the decoupling elastic wave reverse time migration method, wherein the decoupling elastic wave reverse time migration system includes:
the input data acquisition module is used for acquiring input data; wherein the input data comprises: longitudinal wave offset velocity model v p (x) Transverse wave migration velocity model v s (x) Density model rho (x), source function wavelet f (t), and multi-wave multi-component observation data d (x) r ,t)；
A seismic source vector continuation wave field calculation module for calculating the vector continuation wave field of the seismic source according to the input seismic source wavelets f (t), the density model rho (x) and the longitudinal wave velocity model v p (x) And shear wave velocity model v s (x) Calculating the vector continuation wave field u of the seismic source by solving a first-order velocity-stress elastic wave equation s (x,t)；
A wave detection point vector continuation wave field calculation module for calculating the wave field according to the input density model rho (x) and the longitudinal wave velocity model v p (x) Transverse wave velocity model v s (x) And observed data d (x) r T), calculating the vector continuation wave field u of the detection point by solving the elastic wave equation r (x,t)；
The longitudinal and transverse wave separation module is used for performing longitudinal and transverse wave separation on wave fields of the seismic source and the wave detection point by adopting vector Helmholtz decomposition;
the imaging result acquisition module is used for performing cross-correlation imaging by using elastic impedance sensitive nuclear imaging conditions after acquiring the separated seismic source and wave detection point wave fields to acquire PP and PS imaging results;
and the offset imaging section acquisition module is used for adding the imaging results of all shot gathers to obtain a final offset imaging section and improving the balance of deep imaging amplitude by using the seismic source illumination.
It is a further object of the invention to provide a computer device comprising a memory and a processor, the memory storing a computer program which, when executed by the processor, causes the processor to perform the steps of:
obtaining input seismic records, seismic wavelets, density and velocity models; obtaining a seismic source and a wave detection point continuation wave field by solving an elastic wave fluctuation equation; carrying out wave field separation by using vector Helmholtz decomposition to obtain separated amplitude-preserving pure longitudinal (P) wave and pure transverse (S) wave vector wave fields; calculating imaging conditions by using an elastic wave impedance sensitive kernel function to obtain high-precision PP and PS imaging results; and superposing all shot integrated image results to obtain a final offset imaging section.
It is another object of the present invention to provide a computer-readable storage medium storing a computer program which, when executed by a processor, causes the processor to perform the steps of:
obtaining input seismic records, seismic wavelets, density and velocity models; obtaining a seismic source and wave detection point continuation wave field by solving an elastic wave fluctuation equation; performing wave field separation by using vector Helmholtz decomposition to obtain separated pure longitudinal (P) wave and pure transverse (S) wave vector wave fields with amplitude preserved; calculating imaging conditions by using an elastic wave impedance sensitive kernel function to obtain high-precision PP and PS imaging results; and superposing all shot integrated image results to obtain a final offset imaging section.
Another objective of the present invention is to provide an information data processing terminal, which is used for implementing the decoupled elastic wave reverse time migration system.
By combining all the technical schemes, the invention has the advantages and positive effects that: according to the decoupling elastic wave reverse time migration method provided by the invention, firstly, vector Helmholtz decomposition is used for wave field separation to obtain pure longitudinal (P) wave and pure transverse (S) wave vector wave fields with amplitude preservation, and then, an elastic wave impedance sensitive kernel function is used for calculating imaging conditions to obtain high-precision PP and PS imaging results.
According to the scheme of the invention, after input seismic data, a seismic source wavelet and model parameters are obtained, extended seismic source and demodulator probe vector wave fields are obtained by solving an elastic wave field equation, then vertical and horizontal wave field separation is carried out by using vector Helmholtz decomposition, P wave and S wave vector wave fields of the seismic source and the demodulator probe are obtained, and finally cross-correlation imaging is carried out by using imaging conditions based on an elastic impedance sensitive core to obtain a final imaging result. Compared with the existing elastic wave reverse time migration imaging technology, the technical method of the invention adopts vector Helmholtz decomposition, can obtain the separation result of pure P wave field and S wave field of true amplitude, further avoid crosstalk noise in a migration profile and improve the imaging quality; in addition, the technical method uses the elastic impedance sensitive kernel function to calculate the imaging condition, can well avoid background noise in reverse time migration, and improve the imaging resolution and the signal-to-noise ratio so as to assist high-precision longitudinal and transverse wave combined seismic interpretation.
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In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments of the present invention will be briefly described below, and it is obvious that the drawings described below are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a flowchart of a decoupling elastic wave reverse time migration method according to an embodiment of the present invention.
Fig. 2 is a schematic diagram of a decoupling elastic wave reverse time migration method provided in the embodiment of the present invention.
FIG. 3 is a block diagram of a decoupled elastic wave reverse time migration system according to an embodiment of the present invention;
in the figure: 1. an input data acquisition module; 2. a seismic source vector continuation wave field calculation module; 3. a wave detection point vector continuation wave field calculation module; 4. a longitudinal and transverse wave separation module; 5. an imaging result acquisition module; 6. an offset imaging profile acquisition module.
FIG. 4 is a longitudinal wave velocity model v provided by an embodiment of the present invention p (x) Schematic representation of (a).
FIG. 5 shows a shear velocity model v provided by an embodiment of the present invention s (x) Schematic representation of (a).
FIG. 6 is a diagram of the results of conventional elastic wave reverse time migration PP imaging based on divergence and rotation wavefield separation and conventional cross-correlation imaging conditions, provided by an embodiment of the present invention.
FIG. 7 is a diagram illustrating the result of conventional elastic wave reverse time migration PS imaging based on divergence and rotation wave field separation and conventional cross-correlation imaging conditions according to an embodiment of the present invention.
Fig. 8 is a schematic diagram of elastic wave reverse time migration PP imaging results based on vector helmholtz decomposition and conventional cross-correlation imaging conditions according to an embodiment of the present invention.
Fig. 9 is a diagram illustrating elastic wave reverse time migration PS imaging results based on vector helmholtz decomposition and conventional cross-correlation imaging conditions according to an embodiment of the present invention.
FIG. 10 is a graphical illustration of decoupled elastic wave reverse time migration PP imaging results based on vector Helmholtz decomposition and impedance sensitive nuclear imaging conditions as provided by an embodiment of the present invention.
Fig. 11 is a diagram illustrating decoupled elastic wave reverse time migration PS imaging results based on vector helmholtz decomposition and impedance sensitive nuclear imaging conditions according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Aiming at the problems in the prior art, the invention provides a decoupling elastic wave reverse time migration method, an efficient algorithm and a processing flow, and the invention is described in detail below with reference to the accompanying drawings.
As shown in fig. 1, the decoupling elastic wave reverse time migration method provided in the embodiment of the present invention includes the following steps:
s101, obtaining input seismic records, seismic wavelets, density and velocity models;
s102, obtaining a seismic source and a wave detection point continuation wave field by solving an elastic wave fluctuation equation;
s103, obtaining separated true-amplitude pure longitudinal wave and pure transverse wave fields by using vector Helmholtz decomposition;
s104, performing offset imaging by using elastic impedance sensitive nuclear imaging conditions;
and S105, overlapping all shot integrated image results to obtain a final offset imaging section.
A schematic diagram of a decoupling elastic wave reverse time migration method provided by the embodiment of the invention is shown in fig. 2.
As shown in fig. 3, the decoupled elastic wave reverse time migration system provided in the embodiment of the present invention includes:
an input data acquisition module 1 for acquiring input data; wherein the input data comprises: longitudinal wave offset velocity model v p (x) Transverse wave migration velocity model v s (x) Density model rho (x), source function wavelet f (t), and multi-wave multi-component observation data d (x) r T), these inputs enhance the model and data base for subsequent wavefield computations and offset imaging;
a seismic source vector continuation wave field calculation module 2 for calculating the velocity model v according to the input seismic source wavelets f (t), the density model rho (x) and the longitudinal wave velocity model v p (x) And transverse wave velocity model v s (x) Calculating a seismic source vector continuation wave field u by solving a first-order velocity-stress elastic wave equation in a point source excitation mode s (x,t)；
A wave detection point vector continuation wave field calculation module 3 for calculating the wave field according to the input density model rho (x) and the longitudinal wave velocity model v p (x) Transverse wave velocity model v s (x) And observed data d (x) r T), calculating the extended wave field u of the wave detection point vector by solving the elastic wave equation r (x,t)；
The longitudinal and transverse wave separation module 4 is used for performing longitudinal and transverse wave separation on wave fields of a seismic source and a wave detection point by adopting vector Helmholtz decomposition, and the innovative technical step can obtain true-amplitude pure longitudinal wave and pure transverse wave vector wave fields, ensure the amplitude effectiveness of an imaging result and avoid the crosstalk noise of longitudinal and transverse waves;
the imaging result acquisition module 5 is used for performing cross-correlation imaging by using elastic impedance sensitive nuclear imaging conditions after acquiring separated seismic source and wave detection point wave fields, and the innovative processing step can automatically remove low-frequency noise when the imaging conditions are applied so as to obtain PP and PS imaging results with high signal-to-noise ratio and high resolution;
and the offset imaging section acquisition module 6 is used for adding the imaging results of all shot gathers to obtain a final offset imaging section, and improving the balance of deep imaging amplitude by using the seismic source illumination.
The technical solution of the present invention will be further described with reference to the following examples.
Example 1
The invention provides a decoupling elastic reverse time migration imaging method based on vector Helmholtz decomposition and impedance sensitive nuclear imaging conditions, aiming at solving the problems of low-frequency noise and cross wave crosstalk artifact in elastic wave reverse time migration. According to the method, firstly, vector Helmholtz decomposition is used for wave field separation to obtain amplitude-preserved pure longitudinal (P) wave and pure transverse (S) wave vector wave fields, then, an elastic wave impedance sensitive kernel function is used for calculating imaging conditions, and high-precision PP and PS imaging results are obtained.
The invention relates to a decoupling elastic reverse time migration imaging method based on an impedance sensitive nucleus, which comprises the following steps:
(1) obtaining input data, the input data comprising: longitudinal wave offset velocity model v p (x) Transverse wave migration velocity model v s (x) Density model rho (x), source function wavelet f (t), and multi-wave multi-component observation data d (x) r ,t)。
(2) According to the input seismic source wavelets f (t), the density model rho (x) and the longitudinal wave velocity model v p (x) And transverse wave velocity model v s (x) Calculating the vector continuation wave field u of the seismic source by solving a first-order velocity-stress elastic wave equation s (x, t), said first order velocity-stress elastic wave equation being of the form:
where x is the imaging spatial position, x s For the seismic source location, t is the wavefield travel time, u s ＝[u s,x u s,y u s,z ] T For the polarization velocity wave field, σ s ＝[σ s,xx σ s,yy σ s,zz σ s,xy σ s,xz σ s,yz ] T For the stress wavefield, T is the transposed symbol and δ is the kronecker function. L is partial derivativeNumber matrix, c (x) is a parameter matrix having the following expression:
(3) according to the input density model rho (x) and longitudinal wave velocity model v p (x) Transverse wave velocity model v s (x) And observed data d (x) r T), calculating the extended wave field u of the wave detection point vector by solving the elastic wave equation r (x, t), the expression of the elastic wave equation is:
wherein x is r For the detector position, L and C (x) have the same expression as equations (2) and (3).
(4) The method adopts vector Helmholtz decomposition to separate longitudinal waves and transverse waves of wave fields of a seismic source and a wave detection point, and the specific expression is as follows:
wherein,
in order to perform the gradient operation, the method comprises the following steps,
in order to calculate the divergence, the method comprises the following steps,
in order to calculate the rotation degree,
is a longitudinal direction after separationA wave-source wave field of a wave source,
is the shear wave source wavefield and,
is a longitudinal wave demodulator probe wave field,
is the shear wave demodulator point wavefield. w is a s And w r To assist the vector wavefield, it can be obtained by solving the poisson equation:
where Δ is the laplace operator.
(5) After the separated seismic source and wave detection point wave fields are obtained, performing cross-correlation imaging by using elastic impedance sensitive nuclear imaging conditions to obtain PP and PS imaging results, wherein the specific expression is as follows:
wherein,
in order to be able to obtain a shear modulus,
in order to be the bulk modulus,
and I is an identity matrix.
(6) The imaging results of all shot gathers are summed to obtain the final offset imaging profile, and source illumination is used to improve the equalization of deep imaging amplitudes.
The embodiment of the invention adopts at least one technical scheme which can achieve the following beneficial effects:
according to the scheme of the invention, after input seismic data, a seismic source wavelet and model parameters are obtained, extended seismic source and demodulator probe vector wave fields are obtained by solving an elastic wave field equation, then vertical and horizontal wave field separation is carried out by using vector Helmholtz decomposition, P wave and S wave vector wave fields of the seismic source and the demodulator probe are obtained, and finally cross-correlation imaging is carried out by using imaging conditions based on an elastic impedance sensitive core to obtain a final imaging result. Compared with the existing elastic wave reverse time migration imaging technology, the technical method adopts vector Helmholtz decomposition, can obtain an amplitude-preserved wave field separation result, further avoids crosstalk noise in a migration profile, and improves imaging quality; in addition, the technical method uses the elastic impedance sensitive kernel function to calculate the imaging condition, can well avoid background noise in reverse time migration, and improve the imaging resolution and the signal-to-noise ratio so as to assist high-precision longitudinal and transverse wave combined seismic interpretation.
Example 2
The following description is given as an explanation of the practical effects of the embodiment in the model.
The method provided by the invention is applied to the imaging of the international standard Marmousi model, and the ideal PP and PS imaging results are obtained. A longitudinal wave velocity model (as shown in fig. 4), a shear wave velocity model (as shown in fig. 5); adopting an observation aperture of 3km, and carrying out full waveform forward modeling by using a real velocity model to obtain observation seismic records, wherein the total number of the observation seismic records is 103 shot gather data; and inputting the source wavelet and the migration model to carry out source wave field continuation, reversely transmitting and observing the seismic record to obtain a wave detection point continuation wave field, and applying a sensitive kernel function imaging condition to obtain an imaging result (as shown in figures 10 and 11). For contrast imaging effects, imaging results obtained using the conventional elastic wave reverse time migration method based on both the rotation and divergence wave field decomposition and conventional cross-correlation imaging conditions are shown in fig. 6-7, and imaging results obtained using the vector helmholtz decomposition and conventional cross-correlation imaging conditions are shown in fig. 8-9. Compared with the conventional elastic wave reverse time migration imaging result (as shown in fig. 6-9), the scheme of the embodiment of the specification adopts elastic wave reverse time migration based on vector helmholtz decomposition and impedance sensitive nuclear imaging conditions, can automatically eliminate low-frequency noise in the reverse time migration, improves imaging section resolution and signal-to-noise ratio (as shown in fig. 10 and 11), and can greatly improve the accuracy of subsequent seismic interpretation. In the foregoing schematic, Distance corresponds to the abscissa x and Depth corresponds to the ordinate z.
In the above embodiments, the implementation may be wholly or partially realized by software, hardware, firmware, or any combination thereof. When used in whole or in part, can be implemented in a computer program product that includes one or more computer instructions. When loaded or executed on a computer, cause the flow or functions according to embodiments of the invention to occur, in whole or in part. The computer may be a general purpose computer, a special purpose computer, a network of computers, or other programmable device. The computer instructions may be stored in a computer readable storage medium or transmitted from one computer readable storage medium to another computer readable storage medium, for example, the computer instructions may be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wire (e.g., coaxial cable, fiber optic, Digital Subscriber Line (DSL), or wireless (e.g., infrared, wireless, microwave, etc.)). The computer-readable storage medium can be any available medium that can be accessed by a computer or a data storage device, such as a server, a data center, etc., that includes one or more of the available media. The usable medium may be a magnetic medium (e.g., floppy Disk, hard Disk, magnetic tape), an optical medium (e.g., DVD), or a semiconductor medium (e.g., Solid State Disk (SSD)), among others.
The above description is only for the purpose of illustrating the present invention and the appended claims are not to be construed as limiting the scope of the invention, which is intended to cover all modifications, equivalents and improvements that are within the spirit and scope of the invention as defined by the appended claims.
Claims (7)
1. A decoupling elastic wave reverse time migration method is characterized in that the elastic wave reverse time migration method of vector wave field decoupling comprises the following steps: obtaining input seismic records, seismic wavelets, density and longitudinal and transverse wave velocity models; obtaining a seismic source and wave detection point continuation wave field by solving an elastic medium wave equation; elastic wave field separation is carried out by using vector Helmholtz decomposition, and separated true-amplitude pure longitudinal (P) wave and pure transverse (S) wave vector wave fields are obtained; calculating imaging conditions by using an elastic wave impedance sensitive kernel function to obtain high-precision longitudinal wave-longitudinal wave (PP) and longitudinal wave-transverse wave (PS) imaging results; superposing all the single shot imaging results to obtain a final offset imaging section; the elastic wave reverse time migration method for vector wave field decoupling comprises the following steps:
step one, acquiring input data; wherein the input data comprises: longitudinal wave offset velocity model v p (x) Transverse wave migration velocity model v s (x) Density model rho (x), source function wavelet f (t), and multi-wave multi-component observation data d (x) r ,t)；
Secondly, according to the input seismic source wavelet f (t), the density model rho (x) and the longitudinal wave velocity model v p (x) And transverse wave velocity model v s (x) Calculating an elastic vector wave field u extended at one side of the seismic source by solving a first-order velocity-stress elastic medium wave equation in a point source excitation mode s (x,t)；
Thirdly, according to the input density model rho (x) and the longitudinal wave velocity model v p (x) Transverse wave velocity model v s (x) Using the observed data d (x) r T) as boundary condition, calculating extended elastic vector wave field u at one side of detection point by solving elastic wave equation r (x,t)；
Step four, performing vertical and horizontal wave field separation on the coupling elastic wave fields at the seismic source side and the wave detection point side by adopting vector Helmholtz decomposition;
step five, after the separated seismic source and wave field of the wave detection point are obtained, performing zero-delay cross-correlation imaging by using the elastic impedance sensitive nuclear imaging condition to obtain PP and PS imaging results;
adding the imaging results of all shot gathers to obtain a final offset imaging section, and improving the balance of deep imaging amplitude by using seismic source illumination as a preconditioner;
in step four, the vector Helmholtz decomposition is adopted to perform longitudinal and transverse wave separation on the wave fields of the source and the demodulator probe, and the following expression is provided:
wherein,
in order to perform the gradient operation, the method comprises the following steps,
in order to calculate the divergence, the method comprises the following steps,
in order to calculate the rotation degree,
for the separated longitudinal wave source wavefield,
for the separated shear wave source wavefield,
for the separated longitudinal wave demodulator probe wave field,
the separated transverse wave detection point wave field is obtained; w is a s And w r To assist the vector wavefield, it can be obtained by solving the following poisson equation:
wherein, delta is Laplace operator;
in the fifth step, after the separated seismic source and wave detection point wave fields are obtained, performing cross-correlation imaging by using elastic impedance sensitive nuclear imaging conditions to obtain PP and PS imaging results, wherein the PP and PS imaging results have the following expression:
wherein,
in order to be able to obtain a shear modulus,
in order to be the bulk modulus,
and I is an identity matrix.
2. The method for decoupling reverse time migration of an elastic wave according to claim 1, wherein in step two, the first order velocity-stress elastic wave equation is in the form of:
where x is the imaging spatial position, x s For the seismic source location, t is the wavefield travel time, u s ＝[u s,x u s,y u s,z ] T For the seismic source side deflection velocity wave field, σ s ＝[σ s,xx σ s,yy σ s,zz σ s,xy σ s,xz σ s,yz ] T Is a seismic source side stress wave field, T is a transposition symbol, and delta is a kronecker function; l is a first order partial derivative matrix, C (x) is a model parameter matrix, having the following expression:
3. the method for decoupling reverse time migration of an elastic wave according to claim 1, wherein in step three, the expression of the elastic wave equation is:
wherein x is r For the position of the detection point, L is a partial derivative matrix, C (x) is a rigidity matrix formed by model parameters, and the specific expression is as follows:
4. an elastic wave reverse time migration system for implementing the vector wave field decoupling elastic wave reverse time migration method according to any one of claims 1 to 3, wherein the vector wave field decoupling elastic wave reverse time migration method comprises the following steps:
the input data acquisition module is used for acquiring input data; wherein the input data comprises: longitudinal wave offset velocity model v p (x) Transverse wave migration velocity model v s (x) Density model rho (x), source function wavelet f (t), and multi-wave multi-component observation data d (x) r ,t)；
A seismic source vector continuation wave field computing module for calculating the intensity of the seismic source wavelet f (t) according to the input seismic source waveletModel ρ (x) and longitudinal velocity model v p (x) And transverse wave velocity model v s (x) Calculating a seismic source vector continuation wave field u by solving a first-order velocity-stress elastic wave equation in a point source excitation mode s (x,t)；
A wave detection point vector continuation wave field calculation module for calculating the wave field according to the input density model rho (x) and the longitudinal wave velocity model v p (x) Transverse wave velocity model v s (x) Using the observed data d (x) r T) as boundary condition, calculating the extended wave field u of the wave detection point vector by solving the elastic wave equation r (x,t)；
The longitudinal and transverse wave field separation module is used for performing longitudinal and transverse wave separation on wave fields of the seismic source and the wave detection point by adopting vector Helmholtz decomposition;
the imaging result acquisition module is used for performing cross-correlation imaging by using elastic impedance sensitive nuclear imaging conditions after acquiring the separated seismic source and wave detection point wave fields to acquire PP and PS imaging results;
and the offset imaging section acquisition module is used for adding all the single-shot imaging results to obtain a final offset imaging section, and using the seismic source illumination as a preconditioner to improve the balance of the deep imaging amplitude.
5. A computer device comprising a memory and a processor, the memory storing a computer program that, when executed by the processor, causes the processor to perform the vector wavefield decoupling elastic wave reverse time migration method of any one of claims 1-3.
6. A computer readable storage medium storing a computer program which, when executed by a processor, causes the processor to perform the method of vector wavefield decoupling elastic wave reverse time migration of any one of claims 1 to 3.
7. An information data processing terminal, characterized in that the information data processing terminal is used for implementing the decoupled elastic wave reverse time migration system according to claim 4.
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