Single-component data elastic wave reverse time migration algorithm and device

Abstract

The invention provides a single-component data elastic wave reverse time migration algorithm and device. The single-component data elastic wave reverse time migration algorithm comprises the steps of 1, solving an isotropic medium elastic wave equation to obtain a seismic source displacement wave field; 2, solving a seismic source potential field through a seismic source displacement wave field; step 3, carrying out back propagation on the single-component seismic record to obtain a detection point wave field; step 4, using Helmholtz decomposition to respectively obtain longitudinal and transverse wave fields of the seismic source wave field and the detection point wave field; 5, solving a PP offset profile and a PS offset profile; and step 6, superposing multi-shot migration results to obtain a final migration profile. According to the elastic wave reverse time migration algorithm and device for the single-component data, a vector imaging result can be obtained from the single-component data, implementation is easy, the calculated amount is small, and the migration profile imaging resolution is high.

Description

Technical Field

[0001] The invention relates to the technical field of geophysical exploration, and in particular to a single-component data elastic wave reverse time migration algorithm and device. Background Art

[0002] Seismic waves propagate in underground media in the form of coupled P- and S-waves, while traditional scalar wave reverse time migration only considers the propagation characteristics of underground P-waves and ignores S-wave information. Elastic wave reverse time migration technology contains P- and S-wave information, which can effectively improve imaging effects and provide richer data for reservoir prediction.

[0003] However, the current elastic wave imaging method is only for multi-component seismic data, and does not involve single-component data, which accounts for the vast majority of land seismic data. Therefore, the study of elastic wave reverse time migration technology for single-component data not only belongs to the category of elastic wave imaging, but also can adapt to single-component data, meeting the needs of domestic and foreign markets, and has important research significance.

[0004] In the Chinese patent application with application number: CN202110329092.8, a method, system and application of decoupled elastic wave reverse time migration is involved, which obtains input seismic records, seismic wavelets, density and velocity models; obtains the extended wave field of the source and the detector point by solving the wave equation of the elastic medium; uses vector Helmholtz decomposition to separate the elastic wave field and obtains the separated amplitude-preserving pure longitudinal and transverse wave vector wave fields; uses elastic wave impedance sensitive kernel function to calculate the imaging conditions and obtains high signal-to-noise ratio, high-precision longitudinal-longitudinal (PP) and longitudinal-transverse (PS) imaging results; superimposes all the imaging results of the gun collection to obtain the final migration imaging profile. The invention can obtain the separation results of the pure longitudinal and pure transverse wave vector wave fields of true amplitude, improve the fidelity of the imaging amplitude, automatically avoid the low-frequency noise generated by the cross-correlation of the two-way wave field, improve the imaging signal-to-noise ratio and resolution, and assist in high-precision longitudinal and transverse wave joint seismic interpretation.

[0005] In the Chinese patent application with application number: CN202111229275.9, a method, device, electronic device and medium for reverse time migration of elastic waves are involved. The method may include: obtaining a wave field extension formula according to the first-order velocity-stress elastic wave equation of a two-phase medium; obtaining a wave field separation formula; performing wave field extension and wave field separation in sequence for the target gun, obtaining forward wave field extension and reverse wave field extension, and storing the pure longitudinal wave field value at each moment; extracting the imaging value for the pure longitudinal wave field value through the cross-correlation imaging condition; repeating the above steps for all guns to obtain the elastic wave reverse time migration stacking profile. The invention performs elastic wave field separation in the forward and reverse migration extension operators under the two-phase medium model, obtains the pure longitudinal wave component in the two-phase medium, and uses the pure longitudinal wave component for migration imaging. Compared with the traditional two-phase medium elastic wave reverse time migration method using the velocity component containing the mixed wave field for imaging, the imaging accuracy is significantly improved.

[0006] In the Chinese patent application with application number: CN202211447889.9, a composite wavefield elastic wave reverse time migration imaging method based on Hilbert transform is involved, including obtaining HβHt, H-βHt and HβH-β terms respectively through Hilbert transform in time and oblique direction; bringing into the Hilbert full wavefield separation formula in the oblique direction to obtain four wavefield components of the original shot detection wavefield data separated along any β and its symmetric direction; according to the four wavefield components, the corresponding forward composite P wave (longitudinal wave) wavefield and reverse P wave, S wave (transverse wave) composite wavefield are obtained; the forward composite wavefield is cross-correlated with the reverse upgoing wave, and the forward downgoing wave is cross-correlated with the reverse composite wavefield, to obtain PP and PS elastic wave reverse time migration results that retain high steep structures. This invention utilizes the construction of a composite wave field to ensure the elimination of rotation wave artifacts and the weakening of the offset low-frequency noise, while retaining the algorithm's imaging advantage for high-steep structures. In addition, compared with the traditional elastic wave reverse-time migration algorithm, its computational complexity has only increased by about one-fold, providing a new methodological idea for the elastic wave reverse-time migration algorithm in imaging high-steep and complex underground structures.

[0007] In the Chinese patent application with application number: CN201610520574.0, a method and system for least squares reverse time migration imaging of multi-component seismic data is involved. The method is improved on the basis of the elastic wave reverse time migration method, and can directly take multi-component seismic data as input. Under the framework of inversion, different wave field extension operators and new imaging conditions are adopted in different steps of migration, thereby realizing the migration imaging of multi-component seismic data based on inversion. The invention introduces the idea of ​​inversion into elastic wave reverse time migration, and can obtain high-precision, high-resolution, high-signal-to-noise ratio, and amplitude-fidelity pre-stack depth migration profiles compared with conventional elastic wave reverse time migration; it can effectively overcome the destructive interference of the phase axis caused by the reversal of the shear wave polarity, and while completely maintaining the vector characteristics, amplitude and phase characteristics of the longitudinal and transverse waves, it effectively eliminates the migration illusion caused by the crosstalk between the longitudinal and transverse waves, thereby improving the imaging accuracy. It can be applied to the migration of multi-component seismic data in various complex medium models, and the imaging profile is clear, which is convenient for later geological interpretation.

[0008] The above existing technologies are all significantly different from the present invention and fail to solve the technical problem we want to solve. Therefore, we have invented a new single-component data elastic wave reverse time migration algorithm and device. Summary of the invention

[0009] The purpose of the present invention is to provide a single-component data elastic wave reverse time migration algorithm and device with small calculation amount and high migration profile imaging resolution.

[0010] The object of the present invention can be achieved by the following technical measures: a single-component data elastic wave reverse time migration algorithm, the single-component data elastic wave reverse time migration algorithm comprises:

[0011] Step 1, solving the elastic wave equation of isotropic medium to obtain the source displacement wave field;

[0012] Step 2, calculating the source potential field through the source displacement wave field;

[0013] Step 3, invert the single component seismic record to obtain the wave field of the detection point;

[0014] Step 4, using Helmholtz decomposition, obtain the longitudinal and transverse wave fields of the source wave field and the receiver wave field respectively;

[0015] Step 5, solving the PP migration profile and the PS migration profile;

[0016] Step 6: Superimpose the migration results of multiple shots to obtain the final migration profile.

[0017] The purpose of the present invention can also be achieved by the following technical measures:

[0018] In step 1, the elastic wave equation for isotropic media is as follows:

[0019]

[0020] Among them, u source (x,t)=[u x-source ,u y-source ,u z-source ] T represents the source vector wave field, f(x,t) represents the source term, x=[x,y,z] represents the spatial position, t represents the time, ρ represents the density parameter, L represents the partial differential operator, C is the isotropic medium stiffness matrix, represents the partial derivative, L T represents the transposed matrix of L, u x-source represents the displacement wave field of the earthquake source in the x direction at the spatial position x, u y-source represents the displacement wave field of the earthquake source in the y direction at the spatial position x, u z-source Represents the source displacement wave field in the z direction at the spatial position x;

[0021]

[0022] In step 2, the single-component source potential field is obtained through the source wave field;

[0023]

[0024] in, represents the single-component source potential field, is the gradient operation, i, j, k are direction vectors in different directions.

[0025] In step 2, taking the divergence on both sides yields:

[0026]

[0027] That is, solving the Poisson equation gives the single-component source potential field

[0028]

[0029] In step 3, the gradient of the single-component source potential field record is taken as the back propagation source and introduced into the elastic wave equation of the isotropic medium to obtain the wave field of the detection point.

[0030] In step 1, the wave field formula of the detection point is:

[0031]

[0032] in, is the single-component source potential field, represents the wave field at the limited detection point position, u receiver (x,t)=[u x-receiver ,u y-receiver ,uz-receiver ] T represents the vector wave field of the detection point, u x-receiver Represents the displacement wave field of the detector point in the x-coordinate direction of the spatial position x, u y-rece i ver Represents the displacement wave field of the detection point in the y coordinate direction of the spatial position x, u z-receiver Represents the displacement wave field of the detection point in the z-coordinate direction of the spatial position x.

[0033] In step 4, the source wave field and the receiver wave field are subjected to Helmholtz decomposition to obtain the longitudinal and transverse wave fields of the source wave field and the receiver wave field, which have the following expressions:

[0034]

[0035] in, is the divergence operation, is the curl operation, is the P-wave source wave field after Helmholtz decomposition, is the source wave field of the shear wave after Helmholtz decomposition, is the wave field of the longitudinal wave detection point after Helmholtz decomposition, It is the wave field of the shear wave detection point after Helmholtz decomposition.

[0036] In step 5, the PP migration profile is obtained by cross-correlating the longitudinal wave component of the source wave field with the longitudinal wave component of the detection point wave field, and the PS migration profile is obtained by cross-correlating the longitudinal wave component of the source wave field with the transverse wave component of the detection point wave field.

[0037] In step 5, the PP offset profile and the PS offset profile have the following expressions:

[0038]

[0039] Among them, I pp is the PP wave imaging result, I ps is the PS wave imaging result, is the source longitudinal wave field after Helmholtz decomposition, is the longitudinal wave field of the detection point after Helmholtz decomposition, is the shear wave field of the detection point after Helmholtz decomposition.

[0040] The object of the present invention can also be achieved by the following technical measures: a single-component data elastic wave reverse time migration device, the single-component data elastic wave reverse time migration device comprising:

[0041] The earthquake source wave field calculation module obtains the earthquake source wave field by solving the elastic wave equation;

[0042] The single-component data back-transmission module calculates the gradient of the collected single-component data as the source of the elastic wave equation back-transmission, and calculates the wave field of the detection point by solving the elastic wave equation;

[0043] The wave field separation module performs Helmholtz decomposition on the acquired source and receiver wave fields to separate longitudinal and transverse waves;

[0044] The imaging module cross-correlates the longitudinal and transverse wave fields of the seismic source and the receiver points to obtain the single-shot PP and PS imaging results;

[0045] The imaging stacking module stacks all the single-shot imaging results to obtain the final migration profile.

[0046] The single-component data elastic wave reverse time migration algorithm and device in the present invention first solve the elastic wave equation of isotropic medium to obtain the source wave field, then use the single-component seismic record as the potential field to find the gradient as the reverse propagation source to obtain the detection point wave field, then use Helmholtz decomposition on the source wave field and the detection point wave field to obtain the longitudinal and transverse wave fields of the source wave field and the detection point wave field, and finally use the cross-correlation imaging condition to perform PP and PS imaging. The accuracy of the single-component data elastic wave reverse time migration method is proved by the numerical simulation of the Marmousi model. The present invention can obtain vector imaging results from single-component data, is easy to implement, has a small amount of calculation, and has a high resolution of migration profile imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 A schematic diagram of a longitudinal wave velocity model Vp according to a specific embodiment of the present invention;

[0048] Figure 2 A schematic diagram of a shear wave velocity model Vs according to a specific embodiment of the present invention;

[0049] Figure 3 It is a schematic diagram of conventional scalar wave reverse time migration imaging results based on single component data according to a specific embodiment of the present invention;

[0050] Figure 4 It is a schematic diagram of PP results of elastic wave reverse time migration imaging based on single component data according to a specific embodiment of the present invention;

[0051] Figure 5 It is a schematic diagram of PS results of elastic wave reverse time migration imaging based on single component data according to a specific embodiment of the present invention;

[0052] Figure 6 A schematic diagram of the longitudinal wave velocity of a layered model in another specific embodiment of the present invention;

[0053] Figure 7 A schematic diagram of the shear wave velocity of a layered model in another specific embodiment of the present invention;

[0054] Figure 8 A schematic diagram of an imaging result of conventional single-component data of another specific embodiment of the present invention;

[0055] Fig. 9 It is a schematic diagram of PP imaging results obtained by reverse time migration of single-component data elastic waves according to another specific embodiment of the present invention;

[0056] Fig.10 It is a schematic diagram of PS imaging results obtained by reverse time migration of single-component data elastic waves according to another specific embodiment of the present invention;

[0057] Fig.11 The flowchart is a specific embodiment of the single-component data elastic wave reverse time migration algorithm of the present invention. DETAILED DESCRIPTION

[0058] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0059] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations and / or combinations thereof.

[0060] like Fig.11 As shown, Fig.11 The flowchart of the single-component data elastic wave reverse time migration algorithm of the present invention. The single-component data elastic wave reverse time migration algorithm includes:

[0061] Step 101, solving the elastic wave equation of the isotropic medium to obtain the source displacement wave field;

[0062] Step 102, calculating the earthquake source potential field through the earthquake source displacement wave field;

[0063] Step 103, invert the single component seismic record to obtain the detection point wave field;

[0064] Step 104, using Helmholtz decomposition to obtain the longitudinal and transverse wave fields of the source wave field and the receiver wave field respectively;

[0065] Step 105, using the cross-correlation between the longitudinal wave component of the source wave field and the longitudinal wave component of the detection point wave field to obtain the PP migration profile, and using the cross-correlation between the longitudinal wave component of the source wave field and the shear wave component of the detection point wave field to obtain the PS migration profile; P waves are longitudinal waves, and S waves are shear waves.

[0066] Step 106, superimposing the migration results of multiple shots to obtain the final migration profile.

[0067] The present invention can obtain vector imaging results from single-component data, is easy to implement, has a small amount of calculation, and has high resolution of offset profile imaging.

[0068] The following are several specific embodiments of the present invention.

[0069] Example 1

[0070] In a specific embodiment 1 of the present invention, the single-component data elastic wave reverse time migration algorithm includes the following steps:

[0071] Step 1: Solve the elastic wave equation of isotropic medium to obtain the source displacement wave field;

[0072] First, the elastic wave equation of isotropic medium is given as follows:

[0073]

[0074] Among them, u source (x,t)=[u x-source ,u y-source ,u z-source ] T represents the source vector wave field, f(x,t) represents the source term, x=[x,y,z] represents the spatial position, t represents the time, ρ represents the density parameter, L represents the partial differential operator, C is the isotropic medium stiffness matrix, represents the partial derivative, L T represents the transposed matrix of L, u x-source represents the displacement wave field of the earthquake source in the x direction at the spatial position x, u y-source represents the displacement wave field of the earthquake source in the y direction at the spatial position x, u z-source Represents the source displacement wave field in the z direction at spatial position x.

[0075]

[0076] Step 2, obtaining the single-component source potential field through the source wave field;

[0077]

[0078] in, represents the single-component source potential field, is the gradient operation, i, j, k are direction vectors in different directions. Taking the divergence on both sides, we can get:

[0079]

[0080] That is, solving the Poisson equation gives the single-component source potential field

[0081]

[0082] Step 3: Take the single-component source potential field record and calculate the gradient as the back propagation source and bring it into the elastic wave equation of isotropic medium to obtain the wave field of the detection point;

[0083]

[0084] in, is the single-component source potential field, represents the wave field at the limited detection point position, u receiver (x,t)=[u x-receiver ,u y-receiver ,u z-receiver ] T represents the vector wave field of the detection point, u x-receiver Represents the displacement wave field of the detector point in the x-coordinate direction of the spatial position x, u y-receiver Represents the displacement wave field of the detection point in the y coordinate direction of the spatial position x, u z-receiver Represents the displacement wave field of the detection point in the z-coordinate direction of the spatial position x.

[0085] Step 4: Use Helmholtz decomposition on the source wave field and the receiver wave field to obtain the longitudinal and transverse wave fields of the source wave field and the receiver wave field, which have the following expressions:

[0086]

[0087] in, is the divergence operation, is the curl operation, is the P-wave source wave field after Helmholtz decomposition, is the source wave field of the shear wave after Helmholtz decomposition, is the wave field of the longitudinal wave detection point after Helmholtz decomposition, It is the wave field of the shear wave detection point after Helmholtz decomposition.

[0088] Step 5: The PP migration profile is obtained by cross-correlating the P-wave component of the source wave field with the P-wave component of the detection point wave field, and the PS migration profile is obtained by cross-correlating the P-wave component of the source wave field with the S-wave component of the detection point wave field, which has the following expression:

[0089]

[0090] Step six: superimpose the migration results of multiple shots to obtain the final migration profile.

[0091] The single-component elastic wave reverse time migration device of this embodiment includes:

[0092] The earthquake source wave field calculation module obtains the earthquake source wave field by solving the elastic wave equation;

[0093] The single-component data back-transmission module is used to calculate the gradient of the collected single-component data, which is used as the source of the elastic wave equation back-transmission, and the wave field of the detection point is calculated by solving the elastic wave equation;

[0094] The wave field separation module is used to perform Helmholtz decomposition on the acquired source and receiver wave fields to separate longitudinal and transverse waves;

[0095] The imaging module cross-correlates the longitudinal and transverse wave fields of the seismic source and the receiver points to obtain the single-shot PP and PS imaging results;

[0096] The imaging stacking module stacks all the single-shot imaging results to obtain the final migration profile.

[0097] Example 2

[0098] In a specific embodiment 2 of the present invention, Figures 1 to 5 The effect diagram of the two-dimensional Marmous i model test is shown. Figure 1 and Figure 2 are the longitudinal and shear wave velocities of the Marmous i model. Figure 3 is the imaging result of conventional single-component data, while Figure 4 and Figure 5 The PP imaging and PS imaging results obtained by reverse time migration of single-component elastic waves are more advantageous in depicting the skeleton of underground structures than traditional imaging results.

[0099] Example 3

[0100] In a specific embodiment 3 of the present invention, Figures 6 to 10 The effect diagram of the two-dimensional layered model test is shown. Figure 6 and Figure 7 are the longitudinal and shear wave velocities of the layered model. Figure 8 is the imaging result of conventional single-component data, while Fig. 9 and Fig.10 The PP imaging and PS imaging results obtained by reverse time migration of single-component elastic waves are more advantageous in depicting the skeleton of underground structures than traditional imaging results.

[0101] Actual data collection is mainly based on single-component data, so it is necessary to study the single-component data elastic wave reverse time migration method. First, solve the elastic wave equation of isotropic medium to obtain the source wave field, then use the single-component seismic record as the potential field to find the gradient as the reverse propagation source, and obtain the receiver wave field. Then use the Helmholtz decomposition of the source wave field and the receiver wave field to obtain the longitudinal and transverse wave fields of the source wave field and the receiver wave field. Finally, use the cross-correlation imaging condition to perform PP and PS imaging, laying the foundation for future structural interpretation.

[0102] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions recorded in the aforementioned embodiments or replace some of the technical features therein with equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

[0103] Except for the technical features described in the specification, all other technical features are known technologies to those skilled in the art.

Claims

1. Single-component data elastic wave reverse time migration algorithm, characterized by: The single-component data elastic wave reverse time migration algorithm includes: Step 1, solving the elastic wave equation of isotropic medium to obtain the source displacement wave field; Step 2, calculating the source potential field through the source displacement wave field; Step 3, invert the single component seismic record to obtain the wave field of the detection point; Step 4, using Helmholtz decomposition, obtain the longitudinal and transverse wave fields of the source wave field and the receiver wave field respectively; Step 5, solving the PP migration profile and the PS migration profile; Step 6: Superimpose the migration results of multiple shots to obtain the final migration profile.

2. The single component data elastic wave reverse time migration algorithm according to claim 1, characterized in that: In step 1, the elastic wave equation for isotropic media is as follows: Among them, u source (x,t)=[u x-source ,u y-source ,u z-source ] T represents the source vector wave field, f(x,t) represents the source term, x=[x,y,z] represents the spatial position, t represents the time, ρ represents the density parameter, L represents the partial differential operator, C is the isotropic medium stiffness matrix, represents the partial derivative, L T represents the transposed matrix of L, u x-source represents the displacement wave field of the earthquake source in the x direction at the spatial position x, u y-source represents the displacement wave field of the earthquake source in the y direction at the spatial position x, u z-source Represents the source displacement wave field in the z direction at the spatial position x; 3. The single component data elastic wave reverse time migration algorithm according to claim 2, characterized in that: In step 2, the single-component source potential field is obtained through the source wave field; in, represents the single-component source potential field, is the gradient operation, i, j, k are direction vectors in different directions.

4. The single component data elastic wave reverse time migration algorithm according to claim 3, characterized in that: In step 2, taking the divergence on both sides yields: That is, solving the Poisson equation gives the single-component source potential field 5. The single component data elastic wave reverse time migration algorithm according to claim 1, characterized in that: In step 3, the gradient of the single-component source potential field record is taken as the back propagation source and introduced into the elastic wave equation of the isotropic medium to obtain the wave field of the detection point.

6. The single component data elastic wave reverse time migration algorithm according to claim 1, characterized in that: In step 1, the wave field formula of the detection point is: in, is the single-component source potential field, represents the wave field at the limited detection point position, u receiver (x,t)=[u x-receiver ,u y-receiver ,u z-receiver ] T represents the vector wave field of the detection point, u x-receiver Represents the displacement wave field of the detector point in the x-coordinate direction of the spatial position x, u y-rece i ver Represents the displacement wave field of the detection point in the y coordinate direction of the spatial position x, u z-receiver Represents the displacement wave field of the detection point in the z-coordinate direction of the spatial position x.

7. The single component data elastic wave reverse time migration algorithm according to claim 1, characterized in that: In step 4, the source wave field and the receiver wave field are subjected to Helmholtz decomposition to obtain the longitudinal and transverse wave fields of the source wave field and the receiver wave field, which have the following expressions: in, is the divergence operation, is the curl operation, is the P-wave source wave field after Helmholtz decomposition, is the source wave field of the shear wave after Helmholtz decomposition, is the wave field of the longitudinal wave detection point after Helmholtz decomposition, It is the wave field of the shear wave detection point after Helmholtz decomposition.

8. The single component data elastic wave reverse time migration algorithm according to claim 1, characterized in that: In step 5, the PP migration profile is obtained by cross-correlating the longitudinal wave component of the source wave field with the longitudinal wave component of the detection point wave field, and the PS migration profile is obtained by cross-correlating the longitudinal wave component of the source wave field with the transverse wave component of the detection point wave field.

9. The single component data elastic wave reverse time migration algorithm according to claim 8, characterized in that: In step 5, the PP offset profile and the PS offset profile have the following expressions: Among them, I pp is the PP wave imaging result, I ps is the PS wave imaging result, is the source longitudinal wave field after Helmholtz decomposition, is the longitudinal wave field of the detection point after Helmholtz decomposition, is the shear wave field of the detection point after Helmholtz decomposition.

10. A single-component data elastic wave reverse time migration device, characterized in that: The single-component data elastic wave reverse time migration device comprises: The earthquake source wave field calculation module obtains the earthquake source wave field by solving the elastic wave equation; The single-component data back-transmission module calculates the gradient of the collected single-component data as the source of the elastic wave equation back-transmission, and calculates the wave field of the detection point by solving the elastic wave equation; The wave field separation module performs Helmholtz decomposition on the acquired source and receiver wave fields to separate longitudinal and transverse waves; The imaging module cross-correlates the longitudinal and transverse wave fields of the seismic source and the receiver points to obtain the single-shot PP and PS imaging results; The imaging stacking module stacks all the single-shot imaging results to obtain the final migration profile.

Images