Single-component data elastic wave reverse-time migration method and device used in implementation method

Abstract

The application provides a single-component data elastic wave reverse time migration algorithm and device, which comprises the following steps: step 1, solving an isotropic medium elastic wave equation to obtain a source displacement wave field; step 2, obtaining a source potential field through the source displacement wave field; step 3, inversely transmitting single-component seismic records to obtain a receiver wave field; step 4, using a Helmholtz decomposition to respectively obtain longitudinal wave and transverse wave wave fields of the source wave field and the receiver wave field; step 5, solving PP migration profiles and PS migration profiles; and step 6, superimposing multi-shot migration results to obtain final migration profiles. The single-component data elastic wave reverse time migration algorithm and device can obtain vector imaging results from single-component data, is easy to implement, has a small amount of calculation and has high migration profile imaging resolution.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of geophysical exploration, in particular to a single-component data elastic wave reverse time migration method and a device using the same. BACKGROUND

[0002] Seismic waves propagate in the form of coupling between longitudinal and transverse waves in the underground medium, and the traditional scalar wave reverse time migration only considers the propagation characteristics of longitudinal waves in the underground and ignores the transverse wave information. The elastic wave reverse time migration technology contains longitudinal and transverse wave information, which can effectively improve the imaging effect and provide more abundant 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 majority of land seismic data. Therefore, the research on the 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 and meet the needs of the domestic and foreign markets, which has important research significance.

[0004] In the Chinese patent application with the application number CN202110329092.8, a decoupling elastic wave reverse time migration method and system and application are involved. Input seismic records, seismic wavelets, density and velocity models are obtained. By solving the elastic medium wave equation, the source and receiver continuation wave field is obtained. The elastic wave field separation is performed using the vector Helmholtz decomposition to obtain the separated amplitude-preserved pure longitudinal and transverse wave vector wave field. The imaging condition is calculated using the 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. All shot imaging results are stacked to obtain the final migration imaging profile. The invention can obtain true amplitude pure longitudinal and transverse wave vector wave field separation results, improve the imaging amplitude fidelity, automatically avoid low frequency noise generated by double-path wave field cross-correlation, improve the imaging signal-to-noise ratio and resolution, and assist high-precision longitudinal and transverse wave joint seismic interpretation.

[0005] In the Chinese patent application with application number: CN202111229275.9, a method and device for elastic wave reverse time migration are disclosed. The method can include obtaining a wave field continuation formula based on the first-order velocity-stress elastic wave equation of a two-phase medium; obtaining a wave field separation formula; performing wave field continuation and wave field separation for the target shot in sequence to obtain forward and reverse wave field continuation, and storing the pure longitudinal wave field value at each time; extracting the imaging value by cross-correlation imaging condition for the pure longitudinal wave field value; repeating the above steps for all shots to obtain the elastic wave reverse time migration stacking profile. The invention separates the elastic wave field in the forward and reverse migration continuation operators under the two-phase medium model to obtain 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 mixed wave field velocity component for imaging, the imaging accuracy is significantly improved.

[0006] In the Chinese patent application with application number: CN202211447889.9, a method for composite wave field elastic wave reverse time migration imaging based on Hilbert transform is disclosed. The method includes obtaining HβHt, H-βHt and HβH-β terms by Hilbert transform in time and slant direction respectively; obtaining four wave field components of the original shot wave field data along any β and its symmetric direction by inserting the Hilbert full wave field separation formula into the slant direction; obtaining the corresponding forward composite P wave (longitudinal wave) wave field and reverse P wave, S wave (transverse wave) composite wave field according to the four wave field components; performing cross-correlation on the forward composite wave field and the reverse uplink wave, the forward downlink wave and the reverse composite wave field respectively to obtain the PP and PS elastic wave reverse time migration results that preserve high steep structure. The invention uses composite wave field to ensure the elimination of rotation wave artifacts and the weakening of migration low frequency noise while preserving the imaging advantage of high steep structure for this method. Compared with the traditional elastic wave reverse time migration method, the calculation amount is only increased by about one time. The invention provides a new method for elastic wave reverse time migration method in imaging of underground high steep complex structure.

[0007] In the Chinese patent application with the application number CN201610520574.0, a multi-component seismic data least square reverse time migration imaging method and system are related. The method is improved on the basis of the elastic wave reverse time migration method, can directly take the multi-component seismic data as the input, and realizes the multi-component seismic data migration imaging based on the inversion by using different wave field continuation operators and new imaging conditions at different steps of migration in the framework of inversion. The application introduces the idea of inversion into the elastic wave reverse time migration, compared with the conventional elastic wave reverse time migration, can obtain the pre-stack depth migration profile with high precision, high resolution, high signal-to-noise ratio and amplitude fidelity; can effectively overcome the destructive interference of the same phase axis caused by the polarity reversal of the transverse wave, effectively eliminate the migration artifacts caused by the crosstalk between the longitudinal and transverse waves while completely maintaining the vector characteristics, amplitude and phase characteristics of the longitudinal and transverse waves, improve the imaging precision, can be applied to the multi-component seismic data migration of various complex medium models, and the imaging profile is clear, which is convenient for later geological interpretation.

[0008] The above prior art is quite different from the present application, and cannot solve the technical problems we want to solve. Therefore, we have invented a new single-component data elastic wave reverse time migration method and device. SUMMARY

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

[0010] The purpose of the present application can be realized by the following technical measures: a single-component data elastic wave reverse time migration method, which comprises:

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

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

[0013] Step 3, inversely transmitting single-component seismic records to obtain a geophone point wave field;

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

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

[0016] Step 6, superimposing multi-shot migration results to obtain a final migration profile;

[0017] In step 2, a single-component source potential field is obtained through the source wave field;

[0018]

[0019] where, represents single-component source potential field, is gradient operation, i, j, k are direction vectors in different directions;

[0020] In step 2, the divergence of both sides can be obtained as follows:

[0021]

[0022] That is, the single-component source potential field is obtained by solving the Poisson equation

[0023]

[0024] In step 4, the Helmholtz decomposition is used on the source wave field and the receiver wave field to obtain the longitudinal wave and transverse wave wave fields of the source wave field and the receiver wave field, and has the following expression:

[0025]

[0026] where, is divergence operation, is curl operation, is longitudinal wave source wave field after Helmholtz decomposition, is transverse wave source wave field after Helmholtz decomposition, is longitudinal wave receiver wave field after Helmholtz decomposition, is transverse wave receiver wave field after Helmholtz decomposition;

[0027] In step 5, the PP migration section and the PS migration section have the following expression:

[0028]

[0029] Where, 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 receiver longitudinal wave field after Helmholtz decomposition, is the receiver transverse wave field after Helmholtz decomposition.

[0030] The purpose of the application can also be achieved by the following technical measures:

[0031] In step 1, the isotropic medium elastic wave equation is as follows:

[0032]

[0033] Where, u source (x,t)=[u x-source ,u y-source ,uz-source ] T represents a source vector wave field, represents a source term, represents a spatial position, t represents time, p represents a density parameter, L represents a partial differential operator, and C is an isotropic medium stiffness matrix, represents a partial derivative, L T represents a transpose matrix of L, u x-source represents a spatial position of the x-direction source displacement wave field, u y-source represents a spatial position of the y-direction source displacement wave field, u z-source represents a spatial position of the z-direction source displacement wave field;

[0034]

[0035] The single-component source potential field record is taken as a gradient to bring in the isotropic medium elastic wave equation as a reverse transmission source, and a receiver point wave field is obtained.

[0036] In step 1, the receiver point wave field formula is:

[0037]

[0038] wherein, is a single-component source potential field, represents a wave field limited at a receiver point position, represents a receiver point vector wave field, u x-receiver represents a spatial position of the x-coordinate direction receiver point displacement wave field, u y-receiver represents a spatial position of the y-coordinate direction receiver point displacement wave field, u z-receiver represents a spatial position of the z-coordinate direction receiver point displacement wave field.

[0039] In step 5, a PP migration profile is obtained by cross-correlating the longitudinal wave component of the source wave field and the longitudinal wave component of the receiver point wave field, and a PS migration profile is obtained by cross-correlating the longitudinal wave component of the source wave field and the transverse wave component of the receiver point wave field.

[0040] The object of the application can also be achieved by the following technical measures:

[0041] The application provides a device for implementing the single-component data elastic wave reverse time migration method described above, which comprises:

[0042] A source wave field calculation module obtains a source wave field by solving an elastic wave equation;

[0043] The single-component data back-propagation module performs gradient calculation on the collected single-component data as a source of elastic wave equation back-propagation, and calculates the wave field of the receiver by solving the elastic wave equation;

[0044] The wave field separation module performs Helmholtz decomposition on the obtained source and receiver wave field to separate the P and S waves;

[0045] The imaging module performs cross-correlation on the obtained P and S wave fields of the source and receiver to obtain single-shot PP and PS imaging results;

[0046] The imaging and stacking module stacks all single-shot imaging results to obtain the final migration profile.

[0047] The single-component data elastic wave reverse time migration method and device in the application first solve the isotropic medium elastic wave equation to obtain the source wave field, then take the single-component seismic record as the potential field to obtain the gradient as the back-propagation source, obtain the receiver wave field, then use Helmholtz decomposition on the source wave field and the receiver wave field to obtain the P and S wave fields of the source wave field and the receiver wave field, and finally use the cross-correlation imaging condition to perform PP and PS imaging. The numerical simulation of the Marmousi model proves the accuracy of the single-component data elastic wave reverse time migration method. The application can obtain vector imaging results from single-component data, is easy to implement, has small calculation amount, and has high migration profile imaging resolution. BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1 It is a schematic view of the P-wave velocity model Vp of an embodiment of the application;

[0049] Figure 2 It is a schematic view of the S-wave velocity model Vs of an embodiment of the application;

[0050] Figure 3 It is a schematic view of the conventional scalar wave reverse time migration imaging result based on single-component data of an embodiment of the application;

[0051] Figure 4 It is a schematic view of the elastic wave reverse time migration imaging PP result based on single-component data of an embodiment of the application;

[0052] Figure 5 It is a schematic view of the elastic wave reverse time migration imaging PS result based on single-component data of an embodiment of the application;

[0053] Figure 6 It is a schematic view of the P-wave velocity of the layered model in another embodiment of the application;

[0054] Figure 7Fig. 2 is a schematic diagram of the velocity of the transverse wave of the layered model of another embodiment of the present application;

[0055] Figure 8 Fig. 3 is a schematic diagram of the imaging result of the conventional single-component data of another embodiment of the present application;

[0056] Figure 9 Fig. 4 is a schematic diagram of the PP imaging result obtained by the single-component data elastic wave reverse time migration of another embodiment of the present application;

[0057] Figure 10 Fig. 5 is a schematic diagram of the PS imaging result obtained by the single-component data elastic wave reverse time migration of another embodiment of the present application;

[0058] Figure 11 Fig. 6 is a flow chart of a specific embodiment of the single-component data elastic wave reverse time migration method of the present application. DETAILED DESCRIPTION

[0059] It should be noted that the following detailed description is merely exemplary in nature and is intended to provide further description of the present application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0060] It is to be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments consistent with the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, steps, operations, elements, and / or groups thereof, but do not preclude the presence or addition of one or more other features, steps, operations, elements, and / or groups thereof.

[0061] As shown in Fig. 1, Figure 11 Figure 11 Fig. 6 is a flow chart of a specific embodiment of the single-component data elastic wave reverse time migration method of the present application. The single-component data elastic wave reverse time migration method comprises:

[0062] Step 101, solving the elastic wave equation of the isotropic medium to obtain the source displacement wave field;

[0063] Step 102, obtaining the source potential field through the source displacement wave field;

[0064] Step 103, inversely transmitting the single-component seismic record to obtain the receiver wave field;

[0065] Step 104, using the Helmholtz decomposition to respectively obtain the longitudinal and transverse wave fields of the source wave field and the receiver wave field;

[0066] ​Step 105, PP migration profile is obtained by cross-correlation of the longitudinal wave component of the source wave field and the longitudinal wave component of the wave field at the receiver point, and PS migration profile is obtained by cross-correlation of the longitudinal wave component of the source wave field and the transverse wave component of the wave field at the receiver point; P wave is longitudinal wave, and S wave is transverse wave.

[0067] Step 106, superimposing the multi-shot migration results to obtain the final migration profile.

[0068] The application can obtain vector imaging results from single-component data, is easy to implement, has small amount of calculation, and has high migration profile imaging resolution.

[0069] The following are several specific embodiments of the application

[0070] Embodiment 1

[0071] In a specific embodiment 1 of the application, the single-component data elastic wave reverse time migration method comprises the following steps:

[0072] Step one, solving the isotropic medium elastic wave equation to obtain the source displacement wave field;

[0073] First, the isotropic medium elastic wave equation is as follows:

[0074]

[0075] Wherein, 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 time, rho 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 transpose matrix of L, u x-source represents the x-direction source displacement wave field of the spatial position x, u y-source represents the y-direction source displacement wave field of the spatial position x, and u z-source represents the z-direction source displacement wave field of the spatial position x.

[0076]

[0077] Step two, obtaining single-component source potential field through the source wave field;

[0078]

[0079] Wherein, represents the single-component source potential field, For gradient operation, i, j, k are direction vectors in different directions. Taking divergence on both sides can get:

[0080]

[0081] That is, the single-component source potential field is obtained by solving the Poisson equation

[0082]

[0083] Step three, taking the gradient of the single-component source potential field record as the back-propagating source into the isotropic medium elastic wave equation to obtain the wave field at the receiver point;

[0084]

[0085] wherein, is the single-component source potential field, represents the wave field at the receiver point position, u receiver (x, t) = [u x-receiver , u y-receiver , u z-receiver ] T represents the receiver point vector wave field, u x-receiver represents the receiver point displacement wave field in the x coordinate direction of the spatial position x, u y-receiver represents the receiver point displacement wave field in the y coordinate direction of the spatial position x, u z-receiver represents the receiver point displacement wave field in the z coordinate direction of the spatial position x.

[0086] Step four, using the Helmholtz decomposition on the source wave field and the receiver point wave field to obtain the longitudinal and transverse wave fields of the source wave field and the receiver point wave field, which have the following expressions:

[0087]

[0088] wherein, is the divergence operation, is the curl operation, is the longitudinal wave source wave field after Helmholtz decomposition, is the transverse wave source wave field after Helmholtz decomposition, is the longitudinal wave receiver point wave field after Helmholtz decomposition, is the transverse wave receiver point wave field after Helmholtz decomposition.

[0089] Step five, 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 receiver 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 receiver point wave field, which have the following expressions:

[0090]

[0091] Step six, superimposing multi-shot offset results to obtain the final migration profile.

[0092] The single-component elastic wave reverse time migration device of the embodiment comprises:

[0093] A source wave field calculation module obtains a source wave field by solving an elastic wave equation;

[0094] A single-component data back-propagation module is configured to perform gradient calculation on the collected single-component data as a source of elastic wave equation back-propagation, and to calculate a receiver point wave field by solving the elastic wave equation;

[0095] A wave field separation module is configured to perform Hemholtz decomposition on the obtained source and receiver point wave fields to separate P and S waves;

[0096] An imaging module is configured to perform cross-correlation on the obtained P and S wave fields of the source and receiver points to obtain single-shot PP and PS imaging results;

[0097] An imaging superposition module is configured to superimpose all single-shot imaging results to obtain a final migration profile.

[0098] Embodiment 2

[0099] In a specific embodiment 2 of the application, Figures 1 to 5 The effect diagram of the two-dimensional Marmousi model test is shown. Figure 1 and Figure 2 are the P wave velocity and S wave velocity of the Marmousi model. Figure 3 is the imaging result of the conventional single-component data, while Figure 4 and Figure 5 are the PP imaging and PS imaging results obtained by the single-component data elastic wave reverse time migration, which have more advantages in the skeleton description of the underground structure than the conventional imaging results.

[0100] Embodiment 3

[0101] In a specific embodiment 3 of the application, Figures 6 to 10 The effect diagram of the two-dimensional layered model test is shown. Figure 6 and Figure 7 are the P wave velocity and S wave velocity of the layered model. Figure 8 is the imaging result of the conventional single-component data, while Figure 9 and Figure 10 are the PP imaging and PS imaging results obtained by the single-component data elastic wave reverse time migration, which have more advantages in the skeleton description of the underground structure than the conventional imaging results.

[0102] The actual data acquisition is mainly single-component data, so it is necessary to study the single-component data elastic wave reverse time migration method. First, the isotropic medium elastic wave equation is solved to obtain the source wave field, then the single-component seismic record is taken as the potential field gradient as the anti-transmission source to obtain the receiver point wave field, then the Helmholtz decomposition is used for the source wave field and the receiver point wave field to obtain the longitudinal and transverse wave fields of the source wave field and the receiver point wave field, finally, the PP and PS imaging are carried out by using the cross-correlation imaging condition, which lays a foundation for the subsequent structural interpretation.

[0103] Finally, it should be noted that: the above only for the preferred embodiments of the present application, and not for the purpose of limiting the present application, although the foregoing detailed description of the present application is made with reference to the foregoing examples, for those skilled in the art, it still can be modified, or part of the technical features of the equivalent replacement. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application shall be included in the protection scope of the present application.

[0104] In addition to the technical features described in the specification, they are known to those skilled in the art.

Claims

1. A single-component data elastic wave reverse time migration method, characterized in that, The single-component data elastic wave reverse time migration method comprises: Step 1, solving the isotropic medium elastic wave equation to obtain a source displacement wave field; Step 2, obtaining a source potential field through the source displacement wave field; Step 3, transmitting a single-component seismic record in reverse to obtain a receiver wave field; Step 4, using Helmholtz decomposition to obtain longitudinal and transverse wave fields of the source wave field and the receiver wave field respectively; Step 5, solving a PP migration profile and a PS migration profile; Step 6, stacking multi-shot migration results to obtain a final migration profile; In step 2, a single-component source potential field is obtained through the source wave field; ； wherein, represents a single-component source potential field, represents a spatial position of a source displacement wavefield in a direction, represents a spatial position of a source displacement wavefield in a direction, represents a spatial position of a source displacement wavefield in a direction, is a gradient operation, is a directional vector in different directions; In step 2, the divergence of both sides can be obtained as follows: ； That is, a single-component source potential field is obtained by solving the Poisson equation ； In step 4, Helmholtz decomposition is used on the source wave field and the receiver wave field to obtain longitudinal and transverse wave fields of the source wave field and the receiver wave field, which have the following expressions: ； wherein, is a divergence operation, is a curl operation, is a longitudinal wave source wavefield after Helmholtz decomposition, is a transverse wave source wavefield after Helmholtz decomposition, is a longitudinal wave receiver wavefield after Helmholtz decomposition, is a transverse wave receiver wavefield after Helmholtz decomposition; In step 5, the PP migration profile and the PS migration profile have the following expressions: ； wherein, is the PP wave imaging result, is the PS wave imaging result.

2. The single-component data elastic wave reverse time migration method of claim 1, wherein, In step 1, the isotropic medium elastic wave equation is as follows: ； wherein, denotes the source vector wavefield, denotes the source term, denotes the spatial position, denotes the time, denotes the density parameter, denotes the partial differential operator, C is the stiffness matrix of the isotropic medium, denotes the partial derivative, denotes the transpose matrix of 。 3. The single-component data elastic wave reverse time migration method of claim 2, wherein, In step 3, the gradient of the single-component source potential field record is calculated as a reverse transmission source of the isotropic medium elastic wave equation to obtain a receiver wave field.

4. The single-component data elastic wave reverse time migration method of claim 3, wherein, At step 3, the wavefield formula at the receiver point is: ; wherein, represents a wavefield at a defined receiver position, represents a receiver vector wavefield, represents a spatial position of a receiver displacement wavefield in a coordinate direction, represents a spatial position of a receiver displacement wavefield in a coordinate direction, represents a spatial position of a receiver displacement wavefield in a coordinate direction.

5. The single-component data elastic wave reverse time migration method of claim 1, wherein, 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 receiver 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 receiver wave field.

6. An apparatus for implementing the single-component data elastic wave reverse time migration method according to any one of claims 1 to 5, characterized in that, The single-component data elastic wave reverse time migration device comprises: A source wave field calculation module obtains a source wave field by solving an elastic wave equation; A single-component data reverse transmission module calculates the gradient of the collected single-component data as a source of elastic wave equation reverse transmission, and calculates a receiver wave field by solving the elastic wave equation; A wave field separation module separates longitudinal and transverse waves by Helmholtz decomposition on the obtained source and receiver wave fields; An imaging module cross-correlates the obtained source and receiver longitudinal and transverse wave fields to obtain single-shot PP and PS imaging results; An imaging stacking module stacks all single-shot imaging results to obtain a final migration profile.

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