CN-116165702-B - Method, system, equipment and medium for least square reverse time migration of new elastic wave

CN116165702BCN 116165702 BCN116165702 BCN 116165702BCN-116165702-B

Abstract

The invention relates to a new elastic wave least square reverse time migration method, a system, equipment and a medium, which comprise the steps of acquiring a longitudinal wave velocity model, a transverse wave velocity model, a density model and OBS 4C data of an observation system; the method comprises the steps of performing wave field forward extension based on a longitudinal wave velocity model, a transverse wave velocity model and a density model, performing residual reverse extension based on the longitudinal wave velocity model, the transverse wave velocity model, the density model and 4C data, performing cross-correlation calculation on the forward extension and the residual reverse extension to obtain initial multi-parameter imaging, performing forward modeling on the initial multi-parameter imaging based on an ACE equation Born forward modeling to obtain OBS 4C data, performing the residual reverse extension on the OBS 4C data obtained through modeling and the OBS 4C data of an observation system, performing cross-correlation calculation on the forward extension and the residual reverse extension, performing multiple iterations to obtain LSM imaging results, and further obtaining seismic imaging results.

Inventors

DU XIANGDONG
LIU FANG
WANG XIAOJIANG
QU YINGMING
XUE DONGCHUAN
MI FANG
TONG ZHONGFEI
ZHANG HONGLIANG
OUYANG YANG
Bao Tiezhao
XIAO XI

Assignees

中海石油(中国)有限公司
中海石油（中国）有限公司北京研究中心

Dates

Publication Date: 20260512
Application Date: 20221215

Claims (8)

1. A new elastic wave least square reverse time migration method, characterized by comprising: acquiring a longitudinal wave velocity model, a transverse wave velocity model, a density model and OBS 4C data of an observation system; Performing wave field forward continuation based on the longitudinal wave velocity model, the transverse wave velocity model and the density model; performing residual reverse continuation based on the longitudinal wave velocity model, the transverse wave velocity model, the density model and the 4C data; Performing cross-correlation calculation on the forward continuation and the residual reverse continuation to obtain initial multi-parameter imaging; Performing forward modeling on the initial multi-parameter imaging based on an ACE equation, namely, forward modeling to obtain OBS 4C data, performing residual reverse extension on the OBS 4C data obtained by modeling and the OBS 4C data of an observation system, performing cross-correlation calculation on the forward extension and the residual reverse extension, and performing multiple iterations to obtain an LSM imaging result, thereby obtaining a seismic imaging result, wherein the OBS 4C data obtained by performing forward modeling on the initial multi-parameter imaging based on the ACE equation, namely, the forward modeling on the OBS 4C data adopts the following formula: Where δ represents the disturbance, (x, z) is the Cartesian coordinate value on the grid point before coordinate transformation, (ζ, η) is the body coordinate value on the grid point after coordinate transformation, P is the acoustic stress, Is density, t is time, τ xx and τ zz represent positive stress components, τ xz represents shear stress components, v x0 ,v z0 represents velocity components in the horizontal x-direction and the vertical z-direction, respectively, And Respectively is And Lambda, mu, lambda 0 and mu 0 are each a lame constant, v x ,v z represents the velocity component in the horizontal x-direction and in the vertical z-direction respectively, , , And Is the directional partial derivative.
2. The method of claim 1, wherein the forward extension of the wave field based on the longitudinal wave velocity model, the transverse wave velocity model and the density model is as follows: Where f is the source term, τ xx0 and τ zz0 represent the positive stress component, τ xz0 the shear stress component, and P 0 the acoustic stress.
3. The method of claim 1, wherein the calculation formula for residual reverse continuation based on the longitudinal wave velocity model, the transverse wave velocity model, the density model and the 4C data is: Wherein the superscript R denotes the wave field value at the position of the pickup point, x r denotes the position of the pickup point, And Representing the combined data in the horizontal and vertical directions, respectively And observation data The difference between them.
4. The method of elastic wave least square reverse time migration according to claim 1, wherein performing cross-correlation computation on the forward continuation and the residual reverse continuation for a plurality of iterations to obtain LSM imaging results, and further outputting seismic imaging results, comprises: And constructing an objective function, judging whether the objective function meets the set requirement, outputting a final seismic imaging result if the objective function meets the set requirement, if not, updating the LSM imaging result by using a diagonal Hessian operator, solving the step length by a conjugate gradient method for a plurality of times until the iteration meets the set requirement, and outputting the final seismic imaging result.
5. The method of elastic wave least squares reverse time migration according to claim 4, wherein updating the LSM imaging result uses a gradient formula: Where g represents the gradient direction, λ and μ are the lame constants, the superscript R represents the wavefield value at the position of the detector point, τ xx and τ zz represent the positive stress components, and E represents the objective function.
6. A system for implementing the new elastic wave least squares reverse time migration method of any one of claims 1 to 5, the system comprising: A first processing unit configured to acquire a longitudinal wave velocity model, a transverse wave velocity model, and a density model, and observation system OBS 4C data; A second processing unit configured to perform wave field forward continuation based on the longitudinal wave velocity model, the transverse wave velocity model, and the density model; a third processing unit configured to perform residual reverse continuation based on the longitudinal wave velocity model, the transverse wave velocity model, the density model, and the 4C data; the fourth processing unit is configured to perform cross-correlation calculation on the forward continuation and the residual reverse continuation to obtain initial multi-parameter imaging; And the fifth processing unit is configured to perform forward modeling on the initial multi-parameter imaging based on an ACE equation Born to obtain OBS 4C data, perform data residual reverse extension on the OBS 4C data obtained by the modeling and the OBS 4C data of the observation system, perform cross-correlation calculation on the forward extension and the data residual reverse extension, obtain an LSM imaging result through multiple iterations, and further obtain a seismic imaging result.
7. A computer readable storage medium storing one or more programs, wherein the one or more programs comprise instructions, which when executed by a computing device, cause the computing device to perform any of the methods of claims 1-5.
8. An electronic device comprising one or more processors, memory, and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, the one or more programs comprising instructions for performing any of the methods of claims 1-5.

Description

Method, system, equipment and medium for least square reverse time migration of new elastic wave Technical Field The invention relates to a new elastic wave least square reverse time migration method, system, equipment and medium based on a modified heave sound-elastic coupling equation, and relates to the technical field of petroleum geophysical exploration. Background With the rapid development of modern offshore oil and gas seismic exploration in data acquisition methods and processing technologies, the offshore oil and gas seismic exploration is developing from shallow water to deep water, from the sea surface to the sea bottom and from single component to multiple component. In recent years, deep water oil-gas seismic exploration has become an important point and a difficult point for geophysical exploration at home and abroad. The underwater region is elastic and the single component acquisition of the streamer does not meet the needs of the petroleum industry. The seafloor seismic survey deploys four-component (4C) sensors, including three-component (3C) geophones and hydrophones on the seafloor interface, and quantitatively estimates subsurface elastic parameters by processing observed seafloor 4C data. Wide azimuth, multiple coverage, high signal-to-noise ratio, and subsea multi-component observations have become important geophysical methods for offshore oil and gas exploration, development and estimation. The biggest advantage of seafloor seismic acquisition is that 4C seismic data observed above the seafloor carries effective subsurface elasticity information. Thus, these multicomponent data can be used for elastography. Traditional acoustic wave equations in marine environments lack transverse wave information, while single elastic wave equations are unstable, and the problem of numerical dispersion is easy to occur. In addition, the problem to be overcome is a rugged subsea interface, as the severely undulating interface can cause serious disturbances to the imaging results. The complex construction at this boundary produces strong scattering, resulting in complex wavefields and waveform distortions, which present significant difficulties in subsequent seismic processing. Disclosure of Invention The present invention aims to solve at least one of the technical problems existing in the prior art. Therefore, in order to solve the problems, the invention aims to provide a new elastic wave least square reverse time migration method based on a modified fluctuation acoustic-elastic coupling equation, which can solve the problems of artificial angular point scattering caused by low calculation efficiency of acoustic-elastic coupling media and boundary and transverse wave information missing and equation instability existing in a conventional single wave equation, and obtain an accurate imaging result. In order to achieve the above object, the present invention provides a new elastic wave least square reverse time migration method, which is characterized by comprising: acquiring a longitudinal wave velocity model, a transverse wave velocity model, a density model and OBS 4C data of an observation system; Performing wave field forward continuation based on the longitudinal wave velocity model, the transverse wave velocity model and the density model; performing residual reverse continuation based on the longitudinal wave velocity model, the transverse wave velocity model, the density model and the 4C data; Performing cross-correlation calculation on the forward continuation and the residual reverse continuation to obtain initial multi-parameter imaging; And performing forward modeling on the initial multiparameter imaging based on an ACE equation, obtaining OBS 4C data, performing residual reverse extension on the OBS 4C data obtained by modeling and the OBS 4C data of the observation system, performing cross-correlation calculation on the forward extension and the residual reverse extension, and performing multiple iterations to obtain an LSM imaging result, thereby obtaining a seismic imaging result. Further, wave field forward continuation based on a longitudinal wave velocity model, a transverse wave velocity model and a density model adopts the following formula: wherein, (x, z) is Cartesian coordinate values on grid points before coordinate transformation, and (ζ, η) is coordinate values of grid points after coordinate transformation; And Is the directional partial derivative, ρ 0 is the density, t is the time, f is the source term, τ xx0 and τ zz0 represent the positive stress component, τ xz0 represents the shear stress component, v x0,vz0 represents the velocity component in the horizontal x-direction and the vertical z-direction, P 0 is the acoustic stress, λ 0 and μ 0 are the lame constants, respectively. Further, a calculation formula for residual reverse continuation based on the longitudinal wave velocity model, the transverse wave velocity model, the density model and the 4C data is as