Compared with other migration methods, reverse-time migration is based on a precise wave equation, not an approximation, and performs extrapolation in the depth domain rather than the time domain. It is highly accurat...Compared with other migration methods, reverse-time migration is based on a precise wave equation, not an approximation, and performs extrapolation in the depth domain rather than the time domain. It is highly accurate and not affected by strong subsurface structure complexity and horizontal velocity variations. The difference method based on triangular grids maintains the simplicity of the difference method and the precision of the finite element method. It can be used directly for forward modeling on models with complex top surfaces and migration without statics preprocessing. We apply a finite difference method based on triangular grids for post-stack reverse-time migration for the first time. Tests on model data verify that the combination of the two methods can achieve near-perfect results in application.展开更多
Compared with the transverse isotropic(TI)medium,the orthorhombic anisotropic medium has both horizontal and vertical symmetry axes and it can be approximated as a set of vertical fissures developed in a group of hori...Compared with the transverse isotropic(TI)medium,the orthorhombic anisotropic medium has both horizontal and vertical symmetry axes and it can be approximated as a set of vertical fissures developed in a group of horizontal strata.Although the full-elastic orthorhombic anisotropic wave equation can accurately simulate seismic wave propagation in the underground media,a huge computational cost is required in seismic modeling,migration,and inversion.The conventional coupled pseudo-acoustic wave equations based on acoustic approximation can be used to significantly reduce the cost of calculation.However,these equations usually suffer from unwanted shear wave artifacts during wave propagation,and the presence of these artifacts can significantly degrade the imaging quality.To solve these problems,we derived a new pure P-wave equation for orthorhombic media that eliminates shear wave artifacts while compromising computational efficiency and accuracy.In addition,the derived equation involves pseudo-differential operators and it must be solved by 3D FFT algorithms.In order to reduce the number of 3D FFT,we utilized the finite difference and pseudo-spectral methods to conduct 3D forward modeling.Furthermore,we simplified the equation by using elliptic approximation and implemented 3D reverse-time migration(RTM).Forward modeling tests on several homogeneous and heterogeneous models confirm that the accuracy of the new equation is better than that of conventional methods.3D RTM imaging tests on three-layer and SEG/EAGE 3D salt models confirm that the ORT media have better imaging quality.展开更多
Presently the research based on the accurate seismic imaging methods for surface relief, complex structure, and complicated velocity distributions is of great significance. Reverse-time migration is considered to be o...Presently the research based on the accurate seismic imaging methods for surface relief, complex structure, and complicated velocity distributions is of great significance. Reverse-time migration is considered to be one of highly accurate methods. In this paper, we propose a new non-reflecting recursive algorithm for reverse-time migration by introducing the wave impedance function into the acoustic wave equation and the algorithm for the surface relief case is derived from the coordinate transformation principle. Using the exploding reflector principle and the zero-time imaging condition of poststack reverse- time migration, poststack numerical simulation and reverse-time migration with complex conditions can be realized. The results of synthetic and real data calculations show that the method effectively suppresses unwanted internal reflections and also deals with the seismic imaging problems resulting from surface relief. So, we prove that this method has strong adaptability and practicality.展开更多
Reverse-time migration in finite space requires effective boundary processing technology to eliminate the artificial truncation boundary effect in the migration result.On the basis of the elastic velocity-stress equat...Reverse-time migration in finite space requires effective boundary processing technology to eliminate the artificial truncation boundary effect in the migration result.On the basis of the elastic velocity-stress equations in vertical transversely isotropic media and the idea of the conventional split perfectly matched layer（PML）,the PML wave equations in reverse-time migration are derived in this paper and then the high order staggered grid discrete schemes are subsequently given.Aiming at the＂reflections＂from the boundary to the computational domain,as well as the effect of seismic event＇s abrupt changes at the two ends of the seismic array,the PML arrangement in reverse-time migration is given.The synthetic and real elastic,prestack,multi-component,reverse-time depth migration results demonstrate that this method has much better absorbing effects than other methods and the joint migration produces good imaging results.展开更多
The attenuation and anisotropy characteristics of real earth media give rise to amplitude loss and phase dispersion during seismic wave propagation.To address these effects on seismic imaging,viscoacoustic anisotropic...The attenuation and anisotropy characteristics of real earth media give rise to amplitude loss and phase dispersion during seismic wave propagation.To address these effects on seismic imaging,viscoacoustic anisotropic wave equations expressed by the fractional Laplacian have been derived.However,the huge computational expense associated with multiple Fast Fourier transforms for solving these wave equations makes them unsuitable for industrial applications,especially in three dimensions.Therefore,we first derived a cost-effective pure-viscoacoustic wave equation expressed by the memory-variable in tilted transversely isotropic(TTI)media,based on the standard linear solid model.The newly derived wave equation featuring decoupled amplitude dissipation and phase dispersion terms,can be easily solved using the finite-difference method(FDM).Computational efficiency analyses demonstrate that wavefields simulated by our newly derived wave equation are more efficient compared to the previous pure-viscoacoustic TTI wave equations.The decoupling characteristics of the phase dispersion and amplitude dissipation of the proposed wave equation are illustrated in numerical tests.Additionally,we extend the newly derived wave equation to implement Q-compensated reverse time migration(RTM)in attenuating TTI media.Synthetic examples and field data test demonstrate that the proposed Qcompensated TTI RTM effectively migrate the effects of anisotropy and attenuation,providing highquality imaging results.展开更多
With increased computational power, reverse-time prestack depth migration（RT-PSDM） has become a preferred imaging tool in seismic exploration, yet its use has remained relatively limited in ground-penetrating radar...With increased computational power, reverse-time prestack depth migration（RT-PSDM） has become a preferred imaging tool in seismic exploration, yet its use has remained relatively limited in ground-penetrating radar（GPR） applications. Complex topography alters the wavefield kinematics making for a challenging imaging problem. Model simulations show that topographic variation can substantially distort reflection amplitudes due to irregular wavefield spreading, attenuation anomalies due to irregular path lengths, and focusing and defocusing effects at the surface. The effects are magnified when the topographic variations are on the same order as the depth of investigation––a situation that is often encountered in GPR investigations. Here, I use a full wave-equation RT-PSDM algorithm to image GPR data in the presence of large topographic variability relative to the depth of investigation. The source and receiver wavefields are propagated directly from the topographic surface and this approach inherently corrects for irregular kinematics, spreading and attenuation. The results show that when GPR data are acquired in areas of extreme topography, RT-PSDM can accurately reconstruct reflector geometry as well as reflection amplitude.展开更多
Imaging the PP- and PS-wave for the elastic vector wave reverse-time migration requires separating the P- and S-waves during the wave field extrapolation. The amplitude and phase of the P- and S-waves are distorted wh...Imaging the PP- and PS-wave for the elastic vector wave reverse-time migration requires separating the P- and S-waves during the wave field extrapolation. The amplitude and phase of the P- and S-waves are distorted when divergence and curl operators are used to separate the P- and S-waves. We present a P- and S-wave amplitude-preserving separation algorithm for the elastic wavefield extrapolation. First, we add the P-wave pressure and P-wave vibration velocity equation to the conventional elastic wave equation to decompose the P- and S-wave vectors. Then, we synthesize the scalar P- and S-wave from the vector P- and S-wave to obtain the scalar P- and S-wave. The amplitude-preserved separated P- and S-waves are imaged based on the vector wave reverse-time migration (RTM). This method ensures that the amplitude and phase of the separated P- and S-wave remain unchanged compared with the divergence and curl operators. In addition, after decomposition, the P-wave pressure and vibration velocity can be used to suppress the interlayer reflection noise and to correct the S-wave polarity. This improves the image quality of P- and S-wave in multicomponent seismic data and the true-amplitude elastic reverse time migration used in prestack inversion.展开更多
Least squares reverse-time migration （LSRTM） is an inversion method that removes artificial images and preserves the amplitude of reflectivity sections. LSRTM has been used in reservoir exploration and processing of...Least squares reverse-time migration （LSRTM） is an inversion method that removes artificial images and preserves the amplitude of reflectivity sections. LSRTM has been used in reservoir exploration and processing of 4D seismic data. LSRTM is, however, a computationally costly and memory-intensive method. In this study, LSRTM in the pseudodepth domain was combined with the conjugate gradient method to reduce the computational cost while maintaining precision. The velocity field in the depth domain was transformed to the velocity field in the pseudodepth domain; thus, the total number of vertical sampling points was reduced and oversampling was avoided. Synthetic and field data were used to validate the proposed method. LSRTM in the pseudodepth domain in conjunction with the conjugate gradient method shows potential in treating field data.展开更多
Reverse-time migration has attracted more and more attention owing to the advantages of high imaging accuracy, no dip restriction, and adaptation to complex velocity models. Cross-correlation imaging method is typical...Reverse-time migration has attracted more and more attention owing to the advantages of high imaging accuracy, no dip restriction, and adaptation to complex velocity models. Cross-correlation imaging method is typically used in conventional reverse-time migration that produces images with strong low-frequency noise. Wavefield decomposition imaging can suppress such noise; however, some residual noise persists in the imaging results. We propose a 2D multidirectional wavefield decomposition method based on the traditional wavefield decomposition method. First, source wavefields and receiver wavefields are separated into eight subwavefields, respectively. Second, cross-correlation imaging is applied to selected subwavefields to produce subimages. Finally, the subimages are stacked to generate the final image. Numerical examples suggest that the proposed method can eliminate the low-frequency noise effectively and produce high-quality imaging profiles.展开更多
Least-squares reverse-time migration(LSRTM) formulates reverse-time migration(RTM) in the leastsquares inversion framework to obtain the optimal reflectivity image. It can generate images with more accurate amplitudes...Least-squares reverse-time migration(LSRTM) formulates reverse-time migration(RTM) in the leastsquares inversion framework to obtain the optimal reflectivity image. It can generate images with more accurate amplitudes, higher resolution, and fewer artifacts than RTM. However, three problems still exist:(1) inversion can be dominated by strong events in the residual;(2) low-wavenumber artifacts in the gradient affect convergence speed and imaging results;(3) high-wavenumber noise is also amplified as iteration increases. To solve these three problems, we have improved LSRTM: firstly, we use Hubernorm as the objective function to emphasize the weak reflectors during the inversion;secondly, we adapt the de-primary imaging condition to remove the low-wavenumber artifacts above strong reflectors as well as the false high-wavenumber reflectors in the gradient;thirdly, we apply the L1-norm sparse constraint in the curvelet-domain as the regularization term to suppress the high-wavenumber migration noise. As the new inversion objective function contains the non-smooth L1-norm, we use a modified iterative soft thresholding(IST) method to update along the Polak-Ribie re conjugate-gradient direction by using a preconditioned non-linear conjugate-gradient(PNCG) method. The numerical examples,especially the Sigsbee2 A model, demonstrate that the Huber inversion-based RTM can generate highquality images by mitigating migration artifacts and improving the contribution of weak reflection events.展开更多
Research on seismic anisotropy and attenuation plays a significant role in exploration geophysics. To enhance the imaging quality for complicated structures, we develop several effective improvements for anisotropic a...Research on seismic anisotropy and attenuation plays a significant role in exploration geophysics. To enhance the imaging quality for complicated structures, we develop several effective improvements for anisotropic attenuation effects in reverse-time migration (Q-RTM) on surface and vertical seismic profiling (VSP) acquisition geometries. First, to suppress pseudo-shear wave artifact and numerical instability of the commonly used anisotropic pseudo-acoustic wave equations, an optimized pure P-wave dispersion relation is derived and the corresponding pure-mode wave equation is solved by combining the finite-difference and Possion methods. Second, a simplified anisotropic pure-mode visco-acoustic wave equation (PVAWE) based on standard linear solid model is established. Third, a time-dispersion correlation strategy is applied to improve the modeling accuracy. Fourth, we extend a target-oriented scheme to anisotropic attenuated modeling and imaging. Instead of the conventional wavefield modeling and RTM, the proposed approach can extract available wavefield information near the target regions and produce high imaging resolution for target structures. Last, both anisotropic surface and VSP Q-RTMs are executed by combining optimized PVAWE, time-dispersion correlation and target-oriented algorithm. Modeling examples demonstrate the advantages of our schemes. Moreover, our modified Q-compensated imaging workflow can be regarded as a supplement to the classical anisotropic RTM.展开更多
Angle-domain common-image gathers （ADCIGs） transformed from the shot- domain common-offset gathers are input to migration velocity analysis （MVA） and prestack inversion. ADCIGs are non-illusion prestack inversion ...Angle-domain common-image gathers （ADCIGs） transformed from the shot- domain common-offset gathers are input to migration velocity analysis （MVA） and prestack inversion. ADCIGs are non-illusion prestack inversion gathers, and thus, accurate. We studied the extraction of elastic-wave ADCIGs based on amplitude-preserving elastic-wave reverse- time migration for calculating the incidence angle of P- and S-waves at each image point and for different source locations. The P- and S-waves share the same incident angle, namely the incident angle of the source P-waves. The angle of incidence of the source P-wavefield was the difference between the source P-wave propagation angle and the reflector dips. The propagation angle of the source P-waves was obtained from the polarization vector of the decomposed P-waves. The reflectors＇ normal direction angle was obtained using the complex wavenumber of the stacked reverse-time migration （RTM） images. The ADCIGs of P- and S-waves were obtained by rearranging the common-shot migration gathers based on the incident angle. We used a horizontally layered model, the graben medium model, and part of the Marmousi-II elastic model and field data to test the proposed algorithm. The results suggested that the proposed method can efficiently extract the P- and S-wave ADCIGs of the elastic-wave reverse-time migration, the P- and S-wave incident angle, and the angle-gather amplitude fidelity, and improve the MVA and prestack inversion.展开更多
The migration of multi-wave seismic data is aimed at obtaining the P- and S-wave imaging results of the amplitude preserving. But the P- and S-wave stretching effect produced by the reverse time migration of the elast...The migration of multi-wave seismic data is aimed at obtaining the P- and S-wave imaging results of the amplitude preserving. But the P- and S-wave stretching effect produced by the reverse time migration of the elastic wave equation will not only reduce the vertical resolution of the migration results and the amplitude preserving of the large reflection angle. In this paper, the reverse time migration technique of amplitude preserving vector wave-field separating is used. Based on the analysis of the stretch mechanism and the influencing factors of stretch magnitude, the paper gave the stretch correcting factors. Then, realize the stretch correction method at the time that after the reverse extrapolation and before the imaging by solving the problem which is how to calculate the P-wave and Ps-wave propagation directions of imaging points at different times. The stretch correction method can improve the vertical resolution and amplitude fidelity of the imaging results and provide high fidelity input data for seismic data interpretation and inversion.展开更多
In ground-penetrating radar （GPR） imaging, it is common for the depth of investigation to be on the same order as the variability in surface topography, In such cases, migration fails when it is carried out from a d...In ground-penetrating radar （GPR） imaging, it is common for the depth of investigation to be on the same order as the variability in surface topography, In such cases, migration fails when it is carried out from a datum after the application of elevation statics, We introduce a reverse-time migration （RTM） algorithm based on the second-order decoupled form of Maxwell＇s equations, which requires computation of only the electric field, The wavefield extrapolation is computed directly from the acquisition surface without the need for datuming, In a synthetic case study, the algorithm significantly improves image accuracy over a processing sequence in which migration is performed after elevation statics, In addition, we acquired a field dataset at the Coral Pink Sand Dunes （CPSD） in Utah, USA, The data were acquired over rugged topography and have the complex internal stratigraphy of multiply eroded, modern, and ancient eolian deposits, The RTM algorithm significantly improves radar depth images in this challenging environment,展开更多
When seismic exploration is conducted in a special geological environment such as a tunnel space,the traditional imaging method in the Cartesian coordinate system cannot accurately discretize the air column in that en...When seismic exploration is conducted in a special geological environment such as a tunnel space,the traditional imaging method in the Cartesian coordinate system cannot accurately discretize the air column in that environment.Thus,obtaining Thus,obtaining highquality imaging results is diffi cult.Therefore,an elastic-wave reverse-time migration method based on the polar coordinate system is proposed.In this method,three boundary conditions exist:outer,inner,and corner boundaries.In the outer boundary,the polar-coordinated absorbing boundary in the radial direction is used to suppress the artifi cial-boundary refl ection.The free-surface boundary condition is adopted in the tunnel space at the inner boundary.In the angular boundaries,we use two diff erent boundary conditions for two cases.The air column in the tunnel space is usually not an irregular circle.Therefore,the irregular tunnelspace geological body in the polar coordinate system is meshed into curvilinear grids and transformed into a regular one in an auxiliary polar coordinate system using the mapping method.Finally,elastic reverse-time migration technology is applied into the auxiliary polar coordinate system.In the numerical examples,two typical models are used to test the proposed method,which verify that the proposed method can obtain accurate images from the datasets in the tunnel space.展开更多
In real strata anisotropy and viscosity extensively exists. They degraded waveforms in amplitude, resulting in which reducing of image resolution. To obtain high-precision imaging of deep reservoirs, we extended the s...In real strata anisotropy and viscosity extensively exists. They degraded waveforms in amplitude, resulting in which reducing of image resolution. To obtain high-precision imaging of deep reservoirs, we extended the separated viscous and anisotropic reverse time migration （RTM） to a stable viscoacoustic anisotropic RTM for vertical transverse isotropic （VTI） media, based on single generalized standard and linear solid （GSLS） media theory.. We used a pseudo-spectral method to develop the numerical simulation. By introducing a regularization operator to eliminate the high-frequency instability problem, we built a stable inverse propagator and achieved viscoacoustic VTI media RTM. High-resolution imaging results were obtained after correcting for the effects of anisotropy and viscosity. Synthetic tests verify the validity and accuracy of algorithm.展开更多
Correctly locating the tunnel lining cavity is extremely important tunnel quality inspection.High-accuracy imaging results are hard to obtain because conventional one-way wave migration is greatly aff ected by lateral...Correctly locating the tunnel lining cavity is extremely important tunnel quality inspection.High-accuracy imaging results are hard to obtain because conventional one-way wave migration is greatly aff ected by lateral velocity change and inclination limitation and because the diff racted wave cannot be accurately returned to the real spatial position of the lining cavity.This paper presents a tunnel lining cavity imaging method based on the groundpenetrating radar(GPR)reverse-time migration(RTM)algorithm.The principle of GPR RTM is described in detail using the electromagnetic wave equation.The finite-difference timedomain method is employed to calculate the backward extrapolation electromagnetic fi elds,and the zero-time imaging condition based on the exploding-reflector concept is used to obtain the RTM results.On this basis,the GPR RTM program is compiled and applied to the simulated and observed GPR data of a typical tunnel lining cavity GPR model and a physical lining cavity model.Comparison of RTM and Kirchhoff migration results reveals that the RTM can better converge the diff racted waves of steel bar and cavity to their true position and have higher resolution and better suppress the eff ect of multiple interference and clutter scattering waves.In addition,comparison of RTM results of diff erent degrees of noise shows that RTM has strong anti-interference ability and can be used for the accurate interpretation of radar profi le in a strong interference environment.展开更多
In elastic-wave reverse-time migration(ERTM),the reverse-time reconstruction of source wavefield takes advantage of the computing power of GPU,avoids its disadvantages in disk-access efficiency and reading and writing...In elastic-wave reverse-time migration(ERTM),the reverse-time reconstruction of source wavefield takes advantage of the computing power of GPU,avoids its disadvantages in disk-access efficiency and reading and writing of temporary files,and realizes the synchronous extrapolation of source and receiver wavefields.Among the existing source wavefield reverse-time reconstruction algorithms,the random boundary algorithm has been widely used in three-dimensional(3D)ERTM because it requires the least storage of temporary files and low-frequency disk access during reverse-time migration.However,the existing random boundary algorithm cannot completely destroy the coherence of the artificial boundary reflected wavefield.This random boundary reflected wavefield with a strong coherence would be enhanced in the cross-correlation image processing of reverse-time migration,resulting in noise and fictitious image in the migration results,which will reduce the signal-to-noise ratio and resolution of the migration section near the boundary.To overcome the above issues,we present an ERTM random boundary-noise suppression method based on generative adversarial networks.First,we use the Resnet network to construct the generator of CycleGAN,and the discriminator is constructed by using the PatchGAN network.Then,we use the gradient descent methods to train the network.We fix some parameters,update the other parameters,and iterate,alternate,and continuously optimize the generator and discriminator to achieve the Nash equilibrium state and obtain the best network structure.Finally,we apply this network to the process of reverse-time migration.The snapshot of noisy wavefield is regarded as a 2D matrix data picture,which is used for training,testing,noise suppression,and imaging.This method can identify the reflected signal in the wavefield,suppress the noise generated by the random boundary,and achieve denoising.Numerical examples show that the proposed method can significantly improve the imaging quality of ERTM.展开更多
Prestack elastic reverse time migration( RTM) requires multicomponent seismic data. But for multicomponent elastic Kirchhoff migration,there is a limitation that ray theory no longer applies if thegeology becomes comp...Prestack elastic reverse time migration( RTM) requires multicomponent seismic data. But for multicomponent elastic Kirchhoff migration,there is a limitation that ray theory no longer applies if thegeology becomes complicated. In this paper,the authors have created a new 2D migration context for isotropic,elastic RTM,which included decomposition of the elastic source and receiver wavefields into P and S wave vectors by decoupled elastodynamic extrapolation,which retained the same stress and particle velocity components as the input data. Then we appliedsource-normalized crosscorrelation imaging condition in elastic reverse time migration to compensate the energy of deep strata. We found that the resulting images were nearly identical to the velocity model,and the resolution has been improved. Our method is a wavefielddecomposition based on vector,and we can alsoavoid the problem of polarity reversal of converted shear wave imaging. It proved the applicability of the method proposed in our paper.展开更多
A least-squares reverse-time migration scheme is presented for reflectivity imaging. Based on an accurate reflection modeling formula, this scheme produces amplitude-preserved stacked reflectivity images with zero pha...A least-squares reverse-time migration scheme is presented for reflectivity imaging. Based on an accurate reflection modeling formula, this scheme produces amplitude-preserved stacked reflectivity images with zero phase. Spatial preconditioning, weighting and the Barzilai-Borwein method are applied to speed up the convergence of the least-squares inversion. In addition, this scheme compensates the effect of ghost waves to broaden the bandwidth of the reflectivity images. Furthermore, roughness penalty constraint is used to regularize the inversion, which in turn stabilizes inversion and removes high-wavenumber artifacts and mitigates spatial aliasing. The examples of synthetic and field datasets demonstrate the scheme can generate zerophase reflectivity images with broader bandwidth, higher resolution, fewer artifacts and more reliable amplitudes than conventional reverse-time migration.展开更多
基金sponsored by National Natural Science Foundation(40474041)National Symposium of 863(2006AA06Z206)+1 种基金National Symposium of 973(2007CB209605)CNPC Geophysical Key Laboratory of the China University of Petroleum (East China) Research Department
文摘Compared with other migration methods, reverse-time migration is based on a precise wave equation, not an approximation, and performs extrapolation in the depth domain rather than the time domain. It is highly accurate and not affected by strong subsurface structure complexity and horizontal velocity variations. The difference method based on triangular grids maintains the simplicity of the difference method and the precision of the finite element method. It can be used directly for forward modeling on models with complex top surfaces and migration without statics preprocessing. We apply a finite difference method based on triangular grids for post-stack reverse-time migration for the first time. Tests on model data verify that the combination of the two methods can achieve near-perfect results in application.
基金supported by the Marine S&T Fund of Shandong Province for Pilot National Laboratory for Marine Science and Technology(No.2021QNLM020001)the Major Scientific and Technological Projects of Shandong Energy Group(No.SNKJ2022A06-R23)+2 种基金the Funds of Creative Research Groups of China(No.41821002)National Natural Science Foundation of China Outstanding Youth Science Fund Project(Overseas)(No.ZX20230152)the Major Scientific and Technological Projects of CNPC(No.ZD2019-183-003)。
文摘Compared with the transverse isotropic(TI)medium,the orthorhombic anisotropic medium has both horizontal and vertical symmetry axes and it can be approximated as a set of vertical fissures developed in a group of horizontal strata.Although the full-elastic orthorhombic anisotropic wave equation can accurately simulate seismic wave propagation in the underground media,a huge computational cost is required in seismic modeling,migration,and inversion.The conventional coupled pseudo-acoustic wave equations based on acoustic approximation can be used to significantly reduce the cost of calculation.However,these equations usually suffer from unwanted shear wave artifacts during wave propagation,and the presence of these artifacts can significantly degrade the imaging quality.To solve these problems,we derived a new pure P-wave equation for orthorhombic media that eliminates shear wave artifacts while compromising computational efficiency and accuracy.In addition,the derived equation involves pseudo-differential operators and it must be solved by 3D FFT algorithms.In order to reduce the number of 3D FFT,we utilized the finite difference and pseudo-spectral methods to conduct 3D forward modeling.Furthermore,we simplified the equation by using elliptic approximation and implemented 3D reverse-time migration(RTM).Forward modeling tests on several homogeneous and heterogeneous models confirm that the accuracy of the new equation is better than that of conventional methods.3D RTM imaging tests on three-layer and SEG/EAGE 3D salt models confirm that the ORT media have better imaging quality.
基金supported by the National Natural Science Foundation of China (Grant No. 40974073)the National 863 Program (Grant No.2007AA060504)the National 973 Program (Grant No. 2007CB209605) and CNPC Geophysical Laboratories
文摘Presently the research based on the accurate seismic imaging methods for surface relief, complex structure, and complicated velocity distributions is of great significance. Reverse-time migration is considered to be one of highly accurate methods. In this paper, we propose a new non-reflecting recursive algorithm for reverse-time migration by introducing the wave impedance function into the acoustic wave equation and the algorithm for the surface relief case is derived from the coordinate transformation principle. Using the exploding reflector principle and the zero-time imaging condition of poststack reverse- time migration, poststack numerical simulation and reverse-time migration with complex conditions can be realized. The results of synthetic and real data calculations show that the method effectively suppresses unwanted internal reflections and also deals with the seismic imaging problems resulting from surface relief. So, we prove that this method has strong adaptability and practicality.
基金supported by the 863 Program(Grant No.2006AA06Z202)Open Fund of the Key Laboratory of Geophysical Exploration of CNPC(Grant No.GPKL0802)+1 种基金CNPC Young Innovation Fund(Grant No.05E7028)the Program for New Century Excellent Talents in University(Grant No.NCET-07-0845)
文摘Reverse-time migration in finite space requires effective boundary processing technology to eliminate the artificial truncation boundary effect in the migration result.On the basis of the elastic velocity-stress equations in vertical transversely isotropic media and the idea of the conventional split perfectly matched layer（PML）,the PML wave equations in reverse-time migration are derived in this paper and then the high order staggered grid discrete schemes are subsequently given.Aiming at the＂reflections＂from the boundary to the computational domain,as well as the effect of seismic event＇s abrupt changes at the two ends of the seismic array,the PML arrangement in reverse-time migration is given.The synthetic and real elastic,prestack,multi-component,reverse-time depth migration results demonstrate that this method has much better absorbing effects than other methods and the joint migration produces good imaging results.
基金supported by the Marine S&T Fund of Shandong Province for Pilot National Laboratory for Marine Science and Technology(Qingdao)(No.2021QNLM020001)the Major Scientificand Technological Projects of Shandong Energy Group(No.SNKJ2022A06-R23)+1 种基金the National Natural Science Foundation of China(No.42374164)the basic theoretical research of seismic wave imaging technology in complex oilfield of Changqing Oilfield Company(No.2023-10502)。
文摘The attenuation and anisotropy characteristics of real earth media give rise to amplitude loss and phase dispersion during seismic wave propagation.To address these effects on seismic imaging,viscoacoustic anisotropic wave equations expressed by the fractional Laplacian have been derived.However,the huge computational expense associated with multiple Fast Fourier transforms for solving these wave equations makes them unsuitable for industrial applications,especially in three dimensions.Therefore,we first derived a cost-effective pure-viscoacoustic wave equation expressed by the memory-variable in tilted transversely isotropic(TTI)media,based on the standard linear solid model.The newly derived wave equation featuring decoupled amplitude dissipation and phase dispersion terms,can be easily solved using the finite-difference method(FDM).Computational efficiency analyses demonstrate that wavefields simulated by our newly derived wave equation are more efficient compared to the previous pure-viscoacoustic TTI wave equations.The decoupling characteristics of the phase dispersion and amplitude dissipation of the proposed wave equation are illustrated in numerical tests.Additionally,we extend the newly derived wave equation to implement Q-compensated reverse time migration(RTM)in attenuating TTI media.Synthetic examples and field data test demonstrate that the proposed Qcompensated TTI RTM effectively migrate the effects of anisotropy and attenuation,providing highquality imaging results.
基金The Herbette Fondation at the University of Lausanne, Switzerland
文摘With increased computational power, reverse-time prestack depth migration（RT-PSDM） has become a preferred imaging tool in seismic exploration, yet its use has remained relatively limited in ground-penetrating radar（GPR） applications. Complex topography alters the wavefield kinematics making for a challenging imaging problem. Model simulations show that topographic variation can substantially distort reflection amplitudes due to irregular wavefield spreading, attenuation anomalies due to irregular path lengths, and focusing and defocusing effects at the surface. The effects are magnified when the topographic variations are on the same order as the depth of investigation––a situation that is often encountered in GPR investigations. Here, I use a full wave-equation RT-PSDM algorithm to image GPR data in the presence of large topographic variability relative to the depth of investigation. The source and receiver wavefields are propagated directly from the topographic surface and this approach inherently corrects for irregular kinematics, spreading and attenuation. The results show that when GPR data are acquired in areas of extreme topography, RT-PSDM can accurately reconstruct reflector geometry as well as reflection amplitude.
基金supported by Special Research Grant for Non-profit Public Service(No.201511037)National Natural Science Foundation of China(No.41504109,41506084,and 41406071)+1 种基金China Postdoctoral Science Foundation(No.2015M582060)Qingdao Municipal Applied Research Projects(No.2015308)
文摘Imaging the PP- and PS-wave for the elastic vector wave reverse-time migration requires separating the P- and S-waves during the wave field extrapolation. The amplitude and phase of the P- and S-waves are distorted when divergence and curl operators are used to separate the P- and S-waves. We present a P- and S-wave amplitude-preserving separation algorithm for the elastic wavefield extrapolation. First, we add the P-wave pressure and P-wave vibration velocity equation to the conventional elastic wave equation to decompose the P- and S-wave vectors. Then, we synthesize the scalar P- and S-wave from the vector P- and S-wave to obtain the scalar P- and S-wave. The amplitude-preserved separated P- and S-waves are imaged based on the vector wave reverse-time migration (RTM). This method ensures that the amplitude and phase of the separated P- and S-wave remain unchanged compared with the divergence and curl operators. In addition, after decomposition, the P-wave pressure and vibration velocity can be used to suppress the interlayer reflection noise and to correct the S-wave polarity. This improves the image quality of P- and S-wave in multicomponent seismic data and the true-amplitude elastic reverse time migration used in prestack inversion.
基金This research is sponsored by The National Natural Science Fund （No. 41574098）, Shandong Provincial Natural Science Foundation （No. ZR201807080087）, the Fundamental Research Funds for the Central Universities （No. 18CX02059A）, the National Natural Science Fund （No. 41504100）, and the national oil and gas major project （No. 2016ZX05006-002）.
文摘Least squares reverse-time migration （LSRTM） is an inversion method that removes artificial images and preserves the amplitude of reflectivity sections. LSRTM has been used in reservoir exploration and processing of 4D seismic data. LSRTM is, however, a computationally costly and memory-intensive method. In this study, LSRTM in the pseudodepth domain was combined with the conjugate gradient method to reduce the computational cost while maintaining precision. The velocity field in the depth domain was transformed to the velocity field in the pseudodepth domain; thus, the total number of vertical sampling points was reduced and oversampling was avoided. Synthetic and field data were used to validate the proposed method. LSRTM in the pseudodepth domain in conjunction with the conjugate gradient method shows potential in treating field data.
基金This work was supported by National Natural Science Foundation of China （No. 41474110） and the Scientific Research Starting Foundation of China University of Petroleum-Beijing at Karamay （No. RCYJ2018A-01-001）.
文摘Reverse-time migration has attracted more and more attention owing to the advantages of high imaging accuracy, no dip restriction, and adaptation to complex velocity models. Cross-correlation imaging method is typically used in conventional reverse-time migration that produces images with strong low-frequency noise. Wavefield decomposition imaging can suppress such noise; however, some residual noise persists in the imaging results. We propose a 2D multidirectional wavefield decomposition method based on the traditional wavefield decomposition method. First, source wavefields and receiver wavefields are separated into eight subwavefields, respectively. Second, cross-correlation imaging is applied to selected subwavefields to produce subimages. Finally, the subimages are stacked to generate the final image. Numerical examples suggest that the proposed method can eliminate the low-frequency noise effectively and produce high-quality imaging profiles.
基金supported by National Key R&D Program of China (No. 2018YFA0702502)NSFC (Grant No. 41974142, 42074129, and 41674114)+1 种基金Science Foundation of China University of Petroleum (Beijing) (Grant No. 2462020YXZZ005)State Key Laboratory of Petroleum Resources and Prospecting (Grant No. PRP/indep-42012)。
文摘Least-squares reverse-time migration(LSRTM) formulates reverse-time migration(RTM) in the leastsquares inversion framework to obtain the optimal reflectivity image. It can generate images with more accurate amplitudes, higher resolution, and fewer artifacts than RTM. However, three problems still exist:(1) inversion can be dominated by strong events in the residual;(2) low-wavenumber artifacts in the gradient affect convergence speed and imaging results;(3) high-wavenumber noise is also amplified as iteration increases. To solve these three problems, we have improved LSRTM: firstly, we use Hubernorm as the objective function to emphasize the weak reflectors during the inversion;secondly, we adapt the de-primary imaging condition to remove the low-wavenumber artifacts above strong reflectors as well as the false high-wavenumber reflectors in the gradient;thirdly, we apply the L1-norm sparse constraint in the curvelet-domain as the regularization term to suppress the high-wavenumber migration noise. As the new inversion objective function contains the non-smooth L1-norm, we use a modified iterative soft thresholding(IST) method to update along the Polak-Ribie re conjugate-gradient direction by using a preconditioned non-linear conjugate-gradient(PNCG) method. The numerical examples,especially the Sigsbee2 A model, demonstrate that the Huber inversion-based RTM can generate highquality images by mitigating migration artifacts and improving the contribution of weak reflection events.
基金supported by the National Key R&D Program of China(2021YFA0716902)National Natural Science Foundation of China(42004119,42174156)+1 种基金the Fundamental Research Funds for the Central Universities,CHD(300102261306)the National Engineering Research Center of Offshore Oil and Gas Exploration,No.6 Courtyard,Taiyanggong South Street,Chaoyang District,Beijing,100028.
文摘Research on seismic anisotropy and attenuation plays a significant role in exploration geophysics. To enhance the imaging quality for complicated structures, we develop several effective improvements for anisotropic attenuation effects in reverse-time migration (Q-RTM) on surface and vertical seismic profiling (VSP) acquisition geometries. First, to suppress pseudo-shear wave artifact and numerical instability of the commonly used anisotropic pseudo-acoustic wave equations, an optimized pure P-wave dispersion relation is derived and the corresponding pure-mode wave equation is solved by combining the finite-difference and Possion methods. Second, a simplified anisotropic pure-mode visco-acoustic wave equation (PVAWE) based on standard linear solid model is established. Third, a time-dispersion correlation strategy is applied to improve the modeling accuracy. Fourth, we extend a target-oriented scheme to anisotropic attenuated modeling and imaging. Instead of the conventional wavefield modeling and RTM, the proposed approach can extract available wavefield information near the target regions and produce high imaging resolution for target structures. Last, both anisotropic surface and VSP Q-RTMs are executed by combining optimized PVAWE, time-dispersion correlation and target-oriented algorithm. Modeling examples demonstrate the advantages of our schemes. Moreover, our modified Q-compensated imaging workflow can be regarded as a supplement to the classical anisotropic RTM.
基金supported by Financially Supported by Qingdao National Laboratory for Marine Science and Technology(No.QNLM2016ORP0206)National Science and Technology Major Project(No.2016ZX05027-002)+6 种基金China Postdoctoral Science Foundation(No.2017M612219)National Key R&D Plan(Nos.2017YFC0306706 and 2017YFC0307400)Financially Supported by Qingdao National Laboratory for Marine Science and Technology(No.QNLM201708)Natural Science Foundation of Shandong Province(No.ZR2016DB10)National Natural Science Foundation of China(Nos.41674118,41504109,and 41506084)Key Laboratory of Submarine Geosciences Foundation of SOA(No.KLSG1603)Qingdao Municipal Applied Research Projects(No.2016238)
文摘Angle-domain common-image gathers （ADCIGs） transformed from the shot- domain common-offset gathers are input to migration velocity analysis （MVA） and prestack inversion. ADCIGs are non-illusion prestack inversion gathers, and thus, accurate. We studied the extraction of elastic-wave ADCIGs based on amplitude-preserving elastic-wave reverse- time migration for calculating the incidence angle of P- and S-waves at each image point and for different source locations. The P- and S-waves share the same incident angle, namely the incident angle of the source P-waves. The angle of incidence of the source P-wavefield was the difference between the source P-wave propagation angle and the reflector dips. The propagation angle of the source P-waves was obtained from the polarization vector of the decomposed P-waves. The reflectors＇ normal direction angle was obtained using the complex wavenumber of the stacked reverse-time migration （RTM） images. The ADCIGs of P- and S-waves were obtained by rearranging the common-shot migration gathers based on the incident angle. We used a horizontally layered model, the graben medium model, and part of the Marmousi-II elastic model and field data to test the proposed algorithm. The results suggested that the proposed method can efficiently extract the P- and S-wave ADCIGs of the elastic-wave reverse-time migration, the P- and S-wave incident angle, and the angle-gather amplitude fidelity, and improve the MVA and prestack inversion.
基金financially supported by Qingdao National Laboratory for Marine Science and Technology (QNLM2016ORP0206)National Science and Technology Major Project (2016ZX05027-002)+3 种基金National Key R&D Plan (2017YFC0306706-04, 2017YFC0307400)Qingdao National Laboratory for Marine Science and Technology (QNLM201708)China Postdoctoral Science Foundation (No. 2017M612219)Natural Science Foundation of Shandong Province (No. ZR2016DB10).
文摘The migration of multi-wave seismic data is aimed at obtaining the P- and S-wave imaging results of the amplitude preserving. But the P- and S-wave stretching effect produced by the reverse time migration of the elastic wave equation will not only reduce the vertical resolution of the migration results and the amplitude preserving of the large reflection angle. In this paper, the reverse time migration technique of amplitude preserving vector wave-field separating is used. Based on the analysis of the stretch mechanism and the influencing factors of stretch magnitude, the paper gave the stretch correcting factors. Then, realize the stretch correction method at the time that after the reverse extrapolation and before the imaging by solving the problem which is how to calculate the P-wave and Ps-wave propagation directions of imaging points at different times. The stretch correction method can improve the vertical resolution and amplitude fidelity of the imaging results and provide high fidelity input data for seismic data interpretation and inversion.
基金The Herbette Foundation at the University of Lausanne provided support for the development of the RTM algorithm
文摘In ground-penetrating radar （GPR） imaging, it is common for the depth of investigation to be on the same order as the variability in surface topography, In such cases, migration fails when it is carried out from a datum after the application of elevation statics, We introduce a reverse-time migration （RTM） algorithm based on the second-order decoupled form of Maxwell＇s equations, which requires computation of only the electric field, The wavefield extrapolation is computed directly from the acquisition surface without the need for datuming, In a synthetic case study, the algorithm significantly improves image accuracy over a processing sequence in which migration is performed after elevation statics, In addition, we acquired a field dataset at the Coral Pink Sand Dunes （CPSD） in Utah, USA, The data were acquired over rugged topography and have the complex internal stratigraphy of multiply eroded, modern, and ancient eolian deposits, The RTM algorithm significantly improves radar depth images in this challenging environment,
基金financially supported by the National Natural Science Foundation of China (grant Nos. 41904101 and 41774133)Natural Science Foundation of Shandong Province (grant No. ZR2019QD004)+1 种基金Fundamental Research Funds for the Central Universities (grant No. 19CX02010A)the Open Funds of SINOPEC Key Laboratory of Geophysics (grant No. wtyjy-wx2019-01-03)。
文摘When seismic exploration is conducted in a special geological environment such as a tunnel space,the traditional imaging method in the Cartesian coordinate system cannot accurately discretize the air column in that environment.Thus,obtaining Thus,obtaining highquality imaging results is diffi cult.Therefore,an elastic-wave reverse-time migration method based on the polar coordinate system is proposed.In this method,three boundary conditions exist:outer,inner,and corner boundaries.In the outer boundary,the polar-coordinated absorbing boundary in the radial direction is used to suppress the artifi cial-boundary refl ection.The free-surface boundary condition is adopted in the tunnel space at the inner boundary.In the angular boundaries,we use two diff erent boundary conditions for two cases.The air column in the tunnel space is usually not an irregular circle.Therefore,the irregular tunnelspace geological body in the polar coordinate system is meshed into curvilinear grids and transformed into a regular one in an auxiliary polar coordinate system using the mapping method.Finally,elastic reverse-time migration technology is applied into the auxiliary polar coordinate system.In the numerical examples,two typical models are used to test the proposed method,which verify that the proposed method can obtain accurate images from the datasets in the tunnel space.
基金Research is sponsored by the National Natural Science Fund(No.41274117)the National Natural Science Fund(No.41574098)Sinopec Geophysical Key Laboratory Open Fund(No.wtyjy-wx2016-04-2)
文摘In real strata anisotropy and viscosity extensively exists. They degraded waveforms in amplitude, resulting in which reducing of image resolution. To obtain high-precision imaging of deep reservoirs, we extended the separated viscous and anisotropic reverse time migration （RTM） to a stable viscoacoustic anisotropic RTM for vertical transverse isotropic （VTI） media, based on single generalized standard and linear solid （GSLS） media theory.. We used a pseudo-spectral method to develop the numerical simulation. By introducing a regularization operator to eliminate the high-frequency instability problem, we built a stable inverse propagator and achieved viscoacoustic VTI media RTM. High-resolution imaging results were obtained after correcting for the effects of anisotropy and viscosity. Synthetic tests verify the validity and accuracy of algorithm.
基金supported by the National Natural Science Foundation of China (Nos. 41764005, 41604039, 41604102, and 41574078)Guangxi Natural Science Foundation of China (Nos. 2016GXNSFBA380082 and 2016GXNSFBA380215)+2 种基金Guangxi Young and Middle-aged Teacher Basic Ability Improvement Project (No. KY2016YB199)Guangxi Collaborative Innovation Center for Exploration of Hidden Nonferrous Metal Deposits and Development of New Materials Project (No. GXYSXTZX2017-II-5)Guangxi Scholarship Fund of Guangxi Education Department。
文摘Correctly locating the tunnel lining cavity is extremely important tunnel quality inspection.High-accuracy imaging results are hard to obtain because conventional one-way wave migration is greatly aff ected by lateral velocity change and inclination limitation and because the diff racted wave cannot be accurately returned to the real spatial position of the lining cavity.This paper presents a tunnel lining cavity imaging method based on the groundpenetrating radar(GPR)reverse-time migration(RTM)algorithm.The principle of GPR RTM is described in detail using the electromagnetic wave equation.The finite-difference timedomain method is employed to calculate the backward extrapolation electromagnetic fi elds,and the zero-time imaging condition based on the exploding-reflector concept is used to obtain the RTM results.On this basis,the GPR RTM program is compiled and applied to the simulated and observed GPR data of a typical tunnel lining cavity GPR model and a physical lining cavity model.Comparison of RTM and Kirchhoff migration results reveals that the RTM can better converge the diff racted waves of steel bar and cavity to their true position and have higher resolution and better suppress the eff ect of multiple interference and clutter scattering waves.In addition,comparison of RTM results of diff erent degrees of noise shows that RTM has strong anti-interference ability and can be used for the accurate interpretation of radar profi le in a strong interference environment.
基金The study is supported by the National Natural Science Foundation of China(No.41674118)the Fundamental Research Funds for the Central Universities of China(No.201964017).
文摘In elastic-wave reverse-time migration(ERTM),the reverse-time reconstruction of source wavefield takes advantage of the computing power of GPU,avoids its disadvantages in disk-access efficiency and reading and writing of temporary files,and realizes the synchronous extrapolation of source and receiver wavefields.Among the existing source wavefield reverse-time reconstruction algorithms,the random boundary algorithm has been widely used in three-dimensional(3D)ERTM because it requires the least storage of temporary files and low-frequency disk access during reverse-time migration.However,the existing random boundary algorithm cannot completely destroy the coherence of the artificial boundary reflected wavefield.This random boundary reflected wavefield with a strong coherence would be enhanced in the cross-correlation image processing of reverse-time migration,resulting in noise and fictitious image in the migration results,which will reduce the signal-to-noise ratio and resolution of the migration section near the boundary.To overcome the above issues,we present an ERTM random boundary-noise suppression method based on generative adversarial networks.First,we use the Resnet network to construct the generator of CycleGAN,and the discriminator is constructed by using the PatchGAN network.Then,we use the gradient descent methods to train the network.We fix some parameters,update the other parameters,and iterate,alternate,and continuously optimize the generator and discriminator to achieve the Nash equilibrium state and obtain the best network structure.Finally,we apply this network to the process of reverse-time migration.The snapshot of noisy wavefield is regarded as a 2D matrix data picture,which is used for training,testing,noise suppression,and imaging.This method can identify the reflected signal in the wavefield,suppress the noise generated by the random boundary,and achieve denoising.Numerical examples show that the proposed method can significantly improve the imaging quality of ERTM.
基金Supported by the National “863” Project(No.2014AA06A605)
文摘Prestack elastic reverse time migration( RTM) requires multicomponent seismic data. But for multicomponent elastic Kirchhoff migration,there is a limitation that ray theory no longer applies if thegeology becomes complicated. In this paper,the authors have created a new 2D migration context for isotropic,elastic RTM,which included decomposition of the elastic source and receiver wavefields into P and S wave vectors by decoupled elastodynamic extrapolation,which retained the same stress and particle velocity components as the input data. Then we appliedsource-normalized crosscorrelation imaging condition in elastic reverse time migration to compensate the energy of deep strata. We found that the resulting images were nearly identical to the velocity model,and the resolution has been improved. Our method is a wavefielddecomposition based on vector,and we can alsoavoid the problem of polarity reversal of converted shear wave imaging. It proved the applicability of the method proposed in our paper.
基金partly supported by the National Naural Science Foundation of China(Grant No.41272099)the Science Foundation of China University of Petroleum,Beijing(Grant No.2462015YJRC012)
文摘A least-squares reverse-time migration scheme is presented for reflectivity imaging. Based on an accurate reflection modeling formula, this scheme produces amplitude-preserved stacked reflectivity images with zero phase. Spatial preconditioning, weighting and the Barzilai-Borwein method are applied to speed up the convergence of the least-squares inversion. In addition, this scheme compensates the effect of ghost waves to broaden the bandwidth of the reflectivity images. Furthermore, roughness penalty constraint is used to regularize the inversion, which in turn stabilizes inversion and removes high-wavenumber artifacts and mitigates spatial aliasing. The examples of synthetic and field datasets demonstrate the scheme can generate zerophase reflectivity images with broader bandwidth, higher resolution, fewer artifacts and more reliable amplitudes than conventional reverse-time migration.
