Reverse time migration via frequency-adaptive multiscale spatial grids

Geophysics ◽  
2019 ◽  
Vol 84 (2) ◽  
pp. S41-S55 ◽  
Author(s):  
Yongchae Cho ◽  
Richard L. Gibson, Jr.
Keyword(s):  
Coarse Grid ◽  
Image Resolution ◽  
Imaging Method ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Fine Grid ◽  
Wave Modeling ◽  
Time Migration ◽  
Wave Solutions ◽  
Spatial Grid

Reverse time migration (RTM) is widely used because of its ability to recover complex geologic structures. However, RTM also has a drawback in that it requires significant computational cost. In RTM, wave modeling accounts for the largest part of the computing cost for calculating forward- and backward-propagated wavefields before applying an imaging condition. For this reason, we have applied a frequency-adaptive multiscale spatial grid to enhance the efficiency of the wave simulations. To implement wave modeling for different values of the spatial grid interval, we apply a model reduction technique, the generalized multiscale finite-element method (GMsFEM), which solves local spectral problems on a fine grid to simulate wave propagation on a coarser grid. We can enhance the speed of computation without sacrificing accuracy by using coarser grids for lower frequency waves, while applying a finer grid for higher frequency waves. In the proposed method, we can control the size of the coarse grid and level of heterogeneity of the wave solutions to tune the trade-off between speedup and accuracy. As we increase the expected level of complexity of the wave solutions, the GMsFEM wave modeling can capture more detailed features of waves. After computing the forward and backward wavefield on the coarse grid, we reproject the coarse wave solutions to the fine grid to construct the RTM gradient image. Although wave solutions are computed on a coarse grid, we still obtain the RTM images without reducing the image resolution by projecting coarse wave solutions to the fine grid. We determine the efficiency of the proposed imaging method using the Marmousi-2 model. We compare the RTM images using GMsFEM with a fixed coarse mesh and a multiple frequency-adaptive coarse meshes to indicate the image quality and computational speed of the new approach.

scholarly journals Phaseless Imaging by Reverse Time Migration: Acoustic Waves

2017 ◽  
Vol 10 (1) ◽  
pp. 1-21 ◽  
Author(s):  
Zhiming Chen ◽  
Guanghui Huang
Keyword(s):  
Acoustic Waves ◽  
Numerical Experiments ◽  
Cross Correlation ◽  
Scattering Data ◽  
Imaging Method ◽  
Total Field ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Time Migration ◽  
Imaging Results

AbstractWe propose a reliable direct imaging method based on the reverse time migration for finding extended obstacles with phaseless total field data. We prove that the imaging resolution of the method is essentially the same as the imaging results using the scattering data with full phase information when the measurement is far away from the obstacle. The imaginary part of the cross-correlation imaging functional always peaks on the boundary of the obstacle. Numerical experiments are included to illustrate the powerful imaging quality

Some Aspects of Seismic Data Reverse Time Migration for Salt Tectonics Geology of the Dnieper-Donets Basin

2021 ◽  
Author(s):  
Pavlo Kuzmenko ◽  
Viktor Buhrii ◽  
Carlo D'Aguanno ◽  
Viktor Maliar ◽  
Hrigorii Kashuba ◽  
...  
Keyword(s):  
Seismic Data ◽  
Full Range ◽  
Donets Basin ◽  
Salt Tectonics ◽  
Imaging Method ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Time Migration ◽  
Seismic Image ◽  
Complex Geology

Abstract Processing of the seismic data acquired in areas of complex geology of the Dnieper-Donets basin, characterized by the salt tectonics, requires special attention to the salt dome interpretation. For this purpose, Kirchhoff Depth Imaging and Reverse Time Migration (RTM) were applied and compared. This is the first such experience in the Dnieper-Donets basin. According to international experience, RTM is the most accurate seismic imaging method for steep and vertical geological (acoustic contrast) boundaries. Application of the RTM on 3D WAZ land data is a great challenge in Dnieper-Donets Basin because of the poor quality of the data with a low signal-to-noise ratio and irregular spatial sampling due to seismic acquisition gaps and missing traces. The RTM algorithm requires data, organized to native positions of seismic shots. For KPSDM we used regularized data after 5D interpolation. This affects the result for near salt reflection. The analysis of KPSDM and RTM results for the two areas revealed the same features. RTM seismic data looked more smoothed, but for steeply dipping reflections, lateral continuity of reflections was much improved. The upper part (1000 m) of the RTM has shadow zones caused by low fold. Other differences between Kirchhoff data and RTM are in the spectral content, as the former is characterized by the full range of seismic frequency spectrum. Conversely, beneath the salt, the RTM has reflections with steep dips which are not observed on the KPSDM. It is possible to identify new prospects using the RTM seismic image. Reverse Time Migration of 3D seismic data has shown geologically consistent results and has the potential to identify undiscovered hydrocarbon traps and to improve salt flank delineation in the complex geology of the Dnieper-Donets Basin's salt domes.

Diffraction imaging for fault-karst structure by least-squares reverse time migration

2020 ◽  
pp. 1-40
Author(s):  
Xinru Mu ◽  
Jianping Huang ◽  
Liyun Fu ◽  
Shikai Jian ◽  
Bing Hu ◽  
...  
Keyword(s):  
Least Squares ◽  
Western China ◽  
Small Scale ◽  
Imaging Method ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Time Migration ◽  
Imaging Results ◽  
Heterogeneous Structures ◽  
Karst Reservoir

The fault-karst reservoir, which evolved from the deformation and karstification of carbonate rock, is one of the most important reservoir types in western China. Along the deep-seated fault zones, there are a lot widely spread and densely distributed fractures and vugs. The energy of the diffractions generated by heterogeneous structures, such as faults, fractures and vugs, are much weaker than that of the reflections produced by continuous formation interface. When using conventional full wavefield imaging method, the imaging results of continuous layers usually cover small-scale heterogeneities. Given that, we use plane-wave destruction (PWD) filter to separate the diffractions from the full data and image the separated diffractions using least-squares reverse time migration (LSRTM) method. We use several numerical examples to demonstrate that the newly developed diffractions LSRTM (D-LSRTM) can improve the definition of the heterogeneous structures, characterize the configuration and internal structure of the fault-karst structure well and enhance the interpretation accuracy for fault-karst reservoir.

Reverse Time Migration Using the Pseudospectral Time-Domain Algorithm

2016 ◽  
Vol 24 (02) ◽  
pp. 1650005 ◽  
Author(s):  
Jiangang Xie ◽  
Zichao Guo ◽  
Hai Liu ◽  
Qing Huo Liu
Keyword(s):  
Time Domain ◽  
Acoustic Waves ◽  
Fdtd Method ◽  
Pseudospectral Method ◽  
Imaging Method ◽  
Processing Unit ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Eighth Order ◽  
Time Migration

We propose a pre-stack reverse time migration (RTM) seismic imaging method using the pseudospectral time-domain (PSTD) algorithm. Traditional pseudospectral method uses the fast Fourier transform (FFT) algorithm to calculate the spatial derivatives, but is limited by the wraparound effect due to the periodicity assumed in the FFT. The PSTD algorithm combines the pseudospectral method with a perfectly matched layer (PML) for acoustic waves. PML is a highly effective absorbing boundary condition that can eliminate the wraparound effect. It enables a wide application of the pseudospectral method to complex models. RTM based on the PSTD algorithm has advantages in the computational efficiency compared to traditional methods such as the second-order and high order finite difference time-domain (FDTD) methods. In this work, we implement the PSTD algorithm for acoustic wave equation based RTM. By applying the PSTD-RTM method to various seismic models and comparing it with RTM based on the eighth-order FDTD method, we find that PSTD-RTM method has better performance and saves more than 50% memory. The method is suitable for parallel computation, and has been accelerated by general purpose graphics processing unit.

scholarly journals Attenuating multiple-related imaging artifacts using combined imaging conditions

Geophysics ◽  
2016 ◽  
Vol 81 (6) ◽  
pp. S469-S475 ◽  
Author(s):  
Carlos Alberto da Costa Filho ◽  
Andrew Curtis
Keyword(s):  
Small Scale ◽  
Imaging Method ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Depth Migration ◽  
Time Migration ◽  
Migration Method ◽  
Combined Imaging ◽  
Spatial Locations ◽  
Imaging Conditions

The objective of prestack depth migration is to position reflectors at their correct subsurface locations. However, migration methods often also generate artifacts along with physical reflectors, which hamper interpretation. These spurious reflectors often appear at different spatial locations in the image depending on which migration method is used. Therefore, we have devised a postimaging filter that combines two imaging conditions to preserve their similarities and to attenuate their differences. The imaging filter is based on combining the two constituent images and their envelopes that were obtained from the complex vertical traces of the images. We have used the method to combine two images resulting from different migration schemes, which produce dissimilar artifacts: a conventional migration method (equivalent to reverse time migration) and a deconvolution-based imaging method. We show how this combination may be exploited to attenuate migration artifacts in a final image. A synthetic model containing a syncline and stochastically generated small-scale heterogeneities in the velocity and density distributions was used for the numerical example. We compared the images in detail at two locations where spurious events arose and also at a true reflector. We found that the combined imaging condition has significantly fewer artifacts than either constituent image individually.

scholarly journals Reverse Time Migration Based on the Pseudo-Space-Domain First-Order Velocity-Stress Acoustic Wave Equation

2021 ◽  
Vol 9 ◽  
Author(s):  
Xiaobo Zhang ◽  
Xiutian Wang ◽  
Baohua Liu ◽  
Peng Song ◽  
Jun Tan ◽  
...  
Keyword(s):  
Wave Equation ◽  
Acoustic Wave ◽  
Imaging Method ◽  
Acoustic Wave Equation ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Space Domain ◽  
First Order ◽  
Time Migration ◽  
Rectangular Mesh

Reverse time migration (RTM) is an ideal seismic imaging method for complex structures. However, in conventional RTM based on rectangular mesh discretization, the medium interfaces are usually distorted. Besides, reflected waves generated by the two-way wave equation can cause artifacts during imaging. To overcome these problems, a high-order finite-difference (FD) scheme and stability condition for the pseudo-space-domain first-order velocity-stress acoustic wave equation were derived, and based on the staggered-grid FD scheme, the RTM of the pseudo-space-domain acoustic wave equation was implemented. Model experiments showed that the proposed RTM of the pseudo-space-domain acoustic wave equation could systematically avoid the interface distortion problem when the velocity interfaces were considered to compute the pseudo-space-domain intervals. Moreover, this method could effectively suppress the false scattering of dipping interfaces and reflections during wavefield extrapolation, thereby reducing migration artifacts on the profile and significantly improving the quality of migration imaging.

scholarly journals An efficient local imaging strategy based on illumination analysis with deep learning

2021 ◽  
Vol 9 ◽  
Author(s):  
Chao Rong ◽  
Xiaofeng Jia
Keyword(s):  
Deep Learning ◽  
Imaging Method ◽  
Target Area ◽  
Single Shot ◽  
Geological Model ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Energy Propagation ◽  
Time Migration ◽  
Low Illumination

We propose a deep-learning-based illumination analysis and efficient local imaging method. Based on the wavefield forward modeling, seismic illumination can intuitively express the energy propagation of direct waves, reflected waves, and transmitted waves, while it requires high calculation costs. We use a series of convolution operations in deep learning to establish the nonlinear relationship between the model and the illuminations to realize single-shot illumination result of the model. Stacking the single shot illumination results obtained by the network prediction can further help determine the target area. For the target area, we use a deep learning method to obtain the low illumination area of the geological model. Each shot has contribution to the low illuminated area; single shot is selected based on the contribution of the shot being greater than the average illuminance, and the low illumination area is imaged by reverse time migration on the selected shot gather. The trained convolutional neural network can help us quickly obtain the single shot illumination result of the model, which is convenient to analyze the energy distribution of various areas of geological model, and do further imaging for target areas. Using part of the shot gathers to image a local area can recover the complex geological structure of the area and improve the efficiency of reverse time migration especially for 3D problems. This method has universal applicability and is suitable for local imaging of various complex models such as subsalt areas and deep regions.

Amplitude-preserving scalar PP and PS imaging condition for elastic reverse time migration based on a wavefield decoupling method

Geophysics ◽  
2019 ◽  
Vol 84 (3) ◽  
pp. S113-S125 ◽  
Author(s):  
Xiyan Zhou ◽  
Xu Chang ◽  
Yibo Wang ◽  
Zhenxing Yao
Keyword(s):  
Wave Vector ◽  
Numerical Models ◽  
P Wave ◽  
Imaging Method ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
S Wave ◽  
Decoupling Method ◽  
Time Migration ◽  
Imaging Results

To eliminate crosstalk within the imaging results of elastic reverse time migration (ERTM), we can separate the coupled P- and S-waves from the forward source wavefield and the backpropagated receiver wavefield. The P- and S-wave decoupling method retains the original phase, amplitude, and physical meaning in the separated wavefields. Thus, it is a vital wavefield separation method in ERTM. However, because these decomposed wavefields are vectors, we could consider how to retrieve scalar images that reveal the real reflectivity of the subsurface. For this purpose, we derive a scalar P-wave equation from the velocity-stress relationship for PP imaging. The phase and amplitude of this scalar P-wave are consistent with the scalarized P-wave. Therefore, this scalar P-wave can be exploited to perform PP imaging directly, with the imaging result retaining the amplitude characteristics. For PS imaging, it is difficult to calculate a dynamic preserved scalar S-wave. However, we have developed a scalar PS imaging method that divides the PS image into energy and sign components according to the geometric relationship between the wavefield vibration and propagation directions. The energy is calculated through the amplitude crosscorrelation of the forward P-wave and backpropagated S-wave from the receivers. The sign is obtained from the dot product of the forward P-wave vector and the backpropagated S-wave vector. These PP and PS imaging methods are suitable for 2D and 3D isotropic media and maintain the correct amplitude information while eliminating polarity-reversal phenomena. Several numerical models are used to verify the robustness and effectiveness of our method.

Memory-efficient source wavefield reconstruction and its application to 3D reverse time migration

Geophysics ◽  
2021 ◽  
pp. 1-76
Author(s):  
Zhiming Ren ◽  
Qianzong Bao ◽  
Shigang Xu
Keyword(s):  
Conventional Method ◽  
Reconstruction Method ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Time Step ◽  
Time Migration ◽  
Spatial Grid ◽  
Grid Points ◽  
Backward Propagation ◽  
And Storage

Reverse time migration (RTM) generally uses the zero-lag crosscorrelation imaging condition, requiring the source and receiver wavefields to be known at the same time step. However, the receiver wavefield is calculated in time-reversed order, opposite to the order of the forward-propagated source wavefield. The inconvenience can be resolved by storing the source wavefield on a computer memory/disk or by reconstructing the source wavefield on the fly for multiplication with the receiver wavefield. The storage requirements for the former approach can be very large. Hence, we have followed the latter route and developed an efficient source wavefield reconstruction method. During forward propagation, the boundary wavefields at N layers of the spatial grid points and a linear combination of wavefields at M − N layers of the spatial grid points are stored. During backward propagation, it reconstructs the source wavefield using the saved wavefields based on a new finite-difference stencil ( M is the operator length parameter, and 0 ≤  N ≤  M). Unlike existing methods, our method allows a trade-off between accuracy and storage by adjusting N. A maximum-norm-based objective function is constructed to optimize the reconstruction coefficients based on the minimax approximation using the Remez exchange algorithm. Dispersion and stability analyses reveal that our method is more accurate and marginally less stable than the method that requires storage of a combination of boundary wavefields. Our method has been applied to 3D RTM on synthetic and field data. Numerical examples indicate that our method with N = 1 can produce images that are close to those obtained using a conventional method of storing M layers of boundary wavefields. The memory usage of our method is ( N + 1)/ M times that of the conventional method.

Source-receiver, reverse-time imaging of dual-source, vector-acoustic seismic data

Geophysics ◽  
2013 ◽  
Vol 78 (2) ◽  
pp. WA123-WA145 ◽  
Author(s):  
Ivan Vasconcelos
Keyword(s):  
Seismic Data ◽  
Super Resolution ◽  
Imaging Method ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Imaging Condition ◽  
Novel Technologies ◽  
Time Migration ◽  
Consistent Manner ◽  
Dual Source

Novel technologies in seismic data acquisition allow for recording full vector-acoustic (VA) data: pointwise recordings of pressure and its multicomponent gradient, excited by pressure only as well as dipole/gradient sources. Building on recent connections between imaging and seismic interferometry, we present a wave-equation-based, nonlinear, reverse-time imaging approach that takes full advantage of dual-source multicomponent data. The method’s formulation relies on source-receiver scattering reciprocity, thus making proper use of VA fields in the wavefield extrapolation and imaging condition steps in a self-consistent manner. The VA imaging method is capable of simultaneously focusing energy from all in- and outgoing waves: The receiver-side up- and downgoing (receiver ghosts) fields are handled by the VA receiver extrapolation, whereas source-side in- and outgoing (source ghosts) arrivals are accounted for when combining dual-source data at the imaging condition. Additionally, VA imaging handles image amplitudes better than conventional reverse-time migration because it properly handles finite-aperture directivity directly from dual-source, 4C data. For nonlinear imaging, we provide a complete source-receiver framework that relies only on surface integrals, thus being computationally applicable to practical problems. The nonlinear image can be implicitly interpreted as a superposition of several nonlinear interactions between scattering components of data with those corresponding to the extrapolators (i.e., to the model). We demonstrate various features of the method using synthetic examples with complex subsurface features. The numerical results show, e.g., that the dual-source, VA image retrieves subsurface features with “super-resolution”, i.e., with resolution higher than the limits of Born imaging, but at the cost of introducing image artifacts not present in the linear image. Although the method does not require any deghosting as a preprocessing step, it can use separated up- and downgoing fields to generate independent subsurface images.

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