Angle-Weighted Reverse Time Migration With Wavefield Decomposition Based on the Optical Flow Vector

Reverse time migration (RTM) is based on the two-way wave equation, so its imaging results obtained by conventional zero-lag cross-correlation imaging conditions contain a lot of low-wavenumber noises. So far, the wavefield decomposition method based on the Poynting vector has been developed to suppress these noises; however, this method also has some problems, such as unstable calculation of the Poynting vector, low accuracy of wavefield decomposition, and poor effect of large-angle migration artifacts suppression. This article introduces the optical flow vector method to RTM to realize high-precision wavefield decomposition for both the source and receiver wavefields and obtains four directions of wavefields: up-, down-, left-, and right-going. Then, the cross-correlation imaging sections of one-way propagation components of forward- and back-propagated wavefields are optimized and stacked. On this basis, the reflection angle of each imaging point is calculated based on the optical flow vector, and an attenuation factor related to the reflection angle is introduced as the weight to generate the optimal stack images. The tests of theoretical model and field marine seismic data illustrate that compared with the conventional RTM with wavefield decomposition based on the Poynting vector, the angle-weighted RTM with wavefield decomposition based on the optical flow vector proposed in this article can achieve wavefield decomposition for both the source and receiver wavefields and calculate the reflection angle of each imaging point more accurately and stably. Moreover, the proposed method adopts angle weighting processing, which can further eliminate large-angle migration artifacts and effectively improve the imaging accuracy of RTM.

Download Full-text

Angle‐domain common‐image gathers in reverse‐time migration by combining the Poynting vector with local‐wavefield decomposition

Geophysical Prospecting ◽

10.1111/1365-2478.12785 ◽

2019 ◽

Vol 67 (8) ◽

pp. 2035-2060 ◽

Cited By ~ 1

Author(s):

Wu Chengliang ◽

Wang Huazhong ◽

Zhou Yang ◽

Hu Jiangtao

Keyword(s):

Poynting Vector ◽

Reverse Time ◽

Reverse Time Migration ◽

Time Migration ◽

Wavefield Decomposition

Download Full-text

Obliquity-correction imaging condition for reverse time migration

Geophysics ◽

10.1190/1.3110589 ◽

2009 ◽

Vol 74 (3) ◽

pp. S57-S66 ◽

Cited By ~ 34

Author(s):

J. C. Costa ◽

F. A. Silva Neto ◽

M. R. Alcântara ◽

J. Schleicher ◽

A. Novais

Keyword(s):

Poynting Vector ◽

Reverse Time ◽

Reverse Time Migration ◽

Illumination Compensation ◽

Imaging Condition ◽

Time Migration ◽

Imaging Point ◽

Stationary Phase Analysis ◽

Seismic Images

The quality of seismic images obtained by reverse time migration (RTM) strongly depends on the imaging condition. We propose a new imaging condition that is motivated by stationary phase analysis of the classical crosscorrelation imaging condition. Its implementation requires the Poynting vector of the source and receiver wavefields at the imaging point. An obliquity correction is added to compensate for the reflector dip effect on amplitudes of RTM. Numerical experiments show that using an imaging condition with obliquity compensation improves reverse time migration by reducing backscattering artifacts and improving illumination compensation.

Download Full-text

Suppressing residual low-frequency noise in VSP reverse time migration by combining wavefield decomposition imaging condition with Poynting vector filtering

Exploration Geophysics ◽

10.1080/08123985.2020.1804298 ◽

2020 ◽

pp. 1-10

Author(s):

Lele Zhang ◽

Yang Liu ◽

Wanli Jia ◽

Jing Wang

Keyword(s):

Poynting Vector ◽

Low Frequency ◽

Frequency Noise ◽

Low Frequency Noise ◽

Reverse Time ◽

Reverse Time Migration ◽

Imaging Condition ◽

Time Migration ◽

Wavefield Decomposition

Download Full-text

True Amplitude Angle Gathers from Reverse Time Migration by Wavefield Decomposition at Excitation Amplitude Time

Energies ◽

10.3390/en13236204 ◽

2020 ◽

Vol 13 (23) ◽

pp. 6204

Author(s):

Zhe Yan ◽

Yonglong Yang ◽

Shaoyong Liu

Keyword(s):

Poynting Vector ◽

Large Angle ◽

Excitation Amplitude ◽

Angle Measurement ◽

Memory Storage ◽

Frequency Noise ◽

Reverse Time ◽

Reverse Time Migration ◽

Vector Method ◽

Time Migration

Reservoir parameter estimation is one of the goals of amplitude-versus-angle (AVA) inversion and angle-domain common image gathers are the basis of AVA inversion. Therefore, the accuracy of kinematic and kinetic information on angle gathers is very important for reservoir characterization. Reverse time migration is one of the most physically accurate migration method. Generating angle gathers from reverse time migration with the Poynting vector method is very efficient. However, due to inaccurate angle measurement and uneven illumination, angle gathers calculated by the Poynting vector method are often not suitable for AVA inversion. In this paper, we propose an efficient method of angle gathers with accurate angular information and amplitude from reverse time migration. We firstly decompose source and receiver wavefield to their up-going and down-going parts by using analytic wavefield. We calculate propagation directions for source down-going wavefield and receiver up-going wavefield by the Poynting vector method and form the angle gathers with these angle information and decomposed wavefield. To reduce memory storage and improve computational efficiency, we decompose wavefield at excitation amplitude time by using a local spatial Fourier transform. We also use a spatial smoothed Poynting vector to improve the stability of angle measurement. We apply an illumination compensation image condition to recover the true amplitude. Numerical examples on Marmousi model and the SEAM two-dimensional (2D) model demonstrate the advantages of our proposed method. The angle gathers based on our method are cleaner with more focus on events energy and better continuity, suffering from less low-frequency noise in the shallow parts and with a distinct cutoff at large angle where reflection terminates. At last, we demonstrate the effectiveness of proposed method on a 2D marine field data example.

Download Full-text

Application of RTM 3D angle gathers to wide-azimuth data subsalt imaging

Geophysics ◽

10.1190/geo2010-0396.1 ◽

2011 ◽

Vol 76 (5) ◽

pp. WB175-WB182 ◽

Cited By ~ 9

Author(s):

Yan Huang ◽

Bing Bai ◽

Haiyong Quan ◽

Tony Huang ◽

Sheng Xu ◽

...

Keyword(s):

Model Updating ◽

Velocity Model ◽

Azimuth Angle ◽

Reverse Time ◽

Reverse Time Migration ◽

Data Set ◽

Additional Information ◽

Time Migration ◽

Reflection Angle ◽

Subsalt Imaging

The availability of wide-azimuth data and the use of reverse time migration (RTM) have dramatically increased the capabilities of imaging complex subsalt geology. With these improvements, the current obstacle for creating accurate subsalt images now lies in the velocity model. One of the challenges is to generate common image gathers that take full advantage of the additional information provided by wide-azimuth data and the additional accuracy provided by RTM for velocity model updating. A solution is to generate 3D angle domain common image gathers from RTM, which are indexed by subsurface reflection angle and subsurface azimuth angle. We apply these 3D angle gathers to subsalt tomography with the result that there were improvements in velocity updating with a wide-azimuth data set in the Gulf of Mexico.

Download Full-text

Reducing artifacts of elastic reverse time migration by the deprimary technique

Geophysics ◽

10.1190/geo2018-0260.1 ◽

2018 ◽

Vol 83 (6) ◽

pp. S569-S577 ◽

Cited By ~ 10

Author(s):

Yang Zhao ◽

Houzhu Zhang ◽

Jidong Yang ◽

Tong Fei

Keyword(s):

Complex Function ◽

Noise Removal ◽

Pure Mode ◽

Reverse Time ◽

Reverse Time Migration ◽

S Wave ◽

Imaging Condition ◽

Velocity Models ◽

Time Migration ◽

Wavefield Decomposition

Using the two-way elastic-wave equation, elastic reverse time migration (ERTM) is superior to acoustic RTM because ERTM can handle mode conversions and S-wave propagations in complex realistic subsurface. However, ERTM results may not only contain classical backscattering noises, but they may also suffer from false images associated with primary P- and S-wave reflections along their nonphysical paths. These false images are produced by specific wave paths in migration velocity models in the presence of sharp interfaces or strong velocity contrasts. We have addressed these issues explicitly by introducing a primary noise removal strategy into ERTM, in which the up- and downgoing waves are efficiently separated from the pure-mode vector P- and S-wavefields during source- and receiver-side wavefield extrapolation. Specifically, we investigate a new method of vector wavefield decomposition, which allows us to produce the same phases and amplitudes for the separated P- and S-wavefields as those of the input elastic wavefields. A complex function involved with the Hilbert transform is used in up- and downgoing wavefield decomposition. Our approach is cost effective and avoids the large storage of wavefield snapshots that is required by the conventional wavefield separation technique. A modified dot-product imaging condition is proposed to produce multicomponent PP-, PS-, SP-, and SS-images. We apply our imaging condition to two synthetic models, and we demonstrate the improvement on the image quality of ERTM.

Download Full-text