Illumination compensation using Poynting vectors, with special treatment for multiples

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.

Section: Introductionmentioning

confidence: 99%

Attenuating multiple-related imaging artifacts using combined imaging conditions

Filho

Curtis

2016

Separating a wavefield by propagation direction

Richardson

Malcolm

2016

Self Cite

SUMMARYDetermining the propagation direction of waves in a wavefield is important in several seismic imaging techniques and applications. This can be achieved using the Poynting vector method, but it performs poorly when waves overlap, returning incorrect wave amplitude and direction. An alternative, the local slowness method, is capable of separating overlapping waves, but suffers from low angular resolution. We describe modifications of these two approaches that improve the ability to extract the wave amplitude propagating in different directions. The primary modification is the addition of a wavefront orientation separation step. We evaluate the original and modified methods' ability to separate six overlapping waves in a constant velocity model and find that the modifications significantly improve the results.

First-order particle velocity equations of decoupled P- and S-wavefields and their application in elastic reverse time migration

Liu

Liang

et al. 2021

The separation of P- and S-wavefields is considered to be an effective approach for eliminating wave-mode crosstalk in elastic reverse time migration (RTM). At present, the Helmholtz decomposition method is widely used for isotropic media. However, it tends to change the amplitudes and phases of the separated wavefields compared with the original wavefields. Other methods used to obtain pure P- and S-wavefields include the application of the elastic wave equations of the decoupled wavefields. To achieve high computational accuracy, staggered-grid finite-difference (FD) schemes are usually used to numerically solve the equations by introducing an additional stress variable. However, the computational cost of this method is high because a conventional hybrid wavefield (the P- and S-wavefields are mixed together) simulation must be created before the P- and S-wavefields can be calculated. We have developed the first-order particle velocity equations to reduce the computational cost. The equations can describe four types of particle-velocity wavefields: the vector P-wavefield, the scalar P-wavefield, the vector S-wavefield, and the vector S-wavefield rotated in the direction of the curl factor. Without introducing the stress variable, only the four types of particle velocity variables are used to construct the staggered-grid FD schemes; therefore, the computational cost is reduced. We also develop an algorithm to calculate the P and S propagation vectors using the four particle velocities, which is simpler than the Poynting vector. Finally, we apply the velocity equations and propagation vectors to elastic RTM and angle-domain common-image gather computations. These numerical examples illustrate the efficiency of our methods.