Abstract: | Staining algorithms based on two-way wave equation migration methods
have been applied to improve the signal-to-noise ratio (SNR) of poorly illuminated
structures such as those in subsalt zones. In regular staining algorithms, when a source
wavefield reaches the stained area that is associated with the target structures, a new
wavefield called stained wavefield is excited, and this stained wavefield forward extrapolates synchronously with the real source wavefield. The forward-extrapolated
stained and real source wavefields are cross-correlated with the backward-extrapolated
receiver wavefield, and we obtain the stained and the real reverse time migration
(RTM) images. The staining algorithms for RTM can suppress the noise of non-target
regions and obtain high SNR images of the target structures. Whereas RTM methods
are limited by the low computational efficiency and SNR, by contrast, one-way wave
equation migration (OWEM) methods have the advantages of high efficiency and no
interference from multiples. Thus, we developed a new staining method based on the
generalised screen propagator (GSP) as a case of OWEM methods for subsalt imaging.
Furthermore, a new stained wavefield called stained receiver wavefield is proposed
here, forming two new staining strategies for seismic imaging, in which forward-propagated source and backward-propagated receiver wavefields can be conveniently
selected to be stained at the stained area. Numerical experiments demonstrated that
this staining GSP method is more effective in improving the SNR of subsalt structures
compared to conventional GSP migration and RTM methods; moreover, these new
staining strategies as applied to the OWEM methods can greatly improve the SNR of
weakly illuminated structures in subsalt zones, in comparison with regular staining
algorithms for one-way methods. |