Directional-oriented wavefield imaging: a new wave-based subsurface illumination imaging condition for reverse time migration
Y.S. Kim, C. Tsingas and W. Jeong
Journal name: Geophysical Prospecting
Issue: Vol 66, No 6, July 2018 pp. 1097 - 1110
DOI: doi: 10.1111/1365-2478.12631
Info: Article, PDF ( 10.49Mb )
The key objective of an imaging algorithm is to produce accurate and high-resolution images of the subsurface geology. However, significant wavefield distortions occur due to wave propagation through complex structures and irregular acquisition geometries causing uneven wavefield illumination at the target. Therefore, conventional imaging conditions are unable to correctly compensate for variable illumination effects. We propose a generalised wave-based imaging condition, which incorporates a weighting function based on energy illumination at each subsurface reflection and azimuth angles. Our proposed imaging kernel, named as the directional-oriented wavefield imaging, compensates for illumination effects produced by possible surface obstructions during acquisition, sparse geometries employed in the field, and complex velocity models. An integral part of the directional-oriented wavefield imaging condition is a methodology for applying down-going/up-going wavefield decomposition to both source and receiver extrapolated wavefields. This type of wavefield decomposition eliminates low-frequency artefacts and scattering noise caused by the two-way wave equation and can facilitate the robust estimation for energy fluxes of wavefields required for the seismic illumination analysis. Then, based on the estimation of the respective wavefield propagation vectors and associated directions, we evaluate the illumination energy for each subsurface location as a function of image depth point and subsurface azimuth and reflection angles. Thus, the final directionaloriented wavefield imaging kernel is a cross-correlation of the decomposed source and receiver wavefields weighted by the illuminated energy estimated at each depth location. The application of the directional-oriented wavefield imaging condition can be employed during the generation of both depth-stacked images and azimuth–reflection angle-domain common image gathers. Numerical examples using synthetic and real data demonstrate that the new imaging condition can properly image complex wave paths and produce high-fidelity depth sections.