Fresnel volume migration of single-component seismic data

摘要

Standard implementations of Kirchhoff prestack depth migrationPSDM distribute the recorded wavefield along two-waytraveltimeisochrons and an image is generated by constructiveinterference of these isochrons along the actual reflector elements.Beside the recent developments of wave-equation-basedapproaches, Kirchhoff PSDM is still considered widely as astate-of-the-art technique in obtaining high-quality images of thesubsurface, particularly for highly irregular survey layouts andtarget-oriented imaging tasks. However, for sparse samplingor limited aperture, the resulting image is affected by significantmigration noise as a result of limited constructive interference ofthe back-propagated wavefield. Some modifications have beenproposed to reduce these artifacts. These modifications includeconstructing a specular path of wave propagation, derived fromestimates of the emergent angle of coherent phases in the seismogramsection, and the mainly heuristic restriction of the imagingoperator to the neighborhood of that wavepath. Our approachuses Fresnel volumes to restrict the migration operator in a physicallyfrequency-dependent way. Using the emergent angle atthe receiver, determined by a local slowness analysis, a ray ispropagated into the subsurface; the back-propagation of thewavefield is restricted to the vicinity of this ray according to itsapproximated Fresnel volume. This so-called Fresnel volumemigration approach enhances image quality significantly comparedwith standard Kirchhoff PSDM because of the inherent focusingand the restriction of the back-propagation to the regionaround the actual reflection point.