Synthesising Primary Reflections by Marchenko Redatuming and Convolutional Interferometry

Abstract:

Standard active-source seismic processing and imaging steps such as velocity analysis and reverse time migration usually provide best results when all reflected waves in the input data are primaries (waves that reflect only once). Multiples (recorded waves that reflect multiple times) represent a source of coherent noise in data that must be suppressed to avoid imaging artefacts. Consequently, multiple-removal methods have been a primcipal direction of active-source seismic research for decades. We describe a new method to estimate primaries directly, which obviates the need for multiple removal. Primaries are constructed within convolutional interferometry by combining first arriving events of up-going and direct wave down-going Green’s functions to virtual receivers in the subsurface. The required up-going wavefields to virtual receivers along discrete subsurface boundaries can be constructed using Marchenko redatuming. Crucially, this is possible without detailed models of the Earth’s subsurface velocity structure: similarly to most migration techniques, the method only requires surface reflection data and estimates of direct (non-reflected) arrivals between subsurface sources and the acquisition surface. The method is demonstrated on a stratified synclinal model. It is shown both to improve reverse time migration compared to standard methods, and to be particularly robust against errors in the reference velocity model used.