Review Paper: An outlook on the future of seismic imaging, Part Ⅱ: Full-Wavefield Migration

摘要

The next-generation seismic imaging algorithms will consider multiple scattering as indispensable information, being referred to as Full-Wavefield Migration. In addition, these algorithms will also include autonomous velocity updating in the migration process, being referred to as Joint Migration Inversion. Full-Wavefield Migration and Joint Migration Inversion address the industrial needs to improve images of very complex reservoirs as well as the industrial ambition to produce these images in a more automatic manner (automation in seismic processing). In this vision paper on seismic imaging, Full-Wavefield Migration and Joint Migration Inversion are formulated in terms of a closed-loop estimation algorithm that can be physically explained by an iterative double focusing process (full-wavefield common-focus-point technology). A critical module in this formulation is forward modelling, allowing feedback from migrated output to unmigrated input (closing the loop). For this purpose, a full-wavefield modelling module has been developed, which utilizes an operator description of complex geology. The full-wavefield modelling module is pre-eminently suited to function in the feedback path of a closed-loop migration algorithm. 'The Future of Seismic Imaging' is presented as a coherent trilogy, proposing the migration framework of the future in three consecutive parts. In Part Ⅰ, it was shown that the proposed full-wavefield modelling module algorithm differs fundamentally from finite-difference modelling because velocities and densities need not be provided. Instead, an operator description of the subsurface is used. In addition, the concept of reverse modelling was introduced. In Part Ⅱ, it is shown how the theory of Primary Wavefield Migration can be extended to Full-Wavefield Migration by correcting for angle-dependent transmission effects and by utilizing multiple scattering. The potential of the Full-Wavefield Migration algorithm is illustrated with numerical examples. A multidirectional migration strategy is proposed that navigates the Full-Wavefield Migration algorithm through the seismic data cube in different directions.