Very high resolution 3D marine seismic data processing for geotechnical applications
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文摘
The processing of a small-scale, very high resolution (VHR) shallow marine 3D data volume is described. The data were acquired over a small clay diapir, on the river Schelde, in 1990. Using an array of 12 dual-channel microstreamers towed from a catamaran, a network of 1m × 1m bins could be produced over an area of 50m × 180m (<100m penetration). Positioning was performed with an autotracking laser ranging system, assuring an absolute accuracy of a few decimetres. Preliminary processing steps included tidal correction and multiple removal. An important step concerned the application of 3D prestack Kirchhoff depth migration. Indeed, this processing allows easy handling of the exact position of both source and receivers as the latter were not set out on a conventional regular grid due to navigation difficulties. Because of the restricted data volume and the more-or-less stratified medium, a 1D velocity model could be used. This allowed a considerable simplification of the migration algorithm, based on summation. Traveltimes were calculated only once, using a 2D time grid with 0.1m intervals. This migration method proved very efficient, greatly improving the seismic image, and inovlved only limited CPU time on a small computer (Sparc 10 workstation). It clearly demonstrates that advanced seismic processing can form a valuable and economically feasible tool for VHR shallow subsurface 3D seismics, as long as the velocity field is not too complex. This method should therefore no longer be restricted to large computers and hydrocarbon exploration, but should also become a routine for VHR 3D shallow seismic work.