Interactive attenuation of seismic multiples in the radial domain

Abstract

In marine seismic surveys, reverberations in the water layer known as multiples obscure primary reflections from deeper geological boundaries. This is especially a problem in areas of the North West Shelf of Western Australia, where the geology of the area can produce very strong multiple events, often with similar NMO velocity to primary events. Because of this lack of velocity discrimination, conventional multiple attenuation methods often fail. An effective method of multiple attenuation using 1D Feedback Autoconvolution in the Radial Domain has been devised. This does not rely on a velocity discrimination between primary and multiple events, and can be applied interactively via a Motif X11 Graphical User Interface, and with minimal user input. A radial transform has been written that converts either CMP or shot record data, to make both simple water bottom and pegleg multiples from a horizontal sea floor, periodic on each trace, and is suitable for the application of autoconvolution. The extension of the radial transform to a dipping sea floor has been modelled using the mathematical modelling package MAPLE, and an approximate solution has been devised. The technique of successive autoconvolution on each seismic trace in a feedback loop, predicts surface related multiple events, at the correct time, reverse polarity, and theoretically correct amplitudes. In practice a scaling algorithm has been incorporated to match the predicted multiples to the original data. A program module to apply 1D Feedback autoconvolution on radial transformed data for both horizontal layer and dipping water bottom models has been developed, and applied successfully to both simple water bottom multiples and water bottom peg-legs.