Model-Based Multiple Suppression: Application to Seismic Prospecting in Santa Barbara Channel
Larry Morley, Paul Heuermann
The suppression of water-layer-generated multiples is a major problem in processing offshore California seismic data. The hard ocean bottom here can be attributed to a high-energy marine environment that prevents accumulation of younger sediments. Conventional approaches to multiple attenuation fail in this area for several reasons. The relatively shallow water bottom (100-300 msec) makes it difficult to improve primary-to-multiple ratios by exploiting residual normal moveout because the primary and multiple velocities are very similar. Also, the strong subsurface dips combined with a dipping sea floor decrease the stationary position of the multiples and degrade the performance of prestack gapped deconvolution.
A novel method of handling these difficulties involves constructing a prestack model of the multiples and subtracting the model from the data using a statistical fitting procedure. The modeling technique uses a Kirchoff implementation of the wave equation together with an estimate of water depth along the line.
Data from the Santa Barbara Channel show that the technique suppresses multiples to much wider offsets than conventional methods. This leads to better estimates of stacking velocity and improved imaging of subsurface data as confirmed by well ties. Finally, successful prestack multiple elimination is essential for achieving good results with prestack migration, which is necessary for imaging the tight structural folding widely found offshore California.
AAPG Search and Discovery Article #91035©1988 AAPG-SEPM-SEG Pacific Sections and SPWLA Annual Convention, Santa Barbara, California, 17-19 April 1988.