Experimental Analysis of Polarity of Vibroseis Data
Robert A. Brook, Laurent J. Meister
Although our understanding of vibrator source characteristics continues to increase, the fundamental issues of signal polarity and phase remain controversial. Improvements in the accuracy of vibrator control have reduced the potential for phase inconsistencies in processed data, but field setup procedures and variations in data processing still create confusion.
In an experiment comparing a vibrator and two impulsive sources, downgoing and reflected waveforms from these three sources were analyzed at selected stages in the processing sequence. Emphasis was placed on polarity procedures during data collection and on phase considerations during digital processing.
Downhole tests compare first-arrival energy from dynamite, an ARIS (TM) impulse source, and a vibrator producing 45,000 lb peak force. Stacked sections and vertical seismic profile data recorded using the ARIS source and vibrator over a well were compared to a synthetic seismogram derived from the lithology of the well. The results show that controlling the vibrator ground force permits the polarity of the vibrator signal to be defined consistently with respect to impulsive signals for both downgoing and reflected energy.
AAPG Search and Discovery Article #91035©1988 AAPG-SEPM-SEG Pacific Sections and SPWLA Annual Convention, Santa Barbara, California, 17-19 April 1988.