New Technique for Acquisition of High-Quality Seismic Data in Sacramento Delta, California

Allen J. Bertagne, Claude Vuillermoz, Rollin Delzer

The Sacramento delta is typified by relatively flat topography, numerous navigation channels, and extensive peat deposits. Seismic data acquired in the area have generally been poor, probably due to attenuation of seismic energy by the peat and to static problems caused by lateral velocity variations within the peat.

In an attempt to obtain higher quality data, a test line was shot using a new field approach. The peat was penetrated using shothole drills and a seismic source and receiver assembly placed in each hole beneath the peat layer. The source consisted of dynamite and the receiver of a single low-cost disposable hydrophone. Thus, shooting and recording were conducted beneath the problematic peat layer. The line was acquired using an end-on spread, with energy being recorded at a given location until the location became a shotpoint and the hydrophone was destroyed. A geophone was planted at the surface at each location, thereby allowing a conventional line to be simultaneously recorded.

Brute stacks show that high-quality data were recorded in the field using the "downhole hydrophone" technique. The surface geophone line, by contrast, was poor. Regional seismic lines were later acquired using these techniques, and they are of higher quality than lines previously recorded with surface phones. Seismic data acquired using the technique will allow mapping and direct hydrocarbon detection in presently nonproducing areas between Rio Vista and Roberts Island fields, California.

AAPG Search and Discovery Article #91035©1988 AAPG-SEPM-SEG Pacific Sections and SPWLA Annual Convention, Santa Barbara, California, 17-19 April 1988.