Imaging the Base of the Weathering by Stacking Shot Records

Abstract

The generation of a time model of the weathering is the single most important parameter for accurate statics corrections when the replacement statics model is used. The computation of an accurate time model of the weathering is critically dependent upon the signal to noise ratio of the first break refraction data. In arid areas, the signal-to-noise ratios can be very low, often because of the common occurrence of sand dunes. In other areas, biogenic gas generation can result in significant gas saturation in porous formations, which strongly attenuate all seismic energy. This study presents a new method for generating a time model of the weathering, which is of equivalent resolution to that generated with the generalized reciprocal method (GRM), by stacking common receiver gathers. The common receiver stack (CRS) consists of a correction for the refraction equivalent of the normal moveout, balancing of the traces to accommodate the effects of geometrical spreading, and then stacking of the traces. CRS has two major advantages. The first is that in most cases, first breaking picking can be eliminated. The second is that CRS generates high quality time models of the weathering even where the signal-to-noise ratios of the first break data are poor.