The philosophy of top and bottom

Abstract

Interpreting geologic information from seismic data involves the following: Data, their quality and signal-to-noise ratio; workstations, their manipulative capabilities; and people, their mental acumen and experience. Using all our high technology today and our capable workstations, it is easy for seismic interpreters to forget the basics of the reflection process. Reflections come from interfaces where the acoustic (and elastic) properties of the rocks change. Amplitude is thus a property of interfaces, more amplitude coming from more impedance contrast. We know this, of course, but we must think of the implications. A reservoir rock encased in some other rock, sand encased in shale for example, has an interface at the top (shale/sand) and an interface at the bottom (sand/shale). Thus there is a reflection at the reservoir top and a reflection at the reservoir bottom, as illustrated in Figure 1. Does every seismic interpreter realize this, and does every interpreter make full use of both these reflections?