1. Introduction

Abstract

Seismic reflections come from interfaces where the acoustic properties of the rocks change, and this fact is the basis of our understanding of the nature of seismic data. Acoustic impedance of a rock layer is the product of the density and the velocity of that layer, and strictly a reflection is generated by a contrast in acoustic impedance. In fact impedance and lithology normally follow each other, so that impedance boundaries and lithologic boundaries normally concur. Consider a sand encased in shale, perhaps the most common situation forming a hydrocarbon reservoir. The shale-sand interface at the top generates a reflection, and the sand-shale interface at the base generates a reflection (Figure 1-1). Thus a sand has a reflection from the top and another from the base. These two reflections should be considered together in all studies of the reservoir sand.