Quantitative Stratigraphic Correlations
Where thick lithologlc units exist in the subsurface, quantitative approaches to stratigraphic correlations using the tools and methods described can be conceived. By thick units, we mean those whose boundaries are demarked by reflection events having sufficient separation in time to be clearly resolvable. In such a case, the necessary calibarations between arrival time and depth and between arrival time difference and thickness are established using velocity information from nearby well log measurements. If the lithologlc unit is sufficiently well defined and thick it may even be possible to develop the velocity Information from the seismic data itself (see Taner and Koehler (1969) for a basic discussion of seismic velocity determination, and Neidell and Taner (1971) for refined considerations pertaining to such determinations). The barrier bar sand described in the context of using models aptly illustrates a unit of this type.
For normal seismic data, thick lithologic units typically encompass 20 m or more depending on depth of burial, regional velocity variation with depth, and specific characteristic of the effective seismic wavelet. This value is, in fact, very much in line with our usual view of the thickness resolution inherent in our seismic data (see Sheriff, 1976). Because many exploration situations are concerned with beds having less than 20-m thickness, the matter of their resolution in quantitative terms is far from academic. Hence, we must consider in analytical terms the thin-bed stratigraphic resolution potential inherent in seismic data.
The exposition of wavelet-processing concepts and practices gave an indication that the