Synthetic sonic logs—a process for stratigraphic interpretation

Abstract

Modern seismic reflection data may be processed to approximate closely the reflection coefficient series of a sedimentary section. Inversion of the series will produce a low‐cut filtered impedance log. Extension of the technique to include density correction and replacement of missing low‐frequency components leads to generation of a synthetic sonic log having dimensions and characteristics similar to a conventional borehole sonic log. A synthetic sonic log section provides several advantages over conventional seismic sections, particularly for stratigraphic exploration. Direct depth display largely eliminates the vertical scale distortion inherent in time sections and simplifies integration with other subsurface data. Resolution is generally improved. The process is well adapted to automated generation of stratigraphic sections. Individual rock units are mapped by contours of constant transit‐time, to show facies changes and depositional sequences in detail. The detailed measurements of velocity may be used to interpret rock type. Comparison of synthetic sonic log sections to the conventional seismic data from which they were derived, clearly demonstrates improved understanding of subsurface geology.