Interpretation of reflection seismic data by analysis of cumulative energy spectra

Abstract

Where reflection seismic data are available, and in the absence of geologic control (deep reflectors, lack of drill hole data), a positive identification of the structure and lithostratigraphy of the reflectors is desirable. In this study, synthetic geologic models are generated to model thin-bed and velocity transition (constant velocity gradient) structures. These are transformed to displays of frequency vs. horizontal location vs. cumulative percent spectral energy.

The spectra of thin-bed models display a shift to higher frequencies relative to that of the incident wavelet, a consequence of differentiation. The spectra of the transition model show a shift to lower frequencies, a result of integration. Mathematical derivation of these spectra yields a method to estimate layer thickness at horizontal locations which correspond to local maxima and minima of the cumulative percent energy contours.

The synthetic spectra are compared with those of (x, t) windows of seismic record sections. For the reflectors for which there is geologic control, there is a good correlation between the spectra of the synthetic and real data. This suggests that this method of pattern recognition is a useful tool in interpretation of reflection seismic data.

Spectra were generated for data from the Valley and Ridge province, the Piedmont, and the Atlantic Coastal Plain. There is geologic control for the reflectors from the eastern Piedmont and the Coastal Plain. Spectra for reflectors in the western Piedmont and the Valley and Ridge aid in the interpretation of these data, for which there is not good geologic control.