In modern exploration for hydrocarbons there is a great emphasis on the location of stratigraphic traps and estimation of lithologic information like sand‐shale ratios from seismic data. In order to investigate the possibilities of success in this endeavour we have studied the synthetic seismograms for wave form and spectral characteristic for four basic sedimentation models: (I) interbedded sand‐shale model representing the sediments of generally fluviatile origin, (2) interbedded coal‐shale model representing deltaic deposits, (3) sedimentary models representing transgression and regression of shore lines, and (4) a basal sand model. The results have shown that for the first two models a change in the sand‐shale or coal‐shale ratio results in a characteristically different seismogram. The nature of the seismogram, however, is also strongly dependent on how the sand‐shale or coal shale layers are arranged to ultimately give the same number of total layers, thus implying the same coal‐shale or sand‐shale ratios. The transgression, regression, and basal sand models also produce characteristically different seismic signatures. The spectra of these seismograms show attendant characteristic changes. However, it seems that in the case of real data which are disturbed by noise and the effects of overlying layers these characteristic features may not always be distinguishable.

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The analysis of reverberation periodicities is shown to be a promising method to study local crustal structure. It is demonstrated with the help of numerical models, that for an average crust; a data length of only 8 to 12 sec is sufficient to derive a crustal model in contrast to about 40 sec or more needed in the Phinney's spectral ratio matching technique. Examples from numerical models of one- and two-layer crusts are presented. Analysis of five intermediate and deep focus earthquakes, recorded on magnetic tape at the Echery (ECH) observatory of the Institut de Physique du Globe of Strasbourg, shows that while the spectral ratios indicate little overall coherence, the periodicity corresponding to the total crustal thickness is evident in all cases. The possibility of deriving a detailed crustal model is also discussed with the help of results from one of the above events.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractNew innovative approaches are now available that enable three dimensional (3D) seismic data to be rapidly screened, evaluated, and interpreted in a period of weeks, rather than months. This provides a quick and effective way to identify and define prospective targets to help optimize exploration and production (E&P) activities leading to a major impact on the net present value (NPV) of the field.The rapid seismic screening process identifies major structural and stratigraphic features, blends the major stratigraphic features with 3D attributes, and locates amplitude anomalies via 3D Voxel screening. This process applied to 3D data from the Gulf of Mexico has revealed numerous large undrilled structures in the deeper section below and adjacent to existing fields associated with sand-prone low-stand facies. This approach for screening 3D seismic data sets reduces the risks normally associated with conventional evaluation methods. Its use significantly reduces 3D seismic evaluation time and increases information quality, helping asset managers find and evaluate drilling opportunities quickly and accurately.Improvements on project economics through the use of this process are demonstrated in a number of economic impact analyses. Typical values of production, commodity prices, and costs from a Gulf of Mexico region are used in various cases to quantify the economic benefits of the rapid seismic screening process. The economic impact of this rapid seismic screening and interpretation approach can be clearly shown.