Predictive Seismic Modeling Case History from the Niger Delta

Abstract

Seismic modeling techniques provide the mechanics for simulating the geology of the subsurface by depicting the impact of a propagating seismic wavefront on subsurface structures. In practice, seismic data have been used to map the geometry of events in the subsurface, mainly from reflection continuity and the character of reflection packages. In the Niger delta, recent developments in stratigraphic exploration has induced the examination of more subtle features of reflection, mainly polarity, amplitude, and waveform to define the limits of seismic resolution and hence predict the geometry of subsurface fluid and solid interfaces. The case history discussed here involved interpretative study for defining the fluid contents of prospective oil and gas leads as indicated by anomalous seismic events on a Niger delta field located in a water depth of 25 m. An appropriate source signal (5-35 Hertz minimum phase) is selected, and the wavelet is convolved with a practical geologic model to obtain a synthetic seismogram. By an interactive process involving slight modifications in the geologic model, a synthetic seismogram is ultimately derived that matches a field signal, thus providing a more accurate prediction of the geological formation under study. The technique was effect (as confirmed by later drilling) inmore » appraising the fluid contents of the targeted pay zones encountered at gas/water, oil/water, and gas/oil/water contacts in the O field, located in the eastern offshore area of the Niger delta. The method further demonstrated that structural and stratigraphic modeling are effective tools for testing the mapability of a geologic concept and are able to evaluate the significance of reflectivity changes or anomalies on uncalibrated seismic data.« less