RESERVOIR POTENTIAL USING SEISMIC ATTRIBUTES AND DEPOSITIONAL ENVIRONMENT ANALYSIS OF THE EOCENE SUCCESSION SOUTHERN ROVUMA BASIN, MOZAMBIQUE

Abstract

This study examined depositional environments and sand distribution in the Eocene of the southern Rovuma basin using well data and seismic attributes. The succession was deposited in deep water by a major progradational event that occurred in the Tertiary because of a huge influx of sediments and shelf edge collapse which generated turbidity currents that transported shallow water sediments down slope. Seismic amplitude data cannot fully delineate detailed stratigraphic or structural features, so it is important to consider a number of  seismic attributes that can help to easily identify those features. Beyond of many available attributes, RMS, spectral decomposition, variance and coherence were selected due to their proven abilities to delineate stratigraphic, structural discontinuities and bed thickness. Seismic attributes were extracted from a conventional 3D Pre Stack Time-Migration seismic volume. Two main horizon slices were analyzed within the interval. Shallow slice Top Sand RMS and Variance better enhance the sand distribution and the lateral continuity associated with the     channels and depositional lobes, whereas the deeper slice Base Sand can be imaged more efficiently by using Spectral Decomposition, Coherence and Variance. Nevertheless, the base of the      channel are filled by mud. Channel widths vary from 800 m to 2.2 km. These channels are NW-SE oriented. Depositional environment analysis was carried out on the basis of seismic geomorphology supported by well log data. The study interval was divided into 4 units based on well logs and comprise proximal to distal fans. Potential reservoir targets in this interval might be located where there are high amplitudes on RMS combined with Variance, however, the presence of carbonate cement must be considered. Attributes effectively demonstrate lateral continuity and geomorphology of the channels.