AN INTEGRATED ANALYSIS OF WELL DATA & MULTI 3D SEISMIC ATTRIBUTES FOR RESERVOIR CHARACTERIZATION AND FORMATION EVALUATION A CASE STUDY OF DEEP JURASSIC-CRETACEOUS SANDSTONE RESERVOIRS, OFFSHORE ROVUMA BASIN, MOZAMBIQUE

Abstract

The offshore Rovuma basin, northern Mozambique is the study area location. Actually it is a passive margin. The depositional settings of Rovuma basin consists of syn-rift Triassic-Jurassic (200-145Ma) and post-rift Cretaceous-Ne-ogene (145-2.6Ma) sedimentary deposits including the sand facies of the Rovuma Delta complex. Multiple tectonic episodes syn-post depositional took place and the Ibo High Structure growth orientated to (N-S) and the bathymetrical feature, the Davie Ridge are the ancient geological deepest structures (Key et al, 2008). This Research Project was designed for geochronostratigraphic identification of the poroperm lithofacies, characteristics and evaluate the potential controlling factors of distribution throughout the study area. The lower Cretaceous (Hauterian-Albian) holds poroperm (phi ~ 12-32%, K ~ 30-100mD) sandstones reservoirs which are characterized as well sorted, fine-grained sandstone, roundness: angular-sub-angular, clasts: quartz, k-feldspar, plagioclase, amphibole, completely apparent matrix density and transition cement type: limestone-dolomite whereas the upper Jurassic (Oxfordian-Tithonian) are tight sandstone reservoirs and hold the lowest poroperm properties with highest limestone apparent matrix density and cement type (compatible plots and projected throughout the well section evaluation, swc, petrographic and thin-section analysis). The 3D seismic multi attributes which are the spectral decomposition (SDE/SDT), relative acoustic impedance (RAI), trace envelope (TE), Root Mean Square (RMS), Semblance and Curvatures (-ve; +ve), RMS at windows of -+25ms to -+50ms and SDE 8-32Hz applied for the TS1 and Karoo horizons slices enhanced the geospatial lobate, isolated overbank, fans and sheets reservoirs shape/geometries distribution. The SDE at 32Hz brought up thinner fan sand facies shapes/geometries associated with small channels. Thus, the western to eastern meandering and straight single and multiple submarine channels control the geochronostratigraphic sand facies deposition and distribution into mud-sand rich to mud rich systems from the upper Jurassic to lower Cretaceous. The depositional environments (EODs) which tie with the sand facies distribution are the middle-outer Neritic (upper Jurassic) to upper bathyal (lower Cretaceous) whereas the reverse faults and three groups of normal faults: NW/SE, NNW/SSE and NNE/SSW associated with strong lateral lithofacies changes trap and compartmentalize the sandstone reservoirs in the study area.