Abstract

The geometry and distribution of lithofacies are important factors in the geological understanding of subsurface carbonate sequences. High-resolution 3D seismic data commonly provides many geometric and stratigraphic relationships, and is therefore an ideal tool to assess these two factors. A 3D volume from Offshore Northwest Java (ONWJ), illustrates the geometry, amplitude and reflection configurations within two Mid-Late Miocene carbonate sequences. One carbonate sequence, informally named Pre-Parigi in ONWJ, is interpreted as a stack of low-relief sheet-like units containing a series of carbonate buildups which form a small elliptical complex. The overstepping of low-angle clinoforms along the complex's eastern margin, combined with back-stepping of the western margin, suggest that the complex has shifted eastward through geological time. An overlying carbonate sequence, the Parigi Formation, is interpreted as a series of well defined, sub-elliptical buildups with several low-relief linear to slightly sinuous buildups extending to the north. In map view, the linear buildups locally have a geometry similar to that of the tail of a comet, with respect to the elliptical buildups. The linear buildups probably represent the deposition of material in a relatively low-energy setting, leeward of the main elliptical buildups. Seismic facies are mapped within the Pre-Parigi carbonate sequence using a new technique which involves the automated zone-averaging of seismic attributes. Both zone-averaged RMS amplitude and frequency attributes provide images that represent the carbonate sequence as a whole. These results have implications for further use of the zone-averaging technique as a general exploration tool where lateral facies changes are associated with changes in reservoir quality.