oa Presenting seismic stratigraphy and attribute analysis as pioneer techniques for delineation of reservoir quality sand bodies in Indus offshore, southwest Pakistan

It is generally believed that various exploration failures in nearby offshore areas of Pakistan are due to the absence of a mature petroleum system. But a few gas shows and 0.55–3.24% TOC drove us to suggest that Middle-Upper Miocene lowstand systems tract (LST) exist that possesses organic, paleo-environmental and sequence stratigraphic characteristics of a potential source rock. The objective was to highlight the presence and delineate the slope and basinward facies through seismic stratigraphy and seismic attribute analysis as a new approach in southwestern Lower Indus Basin of Pakistan. Working within a sequence stratigraphic framework, four sequences have been marked on the basis of reflection termination patterns, and a sea-level curve was constructed to represent coastal onlap. A hypothetical curve was also generated by employing the spectral analysis Fourier transform function, which was found to be similar to the real one. Two coarse-grained sand wedges in the lowstands were distinguished on the basis of Wheeler’s Diagram, which were the result of fluvial incision following forced regression. Seismic attributes of total amplitude, maximum absolute amplitude and average instantaneous frequency were then studied for these sand bodies to identify their seismic signature as a gas saturation zone. Finally, a cross-plot of these attributes was generated to show the anomaly for these potential zones. It was concluded that good TOC values at a location where incision took place favours the accumulation of a reasonable amount of hydrocarbons in basin floor fans; this was further supported through seismic attributes. The present study has opened new dimensions for identifying the prospective zones for future exploration in the Indus offshore of Pakistan.