ABSTRACT

Several recent projects involving detailed seismic sequence stratigraphic analysis of existing wells near subsalt prospects in the south additions of the offshore Louisiana area in the Gulf of Mexico have demonstrated the utility of using seismic sequence stratigraphic analysis to reduce risk when drilling subsalt plays. First, the thick section of sedimentary rocks that was thought to be above and below the salt was penetrated in the area away from the salt. These sedimentary rocks were accurately dated using maximum flooding surface first occurrence downhole of important bioevent, condensed sections, abundance and diversity histograms, and high-resolution biostratigraphy while the wells were being drilled. Potential reservoir sandstones within specific Vail sequences in these wells were projected using seismic data up to the subsalt and non-subsalt sediment interface. The systems tract above and below the maximum flooding surface and the type of reservoir sandstones that were to be encountered were predictable based on the paleobathymetry, increase and decrease of fauna and flora, recognition of the bottom-set turbidite, slope fan and basin floor fan condensed sections, and superpositional relationship of the Vail sequences and systems tracts to provide a detailed sequence stratigraphic analysis of the well. Subsequently, wells drilled through the salt could be accurately correlated with Vail sequences and systems tracts in wells that were previously correlated away from the salt layer with seismic reflection profiles.

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