Abstract: Subsalt Risk Reduction Using Seismic Sequence-Stratigraphic Analysis

Walter W. Wornardt, Jr.

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 sediments that was thought to be above and below the salt was penetrated in the area away from the salt. These sediments 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 sands within specific Vail sequences in these wells were projected on sei mic up to the subsalt and non-subsalt sediment interface. The systems tract above and below the maximum flooding surface and the type of reservoir sands that were to be encountered were predictable based on the paleobathymetry, increase and decrease of fauna and flora abundance, 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 in question. Subsequently, the wells drilled through the salt could be accurately correlated with the Vail sequences and systems tracts in wells that were previously correlated with seismic reflection profiles away from the salt layer.

AAPG Search and Discovery Article #90983©1994 GCAGS and Gulf Coast SEPM 44th Annual Meeting, Austin, Texas, October 6-7, 1994