PREDICTING AND EXPLAINING RESERVOIR DISTRIBUTIONS IN A GOM INTRASALT BASIN

Seismic data clearly illustrates a number of depositional sequences within the basin-filling stratigraphy of a northern Gulf of Mexico intrasalt basin. Depositional geometries within these sequences are illustrated on 3D seismic data, and characteristics of these deposits are calibrated with log data and high resolution biostratigraphy. Each sequence has an overall fining upward character, and represents an evolution from higher energy to lower energy processes. This superficial similarity masks the presence of a wide variation of depositional processes, reservoir architecture and quality within each sequence.

For example, the basal deposits of these cycles range from debris flows to sheet-like sands or erosional channel fill. Although the best reservoir potential is generally associated with the basal interval of the sequence, in reality, a wide range of reservoir quality (excellent to non-existent) is observed. Above the basal section of each sequence, deposits ranging from leveed channels to muddy turbidites are presents; again, reservoir potential ranges from good to very poor. Where preserved, condensed section and highstand deposits are represented by clean shales, marls or a combination of these litholigies.

Reservoir quality within deepwater depositional sequences can vary dramatically. Seismic facies and geometries, as well as an understanding of the variations in sediment input rate, local tectonics and gradient can be used to differentiate between the wide range of depositional processes within these sequences. These tools help highgrade intervals with best developed reservoirs from those with limited to no reservoir potential.