Use of High-Resolution Biostratigraphic Analysis for Delineation of Reservoir Compartments in the Deepwater Gulf of Mexico

Jeff Coryell¹, John B. Wagner¹, Gerald Ragan², and Ronald W. Morin^3
1 Nexen Petroleum, Dallas, TX
² Ragan Biostrat, Dallas, TX
³ Morin Biostratigraphic Studies, Carrollton, TX

Paleontological analysis of subsurface wells in deep-water environments commonly utilize regional extinction tops associated with condensed sections for both stratigraphic correlation and age determination. However, we recognize that critical interpretation of data rests within the detailed interpretation (extinctions, local assemblages, abundance/diversity curves and paleoecology information) of foraminifers, nannofossils, and often palynological data to establish a high-resolution biostratigraphic framework.

The Aspen Field, Green Canyon Area, Gulf of Mexico, was analyzed using an integration of well log, seismic, paleontologic, pressure, and lithologic information from both whole core and sidewall core data. Work ranged from the identification of condensed sections for regional inter-basinal correlations down to high-resolution correlations of individual reservoir sands. Aspen Field produces from a series of Upper Miocene sandstones deposited in a middle to lower slope paleobathymetric environment that are predominantly characterized as amalgamated sheet sands to low-relief channelized systems. Local variations in reservoir architecture related to paleotopography and local unconformities have been confirmed by detailed analyses of paleontologic and pressure data. These local variations become critical to the economic development of the field.

High-resolution paleontological analysis provided a framework at the field scale for understanding sand presence and connectivity, potential compartmentalization of reservoir units, sedimentation rates, quantification of pressure variances, and the ability to exploit the reservoirs in areas where the reservoirs are below the resolution of seismic. Additionally, the ability to distinguish shales that have sealing capacity from shales that contain an abundant silt-sized fraction is critical to both an understanding of depositional environment and trapping ability.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005