Application of Biostratigraphy to the Resolution of Exploration and Reservoir Architecture Problems

A. E. DuVernay, B. J. O'Neill, M. Rannik, M. J. Styzen

Biostratigraphy plays an important role in Gulf of Mexico exploration and production. Advances in logging and seismic technologies have not eliminated this need, but rather reinforced the importance of high-quality biostratigraphic correlation. At Shell Offshore, exploration in deep water sediments has relied heavily on correlations using foraminifera, calcareous nannoplankton and palynomorphs. The signals from these groups complement each other, allowing internal corroboration of the data increasing confidence in the interpretations even when based upon sparse faunas.

Chronostratigraphic information from paleontology constrains the timing of basin filling events. Prospect Wren (Green Canyon Block 908) was drilled in an isolated intraslope minibasin where pre-drilling control was highly speculative. Biostratigraphic dating of the bounding condensed sections indicates that the basin was filled rapidly during the Pleistocene with approximately 5600 feet of sediment deposited in 100,000 years (Hyalinea balthica Gulf of Mexico LAD to small Gephyrocapsa spp. acme). Age control from up-dip basins can help constrain models for the filling of down-dip basins.

Exploratory drilling in the Mars Basin (Mississippi Canyon Blocks 763, 806 and 807) was aided by the recognition of regional and sub-regional condensed sections between turbidite packages. These shales and marls were critical to correlation of individual reservoir units within the field. Detailed biostratigraphic correlations showed stratigraphic pinch-out of reservoir sands rather than erosional or structural truncation near vertical salt faces effecting volume estimates and planning of well paths.

Local biostratigraphic markers established on changes in planktonic foraminiferal faunas were used within Auger Field (Garden Banks Blocks 426 and 470) to resolve unconformities below the resolution of current 3D seismic. Reservoir models developed from seismic imaging were unique until integrated with detailed biostratigraphy. Refined models indicated that a planned development well would likely have encountered wet sands. Avoiding the dry hole saved approximately $12 million.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995