PALEONTOLOGY: STILL A CRITICAL STRATIGRAPHIC BOREHOLE TOOL IN GULF OF MEXICO EXPLORATION AND EXPLOITATION
BRIAN J. O’NEILL, ALVIN E. DUVERNAY, RICHARD A. GEORGE, 1996. "PALEONTOLOGY: STILL A CRITICAL STRATIGRAPHIC BOREHOLE TOOL IN GULF OF MEXICO EXPLORATION AND EXPLOITATION", Stratigraphic Analysis Utilizing Advanced Geophysical, Wireline and Borehole Technology for Petroleum Exploration and Production, Jory A. Pacht, Robert E. Sheriff, Bob F. Perkins
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Biostratigraphy plays an important role in Gulf of Mexico exploration and exploitation. Advances in wireline logging and seismic technologies have not eliminated this need, but rather reinforced the importance of high-quality biostratigraphic correlation. At Shell Offshore, recent exploration has relied heavily on detailed biostratigraphic correlations using foraminifera and calcareous nannoplankton. The signals from these groups complement each other, providing excellent stratigraphic resolution even in salt flank positions poorly imaged by seismic. Paleontologic data can be acquired while drilling, allowing well path positioning on seismic without a “check-shot” survey.
Exploratory drilling at Shell’s prospect “Bonnie” (Eugene Island Block 95) benefited significantly from paleontology while drilling-With 3D seismic coverage, a deep, near-salt; well was drilled as a farm-in below an existing shallow gas field to the depth of projected amplitude anomalies without encountering significant sand bodies. Detailed paleontologic correlation to nearby control wells verified that the entire objective section had been penetrated. Objective sands were interpreted to be missing because of stratigraphic thinning onto the dome. A sidetrack well was drilled further off-structure and encountered significant hydrocarbon reserves in the projected objective section.
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 absence from erosional or structural truncation near vertical salt faces. This interpretation changed volume estimates and the planning of future wells.