ABSTRACT: Burial Porosity Enhancement of Sunniland Formation Reservoir Facies in the Bear Island Field, Collier County, Florida

FISHER, R. E., Georgia Southern University, Statesboro, GA

Investigation of burial diagenetic fabrics in Cretaceous (Comanchean) grain-supported facies reveals the presence of diagenetic fabrics synchronous and subsequent to hydrocarbon emplacement. These diagenetic fabrics provide evidence of late porosity enhancement, probably by redistribution.

The Sunniland Formation in the Bear Island field contains two bioclastic reservoir facies. The basal portion of the lower reservoir facies exhibits several diagenetic features that were not observed in the upper, oil-saturated portion of the facies.

Late stage diagenetic features include:
1. Microstylolites in which calcium-rich euhedral saddle dolomite rhombs may display evidence of subsequent corrosion along cleavage. These dolomite rhombs presumably precipitated while pressure generated by hydrocarbon generation formed microstylolites and kept them open. Petroleum migration then followed as bitumen is also present within the microstylolites.
2. Another diagenetic fabric observed below the oil-water contact was that of partial replacement of saddle dolomite by anhydrite. Additional calcium that may have been required for replacement to occur may have been available owing to selective dissolution of calcite above the oil-water contact. Absence of these diagenetic

features in the oil-saturated zone, where saddle dolomite is also present, may permit estimation of the range of secondary porosity enhancement that may have taken place.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)