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ABSTRACT: New Oil Exploration Play in Florida: The Upper Fredericksberg Dollar Bay Formation

Hugh J. Mitchell-Tapping

The Fredericksberg of South Florida may have a great oil potential that has been overlooked as a primary target in past decades. Previous exploration in the area has targeted the Lower Cretaceous oil-producing Sunniland Formation lower in the stratigraphic section. The Fredericksberg Dollar Bay Formation has hydrocarbon shows in many wells occurring in limestone biohermal deposits as well as in an upper dolomitic section. The Dollar Bay Formation is part of the Big Cypress Group of the Comanchean Series of the Lower Cretaceous. The Lower Cretaceous lithology is composed of evaporitic-carbonate cycles consisting of anhydrites, dolomites, and limestones. There are also present some calcareous shales, mudstones, salt, lignitic material, and carbonaceous material, especially n the anhydrite and limestone intervals. The limestones are usually micritic, chalky, calcarenitic, sometimes argillaceous, containing skeletal particles of gastropods, pelecypods, ostracods, algae, and forams together with ooids, oncolites, grapestones, and fecal pellets. The color of the limestone ranges from white to gray to tan to dark brown. The anhydrite is usually nodular, microcrystalline, or crystalline and is usually bedded. The dolomite crystals range from euhedral to sucrosic and occur in about 30% of the formation. The expected production in the Dollar Bay Formation will be from a leached calcarenite or a dolomite. Petrological examination of core and cuttings samples show a trapping mechanism and reservoir quality and content similar to the oil pay-zone of the Sunniland For ation in Felda field. In the wells examined the reservoir porosities range from 13.6% to 28.7% with permeabilities ranging from 4.9 md to 119.0 md in a dolomite section, while in the limestone the porosities range from 9.2% to 32.7% with permeabilities from 5.2 md to 59.0 md. More than 20 wells have been evaluated to determine lithology, porosity, diagenesis, cementation, and the direction of hydrocarbon migration. All indicators are that there are strong possibilities that the Dollar Bay Formation should produce oil similar to that of the Sunniland Formation but from an area updip and northeast of the existing oil producing trend.

AAPG Search and Discovery Article #90999©1990 GCAGS and Gulf Coast Section SEPM Meeting, Lafayette, Louisiana, October 17-19, 1990