Petrology of Partially Dolomitized Reservoir: Blackjack Creek Field, Santa Rosa County, Florida

Hugh J. Mitchell-Tapping

In January 1972, Blackjack Creek field was discovered by Exxon drilling the 13-3 St. Regis well in Santa Rosa County in the Florida Panhandle. This well flowed 1,379 BOPD on a 13/64 in. choke from perforations in the Jurassic upper Smackover. The field lies at the eastern end of the Pickens-Pollard-Foshee fault system and is on trend with other major Smackover oil producing fields. At Blackjack Creek field, the Smackover is about 420 ft (128 m) thick, with the pay zone occurring at 15,700 ft (4,785 m). The pay-zone thickness varies throughout the field, but its maximum thickness occurs at the crest of the structure, measuring about 90 ft (27 m) thick. The field was put under waterflood and was estimated in 1977 to reach economic reservoir depletion by the end of 1986. How ver, by the end of 1987, the field was still producing oil and gas. This petrological study examined various cores and electric logs to determine why the oil production of the field continues beyond the estimated recoverable reserves. Other than economic values, the preserved porosity and permeability, effects of leaching, localized fractures and brecciation, and partial dolomitization are considered to be principal contributing factors to continued production.

AAPG Search and Discovery Article #91036©1988 GCAGS and SEPM Gulf Coast Section Meeting; New Orleans, Louisiana, 19-21 October 1988.