ABSTRACT

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, Florida. This well flowed 1379 BOD on a 13/64 inch 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 where it is about 90 ft (27 m). The field was put under waterflood in 1977 and was estimated to reach economic reservoir depletion by the end of 1986. However, by the end of 1987 the field was still producing oil and gas. This petrological and petrophysical study examined various cores and electric logs to determine why the oil production of the field continues beyond the original estimated recoverable reserves. This study found that the preserved porosity and permeability, the effects of leaching, the localized fractures together with partial dolomitization adversely affected reserve calculations but brecciation in one area of the field is considered to be the principal contributing factor.