Abstract: Smackover Oil Prospects in Apalachicola Embayment

A. V. Applegate, F. A. Pontigo, Jr., J. H. Rooke

Although no commercial accumulation of hydrocarbons has been found in the Apalachicola Embayment, core analysis on a well in northwestern Gulf County, Florida, disclosed residual oil locked in a dense, impermeable section of Smackover Limestone.

The Apalachicola Embayment (Southwest Georgia Embayment) is defined by a synclinal axis trending from St. Joseph's Bay north-northeast along the Apalachicola River. The updip limit of the Smackover Limestone is defined by eight wells which encountered this formation in Bay, Calhoun, Franklin, Gulf, and Liberty Counties and by six deep tests updip of the Smackover limits. The area underlain by Smackover in the embayment is about 2,000 sq mi (5,180 sq km), hence drilling density (eight wells) is one per 250 sq mi (648 sq km). All eight tests within the updip limits of the Smackover have been drilled within the last 3 years by Charter, Hunt, Placid, Mobil, and Exxon Oil Companies, except for the Mobil well drilled in 1968. The two wells drilled by Exxon within the area of interest are in confidential status. All other data have been released, and cuttings, cores, and electric logs are in open file at the Florida Bureau of Geology.

During the past 2 years, the Bureau has conducted a regional gravity survey in the area. The results show a very definite positive anomaly centered about 4 mi (6 km) west of the town of Sopchoppy in Franklin County. An additional, but less intense, positive anomaly is centered in Apalachicola Sound, about 5 mi (8 km) east of the community of East Point in Gulf County. These two positive gravity anomalies coincide with positive magnetic anomalies on a regional magnetic map.

A negative gravity anomaly lies northwest of these two positive anomalies. It is believed that it shows the trend of Louann Salt deposits in the embayment. Two wells encountered this salt. One of these wells was drilled through the Smackover and was bottomed in Louann. The other well was outside of the updip limits of the Smackover and was drilled through 705 ft (215 m) of Louann before being bottomed in Eagle Mills.

With the sparse well control in the embayment, indirect evidence indicates possible faulting, which would afford Smackover fault traps. The two positive gravity anomalies have not been tested by drilling. If they formed in pre-Smackover time and were buried by younger sediments, it is unlikely that Smackover Limestone is present over the crests of the anomalies. However, stratigraphic pinchout traps may exist on the flanks of these structures.

AAPG Search and Discovery Article #90967©1977 GCAGS and GC Section SEPM 27th Annual Meeting, Austin, Texas