ABSTRACT

Smackover sandstones in Thomasville Field represent turbidite channel deposits. These sandstones are interbedded with a few thin beds of oolitic grainstones. 969 ft (296 m) of core from three wells were examined, of which 820 ft (252 m) were sandstone. Depths ranged from 20,100 to 20,649 ft (6131 to 6298 m). Electric logs and cores from three wells show abrupt facies changes which may be expected from a shifting channel deposition. Correlations were made between wells and labeled the lower, upper, and anhydrite zones.

Environment of deposition was determined from an examination of core composition, texture, and sedimentary structures. Thick, massive bedsets and massive to laminated bedsets (A and AB units respectively) are common in all cores, although massive (A) units dominate. Quartz grain sizes decrease upwards in most bedsets. Sandstones have a mean grain size of 0.23 mm (fine grained). Carbonates exhibit similar textural trends and sedimentary structures.

Porosity and permeability average 5.1 percent and 0.32 md for sandstone, and average 1.2 percent and 0.01 millidarcy for carbonates. A black, opaque residue, ubiquitous throughout the cores, represents residue of a paleo oil pool.

Resistivity plotted against bulk density shows distinct groups for each rock type. A plot of resistivity versus porosity suggests a gas-water contact further down the section at a depth of about 20,500 ft (6253 m). Based on this study, the gas column is on the order 300 ft (92 m) for about 50 percent water saturation.