The Smackover Formation, which is economically significant throughout the Gulf Coast region, is virtually untested in south Texas. The Smackover and lower part of the Buckner formations comprise a thick regressive sedimentary sequence deposited on a carbonate ramp. Four major depositional systems are recognized: (1) basinal, (2) open shelf, (3) shoal, and (4) sabkha. High-energy grainstone facies were concentrated landward; muddy low-energy facies were deposited seaward.
Basinal facies are dominated by laminated carbonate mudstones, deposited from suspension, and irregularly laminated carbonate mudstones, the product of sediment reworking by oscillatory bottom currents. The outer shelf facies is characterized by burrowed carbonate mudstones containing crustacean pellets and a pelagic fauna. The inner-shelf facies is composed of burrowed wackestones containing a benthic fauna. Burrowed oncolite and pellet packstones characterize the outer-shoal facies and cross-bedded mixed-allochem, oolite-intraclast, and oolite grainstones compose the high-energy, inner-shoal facies. The sabkha system consists of cyclic subtidal to supratidal facies. Subtidal units are burrowed gastropod-pellet wackestones and oolite wackestones to grainstones, whereas the intertidal facies is characterized by cross-laminated sandstones and algal-laminated dolomite mudstones. The supratidal facies consists of anhydrite intercalated with carbonate and terrigenous mud, and siliciclastic sand and silt.
Reservoirs as thick as 33 ft (10 m), with porosity ranging from 4 to 26% and permeabilities ranging from 0.1 to 6.5 md, have been cored at depths below 18,000 ft (5,486 m). Nearly complete dolomitization has resulted in the development of inter-crystalline porosity in inner-shelf wackestones and shoal-complex grainstones. In addition, some grainstones have subsurface-derived secondary oomoldic porosity.