ABSTRACT

The key to new exploration ideas in the Upper Smackover is to use a depositional model that includes the fundamental interrelationships between facies, stacking patterns, cyclicity, and porosity/permeability. Cyclicity has not been addressed well in the Smackover. At Kildare Field, seven cycles of high-energy grainstones are observed. Each cycle is deposited as part of a shallow-water ooid shoal complex located on a paleobathymetric high that was sometimes rimmed by low relief coral-algal reefs. The cycles are high-frequency, small scale, and each shallow upward, suggesting a glacio-eustatic process. Additional modifications occurred from structural growth of the underlying salt anticline contemporaneous with sedimentation. Overall, the style of local basin filling is onlap, followed by aggradation, and then progradation.

The sub-facies are ooid grainstones, ooid siliciclastic grainstones, ooid rhodolith grainstones, ooid intraclast grainstones, ooid peloid grainstones, and coral-algal reef framestone/bindstones, all overlying lower-energy mixed grainstones and packstones. The major sub-environments of deposition are ooid shoal, tidal channel, tidal delta, outer shoal, inner shelf-lagoon, and coral-algal reef.

Porosity and permeability occur as interparticle porosity primarily in the ooid and ooid rhodolith grainstone sub-facies. Poor porosity and permeability are generally caused by early cementation of pore-filling blocky calcite spar, and late cementation and replacement by saddle dolomite, poikilotopic calcite, and anhydrite.

The concept of regional cycles in the Smackover, a result of rising and falling sea level, has positive implications for the development and discovery of new porosity zones.