Abstract: Upper Smackover Depositional Model -- Kildare Field, Cass County, Texas

BARRETT, DAVID
British-Borneo Exploration, Inc., Houston, TX

One key to predicting trends in the Upper Smackover is to use a depositional model that addresses the fundamental interrelationships among facies, cycles, stacking patterns, structural timing, and porosity/permeability. The Kildare Field model does this and suggests that a complete analysis of the above characteristics should help to predict porosity trends on a subregional basis.

At Kildare Field, the depositional model is a shallow-water ooid shoal complex deposited on a paleobathymetric high that is rimmed by low relief coral-algal reefs. The sub-facies identified are ooid grainstones, ooid siliciclastic grainstones, ooid intraclast grainstones, ooid peloid grainstones, and ooid rhodolith grainstones, all overlying lower-energy mixed grainstones. Other sub-facies are inner shelf-lagoon mixed packstones and coralalgal reef framestone/bindstones. Specific subenvironments of the ooid shoal complex are the inner shoal, tidal channel, tidal delta, outer shoal, inner shelf-lagoon, and coral-algal reef. Each sub-facies has a distinct porosity/permeability profile.

Deposition occurs as six high-frequency shallowing-upward cycles of high-energy grainstones progressing from onlap to aggradation to progradation. The cycles and stacking patterns

occurred in response to penecontemporaneous sedimentation during structural growth of the underlying salt anticline, and/or high-frequency glacioeustacy.

Good porosity and permeability occur as interparticle porosity occasionally enhanced by dissolution in slightly emergent areas. Poor porosity and permeability are caused by early precipitation of pore-filling blocky calcite spar from a freshwater phreatic lens. Late occlusion occurs by precipitation of saddle dolomite, poikilotopic calcite, and anhydrite.

AAPG Search and Discovery Article #90932©1998 GCAGS/GCS-SEPM Meeting, Corpus Christi, Texas