The Pettet Formation is a southward-thickening carbonate wedge, deposited during Aptian (Early Cretaceous) time in the region that is now the Gulf coastal plain of east Texas, Arkansas, and Louisiana. Within the Pettet are characteristic oolite sequences which formed in a northwest-southeast-striking belt paralleling the shelf edge.

In southeast Shelby County, Texas, the Pettet oolite shoals were studied, using available well cores and induction-electric logs. The oolite shoals appear to have formed on top of remnant topographic highs in the underlying Travis Peak Formation, in series of vertically stacked cycles of grainstone development.

The oolite shoals display five constituent lithofacies: (1) mudstone, (2) oolitic packstone, (3) skeletal-oolitic packstone, (4) skeletal-oolitic grainstone, and (5) oolitic grainstone. The oolitic grainstone lithofacies is the most volumetrically significant constituent of the Pettet oolite shoal reservoirs, comprising approximately 95% of each sequence.

Three diagenetic environments are seen in the oolite shoals: marine phreatic zone, vadose zone, and freshwater phreatic zone. Porosity is mainly primary interparticle, with some secondary intraparticle and vuggy porosity also being important. The freshwater phreatic diagenesis appears to have had the most effect on the Pettet reservoirs, creating minor recrystallization-induced porosity occlusion and excellent porosity-enhanced dissolution zones.

Hydrocarbon reserves in the Pettet Formation are related to certain structurally modified oolite shoals. Salt swelling and diapirism in the underlying Jurassic Louann Salt appear to be the mechanism responsible for the formation of locally developed anticlinal noses and domes. These small anticlinal features, when occurring beneath or adjacent to an oolite shoal, result in the upward tilting of the strata with subsequent migration and stratigraphic trapping of oil and gas.

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