Abstract Introduction Geologic Setting Stratigraphic Setting Porosity Determination Data Set Porosity vs. Depth Depth vs. Age Effect of Pore- Water Composition Limestone & Dolomite Porosity Summary References

Newly deposited carbonate sediments typically have porosities of 40 to 70%, whereas ancient carbonate strata with porosities greater than a few percent are uncommon (Choquette and Pray, 1970). Thus, the dominant trend of porosity evolution in the subsurface is that of porosity destruction (Choquette and Pray, 1970), but there is little quantitative documentation of these porosity-reducing processes for shallow- water carbonates (Choquette and Steinen, 1980). The problem of theoretically predicting the porosity of carbonate rocks, and in particular of shallow-water carbonate rocks, is a difficult one (Scholle, 1981). The majority of carbonate studies are concerned with either recent or ancient end members, or with individual hydrocarbon reservoirs representing single (and possibly atypical) points along the continuum of porosity diagenesis.

This article describes porosity data from limestones and dolomites of peninsular Florida that span the transition from high-porosity near-surface sediments of Pleistocene age to much denser Mesozoic rocks with porosities of only a few percent. Investigation depths range from the surface to about 18,000 ft (5,500 m). Porosity data are derived from borehole-gravity measurements and from suites of acoustic, neutron, and density logs. Both types of wire-line measurements sample large volumes relative to petrographic methods, and are averaged here over vertical intervals of 5 to 70 ft (1.5 to 21.3 m) that approximate the scale of aquifers and hydrocarbon reservoirs.

Empirically derived curves of porosity versus depth for the South Florida basin and for carbonate strata of different ages and composition are given for a composite carbonate section. These curves reflect large-scale porosity-loss processes in the subsurface.