POROSITY DISTRIBUTION IN THE CEDAR KEYS AND LAWSON FORMATIONS OF THE SOUTH FLORIDA BASIN AND AN EVALUATION OF THEIR POTENTIAL USE AS CO2 STORAGE RESERVOIRS

The shallow reservoirs of the Paleocene Cedar Keys Formation and Upper Cretaceous Lawson Formation have been recognized as potentially suitable for geologic carbon dioxide (CO₂) sequestration, and have already shown to be successful waste-disposal intervals in the subsurface; however, until now, little information was available on the porosity and extent of the formations throughout southern Florida. In this study, the upper member of the Lawson Formation together with the lower portion of the Cedar Keys Formation are collectively identified as a potential composite CO₂ storage reservoir in the South Florida Basin and into south-central Florida where formation-tops are below 914 m. The storage reservoir is mainly composed of porous dolostone sealed by thick anhydrite layers within the overlying middle Cedar Keys Formation. Well-log and rock core analyses indicate that porous intervals within the Cedar Keys-Lawson storage reservoir display lateral continuity within the subsurface, and have an average porosity of 23% but can have values in excess of 40%. Porosity is generally greatest in the most northern and northeastern extents of the basin and into south-central Florida. Overall, porosity is lowest in the central portion of the basin and progressively increases to the north and south. Net-porous intervals within the reservoir tend to thicken toward the north and northwestern portions of the basin and into south-central Florida, and typically range from about 50-70 meters with an average thickness of 67 meters. The high porosity values within the Cedar Keys-Lawson storage reservoir and their vertical and lateral distribution throughout the South Florida Basin and south-central peninsular Florida render the unit promising for CO₂ storage in the southeastern United States. Additionally, the large expanse and relatively shallow depth of the unit make the Cedar Keys-Lawson storage reservoir one of the most cost-effective CO₂ storage resources in the region.