RESERVOIR CHARACTERIZATION OF THE JURASSIC-CRETACEOUS ROCKS IN THE SOUTH FLORIDA BASIN – AN UPDATE TO THE USGS 2001 OIL AND GAS ASSESSMENT

Rocks of Late Jurassic and Cretaceous age in the South Florida Basin (SFB) consist of thick carbonate-evaporite sequences that contain porous rock sealed by surrounding evaporites or low-permeability micritic limestone. Currently, commercial petroleum production only occurs in the Lower Cretaceous Sunniland Formation, and although it has been producing since the 1940s, newfound interest has arisen as industry explores this unit for unconventional oil production. Many of the remaining Jurassic-Cretaceous rocks show signs of hydrocarbons; however, published literature lacks a firm understanding of the geochemistry, organic petrology, and thermal maturity of these rocks, as well as their structure and thickness. In 2001, the USGS published an assessment of undiscovered oil and gas in the onshore and State-waters portion of the SFB. This assessment identified two stacked total petroleum systems (TPS), each with a single assessment unit (AU), that were separated by a regional evaporite seal, the Lower Cretaceous Punta Gorda Anhydrite. The identified TPS and AUs were the: 1) section above the Punta Gorda seal, the Sunniland–Dollar Bay TPS and Lower Cretaceous Shoal-Reef Oil AU; and 2) the section below the Punta Gorda seal, the Pre-Punta Gorda TPS and Pre-Punta Gorda Dolomite Gas and Oil hypothetical AU. Much of this assessment was conducted using published literature, along with some proprietary well information, for intervals of interest; however, a majority of these resources were compiled decades ago and require significant updating. Additionally, some of the Jurassic-Cretaceous rocks in the SFB have never been mapped and lack a thorough understanding of the reservoir quality, organic petrology and thermal maturity, and spatial distribution of these rocks throughout the onshore portion of the SFB and southwest into the State-waters toward the basin center. In preparation for a re-assessment of undiscovered hydrocarbons in the SFB, the USGS is revising and expanding the current understanding of the thickness and extent of the Jurassic-Cretaceous rocks using geophysical logs, and is conducting rock evaluations and geochemical analyses on ~60 rock samples for a better handle on the organic petrology and thermal maturity of these rocks, as well as their potential to serve as unconventional petroleum resources.