ABSTRACT

Reconnaissance geochemical analyses (organic carbon (orgC) and Rock-Eval pyrolysis) were made of drill cuttings of pre-Punta Gorda rocks in seven widely scattered boreholes in South Florida to assess the petroleum source-rock potential. The rocks judged to have the best source characteristics, by virtue of their relatively higher orgC contents (0.4 to 3.2 percent) and total pyrolytic hydrocarbon yields (1 to 16 mg/g rock), occur chiefly in carbonates in the upper half of the Pumpkin Bay Formation (upper Coahuilan) and, to a lesser extent, in parts of the Lehigh Acres Formation (Trinity 'F' of Exxon). Geographically, the richest of these rocks are in the vicinity of the West Felda field and in the lower part of the Florida Keys.

The rocks in the lower part of the Pumpkin Bay and underlying Bone Island (lower Coahuilan) and Wood River (Jurassic?) Formations have very low orgC contents (<0.3 percent) and low pyrolytic hydrocarbon yields (<0.3 mg/g rock). At face value, the oil potential is poor for pre-upper Pumpkin Bay rocks. Potential for natural gas, however, cannot be eliminated on the basis of insufficient organic matter even though the preliminary indications are not favorable. In light of a reported gas show in the Wood River Formation (at about 15,700 ft in the Phillips-Mobil 1-C Seminole well), the lower part of the pre-Punta Gorda section of South Florida may have some potential for gas, provided that other factors (porosity, permeability, traps) are favorable.