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Exploration GIS Analysis of Basin Maturity in the South Florida Basin

By

MITCHELL-TAPPING, HUGH J.

Estero Bay Marine Laboratory Inc., Fort Myers, FL

 

A major problem of thermal maturity exists in the South Florida Basin as the bottom hole temperatures (BHT) of producing wells are below the published minimum temperature required for hydrocarbon generation that has been calculated as 221oF, based on 5,358 oil reservoirs in the Gulf Coast ranging from 221oF and 260oF. Unfortunately, South Florida oil-producing wells have BHTs ranging from 96oF in Corkscrew oilfield to 296oF in one well in Sunniland oilfield. The average for all fields is 114.5oF, indicating that the Sunniland interval is non-mature.

The quantity of organic carbon is a basic property for assessment of the petroleum potential, especially with regard to rocks deficient in organic matter. Regardless of favorable thermal maturity, type, or organic matter, if the rock contains relatively small amounts of TOC it is unlikely to yield commercial amounts of petroleum. Based on previous South Florida studies, 0.4% TOC has been judged as the minimum requirement for source rocks in the basin. The quantity, type, and thermal maturity in the Dollar Bay Formation are better than in the oil-producing Sunniland Formation lower in the stratigraphic column. The Triassic and Jurassic rocks have reported TOC values ranging from 0.07% to 0.90%; however the lower Pumpkin Bay carbonates in the Humble #1-Lehigh Acres range from 0.42 to 0.47%; while there is a 10-ft-thick 0.82% carbonate bed in the Fredericksburg Bone Island Formation in the well Coastal Petroleum #1-Tiedtke in Glades County. This study advocates a revision of the accepted standards for maturity determination.