ABSTRACT

Outer Continental Shelf hydrocarbon exploration of Lower Cretaceous carbonates began in 1968, with the James Limestone and Andrew Formation as targets. Six fields were declared in this carbonate trend: the James Limestone's Formation's Viosca Knoll 252, Viosca Knoll 256 (terminated), Viosca Knoll 69, and Mobile 991 Fields; the Andrew Formation's Main Pass 253 and Main Pass 221 relinquished Fields. Additional James shows are observed in Viosca Knoll lease Block 114 and Viosca Knoll lease Block 117, which initially discovered James Limestone gas during drilling to a deeper target. Relatively unexplored regions of Lower Cretaceous hydrocarbon potential occur on the Southern Platform in the Desoto Canyon/Florida Middle Ground areas, on Sarasota Arch, and in the South Florida Basin adjacent to the Lower Cretaceous shelf-edge-reef-trend.

Stratigraphically between the Dantzler and Paluxy formations, the Andrew Formation is composed of an upper Washita and two Fredericksburg aged carbonate platforms separated by shelf mudstones. The James Limestone, comprising upper and lower members, dominate the thin shale members of the Pearsall Formation. Six facies compose the Lower Cretaceous carbonates where grainstone detritus zones, adjacent to reef/patch reef boundstones, were redistributed by wave action over the interior platform. Shelf mudstones, nearest the paleoshoreline, occurring in central and eastern portions of the Mobile and northern Viosca Knoll areas have no porosity. Oolitic grainstones trend subparallel to the shelf-edge-reef-trend and possess relatively more abundant spar cement destroying porosity. Reef/patch reef boundstones have micrite trapped in their growth structures resulting in poor permeability and interfinger with outer shelf mudstones nearest the shelf-edge.