ABSTRACT

An electric log section 106 miles long through 11 exploratory wells drilled in nearshore waters of southeastern Louisiana and western Mississippi reveals a thick (387-1000 ft) section of carbonates both above and below the Heterostegina Zone. Lithologic logs of four cores (total 229 ft) from the Heterostegina Zone, and petrographic analysis of 45 thin sections cut from these cores, indicates the presence of hermatypic framework and binding organisms that constructed reefal or algal mound accumulations. These buildups accumulated along a Late Oligocene-Early Miocene rimmed accretionary carbonate shelf. About 160 miles of seismic line, shot roughly perpendicular to this shelf edge, confirms the presence of these buildups in the subsurface. Oil shows in the relatively thick porous and permeable carbonates both above and below the Heterostegina Zone interval, regional unconformities at the top and bottom of these carbonates, and the listric faults at the Heterostegina Zone hinge line, indicate that additional Frio-Anahuac hydrocarbon reservoirs await discovery in this area of the Gulf Coast.