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Seismic/Stratigraphic Definition of Lower Cretaceous Carbonate-Bank Prospect

Marc P. Deshowitz

Exploration for Glen Rose (Lower Cretaceous) objectives in central Louisiana requires detailed calibration of well and seismic data. Well control enabled us to determine four gross facies packages in the youngest, southernmost Glen Rose bank. Seismic data allowed us to map the regional extent of the shelf-margin complex.

Lower energy rocks are found both landward and seaward of the bank complex. The fore-reef facies consists of interbedded pelagic lime mudstone, wackestone, and shale, which represent a relatively deeper water environment. The lagoonal facies is shale with thin argillaceous limestone interbeds, which represent a relatively shallow, lower energy environment behind the bank complex.

Higher energy rocks are found in the reef framework and back-reef apron facies that comprise the shelf-margin complex. The reef framework facies is a rudist coralgal boundstone and represents a constructional feature at the shelf margin. The back-reef apron facies consists of skeletal and oolitic grainstones derived from reef debris.

A predominantly shale-filled tidal pass, revealed by seismic and well data, provides a major interruption in the shelf-margin trend. This pass is a lateral seal for hydrocarbons that otherwise might have migrated to the Sabine uplift. Our prospect is located on the east side (downdip) of the pass.

A recent test of this prospect encountered approximately 1,250 ft of shelf-margin complex facies, which for the most part were nonreservoir quality. The lack of hydrocarbon shows in the area may indicate a charge problem.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.