Abstract: Door Point: Buried Volcano in Southeast Louisiana

Jules Braunstein, Claude E. McMichael

An exploratory well, the Shell Oil Co., State Lease 3956 No. 1, offshore St. Bernard Parish, Louisiana, was completed in 1963 at a total depth of 8,538 ft (2,602 m). The last 1,300 ft (3,962 m) of hole was cored and drilled through volcanic material of Late Cretaceous age.

Predrilling seismic data had revealed the presence on this prospect of intrusive material with a density slightly higher than that of the surrounding sedimentary rocks. Gravity data defined a weak maximum here, and no salt was believed to be present.

The igneous material consisted of angular fragments of altered porphyritic mafic rock. In cores it proved to be evenly bedded and cemented by sparry calcite. Radioactivity age dating fixed a minimum age of crystallization of this rock at 82 m.y. + 8, or middle Late Cretaceous (Austin). Bulk density of the igneous rock ranged from 2.02 gm/cc near its top to 2.53 gm/cc near the bottom of the well.

Three gas accumulations, with an aggregate thickness of 38 ft (12 m) were encountered in the Miocene section between 5,092 and 6,219 ft (1,552 and 1,896 m) in the well. Gas bearing sands were not present in two other wells drilled later on the same structure.

Although evidence of Late Cretaceous volcanic activity is widespread in northern Louisiana, as well as in Mississippi, and southeast of Louisiana in the Gulf of Mexico, the Door Point prospect lies within an area that had been designated previously as being free of volcanism.

AAPG Search and Discovery Article #90975©1976 GCAGS- GC Section SEPM Annual Meeting Shreveport, Louisiana