Drilling exploration of structures of the Louisiana Continental Shelf has progressed to such an extent that it appears that a reasonable prediction can be made of the number of the various types of structures that will eventually be found when development of this area has reached a stage comparable with that now existing for the onshore Miocene area of South Louisiana.

Based on a study of the land Miocene area, it is estimated that a total of 540 offshore structures will be found out to water depths of 600 feet, of which 216 will be productive of gas, 124 productive of oil, and 200 productive of both oil and gas. It is estimated that, of this total of 540 structures, 81 are piercement salt domes with the major reserves trapped against the domal core, and 459 are deep-seated features which, though related to deep salt intrusion, have their major oil and gas reserves in reservoirs above the salt core.

The area covered by the average deep-seated salt dome feature is approximately 9 square miles in the land Miocene area, as compared with approximately 19 square miles of structural area encompassed by the average piercement salt dome. The average gas-productive structure is substantially smaller than the average structure productive of oil, or of oil and gas. The same relationships can be anticipated offshore. It also appears reasonable to anticipate that approximately 20 per cent of the total of 24,552 square miles of offshore water bottoms underlain by potentially productive Miocene and younger sediments will be proved to be occupied by structures, restrictive parts of which will be productive of oil or gas.

It is estimated that 288 structures are present in water depths of less than 100 feet, of which 200 undrilled but potentially productive structures still remain to be found. It should be remembered that many of these structures will be proved non-commercial with development drilling. In the essentially unexplored water depths from 100 feet to 600 feet, it is estimated that 252 structures potentially productive of oil or gas will be found eventually, only one of which has been drilled to July, 1961.

The presence of a type of structure not common to the land Miocene area of Louisiana but associated with salt uplift and intrusion is described, and the possibility of additional occurrences of this type of prolific structure elsewhere offshore is discussed.

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