Regional Salt Distribution from 3-D Data Across the South Additions, Offshore Louisiana

George A. Jamieson

A contiguous 3-D dataset comprising 20 surveys covering over 800 OCS blocks in the offshore Louisiana South Additions region formed the primary database for a regional interpretation of top and base salt surfaces. The interpretation was performed on a 800 m by 800 m grid of 3-D time migrated lines extracted from each survey and loaded into a single project on a workstation. After completing the interpretation the top and base salt horizons were depth converted, incorporating representative well velocity information across the study area.

The use of 3-D data has significantly improved interpretation confidence, particularly of the base salt, compared to 2-D data, which, to date, has been the most commonly utilized regional tool. However, 2-D data suffers from out-of-plane effects which can lead to erroneous interpretations of the base of salt and deep welds. A number of significant regional salt-related features and trends have been identified from the top and base salt time and depth maps. Significant identified features on the base of salt and below include keels, welds, fault zones and possible ramps which, in places, display significantly differing trends to those of the suprasalt section. The 3-D data allows the mapping of feeders associated with large counter-regional fault systems down to extreme depths, in plac s to over 7 kms, as well as the location of feeder stock and wall locations beneath salt canopies. This has shown that many large sheets comprise several salt masses which have coalesced along suture zones, for example in the Vermilion and Ship Shoal regions.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California