Integration of Multiple Techniques to Define A Complex Salt Body in The Flex Trend of The Gulf of Mexico

By

Sherrie R. Cronin¹, Brian Mallick¹

(1) Anadarko Petroleum, The Woodlands, TX

 A recent discovery well drilled by Anadarko underscored the wisdom of integrating salt body interpretation from multiple data sources. Seismic clearly showed a top of salt reflector for both the main salt stock and a laterally extensive salt canopy on a prospective block in 150m of water in the Central Gulf of Mexico. However, neither poststack time migrated data nor the initial sediment flood of a PreSDM project in progress showed a convincing salt flank or base of salt.

Concern that strong reflectors under the salt canopy believed to be prospective section might actually be a poorly imaged base of unexpectedly thick salt prompted Anadarko to perform a series of prestack depth migrations on an extracted 2D line using various salt geometries. Thicker salt models resulted in grossly distorted seismic and poor imaging at depth. A thinner salt layer (300m to 500m) such that the top and base of salt reflectors interfered with each other produced more reasonable subsalt images.

To aid in this confirmation, the salt body was analyzed using gravity and magnetic data. To our surprise, this analysis showed two allochthonous salt thicks to the south and west of the prospect, both of which thinned rapidly to zero salt at the proposed well location. The drill bit encountered approximately 10m of salt. A VSP subsequently enabled us to pinpoint the unimaged flank of the salt stock. Ongoing drilling, VSP, and seismic reprocessing have all confirmed that this field is located under a complex and rapidly changing salt canopy.