Lower Tertiary Salt-Sediment Interaction in Walker Ridge, Deep Water Gulf of Mexico

Adam M. Seitchik and Timothy F. Powell
Devon Energy, 1200 Smith Street, Houston, Texas 77002

The Cascade discovery, operated by BHP Billiton, identified a thick Lower Tertiary, Wilcox equivalent, section and opened a new exploration trend in the historically unsuccessful Walker Ridge, Gulf of Mexico protraction area. Subsequent exploration wells confirmed a prolific hydro-carbon trend within an extensive clastic depositional system. The areally extensive, thick sand section generated questions concerning sediment transport, dispersion, and the interaction with salt during the Lower Tertiary period. Log and core data from Cascade suggest the Lower Tertiary sequence is composed of stacked, amalgamated sheet sands deposited as basin floor fans, with the well located in the mid to distal fan. Salt history reconstruction from the Late Cretaceous through Early Eocene depicts an open system for deposition with little restriction from paleo salt relief. Pre-stack depth migrated seismic isopach maps from Top Cretaceous to Early Eocene demonstrate autochthonous salt movement during the Cretaceous and into the Lower Tertiary. This is also evidenced by an increased number of moderate relief, high frequency salt ridges located proximal and sub parallel to mapped autochthonous salt limits. The generation and progression of Walker Ridge folds began in the Northeast with subsequent evolution trending south, south-west. Isopach maps generated with available data, show local variations over the frontal folds yet subtle variations on a regional scale. Conclusions are that Lower Tertiary clastics were deposited in a relatively unrestricted system with minimal basal salt layer influence. Lower Tertiary Deposition may have perpetuated but did not initiate autochthonous salt movement.

AAPG Search and Discovery Article #90080©2005 GCAGS 55th Annual Convention, New Orleans, Louisiana