Shallow Salt Imaging Using 3-D Seismic Attributes Around Orca Basin, Green Canyon and Walker Ridge Areas, Northern Gulf of Mexico

Eugene Brush, Joseph Carl Fiduk, Thomas Schultz, Lynn Anderson, Robert Ayers, Susan Towe, and Charles Bowen
CGG Americas, Inc, Houston, TX

Orca Basin is a mid-slope, silled minibasin, spanning the boarder between Green Canyon and Walker Ridge OCS areas of the northern Gulf of Mexico. Orca Basin is unique amongst the 90+ intraslope minibasins in that it contains an anoxic hypersaline brine lake and salt exposed at the seafloor. The brine lake is a prominent flat seismic reflector at 2234m with a maximum depth of 172m. Bathymetry in the area of the Orca Basin ranges from 1750 to 2425m.

Orca Basin was formed through diapiric movement and lateral convergence of two shallow allochthonous salt tongues. One tongue has moved in from the north/northwest and the other tongue has moved in from the east. Over 30 km2 of salt is exposed at the seafloor on the eastern and northern sides of the basin.

Detailed interpretation of the top salt amplitude reveals various features that are indicative of differential salt movement within allochthonous salt. Construction of a top salt stability maps, using various seismic attributes, can identify possible geohazards as direction of future movement. Some of the features that can be identified are “growth rings” showing extensional salt and “strain fields” related to seafloor faulting.

In the last 10 years exploration 3D seismic have been used to replace shallow geohazard surveys in the deepwater. Interpretation and mapping of the top of shallow salt should also be included when locating geohazards in deepwater subsalt prospects.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005