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The AAPG/Datapages Combined Publications Database
Houston Geological Society Bulletin
Abstract
Abstract: The Geophysical Impact of Salt in the Enchilada Area, N.E. Garden Banks
By
Western Production Asset of Shelf Division,
Shell Offshore, Inc., New Orleans, LA
The Greater Enchilada-Salsa Area (ESA) is located in the Hex trend, offshore Louisiana (water depths 500 to 1,500 ft.), approximately 200 miles southwest of New Orleans. Primary recoverable reserves for the Enchilada project include volumes from a historic discovery at prospect Elmer and recent discoveries at Enchilada, Salsa, and Chimichanga. Subsurface interpretation of ESA involves a series of technical issues. Challenges associated with a strongly sloping water bottom and shallow, rapid lateral velocity changes can result in seismic positioning uncertainties deeper in the section. Additionally, the upper section is characterized by an abrupt transition into "strong overpressures" associated with a subregional layer of highly channelized, rotated blocks at depths of 5,000 to 8,000 ft.
The Aspen salt structurally dominates the
Enchilada area. At its northern edge in the
South Marsh Island area, it rises as a thick
and massive salt dome to nearly the seafloor.
Immediately to the south, the salt
abruptly thins and collapses to form a deep
evacuation, synclinal minibasin. It then
rises again, to a depth of about 6,000 ft,
forming an east-west triangular ridge on
which the Elmer discovery is located. Along
its southern limit, the salt expands as a tabular
body of about 2,000-ft thickness at a
depth of 9,000 ft. Both the Enchilada and
Chimichanga discoveries in the upper
Pliocene section are located adjacent to and/
or under the Aspen salt. This stratigraphic
interval is interpreted to be a near-slope
channel-levee turbidite complex mappable
in a north-south direction for over 10 miles.
Its channelized nature dictates a requirement
for accurate and detailed geophysical
imaging to reduce uncertainty for both
trap definition and early estimation of reservoir
characteristics. The Aspen salt-top
is reasonably well imaged, with numerous
overhangs and a complex, topographically
irregular surface, including mappable
faulted offsets. Data immediately below the
base of salt is degraded by complex ray
paths, multiples
, and converted-mode energy.
Primary Enchilada and Chimichanga
development will take place with wells penetrating
the salt.
Technical challenges associated with imaging,
well planning, and field development
have been successfully tackled with
prestack depth migration and detailed 3-D
volume modeling
. The generation of detailed,
complex salt bodies for immersion
in the sedimentary velocity field has allowed
alternative salt models to be quickly
tested and an improved 3-D depth image
to be ultimately reached.
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