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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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