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The AAPG/Datapages Combined Publications Database
Houston Geological Society Bulletin
Abstract
Abstract: The Effects of Salt Withdrawal of Trap Evolution and
Hydrocarbon Systems in the Gulf of Mexico Basin
By
1Exxon Production Research
2Exxon Exploration
The northern Gulf of Mexico basin margin exhibits a large variety of structural trap styles that resulted from, or were influenced by, salt withdrawal. In the past decade, improved seismic data quality and geological concepts have led to a fundamentally new regional understanding of the distribution of these structural styles and their evolution in the context of allochthonous, laterally moving salt sheets. High quality offshore seismic data, recent onshore deeper seismic, and key deep well penetrations have contributed to the recognition of important similarities between offshore and onshore structures. Concepts developed for offshore exploration using high-quality seismic data are applicable in the onshore where data quality is poorer. Continued exploration success and efficient exploitation of hydrocarbon traps in the environment require an even more in-depth understanding of their geometry, evolution, and structural integrity than has been achieved in the past. Particularly important needs include better methods for predicting fault and trap geometries, evaluating fault seal, and a clearer appreciation for the mechanics of salt movement. Finding and producing economic accumulations in a mature area will depend on applying technology based on an integrated knowledge of the hydrocarbon system. A key piece of this technology is an understanding of the relationship of trap evolution to other play elements an their associated risks.
Extensive normal growth fault detachment
systems have been documented
in the onshore and on the inner
continental shelf and appear to
have been variously influenced by salt
movements. Perhaps the most important
advance in understanding these
detachment systems is the notion that
some of them originated as
allochthonous salt sheets fed from the
Jurassic Louann salt onto the ancient
continental slope. Their subsequent
evolution as growth fault provinces
resulted from sediment influx and accommodation
provided by salt withdrawal,
the end product being a detached
normal fault system with distinctive
structural attributes, including
remnant salt of the detachment surface.
These types of detachment systems can be distinguished from more conventional detached styles through
palinspastic restorations and
geohistory analysis
. Examples exist in
the Frio and Miocene detachment provinces
of south Louisiana and have striking
analogs in the Plio-Pleistocene
trend.
Increased emphasis on the dynamics
of salt movement in environments
like the Gulf of Mexico has led to a significant advance in understanding the
form, emplacement history, and deformation
of allochthonous salt sheets.
Geomechanical modeling is potentially
useful for testing qualitative models of
salt sheet evolution based on purely
geometrical
structural restorations.
Specific aspects include base salt configuration, formation of mini-basins on
tabular salt bodies, and identification
of potential migration pathways.
Intraslope mini-basins formed during
the withdrawal of tabular salt sheets.
Depositional models developed to predict
the lateral and vertical distribution
of reservoir types in these basins indicate
that the fill evolved from older basin-
floor fans to younger shelf-margin
sequences, with sediment progradation
an progressive salt withdrawal. In
many cases, the basins have ponded
high-quality deep water reservoir
sands accounting for a large fraction of
recently discovered hydrocarbon reserves
in the Gulf. Improved knowledge
of the salt withdrawal process
coupled with higher quality seismic
data give rise to concepts with implications
for new hydrocarbon plays beneath salt, higher confidence models of
trap geometry where data are poor,
prediction of secondary migration
pathways, and perhaps the prediction
of controls on subtle trap formation or
favorable reservoir distribution.
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