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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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