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The AAPG/Datapages Combined Publications Database
Houston Geological Society Bulletin
Abstract
Abstract: Subsalt Exploration in the Deepwater Foldbelts of the Gulf of
Mexico:
Regional Analysis of a Giant Petroleum System
By
Chevron North America Exploration and
Production Company, Deepwater Business Unit,
New Orleans, Louisiana
The geologic setting of the distal U.S. waters is characterized by a complex assemblage of salt-related contractional features. In the U.S. western Gulf, the Perdido Foldbelt is a north-south trending zone of shortened Mesozoic through Miocene strata covering an area of over 30,000 square kilometers. In the deep east central U.S. Gulf, the Mississippi Fan Foldbelt is an arcuate trend of folded/thrusted Mesozoic through Pliocene strata encompassing over 25,000 square kilometers. Approximately 80% of each trend is in the subsalt environment. The difficult seismic imaging of these subsalt trends necessitates a regional approach to understand the development and prospect potential in these vast areas.
Our regional methodology employs source rock analyses, potential
field and basement mapping, regional structural
mapping of
key horizons including the top and base of salt, regional
cross
sections
,
stratigraphic studies and depth-migrated seismic
imaging. Basement-controlled thickness and distribution of the
Louann Salt and subsequent sediment loading history are the
primary controls on the location, distribution, and character of
the foldbelts. These primary controls are responsible for
observed changes along the regional strike and dip of the trends
that include
structural
inversion. Contraction in both areas has
lifted objective intervals up to 4 km above regional elevation.
Folding accommodates only a small portion of the total regional
extension, with the emplacement of the Sigsbee salt canopy serving
as the primary balancing mechanism. Understanding the
linkage between contraction of the objective intervals and the
emplacement of the overlying salt canopy is the key to successful
exploration in these trends. Because emplacement of the canopy
is partially synchronous with folding, a correlation exists
between the
structural
grain of the subsalt folds and the base of
allochthonous salt.
Primary reservoir objectives in both foldbelt trends are Tertiary-age
turbidites, although a higher-risk poorly understood
Mesozoic section is present. Hydrocarbon sources for both
trends arc from Upper Jurassic and Lower Cretaceous marls,
with the Perdido Foldbelt also accessing potentially mature
Paleogene intervals. The combination of large structural
traps,
rich source rocks, potentially excellent reservoirs, and a regional
top seal places the subsalt foldbelts in the forefront of future
Gulf of Mexico exploration.
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