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The AAPG/Datapages Combined Publications Database
Houston Geological Society Bulletin
Abstract
Abstract: Salt Morphology and Hydrocarbon Trapping
at Eugene Island 188 Field: Retailed Salt Surface
Mapping Yields New Opportunities in an Old Field
By
Increased reserves, attic wells, a substantial increase in production rates and more efficient field depletion have resulted from detailed mapping of an irregular, rugose salt surface at Eugene Island 188 Field. Forty salt penetrations (of 175 total wells and sidetracks), time and depth migrated versions of a 3-D seismic survey, salt proximity surveys, gravity data, and 3-D visualization were used in the study.
The EI 188 dome is part of a
counter-regional fault
/ salt withdrawal
basin complex which began forming in
the Miocene. A series of sub-regional interval
isopachs used to reconstruct the
mini-basin evolution indicate that basin
shape changed through time. Dome
growth, continuous since the middle
Miocene, reached a maximum growth
rate during the Late Miocene.
The gross salt morphology is a north
dipping tear-drop shape from a depth
of about 25,000 feet to 700 feet from the
sea floor. The salt body is severely overhung
to the south and east with salt
noses extending out to the northeast and
west. The noses, which become more
extensive with depth, are related to the
counter-regional fault
system (and associated
antithetic
fault
system) along
which the dome appears to have grown.
Tangential faults cut into, offset, and
extend out from the salt creating a very
irregular, rugose surface. Radial faults
are not present. Numerous sills and salt
intrusions, defined and mapped by
closely tying the well and seismic data,
were probably formed as extensive salt
flows on or near the sea floor and were
later covered by sediments.
Hydrocarbons are found in 60
hydropressured deltaic sands ranging in
depth from 5,000 to 16,000 feet and in
age from Late Miocene to Pliocene. Trap
types are nearly all related to closure
against salt, whether it is closure within
concave recesses in the salt, beneath salt
sills, or between faults and the salt. Vertical
segregation of hydrocarbons is
present, shallow sands tend to be oil-bearing
and deeper sands gas-bearing.
Areal segregation of hydrocarbons is
also evident. Within a given sand the
structurally lower western flank of the
dome tends to be wet, the northern flank
oil-bearing and the structurally higher
eastern flank, gas-bearing even though
faults separate the sand into numerous
reservoirs.
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