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The AAPG/Datapages Combined Publications Database
Houston Geological Society Bulletin
Abstract
Abstract: Three Dimensional
Seismic
Interpretation
of a Piercement
Salt Dome
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By
1 Hunt Oil Company
2 Geophysical Services, Inc.
Eugene Island Block 77 field is a shallow (1100 feet)
piercement salt dome with a low relief overhang which is
productive from Upper Miocene sands at depths between
13,000 feet and 15,800 feet (or between 3.260 and 3.690
seconds). Hydrocarbon accumulations are trapped in steeply
dipping beds (10-40 degrees by dipmeter) between the salt
mass and the rim syncline. Small radial faults (50 feet of
throw) also affect reservoir limits, as is evidenced by varied
gas/water contacts and reservoir production performance.
This combination of factors (piercement dome, salt overhang,
deep objective, steeply dipping beds, tight rim syncline,
small faults) makes Block 77 field difficult to map accurately
with 2-D In previous interpretations (based on 2-D Salt face maps based on 2-D End_of_Record - Last_Page 2---------------seismic
. Unmigrated lines do not show the dip
between the salt mass and rim syncline; migrated lines
contain migration artifacts, making a salt interface
interpretation
ambiguous and recognition of small faults
impossible. To overcome the problems inherent in the 2-D
seismic
method, a dense grid of
data
(trace spacing of 110 feet in both X and Y directions) was collected over this field and
migrated in three dimensions. This placed events in their
spatial relationship, enhancing both fault delineation
and salt face
interpretation
.
data
), only one
fault was mapped - a large down to the north fault extending
eastward from the northeast quadrant of the dome. The 3-D
data
show a more complicated combination of fault systems
including other large parallel faults (some with compensating
faults), buried, down to the south faults, and an extensive
system of small radial faults.
data
were very inaccurate.
Due to sideswipe problems, only lines shot radially across the
dome were interpretable. This created large areas of no
control. Using a 3-D grid eliminated the sideswipe problem
and increased the amount of control on which to base the
interpretation
. The salt face, as seen on the
seismic
, was tied
to existing well control to make an accurate salt face
interpretation
.