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The AAPG/Datapages Combined Publications Database
Houston Geological Society Bulletin
Abstract
Abstract: Submarine Fan Faces Analysis Using
Well Logs and 3-D
Seismic
:
An Example from the Miocene
of The Texas Gulf Coast
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The horizons of primary interest in the M A 668 Field
are of middle Miocene age. They are present in the field as
fan complexes which prograded from west to east. They
were subsequently folded into a shallow dome with four-way
dips and cut by two generations of orthogonally-oriented
faults, the first down-to-the-west and the second down-to-the-
north. Efficient development of the field required that a
3-D seismic
survey be conducted in advance of development
drilling so the prospective fault blocks could be properly
mapped. Exploration drilling had also revealed the strata at
the prospective horizon(s) to be complex, and we hoped
that the
seismic
program would also help with mapping
stratigraphic variations within the reservoir.
Seismic
-stratigraphic
interpretation
was conducted on
an interactive color terminal which facilitated the selection
of optimum display scales, colors, and orientations. Facies
analyses relied on identification of such features as top-and-bottom-
lap, foresets, top truncations, and hummocky reflectors.
Well log analyses of facies utilized SP and gamma curve shapes: fining upward (increasing gamma and SP), coarsening upward (decreasing gamma and SP), and more blocky and rounded shapes were all identified and compared to record sections printed or displayed at the same scale as the well logs.
Top-lap seismic
sequences were found to correlate
with fining-upward log character, bottom-lap
seismic
sequences
were found to correlate with coarsening-upward
log character, and log forms with shapes intermediate to
these were found to correlate with foreset sequences.
Hummocky reflectors were found in the core of the fan
complex.
Time-slice displays and displays flattened on events
were also helpful in defining the limits of selected fans, and
these could be correlated to limits implied from the log
interpretation
.
Subsurface facies analyses are often done using either
well logs or seismic
-stratigraphic techniques. There are
pitfalls inherent in depending too much on either, but a
high-quality
data
set is not always available for cross-testing
alternate hypotheses. Our analyses suggest specifically that
electric log curve shapes may be interpreted with greater
confidence in the future than has generally been the case.
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