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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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