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The AAPG/Datapages Combined Publications Database
GCAGS Transactions
Abstract
EXTENDED ABSTRACT: Interaction between Submarine Channels and Mass-Transport
Deposits in an Outer Thrust and Fold Belt of the Western Deepwater Niger
Delta
Eddy Lee, Efthymios Tripsanas, R. Craig Shipp, and Larry Gibson
Shell International Exploration and Production Inc., 200 N. Dairy Ashford Rd., Houston, Texas 77079
EXTENDED ABSTRACT
The objectives of this presentation are to use 3D volume visualization tools
to analyze
visually and interactively complex geologic elements in multiple seismic data
volumes
to enhance seismic data interpretation. The study area is located in the western
deepwater Niger Delta and is characterized by a series of imbricated, seaward
thrusts
and folds formed by the downdip movement of strata as a result of sediment
loading and
extension at the shelf margin (Fig. 1). Deepwater channels and mass-transport
deposits
were identified using 3D seismic volume visualization, which allows fast volume
scanning
and extraction of seismic attributes, and multi-volume or attribute
rendering
for use in
geologic interpretation.
Methods
The seismic data presented in this study includes near- and far-angle stack
and
“
dissemblance” volumes. Shell proprietary interpretation software was
used for attribute
analysis
. To highlight channel depositional patterns and relationships, seismic
data
are best visualized, classified, and analyzed along time surfaces. Time slices
are extracted
and displayed using a dissemblance volume that was created by measuring seismic
data discontinuities. This
attribute
is useful for highlighting structural
and stratigraphic
discontinuities that best images channels and faults (Fig. 2). Amplitude scanning
software is used to analyze visually and interactively seismic data volumes
and to
display amplitude
attribute
as a cube or slabs (stacks of time slices). Amplitude
threshold
levels (color bar editing) are set so that insignificant reflections are turned
transparent
and only key features are shown as voxelized images (Fig. 3). Multi-volume
corendering
was also used to reveal the relationships between different attributes at the
same surface. Figure 4 demonstrates amplitude variations along with channel
and masstransport
deposit distribution. High-amplitude reflections (red color in Figure 4) are
identified in channel cutoffs.
Observations
Miocene to Holocene sedimentation in the study area is characterized by alternating periods of channel formation and mass-transport deposition.
Figure
1. Regional topography (upper left) and rendered seafloor map of the
study area (right).
Channels tend to
exhibit higher-amplitude reflections and have linear to meandering paths
that can
easily be
identified using seismic attribute
extractions. These channel pathways were
controlled
by the seafloor morphology, associated with the underlying thrust and fold,
and masstransport
deposits. In Figure 3, two mass-transport deposits appear to have been diverted
by an anticlinal fold in the study area, resulting in the development of a
paleodepression
that “captured” a channel system. The most recent channel system
developed
after a period of significant mass-transport deposition that covered almost
the entire
study area and caused an abrupt change in the channel position (approximately
perpendicular
to older channels) (Fig. 2). The recent channel avulsion just northwest of
the
study area may also contribute to this significant change in channel orientation.
Conclusions
3D seismic volume visualization has increased the understanding of the complex nature of channel migrations that have been modified by the interaction with mass transport deposition and the growth of underlying thrust and fold structures. Combined with traditional structural and stratigraphic interpretation, the geological history of channel systems can be further visualized and evaluated.
![](THUMBS/leeetal_img_1.jpg)
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