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The AAPG/Datapages Combined Publications Database
Houston Geological Society Bulletin
Abstract
Abstract: Cyclic Attributes on
Seismic
Data and Sequence Stratigraphy-New Criteria for Exploration,
New Interpretation Styles
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By
Integrated Geophysics
Corporation, Houston, TX
The application of sequence stratigraphy to seismic
data has
long centered on the process of interpretation of
seismic
reflection geometries of onlap and downlap, and the tying of
well data to
seismic
. But in many basins, and especially in deepwater
areas, well data may be rare or nonexistent. Tying shelf
sequences to basin sequences is often impossible because of long
distances, gaps in
seismic
data, and complex structures. The
concept of aggradation cycles within sequence architectures
offers new criteria for exploration and new ways to interpret
seismic
2D and 3D datasets with modern visualization tools.
Manipulation of
seismic
voxels and attributes become tools to
study stratigraphy. The focus of
seismic
interpretation shifts
from finding reflection geometries to finding
cyclic vertical stacking patterns even if
geometries are absent or subtle. This
framework can give insight into the sediment
delivery system of margins and to
the aggradation of sediments in deep water
in areas of sparse or no geologic control.
These criteria have been applied for almost
a decade to the Offshore Nigeria exploration
areas and key discoveries have been
made using these techniques. Other areas
of application include Gulf of Mexico, NW
Shelf Australia, offshore Brunei, and
Bangladesh.
The key criterion that guides the interpreter
in these settings is the repetitive
cycles of seismic
reflection attributes and
seismic
facies patterns. The most useful
attribute
cycles consist of changes in
seismic
instantaneous amplitude and
frequency. Vertical stacking patterns of
seismic
attributes can be utilized in much
the way that well log curve stacking patterns
are used to guide sequence stratigraphic
analysis. Cyclic
seismic
facies patterns
often change upward from laterally continuous
reflections to
Unnumbered Figure. TRIO attribute
display for offshore Nigeria shows amplitude and frequency cycles build the
deep water
seismic
sequence architecture. An example of a slope well is tied to the
seismic
TRIO
attribute
display from offshore Nigeria. Only the highest amplitudes are visible. The high frequency
(hot pink) and the low frequency (red and yellow) voxels show cycles on the 3rd-order
sequence scale and build the architecture for this slope setting. The sequence boundaries are
marked in orange with the deep-water aggradation cycles in bold white curves. The gamma ray
curve is displayed in the color-coded lathe display and the thickest sands (yellow) match to the
lowest frequency responses. Note that the cycles are not confined to the syncline, but continue
into deeper water.
End_Page 17---------------
subtle mounded patterns or chaotic patterns. The attribute
cycles
and succession of
seismic
facies most often correlate to the 3rdorder
sequence and the different depositional energy and styles
that predominate as sea level falls and then rises. The key parameters
that change through this cycle are bed thickness, lithology
and facies assemblages, and depositional styles such as sheet-forms
or sinuous channel-forms. In deep-water settings, these
cycles are often a very prominent feature of the
seismic
data. Full
analysis of the
seismic
data from these areas typically reveals the
framework on three scales; the mega-architecture basin scale of
2nd-order sea level change and tectonic subsidence, the 3rd-order
"building block" sequence scale of many sea level falls and
rises, and the parasequence scale suitable for well prediction and
reserve calculation. The repetitive nature of the cycles implies a
time of balance for important parameters like sedimentation
rate, subsidence, sea level, and the development of a matured,
efficient sediment delivery system. These patterns also imply a
high potential for recycled sediments stored in an intermediate
position ready to be efficiently delivered to the basin at each lowstand
of sea level. Thus, the more repetitive the cycles, the better
the potential for good-quality reservoir sands occurring in the
deepwater facies.
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