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by Barbara ,. RadovichIntegrated GeophysicsCorporation, Houston, TX

CyclicAttributes on Seismic Data and SequenceStratigraphy-New Criteriafor Exploration,

New Interpretation Styles

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 deep-

water 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 interpretseismic 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 find-

ing cyclic vertical stacking patterns even if

geometries are absent or subtle. This

framework can give insight into the sedi-

ment 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 explo-

ration areas and key discoveries have been

made using these techniques. Other areas

of application include Gulf of Mexico, NW

Shelf ~Australia, offshore Brunei, andBangladesh.

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 fre-quency (hot pink) and the low frequency (red and yellow) voxe/s 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 raycurve 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 continueinto deeper water.

February 2003 Houston Geological Society Bulletin

The key criterion that guides the inter-

preter 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 ofseismic 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 contin-

uous reflections to ~ continuedonpage19

17

subtle mounded patterns or chaotic patterns. The anrbute cycles and sucassion of seismic facies most often correlate to the 3rd- order sequence and the di£ferent depositional energy and styles that predominate as sea level falls and then rises. The key param- eters that change thmugh this cycle are bed thiclmess lithology and fads assemblages, and depositional styles such as sheet-

forms or sinuous channel-forms. In deep-water - these cycles are often a very prominent feature of the seismic data. Full analysis of the seismic data from these areas typically rev& the 'mework on three scales the mega-architecture basin scale of 2nd-order sea level change and tectonic subsidence, the 3rd- order "building blodC sequence scale of many sea level falls and riss, and the parasequence scale suitable for well prediction and - caculation. 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. &dent 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 low- stand of sea level. Thus, the more repetitive the cycles, the better the potential for goodquality reservoir sands occurring in the deepwater hues. . Biogmphlcal Sketch B m u m I. E ~ ~ V I C H is a consultant geophysical advisor for Integrated Geophysics corporation. She has 25 years of world-

wide experience in wismic and well log sequence stratigraphy of dastics and

a carbonates, fluvial to deepwater set- 5 tings, and regional basin to detailed s c reservoir scales of investigation. Key .- accomplishments have included suc-

P cess l l pre-drill predictions in the Norphlet play, South Atlantic margin studies resulting in significant lease acquisitions, and development of inno-

4 3

vative interpretation approaches leading to major discoveries for T a c o in offshore nigeria She was awarded the Texaco technol- 0

ogy group's top honor for deepwater research dons . She was a

retirement symposiums concerning the full utilization of

B featured speaka at the SEF'M D i o n d jubilee and Peter Vail W

a 3D seismic attribute and visualization techniques within a b e w o r k of sequence stratigraphic architechms, espKially as applied to deep-water settings. Her career has spanned both 3 geophysical and geological research topics and Barbara has held

corporate affiliations are Texaco Exploration and Upstream

: a variety of management positions in operations. Former

Technology, Pennzoil, and Exxon Production Research. She received her BS and MS degree in geology from Duke University and Rice University, and a PhD at the University of Michigan. barhar&igcworldcom