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EXTENDED ABSTRACT: Illuminating Seismic Stratigraphic Features
Using 3D Visualization
Paradigm, 820 Gessner Rd., Ste. 400, Houston, Texas 77024
Interpreters use a variety of workflows when performing structural interpretation of seismic data and these workflows are fairly easy to turn into procedures that can be followed by other members of the team. Visualization of 3D seismic data enables interpreters to scan volumes and reveal stratigraphic features. Interpreters can choose to work with amplitude volumes, attribute volumes or mixtures of both. The volumes can be datumed relative to the current sea-level surface, historical surfaces, or flattened horizons. The interpreter can sculpt, varying opacity and lighting to deliver a huge number of potential results. The outcomes can be so numerous that it becomes difficult to know where to stop in this process. Examples from a data set from offshore Indonesia are below. The reader is referred to Yilmaz (2001) for additional information and views of this particular data set.
Interpreters have traditionally used coherency displays to accentuate faults. These have frequently been combined with reflection amplitude displays to show bright spots bounded by faults, which indicate potential reservoirs. Coherency can also emphasize stratigraphic features such as channel boundaries, which are also discontinuities in the reflection amplitude field. A typical stratigraphic workflow begins with the interpreter scanning the 3D seismic data set in section and plan view to look for stratigraphic features. Figure 1 shows a shallow time slice of reflection amplitude data with indications of channels. Figure 2 shows the same time slice with a blend of amplitude and coherence data. It is immediately evident that the channels are more clearly displayed in the combined attribute display.
Flattened and Structural Voxel Displays
Once stratigraphic features have been spotted, the interpreter needs to discover their full extent in the data set. Features are unlikely to lie flat on a particular time or depth slice. Channels may have an almost flat expression at the time of deposition but will typically occupy a depth or time range. Other features such as dunes, reefs, or channel fan complexes were not flat at the time of deposition. Interpreters may examine a thick slab of seismic data by making some amplitude values transparent. Interpreters may also pick a structural horizon and then flatten the volume. A flattened slab can then be examined using transparency. Figure 3 shows a flattened slab where the positive
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