Volume-based interpretation

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Seismic Data Analysis
Series Investigations in Geophysics
Author Öz Yilmaz
DOI http://dx.doi.org/10.1190/1.9781560801580
ISBN ISBN 978-1-56080-094-1
Store SEG Online Store

Interpretation of 3-D seismic data is based on one of the following two strategies:

  1. Image in time, interpret in time to create a set of time structure maps, and then perform time-to-depth conversion to create the corresponding set of depth structure maps, or
  2. Image in depth and interpret directly in depth to create a set of depth structure maps.

Whatever the strategy, the resulting depth structure maps are calibrated to well data.

We demonstrated the first strategy for interpretation in interpretation of 3-D seismic data. We now demonstrate the second strategy for interpretation. Figure 10.8-21 shows selected 3-D views of the image volume from 3-D prestack depth migration of the data as in Figure 10.8-19 in the inline direction, and Figure 10.8-22 shows selected 3-D views of the image volume in the crossline direction as in Figure 10.8-20. Begin the structural interpretation session by 3-D visualization of the image volume in depth to understand and characterize the subsurface structural model. Combine the visualization of the image volume in the inline and crossline directions with the the scanning of the depth slices (Figure 10.8-23). Note that the structural model is based on wrench tectonism that has caused the intensive faulting and folding.

By using the seed detection technique (interpretation of 3-D seismic data), we capture a set of surface patches for each of the depth horizons to be interpreted. Where seed detection fails, as in the complex fault zones, the surface paths are complemented with the horizon strands along the selected inlines and crosslines derived from line-based interpretation. The combination of seed detection and line-based interpretation produce a set of control points for each depth horizon as shown in Figures 10.8-24a through 10.8-29a. The control points are then used to create a complete surface for each horizon by grid-fitting (Section J.5) as shown in Figures 10.8-24b through 10.8-29b. The sixth horizon, which is the deepest, shown in Figure 10.8-29b is deeper in some areas than the maximum depth (4 km) associated with the image volume from 3-D prestack depth migration (Figures 10.8-21 and 10.8-22). All six depth horizons are shown in the 3-D view of Figure 10.8-30.

Stratigraphic interpretation uses an amplitude manipulation technique based on removal of opacity (interpretation of 3-D seismic data). Application of this technique to the depositional unit bounded by surface DH3 at the top and DH4 at its base (Figure 10.8-31a) leads to the discovery of an ancient channel (Figure 10.8-31b). This buried channel within the depositional unit of Figure 10.8-31a resembles the recent channel system at the water bottom which is dramatically manifested by the depth slices shown in Figure 10.8-32.

A close-up view reveals the disruption of the buried channel by the faulting associated with the wrench tectonism in the area (Figure 10.8-33a). By using the subvolume detection (interpretation of 3-D seismic data), the channel can be isolated as shown in Figure 10.8-33b. The color-coded view of the channel shows that elevation changes exist along the channel caused by the faulting that has occurred after the formation of the channel itself (Figure 10.8-34a). After its subvolume detection, the channel can be extracted from the volume associated with the depositional unit (Figure 10.8-31a) and viewed in combination with the surface that corresponds to the base of the unit (Figure 10.8-34b). The objective is to gain a complete understanding of the stratigraphic prospect represented by the channel in relation to the subsurface structural model.

Finally, the results of the structural interpretation (Figures 10.8-24b through 10.8-29b) are combined to build a solid earth model. Figure 10.8-35b shows the layer boundaries represented by the depth horizons that were derived from the structural interpretation. Each layer is then represented by a solid volume bounded by these surfaces as shown in Figure 10.8-35. Explosion of the entire solid model facilitates viewing of the individual depositional units represented by the solid segments (Figure 10.8-36). The solid segment associated with the zone of interest can be subsequently populated by the seismically derived petrophysical properties, which are constrained by the well data, to derive a reservoir model.

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Volume-based interpretation
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