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A session for 3-D stratigraphic interpretation may begin with splitting the image volume as in Figure 7.5-18 into subvolumes that correspond to individual depositional units bounded by the time horizons derived from structural interpretation. Figure 7.5-27 shows the image volume stripped down to each time horizon as in Figure 7.5-22, while Figure 7.5-28 shows the subvolumes that represent the depositional unit for each layer.
The stratigraphic interpretation involves removal of opacity and seed detection.
- Removal of opacity is applied to either a horizontal time slab with a specified thickness, typically a few to tens of time samples, or to a depositional unit bounded by the time horizons derived from structural interpretation. Figure 7.5-29 shows opacity removal applied to a thin horizontal slab that includes the water bottom, the horizontal slab slightly deeper than the water bottom, and the depositional unit labeled as H1 in Figure 7.5-28. Note the enhanced images of a complex channel system at the water bottom, and the intensive fracture system that begins to develop immediately below the water bottom and increases in complexity as we go deeper in the image volume. When we reach horizon H3 as labeled in Figure 7.5-28, we observe a highly complex fault system (Figure 7.5-30).
- Now we look inside a specific depositional unit, in this case the unit bounded by horizon H3 on top as labeled in Figure 7.5-28. The subvolume defined by a horizon-consistent slab associated with this unit is shown also in Figure 7.5-31a. Examine selected vertical cross-sections from this slab as shown in Figure 7.5-31b and identify stratigraphic features of interest. In this case, we note the presence of a buried channel represented by a strong reflection event with a lateral extent up to 400 m (Figure 7.5-31c). Remove the opacity within the subvolume under consideration and uncover a remnant of an ancient channel system as shown in Figure 7.5-32. Note that the fault system, which has been formed by the subsequent tectonic disturbance, disrupts the channel system at several locations.
- Apply seed detection to the event that represents the channel within the subvolume and isolate it completely from the rest of the subvolume. Shown in Figure 7.5-33 is the channel with the surrounding flood plain represented by the white speckles. The color within the channel represents the seismic amplitudes. Also shown in Figure 7.5-33 is horizon H4 which defines the base of the reservoir unit that contains the channel. A close-up view of the structural and stratigraphic interpretation result in Figure 7.5-33 is shown in Figure 7.5-34a.
Figure 7.5-18 Picking of a time horizon from the image volume as in Figure 7.5-14 based on seed detection. Color indicates reflection times.
Figure 7.5-22 Picked time horizons from the image volume as in Figure 7.5-14 based on a combination of seed detection and manual picking. Color indicates reflection times; each horizon has been color-coded, independently.
As for structural interpretation, the result of stratigraphic interpretation needs to be checked for consistency with the image volume of data used in the interpretation. Figure 7.5-34b shows a views of the channel, horizon H4, and an inline section from the image volume derive from 3-D prestack time migration. The color within the channel in this view represents the elevation; note that it varies considerably because of the disturbance of the channel by the subsequent faulting.
- Interpretation of 3-D seismic data
- Time slices
- 3-D visualization
- Removal of opacity
- Seed detection
- Structural interpretation