Changes

==Step 1: Map structure from well data==

==Step 1: Map structure from well data==

Post well depths to key horizons and contour structure maps for key horizons using well control only. These well maps of structure should guide you when making structure maps that integrate both well and seismic data. Comparing this map with the final time structure map gives a good feel for the additional information supplied by the 3-D seismic section.

Post well depths to key horizons and contour structure maps for key horizons using well control only. These well maps of structure should guide you when making structure maps that integrate both well and seismic data. Comparing this map with the final time structure map gives a good feel for the additional information supplied by the 3-D seismic section.

==Step 2: Pick seismic horizons==

==Step 2: Pick seismic horizons==

For 2-D data, only the traveltime to each event of interest is recorded with its coordinate along the line ''t''(''x''). For 3-D data, both traveltime and amplitude at each (''x, y'') are available from the seismic data cube, ''t''(''x, y'') and ''a''(''x, y''). The traveltimes form a time structure map, and the amplitudes are a horizon slice. Figure 12-12A shows a representative line from the Glenn Pool data volume with sonic overlay and tracked events. Horizon amplitude and time structure maps for the Wilcox are shown in Figures 12-12B, C.

For 2-D data, only the traveltime to each event of interest is recorded with its coordinate along the line ''t''(''x''). For 3-D data, both traveltime and amplitude at each (''x, y'') are available from the seismic data cube, ''t''(''x, y'') and ''a''(''x, y''). The traveltimes form a time structure map, and the amplitudes are a horizon slice. [[:file:interpreting-seismic-data_fig12-12.png|Figure 1A]] shows a representative line from the Glenn Pool data volume with sonic overlay and tracked events. Horizon amplitude and time structure maps for the Wilcox are shown in [[:file:interpreting-seismic-data_fig12-12.png|Figures 1B, C]].

[[file:interpreting-seismic-data_fig12-12.png|thumb|{{figure number|12-12}}. Copyright: Liner, 1999; courtesy PennWell.]]

[[file:interpreting-seismic-data_fig12-13.png|thumb|{{figure number|2}}. Copyright: Liner, 1999; courtesy PennWell.]]

==Step 3: Calculate depth conversion velocity==

==Step 3: Calculate depth conversion velocity==

Depth conversion velocities are posted to a map and contoured or gridded to create ''υ''(''x, y'').

Depth conversion velocities are posted to a map and contoured or gridded to create ''υ''(''x, y'').

The figure below shows a hypothetical well with important reference points as well the average velocity map for the Wilcox Formation in the Glenn Pool survey. This map has a fairly strong lateral velocity gradient, i.e., the velocity changes from about 11,400 ft/s for velocity (NE) to 10,200 ft/s (SW) in the space of just over a mile. When this occurs, time structure and depth structure can be significantly different.

[[:file:interpreting-seismic-data_fig12-13.png|Figure 2]] shows a hypothetical well with important reference points as well the average velocity map for the Wilcox Formation in the Glenn Pool survey. This map has a fairly strong lateral velocity gradient, i.e., the velocity changes from about 11,400 ft/s for velocity (NE) to 10,200 ft/s (SW) in the space of just over a mile. When this occurs, time structure and depth structure can be significantly different.

 

[[file:interpreting-seismic-data_fig12-13.png|thumb|{{figure number|12-13}}. Copyright: Liner, 1999; courtesy PennWell.]]

[[file:interpreting-seismic-data_fig12-14.png|left|thumb|{{figure number|3}}. Copyright: Liner, 1999; courtesy PennWell.]]

Convert time to depth by multiplying the time structure map and the depth conversion velocity map, i.e.,

Convert time to depth by multiplying the time structure map and the depth conversion velocity map, i.e.,

:<math>z(x,y) = \frac{\upsilon(x,y)*t(x,y)}{2}</math>

:<math>z(x,y) = \frac{\upsilon(x,y)*t(x,y)}{2}</math>

The factor of one-half is necessary because the times are two-way vertical times and we only want the one-way depth. The figure below shows the process and result for the Glenn Pool Wilcox horizon.

[[file:interpreting-seismic-data_fig12-15.png|thumb|{{figure number|4}}. Copyright: Liner, 1999; courtesy PennWell.]]

[[file:interpreting-seismic-data_fig12-14.png|thumb|{{figure number|12-14}}. Copyright: Liner, 1999; courtesy PennWell.]]

The factor of one-half is necessary because the times are two-way vertical times and we only want the one-way depth. [[:file:interpreting-seismic-data_fig12-14.png|Figure 3]] shows the process and result for the Glenn Pool Wilcox horizon.

==Step 5: Contour map==

==Step 5: Contour map==

[[file:interpreting-seismic-data_fig12-16.png|thumb|{{figure number|5}}. Copyright: Liner, 1999; courtesy PennWell.]]

The final product ''z''(''x'', ''y'') is called an integrated structure map. It honors all well-control depth points (by definition) and uses the seismic events to interpolate between these points. The figure below is a comparison of the first depth map from well control only and the seismic plus well integrated depth map.

[[file:interpreting-seismic-data_fig12-15.png|thumb|{{figure number|12-15}}. Copyright: Liner, 1999; courtesy PennWell.]]

Contour or grid the integrated structure map with the same technique used for the wells-only depth map. This allows head-to-head comparison ([[:file:interpreting-seismic-data_fig12-16.png|Figure 5]]).

Figure 12-16 is a zoom of the central area in the maps in Figure 12-15. Map A uses well control only, and map B uses well control plus [[seismic interpretation]].

The final product ''z''(''x'', ''y'') is called an integrated structure map. It honors all well-control depth points (by definition) and uses the seismic events to interpolate between these points.[[:file:interpreting-seismic-data_fig12-16.png|Figure 5]] is a comparison of the first depth map from well control only and the seismic plus well integrated depth map.

[[file:interpreting-seismic-data_fig12-16.png|thumb|{{figure number|12-16}}. Copyright: Liner, 1999; courtesy PennWell.]]

[[:file:interpreting-seismic-data_fig12-16.png|Figure 5]] is a zoom of the central area in the maps in [[:file:interpreting-seismic-data_fig12-15.png|Figure 4]]. Map A uses well control only, and map B uses well control plus [[seismic interpretation]].

==Conclusion==

==Conclusion==