Geology 290M- 3D seismic Interpretation
Illustrated 3D Interpretation Workshop
Spring 2001

Fault/Horizon Interpretation Using
Seismic Micro-Technology’s 2d/3dPAK

Seismic Micro-Technology's Kingdom software is accessed through the Windows Start Programs Menu.
In your program list select Kingdom Suite and then left-click on Kingdom.

NOTE: Left clicking the mouse is used to start, continue and end an activity. Right clicking is ONLY used for displaying various pop-up menus.

Project files are opened from the initial Kingdom Suite window (Figure 1). Click on Project then Open Project in the drop-down menus.

Figure 1: The initial Kingdom Suite display window provides access to new and old project files.

This exercise uses the Golden 3D data set available on your installation diskette. In this exercise, the C38 formation top is selected from any well and then tied around to the remaining wells. The entire 3D grid is interpreted. It is recommended that major faults be interpreted at the outset, since this will prevent autopicking of select reflection events across fault planes.

Procedures:

When you open a project under Kingdom, the basic windows layout will contain a 3D basemap (right) and project tree (left) (Figure 2a and b).

1. Left click on the 3D grid (Figure 2) to activate it. Line and crossline numbers are plotted along the sides of the basemap. In this example, position the mouse arrow on Line 110. Right click and select Display Line 110. The seismic line will now appear as shown below in Figure 3.

Figure 3: Display of 3D line 110 with color bar.

2. If you prefer another colorbar, left click on View and Colors. Click on File and Open and select a different colorbar. In most cases, the name of the colorbar describes the colors and the number of colors in the colorbar. For example, the default colorbar, brwbl50.clm, is a blue-white-brown colorbar with 50 colors. Close the color editor once you are satisfied with a colorbar.

3. If you are accustomed to wiggle traces, left click on View and Type of Plot and select Wiggle Variable Area. You may need to change the display scale to obtain the desired view. The variable area wiggle trace display will appear as shown below (Figure 4). Note the other display formats for future reference.

Figure 4: Variable area wiggle trace display format of Line 110.

4. To change the display scales, left click on View and Set Display Scales or click on the scale bar at the top of the seismic line display window. Try 8 traces per inch and 10 inches per second to provide a close-up (Figure 5) view of waveform character in the vicinity of the well shown above (Figure 4). Use the scroll bars to position yourself within the line.

Figure 5: Close-up view obtained using 8 traces/ inch and 10 inches/second.

5. You can orient yourself to geographical directions by moving the cursor on the seismic window (Figures 4 or 5) and watch the cursor movement on the map. If the direction is backwards hit the R key on the keyboard to reverse the line direction.

6. The colorbar may or may not be displayed on the seismic window. To display colorbar, left click on View and Toolbars and then Color Bar. A check indicates "on".

7. Display features can also be accessed directly using the buttons (Figure 6) in the upper left corner of the trace window.

8. On the seismic line, several faults are prominently displayed. Many of these faults are easy to correlate others are not. Now would be a good time to assign a name to at least two of the major faults, the down to the south and the antithetic. The others may be picked as assigned or unassigned. To assign the faults, right click on the seismic window and select Fault Management. From there, select the Create tab and enter a name and color for the antithetic fault. Left click on Apply. Enter a name and color for the major fault and then either OK or Apply. Create new faults if desired, You're now in the fault picking mode with the last created fault active.

9. Display the fault toolbar to allow for quicker selection of the faults you wish to pick. To do this left click on View and Toolbars and then Faults. All the displayed faults are present, including Unassigned. Hot keys are available: "D" enters the user into the fault digitization mode, "A" assigns a fault, and "S" de-assigns.

10. To start picking your fault, left click on one of the fault names. To begin digitizing hit the D-key and then left click on the fault break that courses through the seismic data. A rubber band should appear as you go from point to point (Figure 7). Continue left clicking points along the fault until you either need to scroll vertically or horizontally to view fault extensions outside your current view (Figure 7). Use the scroll bar to move the display so that more of the fault is visible. Continue until you can no longer pick this fault. Double click to end.

If you enter a point you don’t like, you can back up or delete the last point by hitting the Esc key

11. Left click on the other fault displayed in the Faults digitizing menu to activate it and then hit the "D" key to begin digitization. Begin picking the second fault. If you choose to pick some of the other faults on the Faults Toolbar, simply activate the appropriate named or unassigned fault, hit the "D" key and start picking. The two faults you just picked should appear as shown in the montage below (Figure 8). The number of points used to digitize the fault will vary from interpreter to interpreter.

12. If you want to edit some of your picks, the fault is active so long as the square dots are present. Note that the red fault in the above display is currently active. When a fault is selected for further editing, little handles appear on each digitized point. To move points, activate the fault and then left click and hold on the digitized fault point. As you move the mouse, the digitized point will also move. If you move a small distance, you may have to use the Esc key to undo the rubber band.

13. If you would like to move the entire fault line, first activate the fault and then hold the Ctrl key and then left click and hold on any part of the fault line. Move the line to wherever you like and then release the mouse button and Ctrl key.

14. To delete a fault segment, make it active and then hit the delete key on your keyboard.

15. To add points, left click on an existing point, add the appropriate intervening points, and double click on another existing point.

16. To remove consecutive points, left click on an existing point, skip the 'bad' points and double click on an existing point.

17. If you'd like to change the active fault, left click on the new fault to activate it or select from the Faults Menu. If the new fault has no existing digital points, you must hit "D" on either the keyboard or Faults Menu.

18. To assign an unnamed fault, activate the fault name, activate the unassigned fault line and then hit the A-key.

19. To de-assign a named fault, activate the fault line and then hit the S-key.

20. Once the faults have been picked on this line, you can begin picking the faults on a grid of lines extending through the entire 3D data base. To set the grid spacing, left click on Line and Set Line Skip Increment. Set the increment to 20 and then OK. Now whenever the right arrow on the keyboard is hit, the line displayed will increase by 20. If the left arrow is hit, the display will decrease by 20. If a cross line is displayed, the up and down arrow keys will work likewise.

21. Go to line 130 and digitize the main down-to-the-south fault and antithetic fault.

22. Once an assigned fault has been picked on at least two lines, a fault surface is automatically created. To view fault surfaces in map view go to the Project Tree and double click on the appropriate fault icon (Figure 9). This opens a new map window where the fault may be displayed as either a fault surface or segments.

Map view of fault surface is shown below (Figure 10).

To toggle from planes to segments, go to View, Fault Display Mode and select either Fault Surface or Fault Segment.

The fault segment display is shown below in Figure 11.

Figure 11: Fault segment display of the main down-to-the-south fault.

23. Display features can also be accessed directly using the buttons (Figure 12) in the upper left corner of the map window (Figure 11).

24. Display the fault surface in seismic view so that any miscorrelation can be quickly seen. To do this, go to a seismic window and right click, go to Fault Management, and Display. Verify that Both is selected for Display Type (Figure 13). If "Both" is selected, two lines are visible in seismic view, the straight line connecting the digitized points and the interpolated fault surface.

25. Complete fault picking: Continue over to the east-end of the survey to Line 145. Note the dashed line representing the extrapolated fault surface (Figure 14). This projection is displayed as a guide only and does not represent the actual fault surface. When complete return to line 90 and continue to the west. To go to line 90, left click on Line and then Select or left click on the arrow button in the seismic display window which brings up the same window. Type in 90 and be sure the line button is on and that the 3D survey is displayed. Hit OK. If you would like to view the faults in strike direction or on an arbitrary line, right click on the desired cross line in the base map window and then display line.

26. To display line with an arbitrary orientation through the survey, right click on a map window, select Digitize Arbitrary Line, left click on the starting point, continue left clicking on each bend in the line (Figure 15) and then double click to end. The digitized line will appear (Figure 16).

Figure 16: Arbitrary 2D line digitized in Figure 15.

At this point, your fault surfaces will be correlated across the entire survey area. The north-dipping (antithetic) fault surface, for example, will appear as shown below (Figure 17).

Figure 17: Color raster display of north-dipping (antithetic) fault surface.

27. Continue picking faults, in the western direction. You can edit interpolated fault picks by first selecting the desired fault as the active fault in the Fault Management Window, and then hitting the D key to digitize. If you wish to correct a portion of the interpolated picks simply begin picking points through the desired region. Double click to complete digitization. Your picks will replace the interpolated picks.

Note: If a fault has been extended too far, you can delete a portion of the interpolated fault line by digitizing the extended portion, and double clicking to replace the interpolated line with your picks. Then click on the bad pick and drag the rubber band to the first good pick and double click. All points beyond the last pick will be deleted.

28. Once you are satisfied with your fault interpretation you can begin picking horizons.

29. As mentioned earlier, the seismic data will be tied to a well using the C38 formation top. Display line 80. Scroll until the well is visible and the C38 top is displayed around 1.3 seconds. If the C38 top is not displayed, left click on Wells and Wellbore Display Options, Left click on Plot Formation Tops and OK. The C38 should be displayed and correlated along a peak (Figure 18).

Figure 18: Horizon C38 tied to two wells on Line 80.

30. Horizons are created in much the same way as faults. Anywhere on the seismic line, right click and select Horizon Management. Select the Create tab and then enter C38 for the horizon name and then select a color. Hit OK. The C38 horizon is now active.

31. Display the horizon in map view by double clicking on the icon next to the C38 Horizon. Since no picks have been made, no horizon is visible.

32. Horizon Picking: Right click on a seismic line and select Picking Parameters. Make sure that Stop at Displayed Fault Surface Intersections is enabled. This feature, when enabled, works with the Autopick-2D Hunt mode. Picking will stop either whenever data goes away or the horizon encounters a fault surface.

33. Display the Horizon Toolbar by left clicking on View, Toolbars, and Horizon bar. Note that the active horizon is highlighted in the toolbar. Hot keys are available, M = manual picking. F = Fill made, H = 2d Hunt. E = Erase. P = Peak, and T = Trough. Hot keys are not available for zero crossings.

34. Note the shape of the cursor and the status bar. The cursor is now represented by a '+' with an E, M, F, or H next to it. Change the picking mode to either F or H, and change the phase to peak. Pick the event as far as you can. Jump the fault if desired. Note that the map display is updated immediately after picking.

35. Once the horizon has been picked across the inlines do the crosslines. Place the cursor on any cross line within any inline seismic display, then right click and display the crossline at that point. A small tick mark is visible where the two lines intersect. The tick mark color will be the same as that of the horizon you are picking. You may also see a vertical red line. This red line is a line overlay and can be disabled by left clicking on View and selecting Line Overlays. A check mark indicates 'on'. If you chose the 2D Hunt mode, left click once on the tick mark and the entire horizon between fault segments is completed.

Increment through your data using the arrow keys and continue picking this horizon, Remember that the skip increment that occurs with each touch of the arrow key can be adjusted using the Line, Seismic Line Skip Increment selections. Then set the increment to the number of lines desired (5 for example). Now is also a good time to check for the consistency of your picks as you make your way through the crosslines. You should end up with picked grid of lines for the C38 horizon (Figure 19).

36. Draw fault polygons around the fault gaps by right clicking on the map and then Enable Fault Polygon Editing. Then select Digitize Fault Polygons. You may find it useful to zoom in on the faults to observe the gaps as shown in Figure 20.

Begin left clicking a series of points, which define the fault gaps. Double click on the final point. The fault polygon is drawn to outline the gap (Figure 20),

Figure 20: Fault gaps in horizon C38 appear in a close-up view of the basemap.

It may help to zoom in and draw polygons around visible segments in a close-up view. Use the slide bars to reposition your viewing area farther along the fault. Continue digitizing the polygon. When the rubber band is returned to the adjoining point on the opposing side of the fault, double click on that point. One continuous polygon will appear. Your fault polygons will look similar to those shown in Figure 21 below.

Alternatively, use Auto Create Fault Polygons. This option is useful whenever the fault surface is easily picked and smooth. Go to the menu bar and select Faults, Auto Create Fault Polygons. You can display fault polygons in several ways: outline only, solid fill or solid fill with an outline. To change the display, right click on the map, select Fault Management then select the Fault Polygons tab. Make your selection and hit OK.

37. With this grid, the horizon is now ready for the autopicker.

38. Left click on Horizons on the Command line and select Polygon Hunt. Using the left mouse button, draw a polygon around one of the fault blocks. Double click to end. Autopicking begins immediately after double clicking. Continue this process using a series of polygons. Not recommended is one giant polygon. Instead, create a series of smaller polygons.

Note that you can bring up a seismic line and go to regions of the data where the Polygon Hunt operations are having trouble. You can manually interpret the data in these regions directly on the seismic lines. When you do this, the active seismic line will show up as a red line. If you want to bring up a line nearby you need only left click on the red line overlay and drag it to the location where you need an interpretation.

Your completed horizon interpretation will look something like the one shown below (Figure 22).

39. If you don't like how 3D Hunt worked in particular area, left click on Horizons and select Polygon 3D Erase. Draw a polygon around the area of interest similar to 3D Hunt. You will he given the option to erase hunted picks, seed picks or both hunted and seed picks. Select hunted picks only. Hit Yes and the polygonal area is wiped clean with only the seed picks remaining. Repick a tighter grid if necessary and rerun 3D Hunt.
40. Once the map is completed, display the amplitudes. Go to the Project Tree and left click on the '+' sign next to the C38 horizon line. This opens the horizon showing you the additional surfaces available (Figure 23). Drag the amplitudes from the Project Tree to the map window.

Dragging the amplitudes from the Project Tree list to the base map will cause reflection event amplitude to be displayed.

Horizon travel times are shown in Figure 22. Horizon amplitudes are shown below (Figure 24).

Figure 24: Horizon amplitudes for C38 Seed.

41. Generate a time-structure contour map by selecting Map and Select Contour Overlay. Select the horizon and data type (Time) (Figure 25). Click on OK.

After you click OK, the Contour Parameters will automatically appear. You can also change the contour parameters by clicking on the Set Contour Parameters Icon to see what the effect is. You can check the effect of various parameter selections by leaving the contour parameters window active and selecting Apply. Your result may appear similar to that shown below (Figure 26).

Figure 26: Contour Overlay on C38.

42. Creation of a depth map is a two-stage effort that begins with construction of an average velocity map. To create a velocity map, select Tools from the main Menu Bar and then Depth from the drop down list. Under Depth there are several selections. Click on Compute Average Velocity Map. For Type, select Horizon. The program computes the average velocity at each well using one of three options (Apparent, Time Grid or Formation Top) (Figure 27).

The Apparent method used to construct the average velocity map uses the horizon time and formation top depth. You must provide a velocity map name (Figure 27). Gridding parameters can be tailored to individual needs (Figure 28). Time and depth pairs are then combined to form an average velocity grid.

Figure 28: Gridding parameters selections menu.

Average velocity in this (Apparent) approach is computed by dividing formation top depth by half the horizon time. Whether you Extrapolate (Figures 27 and 29) or not (Figure 30) will yield two different results. Extrapolation will project the resulting velocity grid outside the area of well control.

Figure 29: Velocity map formed by extrapolation.

The Time Grid method of deriving the velocity map uses the horizon time picks, converts them to depth using the well time/depth function and then generates a velocity grid. This velocity map (Figure 31) is considerably different from that obtained using the apparent method.

Figure 31: Velocity grid from Time Gridding (no extrapolation).

Figure 32: Velocity grid from time gridding with extrapolation.

Comparison of Figures 29 and 32 reveal notable but minor differences in this example.

The Formation Top method of deriving a velocity map starts with the formation top depth, converts it to time using the well time/depth function and then generates a velocity grid. If the horizon and formation top do not tie, three different velocities can be generated. Use the default grid parameters as a first pass for each velocity map. Depths obtained from this approach (Figure 33 and 34) reveal subtle differences.

43. Once the velocity map has been generated, you are ready to convert times to depth. From the top menu bar click on Tools then Depth, then Depth Map by Average Velocity Map. This will open up the menu shown below (Figure 35).

Supply the appropriate information in the above menu (Figure 35) and then click OK. The Grid Parameters window (not shown) will then appear. Parameters can be tailored to your specific project. Click OK to generate the Depth Map (Figure 36).

Edge effects may be noticeable on your depth map. These areas can easily be removed using the Grids, Polygon Erase utility. Polygon erase will provide you with a "rubber band" that you can use to define an enclosed region to delete. The operation is identical to that used to digitize fault polygons. Digitize the points around the region you wish to delete and double click to complete the operation.

44. Contour the depth map and display the amplitudes under the contours. Remember that you can contour your maps using the Map Select Contour Overlay options. Contours of velocity for the C38 horizon are shown below (Figure 37).

Amplitudes of the C38 reflection event can then be followed along the structure by dragging the amplitude horizon from the project menu onto the map (see montage Figure 38). Note the association of amplitude anomalies with the faults in this example.