Geology 554Environmental and Exploration Geophysics II

Seismic Attribute Analysis

This exercise is intended to allow you to delve into additional features of your data; to provide you with different views that may help you see some of the geology in your data you expect is there but haven’t been able to uncover or resolve. There are a variety of common attributes in use and this exercise is intended to get you to look at some of them and think about what they may tell you about your data.

Getting a quick look at attributes in vertical displays1. Get into the Gulf Coast data and bring up an inline, crossline or arbitrary line – doesn’t

matter.

Figure 1: Seismic line from the Gulf Coast area.

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2. With the seismic line the active window in your view, select Line> Seismic Attributes >

and pick an attribute from the list. Phase for example gives you the ,

where the Quadrature component is computed from the Hilbert Transform.

That will give you vertical display that looks like that shown below.

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3. Slide your cursor up and down a trace over one of the transitions and note that the values going from gray areas to brown are very abrupt. The values will go from about 180 in the gray to -180 in the brown. The phase is actually continuous but makes these abrupt jumps depending on how the scale is defined.

4. Repeat the process to view the influence of different attributes on the data.5. Bring up a crossline (EW line) in the northern part of the survey area and turn on the B46

Horizon. We picked this on a peak. Display the Hilbert transform. Note where the pick is now displayed. Remember that the Hilbert transform is nothing more than a 90 degree phase shift in the data. The positive peak in your data became a negative to positive zero crossing. In fact, if you want to map a zero crossing, the best way to do it is to take the Hilbert transform and map the peak or trough in the Hilbert transformed data. Troughs in the amplitude display become positive to negative zero-crossings.

Locate the Channel Mapped earlier and see if you can enhance it1. On the preceding crossline locate the channel we discussed earlier in the semester. On

Crossline 40 look between inlines 40 to 50 (see below).

2. Turn on the different attributes. Do any of them improve your ability to see this amplitude anomaly?

Flattening and Time-slicing

1. With your seismic display window active, click on Horizon

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2. Select the Flatten or Unflatten item.

3. The horizons appearing in this window are the ones you have turned on in your display or Project Tree. Select the B46. Click OK.

4. Note that your vertical display is now flattened on this horizon (display below is of the envelope)

5. Select > Display Flattened Timeslice6. Uncheck the horizon in your Project Tree.

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7. On the scale bar in your TimeSlice view open the Seismic tab (see below).

8. Change the skip increment to 0.002 (i.e. 2 milliseconds). 9. Notice that in the map display that you are displaying the Amplitude volume (see below).

Figure 2: Note the channel in this amplitude display.

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Generate attribute volumes1. To get attributes views in timeslice or map view you’ll have to generate an attribute

volume.2. Go to Tools > TracePak > Process Multiple Traces

3. The following window should come up>

4. Next

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Make the following selections

5. Next 6. Click apply or Finish

7. OK to the Summary Window and Finish8. In the new map display window bring up a line. It should come up in the new attribute

volume you just computed. 9. Flatten the horizon on the B46 and generate a time slice through the attribute volume.

This may take a minute and you’ll get a window telling you that the processing is taking place. Below I show a time-slice from an Envelope volume.

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Figure 3: Timeslice through the top of the channel as it appears in the envelope attribute volume.

Exercise 1. Generate Average Energy, Peak-to-Trough ratio, Frequency and Phase volumes, 2. Create a time slice flattened on the B46 for each3. Shift up and down through time and examine the influence individual attributes have on

channel appearance. 4. To capture the screen view go to View > Copy active window to Clipboard and paste in a

word file. 5. Make at least three screen captures to illustrate the appearance of the channel with

amplitude and two additional attributes.6. Place captions beneath each figure.7. In a couple sentences beneath each figure caption describe what you see. This description

can take the form of a simple comparison to the amplitude display. Doe phase reveal more detail in the channel? What kind of detail do you see? How does the attribute view differ from the original amplitude view?

Due next Wednesday.

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