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The presence of gas in a formation can skew density and porosity readings causing these curves to cross in what is called gas effect. You can display gas effect by filling the areas where density and porosity curves crossover with unique colors for the negative and positive crossover. |
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DT of a formation is not just increased for gas-saturated layers, the interval transit time may also significantly increase for unconsolidated sands.
To create neutron sonic crossovers
1. Double-click the log or well header, not a curve or top.
The Single Well Properties: Crossover
dialog box appears.
2. Select the crossover tab, and then click add.
The Selection
dialog box appears.
3. Select options for the basic curve and second curve boxes, and then click OK.
4. If desired, in the crossover list of the Single Well Properties dialog box, select the crossover you created in the above step, double-click the positive color and negative color to select fill colors from the popup color palette, and then click OK.
5. In the Cross Section Viewer, select the basic or second curve and using the left and right arrow keys on the keyboard, move the curve to adjust the crossover.
Note:
Color fill for positive and negative
differences appear only if engineering values for both curves are located
between left and right limits for the main scale (not the backup scale).
For example if the main scale for DT is 300–100 usec/m and the average
value for the target layer is 510 usec/m, no color fill appears. You must
set a suitable left and right scale for DT (in this case 600–400 usec/m)
using the Single Curve
Properties dialog box
or by moving the curve using the keyboard (wrapping method).
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