# Defining Log Curves (Synthetics)

You can define the particular elastic log curves for P slowness, S slowness and density from the LAS file for each well in Synthetics. Define your own equation or use a standard equation for the log curves if the well log is not defined in certain parts or the entire well log is missing.

## Define log curves 1. In the Synthetics window, open the Well tab.
2. Go to the Log Curves (filtered by class) section.
3. At P Slowness, S Slowness and Density, select the P slowness curve, S slowness curve and density curve, and their respective units of measurement.
4. Click the Where undefined check box to input your own equation or use a standard interpolation equation to define parts of the well log that are undefined (see below).
5. You can define one additional log curve to be displayed at Extra.

### Where undefined... If the S slowness and density curves contain undefined points, the log curve will be broken into multiple sections separated by those points. In this case, Insight will only display the synthetics of the longest defined section of the curve.

Select the Where undefined check box and choose the formula to be used to help Insight define the points and fill in the gaps.

• For the P Slowness curve:
• Select use linear interpolation to do a simple linear interpolation to fill gaps in the P slowness curve.
• For the S Slowness curve:
• Select use 'mudrock line' formula to use the standard mudrock line formula where Vs = 0.862*Vp - 1172 (m/s).
• Otherwise, select use custom formula to define your own formula using the standard operators.
Tip: Click on the Help icon (?) for more information on building S slowness curves.
• For the density curve:
• Select use power-law GGG relationship to use the standard Gardner/Gardner/Gregory (GGG) formula where rho_bulk = 1.75*(Vp/1000)^0.265 (g/cc).
• You can also select use polynomial GGG relationship to use the polynomial form of the GGG relationship where rho_bulk = -0.0261 * (Vp/1000)^2 + 0.373 * (Vp/1000) + 1.458.
• Otherwise, select use custom formula to define your own equation using the standard operators. 