Time/Depth Velocity Modeling: Calculations

The following calculations are use in the Time/Depth Velocity Modeling application. Note: In all cases a constant value of 2000 is used to convert to two–way time, and to convert from milliseconds to seconds.

Converting Time to Depth

When using formation tops or velocity curves, velocity points are calculated at the well locations and then these velocities are gridded to produce a velocity grid. The final depth grid will then either use the time and the velocity grid to produce a depth grid, or use the time and the velocity at the well locations to calculate the depth at the well locations and then these depths are gridded to produce the final depth grid, depending on the setting of Calculate final grid option.

Velocity / Depth Options

Uses the time grid and the top formation to calculate velocity points at each of the well locations. The equations used are as follows:

Using formation tops - subsequent layers

Uses multiple time grids and multiple top formations to create the velocity grid by computing interval times and interval depths.  The calculations are as follows where Depth1 and Time1 represent the values for the previous layer:

Using a velocity curve - first layer

Uses the Time/Depth pairs (or check shots) in the velocity curve along with the time grid to calculate velocity points at each of the well locations.  Note:  All wells using this method must have a velocity curve and must be properly tied to the data. The equations used are as follows:

Using a velocity curve - subsequent layers

Uses the Time/Depth pairs (or check shots) in the velocity curve along with multiple time grids to calculate velocity points at each of the well locations.  Note:  All wells using this method must have a velocity curve and must be properly tied to the data. The equations used are as follows where Depth1 and Time1 represent the values for the previous layer:

Using a constant velocity

Uses the time grid and the entered velocity value to calculate the depth grid. The equation used is as follows:

Using a velocity function

Uses the time grid and the entered equation coefficients to calculate the depth grid. The equation used for a cubic function is as follows where A, B, C, and D are the coefficients entered for the equation:

Converting Depth to Time

First layer

Uses the velocities in your Time/Depth pairs along with well top information to compute time grid. The equation used is as follows:

Subsequent layers

Uses the velocities in your Time/Depth pairs along with the multiple well tops to compute an interval time grid. The equation used is as follows where Depth1 and Time1 represent the values for the previous layer: