The conversion lives in a spreadsheet that has been copied through three jobs. It has one velocity in it, nobody remembers whether the two in the denominator is already there, and the last person who checked it against a well tie has left. So the prospect gets picked in time, the well comes in forty feet off, and the argument that follows is about whose number it was rather than which formula it came from.
You enter the horizon table you already have: name, two-way time in milliseconds, stacking velocity in ft/s, and a measured TVD wherever you have a well that reached it. Everything else is computed in front of you, in order, with the arithmetic printed line by line.
Dix inversion on two-way time in seconds, with the datum at t = 0 handled explicitly so the shallowest layer is not a special case you have to remember. Interval thickness shown for every layer.
Where you supply a well TVD you get the mis-tie, the dimensionless scale factor k, and the average velocity the well actually implies, not a residual you have to back out by hand.
One two-way time for an undrilled location, one horizon to calibrate on, and the depth both ways: uncalibrated and calibrated, with the correction in feet stated separately.
Inconsistent stacking velocities, two horizons on the same time, a horizon at zero: each is refused by name, with the offending pair identified. No silent NaN, no blank cell you mistake for a zero.
The example table loads with one click, so you can see every column populated before you type anything of your own.
| Horizon | TWT ms | Vrms ft/s | Vint ft/s | Z ft | Vavg ft/s | Well ft | Mis-tie ft | k | Vavg,cal |
|---|---|---|---|---|---|---|---|---|---|
| Top Chalk | 600 | 6500 | 6500.00 | 1950.00 | 6500.00 | 1902.00 | -48.00 | 0.975385 | 6340.00 |
| Top Sand | 1200 | 8000 | 9260.13 | 4728.04 | 7880.06 | 4810.00 | +81.96 | 1.017335 | 8016.67 |
| Top Shale | 1800 | 9200 | 11221.41 | 8094.46 | 8993.85 | 8040.00 | -54.46 | 0.993272 | 8933.33 |
Built by people who have picked horizons in time and then had to explain the depth to a drilling engineer. The formulas are the standard ones and they are printed on the screen with their symbols defined and their units stated, so you can check the tool rather than trust it.
One HTML file. No account, no sign-in, no upload: your horizon table never leaves the device it is typed into.
No subscription and nothing to renew.