Calculator

Rig Floor (ODF) Depth Correction

Reconcile drill pipe tally depth against wireline depth after a rig floor elevation change, with an optional cross-check against a fresh wireline run.

📐 1st Correction — Rig Floor Elevation Change
🔗 2nd Correction — Cross-Check Against Wireline (optional)
1st Correction (rig floor change)—
2nd Correction (drill pipe vs wireline)—
Final Correction to Apply—
Reference only. Confirm both elevations against the actual rig documentation before applying a correction to a live well's depth records.

The Formulas Used

1st Correction
C1 = Original Rig Floor Elevation − Present Rig Floor Elevation
Applied to both drill pipe and wireline depths, since both were referenced to the original elevation.
2nd Correction
C2 = Drill Pipe Tally Depth − Wireline Measured Depth
Only meaningful once both depths are read from the same reference point — apply C1 first if the rig floor also changed.
Final Correction
Final = C1 + C2
The total correction to apply to the drill pipe tally to get true depth against the new reference.

This is a datum reconciliation, not a stretch calculation — it doesn't account for drill pipe or wireline stretch over depth on its own. For the capacity and volume math that depth feeds into elsewhere, see the drilling formulas cheat sheet.

Frequently Asked Questions

What does ODF stand for and why does rig floor elevation change?

ODF is the original datum from which depths on a well are referenced — usually rig floor elevation above sea level or ground level. It can change between operations on the same well: a workover rig with a different substructure height, a platform deck modification, or simply moving to a different rig on a re-entry all shift where "zero" actually sits.

Why does this need two separate corrections?

The first correction reconciles a physical change in rig floor height, so drill pipe tally and wireline depths are both talking about the same reference point again. The second reconciles drill pipe tally against a wireline run at that same reference point, since drill pipe stretch and wireline stretch drift apart from each other over depth and time even when the datum hasn't moved.

Which correction do I apply if only the rig floor changed?

Just the first one — leave both wireline fields at zero and the calculator applies only the elevation-change correction. The second correction is a separate, optional cross-check for whenever you actually have a fresh wireline depth to compare against your pipe tally.

Does a positive or negative correction mean the depth is deeper or shallower?

A positive final correction means the drill pipe tally under-reads the true depth relative to the new reference — add it to get true depth. A negative correction means the tally over-reads. Always apply the sign as calculated rather than assuming which direction it should go.