Calculate drilling lag time or required flow from annular volume or hole-and-pipe geometry, with bbl, gallons, m³, pump strokes, SPM, and 0.5× to 2× circulation checkpoints.

Ideal annular displacement at constant flow. Actual cuttings arrival and well conditions can differ; this is not a well-control or operating procedure.

Optional pump cross-check

Leave both pump fields blank to omit this check.

Lag Time Formula

The following two example problems outline the steps and information needed to calculate the Lag Time.

LT = AV / FR

Variables:

  • LT is the Lag Time (min)
  • AV is the total annular volume (bbls) 
  • FR is the total flow rate (bbl/min) 

To calculate ideal annular displacement time, divide the annular volume by a constant circulation flow rate. This assumes ideal displacement; actual cuttings arrival may differ. Geometry mode covers one uniform annular section. Optional pump output and speed provide an arithmetic cross-check, not an operating tolerance.

How to Calculate Lag Time?

The following steps outline how to calculate the Lag Time.

  1. First, determine the total annular volume (bbls). 
  2. Next, determine the total flow rate (bbl/min). 
  3. Next, gather the formula from above = LT = AV / FR.
  4. Finally, calculate the Lag Time.
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

total annular volume (bbls) = 50

total flow rate (bbl/min) = 20

LT = AV / FR = 50 / 20 = 2.5 min