Lag Time Calculation

Description:

Lag time is the time taken for the mud to travel from the pump to the bit and back to the surface. It is important to know the lag time to prevent the pump from running dry and to avoid swabbing the hole.

Equation:

Lag time in minutes: $$\text{Lag time} = \frac{AV}{Q/42}$$ Lag time in strokes: $$\text{Lag time} = \frac{AV}{Q_{po}}$$

Where:

\( AV \) = Annular volume, bbl

\( Q \) = Pump rate, gpm

\(Q_{po}\) = Triplex pump output, bbl/stroke

Practical Consideration:

The lag time always changes when a well becomes deeper and/or pumping speed change.