LAG TIME CALCULATIONS Lag time is traveling time interval required for pumping cuttings from each particular depth to surface. It can be expressed in terms of time (minutes) and pump strokes. The lag time always changes when a well becomes deeper and/or pumping speed change. Two factors, affecting lag time calculation, are annulus volume of drilling fluid in and drilling mud flow rate. With certain annular volume, the lag time, normally expressed in minutes, can be determined by dividing the annular volume (bbls) by the flow rate (bbl/min). If there are changes in mud flow rate, the lag time figure will be changed as well. In order compensate for any changes, the lag time is transformed into pump strokes too; therefore, a change in speed of pump will not affect the lag time.
Lag time is traveling time interval required for pumping
cuttings from each particular depth to surface. It can be expressed
in terms of time (minutes) and pump strokes. The lag time always
changes when a well becomes deeper and/or pumping speed change. Two
factors, affecting lag time calculation, are annulus volume of
drilling fluid in and drilling mud flow rate.
With certain annular volume, the lag time, normally expressed in
minutes, can be determined by dividing the annular volume (bbls) by
the flow rate (bbl/min).
If there are changes in mud flow rate, the lag time figure will
be changed as well. In order compensate for any changes, the lag
time is transformed into pump strokes too; therefore, a change in
speed of pump will not affect the lag time.
How to Calculate Theoretical Lag Time
There are 3 steps to do in order to calculate lag time as listed
below;
1. Calculate pump output 2. Calculate annular volume at certain
depth of hole 3. Calculate the theoretical lag time
Example Determine lag time from bottom to surface with the
following information;
