We still have the same question as the previous post, Pressure Loss and Equivalent Circulating Density Review, but this case we will do reverser circulation, circulating from annulus to tubing , and see how much pressure and equivalent circulating density at bottom hole.
This example that I got from my junior member is very simple but it helps you a lot to understand about how to determine pressure loss during normal circulation.
Information given is listed below;
Circulate at 3 bottom up through open end tubing (Down tubing and up annulus) with 12.7 ppg mud.
Pump pressure = 1000 psi
Annulus friction loss = 50 psi
Inside tubing friction loss = 925 psi
Surface line friction loss = 25 psi
I still have the simple but interesting question about hydrostatic pressure which you can apply this calculation into drilling/cementing operation. The question I got about how much pressure we will see at cement head in case of float shoe fail.
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;
Bit depth = 9500’ MD
Pump rate = 300 GPM
Annular volume at 9500’ MD = 250 bbl
Triplex pump output = 0.102 bbl/stroke
Solution;
Pump rate = 300 GPM ÷ 42 = 7.14 bbl / minute
Lag time in minutes = 250 bbl ÷ 7.14 bbl / minute = 35 minutes
Lag time in strokes = 250 bbl ÷ 0.102 bbl/stroke = 2451 strokes
Bit depth = 3,300 m
Pump rate = 1,200 liter/min
Annular volume at 3,300 m = 40 m3
Triplex pump output = 0.01622 m3/stroke
Solution;
Lag time in minutes = 40 m3 ÷ (1,200 ÷ 1,000 m3/ min) = 33.3 minutes
Lag time in strokes = 40 m3 ÷ 0.01622 m3/stroke = 2466 strokes
Download Lag Time Calculation Spreadsheet
Ref books:
Lapeyrouse, N.J., 2002. Formulas and calculations for drilling, production and workover, Boston: Gulf Professional publishing.
Bourgoyne, A.J.T., Chenevert , M.E. & Millheim, K.K., 1986. SPE Textbook Series, Volume 2: Applied Drilling Engineering, Society of Petroleum Engineers.
Mitchell, R.F., Miska, S. & Aadny, B.S., 2011. Fundamentals of drilling engineering, Richardson, TX: Society of Petroleum Engineers.
The ton-miles of work performed in short trip operation is also in term of round trips.
The ton-miles of work done in making a short trip is equal to the difference between round ton-miles of end depth and starting depth. The formula for short trip ton-miles is listed below;
Tst = T6 – T5
Where; Tst = ton-miles for short trip
T6 = ton-miles for one round trip at the deeper depth
T5 = ton-miles for one round trip at the shallower depth
Example;
Please determine short trip ton-miles from 8000 ft to 8050 ft
Ton-miles @ 8050 ft = 200
Ton-miles @ 8000 ft = 190
Tst = (200 – 190)
Tst = 10 ton-miles
Ref book: Formulas and Calculations for Drilling, Production and Workover, Second Edition
