You’ve learn how to determine surge and swab pressure from the previous topic (Surge and swab pressure method 1) and this topic will demonstrate you how to use those equations to determine surge and swab pressure for the open-ended pipe.
Example
The well information is listed below:
θ300 = 85
θ600 = 130
Hole diameter = 9 inch
Drill Collar = 6.25 inch
ID of drill collar = 2.5 inch
Drillpipe diameter = 5 inch
ID of drill pipe = 3.5 inch
Average pipe running or pulling speed = 250 ft/min
Drill Pipe Length = 12000 ft
Drill Collar Length = 800 ft
Current Mud Weight = 12.5 ppg
Well TVD = 9000 ft
1st case – open ended pipe
Determine pressure loss around drill pipe
1. Determine n
n= 0.613
2. Determine K
K=1.863
3. Determine fluid velocity around drill pipe
For open-ended pipe
Vdp = 159.2 ft/min
4. Maximum pipe velocity
Vm = 159.2 x 1.5 = 239 ft/min
5. Pressure loss around drill pipe
Pdp =438.5 psi
Determine pressure loss around drill collar
We still use the same n and K.
1. Determine fluid velocity around drill collar
For open ended pipe
Vdc = 282.7 ft/min
2. Maximum pipe velocity
Vm = 282.7 x 1.5 = 424 ft/min
3. Pressure loss around drill collar
Pdc = 76.1 psi
Total pressure loss = Pdp + Pdc
Total pressure loss = 438.5 + 76.1 = 514.6 psi
If surge pressure is required:
Surge pressure = hydrostatic pressure + total pressure loss
Surge pressure = (0.052 x 9000 x 12.5) + 514.6 = 6364.6 psi
If swab pressure is required:
Swab pressure = hydrostatic pressure – total pressure loss
Swab pressure = (0.052 x 9000 x 12.5) – 514.6 = 5335.4 psi
Reference book: 
Formulas and Calculations for Drilling, Production and Workover, Second Edition
