I would like to show more calculation about surge and swab pressure. In this article, I will show how to use the previous formulas (Surge and swab pressure method 1) to figure out surge and swab pressure for close-ended pipe (plug flow). The calculation concept is pretty much the same but I would like to show you how much difference between surge/swab if you have the close-ended pipe.
I still use the same data but this time so I can compare apple to apple with the previous calculation.
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
2nd case – closed ended pipe
Determine pressure loss around drill pipe
1. Determine n
2. Determine K
3. Determine fluid velocity around drill pipe
For closed ended pipe
Vdp = 224.1 ft/min
4. Maximum pipe velocity
Vm = 224.1 x 1.5 = 336 ft/min
5. Pressure loss around drill pipe
Pdp =540.7 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 = 345.4 ft/min
2. Maximum pipe velocity
Vm = 345.4 x 1.5 = 518 ft/min
3. Pressure loss around drill collar
Pdc = 86 psi
Total pressure loss = Pdp + Pdc
Total pressure loss = 540.7 + 86 = 626.7 psi
Determine surge pressure with the following equation.
Surge pressure = hydrostatic pressure + total pressure loss
Surge pressure = (0.052 x 9000 x 12.5) + 626.7 = 6,476.6 psi
Determine swab pressure with the following equation.
Swab pressure = hydrostatic pressure – total pressure loss
Swab pressure = (0.052 x 9000 x 12.5) – 626.7 = 5,223.3 psi
When compared with 1st case (surge and swab pressure for open-ended pipe), you can see that the closed ended pipe creates more surge and swab effect.