This articles demonstrates how to determine pressure losses through drill string.
To determine pressure drop while the drilling mud is passing through a circular pipe (drill pipe and drill collar), you can calculate pressure loss with the following equation:
Turbulent viscosity = 3 cp
Friction factor = 0.378(Q/D)-0.14
The first equation has a coefficient (C) to take into account the friction and the geometry of the bore ID.
P = pressure loss, psi
L = length of pipe, ft
W = mud density, ppg
Vf = viscosity correction factor
PV = plastic viscosity, centipoises
Q = flow rate, gpm
Di = inside diameter of pipe, inch
C = general coefficient for internal diameter of pipe
Determine the pressure loss in the drill string based on the following information
Drill pipe length = 5000 ft
ID of drill pipe = 3.34 inch
Drill collar length = 500 ft
ID of drill collar = 2.8 inch
Mud Weight = 9.5 ppg
Plastic Viscosity = 12 centipoise
Flow rate = 600 gpm
Pressure loss in the drill string composes of two parts which are pressure loss in drill pipe and drill collar.
We can write the relationship like this:
Pt = Pdp + Pdc
Where; Pt = total pressure loss in drill string
Pdp = pressure loss in drill pipe
Pdc = pressure loss in drill collar
Determine pressure loss in drill pipe with following steps:
Pdp = 1254
Determine pressure loss in drill collar with following steps:
Pdc = 295
Pt = 1254 + 295 = 1,549 psi
Total pressure loss in the drill string equates to 1,549 psi.
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.