Page 12 - Air and Gas Drilling Manual

n
= drill bit speed of the motor, rpm
N m
= estimated number of piston cycles, strike/minute
N p = number of equal diameter orifices xiii List of Symbols
N R = classic expression for Reynolds number
N rb = runaway speed of the drive shaft, rpm
N Rl = Reynolds number for the volumetric flow rate derived for the laminar flow
terminal velocity equation
N rr = theoretical runaway speed of the rotor, rpm
N Rsfa = Reynolds number of foam exiting the cased annulus and starts into the Tee
N Rsfbp = Reynolds number of foam flow upstream of the back pressure valve
N Rsr = Reynolds number of the aerated drilling fluid exiting the surface return
flow line
n s = number of compression stages in the multistage compressor
2
P = fluid pressure, lb/ft abs
P ac = pressure in the annulus at the bottom of the cased section of the borehole,
lb/ft 2
p ac = pressure in the annulus at the bottom of the cased section of the borehole,
psia
2
P ai = pressure above the bit inside the drill string, lb/ft abs
2
P am = pressure above the motor cavity, lb/ft abs
p am = pressure above the motor cavity, psia
2
P at = atmospheric pressure, lb/ft abs
p at = atmospheric pressure, psia
2
P bca = pressure at bottom of casing in annulus, lb/ft abs
2
P bdca = pressure at bottom of drill collars in the annulus, lb/ft abs
2
P bdci = pressure at bottom of drill collars inside the drill string, lb/ft abs
2
P bdpa = pressure at bottom of drill pipe in annulus, lb/ft abs
2
P bdpi = pressure at the bottom of drill pipe inside the drill string, lb/ft abs
2
P bh = bottomhole pressure in the annulus, lb/ft abs