STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

858 Drilling and Well Completions
8$ in. bit will have three open orifices and each orifice has an opening of 0.80
in. in diameter. The inside diameter of drill pipe is 3.640 in. The surface
compressors and booster available at the drilling location are
Compressor (primary)
Atlas Copco PN1200
Positive displacement screw-type, three stages
700 HP
1200 actual cfm
Fixed maximum pressure, 300 psig
Turbocharged
em 80%
Booster (secondary)
-,
TOY WB-12
Positive displacement, piston-type, three stages
500 HP
Maximum pressure, 1500 psig
Naturally aspirated
em E 80%
The minimum volumetric flowrate has been found to be Qin = 2,110 actual
cfm. Therefore, the real air volumetric flowrate must be provided by two of
the compressors given above. Thus the Q will be
or
Q = Z(1200)
= 2400 actual cfm
Using the above Q, Equations 4-123 and 4-124 are
a = 0.0274
b = 170.62
From Equation 4-128 the bottomhole pressure is
P, = { [( 1694.7)2 + 170.62(547.6)2]e2~00274~('o~ooo~~547~6 - 170.62(547.6)2}0.5
= 9789.1 lb/ft2 abs
pb = 68.0 psia
The specific weight of the air at the bottom of the hole is
y,=b_= P
9789' = 0.3073 lb/ft3
RT, 53.3(597.6)
From Equation 4-129 the total area of the orifice openings is