STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

Air and Gas Drilling 859
From Equation 4-130 the weight rate of flow through the system is
The pressure above the bit can be found from Equation 4-131. Equation 4-131 is
2.556 = 0.01047 ~2(32.z)~1~4)(9789.~)(0.~073){ 9789.1 I}]
0.4 [ATm7-
0.5
Solving the above
Pa = 13,144.9 lb/ft2 abs
or
pa = 91.3 psia
Equations 4-133 and 4134 are
a' = 0.0188
b' = 3790.7
Equation 4-132 is
or
13, 144.9)2 + 3790.7(547.6)2(e2~0-0'88~~'0~0"~547~6 - 1)
e2(0. 0188)(10.000)/547.6
= 25,526.4 lb/ft2 psia
pi = 177.3 psia
The above injection pressure is the expected standpipe pressure when drilling
at 10,000 ft of depth. The injection pressure will be somewhat less than the
above when drilling the upper portion of the interval (Le. at 8500').
Thus the primary compressors will have sufficient pressure capability to drill
the interval from 8,500 to 10,000 ft. A third primary compressor should be on
site and hooked up for immediate service in the event of downhole problems
or the necessity to shut down one of the operating compressors. Also, the
booster should be hooked up for immediate service in the event of downhole
problems. For more information and engineering calculations pertaining to
compressors and boosters see reference 64.