Page 241 - Air and gas Drilling Field Guide 3rd Edition

232 CHAPTER 9 Aerated Fluids Drilling

Equation (9-7) can be solved by trial and error. The value of q g is selected and
_ w g determined from
_ w g ¼ g Q g :
g
Substituting the values of H, _ w f ; _ w g ; _ w s ; Q f ,P s ,P bh ,T g , and T av into Equation
(9-7), a value of Q g can be determined. The trial and error process is carried
out until the right side and the left side equal each other. This gives an air
volumetric flow rate of
3
Q g ¼ 6:617 actual ft =sec:
The air volumetric flow rate in field units is
q g ¼ 6:617Þ 60Þ
ð
ð
q g ¼ 397 acfm
or
q g ¼ 353 scfm:

SI Units
2
Table 5-1 gives an average atmospheric pressure of 8.749 N/cm abs for a surface
location of 1219.1 m above sea level (also see Appendix B). The actual atmo-
spheric pressure for the air at the drilling location (used by the compressor) is
2
P at ¼ 8:749 N=cm abs
P at ¼ P at 10000
2
P at ¼ 87490:0N=m abs:
The actual atmospheric temperature of the air at the drilling location (used by the
compressor) is
t at ¼ 7:08 C

T at ¼ t at þ 273:15
T at ¼ 280:23 K:
Thus, P g and T g become
2
P g ¼ P at ¼ 8:749 N=cm abs
T g ¼ T at ¼ 280:23 K:

Using Equation (4-11), the specific weight of the gas entering the compressor
is

ð
ð 87490:0Þ 1:0Þ
g ¼
g
ð
ð 29:31Þ 280:23Þ
2
g ¼ 10:652 N=m :
g