Page 340 - Air and Gas Drilling Manual

Chapter 8: Air, Gas, and Unstable Foam Drilling 8-23
Note the above specific weight value can also be obtained from Figure D-4 in
Appendix D.
The selected reciprocating piston compressor has an actual volumetric flow rate
of 1,200 acfm. Two of these compressor are required to adequately drill this well.
Therefore, the actual volumetric flow rate to the well while drilling the openhole
interval from 7,000 ft to 10,000 ft will be 2,400 acfm. Thus,
,
q g = 2 400 acfm
The value of Q g is
q g
Q g =
60
3
.
Q g = 40 00 ft /sec
The weight rate of flow of the gas, ˙ w , is
g
˙ w = γ Q
g g g
˙ w = . 0 0659 (40 .00 )
g
˙ w = . 2 635 lb/sec
g
The openhole interval of this well has an inside diameter of the drill bit. The
drill bit diameter, D h, is

d h = 7 875 inches
.
d
D = h
h
12
D = 0 656. ft
h

The estimated drilling rate of penetration is 60 ft/hr. From Equation 8-1, ˙ w ,
s
in the annulus is
π
.) (. ) 
2
˙ w =   (. 0 656 ) (62 4 2 7  60  
s     (60 ) (60 )  
4
˙ w = . 0 950 lb/sec
s