Page 199 - Air and Gas Drilling Manual

,
Q
60
Q g = 1 400 3 Chapter 5: Shallow Well Drilling Applications 5-41
.
= 23 3 ft /sec
g
The weight rate of flow of air through the well is
˙ w = . 0 0690 (23 3
. )
g
˙ w = . 1 599 lb/sec
g
The borehole diameter, D h, is
d h = 625 inches
.
d
D = h
h
12
D = 0 521. ft
h
Using Equation 5-4, the weight rate of flow of the solid rock cuttings in the annulus
is
π
2
.) (. ) 
˙ w =   (. 0 521 ) (62 4 2 7  90  
s     (60 ) (60 )  
4
˙ w s = . 0 897 lb/sec
The drill pipe outside diameter, D p, is

.
d p = 2 875 inches
d p
D p =
12
D p = 0 240 ft
.
The sedimentary rock borehole wall absolute surface roughness is assumed to be
0.005 ft (see Table 8-1). Using Equation 5-6, the average surface roughness for the
annulus becomes