Page 192 - Air and Gas Drilling Manual

5-34 Air and Gas Drilling Manual
The weight rate of flow of air in the circulating system in the well is
( . )
=
. 0 700 lb/sec
˙ w ˙ w g = . 0 0600 11 7
g
The borehole diameter, D h, is
d h = 475 inches
.
d
D = h
h
12
D = 0 396. ft
h
In this illustrative example the formations to be drilled are metamorphic rock.
Therefore, unless actual data are available the average specific gravity of metamorphic
rock (i.e., S s = 3.0) is used in Equation 5-4. Using Equation 5-4, the weight rate of
flow of the solid rock cuttings in the annulus is
π
.) ( . ) 
2
˙ w =   (. 0 396 ) (62 4 3 0  30  
s     (60 ) (60 )  
4
˙ w = . 0 192 lb/sec
s
The drill pipe outside diameter, D p, is
d p = 2 375 inches
.
d p
D p =
12
D = 0 198 ft
.
p
Using Equation 5-6, the average surface roughness for the annulus becomes
π
π
  2   2
0
(.005 )   (.396 ) + (.0 00015 )   (.198 )
0
0
e = 4 4
π
π
av   2   2
  (. 0 396 ) +   (. 0 198 )
4
4
.
e av = 0 0040 ft