Page 358 - Air and Gas Drilling Manual

Chapter 8: Air, Gas, and Unstable Foam Drilling 8-41
D =
0 319 ft
.
7
Inside the Drill String (10,000 ft to 7,000 ft)
The fifth drill string section increment is denoted by the length H 5. The
temperature at the bottom of the drill collars (bottomhole tempreature) in the
openhole section is
T = 604 41 R
o
.
5
The average temperature of the drill collar length H 5 and, thus, the temperature of the
gas flow inside the drill collars is
o
.
T av5 = 601 91 R
The inside surface of the drill collars has the surface roughness of commercial steel.
Therefore, over this drill collar length the surface roughness is
.
e = 0 00015 ft
p
With the above, Equation 6-73 becomes
  2
 
f =  1 
i5
  0 234  
.
114
 2 log 0 00015  + . 
  . 
.
f i5 = 0 018
Equations 6-67 and 6-68 become, respectively,
a = 10 .
i5
.
53 36
a = 0 019
.
i5
and
2 635)
.
.
b i5 = 0 018   53 36  2 (. 2
π
.
232 2 . ) 10    2 5
(
0 234)
 4  (.
,
b i5 = 12 420