Page 602 - Air and Gas Drilling Manual

11-40 Air and Gas Drilling Manual
.
604 41˚R
T
5
The average temperature of the drill collar length H 5 and, thus, the temperature of the
gas flow inside the drill collars is
T 601 91˚R
.
av5
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 p 0 00015 ft
.
With the above, Equation 6-73 becomes
2
1
f
i5 0 234
.
.
2 log 114
0 00015
.
f i5 0 018
.
Equations 6-67 and 6-68 become, respectively,
.
10
a i5
53 36
.
.
a i5 0 019
and

.
2 635)
.
0 018 53 36 2 (. 2
b
i5 2
232 2 . ) 10 . 5
(
(.
0 234)
4
,
b i5 12 420
The pressure above the motor, P , is the approximate pressure at the bottom of the
am
inside of the drill string. Thus, Equation 6-72 becomes