Page 584 - Air and Gas Drilling Manual

11-22 Air and Gas Drilling Manual
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 temperature) in the
openhole section is
T 5 604 41˚R
.
The average temperature of the drill collar length H 5 and, thus, the temperature of the
gas flow inside the drill collars is
.
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
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 2
.
0 018 53 36 (.
.
2 635)
b i5
232 2 . ) 10 . 2 5
(
(.
0 234)
4
,
b i5 12 420
Equation 6-72 becomes