Page 362 - Air and Gas Drilling Manual

P
i2
144
=
.
p p i2 = 225 9 psia Chapter 8: Air, Gas, and Unstable Foam Drilling 8-45
i2
The pressure given above is the flowing air pressure at the top of the lumped drill
pipe body length inside the drill string in the openhole section of the borehole.
Inside the Drill String (7,000 ft to Surface)
The second drill string section increment is denoted by the length H 2. The
temperature at the bottom drill pipe tool joints lumped geometry length in the cased
section is
T = 574 41 R
o
.
2
The average temperature of the drill pipe tool joints lumped geometry along H 2 and,
thus, the temperature of the gas flow inside this drill string length is
o
T = 572 66 R
.
av2
The inside surface of the drill pipe body has the surface roughness of commercial
steel. Therefore, over this lumped drill pipe body length the surface roughness is
.
e p = 0 00015 ft
With the above, Equation 6-73 becomes
  2
 
f =  1 
  0 292  
i2
.
114
 2 log  . + . 
0 00015 
 
f i2 = 0 017
.
Equations 6-67 and 6-68 become, respectively,
.
a = 10
i2
53 36
.
a i2 = 0 019
.
and