Page 359 - Air and Gas Drilling Manual

8-42 Air and Gas Drilling Manual
Equation 6-72 becomes
(.
  (, 2 + ( , 601 91) 2  e  2 0 019) ( 500) − 1    05 .
601 91
.
12 420) (
31 330)
.
    

P =  
i4  2 0 019) ( 500) 
(.
 e 601 91 
.
 
 
2
,
P i4 = 33 010 lb/ft abs
P i4
p =
i4
144
p i4 = 229 2 psia
.
The pressure given above is the flowing air pressure at the top of the drill collar
length inside the drill string in the openhole section of the borehole.
The fourth drill string section increment is denoted by the length H 4. The
temperature at the bottom of the drill pipe tool joints lumped geometry length in the
openhole section is
T = 599 41 R
o
.
4
The average temperature of the drill pipe tool joints lumped length along H 4 and,
thus, the temperature of the gas flow inside this drill string length is
o
.
T av4 = 598 79 R
The inside surface of the drill pipe tool joint has the surface roughness of
commercial steel. Therefore, over this lumped drill pipe tool joint length the surface
roughness is
.
e p = 0 00015 ft
With the above, Equation 6-73 becomes
  2
 
f =  1 
i4   0 292  
.
114
 2 log 0 00015  + . 
  . 