Page 363 - Air and Gas Drilling Manual

8-46 Air and Gas Drilling Manual
.
.
0 017
2 635)
10 
2
π
232 2 . )
.
(
0 292)
4 

=
b b i2 = 3 958   53 36  2   (. (. 2 5
,
i2
Equation 6-72 becomes
  2 0 019) ( 350)   05 .
(.
 (, 2 + ( , 572 66) 2 e  572 66 − 1 
.
.
32 540)
3 958) (
    

P i1 =   2 0 019) ( 350)  
(.
 e 572 66 
.
 
 
2
P i1 = 32 620 lb/ft abs
,
P i1
p i1 =
144
p i1 = 226 5 psia
.
The pressure given above is the flowing air pressure at the top of the lumped drill
pipe tool joints length inside the drill string in the cased section of the borehole.
The first drill string section increment is denoted by the length H 1. The
temperature at the bottom drill pipe body lumped geometry length in the cased
section is
o
T = 570 91 R
.
1
The average temperature of the drill pipe body lumped geometry along H 1 and, thus,
the temperature of the gas flow inside this drill string length is
o
.
T av1 = 537 66 R
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