Page 195 - Air and Gas Drilling Manual

The inside surface of the drill pipe is assumed to have the surface roughness of
commercial steel which is 0.00015 ft. Equation 5-10 becomes
2
 Chapter 5: Shallow Well Drilling Applications 5-37

 
f =  1 
  0 166  
.
.
 2 log  + 114 
  0 00015 
.
f = 0 019
.
Equations 5-8 and 5-9 become, respectively,
.
a = 10
i
.
53 36
a = 0 019.
i
and
0 700)
.
b = 0 019  53.36  2 (. 2
i  2
π
0166)
(
2 322 . ) ( .  10 .   4
0 166)
  (.
4
,
b = 5 285
i
Equation 5-7 becomes
  2 (. 0 019 ) ( , 1 200 )   . 05
 (, 4 732 ) 2 + ( , 5 285 ) (503 27 2 e  503 .27 −  1 
. )
    

P =  
in
 2 (. 0 019 ) ( , 1 200 ) 
 e 503 .27 
 
 
2
P = 11 620 lb/ft abs
,
in
P in
p in =
144
p = 80 7 psia
.
in
The above pressure is the approximate injection pressure to the top of the inside
of the drill string. Again, these calculations have been carried out neglecting the