Page 329 - Air and Gas Drilling Manual

8-12 Air and Gas Drilling Manual
.
D
= 0 375 ft
p
where d p is the outside diameter of the drill pipe (inches),
D p is the outside diameter of the drill pipe (ft).
In what follows, Equations 6-52, 6-53, 6-57, and 6-58 from Chapter 6 will be
used to complete this illustrative example. These equations will be used in
sequential calculations through the annulus. The values of the constants and the
pressures obtained will be denoted by the subscripts ac or ao for the annulus cased
section and the annulus openhole section, respectively.
The Fanning friction factor, f ac, for flow in the cased section of the annulus is
determined from the von Karman empirical relationship for turbulent flow conditions
[12]. This empirical relationship is given by Equation 6-58. This is
  2
 
 
f =  1 
ac D − D 
  h p 
 2 log. 

+1 14

   e p   
where e p is the absolute surface roughness of the cased section of the annulus (ft).
Both surfaces of the annulus in the cased section of the borehole is commercial pipe
surfaces (i.e., the inside surface of the casing and the outside surface of the drill
pipe). Thus, the absolute surface roughness of the annulus is the commercial pipe
roughness. Therefore, e p, is given as 0.00015 ft [12]. Equation 6-58 becomes
  2
 
1
f ac =   . − 0 375   
.

2 log  0 656  +114 
.
   0 00015   
.
f ac = 0 017
.
With the above values Equations 6-52 and 6-53 become, respectively,
a ac =  10.    1 +  0 950.   
 53 36.    2 019.  
a = 0 028
.
ac
and