Page 350 - Air and Gas Drilling Manual

b
,
a2
Equation 6-57 becomes
05 .
  = 4 476 Chapter 8: Air, Gas, and Unstable Foam Drilling 8-33

350)
2 0 025) (
(.
[
2 
.
,
(
9 285)
)
,
(
.
.
P a2 =  ( , 2 + 4 476 572 66) 2 ] e 572 66 − 4 476 572 66 
  

2
P a2 = 11 640 lb/ft abs
,
P a2
p a2 =
144
p a2 = 80 8 psia
.
Openhole Section of the Annulus (7,000 ft to 10,000 ft)
The third annulus seciton increment is denoted by the length H 3. The
temperature at the bottom of the length H 3 in the openhole annulus section (bottom
of the drill pipe body lumped geometry), T 3, is
T = T + 001 ( H + H + H )
.
3 r 1 2 3
T = T + 0 01 9 375)
(
.
,
r
3
T = 598 16 R
o
.
3
The average temperature of this openhole annulus section H 3 is
T + T
T av3 = 2 3
2
o
.
T av3 = 586 29 R
It is assumed that the inside surface of the openhole annulus section has a surface
roughness of 0.01 ft (see Table 8-1). The inner surface of this annulus section is the
outer surface of the drill pipe body which has an absolute surface roughness of
0.00015 ft. Using Equation 8-2, the average absolute surface roughness of this
annulus section, e av3, is