Page 490 - Air and Gas Drilling Manual

w ˙
g
Q
g
g
.
1 456 Chapter 10: Stable Foam drilling 10-15
Q
g
.
0 0659
3
Q g 22 11 ft /sec
.
q g Q 60
g
,
q g 1 327 acfm
With the above values, Equation 10-1 can be used to obtain by trial and error
the bottomhole pressure. Equation 10-1 is rearranged in the form
T av P bh
Q g P g ln g H w ˙ w w ˙ s H P bh P bp Q w
T P
g bp
In the above, P s has been replaced by P bp, ˙ w replaced by ˙ w , and Q f replaced by
w
f
Q w.
All values in the above equation are known except for bottomhole pressure P bh.
The value of P bh must be obtained by a trial and error process. The bottomhole
pressure is assumed to be
p 547 psig
bh
or

.
p bh 547 12 685
.
p 559 685 psia
bh
P bh p bh 144
P (559 .685 144
)
bh
2
P 80 595 lb/ft abs
,
bh
Substituting the values of H, ˙ w , ˙ w , g, Q g, Q w, P g, P bp, P bh, T g, and T av into
s
w
the above equation yields