Page 495 - Air and Gas Drilling Manual

10-20 Air and Gas Drilling Manual
The back pressure at the top of the annulus is 17 psig. The back pressure, P bp,
in absolute pressure is
p bp 17 0 12 685
.
.
.
p 29 685 psia
bp
P bp p bp 144
2
,
P bp 4 275 lb/ft abs
Note that the back pressure can be adjusted to improve the annulus foam quality and
kinetic energy per unit volume values.
The trial and error q w that will satisfy these limitations is
q w 105 0 gal/min
.
The volumetric flow rate of water, Q w, in consistent units is

105 0 231
.
Q w 3
12 60
3
.
Q w 0 234 ft /sec
The specific weight of the incompressible fluid is

3
.
62 4 lb/ft
w
The weight rate of flow of the incompressible fluid, ˙ w is
w
˙ w Q
w w w
˙ w (62 4 )
. ) ( . 0 234
w
˙ w w 14 .60 lb/sec

Solving Equation 10-3 for Q gbp gives

bp
Q gbp Q w
1
bp